Sync to upstream/release/672 (#1800)

# What's Changed?

Hi there, folks! It's been another busy week in the type mines, trying
to bring you all the very best type inference system we can. We've got a
bunch of updates to large pain points across the new type solver, and
our next big update (currently under a debug flag) improving type
generalization is finally nearing completion (and should hopefully
eliminate quite a lot of "type solver failed to complete" errors). We've
also continued polishing both the CST Parser and the `Luau.Require`
library we introduced a few releases ago based on user feedback and bug
reports, and we're really happy with how they're turning out.

# Parser
- Fixes a bug in the CST tooling where the spacing on return type
annotations for functions was not being printed correctly.
- Resolves some issues with the JSON encoding of `AstGenericType` and
`AstGenericTypePack`

# Runtime
- Implements support for yielding requires in `Luau.Require` library.
- Improves the error messages for require-by-string to include the chunk
name that was problematic where possible and the overall require path
that failed to be required.
- Fixes a bug that prevented the use of `require` within C functions and
`pcall`.
- Adds an API to support selectively removing chunks from the require
cache in `Luau.Require`
- Adds an API to support clearing the entire require cache in
`Luau.Require`

# New Type Solver

- Fixes a crash in the new non-strict mode when visiting function return
types in incomplete ASTs (e.g. during editing).
- Improves type simplification to support intersections of tables with
extern types, resolving _one_ of the causes of frequent refinements
unexpectedly leading to `never`.
- Improves type inference to better understand diverging branches in
functions, reducing false negatives where the type system fails to learn
that a binding must now always be initialized.
- Fixes a typo in the type definitions for user-defined function types
where the `intersection` tag was misspelled.
- Improves the overall accuracy of free type tracking during constraint
solving, leading to better inference results overall.
- Implements `types.optional` as a new library function for user-defined
type functions to make it easier to union a type with `nil`.
- Resolves a number of bugs caused by local type inference expanding the
domain of upvalues

# Internal Contributors

Co-authored-by: Andy Friesen <afriesen@roblox.com>
Co-authored-by: Ariel Weiss <aaronweiss@roblox.com>
Co-authored-by: Hunter Goldstein <hgoldstein@roblox.com>
Co-authored-by: Talha Pathan <tpathan@roblox.com>
Co-authored-by: Varun Saini <vsaini@roblox.com>
Co-authored-by: Vighnesh Vijay <vvijay@roblox.com>

---------

Co-authored-by: Hunter Goldstein <hgoldstein@roblox.com>
Co-authored-by: Varun Saini <61795485+vrn-sn@users.noreply.github.com>
Co-authored-by: Alexander Youngblood <ayoungblood@roblox.com>
Co-authored-by: Menarul Alam <malam@roblox.com>
Co-authored-by: Aviral Goel <agoel@roblox.com>
Co-authored-by: Vighnesh <vvijay@roblox.com>
Co-authored-by: Vyacheslav Egorov <vegorov@roblox.com>
Co-authored-by: Andy Friesen <afriesen@roblox.com>

.github/workflows/build.yml

@@ -46,9 +46,9 @@ jobs:
     - name: make cli
       run: |
          make -j2 config=sanitize werror=1 luau luau-analyze luau-compile # match config with tests to improve build time
-         ./luau tests/conformance/assert.lua
+         ./luau tests/conformance/assert.luau
-         ./luau-analyze tests/conformance/assert.lua
+         ./luau-analyze tests/conformance/assert.luau
-         ./luau-compile tests/conformance/assert.lua
+         ./luau-compile tests/conformance/assert.luau
 
   windows:
     runs-on: windows-latest
@@ -81,12 +81,12 @@ jobs:
       shell: bash # necessary for fail-fast
       run: |
         cmake --build . --target Luau.Repl.CLI Luau.Analyze.CLI Luau.Compile.CLI --config Debug # match config with tests to improve build time
-        Debug/luau tests/conformance/assert.lua
+        Debug/luau tests/conformance/assert.luau
-        Debug/luau-analyze tests/conformance/assert.lua
+        Debug/luau-analyze tests/conformance/assert.luau
-        Debug/luau-compile tests/conformance/assert.lua
+        Debug/luau-compile tests/conformance/assert.luau
 
   coverage:
-    runs-on: ubuntu-20.04 # needed for clang++-10 to avoid gcov compatibility issues
+    runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v2
     - name: install
@@ -94,7 +94,7 @@ jobs:
         sudo apt install llvm
     - name: make coverage
       run: |
-        CXX=clang++-10 make -j2 config=coverage native=1 coverage
+        CXX=clang++ make -j2 config=coverage native=1 coverage
     - name: upload coverage
       uses: codecov/codecov-action@v3
       with:

.github/workflows/new-release.yml

@@ -29,8 +29,8 @@ jobs:
   build:
     needs: ["create-release"]
     strategy:
-      matrix: # using ubuntu-20.04 to build a Linux binary targeting older glibc to improve compatibility
+      matrix: # not using ubuntu-latest to improve compatibility
-        os: [{name: ubuntu, version: ubuntu-20.04}, {name: macos, version: macos-latest}, {name: windows, version: windows-latest}]
+        os: [{name: ubuntu, version: ubuntu-22.04}, {name: macos, version: macos-latest}, {name: windows, version: windows-latest}]
     name: ${{matrix.os.name}}
     runs-on: ${{matrix.os.version}}
     steps:

.github/workflows/release.yml

@@ -13,8 +13,8 @@ on:
 jobs:
   build:
     strategy:
-      matrix: # using ubuntu-20.04 to build a Linux binary targeting older glibc to improve compatibility
+      matrix: # not using ubuntu-latest to improve compatibility
-        os: [{name: ubuntu, version: ubuntu-20.04}, {name: macos, version: macos-latest}, {name: windows, version: windows-latest}]
+        os: [{name: ubuntu, version: ubuntu-22.04}, {name: macos, version: macos-latest}, {name: windows, version: windows-latest}]
     name: ${{matrix.os.name}}
     runs-on: ${{matrix.os.version}}
     steps:

.gitignore

@@ -13,6 +13,7 @@
 /luau
 /luau-tests
 /luau-analyze
+/luau-bytecode
 /luau-compile
 __pycache__
 .cache

Analysis/include/Luau/AnyTypeSummary.h

@@ -1,148 +0,0 @@
-// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
-#pragma once
-
-#include "Luau/AstQuery.h"
-#include "Luau/Config.h"
-#include "Luau/ModuleResolver.h"
-#include "Luau/Scope.h"
-#include "Luau/Variant.h"
-#include "Luau/Normalize.h"
-#include "Luau/TypePack.h"
-#include "Luau/TypeArena.h"
-
-#include <mutex>
-#include <string>
-#include <vector>
-#include <optional>
-
-namespace Luau
-{
-
-class AstStat;
-class ParseError;
-struct TypeError;
-struct LintWarning;
-struct GlobalTypes;
-struct ModuleResolver;
-struct ParseResult;
-struct DcrLogger;
-
-struct TelemetryTypePair
-{
-    std::string annotatedType;
-    std::string inferredType;
-};
-
-struct AnyTypeSummary
-{
-    TypeArena arena;
-
-    AstStatBlock* rootSrc = nullptr;
-    DenseHashSet<TypeId> seenTypeFamilyInstances{nullptr};
-
-    int recursionCount = 0;
-
-    std::string root;
-    int strictCount = 0;
-
-    DenseHashMap<const void*, bool> seen{nullptr};
-
-    AnyTypeSummary();
-
-    void traverse(const Module* module, AstStat* src, NotNull<BuiltinTypes> builtinTypes);
-
-    std::pair<bool, TypeId> checkForAnyCast(const Scope* scope, AstExprTypeAssertion* expr);
-
-    bool containsAny(TypePackId typ);
-    bool containsAny(TypeId typ);
-
-    bool isAnyCast(const Scope* scope, AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    bool isAnyCall(const Scope* scope, AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-
-    bool hasVariadicAnys(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    bool hasArgAnys(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    bool hasAnyReturns(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-
-    TypeId checkForFamilyInhabitance(const TypeId instance, Location location);
-    TypeId lookupType(const AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    TypePackId reconstructTypePack(const AstArray<AstExpr*> exprs, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-
-    DenseHashSet<TypeId> seenTypeFunctionInstances{nullptr};
-    TypeId lookupAnnotation(AstType* annotation, const Module* module, NotNull<BuiltinTypes> builtintypes);
-    std::optional<TypePackId> lookupPackAnnotation(AstTypePack* annotation, const Module* module);
-    TypeId checkForTypeFunctionInhabitance(const TypeId instance, const Location location);
-
-    enum Pattern : uint64_t
-    {
-        Casts,
-        FuncArg,
-        FuncRet,
-        FuncApp,
-        VarAnnot,
-        VarAny,
-        TableProp,
-        Alias,
-        Assign,
-        TypePk
-    };
-
-    struct TypeInfo
-    {
-        Pattern code;
-        std::string node;
-        TelemetryTypePair type;
-
-        explicit TypeInfo(Pattern code, std::string node, TelemetryTypePair type);
-    };
-
-    struct FindReturnAncestry final : public AstVisitor
-    {
-        AstNode* currNode{nullptr};
-        AstNode* stat{nullptr};
-        Position rootEnd;
-        bool found = false;
-
-        explicit FindReturnAncestry(AstNode* stat, Position rootEnd);
-
-        bool visit(AstType* node) override;
-        bool visit(AstNode* node) override;
-        bool visit(AstStatFunction* node) override;
-        bool visit(AstStatLocalFunction* node) override;
-    };
-
-    std::vector<TypeInfo> typeInfo;
-
-    /**
-     * Fabricates a scope that is a child of another scope.
-     * @param node the lexical node that the scope belongs to.
-     * @param parent the parent scope of the new scope. Must not be null.
-     */
-    const Scope* childScope(const AstNode* node, const Scope* parent);
-
-    std::optional<AstExpr*> matchRequire(const AstExprCall& call);
-    AstNode* getNode(AstStatBlock* root, AstNode* node);
-    const Scope* findInnerMostScope(const Location location, const Module* module);
-    const AstNode* findAstAncestryAtLocation(const AstStatBlock* root, AstNode* node);
-
-    void visit(const Scope* scope, AstStat* stat, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatBlock* block, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatIf* ifStatement, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatWhile* while_, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatRepeat* repeat, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatReturn* ret, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatLocal* local, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatFor* for_, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatForIn* forIn, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatAssign* assign, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatCompoundAssign* assign, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatFunction* function, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatLocalFunction* function, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatTypeAlias* alias, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatDeclareGlobal* declareGlobal, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatDeclareClass* declareClass, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatDeclareFunction* declareFunction, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-    void visit(const Scope* scope, AstStatError* error, const Module* module, NotNull<BuiltinTypes> builtinTypes);
-};
-
-} // namespace Luau

Analysis/include/Luau/AutocompleteTypes.h

@@ -57,7 +57,7 @@ struct AutocompleteEntry
     // Set if this suggestion matches the type expected in the context
     TypeCorrectKind typeCorrect = TypeCorrectKind::None;
 
-    std::optional<const ClassType*> containingClass = std::nullopt;
+    std::optional<const ExternType*> containingExternType = std::nullopt;
     std::optional<const Property*> prop = std::nullopt;
     std::optional<std::string> documentationSymbol = std::nullopt;
     Tags tags;
@@ -85,7 +85,7 @@ struct AutocompleteResult
 };
 
 using StringCompletionCallback =
-    std::function<std::optional<AutocompleteEntryMap>(std::string tag, std::optional<const ClassType*> ctx, std::optional<std::string> contents)>;
+    std::function<std::optional<AutocompleteEntryMap>(std::string tag, std::optional<const ExternType*> ctx, std::optional<std::string> contents)>;
 
 constexpr char kGeneratedAnonymousFunctionEntryName[] = "function (anonymous autofilled)";
 

Analysis/include/Luau/BuiltinDefinitions.h

@@ -65,14 +65,12 @@ TypeId makeFunction( // Polymorphic
     bool checked = false
 );
 
-void attachMagicFunction(TypeId ty, MagicFunction fn);
+void attachMagicFunction(TypeId ty, std::shared_ptr<MagicFunction> fn);
-void attachDcrMagicFunction(TypeId ty, DcrMagicFunction fn);
-void attachDcrMagicRefinement(TypeId ty, DcrMagicRefinement fn);
-void attachDcrMagicFunctionTypeCheck(TypeId ty, DcrMagicFunctionTypeCheck fn);
 Property makeProperty(TypeId ty, std::optional<std::string> documentationSymbol = std::nullopt);
 void assignPropDocumentationSymbols(TableType::Props& props, const std::string& baseName);
 
 std::string getBuiltinDefinitionSource();
+std::string getTypeFunctionDefinitionSource();
 
 void addGlobalBinding(GlobalTypes& globals, const std::string& name, TypeId ty, const std::string& packageName);
 void addGlobalBinding(GlobalTypes& globals, const std::string& name, Binding binding);

Analysis/include/Luau/Clone.h

@@ -4,6 +4,7 @@
 #include <Luau/NotNull.h>
 #include "Luau/TypeArena.h"
 #include "Luau/Type.h"
+#include "Luau/Scope.h"
 
 #include <unordered_map>
 
@@ -26,13 +27,22 @@ struct CloneState
  * while `clone` will make a deep copy of the entire type and its every component.
  *
  * Be mindful about which behavior you actually _want_.
+ *
+ * Persistent types are not cloned as an optimization.
+ * If a type is cloned in order to mutate it, 'ignorePersistent' has to be set
  */
 
-TypePackId shallowClone(TypePackId tp, TypeArena& dest, CloneState& cloneState);
+TypePackId shallowClone(TypePackId tp, TypeArena& dest, CloneState& cloneState, bool ignorePersistent = false);
-TypeId shallowClone(TypeId typeId, TypeArena& dest, CloneState& cloneState);
+TypeId shallowClone(TypeId typeId, TypeArena& dest, CloneState& cloneState, bool ignorePersistent = false);
 
 TypePackId clone(TypePackId tp, TypeArena& dest, CloneState& cloneState);
 TypeId clone(TypeId tp, TypeArena& dest, CloneState& cloneState);
 TypeFun clone(const TypeFun& typeFun, TypeArena& dest, CloneState& cloneState);
+Binding clone(const Binding& binding, TypeArena& dest, CloneState& cloneState);
+
+TypePackId cloneIncremental(TypePackId tp, TypeArena& dest, CloneState& cloneState, Scope* freshScopeForFreeTypes);
+TypeId cloneIncremental(TypeId typeId, TypeArena& dest, CloneState& cloneState, Scope* freshScopeForFreeTypes);
+TypeFun cloneIncremental(const TypeFun& typeFun, TypeArena& dest, CloneState& cloneState, Scope* freshScopeForFreeTypes);
+Binding cloneIncremental(const Binding& binding, TypeArena& dest, CloneState& cloneState, Scope* freshScopeForFreeTypes);
 
 } // namespace Luau

Analysis/include/Luau/Constraint.h

@@ -50,6 +50,7 @@ struct GeneralizationConstraint
     TypeId sourceType;
 
     std::vector<TypeId> interiorTypes;
+    bool hasDeprecatedAttribute = false;
 };
 
 // variables ~ iterate iterator
@@ -109,6 +110,21 @@ struct FunctionCheckConstraint
     NotNull<DenseHashMap<const AstExpr*, TypeId>> astExpectedTypes;
 };
 
+// table_check expectedType exprType
+//
+// If `expectedType` is a table type and `exprType` is _also_ a table type,
+// propogate the member types of `expectedType` into the types of `exprType`.
+// This is used to implement bidirectional inference on table assignment.
+// Also see: FunctionCheckConstraint.
+struct TableCheckConstraint
+{
+    TypeId expectedType;
+    TypeId exprType;
+    AstExprTable* table = nullptr;
+    NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes;
+    NotNull<DenseHashMap<const AstExpr*, TypeId>> astExpectedTypes;
+};
+
 // prim FreeType ExpectedType PrimitiveType
 //
 // FreeType is bounded below by the singleton type and above by PrimitiveType
@@ -273,7 +289,8 @@ using ConstraintV = Variant<
     UnpackConstraint,
     ReduceConstraint,
     ReducePackConstraint,
-    EqualityConstraint>;
+    EqualityConstraint,
+    TableCheckConstraint>;
 
 struct Constraint
 {

Analysis/include/Luau/ConstraintGenerator.h

@@ -3,6 +3,7 @@
 
 #include "Luau/Ast.h"
 #include "Luau/Constraint.h"
+#include "Luau/ConstraintSet.h"
 #include "Luau/ControlFlow.h"
 #include "Luau/DataFlowGraph.h"
 #include "Luau/EqSatSimplification.h"
@@ -11,15 +12,14 @@
 #include "Luau/ModuleResolver.h"
 #include "Luau/Normalize.h"
 #include "Luau/NotNull.h"
+#include "Luau/Polarity.h"
 #include "Luau/Refinement.h"
 #include "Luau/Symbol.h"
 #include "Luau/TypeFwd.h"
 #include "Luau/TypeUtils.h"
-#include "Luau/Variant.h"
 
 #include <memory>
 #include <vector>
-#include <unordered_map>
 
 namespace Luau
 {
@@ -92,9 +92,11 @@ struct ConstraintGenerator
     // Constraints that go straight to the solver.
     std::vector<ConstraintPtr> constraints;
 
-    // Constraints that do not go to the solver right away.  Other constraints
+    // The set of all free types introduced during constraint generation.
-    // will enqueue them during solving.
+    DenseHashSet<TypeId> freeTypes{nullptr};
-    std::vector<ConstraintPtr> unqueuedConstraints;
+
+    // Map a function's signature scope back to its signature type.
+    DenseHashMap<Scope*, TypeId> scopeToFunction{nullptr};
 
     // The private scope of type aliases for which the type parameters belong to.
     DenseHashMap<const AstStatTypeAlias*, ScopePtr> astTypeAliasDefiningScopes{nullptr};
@@ -114,18 +116,23 @@ struct ConstraintGenerator
 
     // Needed to register all available type functions for execution at later stages.
     NotNull<TypeFunctionRuntime> typeFunctionRuntime;
+    DenseHashMap<const AstStatTypeFunction*, ScopePtr> astTypeFunctionEnvironmentScopes{nullptr};
+
     // Needed to resolve modules to make 'require' import types properly.
     NotNull<ModuleResolver> moduleResolver;
     // Occasionally constraint generation needs to produce an ICE.
     const NotNull<InternalErrorReporter> ice;
 
     ScopePtr globalScope;
+    ScopePtr typeFunctionScope;
 
     std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope;
     std::vector<RequireCycle> requireCycles;
 
     DenseHashMap<TypeId, TypeIds> localTypes{nullptr};
 
+    DenseHashMap<AstExpr*, Inference> inferredExprCache{nullptr};
+
     DcrLogger* logger;
 
     ConstraintGenerator(
@@ -137,12 +144,16 @@ struct ConstraintGenerator
         NotNull<BuiltinTypes> builtinTypes,
         NotNull<InternalErrorReporter> ice,
         const ScopePtr& globalScope,
+        const ScopePtr& typeFunctionScope,
         std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope,
         DcrLogger* logger,
         NotNull<DataFlowGraph> dfg,
         std::vector<RequireCycle> requireCycles
     );
 
+    ConstraintSet run(AstStatBlock* block);
+    ConstraintSet runOnFragment(const ScopePtr& resumeScope, AstStatBlock* block);
+
     /**
      * The entry point to the ConstraintGenerator. This will construct a set
      * of scopes, constraints, and free types that can be solved later.
@@ -153,19 +164,26 @@ struct ConstraintGenerator
     void visitFragmentRoot(const ScopePtr& resumeScope, AstStatBlock* block);
 
 private:
-    std::vector<std::vector<TypeId>> interiorTypes;
+    struct InteriorFreeTypes
+    {
+        std::vector<TypeId> types;
+        std::vector<TypePackId> typePacks;
+    };
+
+    std::vector<std::vector<TypeId>> DEPRECATED_interiorTypes;
+    std::vector<InteriorFreeTypes> interiorFreeTypes;
 
     /**
      * Fabricates a new free type belonging to a given scope.
      * @param scope the scope the free type belongs to.
      */
-    TypeId freshType(const ScopePtr& scope);
+    TypeId freshType(const ScopePtr& scope, Polarity polarity = Polarity::Unknown);
 
     /**
      * Fabricates a new free type pack belonging to a given scope.
      * @param scope the scope the free type pack belongs to.
      */
-    TypePackId freshTypePack(const ScopePtr& scope);
+    TypePackId freshTypePack(const ScopePtr& scope, Polarity polarity = Polarity::Unknown);
 
     /**
      * Allocate a new TypePack with the given head and tail.
@@ -254,7 +272,7 @@ private:
     ControlFlow visit(const ScopePtr& scope, AstStatTypeAlias* alias);
     ControlFlow visit(const ScopePtr& scope, AstStatTypeFunction* function);
     ControlFlow visit(const ScopePtr& scope, AstStatDeclareGlobal* declareGlobal);
-    ControlFlow visit(const ScopePtr& scope, AstStatDeclareClass* declareClass);
+    ControlFlow visit(const ScopePtr& scope, AstStatDeclareExternType* declareExternType);
     ControlFlow visit(const ScopePtr& scope, AstStatDeclareFunction* declareFunction);
     ControlFlow visit(const ScopePtr& scope, AstStatError* error);
 
@@ -286,7 +304,7 @@ private:
     );
 
     Inference check(const ScopePtr& scope, AstExprConstantString* string, std::optional<TypeId> expectedType, bool forceSingleton);
-    Inference check(const ScopePtr& scope, AstExprConstantBool* bool_, std::optional<TypeId> expectedType, bool forceSingleton);
+    Inference check(const ScopePtr& scope, AstExprConstantBool* boolExpr, std::optional<TypeId> expectedType, bool forceSingleton);
     Inference check(const ScopePtr& scope, AstExprLocal* local);
     Inference check(const ScopePtr& scope, AstExprGlobal* global);
     Inference checkIndexName(const ScopePtr& scope, const RefinementKey* key, AstExpr* indexee, const std::string& index, Location indexLocation);
@@ -295,11 +313,25 @@ private:
     Inference check(const ScopePtr& scope, AstExprFunction* func, std::optional<TypeId> expectedType, bool generalize);
     Inference check(const ScopePtr& scope, AstExprUnary* unary);
     Inference check(const ScopePtr& scope, AstExprBinary* binary, std::optional<TypeId> expectedType);
+    Inference checkAstExprBinary(
+        const ScopePtr& scope,
+        const Location& location,
+        AstExprBinary::Op op,
+        AstExpr* left,
+        AstExpr* right,
+        std::optional<TypeId> expectedType
+    );
     Inference check(const ScopePtr& scope, AstExprIfElse* ifElse, std::optional<TypeId> expectedType);
     Inference check(const ScopePtr& scope, AstExprTypeAssertion* typeAssert);
     Inference check(const ScopePtr& scope, AstExprInterpString* interpString);
     Inference check(const ScopePtr& scope, AstExprTable* expr, std::optional<TypeId> expectedType);
-    std::tuple<TypeId, TypeId, RefinementId> checkBinary(const ScopePtr& scope, AstExprBinary* binary, std::optional<TypeId> expectedType);
+    std::tuple<TypeId, TypeId, RefinementId> checkBinary(
+        const ScopePtr& scope,
+        AstExprBinary::Op op,
+        AstExpr* left,
+        AstExpr* right,
+        std::optional<TypeId> expectedType
+    );
 
     void visitLValue(const ScopePtr& scope, AstExpr* expr, TypeId rhsType);
     void visitLValue(const ScopePtr& scope, AstExprLocal* local, TypeId rhsType);
@@ -348,6 +380,11 @@ private:
      **/
     TypeId resolveType(const ScopePtr& scope, AstType* ty, bool inTypeArguments, bool replaceErrorWithFresh = false);
 
+    // resolveType() is recursive, but we only want to invoke
+    // inferGenericPolarities() once at the very end.  We thus isolate the
+    // recursive part of the algorithm to this internal helper.
+    TypeId resolveType_(const ScopePtr& scope, AstType* ty, bool inTypeArguments, bool replaceErrorWithFresh = false);
+
     /**
      * Resolves a type pack from its AST annotation.
      * @param scope the scope that the type annotation appears within.
@@ -357,6 +394,9 @@ private:
      **/
     TypePackId resolveTypePack(const ScopePtr& scope, AstTypePack* tp, bool inTypeArguments, bool replaceErrorWithFresh = false);
 
+    // Inner hepler for resolveTypePack
+    TypePackId resolveTypePack_(const ScopePtr& scope, AstTypePack* tp, bool inTypeArguments, bool replaceErrorWithFresh = false);
+
     /**
      * Resolves a type pack from its AST annotation.
      * @param scope the scope that the type annotation appears within.
@@ -378,7 +418,7 @@ private:
      **/
     std::vector<std::pair<Name, GenericTypeDefinition>> createGenerics(
         const ScopePtr& scope,
-        AstArray<AstGenericType> generics,
+        AstArray<AstGenericType*> generics,
         bool useCache = false,
         bool addTypes = true
     );
@@ -395,7 +435,7 @@ private:
      **/
     std::vector<std::pair<Name, GenericTypePackDefinition>> createGenericPacks(
         const ScopePtr& scope,
-        AstArray<AstGenericTypePack> packs,
+        AstArray<AstGenericTypePack*> generics,
         bool useCache = false,
         bool addTypes = true
     );
@@ -444,9 +484,4 @@ private:
     TypeId simplifyUnion(const ScopePtr& scope, Location location, TypeId left, TypeId right);
 };
 
-/** Borrow a vector of pointers from a vector of owning pointers to constraints.
- */
-std::vector<NotNull<Constraint>> borrowConstraints(const std::vector<ConstraintPtr>& constraints);
-
-
 } // namespace Luau

Analysis/include/Luau/ConstraintSet.h

@@ -0,0 +1,32 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#pragma once
+
+#include "Luau/Constraint.h"
+#include "Luau/DenseHash.h"
+#include "Luau/Error.h"
+
+#include <vector>
+
+namespace Luau
+{
+
+struct ConstraintSet
+{
+    NotNull<Scope> rootScope;
+
+    std::vector<ConstraintPtr> constraints;
+
+    // The set of all free types created during constraint generation
+    DenseHashSet<TypeId> freeTypes{nullptr};
+
+    // Map a function's signature scope back to its signature type.   Once we've
+    // dispatched all of the constraints pertaining to a particular free type,
+    // we use this mapping to generalize that free type.
+    DenseHashMap<Scope*, TypeId> scopeToFunction{nullptr};
+
+    // It is pretty uncommon for constraint generation to itself produce errors, but it can happen.
+    std::vector<TypeError> errors;
+};
+
+}

Analysis/include/Luau/ConstraintSolver.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include "Luau/Constraint.h"
+#include "Luau/ConstraintSet.h"
 #include "Luau/DataFlowGraph.h"
 #include "Luau/DenseHash.h"
 #include "Luau/EqSatSimplification.h"
@@ -59,6 +60,25 @@ struct HashInstantiationSignature
     size_t operator()(const InstantiationSignature& signature) const;
 };
 
+
+struct TablePropLookupResult
+{
+    // What types are we blocked on for determining this type?
+    std::vector<TypeId> blockedTypes;
+    // The type of the property (if we were able to determine it).
+    std::optional<TypeId> propType;
+    // Whether or not this is _definitely_ derived as the result of an indexer.
+    // We use this to determine whether or not code like:
+    //
+    //   t.lol = nil;
+    //
+    // ... is legal. If `t: { [string]: ~nil }` then this is legal as
+    // there's no guarantee on whether "lol" specifically exists.
+    // However, if `t: { lol: ~nil }`, then we cannot allow assignment as
+    // that would remove "lol" from the table entirely.
+    bool isIndex = false;
+};
+
 struct ConstraintSolver
 {
     NotNull<TypeArena> arena;
@@ -68,7 +88,9 @@ struct ConstraintSolver
     NotNull<Simplifier> simplifier;
     NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     // The entire set of constraints that the solver is trying to resolve.
+    ConstraintSet constraintSet;
     std::vector<NotNull<Constraint>> constraints;
+    NotNull<DenseHashMap<Scope*, TypeId>> scopeToFunction;
     NotNull<Scope> rootScope;
     ModuleName currentModuleName;
 
@@ -99,6 +121,9 @@ struct ConstraintSolver
     // A mapping from free types to the number of unresolved constraints that mention them.
     DenseHashMap<TypeId, size_t> unresolvedConstraints{{}};
 
+    std::unordered_map<NotNull<const Constraint>, DenseHashSet<TypeId>> maybeMutatedFreeTypes;
+    std::unordered_map<TypeId, DenseHashSet<const Constraint*>> mutatedFreeTypeToConstraint;
+
     // Irreducible/uninhabited type functions or type pack functions.
     DenseHashSet<const void*> uninhabitedTypeFunctions{{}};
 
@@ -117,12 +142,26 @@ struct ConstraintSolver
 
     DenseHashMap<TypeId, const Constraint*> typeFunctionsToFinalize{nullptr};
 
+    explicit ConstraintSolver(
+        NotNull<Normalizer> normalizer,
+        NotNull<Simplifier> simplifier,
+        NotNull<TypeFunctionRuntime> typeFunctionRuntime,
+        ModuleName moduleName,
+        NotNull<ModuleResolver> moduleResolver,
+        std::vector<RequireCycle> requireCycles,
+        DcrLogger* logger,
+        NotNull<const DataFlowGraph> dfg,
+        TypeCheckLimits limits,
+        ConstraintSet constraintSet
+    );
+
     explicit ConstraintSolver(
         NotNull<Normalizer> normalizer,
         NotNull<Simplifier> simplifier,
         NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<Scope> rootScope,
         std::vector<NotNull<Constraint>> constraints,
+        NotNull<DenseHashMap<Scope*, TypeId>> scopeToFunction,
         ModuleName moduleName,
         NotNull<ModuleResolver> moduleResolver,
         std::vector<RequireCycle> requireCycles,
@@ -147,9 +186,14 @@ struct ConstraintSolver
      **/
     void finalizeTypeFunctions();
 
-    bool isDone();
+    bool isDone() const;
 
 private:
+    /// A helper that does most of the setup work that is shared between the two constructors.
+    void initFreeTypeTracking();
+
+    void generalizeOneType(TypeId ty);
+
     /**
      * Bind a type variable to another type.
      *
@@ -182,6 +226,7 @@ public:
     bool tryDispatch(const NameConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const TypeAliasExpansionConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const FunctionCallConstraint& c, NotNull<const Constraint> constraint);
+    bool tryDispatch(const TableCheckConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const FunctionCheckConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const PrimitiveTypeConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const HasPropConstraint& c, NotNull<const Constraint> constraint);
@@ -211,7 +256,7 @@ public:
     // for a, ... in next_function, t, ... do
     bool tryDispatchIterableFunction(TypeId nextTy, TypeId tableTy, const IterableConstraint& c, NotNull<const Constraint> constraint);
 
-    std::pair<std::vector<TypeId>, std::optional<TypeId>> lookupTableProp(
+    TablePropLookupResult lookupTableProp(
         NotNull<const Constraint> constraint,
         TypeId subjectType,
         const std::string& propName,
@@ -219,7 +264,8 @@ public:
         bool inConditional = false,
         bool suppressSimplification = false
     );
-    std::pair<std::vector<TypeId>, std::optional<TypeId>> lookupTableProp(
+
+    TablePropLookupResult lookupTableProp(
         NotNull<const Constraint> constraint,
         TypeId subjectType,
         const std::string& propName,
@@ -278,10 +324,10 @@ public:
     // FIXME: This use of a boolean for the return result is an appalling
     // interface.
     bool blockOnPendingTypes(TypeId target, NotNull<const Constraint> constraint);
-    bool blockOnPendingTypes(TypePackId target, NotNull<const Constraint> constraint);
+    bool blockOnPendingTypes(TypePackId targetPack, NotNull<const Constraint> constraint);
 
     void unblock(NotNull<const Constraint> progressed);
-    void unblock(TypeId progressed, Location location);
+    void unblock(TypeId ty, Location location);
     void unblock(TypePackId progressed, Location location);
     void unblock(const std::vector<TypeId>& types, Location location);
     void unblock(const std::vector<TypePackId>& packs, Location location);
@@ -316,7 +362,7 @@ public:
      * @param location the location where the require is taking place; used for
      * error locations.
      **/
-    TypeId resolveModule(const ModuleInfo& module, const Location& location);
+    TypeId resolveModule(const ModuleInfo& info, const Location& location);
 
     void reportError(TypeErrorData&& data, const Location& location);
     void reportError(TypeError e);
@@ -337,7 +383,7 @@ public:
      * @returns a non-free type that generalizes the argument, or `std::nullopt` if one
      * does not exist
      */
-    std::optional<TypeId> generalizeFreeType(NotNull<Scope> scope, TypeId type, bool avoidSealingTables = false);
+    std::optional<TypeId> generalizeFreeType(NotNull<Scope> scope, TypeId type);
 
     /**
      * Checks the existing set of constraints to see if there exist any that contain
@@ -400,8 +446,14 @@ public:
     void throwUserCancelError() const;
 
     ToStringOptions opts;
+
+    void fillInDiscriminantTypes(NotNull<const Constraint> constraint, const std::vector<std::optional<TypeId>>& discriminantTypes);
 };
 
+/** Borrow a vector of pointers from a vector of owning pointers to constraints.
+ */
+std::vector<NotNull<Constraint>> borrowConstraints(const std::vector<ConstraintPtr>& constraints);
+
 void dump(NotNull<Scope> rootScope, struct ToStringOptions& opts);
 
 } // namespace Luau

Analysis/include/Luau/DataFlowGraph.h

@@ -6,6 +6,7 @@
 #include "Luau/ControlFlow.h"
 #include "Luau/DenseHash.h"
 #include "Luau/Def.h"
+#include "Luau/NotNull.h"
 #include "Luau/Symbol.h"
 #include "Luau/TypedAllocator.h"
 
@@ -37,8 +38,6 @@ struct DataFlowGraph
     DefId getDef(const AstExpr* expr) const;
     // Look up the definition optionally, knowing it may not be present.
     std::optional<DefId> getDefOptional(const AstExpr* expr) const;
-    // Look up for the rvalue def for a compound assignment.
-    std::optional<DefId> getRValueDefForCompoundAssign(const AstExpr* expr) const;
 
     DefId getDef(const AstLocal* local) const;
 
@@ -48,13 +47,13 @@ struct DataFlowGraph
     const RefinementKey* getRefinementKey(const AstExpr* expr) const;
 
 private:
-    DataFlowGraph() = default;
+    DataFlowGraph(NotNull<DefArena> defArena, NotNull<RefinementKeyArena> keyArena);
 
     DataFlowGraph(const DataFlowGraph&) = delete;
     DataFlowGraph& operator=(const DataFlowGraph&) = delete;
 
-    DefArena defArena;
+    NotNull<DefArena> defArena;
-    RefinementKeyArena keyArena;
+    NotNull<RefinementKeyArena> keyArena;
 
     DenseHashMap<const AstExpr*, const Def*> astDefs{nullptr};
 
@@ -65,10 +64,6 @@ private:
     // All keys in this maps are really only statements that ambiently declares a symbol.
     DenseHashMap<const AstStat*, const Def*> declaredDefs{nullptr};
 
-    // Compound assignments are in a weird situation where the local being assigned to is also being used at its
-    // previous type implicitly in an rvalue position. This map provides the previous binding.
-    DenseHashMap<const AstExpr*, const Def*> compoundAssignDefs{nullptr};
-
     DenseHashMap<const AstExpr*, const RefinementKey*> astRefinementKeys{nullptr};
     friend struct DataFlowGraphBuilder;
 };
@@ -84,7 +79,6 @@ struct DfgScope
 
     DfgScope* parent;
     ScopeType scopeType;
-    Location location;
 
     using Bindings = DenseHashMap<Symbol, const Def*>;
     using Props = DenseHashMap<const Def*, std::unordered_map<std::string, const Def*>>;
@@ -111,49 +105,22 @@ using ScopeStack = std::vector<DfgScope*>;
 
 struct DataFlowGraphBuilder
 {
-    static DataFlowGraph build(AstStatBlock* root, NotNull<struct InternalErrorReporter> handle);
+    static DataFlowGraph build(
-
-    /**
-     * This method is identical to the build method above, but returns a pair of dfg, scopes as the data flow graph
-     * here is intended to live on the module between runs of typechecking. Before, the DFG only needed to live as
-     * long as the typecheck, but in a world with incremental typechecking, we need the information on the dfg to incrementally
-     * typecheck small fragments of code.
-     * @param block - pointer to the ast to build the dfg for
-     * @param handle - for raising internal errors while building the dfg
-     */
-    static std::pair<std::shared_ptr<DataFlowGraph>, std::vector<std::unique_ptr<DfgScope>>> buildShared(
         AstStatBlock* block,
-        NotNull<InternalErrorReporter> handle
+        NotNull<DefArena> defArena,
-    );
+        NotNull<RefinementKeyArena> keyArena,
-
+        NotNull<struct InternalErrorReporter> handle
-    /**
-     * Takes a stale graph along with a list of scopes, a small fragment of the ast, and a cursor position
-     * and constructs the DataFlowGraph for just that fragment. This method will fabricate defs in the final
-     * DFG for things that have been referenced and exist in the stale dfg.
-     * For example, the fragment local z = x + y will populate defs for x and y from the stale graph.
-     * @param staleGraph - the old DFG
-     * @param scopes - the old DfgScopes in the graph
-     * @param fragment - the Ast Fragment to re-build the root for
-     * @param cursorPos - the current location of the cursor - used to determine which scope we are currently in
-     * @param handle - for internal compiler errors
-     */
-    static DataFlowGraph updateGraph(
-        const DataFlowGraph& staleGraph,
-        const std::vector<std::unique_ptr<DfgScope>>& scopes,
-        AstStatBlock* fragment,
-        const Position& cursorPos,
-        NotNull<InternalErrorReporter> handle
     );
 
 private:
-    DataFlowGraphBuilder() = default;
+    DataFlowGraphBuilder(NotNull<DefArena> defArena, NotNull<RefinementKeyArena> keyArena);
 
     DataFlowGraphBuilder(const DataFlowGraphBuilder&) = delete;
     DataFlowGraphBuilder& operator=(const DataFlowGraphBuilder&) = delete;
 
     DataFlowGraph graph;
-    NotNull<DefArena> defArena{&graph.defArena};
+    NotNull<DefArena> defArena;
-    NotNull<RefinementKeyArena> keyArena{&graph.keyArena};
+    NotNull<RefinementKeyArena> keyArena;
 
     struct InternalErrorReporter* handle = nullptr;
 
@@ -162,8 +129,8 @@ private:
 
     /// A stack of scopes used by the visitor to see where we are.
     ScopeStack scopeStack;
-
+    NotNull<DfgScope> currentScope();
-    DfgScope* currentScope();
+    DfgScope* currentScope_DEPRECATED();
 
     struct FunctionCapture
     {
@@ -175,14 +142,14 @@ private:
     DenseHashMap<Symbol, FunctionCapture> captures{Symbol{}};
     void resolveCaptures();
 
-    DfgScope* makeChildScope(Location loc, DfgScope::ScopeType scopeType = DfgScope::Linear);
+    DfgScope* makeChildScope(DfgScope::ScopeType scopeType = DfgScope::Linear);
 
     void join(DfgScope* p, DfgScope* a, DfgScope* b);
     void joinBindings(DfgScope* p, const DfgScope& a, const DfgScope& b);
     void joinProps(DfgScope* p, const DfgScope& a, const DfgScope& b);
 
-    DefId lookup(Symbol symbol);
+    DefId lookup(Symbol symbol, Location location);
-    DefId lookup(DefId def, const std::string& key);
+    DefId lookup(DefId def, const std::string& key, Location location);
 
     ControlFlow visit(AstStatBlock* b);
     ControlFlow visitBlockWithoutChildScope(AstStatBlock* b);
@@ -206,7 +173,7 @@ private:
     ControlFlow visit(AstStatTypeFunction* f);
     ControlFlow visit(AstStatDeclareGlobal* d);
     ControlFlow visit(AstStatDeclareFunction* d);
-    ControlFlow visit(AstStatDeclareClass* d);
+    ControlFlow visit(AstStatDeclareExternType* d);
     ControlFlow visit(AstStatError* error);
 
     DataFlowResult visitExpr(AstExpr* e);
@@ -248,8 +215,8 @@ private:
 
     void visitTypeList(AstTypeList l);
 
-    void visitGenerics(AstArray<AstGenericType> g);
+    void visitGenerics(AstArray<AstGenericType*> g);
-    void visitGenericPacks(AstArray<AstGenericTypePack> g);
+    void visitGenericPacks(AstArray<AstGenericTypePack*> g);
 };
 
 } // namespace Luau

Analysis/include/Luau/Def.h

@@ -4,7 +4,8 @@
 #include "Luau/NotNull.h"
 #include "Luau/TypedAllocator.h"
 #include "Luau/Variant.h"
-
+#include "Luau/Location.h"
+#include "Luau/Symbol.h"
 #include <string>
 #include <optional>
 
@@ -13,6 +14,7 @@ namespace Luau
 
 struct Def;
 using DefId = NotNull<const Def>;
+struct AstLocal;
 
 /**
  * A cell is a "single-object" value.
@@ -64,6 +66,8 @@ struct Def
     using V = Variant<struct Cell, struct Phi>;
 
     V v;
+    Symbol name;
+    Location location;
 };
 
 template<typename T>
@@ -79,7 +83,7 @@ struct DefArena
 {
     TypedAllocator<Def> allocator;
 
-    DefId freshCell(bool subscripted = false);
+    DefId freshCell(Symbol sym, Location location, bool subscripted = false);
     DefId phi(DefId a, DefId b);
     DefId phi(const std::vector<DefId>& defs);
 };

Analysis/include/Luau/EqSatSimplificationImpl.h

@@ -53,7 +53,7 @@ LUAU_EQSAT_NODE_SET(Intersection);
 
 LUAU_EQSAT_NODE_ARRAY(Negation, 1);
 
-LUAU_EQSAT_NODE_ATOM_WITH_VECTOR(TTypeFun, const TypeFunction*);
+LUAU_EQSAT_NODE_ATOM_WITH_VECTOR(TTypeFun, std::shared_ptr<const TypeFunctionInstanceType>);
 
 LUAU_EQSAT_UNIT(TNoRefine);
 LUAU_EQSAT_UNIT(Invalid);
@@ -105,6 +105,9 @@ private:
     std::vector<Id> storage;
 };
 
+template<typename L>
+using Node = EqSat::Node<L>;
+
 using EType = EqSat::Language<
     TNil,
     TBoolean,
@@ -146,7 +149,7 @@ using EType = EqSat::Language<
 struct StringCache
 {
     Allocator allocator;
-    DenseHashMap<size_t, StringId> strings{{}};
+    DenseHashMap<std::string_view, StringId> strings{{}};
     std::vector<std::string_view> views;
 
     StringId add(std::string_view s);
@@ -171,6 +174,9 @@ struct Subst
     Id eclass;
     Id newClass;
 
+    // The node into eclass which is boring, if any
+    std::optional<size_t> boringIndex;
+
     std::string desc;
 
     Subst(Id eclass, Id newClass, std::string desc = "");
@@ -211,6 +217,7 @@ struct Simplifier
     void subst(Id from, Id to);
     void subst(Id from, Id to, const std::string& ruleName);
     void subst(Id from, Id to, const std::string& ruleName, const std::unordered_map<Id, size_t>& forceNodes);
+    void subst(Id from, size_t boringIndex, Id to, const std::string& ruleName, const std::unordered_map<Id, size_t>& forceNodes);
 
     void unionClasses(std::vector<Id>& hereParts, Id there);
 
@@ -218,6 +225,7 @@ struct Simplifier
     void simplifyUnion(Id id);
     void uninhabitedIntersection(Id id);
     void intersectWithNegatedClass(Id id);
+    void intersectWithNegatedAtom(Id id);
     void intersectWithNoRefine(Id id);
     void cyclicIntersectionOfUnion(Id id);
     void cyclicUnionOfIntersection(Id id);
@@ -228,6 +236,7 @@ struct Simplifier
     void unneededTableModification(Id id);
     void builtinTypeFunctions(Id id);
     void iffyTypeFunctions(Id id);
+    void strictMetamethods(Id id);
 };
 
 template<typename Tag>
@@ -293,13 +302,13 @@ QueryIterator<Tag>::QueryIterator(EGraph* egraph_, Id eclass)
 
     for (const auto& enode : ecl.nodes)
     {
-        if (enode.index() < idx)
+        if (enode.node.index() < idx)
             ++index;
         else
             break;
     }
 
-    if (index >= ecl.nodes.size() || ecl.nodes[index].index() != idx)
+    if (index >= ecl.nodes.size() || ecl.nodes[index].node.index() != idx)
     {
         egraph = nullptr;
         index = 0;
@@ -329,7 +338,7 @@ std::pair<const Tag*, size_t> QueryIterator<Tag>::operator*() const
     EGraph::EClassT& ecl = (*egraph)[eclass];
 
     LUAU_ASSERT(index < ecl.nodes.size());
-    auto& enode = ecl.nodes[index];
+    auto& enode = ecl.nodes[index].node;
     Tag* result = enode.template get<Tag>();
     LUAU_ASSERT(result);
     return {result, index};
@@ -341,12 +350,16 @@ QueryIterator<Tag>& QueryIterator<Tag>::operator++()
 {
     const auto& ecl = (*egraph)[eclass];
 
-    ++index;
+    do
-    if (index >= ecl.nodes.size() || ecl.nodes[index].index() != EType::VariantTy::getTypeId<Tag>())
     {
-        egraph = nullptr;
+        ++index;
-        index = 0;
+        if (index >= ecl.nodes.size() || ecl.nodes[index].node.index() != EType::VariantTy::getTypeId<Tag>())
-    }
+        {
+            egraph = nullptr;
+            index = 0;
+            break;
+        }
+    } while (ecl.nodes[index].boring);
 
     return *this;
 }

Analysis/include/Luau/Error.h

@@ -332,11 +332,11 @@ struct TypePackMismatch
     bool operator==(const TypePackMismatch& rhs) const;
 };
 
-struct DynamicPropertyLookupOnClassesUnsafe
+struct DynamicPropertyLookupOnExternTypesUnsafe
 {
     TypeId ty;
 
-    bool operator==(const DynamicPropertyLookupOnClassesUnsafe& rhs) const;
+    bool operator==(const DynamicPropertyLookupOnExternTypesUnsafe& rhs) const;
 };
 
 struct UninhabitedTypeFunction
@@ -455,6 +455,13 @@ struct UserDefinedTypeFunctionError
     bool operator==(const UserDefinedTypeFunctionError& rhs) const;
 };
 
+struct ReservedIdentifier
+{
+    std::string name;
+
+    bool operator==(const ReservedIdentifier& rhs) const;
+};
+
 using TypeErrorData = Variant<
     TypeMismatch,
     UnknownSymbol,
@@ -492,7 +499,7 @@ using TypeErrorData = Variant<
     TypesAreUnrelated,
     NormalizationTooComplex,
     TypePackMismatch,
-    DynamicPropertyLookupOnClassesUnsafe,
+    DynamicPropertyLookupOnExternTypesUnsafe,
     UninhabitedTypeFunction,
     UninhabitedTypePackFunction,
     WhereClauseNeeded,
@@ -504,7 +511,8 @@ using TypeErrorData = Variant<
     UnexpectedTypeInSubtyping,
     UnexpectedTypePackInSubtyping,
     ExplicitFunctionAnnotationRecommended,
-    UserDefinedTypeFunctionError>;
+    UserDefinedTypeFunctionError,
+    ReservedIdentifier>;
 
 struct TypeErrorSummary
 {

Analysis/include/Luau/FileResolver.h

@@ -1,8 +1,9 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
-#include <string>
+#include <memory>
 #include <optional>
+#include <string>
 #include <vector>
 
 namespace Luau
@@ -19,7 +20,7 @@ struct SourceCode
         None,
         Module,
         Script,
-        Local
+        Local_DEPRECATED
     };
 
     std::string source;
@@ -32,15 +33,71 @@ struct ModuleInfo
     bool optional = false;
 };
 
+struct RequireAlias
+{
+    std::string alias; // Unprefixed alias name (no leading `@`).
+    std::vector<std::string> tags = {};
+};
+
+struct RequireNode
+{
+    virtual ~RequireNode() {}
+
+    // Get the path component representing this node.
+    virtual std::string getPathComponent() const = 0;
+
+    // Get the displayed user-facing label for this node, defaults to getPathComponent()
+    virtual std::string getLabel() const
+    {
+        return getPathComponent();
+    }
+
+    // Get tags to attach to this node's RequireSuggestion (defaults to none).
+    virtual std::vector<std::string> getTags() const
+    {
+        return {};
+    }
+
+    // TODO: resolvePathToNode() can ultimately be replaced with a call into
+    // require-by-string's path resolution algorithm. This will first require
+    // generalizing that algorithm to work with a virtual file system.
+    virtual std::unique_ptr<RequireNode> resolvePathToNode(const std::string& path) const = 0;
+
+    // Get children of this node, if any (if this node represents a directory).
+    virtual std::vector<std::unique_ptr<RequireNode>> getChildren() const = 0;
+
+    // A list of the aliases available to this node.
+    virtual std::vector<RequireAlias> getAvailableAliases() const = 0;
+};
+
 struct RequireSuggestion
 {
     std::string label;
     std::string fullPath;
+    std::vector<std::string> tags;
 };
 using RequireSuggestions = std::vector<RequireSuggestion>;
 
+struct RequireSuggester
+{
+    virtual ~RequireSuggester() {}
+    std::optional<RequireSuggestions> getRequireSuggestions(const ModuleName& requirer, const std::optional<std::string>& pathString) const;
+
+protected:
+    virtual std::unique_ptr<RequireNode> getNode(const ModuleName& name) const = 0;
+
+private:
+    std::optional<RequireSuggestions> getRequireSuggestionsImpl(const ModuleName& requirer, const std::optional<std::string>& path) const;
+};
+
 struct FileResolver
 {
+    FileResolver() = default;
+    FileResolver(std::shared_ptr<RequireSuggester> requireSuggester)
+        : requireSuggester(std::move(requireSuggester))
+    {
+    }
+
     virtual ~FileResolver() {}
 
     virtual std::optional<SourceCode> readSource(const ModuleName& name) = 0;
@@ -60,10 +117,9 @@ struct FileResolver
         return std::nullopt;
     }
 
-    virtual std::optional<RequireSuggestions> getRequireSuggestions(const ModuleName& requirer, const std::optional<std::string>& pathString) const
+    std::optional<RequireSuggestions> getRequireSuggestions(const ModuleName& requirer, const std::optional<std::string>& pathString) const;
-    {
+
-        return std::nullopt;
+    std::shared_ptr<RequireSuggester> requireSuggester;
-    }
 };
 
 struct NullFileResolver : FileResolver

Analysis/include/Luau/FragmentAutocomplete.h

@@ -15,12 +15,42 @@ namespace Luau
 {
 struct FrontendOptions;
 
+enum class FragmentAutocompleteWaypoint
+{
+    ParseFragmentEnd,
+    CloneModuleStart,
+    CloneModuleEnd,
+    DfgBuildEnd,
+    CloneAndSquashScopeStart,
+    CloneAndSquashScopeEnd,
+    ConstraintSolverStart,
+    ConstraintSolverEnd,
+    TypecheckFragmentEnd,
+    AutocompleteEnd,
+    COUNT,
+};
+
+class IFragmentAutocompleteReporter
+{
+public:
+    virtual void reportWaypoint(FragmentAutocompleteWaypoint) = 0;
+    virtual void reportFragmentString(std::string_view) = 0;
+};
+
+enum class FragmentTypeCheckStatus
+{
+    SkipAutocomplete,
+    Success,
+};
+
 struct FragmentAutocompleteAncestryResult
 {
     DenseHashMap<AstName, AstLocal*> localMap{AstName()};
     std::vector<AstLocal*> localStack;
     std::vector<AstNode*> ancestry;
     AstStat* nearestStatement = nullptr;
+    AstStatBlock* parentBlock = nullptr;
+    Location fragmentSelectionRegion;
 };
 
 struct FragmentParseResult
@@ -29,7 +59,9 @@ struct FragmentParseResult
     AstStatBlock* root = nullptr;
     std::vector<AstNode*> ancestry;
     AstStat* nearestStatement = nullptr;
+    std::vector<Comment> commentLocations;
     std::unique_ptr<Allocator> alloc = std::make_unique<Allocator>();
+    Position scopePos{0, 0};
 };
 
 struct FragmentTypeCheckResult
@@ -43,20 +75,48 @@ struct FragmentAutocompleteResult
 {
     ModulePtr incrementalModule;
     Scope* freshScope;
-    TypeArena arenaForAutocomplete;
+    TypeArena arenaForAutocomplete_DEPRECATED;
     AutocompleteResult acResults;
 };
 
-FragmentAutocompleteAncestryResult findAncestryForFragmentParse(AstStatBlock* root, const Position& cursorPos);
+struct FragmentRegion
+{
+    Location fragmentLocation;
+    AstStat* nearestStatement = nullptr; // used for tests
+    AstStatBlock* parentBlock = nullptr; // used for scope detection
+};
 
-FragmentParseResult parseFragment(const SourceModule& srcModule, std::string_view src, const Position& cursorPos);
+std::optional<Position> blockDiffStart(AstStatBlock* blockOld, AstStatBlock* blockNew, AstStat* nearestStatementNewAst);
+FragmentRegion getFragmentRegion(AstStatBlock* root, const Position& cursorPosition);
+FragmentAutocompleteAncestryResult findAncestryForFragmentParse(AstStatBlock* stale, const Position& cursorPos, AstStatBlock* lastGoodParse);
+FragmentAutocompleteAncestryResult findAncestryForFragmentParse_DEPRECATED(AstStatBlock* root, const Position& cursorPos);
 
-FragmentTypeCheckResult typecheckFragment(
+std::optional<FragmentParseResult> parseFragment_DEPRECATED(
+    AstStatBlock* root,
+    AstNameTable* names,
+    std::string_view src,
+    const Position& cursorPos,
+    std::optional<Position> fragmentEndPosition
+);
+
+std::optional<FragmentParseResult> parseFragment(
+    AstStatBlock* stale,
+    AstStatBlock* mostRecentParse,
+    AstNameTable* names,
+    std::string_view src,
+    const Position& cursorPos,
+    std::optional<Position> fragmentEndPosition
+);
+
+std::pair<FragmentTypeCheckStatus, FragmentTypeCheckResult> typecheckFragment(
     Frontend& frontend,
     const ModuleName& moduleName,
     const Position& cursorPos,
     std::optional<FrontendOptions> opts,
-    std::string_view src
+    std::string_view src,
+    std::optional<Position> fragmentEndPosition,
+    AstStatBlock* recentParse = nullptr,
+    IFragmentAutocompleteReporter* reporter = nullptr
 );
 
 FragmentAutocompleteResult fragmentAutocomplete(
@@ -65,8 +125,72 @@ FragmentAutocompleteResult fragmentAutocomplete(
     const ModuleName& moduleName,
     Position cursorPosition,
     std::optional<FrontendOptions> opts,
-    StringCompletionCallback callback
+    StringCompletionCallback callback,
+    std::optional<Position> fragmentEndPosition = std::nullopt,
+    AstStatBlock* recentParse = nullptr,
+    IFragmentAutocompleteReporter* reporter = nullptr
 );
 
+enum class FragmentAutocompleteStatus
+{
+    Success,
+    FragmentTypeCheckFail,
+    InternalIce
+};
+
+struct FragmentAutocompleteStatusResult
+{
+    FragmentAutocompleteStatus status;
+    std::optional<FragmentAutocompleteResult> result;
+};
+
+struct FragmentContext
+{
+    std::string_view newSrc;
+    const ParseResult& freshParse;
+    std::optional<FrontendOptions> opts;
+    std::optional<Position> DEPRECATED_fragmentEndPosition;
+    IFragmentAutocompleteReporter* reporter = nullptr;
+};
+
+/**
+ * @brief Attempts to compute autocomplete suggestions from the fragment context.
+ *
+ * This function computes autocomplete suggestions using outdated frontend typechecking data
+ * by patching the fragment context of the new script source content.
+ *
+ * @param frontend The Luau Frontend data structure, which may contain outdated typechecking data.
+ *
+ * @param moduleName The name of the target module, specifying which script the caller wants to request autocomplete for.
+ *
+ * @param cursorPosition The position in the script where the caller wants to trigger autocomplete.
+ *
+ * @param context The fragment context that this API will use to patch the outdated typechecking data.
+ *
+ * @param stringCompletionCB A callback function that provides autocomplete suggestions for string contexts.
+ *
+ * @return
+ * The status indicating whether `fragmentAutocomplete` ran successfully or failed, along with the reason for failure.
+ * Also includes autocomplete suggestions if the status is successful.
+ *
+ * @usage
+ * FragmentAutocompleteStatusResult acStatusResult;
+ * if (shouldFragmentAC)
+ *     acStatusResult = Luau::tryFragmentAutocomplete(...);
+ *
+ * if (acStatusResult.status != Successful)
+ * {
+ *     frontend.check(moduleName, options);
+ *     acStatusResult.acResult = Luau::autocomplete(...);
+ * }
+ * return convertResultWithContext(acStatusResult.acResult);
+ */
+FragmentAutocompleteStatusResult tryFragmentAutocomplete(
+    Frontend& frontend,
+    const ModuleName& moduleName,
+    Position cursorPosition,
+    FragmentContext context,
+    StringCompletionCallback stringCompletionCB
+);
 
 } // namespace Luau

Analysis/include/Luau/Frontend.h

@@ -7,9 +7,9 @@
 #include "Luau/ModuleResolver.h"
 #include "Luau/RequireTracer.h"
 #include "Luau/Scope.h"
+#include "Luau/Set.h"
 #include "Luau/TypeCheckLimits.h"
 #include "Luau/Variant.h"
-#include "Luau/AnyTypeSummary.h"
 
 #include <mutex>
 #include <string>
@@ -31,8 +31,8 @@ struct ModuleResolver;
 struct ParseResult;
 struct HotComment;
 struct BuildQueueItem;
+struct BuildQueueWorkState;
 struct FrontendCancellationToken;
-struct AnyTypeSummary;
 
 struct LoadDefinitionFileResult
 {
@@ -56,13 +56,32 @@ struct SourceNode
         return forAutocomplete ? dirtyModuleForAutocomplete : dirtyModule;
     }
 
+    bool hasInvalidModuleDependency(bool forAutocomplete) const
+    {
+        return forAutocomplete ? invalidModuleDependencyForAutocomplete : invalidModuleDependency;
+    }
+
+    void setInvalidModuleDependency(bool value, bool forAutocomplete)
+    {
+        if (forAutocomplete)
+            invalidModuleDependencyForAutocomplete = value;
+        else
+            invalidModuleDependency = value;
+    }
+
     ModuleName name;
     std::string humanReadableName;
     DenseHashSet<ModuleName> requireSet{{}};
     std::vector<std::pair<ModuleName, Location>> requireLocations;
+    Set<ModuleName> dependents{{}};
+
     bool dirtySourceModule = true;
     bool dirtyModule = true;
     bool dirtyModuleForAutocomplete = true;
+
+    bool invalidModuleDependency = true;
+    bool invalidModuleDependencyForAutocomplete = true;
+
     double autocompleteLimitsMult = 1.0;
 };
 
@@ -117,7 +136,7 @@ struct FrontendModuleResolver : ModuleResolver
     std::optional<ModuleInfo> resolveModuleInfo(const ModuleName& currentModuleName, const AstExpr& pathExpr) override;
     std::string getHumanReadableModuleName(const ModuleName& moduleName) const override;
 
-    void setModule(const ModuleName& moduleName, ModulePtr module);
+    bool setModule(const ModuleName& moduleName, ModulePtr module);
     void clearModules();
 
 private:
@@ -151,9 +170,13 @@ struct Frontend
     // Parse and typecheck module graph
     CheckResult check(const ModuleName& name, std::optional<FrontendOptions> optionOverride = {}); // new shininess
 
+    bool allModuleDependenciesValid(const ModuleName& name, bool forAutocomplete = false) const;
+
     bool isDirty(const ModuleName& name, bool forAutocomplete = false) const;
     void markDirty(const ModuleName& name, std::vector<ModuleName>* markedDirty = nullptr);
 
+    void traverseDependents(const ModuleName& name, std::function<bool(SourceNode&)> processSubtree);
+
     /** Borrow a pointer into the SourceModule cache.
      *
      * Returns nullptr if we don't have it.  This could mean that the script
@@ -194,6 +217,7 @@ struct Frontend
     );
 
     std::optional<CheckResult> getCheckResult(const ModuleName& name, bool accumulateNested, bool forAutocomplete = false);
+    std::vector<ModuleName> getRequiredScripts(const ModuleName& name);
 
 private:
     ModulePtr check(
@@ -226,6 +250,9 @@ private:
     void checkBuildQueueItem(BuildQueueItem& item);
     void checkBuildQueueItems(std::vector<BuildQueueItem>& items);
     void recordItemResult(const BuildQueueItem& item);
+    void performQueueItemTask(std::shared_ptr<BuildQueueWorkState> state, size_t itemPos);
+    void sendQueueItemTask(std::shared_ptr<BuildQueueWorkState> state, size_t itemPos);
+    void sendQueueCycleItemTask(std::shared_ptr<BuildQueueWorkState> state);
 
     static LintResult classifyLints(const std::vector<LintWarning>& warnings, const Config& config);
 
@@ -271,6 +298,7 @@ ModulePtr check(
     NotNull<ModuleResolver> moduleResolver,
     NotNull<FileResolver> fileResolver,
     const ScopePtr& globalScope,
+    const ScopePtr& typeFunctionScope,
     std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope,
     FrontendOptions options,
     TypeCheckLimits limits
@@ -285,6 +313,7 @@ ModulePtr check(
     NotNull<ModuleResolver> moduleResolver,
     NotNull<FileResolver> fileResolver,
     const ScopePtr& globalScope,
+    const ScopePtr& typeFunctionScope,
     std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope,
     FrontendOptions options,
     TypeCheckLimits limits,

Analysis/include/Luau/Generalization.h

@@ -8,12 +8,75 @@
 namespace Luau
 {
 
+template<typename TID>
+struct GeneralizationParams
+{
+    bool foundOutsideFunctions = false;
+    size_t useCount = 0;
+    Polarity polarity = Polarity::None;
+};
+
+template<typename TID>
+struct GeneralizationResult
+{
+    std::optional<TID> result;
+
+    // True if the provided type was replaced with a generic.
+    bool wasReplacedByGeneric = false;
+
+    bool resourceLimitsExceeded = false;
+
+    explicit operator bool() const
+    {
+        return bool(result);
+    }
+};
+
+// Replace a single free type by its bounds according to the polarity provided.
+GeneralizationResult<TypeId> generalizeType(
+    NotNull<TypeArena> arena,
+    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Scope> scope,
+    TypeId freeTy,
+    const GeneralizationParams<TypeId>& params
+);
+
+// Generalize one type pack
+GeneralizationResult<TypePackId> generalizeTypePack(
+    NotNull<TypeArena> arena,
+    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Scope> scope,
+    TypePackId tp,
+    const GeneralizationParams<TypePackId>& params
+);
+
+void sealTable(NotNull<Scope> scope, TypeId ty);
+
+/** Attempt to generalize a type.
+ *
+ * If generalizationTarget is set, then only that type will be replaced by its
+ * bounds.  The way this is intended to be used is that ty is some function that
+ * is not fully generalized, and generalizationTarget is a type within its
+ * signature.  There should be no further constraints that could affect the
+ * bounds of generalizationTarget.
+ *
+ * Returns nullopt if generalization failed due to resources limits.
+ */
 std::optional<TypeId> generalize(
     NotNull<TypeArena> arena,
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<Scope> scope,
-    NotNull<DenseHashSet<TypeId>> bakedTypes,
+    NotNull<DenseHashSet<TypeId>> cachedTypes,
     TypeId ty,
-    /* avoid sealing tables*/ bool avoidSealingTables = false
+    std::optional<TypeId> generalizationTarget = {}
 );
-}
+
+void pruneUnnecessaryGenerics(
+    NotNull<TypeArena> arena,
+    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Scope> scope,
+    NotNull<DenseHashSet<TypeId>> cachedTypes,
+    TypeId ty
+);
+
+} // namespace Luau

Analysis/include/Luau/GlobalTypes.h

@@ -19,7 +19,9 @@ struct GlobalTypes
 
     TypeArena globalTypes;
     SourceModule globalNames; // names for symbols entered into globalScope
+
     ScopePtr globalScope;     // shared by all modules
+    ScopePtr globalTypeFunctionScope; // shared by all modules
 };
 
 } // namespace Luau

Analysis/include/Luau/InferPolarity.h

@@ -0,0 +1,16 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/NotNull.h"
+#include "Luau/TypeFwd.h"
+
+namespace Luau
+{
+
+struct Scope;
+struct TypeArena;
+
+void inferGenericPolarities(NotNull<TypeArena> arena, NotNull<Scope> scope, TypeId ty);
+void inferGenericPolarities(NotNull<TypeArena> arena, NotNull<Scope> scope, TypePackId tp);
+
+} // namespace Luau

Analysis/include/Luau/InsertionOrderedMap.h

@@ -67,6 +67,19 @@ public:
             return &pairs.at(it->second).second;
     }
 
+    V& operator[](const K& k)
+    {
+        auto it = indices.find(k);
+        if (it == indices.end())
+        {
+            pairs.push_back(std::make_pair(k, V()));
+            indices[k] = pairs.size() - 1;
+            return pairs.back().second;
+        }
+        else
+            return pairs.at(it->second).second;
+    }
+
     const_iterator begin() const
     {
         return pairs.begin();

Analysis/include/Luau/Instantiation.h

@@ -133,9 +133,9 @@ struct GenericTypeFinder : TypeOnceVisitor
         return false;
     }
 
-    bool visit(TypeId ty, const Luau::ClassType&) override
+    bool visit(TypeId ty, const Luau::ExternType&) override
     {
-        // During function instantiation, classes are not traversed even if they have generics
+        // During function instantiation, extern types are not traversed even if they have generics
         return false;
     }
 };

Analysis/include/Luau/Instantiation2.h

@@ -53,7 +53,7 @@ struct Replacer : Substitution
 };
 
 // A substitution which replaces generic functions by monomorphic functions
-struct Instantiation2 : Substitution
+struct Instantiation2 final : Substitution
 {
     // Mapping from generic types to free types to be used in instantiation.
     DenseHashMap<TypeId, TypeId> genericSubstitutions{nullptr};

Analysis/include/Luau/Module.h

@@ -8,7 +8,6 @@
 #include "Luau/ParseResult.h"
 #include "Luau/Scope.h"
 #include "Luau/TypeArena.h"
-#include "Luau/AnyTypeSummary.h"
 #include "Luau/DataFlowGraph.h"
 
 #include <memory>
@@ -19,8 +18,13 @@
 namespace Luau
 {
 
+using LogLuauProc = void (*)(std::string_view, std::string_view);
+extern LogLuauProc logLuau;
+
+void setLogLuau(LogLuauProc ll);
+void resetLogLuauProc();
+
 struct Module;
-struct AnyTypeSummary;
 
 using ScopePtr = std::shared_ptr<struct Scope>;
 using ModulePtr = std::shared_ptr<Module>;
@@ -55,6 +59,7 @@ struct SourceModule
     }
 };
 
+bool isWithinComment(const std::vector<Comment>& commentLocations, Position pos);
 bool isWithinComment(const SourceModule& sourceModule, Position pos);
 bool isWithinComment(const ParseResult& result, Position pos);
 
@@ -68,19 +73,19 @@ struct Module
 {
     ~Module();
 
+    // TODO: Clip this when we clip FFlagLuauSolverV2
+    bool checkedInNewSolver = false;
+
     ModuleName name;
     std::string humanReadableName;
 
     TypeArena interfaceTypes;
     TypeArena internalTypes;
 
-    // Summary of Ast Nodes that either contain
-    // user annotated anys or typechecker inferred anys
-    AnyTypeSummary ats{};
-
     // Scopes and AST types refer to parse data, so we need to keep that alive
     std::shared_ptr<Allocator> allocator;
     std::shared_ptr<AstNameTable> names;
+    AstStatBlock* root = nullptr;
 
     std::vector<std::pair<Location, ScopePtr>> scopes; // never empty
 
@@ -132,9 +137,11 @@ struct Module
 
     TypePackId returnType = nullptr;
     std::unordered_map<Name, TypeFun> exportedTypeBindings;
-    // We also need to keep DFG data alive between runs
+
-    std::shared_ptr<DataFlowGraph> dataFlowGraph = nullptr;
+    // Arenas related to the DFG must persist after the DFG no longer exists, as
-    std::vector<std::unique_ptr<DfgScope>> dfgScopes;
+    // Module objects maintain raw pointers to objects in these arenas.
+    DefArena defArena;
+    RefinementKeyArena keyArena;
 
     bool hasModuleScope() const;
     ScopePtr getModuleScope() const;

Analysis/include/Luau/NonStrictTypeChecker.h

@@ -1,9 +1,10 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/DataFlowGraph.h"
+#include "Luau/EqSatSimplification.h"
 #include "Luau/Module.h"
 #include "Luau/NotNull.h"
-#include "Luau/DataFlowGraph.h"
 
 namespace Luau
 {
@@ -15,6 +16,7 @@ struct TypeCheckLimits;
 
 void checkNonStrict(
     NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
     NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<InternalErrorReporter> ice,
     NotNull<UnifierSharedState> unifierState,

Analysis/include/Luau/Normalize.h

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/EqSatSimplification.h"
 #include "Luau/NotNull.h"
 #include "Luau/Set.h"
 #include "Luau/TypeFwd.h"
@@ -21,8 +22,22 @@ struct Scope;
 
 using ModulePtr = std::shared_ptr<Module>;
 
-bool isSubtype(TypeId subTy, TypeId superTy, NotNull<Scope> scope, NotNull<BuiltinTypes> builtinTypes, InternalErrorReporter& ice);
+bool isSubtype(
-bool isSubtype(TypePackId subTy, TypePackId superTy, NotNull<Scope> scope, NotNull<BuiltinTypes> builtinTypes, InternalErrorReporter& ice);
+    TypeId subTy,
+    TypeId superTy,
+    NotNull<Scope> scope,
+    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
+    InternalErrorReporter& ice
+);
+bool isSubtype(
+    TypePackId subPack,
+    TypePackId superPack,
+    NotNull<Scope> scope,
+    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
+    InternalErrorReporter& ice
+);
 
 class TypeIds
 {
@@ -166,7 +181,7 @@ struct NormalizedStringType
 
 bool isSubtype(const NormalizedStringType& subStr, const NormalizedStringType& superStr);
 
-struct NormalizedClassType
+struct NormalizedExternType
 {
     /** Has the following structure:
      *
@@ -177,7 +192,7 @@ struct NormalizedClassType
      *
      * Each TypeId is a class type.
      */
-    std::unordered_map<TypeId, TypeIds> classes;
+    std::unordered_map<TypeId, TypeIds> externTypes;
 
     /**
      * In order to maintain a consistent insertion order, we use this vector to
@@ -230,7 +245,7 @@ enum class NormalizationResult
 };
 
 // A normalized type is either any, unknown, or one of the form P | T | F | G where
-// * P is a union of primitive types (including singletons, classes and the error type)
+// * P is a union of primitive types (including singletons, extern types and the error type)
 // * T is a union of table types
 // * F is a union of an intersection of function types
 // * G is a union of generic/free/blocked types, intersected with a normalized type
@@ -245,7 +260,7 @@ struct NormalizedType
     // This type is either never, boolean type, or a boolean singleton.
     TypeId booleans;
 
-    NormalizedClassType classes;
+    NormalizedExternType externTypes;
 
     // The error part of the type.
     // This type is either never or the error type.
@@ -318,7 +333,7 @@ struct NormalizedType
     // Helpers that improve readability of the above (they just say if the component is present)
     bool hasTops() const;
     bool hasBooleans() const;
-    bool hasClasses() const;
+    bool hasExternTypes() const;
     bool hasErrors() const;
     bool hasNils() const;
     bool hasNumbers() const;
@@ -376,10 +391,10 @@ public:
     void unionTysWithTy(TypeIds& here, TypeId there);
     TypeId unionOfTops(TypeId here, TypeId there);
     TypeId unionOfBools(TypeId here, TypeId there);
-    void unionClassesWithClass(TypeIds& heres, TypeId there);
+    void unionExternTypesWithExternType(TypeIds& heres, TypeId there);
-    void unionClasses(TypeIds& heres, const TypeIds& theres);
+    void unionExternTypes(TypeIds& heres, const TypeIds& theres);
-    void unionClassesWithClass(NormalizedClassType& heres, TypeId there);
+    void unionExternTypesWithExternType(NormalizedExternType& heres, TypeId there);
-    void unionClasses(NormalizedClassType& heres, const NormalizedClassType& theres);
+    void unionExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres);
     void unionStrings(NormalizedStringType& here, const NormalizedStringType& there);
     std::optional<TypePackId> unionOfTypePacks(TypePackId here, TypePackId there);
     std::optional<TypeId> unionOfFunctions(TypeId here, TypeId there);
@@ -408,8 +423,8 @@ public:
     // ------- Normalizing intersections
     TypeId intersectionOfTops(TypeId here, TypeId there);
     TypeId intersectionOfBools(TypeId here, TypeId there);
-    void intersectClasses(NormalizedClassType& heres, const NormalizedClassType& theres);
+    void intersectExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres);
-    void intersectClassesWithClass(NormalizedClassType& heres, TypeId there);
+    void intersectExternTypesWithExternType(NormalizedExternType& heres, TypeId there);
     void intersectStrings(NormalizedStringType& here, const NormalizedStringType& there);
     std::optional<TypePackId> intersectionOfTypePacks(TypePackId here, TypePackId there);
     std::optional<TypeId> intersectionOfTables(TypeId here, TypeId there, SeenTablePropPairs& seenTablePropPairs, Set<TypeId>& seenSet);

Analysis/include/Luau/OverloadResolution.h

@@ -2,12 +2,13 @@
 #pragma once
 
 #include "Luau/Ast.h"
-#include "Luau/InsertionOrderedMap.h"
+#include "Luau/EqSatSimplification.h"
-#include "Luau/NotNull.h"
-#include "Luau/TypeFwd.h"
-#include "Luau/Location.h"
 #include "Luau/Error.h"
+#include "Luau/InsertionOrderedMap.h"
+#include "Luau/Location.h"
+#include "Luau/NotNull.h"
 #include "Luau/Subtyping.h"
+#include "Luau/TypeFwd.h"
 
 namespace Luau
 {
@@ -34,6 +35,7 @@ struct OverloadResolver
     OverloadResolver(
         NotNull<BuiltinTypes> builtinTypes,
         NotNull<TypeArena> arena,
+        NotNull<Simplifier> simplifier,
         NotNull<Normalizer> normalizer,
         NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<Scope> scope,
@@ -44,6 +46,7 @@ struct OverloadResolver
 
     NotNull<BuiltinTypes> builtinTypes;
     NotNull<TypeArena> arena;
+    NotNull<Simplifier> simplifier;
     NotNull<Normalizer> normalizer;
     NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     NotNull<Scope> scope;
@@ -110,6 +113,7 @@ struct SolveResult
 SolveResult solveFunctionCall(
     NotNull<TypeArena> arena,
     NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
     NotNull<Normalizer> normalizer,
     NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<InternalErrorReporter> iceReporter,

Analysis/include/Luau/Polarity.h

@@ -0,0 +1,68 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include <cstdint>
+
+namespace Luau
+{
+
+enum struct Polarity : uint8_t
+{
+    None = 0b000,
+    Positive = 0b001,
+    Negative = 0b010,
+    Mixed = 0b011,
+    Unknown = 0b100,
+};
+
+inline Polarity operator|(Polarity lhs, Polarity rhs)
+{
+    return Polarity(uint8_t(lhs) | uint8_t(rhs));
+}
+
+inline Polarity& operator|=(Polarity& lhs, Polarity rhs)
+{
+    lhs = lhs | rhs;
+    return lhs;
+}
+
+inline Polarity operator&(Polarity lhs, Polarity rhs)
+{
+    return Polarity(uint8_t(lhs) & uint8_t(rhs));
+}
+
+inline Polarity& operator&=(Polarity& lhs, Polarity rhs)
+{
+    lhs = lhs & rhs;
+    return lhs;
+}
+
+inline bool isPositive(Polarity p)
+{
+    return bool(p & Polarity::Positive);
+}
+
+inline bool isNegative(Polarity p)
+{
+    return bool(p & Polarity::Negative);
+}
+
+inline bool isKnown(Polarity p)
+{
+    return p != Polarity::Unknown;
+}
+
+inline Polarity invert(Polarity p)
+{
+    switch (p)
+    {
+    case Polarity::Positive:
+        return Polarity::Negative;
+    case Polarity::Negative:
+        return Polarity::Positive;
+    default:
+        return p;
+    }
+}
+
+} // namespace Luau

Analysis/include/Luau/Quantify.h

@@ -16,7 +16,7 @@ struct Scope;
 
 void quantify(TypeId ty, TypeLevel level);
 
-// TODO: This is eerily similar to the pattern that NormalizedClassType
+// TODO: This is eerily similar to the pattern that NormalizedExternType
 // implements. We could, and perhaps should, merge them together.
 template<typename K, typename V>
 struct OrderedMap
@@ -31,13 +31,4 @@ struct OrderedMap
     }
 };
 
-struct QuantifierResult
-{
-    TypeId result;
-    OrderedMap<TypeId, TypeId> insertedGenerics;
-    OrderedMap<TypePackId, TypePackId> insertedGenericPacks;
-};
-
-std::optional<QuantifierResult> quantify(TypeArena* arena, TypeId ty, Scope* scope);
-
 } // namespace Luau

Analysis/include/Luau/Refinement.h

@@ -53,6 +53,7 @@ struct Proposition
 {
     const RefinementKey* key;
     TypeId discriminantTy;
+    bool implicitFromCall;
 };
 
 template<typename T>
@@ -69,6 +70,7 @@ struct RefinementArena
     RefinementId disjunction(RefinementId lhs, RefinementId rhs);
     RefinementId equivalence(RefinementId lhs, RefinementId rhs);
     RefinementId proposition(const RefinementKey* key, TypeId discriminantTy);
+    RefinementId implicitProposition(const RefinementKey* key, TypeId discriminantTy);
 
 private:
     TypedAllocator<Refinement> allocator;

Analysis/include/Luau/RequireTracer.h

@@ -11,14 +11,12 @@
 namespace Luau
 {
 
-class AstStat;
+class AstNode;
-class AstExpr;
 class AstStatBlock;
-struct AstLocal;
 
 struct RequireTraceResult
 {
-    DenseHashMap<const AstExpr*, ModuleInfo> exprs{nullptr};
+    DenseHashMap<const AstNode*, ModuleInfo> exprs{nullptr};
 
     std::vector<std::pair<ModuleName, Location>> requireList;
 };

Analysis/include/Luau/Scope.h

@@ -35,12 +35,12 @@ struct Scope
     explicit Scope(TypePackId returnType);                    // root scope
     explicit Scope(const ScopePtr& parent, int subLevel = 0); // child scope.  Parent must not be nullptr.
 
-    const ScopePtr parent; // null for the root
+    ScopePtr parent; // null for the root
 
     // All the children of this scope.
     std::vector<NotNull<Scope>> children;
     std::unordered_map<Symbol, Binding> bindings;
-    TypePackId returnType;
+    TypePackId returnType = nullptr;
     std::optional<TypePackId> varargPack;
 
     TypeLevel level;
@@ -59,6 +59,8 @@ struct Scope
 
     std::optional<TypeId> lookup(Symbol sym) const;
     std::optional<TypeId> lookupUnrefinedType(DefId def) const;
+
+    std::optional<TypeId> lookupRValueRefinementType(DefId def) const;
     std::optional<TypeId> lookup(DefId def) const;
     std::optional<std::pair<TypeId, Scope*>> lookupEx(DefId def);
     std::optional<std::pair<Binding*, Scope*>> lookupEx(Symbol sym);
@@ -71,6 +73,7 @@ struct Scope
 
     // WARNING: This function linearly scans for a string key of equal value!  It is thus O(n**2)
     std::optional<Binding> linearSearchForBinding(const std::string& name, bool traverseScopeChain = true) const;
+    std::optional<std::pair<Symbol, Binding>> linearSearchForBindingPair(const std::string& name, bool traverseScopeChain) const;
 
     RefinementMap refinements;
 
@@ -85,12 +88,19 @@ struct Scope
     void inheritAssignments(const ScopePtr& childScope);
     void inheritRefinements(const ScopePtr& childScope);
 
+    // Track globals that should emit warnings during type checking.
+    DenseHashSet<std::string> globalsToWarn{""};
+    bool shouldWarnGlobal(std::string name) const;
+
     // For mutually recursive type aliases, it's important that
     // they use the same types for the same names.
     // For instance, in `type Tree<T> { data: T, children: Forest<T> } type Forest<T> = {Tree<T>}`
     // we need that the generic type `T` in both cases is the same, so we use a cache.
     std::unordered_map<Name, TypeId> typeAliasTypeParameters;
     std::unordered_map<Name, TypePackId> typeAliasTypePackParameters;
+
+    std::optional<std::vector<TypeId>> interiorFreeTypes;
+    std::optional<std::vector<TypePackId>> interiorFreeTypePacks;
 };
 
 // Returns true iff the left scope encloses the right scope.  A Scope* equal to

Analysis/include/Luau/Simplify.h

@@ -19,10 +19,13 @@ struct SimplifyResult
     DenseHashSet<TypeId> blockedTypes;
 };
 
-SimplifyResult simplifyIntersection(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId ty, TypeId discriminant);
+SimplifyResult simplifyIntersection(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId left, TypeId right);
 SimplifyResult simplifyIntersection(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, std::set<TypeId> parts);
 
-SimplifyResult simplifyUnion(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId ty, TypeId discriminant);
+SimplifyResult simplifyUnion(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId left, TypeId right);
+
+SimplifyResult simplifyIntersectWithTruthy(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId target);
+SimplifyResult simplifyIntersectWithFalsy(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId target);
 
 enum class Relation
 {

Analysis/include/Luau/Substitution.h

@@ -86,6 +86,7 @@ struct TarjanNode
 struct Tarjan
 {
     Tarjan();
+    virtual ~Tarjan() = default;
 
     // Vertices (types and type packs) are indexed, using pre-order traversal.
     DenseHashMap<TypeId, int> typeToIndex{nullptr};
@@ -121,7 +122,7 @@ struct Tarjan
     void visitChildren(TypePackId tp, int index);
 
     void visitChild(TypeId ty);
-    void visitChild(TypePackId ty);
+    void visitChild(TypePackId tp);
 
     template<typename Ty>
     void visitChild(std::optional<Ty> ty)
@@ -132,7 +133,7 @@ struct Tarjan
 
     // Visit the root vertex.
     TarjanResult visitRoot(TypeId ty);
-    TarjanResult visitRoot(TypePackId ty);
+    TarjanResult visitRoot(TypePackId tp);
 
     // Used to reuse the object for a new operation
     void clearTarjan(const TxnLog* log);
@@ -150,26 +151,12 @@ struct Tarjan
     void visitSCC(int index);
 
     // Each subclass can decide to ignore some nodes.
-    virtual bool ignoreChildren(TypeId ty)
+    virtual bool ignoreChildren(TypeId ty);
-    {
+    virtual bool ignoreChildren(TypePackId ty);
-        return false;
-    }
-
-    virtual bool ignoreChildren(TypePackId ty)
-    {
-        return false;
-    }
 
     // Some subclasses might ignore children visit, but not other actions like replacing the children
-    virtual bool ignoreChildrenVisit(TypeId ty)
+    virtual bool ignoreChildrenVisit(TypeId ty);
-    {
+    virtual bool ignoreChildrenVisit(TypePackId ty);
-        return ignoreChildren(ty);
-    }
-
-    virtual bool ignoreChildrenVisit(TypePackId ty)
-    {
-        return ignoreChildren(ty);
-    }
 
     // Subclasses should say which vertices are dirty,
     // and what to do with dirty vertices.
@@ -184,6 +171,7 @@ struct Tarjan
 struct Substitution : Tarjan
 {
 protected:
+    explicit Substitution(TypeArena* arena);
     Substitution(const TxnLog* log_, TypeArena* arena);
 
     /*
@@ -232,28 +220,23 @@ public:
     virtual TypeId clean(TypeId ty) = 0;
     virtual TypePackId clean(TypePackId tp) = 0;
 
+protected:
     // Helper functions to create new types (used by subclasses)
     template<typename T>
-    TypeId addType(const T& tv)
+    TypeId addType(T tv)
     {
-        return arena->addType(tv);
+        return arena->addType(std::move(tv));
     }
 
     template<typename T>
-    TypePackId addTypePack(const T& tp)
+    TypePackId addTypePack(T tp)
     {
-        return arena->addTypePack(TypePackVar{tp});
+        return arena->addTypePack(TypePackVar{std::move(tp)});
     }
 
 private:
     template<typename Ty>
-    std::optional<Ty> replace(std::optional<Ty> ty)
+    std::optional<Ty> replace(std::optional<Ty> ty);
-    {
-        if (ty)
-            return replace(*ty);
-        else
-            return std::nullopt;
-    }
 };
 
 } // namespace Luau

Analysis/include/Luau/Subtyping.h

@@ -1,13 +1,14 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/DenseHash.h"
+#include "Luau/EqSatSimplification.h"
 #include "Luau/Set.h"
+#include "Luau/TypeCheckLimits.h"
+#include "Luau/TypeFunction.h"
 #include "Luau/TypeFwd.h"
 #include "Luau/TypePairHash.h"
 #include "Luau/TypePath.h"
-#include "Luau/TypeFunction.h"
-#include "Luau/TypeCheckLimits.h"
-#include "Luau/DenseHash.h"
 
 #include <vector>
 #include <optional>
@@ -21,7 +22,7 @@ struct InternalErrorReporter;
 
 class TypeIds;
 class Normalizer;
-struct NormalizedClassType;
+struct NormalizedExternType;
 struct NormalizedFunctionType;
 struct NormalizedStringType;
 struct NormalizedType;
@@ -120,7 +121,7 @@ struct SubtypingEnvironment
     DenseHashMap<TypePackId, TypePackId> mappedGenericPacks{nullptr};
 
     /*
-     * See the test cyclic_tables_are_assumed_to_be_compatible_with_classes for
+     * See the test cyclic_tables_are_assumed_to_be_compatible_with_extern_types for
      * details.
      *
      * An empty value is equivalent to a nonexistent key.
@@ -134,6 +135,7 @@ struct Subtyping
 {
     NotNull<BuiltinTypes> builtinTypes;
     NotNull<TypeArena> arena;
+    NotNull<Simplifier> simplifier;
     NotNull<Normalizer> normalizer;
     NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     NotNull<InternalErrorReporter> iceReporter;
@@ -155,6 +157,7 @@ struct Subtyping
     Subtyping(
         NotNull<BuiltinTypes> builtinTypes,
         NotNull<TypeArena> typeArena,
+        NotNull<Simplifier> simplifier,
         NotNull<Normalizer> normalizer,
         NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<InternalErrorReporter> iceReporter
@@ -226,9 +229,8 @@ private:
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const TableType* subTable, const TableType* superTable, NotNull<Scope> scope);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const MetatableType* subMt, const MetatableType* superMt, NotNull<Scope> scope);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const MetatableType* subMt, const TableType* superTable, NotNull<Scope> scope);
-    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const ClassType* subClass, const ClassType* superClass, NotNull<Scope> scope);
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const ExternType* subExternType, const ExternType* superExternType, NotNull<Scope> scope);
-    SubtypingResult
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, TypeId subTy, const ExternType* subExternType, TypeId superTy, const TableType* superTable, NotNull<Scope>);
-    isCovariantWith(SubtypingEnvironment& env, TypeId subTy, const ClassType* subClass, TypeId superTy, const TableType* superTable, NotNull<Scope>);
     SubtypingResult isCovariantWith(
         SubtypingEnvironment& env,
         const FunctionType* subFunction,
@@ -256,11 +258,11 @@ private:
     );
     SubtypingResult isCovariantWith(
         SubtypingEnvironment& env,
-        const NormalizedClassType& subClass,
+        const NormalizedExternType& subExternType,
-        const NormalizedClassType& superClass,
+        const NormalizedExternType& superExternType,
         NotNull<Scope> scope
     );
-    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const NormalizedClassType& subClass, const TypeIds& superTables, NotNull<Scope> scope);
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const NormalizedExternType& subExternType, const TypeIds& superTables, NotNull<Scope> scope);
     SubtypingResult isCovariantWith(
         SubtypingEnvironment& env,
         const NormalizedStringType& subString,

Analysis/include/Luau/TableLiteralInference.h

@@ -6,12 +6,15 @@
 #include "Luau/NotNull.h"
 #include "Luau/TypeFwd.h"
 
+#include <vector>
+
 namespace Luau
 {
 
 struct TypeArena;
 struct BuiltinTypes;
 struct Unifier2;
+struct Subtyping;
 class AstExpr;
 
 TypeId matchLiteralType(
@@ -20,6 +23,7 @@ TypeId matchLiteralType(
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<TypeArena> arena,
     NotNull<Unifier2> unifier,
+    NotNull<Subtyping> subtyping,
     TypeId expectedType,
     TypeId exprType,
     const AstExpr* expr,

Analysis/include/Luau/ToString.h

@@ -44,6 +44,7 @@ struct ToStringOptions
     bool hideTableKind = false;                   // If true, all tables will be surrounded with plain '{}'
     bool hideNamedFunctionTypeParameters = false; // If true, type parameters of functions will be hidden at top-level.
     bool hideFunctionSelfArgument = false;        // If true, `self: X` will be omitted from the function signature if the function has self
+    bool hideTableAliasExpansions = false;        // If true, all table aliases will not be expanded
     bool useQuestionMarks = true;                 // If true, use a postfix ? for options, else write them out as unions that include nil.
     size_t maxTableLength = size_t(FInt::LuauTableTypeMaximumStringifierLength); // Only applied to TableTypes
     size_t maxTypeLength = size_t(FInt::LuauTypeMaximumStringifierLength);

Analysis/include/Luau/TxnLog.h

@@ -65,11 +65,10 @@ T* getMutable(PendingTypePack* pending)
 // Log of what TypeIds we are rebinding, to be committed later.
 struct TxnLog
 {
-    explicit TxnLog(bool useScopes = false)
+    explicit TxnLog()
         : typeVarChanges(nullptr)
         , typePackChanges(nullptr)
         , ownedSeen()
-        , useScopes(useScopes)
         , sharedSeen(&ownedSeen)
     {
     }
@@ -193,16 +192,6 @@ struct TxnLog
     // The pointer returned lives until `commit` or `clear` is called.
     PendingTypePack* changeLevel(TypePackId tp, TypeLevel newLevel);
 
-    // Queues the replacement of a type's scope with the provided scope.
-    //
-    // The pointer returned lives until `commit` or `clear` is called.
-    PendingType* changeScope(TypeId ty, NotNull<Scope> scope);
-
-    // Queues the replacement of a type pack's scope with the provided scope.
-    //
-    // The pointer returned lives until `commit` or `clear` is called.
-    PendingTypePack* changeScope(TypePackId tp, NotNull<Scope> scope);
-
     // Queues a replacement of a table type with another table type with a new
     // indexer.
     //

Analysis/include/Luau/Type.h

@@ -5,10 +5,11 @@
 
 #include "Luau/Ast.h"
 #include "Luau/Common.h"
-#include "Luau/Refinement.h"
 #include "Luau/DenseHash.h"
 #include "Luau/NotNull.h"
+#include "Luau/Polarity.h"
 #include "Luau/Predicate.h"
+#include "Luau/Refinement.h"
 #include "Luau/Unifiable.h"
 #include "Luau/Variant.h"
 #include "Luau/VecDeque.h"
@@ -19,7 +20,6 @@
 #include <optional>
 #include <set>
 #include <string>
-#include <unordered_map>
 #include <vector>
 
 LUAU_FASTINT(LuauTableTypeMaximumStringifierLength)
@@ -69,11 +69,11 @@ using Name = std::string;
 // A free type is one whose exact shape has yet to be fully determined.
 struct FreeType
 {
-    explicit FreeType(TypeLevel level);
+    // New constructors
-    explicit FreeType(Scope* scope);
+    explicit FreeType(TypeLevel level, TypeId lowerBound, TypeId upperBound);
-    FreeType(Scope* scope, TypeLevel level);
+    // This one got promoted to explicit
-
+    explicit FreeType(Scope* scope, TypeId lowerBound, TypeId upperBound, Polarity polarity = Polarity::Unknown);
-    FreeType(Scope* scope, TypeId lowerBound, TypeId upperBound);
+    explicit FreeType(Scope* scope, TypeLevel level, TypeId lowerBound, TypeId upperBound);
 
     int index;
     TypeLevel level;
@@ -87,6 +87,8 @@ struct FreeType
     // Only used under local type inference
     TypeId lowerBound = nullptr;
     TypeId upperBound = nullptr;
+
+    Polarity polarity = Polarity::Unknown;
 };
 
 struct GenericType
@@ -95,8 +97,8 @@ struct GenericType
     GenericType();
 
     explicit GenericType(TypeLevel level);
-    explicit GenericType(const Name& name);
+    explicit GenericType(const Name& name, Polarity polarity = Polarity::Unknown);
-    explicit GenericType(Scope* scope);
+    explicit GenericType(Scope* scope, Polarity polarity = Polarity::Unknown);
 
     GenericType(TypeLevel level, const Name& name);
     GenericType(Scope* scope, const Name& name);
@@ -106,6 +108,8 @@ struct GenericType
     Scope* scope = nullptr;
     Name name;
     bool explicitName = false;
+
+    Polarity polarity = Polarity::Unknown;
 };
 
 // When an equality constraint is found, it is then "bound" to that type,
@@ -131,14 +135,14 @@ struct BlockedType
     BlockedType();
     int index;
 
-    Constraint* getOwner() const;
+    const Constraint* getOwner() const;
-    void setOwner(Constraint* newOwner);
+    void setOwner(const Constraint* newOwner);
-    void replaceOwner(Constraint* newOwner);
+    void replaceOwner(const Constraint* newOwner);
 
 private:
     // The constraint that is intended to unblock this type. Other constraints
     // should block on this constraint if present.
-    Constraint* owner = nullptr;
+    const Constraint* owner = nullptr;
 };
 
 struct PrimitiveType
@@ -279,19 +283,15 @@ struct WithPredicate
     }
 };
 
-using MagicFunction = std::function<std::optional<
-    WithPredicate<TypePackId>>(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>)>;
-
 struct MagicFunctionCallContext
 {
     NotNull<struct ConstraintSolver> solver;
     NotNull<const Constraint> constraint;
-    const class AstExprCall* callSite;
+    NotNull<const AstExprCall> callSite;
     TypePackId arguments;
     TypePackId result;
 };
 
-using DcrMagicFunction = std::function<bool(MagicFunctionCallContext)>;
 struct MagicRefinementContext
 {
     NotNull<Scope> scope;
@@ -308,8 +308,30 @@ struct MagicFunctionTypeCheckContext
     NotNull<Scope> checkScope;
 };
 
-using DcrMagicRefinement = void (*)(const MagicRefinementContext&);
+struct MagicFunction
-using DcrMagicFunctionTypeCheck = std::function<void(const MagicFunctionTypeCheckContext&)>;
+{
+    virtual std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) = 0;
+
+    // Callback to allow custom typechecking of builtin function calls whose argument types
+    // will only be resolved after constraint solving. For example, the arguments to string.format
+    // have types that can only be decided after parsing the format string and unifying
+    // with the passed in values, but the correctness of the call can only be decided after
+    // all the types have been finalized.
+    virtual bool infer(const MagicFunctionCallContext&) = 0;
+    virtual void refine(const MagicRefinementContext&) {}
+
+    // If a magic function needs to do its own special typechecking, do it here.
+    // Returns true if magic typechecking was performed.  Return false if the
+    // default typechecking logic should run.
+    virtual bool typeCheck(const MagicFunctionTypeCheckContext&)
+    {
+        return false;
+    }
+
+    virtual ~MagicFunction() {}
+};
+
 struct FunctionType
 {
     // Global monomorphic function
@@ -326,10 +348,8 @@ struct FunctionType
     );
 
     // Local monomorphic function
-    FunctionType(TypeLevel level, TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn = {}, bool hasSelf = false);
     FunctionType(
         TypeLevel level,
-        Scope* scope,
         TypePackId argTypes,
         TypePackId retTypes,
         std::optional<FunctionDefinition> defn = {},
@@ -346,16 +366,6 @@ struct FunctionType
         std::optional<FunctionDefinition> defn = {},
         bool hasSelf = false
     );
-    FunctionType(
-        TypeLevel level,
-        Scope* scope,
-        std::vector<TypeId> generics,
-        std::vector<TypePackId> genericPacks,
-        TypePackId argTypes,
-        TypePackId retTypes,
-        std::optional<FunctionDefinition> defn = {},
-        bool hasSelf = false
-    );
 
     std::optional<FunctionDefinition> definition;
     /// These should all be generic
@@ -364,25 +374,16 @@ struct FunctionType
     std::vector<std::optional<FunctionArgument>> argNames;
     Tags tags;
     TypeLevel level;
-    Scope* scope = nullptr;
     TypePackId argTypes;
     TypePackId retTypes;
-    MagicFunction magicFunction = nullptr;
+    std::shared_ptr<MagicFunction> magic = nullptr;
-    DcrMagicFunction dcrMagicFunction = nullptr;
-    DcrMagicRefinement dcrMagicRefinement = nullptr;
-
-    // Callback to allow custom typechecking of builtin function calls whose argument types
-    // will only be resolved after constraint solving. For example, the arguments to string.format
-    // have types that can only be decided after parsing the format string and unifying
-    // with the passed in values, but the correctness of the call can only be decided after
-    // all the types have been finalized.
-    DcrMagicFunctionTypeCheck dcrMagicTypeCheck = nullptr;
 
     bool hasSelf;
     // `hasNoFreeOrGenericTypes` should be true if and only if the type does not have any free or generic types present inside it.
     // this flag is used as an optimization to exit early from procedures that manipulate free or generic types.
     bool hasNoFreeOrGenericTypes = false;
     bool isCheckedFunction = false;
+    bool isDeprecatedFunction = false;
 };
 
 enum class TableState
@@ -459,7 +460,9 @@ struct Property
     TypeId type() const;
     void setType(TypeId ty);
 
-    // Sets the write type of this property to the read type.
+    // If this property has a present `writeTy`, set it equal to the `readTy`.
+    // This is to ensure that if we normalize a property that has divergent
+    // read and write types, we make them converge (for now).
     void makeShared();
 
     bool isShared() const;
@@ -504,9 +507,6 @@ struct TableType
     std::optional<TypeId> boundTo;
     Tags tags;
 
-    // Methods of this table that have an untyped self will use the same shared self type.
-    std::optional<TypeId> selfTy;
-
     // We track the number of as-yet-unadded properties to unsealed tables.
     // Some constraints will use this information to decide whether or not they
     // are able to dispatch.
@@ -532,15 +532,15 @@ struct ClassUserData
     virtual ~ClassUserData() {}
 };
 
-/** The type of a class.
+/** The type of an external userdata exposed to Luau.
  *
- * Classes behave like tables in many ways, but there are some important differences:
+ * Extern types behave like tables in many ways, but there are some important differences:
  *
  * The properties of a class are always exactly known.
- * Classes optionally have a parent class.
+ * Extern types optionally have a parent type.
- * Two different classes that share the same properties are nevertheless distinct and mutually incompatible.
+ * Two different extern types that share the same properties are nevertheless distinct and mutually incompatible.
  */
-struct ClassType
+struct ExternType
 {
     using Props = TableType::Props;
 
@@ -554,7 +554,7 @@ struct ClassType
     std::optional<Location> definitionLocation;
     std::optional<TableIndexer> indexer;
 
-    ClassType(
+    ExternType(
         Name name,
         Props props,
         std::optional<TypeId> parent,
@@ -575,7 +575,7 @@ struct ClassType
     {
     }
 
-    ClassType(
+    ExternType(
         Name name,
         Props props,
         std::optional<TypeId> parent,
@@ -608,7 +608,7 @@ struct UserDefinedFunctionData
     // References to AST elements are owned by the Module allocator which also stores this type
     AstStatTypeFunction* definition = nullptr;
 
-    DenseHashMap<Name, AstStatTypeFunction*> environment{""};
+    DenseHashMap<Name, std::pair<AstStatTypeFunction*, size_t>> environment{""};
 };
 
 /**
@@ -625,7 +625,7 @@ struct TypeFunctionInstanceType
     std::vector<TypeId> typeArguments;
     std::vector<TypePackId> packArguments;
 
-    std::optional<AstName> userFuncName;          // Name of the user-defined type function; only available for UDTFs
+    std::optional<AstName> userFuncName; // Name of the user-defined type function; only available for UDTFs
     UserDefinedFunctionData userFuncData;
 
     TypeFunctionInstanceType(
@@ -762,7 +762,7 @@ struct NegationType
     TypeId ty;
 };
 
-using ErrorType = Unifiable::Error;
+using ErrorType = Unifiable::Error<TypeId>;
 
 using TypeVariant = Unifiable::Variant<
     TypeId,
@@ -775,7 +775,7 @@ using TypeVariant = Unifiable::Variant<
     FunctionType,
     TableType,
     MetatableType,
-    ClassType,
+    ExternType,
     AnyType,
     UnionType,
     IntersectionType,
@@ -868,6 +868,9 @@ struct TypeFun
      */
     TypeId type;
 
+    // The location of where this TypeFun was defined, if available
+    std::optional<Location> definitionLocation;
+
     TypeFun() = default;
 
     explicit TypeFun(TypeId ty)
@@ -875,16 +878,23 @@ struct TypeFun
     {
     }
 
-    TypeFun(std::vector<GenericTypeDefinition> typeParams, TypeId type)
+    TypeFun(std::vector<GenericTypeDefinition> typeParams, TypeId type, std::optional<Location> definitionLocation = std::nullopt)
         : typeParams(std::move(typeParams))
         , type(type)
+        , definitionLocation(definitionLocation)
     {
     }
 
-    TypeFun(std::vector<GenericTypeDefinition> typeParams, std::vector<GenericTypePackDefinition> typePackParams, TypeId type)
+    TypeFun(
+        std::vector<GenericTypeDefinition> typeParams,
+        std::vector<GenericTypePackDefinition> typePackParams,
+        TypeId type,
+        std::optional<Location> definitionLocation = std::nullopt
+    )
         : typeParams(std::move(typeParams))
         , typePackParams(std::move(typePackParams))
         , type(type)
+        , definitionLocation(definitionLocation)
     {
     }
 
@@ -976,7 +986,7 @@ public:
     const TypeId threadType;
     const TypeId bufferType;
     const TypeId functionType;
-    const TypeId classType;
+    const TypeId externType;
     const TypeId tableType;
     const TypeId emptyTableType;
     const TypeId trueType;
@@ -988,6 +998,7 @@ public:
     const TypeId noRefineType;
     const TypeId falsyType;
     const TypeId truthyType;
+    const TypeId notNilType;
 
     const TypeId optionalNumberType;
     const TypeId optionalStringType;
@@ -1008,10 +1019,10 @@ TypeLevel* getMutableLevel(TypeId ty);
 
 std::optional<TypeLevel> getLevel(TypePackId tp);
 
-const Property* lookupClassProp(const ClassType* cls, const Name& name);
+const Property* lookupExternTypeProp(const ExternType* cls, const Name& name);
 
 // Whether `cls` is a subclass of `parent`
-bool isSubclass(const ClassType* cls, const ClassType* parent);
+bool isSubclass(const ExternType* cls, const ExternType* parent);
 
 Type* asMutable(TypeId ty);
 
@@ -1188,7 +1199,7 @@ private:
     }
 };
 
-TypeId freshType(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, Scope* scope);
+TypeId freshType(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, Scope* scope, Polarity polarity = Polarity::Unknown);
 
 using TypeIdPredicate = std::function<std::optional<TypeId>(TypeId)>;
 std::vector<TypeId> filterMap(TypeId type, TypeIdPredicate predicate);

Analysis/include/Luau/TypeArena.h

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/Polarity.h"
 #include "Luau/TypedAllocator.h"
 #include "Luau/Type.h"
 #include "Luau/TypePack.h"
@@ -32,11 +33,11 @@ struct TypeArena
 
     TypeId addTV(Type&& tv);
 
-    TypeId freshType(TypeLevel level);
+    TypeId freshType(NotNull<BuiltinTypes> builtins, TypeLevel level);
-    TypeId freshType(Scope* scope);
+    TypeId freshType(NotNull<BuiltinTypes> builtins, Scope* scope);
-    TypeId freshType(Scope* scope, TypeLevel level);
+    TypeId freshType(NotNull<BuiltinTypes> builtins, Scope* scope, TypeLevel level);
 
-    TypePackId freshTypePack(Scope* scope);
+    TypePackId freshTypePack(Scope* scope, Polarity polarity = Polarity::Unknown);
 
     TypePackId addTypePack(std::initializer_list<TypeId> types);
     TypePackId addTypePack(std::vector<TypeId> types, std::optional<TypePackId> tail = {});

Analysis/include/Luau/TypeAttach.h

@@ -11,7 +11,7 @@ namespace Luau
 struct TypeRehydrationOptions
 {
     std::unordered_set<std::string> bannedNames;
-    bool expandClassProps = false;
+    bool expandExternTypeProps = false;
 };
 
 void attachTypeData(SourceModule& source, Module& result);

Analysis/include/Luau/TypeChecker2.h

@@ -2,15 +2,18 @@
 
 #pragma once
 
-#include "Luau/Error.h"
-#include "Luau/NotNull.h"
 #include "Luau/Common.h"
-#include "Luau/TypeUtils.h"
+#include "Luau/EqSatSimplification.h"
+#include "Luau/Error.h"
+#include "Luau/Normalize.h"
+#include "Luau/NotNull.h"
+#include "Luau/Subtyping.h"
 #include "Luau/Type.h"
 #include "Luau/TypeFwd.h"
 #include "Luau/TypeOrPack.h"
-#include "Luau/Normalize.h"
+#include "Luau/TypeUtils.h"
-#include "Luau/Subtyping.h"
+
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
 
 namespace Luau
 {
@@ -37,18 +40,29 @@ struct Reasonings
 
     std::string toString()
     {
+        if (FFlag::LuauImproveTypePathsInErrors && reasons.empty())
+            return "";
+
         // DenseHashSet ordering is entirely undefined, so we want to
         // sort the reasons here to achieve a stable error
         // stringification.
         std::sort(reasons.begin(), reasons.end());
-        std::string allReasons;
+        std::string allReasons = FFlag::LuauImproveTypePathsInErrors ? "\nthis is because " : "";
         bool first = true;
         for (const std::string& reason : reasons)
         {
-            if (first)
+            if (FFlag::LuauImproveTypePathsInErrors)
-                first = false;
+            {
+                if (reasons.size() > 1)
+                    allReasons += "\n\t * ";
+            }
             else
-                allReasons += "\n\t";
+            {
+                if (first)
+                    first = false;
+                else
+                    allReasons += "\n\t";
+            }
 
             allReasons += reason;
         }
@@ -60,8 +74,9 @@ struct Reasonings
 
 void check(
     NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
     NotNull<TypeFunctionRuntime> typeFunctionRuntime,
-    NotNull<UnifierSharedState> sharedState,
+    NotNull<UnifierSharedState> unifierState,
     NotNull<TypeCheckLimits> limits,
     DcrLogger* logger,
     const SourceModule& sourceModule,
@@ -71,6 +86,7 @@ void check(
 struct TypeChecker2
 {
     NotNull<BuiltinTypes> builtinTypes;
+    NotNull<Simplifier> simplifier;
     NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     DcrLogger* logger;
     const NotNull<TypeCheckLimits> limits;
@@ -90,6 +106,7 @@ struct TypeChecker2
 
     TypeChecker2(
         NotNull<BuiltinTypes> builtinTypes,
+        NotNull<Simplifier> simplifier,
         NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<UnifierSharedState> unifierState,
         NotNull<TypeCheckLimits> limits,
@@ -112,14 +129,14 @@ private:
     std::optional<StackPusher> pushStack(AstNode* node);
     void checkForInternalTypeFunction(TypeId ty, Location location);
     TypeId checkForTypeFunctionInhabitance(TypeId instance, Location location);
-    TypePackId lookupPack(AstExpr* expr);
+    TypePackId lookupPack(AstExpr* expr) const;
     TypeId lookupType(AstExpr* expr);
     TypeId lookupAnnotation(AstType* annotation);
-    std::optional<TypePackId> lookupPackAnnotation(AstTypePack* annotation);
+    std::optional<TypePackId> lookupPackAnnotation(AstTypePack* annotation) const;
-    TypeId lookupExpectedType(AstExpr* expr);
+    TypeId lookupExpectedType(AstExpr* expr) const;
-    TypePackId lookupExpectedPack(AstExpr* expr, TypeArena& arena);
+    TypePackId lookupExpectedPack(AstExpr* expr, TypeArena& arena) const;
     TypePackId reconstructPack(AstArray<AstExpr*> exprs, TypeArena& arena);
-    Scope* findInnermostScope(Location location);
+    Scope* findInnermostScope(Location location) const;
     void visit(AstStat* stat);
     void visit(AstStatIf* ifStatement);
     void visit(AstStatWhile* whileStatement);
@@ -143,7 +160,7 @@ private:
     void visit(AstTypeList types);
     void visit(AstStatDeclareFunction* stat);
     void visit(AstStatDeclareGlobal* stat);
-    void visit(AstStatDeclareClass* stat);
+    void visit(AstStatDeclareExternType* stat);
     void visit(AstStatError* stat);
     void visit(AstExpr* expr, ValueContext context);
     void visit(AstExprGroup* expr, ValueContext context);
@@ -156,7 +173,7 @@ private:
     void visit(AstExprVarargs* expr);
     void visitCall(AstExprCall* call);
     void visit(AstExprCall* call);
-    std::optional<TypeId> tryStripUnionFromNil(TypeId ty);
+    std::optional<TypeId> tryStripUnionFromNil(TypeId ty) const;
     TypeId stripFromNilAndReport(TypeId ty, const Location& location);
     void visitExprName(AstExpr* expr, Location location, const std::string& propName, ValueContext context, TypeId astIndexExprTy);
     void visit(AstExprIndexName* indexName, ValueContext context);
@@ -171,7 +188,7 @@ private:
     void visit(AstExprInterpString* interpString);
     void visit(AstExprError* expr);
     TypeId flattenPack(TypePackId pack);
-    void visitGenerics(AstArray<AstGenericType> generics, AstArray<AstGenericTypePack> genericPacks);
+    void visitGenerics(AstArray<AstGenericType*> generics, AstArray<AstGenericTypePack*> genericPacks);
     void visit(AstType* ty);
     void visit(AstTypeReference* ty);
     void visit(AstTypeTable* table);
@@ -213,6 +230,9 @@ private:
         std::vector<TypeError>& errors
     );
 
+    // Avoid duplicate warnings being emitted for the same global variable.
+    DenseHashSet<std::string> warnedGlobals{""};
+
     void diagnoseMissingTableKey(UnknownProperty* utk, TypeErrorData& data) const;
     bool isErrorSuppressing(Location loc, TypeId ty);
     bool isErrorSuppressing(Location loc1, TypeId ty1, Location loc2, TypeId ty2);

Analysis/include/Luau/TypeFunction.h

@@ -2,6 +2,7 @@
 #pragma once
 
 #include "Luau/Constraint.h"
+#include "Luau/EqSatSimplification.h"
 #include "Luau/Error.h"
 #include "Luau/NotNull.h"
 #include "Luau/TypeCheckLimits.h"
@@ -41,9 +42,18 @@ struct TypeFunctionRuntime
 
     StateRef state;
 
+    // Set of functions which have their environment table initialized
+    DenseHashSet<AstStatTypeFunction*> initialized{nullptr};
+
     // Evaluation of type functions should only be performed in the absence of parse errors in the source module
     bool allowEvaluation = true;
 
+    // Root scope in which the type function operates in, set up by ConstraintGenerator
+    ScopePtr rootScope;
+
+    // Output created by 'print' function
+    std::vector<std::string> messages;
+
 private:
     void prepareState();
 };
@@ -53,6 +63,7 @@ struct TypeFunctionContext
     NotNull<TypeArena> arena;
     NotNull<BuiltinTypes> builtins;
     NotNull<Scope> scope;
+    NotNull<Simplifier> simplifier;
     NotNull<Normalizer> normalizer;
     NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     NotNull<InternalErrorReporter> ice;
@@ -63,7 +74,7 @@ struct TypeFunctionContext
     // The constraint being reduced in this run of the reduction
     const Constraint* constraint;
 
-    std::optional<AstName> userFuncName;          // Name of the user-defined type function; only available for UDTFs
+    std::optional<AstName> userFuncName; // Name of the user-defined type function; only available for UDTFs
 
     TypeFunctionContext(NotNull<ConstraintSolver> cs, NotNull<Scope> scope, NotNull<const Constraint> constraint);
 
@@ -71,6 +82,7 @@ struct TypeFunctionContext
         NotNull<TypeArena> arena,
         NotNull<BuiltinTypes> builtins,
         NotNull<Scope> scope,
+        NotNull<Simplifier> simplifier,
         NotNull<Normalizer> normalizer,
         NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<InternalErrorReporter> ice,
@@ -79,6 +91,7 @@ struct TypeFunctionContext
         : arena(arena)
         , builtins(builtins)
         , scope(scope)
+        , simplifier(simplifier)
         , normalizer(normalizer)
         , typeFunctionRuntime(typeFunctionRuntime)
         , ice(ice)
@@ -91,19 +104,31 @@ struct TypeFunctionContext
     NotNull<Constraint> pushConstraint(ConstraintV&& c) const;
 };
 
+enum class Reduction
+{
+    // The type function is either known to be reducible or the determination is blocked.
+    MaybeOk,
+    // The type function is known to be irreducible, but maybe not be erroneous, e.g. when it's over generics or free types.
+    Irreducible,
+    // The type function is known to be irreducible, and is definitely erroneous.
+    Erroneous,
+};
+
 /// Represents a reduction result, which may have successfully reduced the type,
 /// may have concretely failed to reduce the type, or may simply be stuck
 /// without more information.
 template<typename Ty>
 struct TypeFunctionReductionResult
 {
+
     /// The result of the reduction, if any. If this is nullopt, the type function
     /// could not be reduced.
     std::optional<Ty> result;
-    /// Whether the result is uninhabited: whether we know, unambiguously and
+    /// Indicates the status of this reduction: is `Reduction::Irreducible` if
-    /// permanently, whether this type function reduction results in an
+    /// the this result indicates the type function is irreducible, and
-    /// uninhabitable type. This will trigger an error to be reported.
+    /// `Reduction::Erroneous` if this result indicates the type function is
-    bool uninhabited;
+    /// erroneous. `Reduction::MaybeOk` otherwise.
+    Reduction reductionStatus;
     /// Any types that need to be progressed or mutated before the reduction may
     /// proceed.
     std::vector<TypeId> blockedTypes;
@@ -112,6 +137,8 @@ struct TypeFunctionReductionResult
     std::vector<TypePackId> blockedPacks;
     /// A runtime error message from user-defined type functions
     std::optional<std::string> error;
+    /// Messages printed out from user-defined type functions
+    std::vector<std::string> messages;
 };
 
 template<typename T>
@@ -128,6 +155,9 @@ struct TypeFunction
 
     /// The reducer function for the type function.
     ReducerFunction<TypeId> reducer;
+
+    /// If true, this type function can reduce even if it is parameterized on a generic.
+    bool canReduceGenerics = false;
 };
 
 /// Represents a type function that may be applied to map a series of types and
@@ -140,15 +170,20 @@ struct TypePackFunction
 
     /// The reducer function for the type pack function.
     ReducerFunction<TypePackId> reducer;
+
+    /// If true, this type function can reduce even if it is parameterized on a generic.
+    bool canReduceGenerics = false;
 };
 
 struct FunctionGraphReductionResult
 {
     ErrorVec errors;
+    ErrorVec messages;
     DenseHashSet<TypeId> blockedTypes{nullptr};
     DenseHashSet<TypePackId> blockedPacks{nullptr};
     DenseHashSet<TypeId> reducedTypes{nullptr};
     DenseHashSet<TypePackId> reducedPacks{nullptr};
+    DenseHashSet<TypeId> irreducibleTypes{nullptr};
 };
 
 /**
@@ -216,6 +251,11 @@ struct BuiltinTypeFunctions
     TypeFunction indexFunc;
     TypeFunction rawgetFunc;
 
+    TypeFunction setmetatableFunc;
+    TypeFunction getmetatableFunc;
+
+    TypeFunction weakoptionalFunc;
+
     void addToScope(NotNull<TypeArena> arena, NotNull<Scope> scope) const;
 };
 

Analysis/include/Luau/TypeFunctionRuntime.h

@@ -3,6 +3,7 @@
 
 #include "Luau/Common.h"
 #include "Luau/Variant.h"
+#include "Luau/TypeFwd.h"
 
 #include <optional>
 #include <string>
@@ -31,6 +32,8 @@ struct TypeFunctionPrimitiveType
         Boolean,
         Number,
         String,
+        Thread,
+        Buffer,
     };
 
     Type type;
@@ -117,7 +120,14 @@ struct TypeFunctionVariadicTypePack
     TypeFunctionTypeId type;
 };
 
-using TypeFunctionTypePackVariant = Variant<TypeFunctionTypePack, TypeFunctionVariadicTypePack>;
+struct TypeFunctionGenericTypePack
+{
+    bool isNamed = false;
+
+    std::string name;
+};
+
+using TypeFunctionTypePackVariant = Variant<TypeFunctionTypePack, TypeFunctionVariadicTypePack, TypeFunctionGenericTypePack>;
 
 struct TypeFunctionTypePackVar
 {
@@ -133,6 +143,9 @@ struct TypeFunctionTypePackVar
 
 struct TypeFunctionFunctionType
 {
+    std::vector<TypeFunctionTypeId> generics;
+    std::vector<TypeFunctionTypePackId> genericPacks;
+
     TypeFunctionTypePackId argTypes;
     TypeFunctionTypePackId retTypes;
 };
@@ -192,7 +205,7 @@ struct TypeFunctionTableType
     std::optional<TypeFunctionTypeId> metatable;
 };
 
-struct TypeFunctionClassType
+struct TypeFunctionExternType
 {
     using Name = std::string;
     using Props = std::map<Name, TypeFunctionProperty>;
@@ -203,7 +216,19 @@ struct TypeFunctionClassType
 
     std::optional<TypeFunctionTypeId> metatable; // metaclass?
 
-    std::optional<TypeFunctionTypeId> parent;
+    // this was mistaken, and we should actually be keeping separate read/write types here.
+    std::optional<TypeFunctionTypeId> parent_DEPRECATED;
+
+    std::optional<TypeFunctionTypeId> readParent;
+    std::optional<TypeFunctionTypeId> writeParent;
+
+    TypeId externTy;
+};
+
+struct TypeFunctionGenericType
+{
+    bool isNamed = false;
+    bool isPack = false;
 
     std::string name;
 };
@@ -219,7 +244,8 @@ using TypeFunctionTypeVariant = Luau::Variant<
     TypeFunctionNegationType,
     TypeFunctionFunctionType,
     TypeFunctionTableType,
-    TypeFunctionClassType>;
+    TypeFunctionExternType,
+    TypeFunctionGenericType>;
 
 struct TypeFunctionType
 {

Analysis/include/Luau/TypeFunctionRuntimeBuilder.h

@@ -28,20 +28,12 @@ struct TypeFunctionRuntimeBuilderState
 {
     NotNull<TypeFunctionContext> ctx;
 
-    // Mapping of class name to ClassType
-    // Invariant: users can not create a new class types -> any class types that get deserialized must have been an argument to the type function
-    // Using this invariant, whenever a ClassType is serialized, we can put it into this map
-    // whenever a ClassType is deserialized, we can use this map to return the corresponding value
-    DenseHashMap<std::string, TypeId> classesSerialized{{}};
-
     // List of errors that occur during serialization/deserialization
-    // At every iteration of serialization/deserialzation, if this list.size() != 0, we halt the process
+    // At every iteration of serialization/deserialization, if this list.size() != 0, we halt the process
     std::vector<std::string> errors{};
 
     TypeFunctionRuntimeBuilderState(NotNull<TypeFunctionContext> ctx)
         : ctx(ctx)
-        , classesSerialized({})
-        , errors({})
     {
     }
 };

Analysis/include/Luau/TypeFwd.h

@@ -29,7 +29,7 @@ struct SingletonType;
 struct FunctionType;
 struct TableType;
 struct MetatableType;
-struct ClassType;
+struct ExternType;
 struct AnyType;
 struct UnionType;
 struct IntersectionType;

Analysis/include/Luau/TypeInfer.h

@@ -90,11 +90,11 @@ struct TypeChecker
     ControlFlow check(const ScopePtr& scope, TypeId ty, const ScopePtr& funScope, const AstStatLocalFunction& function);
     ControlFlow check(const ScopePtr& scope, const AstStatTypeAlias& typealias);
     ControlFlow check(const ScopePtr& scope, const AstStatTypeFunction& typefunction);
-    ControlFlow check(const ScopePtr& scope, const AstStatDeclareClass& declaredClass);
+    ControlFlow check(const ScopePtr& scope, const AstStatDeclareExternType& declaredExternType);
     ControlFlow check(const ScopePtr& scope, const AstStatDeclareFunction& declaredFunction);
 
     void prototype(const ScopePtr& scope, const AstStatTypeAlias& typealias, int subLevel = 0);
-    void prototype(const ScopePtr& scope, const AstStatDeclareClass& declaredClass);
+    void prototype(const ScopePtr& scope, const AstStatDeclareExternType& declaredExternType);
 
     ControlFlow checkBlock(const ScopePtr& scope, const AstStatBlock& statement);
     ControlFlow checkBlockWithoutRecursionCheck(const ScopePtr& scope, const AstStatBlock& statement);
@@ -130,6 +130,7 @@ struct TypeChecker
         const PredicateVec& predicates = {}
     );
     WithPredicate<TypeId> checkExpr(const ScopePtr& scope, const AstExprBinary& expr, std::optional<TypeId> expectedType = std::nullopt);
+    WithPredicate<TypeId> checkExpr_DEPRECATED(const ScopePtr& scope, const AstExprBinary& expr, std::optional<TypeId> expectedType = std::nullopt);
     WithPredicate<TypeId> checkExpr(const ScopePtr& scope, const AstExprTypeAssertion& expr);
     WithPredicate<TypeId> checkExpr(const ScopePtr& scope, const AstExprError& expr);
     WithPredicate<TypeId> checkExpr(const ScopePtr& scope, const AstExprIfElse& expr, std::optional<TypeId> expectedType = std::nullopt);
@@ -399,8 +400,8 @@ private:
         const ScopePtr& scope,
         std::optional<TypeLevel> levelOpt,
         const AstNode& node,
-        const AstArray<AstGenericType>& genericNames,
+        const AstArray<AstGenericType*>& genericNames,
-        const AstArray<AstGenericTypePack>& genericPackNames,
+        const AstArray<AstGenericTypePack*>& genericPackNames,
         bool useCache = false
     );
 
@@ -486,7 +487,7 @@ private:
     /**
      * A set of incorrect class definitions which is used to avoid a second-pass analysis.
      */
-    DenseHashSet<const AstStatDeclareClass*> incorrectClassDefinitions{nullptr};
+    DenseHashSet<const AstStatDeclareExternType*> incorrectExternTypeDefinitions{nullptr};
 
     std::vector<std::pair<TypeId, ScopePtr>> deferredQuantification;
 };

Analysis/include/Luau/TypePack.h

@@ -1,11 +1,12 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/Common.h"
+#include "Luau/NotNull.h"
+#include "Luau/Polarity.h"
+#include "Luau/TypeFwd.h"
 #include "Luau/Unifiable.h"
 #include "Luau/Variant.h"
-#include "Luau/TypeFwd.h"
-#include "Luau/NotNull.h"
-#include "Luau/Common.h"
 
 #include <optional>
 #include <set>
@@ -26,12 +27,14 @@ struct TypeFunctionInstanceTypePack;
 struct FreeTypePack
 {
     explicit FreeTypePack(TypeLevel level);
-    explicit FreeTypePack(Scope* scope);
+    explicit FreeTypePack(Scope* scope, Polarity polarity = Polarity::Unknown);
     FreeTypePack(Scope* scope, TypeLevel level);
 
     int index;
     TypeLevel level;
     Scope* scope = nullptr;
+
+    Polarity polarity = Polarity::Unknown;
 };
 
 struct GenericTypePack
@@ -40,7 +43,7 @@ struct GenericTypePack
     GenericTypePack();
     explicit GenericTypePack(TypeLevel level);
     explicit GenericTypePack(const Name& name);
-    explicit GenericTypePack(Scope* scope);
+    explicit GenericTypePack(Scope* scope, Polarity polarity = Polarity::Unknown);
     GenericTypePack(TypeLevel level, const Name& name);
     GenericTypePack(Scope* scope, const Name& name);
 
@@ -49,10 +52,12 @@ struct GenericTypePack
     Scope* scope = nullptr;
     Name name;
     bool explicitName = false;
+
+    Polarity polarity = Polarity::Unknown;
 };
 
 using BoundTypePack = Unifiable::Bound<TypePackId>;
-using ErrorTypePack = Unifiable::Error;
+using ErrorTypePack = Unifiable::Error<TypePackId>;
 
 using TypePackVariant =
     Unifiable::Variant<TypePackId, FreeTypePack, GenericTypePack, TypePack, VariadicTypePack, BlockedTypePack, TypeFunctionInstanceTypePack>;
@@ -100,9 +105,9 @@ struct TypeFunctionInstanceTypePack
 
 struct TypePackVar
 {
-    explicit TypePackVar(const TypePackVariant& ty);
+    explicit TypePackVar(const TypePackVariant& tp);
-    explicit TypePackVar(TypePackVariant&& ty);
+    explicit TypePackVar(TypePackVariant&& tp);
-    TypePackVar(TypePackVariant&& ty, bool persistent);
+    TypePackVar(TypePackVariant&& tp, bool persistent);
 
     bool operator==(const TypePackVar& rhs) const;
 
@@ -169,6 +174,7 @@ struct TypePackIterator
 
 private:
     TypePackId currentTypePack = nullptr;
+    TypePackId tailCycleCheck = nullptr;
     const TypePack* tp = nullptr;
     size_t currentIndex = 0;
 
@@ -179,6 +185,8 @@ TypePackIterator begin(TypePackId tp);
 TypePackIterator begin(TypePackId tp, const TxnLog* log);
 TypePackIterator end(TypePackId tp);
 
+TypePackId getTail(TypePackId tp);
+
 using SeenSet = std::set<std::pair<const void*, const void*>>;
 
 bool areEqual(SeenSet& seen, const TypePackVar& lhs, const TypePackVar& rhs);

Analysis/include/Luau/TypePath.h

@@ -42,9 +42,19 @@ struct Property
 /// element.
 struct Index
 {
+    enum class Variant
+    {
+        Pack,
+        Union,
+        Intersection
+    };
+
     /// The 0-based index to use for the lookup.
     size_t index;
 
+    /// The sort of thing we're indexing from, this is used in stringifying the type path for errors.
+    Variant variant;
+
     bool operator==(const Index& other) const;
 };
 
@@ -205,6 +215,9 @@ using Path = TypePath::Path;
 /// terribly clear to end users of the Luau type system.
 std::string toString(const TypePath::Path& path, bool prefixDot = false);
 
+/// Converts a Path to a human readable string for error reporting.
+std::string toStringHuman(const TypePath::Path& path);
+
 std::optional<TypeOrPack> traverse(TypeId root, const Path& path, NotNull<BuiltinTypes> builtinTypes);
 std::optional<TypeOrPack> traverse(TypePackId root, const Path& path, NotNull<BuiltinTypes> builtinTypes);
 

Analysis/include/Luau/TypeUtils.h

@@ -40,7 +40,7 @@ struct InConditionalContext
     TypeContext* typeContext;
     TypeContext oldValue;
 
-    InConditionalContext(TypeContext* c)
+    explicit InConditionalContext(TypeContext* c)
         : typeContext(c)
         , oldValue(*c)
     {
@@ -269,8 +269,8 @@ bool isLiteral(const AstExpr* expr);
 std::vector<TypeId> findBlockedTypesIn(AstExprTable* expr, NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes);
 
 /**
- * Given a function call and a mapping from expression to type, determine 
+ * Given a function call and a mapping from expression to type, determine
- * whether the type of any argument in said call in depends on a blocked types. 
+ * whether the type of any argument in said call in depends on a blocked types.
  * This is used as a precondition for bidirectional inference: be warned that
  * the behavior of this algorithm is tightly coupled to that of bidirectional
  * inference.
@@ -280,4 +280,15 @@ std::vector<TypeId> findBlockedTypesIn(AstExprTable* expr, NotNull<DenseHashMap<
  */
 std::vector<TypeId> findBlockedArgTypesIn(AstExprCall* expr, NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes);
 
+/**
+ * Given a scope and a free type, find the closest parent that has a present
+ * `interiorFreeTypes` and append the given type to said list. This list will
+ * be generalized when the requiste `GeneralizationConstraint` is resolved.
+ * @param scope Initial scope this free type was attached to
+ * @param ty Free type to track.
+ */
+void trackInteriorFreeType(Scope* scope, TypeId ty);
+
+void trackInteriorFreeTypePack(Scope* scope, TypePackId tp);
+
 } // namespace Luau

Analysis/include/Luau/Unifiable.h

@@ -3,6 +3,7 @@
 
 #include "Luau/Variant.h"
 
+#include <optional>
 #include <string>
 
 namespace Luau
@@ -94,19 +95,29 @@ struct Bound
     Id boundTo;
 };
 
+template<typename Id>
 struct Error
 {
     // This constructor has to be public, since it's used in Type and TypePack,
     // but shouldn't be called directly. Please use errorRecoveryType() instead.
-    Error();
+    explicit Error();
+
+    explicit Error(Id synthetic)
+        : synthetic{synthetic}
+    {
+    }
 
     int index;
 
+    // This is used to create an error that can be rendered out using this field
+    // as appropriate metadata for communicating it to the user.
+    std::optional<Id> synthetic;
+
 private:
     static int nextIndex;
 };
 
 template<typename Id, typename... Value>
-using Variant = Luau::Variant<Bound<Id>, Error, Value...>;
+using Variant = Luau::Variant<Bound<Id>, Error<Id>, Value...>;
 
 } // namespace Luau::Unifiable

Analysis/include/Luau/Unifier.h

@@ -93,10 +93,6 @@ struct Unifier
 
     Unifier(NotNull<Normalizer> normalizer, NotNull<Scope> scope, const Location& location, Variance variance, TxnLog* parentLog = nullptr);
 
-    // Configure the Unifier to test for scope subsumption via embedded Scope
-    // pointers rather than TypeLevels.
-    void enableNewSolver();
-
     // Test whether the two type vars unify.  Never commits the result.
     ErrorVec canUnify(TypeId subTy, TypeId superTy);
     ErrorVec canUnify(TypePackId subTy, TypePackId superTy, bool isFunctionCall = false);
@@ -144,7 +140,7 @@ private:
     void tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection = false, const LiteralProperties* aliasableMap = nullptr);
     void tryUnifyScalarShape(TypeId subTy, TypeId superTy, bool reversed);
     void tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed);
-    void tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed);
+    void tryUnifyWithExternType(TypeId subTy, TypeId superTy, bool reversed);
     void tryUnifyNegations(TypeId subTy, TypeId superTy);
 
     TypePackId tryApplyOverloadedFunction(TypeId function, const NormalizedFunctionType& overloads, TypePackId args);
@@ -169,7 +165,6 @@ private:
 
     std::optional<TypeId> findTablePropertyRespectingMeta(TypeId lhsType, Name name);
 
-    TxnLog combineLogsIntoIntersection(std::vector<TxnLog> logs);
     TxnLog combineLogsIntoUnion(std::vector<TxnLog> logs);
 
 public:
@@ -195,11 +190,6 @@ private:
 
     // Available after regular type pack unification errors
     std::optional<int> firstPackErrorPos;
-
-    // If true, we do a bunch of small things differently to work better with
-    // the new type inference engine. Most notably, we use the Scope hierarchy
-    // directly rather than using TypeLevels.
-    bool useNewSolver = false;
 };
 
 void promoteTypeLevels(TxnLog& log, const TypeArena* arena, TypeLevel minLevel, Scope* outerScope, bool useScope, TypePackId tp);

Analysis/include/Luau/Unifier2.h

@@ -44,6 +44,12 @@ struct Unifier2
     // Mapping from generic type packs to `TypePack`s of free types to be used in instantiation.
     DenseHashMap<TypePackId, TypePackId> genericPackSubstitutions{nullptr};
 
+    // Unification sometimes results in the creation of new free types.
+    // We collect them here so that other systems can perform necessary
+    // bookkeeping.
+    std::vector<TypeId> newFreshTypes;
+    std::vector<TypePackId> newFreshTypePacks;
+
     int recursionCount = 0;
     int recursionLimit = 0;
 
@@ -87,6 +93,9 @@ struct Unifier2
     bool unify(const AnyType* subAny, const TableType* superTable);
     bool unify(const TableType* subTable, const AnyType* superAny);
 
+    bool unify(const MetatableType* subMetatable, const AnyType*);
+    bool unify(const AnyType*, const MetatableType* superMetatable);
+
     // TODO think about this one carefully.  We don't do unions or intersections of type packs
     bool unify(TypePackId subTp, TypePackId superTp);
 
@@ -110,6 +119,9 @@ private:
     // Returns true if needle occurs within haystack already.  ie if we bound
     // needle to haystack, would a cyclic TypePack result?
     OccursCheckResult occursCheck(DenseHashSet<TypePackId>& seen, TypePackId needle, TypePackId haystack);
+
+    TypeId freshType(NotNull<Scope> scope, Polarity polarity);
+    TypePackId freshTypePack(NotNull<Scope> scope, Polarity polarity);
 };
 
 } // namespace Luau

Analysis/include/Luau/UnifierSharedState.h

@@ -49,6 +49,26 @@ struct UnifierSharedState
     DenseHashSet<TypePackId> tempSeenTp{nullptr};
 
     UnifierCounters counters;
+
+    bool reentrantTypeReduction = false;
+};
+
+struct TypeReductionRentrancyGuard final
+{
+    explicit TypeReductionRentrancyGuard(NotNull<UnifierSharedState> sharedState)
+        : sharedState{sharedState}
+    {
+        sharedState->reentrantTypeReduction = true;
+    }
+    ~TypeReductionRentrancyGuard()
+    {
+        sharedState->reentrantTypeReduction = false;
+    }
+    TypeReductionRentrancyGuard(const TypeReductionRentrancyGuard&) = delete;
+    TypeReductionRentrancyGuard(TypeReductionRentrancyGuard&&) = delete;
+
+private:
+    NotNull<UnifierSharedState> sharedState;
 };
 
 } // namespace Luau

Analysis/include/Luau/VisitType.h

@@ -10,7 +10,6 @@
 #include "Type.h"
 
 LUAU_FASTINT(LuauVisitRecursionLimit)
-LUAU_FASTFLAG(LuauBoundLazyTypes2)
 LUAU_FASTFLAG(LuauSolverV2)
 
 namespace Luau
@@ -86,6 +85,8 @@ struct GenericTypeVisitor
     {
     }
 
+    virtual ~GenericTypeVisitor() {}
+
     virtual void cycle(TypeId) {}
     virtual void cycle(TypePackId) {}
 
@@ -125,7 +126,7 @@ struct GenericTypeVisitor
     {
         return visit(ty);
     }
-    virtual bool visit(TypeId ty, const ClassType& ctv)
+    virtual bool visit(TypeId ty, const ExternType& etv)
     {
         return visit(ty);
     }
@@ -190,7 +191,7 @@ struct GenericTypeVisitor
     {
         return visit(tp);
     }
-    virtual bool visit(TypePackId tp, const Unifiable::Error& etp)
+    virtual bool visit(TypePackId tp, const ErrorTypePack& etp)
     {
         return visit(tp);
     }
@@ -312,11 +313,11 @@ struct GenericTypeVisitor
                 traverse(mtv->metatable);
             }
         }
-        else if (auto ctv = get<ClassType>(ty))
+        else if (auto etv = get<ExternType>(ty))
         {
-            if (visit(ty, *ctv))
+            if (visit(ty, *etv))
             {
-                for (const auto& [name, prop] : ctv->props)
+                for (const auto& [name, prop] : etv->props)
                 {
                     if (FFlag::LuauSolverV2)
                     {
@@ -334,16 +335,16 @@ struct GenericTypeVisitor
                         traverse(prop.type());
                 }
 
-                if (ctv->parent)
+                if (etv->parent)
-                    traverse(*ctv->parent);
+                    traverse(*etv->parent);
 
-                if (ctv->metatable)
+                if (etv->metatable)
-                    traverse(*ctv->metatable);
+                    traverse(*etv->metatable);
 
-                if (ctv->indexer)
+                if (etv->indexer)
                 {
-                    traverse(ctv->indexer->indexType);
+                    traverse(etv->indexer->indexType);
-                    traverse(ctv->indexer->indexResultType);
+                    traverse(etv->indexer->indexResultType);
                 }
             }
         }
@@ -395,7 +396,7 @@ struct GenericTypeVisitor
                 traverse(unwrapped);
 
             // Visiting into LazyType that hasn't been unwrapped may necessarily cause infinite expansion, so we don't do that on purpose.
-            // Asserting also makes no sense, because the type _will_ happen here, most likely as a property of some ClassType
+            // Asserting also makes no sense, because the type _will_ happen here, most likely as a property of some ExternType
             // that doesn't need to be expanded.
         }
         else if (auto stv = get<SingletonType>(ty))
@@ -461,7 +462,7 @@ struct GenericTypeVisitor
         else if (auto gtv = get<GenericTypePack>(tp))
             visit(tp, *gtv);
 
-        else if (auto etv = get<Unifiable::Error>(tp))
+        else if (auto etv = get<ErrorTypePack>(tp))
             visit(tp, *etv);
 
         else if (auto pack = get<TypePack>(tp))

Analysis/src/AnyTypeSummary.cpp

@@ -1,903 +0,0 @@
-// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
-#include "Luau/AnyTypeSummary.h"
-
-#include "Luau/BuiltinDefinitions.h"
-#include "Luau/Clone.h"
-#include "Luau/Common.h"
-#include "Luau/Config.h"
-#include "Luau/ConstraintGenerator.h"
-#include "Luau/ConstraintSolver.h"
-#include "Luau/DataFlowGraph.h"
-#include "Luau/DcrLogger.h"
-#include "Luau/Module.h"
-#include "Luau/Parser.h"
-#include "Luau/Scope.h"
-#include "Luau/StringUtils.h"
-#include "Luau/TimeTrace.h"
-#include "Luau/ToString.h"
-#include "Luau/Transpiler.h"
-#include "Luau/TypeArena.h"
-#include "Luau/TypeChecker2.h"
-#include "Luau/NonStrictTypeChecker.h"
-#include "Luau/TypeInfer.h"
-#include "Luau/Variant.h"
-#include "Luau/VisitType.h"
-#include "Luau/TypePack.h"
-#include "Luau/TypeOrPack.h"
-
-#include <algorithm>
-#include <memory>
-#include <chrono>
-#include <condition_variable>
-#include <exception>
-#include <mutex>
-#include <stdexcept>
-#include <string>
-#include <iostream>
-
-
-#include <stdio.h>
-
-LUAU_FASTFLAGVARIABLE(StudioReportLuauAny2);
-LUAU_FASTINTVARIABLE(LuauAnySummaryRecursionLimit, 300);
-
-LUAU_FASTFLAG(DebugLuauMagicTypes);
-
-namespace Luau
-{
-
-void AnyTypeSummary::traverse(const Module* module, AstStat* src, NotNull<BuiltinTypes> builtinTypes)
-{
-    visit(findInnerMostScope(src->location, module), src, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStat* stat, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    RecursionLimiter limiter{&recursionCount, FInt::LuauAnySummaryRecursionLimit};
-
-    if (auto s = stat->as<AstStatBlock>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto i = stat->as<AstStatIf>())
-        return visit(scope, i, module, builtinTypes);
-    else if (auto s = stat->as<AstStatWhile>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatRepeat>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto r = stat->as<AstStatReturn>())
-        return visit(scope, r, module, builtinTypes);
-    else if (auto e = stat->as<AstStatExpr>())
-        return visit(scope, e, module, builtinTypes);
-    else if (auto s = stat->as<AstStatLocal>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatFor>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatForIn>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto a = stat->as<AstStatAssign>())
-        return visit(scope, a, module, builtinTypes);
-    else if (auto a = stat->as<AstStatCompoundAssign>())
-        return visit(scope, a, module, builtinTypes);
-    else if (auto f = stat->as<AstStatFunction>())
-        return visit(scope, f, module, builtinTypes);
-    else if (auto f = stat->as<AstStatLocalFunction>())
-        return visit(scope, f, module, builtinTypes);
-    else if (auto a = stat->as<AstStatTypeAlias>())
-        return visit(scope, a, module, builtinTypes);
-    else if (auto s = stat->as<AstStatDeclareGlobal>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatDeclareFunction>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatDeclareClass>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatError>())
-        return visit(scope, s, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatBlock* block, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    RecursionCounter counter{&recursionCount};
-
-    if (recursionCount >= FInt::LuauAnySummaryRecursionLimit)
-        return; // don't report
-
-    for (AstStat* stat : block->body)
-        visit(scope, stat, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatIf* ifStatement, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (ifStatement->thenbody)
-    {
-        const Scope* thenScope = findInnerMostScope(ifStatement->thenbody->location, module);
-        visit(thenScope, ifStatement->thenbody, module, builtinTypes);
-    }
-
-    if (ifStatement->elsebody)
-    {
-        const Scope* elseScope = findInnerMostScope(ifStatement->elsebody->location, module);
-        visit(elseScope, ifStatement->elsebody, module, builtinTypes);
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatWhile* while_, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* whileScope = findInnerMostScope(while_->location, module);
-    visit(whileScope, while_->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatRepeat* repeat, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* repeatScope = findInnerMostScope(repeat->location, module);
-    visit(repeatScope, repeat->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatReturn* ret, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* retScope = findInnerMostScope(ret->location, module);
-
-    auto ctxNode = getNode(rootSrc, ret);
-    bool seenTP = false;
-
-    for (auto val : ret->list)
-    {
-        if (isAnyCall(retScope, val, module, builtinTypes))
-        {
-            TelemetryTypePair types;
-            types.inferredType = toString(lookupType(val, module, builtinTypes));
-            TypeInfo ti{Pattern::FuncApp, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-
-        if (isAnyCast(retScope, val, module, builtinTypes))
-        {
-            if (auto cast = val->as<AstExprTypeAssertion>())
-            {
-                TelemetryTypePair types;
-
-                types.annotatedType = toString(lookupAnnotation(cast->annotation, module, builtinTypes));
-                types.inferredType = toString(lookupType(cast->expr, module, builtinTypes));
-
-                TypeInfo ti{Pattern::Casts, toString(ctxNode), types};
-                typeInfo.push_back(ti);
-            }
-        }
-
-        if (ret->list.size > 1 && !seenTP)
-        {
-            if (containsAny(retScope->returnType))
-            {
-                seenTP = true;
-
-                TelemetryTypePair types;
-
-                types.inferredType = toString(retScope->returnType);
-
-                TypeInfo ti{Pattern::TypePk, toString(ctxNode), types};
-                typeInfo.push_back(ti);
-            }
-        }
-    }
-
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatLocal* local, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, local);
-
-    TypePackId values = reconstructTypePack(local->values, module, builtinTypes);
-    auto [head, tail] = flatten(values);
-
-    size_t posn = 0;
-    for (AstLocal* loc : local->vars)
-    {
-        if (local->vars.data[0] == loc && posn < local->values.size)
-        {
-            if (loc->annotation)
-            {
-                auto annot = lookupAnnotation(loc->annotation, module, builtinTypes);
-                if (containsAny(annot))
-                {
-                    TelemetryTypePair types;
-
-                    types.annotatedType = toString(annot);
-                    types.inferredType = toString(lookupType(local->values.data[posn], module, builtinTypes));
-
-                    TypeInfo ti{Pattern::VarAnnot, toString(ctxNode), types};
-                    typeInfo.push_back(ti);
-                }
-            }
-
-            const AstExprTypeAssertion* maybeRequire = local->values.data[posn]->as<AstExprTypeAssertion>();
-            if (!maybeRequire)
-                continue;
-
-            if (std::min(local->values.size - 1, posn) < head.size())
-            {
-                if (isAnyCast(scope, local->values.data[posn], module, builtinTypes))
-                {
-                    TelemetryTypePair types;
-
-                    types.inferredType = toString(head[std::min(local->values.size - 1, posn)]);
-
-                    TypeInfo ti{Pattern::Casts, toString(ctxNode), types};
-                    typeInfo.push_back(ti);
-                }
-            }
-        }
-        else
-        {
-
-            if (std::min(local->values.size - 1, posn) < head.size())
-            {
-                if (loc->annotation)
-                {
-                    auto annot = lookupAnnotation(loc->annotation, module, builtinTypes);
-                    if (containsAny(annot))
-                    {
-                        TelemetryTypePair types;
-
-                        types.annotatedType = toString(annot);
-                        types.inferredType = toString(head[std::min(local->values.size - 1, posn)]);
-
-                        TypeInfo ti{Pattern::VarAnnot, toString(ctxNode), types};
-                        typeInfo.push_back(ti);
-                    }
-                }
-            }
-            else
-            {
-                if (tail)
-                {
-                    if (containsAny(*tail))
-                    {
-                        TelemetryTypePair types;
-
-                        types.inferredType = toString(*tail);
-
-                        TypeInfo ti{Pattern::VarAny, toString(ctxNode), types};
-                        typeInfo.push_back(ti);
-                    }
-                }
-            }
-        }
-
-        ++posn;
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatFor* for_, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* forScope = findInnerMostScope(for_->location, module);
-    visit(forScope, for_->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatForIn* forIn, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* loopScope = findInnerMostScope(forIn->location, module);
-    visit(loopScope, forIn->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatAssign* assign, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, assign);
-
-    TypePackId values = reconstructTypePack(assign->values, module, builtinTypes);
-    auto [head, tail] = flatten(values);
-
-    size_t posn = 0;
-    for (AstExpr* var : assign->vars)
-    {
-        TypeId tp = lookupType(var, module, builtinTypes);
-        if (containsAny(tp))
-        {
-            TelemetryTypePair types;
-
-            types.annotatedType = toString(tp);
-
-            auto loc = std::min(assign->vars.size - 1, posn);
-            if (head.size() >= assign->vars.size && posn < head.size())
-            {
-                types.inferredType = toString(head[posn]);
-            }
-            else if (loc < head.size())
-                types.inferredType = toString(head[loc]);
-            else
-                types.inferredType = toString(builtinTypes->nilType);
-
-            TypeInfo ti{Pattern::Assign, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-        ++posn;
-    }
-
-    for (AstExpr* val : assign->values)
-    {
-        if (isAnyCall(scope, val, module, builtinTypes))
-        {
-            TelemetryTypePair types;
-
-            types.inferredType = toString(lookupType(val, module, builtinTypes));
-
-            TypeInfo ti{Pattern::FuncApp, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-
-        if (isAnyCast(scope, val, module, builtinTypes))
-        {
-            if (auto cast = val->as<AstExprTypeAssertion>())
-            {
-                TelemetryTypePair types;
-
-                types.annotatedType = toString(lookupAnnotation(cast->annotation, module, builtinTypes));
-                types.inferredType = toString(lookupType(val, module, builtinTypes));
-
-                TypeInfo ti{Pattern::Casts, toString(ctxNode), types};
-                typeInfo.push_back(ti);
-            }
-        }
-    }
-
-    if (tail)
-    {
-        if (containsAny(*tail))
-        {
-            TelemetryTypePair types;
-
-            types.inferredType = toString(*tail);
-
-            TypeInfo ti{Pattern::Assign, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatCompoundAssign* assign, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, assign);
-
-    TelemetryTypePair types;
-
-    types.inferredType = toString(lookupType(assign->value, module, builtinTypes));
-    types.annotatedType = toString(lookupType(assign->var, module, builtinTypes));
-
-    if (module->astTypes.contains(assign->var))
-    {
-        if (containsAny(*module->astTypes.find(assign->var)))
-        {
-            TypeInfo ti{Pattern::Assign, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-    }
-    else if (module->astTypePacks.contains(assign->var))
-    {
-        if (containsAny(*module->astTypePacks.find(assign->var)))
-        {
-            TypeInfo ti{Pattern::Assign, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-    }
-
-    if (isAnyCall(scope, assign->value, module, builtinTypes))
-    {
-        TypeInfo ti{Pattern::FuncApp, toString(ctxNode), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (isAnyCast(scope, assign->value, module, builtinTypes))
-    {
-        if (auto cast = assign->value->as<AstExprTypeAssertion>())
-        {
-            types.annotatedType = toString(lookupAnnotation(cast->annotation, module, builtinTypes));
-            types.inferredType = toString(lookupType(cast->expr, module, builtinTypes));
-
-            TypeInfo ti{Pattern::Casts, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatFunction* function, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    TelemetryTypePair types;
-    types.inferredType = toString(lookupType(function->func, module, builtinTypes));
-
-    if (hasVariadicAnys(scope, function->func, module, builtinTypes))
-    {
-        TypeInfo ti{Pattern::VarAny, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (hasArgAnys(scope, function->func, module, builtinTypes))
-    {
-        TypeInfo ti{Pattern::FuncArg, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (hasAnyReturns(scope, function->func, module, builtinTypes))
-    {
-        TypeInfo ti{Pattern::FuncRet, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (function->func->body->body.size > 0)
-        visit(scope, function->func->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatLocalFunction* function, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    TelemetryTypePair types;
-
-    if (hasVariadicAnys(scope, function->func, module, builtinTypes))
-    {
-        types.inferredType = toString(lookupType(function->func, module, builtinTypes));
-        TypeInfo ti{Pattern::VarAny, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (hasArgAnys(scope, function->func, module, builtinTypes))
-    {
-        types.inferredType = toString(lookupType(function->func, module, builtinTypes));
-        TypeInfo ti{Pattern::FuncArg, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (hasAnyReturns(scope, function->func, module, builtinTypes))
-    {
-        types.inferredType = toString(lookupType(function->func, module, builtinTypes));
-        TypeInfo ti{Pattern::FuncRet, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (function->func->body->body.size > 0)
-        visit(scope, function->func->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatTypeAlias* alias, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, alias);
-
-    auto annot = lookupAnnotation(alias->type, module, builtinTypes);
-    if (containsAny(annot))
-    {
-        // no expr => no inference for aliases
-        TelemetryTypePair types;
-
-        types.annotatedType = toString(annot);
-        TypeInfo ti{Pattern::Alias, toString(ctxNode), types};
-        typeInfo.push_back(ti);
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, expr);
-
-    if (isAnyCall(scope, expr->expr, module, builtinTypes))
-    {
-        TelemetryTypePair types;
-        types.inferredType = toString(lookupType(expr->expr, module, builtinTypes));
-
-        TypeInfo ti{Pattern::FuncApp, toString(ctxNode), types};
-        typeInfo.push_back(ti);
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatDeclareGlobal* declareGlobal, const Module* module, NotNull<BuiltinTypes> builtinTypes) {}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatDeclareClass* declareClass, const Module* module, NotNull<BuiltinTypes> builtinTypes) {}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatDeclareFunction* declareFunction, const Module* module, NotNull<BuiltinTypes> builtinTypes) {}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatError* error, const Module* module, NotNull<BuiltinTypes> builtinTypes) {}
-
-TypeId AnyTypeSummary::checkForFamilyInhabitance(const TypeId instance, const Location location)
-{
-    if (seenTypeFamilyInstances.find(instance))
-        return instance;
-
-    seenTypeFamilyInstances.insert(instance);
-    return instance;
-}
-
-TypeId AnyTypeSummary::lookupType(const AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const TypeId* ty = module->astTypes.find(expr);
-    if (ty)
-        return checkForFamilyInhabitance(follow(*ty), expr->location);
-
-    const TypePackId* tp = module->astTypePacks.find(expr);
-    if (tp)
-    {
-        if (auto fst = first(*tp, /*ignoreHiddenVariadics*/ false))
-            return checkForFamilyInhabitance(*fst, expr->location);
-        else if (finite(*tp) && size(*tp) == 0)
-            return checkForFamilyInhabitance(builtinTypes->nilType, expr->location);
-    }
-
-    return builtinTypes->errorRecoveryType();
-}
-
-TypePackId AnyTypeSummary::reconstructTypePack(AstArray<AstExpr*> exprs, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (exprs.size == 0)
-        return arena.addTypePack(TypePack{{}, std::nullopt});
-
-    std::vector<TypeId> head;
-
-    for (size_t i = 0; i < exprs.size - 1; ++i)
-    {
-        head.push_back(lookupType(exprs.data[i], module, builtinTypes));
-    }
-
-    const TypePackId* tail = module->astTypePacks.find(exprs.data[exprs.size - 1]);
-    if (tail)
-        return arena.addTypePack(TypePack{std::move(head), follow(*tail)});
-    else
-        return arena.addTypePack(TypePack{std::move(head), builtinTypes->errorRecoveryTypePack()});
-}
-
-bool AnyTypeSummary::isAnyCall(const Scope* scope, AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (auto call = expr->as<AstExprCall>())
-    {
-        TypePackId args = reconstructTypePack(call->args, module, builtinTypes);
-        if (containsAny(args))
-            return true;
-
-        TypeId func = lookupType(call->func, module, builtinTypes);
-        if (containsAny(func))
-            return true;
-    }
-    return false;
-}
-
-bool AnyTypeSummary::hasVariadicAnys(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (expr->vararg && expr->varargAnnotation)
-    {
-        auto annot = lookupPackAnnotation(expr->varargAnnotation, module);
-        if (annot && containsAny(*annot))
-        {
-            return true;
-        }
-    }
-    return false;
-}
-
-bool AnyTypeSummary::hasArgAnys(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (expr->args.size > 0)
-    {
-        for (const AstLocal* arg : expr->args)
-        {
-            if (arg->annotation)
-            {
-                auto annot = lookupAnnotation(arg->annotation, module, builtinTypes);
-                if (containsAny(annot))
-                {
-                    return true;
-                }
-            }
-        }
-    }
-    return false;
-}
-
-bool AnyTypeSummary::hasAnyReturns(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (!expr->returnAnnotation)
-    {
-        return false;
-    }
-
-    for (AstType* ret : expr->returnAnnotation->types)
-    {
-        if (containsAny(lookupAnnotation(ret, module, builtinTypes)))
-        {
-            return true;
-        }
-    }
-
-    if (expr->returnAnnotation->tailType)
-    {
-        auto annot = lookupPackAnnotation(expr->returnAnnotation->tailType, module);
-        if (annot && containsAny(*annot))
-        {
-            return true;
-        }
-    }
-
-    return false;
-}
-
-bool AnyTypeSummary::isAnyCast(const Scope* scope, AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (auto cast = expr->as<AstExprTypeAssertion>())
-    {
-        auto annot = lookupAnnotation(cast->annotation, module, builtinTypes);
-        if (containsAny(annot))
-        {
-            return true;
-        }
-    }
-    return false;
-}
-
-TypeId AnyTypeSummary::lookupAnnotation(AstType* annotation, const Module* module, NotNull<BuiltinTypes> builtintypes)
-{
-    if (FFlag::DebugLuauMagicTypes)
-    {
-        if (auto ref = annotation->as<AstTypeReference>(); ref && ref->parameters.size > 0)
-        {
-            if (auto ann = ref->parameters.data[0].type)
-            {
-                TypeId argTy = lookupAnnotation(ref->parameters.data[0].type, module, builtintypes);
-                return follow(argTy);
-            }
-        }
-    }
-
-    const TypeId* ty = module->astResolvedTypes.find(annotation);
-    if (ty)
-        return checkForTypeFunctionInhabitance(follow(*ty), annotation->location);
-    else
-        return checkForTypeFunctionInhabitance(builtintypes->errorRecoveryType(), annotation->location);
-}
-
-TypeId AnyTypeSummary::checkForTypeFunctionInhabitance(const TypeId instance, const Location location)
-{
-    if (seenTypeFunctionInstances.find(instance))
-        return instance;
-    seenTypeFunctionInstances.insert(instance);
-
-    return instance;
-}
-
-std::optional<TypePackId> AnyTypeSummary::lookupPackAnnotation(AstTypePack* annotation, const Module* module)
-{
-    const TypePackId* tp = module->astResolvedTypePacks.find(annotation);
-    if (tp != nullptr)
-        return {follow(*tp)};
-    return {};
-}
-
-bool AnyTypeSummary::containsAny(TypeId typ)
-{
-    typ = follow(typ);
-
-    if (auto t = seen.find(typ); t && !*t)
-    {
-        return false;
-    }
-
-    seen[typ] = false;
-
-    RecursionCounter counter{&recursionCount};
-    if (recursionCount >= FInt::LuauAnySummaryRecursionLimit)
-    {
-        return false;
-    }
-
-    bool found = false;
-
-    if (auto ty = get<AnyType>(typ))
-    {
-        found = true;
-    }
-    else if (auto ty = get<UnknownType>(typ))
-    {
-        found = true;
-    }
-    else if (auto ty = get<TableType>(typ))
-    {
-        for (auto& [_name, prop] : ty->props)
-        {
-            if (FFlag::LuauSolverV2)
-            {
-                if (auto newT = follow(prop.readTy))
-                {
-                    if (containsAny(*newT))
-                        found = true;
-                }
-                else if (auto newT = follow(prop.writeTy))
-                {
-                    if (containsAny(*newT))
-                        found = true;
-                }
-            }
-            else
-            {
-                if (containsAny(prop.type()))
-                    found = true;
-            }
-        }
-    }
-    else if (auto ty = get<IntersectionType>(typ))
-    {
-        for (auto part : ty->parts)
-        {
-            if (containsAny(part))
-            {
-                found = true;
-            }
-        }
-    }
-    else if (auto ty = get<UnionType>(typ))
-    {
-        for (auto option : ty->options)
-        {
-            if (containsAny(option))
-            {
-                found = true;
-            }
-        }
-    }
-    else if (auto ty = get<FunctionType>(typ))
-    {
-        if (containsAny(ty->argTypes))
-            found = true;
-        else if (containsAny(ty->retTypes))
-            found = true;
-    }
-
-    seen[typ] = found;
-
-    return found;
-}
-
-bool AnyTypeSummary::containsAny(TypePackId typ)
-{
-    typ = follow(typ);
-
-    if (auto t = seen.find(typ); t && !*t)
-    {
-        return false;
-    }
-
-    seen[typ] = false;
-
-    auto [head, tail] = flatten(typ);
-    bool found = false;
-
-    for (auto tp : head)
-    {
-        if (containsAny(tp))
-            found = true;
-    }
-
-    if (tail)
-    {
-        if (auto vtp = get<VariadicTypePack>(tail))
-        {
-            if (auto ty = get<AnyType>(follow(vtp->ty)))
-            {
-                found = true;
-            }
-        }
-        else if (auto tftp = get<TypeFunctionInstanceTypePack>(tail))
-        {
-
-            for (TypePackId tp : tftp->packArguments)
-            {
-                if (containsAny(tp))
-                {
-                    found = true;
-                }
-            }
-
-            for (TypeId t : tftp->typeArguments)
-            {
-                if (containsAny(t))
-                {
-                    found = true;
-                }
-            }
-        }
-    }
-
-    seen[typ] = found;
-
-    return found;
-}
-
-const Scope* AnyTypeSummary::findInnerMostScope(const Location location, const Module* module)
-{
-    const Scope* bestScope = module->getModuleScope().get();
-
-    bool didNarrow = false;
-    do
-    {
-        didNarrow = false;
-        for (auto scope : bestScope->children)
-        {
-            if (scope->location.encloses(location))
-            {
-                bestScope = scope.get();
-                didNarrow = true;
-                break;
-            }
-        }
-    } while (didNarrow && bestScope->children.size() > 0);
-
-    return bestScope;
-}
-
-std::optional<AstExpr*> AnyTypeSummary::matchRequire(const AstExprCall& call)
-{
-    const char* require = "require";
-
-    if (call.args.size != 1)
-        return std::nullopt;
-
-    const AstExprGlobal* funcAsGlobal = call.func->as<AstExprGlobal>();
-    if (!funcAsGlobal || funcAsGlobal->name != require)
-        return std::nullopt;
-
-    if (call.args.size != 1)
-        return std::nullopt;
-
-    return call.args.data[0];
-}
-
-AstNode* AnyTypeSummary::getNode(AstStatBlock* root, AstNode* node)
-{
-    FindReturnAncestry finder(node, root->location.end);
-    root->visit(&finder);
-
-    if (!finder.currNode)
-        finder.currNode = node;
-
-    LUAU_ASSERT(finder.found && finder.currNode);
-    return finder.currNode;
-}
-
-bool AnyTypeSummary::FindReturnAncestry::visit(AstStatLocalFunction* node)
-{
-    currNode = node;
-    return !found;
-}
-
-bool AnyTypeSummary::FindReturnAncestry::visit(AstStatFunction* node)
-{
-    currNode = node;
-    return !found;
-}
-
-bool AnyTypeSummary::FindReturnAncestry::visit(AstType* node)
-{
-    return !found;
-}
-
-bool AnyTypeSummary::FindReturnAncestry::visit(AstNode* node)
-{
-    if (node == stat)
-    {
-        found = true;
-    }
-
-    if (node->location.end == rootEnd && stat->location.end >= rootEnd)
-    {
-        currNode = node;
-        found = true;
-    }
-
-    return !found;
-}
-
-
-AnyTypeSummary::TypeInfo::TypeInfo(Pattern code, std::string node, TelemetryTypePair type)
-    : code(code)
-    , node(node)
-    , type(type)
-{
-}
-
-AnyTypeSummary::FindReturnAncestry::FindReturnAncestry(AstNode* stat, Position rootEnd)
-    : stat(stat)
-    , rootEnd(rootEnd)
-{
-}
-
-AnyTypeSummary::AnyTypeSummary() {}
-
-} // namespace Luau

Analysis/src/Anyification.cpp

@@ -88,7 +88,7 @@ TypePackId Anyification::clean(TypePackId tp)
 
 bool Anyification::ignoreChildren(TypeId ty)
 {
-    if (get<ClassType>(ty))
+    if (get<ExternType>(ty))
         return true;
 
     return ty->persistent;

Analysis/src/ApplyTypeFunction.cpp

@@ -31,7 +31,7 @@ bool ApplyTypeFunction::ignoreChildren(TypeId ty)
 {
     if (get<GenericType>(ty))
         return true;
-    else if (get<ClassType>(ty))
+    else if (get<ExternType>(ty))
         return true;
     else
         return false;

Analysis/src/AstJsonEncoder.cpp

@@ -8,6 +8,8 @@
 
 #include <math.h>
 
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+
 namespace Luau
 {
 
@@ -431,8 +433,16 @@ struct AstJsonEncoder : public AstVisitor
                 if (node->self)
                     PROP(self);
                 PROP(args);
-                if (node->returnAnnotation)
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
-                    PROP(returnAnnotation);
+                {
+                    if (node->returnAnnotation)
+                        PROP(returnAnnotation);
+                }
+                else
+                {
+                    if (node->returnAnnotation_DEPRECATED)
+                        write("returnAnnotation", node->returnAnnotation_DEPRECATED);
+                }
                 PROP(vararg);
                 PROP(varargLocation);
                 if (node->varargAnnotation)
@@ -465,26 +475,26 @@ struct AstJsonEncoder : public AstVisitor
         writeRaw("}");
     }
 
-    void write(const AstGenericType& genericType)
+    void write(class AstGenericType* genericType)
     {
         writeRaw("{");
         bool c = pushComma();
         writeType("AstGenericType");
-        write("name", genericType.name);
+        write("name", genericType->name);
-        if (genericType.defaultValue)
+        if (genericType->defaultValue)
-            write("luauType", genericType.defaultValue);
+            write("luauType", genericType->defaultValue);
         popComma(c);
         writeRaw("}");
     }
 
-    void write(const AstGenericTypePack& genericTypePack)
+    void write(class AstGenericTypePack* genericTypePack)
     {
         writeRaw("{");
         bool c = pushComma();
         writeType("AstGenericTypePack");
-        write("name", genericTypePack.name);
+        write("name", genericTypePack->name);
-        if (genericTypePack.defaultValue)
+        if (genericTypePack->defaultValue)
-            write("luauType", genericTypePack.defaultValue);
+            write("luauType", genericTypePack->defaultValue);
         popComma(c);
         writeRaw("}");
     }
@@ -902,7 +912,10 @@ struct AstJsonEncoder : public AstVisitor
                 PROP(paramNames);
                 PROP(vararg);
                 PROP(varargLocation);
-                PROP(retTypes);
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                    PROP(retTypes);
+                else
+                    write("retTypes", node->retTypes_DEPRECATED);
                 PROP(generics);
                 PROP(genericPacks);
             }
@@ -923,7 +936,7 @@ struct AstJsonEncoder : public AstVisitor
         );
     }
 
-    void write(const AstDeclaredClassProp& prop)
+    void write(const AstDeclaredExternTypeProperty& prop)
     {
         writeRaw("{");
         bool c = pushComma();
@@ -936,7 +949,7 @@ struct AstJsonEncoder : public AstVisitor
         writeRaw("}");
     }
 
-    void write(class AstStatDeclareClass* node)
+    void write(class AstStatDeclareExternType* node)
     {
         writeNode(
             node,
@@ -1048,7 +1061,10 @@ struct AstJsonEncoder : public AstVisitor
                 PROP(genericPacks);
                 PROP(argTypes);
                 PROP(argNames);
-                PROP(returnTypes);
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                    PROP(returnTypes);
+                else
+                    write("returnTypes", node->returnTypes_DEPRECATED);
             }
         );
     }
@@ -1065,6 +1081,11 @@ struct AstJsonEncoder : public AstVisitor
         );
     }
 
+    void write(class AstTypeOptional* node)
+    {
+        writeNode(node, "AstTypeOptional", [&]() {});
+    }
+
     void write(class AstTypeUnion* node)
     {
         writeNode(
@@ -1146,6 +1167,8 @@ struct AstJsonEncoder : public AstVisitor
             return writeString("checked");
         case AstAttr::Type::Native:
             return writeString("native");
+        case AstAttr::Type::Deprecated:
+            return writeString("deprecated");
         }
     }
 
@@ -1161,6 +1184,19 @@ struct AstJsonEncoder : public AstVisitor
         );
     }
 
+    bool visit(class AstTypeGroup* node) override
+    {
+        writeNode(
+            node,
+            "AstTypeGroup",
+            [&]()
+            {
+                write("inner", node->type);
+            }
+        );
+        return false;
+    }
+
     bool visit(class AstTypeSingletonBool* node) override
     {
         writeNode(
@@ -1409,7 +1445,7 @@ struct AstJsonEncoder : public AstVisitor
         return false;
     }
 
-    bool visit(class AstStatDeclareClass* node) override
+    bool visit(class AstStatDeclareExternType* node) override
     {
         write(node);
         return false;

Analysis/src/AstQuery.cpp

@@ -13,8 +13,6 @@
 
 LUAU_FASTFLAG(LuauSolverV2)
 
-LUAU_FASTFLAGVARIABLE(LuauDocumentationAtPosition)
-
 namespace Luau
 {
 
@@ -43,11 +41,15 @@ struct AutocompleteNodeFinder : public AstVisitor
 
     bool visit(AstStat* stat) override
     {
-        if (stat->location.begin < pos && pos <= stat->location.end)
+        // Consider 'local myLocal = 4;|' and 'local myLocal = 4', where '|' is the cursor position. In both cases, the cursor position is equal
+        // to `AstStatLocal.location.end`. However, in the first case (semicolon), we are starting a new statement, whilst in the second case
+        // (no semicolon) we are still part of the AstStatLocal, hence the different comparison check.
+        if (stat->location.begin < pos && (stat->hasSemicolon ? pos < stat->location.end : pos <= stat->location.end))
         {
             ancestry.push_back(stat);
             return true;
         }
+
         return false;
     }
 
@@ -518,7 +520,6 @@ static std::optional<DocumentationSymbol> getMetatableDocumentation(
     const AstName& index
 )
 {
-    LUAU_ASSERT(FFlag::LuauDocumentationAtPosition);
     auto indexIt = mtable->props.find("__index");
     if (indexIt == mtable->props.end())
         return std::nullopt;
@@ -573,30 +574,11 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
                             return checkOverloadedDocumentationSymbol(module, propIt->second.type(), parentExpr, propIt->second.documentationSymbol);
                     }
                 }
-                else if (const ClassType* ctv = get<ClassType>(parentTy))
+                else if (const ExternType* etv = get<ExternType>(parentTy))
                 {
-                    if (FFlag::LuauDocumentationAtPosition)
+                    while (etv)
                     {
-                        while (ctv)
+                        if (auto propIt = etv->props.find(indexName->index.value); propIt != etv->props.end())
-                        {
-                            if (auto propIt = ctv->props.find(indexName->index.value); propIt != ctv->props.end())
-                            {
-                                if (FFlag::LuauSolverV2)
-                                {
-                                    if (auto ty = propIt->second.readTy)
-                                        return checkOverloadedDocumentationSymbol(module, *ty, parentExpr, propIt->second.documentationSymbol);
-                                }
-                                else
-                                    return checkOverloadedDocumentationSymbol(
-                                        module, propIt->second.type(), parentExpr, propIt->second.documentationSymbol
-                                    );
-                            }
-                            ctv = ctv->parent ? Luau::get<Luau::ClassType>(*ctv->parent) : nullptr;
-                        }
-                    }
-                    else
-                    {
-                        if (auto propIt = ctv->props.find(indexName->index.value); propIt != ctv->props.end())
                         {
                             if (FFlag::LuauSolverV2)
                             {
@@ -608,17 +590,15 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
                                     module, propIt->second.type(), parentExpr, propIt->second.documentationSymbol
                                 );
                         }
+                        etv = etv->parent ? Luau::get<Luau::ExternType>(*etv->parent) : nullptr;
                     }
                 }
-                else if (FFlag::LuauDocumentationAtPosition)
+                else if (const PrimitiveType* ptv = get<PrimitiveType>(parentTy); ptv && ptv->metatable)
                 {
-                    if (const PrimitiveType* ptv = get<PrimitiveType>(parentTy); ptv && ptv->metatable)
+                    if (auto mtable = get<TableType>(*ptv->metatable))
                     {
-                        if (auto mtable = get<TableType>(*ptv->metatable))
+                        if (std::optional<std::string> docSymbol = getMetatableDocumentation(module, parentExpr, mtable, indexName->index))
-                        {
+                            return docSymbol;
-                            if (std::optional<std::string> docSymbol = getMetatableDocumentation(module, parentExpr, mtable, indexName->index))
-                                return docSymbol;
-                        }
                     }
                 }
             }

Analysis/src/Autocomplete.cpp

@@ -2,6 +2,7 @@
 #include "Luau/Autocomplete.h"
 
 #include "Luau/AstQuery.h"
+#include "Luau/TimeTrace.h"
 #include "Luau/TypeArena.h"
 #include "Luau/Module.h"
 #include "Luau/Frontend.h"
@@ -15,6 +16,9 @@ namespace Luau
 
 AutocompleteResult autocomplete(Frontend& frontend, const ModuleName& moduleName, Position position, StringCompletionCallback callback)
 {
+    LUAU_TIMETRACE_SCOPE("Luau::autocomplete", "Autocomplete");
+    LUAU_TIMETRACE_ARGUMENT("name", moduleName.c_str());
+
     const SourceModule* sourceModule = frontend.getSourceModule(moduleName);
     if (!sourceModule)
         return {};

Analysis/src/AutocompleteCore.cpp

@@ -10,6 +10,7 @@
 #include "Luau/Common.h"
 #include "Luau/FileResolver.h"
 #include "Luau/Frontend.h"
+#include "Luau/TimeTrace.h"
 #include "Luau/ToString.h"
 #include "Luau/Subtyping.h"
 #include "Luau/TypeInfer.h"
@@ -20,12 +21,13 @@
 #include <utility>
 
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAGVARIABLE(AutocompleteRequirePathSuggestions2)
-LUAU_DYNAMIC_FASTINT(LuauTypeSolverRelease)
 LUAU_FASTINT(LuauTypeInferIterationLimit)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
-
+LUAU_FASTFLAGVARIABLE(DebugLuauMagicVariableNames)
-LUAU_FASTFLAGVARIABLE(LuauAutocompleteRefactorsForIncrementalAutocomplete)
+LUAU_FASTFLAGVARIABLE(LuauAutocompleteUsesModuleForTypeCompatibility)
+LUAU_FASTFLAGVARIABLE(LuauAutocompleteUnionCopyPreviousSeen)
+LUAU_FASTFLAGVARIABLE(LuauAutocompleteMissingFollows)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 static const std::unordered_set<std::string> kStatementStartingKeywords =
     {"while", "if", "local", "repeat", "function", "do", "for", "return", "break", "continue", "type", "export"};
@@ -78,6 +80,8 @@ static ParenthesesRecommendation getParenRecommendationForIntersect(const Inters
     ParenthesesRecommendation rec = ParenthesesRecommendation::None;
     for (Luau::TypeId partId : intersect->parts)
     {
+        if (FFlag::LuauAutocompleteMissingFollows)
+            partId = follow(partId);
         if (auto partFunc = Luau::get<FunctionType>(partId))
         {
             rec = std::max(rec, getParenRecommendationForFunc(partFunc, nodes));
@@ -147,35 +151,91 @@ static std::optional<TypeId> findExpectedTypeAt(const Module& module, AstNode* n
     return *it;
 }
 
-static bool checkTypeMatch(TypeId subTy, TypeId superTy, NotNull<Scope> scope, TypeArena* typeArena, NotNull<BuiltinTypes> builtinTypes)
+static bool checkTypeMatch(
+    const Module& module,
+    TypeId subTy,
+    TypeId superTy,
+    NotNull<Scope> scope,
+    TypeArena* typeArena,
+    NotNull<BuiltinTypes> builtinTypes
+)
 {
     InternalErrorReporter iceReporter;
     UnifierSharedState unifierState(&iceReporter);
+    SimplifierPtr simplifier = newSimplifier(NotNull{typeArena}, builtinTypes);
     Normalizer normalizer{typeArena, builtinTypes, NotNull{&unifierState}};
-
+    if (FFlag::LuauAutocompleteUsesModuleForTypeCompatibility)
-    if (FFlag::LuauSolverV2)
     {
-        TypeCheckLimits limits;
+        if (module.checkedInNewSolver)
-        TypeFunctionRuntime typeFunctionRuntime{
+        {
-            NotNull{&iceReporter}, NotNull{&limits}
+            TypeCheckLimits limits;
-        }; // TODO: maybe subtyping checks should not invoke user-defined type function runtime
+            TypeFunctionRuntime typeFunctionRuntime{
+                NotNull{&iceReporter}, NotNull{&limits}
+            }; // TODO: maybe subtyping checks should not invoke user-defined type function runtime
 
-        unifierState.counters.recursionLimit = FInt::LuauTypeInferRecursionLimit;
+            unifierState.counters.recursionLimit = FInt::LuauTypeInferRecursionLimit;
-        unifierState.counters.iterationLimit = FInt::LuauTypeInferIterationLimit;
+            unifierState.counters.iterationLimit = FInt::LuauTypeInferIterationLimit;
 
-        Subtyping subtyping{builtinTypes, NotNull{typeArena}, NotNull{&normalizer}, NotNull{&typeFunctionRuntime}, NotNull{&iceReporter}};
+            Subtyping subtyping{
+                builtinTypes,
+                NotNull{typeArena},
+                NotNull{simplifier.get()},
+                NotNull{&normalizer},
+                NotNull{&typeFunctionRuntime},
+                NotNull{&iceReporter}
+            };
 
-        return subtyping.isSubtype(subTy, superTy, scope).isSubtype;
+            return subtyping.isSubtype(subTy, superTy, scope).isSubtype;
+        }
+        else
+        {
+            Unifier unifier(NotNull<Normalizer>{&normalizer}, scope, Location(), Variance::Covariant);
+
+            // Cost of normalization can be too high for autocomplete response time requirements
+            unifier.normalize = false;
+            unifier.checkInhabited = false;
+
+            unifierState.counters.recursionLimit = FInt::LuauTypeInferRecursionLimit;
+            unifierState.counters.iterationLimit = FInt::LuauTypeInferIterationLimit;
+
+            return unifier.canUnify(subTy, superTy).empty();
+        }
     }
     else
     {
-        Unifier unifier(NotNull<Normalizer>{&normalizer}, scope, Location(), Variance::Covariant);
+        if (FFlag::LuauSolverV2)
+        {
+            TypeCheckLimits limits;
+            TypeFunctionRuntime typeFunctionRuntime{
+                NotNull{&iceReporter}, NotNull{&limits}
+            }; // TODO: maybe subtyping checks should not invoke user-defined type function runtime
 
-        // Cost of normalization can be too high for autocomplete response time requirements
+            unifierState.counters.recursionLimit = FInt::LuauTypeInferRecursionLimit;
-        unifier.normalize = false;
+            unifierState.counters.iterationLimit = FInt::LuauTypeInferIterationLimit;
-        unifier.checkInhabited = false;
 
-        return unifier.canUnify(subTy, superTy).empty();
+            Subtyping subtyping{
+                builtinTypes,
+                NotNull{typeArena},
+                NotNull{simplifier.get()},
+                NotNull{&normalizer},
+                NotNull{&typeFunctionRuntime},
+                NotNull{&iceReporter}
+            };
+
+            return subtyping.isSubtype(subTy, superTy, scope).isSubtype;
+        }
+        else
+        {
+            Unifier unifier(NotNull<Normalizer>{&normalizer}, scope, Location(), Variance::Covariant);
+
+            // Cost of normalization can be too high for autocomplete response time requirements
+            unifier.normalize = false;
+            unifier.checkInhabited = false;
+            unifierState.counters.recursionLimit = FInt::LuauTypeInferRecursionLimit;
+            unifierState.counters.iterationLimit = FInt::LuauTypeInferIterationLimit;
+
+            return unifier.canUnify(subTy, superTy).empty();
+        }
     }
 }
 
@@ -201,10 +261,10 @@ static TypeCorrectKind checkTypeCorrectKind(
 
     TypeId expectedType = follow(*typeAtPosition);
 
-    auto checkFunctionType = [typeArena, builtinTypes, moduleScope, &expectedType](const FunctionType* ftv)
+    auto checkFunctionType = [typeArena, builtinTypes, moduleScope, &expectedType, &module](const FunctionType* ftv)
     {
         if (std::optional<TypeId> firstRetTy = first(ftv->retTypes))
-            return checkTypeMatch(*firstRetTy, expectedType, moduleScope, typeArena, builtinTypes);
+            return checkTypeMatch(module, *firstRetTy, expectedType, moduleScope, typeArena, builtinTypes);
 
         return false;
     };
@@ -227,7 +287,7 @@ static TypeCorrectKind checkTypeCorrectKind(
         }
     }
 
-    return checkTypeMatch(ty, expectedType, moduleScope, typeArena, builtinTypes) ? TypeCorrectKind::Correct : TypeCorrectKind::None;
+    return checkTypeMatch(module, ty, expectedType, moduleScope, typeArena, builtinTypes) ? TypeCorrectKind::Correct : TypeCorrectKind::None;
 }
 
 enum class PropIndexType
@@ -247,7 +307,7 @@ static void autocompleteProps(
     const std::vector<AstNode*>& nodes,
     AutocompleteEntryMap& result,
     std::unordered_set<TypeId>& seen,
-    std::optional<const ClassType*> containingClass = std::nullopt
+    std::optional<const ExternType*> containingExternType = std::nullopt
 )
 {
     rootTy = follow(rootTy);
@@ -270,15 +330,15 @@ static void autocompleteProps(
             if (calledWithSelf == ftv->hasSelf)
                 return true;
 
-            // Calls on classes require strict match between how function is declared and how it's called
+            // Calls on extern types require strict match between how function is declared and how it's called
-            if (get<ClassType>(rootTy))
+            if (get<ExternType>(rootTy))
                 return false;
 
             // When called with ':', but declared without 'self', it is invalid if a function has incompatible first argument or no arguments at all
             // When called with '.', but declared with 'self', it is considered invalid if first argument is compatible
             if (std::optional<TypeId> firstArgTy = first(ftv->argTypes))
             {
-                if (checkTypeMatch(rootTy, *firstArgTy, NotNull{module.getModuleScope().get()}, typeArena, builtinTypes))
+                if (checkTypeMatch(module, rootTy, *firstArgTy, NotNull{module.getModuleScope().get()}, typeArena, builtinTypes))
                     return calledWithSelf;
             }
 
@@ -304,7 +364,7 @@ static void autocompleteProps(
         return calledWithSelf;
     };
 
-    auto fillProps = [&](const ClassType::Props& props)
+    auto fillProps = [&](const ExternType::Props& props)
     {
         for (const auto& [name, prop] : props)
         {
@@ -337,7 +397,7 @@ static void autocompleteProps(
                     prop.deprecated,
                     isWrongIndexer(type),
                     typeCorrect,
-                    containingClass,
+                    containingExternType,
                     &prop,
                     prop.documentationSymbol,
                     {},
@@ -368,12 +428,12 @@ static void autocompleteProps(
         }
     };
 
-    if (auto cls = get<ClassType>(ty))
+    if (auto cls = get<ExternType>(ty))
     {
-        containingClass = containingClass.value_or(cls);
+        containingExternType = containingExternType.value_or(cls);
         fillProps(cls->props);
         if (cls->parent)
-            autocompleteProps(module, typeArena, builtinTypes, rootTy, *cls->parent, indexType, nodes, result, seen, containingClass);
+            autocompleteProps(module, typeArena, builtinTypes, rootTy, *cls->parent, indexType, nodes, result, seen, containingExternType);
     }
     else if (auto tbl = get<TableType>(ty))
         fillProps(tbl->props);
@@ -424,6 +484,21 @@ static void autocompleteProps(
             AutocompleteEntryMap inner;
             std::unordered_set<TypeId> innerSeen;
 
+            // If we don't do this, and we have the misfortune of receiving a
+            // recursive union like:
+            //
+            //  t1 where t1 = t1 | ExternType
+            //
+            // Then we are on a one way journey to a stack overflow.
+            if (FFlag::LuauAutocompleteUnionCopyPreviousSeen)
+            {
+                for (auto ty : seen)
+                {
+                    if (is<UnionType, IntersectionType>(ty))
+                        innerSeen.insert(ty);
+                }
+            }
+
             if (isNil(*iter))
             {
                 ++iter;
@@ -512,7 +587,7 @@ AutocompleteEntryMap autocompleteProps(
 AutocompleteEntryMap autocompleteModuleTypes(const Module& module, const ScopePtr& scopeAtPosition, Position position, std::string_view moduleName)
 {
     AutocompleteEntryMap result;
-    ScopePtr startScope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position);
+    ScopePtr startScope = scopeAtPosition;
     for (ScopePtr& scope = startScope; scope; scope = scope->parent)
     {
         if (auto it = scope->importedTypeBindings.find(std::string(moduleName)); it != scope->importedTypeBindings.end())
@@ -624,6 +699,30 @@ static std::optional<TypeId> findTypeElementAt(const AstTypeList& astTypeList, T
     return {};
 }
 
+static std::optional<TypeId> findTypeElementAt(AstTypePack* astTypePack, TypePackId tp, Position position)
+{
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
+    if (const auto typePack = astTypePack->as<AstTypePackExplicit>())
+    {
+        return findTypeElementAt(typePack->typeList, tp, position);
+    }
+    else if (const auto variadic = astTypePack->as<AstTypePackVariadic>())
+    {
+        if (variadic->location.containsClosed(position))
+        {
+            auto [_, tail] = flatten(tp);
+
+            if (tail)
+            {
+                if (const VariadicTypePack* vtp = get<VariadicTypePack>(follow(*tail)))
+                    return findTypeElementAt(variadic->variadicType, vtp->ty, position);
+            }
+        }
+    }
+
+    return {};
+}
+
 static std::optional<TypeId> findTypeElementAt(AstType* astType, TypeId ty, Position position)
 {
     ty = follow(ty);
@@ -644,8 +743,16 @@ static std::optional<TypeId> findTypeElementAt(AstType* astType, TypeId ty, Posi
         if (auto element = findTypeElementAt(type->argTypes, ftv->argTypes, position))
             return element;
 
-        if (auto element = findTypeElementAt(type->returnTypes, ftv->retTypes, position))
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
-            return element;
+        {
+            if (auto element = findTypeElementAt(type->returnTypes, ftv->retTypes, position))
+                return element;
+        }
+        else
+        {
+            if (auto element = findTypeElementAt(type->returnTypes_DEPRECATED, ftv->retTypes, position))
+                return element;
+        }
     }
 
     // It's possible to walk through other types like intrsection and unions if we find value in doing that
@@ -654,7 +761,7 @@ static std::optional<TypeId> findTypeElementAt(AstType* astType, TypeId ty, Posi
 
 std::optional<TypeId> getLocalTypeInScopeAt(const Module& module, const ScopePtr& scopeAtPosition, Position position, AstLocal* local)
 {
-    if (ScopePtr scope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position))
+    if (ScopePtr scope = scopeAtPosition)
     {
         for (const auto& [name, binding] : scope->bindings)
         {
@@ -796,7 +903,7 @@ AutocompleteEntryMap autocompleteTypeNames(
 {
     AutocompleteEntryMap result;
 
-    ScopePtr startScope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position);
+    ScopePtr startScope = scopeAtPosition;
 
     for (ScopePtr scope = startScope; scope; scope = scope->parent)
     {
@@ -975,29 +1082,46 @@ AutocompleteEntryMap autocompleteTypeNames(
             }
         }
 
-        if (!node->returnAnnotation)
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
-            return result;
-
-        for (size_t i = 0; i < node->returnAnnotation->types.size; i++)
         {
-            AstType* ret = node->returnAnnotation->types.data[i];
+            if (!node->returnAnnotation)
+                return result;
 
-            if (ret->location.containsClosed(position))
+            if (const auto typePack = node->returnAnnotation->as<AstTypePackExplicit>())
             {
-                if (const FunctionType* ftv = tryGetExpectedFunctionType(module, node))
+                for (size_t i = 0; i < typePack->typeList.types.size; i++)
                 {
-                    if (auto ty = tryGetTypePackTypeAt(ftv->retTypes, i))
+                    AstType* ret = typePack->typeList.types.data[i];
-                        tryAddTypeCorrectSuggestion(result, startScope, topType, *ty, position);
+
+                    if (ret->location.containsClosed(position))
+                    {
+                        if (const FunctionType* ftv = tryGetExpectedFunctionType(module, node))
+                        {
+                            if (auto ty = tryGetTypePackTypeAt(ftv->retTypes, i))
+                                tryAddTypeCorrectSuggestion(result, startScope, topType, *ty, position);
+                        }
+
+                        // TODO: with additional type information, we could suggest inferred return type here
+                        break;
+                    }
                 }
 
-                // TODO: with additional type information, we could suggest inferred return type here
+                if (AstTypePack* retTp = typePack->typeList.tailType)
-                break;
+                {
+                    if (auto variadic = retTp->as<AstTypePackVariadic>())
+                    {
+                        if (variadic->location.containsClosed(position))
+                        {
+                            if (const FunctionType* ftv = tryGetExpectedFunctionType(module, node))
+                            {
+                                if (auto ty = tryGetTypePackTypeAt(ftv->retTypes, ~0u))
+                                    tryAddTypeCorrectSuggestion(result, startScope, topType, *ty, position);
+                            }
+                        }
+                    }
+                }
             }
-        }
+            else if (auto variadic = node->returnAnnotation->as<AstTypePackVariadic>())
-
-        if (AstTypePack* retTp = node->returnAnnotation->tailType)
-        {
-            if (auto variadic = retTp->as<AstTypePackVariadic>())
             {
                 if (variadic->location.containsClosed(position))
                 {
@@ -1009,6 +1133,43 @@ AutocompleteEntryMap autocompleteTypeNames(
                 }
             }
         }
+        else
+        {
+            if (!node->returnAnnotation_DEPRECATED)
+                return result;
+
+            for (size_t i = 0; i < node->returnAnnotation_DEPRECATED->types.size; i++)
+            {
+                AstType* ret = node->returnAnnotation_DEPRECATED->types.data[i];
+
+                if (ret->location.containsClosed(position))
+                {
+                    if (const FunctionType* ftv = tryGetExpectedFunctionType(module, node))
+                    {
+                        if (auto ty = tryGetTypePackTypeAt(ftv->retTypes, i))
+                            tryAddTypeCorrectSuggestion(result, startScope, topType, *ty, position);
+                    }
+
+                    // TODO: with additional type information, we could suggest inferred return type here
+                    break;
+                }
+            }
+
+            if (AstTypePack* retTp = node->returnAnnotation_DEPRECATED->tailType)
+            {
+                if (auto variadic = retTp->as<AstTypePackVariadic>())
+                {
+                    if (variadic->location.containsClosed(position))
+                    {
+                        if (const FunctionType* ftv = tryGetExpectedFunctionType(module, node))
+                        {
+                            if (auto ty = tryGetTypePackTypeAt(ftv->retTypes, ~0u))
+                                tryAddTypeCorrectSuggestion(result, startScope, topType, *ty, position);
+                        }
+                    }
+                }
+            }
+        }
     }
 
     return result;
@@ -1129,7 +1290,7 @@ static AutocompleteEntryMap autocompleteStatement(
 )
 {
     // This is inefficient. :(
-    ScopePtr scope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position);
+    ScopePtr scope = scopeAtPosition;
 
     AutocompleteEntryMap result;
 
@@ -1286,6 +1447,15 @@ static AutocompleteContext autocompleteExpression(
 
     AstNode* node = ancestry.rbegin()[0];
 
+    if (FFlag::DebugLuauMagicVariableNames)
+    {
+        InternalErrorReporter ice;
+        if (auto local = node->as<AstExprLocal>(); local && local->local->name == "_luau_autocomplete_ice")
+            ice.ice("_luau_autocomplete_ice encountered", local->location);
+        if (auto global = node->as<AstExprGlobal>(); global && global->name == "_luau_autocomplete_ice")
+            ice.ice("_luau_autocomplete_ice encountered", global->location);
+    }
+
     if (node->is<AstExprIndexName>())
     {
         if (auto it = module.astTypes.find(node->asExpr()))
@@ -1298,7 +1468,7 @@ static AutocompleteContext autocompleteExpression(
     else
     {
         // This is inefficient. :(
-        ScopePtr scope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position);
+        ScopePtr scope = scopeAtPosition;
 
         while (scope)
         {
@@ -1367,7 +1537,7 @@ static AutocompleteResult autocompleteExpression(
     return {result, ancestry, context};
 }
 
-static std::optional<const ClassType*> getMethodContainingClass(const ModulePtr& module, AstExpr* funcExpr)
+static std::optional<const ExternType*> getMethodContainingExternType(const ModulePtr& module, AstExpr* funcExpr)
 {
     AstExpr* parentExpr = nullptr;
     if (auto indexName = funcExpr->as<AstExprIndexName>())
@@ -1391,14 +1561,14 @@ static std::optional<const ClassType*> getMethodContainingClass(const ModulePtr&
 
     Luau::TypeId parentType = Luau::follow(*parentIt);
 
-    if (auto parentClass = Luau::get<ClassType>(parentType))
+    if (auto parentExternType = Luau::get<ExternType>(parentType))
     {
-        return parentClass;
+        return parentExternType;
     }
 
     if (auto parentUnion = Luau::get<UnionType>(parentType))
     {
-        return returnFirstNonnullOptionOfType<ClassType>(parentUnion);
+        return returnFirstNonnullOptionOfType<ExternType>(parentUnion);
     }
 
     return std::nullopt;
@@ -1452,10 +1622,11 @@ static std::optional<AutocompleteEntryMap> convertRequireSuggestionsToAutocomple
         return std::nullopt;
 
     AutocompleteEntryMap result;
-    for (const RequireSuggestion& suggestion : *suggestions)
+    for (RequireSuggestion& suggestion : *suggestions)
     {
         AutocompleteEntry entry = {AutocompleteEntryKind::RequirePath};
         entry.insertText = std::move(suggestion.fullPath);
+        entry.tags = std::move(suggestion.tags);
         result[std::move(suggestion.label)] = std::move(entry);
     }
     return result;
@@ -1512,14 +1683,11 @@ static std::optional<AutocompleteEntryMap> autocompleteStringParams(
     {
         for (const std::string& tag : funcType->tags)
         {
-            if (FFlag::AutocompleteRequirePathSuggestions2)
+            if (tag == kRequireTagName && fileResolver)
             {
-                if (tag == kRequireTagName && fileResolver)
+                return convertRequireSuggestionsToAutocompleteEntryMap(fileResolver->getRequireSuggestions(module->name, candidateString));
-                {
-                    return convertRequireSuggestionsToAutocompleteEntryMap(fileResolver->getRequireSuggestions(module->name, candidateString));
-                }
             }
-            if (std::optional<AutocompleteEntryMap> ret = callback(tag, getMethodContainingClass(module, candidate->func), candidateString))
+            if (std::optional<AutocompleteEntryMap> ret = callback(tag, getMethodContainingExternType(module, candidate->func), candidateString))
             {
                 return ret;
             }
@@ -1537,6 +1705,8 @@ static std::optional<AutocompleteEntryMap> autocompleteStringParams(
     {
         for (TypeId part : intersect->parts)
         {
+            if (FFlag::LuauAutocompleteMissingFollows)
+                part = follow(part);
             if (auto candidateFunctionType = Luau::get<FunctionType>(part))
             {
                 if (std::optional<AutocompleteEntryMap> ret = performCallback(candidateFunctionType))
@@ -1685,7 +1855,7 @@ static std::optional<AutocompleteEntry> makeAnonymousAutofilled(
     if (!type)
         return std::nullopt;
 
-    const ScopePtr scope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(*module, position);
+    const ScopePtr scope = scopeAtPosition;
     if (!scope)
         return std::nullopt;
 
@@ -1702,13 +1872,14 @@ AutocompleteResult autocomplete_(
     NotNull<BuiltinTypes> builtinTypes,
     TypeArena* typeArena,
     std::vector<AstNode*>& ancestry,
-    Scope* globalScope,
+    Scope* globalScope, // [TODO] This is unused argument, do we really need this?
     const ScopePtr& scopeAtPosition,
     Position position,
     FileResolver* fileResolver,
     StringCompletionCallback callback
 )
 {
+    LUAU_TIMETRACE_SCOPE("Luau::autocomplete_", "AutocompleteCore");
     AstNode* node = ancestry.back();
 
     AstExprConstantNil dummy{Location{}};

Analysis/src/BuiltinDefinitions.cpp

@@ -3,22 +3,23 @@
 
 #include "Luau/Ast.h"
 #include "Luau/Clone.h"
+#include "Luau/Common.h"
+#include "Luau/ConstraintGenerator.h"
+#include "Luau/ConstraintSolver.h"
 #include "Luau/DenseHash.h"
 #include "Luau/Error.h"
 #include "Luau/Frontend.h"
-#include "Luau/Symbol.h"
+#include "Luau/InferPolarity.h"
-#include "Luau/Common.h"
-#include "Luau/ToString.h"
-#include "Luau/ConstraintSolver.h"
-#include "Luau/ConstraintGenerator.h"
 #include "Luau/NotNull.h"
-#include "Luau/TypeInfer.h"
+#include "Luau/Subtyping.h"
+#include "Luau/Symbol.h"
+#include "Luau/ToString.h"
+#include "Luau/Type.h"
 #include "Luau/TypeChecker2.h"
 #include "Luau/TypeFunction.h"
+#include "Luau/TypeInfer.h"
 #include "Luau/TypePack.h"
-#include "Luau/Type.h"
 #include "Luau/TypeUtils.h"
-#include "Luau/Subtyping.h"
 
 #include <algorithm>
 
@@ -29,51 +30,92 @@
  */
 
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_DYNAMIC_FASTINT(LuauTypeSolverRelease)
+LUAU_FASTFLAG(LuauNonReentrantGeneralization2)
-LUAU_FASTFLAGVARIABLE(LuauTypestateBuiltins2)
+LUAU_FASTFLAGVARIABLE(LuauTableCloneClonesType3)
-LUAU_FASTFLAGVARIABLE(LuauStringFormatArityFix)
+LUAU_FASTFLAGVARIABLE(LuauUserTypeFunTypecheck)
-
+LUAU_FASTFLAGVARIABLE(LuauMagicFreezeCheckBlocked)
-LUAU_FASTFLAG(AutocompleteRequirePathSuggestions2);
+LUAU_FASTFLAGVARIABLE(LuauFormatUseLastPosition)
 
 namespace Luau
 {
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionSelect(
+struct MagicSelect final : MagicFunction
-    TypeChecker& typechecker,
+{
-    const ScopePtr& scope,
+    std::optional<WithPredicate<TypePackId>>
-    const AstExprCall& expr,
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
-    WithPredicate<TypePackId> withPredicate
+    bool infer(const MagicFunctionCallContext& ctx) override;
-);
+};
-static std::optional<WithPredicate<TypePackId>> magicFunctionSetMetaTable(
-    TypeChecker& typechecker,
-    const ScopePtr& scope,
-    const AstExprCall& expr,
-    WithPredicate<TypePackId> withPredicate
-);
-static std::optional<WithPredicate<TypePackId>> magicFunctionAssert(
-    TypeChecker& typechecker,
-    const ScopePtr& scope,
-    const AstExprCall& expr,
-    WithPredicate<TypePackId> withPredicate
-);
-static std::optional<WithPredicate<TypePackId>> magicFunctionPack(
-    TypeChecker& typechecker,
-    const ScopePtr& scope,
-    const AstExprCall& expr,
-    WithPredicate<TypePackId> withPredicate
-);
-static std::optional<WithPredicate<TypePackId>> magicFunctionRequire(
-    TypeChecker& typechecker,
-    const ScopePtr& scope,
-    const AstExprCall& expr,
-    WithPredicate<TypePackId> withPredicate
-);
 
+struct MagicSetMetatable final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
 
-static bool dcrMagicFunctionSelect(MagicFunctionCallContext context);
+struct MagicAssert final : MagicFunction
-static bool dcrMagicFunctionRequire(MagicFunctionCallContext context);
+{
-static bool dcrMagicFunctionPack(MagicFunctionCallContext context);
+    std::optional<WithPredicate<TypePackId>>
-static bool dcrMagicFunctionFreeze(MagicFunctionCallContext context);
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
+
+struct MagicPack final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
+
+struct MagicRequire final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
+
+struct MagicClone final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
+
+struct MagicFreeze final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
+
+struct MagicFormat final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+    bool typeCheck(const MagicFunctionTypeCheckContext& ctx) override;
+};
+
+struct MagicMatch final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
+
+struct MagicGmatch final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
+
+struct MagicFind final : MagicFunction
+{
+    std::optional<WithPredicate<TypePackId>>
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>) override;
+    bool infer(const MagicFunctionCallContext& ctx) override;
+};
 
 TypeId makeUnion(TypeArena& arena, std::vector<TypeId>&& types)
 {
@@ -168,34 +210,10 @@ TypeId makeFunction(
     return arena.addType(std::move(ftv));
 }
 
-void attachMagicFunction(TypeId ty, MagicFunction fn)
+void attachMagicFunction(TypeId ty, std::shared_ptr<MagicFunction> magic)
 {
     if (auto ftv = getMutable<FunctionType>(ty))
-        ftv->magicFunction = fn;
+        ftv->magic = std::move(magic);
-    else
-        LUAU_ASSERT(!"Got a non functional type");
-}
-
-void attachDcrMagicFunction(TypeId ty, DcrMagicFunction fn)
-{
-    if (auto ftv = getMutable<FunctionType>(ty))
-        ftv->dcrMagicFunction = fn;
-    else
-        LUAU_ASSERT(!"Got a non functional type");
-}
-
-void attachDcrMagicRefinement(TypeId ty, DcrMagicRefinement fn)
-{
-    if (auto ftv = getMutable<FunctionType>(ty))
-        ftv->dcrMagicRefinement = fn;
-    else
-        LUAU_ASSERT(!"Got a non functional type");
-}
-
-void attachDcrMagicFunctionTypeCheck(TypeId ty, DcrMagicFunctionTypeCheck fn)
-{
-    if (auto ftv = getMutable<FunctionType>(ty))
-        ftv->dcrMagicTypeCheck = fn;
     else
         LUAU_ASSERT(!"Got a non functional type");
 }
@@ -230,6 +248,7 @@ void addGlobalBinding(GlobalTypes& globals, const ScopePtr& scope, const std::st
 
 void addGlobalBinding(GlobalTypes& globals, const ScopePtr& scope, const std::string& name, Binding binding)
 {
+    inferGenericPolarities(NotNull{&globals.globalTypes}, NotNull{scope.get()}, binding.typeId);
     scope->bindings[globals.globalNames.names->getOrAdd(name.c_str())] = binding;
 }
 
@@ -271,6 +290,22 @@ void assignPropDocumentationSymbols(TableType::Props& props, const std::string&
     }
 }
 
+static void finalizeGlobalBindings(ScopePtr scope)
+{
+    LUAU_ASSERT(FFlag::LuauUserTypeFunTypecheck);
+
+    for (const auto& pair : scope->bindings)
+    {
+        persist(pair.second.typeId);
+
+        if (TableType* ttv = getMutable<TableType>(pair.second.typeId))
+        {
+            if (!ttv->name)
+                ttv->name = "typeof(" + toString(pair.first) + ")";
+        }
+    }
+}
+
 void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeCheckForAutocomplete)
 {
     LUAU_ASSERT(!globals.globalTypes.types.isFrozen());
@@ -278,6 +313,9 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
 
     TypeArena& arena = globals.globalTypes;
     NotNull<BuiltinTypes> builtinTypes = globals.builtinTypes;
+    Scope* globalScope = nullptr; // NotNull<Scope> when removing FFlag::LuauNonReentrantGeneralization2
+    if (FFlag::LuauNonReentrantGeneralization2)
+        globalScope = globals.globalScope.get();
 
     if (FFlag::LuauSolverV2)
         builtinTypeFunctions().addToScope(NotNull{&arena}, NotNull{globals.globalScope.get()});
@@ -287,8 +325,8 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
     );
     LUAU_ASSERT(loadResult.success);
 
-    TypeId genericK = arena.addType(GenericType{"K"});
+    TypeId genericK = arena.addType(GenericType{globalScope, "K"});
-    TypeId genericV = arena.addType(GenericType{"V"});
+    TypeId genericV = arena.addType(GenericType{globalScope, "V"});
     TypeId mapOfKtoV = arena.addType(TableType{{}, TableIndexer(genericK, genericV), globals.globalScope->level, TableState::Generic});
 
     std::optional<TypeId> stringMetatableTy = getMetatable(builtinTypes->stringType, builtinTypes);
@@ -301,6 +339,28 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
 
     addGlobalBinding(globals, "string", it->second.type(), "@luau");
 
+    // Setup 'vector' metatable
+    if (auto it = globals.globalScope->exportedTypeBindings.find("vector"); it != globals.globalScope->exportedTypeBindings.end())
+    {
+        TypeId vectorTy = it->second.type;
+        ExternType* vectorCls = getMutable<ExternType>(vectorTy);
+
+        vectorCls->metatable = arena.addType(TableType{{}, std::nullopt, TypeLevel{}, TableState::Sealed});
+        TableType* metatableTy = Luau::getMutable<TableType>(vectorCls->metatable);
+
+        metatableTy->props["__add"] = {makeFunction(arena, vectorTy, {vectorTy}, {vectorTy})};
+        metatableTy->props["__sub"] = {makeFunction(arena, vectorTy, {vectorTy}, {vectorTy})};
+        metatableTy->props["__unm"] = {makeFunction(arena, vectorTy, {}, {vectorTy})};
+
+        std::initializer_list<TypeId> mulOverloads{
+            makeFunction(arena, vectorTy, {vectorTy}, {vectorTy}),
+            makeFunction(arena, vectorTy, {builtinTypes->numberType}, {vectorTy}),
+        };
+        metatableTy->props["__mul"] = {makeIntersection(arena, mulOverloads)};
+        metatableTy->props["__div"] = {makeIntersection(arena, mulOverloads)};
+        metatableTy->props["__idiv"] = {makeIntersection(arena, mulOverloads)};
+    }
+
     // next<K, V>(t: Table<K, V>, i: K?) -> (K?, V)
     TypePackId nextArgsTypePack = arena.addTypePack(TypePack{{mapOfKtoV, makeOption(builtinTypes, arena, genericK)}});
     TypePackId nextRetsTypePack = arena.addTypePack(TypePack{{makeOption(builtinTypes, arena, genericK), genericV}});
@@ -314,7 +374,7 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
     // pairs<K, V>(t: Table<K, V>) -> ((Table<K, V>, K?) -> (K, V), Table<K, V>, nil)
     addGlobalBinding(globals, "pairs", arena.addType(FunctionType{{genericK, genericV}, {}, pairsArgsTypePack, pairsReturnTypePack}), "@luau");
 
-    TypeId genericMT = arena.addType(GenericType{"MT"});
+    TypeId genericMT = arena.addType(GenericType{globalScope, "MT"});
 
     TableType tab{TableState::Generic, globals.globalScope->level};
     TypeId tabTy = arena.addType(tab);
@@ -326,7 +386,7 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
 
     if (FFlag::LuauSolverV2)
     {
-        TypeId genericT = arena.addType(GenericType{"T"});
+        TypeId genericT = arena.addType(GenericType{globalScope, "T"});
         TypeId tMetaMT = arena.addType(MetatableType{genericT, genericMT});
 
         // clang-format off
@@ -360,23 +420,30 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
         // clang-format on
     }
 
-    for (const auto& pair : globals.globalScope->bindings)
+    if (FFlag::LuauUserTypeFunTypecheck)
     {
-        persist(pair.second.typeId);
+        finalizeGlobalBindings(globals.globalScope);
-
+    }
-        if (TableType* ttv = getMutable<TableType>(pair.second.typeId))
+    else
+    {
+        for (const auto& pair : globals.globalScope->bindings)
         {
-            if (!ttv->name)
+            persist(pair.second.typeId);
-                ttv->name = "typeof(" + toString(pair.first) + ")";
+
+            if (TableType* ttv = getMutable<TableType>(pair.second.typeId))
+            {
+                if (!ttv->name)
+                    ttv->name = "typeof(" + toString(pair.first) + ")";
+            }
         }
     }
 
-    attachMagicFunction(getGlobalBinding(globals, "assert"), magicFunctionAssert);
+    attachMagicFunction(getGlobalBinding(globals, "assert"), std::make_shared<MagicAssert>());
 
     if (FFlag::LuauSolverV2)
     {
         // declare function assert<T>(value: T, errorMessage: string?): intersect<T, ~(false?)>
-        TypeId genericT = arena.addType(GenericType{"T"});
+        TypeId genericT = arena.addType(GenericType{globalScope, "T"});
         TypeId refinedTy = arena.addType(TypeFunctionInstanceType{
             NotNull{&builtinTypeFunctions().intersectFunc}, {genericT, arena.addType(NegationType{builtinTypes->falsyType})}, {}
         });
@@ -387,9 +454,8 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
         addGlobalBinding(globals, "assert", assertTy, "@luau");
     }
 
-    attachMagicFunction(getGlobalBinding(globals, "setmetatable"), magicFunctionSetMetaTable);
+    attachMagicFunction(getGlobalBinding(globals, "setmetatable"), std::make_shared<MagicSetMetatable>());
-    attachMagicFunction(getGlobalBinding(globals, "select"), magicFunctionSelect);
+    attachMagicFunction(getGlobalBinding(globals, "select"), std::make_shared<MagicSelect>());
-    attachDcrMagicFunction(getGlobalBinding(globals, "select"), dcrMagicFunctionSelect);
 
     if (TableType* ttv = getMutable<TableType>(getGlobalBinding(globals, "table")))
     {
@@ -400,12 +466,16 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
             // the top table type.  We do the best we can by modelling these
             // functions using unconstrained generics.  It's not quite right,
             // but it'll be ok for now.
-            TypeId genericTy = arena.addType(GenericType{"T"});
+            TypeId genericTy = arena.addType(GenericType{globalScope, "T"});
             TypePackId thePack = arena.addTypePack({genericTy});
             TypeId idTyWithMagic = arena.addType(FunctionType{{genericTy}, {}, thePack, thePack});
             ttv->props["freeze"] = makeProperty(idTyWithMagic, "@luau/global/table.freeze");
+            if (globalScope)
+                inferGenericPolarities(NotNull{&globals.globalTypes}, NotNull{globalScope}, idTyWithMagic);
 
             TypeId idTy = arena.addType(FunctionType{{genericTy}, {}, thePack, thePack});
+            if (globalScope)
+                inferGenericPolarities(NotNull{&globals.globalTypes}, NotNull{globalScope}, idTy);
             ttv->props["clone"] = makeProperty(idTy, "@luau/global/table.clone");
         }
         else
@@ -420,23 +490,67 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
         ttv->props["foreach"].deprecated = true;
         ttv->props["foreachi"].deprecated = true;
 
-        attachMagicFunction(ttv->props["pack"].type(), magicFunctionPack);
+        attachMagicFunction(ttv->props["pack"].type(), std::make_shared<MagicPack>());
-        attachDcrMagicFunction(ttv->props["pack"].type(), dcrMagicFunctionPack);
+        if (FFlag::LuauTableCloneClonesType3)
-        if (FFlag::LuauTypestateBuiltins2)
+            attachMagicFunction(ttv->props["clone"].type(), std::make_shared<MagicClone>());
-            attachDcrMagicFunction(ttv->props["freeze"].type(), dcrMagicFunctionFreeze);
+        attachMagicFunction(ttv->props["freeze"].type(), std::make_shared<MagicFreeze>());
     }
 
-    if (FFlag::AutocompleteRequirePathSuggestions2)
+    TypeId requireTy = getGlobalBinding(globals, "require");
+    attachTag(requireTy, kRequireTagName);
+    attachMagicFunction(requireTy, std::make_shared<MagicRequire>());
+
+    if (FFlag::LuauUserTypeFunTypecheck)
     {
-        TypeId requireTy = getGlobalBinding(globals, "require");
+        // Global scope cannot be the parent of the type checking environment because it can be changed by the embedder
-        attachTag(requireTy, kRequireTagName);
+        globals.globalTypeFunctionScope->exportedTypeBindings = globals.globalScope->exportedTypeBindings;
-        attachMagicFunction(requireTy, magicFunctionRequire);
+        globals.globalTypeFunctionScope->builtinTypeNames = globals.globalScope->builtinTypeNames;
-        attachDcrMagicFunction(requireTy, dcrMagicFunctionRequire);
+
-    }
+        // Type function runtime also removes a few standard libraries and globals, so we will take only the ones that are defined
-    else
+        static const char* typeFunctionRuntimeBindings[] = {
-    {
+            // Libraries
-        attachMagicFunction(getGlobalBinding(globals, "require"), magicFunctionRequire);
+            "math",
-        attachDcrMagicFunction(getGlobalBinding(globals, "require"), dcrMagicFunctionRequire);
+            "table",
+            "string",
+            "bit32",
+            "utf8",
+            "buffer",
+
+            // Globals
+            "assert",
+            "error",
+            "print",
+            "next",
+            "ipairs",
+            "pairs",
+            "select",
+            "unpack",
+            "getmetatable",
+            "setmetatable",
+            "rawget",
+            "rawset",
+            "rawlen",
+            "rawequal",
+            "tonumber",
+            "tostring",
+            "type",
+            "typeof",
+        };
+
+        for (auto& name : typeFunctionRuntimeBindings)
+        {
+            AstName astName = globals.globalNames.names->get(name);
+            LUAU_ASSERT(astName.value);
+
+            globals.globalTypeFunctionScope->bindings[astName] = globals.globalScope->bindings[astName];
+        }
+
+        LoadDefinitionFileResult typeFunctionLoadResult = frontend.loadDefinitionFile(
+            globals, globals.globalTypeFunctionScope, getTypeFunctionDefinitionSource(), "@luau", /* captureComments */ false, false
+        );
+        LUAU_ASSERT(typeFunctionLoadResult.success);
+
+        finalizeGlobalBindings(globals.globalTypeFunctionScope);
     }
 }
 
@@ -476,7 +590,7 @@ static std::vector<TypeId> parseFormatString(NotNull<BuiltinTypes> builtinTypes,
     return result;
 }
 
-std::optional<WithPredicate<TypePackId>> magicFunctionFormat(
+std::optional<WithPredicate<TypePackId>> MagicFormat::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -526,7 +640,7 @@ std::optional<WithPredicate<TypePackId>> magicFunctionFormat(
     return WithPredicate<TypePackId>{arena.addTypePack({typechecker.stringType})};
 }
 
-static bool dcrMagicFunctionFormat(MagicFunctionCallContext context)
+bool MagicFormat::infer(const MagicFunctionCallContext& context)
 {
     TypeArena* arena = context.solver->arena;
 
@@ -570,7 +684,7 @@ static bool dcrMagicFunctionFormat(MagicFunctionCallContext context)
     return true;
 }
 
-static void dcrMagicFunctionTypeCheckFormat(MagicFunctionTypeCheckContext context)
+bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
 {
     AstExprConstantString* fmt = nullptr;
     if (auto index = context.callSite->func->as<AstExprIndexName>(); index && context.callSite->self)
@@ -586,11 +700,18 @@ static void dcrMagicFunctionTypeCheckFormat(MagicFunctionTypeCheckContext contex
 
     if (!fmt)
     {
-        if (FFlag::LuauStringFormatArityFix)
+        context.typechecker->reportError(CountMismatch{1, std::nullopt, 0, CountMismatch::Arg, true, "string.format"}, context.callSite->location);
-            context.typechecker->reportError(CountMismatch{1, std::nullopt, 0, CountMismatch::Arg, true, "string.format"}, context.callSite->location);
+        return true;
-        return;
     }
 
+    // CLI-150726: The block below effectively constructs a type pack and then type checks it by going parameter-by-parameter.
+    // This does _not_ handle cases like:
+    //
+    //  local foo : () -> (...string) = (nil :: any)
+    //  print(string.format("%s %d %s", foo()))
+    //
+    // ... which should be disallowed.
+
     std::vector<TypeId> expected = parseFormatString(context.builtinTypes, fmt->value.data, fmt->value.size);
     const auto& [params, tail] = flatten(context.arguments);
 
@@ -602,15 +723,30 @@ static void dcrMagicFunctionTypeCheckFormat(MagicFunctionTypeCheckContext contex
     {
         TypeId actualTy = params[i + paramOffset];
         TypeId expectedTy = expected[i];
-        Location location = context.callSite->args.data[i + (calledWithSelf ? 0 : paramOffset)]->location;
+        Location location = FFlag::LuauFormatUseLastPosition
+            ? context.callSite->args.data[std::min(context.callSite->args.size - 1, i + (calledWithSelf ? 0 : paramOffset))]->location
+            : context.callSite->args.data[i + (calledWithSelf ? 0 : paramOffset)]->location;
         // use subtyping instead here
         SubtypingResult result = context.typechecker->subtyping->isSubtype(actualTy, expectedTy, context.checkScope);
+
         if (!result.isSubtype)
         {
-            Reasonings reasonings = context.typechecker->explainReasonings(actualTy, expectedTy, location, result);
+            switch (shouldSuppressErrors(NotNull{&context.typechecker->normalizer}, actualTy))
-            context.typechecker->reportError(TypeMismatch{expectedTy, actualTy, reasonings.toString()}, location);
+            {
+            case ErrorSuppression::Suppress:
+                break;
+            case ErrorSuppression::NormalizationFailed:
+                break;
+            case ErrorSuppression::DoNotSuppress:
+                Reasonings reasonings = context.typechecker->explainReasonings(actualTy, expectedTy, location, result);
+
+                if (!reasonings.suppressed)
+                    context.typechecker->reportError(TypeMismatch{expectedTy, actualTy, reasonings.toString()}, location);
+            }
         }
     }
+
+    return true;
 }
 
 static std::vector<TypeId> parsePatternString(NotNull<BuiltinTypes> builtinTypes, const char* data, size_t size)
@@ -673,7 +809,7 @@ static std::vector<TypeId> parsePatternString(NotNull<BuiltinTypes> builtinTypes
     return result;
 }
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionGmatch(
+std::optional<WithPredicate<TypePackId>> MagicGmatch::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -709,7 +845,7 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionGmatch(
     return WithPredicate<TypePackId>{arena.addTypePack({iteratorType})};
 }
 
-static bool dcrMagicFunctionGmatch(MagicFunctionCallContext context)
+bool MagicGmatch::infer(const MagicFunctionCallContext& context)
 {
     const auto& [params, tail] = flatten(context.arguments);
 
@@ -742,7 +878,7 @@ static bool dcrMagicFunctionGmatch(MagicFunctionCallContext context)
     return true;
 }
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionMatch(
+std::optional<WithPredicate<TypePackId>> MagicMatch::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -782,7 +918,7 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionMatch(
     return WithPredicate<TypePackId>{returnList};
 }
 
-static bool dcrMagicFunctionMatch(MagicFunctionCallContext context)
+bool MagicMatch::infer(const MagicFunctionCallContext& context)
 {
     const auto& [params, tail] = flatten(context.arguments);
 
@@ -818,7 +954,7 @@ static bool dcrMagicFunctionMatch(MagicFunctionCallContext context)
     return true;
 }
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionFind(
+std::optional<WithPredicate<TypePackId>> MagicFind::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -876,7 +1012,7 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionFind(
     return WithPredicate<TypePackId>{returnList};
 }
 
-static bool dcrMagicFunctionFind(MagicFunctionCallContext context)
+bool MagicFind::infer(const MagicFunctionCallContext& context)
 {
     const auto& [params, tail] = flatten(context.arguments);
 
@@ -953,11 +1089,9 @@ TypeId makeStringMetatable(NotNull<BuiltinTypes> builtinTypes)
 
 
     FunctionType formatFTV{arena->addTypePack(TypePack{{stringType}, variadicTailPack}), oneStringPack};
-    formatFTV.magicFunction = &magicFunctionFormat;
     formatFTV.isCheckedFunction = true;
     const TypeId formatFn = arena->addType(formatFTV);
-    attachDcrMagicFunction(formatFn, dcrMagicFunctionFormat);
+    attachMagicFunction(formatFn, std::make_shared<MagicFormat>());
-    attachDcrMagicFunctionTypeCheck(formatFn, dcrMagicFunctionTypeCheckFormat);
 
 
     const TypeId stringToStringType = makeFunction(*arena, std::nullopt, {}, {}, {stringType}, {}, {stringType}, /* checked */ true);
@@ -971,16 +1105,14 @@ TypeId makeStringMetatable(NotNull<BuiltinTypes> builtinTypes)
         makeFunction(*arena, stringType, {}, {}, {stringType, replArgType, optionalNumber}, {}, {stringType, numberType}, /* checked */ false);
     const TypeId gmatchFunc =
         makeFunction(*arena, stringType, {}, {}, {stringType}, {}, {arena->addType(FunctionType{emptyPack, stringVariadicList})}, /* checked */ true);
-    attachMagicFunction(gmatchFunc, magicFunctionGmatch);
+    attachMagicFunction(gmatchFunc, std::make_shared<MagicGmatch>());
-    attachDcrMagicFunction(gmatchFunc, dcrMagicFunctionGmatch);
 
     FunctionType matchFuncTy{
         arena->addTypePack({stringType, stringType, optionalNumber}), arena->addTypePack(TypePackVar{VariadicTypePack{stringType}})
     };
     matchFuncTy.isCheckedFunction = true;
     const TypeId matchFunc = arena->addType(matchFuncTy);
-    attachMagicFunction(matchFunc, magicFunctionMatch);
+    attachMagicFunction(matchFunc, std::make_shared<MagicMatch>());
-    attachDcrMagicFunction(matchFunc, dcrMagicFunctionMatch);
 
     FunctionType findFuncTy{
         arena->addTypePack({stringType, stringType, optionalNumber, optionalBoolean}),
@@ -988,8 +1120,7 @@ TypeId makeStringMetatable(NotNull<BuiltinTypes> builtinTypes)
     };
     findFuncTy.isCheckedFunction = true;
     const TypeId findFunc = arena->addType(findFuncTy);
-    attachMagicFunction(findFunc, magicFunctionFind);
+    attachMagicFunction(findFunc, std::make_shared<MagicFind>());
-    attachDcrMagicFunction(findFunc, dcrMagicFunctionFind);
 
     // string.byte : string -> number? -> number? -> ...number
     FunctionType stringDotByte{arena->addTypePack({stringType, optionalNumber, optionalNumber}), numberVariadicList};
@@ -1050,7 +1181,7 @@ TypeId makeStringMetatable(NotNull<BuiltinTypes> builtinTypes)
     return arena->addType(TableType{{{{"__index", {tableType}}}}, std::nullopt, TypeLevel{}, TableState::Sealed});
 }
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionSelect(
+std::optional<WithPredicate<TypePackId>> MagicSelect::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -1095,7 +1226,7 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionSelect(
     return std::nullopt;
 }
 
-static bool dcrMagicFunctionSelect(MagicFunctionCallContext context)
+bool MagicSelect::infer(const MagicFunctionCallContext& context)
 {
     if (context.callSite->args.size <= 0)
     {
@@ -1140,7 +1271,7 @@ static bool dcrMagicFunctionSelect(MagicFunctionCallContext context)
     return false;
 }
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionSetMetaTable(
+std::optional<WithPredicate<TypePackId>> MagicSetMetatable::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -1222,7 +1353,12 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionSetMetaTable(
     return WithPredicate<TypePackId>{arena.addTypePack({target})};
 }
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionAssert(
+bool MagicSetMetatable::infer(const MagicFunctionCallContext&)
+{
+    return false;
+}
+
+std::optional<WithPredicate<TypePackId>> MagicAssert::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -1256,7 +1392,12 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionAssert(
     return WithPredicate<TypePackId>{arena.addTypePack(TypePack{std::move(head), tail})};
 }
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionPack(
+bool MagicAssert::infer(const MagicFunctionCallContext&)
+{
+    return false;
+}
+
+std::optional<WithPredicate<TypePackId>> MagicPack::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -1299,7 +1440,7 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionPack(
     return WithPredicate<TypePackId>{arena.addTypePack({packedTable})};
 }
 
-static bool dcrMagicFunctionPack(MagicFunctionCallContext context)
+bool MagicPack::infer(const MagicFunctionCallContext& context)
 {
 
     TypeArena* arena = context.solver->arena;
@@ -1339,10 +1480,76 @@ static bool dcrMagicFunctionPack(MagicFunctionCallContext context)
     return true;
 }
 
-static std::optional<TypeId> freezeTable(TypeId inputType, MagicFunctionCallContext& context)
+std::optional<WithPredicate<TypePackId>> MagicClone::handleOldSolver(
+    TypeChecker& typechecker,
+    const ScopePtr& scope,
+    const AstExprCall& expr,
+    WithPredicate<TypePackId> withPredicate
+)
 {
+    LUAU_ASSERT(FFlag::LuauTableCloneClonesType3);
+
+    auto [paramPack, _predicates] = withPredicate;
+
+    TypeArena& arena = typechecker.currentModule->internalTypes;
+
+    const auto& [paramTypes, paramTail] = flatten(paramPack);
+    if (paramTypes.empty() || expr.args.size == 0)
+    {
+        typechecker.reportError(expr.argLocation, CountMismatch{1, std::nullopt, 0});
+        return std::nullopt;
+    }
+
+    TypeId inputType = follow(paramTypes[0]);
+
+    if (!get<TableType>(inputType))
+        return std::nullopt;
+
+    CloneState cloneState{typechecker.builtinTypes};
+    TypeId resultType = shallowClone(inputType, arena, cloneState);
+
+    TypePackId clonedTypePack = arena.addTypePack({resultType});
+    return WithPredicate<TypePackId>{clonedTypePack};
+}
+
+bool MagicClone::infer(const MagicFunctionCallContext& context)
+{
+    LUAU_ASSERT(FFlag::LuauTableCloneClonesType3);
+
     TypeArena* arena = context.solver->arena;
 
+    const auto& [paramTypes, paramTail] = flatten(context.arguments);
+    if (paramTypes.empty() || context.callSite->args.size == 0)
+    {
+        context.solver->reportError(CountMismatch{1, std::nullopt, 0}, context.callSite->argLocation);
+        return false;
+    }
+
+    TypeId inputType = follow(paramTypes[0]);
+
+    if (!get<TableType>(inputType))
+        return false;
+
+    CloneState cloneState{context.solver->builtinTypes};
+    TypeId resultType = shallowClone(inputType, *arena, cloneState, /* ignorePersistent */ true);
+
+    if (auto tableType = getMutable<TableType>(resultType))
+    {
+        tableType->scope = context.constraint->scope.get();
+    }
+
+    trackInteriorFreeType(context.constraint->scope.get(), resultType);
+
+    TypePackId clonedTypePack = arena->addTypePack({resultType});
+    asMutable(context.result)->ty.emplace<BoundTypePack>(clonedTypePack);
+
+    return true;
+}
+
+static std::optional<TypeId> freezeTable(TypeId inputType, const MagicFunctionCallContext& context)
+{
+    TypeArena* arena = context.solver->arena;
+    inputType = follow(inputType);
     if (auto mt = get<MetatableType>(inputType))
     {
         std::optional<TypeId> frozenTable = freezeTable(mt->table, context);
@@ -1359,7 +1566,7 @@ static std::optional<TypeId> freezeTable(TypeId inputType, MagicFunctionCallCont
     {
         // Clone the input type, this will become our final result type after we mutate it.
         CloneState cloneState{context.solver->builtinTypes};
-        TypeId resultType = shallowClone(inputType, *arena, cloneState);
+        TypeId resultType = shallowClone(inputType, *arena, cloneState, /* ignorePersistent */ true);
         auto tableTy = getMutable<TableType>(resultType);
         // `clone` should not break this.
         LUAU_ASSERT(tableTy);
@@ -1384,10 +1591,14 @@ static std::optional<TypeId> freezeTable(TypeId inputType, MagicFunctionCallCont
     return std::nullopt;
 }
 
-static bool dcrMagicFunctionFreeze(MagicFunctionCallContext context)
+std::optional<WithPredicate<TypePackId>> MagicFreeze::
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>)
 {
-    LUAU_ASSERT(FFlag::LuauTypestateBuiltins2);
+    return std::nullopt;
+}
 
+bool MagicFreeze::infer(const MagicFunctionCallContext& context)
+{
     TypeArena* arena = context.solver->arena;
     const DataFlowGraph* dfg = context.solver->dfg.get();
     Scope* scope = context.constraint->scope.get();
@@ -1405,6 +1616,17 @@ static bool dcrMagicFunctionFreeze(MagicFunctionCallContext context)
     std::optional<DefId> resultDef = dfg->getDefOptional(targetExpr);
     std::optional<TypeId> resultTy = resultDef ? scope->lookup(*resultDef) : std::nullopt;
 
+    if (FFlag::LuauMagicFreezeCheckBlocked)
+    {
+        if (resultTy && !get<BlockedType>(resultTy))
+        {
+            // If there's an existing result type but it's _not_ blocked, then
+            // we aren't type stating this builtin and should fall back to
+            // regular inference.
+            return false;
+        }
+    }
+
     std::optional<TypeId> frozenType = freezeTable(inputType, context);
 
     if (!frozenType)
@@ -1445,7 +1667,7 @@ static bool checkRequirePath(TypeChecker& typechecker, AstExpr* expr)
     return good;
 }
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionRequire(
+std::optional<WithPredicate<TypePackId>> MagicRequire::handleOldSolver(
     TypeChecker& typechecker,
     const ScopePtr& scope,
     const AstExprCall& expr,
@@ -1491,7 +1713,7 @@ static bool checkRequirePathDcr(NotNull<ConstraintSolver> solver, AstExpr* expr)
     return good;
 }
 
-static bool dcrMagicFunctionRequire(MagicFunctionCallContext context)
+bool MagicRequire::infer(const MagicFunctionCallContext& context)
 {
     if (context.callSite->args.size != 1)
     {

Analysis/src/Clone.cpp

@@ -1,16 +1,20 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Clone.h"
 
+#include "Luau/Common.h"
 #include "Luau/NotNull.h"
 #include "Luau/Type.h"
 #include "Luau/TypePack.h"
 #include "Luau/Unifiable.h"
+#include "Luau/VisitType.h"
 
 LUAU_FASTFLAG(LuauSolverV2)
 
 // For each `Luau::clone` call, we will clone only up to N amount of types _and_ packs, as controlled by this limit.
 LUAU_FASTINTVARIABLE(LuauTypeCloneIterationLimit, 100'000)
-
+LUAU_FASTFLAGVARIABLE(LuauClonedTableAndFunctionTypesMustHaveScopes)
+LUAU_FASTFLAGVARIABLE(LuauDoNotClonePersistentBindings)
+LUAU_FASTFLAG(LuauIncrementalAutocompleteDemandBasedCloning)
 namespace Luau
 {
 
@@ -27,6 +31,8 @@ const T* get(const Kind& kind)
 
 class TypeCloner
 {
+
+protected:
     NotNull<TypeArena> arena;
     NotNull<BuiltinTypes> builtinTypes;
 
@@ -38,17 +44,31 @@ class TypeCloner
     NotNull<SeenTypes> types;
     NotNull<SeenTypePacks> packs;
 
+    TypeId forceTy = nullptr;
+    TypePackId forceTp = nullptr;
+
     int steps = 0;
 
 public:
-    TypeCloner(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, NotNull<SeenTypes> types, NotNull<SeenTypePacks> packs)
+    TypeCloner(
+        NotNull<TypeArena> arena,
+        NotNull<BuiltinTypes> builtinTypes,
+        NotNull<SeenTypes> types,
+        NotNull<SeenTypePacks> packs,
+        TypeId forceTy,
+        TypePackId forceTp
+    )
         : arena(arena)
         , builtinTypes(builtinTypes)
         , types(types)
         , packs(packs)
+        , forceTy(forceTy)
+        , forceTp(forceTp)
     {
     }
 
+    virtual ~TypeCloner() = default;
+
     TypeId clone(TypeId ty)
     {
         shallowClone(ty);
@@ -107,12 +127,13 @@ private:
         }
     }
 
+protected:
     std::optional<TypeId> find(TypeId ty) const
     {
         ty = follow(ty, FollowOption::DisableLazyTypeThunks);
         if (auto it = types->find(ty); it != types->end())
             return it->second;
-        else if (ty->persistent)
+        else if (ty->persistent && ty != forceTy)
             return ty;
         return std::nullopt;
     }
@@ -122,7 +143,7 @@ private:
         tp = follow(tp);
         if (auto it = packs->find(tp); it != packs->end())
             return it->second;
-        else if (tp->persistent)
+        else if (tp->persistent && tp != forceTp)
             return tp;
         return std::nullopt;
     }
@@ -141,14 +162,14 @@ private:
     }
 
 public:
-    TypeId shallowClone(TypeId ty)
+    virtual TypeId shallowClone(TypeId ty)
     {
         // We want to [`Luau::follow`] but without forcing the expansion of [`LazyType`]s.
         ty = follow(ty, FollowOption::DisableLazyTypeThunks);
 
         if (auto clone = find(ty))
             return *clone;
-        else if (ty->persistent)
+        else if (ty->persistent && ty != forceTy)
             return ty;
 
         TypeId target = arena->addType(ty->ty);
@@ -158,8 +179,6 @@ public:
             generic->scope = nullptr;
         else if (auto free = getMutable<FreeType>(target))
             free->scope = nullptr;
-        else if (auto fn = getMutable<FunctionType>(target))
-            fn->scope = nullptr;
         else if (auto table = getMutable<TableType>(target))
             table->scope = nullptr;
 
@@ -168,13 +187,13 @@ public:
         return target;
     }
 
-    TypePackId shallowClone(TypePackId tp)
+    virtual TypePackId shallowClone(TypePackId tp)
     {
         tp = follow(tp);
 
         if (auto clone = find(tp))
             return *clone;
-        else if (tp->persistent)
+        else if (tp->persistent && tp != forceTp)
             return tp;
 
         TypePackId target = arena->addTypePack(tp->ty);
@@ -257,8 +276,7 @@ private:
             LUAU_ASSERT(!"Item holds neither TypeId nor TypePackId when enqueuing its children?");
     }
 
-    // ErrorType and ErrorTypePack is an alias to this type.
+    void cloneChildren(ErrorType* t)
-    void cloneChildren(Unifiable::Error* t)
     {
         // noop.
     }
@@ -337,7 +355,7 @@ private:
         t->metatable = shallowClone(t->metatable);
     }
 
-    void cloneChildren(ClassType* t)
+    void cloneChildren(ExternType* t)
     {
         for (auto& [_, p] : t->props)
             p = shallowClone(p);
@@ -377,7 +395,7 @@ private:
             ty = shallowClone(ty);
     }
 
-    void cloneChildren(LazyType* t)
+    virtual void cloneChildren(LazyType* t)
     {
         if (auto unwrapped = t->unwrapped.load())
             t->unwrapped.store(shallowClone(unwrapped));
@@ -428,6 +446,11 @@ private:
         t->boundTo = shallowClone(t->boundTo);
     }
 
+    void cloneChildren(ErrorTypePack* t)
+    {
+        // noop.
+    }
+
     void cloneChildren(VariadicTypePack* t)
     {
         t->ty = shallowClone(t->ty);
@@ -452,23 +475,122 @@ private:
     }
 };
 
+class FragmentAutocompleteTypeCloner final : public TypeCloner
+{
+    Scope* replacementForNullScope = nullptr;
+
+public:
+    FragmentAutocompleteTypeCloner(
+        NotNull<TypeArena> arena,
+        NotNull<BuiltinTypes> builtinTypes,
+        NotNull<SeenTypes> types,
+        NotNull<SeenTypePacks> packs,
+        TypeId forceTy,
+        TypePackId forceTp,
+        Scope* replacementForNullScope
+    )
+        : TypeCloner(arena, builtinTypes, types, packs, forceTy, forceTp)
+        , replacementForNullScope(replacementForNullScope)
+    {
+        LUAU_ASSERT(replacementForNullScope);
+    }
+
+    TypeId shallowClone(TypeId ty) override
+    {
+        // We want to [`Luau::follow`] but without forcing the expansion of [`LazyType`]s.
+        ty = follow(ty, FollowOption::DisableLazyTypeThunks);
+
+        if (auto clone = find(ty))
+            return *clone;
+        else if (ty->persistent && ty != forceTy)
+            return ty;
+
+        TypeId target = arena->addType(ty->ty);
+        asMutable(target)->documentationSymbol = ty->documentationSymbol;
+
+        if (auto generic = getMutable<GenericType>(target))
+            generic->scope = nullptr;
+        else if (auto free = getMutable<FreeType>(target))
+        {
+            free->scope = replacementForNullScope;
+        }
+        else if (auto tt = getMutable<TableType>(target))
+        {
+            if (FFlag::LuauClonedTableAndFunctionTypesMustHaveScopes)
+                tt->scope = replacementForNullScope;
+        }
+
+        (*types)[ty] = target;
+        queue.emplace_back(target);
+        return target;
+    }
+
+    TypePackId shallowClone(TypePackId tp) override
+    {
+        tp = follow(tp);
+
+        if (auto clone = find(tp))
+            return *clone;
+        else if (tp->persistent && tp != forceTp)
+            return tp;
+
+        TypePackId target = arena->addTypePack(tp->ty);
+
+        if (auto generic = getMutable<GenericTypePack>(target))
+            generic->scope = nullptr;
+        else if (auto free = getMutable<FreeTypePack>(target))
+            free->scope = replacementForNullScope;
+
+        (*packs)[tp] = target;
+        queue.emplace_back(target);
+        return target;
+    }
+
+    void cloneChildren(LazyType* t) override
+    {
+        // Do not clone lazy types
+        if (!FFlag::LuauIncrementalAutocompleteDemandBasedCloning)
+        {
+            if (auto unwrapped = t->unwrapped.load())
+                t->unwrapped.store(shallowClone(unwrapped));
+        }
+    }
+};
+
+
 } // namespace
 
-TypePackId shallowClone(TypePackId tp, TypeArena& dest, CloneState& cloneState)
+TypePackId shallowClone(TypePackId tp, TypeArena& dest, CloneState& cloneState, bool ignorePersistent)
 {
-    if (tp->persistent)
+    if (tp->persistent && !ignorePersistent)
         return tp;
 
-    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}};
+    TypeCloner cloner{
+        NotNull{&dest},
+        cloneState.builtinTypes,
+        NotNull{&cloneState.seenTypes},
+        NotNull{&cloneState.seenTypePacks},
+        nullptr,
+        ignorePersistent ? tp : nullptr
+    };
+
     return cloner.shallowClone(tp);
 }
 
-TypeId shallowClone(TypeId typeId, TypeArena& dest, CloneState& cloneState)
+TypeId shallowClone(TypeId typeId, TypeArena& dest, CloneState& cloneState, bool ignorePersistent)
 {
-    if (typeId->persistent)
+    if (typeId->persistent && !ignorePersistent)
         return typeId;
 
-    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}};
+    TypeCloner cloner{
+        NotNull{&dest},
+        cloneState.builtinTypes,
+        NotNull{&cloneState.seenTypes},
+        NotNull{&cloneState.seenTypePacks},
+        ignorePersistent ? typeId : nullptr,
+        nullptr
+    };
+
     return cloner.shallowClone(typeId);
 }
 
@@ -477,7 +599,7 @@ TypePackId clone(TypePackId tp, TypeArena& dest, CloneState& cloneState)
     if (tp->persistent)
         return tp;
 
-    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}};
+    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}, nullptr, nullptr};
     return cloner.clone(tp);
 }
 
@@ -486,13 +608,13 @@ TypeId clone(TypeId typeId, TypeArena& dest, CloneState& cloneState)
     if (typeId->persistent)
         return typeId;
 
-    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}};
+    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}, nullptr, nullptr};
     return cloner.clone(typeId);
 }
 
 TypeFun clone(const TypeFun& typeFun, TypeArena& dest, CloneState& cloneState)
 {
-    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}};
+    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}, nullptr, nullptr};
 
     TypeFun copy = typeFun;
 
@@ -517,4 +639,110 @@ TypeFun clone(const TypeFun& typeFun, TypeArena& dest, CloneState& cloneState)
     return copy;
 }
 
+Binding clone(const Binding& binding, TypeArena& dest, CloneState& cloneState)
+{
+    TypeCloner cloner{NotNull{&dest}, cloneState.builtinTypes, NotNull{&cloneState.seenTypes}, NotNull{&cloneState.seenTypePacks}, nullptr, nullptr};
+
+    Binding b;
+    b.deprecated = binding.deprecated;
+    b.deprecatedSuggestion = binding.deprecatedSuggestion;
+    b.documentationSymbol = binding.documentationSymbol;
+    b.location = binding.location;
+    b.typeId = cloner.clone(binding.typeId);
+
+    return b;
+}
+
+TypePackId cloneIncremental(TypePackId tp, TypeArena& dest, CloneState& cloneState, Scope* freshScopeForFreeTypes)
+{
+    if (tp->persistent)
+        return tp;
+
+    FragmentAutocompleteTypeCloner cloner{
+        NotNull{&dest},
+        cloneState.builtinTypes,
+        NotNull{&cloneState.seenTypes},
+        NotNull{&cloneState.seenTypePacks},
+        nullptr,
+        nullptr,
+        freshScopeForFreeTypes
+    };
+    return cloner.clone(tp);
+}
+
+TypeId cloneIncremental(TypeId typeId, TypeArena& dest, CloneState& cloneState, Scope* freshScopeForFreeTypes)
+{
+    if (typeId->persistent)
+        return typeId;
+
+    FragmentAutocompleteTypeCloner cloner{
+        NotNull{&dest},
+        cloneState.builtinTypes,
+        NotNull{&cloneState.seenTypes},
+        NotNull{&cloneState.seenTypePacks},
+        nullptr,
+        nullptr,
+        freshScopeForFreeTypes
+    };
+    return cloner.clone(typeId);
+}
+
+TypeFun cloneIncremental(const TypeFun& typeFun, TypeArena& dest, CloneState& cloneState, Scope* freshScopeForFreeTypes)
+{
+    FragmentAutocompleteTypeCloner cloner{
+        NotNull{&dest},
+        cloneState.builtinTypes,
+        NotNull{&cloneState.seenTypes},
+        NotNull{&cloneState.seenTypePacks},
+        nullptr,
+        nullptr,
+        freshScopeForFreeTypes
+    };
+
+    TypeFun copy = typeFun;
+
+    for (auto& param : copy.typeParams)
+    {
+        param.ty = cloner.clone(param.ty);
+
+        if (param.defaultValue)
+            param.defaultValue = cloner.clone(*param.defaultValue);
+    }
+
+    for (auto& param : copy.typePackParams)
+    {
+        param.tp = cloner.clone(param.tp);
+
+        if (param.defaultValue)
+            param.defaultValue = cloner.clone(*param.defaultValue);
+    }
+
+    copy.type = cloner.clone(copy.type);
+
+    return copy;
+}
+
+Binding cloneIncremental(const Binding& binding, TypeArena& dest, CloneState& cloneState, Scope* freshScopeForFreeTypes)
+{
+    FragmentAutocompleteTypeCloner cloner{
+        NotNull{&dest},
+        cloneState.builtinTypes,
+        NotNull{&cloneState.seenTypes},
+        NotNull{&cloneState.seenTypePacks},
+        nullptr,
+        nullptr,
+        freshScopeForFreeTypes
+    };
+
+    Binding b;
+    b.deprecated = binding.deprecated;
+    b.deprecatedSuggestion = binding.deprecatedSuggestion;
+    b.documentationSymbol = binding.documentationSymbol;
+    b.location = binding.location;
+    b.typeId = FFlag::LuauDoNotClonePersistentBindings && binding.typeId->persistent ? binding.typeId : cloner.clone(binding.typeId);
+
+    return b;
+}
+
+
 } // namespace Luau

Analysis/src/Constraint.cpp

@@ -3,7 +3,7 @@
 #include "Luau/Constraint.h"
 #include "Luau/VisitType.h"
 
-LUAU_FASTFLAGVARIABLE(LuauDontRefCountTypesInTypeFunctions)
+LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
 
 namespace Luau
 {
@@ -20,7 +20,7 @@ struct ReferenceCountInitializer : TypeOnceVisitor
 
     DenseHashSet<TypeId>* result;
 
-    ReferenceCountInitializer(DenseHashSet<TypeId>* result)
+    explicit ReferenceCountInitializer(DenseHashSet<TypeId>* result)
         : result(result)
     {
     }
@@ -43,26 +43,16 @@ struct ReferenceCountInitializer : TypeOnceVisitor
         return false;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
-        // ClassTypes never contain free types.
+        // ExternTypes never contain free types.
         return false;
     }
 
     bool visit(TypeId, const TypeFunctionInstanceType&) override
     {
-        // We do not consider reference counted types that are inside a type
+        return FFlag::DebugLuauGreedyGeneralization;
-        // function to be part of the reachable reference counted types.
-        // Otherwise, code can be constructed in just the right way such
-        // that two type functions both claim to mutate a free type, which
-        // prevents either type function from trying to generalize it, so
-        // we potentially get stuck.
-        //
-        // The default behavior here is `true` for "visit the child types"
-        // of this type, hence:
-        return !FFlag::LuauDontRefCountTypesInTypeFunctions;
     }
-
 };
 
 bool isReferenceCountedType(const TypeId typ)
@@ -114,6 +104,11 @@ DenseHashSet<TypeId> Constraint::getMaybeMutatedFreeTypes() const
     {
         rci.traverse(fchc->argsPack);
     }
+    else if (auto fcc = get<FunctionCallConstraint>(*this); fcc && FFlag::DebugLuauGreedyGeneralization)
+    {
+        rci.traverse(fcc->fn);
+        rci.traverse(fcc->argsPack);
+    }
     else if (auto ptc = get<PrimitiveTypeConstraint>(*this))
     {
         rci.traverse(ptc->freeType);
@@ -121,12 +116,15 @@ DenseHashSet<TypeId> Constraint::getMaybeMutatedFreeTypes() const
     else if (auto hpc = get<HasPropConstraint>(*this))
     {
         rci.traverse(hpc->resultType);
-        // `HasPropConstraints` should not mutate `subjectType`.
+        if (FFlag::DebugLuauGreedyGeneralization)
+            rci.traverse(hpc->subjectType);
     }
     else if (auto hic = get<HasIndexerConstraint>(*this))
     {
+        if (FFlag::DebugLuauGreedyGeneralization)
+            rci.traverse(hic->subjectType);
         rci.traverse(hic->resultType);
-        // `HasIndexerConstraint` should not mutate `subjectType` or `indexType`.
+        // `HasIndexerConstraint` should not mutate `indexType`.
     }
     else if (auto apc = get<AssignPropConstraint>(*this))
     {
@@ -145,10 +143,18 @@ DenseHashSet<TypeId> Constraint::getMaybeMutatedFreeTypes() const
             rci.traverse(ty);
         // `UnpackConstraint` should not mutate `sourcePack`.
     }
+    else if (auto rpc = get<ReduceConstraint>(*this); FFlag::DebugLuauGreedyGeneralization && rpc)
+    {
+        rci.traverse(rpc->ty);
+    }
     else if (auto rpc = get<ReducePackConstraint>(*this))
     {
         rci.traverse(rpc->tp);
     }
+    else if (auto tcc = get<TableCheckConstraint>(*this))
+    {
+        rci.traverse(tcc->exprType);
+    }
 
     return types;
 }

Analysis/src/DataFlowGraph.cpp

@@ -13,33 +13,25 @@
 
 LUAU_FASTFLAG(DebugLuauFreezeArena)
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAG(LuauTypestateBuiltins2)
+LUAU_FASTFLAGVARIABLE(LuauPreprocessTypestatedArgument)
-
+LUAU_FASTFLAGVARIABLE(LuauDfgScopeStackTrueReset)
+LUAU_FASTFLAGVARIABLE(LuauDfgScopeStackNotNull)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+LUAU_FASTFLAGVARIABLE(LuauDoNotAddUpvalueTypesToLocalType)
+LUAU_FASTFLAGVARIABLE(LuauDfgIfBlocksShouldRespectControlFlow)
 namespace Luau
 {
 
 bool doesCallError(const AstExprCall* call); // TypeInfer.cpp
 
-struct ReferencedDefFinder : public AstVisitor
-{
-    bool visit(AstExprLocal* local) override
-    {
-        referencedLocalDefs.push_back(local->local);
-        return true;
-    }
-    // ast defs is just a mapping from expr -> def in general
-    // will get built up by the dfg builder
-
-    // localDefs, we need to copy over
-    std::vector<AstLocal*> referencedLocalDefs;
-};
-
 struct PushScope
 {
     ScopeStack& stack;
+    size_t previousSize;
 
     PushScope(ScopeStack& stack, DfgScope* scope)
         : stack(stack)
+        , previousSize(stack.size())
     {
         // `scope` should never be `nullptr` here.
         LUAU_ASSERT(scope);
@@ -48,7 +40,18 @@ struct PushScope
 
     ~PushScope()
     {
-        stack.pop_back();
+        if (FFlag::LuauDfgScopeStackTrueReset)
+        {
+            // If somehow this stack has _shrunk_ to be smaller than we expect,
+            // something very strange has happened.
+            LUAU_ASSERT(stack.size() > previousSize);
+            while (stack.size() > previousSize)
+                stack.pop_back();
+        }
+        else
+        {
+            stack.pop_back();
+        }
     }
 };
 
@@ -62,6 +65,12 @@ const RefinementKey* RefinementKeyArena::node(const RefinementKey* parent, DefId
     return allocator.allocate(RefinementKey{parent, def, propName});
 }
 
+DataFlowGraph::DataFlowGraph(NotNull<DefArena> defArena, NotNull<RefinementKeyArena> keyArena)
+    : defArena{defArena}
+    , keyArena{keyArena}
+{
+}
+
 DefId DataFlowGraph::getDef(const AstExpr* expr) const
 {
     auto def = astDefs.find(expr);
@@ -77,12 +86,6 @@ std::optional<DefId> DataFlowGraph::getDefOptional(const AstExpr* expr) const
     return NotNull{*def};
 }
 
-std::optional<DefId> DataFlowGraph::getRValueDefForCompoundAssign(const AstExpr* expr) const
-{
-    auto def = compoundAssignDefs.find(expr);
-    return def ? std::optional<DefId>(*def) : std::nullopt;
-}
-
 DefId DataFlowGraph::getDef(const AstLocal* local) const
 {
     auto def = localDefs.find(local);
@@ -178,41 +181,33 @@ bool DfgScope::canUpdateDefinition(DefId def, const std::string& key) const
     return true;
 }
 
-DataFlowGraph DataFlowGraphBuilder::build(AstStatBlock* block, NotNull<InternalErrorReporter> handle)
+DataFlowGraphBuilder::DataFlowGraphBuilder(NotNull<DefArena> defArena, NotNull<RefinementKeyArena> keyArena)
+    : graph{defArena, keyArena}
+    , defArena{defArena}
+    , keyArena{keyArena}
 {
-    LUAU_TIMETRACE_SCOPE("DataFlowGraphBuilder::build", "Typechecking");
-
-    LUAU_ASSERT(FFlag::LuauSolverV2);
-
-    DataFlowGraphBuilder builder;
-    builder.handle = handle;
-    DfgScope* moduleScope = builder.makeChildScope(block->location);
-    PushScope ps{builder.scopeStack, moduleScope};
-    builder.visitBlockWithoutChildScope(block);
-    builder.resolveCaptures();
-
-    if (FFlag::DebugLuauFreezeArena)
-    {
-        builder.defArena->allocator.freeze();
-        builder.keyArena->allocator.freeze();
-    }
-
-    return std::move(builder.graph);
 }
 
-std::pair<std::shared_ptr<DataFlowGraph>, std::vector<std::unique_ptr<DfgScope>>> DataFlowGraphBuilder::buildShared(
+DataFlowGraph DataFlowGraphBuilder::build(
     AstStatBlock* block,
-    NotNull<InternalErrorReporter> handle
+    NotNull<DefArena> defArena,
+    NotNull<RefinementKeyArena> keyArena,
+    NotNull<struct InternalErrorReporter> handle
 )
 {
-
     LUAU_TIMETRACE_SCOPE("DataFlowGraphBuilder::build", "Typechecking");
 
-    LUAU_ASSERT(FFlag::LuauSolverV2);
+    DataFlowGraphBuilder builder(defArena, keyArena);
-
-    DataFlowGraphBuilder builder;
     builder.handle = handle;
-    DfgScope* moduleScope = builder.makeChildScope(block->location);
+
+    DfgScope* moduleScope;
+    // We're not explicitly calling makeChildScope here because that function relies on currentScope
+    // which guarantees that the scope being returned is NotNull
+    // This means that while the scope stack is empty, we'll have to manually initialize the global scope
+    if (FFlag::LuauDfgScopeStackNotNull)
+        moduleScope = builder.scopes.emplace_back(new DfgScope{nullptr, DfgScope::ScopeType::Linear}).get();
+    else
+        moduleScope = builder.makeChildScope();
     PushScope ps{builder.scopeStack, moduleScope};
     builder.visitBlockWithoutChildScope(block);
     builder.resolveCaptures();
@@ -223,56 +218,6 @@ std::pair<std::shared_ptr<DataFlowGraph>, std::vector<std::unique_ptr<DfgScope>>
         builder.keyArena->allocator.freeze();
     }
 
-    return {std::make_shared<DataFlowGraph>(std::move(builder.graph)), std::move(builder.scopes)};
-}
-
-DataFlowGraph DataFlowGraphBuilder::updateGraph(
-    const DataFlowGraph& staleGraph,
-    const std::vector<std::unique_ptr<DfgScope>>& scopes,
-    AstStatBlock* fragment,
-    const Position& cursorPos,
-    NotNull<InternalErrorReporter> handle
-)
-{
-    LUAU_TIMETRACE_SCOPE("DataFlowGraphBuilder::build", "Typechecking");
-    LUAU_ASSERT(FFlag::LuauSolverV2);
-
-    DataFlowGraphBuilder builder;
-    builder.handle = handle;
-    // Generate a list of prepopulated locals
-    ReferencedDefFinder finder;
-    fragment->visit(&finder);
-    for (AstLocal* loc : finder.referencedLocalDefs)
-    {
-        if (staleGraph.localDefs.contains(loc))
-        {
-            builder.graph.localDefs[loc] = *staleGraph.localDefs.find(loc);
-        }
-    }
-
-    // Figure out which scope we should start re-accumulating DFG information from again
-    DfgScope* nearest = nullptr;
-    for (auto& sc : scopes)
-    {
-        if (nearest == nullptr || (sc->location.begin <= cursorPos && nearest->location.begin < sc->location.begin))
-            nearest = sc.get();
-    }
-
-    // The scope stack should start with the nearest enclosing scope so we can resume DFG'ing correctly
-    PushScope ps{builder.scopeStack, nearest};
-    // Conspire for the current scope in the scope stack to be a fresh dfg scope, parented to the above nearest enclosing scope, so any insertions are
-    // isolated there
-    DfgScope* scope = builder.makeChildScope(fragment->location);
-    PushScope psAgain{builder.scopeStack, scope};
-
-    builder.visitBlockWithoutChildScope(fragment);
-
-    if (FFlag::DebugLuauFreezeArena)
-    {
-        builder.defArena->allocator.freeze();
-        builder.keyArena->allocator.freeze();
-    }
-
     return std::move(builder.graph);
 }
 
@@ -294,16 +239,25 @@ void DataFlowGraphBuilder::resolveCaptures()
     }
 }
 
-DfgScope* DataFlowGraphBuilder::currentScope()
+NotNull<DfgScope> DataFlowGraphBuilder::currentScope()
+{
+    LUAU_ASSERT(!scopeStack.empty());
+    return NotNull{scopeStack.back()};
+}
+
+DfgScope* DataFlowGraphBuilder::currentScope_DEPRECATED()
 {
     if (scopeStack.empty())
         return nullptr; // nullptr is the root DFG scope.
     return scopeStack.back();
 }
 
-DfgScope* DataFlowGraphBuilder::makeChildScope(Location loc, DfgScope::ScopeType scopeType)
+DfgScope* DataFlowGraphBuilder::makeChildScope(DfgScope::ScopeType scopeType)
 {
-    return scopes.emplace_back(new DfgScope{currentScope(), scopeType, loc}).get();
+    if (FFlag::LuauDfgScopeStackNotNull)
+        return scopes.emplace_back(new DfgScope{currentScope(), scopeType}).get();
+    else
+        return scopes.emplace_back(new DfgScope{currentScope_DEPRECATED(), scopeType}).get();
 }
 
 void DataFlowGraphBuilder::join(DfgScope* p, DfgScope* a, DfgScope* b)
@@ -378,9 +332,9 @@ void DataFlowGraphBuilder::joinProps(DfgScope* result, const DfgScope& a, const
     }
 }
 
-DefId DataFlowGraphBuilder::lookup(Symbol symbol)
+DefId DataFlowGraphBuilder::lookup(Symbol symbol, Location location)
 {
-    DfgScope* scope = currentScope();
+    DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
 
     // true if any of the considered scopes are a loop.
     bool outsideLoopScope = false;
@@ -405,15 +359,15 @@ DefId DataFlowGraphBuilder::lookup(Symbol symbol)
         }
     }
 
-    DefId result = defArena->freshCell();
+    DefId result = defArena->freshCell(symbol, location);
     scope->bindings[symbol] = result;
     captures[symbol].allVersions.push_back(result);
     return result;
 }
 
-DefId DataFlowGraphBuilder::lookup(DefId def, const std::string& key)
+DefId DataFlowGraphBuilder::lookup(DefId def, const std::string& key, Location location)
 {
-    DfgScope* scope = currentScope();
+    DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
     for (DfgScope* current = scope; current; current = current->parent)
     {
         if (auto props = current->props.find(def))
@@ -423,7 +377,7 @@ DefId DataFlowGraphBuilder::lookup(DefId def, const std::string& key)
         }
         else if (auto phi = get<Phi>(def); phi && phi->operands.empty()) // Unresolved phi nodes
         {
-            DefId result = defArena->freshCell();
+            DefId result = defArena->freshCell(def->name, location);
             scope->props[def][key] = result;
             return result;
         }
@@ -433,7 +387,7 @@ DefId DataFlowGraphBuilder::lookup(DefId def, const std::string& key)
     {
         std::vector<DefId> defs;
         for (DefId operand : phi->operands)
-            defs.push_back(lookup(operand, key));
+            defs.push_back(lookup(operand, key, location));
 
         DefId result = defArena->phi(defs);
         scope->props[def][key] = result;
@@ -441,7 +395,7 @@ DefId DataFlowGraphBuilder::lookup(DefId def, const std::string& key)
     }
     else if (get<Cell>(def))
     {
-        DefId result = defArena->freshCell();
+        DefId result = defArena->freshCell(def->name, location);
         scope->props[def][key] = result;
         return result;
     }
@@ -451,7 +405,7 @@ DefId DataFlowGraphBuilder::lookup(DefId def, const std::string& key)
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatBlock* b)
 {
-    DfgScope* child = makeChildScope(b->location);
+    DfgScope* child = makeChildScope();
 
     ControlFlow cf;
     {
@@ -459,7 +413,10 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatBlock* b)
         cf = visitBlockWithoutChildScope(b);
     }
 
-    currentScope()->inherit(child);
+    if (FFlag::LuauDfgScopeStackNotNull)
+        currentScope()->inherit(child);
+    else
+        currentScope_DEPRECATED()->inherit(child);
     return cf;
 }
 
@@ -516,7 +473,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStat* s)
         return visit(d);
     else if (auto d = s->as<AstStatDeclareFunction>())
         return visit(d);
-    else if (auto d = s->as<AstStatDeclareClass>())
+    else if (auto d = s->as<AstStatDeclareExternType>())
         return visit(d);
     else if (auto error = s->as<AstStatError>())
         return visit(error);
@@ -528,8 +485,8 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatIf* i)
 {
     visitExpr(i->condition);
 
-    DfgScope* thenScope = makeChildScope(i->thenbody->location);
+    DfgScope* thenScope = makeChildScope();
-    DfgScope* elseScope = makeChildScope(i->elsebody ? i->elsebody->location : i->location);
+    DfgScope* elseScope = makeChildScope();
 
     ControlFlow thencf;
     {
@@ -544,13 +501,27 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatIf* i)
         elsecf = visit(i->elsebody);
     }
 
-    DfgScope* scope = currentScope();
+    DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
-    if (thencf != ControlFlow::None && elsecf == ControlFlow::None)
+    if (FFlag::LuauDfgIfBlocksShouldRespectControlFlow)
-        join(scope, scope, elseScope);
+    {
-    else if (thencf == ControlFlow::None && elsecf != ControlFlow::None)
+        // If the control flow from the `if` or `else` block is non-linear,
-        join(scope, thenScope, scope);
+        // then we should assume that the _other_ branch is the one taken.
-    else if ((thencf | elsecf) == ControlFlow::None)
+        if (thencf != ControlFlow::None && elsecf == ControlFlow::None)
-        join(scope, thenScope, elseScope);
+            scope->inherit(elseScope);
+        else if (thencf == ControlFlow::None && elsecf != ControlFlow::None)
+            scope->inherit(thenScope);
+        else if ((thencf | elsecf) == ControlFlow::None)
+            join(scope, thenScope, elseScope);
+    }
+    else
+    {
+        if (thencf != ControlFlow::None && elsecf == ControlFlow::None)
+            join(scope, scope, elseScope);
+        else if (thencf == ControlFlow::None && elsecf != ControlFlow::None)
+            join(scope, thenScope, scope);
+        else if ((thencf | elsecf) == ControlFlow::None)
+            join(scope, thenScope, elseScope);
+    }
 
     if (thencf == elsecf)
         return thencf;
@@ -563,7 +534,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatIf* i)
 ControlFlow DataFlowGraphBuilder::visit(AstStatWhile* w)
 {
     // TODO(controlflow): entry point has a back edge from exit point
-    DfgScope* whileScope = makeChildScope(w->location, DfgScope::Loop);
+    DfgScope* whileScope = makeChildScope(DfgScope::Loop);
 
     {
         PushScope ps{scopeStack, whileScope};
@@ -571,7 +542,10 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatWhile* w)
         visit(w->body);
     }
 
-    currentScope()->inherit(whileScope);
+    if (FFlag::LuauDfgScopeStackNotNull)
+        currentScope()->inherit(whileScope);
+    else
+        currentScope_DEPRECATED()->inherit(whileScope);
 
     return ControlFlow::None;
 }
@@ -579,7 +553,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatWhile* w)
 ControlFlow DataFlowGraphBuilder::visit(AstStatRepeat* r)
 {
     // TODO(controlflow): entry point has a back edge from exit point
-    DfgScope* repeatScope = makeChildScope(r->location, DfgScope::Loop);
+    DfgScope* repeatScope = makeChildScope(DfgScope::Loop);
 
     {
         PushScope ps{scopeStack, repeatScope};
@@ -587,7 +561,10 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatRepeat* r)
         visitExpr(r->condition);
     }
 
-    currentScope()->inherit(repeatScope);
+    if (FFlag::LuauDfgScopeStackNotNull)
+        currentScope()->inherit(repeatScope);
+    else
+        currentScope_DEPRECATED()->inherit(repeatScope);
 
     return ControlFlow::None;
 }
@@ -636,7 +613,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatLocal* l)
         // We need to create a new def to intentionally avoid alias tracking, but we'd like to
         // make sure that the non-aliased defs are also marked as a subscript for refinements.
         bool subscripted = i < defs.size() && containsSubscriptedDefinition(defs[i]);
-        DefId def = defArena->freshCell(subscripted);
+        DefId def = defArena->freshCell(local, local->location, subscripted);
         if (i < l->values.size)
         {
             AstExpr* e = l->values.data[i];
@@ -646,7 +623,10 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatLocal* l)
             }
         }
         graph.localDefs[local] = def;
-        currentScope()->bindings[local] = def;
+        if (FFlag::LuauDfgScopeStackNotNull)
+            currentScope()->bindings[local] = def;
+        else
+            currentScope_DEPRECATED()->bindings[local] = def;
         captures[local].allVersions.push_back(def);
     }
 
@@ -655,7 +635,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatLocal* l)
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatFor* f)
 {
-    DfgScope* forScope = makeChildScope(f->location, DfgScope::Loop);
+    DfgScope* forScope = makeChildScope(DfgScope::Loop);
 
     visitExpr(f->from);
     visitExpr(f->to);
@@ -668,23 +648,29 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatFor* f)
         if (f->var->annotation)
             visitType(f->var->annotation);
 
-        DefId def = defArena->freshCell();
+        DefId def = defArena->freshCell(f->var, f->var->location);
         graph.localDefs[f->var] = def;
-        currentScope()->bindings[f->var] = def;
+        if (FFlag::LuauDfgScopeStackNotNull)
+            currentScope()->bindings[f->var] = def;
+        else
+            currentScope_DEPRECATED()->bindings[f->var] = def;
         captures[f->var].allVersions.push_back(def);
 
         // TODO(controlflow): entry point has a back edge from exit point
         visit(f->body);
     }
 
-    currentScope()->inherit(forScope);
+    if (FFlag::LuauDfgScopeStackNotNull)
+        currentScope()->inherit(forScope);
+    else
+        currentScope_DEPRECATED()->inherit(forScope);
 
     return ControlFlow::None;
 }
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatForIn* f)
 {
-    DfgScope* forScope = makeChildScope(f->location, DfgScope::Loop);
+    DfgScope* forScope = makeChildScope(DfgScope::Loop);
 
     {
         PushScope ps{scopeStack, forScope};
@@ -694,9 +680,12 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatForIn* f)
             if (local->annotation)
                 visitType(local->annotation);
 
-            DefId def = defArena->freshCell();
+            DefId def = defArena->freshCell(local, local->location);
             graph.localDefs[local] = def;
-            currentScope()->bindings[local] = def;
+            if (FFlag::LuauDfgScopeStackNotNull)
+                currentScope()->bindings[local] = def;
+            else
+                currentScope_DEPRECATED()->bindings[local] = def;
             captures[local].allVersions.push_back(def);
         }
 
@@ -707,8 +696,10 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatForIn* f)
 
         visit(f->body);
     }
-
+    if (FFlag::LuauDfgScopeStackNotNull)
-    currentScope()->inherit(forScope);
+        currentScope()->inherit(forScope);
+    else
+        currentScope_DEPRECATED()->inherit(forScope);
 
     return ControlFlow::None;
 }
@@ -723,7 +714,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatAssign* a)
     for (size_t i = 0; i < a->vars.size; ++i)
     {
         AstExpr* v = a->vars.data[i];
-        visitLValue(v, i < defs.size() ? defs[i] : defArena->freshCell());
+        visitLValue(v, i < defs.size() ? defs[i] : defArena->freshCell(Symbol{}, v->location));
     }
 
     return ControlFlow::None;
@@ -749,7 +740,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatFunction* f)
     //
     // which is evidence that references to variables must be a phi node of all possible definitions,
     // but for bug compatibility, we'll assume the same thing here.
-    visitLValue(f->name, defArena->freshCell());
+    visitLValue(f->name, defArena->freshCell(Symbol{}, f->name->location));
     visitExpr(f->func);
 
     if (auto local = f->name->as<AstExprLocal>())
@@ -769,9 +760,12 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatFunction* f)
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatLocalFunction* l)
 {
-    DefId def = defArena->freshCell();
+    DefId def = defArena->freshCell(l->name, l->location);
     graph.localDefs[l->name] = def;
-    currentScope()->bindings[l->name] = def;
+    if (FFlag::LuauDfgScopeStackNotNull)
+        currentScope()->bindings[l->name] = def;
+    else
+        currentScope_DEPRECATED()->bindings[l->name] = def;
     captures[l->name].allVersions.push_back(def);
     visitExpr(l->func);
 
@@ -780,7 +774,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatLocalFunction* l)
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatTypeAlias* t)
 {
-    DfgScope* unreachable = makeChildScope(t->location);
+    DfgScope* unreachable = makeChildScope();
     PushScope ps{scopeStack, unreachable};
 
     visitGenerics(t->generics);
@@ -792,7 +786,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatTypeAlias* t)
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatTypeFunction* f)
 {
-    DfgScope* unreachable = makeChildScope(f->location);
+    DfgScope* unreachable = makeChildScope();
     PushScope ps{scopeStack, unreachable};
 
     visitExpr(f->body);
@@ -802,9 +796,12 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatTypeFunction* f)
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareGlobal* d)
 {
-    DefId def = defArena->freshCell();
+    DefId def = defArena->freshCell(d->name, d->nameLocation);
     graph.declaredDefs[d] = def;
-    currentScope()->bindings[d->name] = def;
+    if (FFlag::LuauDfgScopeStackNotNull)
+        currentScope()->bindings[d->name] = def;
+    else
+        currentScope_DEPRECATED()->bindings[d->name] = def;
     captures[d->name].allVersions.push_back(def);
 
     visitType(d->type);
@@ -814,31 +811,37 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareGlobal* d)
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareFunction* d)
 {
-    DefId def = defArena->freshCell();
+    DefId def = defArena->freshCell(d->name, d->nameLocation);
     graph.declaredDefs[d] = def;
-    currentScope()->bindings[d->name] = def;
+    if (FFlag::LuauDfgScopeStackNotNull)
+        currentScope()->bindings[d->name] = def;
+    else
+        currentScope_DEPRECATED()->bindings[d->name] = def;
     captures[d->name].allVersions.push_back(def);
 
-    DfgScope* unreachable = makeChildScope(d->location);
+    DfgScope* unreachable = makeChildScope();
     PushScope ps{scopeStack, unreachable};
 
     visitGenerics(d->generics);
     visitGenericPacks(d->genericPacks);
     visitTypeList(d->params);
-    visitTypeList(d->retTypes);
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        visitTypePack(d->retTypes);
+    else
+        visitTypeList(d->retTypes_DEPRECATED);
 
     return ControlFlow::None;
 }
 
-ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareClass* d)
+ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareExternType* d)
 {
     // This declaration does not "introduce" any bindings in value namespace,
     // so there's no symbolic value to begin with. We'll traverse the properties
     // because their type annotations may depend on something in the value namespace.
-    DfgScope* unreachable = makeChildScope(d->location);
+    DfgScope* unreachable = makeChildScope();
     PushScope ps{scopeStack, unreachable};
 
-    for (AstDeclaredClassProp prop : d->props)
+    for (AstDeclaredExternTypeProperty prop : d->props)
         visitType(prop.ty);
 
     return ControlFlow::None;
@@ -846,7 +849,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareClass* d)
 
 ControlFlow DataFlowGraphBuilder::visit(AstStatError* error)
 {
-    DfgScope* unreachable = makeChildScope(error->location);
+    DfgScope* unreachable = makeChildScope();
     PushScope ps{scopeStack, unreachable};
 
     for (AstStat* s : error->statements)
@@ -871,19 +874,19 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExpr* e)
         if (auto g = e->as<AstExprGroup>())
             return visitExpr(g);
         else if (auto c = e->as<AstExprConstantNil>())
-            return {defArena->freshCell(), nullptr}; // ok
+            return {defArena->freshCell(Symbol{}, c->location), nullptr}; // ok
         else if (auto c = e->as<AstExprConstantBool>())
-            return {defArena->freshCell(), nullptr}; // ok
+            return {defArena->freshCell(Symbol{}, c->location), nullptr}; // ok
         else if (auto c = e->as<AstExprConstantNumber>())
-            return {defArena->freshCell(), nullptr}; // ok
+            return {defArena->freshCell(Symbol{}, c->location), nullptr}; // ok
         else if (auto c = e->as<AstExprConstantString>())
-            return {defArena->freshCell(), nullptr}; // ok
+            return {defArena->freshCell(Symbol{}, c->location), nullptr}; // ok
         else if (auto l = e->as<AstExprLocal>())
             return visitExpr(l);
         else if (auto g = e->as<AstExprGlobal>())
             return visitExpr(g);
         else if (auto v = e->as<AstExprVarargs>())
-            return {defArena->freshCell(), nullptr}; // ok
+            return {defArena->freshCell(Symbol{}, v->location), nullptr}; // ok
         else if (auto c = e->as<AstExprCall>())
             return visitExpr(c);
         else if (auto i = e->as<AstExprIndexName>())
@@ -924,14 +927,14 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprGroup* group)
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprLocal* l)
 {
-    DefId def = lookup(l->local);
+    DefId def = lookup(l->local, l->local->location);
     const RefinementKey* key = keyArena->leaf(def);
     return {def, key};
 }
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprGlobal* g)
 {
-    DefId def = lookup(g->name);
+    DefId def = lookup(g->name, g->location);
     return {def, keyArena->leaf(def)};
 }
 
@@ -939,7 +942,13 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprCall* c)
 {
     visitExpr(c->func);
 
-    if (FFlag::LuauTypestateBuiltins2 && shouldTypestateForFirstArgument(*c) && c->args.size > 1 && isLValue(*c->args.begin()))
+    if (FFlag::LuauPreprocessTypestatedArgument)
+    {
+        for (AstExpr* arg : c->args)
+            visitExpr(arg);
+    }
+
+    if (shouldTypestateForFirstArgument(*c) && c->args.size > 1 && isLValue(*c->args.begin()))
     {
         AstExpr* firstArg = *c->args.begin();
 
@@ -958,10 +967,7 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprCall* c)
 
         LUAU_ASSERT(result);
 
-        Location location = currentScope()->location;
+        DfgScope* child = makeChildScope();
-        // This scope starts at the end of the call site and continues to the end of the original scope.
-        location.begin = c->location.end;
-        DfgScope* child = makeChildScope(location);
         scopeStack.push_back(child);
 
         auto [def, key] = *result;
@@ -972,20 +978,31 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprCall* c)
         visitLValue(firstArg, def);
     }
 
-    for (AstExpr* arg : c->args)
+    if (!FFlag::LuauPreprocessTypestatedArgument)
-        visitExpr(arg);
+    {
+        for (AstExpr* arg : c->args)
+            visitExpr(arg);
+    }
 
-    // calls should be treated as subscripted.
+    // We treat function calls as "subscripted" as they could potentially
-    return {defArena->freshCell(/* subscripted */ true), nullptr};
+    // return a subscripted value, consider:
+    //
+    //  local function foo(tbl: {[string]: woof)
+    //      return tbl["foobarbaz"]
+    //  end
+    //
+    //  local v = foo({})
+    //
+    // We want to consider `v` to be subscripted here.
+    return {defArena->freshCell(Symbol{}, c->location, /*subscripted=*/true)};
 }
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprIndexName* i)
 {
     auto [parentDef, parentKey] = visitExpr(i->expr);
-
     std::string index = i->index.value;
 
-    DefId def = lookup(parentDef, index);
+    DefId def = lookup(parentDef, index, i->location);
     return {def, keyArena->node(parentKey, def, index)};
 }
 
@@ -998,16 +1015,16 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprIndexExpr* i)
     {
         std::string index{string->value.data, string->value.size};
 
-        DefId def = lookup(parentDef, index);
+        DefId def = lookup(parentDef, index, i->location);
         return {def, keyArena->node(parentKey, def, index)};
     }
 
-    return {defArena->freshCell(/* subscripted= */ true), nullptr};
+    return {defArena->freshCell(Symbol{}, i->location, /* subscripted= */ true), nullptr};
 }
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprFunction* f)
 {
-    DfgScope* signatureScope = makeChildScope(f->location, DfgScope::Function);
+    DfgScope* signatureScope = makeChildScope(DfgScope::Function);
     PushScope ps{scopeStack, signatureScope};
 
     if (AstLocal* self = f->self)
@@ -1015,7 +1032,7 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprFunction* f)
         // There's no syntax for `self` to have an annotation if using `function t:m()`
         LUAU_ASSERT(!self->annotation);
 
-        DefId def = defArena->freshCell();
+        DefId def = defArena->freshCell(f->debugname, f->location);
         graph.localDefs[self] = def;
         signatureScope->bindings[self] = def;
         captures[self].allVersions.push_back(def);
@@ -1026,7 +1043,7 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprFunction* f)
         if (param->annotation)
             visitType(param->annotation);
 
-        DefId def = defArena->freshCell();
+        DefId def = defArena->freshCell(param, param->location);
         graph.localDefs[param] = def;
         signatureScope->bindings[param] = def;
         captures[param].allVersions.push_back(def);
@@ -1035,8 +1052,16 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprFunction* f)
     if (f->varargAnnotation)
         visitTypePack(f->varargAnnotation);
 
-    if (f->returnAnnotation)
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
-        visitTypeList(*f->returnAnnotation);
+    {
+        if (f->returnAnnotation)
+            visitTypePack(f->returnAnnotation);
+    }
+    else
+    {
+        if (f->returnAnnotation_DEPRECATED)
+            visitTypeList(*f->returnAnnotation_DEPRECATED);
+    }
 
     // TODO: function body can be re-entrant, as in mutations that occurs at the end of the function can also be
     // visible to the beginning of the function, so statically speaking, the body of the function has an exit point
@@ -1048,13 +1073,16 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprFunction* f)
     // g() --> 5
     visit(f->body);
 
-    return {defArena->freshCell(), nullptr};
+    return {defArena->freshCell(f->debugname, f->location), nullptr};
 }
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprTable* t)
 {
-    DefId tableCell = defArena->freshCell();
+    DefId tableCell = defArena->freshCell(Symbol{}, t->location);
-    currentScope()->props[tableCell] = {};
+    if (FFlag::LuauDfgScopeStackNotNull)
+        currentScope()->props[tableCell] = {};
+    else
+        currentScope_DEPRECATED()->props[tableCell] = {};
     for (AstExprTable::Item item : t->items)
     {
         DataFlowResult result = visitExpr(item.value);
@@ -1062,7 +1090,12 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprTable* t)
         {
             visitExpr(item.key);
             if (auto string = item.key->as<AstExprConstantString>())
-                currentScope()->props[tableCell][string->value.data] = result.def;
+            {
+                if (FFlag::LuauDfgScopeStackNotNull)
+                    currentScope()->props[tableCell][string->value.data] = result.def;
+                else
+                    currentScope_DEPRECATED()->props[tableCell][string->value.data] = result.def;
+            }
         }
     }
 
@@ -1073,7 +1106,7 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprUnary* u)
 {
     visitExpr(u->expr);
 
-    return {defArena->freshCell(), nullptr};
+    return {defArena->freshCell(Symbol{}, u->location), nullptr};
 }
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprBinary* b)
@@ -1081,7 +1114,7 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprBinary* b)
     visitExpr(b->left);
     visitExpr(b->right);
 
-    return {defArena->freshCell(), nullptr};
+    return {defArena->freshCell(Symbol{}, b->location), nullptr};
 }
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprTypeAssertion* t)
@@ -1098,7 +1131,7 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprIfElse* i)
     visitExpr(i->trueExpr);
     visitExpr(i->falseExpr);
 
-    return {defArena->freshCell(), nullptr};
+    return {defArena->freshCell(Symbol{}, i->location), nullptr};
 }
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprInterpString* i)
@@ -1106,18 +1139,18 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprInterpString* i)
     for (AstExpr* e : i->expressions)
         visitExpr(e);
 
-    return {defArena->freshCell(), nullptr};
+    return {defArena->freshCell(Symbol{}, i->location), nullptr};
 }
 
 DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprError* error)
 {
-    DfgScope* unreachable = makeChildScope(error->location);
+    DfgScope* unreachable = makeChildScope();
     PushScope ps{scopeStack, unreachable};
 
     for (AstExpr* e : error->expressions)
         visitExpr(e);
 
-    return {defArena->freshCell(), nullptr};
+    return {defArena->freshCell(Symbol{}, error->location), nullptr};
 }
 
 void DataFlowGraphBuilder::visitLValue(AstExpr* e, DefId incomingDef)
@@ -1143,12 +1176,12 @@ void DataFlowGraphBuilder::visitLValue(AstExpr* e, DefId incomingDef)
 
 DefId DataFlowGraphBuilder::visitLValue(AstExprLocal* l, DefId incomingDef)
 {
-    DfgScope* scope = currentScope();
+    DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
 
     // In order to avoid alias tracking, we need to clip the reference to the parent def.
-    if (scope->canUpdateDefinition(l->local))
+    if (scope->canUpdateDefinition(l->local) && !(FFlag::LuauDoNotAddUpvalueTypesToLocalType && l->upvalue))
     {
-        DefId updated = defArena->freshCell(containsSubscriptedDefinition(incomingDef));
+        DefId updated = defArena->freshCell(l->local, l->location, containsSubscriptedDefinition(incomingDef));
         scope->bindings[l->local] = updated;
         captures[l->local].allVersions.push_back(updated);
         return updated;
@@ -1159,12 +1192,12 @@ DefId DataFlowGraphBuilder::visitLValue(AstExprLocal* l, DefId incomingDef)
 
 DefId DataFlowGraphBuilder::visitLValue(AstExprGlobal* g, DefId incomingDef)
 {
-    DfgScope* scope = currentScope();
+    DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
 
     // In order to avoid alias tracking, we need to clip the reference to the parent def.
     if (scope->canUpdateDefinition(g->name))
     {
-        DefId updated = defArena->freshCell(containsSubscriptedDefinition(incomingDef));
+        DefId updated = defArena->freshCell(g->name, g->location, containsSubscriptedDefinition(incomingDef));
         scope->bindings[g->name] = updated;
         captures[g->name].allVersions.push_back(updated);
         return updated;
@@ -1177,10 +1210,10 @@ DefId DataFlowGraphBuilder::visitLValue(AstExprIndexName* i, DefId incomingDef)
 {
     DefId parentDef = visitExpr(i->expr).def;
 
-    DfgScope* scope = currentScope();
+    DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
     if (scope->canUpdateDefinition(parentDef, i->index.value))
     {
-        DefId updated = defArena->freshCell(containsSubscriptedDefinition(incomingDef));
+        DefId updated = defArena->freshCell(i->index, i->location, containsSubscriptedDefinition(incomingDef));
         scope->props[parentDef][i->index.value] = updated;
         return updated;
     }
@@ -1193,12 +1226,12 @@ DefId DataFlowGraphBuilder::visitLValue(AstExprIndexExpr* i, DefId incomingDef)
     DefId parentDef = visitExpr(i->expr).def;
     visitExpr(i->index);
 
-    DfgScope* scope = currentScope();
+    DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
     if (auto string = i->index->as<AstExprConstantString>())
     {
         if (scope->canUpdateDefinition(parentDef, string->value.data))
         {
-            DefId updated = defArena->freshCell(containsSubscriptedDefinition(incomingDef));
+            DefId updated = defArena->freshCell(Symbol{}, i->location, containsSubscriptedDefinition(incomingDef));
             scope->props[parentDef][string->value.data] = updated;
             return updated;
         }
@@ -1206,7 +1239,7 @@ DefId DataFlowGraphBuilder::visitLValue(AstExprIndexExpr* i, DefId incomingDef)
             return visitExpr(static_cast<AstExpr*>(i)).def;
     }
     else
-        return defArena->freshCell(/*subscripted=*/true);
+        return defArena->freshCell(Symbol{}, i->location, /*subscripted=*/true);
 }
 
 DefId DataFlowGraphBuilder::visitLValue(AstExprError* error, DefId incomingDef)
@@ -1224,6 +1257,8 @@ void DataFlowGraphBuilder::visitType(AstType* t)
         return visitType(f);
     else if (auto tyof = t->as<AstTypeTypeof>())
         return visitType(tyof);
+    else if (auto o = t->as<AstTypeOptional>())
+        return;
     else if (auto u = t->as<AstTypeUnion>())
         return visitType(u);
     else if (auto i = t->as<AstTypeIntersection>())
@@ -1234,6 +1269,8 @@ void DataFlowGraphBuilder::visitType(AstType* t)
         return; // ok
     else if (auto s = t->as<AstTypeSingletonString>())
         return; // ok
+    else if (auto g = t->as<AstTypeGroup>())
+        return visitType(g->type);
     else
         handle->ice("Unknown AstType in DataFlowGraphBuilder::visitType");
 }
@@ -1266,7 +1303,10 @@ void DataFlowGraphBuilder::visitType(AstTypeFunction* f)
     visitGenerics(f->generics);
     visitGenericPacks(f->genericPacks);
     visitTypeList(f->argTypes);
-    visitTypeList(f->returnTypes);
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        visitTypePack(f->returnTypes);
+    else
+        visitTypeList(f->returnTypes_DEPRECATED);
 }
 
 void DataFlowGraphBuilder::visitType(AstTypeTypeof* t)
@@ -1323,21 +1363,21 @@ void DataFlowGraphBuilder::visitTypeList(AstTypeList l)
         visitTypePack(l.tailType);
 }
 
-void DataFlowGraphBuilder::visitGenerics(AstArray<AstGenericType> g)
+void DataFlowGraphBuilder::visitGenerics(AstArray<AstGenericType*> g)
 {
-    for (AstGenericType generic : g)
+    for (AstGenericType* generic : g)
     {
-        if (generic.defaultValue)
+        if (generic->defaultValue)
-            visitType(generic.defaultValue);
+            visitType(generic->defaultValue);
     }
 }
 
-void DataFlowGraphBuilder::visitGenericPacks(AstArray<AstGenericTypePack> g)
+void DataFlowGraphBuilder::visitGenericPacks(AstArray<AstGenericTypePack*> g)
 {
-    for (AstGenericTypePack generic : g)
+    for (AstGenericTypePack* generic : g)
     {
-        if (generic.defaultValue)
+        if (generic->defaultValue)
-            visitTypePack(generic.defaultValue);
+            visitTypePack(generic->defaultValue);
     }
 }
 

Analysis/src/Def.cpp

@@ -36,9 +36,9 @@ void collectOperands(DefId def, std::vector<DefId>* operands)
     }
 }
 
-DefId DefArena::freshCell(bool subscripted)
+DefId DefArena::freshCell(Symbol sym, Location location, bool subscripted)
 {
-    return NotNull{allocator.allocate(Def{Cell{subscripted}})};
+    return NotNull{allocator.allocate(Def{Cell{subscripted}, sym, location})};
 }
 
 DefId DefArena::phi(DefId a, DefId b)

Analysis/src/Differ.cpp

@@ -13,7 +13,6 @@
 
 namespace Luau
 {
-
 std::string DiffPathNode::toString() const
 {
     switch (kind)
@@ -278,7 +277,7 @@ static DifferResult diffSingleton(DifferEnvironment& env, TypeId left, TypeId ri
 static DifferResult diffFunction(DifferEnvironment& env, TypeId left, TypeId right);
 static DifferResult diffGeneric(DifferEnvironment& env, TypeId left, TypeId right);
 static DifferResult diffNegation(DifferEnvironment& env, TypeId left, TypeId right);
-static DifferResult diffClass(DifferEnvironment& env, TypeId left, TypeId right);
+static DifferResult diffExternType(DifferEnvironment& env, TypeId left, TypeId right);
 struct FindSeteqCounterexampleResult
 {
     // nullopt if no counterexample found
@@ -482,14 +481,14 @@ static DifferResult diffNegation(DifferEnvironment& env, TypeId left, TypeId rig
     return differResult;
 }
 
-static DifferResult diffClass(DifferEnvironment& env, TypeId left, TypeId right)
+static DifferResult diffExternType(DifferEnvironment& env, TypeId left, TypeId right)
 {
-    const ClassType* leftClass = get<ClassType>(left);
+    const ExternType* leftExternType = get<ExternType>(left);
-    const ClassType* rightClass = get<ClassType>(right);
+    const ExternType* rightExternType = get<ExternType>(right);
-    LUAU_ASSERT(leftClass);
+    LUAU_ASSERT(leftExternType);
-    LUAU_ASSERT(rightClass);
+    LUAU_ASSERT(rightExternType);
 
-    if (leftClass == rightClass)
+    if (leftExternType == rightExternType)
     {
         return DifferResult{};
     }
@@ -652,9 +651,9 @@ static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId rig
         {
             return diffNegation(env, left, right);
         }
-        else if (auto lc = get<ClassType>(left))
+        else if (auto lc = get<ExternType>(left))
         {
-            return diffClass(env, left, right);
+            return diffExternType(env, left, right);
         }
 
         throw InternalCompilerError{"Unimplemented Simple TypeId variant for diffing"};
@@ -719,7 +718,7 @@ static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId rig
         env.popVisiting();
         return diffRes;
     }
-    if (auto le = get<Luau::Unifiable::Error>(left))
+    if (auto le = get<ErrorType>(left))
     {
         // TODO: return debug-friendly result state
         env.popVisiting();
@@ -945,14 +944,12 @@ std::vector<std::pair<TypeId, TypeId>>::const_reverse_iterator DifferEnvironment
     return visitingStack.crend();
 }
 
-
 DifferResult diff(TypeId ty1, TypeId ty2)
 {
     DifferEnvironment differEnv{ty1, ty2, std::nullopt, std::nullopt};
     return diffUsingEnv(differEnv, ty1, ty2);
 }
 
-
 DifferResult diffWithSymbols(TypeId ty1, TypeId ty2, std::optional<std::string> symbol1, std::optional<std::string> symbol2)
 {
     DifferEnvironment differEnv{ty1, ty2, symbol1, symbol2};
@@ -963,7 +960,7 @@ bool isSimple(TypeId ty)
 {
     ty = follow(ty);
     // TODO: think about GenericType, etc.
-    return get<PrimitiveType>(ty) || get<SingletonType>(ty) || get<AnyType>(ty) || get<NegationType>(ty) || get<ClassType>(ty) ||
+    return get<PrimitiveType>(ty) || get<SingletonType>(ty) || get<AnyType>(ty) || get<NegationType>(ty) || get<ExternType>(ty) ||
            get<UnknownType>(ty) || get<NeverType>(ty);
 }
 

Analysis/src/EmbeddedBuiltinDefinitions.cpp

@@ -1,107 +1,13 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/BuiltinDefinitions.h"
 
-LUAU_FASTFLAG(LuauMathMap)
+LUAU_FASTFLAG(LuauDeclareExternType)
-
+LUAU_FASTFLAG(LuauTypeFunOptional)
-LUAU_FASTFLAGVARIABLE(LuauVectorDefinitions)
 
 namespace Luau
 {
 
-// TODO: there has to be a better way, like splitting up per library
+static const std::string kBuiltinDefinitionBaseSrc = R"BUILTIN_SRC(
-static const std::string kBuiltinDefinitionLuaSrcChecked_DEPRECATED = R"BUILTIN_SRC(
-
-declare bit32: {
-    band: @checked (...number) -> number,
-    bor: @checked (...number) -> number,
-    bxor: @checked (...number) -> number,
-    btest: @checked (number, ...number) -> boolean,
-    rrotate: @checked (x: number, disp: number) -> number,
-    lrotate: @checked (x: number, disp: number) -> number,
-    lshift: @checked (x: number, disp: number) -> number,
-    arshift: @checked (x: number, disp: number) -> number,
-    rshift: @checked (x: number, disp: number) -> number,
-    bnot: @checked (x: number) -> number,
-    extract: @checked (n: number, field: number, width: number?) -> number,
-    replace: @checked (n: number, v: number, field: number, width: number?) -> number,
-    countlz: @checked (n: number) -> number,
-    countrz: @checked (n: number) -> number,
-    byteswap: @checked (n: number) -> number,
-}
-
-declare math: {
-    frexp: @checked (n: number) -> (number, number),
-    ldexp: @checked (s: number, e: number) -> number,
-    fmod: @checked (x: number, y: number) -> number,
-    modf: @checked (n: number) -> (number, number),
-    pow: @checked (x: number, y: number) -> number,
-    exp: @checked (n: number) -> number,
-
-    ceil: @checked (n: number) -> number,
-    floor: @checked (n: number) -> number,
-    abs: @checked (n: number) -> number,
-    sqrt: @checked (n: number) -> number,
-
-    log: @checked (n: number, base: number?) -> number,
-    log10: @checked (n: number) -> number,
-
-    rad: @checked (n: number) -> number,
-    deg: @checked (n: number) -> number,
-
-    sin: @checked (n: number) -> number,
-    cos: @checked (n: number) -> number,
-    tan: @checked (n: number) -> number,
-    sinh: @checked (n: number) -> number,
-    cosh: @checked (n: number) -> number,
-    tanh: @checked (n: number) -> number,
-    atan: @checked (n: number) -> number,
-    acos: @checked (n: number) -> number,
-    asin: @checked (n: number) -> number,
-    atan2: @checked (y: number, x: number) -> number,
-
-    min: @checked (number, ...number) -> number,
-    max: @checked (number, ...number) -> number,
-
-    pi: number,
-    huge: number,
-
-    randomseed: @checked (seed: number) -> (),
-    random: @checked (number?, number?) -> number,
-
-    sign: @checked (n: number) -> number,
-    clamp: @checked (n: number, min: number, max: number) -> number,
-    noise: @checked (x: number, y: number?, z: number?) -> number,
-    round: @checked (n: number) -> number,
-}
-
-type DateTypeArg = {
-    year: number,
-    month: number,
-    day: number,
-    hour: number?,
-    min: number?,
-    sec: number?,
-    isdst: boolean?,
-}
-
-type DateTypeResult = {
-    year: number,
-    month: number,
-    wday: number,
-    yday: number,
-    day: number,
-    hour: number,
-    min: number,
-    sec: number,
-    isdst: boolean,
-}
-
-declare os: {
-    time: (time: DateTypeArg?) -> number,
-    date: ((formatString: "*t" | "!*t", time: number?) -> DateTypeResult) & ((formatString: string?, time: number?) -> string),
-    difftime: (t2: DateTypeResult | number, t1: DateTypeResult | number) -> number,
-    clock: () -> number,
-}
 
 @checked declare function require(target: any): any
 
@@ -149,88 +55,12 @@ declare function loadstring<A...>(src: string, chunkname: string?): (((A...) ->
 
 @checked declare function newproxy(mt: boolean?): any
 
-declare coroutine: {
-    create: <A..., R...>(f: (A...) -> R...) -> thread,
-    resume: <A..., R...>(co: thread, A...) -> (boolean, R...),
-    running: () -> thread,
-    status: @checked (co: thread) -> "dead" | "running" | "normal" | "suspended",
-    wrap: <A..., R...>(f: (A...) -> R...) -> ((A...) -> R...),
-    yield: <A..., R...>(A...) -> R...,
-    isyieldable: () -> boolean,
-    close: @checked (co: thread) -> (boolean, any)
-}
-
-declare table: {
-    concat: <V>(t: {V}, sep: string?, i: number?, j: number?) -> string,
-    insert: (<V>(t: {V}, value: V) -> ()) & (<V>(t: {V}, pos: number, value: V) -> ()),
-    maxn: <V>(t: {V}) -> number,
-    remove: <V>(t: {V}, number?) -> V?,
-    sort: <V>(t: {V}, comp: ((V, V) -> boolean)?) -> (),
-    create: <V>(count: number, value: V?) -> {V},
-    find: <V>(haystack: {V}, needle: V, init: number?) -> number?,
-
-    unpack: <V>(list: {V}, i: number?, j: number?) -> ...V,
-    pack: <V>(...V) -> { n: number, [number]: V },
-
-    getn: <V>(t: {V}) -> number,
-    foreach: <K, V>(t: {[K]: V}, f: (K, V) -> ()) -> (),
-    foreachi: <V>({V}, (number, V) -> ()) -> (),
-
-    move: <V>(src: {V}, a: number, b: number, t: number, dst: {V}?) -> {V},
-    clear: <K, V>(table: {[K]: V}) -> (),
-
-    isfrozen: <K, V>(t: {[K]: V}) -> boolean,
-}
-
-declare debug: {
-    info: (<R...>(thread: thread, level: number, options: string) -> R...) & (<R...>(level: number, options: string) -> R...) & (<A..., R1..., R2...>(func: (A...) -> R1..., options: string) -> R2...),
-    traceback: ((message: string?, level: number?) -> string) & ((thread: thread, message: string?, level: number?) -> string),
-}
-
-declare utf8: {
-    char: @checked (...number) -> string,
-    charpattern: string,
-    codes: @checked (str: string) -> ((string, number) -> (number, number), string, number),
-    codepoint: @checked (str: string, i: number?, j: number?) -> ...number,
-    len: @checked (s: string, i: number?, j: number?) -> (number?, number?),
-    offset: @checked (s: string, n: number?, i: number?) -> number,
-}
-
 -- Cannot use `typeof` here because it will produce a polytype when we expect a monotype.
 declare function unpack<V>(tab: {V}, i: number?, j: number?): ...V
 
-
---- Buffer API
-declare buffer: {
-    create: @checked (size: number) -> buffer,
-    fromstring: @checked (str: string) -> buffer,
-    tostring: @checked (b: buffer) -> string,
-    len: @checked (b: buffer) -> number,
-    copy: @checked (target: buffer, targetOffset: number, source: buffer, sourceOffset: number?, count: number?) -> (),
-    fill: @checked (b: buffer, offset: number, value: number, count: number?) -> (),
-    readi8: @checked (b: buffer, offset: number) -> number,
-    readu8: @checked (b: buffer, offset: number) -> number,
-    readi16: @checked (b: buffer, offset: number) -> number,
-    readu16: @checked (b: buffer, offset: number) -> number,
-    readi32: @checked (b: buffer, offset: number) -> number,
-    readu32: @checked (b: buffer, offset: number) -> number,
-    readf32: @checked (b: buffer, offset: number) -> number,
-    readf64: @checked (b: buffer, offset: number) -> number,
-    writei8: @checked (b: buffer, offset: number, value: number) -> (),
-    writeu8: @checked (b: buffer, offset: number, value: number) -> (),
-    writei16: @checked (b: buffer, offset: number, value: number) -> (),
-    writeu16: @checked (b: buffer, offset: number, value: number) -> (),
-    writei32: @checked (b: buffer, offset: number, value: number) -> (),
-    writeu32: @checked (b: buffer, offset: number, value: number) -> (),
-    writef32: @checked (b: buffer, offset: number, value: number) -> (),
-    writef64: @checked (b: buffer, offset: number, value: number) -> (),
-    readstring: @checked (b: buffer, offset: number, count: number) -> string,
-    writestring: @checked (b: buffer, offset: number, value: string, count: number?) -> (),
-}
-
 )BUILTIN_SRC";
 
-static const std::string kBuiltinDefinitionLuaSrcChecked = R"BUILTIN_SRC(
+static const std::string kBuiltinDefinitionBit32Src = R"BUILTIN_SRC(
 
 declare bit32: {
     band: @checked (...number) -> number,
@@ -250,6 +80,10 @@ declare bit32: {
     byteswap: @checked (n: number) -> number,
 }
 
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionMathSrc = R"BUILTIN_SRC(
+
 declare math: {
     frexp: @checked (n: number) -> (number, number),
     ldexp: @checked (s: number, e: number) -> number,
@@ -294,8 +128,13 @@ declare math: {
     noise: @checked (x: number, y: number?, z: number?) -> number,
     round: @checked (n: number) -> number,
     map: @checked (x: number, inmin: number, inmax: number, outmin: number, outmax: number) -> number,
+    lerp: @checked (a: number, b: number, t: number) -> number,
 }
 
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionOsSrc = R"BUILTIN_SRC(
+
 type DateTypeArg = {
     year: number,
     month: number,
@@ -325,51 +164,9 @@ declare os: {
     clock: () -> number,
 }
 
-@checked declare function require(target: any): any
+)BUILTIN_SRC";
 
-@checked declare function getfenv(target: any): { [string]: any }
+static const std::string kBuiltinDefinitionCoroutineSrc = R"BUILTIN_SRC(
-
-declare _G: any
-declare _VERSION: string
-
-declare function gcinfo(): number
-
-declare function print<T...>(...: T...)
-
-declare function type<T>(value: T): string
-declare function typeof<T>(value: T): string
-
--- `assert` has a magic function attached that will give more detailed type information
-declare function assert<T>(value: T, errorMessage: string?): T
-declare function error<T>(message: T, level: number?): never
-
-declare function tostring<T>(value: T): string
-declare function tonumber<T>(value: T, radix: number?): number?
-
-declare function rawequal<T1, T2>(a: T1, b: T2): boolean
-declare function rawget<K, V>(tab: {[K]: V}, k: K): V
-declare function rawset<K, V>(tab: {[K]: V}, k: K, v: V): {[K]: V}
-declare function rawlen<K, V>(obj: {[K]: V} | string): number
-
-declare function setfenv<T..., R...>(target: number | (T...) -> R..., env: {[string]: any}): ((T...) -> R...)?
-
-declare function ipairs<V>(tab: {V}): (({V}, number) -> (number?, V), {V}, number)
-
-declare function pcall<A..., R...>(f: (A...) -> R..., ...: A...): (boolean, R...)
-
--- FIXME: The actual type of `xpcall` is:
--- <E, A..., R1..., R2...>(f: (A...) -> R1..., err: (E) -> R2..., A...) -> (true, R1...) | (false, R2...)
--- Since we can't represent the return value, we use (boolean, R1...).
-declare function xpcall<E, A..., R1..., R2...>(f: (A...) -> R1..., err: (E) -> R2..., ...: A...): (boolean, R1...)
-
--- `select` has a magic function attached to provide more detailed type information
-declare function select<A...>(i: string | number, ...: A...): ...any
-
--- FIXME: This type is not entirely correct - `loadstring` returns a function or
--- (nil, string).
-declare function loadstring<A...>(src: string, chunkname: string?): (((A...) -> any)?, string?)
-
-@checked declare function newproxy(mt: boolean?): any
 
 declare coroutine: {
     create: <A..., R...>(f: (A...) -> R...) -> thread,
@@ -382,6 +179,10 @@ declare coroutine: {
     close: @checked (co: thread) -> (boolean, any)
 }
 
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionTableSrc = R"BUILTIN_SRC(
+
 declare table: {
     concat: <V>(t: {V}, sep: string?, i: number?, j: number?) -> string,
     insert: (<V>(t: {V}, value: V) -> ()) & (<V>(t: {V}, pos: number, value: V) -> ()),
@@ -404,11 +205,19 @@ declare table: {
     isfrozen: <K, V>(t: {[K]: V}) -> boolean,
 }
 
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionDebugSrc = R"BUILTIN_SRC(
+
 declare debug: {
-    info: (<R...>(thread: thread, level: number, options: string) -> R...) & (<R...>(level: number, options: string) -> R...) & (<A..., R1..., R2...>(func: (A...) -> R1..., options: string) -> R2...),
+    info: ((thread: thread, level: number, options: string) -> ...any) & ((level: number, options: string) -> ...any) & (<A..., R1...>(func: (A...) -> R1..., options: string) -> ...any),
     traceback: ((message: string?, level: number?) -> string) & ((thread: thread, message: string?, level: number?) -> string),
 }
 
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionUtf8Src = R"BUILTIN_SRC(
+
 declare utf8: {
     char: @checked (...number) -> string,
     charpattern: string,
@@ -418,10 +227,9 @@ declare utf8: {
     offset: @checked (s: string, n: number?, i: number?) -> number,
 }
 
--- Cannot use `typeof` here because it will produce a polytype when we expect a monotype.
+)BUILTIN_SRC";
-declare function unpack<V>(tab: {V}, i: number?, j: number?): ...V
-
 
+static const std::string kBuiltinDefinitionBufferSrc = R"BUILTIN_SRC(
 --- Buffer API
 declare buffer: {
     create: @checked (size: number) -> buffer,
@@ -448,17 +256,53 @@ declare buffer: {
     writef64: @checked (b: buffer, offset: number, value: number) -> (),
     readstring: @checked (b: buffer, offset: number, count: number) -> string,
     writestring: @checked (b: buffer, offset: number, value: string, count: number?) -> (),
+    readbits: @checked (b: buffer, bitOffset: number, bitCount: number) -> number,
+    writebits: @checked (b: buffer, bitOffset: number, bitCount: number, value: number) -> (),
 }
 
 )BUILTIN_SRC";
 
-static const std::string kBuiltinDefinitionVectorSrc = R"BUILTIN_SRC(
+static const std::string kBuiltinDefinitionVectorSrc = (FFlag::LuauDeclareExternType)
+    ? R"BUILTIN_SRC(
 
--- TODO: this will be replaced with a built-in primitive type
+-- While vector would have been better represented as a built-in primitive type, type solver extern type handling covers most of the properties
-declare class vector end
+declare extern type vector with
+    x: number
+    y: number
+    z: number
+end
 
 declare vector: {
-    create: @checked (x: number, y: number, z: number) -> vector,
+    create: @checked (x: number, y: number, z: number?) -> vector,
+    magnitude: @checked (vec: vector) -> number,
+    normalize: @checked (vec: vector) -> vector,
+    cross: @checked (vec1: vector, vec2: vector) -> vector,
+    dot: @checked (vec1: vector, vec2: vector) -> number,
+    angle: @checked (vec1: vector, vec2: vector, axis: vector?) -> number,
+    floor: @checked (vec: vector) -> vector,
+    ceil: @checked (vec: vector) -> vector,
+    abs: @checked (vec: vector) -> vector,
+    sign: @checked (vec: vector) -> vector,
+    clamp: @checked (vec: vector, min: vector, max: vector) -> vector,
+    max: @checked (vector, ...vector) -> vector,
+    min: @checked (vector, ...vector) -> vector,
+
+    zero: vector,
+    one: vector,
+}
+
+)BUILTIN_SRC"
+    : R"BUILTIN_SRC(
+
+-- While vector would have been better represented as a built-in primitive type, type solver class handling covers most of the properties
+declare class vector
+    x: number
+    y: number
+    z: number
+end
+
+declare vector: {
+    create: @checked (x: number, y: number, z: number?) -> vector,
     magnitude: @checked (vec: vector) -> number,
     normalize: @checked (vec: vector) -> vector,
     cross: @checked (vec1: vector, vec2: vector) -> vector,
@@ -480,10 +324,132 @@ declare vector: {
 
 std::string getBuiltinDefinitionSource()
 {
-    std::string result = FFlag::LuauMathMap ? kBuiltinDefinitionLuaSrcChecked : kBuiltinDefinitionLuaSrcChecked_DEPRECATED;
+    std::string result = kBuiltinDefinitionBaseSrc;
 
-    if (FFlag::LuauVectorDefinitions)
+    result += kBuiltinDefinitionBit32Src;
-        result += kBuiltinDefinitionVectorSrc;
+    result += kBuiltinDefinitionMathSrc;
+    result += kBuiltinDefinitionOsSrc;
+    result += kBuiltinDefinitionCoroutineSrc;
+    result += kBuiltinDefinitionTableSrc;
+    result += kBuiltinDefinitionDebugSrc;
+    result += kBuiltinDefinitionUtf8Src;
+    result += kBuiltinDefinitionBufferSrc;
+    result += kBuiltinDefinitionVectorSrc;
+
+    return result;
+}
+
+// TODO: split into separate tagged unions when the new solver can appropriately handle that.
+static const std::string kBuiltinDefinitionTypeMethodSrc = R"BUILTIN_SRC(
+
+export type type = {
+    tag: "nil" | "unknown" | "never" | "any" | "boolean" | "number" | "string" | "buffer" | "thread" |
+         "singleton" | "negation" | "union" | "intersection" | "table" | "function" | "class" | "generic",
+
+    is: (self: type, arg: string) -> boolean,
+
+    -- for singleton type
+    value: (self: type) -> (string | boolean | nil),
+
+    -- for negation type
+    inner: (self: type) -> type,
+
+    -- for union and intersection types
+    components: (self: type) -> {type},
+
+    -- for table type
+    setproperty: (self: type, key: type, value: type?) -> (),
+    setreadproperty: (self: type, key: type, value: type?) -> (),
+    setwriteproperty: (self: type, key: type, value: type?) -> (),
+    readproperty: (self: type, key: type) -> type?,
+    writeproperty: (self: type, key: type) -> type?,
+    properties: (self: type) -> { [type]: { read: type?, write: type? } },
+    setindexer: (self: type, index: type, result: type) -> (),
+    setreadindexer: (self: type, index: type, result: type) -> (),
+    setwriteindexer: (self: type, index: type, result: type) -> (),
+    indexer: (self: type) -> { index: type, readresult: type, writeresult: type }?,
+    readindexer: (self: type) -> { index: type, result: type }?,
+    writeindexer: (self: type) -> { index: type, result: type }?,
+    setmetatable: (self: type, arg: type) -> (),
+    metatable: (self: type) -> type?,
+
+    -- for function type
+    setparameters: (self: type, head: {type}?, tail: type?) -> (),
+    parameters: (self: type) -> { head: {type}?, tail: type? },
+    setreturns: (self: type, head: {type}?, tail: type? ) -> (),
+    returns: (self: type) -> { head: {type}?, tail: type? },
+    setgenerics: (self: type, {type}?) -> (),
+    generics: (self: type) -> {type},
+
+    -- for class type
+    -- 'properties', 'metatable', 'indexer', 'readindexer' and 'writeindexer' are shared with table type
+    readparent: (self: type) -> type?,
+    writeparent: (self: type) -> type?,
+
+    -- for generic type
+    name: (self: type) -> string?,
+    ispack: (self: type) -> boolean,
+}
+
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionTypesLibSrc = R"BUILTIN_SRC(
+
+declare types: {
+    unknown: type,
+    never: type,
+    any: type,
+    boolean: type,
+    number: type,
+    string: type,
+    thread: type,
+    buffer: type,
+
+    singleton: @checked (arg: string | boolean | nil) -> type,
+    generic: @checked (name: string, ispack: boolean?) -> type,
+    negationof: @checked (arg: type) -> type,
+    unionof: @checked (...type) -> type,
+    intersectionof: @checked (...type) -> type,
+    newtable: @checked (props: {[type]: type} | {[type]: { read: type, write: type } } | nil, indexer: { index: type, readresult: type, writeresult: type }?, metatable: type?) -> type,
+    newfunction: @checked (parameters: { head: {type}?, tail: type? }?, returns: { head: {type}?, tail: type? }?, generics: {type}?) -> type,
+    copy: @checked (arg: type) -> type,
+}
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionTypesLibWithOptionalSrc = R"BUILTIN_SRC(
+
+declare types: {
+    unknown: type,
+    never: type,
+    any: type,
+    boolean: type,
+    number: type,
+    string: type,
+    thread: type,
+    buffer: type,
+
+    singleton: @checked (arg: string | boolean | nil) -> type,
+    optional: @checked (arg: type) -> type,
+    generic: @checked (name: string, ispack: boolean?) -> type,
+    negationof: @checked (arg: type) -> type,
+    unionof: @checked (...type) -> type,
+    intersectionof: @checked (...type) -> type,
+    newtable: @checked (props: {[type]: type} | {[type]: { read: type, write: type } } | nil, indexer: { index: type, readresult: type, writeresult: type }?, metatable: type?) -> type,
+    newfunction: @checked (parameters: { head: {type}?, tail: type? }?, returns: { head: {type}?, tail: type? }?, generics: {type}?) -> type,
+    copy: @checked (arg: type) -> type,
+}
+)BUILTIN_SRC";
+
+
+std::string getTypeFunctionDefinitionSource()
+{
+
+    std::string result = kBuiltinDefinitionTypeMethodSrc;
+
+    if (FFlag::LuauTypeFunOptional)
+        result += kBuiltinDefinitionTypesLibWithOptionalSrc;
+    else
+        result += kBuiltinDefinitionTypesLibSrc;
 
     return result;
 }

Analysis/src/EqSatSimplification.cpp

@@ -23,6 +23,7 @@
 #include <vector>
 
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSimplification)
+LUAU_FASTFLAGVARIABLE(DebugLuauLogSimplificationToDot)
 LUAU_FASTFLAGVARIABLE(DebugLuauExtraEqSatSanityChecks)
 
 namespace Luau::EqSatSimplification
@@ -91,18 +92,24 @@ size_t TTable::Hash::operator()(const TTable& value) const
     return hash;
 }
 
-uint32_t StringCache::add(std::string_view s)
+StringId StringCache::add(std::string_view s)
 {
-    size_t hash = std::hash<std::string_view>()(s);
+    /* Important subtlety: This use of DenseHashMap<std::string_view, StringId>
-    if (uint32_t* it = strings.find(hash))
+     * is okay because std::hash<std::string_view> works solely on the bytes
+     * referred by the string_view.
+     *
+     * In other words, two string views which contain the same bytes will have
+     * the same hash whether or not their addresses are the same.
+     */
+    if (StringId* it = strings.find(s))
         return *it;
 
     char* storage = static_cast<char*>(allocator.allocate(s.size()));
     memcpy(storage, s.data(), s.size());
 
-    uint32_t result = uint32_t(views.size());
+    StringId result = StringId(views.size());
     views.emplace_back(storage, s.size());
-    strings[hash] = result;
+    strings[s] = result;
     return result;
 }
 
@@ -142,6 +149,61 @@ static bool isTerminal(const EType& node)
            node.get<TNever>() || node.get<TNoRefine>();
 }
 
+static bool areTerminalAndDefinitelyDisjoint(const EType& lhs, const EType& rhs)
+{
+    // If either node is non-terminal, then we early exit: we're not going to
+    // do a state space search for whether something like:
+    //  (A | B | C | D) & (E | F | G | H)
+    // ... is a disjoint intersection.
+    if (!isTerminal(lhs) || !isTerminal(rhs))
+        return false;
+
+    // Special case some types that aren't strict, disjoint subsets.
+    if (lhs.get<TTopClass>() || lhs.get<TClass>())
+        return !(rhs.get<TTopClass>() || rhs.get<TClass>());
+
+    // Handling strings / booleans: these are the types for which we
+    // expect something like:
+    //
+    //  "foo" & ~"bar"
+    //
+    // ... to simplify to "foo".
+    if (lhs.get<TString>())
+        return !(rhs.get<TString>() || rhs.get<SString>());
+
+    if (lhs.get<TBoolean>())
+        return !(rhs.get<TBoolean>() || rhs.get<SBoolean>());
+
+    if (auto lhsSString = lhs.get<SString>())
+    {
+        auto rhsSString = rhs.get<SString>();
+        if (!rhsSString)
+            return !rhs.get<TString>();
+        return lhsSString->value() != rhsSString->value();
+    }
+
+    if (auto lhsSBoolean = lhs.get<SBoolean>())
+    {
+        auto rhsSBoolean = rhs.get<SBoolean>();
+        if (!rhsSBoolean)
+            return !rhs.get<TBoolean>();
+        return lhsSBoolean->value() != rhsSBoolean->value();
+    }
+
+    // At this point:
+    // - We know both nodes are terminal
+    // - We know that the LHS is not any boolean, string, or class
+    // At this point, we have two classes of checks left:
+    // - Whether the two enodes are exactly the same set (now that the static
+    //   sets have been covered).
+    // - Whether one of the enodes is a large semantic set such as TAny,
+    //   TUnknown, or TError.
+    return !(
+        lhs.index() == rhs.index() || lhs.get<TUnknown>() || rhs.get<TUnknown>() || lhs.get<TAny>() || rhs.get<TAny>() || lhs.get<TNoRefine>() ||
+        rhs.get<TNoRefine>() || lhs.get<TError>() || rhs.get<TError>() || lhs.get<TOpaque>() || rhs.get<TOpaque>()
+    );
+}
+
 static bool isTerminal(const EGraph& egraph, Id eclass)
 {
     const auto& nodes = egraph[eclass].nodes;
@@ -150,7 +212,7 @@ static bool isTerminal(const EGraph& egraph, Id eclass)
         nodes.end(),
         [](auto& a)
         {
-            return isTerminal(a);
+            return isTerminal(a.node);
         }
     );
 }
@@ -268,9 +330,9 @@ Id toId(
         return egraph.add(TOpaque{ty});
     else if (get<FunctionType>(ty))
         return egraph.add(TFunction{ty});
-    else if (ty == builtinTypes->classType)
+    else if (ty == builtinTypes->externType)
         return egraph.add(TTopClass{});
-    else if (get<ClassType>(ty))
+    else if (get<ExternType>(ty))
         return egraph.add(TClass{ty});
     else if (get<AnyType>(ty))
         return egraph.add(TAny{});
@@ -334,11 +396,32 @@ Id toId(
     {
         LUAU_ASSERT(tfun->packArguments.empty());
 
+        if (tfun->userFuncName)
+        {
+            // TODO: User defined type functions are pseudo-effectful: error
+            // reporting is done via the `print` statement, so running a
+            // UDTF multiple times may end up double erroring. egraphs
+            // currently may induce type functions to be reduced multiple
+            // times. We should probably opt _not_ to process user defined
+            // type functions at all.
+            return egraph.add(TOpaque{ty});
+        }
+
         std::vector<Id> parts;
+        parts.reserve(tfun->typeArguments.size());
         for (TypeId part : tfun->typeArguments)
             parts.push_back(toId(egraph, builtinTypes, mappingIdToClass, typeToMappingId, boundNodes, strings, part));
 
-        return cache(egraph.add(TTypeFun{tfun->function.get(), std::move(parts)}));
+        // This looks sily, but we're making a copy of the specific
+        // `TypeFunctionInstanceType` outside of the provided arena so that
+        // we can access the members without fear of the specific TFIT being
+        // overwritten with a bound type.
+        return cache(egraph.add(TTypeFun{
+            std::make_shared<const TypeFunctionInstanceType>(
+                tfun->function, tfun->typeArguments, tfun->packArguments, tfun->userFuncName, tfun->userFuncData
+            ),
+            std::move(parts)
+        }));
     }
     else if (get<NoRefineType>(ty))
         return egraph.add(TNoRefine{});
@@ -398,7 +481,7 @@ static size_t computeCost(std::unordered_map<Id, size_t>& bestNodes, const EGrap
     if (auto it = costs.find(id); it != costs.end())
         return it->second;
 
-    const std::vector<EType>& nodes = egraph[id].nodes;
+    const std::vector<Node<EType>>& nodes = egraph[id].nodes;
 
     size_t minCost = std::numeric_limits<size_t>::max();
     size_t bestNode = std::numeric_limits<size_t>::max();
@@ -415,7 +498,7 @@ static size_t computeCost(std::unordered_map<Id, size_t>& bestNodes, const EGrap
     // First, quickly scan for a terminal type.  If we can find one, it is obviously the best.
     for (size_t index = 0; index < nodes.size(); ++index)
     {
-        if (isTerminal(nodes[index]))
+        if (isTerminal(nodes[index].node))
         {
             minCost = 1;
             bestNode = index;
@@ -467,44 +550,44 @@ static size_t computeCost(std::unordered_map<Id, size_t>& bestNodes, const EGrap
     {
         const auto& node = nodes[index];
 
-        if (node.get<TBound>())
+        if (node.node.get<TBound>())
             updateCost(BOUND_PENALTY, index); // TODO: This could probably be an assert now that we don't need rewrite rules to handle TBound.
-        else if (node.get<TFunction>())
+        else if (node.node.get<TFunction>())
         {
             minCost = 1;
             bestNode = index;
         }
-        else if (auto tbl = node.get<TTable>())
+        else if (auto tbl = node.node.get<TTable>())
         {
             // TODO: We could make the penalty a parameter to computeChildren.
             std::optional<size_t> maybeCost = computeChildren(tbl->operands(), minCost);
             if (maybeCost)
                 updateCost(TABLE_TYPE_PENALTY + *maybeCost, index);
         }
-        else if (node.get<TImportedTable>())
+        else if (node.node.get<TImportedTable>())
         {
             minCost = IMPORTED_TABLE_PENALTY;
             bestNode = index;
         }
-        else if (auto u = node.get<Union>())
+        else if (auto u = node.node.get<Union>())
         {
             std::optional<size_t> maybeCost = computeChildren(u->operands(), minCost);
             if (maybeCost)
                 updateCost(SET_TYPE_PENALTY + *maybeCost, index);
         }
-        else if (auto i = node.get<Intersection>())
+        else if (auto i = node.node.get<Intersection>())
         {
             std::optional<size_t> maybeCost = computeChildren(i->operands(), minCost);
             if (maybeCost)
                 updateCost(SET_TYPE_PENALTY + *maybeCost, index);
         }
-        else if (auto negation = node.get<Negation>())
+        else if (auto negation = node.node.get<Negation>())
         {
             std::optional<size_t> maybeCost = computeChildren(negation->operands(), minCost);
             if (maybeCost)
                 updateCost(NEGATION_PENALTY + *maybeCost, index);
         }
-        else if (auto tfun = node.get<TTypeFun>())
+        else if (auto tfun = node.node.get<TTypeFun>())
         {
             std::optional<size_t> maybeCost = computeChildren(tfun->operands(), minCost);
             if (maybeCost)
@@ -573,28 +656,34 @@ TypeId flattenTableNode(
             // If a TTable is its own basis, it must be the case that some other
             // node on this eclass is a TImportedTable.  Let's use that.
 
+            bool found = false;
+
             for (size_t i = 0; i < eclass.nodes.size(); ++i)
             {
-                if (eclass.nodes[i].get<TImportedTable>())
+                if (eclass.nodes[i].node.get<TImportedTable>())
                 {
+                    found = true;
                     index = i;
                     break;
                 }
             }
 
-            // If we couldn't find one, we don't know what to do.  Use ErrorType.
+            if (!found)
-            LUAU_ASSERT(0);
+            {
-            return builtinTypes->errorType;
+                // If we couldn't find one, we don't know what to do.  Use ErrorType.
+                LUAU_ASSERT(0);
+                return builtinTypes->errorType;
+            }
         }
 
         const auto& node = eclass.nodes[index];
-        if (const TTable* ttable = node.get<TTable>())
+        if (const TTable* ttable = node.node.get<TTable>())
         {
             stack.push_back(ttable);
             id = ttable->getBasis();
             continue;
         }
-        else if (const TImportedTable* ti = node.get<TImportedTable>())
+        else if (const TImportedTable* ti = node.node.get<TImportedTable>())
         {
             importedTable = ti;
             break;
@@ -621,7 +710,8 @@ TypeId flattenTableNode(
             StringId propName = t->propNames[i];
             const Id propType = t->propTypes()[i];
 
-            resultTable.props[strings.asString(propName)] = Property{fromId(egraph, strings, builtinTypes, arena, bestNodes, seen, newTypeFunctions, propType)};
+            resultTable.props[strings.asString(propName)] =
+                Property{fromId(egraph, strings, builtinTypes, arena, bestNodes, seen, newTypeFunctions, propType)};
         }
     }
 
@@ -645,7 +735,7 @@ TypeId fromId(
     size_t index = bestNodes.at(rootId);
     LUAU_ASSERT(index <= egraph[rootId].nodes.size());
 
-    const EType& node = egraph[rootId].nodes[index];
+    const EType& node = egraph[rootId].nodes[index].node;
 
     if (node.get<TNil>())
         return builtinTypes->nilType;
@@ -662,7 +752,7 @@ TypeId fromId(
     else if (node.get<TTopTable>())
         return builtinTypes->tableType;
     else if (node.get<TTopClass>())
-        return builtinTypes->classType;
+        return builtinTypes->externType;
     else if (node.get<TBuffer>())
         return builtinTypes->bufferType;
     else if (auto opaque = node.get<TOpaque>())
@@ -702,7 +792,20 @@ TypeId fromId(
         if (parts.empty())
             return builtinTypes->neverType;
         else if (parts.size() == 1)
-            return fromId(egraph, strings, builtinTypes, arena, bestNodes, seen, newTypeFunctions, parts[0]);
+        {
+            TypeId placeholder = arena->addType(BlockedType{});
+            seen[rootId] = placeholder;
+            auto result = fromId(egraph, strings, builtinTypes, arena, bestNodes, seen, newTypeFunctions, parts[0]);
+            if (follow(result) == placeholder)
+            {
+                emplaceType<GenericType>(asMutable(placeholder), "EGRAPH-SINGLETON-CYCLE");
+            }
+            else
+            {
+                emplaceType<BoundType>(asMutable(placeholder), result);
+            }
+            return result;
+        }
         else
         {
             TypeId res = arena->addType(BlockedType{});
@@ -767,7 +870,11 @@ TypeId fromId(
         for (Id part : tfun->operands())
             args.push_back(fromId(egraph, strings, builtinTypes, arena, bestNodes, seen, newTypeFunctions, part));
 
-        asMutable(res)->ty.emplace<TypeFunctionInstanceType>(*tfun->value(), std::move(args));
+        auto oldInstance = tfun->value();
+
+        asMutable(res)->ty.emplace<TypeFunctionInstanceType>(
+            oldInstance->function, std::move(args), std::vector<TypePackId>(), oldInstance->userFuncName, oldInstance->userFuncData
+        );
 
         newTypeFunctions.push_back(res);
 
@@ -847,12 +954,20 @@ std::string mkDesc(
     const int RULE_PADDING = 35;
     const std::string rulePadding(std::max<size_t>(0, RULE_PADDING - rule.size()), ' ');
     const std::string fromIdStr = ""; // "(" + std::to_string(uint32_t(from)) + ") ";
-    const std::string toIdStr = ""; // "(" + std::to_string(uint32_t(to)) + ") ";
+    const std::string toIdStr = "";   // "(" + std::to_string(uint32_t(to)) + ") ";
 
     return rule + ":" + rulePadding + fromIdStr + toString(fromTy, opts) + " <=> " + toIdStr + toString(toTy, opts);
 }
 
-std::string mkDesc(EGraph& egraph, const StringCache& strings, NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, Id from, Id to, const std::string& rule)
+std::string mkDesc(
+    EGraph& egraph,
+    const StringCache& strings,
+    NotNull<TypeArena> arena,
+    NotNull<BuiltinTypes> builtinTypes,
+    Id from,
+    Id to,
+    const std::string& rule
+)
 {
     if (!FFlag::DebugLuauLogSimplification)
         return "";
@@ -892,7 +1007,7 @@ static std::string getNodeName(const StringCache& strings, const EType& node)
         return "\xe2\x88\xa9";
     else if (auto cls = node.get<TClass>())
     {
-        const ClassType* ct = get<ClassType>(cls->value());
+        const ExternType* ct = get<ExternType>(cls->value());
         LUAU_ASSERT(ct);
         return ct->name;
     }
@@ -905,7 +1020,7 @@ static std::string getNodeName(const StringCache& strings, const EType& node)
     else if (node.get<TNever>())
         return "never";
     else if (auto tfun = node.get<TTypeFun>())
-        return "tfun " + tfun->value()->name;
+        return "tfun " + tfun->value()->function->name;
     else if (node.get<Negation>())
         return "~";
     else if (node.get<Invalid>())
@@ -927,8 +1042,9 @@ std::string toDot(const StringCache& strings, const EGraph& egraph)
 
     for (const auto& [id, eclass] : egraph.getAllClasses())
     {
-        for (const auto& node : eclass.nodes)
+        for (const auto& n : eclass.nodes)
         {
+            const EType& node = n.node;
             if (!node.operands().empty())
                 populated.insert(id);
             for (Id op : node.operands())
@@ -949,7 +1065,7 @@ std::string toDot(const StringCache& strings, const EGraph& egraph)
 
         for (size_t index = 0; index < eclass.nodes.size(); ++index)
         {
-            const auto& node = eclass.nodes[index];
+            const auto& node = eclass.nodes[index].node;
 
             const std::string label = getNodeName(strings, node);
             const std::string nodeName = "n" + std::to_string(uint32_t(id)) + "_" + std::to_string(index);
@@ -964,7 +1080,7 @@ std::string toDot(const StringCache& strings, const EGraph& egraph)
     {
         for (size_t index = 0; index < eclass.nodes.size(); ++index)
         {
-            const auto& node = eclass.nodes[index];
+            const auto& node = eclass.nodes[index].node;
 
             const std::string label = getNodeName(strings, node);
             const std::string nodeName = "n" + std::to_string(uint32_t(egraph.find(id))) + "_" + std::to_string(index);
@@ -1000,7 +1116,7 @@ static Tag const* isTag(const EGraph& egraph, Id id)
 {
     for (const auto& node : egraph[id].nodes)
     {
-        if (auto n = isTag<Tag>(node))
+        if (auto n = isTag<Tag>(node.node))
             return n;
     }
     return nullptr;
@@ -1036,7 +1152,7 @@ protected:
     {
         for (const auto& node : (*egraph)[id].nodes)
         {
-            if (auto n = node.get<Tag>())
+            if (auto n = node.node.get<Tag>())
                 return n;
         }
         return nullptr;
@@ -1061,12 +1177,12 @@ enum SubclassRelationship
 
 static SubclassRelationship relateClasses(const TClass* leftClass, const TClass* rightClass)
 {
-    const ClassType* leftClassType = Luau::get<ClassType>(leftClass->value());
+    const ExternType* leftExternType = Luau::get<ExternType>(leftClass->value());
-    const ClassType* rightClassType = Luau::get<ClassType>(rightClass->value());
+    const ExternType* rightExternType = Luau::get<ExternType>(rightClass->value());
 
-    if (isSubclass(leftClassType, rightClassType))
+    if (isSubclass(leftExternType, rightExternType))
         return RightSuper;
-    else if (isSubclass(rightClassType, leftClassType))
+    else if (isSubclass(rightExternType, leftExternType))
         return LeftSuper;
     else
         return Unrelated;
@@ -1224,8 +1340,10 @@ const EType* findSubtractableClass(const EGraph& egraph, std::unordered_set<Id>&
     const EType* bestUnion = nullptr;
     std::optional<size_t> unionSize;
 
-    for (const auto& node : egraph[id].nodes)
+    for (const auto& n : egraph[id].nodes)
     {
+        const EType& node = n.node;
+
         if (isTerminal(node))
             return &node;
 
@@ -1341,14 +1459,14 @@ bool subtract(EGraph& egraph, CanonicalizedType& ct, Id part)
     return true;
 }
 
-Id fromCanonicalized(EGraph& egraph, CanonicalizedType& ct)
+static std::pair<Id, size_t> fromCanonicalized(EGraph& egraph, CanonicalizedType& ct)
 {
     if (ct.isUnknown())
     {
         if (ct.errorPart)
-            return egraph.add(TAny{});
+            return {egraph.add(TAny{}), 1};
         else
-            return egraph.add(TUnknown{});
+            return {egraph.add(TUnknown{}), 1};
     }
 
     std::vector<Id> parts;
@@ -1386,7 +1504,12 @@ Id fromCanonicalized(EGraph& egraph, CanonicalizedType& ct)
     parts.insert(parts.end(), ct.functionParts.begin(), ct.functionParts.end());
     parts.insert(parts.end(), ct.otherParts.begin(), ct.otherParts.end());
 
-    return mkUnion(egraph, std::move(parts));
+    std::sort(parts.begin(), parts.end());
+    auto it = std::unique(parts.begin(), parts.end());
+    parts.erase(it, parts.end());
+
+    const size_t size = parts.size();
+    return {mkUnion(egraph, std::move(parts)), size};
 }
 
 void addChildren(const EGraph& egraph, const EType* enode, VecDeque<Id>& worklist)
@@ -1432,7 +1555,7 @@ const Tag* Simplifier::isTag(Id id) const
 {
     for (const auto& node : get(id).nodes)
     {
-        if (const Tag* ty = node.get<Tag>())
+        if (const Tag* ty = node.node.get<Tag>())
             return ty;
     }
 
@@ -1466,6 +1589,16 @@ void Simplifier::subst(Id from, Id to, const std::string& ruleName, const std::u
     substs.emplace_back(from, to, desc);
 }
 
+void Simplifier::subst(Id from, size_t boringIndex, Id to, const std::string& ruleName, const std::unordered_map<Id, size_t>& forceNodes)
+{
+    std::string desc;
+    if (FFlag::DebugLuauLogSimplification)
+        desc = mkDesc(egraph, stringCache, arena, builtinTypes, from, to, forceNodes, ruleName);
+
+    egraph.markBoring(from, boringIndex);
+    substs.emplace_back(from, to, desc);
+}
+
 void Simplifier::unionClasses(std::vector<Id>& hereParts, Id there)
 {
     if (1 == hereParts.size() && isTag<TTopClass>(hereParts[0]))
@@ -1516,9 +1649,12 @@ void Simplifier::simplifyUnion(Id id)
         for (Id part : u->operands())
             unionWithType(egraph, canonicalized, find(part));
 
-        Id resultId = fromCanonicalized(egraph, canonicalized);
+        const auto [resultId, newSize] = fromCanonicalized(egraph, canonicalized);
 
-        subst(id, resultId, "simplifyUnion", {{id, unionIndex}});
+        if (newSize < u->operands().size())
+            subst(id, unionIndex, resultId, "simplifyUnion", {{id, unionIndex}});
+        else
+            subst(id, resultId, "simplifyUnion", {{id, unionIndex}});
     }
 }
 
@@ -1551,11 +1687,6 @@ std::optional<EType> intersectOne(EGraph& egraph, Id hereId, const EType* hereNo
         thereNode->get<Intersection>() || thereNode->get<Negation>() || hereNode->get<TOpaque>() || thereNode->get<TOpaque>())
         return std::nullopt;
 
-    if (hereNode->get<TAny>())
-        return *thereNode;
-    if (thereNode->get<TAny>())
-        return *hereNode;
-
     if (hereNode->get<TUnknown>())
         return *thereNode;
     if (thereNode->get<TUnknown>())
@@ -1731,7 +1862,7 @@ void Simplifier::uninhabitedIntersection(Id id)
             const auto& partNodes = egraph[partId].nodes;
             for (size_t partIndex = 0; partIndex < partNodes.size(); ++partIndex)
             {
-                const EType& N = partNodes[partIndex];
+                const EType& N = partNodes[partIndex].node;
                 if (std::optional<EType> intersection = intersectOne(egraph, accumulator, &accumulatorNode, partId, &N))
                 {
                     if (isTag<TNever>(*intersection))
@@ -1754,9 +1885,14 @@ void Simplifier::uninhabitedIntersection(Id id)
         if ((unsimplified.empty() || !isTag<TUnknown>(accumulator)) && find(accumulator) != id)
             unsimplified.push_back(accumulator);
 
+        const bool isSmaller = unsimplified.size() < parts.size();
+
         const Id result = mkIntersection(egraph, std::move(unsimplified));
 
-        subst(id, result, "uninhabitedIntersection", {{id, index}});
+        if (isSmaller)
+            subst(id, index, result, "uninhabitedIntersection", {{id, index}});
+        else
+            subst(id, result, "uninhabitedIntersection", {{id, index}});
     }
 }
 
@@ -1787,14 +1923,19 @@ void Simplifier::intersectWithNegatedClass(Id id)
                     const auto& iNodes = egraph[iId].nodes;
                     for (size_t iIndex = 0; iIndex < iNodes.size(); ++iIndex)
                     {
-                        const EType& iNode = iNodes[iIndex];
+                        const EType& iNode = iNodes[iIndex].node;
                         if (isTag<TNil>(iNode) || isTag<TBoolean>(iNode) || isTag<TNumber>(iNode) || isTag<TString>(iNode) || isTag<TThread>(iNode) ||
                             isTag<TTopFunction>(iNode) ||
                             // isTag<TTopTable>(iNode) || // I'm not sure about this one.
                             isTag<SBoolean>(iNode) || isTag<SString>(iNode) || isTag<TFunction>(iNode) || isTag<TNever>(iNode))
                         {
                             // eg string & ~SomeClass
-                            subst(id, iId, "intersectClassWithNegatedClass", {{id, intersectionIndex}, {iId, iIndex}, {jId, negationIndex}, {negated, negatedClassIndex}});
+                            subst(
+                                id,
+                                iId,
+                                "intersectClassWithNegatedClass",
+                                {{id, intersectionIndex}, {iId, iIndex}, {jId, negationIndex}, {negated, negatedClassIndex}}
+                            );
                             return;
                         }
 
@@ -1802,27 +1943,37 @@ void Simplifier::intersectWithNegatedClass(Id id)
                         {
                             switch (relateClasses(class_, negatedClass))
                             {
-                                case LeftSuper:
+                            case LeftSuper:
-                                    // eg Instance & ~Part
+                                // eg Instance & ~Part
-                                    // This cannot be meaningfully reduced.
+                                // This cannot be meaningfully reduced.
-                                    continue;
+                                continue;
-                                case RightSuper:
+                            case RightSuper:
-                                    subst(id, egraph.add(TNever{}), "intersectClassWithNegatedClass", {{id, intersectionIndex}, {iId, iIndex}, {jId, negationIndex}, {negated, negatedClassIndex}});
+                                subst(
-                                    return;
+                                    id,
-                                case Unrelated:
+                                    egraph.add(TNever{}),
-                                    // Part & ~Folder == Part
+                                    "intersectClassWithNegatedClass",
+                                    {{id, intersectionIndex}, {iId, iIndex}, {jId, negationIndex}, {negated, negatedClassIndex}}
+                                );
+                                return;
+                            case Unrelated:
+                                // Part & ~Folder == Part
+                                {
+                                    std::vector<Id> newParts;
+                                    newParts.reserve(intersection->operands().size() - 1);
+                                    for (Id part : intersection->operands())
                                     {
-                                        std::vector<Id> newParts;
+                                        if (part != jId)
-                                        newParts.reserve(intersection->operands().size() - 1);
+                                            newParts.push_back(part);
-                                        for (Id part : intersection->operands())
-                                        {
-                                            if (part != jId)
-                                                newParts.push_back(part);
-                                        }
-
-                                        Id substId = egraph.add(Intersection{newParts.begin(), newParts.end()});
-                                        subst(id, substId, "intersectClassWithNegatedClass", {{id, intersectionIndex}, {iId, iIndex}, {jId, negationIndex}, {negated, negatedClassIndex}});
                                     }
+
+                                    Id substId = mkIntersection(egraph, newParts);
+                                    subst(
+                                        id,
+                                        substId,
+                                        "intersectClassWithNegatedClass",
+                                        {{id, intersectionIndex}, {iId, iIndex}, {jId, negationIndex}, {negated, negatedClassIndex}}
+                                    );
+                                }
                             }
                         }
                     }
@@ -1838,6 +1989,74 @@ void Simplifier::intersectWithNegatedClass(Id id)
     }
 }
 
+void Simplifier::intersectWithNegatedAtom(Id id)
+{
+    // Let I and ~J be two arbitrary distinct operands of an intersection where
+    // I and J are terminal but are not type variables. (free, generic, or
+    // otherwise opaque)
+    //
+    // If I and J are equal, then the whole intersection is equivalent to never.
+    //
+    // If I and J are inequal, then J & ~I == J
+
+    for (const auto [intersection, intersectionIndex] : Query<Intersection>(&egraph, id))
+    {
+        const Slice<const Id>& intersectionOperands = intersection->operands();
+        for (size_t i = 0; i < intersectionOperands.size(); ++i)
+        {
+            for (const auto [negation, negationIndex] : Query<Negation>(&egraph, intersectionOperands[i]))
+            {
+                for (size_t negationOperandIndex = 0; negationOperandIndex < egraph[negation->operands()[0]].nodes.size(); ++negationOperandIndex)
+                {
+                    const EType* negationOperand = &egraph[negation->operands()[0]].nodes[negationOperandIndex].node;
+                    if (!isTerminal(*negationOperand) || negationOperand->get<TOpaque>())
+                        continue;
+
+                    for (size_t j = 0; j < intersectionOperands.size(); ++j)
+                    {
+                        if (j == i)
+                            continue;
+
+                        for (size_t jNodeIndex = 0; jNodeIndex < egraph[intersectionOperands[j]].nodes.size(); ++jNodeIndex)
+                        {
+                            const EType* jNode = &egraph[intersectionOperands[j]].nodes[jNodeIndex].node;
+                            if (!isTerminal(*jNode) || jNode->get<TOpaque>())
+                                continue;
+
+                            if (*negationOperand == *jNode)
+                            {
+                                // eg "Hello" & ~"Hello"
+                                // or boolean & ~boolean
+                                subst(
+                                    id,
+                                    egraph.add(TNever{}),
+                                    "intersectWithNegatedAtom",
+                                    {{id, intersectionIndex}, {intersectionOperands[i], negationIndex}, {intersectionOperands[j], jNodeIndex}}
+                                );
+                                return;
+                            }
+                            else if (areTerminalAndDefinitelyDisjoint(*jNode, *negationOperand))
+                            {
+                                // eg "Hello" & ~"World"
+                                // or boolean & ~string
+                                std::vector<Id> newOperands(intersectionOperands.begin(), intersectionOperands.end());
+                                newOperands.erase(newOperands.begin() + std::vector<Id>::difference_type(i));
+
+                                subst(
+                                    id,
+                                    mkIntersection(egraph, std::move(newOperands)),
+                                    "intersectWithNegatedAtom",
+                                    {{id, intersectionIndex}, {intersectionOperands[i], negationIndex}, {intersectionOperands[j], jNodeIndex}}
+                                );
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
 void Simplifier::intersectWithNoRefine(Id id)
 {
     for (const auto pair : Query<Intersection>(&egraph, id))
@@ -2002,7 +2221,7 @@ void Simplifier::expandNegation(Id id)
         if (!ok)
             continue;
 
-        subst(id, fromCanonicalized(egraph, canonicalized), "expandNegation", {{id, index}});
+        subst(id, fromCanonicalized(egraph, canonicalized).first, "expandNegation", {{id, index}});
     }
 }
 
@@ -2159,7 +2378,7 @@ void Simplifier::intersectTableProperty(Id id)
 
                             subst(
                                 id,
-                                egraph.add(Intersection{std::move(newIntersectionParts)}),
+                                mkIntersection(egraph, std::move(newIntersectionParts)),
                                 "intersectTableProperty",
                                 {{id, intersectionIndex}, {iId, table1Index}, {jId, table2Index}}
                             );
@@ -2249,7 +2468,7 @@ void Simplifier::builtinTypeFunctions(Id id)
         if (args.size() != 2)
             continue;
 
-        const std::string& name = tfun->value()->name;
+        const std::string& name = tfun->value()->function->name;
         if (name == "add" || name == "sub" || name == "mul" || name == "div" || name == "idiv" || name == "pow" || name == "mod")
         {
             if (isTag<TNumber>(args[0]) && isTag<TNumber>(args[1]))
@@ -2271,15 +2490,43 @@ void Simplifier::iffyTypeFunctions(Id id)
     {
         const Slice<const Id>& args = tfun->operands();
 
-        const std::string& name = tfun->value()->name;
+        const std::string& name = tfun->value()->function->name;
 
         if (name == "union")
             subst(id, add(Union{std::vector(args.begin(), args.end())}), "iffyTypeFunctions", {{id, index}});
-        else if (name == "intersect" || name == "refine")
+        else if (name == "intersect")
             subst(id, add(Intersection{std::vector(args.begin(), args.end())}), "iffyTypeFunctions", {{id, index}});
     }
 }
 
+// Replace instances of `lt<X, Y>` and `le<X, Y>` when either X or Y is `number`
+// or `string` with `boolean`. Lua semantics are that if we see the expression:
+//
+//   x < y
+//
+// ... we error if `x` and `y` don't have the same type. We know that for
+// `string` and `number`, comparisons will always return a boolean. So if either
+// of the arguments to `lt<>` are equivalent to `number` or `string`, then the
+// type is effectively `boolean`: either the other type is equivalent, in which
+// case we eval to `boolean`, or we diverge (raise an error).
+void Simplifier::strictMetamethods(Id id)
+{
+    for (const auto [tfun, index] : Query<TTypeFun>(&egraph, id))
+    {
+        const Slice<const Id>& args = tfun->operands();
+
+        const std::string& name = tfun->value()->function->name;
+
+        if (!(name == "lt" || name == "le") || args.size() != 2)
+            continue;
+
+        if (isTag<TNumber>(args[0]) || isTag<TString>(args[0]) || isTag<TNumber>(args[1]) || isTag<TString>(args[1]))
+        {
+            subst(id, add(TBoolean{}), __FUNCTION__, {{id, index}});
+        }
+    }
+}
+
 static void deleteSimplifier(Simplifier* s)
 {
     delete s;
@@ -2307,6 +2554,7 @@ std::optional<EqSatSimplificationResult> eqSatSimplify(NotNull<Simplifier> simpl
         &Simplifier::simplifyUnion,
         &Simplifier::uninhabitedIntersection,
         &Simplifier::intersectWithNegatedClass,
+        &Simplifier::intersectWithNegatedAtom,
         &Simplifier::intersectWithNoRefine,
         &Simplifier::cyclicIntersectionOfUnion,
         &Simplifier::cyclicUnionOfIntersection,
@@ -2317,6 +2565,7 @@ std::optional<EqSatSimplificationResult> eqSatSimplify(NotNull<Simplifier> simpl
         &Simplifier::unneededTableModification,
         &Simplifier::builtinTypeFunctions,
         &Simplifier::iffyTypeFunctions,
+        &Simplifier::strictMetamethods,
     };
 
     std::unordered_set<Id> seen;
@@ -2327,7 +2576,7 @@ std::optional<EqSatSimplificationResult> eqSatSimplify(NotNull<Simplifier> simpl
     int count = 0;
     const int MAX_COUNT = 1000;
 
-    if (FFlag::DebugLuauLogSimplification)
+    if (FFlag::DebugLuauLogSimplificationToDot)
         std::ofstream("begin.dot") << toDot(simplifier->stringCache, simplifier->egraph);
 
     auto& egraph = simplifier->egraph;
@@ -2370,9 +2619,9 @@ std::optional<EqSatSimplificationResult> eqSatSimplify(NotNull<Simplifier> simpl
             // try to run any rules on it.
             bool shouldAbort = false;
 
-            for (const EType& enode : egraph[id].nodes)
+            for (const auto& enode : egraph[id].nodes)
             {
-                if (isTerminal(enode))
+                if (isTerminal(enode.node))
                 {
                     shouldAbort = true;
                     break;
@@ -2382,8 +2631,8 @@ std::optional<EqSatSimplificationResult> eqSatSimplify(NotNull<Simplifier> simpl
             if (shouldAbort)
                 continue;
 
-            for (const EType& enode : egraph[id].nodes)
+            for (const auto& enode : egraph[id].nodes)
-                addChildren(egraph, &enode, worklist);
+                addChildren(egraph, &enode.node, worklist);
 
             for (Simplifier::RewriteRuleFn rule : rules)
                 (simplifier.get()->*rule)(id);
@@ -2409,11 +2658,11 @@ std::optional<EqSatSimplificationResult> eqSatSimplify(NotNull<Simplifier> simpl
 
                 ++count;
 
-                if (FFlag::DebugLuauLogSimplification)
+                if (FFlag::DebugLuauLogSimplification && isFresh)
-                {
+                    std::cout << "count=" << std::setw(3) << count << "\t" << subst.desc << '\n';
-                    if (isFresh)
-                        std::cout << "count=" << std::setw(3) << count << "\t" << subst.desc << '\n';
 
+                if (FFlag::DebugLuauLogSimplificationToDot)
+                {
                     std::string filename = format("step%03d.dot", count);
                     std::ofstream(filename) << toDot(simplifier->stringCache, egraph);
                 }

Analysis/src/Error.cpp

@@ -8,6 +8,7 @@
 #include "Luau/StringUtils.h"
 #include "Luau/ToString.h"
 #include "Luau/Type.h"
+#include "Luau/TypeChecker2.h"
 #include "Luau/TypeFunction.h"
 
 #include <optional>
@@ -17,6 +18,7 @@
 #include <unordered_set>
 
 LUAU_FASTINTVARIABLE(LuauIndentTypeMismatchMaxTypeLength, 10)
+LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
 
 static std::string wrongNumberOfArgsString(
     size_t expectedCount,
@@ -68,7 +70,7 @@ namespace Luau
 {
 
 // this list of binary operator type functions is used for better stringification of type functions errors
-static const std::unordered_map<std::string, const char*> kBinaryOps{
+static const std::unordered_map<std::string, const char*> DEPRECATED_kBinaryOps{
     {"add", "+"},
     {"sub", "-"},
     {"mul", "*"},
@@ -84,12 +86,27 @@ static const std::unordered_map<std::string, const char*> kBinaryOps{
     {"eq", "== or ~="}
 };
 
+static const std::unordered_map<std::string, const char*> kBinaryOps{
+    {"add", "+"},
+    {"sub", "-"},
+    {"mul", "*"},
+    {"div", "/"},
+    {"idiv", "//"},
+    {"pow", "^"},
+    {"mod", "%"},
+    {"concat", ".."},
+    {"lt", "< or >="},
+    {"le", "<= or >"},
+    {"eq", "== or ~="}
+};
+
 // this list of unary operator type functions is used for better stringification of type functions errors
 static const std::unordered_map<std::string, const char*> kUnaryOps{{"unm", "-"}, {"len", "#"}, {"not", "not"}};
 
 // this list of type functions will receive a special error indicating that the user should file a bug on the GitHub repository
 // putting a type function in this list indicates that it is expected to _always_ reduce
-static const std::unordered_set<std::string> kUnreachableTypeFunctions{"refine", "singleton", "union", "intersect"};
+static const std::unordered_set<std::string> DEPRECATED_kUnreachableTypeFunctions{"refine", "singleton", "union", "intersect"};
+static const std::unordered_set<std::string> kUnreachableTypeFunctions{"refine", "singleton", "union", "intersect", "and", "or"};
 
 struct ErrorConverter
 {
@@ -116,7 +133,10 @@ struct ErrorConverter
             size_t luauIndentTypeMismatchMaxTypeLength = size_t(FInt::LuauIndentTypeMismatchMaxTypeLength);
             if (givenType.length() <= luauIndentTypeMismatchMaxTypeLength || wantedType.length() <= luauIndentTypeMismatchMaxTypeLength)
                 return "Type " + given + " could not be converted into " + wanted;
-            return "Type\n    " + given + "\ncould not be converted into\n    " + wanted;
+            if (FFlag::LuauImproveTypePathsInErrors)
+                return "Type\n\t" + given + "\ncould not be converted into\n\t" + wanted;
+            else
+                return "Type\n    " + given + "\ncould not be converted into\n    " + wanted;
         };
 
         if (givenTypeName == wantedTypeName)
@@ -183,7 +203,7 @@ struct ErrorConverter
         TypeId t = follow(e.table);
         if (get<TableType>(t))
             return "Key '" + e.key + "' not found in table '" + Luau::toString(t) + "'";
-        else if (get<ClassType>(t))
+        else if (get<ExternType>(t))
             return "Key '" + e.key + "' not found in class '" + Luau::toString(t) + "'";
         else
             return "Type '" + Luau::toString(e.table) + "' does not have key '" + e.key + "'";
@@ -351,7 +371,7 @@ struct ErrorConverter
         std::string s = "Key '" + e.key + "' not found in ";
 
         TypeId t = follow(e.table);
-        if (get<ClassType>(t))
+        if (get<ExternType>(t))
             s += "class";
         else
             s += "table";
@@ -382,8 +402,8 @@ struct ErrorConverter
         std::optional<TypeId> metatable;
         if (const MetatableType* mtType = get<MetatableType>(type))
             metatable = mtType->metatable;
-        else if (const ClassType* classType = get<ClassType>(type))
+        else if (const ExternType* externType = get<ExternType>(type))
-            metatable = classType->metatable;
+            metatable = externType->metatable;
 
         if (!metatable)
             return std::nullopt;
@@ -591,7 +611,7 @@ struct ErrorConverter
         return ss;
     }
 
-    std::string operator()(const DynamicPropertyLookupOnClassesUnsafe& e) const
+    std::string operator()(const DynamicPropertyLookupOnExternTypesUnsafe& e) const
     {
         return "Attempting a dynamic property access on type '" + Luau::toString(e.ty) + "' is unsafe and may cause exceptions at runtime";
     }
@@ -601,7 +621,7 @@ struct ErrorConverter
         auto tfit = get<TypeFunctionInstanceType>(e.ty);
         LUAU_ASSERT(tfit); // Luau analysis has actually done something wrong if this type is not a type function.
         if (!tfit)
-            return "Unexpected type " + Luau::toString(e.ty) + " flagged as an uninhabited type function.";
+            return "Internal error: Unexpected type " + Luau::toString(e.ty) + " flagged as an uninhabited type function.";
 
         // unary operators
         if (auto unaryString = kUnaryOps.find(tfit->function->name); unaryString != kUnaryOps.end())
@@ -638,7 +658,8 @@ struct ErrorConverter
         }
 
         // binary operators
-        if (auto binaryString = kBinaryOps.find(tfit->function->name); binaryString != kBinaryOps.end())
+        const auto binaryOps = FFlag::DebugLuauGreedyGeneralization ? kBinaryOps : DEPRECATED_kBinaryOps;
+        if (auto binaryString = binaryOps.find(tfit->function->name); binaryString != binaryOps.end())
         {
             std::string result = "Operator '" + std::string(binaryString->second) + "' could not be applied to operands of types ";
 
@@ -692,10 +713,10 @@ struct ErrorConverter
                        "'";
         }
 
-        if (kUnreachableTypeFunctions.count(tfit->function->name))
+        if ((FFlag::DebugLuauGreedyGeneralization ? kUnreachableTypeFunctions : DEPRECATED_kUnreachableTypeFunctions).count(tfit->function->name))
         {
             return "Type function instance " + Luau::toString(e.ty) + " is uninhabited\n" +
-                   "This is likely to be a bug, please report it at https://github.com/luau-lang/luau/issues";
+                "This is likely to be a bug, please report it at https://github.com/luau-lang/luau/issues";
         }
 
         // Everything should be specialized above to report a more descriptive error that hopefully does not mention "type functions" explicitly.
@@ -751,8 +772,15 @@ struct ErrorConverter
 
     std::string operator()(const NonStrictFunctionDefinitionError& e) const
     {
-        return "Argument " + e.argument + " with type '" + toString(e.argumentType) + "' in function '" + e.functionName +
+        if (e.functionName.empty())
-               "' is used in a way that will run time error";
+        {
+            return "Argument " + e.argument + " with type '" + toString(e.argumentType) + "' is used in a way that will run time error";
+        }
+        else
+        {
+            return "Argument " + e.argument + " with type '" + toString(e.argumentType) + "' in function '" + e.functionName +
+                   "' is used in a way that will run time error";
+        }
     }
 
     std::string operator()(const PropertyAccessViolation& e) const
@@ -791,6 +819,11 @@ struct ErrorConverter
         return e.message;
     }
 
+    std::string operator()(const ReservedIdentifier& e) const
+    {
+        return e.name + " cannot be used as an identifier for a type function or alias";
+    }
+
     std::string operator()(const CannotAssignToNever& e) const
     {
         std::string result = "Cannot assign a value of type " + toString(e.rhsType) + " to a field of type never";
@@ -1116,7 +1149,7 @@ bool TypePackMismatch::operator==(const TypePackMismatch& rhs) const
     return *wantedTp == *rhs.wantedTp && *givenTp == *rhs.givenTp;
 }
 
-bool DynamicPropertyLookupOnClassesUnsafe::operator==(const DynamicPropertyLookupOnClassesUnsafe& rhs) const
+bool DynamicPropertyLookupOnExternTypesUnsafe::operator==(const DynamicPropertyLookupOnExternTypesUnsafe& rhs) const
 {
     return ty == rhs.ty;
 }
@@ -1178,6 +1211,11 @@ bool UserDefinedTypeFunctionError::operator==(const UserDefinedTypeFunctionError
     return message == rhs.message;
 }
 
+bool ReservedIdentifier::operator==(const ReservedIdentifier& rhs) const
+{
+    return name == rhs.name;
+}
+
 bool CannotAssignToNever::operator==(const CannotAssignToNever& rhs) const
 {
     if (cause.size() != rhs.cause.size())
@@ -1353,7 +1391,7 @@ void copyError(T& e, TypeArena& destArena, CloneState& cloneState)
         e.wantedTp = clone(e.wantedTp);
         e.givenTp = clone(e.givenTp);
     }
-    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnClassesUnsafe>)
+    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnExternTypesUnsafe>)
         e.ty = clone(e.ty);
     else if constexpr (std::is_same_v<T, UninhabitedTypeFunction>)
         e.ty = clone(e.ty);
@@ -1397,6 +1435,9 @@ void copyError(T& e, TypeArena& destArena, CloneState& cloneState)
         for (auto& ty : e.cause)
             ty = clone(ty);
     }
+    else if constexpr (std::is_same_v<T, ReservedIdentifier>)
+    {
+    }
     else
         static_assert(always_false_v<T>, "Non-exhaustive type switch");
 }

Analysis/src/FileResolver.cpp

@@ -0,0 +1,160 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#include "Luau/FileResolver.h"
+
+#include "Luau/Common.h"
+#include "Luau/StringUtils.h"
+
+#include <algorithm>
+#include <memory>
+#include <optional>
+#include <string_view>
+#include <utility>
+
+namespace Luau
+{
+
+static std::optional<RequireSuggestions> processRequireSuggestions(std::optional<RequireSuggestions> suggestions)
+{
+    if (!suggestions)
+        return suggestions;
+
+    for (RequireSuggestion& suggestion : *suggestions)
+    {
+        suggestion.fullPath = escape(suggestion.fullPath);
+    }
+
+    return suggestions;
+}
+
+static RequireSuggestions makeSuggestionsFromAliases(std::vector<RequireAlias> aliases)
+{
+    RequireSuggestions result;
+    for (RequireAlias& alias : aliases)
+    {
+        RequireSuggestion suggestion;
+        suggestion.label = "@" + std::move(alias.alias);
+        suggestion.fullPath = suggestion.label;
+        suggestion.tags = std::move(alias.tags);
+        result.push_back(std::move(suggestion));
+    }
+    return result;
+}
+
+static RequireSuggestions makeSuggestionsForFirstComponent(std::unique_ptr<RequireNode> node)
+{
+    RequireSuggestions result = makeSuggestionsFromAliases(node->getAvailableAliases());
+    result.push_back(RequireSuggestion{"./", "./", {}});
+    result.push_back(RequireSuggestion{"../", "../", {}});
+    return result;
+}
+
+static RequireSuggestions makeSuggestionsFromNode(std::unique_ptr<RequireNode> node, const std::string_view path, bool isPartialPath)
+{
+    LUAU_ASSERT(!path.empty());
+
+    RequireSuggestions result;
+
+    const size_t lastSlashInPath = path.find_last_of('/');
+
+    if (lastSlashInPath != std::string_view::npos)
+    {
+        // Add a suggestion for the parent directory
+        RequireSuggestion parentSuggestion;
+        parentSuggestion.label = "..";
+
+        // TODO: after exposing require-by-string's path normalization API, this
+        // if-else can be replaced. Instead, we can simply normalize the result
+        // of inserting ".." at the end of the current path.
+        if (lastSlashInPath >= 2 && path.substr(lastSlashInPath - 2, 3) == "../")
+        {
+            parentSuggestion.fullPath = path.substr(0, lastSlashInPath + 1);
+            parentSuggestion.fullPath += "..";
+        }
+        else
+        {
+            parentSuggestion.fullPath = path.substr(0, lastSlashInPath);
+        }
+
+        result.push_back(std::move(parentSuggestion));
+    }
+
+    std::string fullPathPrefix;
+    if (isPartialPath)
+    {
+        // ./path/to/chi -> ./path/to/
+        fullPathPrefix += path.substr(0, lastSlashInPath + 1);
+    }
+    else
+    {
+        if (path.back() == '/')
+        {
+            // ./path/to/ -> ./path/to/
+            fullPathPrefix += path;
+        }
+        else
+        {
+            // ./path/to -> ./path/to/
+            fullPathPrefix += path;
+            fullPathPrefix += "/";
+        }
+    }
+
+    for (const std::unique_ptr<RequireNode>& child : node->getChildren())
+    {
+        if (!child)
+            continue;
+
+        std::string pathComponent = child->getPathComponent();
+
+        // If path component contains a slash, it cannot be required by string.
+        // There's no point suggesting it.
+        if (pathComponent.find('/') != std::string::npos)
+            continue;
+
+        RequireSuggestion suggestion;
+        suggestion.label = isPartialPath || path.back() == '/' ? child->getLabel() : "/" + child->getLabel();
+        suggestion.fullPath = fullPathPrefix + std::move(pathComponent);
+        suggestion.tags = child->getTags();
+        result.push_back(std::move(suggestion));
+    }
+
+    return result;
+}
+
+std::optional<RequireSuggestions> RequireSuggester::getRequireSuggestionsImpl(const ModuleName& requirer, const std::optional<std::string>& path)
+    const
+{
+    if (!path)
+        return std::nullopt;
+
+    std::unique_ptr<RequireNode> requirerNode = getNode(requirer);
+    if (!requirerNode)
+        return std::nullopt;
+
+    const size_t slashPos = path->find_last_of('/');
+
+    if (slashPos == std::string::npos)
+        return makeSuggestionsForFirstComponent(std::move(requirerNode));
+
+    // If path already points at a Node, return the Node's children as paths.
+    if (std::unique_ptr<RequireNode> node = requirerNode->resolvePathToNode(*path))
+        return makeSuggestionsFromNode(std::move(node), *path, /* isPartialPath = */ false);
+
+    // Otherwise, recover a partial path and use this to generate suggestions.
+    if (std::unique_ptr<RequireNode> partialNode = requirerNode->resolvePathToNode(path->substr(0, slashPos)))
+        return makeSuggestionsFromNode(std::move(partialNode), *path, /* isPartialPath = */ true);
+
+    return std::nullopt;
+}
+
+std::optional<RequireSuggestions> RequireSuggester::getRequireSuggestions(const ModuleName& requirer, const std::optional<std::string>& path) const
+{
+    return processRequireSuggestions(getRequireSuggestionsImpl(requirer, path));
+}
+
+std::optional<RequireSuggestions> FileResolver::getRequireSuggestions(const ModuleName& requirer, const std::optional<std::string>& path) const
+{
+    return requireSuggester ? requireSuggester->getRequireSuggestions(requirer, path) : std::nullopt;
+}
+
+} // namespace Luau

Analysis/src/Frontend.cpp

@@ -1,7 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Frontend.h"
 
-#include "Luau/AnyTypeSummary.h"
 #include "Luau/BuiltinDefinitions.h"
 #include "Luau/Clone.h"
 #include "Luau/Common.h"
@@ -13,6 +12,7 @@
 #include "Luau/EqSatSimplification.h"
 #include "Luau/FileResolver.h"
 #include "Luau/NonStrictTypeChecker.h"
+#include "Luau/NotNull.h"
 #include "Luau/Parser.h"
 #include "Luau/Scope.h"
 #include "Luau/StringUtils.h"
@@ -38,18 +38,16 @@ LUAU_FASTINT(LuauTypeInferRecursionLimit)
 LUAU_FASTINT(LuauTarjanChildLimit)
 LUAU_FASTFLAG(LuauInferInNoCheckMode)
 LUAU_FASTFLAGVARIABLE(LuauKnowsTheDataModel3)
-LUAU_FASTFLAGVARIABLE(LuauStoreCommentsForDefinitionFiles)
 LUAU_FASTFLAG(LuauSolverV2)
+LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauRethrowKnownExceptions, false)
+LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJson)
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJsonFile)
 LUAU_FASTFLAGVARIABLE(DebugLuauForbidInternalTypes)
 LUAU_FASTFLAGVARIABLE(DebugLuauForceStrictMode)
 LUAU_FASTFLAGVARIABLE(DebugLuauForceNonStrictMode)
-LUAU_FASTFLAGVARIABLE(LuauUserDefinedTypeFunctionNoEvaluation)
-LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauRunCustomModuleChecks, false)
 
-LUAU_FASTFLAG(StudioReportLuauAny2)
+LUAU_FASTFLAG(LuauTypeFunResultInAutocomplete)
-LUAU_FASTFLAGVARIABLE(LuauStoreDFGOnModule2)
 
 namespace Luau
 {
@@ -79,6 +77,20 @@ struct BuildQueueItem
     Frontend::Stats stats;
 };
 
+struct BuildQueueWorkState
+{
+    std::function<void(std::function<void()> task)> executeTask;
+
+    std::vector<BuildQueueItem> buildQueueItems;
+
+    std::mutex mtx;
+    std::condition_variable cv;
+    std::vector<size_t> readyQueueItems;
+
+    size_t processing = 0;
+    size_t remaining = 0;
+};
+
 std::optional<Mode> parseMode(const std::vector<HotComment>& hotcomments)
 {
     for (const HotComment& hc : hotcomments)
@@ -117,9 +129,9 @@ static void generateDocumentationSymbols(TypeId ty, const std::string& rootName)
             prop.documentationSymbol = rootName + "." + name;
         }
     }
-    else if (ClassType* ctv = getMutable<ClassType>(ty))
+    else if (ExternType* etv = getMutable<ExternType>(ty))
     {
-        for (auto& [name, prop] : ctv->props)
+        for (auto& [name, prop] : etv->props)
         {
             prop.documentationSymbol = rootName + "." + name;
         }
@@ -136,7 +148,7 @@ static ParseResult parseSourceForModule(std::string_view source, Luau::SourceMod
     sourceModule.root = parseResult.root;
     sourceModule.mode = Mode::Definition;
 
-    if (FFlag::LuauStoreCommentsForDefinitionFiles && options.captureComments)
+    if (options.captureComments)
     {
         sourceModule.hotcomments = parseResult.hotcomments;
         sourceModule.commentLocations = parseResult.commentLocations;
@@ -443,20 +455,6 @@ CheckResult Frontend::check(const ModuleName& name, std::optional<FrontendOption
 
         if (item.name == name)
             checkResult.lintResult = item.module->lintResult;
-
-        if (FFlag::StudioReportLuauAny2 && item.options.retainFullTypeGraphs)
-        {
-            if (item.module)
-            {
-                const SourceModule& sourceModule = *item.sourceModule;
-                if (sourceModule.mode == Luau::Mode::Strict)
-                {
-                    item.module->ats.root = toString(sourceModule.root);
-                }
-                item.module->ats.rootSrc = sourceModule.root;
-                item.module->ats.traverse(item.module.get(), sourceModule.root, NotNull{&builtinTypes_});
-            }
-        }
     }
 
     return checkResult;
@@ -487,7 +485,8 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
     std::swap(currModuleQueue, moduleQueue);
 
     DenseHashSet<Luau::ModuleName> seen{{}};
-    std::vector<BuildQueueItem> buildQueueItems;
+
+    std::shared_ptr<BuildQueueWorkState> state = std::make_shared<BuildQueueWorkState>();
 
     for (const ModuleName& name : currModuleQueue)
     {
@@ -511,18 +510,18 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
             }
         );
 
-        addBuildQueueItems(buildQueueItems, queue, cycleDetected, seen, frontendOptions);
+        addBuildQueueItems(state->buildQueueItems, queue, cycleDetected, seen, frontendOptions);
     }
 
-    if (buildQueueItems.empty())
+    if (state->buildQueueItems.empty())
         return {};
 
     // We need a mapping from modules to build queue slots
     std::unordered_map<ModuleName, size_t> moduleNameToQueue;
 
-    for (size_t i = 0; i < buildQueueItems.size(); i++)
+    for (size_t i = 0; i < state->buildQueueItems.size(); i++)
     {
-        BuildQueueItem& item = buildQueueItems[i];
+        BuildQueueItem& item = state->buildQueueItems[i];
         moduleNameToQueue[item.name] = i;
     }
 
@@ -535,67 +534,13 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
         };
     }
 
-    std::mutex mtx;
+    state->executeTask = executeTask;
-    std::condition_variable cv;
+    state->remaining = state->buildQueueItems.size();
-    std::vector<size_t> readyQueueItems;
 
-    size_t processing = 0;
+    // Record dependencies between modules
-    size_t remaining = buildQueueItems.size();
+    for (size_t i = 0; i < state->buildQueueItems.size(); i++)
-
-    auto itemTask = [&](size_t i)
     {
-        BuildQueueItem& item = buildQueueItems[i];
+        BuildQueueItem& item = state->buildQueueItems[i];
-
-        try
-        {
-            checkBuildQueueItem(item);
-        }
-        catch (...)
-        {
-            item.exception = std::current_exception();
-        }
-
-        {
-            std::unique_lock guard(mtx);
-            readyQueueItems.push_back(i);
-        }
-
-        cv.notify_one();
-    };
-
-    auto sendItemTask = [&](size_t i)
-    {
-        BuildQueueItem& item = buildQueueItems[i];
-
-        item.processing = true;
-        processing++;
-
-        executeTask(
-            [&itemTask, i]()
-            {
-                itemTask(i);
-            }
-        );
-    };
-
-    auto sendCycleItemTask = [&]
-    {
-        for (size_t i = 0; i < buildQueueItems.size(); i++)
-        {
-            BuildQueueItem& item = buildQueueItems[i];
-
-            if (!item.processing)
-            {
-                sendItemTask(i);
-                break;
-            }
-        }
-    };
-
-    // In a first pass, check modules that have no dependencies and record info of those modules that wait
-    for (size_t i = 0; i < buildQueueItems.size(); i++)
-    {
-        BuildQueueItem& item = buildQueueItems[i];
 
         for (const ModuleName& dep : item.sourceNode->requireSet)
         {
@@ -605,41 +550,45 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
                 {
                     item.dirtyDependencies++;
 
-                    buildQueueItems[moduleNameToQueue[dep]].reverseDeps.push_back(i);
+                    state->buildQueueItems[moduleNameToQueue[dep]].reverseDeps.push_back(i);
                 }
             }
         }
-
-        if (item.dirtyDependencies == 0)
-            sendItemTask(i);
     }
 
-    // Not a single item was found, a cycle in the graph was hit
+    // In the first pass, check all modules with no pending dependencies
-    if (processing == 0)
+    for (size_t i = 0; i < state->buildQueueItems.size(); i++)
-        sendCycleItemTask();
+    {
+        if (state->buildQueueItems[i].dirtyDependencies == 0)
+            sendQueueItemTask(state, i);
+    }
+
+    // If not a single item was found, a cycle in the graph was hit
+    if (state->processing == 0)
+        sendQueueCycleItemTask(state);
 
     std::vector<size_t> nextItems;
     std::optional<size_t> itemWithException;
     bool cancelled = false;
 
-    while (remaining != 0)
+    while (state->remaining != 0)
     {
         {
-            std::unique_lock guard(mtx);
+            std::unique_lock guard(state->mtx);
 
             // If nothing is ready yet, wait
-            cv.wait(
+            state->cv.wait(
                 guard,
-                [&readyQueueItems]
+                [state]
                 {
-                    return !readyQueueItems.empty();
+                    return !state->readyQueueItems.empty();
                 }
             );
 
             // Handle checked items
-            for (size_t i : readyQueueItems)
+            for (size_t i : state->readyQueueItems)
             {
-                const BuildQueueItem& item = buildQueueItems[i];
+                const BuildQueueItem& item = state->buildQueueItems[i];
 
                 // If exception was thrown, stop adding new items and wait for processing items to complete
                 if (item.exception)
@@ -656,7 +605,7 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
                 // Notify items that were waiting for this dependency
                 for (size_t reverseDep : item.reverseDeps)
                 {
-                    BuildQueueItem& reverseDepItem = buildQueueItems[reverseDep];
+                    BuildQueueItem& reverseDepItem = state->buildQueueItems[reverseDep];
 
                     LUAU_ASSERT(reverseDepItem.dirtyDependencies != 0);
                     reverseDepItem.dirtyDependencies--;
@@ -667,26 +616,26 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
                 }
             }
 
-            LUAU_ASSERT(processing >= readyQueueItems.size());
+            LUAU_ASSERT(state->processing >= state->readyQueueItems.size());
-            processing -= readyQueueItems.size();
+            state->processing -= state->readyQueueItems.size();
 
-            LUAU_ASSERT(remaining >= readyQueueItems.size());
+            LUAU_ASSERT(state->remaining >= state->readyQueueItems.size());
-            remaining -= readyQueueItems.size();
+            state->remaining -= state->readyQueueItems.size();
-            readyQueueItems.clear();
+            state->readyQueueItems.clear();
         }
 
         if (progress)
         {
-            if (!progress(buildQueueItems.size() - remaining, buildQueueItems.size()))
+            if (!progress(state->buildQueueItems.size() - state->remaining, state->buildQueueItems.size()))
                 cancelled = true;
         }
 
         // Items cannot be submitted while holding the lock
         for (size_t i : nextItems)
-            sendItemTask(i);
+            sendQueueItemTask(state, i);
         nextItems.clear();
 
-        if (processing == 0)
+        if (state->processing == 0)
         {
             // Typechecking might have been cancelled by user, don't return partial results
             if (cancelled)
@@ -694,19 +643,19 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
 
             // We might have stopped because of a pending exception
             if (itemWithException)
-                recordItemResult(buildQueueItems[*itemWithException]);
+                recordItemResult(state->buildQueueItems[*itemWithException]);
         }
 
         // If we aren't done, but don't have anything processing, we hit a cycle
-        if (remaining != 0 && processing == 0)
+        if (state->remaining != 0 && state->processing == 0)
-            sendCycleItemTask();
+            sendQueueCycleItemTask(state);
     }
 
     std::vector<ModuleName> checkedModules;
-    checkedModules.reserve(buildQueueItems.size());
+    checkedModules.reserve(state->buildQueueItems.size());
 
-    for (size_t i = 0; i < buildQueueItems.size(); i++)
+    for (size_t i = 0; i < state->buildQueueItems.size(); i++)
-        checkedModules.push_back(std::move(buildQueueItems[i].name));
+        checkedModules.push_back(std::move(state->buildQueueItems[i].name));
 
     return checkedModules;
 }
@@ -744,6 +693,32 @@ std::optional<CheckResult> Frontend::getCheckResult(const ModuleName& name, bool
     return checkResult;
 }
 
+std::vector<ModuleName> Frontend::getRequiredScripts(const ModuleName& name)
+{
+    RequireTraceResult require = requireTrace[name];
+    if (isDirty(name))
+    {
+        std::optional<SourceCode> source = fileResolver->readSource(name);
+        if (!source)
+        {
+            return {};
+        }
+        const Config& config = configResolver->getConfig(name);
+        ParseOptions opts = config.parseOptions;
+        opts.captureComments = true;
+        SourceModule result = parse(name, source->source, opts);
+        result.type = source->type;
+        require = traceRequires(fileResolver, result.root, name);
+    }
+    std::vector<std::string> requiredModuleNames;
+    requiredModuleNames.reserve(require.requireList.size());
+    for (const auto& [moduleName, _] : require.requireList)
+    {
+        requiredModuleNames.push_back(moduleName);
+    }
+    return requiredModuleNames;
+}
+
 bool Frontend::parseGraph(
     std::vector<ModuleName>& buildQueue,
     const ModuleName& root,
@@ -792,6 +767,13 @@ bool Frontend::parseGraph(
             topseen = Permanent;
 
             buildQueue.push_back(top->name);
+
+            // at this point we know all valid dependencies are processed into SourceNodes
+            for (const ModuleName& dep : top->requireSet)
+            {
+                if (auto it = sourceNodes.find(dep); it != sourceNodes.end())
+                    it->second->dependents.insert(top->name);
+            }
         }
         else
         {
@@ -969,7 +951,7 @@ void Frontend::checkBuildQueueItem(BuildQueueItem& item)
         item.stats.timeCheck += duration;
         item.stats.filesStrict += 1;
 
-        if (DFFlag::LuauRunCustomModuleChecks && item.options.customModuleCheck)
+        if (item.options.customModuleCheck)
             item.options.customModuleCheck(sourceModule, *moduleForAutocomplete);
 
         item.module = moduleForAutocomplete;
@@ -989,7 +971,7 @@ void Frontend::checkBuildQueueItem(BuildQueueItem& item)
     item.stats.filesStrict += mode == Mode::Strict;
     item.stats.filesNonstrict += mode == Mode::Nonstrict;
 
-    if (DFFlag::LuauRunCustomModuleChecks && item.options.customModuleCheck)
+    if (item.options.customModuleCheck)
         item.options.customModuleCheck(sourceModule, *module);
 
     if (FFlag::LuauSolverV2 && mode == Mode::NoCheck)
@@ -1021,6 +1003,8 @@ void Frontend::checkBuildQueueItem(BuildQueueItem& item)
         freeze(module->interfaceTypes);
 
         module->internalTypes.clear();
+        module->defArena.allocator.clear();
+        module->keyArena.allocator.clear();
 
         module->astTypes.clear();
         module->astTypePacks.clear();
@@ -1074,17 +1058,35 @@ void Frontend::recordItemResult(const BuildQueueItem& item)
     if (item.exception)
         std::rethrow_exception(item.exception);
 
+    bool replacedModule = false;
     if (item.options.forAutocomplete)
     {
-        moduleResolverForAutocomplete.setModule(item.name, item.module);
+        replacedModule = moduleResolverForAutocomplete.setModule(item.name, item.module);
         item.sourceNode->dirtyModuleForAutocomplete = false;
     }
     else
     {
-        moduleResolver.setModule(item.name, item.module);
+        replacedModule = moduleResolver.setModule(item.name, item.module);
         item.sourceNode->dirtyModule = false;
     }
 
+    if (replacedModule)
+    {
+        LUAU_TIMETRACE_SCOPE("Frontend::invalidateDependentModules", "Frontend");
+        LUAU_TIMETRACE_ARGUMENT("name", item.name.c_str());
+        traverseDependents(
+            item.name,
+            [forAutocomplete = item.options.forAutocomplete](SourceNode& sourceNode)
+            {
+                bool traverseSubtree = !sourceNode.hasInvalidModuleDependency(forAutocomplete);
+                sourceNode.setInvalidModuleDependency(true, forAutocomplete);
+                return traverseSubtree;
+            }
+        );
+    }
+
+    item.sourceNode->setInvalidModuleDependency(false, item.options.forAutocomplete);
+
     stats.timeCheck += item.stats.timeCheck;
     stats.timeLint += item.stats.timeLint;
 
@@ -1092,6 +1094,72 @@ void Frontend::recordItemResult(const BuildQueueItem& item)
     stats.filesNonstrict += item.stats.filesNonstrict;
 }
 
+void Frontend::performQueueItemTask(std::shared_ptr<BuildQueueWorkState> state, size_t itemPos)
+{
+    BuildQueueItem& item = state->buildQueueItems[itemPos];
+
+    if (DFFlag::LuauRethrowKnownExceptions)
+    {
+        try
+        {
+            checkBuildQueueItem(item);
+        }
+        catch (const Luau::InternalCompilerError&)
+        {
+            item.exception = std::current_exception();
+        }
+    }
+    else
+    {
+        try
+        {
+            checkBuildQueueItem(item);
+        }
+        catch (...)
+        {
+            item.exception = std::current_exception();
+        }
+    }
+
+    {
+        std::unique_lock guard(state->mtx);
+        state->readyQueueItems.push_back(itemPos);
+    }
+
+    state->cv.notify_one();
+}
+
+void Frontend::sendQueueItemTask(std::shared_ptr<BuildQueueWorkState> state, size_t itemPos)
+{
+    BuildQueueItem& item = state->buildQueueItems[itemPos];
+
+    LUAU_ASSERT(!item.processing);
+    item.processing = true;
+
+    state->processing++;
+
+    state->executeTask(
+        [this, state, itemPos]()
+        {
+            performQueueItemTask(state, itemPos);
+        }
+    );
+}
+
+void Frontend::sendQueueCycleItemTask(std::shared_ptr<BuildQueueWorkState> state)
+{
+    for (size_t i = 0; i < state->buildQueueItems.size(); i++)
+    {
+        BuildQueueItem& item = state->buildQueueItems[i];
+
+        if (!item.processing)
+        {
+            sendQueueItemTask(state, i);
+            break;
+        }
+    }
+}
+
 ScopePtr Frontend::getModuleEnvironment(const SourceModule& module, const Config& config, bool forAutocomplete) const
 {
     ScopePtr result;
@@ -1119,6 +1187,12 @@ ScopePtr Frontend::getModuleEnvironment(const SourceModule& module, const Config
     return result;
 }
 
+bool Frontend::allModuleDependenciesValid(const ModuleName& name, bool forAutocomplete) const
+{
+    auto it = sourceNodes.find(name);
+    return it != sourceNodes.end() && !it->second->hasInvalidModuleDependency(forAutocomplete);
+}
+
 bool Frontend::isDirty(const ModuleName& name, bool forAutocomplete) const
 {
     auto it = sourceNodes.find(name);
@@ -1133,16 +1207,35 @@ bool Frontend::isDirty(const ModuleName& name, bool forAutocomplete) const
  */
 void Frontend::markDirty(const ModuleName& name, std::vector<ModuleName>* markedDirty)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::markDirty", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("name", name.c_str());
+
+    traverseDependents(
+        name,
+        [markedDirty](SourceNode& sourceNode)
+        {
+            if (markedDirty)
+                markedDirty->push_back(sourceNode.name);
+
+            if (sourceNode.dirtySourceModule && sourceNode.dirtyModule && sourceNode.dirtyModuleForAutocomplete)
+                return false;
+
+            sourceNode.dirtySourceModule = true;
+            sourceNode.dirtyModule = true;
+            sourceNode.dirtyModuleForAutocomplete = true;
+
+            return true;
+        }
+    );
+}
+
+void Frontend::traverseDependents(const ModuleName& name, std::function<bool(SourceNode&)> processSubtree)
+{
+    LUAU_TIMETRACE_SCOPE("Frontend::traverseDependents", "Frontend");
+
     if (sourceNodes.count(name) == 0)
         return;
 
-    std::unordered_map<ModuleName, std::vector<ModuleName>> reverseDeps;
-    for (const auto& module : sourceNodes)
-    {
-        for (const auto& dep : module.second->requireSet)
-            reverseDeps[dep].push_back(module.first);
-    }
-
     std::vector<ModuleName> queue{name};
 
     while (!queue.empty())
@@ -1153,22 +1246,10 @@ void Frontend::markDirty(const ModuleName& name, std::vector<ModuleName>* marked
         LUAU_ASSERT(sourceNodes.count(next) > 0);
         SourceNode& sourceNode = *sourceNodes[next];
 
-        if (markedDirty)
+        if (!processSubtree(sourceNode))
-            markedDirty->push_back(next);
-
-        if (sourceNode.dirtySourceModule && sourceNode.dirtyModule && sourceNode.dirtyModuleForAutocomplete)
             continue;
 
-        sourceNode.dirtySourceModule = true;
+        const Set<ModuleName>& dependents = sourceNode.dependents;
-        sourceNode.dirtyModule = true;
-        sourceNode.dirtyModuleForAutocomplete = true;
-
-        if (0 == reverseDeps.count(next))
-            continue;
-
-        sourceModules.erase(next);
-
-        const std::vector<ModuleName>& dependents = reverseDeps[next];
         queue.insert(queue.end(), dependents.begin(), dependents.end());
     }
 }
@@ -1196,6 +1277,7 @@ ModulePtr check(
     NotNull<ModuleResolver> moduleResolver,
     NotNull<FileResolver> fileResolver,
     const ScopePtr& parentScope,
+    const ScopePtr& typeFunctionScope,
     std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope,
     FrontendOptions options,
     TypeCheckLimits limits,
@@ -1212,6 +1294,7 @@ ModulePtr check(
         moduleResolver,
         fileResolver,
         parentScope,
+        typeFunctionScope,
         std::move(prepareModuleScope),
         options,
         limits,
@@ -1222,7 +1305,7 @@ ModulePtr check(
 
 struct InternalTypeFinder : TypeOnceVisitor
 {
-    bool visit(TypeId, const ClassType&) override
+    bool visit(TypeId, const ExternType&) override
     {
         return false;
     }
@@ -1273,6 +1356,7 @@ ModulePtr check(
     NotNull<ModuleResolver> moduleResolver,
     NotNull<FileResolver> fileResolver,
     const ScopePtr& parentScope,
+    const ScopePtr& typeFunctionScope,
     std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope,
     FrontendOptions options,
     TypeCheckLimits limits,
@@ -1285,11 +1369,15 @@ ModulePtr check(
     LUAU_TIMETRACE_ARGUMENT("name", sourceModule.humanReadableName.c_str());
 
     ModulePtr result = std::make_shared<Module>();
+    result->checkedInNewSolver = true;
     result->name = sourceModule.name;
     result->humanReadableName = sourceModule.humanReadableName;
     result->mode = mode;
     result->internalTypes.owningModule = result.get();
     result->interfaceTypes.owningModule = result.get();
+    result->allocator = sourceModule.allocator;
+    result->names = sourceModule.names;
+    result->root = sourceModule.root;
 
     iceHandler->moduleName = sourceModule.name;
 
@@ -1304,19 +1392,7 @@ ModulePtr check(
         }
     }
 
-    DataFlowGraph oldDfg = DataFlowGraphBuilder::build(sourceModule.root, iceHandler);
+    DataFlowGraph dfg = DataFlowGraphBuilder::build(sourceModule.root, NotNull{&result->defArena}, NotNull{&result->keyArena}, iceHandler);
-    DataFlowGraph* dfgForConstraintGeneration = nullptr;
-    if (FFlag::LuauStoreDFGOnModule2)
-    {
-        auto [dfg, scopes] = DataFlowGraphBuilder::buildShared(sourceModule.root, iceHandler);
-        result->dataFlowGraph = std::move(dfg);
-        result->dfgScopes = std::move(scopes);
-        dfgForConstraintGeneration = result->dataFlowGraph.get();
-    }
-    else
-    {
-        dfgForConstraintGeneration = &oldDfg;
-    }
 
     UnifierSharedState unifierState{iceHandler};
     unifierState.counters.recursionLimit = FInt::LuauTypeInferRecursionLimit;
@@ -1326,8 +1402,7 @@ ModulePtr check(
     SimplifierPtr simplifier = newSimplifier(NotNull{&result->internalTypes}, builtinTypes);
     TypeFunctionRuntime typeFunctionRuntime{iceHandler, NotNull{&limits}};
 
-    if (FFlag::LuauUserDefinedTypeFunctionNoEvaluation)
+    typeFunctionRuntime.allowEvaluation = FFlag::LuauTypeFunResultInAutocomplete || sourceModule.parseErrors.empty();
-        typeFunctionRuntime.allowEvaluation = sourceModule.parseErrors.empty();
 
     ConstraintGenerator cg{
         result,
@@ -1338,35 +1413,66 @@ ModulePtr check(
         builtinTypes,
         iceHandler,
         parentScope,
+        typeFunctionScope,
         std::move(prepareModuleScope),
         logger.get(),
-        NotNull{dfgForConstraintGeneration},
+        NotNull{&dfg},
         requireCycles
     };
 
-    cg.visitModuleRoot(sourceModule.root);
+    // FIXME: Delete this flag when clipping FFlag::DebugLuauGreedyGeneralization.
-    result->errors = std::move(cg.errors);
+    //
+    // This optional<> only exists so that we can run one constructor when the flag
+    // is set, and another when it is unset.
+    std::optional<ConstraintSolver> cs;
 
-    ConstraintSolver cs{
+    if (FFlag::DebugLuauGreedyGeneralization)
-        NotNull{&normalizer},
+    {
-        NotNull{simplifier.get()},
+        ConstraintSet constraintSet = cg.run(sourceModule.root);
-        NotNull{&typeFunctionRuntime},
+        result->errors = std::move(constraintSet.errors);
-        NotNull(cg.rootScope),
+
-        borrowConstraints(cg.constraints),
+        cs.emplace(
-        result->name,
+            NotNull{&normalizer},
-        moduleResolver,
+            NotNull{simplifier.get()},
-        requireCycles,
+            NotNull{&typeFunctionRuntime},
-        logger.get(),
+            result->name,
-        NotNull{dfgForConstraintGeneration},
+            moduleResolver,
-        limits
+            requireCycles,
-    };
+            logger.get(),
+            NotNull{&dfg},
+            limits,
+            std::move(constraintSet)
+        );
+    }
+    else
+    {
+        cg.visitModuleRoot(sourceModule.root);
+        result->errors = std::move(cg.errors);
+
+        cs.emplace(
+            NotNull{&normalizer},
+            NotNull{simplifier.get()},
+            NotNull{&typeFunctionRuntime},
+            NotNull(cg.rootScope),
+            borrowConstraints(cg.constraints),
+            NotNull{&cg.scopeToFunction},
+            result->name,
+            moduleResolver,
+            requireCycles,
+            logger.get(),
+            NotNull{&dfg},
+            limits
+        );
+    }
+
+    LUAU_ASSERT(bool(cs));
 
     if (options.randomizeConstraintResolutionSeed)
-        cs.randomize(*options.randomizeConstraintResolutionSeed);
+        cs->randomize(*options.randomizeConstraintResolutionSeed);
 
     try
     {
-        cs.run();
+        cs->run();
     }
     catch (const TimeLimitError&)
     {
@@ -1386,12 +1492,12 @@ ModulePtr check(
             printf("%s\n", output.c_str());
     }
 
-    for (TypeError& e : cs.errors)
+    for (TypeError& e : cs->errors)
         result->errors.emplace_back(std::move(e));
 
     result->scopes = std::move(cg.scopes);
     result->type = sourceModule.type;
-    result->upperBoundContributors = std::move(cs.upperBoundContributors);
+    result->upperBoundContributors = std::move(cs->upperBoundContributors);
 
     if (result->timeout || result->cancelled)
     {
@@ -1411,38 +1517,30 @@ ModulePtr check(
         switch (mode)
         {
         case Mode::Nonstrict:
-            if (FFlag::LuauStoreDFGOnModule2)
+            Luau::checkNonStrict(
-            {
+                builtinTypes,
-                Luau::checkNonStrict(
+                NotNull{simplifier.get()},
-                    builtinTypes,
+                NotNull{&typeFunctionRuntime},
-                    NotNull{&typeFunctionRuntime},
+                iceHandler,
-                    iceHandler,
+                NotNull{&unifierState},
-                    NotNull{&unifierState},
+                NotNull{&dfg},
-                    NotNull{dfgForConstraintGeneration},
+                NotNull{&limits},
-                    NotNull{&limits},
+                sourceModule,
-                    sourceModule,
+                result.get()
-                    result.get()
+            );
-                );
-            }
-            else
-            {
-                Luau::checkNonStrict(
-                    builtinTypes,
-                    NotNull{&typeFunctionRuntime},
-                    iceHandler,
-                    NotNull{&unifierState},
-                    NotNull{&oldDfg},
-                    NotNull{&limits},
-                    sourceModule,
-                    result.get()
-                );
-            }
             break;
         case Mode::Definition:
             // fallthrough intentional
         case Mode::Strict:
             Luau::check(
-                builtinTypes, NotNull{&typeFunctionRuntime}, NotNull{&unifierState}, NotNull{&limits}, logger.get(), sourceModule, result.get()
+                builtinTypes,
+                NotNull{simplifier.get()},
+                NotNull{&typeFunctionRuntime},
+                NotNull{&unifierState},
+                NotNull{&limits},
+                logger.get(),
+                sourceModule,
+                result.get()
             );
             break;
         case Mode::NoCheck:
@@ -1527,6 +1625,7 @@ ModulePtr Frontend::check(
                 NotNull{forAutocomplete ? &moduleResolverForAutocomplete : &moduleResolver},
                 NotNull{fileResolver},
                 environmentScope ? *environmentScope : globals.globalScope,
+                globals.globalTypeFunctionScope,
                 prepareModuleScopeWrap,
                 options,
                 typeCheckLimits,
@@ -1624,6 +1723,14 @@ std::pair<SourceNode*, SourceModule*> Frontend::getSourceNode(const ModuleName&
 
     sourceNode->name = sourceModule->name;
     sourceNode->humanReadableName = sourceModule->humanReadableName;
+
+    // clear all prior dependents. we will re-add them after parsing the rest of the graph
+    for (const auto& [moduleName, _] : sourceNode->requireLocations)
+    {
+        if (auto depIt = sourceNodes.find(moduleName); depIt != sourceNodes.end())
+            depIt->second->dependents.erase(sourceNode->name);
+    }
+
     sourceNode->requireSet.clear();
     sourceNode->requireLocations.clear();
     sourceNode->dirtySourceModule = false;
@@ -1745,11 +1852,13 @@ std::string FrontendModuleResolver::getHumanReadableModuleName(const ModuleName&
     return frontend->fileResolver->getHumanReadableModuleName(moduleName);
 }
 
-void FrontendModuleResolver::setModule(const ModuleName& moduleName, ModulePtr module)
+bool FrontendModuleResolver::setModule(const ModuleName& moduleName, ModulePtr module)
 {
     std::scoped_lock lock(moduleMutex);
 
+    bool replaced = modules.count(moduleName) > 0;
     modules[moduleName] = std::move(module);
+    return replaced;
 }
 
 void FrontendModuleResolver::clearModules()

Analysis/src/GlobalTypes.cpp

@@ -9,6 +9,7 @@ GlobalTypes::GlobalTypes(NotNull<BuiltinTypes> builtinTypes)
     : builtinTypes(builtinTypes)
 {
     globalScope = std::make_shared<Scope>(globalTypes.addTypePack(TypePackVar{FreeTypePack{TypeLevel{}}}));
+    globalTypeFunctionScope = std::make_shared<Scope>(globalTypes.addTypePack(TypePackVar{FreeTypePack{TypeLevel{}}}));
 
     globalScope->addBuiltinTypeBinding("any", TypeFun{{}, builtinTypes->anyType});
     globalScope->addBuiltinTypeBinding("nil", TypeFun{{}, builtinTypes->nilType});

Analysis/src/InferPolarity.cpp

@@ -0,0 +1,169 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#include "Luau/DenseHash.h"
+#include "Luau/Polarity.h"
+#include "Luau/Scope.h"
+#include "Luau/VisitType.h"
+
+LUAU_FASTFLAG(LuauNonReentrantGeneralization2)
+
+namespace Luau
+{
+
+struct InferPolarity : TypeVisitor
+{
+    NotNull<TypeArena> arena;
+    NotNull<Scope> scope;
+
+    DenseHashMap<TypeId, Polarity> types{nullptr};
+    DenseHashMap<TypePackId, Polarity> packs{nullptr};
+
+    Polarity polarity = Polarity::Positive;
+
+    explicit InferPolarity(NotNull<TypeArena> arena, NotNull<Scope> scope)
+        : arena(arena)
+        , scope(scope)
+    {
+    }
+
+    void flip()
+    {
+        polarity = invert(polarity);
+    }
+
+    bool visit(TypeId ty, const GenericType& gt) override
+    {
+        if (ty->owningArena != arena)
+            return false;
+
+        if (subsumes(scope, gt.scope))
+            types[ty] |= polarity;
+
+        return false;
+    }
+
+    bool visit(TypeId ty, const TableType& tt) override
+    {
+        if (ty->owningArena != arena)
+            return false;
+
+        const Polarity p = polarity;
+        for (const auto& [name, prop] : tt.props)
+        {
+            if (prop.isShared())
+            {
+                polarity = Polarity::Mixed;
+                traverse(prop.type());
+            }
+            else if (prop.isReadOnly())
+            {
+                polarity = p;
+                traverse(*prop.readTy);
+            }
+            else if (prop.isWriteOnly())
+            {
+                polarity = invert(p);
+                traverse(*prop.writeTy);
+            }
+            else
+                LUAU_ASSERT(!"Unreachable");
+        }
+
+        if (tt.indexer)
+        {
+            polarity = Polarity::Mixed;
+            traverse(tt.indexer->indexType);
+            traverse(tt.indexer->indexResultType);
+        }
+
+        polarity = p;
+
+        return false;
+    }
+
+    bool visit(TypeId ty, const FunctionType& ft) override
+    {
+        if (ty->owningArena != arena)
+            return false;
+
+        const Polarity p = polarity;
+
+        polarity = Polarity::Positive;
+
+        // If these types actually occur within the function signature, their
+        // polarity will be overwritten. If not, we infer that they are phantom
+        // types.
+        for (TypeId generic : ft.generics)
+        {
+            generic = follow(generic);
+            const auto gen = get<GenericType>(generic);
+            if (gen && subsumes(scope, gen->scope))
+                types[generic] = Polarity::None;
+        }
+        for (TypePackId genericPack : ft.genericPacks)
+        {
+            genericPack = follow(genericPack);
+            const auto gen = get<GenericTypePack>(genericPack);
+            if (gen && subsumes(scope, gen->scope))
+                packs[genericPack] = Polarity::None;
+        }
+
+        flip();
+        traverse(ft.argTypes);
+        flip();
+        traverse(ft.retTypes);
+
+        polarity = p;
+
+        return false;
+    }
+
+    bool visit(TypeId, const ExternType&) override
+    {
+        return false;
+    }
+
+    bool visit(TypePackId tp, const GenericTypePack& gtp) override
+    {
+        packs[tp] |= polarity;
+        return false;
+    }
+};
+
+template<typename TID>
+static void inferGenericPolarities_(NotNull<TypeArena> arena, NotNull<Scope> scope, TID ty)
+{
+    if (!FFlag::LuauNonReentrantGeneralization2)
+        return;
+
+    InferPolarity infer{arena, scope};
+    infer.traverse(ty);
+
+    for (const auto& [ty, polarity] : infer.types)
+    {
+        auto gt = getMutable<GenericType>(ty);
+        LUAU_ASSERT(gt);
+        gt->polarity = polarity;
+    }
+
+    for (const auto& [tp, polarity] : infer.packs)
+    {
+        if (tp->owningArena != arena)
+            continue;
+        auto gp = getMutable<GenericTypePack>(tp);
+        LUAU_ASSERT(gp);
+        gp->polarity = polarity;
+    }
+}
+
+void inferGenericPolarities(NotNull<TypeArena> arena, NotNull<Scope> scope, TypeId ty)
+{
+    inferGenericPolarities_(arena, scope, ty);
+}
+
+void inferGenericPolarities(NotNull<TypeArena> arena, NotNull<Scope> scope, TypePackId tp)
+{
+    inferGenericPolarities_(arena, scope, tp);
+}
+
+} // namespace Luau

Analysis/src/Instantiation.cpp

@@ -49,7 +49,7 @@ bool Instantiation::ignoreChildren(TypeId ty)
 {
     if (log->getMutable<FunctionType>(ty))
         return true;
-    else if (get<ClassType>(ty))
+    else if (get<ExternType>(ty))
         return true;
     else
         return false;
@@ -60,10 +60,8 @@ TypeId Instantiation::clean(TypeId ty)
     const FunctionType* ftv = log->getMutable<FunctionType>(ty);
     LUAU_ASSERT(ftv);
 
-    FunctionType clone = FunctionType{level, scope, ftv->argTypes, ftv->retTypes, ftv->definition, ftv->hasSelf};
+    FunctionType clone = FunctionType{level, ftv->argTypes, ftv->retTypes, ftv->definition, ftv->hasSelf};
-    clone.magicFunction = ftv->magicFunction;
+    clone.magic = ftv->magic;
-    clone.dcrMagicFunction = ftv->dcrMagicFunction;
-    clone.dcrMagicRefinement = ftv->dcrMagicRefinement;
     clone.tags = ftv->tags;
     clone.argNames = ftv->argNames;
     TypeId result = addType(std::move(clone));
@@ -121,7 +119,7 @@ bool ReplaceGenerics::ignoreChildren(TypeId ty)
         // whenever we quantify, so the vectors overlap if and only if they are equal.
         return (!generics.empty() || !genericPacks.empty()) && (ftv->generics == generics) && (ftv->genericPacks == genericPacks);
     }
-    else if (get<ClassType>(ty))
+    else if (get<ExternType>(ty))
         return true;
     else
     {
@@ -165,7 +163,7 @@ TypeId ReplaceGenerics::clean(TypeId ty)
     }
     else
     {
-        return addType(FreeType{scope, level});
+        return arena->freshType(builtinTypes, scope, level);
     }
 }
 

Analysis/src/Instantiation2.cpp

@@ -6,7 +6,7 @@ namespace Luau
 
 bool Instantiation2::ignoreChildren(TypeId ty)
 {
-    if (get<ClassType>(ty))
+    if (get<ExternType>(ty))
         return true;
 
     if (auto ftv = get<FunctionType>(ty))

Analysis/src/IostreamHelpers.cpp

@@ -193,8 +193,8 @@ static void errorToString(std::ostream& stream, const T& err)
         stream << "NormalizationTooComplex { }";
     else if constexpr (std::is_same_v<T, TypePackMismatch>)
         stream << "TypePackMismatch { wanted = '" + toString(err.wantedTp) + "', given = '" + toString(err.givenTp) + "' }";
-    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnClassesUnsafe>)
+    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnExternTypesUnsafe>)
-        stream << "DynamicPropertyLookupOnClassesUnsafe { " << toString(err.ty) << " }";
+        stream << "DynamicPropertyLookupOnExternTypesUnsafe { " << toString(err.ty) << " }";
     else if constexpr (std::is_same_v<T, UninhabitedTypeFunction>)
         stream << "UninhabitedTypeFunction { " << toString(err.ty) << " }";
     else if constexpr (std::is_same_v<T, ExplicitFunctionAnnotationRecommended>)
@@ -229,6 +229,8 @@ static void errorToString(std::ostream& stream, const T& err)
         stream << "UnexpectedTypePackInSubtyping {  tp = '" + toString(err.tp) + "' }";
     else if constexpr (std::is_same_v<T, UserDefinedTypeFunctionError>)
         stream << "UserDefinedTypeFunctionError { " << err.message << " }";
+    else if constexpr (std::is_same_v<T, ReservedIdentifier>)
+        stream << "ReservedIdentifier { " << err.name << " }";
     else if constexpr (std::is_same_v<T, CannotAssignToNever>)
     {
         stream << "CannotAssignToNever { rvalueType = '" << toString(err.rhsType) << "', reason = '" << err.reason << "', cause = { ";

Analysis/src/Linter.cpp

@@ -17,9 +17,11 @@ LUAU_FASTINTVARIABLE(LuauSuggestionDistance, 4)
 LUAU_FASTFLAG(LuauSolverV2)
 
 LUAU_FASTFLAG(LuauAttribute)
-LUAU_FASTFLAG(LuauNativeAttribute)
 LUAU_FASTFLAGVARIABLE(LintRedundantNativeAttribute)
 
+LUAU_FASTFLAG(LuauDeprecatedAttribute)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+
 namespace Luau
 {
 
@@ -907,6 +909,11 @@ private:
         return true;
     }
 
+    bool visit(AstTypePack* node) override
+    {
+        return FFlag::LuauStoreReturnTypesAsPackOnAst;
+    }
+
     bool visit(AstTypeReference* node) override
     {
         if (!node->prefix)
@@ -1969,6 +1976,11 @@ private:
         return true;
     }
 
+    bool visit(AstTypePack* node) override
+    {
+        return FFlag::LuauStoreReturnTypesAsPackOnAst;
+    }
+
     bool visit(AstTypeTable* node) override
     {
         if (FFlag::LuauSolverV2)
@@ -2281,6 +2293,57 @@ private:
     {
     }
 
+    bool visit(AstExprLocal* node) override
+    {
+        if (FFlag::LuauDeprecatedAttribute)
+        {
+
+            const FunctionType* fty = getFunctionType(node);
+            bool shouldReport = fty && fty->isDeprecatedFunction && !inScope(fty);
+
+            if (shouldReport)
+                report(node->location, node->local->name.value);
+        }
+
+        return true;
+    }
+
+    bool visit(AstExprGlobal* node) override
+    {
+        if (FFlag::LuauDeprecatedAttribute)
+        {
+            const FunctionType* fty = getFunctionType(node);
+            bool shouldReport = fty && fty->isDeprecatedFunction && !inScope(fty);
+
+            if (shouldReport)
+                report(node->location, node->name.value);
+        }
+
+        return true;
+    }
+
+    bool visit(AstStatLocalFunction* node) override
+    {
+        if (FFlag::LuauDeprecatedAttribute)
+        {
+            check(node->func);
+            return false;
+        }
+        else
+            return true;
+    }
+
+    bool visit(AstStatFunction* node) override
+    {
+        if (FFlag::LuauDeprecatedAttribute)
+        {
+            check(node->func);
+            return false;
+        }
+        else
+            return true;
+    }
+
     bool visit(AstExprIndexName* node) override
     {
         if (std::optional<TypeId> ty = context->getType(node->expr))
@@ -2320,24 +2383,65 @@ private:
 
     void check(AstExprIndexName* node, TypeId ty)
     {
-        if (const ClassType* cty = get<ClassType>(ty))
+        if (const ExternType* cty = get<ExternType>(ty))
         {
-            const Property* prop = lookupClassProp(cty, node->index.value);
+            const Property* prop = lookupExternTypeProp(cty, node->index.value);
 
             if (prop && prop->deprecated)
                 report(node->location, *prop, cty->name.c_str(), node->index.value);
+            else if (FFlag::LuauDeprecatedAttribute && prop)
+            {
+                if (std::optional<TypeId> ty = prop->readTy)
+                {
+                    const FunctionType* fty = get<FunctionType>(follow(ty));
+                    bool shouldReport = fty && fty->isDeprecatedFunction && !inScope(fty);
+
+                    if (shouldReport)
+                    {
+                        const char* className = nullptr;
+                        if (AstExprGlobal* global = node->expr->as<AstExprGlobal>())
+                            className = global->name.value;
+
+                        const char* functionName = node->index.value;
+
+                        report(node->location, className, functionName);
+                    }
+                }
+            }
         }
         else if (const TableType* tty = get<TableType>(ty))
         {
             auto prop = tty->props.find(node->index.value);
 
-            if (prop != tty->props.end() && prop->second.deprecated)
+            if (prop != tty->props.end())
             {
-                // strip synthetic typeof() for builtin tables
+                if (prop->second.deprecated)
-                if (tty->name && tty->name->compare(0, 7, "typeof(") == 0 && tty->name->back() == ')')
+                {
-                    report(node->location, prop->second, tty->name->substr(7, tty->name->length() - 8).c_str(), node->index.value);
+                    // strip synthetic typeof() for builtin tables
-                else
+                    if (tty->name && tty->name->compare(0, 7, "typeof(") == 0 && tty->name->back() == ')')
-                    report(node->location, prop->second, tty->name ? tty->name->c_str() : nullptr, node->index.value);
+                        report(node->location, prop->second, tty->name->substr(7, tty->name->length() - 8).c_str(), node->index.value);
+                    else
+                        report(node->location, prop->second, tty->name ? tty->name->c_str() : nullptr, node->index.value);
+                }
+                else if (FFlag::LuauDeprecatedAttribute)
+                {
+                    if (std::optional<TypeId> ty = prop->second.readTy)
+                    {
+                        const FunctionType* fty = get<FunctionType>(follow(ty));
+                        bool shouldReport = fty && fty->isDeprecatedFunction && !inScope(fty);
+
+                        if (shouldReport)
+                        {
+                            const char* className = nullptr;
+                            if (AstExprGlobal* global = node->expr->as<AstExprGlobal>())
+                                className = global->name.value;
+
+                            const char* functionName = node->index.value;
+
+                            report(node->location, className, functionName);
+                        }
+                    }
+                }
             }
         }
     }
@@ -2356,6 +2460,26 @@ private:
         }
     }
 
+    void check(AstExprFunction* func)
+    {
+        LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+        LUAU_ASSERT(func);
+
+        const FunctionType* fty = getFunctionType(func);
+        bool isDeprecated = fty && fty->isDeprecatedFunction;
+
+        // If a function is deprecated, we don't want to flag its recursive uses.
+        // So we push it on a stack while its body is being analyzed.
+        // When a deprecated function is used, we check the stack to ensure that we are not inside that function.
+        if (isDeprecated)
+            pushScope(fty);
+
+        func->visit(this);
+
+        if (isDeprecated)
+            popScope(fty);
+    }
+
     void report(const Location& location, const Property& prop, const char* container, const char* field)
     {
         std::string suggestion = prop.deprecatedSuggestion.empty() ? "" : format(", use '%s' instead", prop.deprecatedSuggestion.c_str());
@@ -2365,6 +2489,63 @@ private:
         else
             emitWarning(*context, LintWarning::Code_DeprecatedApi, location, "Member '%s' is deprecated%s", field, suggestion.c_str());
     }
+
+    void report(const Location& location, const char* tableName, const char* functionName)
+    {
+        LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+
+        if (tableName)
+            emitWarning(*context, LintWarning::Code_DeprecatedApi, location, "Member '%s.%s' is deprecated", tableName, functionName);
+        else
+            emitWarning(*context, LintWarning::Code_DeprecatedApi, location, "Member '%s' is deprecated", functionName);
+    }
+
+    void report(const Location& location, const char* functionName)
+    {
+        LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+
+        emitWarning(*context, LintWarning::Code_DeprecatedApi, location, "Function '%s' is deprecated", functionName);
+    }
+
+    std::vector<const FunctionType*> functionTypeScopeStack;
+
+    void pushScope(const FunctionType* fty)
+    {
+        LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+        LUAU_ASSERT(fty);
+
+        functionTypeScopeStack.push_back(fty);
+    }
+
+    void popScope(const FunctionType* fty)
+    {
+        LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+        LUAU_ASSERT(fty);
+
+        LUAU_ASSERT(fty == functionTypeScopeStack.back());
+        functionTypeScopeStack.pop_back();
+    }
+
+    bool inScope(const FunctionType* fty) const
+    {
+        LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+        LUAU_ASSERT(fty);
+
+        return std::find(functionTypeScopeStack.begin(), functionTypeScopeStack.end(), fty) != functionTypeScopeStack.end();
+    }
+
+    const FunctionType* getFunctionType(AstExpr* node)
+    {
+        LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+
+        std::optional<TypeId> ty = context->getType(node);
+        if (!ty)
+            return nullptr;
+
+        const FunctionType* fty = get<FunctionType>(follow(ty));
+
+        return fty;
+    }
 };
 
 class LintTableOperations : AstVisitor
@@ -3239,7 +3420,6 @@ static void lintComments(LintContext& context, const std::vector<HotComment>& ho
 
 static bool hasNativeCommentDirective(const std::vector<HotComment>& hotcomments)
 {
-    LUAU_ASSERT(FFlag::LuauNativeAttribute);
     LUAU_ASSERT(FFlag::LintRedundantNativeAttribute);
 
     for (const HotComment& hc : hotcomments)
@@ -3265,7 +3445,6 @@ struct LintRedundantNativeAttribute : AstVisitor
 public:
     LUAU_NOINLINE static void process(LintContext& context)
     {
-        LUAU_ASSERT(FFlag::LuauNativeAttribute);
         LUAU_ASSERT(FFlag::LintRedundantNativeAttribute);
 
         LintRedundantNativeAttribute pass;
@@ -3389,7 +3568,7 @@ std::vector<LintWarning> lint(
     if (context.warningEnabled(LintWarning::Code_ComparisonPrecedence))
         LintComparisonPrecedence::process(context);
 
-    if (FFlag::LuauNativeAttribute && FFlag::LintRedundantNativeAttribute && context.warningEnabled(LintWarning::Code_RedundantNativeAttribute))
+    if (FFlag::LintRedundantNativeAttribute && context.warningEnabled(LintWarning::Code_RedundantNativeAttribute))
     {
         if (hasNativeCommentDirective(hotcomments))
             LintRedundantNativeAttribute::process(context);

Analysis/src/Module.cpp

@@ -15,11 +15,29 @@
 #include <algorithm>
 
 LUAU_FASTFLAG(LuauSolverV2);
-LUAU_DYNAMIC_FASTINT(LuauTypeSolverRelease)
+LUAU_FASTFLAG(LuauRetainDefinitionAliasLocations)
 
 namespace Luau
 {
 
+static void defaultLogLuau(std::string_view context, std::string_view input)
+{
+    // The default is to do nothing because we don't want to mess with
+    // the xml parsing done by the dcr script.
+}
+
+Luau::LogLuauProc logLuau = &defaultLogLuau;
+
+void setLogLuau(LogLuauProc ll)
+{
+    logLuau = ll;
+}
+
+void resetLogLuauProc()
+{
+    logLuau = &defaultLogLuau;
+}
+
 static bool contains(Position pos, Comment comment)
 {
     if (comment.location.contains(pos))
@@ -27,13 +45,15 @@ static bool contains(Position pos, Comment comment)
     else if (comment.type == Lexeme::BrokenComment && comment.location.begin <= pos) // Broken comments are broken specifically because they don't
                                                                                      // have an end
         return true;
-    else if (comment.type == Lexeme::Comment && comment.location.end == pos)
+    // comments actually span the whole line - in incremental mode, we could pass a cursor outside of the current parsed comment range span, but it
+    // would still be 'within' the comment So, the cursor must be on the same line and the comment itself must come strictly after the `begin`
+    else if (comment.type == Lexeme::Comment && comment.location.end.line == pos.line && comment.location.begin <= pos)
         return true;
     else
         return false;
 }
 
-static bool isWithinComment(const std::vector<Comment>& commentLocations, Position pos)
+bool isWithinComment(const std::vector<Comment>& commentLocations, Position pos)
 {
     auto iter = std::lower_bound(
         commentLocations.begin(),
@@ -41,6 +61,8 @@ static bool isWithinComment(const std::vector<Comment>& commentLocations, Positi
         Comment{Lexeme::Comment, Location{pos, pos}},
         [](const Comment& a, const Comment& b)
         {
+            if (a.type == Lexeme::Comment)
+                return a.location.end.line < b.location.end.line;
             return a.location.end < b.location.end;
         }
     );
@@ -132,34 +154,25 @@ struct ClonePublicInterface : Substitution
             }
 
             ftv->level = TypeLevel{0, 0};
-            if (FFlag::LuauSolverV2 && DFInt::LuauTypeSolverRelease >= 645)
-                ftv->scope = nullptr;
         }
         else if (TableType* ttv = getMutable<TableType>(result))
         {
             ttv->level = TypeLevel{0, 0};
-            if (FFlag::LuauSolverV2 && DFInt::LuauTypeSolverRelease >= 645)
+            if (FFlag::LuauSolverV2)
                 ttv->scope = nullptr;
         }
 
-        if (FFlag::LuauSolverV2 && DFInt::LuauTypeSolverRelease >= 645)
+        if (FFlag::LuauSolverV2)
         {
             if (auto freety = getMutable<FreeType>(result))
             {
-                if (DFInt::LuauTypeSolverRelease >= 646)
+                module->errors.emplace_back(
-                {
+                    freety->scope->location,
-                    module->errors.emplace_back(
+                    module->name,
-                        freety->scope->location,
+                    InternalError{"Free type is escaping its module; please report this bug at "
-                        module->name,
+                                  "https://github.com/luau-lang/luau/issues"}
-                        InternalError{"Free type is escaping its module; please report this bug at "
+                );
-                                      "https://github.com/luau-lang/luau/issues"}
+                result = builtinTypes->errorRecoveryType();
-                    );
-                    result = builtinTypes->errorRecoveryType();
-                }
-                else
-                {
-                    freety->scope = nullptr;
-                }
             }
             else if (auto genericty = getMutable<GenericType>(result))
             {
@@ -172,26 +185,18 @@ struct ClonePublicInterface : Substitution
 
     TypePackId clean(TypePackId tp) override
     {
-        if (FFlag::LuauSolverV2 && DFInt::LuauTypeSolverRelease >= 645)
+        if (FFlag::LuauSolverV2)
         {
             auto clonedTp = clone(tp);
             if (auto ftp = getMutable<FreeTypePack>(clonedTp))
             {
-
+                module->errors.emplace_back(
-                if (DFInt::LuauTypeSolverRelease >= 646)
+                    ftp->scope->location,
-                {
+                    module->name,
-                    module->errors.emplace_back(
+                    InternalError{"Free type pack is escaping its module; please report this bug at "
-                        ftp->scope->location,
+                                  "https://github.com/luau-lang/luau/issues"}
-                        module->name,
+                );
-                        InternalError{"Free type pack is escaping its module; please report this bug at "
+                clonedTp = builtinTypes->errorRecoveryTypePack();
-                                      "https://github.com/luau-lang/luau/issues"}
-                    );
-                    clonedTp = builtinTypes->errorRecoveryTypePack();
-                }
-                else
-                {
-                    ftp->scope = nullptr;
-                }
             }
             else if (auto gtp = getMutable<GenericTypePack>(clonedTp))
                 gtp->scope = nullptr;
@@ -260,7 +265,10 @@ struct ClonePublicInterface : Substitution
 
         TypeId type = cloneType(tf.type);
 
-        return TypeFun{typeParams, typePackParams, type};
+        if (FFlag::LuauRetainDefinitionAliasLocations)
+            return TypeFun{typeParams, typePackParams, type, tf.definitionLocation};
+        else
+            return TypeFun{typeParams, typePackParams, type};
     }
 };
 

Analysis/src/Normalize.cpp

@@ -17,12 +17,12 @@
 
 LUAU_FASTFLAGVARIABLE(DebugLuauCheckNormalizeInvariant)
 
-LUAU_FASTINTVARIABLE(LuauNormalizeCacheLimit, 100000);
+LUAU_FASTINTVARIABLE(LuauNormalizeCacheLimit, 100000)
-LUAU_FASTFLAG(LuauSolverV2);
-
 LUAU_FASTINTVARIABLE(LuauNormalizeIntersectionLimit, 200)
-LUAU_FASTFLAGVARIABLE(LuauNormalizationTracksCyclicPairsThroughInhabitance);
+LUAU_FASTINTVARIABLE(LuauNormalizeUnionLimit, 100)
-LUAU_FASTFLAGVARIABLE(LuauIntersectNormalsNeedsToTrackResourceLimits);
+LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAGVARIABLE(LuauFixInfiniteRecursionInNormalization)
+LUAU_FASTFLAGVARIABLE(LuauNormalizationCatchMetatableCycles)
 
 namespace Luau
 {
@@ -249,23 +249,23 @@ bool isSubtype(const NormalizedStringType& subStr, const NormalizedStringType& s
     return true;
 }
 
-void NormalizedClassType::pushPair(TypeId ty, TypeIds negations)
+void NormalizedExternType::pushPair(TypeId ty, TypeIds negations)
 {
-    auto result = classes.insert(std::make_pair(ty, std::move(negations)));
+    auto result = externTypes.insert(std::make_pair(ty, std::move(negations)));
     if (result.second)
         ordering.push_back(ty);
-    LUAU_ASSERT(ordering.size() == classes.size());
+    LUAU_ASSERT(ordering.size() == externTypes.size());
 }
 
-void NormalizedClassType::resetToNever()
+void NormalizedExternType::resetToNever()
 {
     ordering.clear();
-    classes.clear();
+    externTypes.clear();
 }
 
-bool NormalizedClassType::isNever() const
+bool NormalizedExternType::isNever() const
 {
-    return classes.empty();
+    return externTypes.empty();
 }
 
 void NormalizedFunctionType::resetToTop()
@@ -304,17 +304,17 @@ bool NormalizedType::isUnknown() const
 
     // Otherwise, we can still be unknown!
     bool hasAllPrimitives = isPrim(booleans, PrimitiveType::Boolean) && isPrim(nils, PrimitiveType::NilType) && isNumber(numbers) &&
-                            strings.isString() && isPrim(threads, PrimitiveType::Thread) && isThread(threads);
+                            strings.isString() && isThread(threads) && isBuffer(buffers);
 
     // Check is class
-    bool isTopClass = false;
+    bool isTopExternType = false;
-    for (auto [t, disj] : classes.classes)
+    for (const auto& [t, disj] : externTypes.externTypes)
     {
-        if (auto ct = get<ClassType>(t))
+        if (auto ct = get<ExternType>(t))
         {
             if (ct->name == "class" && disj.empty())
             {
-                isTopClass = true;
+                isTopExternType = true;
                 break;
             }
         }
@@ -330,24 +330,24 @@ bool NormalizedType::isUnknown() const
         }
     }
     // any = unknown or error ==> we need to make sure we have all the unknown components, but not errors
-    return get<NeverType>(errors) && hasAllPrimitives && isTopClass && isTopTable && functions.isTop;
+    return get<NeverType>(errors) && hasAllPrimitives && isTopExternType && isTopTable && functions.isTop;
 }
 
 bool NormalizedType::isExactlyNumber() const
 {
-    return hasNumbers() && !hasTops() && !hasBooleans() && !hasClasses() && !hasErrors() && !hasNils() && !hasStrings() && !hasThreads() &&
+    return hasNumbers() && !hasTops() && !hasBooleans() && !hasExternTypes() && !hasErrors() && !hasNils() && !hasStrings() && !hasThreads() &&
            !hasBuffers() && !hasTables() && !hasFunctions() && !hasTyvars();
 }
 
 bool NormalizedType::isSubtypeOfString() const
 {
-    return hasStrings() && !hasTops() && !hasBooleans() && !hasClasses() && !hasErrors() && !hasNils() && !hasNumbers() && !hasThreads() &&
+    return hasStrings() && !hasTops() && !hasBooleans() && !hasExternTypes() && !hasErrors() && !hasNils() && !hasNumbers() && !hasThreads() &&
            !hasBuffers() && !hasTables() && !hasFunctions() && !hasTyvars();
 }
 
 bool NormalizedType::isSubtypeOfBooleans() const
 {
-    return hasBooleans() && !hasTops() && !hasClasses() && !hasErrors() && !hasNils() && !hasNumbers() && !hasStrings() && !hasThreads() &&
+    return hasBooleans() && !hasTops() && !hasExternTypes() && !hasErrors() && !hasNils() && !hasNumbers() && !hasStrings() && !hasThreads() &&
            !hasBuffers() && !hasTables() && !hasFunctions() && !hasTyvars();
 }
 
@@ -380,9 +380,9 @@ bool NormalizedType::hasBooleans() const
     return !get<NeverType>(booleans);
 }
 
-bool NormalizedType::hasClasses() const
+bool NormalizedType::hasExternTypes() const
 {
-    return !classes.isNever();
+    return !externTypes.isNever();
 }
 
 bool NormalizedType::hasErrors() const
@@ -440,7 +440,7 @@ bool NormalizedType::isFalsy() const
             hasAFalse = !bs->value;
     }
 
-    return (hasAFalse || hasNils()) && (!hasTops() && !hasClasses() && !hasErrors() && !hasNumbers() && !hasStrings() && !hasThreads() &&
+    return (hasAFalse || hasNils()) && (!hasTops() && !hasExternTypes() && !hasErrors() && !hasNumbers() && !hasStrings() && !hasThreads() &&
                                         !hasBuffers() && !hasTables() && !hasFunctions() && !hasTyvars());
 }
 
@@ -452,7 +452,7 @@ bool NormalizedType::isTruthy() const
 static bool isShallowInhabited(const NormalizedType& norm)
 {
     // This test is just a shallow check, for example it returns `true` for `{ p : never }`
-    return !get<NeverType>(norm.tops) || !get<NeverType>(norm.booleans) || !norm.classes.isNever() || !get<NeverType>(norm.errors) ||
+    return !get<NeverType>(norm.tops) || !get<NeverType>(norm.booleans) || !norm.externTypes.isNever() || !get<NeverType>(norm.errors) ||
            !get<NeverType>(norm.nils) || !get<NeverType>(norm.numbers) || !norm.strings.isNever() || !get<NeverType>(norm.threads) ||
            !get<NeverType>(norm.buffers) || !norm.functions.isNever() || !norm.tables.empty() || !norm.tyvars.empty();
 }
@@ -471,7 +471,7 @@ NormalizationResult Normalizer::isInhabited(const NormalizedType* norm, Set<Type
         return NormalizationResult::HitLimits;
 
     if (!get<NeverType>(norm->tops) || !get<NeverType>(norm->booleans) || !get<NeverType>(norm->errors) || !get<NeverType>(norm->nils) ||
-        !get<NeverType>(norm->numbers) || !get<NeverType>(norm->threads) || !get<NeverType>(norm->buffers) || !norm->classes.isNever() ||
+        !get<NeverType>(norm->numbers) || !get<NeverType>(norm->threads) || !get<NeverType>(norm->buffers) || !norm->externTypes.isNever() ||
         !norm->strings.isNever() || !norm->functions.isNever())
         return NormalizationResult::True;
 
@@ -579,7 +579,7 @@ NormalizationResult Normalizer::isIntersectionInhabited(TypeId left, TypeId righ
 {
     left = follow(left);
     right = follow(right);
-    // We're asking if intersection is inahbited between left and right but we've already seen them ....
+    // We're asking if intersection is inhabited between left and right but we've already seen them ....
 
     if (cacheInhabitance)
     {
@@ -619,13 +619,13 @@ static int tyvarIndex(TypeId ty)
         return 0;
 }
 
-static bool isTop(NotNull<BuiltinTypes> builtinTypes, const NormalizedClassType& classes)
+static bool isTop(NotNull<BuiltinTypes> builtinTypes, const NormalizedExternType& externTypes)
 {
-    if (classes.classes.size() != 1)
+    if (externTypes.externTypes.size() != 1)
         return false;
 
-    auto first = classes.classes.begin();
+    auto first = externTypes.externTypes.begin();
-    if (first->first != builtinTypes->classType)
+    if (first->first != builtinTypes->externType)
         return false;
 
     if (!first->second.empty())
@@ -634,11 +634,11 @@ static bool isTop(NotNull<BuiltinTypes> builtinTypes, const NormalizedClassType&
     return true;
 }
 
-static void resetToTop(NotNull<BuiltinTypes> builtinTypes, NormalizedClassType& classes)
+static void resetToTop(NotNull<BuiltinTypes> builtinTypes, NormalizedExternType& externTypes)
 {
-    classes.ordering.clear();
+    externTypes.ordering.clear();
-    classes.classes.clear();
+    externTypes.externTypes.clear();
-    classes.pushPair(builtinTypes->classType, TypeIds{});
+    externTypes.pushPair(builtinTypes->externType, TypeIds{});
 }
 
 #ifdef LUAU_ASSERTENABLED
@@ -762,50 +762,50 @@ static bool areNormalizedTables(const TypeIds& tys)
     return true;
 }
 
-static bool areNormalizedClasses(const NormalizedClassType& tys)
+static bool areNormalizedExternTypes(const NormalizedExternType& tys)
 {
-    for (const auto& [ty, negations] : tys.classes)
+    for (const auto& [ty, negations] : tys.externTypes)
     {
-        const ClassType* ctv = get<ClassType>(ty);
+        const ExternType* etv = get<ExternType>(ty);
-        if (!ctv)
+        if (!etv)
         {
             return false;
         }
 
         for (TypeId negation : negations)
         {
-            const ClassType* nctv = get<ClassType>(negation);
+            const ExternType* nctv = get<ExternType>(negation);
             if (!nctv)
             {
                 return false;
             }
 
-            if (!isSubclass(nctv, ctv))
+            if (!isSubclass(nctv, etv))
             {
                 return false;
             }
         }
 
-        for (const auto& [otherTy, otherNegations] : tys.classes)
+        for (const auto& [otherTy, otherNegations] : tys.externTypes)
         {
             if (otherTy == ty)
                 continue;
 
-            const ClassType* octv = get<ClassType>(otherTy);
+            const ExternType* octv = get<ExternType>(otherTy);
             if (!octv)
             {
                 return false;
             }
 
-            if (isSubclass(ctv, octv))
+            if (isSubclass(etv, octv))
             {
-                auto iss = [ctv](TypeId t)
+                auto iss = [etv](TypeId t)
                 {
-                    const ClassType* c = get<ClassType>(t);
+                    const ExternType* c = get<ExternType>(t);
                     if (!c)
                         return false;
 
-                    return isSubclass(ctv, c);
+                    return isSubclass(etv, c);
                 };
 
                 if (!std::any_of(otherNegations.begin(), otherNegations.end(), iss))
@@ -847,7 +847,7 @@ static void assertInvariant(const NormalizedType& norm)
 
     LUAU_ASSERT(isNormalizedTop(norm.tops));
     LUAU_ASSERT(isNormalizedBoolean(norm.booleans));
-    LUAU_ASSERT(areNormalizedClasses(norm.classes));
+    LUAU_ASSERT(areNormalizedExternTypes(norm.externTypes));
     LUAU_ASSERT(isNormalizedError(norm.errors));
     LUAU_ASSERT(isNormalizedNil(norm.nils));
     LUAU_ASSERT(isNormalizedNumber(norm.numbers));
@@ -988,7 +988,7 @@ void Normalizer::clearNormal(NormalizedType& norm)
 {
     norm.tops = builtinTypes->neverType;
     norm.booleans = builtinTypes->neverType;
-    norm.classes.resetToNever();
+    norm.externTypes.resetToNever();
     norm.errors = builtinTypes->neverType;
     norm.nils = builtinTypes->neverType;
     norm.numbers = builtinTypes->neverType;
@@ -1138,17 +1138,17 @@ TypeId Normalizer::unionOfBools(TypeId here, TypeId there)
     return builtinTypes->booleanType;
 }
 
-void Normalizer::unionClassesWithClass(TypeIds& heres, TypeId there)
+void Normalizer::unionExternTypesWithExternType(TypeIds& heres, TypeId there)
 {
     if (heres.count(there))
         return;
 
-    const ClassType* tctv = get<ClassType>(there);
+    const ExternType* tctv = get<ExternType>(there);
 
     for (auto it = heres.begin(); it != heres.end();)
     {
         TypeId here = *it;
-        const ClassType* hctv = get<ClassType>(here);
+        const ExternType* hctv = get<ExternType>(here);
         if (isSubclass(tctv, hctv))
             return;
         else if (isSubclass(hctv, tctv))
@@ -1160,16 +1160,16 @@ void Normalizer::unionClassesWithClass(TypeIds& heres, TypeId there)
     heres.insert(there);
 }
 
-void Normalizer::unionClasses(TypeIds& heres, const TypeIds& theres)
+void Normalizer::unionExternTypes(TypeIds& heres, const TypeIds& theres)
 {
     for (TypeId there : theres)
-        unionClassesWithClass(heres, there);
+        unionExternTypesWithExternType(heres, there);
 }
 
 static bool isSubclass(TypeId test, TypeId parent)
 {
-    const ClassType* testCtv = get<ClassType>(test);
+    const ExternType* testCtv = get<ExternType>(test);
-    const ClassType* parentCtv = get<ClassType>(parent);
+    const ExternType* parentCtv = get<ExternType>(parent);
 
     LUAU_ASSERT(testCtv);
     LUAU_ASSERT(parentCtv);
@@ -1177,12 +1177,12 @@ static bool isSubclass(TypeId test, TypeId parent)
     return isSubclass(testCtv, parentCtv);
 }
 
-void Normalizer::unionClassesWithClass(NormalizedClassType& heres, TypeId there)
+void Normalizer::unionExternTypesWithExternType(NormalizedExternType& heres, TypeId there)
 {
     for (auto it = heres.ordering.begin(); it != heres.ordering.end();)
     {
         TypeId hereTy = *it;
-        TypeIds& hereNegations = heres.classes.at(hereTy);
+        TypeIds& hereNegations = heres.externTypes.at(hereTy);
 
         // If the incoming class is a subclass of another class in the map, we
         // must ensure that it is negated by one of the negations in the same
@@ -1204,7 +1204,7 @@ void Normalizer::unionClassesWithClass(NormalizedClassType& heres, TypeId there)
                 }
                 // If the incoming class is a superclass of one of the
                 // negations, then the negation no longer applies and must be
-                // removed. This is also true if they are equal. Since classes
+                // removed. This is also true if they are equal. Since extern types
                 // are, at this time, entirely persistent (we do not clone
                 // them), a pointer identity check is sufficient.
                 else if (isSubclass(hereNegation, there))
@@ -1231,7 +1231,7 @@ void Normalizer::unionClassesWithClass(NormalizedClassType& heres, TypeId there)
         {
             TypeIds negations = std::move(hereNegations);
             it = heres.ordering.erase(it);
-            heres.classes.erase(hereTy);
+            heres.externTypes.erase(hereTy);
 
             heres.pushPair(there, std::move(negations));
             return;
@@ -1248,10 +1248,10 @@ void Normalizer::unionClassesWithClass(NormalizedClassType& heres, TypeId there)
     heres.pushPair(there, TypeIds{});
 }
 
-void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassType& theres)
+void Normalizer::unionExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres)
 {
-    // This method bears much similarity with unionClassesWithClass, but is
+    // This method bears much similarity with unionExternTypesWithExternType, but is
-    // solving a more general problem. In unionClassesWithClass, we are dealing
+    // solving a more general problem. In unionExternTypesWithExternType, we are dealing
     // with a singular positive type. Since it's one type, we can use early
     // returns as control flow. Since it's guaranteed to be positive, we do not
     // have negations to worry about combining. The two aspects combine to make
@@ -1260,9 +1260,9 @@ void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassT
 
     for (const TypeId thereTy : theres.ordering)
     {
-        const TypeIds& thereNegations = theres.classes.at(thereTy);
+        const TypeIds& thereNegations = theres.externTypes.at(thereTy);
 
-        // If it happens that there are _no_ classes in the current map, or the
+        // If it happens that there are _no_ extern types in the current map, or the
         // incoming class is completely unrelated to any class in the current
         // map, we must insert the incoming pair as-is.
         bool insert = true;
@@ -1270,7 +1270,7 @@ void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassT
         for (auto it = heres.ordering.begin(); it != heres.ordering.end();)
         {
             TypeId hereTy = *it;
-            TypeIds& hereNegations = heres.classes.at(hereTy);
+            TypeIds& hereNegations = heres.externTypes.at(hereTy);
 
             if (isSubclass(thereTy, hereTy))
             {
@@ -1294,7 +1294,7 @@ void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassT
                     // If the incoming class is a superclass of one of the
                     // negations, then the negation no longer applies and must
                     // be removed. This is also true if they are equal. Since
-                    // classes are, at this time, entirely persistent (we do not
+                    // extern types are, at this time, entirely persistent (we do not
                     // clone them), a pointer identity check is sufficient.
                     else if (isSubclass(hereNegateTy, thereTy))
                     {
@@ -1319,17 +1319,17 @@ void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassT
             else if (isSubclass(hereTy, thereTy))
             {
                 TypeIds negations = std::move(hereNegations);
-                unionClasses(negations, thereNegations);
+                unionExternTypes(negations, thereNegations);
 
                 it = heres.ordering.erase(it);
-                heres.classes.erase(hereTy);
+                heres.externTypes.erase(hereTy);
                 heres.pushPair(thereTy, std::move(negations));
                 insert = false;
                 break;
             }
             else if (hereTy == thereTy)
             {
-                unionClasses(hereNegations, thereNegations);
+                unionExternTypes(hereNegations, thereNegations);
                 insert = false;
                 break;
             }
@@ -1685,8 +1685,12 @@ NormalizationResult Normalizer::unionNormals(NormalizedType& here, const Normali
             return res;
     }
 
+    // Limit based on worst-case expansion of the function unions
+    if (here.functions.parts.size() * there.functions.parts.size() >= size_t(FInt::LuauNormalizeUnionLimit))
+        return NormalizationResult::HitLimits;
+
     here.booleans = unionOfBools(here.booleans, there.booleans);
-    unionClasses(here.classes, there.classes);
+    unionExternTypes(here.externTypes, there.externTypes);
 
     here.errors = (get<NeverType>(there.errors) ? here.errors : there.errors);
     here.nils = (get<NeverType>(there.nils) ? here.nils : there.nils);
@@ -1696,6 +1700,7 @@ NormalizationResult Normalizer::unionNormals(NormalizedType& here, const Normali
     here.buffers = (get<NeverType>(there.buffers) ? here.buffers : there.buffers);
     unionFunctions(here.functions, there.functions);
     unionTables(here.tables, there.tables);
+
     return NormalizationResult::True;
 }
 
@@ -1735,7 +1740,7 @@ NormalizationResult Normalizer::intersectNormalWithNegationTy(TypeId toNegate, N
     return NormalizationResult::True;
 }
 
-// See above for an explaination of `ignoreSmallerTyvars`.
+// See above for an explanation of `ignoreSmallerTyvars`.
 NormalizationResult Normalizer::unionNormalWithTy(
     NormalizedType& here,
     TypeId there,
@@ -1809,7 +1814,8 @@ NormalizationResult Normalizer::unionNormalWithTy(
     }
     else if (get<UnknownType>(here.tops))
         return NormalizationResult::True;
-    else if (get<GenericType>(there) || get<FreeType>(there) || get<BlockedType>(there) || get<PendingExpansionType>(there) || get<TypeFunctionInstanceType>(there))
+    else if (get<GenericType>(there) || get<FreeType>(there) || get<BlockedType>(there) || get<PendingExpansionType>(there) ||
+             get<TypeFunctionInstanceType>(there))
     {
         if (tyvarIndex(there) <= ignoreSmallerTyvars)
             return NormalizationResult::True;
@@ -1824,8 +1830,8 @@ NormalizationResult Normalizer::unionNormalWithTy(
         unionFunctionsWithFunction(here.functions, there);
     else if (get<TableType>(there) || get<MetatableType>(there))
         unionTablesWithTable(here.tables, there);
-    else if (get<ClassType>(there))
+    else if (get<ExternType>(there))
-        unionClassesWithClass(here.classes, there);
+        unionExternTypesWithExternType(here.externTypes, there);
     else if (get<ErrorType>(there))
         here.errors = there;
     else if (const PrimitiveType* ptv = get<PrimitiveType>(there))
@@ -1938,29 +1944,29 @@ std::optional<NormalizedType> Normalizer::negateNormal(const NormalizedType& her
             result.booleans = builtinTypes->trueType;
     }
 
-    if (here.classes.isNever())
+    if (here.externTypes.isNever())
     {
-        resetToTop(builtinTypes, result.classes);
+        resetToTop(builtinTypes, result.externTypes);
     }
-    else if (isTop(builtinTypes, result.classes))
+    else if (isTop(builtinTypes, result.externTypes))
     {
-        result.classes.resetToNever();
+        result.externTypes.resetToNever();
     }
     else
     {
         TypeIds rootNegations{};
 
-        for (const auto& [hereParent, hereNegations] : here.classes.classes)
+        for (const auto& [hereParent, hereNegations] : here.externTypes.externTypes)
         {
-            if (hereParent != builtinTypes->classType)
+            if (hereParent != builtinTypes->externType)
                 rootNegations.insert(hereParent);
 
             for (TypeId hereNegation : hereNegations)
-                unionClassesWithClass(result.classes, hereNegation);
+                unionExternTypesWithExternType(result.externTypes, hereNegation);
         }
 
         if (!rootNegations.empty())
-            result.classes.pushPair(builtinTypes->classType, rootNegations);
+            result.externTypes.pushPair(builtinTypes->externType, rootNegations);
     }
 
     result.nils = get<NeverType>(here.nils) ? builtinTypes->nilType : builtinTypes->neverType;
@@ -2138,7 +2144,7 @@ TypeId Normalizer::intersectionOfBools(TypeId here, TypeId there)
         return there;
 }
 
-void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedClassType& theres)
+void Normalizer::intersectExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres)
 {
     if (theres.isNever())
     {
@@ -2172,12 +2178,12 @@ void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedCl
     //   declare the result of the intersection operation to be never.
     for (const TypeId thereTy : theres.ordering)
     {
-        const TypeIds& thereNegations = theres.classes.at(thereTy);
+        const TypeIds& thereNegations = theres.externTypes.at(thereTy);
 
         for (auto it = heres.ordering.begin(); it != heres.ordering.end();)
         {
             TypeId hereTy = *it;
-            TypeIds& hereNegations = heres.classes.at(hereTy);
+            TypeIds& hereNegations = heres.externTypes.at(hereTy);
 
             if (isSubclass(thereTy, hereTy))
             {
@@ -2200,10 +2206,10 @@ void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedCl
                     }
                 }
 
-                unionClasses(negations, thereNegations);
+                unionExternTypes(negations, thereNegations);
 
                 it = heres.ordering.erase(it);
-                heres.classes.erase(hereTy);
+                heres.externTypes.erase(hereTy);
                 heres.pushPair(thereTy, std::move(negations));
                 break;
             }
@@ -2228,15 +2234,15 @@ void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedCl
                 {
                     if (isSubclass(hereTy, *nIt))
                     {
-                        // eg SomeClass & (class & ~SomeClass)
+                        // eg SomeExternType & (class & ~SomeExternType)
-                        // or SomeClass & (class & ~ParentClass)
+                        // or SomeExternType & (class & ~ParentExternType)
-                        heres.classes.erase(hereTy);
+                        heres.externTypes.erase(hereTy);
                         it = heres.ordering.erase(it);
                         erasedHere = true;
                         break;
                     }
 
-                    // eg SomeClass & (class & ~Unrelated)
+                    // eg SomeExternType & (class & ~Unrelated)
                     if (!isSubclass(*nIt, hereTy))
                         nIt = negations.erase(nIt);
                     else
@@ -2245,30 +2251,30 @@ void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedCl
 
                 if (!erasedHere)
                 {
-                    unionClasses(hereNegations, negations);
+                    unionExternTypes(hereNegations, negations);
                     ++it;
                 }
             }
             else if (hereTy == thereTy)
             {
-                unionClasses(hereNegations, thereNegations);
+                unionExternTypes(hereNegations, thereNegations);
                 break;
             }
             else
             {
                 it = heres.ordering.erase(it);
-                heres.classes.erase(hereTy);
+                heres.externTypes.erase(hereTy);
             }
         }
     }
 }
 
-void Normalizer::intersectClassesWithClass(NormalizedClassType& heres, TypeId there)
+void Normalizer::intersectExternTypesWithExternType(NormalizedExternType& heres, TypeId there)
 {
     for (auto it = heres.ordering.begin(); it != heres.ordering.end();)
     {
         TypeId hereTy = *it;
-        const TypeIds& hereNegations = heres.classes.at(hereTy);
+        const TypeIds& hereNegations = heres.externTypes.at(hereTy);
 
         // If the incoming class _is_ the current class, we skip it. Maybe
         // another entry will have a different story. We check for this first
@@ -2284,9 +2290,24 @@ void Normalizer::intersectClassesWithClass(NormalizedClassType& heres, TypeId th
         else if (isSubclass(there, hereTy))
         {
             TypeIds negations = std::move(hereNegations);
+            bool emptyIntersectWithNegation = false;
 
             for (auto nIt = negations.begin(); nIt != negations.end();)
             {
+                if (isSubclass(there, *nIt))
+                {
+                    // Hitting this block means that the incoming class is a
+                    // subclass of this type, _and_ one of its negations is a
+                    // superclass of this type, e.g.:
+                    //
+                    //  Dog & ~Animal
+                    //
+                    // Clearly this intersects to never, so we mark this class as
+                    // being removed from the normalized class type.
+                    emptyIntersectWithNegation = true;
+                    break;
+                }
+
                 if (!isSubclass(*nIt, there))
                 {
                     nIt = negations.erase(nIt);
@@ -2298,8 +2319,9 @@ void Normalizer::intersectClassesWithClass(NormalizedClassType& heres, TypeId th
             }
 
             it = heres.ordering.erase(it);
-            heres.classes.erase(hereTy);
+            heres.externTypes.erase(hereTy);
-            heres.pushPair(there, std::move(negations));
+            if (!emptyIntersectWithNegation)
+                heres.pushPair(there, std::move(negations));
             break;
         }
         // If the incoming class is a superclass of the current class, we don't
@@ -2313,7 +2335,7 @@ void Normalizer::intersectClassesWithClass(NormalizedClassType& heres, TypeId th
         else
         {
             it = heres.ordering.erase(it);
-            heres.classes.erase(hereTy);
+            heres.externTypes.erase(hereTy);
         }
     }
 }
@@ -2584,11 +2606,31 @@ std::optional<TypeId> Normalizer::intersectionOfTables(TypeId here, TypeId there
                 {
                     if (tprop.readTy.has_value())
                     {
-                        // if the intersection of the read types of a property is uninhabited, the whole table is `never`.
+                        if (FFlag::LuauFixInfiniteRecursionInNormalization)
-                        // We've seen these table prop elements before and we're about to ask if their intersection
-                        // is inhabited
-                        if (FFlag::LuauNormalizationTracksCyclicPairsThroughInhabitance)
                         {
+                            TypeId ty = simplifyIntersection(builtinTypes, NotNull{arena}, *hprop.readTy, *tprop.readTy).result;
+
+                            // If any property is going to get mapped to `never`, we can just call the entire table `never`.
+                            // Since this check is syntactic, we may sometimes miss simplifying tables with complex uninhabited properties.
+                            // Prior versions of this code attempted to do this semantically using the normalization machinery, but this
+                            // mistakenly causes infinite loops when giving more complex recursive table types. As it stands, this approach
+                            // will continue to scale as simplification is improved, but we may wish to reintroduce the semantic approach
+                            // once we have revisited the usage of seen sets systematically (and possibly with some additional guarding to recognize
+                            // when types are infinitely-recursive with non-pointer identical instances of them, or some guard to prevent that
+                            // construction altogether). See also: `gh1632_no_infinite_recursion_in_normalization`
+                            if (get<NeverType>(ty))
+                                return {builtinTypes->neverType};
+
+                            prop.readTy = ty;
+                            hereSubThere &= (ty == hprop.readTy);
+                            thereSubHere &= (ty == tprop.readTy);
+                        }
+                        else
+                        {
+                            // if the intersection of the read types of a property is uninhabited, the whole table is `never`.
+                            // We've seen these table prop elements before and we're about to ask if their intersection
+                            // is inhabited
+
                             auto pair1 = std::pair{*hprop.readTy, *tprop.readTy};
                             auto pair2 = std::pair{*tprop.readTy, *hprop.readTy};
                             if (seenTablePropPairs.contains(pair1) || seenTablePropPairs.contains(pair2))
@@ -2603,6 +2645,8 @@ std::optional<TypeId> Normalizer::intersectionOfTables(TypeId here, TypeId there
                                 seenTablePropPairs.insert(pair2);
                             }
 
+                            // FIXME(ariel): this is being added in a flag removal, so not changing the semantics here, but worth noting that this
+                            // fresh `seenSet` is definitely a bug. we already have `seenSet` from the parameter that _should_ have been used here.
                             Set<TypeId> seenSet{nullptr};
                             NormalizationResult res = isIntersectionInhabited(*hprop.readTy, *tprop.readTy, seenTablePropPairs, seenSet);
 
@@ -2616,34 +2660,6 @@ std::optional<TypeId> Normalizer::intersectionOfTables(TypeId here, TypeId there
                             hereSubThere &= (ty == hprop.readTy);
                             thereSubHere &= (ty == tprop.readTy);
                         }
-                        else
-                        {
-
-                            if (seenSet.contains(*hprop.readTy) && seenSet.contains(*tprop.readTy))
-                            {
-                                seenSet.erase(*hprop.readTy);
-                                seenSet.erase(*tprop.readTy);
-                                return {builtinTypes->neverType};
-                            }
-                            else
-                            {
-                                seenSet.insert(*hprop.readTy);
-                                seenSet.insert(*tprop.readTy);
-                            }
-
-                            NormalizationResult res = isIntersectionInhabited(*hprop.readTy, *tprop.readTy);
-
-                            seenSet.erase(*hprop.readTy);
-                            seenSet.erase(*tprop.readTy);
-
-                            if (NormalizationResult::True != res)
-                                return {builtinTypes->neverType};
-
-                            TypeId ty = simplifyIntersection(builtinTypes, NotNull{arena}, *hprop.readTy, *tprop.readTy).result;
-                            prop.readTy = ty;
-                            hereSubThere &= (ty == hprop.readTy);
-                            thereSubHere &= (ty == tprop.readTy);
-                        }
                     }
                     else
                     {
@@ -3039,15 +3055,12 @@ NormalizationResult Normalizer::intersectTyvarsWithTy(
     return NormalizationResult::True;
 }
 
-// See above for an explaination of `ignoreSmallerTyvars`.
+// See above for an explanation of `ignoreSmallerTyvars`.
 NormalizationResult Normalizer::intersectNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars)
 {
-    if (FFlag::LuauIntersectNormalsNeedsToTrackResourceLimits)
+    RecursionCounter _rc(&sharedState->counters.recursionCount);
-    {
+    if (!withinResourceLimits())
-        RecursionCounter _rc(&sharedState->counters.recursionCount);
+        return NormalizationResult::HitLimits;
-        if (!withinResourceLimits())
-            return NormalizationResult::HitLimits;
-    }
 
     if (!get<NeverType>(there.tops))
     {
@@ -3060,14 +3073,17 @@ NormalizationResult Normalizer::intersectNormals(NormalizedType& here, const Nor
         return unionNormals(here, there, ignoreSmallerTyvars);
     }
 
-    // Limit based on worst-case expansion of the table intersection
+    // Limit based on worst-case expansion of the table/function intersections
     // This restriction can be relaxed when table intersection simplification is improved
     if (here.tables.size() * there.tables.size() >= size_t(FInt::LuauNormalizeIntersectionLimit))
         return NormalizationResult::HitLimits;
 
+    if (here.functions.parts.size() * there.functions.parts.size() >= size_t(FInt::LuauNormalizeIntersectionLimit))
+        return NormalizationResult::HitLimits;
+
     here.booleans = intersectionOfBools(here.booleans, there.booleans);
 
-    intersectClasses(here.classes, there.classes);
+    intersectExternTypes(here.externTypes, there.externTypes);
     here.errors = (get<NeverType>(there.errors) ? there.errors : here.errors);
     here.nils = (get<NeverType>(there.nils) ? there.nils : here.nils);
     here.numbers = (get<NeverType>(there.numbers) ? there.numbers : here.numbers);
@@ -3162,7 +3178,8 @@ NormalizationResult Normalizer::intersectNormalWithTy(
         }
         return NormalizationResult::True;
     }
-    else if (get<GenericType>(there) || get<FreeType>(there) || get<BlockedType>(there) || get<PendingExpansionType>(there) || get<TypeFunctionInstanceType>(there))
+    else if (get<GenericType>(there) || get<FreeType>(there) || get<BlockedType>(there) || get<PendingExpansionType>(there) ||
+             get<TypeFunctionInstanceType>(there))
     {
         NormalizedType thereNorm{builtinTypes};
         NormalizedType topNorm{builtinTypes};
@@ -3188,18 +3205,18 @@ NormalizationResult Normalizer::intersectNormalWithTy(
         intersectTablesWithTable(tables, there, seenTablePropPairs, seenSetTypes);
         here.tables = std::move(tables);
     }
-    else if (get<ClassType>(there))
+    else if (get<ExternType>(there))
     {
-        NormalizedClassType nct = std::move(here.classes);
+        NormalizedExternType nct = std::move(here.externTypes);
         clearNormal(here);
-        intersectClassesWithClass(nct, there);
+        intersectExternTypesWithExternType(nct, there);
-        here.classes = std::move(nct);
+        here.externTypes = std::move(nct);
     }
     else if (get<ErrorType>(there))
     {
         TypeId errors = here.errors;
         clearNormal(here);
-        here.errors = errors;
+        here.errors = get<ErrorType>(errors) ? errors : there;
     }
     else if (const PrimitiveType* ptv = get<PrimitiveType>(there))
     {
@@ -3257,7 +3274,7 @@ NormalizationResult Normalizer::intersectNormalWithTy(
             subtractPrimitive(here, ntv->ty);
         else if (const SingletonType* stv = get<SingletonType>(t))
             subtractSingleton(here, follow(ntv->ty));
-        else if (get<ClassType>(t))
+        else if (get<ExternType>(t))
         {
             NormalizationResult res = intersectNormalWithNegationTy(t, here);
             if (shouldEarlyExit(res))
@@ -3296,8 +3313,18 @@ NormalizationResult Normalizer::intersectNormalWithTy(
             clearNormal(here);
             return NormalizationResult::True;
         }
+        else if (get<ErrorType>(t))
+        {
+            // ~error is still an error, so intersecting with the negation is the same as intersecting with a type
+            TypeId errors = here.errors;
+            clearNormal(here);
+            here.errors = get<ErrorType>(errors) ? errors : t;
+        }
         else if (auto nt = get<NegationType>(t))
+        {
+            here.tyvars = std::move(tyvars);
             return intersectNormalWithTy(here, nt->ty, seenTablePropPairs, seenSetTypes);
+        }
         else
         {
             // TODO negated unions, intersections, table, and function.
@@ -3307,7 +3334,7 @@ NormalizationResult Normalizer::intersectNormalWithTy(
     }
     else if (get<NeverType>(there))
     {
-        here.classes.resetToNever();
+        here.externTypes.resetToNever();
     }
     else if (get<NoRefineType>(there))
     {
@@ -3325,7 +3352,7 @@ NormalizationResult Normalizer::intersectNormalWithTy(
     return NormalizationResult::True;
 }
 
-void makeTableShared(TypeId ty)
+void makeTableShared_DEPRECATED(TypeId ty)
 {
     ty = follow(ty);
     if (auto tableTy = getMutable<TableType>(ty))
@@ -3335,11 +3362,35 @@ void makeTableShared(TypeId ty)
     }
     else if (auto metatableTy = get<MetatableType>(ty))
     {
-        makeTableShared(metatableTy->metatable);
+        makeTableShared_DEPRECATED(metatableTy->metatable);
-        makeTableShared(metatableTy->table);
+        makeTableShared_DEPRECATED(metatableTy->table);
     }
 }
 
+void makeTableShared(TypeId ty, DenseHashSet<TypeId>& seen)
+{
+    ty = follow(ty);
+    if (seen.contains(ty))
+        return;
+    seen.insert(ty);
+    if (auto tableTy = getMutable<TableType>(ty))
+    {
+        for (auto& [_, prop] : tableTy->props)
+            prop.makeShared();
+    }
+    else if (auto metatableTy = get<MetatableType>(ty))
+    {
+        makeTableShared(metatableTy->metatable, seen);
+        makeTableShared(metatableTy->table, seen);
+    }
+}
+
+void makeTableShared(TypeId ty)
+{
+    DenseHashSet<TypeId> seen{nullptr};
+    makeTableShared(ty, seen);
+}
+
 // -------- Convert back from a normalized type to a type
 TypeId Normalizer::typeFromNormal(const NormalizedType& norm)
 {
@@ -3352,18 +3403,18 @@ TypeId Normalizer::typeFromNormal(const NormalizedType& norm)
     if (!get<NeverType>(norm.booleans))
         result.push_back(norm.booleans);
 
-    if (isTop(builtinTypes, norm.classes))
+    if (isTop(builtinTypes, norm.externTypes))
     {
-        result.push_back(builtinTypes->classType);
+        result.push_back(builtinTypes->externType);
     }
-    else if (!norm.classes.isNever())
+    else if (!norm.externTypes.isNever())
     {
         std::vector<TypeId> parts;
-        parts.reserve(norm.classes.classes.size());
+        parts.reserve(norm.externTypes.externTypes.size());
 
-        for (const TypeId normTy : norm.classes.ordering)
+        for (const TypeId normTy : norm.externTypes.ordering)
         {
-            const TypeIds& normNegations = norm.classes.classes.at(normTy);
+            const TypeIds& normNegations = norm.externTypes.externTypes.at(normTy);
 
             if (normNegations.empty())
             {
@@ -3439,7 +3490,10 @@ TypeId Normalizer::typeFromNormal(const NormalizedType& norm)
         result.reserve(result.size() + norm.tables.size());
         for (auto table : norm.tables)
         {
-            makeTableShared(table);
+            if (FFlag::LuauNormalizationCatchMetatableCycles)
+                makeTableShared(table);
+            else
+                makeTableShared_DEPRECATED(table);
             result.push_back(table);
         }
     }
@@ -3465,7 +3519,14 @@ TypeId Normalizer::typeFromNormal(const NormalizedType& norm)
         return arena->addType(UnionType{std::move(result)});
 }
 
-bool isSubtype(TypeId subTy, TypeId superTy, NotNull<Scope> scope, NotNull<BuiltinTypes> builtinTypes, InternalErrorReporter& ice)
+bool isSubtype(
+    TypeId subTy,
+    TypeId superTy,
+    NotNull<Scope> scope,
+    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
+    InternalErrorReporter& ice
+)
 {
     UnifierSharedState sharedState{&ice};
     TypeArena arena;
@@ -3478,7 +3539,7 @@ bool isSubtype(TypeId subTy, TypeId superTy, NotNull<Scope> scope, NotNull<Built
     // Subtyping under DCR is not implemented using unification!
     if (FFlag::LuauSolverV2)
     {
-        Subtyping subtyping{builtinTypes, NotNull{&arena}, NotNull{&normalizer}, NotNull{&typeFunctionRuntime}, NotNull{&ice}};
+        Subtyping subtyping{builtinTypes, NotNull{&arena}, simplifier, NotNull{&normalizer}, NotNull{&typeFunctionRuntime}, NotNull{&ice}};
 
         return subtyping.isSubtype(subTy, superTy, scope).isSubtype;
     }
@@ -3491,7 +3552,14 @@ bool isSubtype(TypeId subTy, TypeId superTy, NotNull<Scope> scope, NotNull<Built
     }
 }
 
-bool isSubtype(TypePackId subPack, TypePackId superPack, NotNull<Scope> scope, NotNull<BuiltinTypes> builtinTypes, InternalErrorReporter& ice)
+bool isSubtype(
+    TypePackId subPack,
+    TypePackId superPack,
+    NotNull<Scope> scope,
+    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
+    InternalErrorReporter& ice
+)
 {
     UnifierSharedState sharedState{&ice};
     TypeArena arena;
@@ -3504,7 +3572,7 @@ bool isSubtype(TypePackId subPack, TypePackId superPack, NotNull<Scope> scope, N
     // Subtyping under DCR is not implemented using unification!
     if (FFlag::LuauSolverV2)
     {
-        Subtyping subtyping{builtinTypes, NotNull{&arena}, NotNull{&normalizer}, NotNull{&typeFunctionRuntime}, NotNull{&ice}};
+        Subtyping subtyping{builtinTypes, NotNull{&arena}, simplifier, NotNull{&normalizer}, NotNull{&typeFunctionRuntime}, NotNull{&ice}};
 
         return subtyping.isSubtype(subPack, superPack, scope).isSubtype;
     }

Analysis/src/OverloadResolution.cpp

@@ -10,12 +10,15 @@
 #include "Luau/TypeUtils.h"
 #include "Luau/Unifier2.h"
 
+LUAU_FASTFLAGVARIABLE(LuauArityMismatchOnUndersaturatedUnknownArguments)
+
 namespace Luau
 {
 
 OverloadResolver::OverloadResolver(
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<TypeArena> arena,
+    NotNull<Simplifier> simplifier,
     NotNull<Normalizer> normalizer,
     NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<Scope> scope,
@@ -25,12 +28,13 @@ OverloadResolver::OverloadResolver(
 )
     : builtinTypes(builtinTypes)
     , arena(arena)
+    , simplifier(simplifier)
     , normalizer(normalizer)
     , typeFunctionRuntime(typeFunctionRuntime)
     , scope(scope)
     , ice(reporter)
     , limits(limits)
-    , subtyping({builtinTypes, arena, normalizer, typeFunctionRuntime, ice})
+    , subtyping({builtinTypes, arena, simplifier, normalizer, typeFunctionRuntime, ice})
     , callLoc(callLocation)
 {
 }
@@ -202,7 +206,7 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
 )
 {
     FunctionGraphReductionResult result = reduceTypeFunctions(
-        fnTy, callLoc, TypeFunctionContext{arena, builtinTypes, scope, normalizer, typeFunctionRuntime, ice, limits}, /*force=*/true
+        fnTy, callLoc, TypeFunctionContext{arena, builtinTypes, scope, simplifier, normalizer, typeFunctionRuntime, ice, limits}, /*force=*/true
     );
     if (!result.errors.empty())
         return {OverloadIsNonviable, result.errors};
@@ -252,15 +256,32 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
             }
 
             // If any of the unsatisfied arguments are not supertypes of
-            // nil, then this overload does not match.
+            // nil or are `unknown`, then this overload does not match.
             for (size_t i = firstUnsatisfiedArgument; i < requiredHead.size(); ++i)
             {
-                if (!subtyping.isSubtype(builtinTypes->nilType, requiredHead[i], scope).isSubtype)
+                if (FFlag::LuauArityMismatchOnUndersaturatedUnknownArguments)
                 {
-                    auto [minParams, optMaxParams] = getParameterExtents(TxnLog::empty(), fn->argTypes);
+                    if (get<UnknownType>(follow(requiredHead[i])) || !subtyping.isSubtype(builtinTypes->nilType, requiredHead[i], scope).isSubtype)
-                    TypeError error{fnExpr->location, CountMismatch{minParams, optMaxParams, args->head.size(), CountMismatch::Arg, isVariadic}};
+                    {
+                        auto [minParams, optMaxParams] = getParameterExtents(TxnLog::empty(), fn->argTypes);
+                        for (auto arg : fn->argTypes)
+                            if (get<UnknownType>(follow(arg)))
+                                minParams += 1;
 
-                    return {Analysis::ArityMismatch, {error}};
+                        TypeError error{fnExpr->location, CountMismatch{minParams, optMaxParams, args->head.size(), CountMismatch::Arg, isVariadic}};
+
+                        return {Analysis::ArityMismatch, {error}};
+                    }
+                }
+                else
+                {
+                    if (!subtyping.isSubtype(builtinTypes->nilType, requiredHead[i], scope).isSubtype)
+                    {
+                        auto [minParams, optMaxParams] = getParameterExtents(TxnLog::empty(), fn->argTypes);
+                        TypeError error{fnExpr->location, CountMismatch{minParams, optMaxParams, args->head.size(), CountMismatch::Arg, isVariadic}};
+
+                        return {Analysis::ArityMismatch, {error}};
+                    }
                 }
             }
 
@@ -404,9 +425,10 @@ void OverloadResolver::add(Analysis analysis, TypeId ty, ErrorVec&& errors)
 
 // we wrap calling the overload resolver in a separate function to reduce overall stack pressure in `solveFunctionCall`.
 // this limits the lifetime of `OverloadResolver`, a large type, to only as long as it is actually needed.
-std::optional<TypeId> selectOverload(
+static std::optional<TypeId> selectOverload(
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<TypeArena> arena,
+    NotNull<Simplifier> simplifier,
     NotNull<Normalizer> normalizer,
     NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<Scope> scope,
@@ -417,8 +439,9 @@ std::optional<TypeId> selectOverload(
     TypePackId argsPack
 )
 {
-    OverloadResolver resolver{builtinTypes, arena, normalizer, typeFunctionRuntime, scope, iceReporter, limits, location};
+    auto resolver =
-    auto [status, overload] = resolver.selectOverload(fn, argsPack);
+        std::make_unique<OverloadResolver>(builtinTypes, arena, simplifier, normalizer, typeFunctionRuntime, scope, iceReporter, limits, location);
+    auto [status, overload] = resolver->selectOverload(fn, argsPack);
 
     if (status == OverloadResolver::Analysis::Ok)
         return overload;
@@ -432,6 +455,7 @@ std::optional<TypeId> selectOverload(
 SolveResult solveFunctionCall(
     NotNull<TypeArena> arena,
     NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
     NotNull<Normalizer> normalizer,
     NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<InternalErrorReporter> iceReporter,
@@ -443,22 +467,22 @@ SolveResult solveFunctionCall(
 )
 {
     std::optional<TypeId> overloadToUse =
-        selectOverload(builtinTypes, arena, normalizer, typeFunctionRuntime, scope, iceReporter, limits, location, fn, argsPack);
+        selectOverload(builtinTypes, arena, simplifier, normalizer, typeFunctionRuntime, scope, iceReporter, limits, location, fn, argsPack);
     if (!overloadToUse)
         return {SolveResult::NoMatchingOverload};
 
     TypePackId resultPack = arena->freshTypePack(scope);
 
-    TypeId inferredTy = arena->addType(FunctionType{TypeLevel{}, scope.get(), argsPack, resultPack});
+    TypeId inferredTy = arena->addType(FunctionType{TypeLevel{}, argsPack, resultPack});
     Unifier2 u2{NotNull{arena}, builtinTypes, scope, iceReporter};
 
     const bool occursCheckPassed = u2.unify(*overloadToUse, inferredTy);
 
     if (!u2.genericSubstitutions.empty() || !u2.genericPackSubstitutions.empty())
     {
-        Instantiation2 instantiation{arena, std::move(u2.genericSubstitutions), std::move(u2.genericPackSubstitutions)};
+        auto instantiation = std::make_unique<Instantiation2>(arena, std::move(u2.genericSubstitutions), std::move(u2.genericPackSubstitutions));
 
-        std::optional<TypePackId> subst = instantiation.substitute(resultPack);
+        std::optional<TypePackId> subst = instantiation->substitute(resultPack);
 
         if (!subst)
             return {SolveResult::CodeTooComplex};

Analysis/src/Quantify.cpp

@@ -107,134 +107,4 @@ void quantify(TypeId ty, TypeLevel level)
     ftv->genericPacks.insert(ftv->genericPacks.end(), q.genericPacks.begin(), q.genericPacks.end());
 }
 
-struct PureQuantifier : Substitution
-{
-    Scope* scope;
-    OrderedMap<TypeId, TypeId> insertedGenerics;
-    OrderedMap<TypePackId, TypePackId> insertedGenericPacks;
-    bool seenMutableType = false;
-    bool seenGenericType = false;
-
-    PureQuantifier(TypeArena* arena, Scope* scope)
-        : Substitution(TxnLog::empty(), arena)
-        , scope(scope)
-    {
-    }
-
-    bool isDirty(TypeId ty) override
-    {
-        LUAU_ASSERT(ty == follow(ty));
-
-        if (auto ftv = get<FreeType>(ty))
-        {
-            bool result = subsumes(scope, ftv->scope);
-            seenMutableType |= result;
-            return result;
-        }
-        else if (auto ttv = get<TableType>(ty))
-        {
-            if (ttv->state == TableState::Free)
-                seenMutableType = true;
-            else if (ttv->state == TableState::Generic)
-                seenGenericType = true;
-
-            return (ttv->state == TableState::Unsealed || ttv->state == TableState::Free) && subsumes(scope, ttv->scope);
-        }
-
-        return false;
-    }
-
-    bool isDirty(TypePackId tp) override
-    {
-        if (auto ftp = get<FreeTypePack>(tp))
-        {
-            return subsumes(scope, ftp->scope);
-        }
-
-        return false;
-    }
-
-    TypeId clean(TypeId ty) override
-    {
-        if (auto ftv = get<FreeType>(ty))
-        {
-            TypeId result = arena->addType(GenericType{scope});
-            insertedGenerics.push(ty, result);
-            return result;
-        }
-        else if (auto ttv = get<TableType>(ty))
-        {
-            TypeId result = arena->addType(TableType{});
-            TableType* resultTable = getMutable<TableType>(result);
-            LUAU_ASSERT(resultTable);
-
-            *resultTable = *ttv;
-            resultTable->level = TypeLevel{};
-            resultTable->scope = scope;
-
-            if (ttv->state == TableState::Free)
-            {
-                resultTable->state = TableState::Generic;
-                insertedGenerics.push(ty, result);
-            }
-            else if (ttv->state == TableState::Unsealed)
-                resultTable->state = TableState::Sealed;
-
-            return result;
-        }
-
-        return ty;
-    }
-
-    TypePackId clean(TypePackId tp) override
-    {
-        if (auto ftp = get<FreeTypePack>(tp))
-        {
-            TypePackId result = arena->addTypePack(TypePackVar{GenericTypePack{scope}});
-            insertedGenericPacks.push(tp, result);
-            return result;
-        }
-
-        return tp;
-    }
-
-    bool ignoreChildren(TypeId ty) override
-    {
-        if (get<ClassType>(ty))
-            return true;
-
-        return ty->persistent;
-    }
-    bool ignoreChildren(TypePackId ty) override
-    {
-        return ty->persistent;
-    }
-};
-
-std::optional<QuantifierResult> quantify(TypeArena* arena, TypeId ty, Scope* scope)
-{
-    PureQuantifier quantifier{arena, scope};
-    std::optional<TypeId> result = quantifier.substitute(ty);
-    if (!result)
-        return std::nullopt;
-
-    FunctionType* ftv = getMutable<FunctionType>(*result);
-    LUAU_ASSERT(ftv);
-    ftv->scope = scope;
-
-    for (auto k : quantifier.insertedGenerics.keys)
-    {
-        TypeId g = quantifier.insertedGenerics.pairings[k];
-        if (get<GenericType>(g))
-            ftv->generics.push_back(g);
-    }
-
-    for (auto k : quantifier.insertedGenericPacks.keys)
-        ftv->genericPacks.push_back(quantifier.insertedGenericPacks.pairings[k]);
-
-    ftv->hasNoFreeOrGenericTypes = ftv->generics.empty() && ftv->genericPacks.empty() && !quantifier.seenGenericType && !quantifier.seenMutableType;
-
-    return std::optional<QuantifierResult>({*result, std::move(quantifier.insertedGenerics), std::move(quantifier.insertedGenericPacks)});
-}
-
 } // namespace Luau

Analysis/src/Refinement.cpp

@@ -54,7 +54,15 @@ RefinementId RefinementArena::proposition(const RefinementKey* key, TypeId discr
     if (!key)
         return nullptr;
 
-    return NotNull{allocator.allocate(Proposition{key, discriminantTy})};
+    return NotNull{allocator.allocate(Proposition{key, discriminantTy, false})};
+}
+
+RefinementId RefinementArena::implicitProposition(const RefinementKey* key, TypeId discriminantTy)
+{
+    if (!key)
+        return nullptr;
+
+    return NotNull{allocator.allocate(Proposition{key, discriminantTy, true})};
 }
 
 } // namespace Luau

Analysis/src/RequireTracer.cpp

@@ -4,6 +4,8 @@
 #include "Luau/Ast.h"
 #include "Luau/Module.h"
 
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+
 namespace Luau
 {
 
@@ -65,7 +67,13 @@ struct RequireTracer : AstVisitor
         return true;
     }
 
-    AstExpr* getDependent(AstExpr* node)
+    bool visit(AstTypePack* node) override
+    {
+        // allow resolving require inside `typeof` annotations
+        return FFlag::LuauStoreReturnTypesAsPackOnAst;
+    }
+
+    AstExpr* getDependent_DEPRECATED(AstExpr* node)
     {
         if (AstExprLocal* expr = node->as<AstExprLocal>())
             return locals[expr->local];
@@ -78,6 +86,27 @@ struct RequireTracer : AstVisitor
         else
             return nullptr;
     }
+    AstNode* getDependent(AstNode* node)
+    {
+        if (AstExprLocal* expr = node->as<AstExprLocal>())
+            return locals[expr->local];
+        else if (AstExprIndexName* expr = node->as<AstExprIndexName>())
+            return expr->expr;
+        else if (AstExprIndexExpr* expr = node->as<AstExprIndexExpr>())
+            return expr->expr;
+        else if (AstExprCall* expr = node->as<AstExprCall>(); expr && expr->self)
+            return expr->func->as<AstExprIndexName>()->expr;
+        else if (AstExprGroup* expr = node->as<AstExprGroup>())
+            return expr->expr;
+        else if (AstExprTypeAssertion* expr = node->as<AstExprTypeAssertion>())
+            return expr->annotation;
+        else if (AstTypeGroup* expr = node->as<AstTypeGroup>())
+            return expr->type;
+        else if (AstTypeTypeof* expr = node->as<AstTypeTypeof>())
+            return expr->expr;
+        else
+            return nullptr;
+    }
 
     void process()
     {
@@ -91,13 +120,15 @@ struct RequireTracer : AstVisitor
 
         // push all dependent expressions to the work stack; note that the vector is modified during traversal
         for (size_t i = 0; i < work.size(); ++i)
-            if (AstExpr* dep = getDependent(work[i]))
+        {
+            if (AstNode* dep = getDependent(work[i]))
                 work.push_back(dep);
+        }
 
         // resolve all expressions to a module info
         for (size_t i = work.size(); i > 0; --i)
         {
-            AstExpr* expr = work[i - 1];
+            AstNode* expr = work[i - 1];
 
             // when multiple expressions depend on the same one we push it to work queue multiple times
             if (result.exprs.contains(expr))
@@ -105,19 +136,22 @@ struct RequireTracer : AstVisitor
 
             std::optional<ModuleInfo> info;
 
-            if (AstExpr* dep = getDependent(expr))
+            if (AstNode* dep = getDependent(expr))
             {
                 const ModuleInfo* context = result.exprs.find(dep);
 
-                // locals just inherit their dependent context, no resolution required
+                if (context && expr->is<AstExprLocal>())
-                if (expr->is<AstExprLocal>())
+                    info = *context; // locals just inherit their dependent context, no resolution required
-                    info = context ? std::optional<ModuleInfo>(*context) : std::nullopt;
+                else if (context && (expr->is<AstExprGroup>() || expr->is<AstTypeGroup>()))
-                else
+                    info = *context; // simple group nodes propagate their value
-                    info = fileResolver->resolveModule(context, expr);
+                else if (context && (expr->is<AstTypeTypeof>() || expr->is<AstExprTypeAssertion>()))
+                    info = *context; // typeof type annotations will resolve to the typeof content
+                else if (AstExpr* asExpr = expr->asExpr())
+                    info = fileResolver->resolveModule(context, asExpr);
             }
-            else
+            else if (AstExpr* asExpr = expr->asExpr())
             {
-                info = fileResolver->resolveModule(&moduleContext, expr);
+                info = fileResolver->resolveModule(&moduleContext, asExpr);
             }
 
             if (info)
@@ -150,7 +184,7 @@ struct RequireTracer : AstVisitor
     ModuleName currentModuleName;
 
     DenseHashMap<AstLocal*, AstExpr*> locals;
-    std::vector<AstExpr*> work;
+    std::vector<AstNode*> work;
     std::vector<AstExprCall*> requireCalls;
 };
 

Analysis/src/Scope.cpp

@@ -84,6 +84,17 @@ std::optional<TypeId> Scope::lookupUnrefinedType(DefId def) const
     return std::nullopt;
 }
 
+std::optional<TypeId> Scope::lookupRValueRefinementType(DefId def) const
+{
+    for (const Scope* current = this; current; current = current->parent.get())
+    {
+        if (auto ty = current->rvalueRefinements.find(def))
+            return *ty;
+    }
+
+    return std::nullopt;
+}
+
 std::optional<TypeId> Scope::lookup(DefId def) const
 {
     for (const Scope* current = this; current; current = current->parent.get())
@@ -181,6 +192,29 @@ std::optional<Binding> Scope::linearSearchForBinding(const std::string& name, bo
     return std::nullopt;
 }
 
+std::optional<std::pair<Symbol, Binding>> Scope::linearSearchForBindingPair(const std::string& name, bool traverseScopeChain) const
+{
+    const Scope* scope = this;
+
+    while (scope)
+    {
+        for (auto& [n, binding] : scope->bindings)
+        {
+            if (n.local && n.local->name == name.c_str())
+                return {{n, binding}};
+            else if (n.global.value && n.global == name.c_str())
+                return {{n, binding}};
+        }
+
+        scope = scope->parent.get();
+
+        if (!traverseScopeChain)
+            break;
+    }
+
+    return std::nullopt;
+}
+
 // Updates the `this` scope with the assignments from the `childScope` including ones that doesn't exist in `this`.
 void Scope::inheritAssignments(const ScopePtr& childScope)
 {
@@ -211,6 +245,16 @@ void Scope::inheritRefinements(const ScopePtr& childScope)
     }
 }
 
+bool Scope::shouldWarnGlobal(std::string name) const
+{
+    for (const Scope* current = this; current; current = current->parent.get())
+    {
+        if (current->globalsToWarn.contains(name))
+            return true;
+    }
+    return false;
+}
+
 bool subsumesStrict(Scope* left, Scope* right)
 {
     while (right)

Analysis/src/Simplify.cpp

@@ -6,6 +6,7 @@
 #include "Luau/DenseHash.h"
 #include "Luau/RecursionCounter.h"
 #include "Luau/Set.h"
+#include "Luau/Type.h"
 #include "Luau/TypeArena.h"
 #include "Luau/TypePairHash.h"
 #include "Luau/TypeUtils.h"
@@ -14,8 +15,10 @@
 
 LUAU_FASTINT(LuauTypeReductionRecursionLimit)
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_DYNAMIC_FASTINTVARIABLE(LuauSimplificationComplexityLimit, 8);
+LUAU_DYNAMIC_FASTINTVARIABLE(LuauSimplificationComplexityLimit, 8)
-LUAU_FASTFLAGVARIABLE(LuauFlagBasicIntersectFollows);
+LUAU_FASTFLAGVARIABLE(LuauSimplificationRecheckAssumption)
+LUAU_FASTFLAGVARIABLE(LuauOptimizeFalsyAndTruthyIntersect)
+LUAU_FASTFLAGVARIABLE(LuauSimplificationTableExternType)
 
 namespace Luau
 {
@@ -31,25 +34,27 @@ struct TypeSimplifier
 
     int recursionDepth = 0;
 
-    TypeId mkNegation(TypeId ty);
+    TypeId mkNegation(TypeId ty) const;
 
     TypeId intersectFromParts(std::set<TypeId> parts);
 
-    TypeId intersectUnionWithType(TypeId unionTy, TypeId right);
+    TypeId intersectUnionWithType(TypeId left, TypeId right);
     TypeId intersectUnions(TypeId left, TypeId right);
-    TypeId intersectNegatedUnion(TypeId unionTy, TypeId right);
+    TypeId intersectNegatedUnion(TypeId left, TypeId right);
 
-    TypeId intersectTypeWithNegation(TypeId a, TypeId b);
+    TypeId intersectTypeWithNegation(TypeId left, TypeId right);
-    TypeId intersectNegations(TypeId a, TypeId b);
+    TypeId intersectNegations(TypeId left, TypeId right);
 
     TypeId intersectIntersectionWithType(TypeId left, TypeId right);
 
     // Attempt to intersect the two types.  Does not recurse.  Does not handle
     // unions, intersections, or negations.
     std::optional<TypeId> basicIntersect(TypeId left, TypeId right);
+    std::optional<TypeId> basicIntersectWithTruthy(TypeId target) const;
+    std::optional<TypeId> basicIntersectWithFalsy(TypeId target) const;
 
-    TypeId intersect(TypeId ty, TypeId discriminant);
+    TypeId intersect(TypeId left, TypeId right);
-    TypeId union_(TypeId ty, TypeId discriminant);
+    TypeId union_(TypeId left, TypeId right);
 
     TypeId simplify(TypeId ty);
     TypeId simplify(TypeId ty, DenseHashSet<TypeId>& seen);
@@ -313,12 +318,14 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     {
         if (get<AnyType>(right))
             return Relation::Subset;
-        else if (get<UnknownType>(right))
+
+        if (get<UnknownType>(right))
             return Relation::Coincident;
-        else if (get<ErrorType>(right))
+
+        if (get<ErrorType>(right))
             return Relation::Disjoint;
-        else
+
-            return Relation::Superset;
+        return Relation::Superset;
     }
 
     if (get<UnknownType>(right))
@@ -328,8 +335,8 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     {
         if (get<AnyType>(right))
             return Relation::Coincident;
-        else
+
-            return Relation::Superset;
+        return Relation::Superset;
     }
 
     if (get<AnyType>(right))
@@ -353,7 +360,7 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     // * FunctionType
     // * TableType
     // * MetatableType
-    // * ClassType
+    // * ExternType
     // * UnionType
     // * IntersectionType
     // * NegationType
@@ -361,26 +368,33 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     if (isTypeVariable(left) || isTypeVariable(right))
         return Relation::Intersects;
 
+    if (FFlag::LuauSimplificationTableExternType)
+    {
+        // if either type is a type function, we cannot know if they'll be related.
+        if (get<TypeFunctionInstanceType>(left) || get<TypeFunctionInstanceType>(right))
+            return Relation::Intersects;
+    }
+
     if (get<ErrorType>(left))
     {
         if (get<ErrorType>(right))
             return Relation::Coincident;
         else if (get<AnyType>(right))
             return Relation::Subset;
-        else
+
-            return Relation::Disjoint;
+        return Relation::Disjoint;
     }
-    if (get<ErrorType>(right))
+    else if (get<ErrorType>(right))
         return flip(relate(right, left, seen));
 
     if (get<NeverType>(left))
     {
         if (get<NeverType>(right))
             return Relation::Coincident;
-        else
+
-            return Relation::Subset;
+        return Relation::Subset;
     }
-    if (get<NeverType>(right))
+    else if (get<NeverType>(right))
         return flip(relate(right, left, seen));
 
     if (auto ut = get<IntersectionType>(left))
@@ -444,52 +458,54 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
         {
             if (lp->type == rp->type)
                 return Relation::Coincident;
-            else
+
-                return Relation::Disjoint;
+            return Relation::Disjoint;
         }
 
         if (auto rs = get<SingletonType>(right))
         {
             if (lp->type == PrimitiveType::String && rs->variant.get_if<StringSingleton>())
                 return Relation::Superset;
-            else if (lp->type == PrimitiveType::Boolean && rs->variant.get_if<BooleanSingleton>())
+
+            if (lp->type == PrimitiveType::Boolean && rs->variant.get_if<BooleanSingleton>())
                 return Relation::Superset;
-            else
+
-                return Relation::Disjoint;
+            return Relation::Disjoint;
         }
 
         if (lp->type == PrimitiveType::Function)
         {
             if (get<FunctionType>(right))
                 return Relation::Superset;
-            else
+
-                return Relation::Disjoint;
+            return Relation::Disjoint;
         }
         if (lp->type == PrimitiveType::Table)
         {
             if (get<TableType>(right))
                 return Relation::Superset;
-            else
+
-                return Relation::Disjoint;
+            return Relation::Disjoint;
         }
 
-        if (get<FunctionType>(right) || get<TableType>(right) || get<MetatableType>(right) || get<ClassType>(right))
+        if (get<FunctionType>(right) || get<TableType>(right) || get<MetatableType>(right) || get<ExternType>(right))
             return Relation::Disjoint;
     }
 
     if (auto ls = get<SingletonType>(left))
     {
-        if (get<FunctionType>(right) || get<TableType>(right) || get<MetatableType>(right) || get<ClassType>(right))
+        if (get<FunctionType>(right) || get<TableType>(right) || get<MetatableType>(right) || get<ExternType>(right))
             return Relation::Disjoint;
 
         if (get<PrimitiveType>(right))
             return flip(relate(right, left, seen));
+
         if (auto rs = get<SingletonType>(right))
         {
             if (ls->variant == rs->variant)
                 return Relation::Coincident;
-            else
+
-                return Relation::Disjoint;
+            return Relation::Disjoint;
         }
     }
 
@@ -499,11 +515,11 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
         {
             if (rp->type == PrimitiveType::Function)
                 return Relation::Subset;
-            else
+
-                return Relation::Disjoint;
+            return Relation::Disjoint;
         }
-        else
+
-            return Relation::Intersects;
+        return Relation::Intersects;
     }
 
     if (auto lt = get<TableType>(left))
@@ -512,10 +528,11 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
         {
             if (rp->type == PrimitiveType::Table)
                 return Relation::Subset;
-            else
+
-                return Relation::Disjoint;
+            return Relation::Disjoint;
         }
-        else if (auto rt = get<TableType>(right))
+
+        if (auto rt = get<TableType>(right))
         {
             // TODO PROBABLY indexers and metatables.
             if (1 == rt->props.size())
@@ -535,29 +552,58 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
                  */
                 if (lt->props.size() > 1 && r == Relation::Superset)
                     return Relation::Intersects;
-                else
+
-                    return r;
+                return r;
             }
-            else if (1 == lt->props.size())
+
+            if (1 == lt->props.size())
                 return flip(relate(right, left, seen));
-            else
+
-                return Relation::Intersects;
+            return Relation::Intersects;
         }
+
+        if (FFlag::LuauSimplificationTableExternType)
+        {
+            if (auto re = get<ExternType>(right))
+            {
+                Relation overall = Relation::Coincident;
+
+                for (auto& [name, prop] : lt->props)
+                {
+                    if (auto propInExternType = re->props.find(name); propInExternType != re->props.end())
+                    {
+                        Relation propRel = relate(prop.type(), propInExternType->second.type());
+
+                        if (propRel == Relation::Disjoint)
+                            return Relation::Disjoint;
+
+                        if (propRel == Relation::Coincident)
+                            continue;
+
+                        overall = Relation::Intersects;
+                    }
+                }
+
+                return overall;
+            }
+        }
+
         // TODO metatables
 
         return Relation::Disjoint;
     }
 
-    if (auto ct = get<ClassType>(left))
+    if (auto ct = get<ExternType>(left))
     {
-        if (auto rct = get<ClassType>(right))
+        if (auto rct = get<ExternType>(right))
         {
             if (isSubclass(ct, rct))
                 return Relation::Subset;
-            else if (isSubclass(rct, ct))
+
+            if (isSubclass(rct, ct))
                 return Relation::Superset;
-            else
+
-                return Relation::Disjoint;
+            return Relation::Disjoint;
         }
 
         return Relation::Disjoint;
@@ -573,7 +619,7 @@ Relation relate(TypeId left, TypeId right)
     return relate(left, right, seen);
 }
 
-TypeId TypeSimplifier::mkNegation(TypeId ty)
+TypeId TypeSimplifier::mkNegation(TypeId ty) const
 {
     TypeId result = nullptr;
 
@@ -707,7 +753,9 @@ TypeId TypeSimplifier::intersectUnionWithType(TypeId left, TypeId right)
     bool changed = false;
     std::set<TypeId> newParts;
 
-    if (leftUnion->options.size() > (size_t)DFInt::LuauSimplificationComplexityLimit)
+    size_t maxSize = DFInt::LuauSimplificationComplexityLimit;
+
+    if (leftUnion->options.size() > maxSize)
         return arena->addType(IntersectionType{{left, right}});
 
     for (TypeId part : leftUnion)
@@ -722,6 +770,13 @@ TypeId TypeSimplifier::intersectUnionWithType(TypeId left, TypeId right)
         }
 
         newParts.insert(simplified);
+
+        if (FFlag::LuauSimplificationRecheckAssumption)
+        {
+            // Initial combination size check could not predict nested union iteration
+            if (newParts.size() > maxSize)
+                return arena->addType(IntersectionType{{left, right}});
+        }
     }
 
     if (!changed)
@@ -762,6 +817,13 @@ TypeId TypeSimplifier::intersectUnions(TypeId left, TypeId right)
                 continue;
 
             newParts.insert(simplified);
+
+            if (FFlag::LuauSimplificationRecheckAssumption)
+            {
+                // Initial combination size check could not predict nested union iteration
+                if (newParts.size() > maxSize)
+                    return arena->addType(IntersectionType{{left, right}});
+            }
         }
     }
 
@@ -840,6 +902,78 @@ TypeId TypeSimplifier::intersectNegatedUnion(TypeId left, TypeId right)
         return intersectFromParts(std::move(newParts));
 }
 
+std::optional<TypeId> TypeSimplifier::basicIntersectWithTruthy(TypeId target) const
+{
+    target = follow(target);
+
+    if (is<UnknownType>(target))
+        return builtinTypes->truthyType;
+
+    if (is<AnyType>(target))
+        // any = *error-type* | unknown, so truthy & any = *error-type* | truthy
+        return arena->addType(UnionType{{builtinTypes->truthyType, builtinTypes->errorType}});
+
+    if (is<NeverType, ErrorType>(target))
+        return target;
+
+    if (is<FunctionType, TableType, MetatableType, ExternType>(target))
+        return target;
+
+    if (auto pt = get<PrimitiveType>(target))
+    {
+        switch (pt->type)
+        {
+        case PrimitiveType::NilType:
+            return builtinTypes->neverType;
+        case PrimitiveType::Boolean:
+            return builtinTypes->trueType;
+        default:
+            return target;
+        }
+    }
+
+    if (auto st = get<SingletonType>(target))
+        return st->variant == BooleanSingleton{false} ? builtinTypes->neverType : target;
+
+    return std::nullopt;
+}
+
+std::optional<TypeId> TypeSimplifier::basicIntersectWithFalsy(TypeId target) const
+{
+    target = follow(target);
+
+    if (is<NeverType, ErrorType>(target))
+        return target;
+
+    if (is<AnyType>(target))
+        // any = *error-type* | unknown, so falsy & any = *error-type* | falsy
+        return arena->addType(UnionType{{builtinTypes->falsyType, builtinTypes->errorType}});
+
+    if (is<UnknownType>(target))
+        return builtinTypes->falsyType;
+
+    if (is<FunctionType, TableType, MetatableType, ExternType>(target))
+        return builtinTypes->neverType;
+
+    if (auto pt = get<PrimitiveType>(target))
+    {
+        switch (pt->type)
+        {
+        case PrimitiveType::NilType:
+            return builtinTypes->nilType;
+        case PrimitiveType::Boolean:
+            return builtinTypes->falseType;
+        default:
+            return builtinTypes->neverType;
+        }
+    }
+
+    if (auto st = get<SingletonType>(target))
+        return st->variant == BooleanSingleton{false} ? builtinTypes->falseType : builtinTypes->neverType;
+
+    return std::nullopt;
+}
+
 TypeId TypeSimplifier::intersectTypeWithNegation(TypeId left, TypeId right)
 {
     const NegationType* leftNegation = get<NegationType>(left);
@@ -1066,11 +1200,8 @@ TypeId TypeSimplifier::intersectIntersectionWithType(TypeId left, TypeId right)
 
 std::optional<TypeId> TypeSimplifier::basicIntersect(TypeId left, TypeId right)
 {
-    if (FFlag::LuauFlagBasicIntersectFollows)
+    left = follow(left);
-    {
+    right = follow(right);
-        left = follow(left);
-        right = follow(right);
-    }
 
     if (get<AnyType>(left) && get<ErrorType>(right))
         return right;
@@ -1179,6 +1310,25 @@ std::optional<TypeId> TypeSimplifier::basicIntersect(TypeId left, TypeId right)
         return std::nullopt;
     }
 
+    if (FFlag::LuauOptimizeFalsyAndTruthyIntersect)
+    {
+        if (isTruthyType(left))
+            if (auto res = basicIntersectWithTruthy(right))
+                return res;
+
+        if (isTruthyType(right))
+            if (auto res = basicIntersectWithTruthy(left))
+                return res;
+
+        if (isFalsyType(left))
+            if (auto res = basicIntersectWithFalsy(right))
+                return res;
+
+        if (isFalsyType(right))
+            if (auto res = basicIntersectWithFalsy(left))
+                return res;
+    }
+
     Relation relation = relate(left, right);
     if (left == right || Relation::Coincident == relation)
         return left;
@@ -1411,8 +1561,6 @@ TypeId TypeSimplifier::simplify(TypeId ty, DenseHashSet<TypeId>& seen)
 
 SimplifyResult simplifyIntersection(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId left, TypeId right)
 {
-    LUAU_ASSERT(FFlag::LuauSolverV2);
-
     TypeSimplifier s{builtinTypes, arena};
 
     // fprintf(stderr, "Intersect %s and %s ...\n", toString(left).c_str(), toString(right).c_str());
@@ -1426,8 +1574,6 @@ SimplifyResult simplifyIntersection(NotNull<BuiltinTypes> builtinTypes, NotNull<
 
 SimplifyResult simplifyIntersection(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, std::set<TypeId> parts)
 {
-    LUAU_ASSERT(FFlag::LuauSolverV2);
-
     TypeSimplifier s{builtinTypes, arena};
 
     TypeId res = s.intersectFromParts(std::move(parts));
@@ -1437,8 +1583,6 @@ SimplifyResult simplifyIntersection(NotNull<BuiltinTypes> builtinTypes, NotNull<
 
 SimplifyResult simplifyUnion(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId left, TypeId right)
 {
-    LUAU_ASSERT(FFlag::LuauSolverV2);
-
     TypeSimplifier s{builtinTypes, arena};
 
     TypeId res = s.union_(left, right);

Analysis/src/Substitution.cpp

@@ -2,22 +2,23 @@
 #include "Luau/Substitution.h"
 
 #include "Luau/Common.h"
-#include "Luau/Clone.h"
 #include "Luau/TxnLog.h"
+#include "Luau/Type.h"
 
 #include <algorithm>
-#include <stdexcept>
 
 LUAU_FASTINTVARIABLE(LuauTarjanChildLimit, 10000)
-LUAU_FASTFLAG(LuauSolverV2);
+LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTINTVARIABLE(LuauTarjanPreallocationSize, 256);
+LUAU_FASTINTVARIABLE(LuauTarjanPreallocationSize, 256)
+LUAU_FASTFLAG(LuauSyntheticErrors)
+LUAU_FASTFLAG(LuauDeprecatedAttribute)
 
 namespace Luau
 {
 
-static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool alwaysClone)
+static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log)
 {
-    auto go = [ty, &dest, alwaysClone](auto&& a)
+    auto go = [ty, &dest](auto&& a)
     {
         using T = std::decay_t<decltype(a)>;
 
@@ -57,8 +58,25 @@ static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool a
         }
         else if constexpr (std::is_same_v<T, ErrorType>)
         {
-            LUAU_ASSERT(ty->persistent);
+            if (FFlag::LuauSyntheticErrors)
-            return ty;
+            {
+                LUAU_ASSERT(ty->persistent || a.synthetic);
+
+                if (ty->persistent)
+                    return ty;
+
+                // While this code intentionally works (and clones) even if `a.synthetic` is `std::nullopt`,
+                // we still assert above because we consider it a bug to have a non-persistent error type
+                // without any associated metadata. We should always use the persistent version in such cases.
+                ErrorType clone = ErrorType{};
+                clone.synthetic = a.synthetic;
+                return dest.addType(clone);
+            }
+            else
+            {
+                LUAU_ASSERT(ty->persistent);
+                return ty;
+            }
         }
         else if constexpr (std::is_same_v<T, UnknownType>)
         {
@@ -76,15 +94,15 @@ static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool a
             return dest.addType(a);
         else if constexpr (std::is_same_v<T, FunctionType>)
         {
-            FunctionType clone = FunctionType{a.level, a.scope, a.argTypes, a.retTypes, a.definition, a.hasSelf};
+            FunctionType clone = FunctionType{a.level, a.argTypes, a.retTypes, a.definition, a.hasSelf};
             clone.generics = a.generics;
             clone.genericPacks = a.genericPacks;
-            clone.magicFunction = a.magicFunction;
+            clone.magic = a.magic;
-            clone.dcrMagicFunction = a.dcrMagicFunction;
-            clone.dcrMagicRefinement = a.dcrMagicRefinement;
             clone.tags = a.tags;
             clone.argNames = a.argNames;
             clone.isCheckedFunction = a.isCheckedFunction;
+            if (FFlag::LuauDeprecatedAttribute)
+                clone.isDeprecatedFunction = a.isDeprecatedFunction;
             return dest.addType(std::move(clone));
         }
         else if constexpr (std::is_same_v<T, TableType>)
@@ -118,15 +136,10 @@ static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool a
             clone.parts = a.parts;
             return dest.addType(std::move(clone));
         }
-        else if constexpr (std::is_same_v<T, ClassType>)
+        else if constexpr (std::is_same_v<T, ExternType>)
         {
-            if (alwaysClone)
+            ExternType clone{a.name, a.props, a.parent, a.metatable, a.tags, a.userData, a.definitionModuleName, a.definitionLocation, a.indexer};
-            {
+            return dest.addType(std::move(clone));
-                ClassType clone{a.name, a.props, a.parent, a.metatable, a.tags, a.userData, a.definitionModuleName, a.definitionLocation, a.indexer};
-                return dest.addType(std::move(clone));
-            }
-            else
-                return ty;
         }
         else if constexpr (std::is_same_v<T, NegationType>)
             return dest.addType(NegationType{a.ty});
@@ -239,21 +252,21 @@ void Tarjan::visitChildren(TypeId ty, int index)
         for (TypePackId a : tfit->packArguments)
             visitChild(a);
     }
-    else if (const ClassType* ctv = get<ClassType>(ty))
+    else if (const ExternType* etv = get<ExternType>(ty))
     {
-        for (const auto& [name, prop] : ctv->props)
+        for (const auto& [name, prop] : etv->props)
             visitChild(prop.type());
 
-        if (ctv->parent)
+        if (etv->parent)
-            visitChild(*ctv->parent);
+            visitChild(*etv->parent);
 
-        if (ctv->metatable)
+        if (etv->metatable)
-            visitChild(*ctv->metatable);
+            visitChild(*etv->metatable);
 
-        if (ctv->indexer)
+        if (etv->indexer)
         {
-            visitChild(ctv->indexer->indexType);
+            visitChild(etv->indexer->indexType);
-            visitChild(ctv->indexer->indexResultType);
+            visitChild(etv->indexer->indexResultType);
         }
     }
     else if (const NegationType* ntv = get<NegationType>(ty))
@@ -527,6 +540,27 @@ void Tarjan::visitSCC(int index)
     }
 }
 
+bool Tarjan::ignoreChildren(TypeId ty)
+{
+    return false;
+}
+
+bool Tarjan::ignoreChildren(TypePackId ty)
+{
+    return false;
+}
+
+// Some subclasses might ignore children visit, but not other actions like replacing the children
+bool Tarjan::ignoreChildrenVisit(TypeId ty)
+{
+    return ignoreChildren(ty);
+}
+
+bool Tarjan::ignoreChildrenVisit(TypePackId ty)
+{
+    return ignoreChildren(ty);
+}
+
 TarjanResult Tarjan::findDirty(TypeId ty)
 {
     return visitRoot(ty);
@@ -537,6 +571,11 @@ TarjanResult Tarjan::findDirty(TypePackId tp)
     return visitRoot(tp);
 }
 
+Substitution::Substitution(TypeArena* arena)
+    : Substitution(TxnLog::empty(), arena)
+{
+}
+
 Substitution::Substitution(const TxnLog* log_, TypeArena* arena)
     : arena(arena)
 {
@@ -637,7 +676,7 @@ void Substitution::resetState(const TxnLog* log, TypeArena* arena)
 
 TypeId Substitution::clone(TypeId ty)
 {
-    return shallowClone(ty, *arena, log, /* alwaysClone */ true);
+    return shallowClone(ty, *arena, log);
 }
 
 TypePackId Substitution::clone(TypePackId tp)
@@ -799,21 +838,21 @@ void Substitution::replaceChildren(TypeId ty)
         for (TypePackId& a : tfit->packArguments)
             a = replace(a);
     }
-    else if (ClassType* ctv = getMutable<ClassType>(ty))
+    else if (ExternType* etv = getMutable<ExternType>(ty))
     {
-        for (auto& [name, prop] : ctv->props)
+        for (auto& [name, prop] : etv->props)
             prop.setType(replace(prop.type()));
 
-        if (ctv->parent)
+        if (etv->parent)
-            ctv->parent = replace(*ctv->parent);
+            etv->parent = replace(*etv->parent);
 
-        if (ctv->metatable)
+        if (etv->metatable)
-            ctv->metatable = replace(*ctv->metatable);
+            etv->metatable = replace(*etv->metatable);
 
-        if (ctv->indexer)
+        if (etv->indexer)
         {
-            ctv->indexer->indexType = replace(ctv->indexer->indexType);
+            etv->indexer->indexType = replace(etv->indexer->indexType);
-            ctv->indexer->indexResultType = replace(ctv->indexer->indexResultType);
+            etv->indexer->indexResultType = replace(etv->indexer->indexResultType);
         }
     }
     else if (NegationType* ntv = getMutable<NegationType>(ty))
@@ -853,4 +892,13 @@ void Substitution::replaceChildren(TypePackId tp)
     }
 }
 
+template<typename Ty>
+std::optional<Ty> Substitution::replace(std::optional<Ty> ty)
+{
+    if (ty)
+        return replace(*ty);
+    else
+        return std::nullopt;
+}
+
 } // namespace Luau

Analysis/src/Subtyping.cpp

@@ -7,13 +7,11 @@
 #include "Luau/Normalize.h"
 #include "Luau/RecursionCounter.h"
 #include "Luau/Scope.h"
-#include "Luau/StringUtils.h"
 #include "Luau/Substitution.h"
 #include "Luau/ToString.h"
 #include "Luau/TxnLog.h"
 #include "Luau/Type.h"
 #include "Luau/TypeArena.h"
-#include "Luau/TypeCheckLimits.h"
 #include "Luau/TypeFunction.h"
 #include "Luau/TypePack.h"
 #include "Luau/TypePath.h"
@@ -22,8 +20,8 @@
 #include <algorithm>
 
 LUAU_FASTFLAGVARIABLE(DebugLuauSubtypingCheckPathValidity)
-LUAU_DYNAMIC_FASTINT(LuauTypeSolverRelease)
+LUAU_FASTINTVARIABLE(LuauSubtypingReasoningLimit, 100)
-LUAU_FASTFLAGVARIABLE(LuauRetrySubtypingWithoutHiddenPack)
+LUAU_FASTFLAGVARIABLE(LuauSubtypingEnableReasoningLimit)
 
 namespace Luau
 {
@@ -33,7 +31,7 @@ struct VarianceFlipper
     Subtyping::Variance* variance;
     Subtyping::Variance oldValue;
 
-    VarianceFlipper(Subtyping::Variance* v)
+    explicit VarianceFlipper(Subtyping::Variance* v)
         : variance(v)
         , oldValue(*v)
     {
@@ -101,6 +99,9 @@ static SubtypingReasonings mergeReasonings(const SubtypingReasonings& a, const S
             else
                 result.insert(r);
         }
+
+        if (FFlag::LuauSubtypingEnableReasoningLimit && result.size() >= size_t(FInt::LuauSubtypingReasoningLimit))
+            return result;
     }
 
     for (const SubtypingReasoning& r : b)
@@ -117,6 +118,9 @@ static SubtypingReasonings mergeReasonings(const SubtypingReasonings& a, const S
             else
                 result.insert(r);
         }
+
+        if (FFlag::LuauSubtypingEnableReasoningLimit && result.size() >= size_t(FInt::LuauSubtypingReasoningLimit))
+            return result;
     }
 
     return result;
@@ -309,7 +313,7 @@ struct ApplyMappedGenerics : Substitution
 
     bool ignoreChildren(TypeId ty) override
     {
-        if (get<ClassType>(ty))
+        if (get<ExternType>(ty))
             return true;
 
         return ty->persistent;
@@ -397,12 +401,14 @@ TypePackId* SubtypingEnvironment::getMappedPackBounds(TypePackId tp)
 Subtyping::Subtyping(
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<TypeArena> typeArena,
+    NotNull<Simplifier> simplifier,
     NotNull<Normalizer> normalizer,
     NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<InternalErrorReporter> iceReporter
 )
     : builtinTypes(builtinTypes)
     , arena(typeArena)
+    , simplifier(simplifier)
     , normalizer(normalizer)
     , typeFunctionRuntime(typeFunctionRuntime)
     , iceReporter(iceReporter)
@@ -415,6 +421,14 @@ SubtypingResult Subtyping::isSubtype(TypeId subTy, TypeId superTy, NotNull<Scope
 
     SubtypingResult result = isCovariantWith(env, subTy, superTy, scope);
 
+    if (result.normalizationTooComplex)
+    {
+        if (result.isCacheable)
+            resultCache[{subTy, superTy}] = result;
+
+        return result;
+    }
+
     for (const auto& [subTy, bounds] : env.mappedGenerics)
     {
         const auto& lb = bounds.lowerBound;
@@ -592,7 +606,12 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
         if (!result.isSubtype && !result.normalizationTooComplex)
         {
             SubtypingResult semantic = isCovariantWith(env, normalizer->normalize(subTy), normalizer->normalize(superTy), scope);
-            if (semantic.isSubtype)
+
+            if (semantic.normalizationTooComplex)
+            {
+                result = semantic;
+            }
+            else if (semantic.isSubtype)
             {
                 semantic.reasoning.clear();
                 result = semantic;
@@ -607,7 +626,12 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
         if (!result.isSubtype && !result.normalizationTooComplex)
         {
             SubtypingResult semantic = isCovariantWith(env, normalizer->normalize(subTy), normalizer->normalize(superTy), scope);
-            if (semantic.isSubtype)
+
+            if (semantic.normalizationTooComplex)
+            {
+                result = semantic;
+            }
+            else if (semantic.isSubtype)
             {
                 // Clear the semantic reasoning, as any reasonings within
                 // potentially contain invalid paths.
@@ -718,9 +742,9 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
         result = isCovariantWith(env, p, scope);
     else if (auto p = get2<MetatableType, TableType>(subTy, superTy))
         result = isCovariantWith(env, p, scope);
-    else if (auto p = get2<ClassType, ClassType>(subTy, superTy))
+    else if (auto p = get2<ExternType, ExternType>(subTy, superTy))
         result = isCovariantWith(env, p, scope);
-    else if (auto p = get2<ClassType, TableType>(subTy, superTy))
+    else if (auto p = get2<ExternType, TableType>(subTy, superTy))
         result = isCovariantWith(env, subTy, p.first, superTy, p.second, scope);
     else if (auto p = get2<TableType, PrimitiveType>(subTy, superTy))
         result = isCovariantWith(env, p, scope);
@@ -753,7 +777,8 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
     // Match head types pairwise
 
     for (size_t i = 0; i < headSize; ++i)
-        results.push_back(isCovariantWith(env, subHead[i], superHead[i], scope).withBothComponent(TypePath::Index{i}));
+        results.push_back(isCovariantWith(env, subHead[i], superHead[i], scope).withBothComponent(TypePath::Index{i, TypePath::Index::Variant::Pack})
+        );
 
     // Handle mismatched head sizes
 
@@ -766,7 +791,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
                 for (size_t i = headSize; i < superHead.size(); ++i)
                     results.push_back(isCovariantWith(env, vt->ty, superHead[i], scope)
                                           .withSubPath(TypePath::PathBuilder().tail().variadic().build())
-                                          .withSuperComponent(TypePath::Index{i}));
+                                          .withSuperComponent(TypePath::Index{i, TypePath::Index::Variant::Pack}));
             }
             else if (auto gt = get<GenericTypePack>(*subTail))
             {
@@ -820,7 +845,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
             {
                 for (size_t i = headSize; i < subHead.size(); ++i)
                     results.push_back(isCovariantWith(env, subHead[i], vt->ty, scope)
-                                          .withSubComponent(TypePath::Index{i})
+                                          .withSubComponent(TypePath::Index{i, TypePath::Index::Variant::Pack})
                                           .withSuperPath(TypePath::PathBuilder().tail().variadic().build()));
             }
             else if (auto gt = get<GenericTypePack>(*superTail))
@@ -858,7 +883,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
             else
                 return SubtypingResult{false}
                     .withSuperComponent(TypePath::PackField::Tail)
-                    .withError({scope->location, UnexpectedTypePackInSubtyping{*subTail}});
+                    .withError({scope->location, UnexpectedTypePackInSubtyping{*superTail}});
         }
         else
             return {false};
@@ -1081,6 +1106,10 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     for (TypeId ty : superUnion)
     {
         SubtypingResult next = isCovariantWith(env, subTy, ty, scope);
+
+        if (next.normalizationTooComplex)
+            return SubtypingResult{false, /* normalizationTooComplex */ true};
+
         if (next.isSubtype)
             return SubtypingResult{true};
     }
@@ -1099,7 +1128,13 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Unio
     std::vector<SubtypingResult> subtypings;
     size_t i = 0;
     for (TypeId ty : subUnion)
-        subtypings.push_back(isCovariantWith(env, ty, superTy, scope).withSubComponent(TypePath::Index{i++}));
+    {
+        subtypings.push_back(isCovariantWith(env, ty, superTy, scope).withSubComponent(TypePath::Index{i++, TypePath::Index::Variant::Union}));
+
+        if (subtypings.back().normalizationTooComplex)
+            return SubtypingResult{false, /* normalizationTooComplex */ true};
+    }
+
     return SubtypingResult::all(subtypings);
 }
 
@@ -1109,7 +1144,13 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     std::vector<SubtypingResult> subtypings;
     size_t i = 0;
     for (TypeId ty : superIntersection)
-        subtypings.push_back(isCovariantWith(env, subTy, ty, scope).withSuperComponent(TypePath::Index{i++}));
+    {
+        subtypings.push_back(isCovariantWith(env, subTy, ty, scope).withSuperComponent(TypePath::Index{i++, TypePath::Index::Variant::Intersection}));
+
+        if (subtypings.back().normalizationTooComplex)
+            return SubtypingResult{false, /* normalizationTooComplex */ true};
+    }
+
     return SubtypingResult::all(subtypings);
 }
 
@@ -1119,7 +1160,13 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Inte
     std::vector<SubtypingResult> subtypings;
     size_t i = 0;
     for (TypeId ty : subIntersection)
-        subtypings.push_back(isCovariantWith(env, ty, superTy, scope).withSubComponent(TypePath::Index{i++}));
+    {
+        subtypings.push_back(isCovariantWith(env, ty, superTy, scope).withSubComponent(TypePath::Index{i++, TypePath::Index::Variant::Intersection}));
+
+        if (subtypings.back().normalizationTooComplex)
+            return SubtypingResult{false, /* normalizationTooComplex */ true};
+    }
+
     return SubtypingResult::any(subtypings);
 }
 
@@ -1287,7 +1334,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
     }
     // the top class type is not actually a primitive type, so the negation of
     // any one of them includes the top class type.
-    else if (auto p = get2<ClassType, PrimitiveType>(subTy, negatedTy))
+    else if (auto p = get2<ExternType, PrimitiveType>(subTy, negatedTy))
         result = {true};
     else if (auto p = get<PrimitiveType>(negatedTy); p && is<TableType, MetatableType>(subTy))
         result = {p->type != PrimitiveType::Table};
@@ -1295,9 +1342,9 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
         result = {p.second->type != PrimitiveType::Function};
     else if (auto p = get2<SingletonType, SingletonType>(subTy, negatedTy))
         result = {*p.first != *p.second};
-    else if (auto p = get2<ClassType, ClassType>(subTy, negatedTy))
+    else if (auto p = get2<ExternType, ExternType>(subTy, negatedTy))
         result = SubtypingResult::negate(isCovariantWith(env, p.first, p.second, scope));
-    else if (get2<FunctionType, ClassType>(subTy, negatedTy))
+    else if (get2<FunctionType, ExternType>(subTy, negatedTy))
         result = {true};
     else if (is<ErrorType, FunctionType, TableType, MetatableType>(negatedTy))
         iceReporter->ice("attempting to negate a non-testable type");
@@ -1395,17 +1442,9 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Tabl
 
 SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const MetatableType* subMt, const MetatableType* superMt, NotNull<Scope> scope)
 {
-    if (DFInt::LuauTypeSolverRelease >= 646)
+    return isCovariantWith(env, subMt->table, superMt->table, scope)
-    {
+        .withBothComponent(TypePath::TypeField::Table)
-        return isCovariantWith(env, subMt->table, superMt->table, scope)
+        .andAlso(isCovariantWith(env, subMt->metatable, superMt->metatable, scope).withBothComponent(TypePath::TypeField::Metatable));
-            .withBothComponent(TypePath::TypeField::Table)
-            .andAlso(isCovariantWith(env, subMt->metatable, superMt->metatable, scope).withBothComponent(TypePath::TypeField::Metatable));
-    }
-    else
-    {
-        return isCovariantWith(env, subMt->table, superMt->table, scope)
-            .andAlso(isCovariantWith(env, subMt->metatable, superMt->metatable, scope).withBothComponent(TypePath::TypeField::Metatable));
-    }
 }
 
 SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const MetatableType* subMt, const TableType* superTable, NotNull<Scope> scope)
@@ -1417,7 +1456,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Meta
         // of the supertype table.
         //
         // There's a flaw here in that if the __index metamethod contributes a new
-        // field that would satisfy the subtyping relationship, we'll erronously say
+        // field that would satisfy the subtyping relationship, we'll erroneously say
         // that the metatable isn't a subtype of the table, even though they have
         // compatible properties/shapes. We'll revisit this later when we have a
         // better understanding of how important this is.
@@ -1430,15 +1469,15 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Meta
     }
 }
 
-SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const ClassType* subClass, const ClassType* superClass, NotNull<Scope> scope)
+SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const ExternType* subExternType, const ExternType* superExternType, NotNull<Scope> scope)
 {
-    return {isSubclass(subClass, superClass)};
+    return {isSubclass(subExternType, superExternType)};
 }
 
 SubtypingResult Subtyping::isCovariantWith(
     SubtypingEnvironment& env,
     TypeId subTy,
-    const ClassType* subClass,
+    const ExternType* subExternType,
     TypeId superTy,
     const TableType* superTable,
     NotNull<Scope> scope
@@ -1450,7 +1489,7 @@ SubtypingResult Subtyping::isCovariantWith(
 
     for (const auto& [name, prop] : superTable->props)
     {
-        if (auto classProp = lookupClassProp(subClass, name))
+        if (auto classProp = lookupExternTypeProp(subExternType, name))
         {
             result.andAlso(isCovariantWith(env, *classProp, prop, name, scope));
         }
@@ -1481,15 +1520,14 @@ SubtypingResult Subtyping::isCovariantWith(
 
         // If subtyping failed in the argument packs, we should check if there's a hidden variadic tail and try ignoring it.
         // This might cause subtyping correctly because the sub type here may not have a hidden variadic tail or equivalent.
-        if (FFlag::LuauRetrySubtypingWithoutHiddenPack && !result.isSubtype)
+        if (!result.isSubtype)
         {
             auto [arguments, tail] = flatten(superFunction->argTypes);
 
             if (auto variadic = get<VariadicTypePack>(tail); variadic && variadic->hidden)
             {
-                result.orElse(
+                result.orElse(isContravariantWith(env, subFunction->argTypes, arena->addTypePack(TypePack{arguments}), scope)
-                    isContravariantWith(env, subFunction->argTypes, arena->addTypePack(TypePack{arguments}), scope).withBothComponent(TypePath::PackField::Arguments)
+                                  .withBothComponent(TypePath::PackField::Arguments));
-                );
             }
         }
     }
@@ -1621,7 +1659,7 @@ SubtypingResult Subtyping::isCovariantWith(
     SubtypingResult result = isCovariantWith(env, subNorm->tops, superNorm->tops, scope);
     result.andAlso(isCovariantWith(env, subNorm->booleans, superNorm->booleans, scope));
     result.andAlso(
-        isCovariantWith(env, subNorm->classes, superNorm->classes, scope).orElse(isCovariantWith(env, subNorm->classes, superNorm->tables, scope))
+        isCovariantWith(env, subNorm->externTypes, superNorm->externTypes, scope).orElse(isCovariantWith(env, subNorm->externTypes, superNorm->tables, scope))
     );
     result.andAlso(isCovariantWith(env, subNorm->errors, superNorm->errors, scope));
     result.andAlso(isCovariantWith(env, subNorm->nils, superNorm->nils, scope));
@@ -1638,24 +1676,24 @@ SubtypingResult Subtyping::isCovariantWith(
 
 SubtypingResult Subtyping::isCovariantWith(
     SubtypingEnvironment& env,
-    const NormalizedClassType& subClass,
+    const NormalizedExternType& subExternType,
-    const NormalizedClassType& superClass,
+    const NormalizedExternType& superExternType,
     NotNull<Scope> scope
 )
 {
-    for (const auto& [subClassTy, _] : subClass.classes)
+    for (const auto& [subExternTypeTy, _] : subExternType.externTypes)
     {
         SubtypingResult result;
 
-        for (const auto& [superClassTy, superNegations] : superClass.classes)
+        for (const auto& [superExternTypeTy, superNegations] : superExternType.externTypes)
         {
-            result.orElse(isCovariantWith(env, subClassTy, superClassTy, scope));
+            result.orElse(isCovariantWith(env, subExternTypeTy, superExternTypeTy, scope));
             if (!result.isSubtype)
                 continue;
 
             for (TypeId negation : superNegations)
             {
-                result.andAlso(SubtypingResult::negate(isCovariantWith(env, subClassTy, negation, scope)));
+                result.andAlso(SubtypingResult::negate(isCovariantWith(env, subExternTypeTy, negation, scope)));
                 if (result.isSubtype)
                     break;
             }
@@ -1670,17 +1708,17 @@ SubtypingResult Subtyping::isCovariantWith(
 
 SubtypingResult Subtyping::isCovariantWith(
     SubtypingEnvironment& env,
-    const NormalizedClassType& subClass,
+    const NormalizedExternType& subExternType,
     const TypeIds& superTables,
     NotNull<Scope> scope
 )
 {
-    for (const auto& [subClassTy, _] : subClass.classes)
+    for (const auto& [subExternTypeTy, _] : subExternType.externTypes)
     {
         SubtypingResult result;
 
         for (TypeId superTableTy : superTables)
-            result.orElse(isCovariantWith(env, subClassTy, superTableTy, scope));
+            result.orElse(isCovariantWith(env, subExternTypeTy, superTableTy, scope));
 
         if (!result.isSubtype)
             return result;
@@ -1768,7 +1806,12 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
     {
         results.emplace_back();
         for (TypeId superTy : superTypes)
+        {
             results.back().orElse(isCovariantWith(env, subTy, superTy, scope));
+
+            if (results.back().normalizationTooComplex)
+                return SubtypingResult{false, /* normalizationTooComplex */ true};
+        }
     }
 
     return SubtypingResult::all(results);
@@ -1870,7 +1913,7 @@ TypeId Subtyping::makeAggregateType(const Container& container, TypeId orElse)
 
 std::pair<TypeId, ErrorVec> Subtyping::handleTypeFunctionReductionResult(const TypeFunctionInstanceType* functionInstance, NotNull<Scope> scope)
 {
-    TypeFunctionContext context{arena, builtinTypes, scope, normalizer, typeFunctionRuntime, iceReporter, NotNull{&limits}};
+    TypeFunctionContext context{arena, builtinTypes, scope, simplifier, normalizer, typeFunctionRuntime, iceReporter, NotNull{&limits}};
     TypeId function = arena->addType(*functionInstance);
     FunctionGraphReductionResult result = reduceTypeFunctions(function, {}, context, true);
     ErrorVec errors;

Analysis/src/Symbol.cpp

@@ -4,7 +4,6 @@
 #include "Luau/Common.h"
 
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAGVARIABLE(LuauSymbolEquality)
 
 namespace Luau
 {
@@ -15,10 +14,8 @@ bool Symbol::operator==(const Symbol& rhs) const
         return local == rhs.local;
     else if (global.value)
         return rhs.global.value && global == rhs.global.value; // Subtlety: AstName::operator==(const char*) uses strcmp, not pointer identity.
-    else if (FFlag::LuauSolverV2 || FFlag::LuauSymbolEquality)
-        return !rhs.local && !rhs.global.value; // Reflexivity: we already know `this` Symbol is empty, so check that rhs is.
     else
-        return false;
+        return !rhs.local && !rhs.global.value; // Reflexivity: we already know `this` Symbol is empty, so check that rhs is.
 }
 
 std::string toString(const Symbol& name)

Analysis/src/TableLiteralInference.cpp

@@ -1,15 +1,21 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 
+#include "Luau/TableLiteralInference.h"
+
 #include "Luau/Ast.h"
+#include "Luau/Common.h"
 #include "Luau/Normalize.h"
 #include "Luau/Simplify.h"
+#include "Luau/Subtyping.h"
 #include "Luau/Type.h"
 #include "Luau/ToString.h"
 #include "Luau/TypeArena.h"
 #include "Luau/TypeUtils.h"
 #include "Luau/Unifier2.h"
 
-LUAU_DYNAMIC_FASTINT(LuauTypeSolverRelease)
+LUAU_FASTFLAGVARIABLE(LuauBidirectionalInferenceCollectIndexerTypes)
+LUAU_FASTFLAGVARIABLE(LuauBidirectionalFailsafe)
+LUAU_FASTFLAGVARIABLE(LuauBidirectionalInferenceElideAssert)
 
 namespace Luau
 {
@@ -111,6 +117,7 @@ TypeId matchLiteralType(
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<TypeArena> arena,
     NotNull<Unifier2> unifier,
+    NotNull<Subtyping> subtyping,
     TypeId expectedType,
     TypeId exprType,
     const AstExpr* expr,
@@ -131,17 +138,33 @@ TypeId matchLiteralType(
      * things like replace explicit named properties with indexers as required
      * by the expected type.
      */
+
     if (!isLiteral(expr))
-        return exprType;
+    {
+        auto result = subtyping->isSubtype(/*subTy=*/exprType, /*superTy=*/expectedType, unifier->scope);
+        return result.isSubtype ? expectedType : exprType;
+    }
 
     expectedType = follow(expectedType);
     exprType = follow(exprType);
 
-    if (get<AnyType>(expectedType) || get<UnknownType>(expectedType))
+    if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
     {
-        // "Narrowing" to unknown or any is not going to do anything useful.
+        // The intent of `matchLiteralType` is to upcast values when it's safe
-        return exprType;
+        // to do so. it's always safe to upcast to `any` or `unknown`, so we
+        // can unconditionally do so here.
+        if (is<AnyType, UnknownType>(expectedType))
+            return expectedType;
     }
+    else
+    {
+        if (get<AnyType>(expectedType) || get<UnknownType>(expectedType))
+        {
+            // "Narrowing" to unknown or any is not going to do anything useful.
+            return exprType;
+        }
+    }
+
 
     if (expr->is<AstExprConstantString>())
     {
@@ -209,11 +232,27 @@ TypeId matchLiteralType(
         return exprType;
     }
 
-    // TODO: lambdas
+
+    if (expr->is<AstExprFunction>())
+    {
+        // TODO: Push argument / return types into the lambda. For now, just do
+        // the non-literal thing: check for a subtype and upcast if valid.
+        auto result = subtyping->isSubtype(/*subTy=*/exprType, /*superTy=*/expectedType, unifier->scope);
+        return result.isSubtype ? expectedType : exprType;
+    }
 
     if (auto exprTable = expr->as<AstExprTable>())
     {
         TableType* const tableTy = getMutable<TableType>(exprType);
+
+        // This can occur if we have an expression like:
+        //
+        //  { x = {}, x = 42 }
+        //
+        // The type of this will be `{ x: number }`
+        if (FFlag::LuauBidirectionalFailsafe && !tableTy)
+            return exprType;
+
         LUAU_ASSERT(tableTy);
 
         const TableType* expectedTableTy = get<TableType>(expectedType);
@@ -228,7 +267,7 @@ TypeId matchLiteralType(
 
                 if (tt)
                 {
-                    TypeId res = matchLiteralType(astTypes, astExpectedTypes, builtinTypes, arena, unifier, *tt, exprType, expr, toBlock);
+                    TypeId res = matchLiteralType(astTypes, astExpectedTypes, builtinTypes, arena, unifier, subtyping, *tt, exprType, expr, toBlock);
 
                     parts.push_back(res);
                     return arena->addType(UnionType{std::move(parts)});
@@ -238,6 +277,11 @@ TypeId matchLiteralType(
             return exprType;
         }
 
+        DenseHashSet<AstExprConstantString*> keysToDelete{nullptr};
+
+        DenseHashSet<TypeId> indexerKeyTypes{nullptr};
+        DenseHashSet<TypeId> indexerValueTypes{nullptr};
+
         for (const AstExprTable::Item& item : exprTable->items)
         {
             if (isRecord(item))
@@ -245,12 +289,20 @@ TypeId matchLiteralType(
                 const AstArray<char>& s = item.key->as<AstExprConstantString>()->value;
                 std::string keyStr{s.data, s.data + s.size};
                 auto it = tableTy->props.find(keyStr);
+
+                // This can occur, potentially, if we are re-entrant.
+                if (FFlag::LuauBidirectionalFailsafe && it == tableTy->props.end())
+                    continue;
+
                 LUAU_ASSERT(it != tableTy->props.end());
 
                 Property& prop = it->second;
 
-                // Table literals always initially result in shared read-write types
+                // If we encounter a duplcate property, we may have already
-                LUAU_ASSERT(prop.isShared());
+                // set it to be read-only. If that's the case, the only thing
+                // that will definitely crash is trying to access a write
+                // only property.
+                LUAU_ASSERT(!prop.isWriteOnly());
                 TypeId propTy = *prop.readTy;
 
                 auto it2 = expectedTableTy->props.find(keyStr);
@@ -271,18 +323,27 @@ TypeId matchLiteralType(
                             builtinTypes,
                             arena,
                             unifier,
+                            subtyping,
                             expectedTableTy->indexer->indexResultType,
                             propTy,
                             item.value,
                             toBlock
                         );
 
-                        if (tableTy->indexer)
+                        if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
-                            unifier->unify(matchedType, tableTy->indexer->indexResultType);
+                        {
+                            indexerKeyTypes.insert(arena->addType(SingletonType{StringSingleton{keyStr}}));
+                            indexerValueTypes.insert(matchedType);
+                        }
                         else
-                            tableTy->indexer = TableIndexer{expectedTableTy->indexer->indexType, matchedType};
+                        {
+                            if (tableTy->indexer)
+                                unifier->unify(matchedType, tableTy->indexer->indexResultType);
+                            else
+                                tableTy->indexer = TableIndexer{expectedTableTy->indexer->indexType, matchedType};
+                        }
 
-                        tableTy->props.erase(keyStr);
+                        keysToDelete.insert(item.key->as<AstExprConstantString>());
                     }
 
                     // If it's just an extra property and the expected type
@@ -305,22 +366,25 @@ TypeId matchLiteralType(
                 // quadratic in a hurry.
                 if (expectedProp.isShared())
                 {
-                    matchedType =
+                    matchedType = matchLiteralType(
-                        matchLiteralType(astTypes, astExpectedTypes, builtinTypes, arena, unifier, *expectedReadTy, propTy, item.value, toBlock);
+                        astTypes, astExpectedTypes, builtinTypes, arena, unifier, subtyping, *expectedReadTy, propTy, item.value, toBlock
+                    );
                     prop.readTy = matchedType;
                     prop.writeTy = matchedType;
                 }
                 else if (expectedReadTy)
                 {
-                    matchedType =
+                    matchedType = matchLiteralType(
-                        matchLiteralType(astTypes, astExpectedTypes, builtinTypes, arena, unifier, *expectedReadTy, propTy, item.value, toBlock);
+                        astTypes, astExpectedTypes, builtinTypes, arena, unifier, subtyping, *expectedReadTy, propTy, item.value, toBlock
+                    );
                     prop.readTy = matchedType;
                     prop.writeTy.reset();
                 }
                 else if (expectedWriteTy)
                 {
-                    matchedType =
+                    matchedType = matchLiteralType(
-                        matchLiteralType(astTypes, astExpectedTypes, builtinTypes, arena, unifier, *expectedWriteTy, propTy, item.value, toBlock);
+                        astTypes, astExpectedTypes, builtinTypes, arena, unifier, subtyping, *expectedWriteTy, propTy, item.value, toBlock
+                    );
                     prop.readTy.reset();
                     prop.writeTy = matchedType;
                 }
@@ -337,10 +401,16 @@ TypeId matchLiteralType(
                 LUAU_ASSERT(matchedType);
 
                 (*astExpectedTypes)[item.value] = matchedType;
+                // NOTE: We do *not* add to the potential indexer types here.
+                // I think this is correct to support something like:
+                //
+                //  { [string]: number, foo: boolean }
+                //
             }
             else if (item.kind == AstExprTable::Item::List)
             {
-                LUAU_ASSERT(tableTy->indexer);
+                if (!FFlag::LuauBidirectionalInferenceCollectIndexerTypes || !FFlag::LuauBidirectionalInferenceElideAssert)
+                    LUAU_ASSERT(tableTy->indexer);
 
                 if (expectedTableTy->indexer)
                 {
@@ -354,15 +424,24 @@ TypeId matchLiteralType(
                         builtinTypes,
                         arena,
                         unifier,
+                        subtyping,
                         expectedTableTy->indexer->indexResultType,
                         *propTy,
                         item.value,
                         toBlock
                     );
 
-                    // if the index result type is the prop type, we can replace it with the matched type here.
+                    if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
-                    if (tableTy->indexer->indexResultType == *propTy)
+                    {
-                        tableTy->indexer->indexResultType = matchedType;
+                        indexerKeyTypes.insert(builtinTypes->numberType);
+                        indexerValueTypes.insert(matchedType);
+                    }
+                    else
+                    {
+                        // if the index result type is the prop type, we can replace it with the matched type here.
+                        if (tableTy->indexer->indexResultType == *propTy)
+                            tableTy->indexer->indexResultType = matchedType;
+                    }
                 }
             }
             else if (item.kind == AstExprTable::Item::General)
@@ -376,29 +455,32 @@ TypeId matchLiteralType(
                 const TypeId* keyTy = astTypes->find(item.key);
                 LUAU_ASSERT(keyTy);
                 TypeId tKey = follow(*keyTy);
-                if (DFInt::LuauTypeSolverRelease >= 648)
+                LUAU_ASSERT(!is<BlockedType>(tKey));
-                {
-                    LUAU_ASSERT(!is<BlockedType>(tKey));
-                }
-                else if (get<BlockedType>(tKey))
-                    toBlock.push_back(tKey);
                 const TypeId* propTy = astTypes->find(item.value);
                 LUAU_ASSERT(propTy);
                 TypeId tProp = follow(*propTy);
-                if (DFInt::LuauTypeSolverRelease >= 648)
+                LUAU_ASSERT(!is<BlockedType>(tProp));
-                {
-                    LUAU_ASSERT(!is<BlockedType>(tKey));
-                }
-                else if (get<BlockedType>(tProp))
-                    toBlock.push_back(tProp);
                 // Populate expected types for non-string keys declared with [] (the code below will handle the case where they are strings)
                 if (!item.key->as<AstExprConstantString>() && expectedTableTy->indexer)
                     (*astExpectedTypes)[item.key] = expectedTableTy->indexer->indexType;
+
+                if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
+                {
+                    indexerKeyTypes.insert(tKey);
+                    indexerValueTypes.insert(tProp);
+                }
             }
             else
                 LUAU_ASSERT(!"Unexpected");
         }
 
+        for (const auto& key : keysToDelete)
+        {
+            const AstArray<char>& s = key->value;
+            std::string keyStr{s.data, s.data + s.size};
+            tableTy->props.erase(keyStr);
+        }
+
         // Keys that the expectedType says we should have, but that aren't
         // specified by the AST fragment.
         //
@@ -448,9 +530,39 @@ TypeId matchLiteralType(
         // have one too.
         // TODO: If the expected table also has an indexer, we might want to
         // push the expected indexer's types into it.
-        if (expectedTableTy->indexer && !tableTy->indexer)
+        if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes && expectedTableTy->indexer)
         {
-            tableTy->indexer = expectedTableTy->indexer;
+            if (indexerValueTypes.size() > 0 && indexerKeyTypes.size() > 0)
+            {
+                TypeId inferredKeyType = builtinTypes->neverType;
+                TypeId inferredValueType = builtinTypes->neverType;
+                for (auto kt : indexerKeyTypes)
+                {
+                    auto simplified = simplifyUnion(builtinTypes, arena, inferredKeyType, kt);
+                    inferredKeyType = simplified.result;
+                }
+                for (auto vt : indexerValueTypes)
+                {
+                    auto simplified = simplifyUnion(builtinTypes, arena, inferredValueType, vt);
+                    inferredValueType = simplified.result;
+                }
+                tableTy->indexer = TableIndexer{inferredKeyType, inferredValueType};
+                auto keyCheck = subtyping->isSubtype(inferredKeyType, expectedTableTy->indexer->indexType, unifier->scope);
+                if (keyCheck.isSubtype)
+                    tableTy->indexer->indexType = expectedTableTy->indexer->indexType;
+                auto valueCheck = subtyping->isSubtype(inferredValueType, expectedTableTy->indexer->indexResultType, unifier->scope);
+                if (valueCheck.isSubtype)
+                    tableTy->indexer->indexResultType = expectedTableTy->indexer->indexResultType;
+            }
+            else
+                LUAU_ASSERT(indexerKeyTypes.empty() && indexerValueTypes.empty());
+        }
+        else
+        {
+            if (expectedTableTy->indexer && !tableTy->indexer)
+            {
+                tableTy->indexer = expectedTableTy->indexer;
+            }
         }
     }
 

Analysis/src/ToDot.cpp

@@ -299,9 +299,9 @@ void StateDot::visitChildren(TypeId ty, int index)
             finishNodeLabel(ty);
             finishNode();
         }
-        else if constexpr (std::is_same_v<T, ClassType>)
+        else if constexpr (std::is_same_v<T, ExternType>)
         {
-            formatAppend(result, "ClassType %s", t.name.c_str());
+            formatAppend(result, "ExternType %s", t.name.c_str());
             finishNodeLabel(ty);
             finishNode();
 
@@ -420,7 +420,7 @@ void StateDot::visitChildren(TypePackId tp, int index)
         finishNodeLabel(tp);
         finishNode();
     }
-    else if (get<Unifiable::Error>(tp))
+    else if (get<ErrorTypePack>(tp))
     {
         formatAppend(result, "ErrorTypePack %d", index);
         finishNodeLabel(tp);

Analysis/src/ToString.cpp

@@ -19,7 +19,11 @@
 #include <stdexcept>
 #include <string>
 
+LUAU_FASTFLAGVARIABLE(LuauEnableDenseTableAlias)
+
 LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAGVARIABLE(LuauSyntheticErrors)
+LUAU_FASTFLAGVARIABLE(LuauStringPartLengthLimit)
 
 /*
  * Enables increasing levels of verbosity for Luau type names when stringifying.
@@ -119,7 +123,7 @@ struct FindCyclicTypes final : TypeVisitor
         return true;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -300,6 +304,28 @@ struct StringifierState
         emit(std::to_string(i).c_str());
     }
 
+    void emit(Polarity p)
+    {
+        switch (p)
+        {
+        case Polarity::None:
+            emit("  ");
+            break;
+        case Polarity::Negative:
+            emit(" -");
+            break;
+        case Polarity::Positive:
+            emit("+ ");
+            break;
+        case Polarity::Mixed:
+            emit("+-");
+            break;
+        default:
+            emit("!!");
+            break;
+        }
+    }
+
     void indent()
     {
         indentation += 4;
@@ -481,6 +507,8 @@ struct TypeStringifier
             {
                 state.emit("'");
                 state.emit(state.getName(ty));
+                if (FInt::DebugLuauVerboseTypeNames >= 1)
+                    state.emit(ftv.polarity);
             }
             else
             {
@@ -493,6 +521,9 @@ struct TypeStringifier
                 state.emit("'");
                 state.emit(state.getName(ty));
 
+                if (FInt::DebugLuauVerboseTypeNames >= 1)
+                    state.emit(ftv.polarity);
+
                 if (!get<UnknownType>(upperBound))
                 {
                     state.emit(" <: ");
@@ -508,6 +539,9 @@ struct TypeStringifier
 
         state.emit(state.getName(ty));
 
+        if (FFlag::LuauSolverV2 && FInt::DebugLuauVerboseTypeNames >= 1)
+            state.emit(ftv.polarity);
+
         if (FInt::DebugLuauVerboseTypeNames >= 2)
         {
             state.emit("-");
@@ -537,6 +571,9 @@ struct TypeStringifier
         else
             state.emit(state.getName(ty));
 
+        if (FInt::DebugLuauVerboseTypeNames >= 1)
+            state.emit(gtv.polarity);
+
         if (FInt::DebugLuauVerboseTypeNames >= 2)
         {
             state.emit("-");
@@ -685,7 +722,13 @@ struct TypeStringifier
         if (ttv.boundTo)
             return stringify(*ttv.boundTo);
 
-        if (!state.exhaustive)
+        bool showName = !state.exhaustive;
+        if (FFlag::LuauEnableDenseTableAlias)
+        {
+            // if hide table alias expansions are enabled and there is a name found for the table, use it
+            showName = !state.exhaustive || state.opts.hideTableAliasExpansions;
+        }
+        if (showName)
         {
             if (ttv.name)
             {
@@ -708,6 +751,10 @@ struct TypeStringifier
                 stringify(ttv.instantiatedTypeParams, ttv.instantiatedTypePackParams);
                 return;
             }
+        }
+
+        if (!state.exhaustive)
+        {
             if (ttv.syntheticName)
             {
                 state.result.invalid = true;
@@ -846,9 +893,9 @@ struct TypeStringifier
         state.emit(" }");
     }
 
-    void operator()(TypeId, const ClassType& ctv)
+    void operator()(TypeId, const ExternType& etv)
     {
-        state.emit(ctv.name);
+        state.emit(etv.name);
     }
 
     void operator()(TypeId, const AnyType&)
@@ -876,6 +923,9 @@ struct TypeStringifier
         bool hasNonNilDisjunct = false;
 
         std::vector<std::string> results = {};
+        size_t resultsLength = 0;
+        bool lengthLimitHit = false;
+
         for (auto el : &uv)
         {
             el = follow(el);
@@ -902,14 +952,34 @@ struct TypeStringifier
             if (needParens)
                 state.emit(")");
 
+            if (FFlag::LuauStringPartLengthLimit)
+                resultsLength += state.result.name.length();
+
             results.push_back(std::move(state.result.name));
+
             state.result.name = std::move(saved);
+
+            if (FFlag::LuauStringPartLengthLimit)
+            {
+                lengthLimitHit = state.opts.maxTypeLength > 0 && resultsLength > state.opts.maxTypeLength;
+
+                if (lengthLimitHit)
+                    break;
+            }
         }
 
         state.unsee(&uv);
 
-        if (!FFlag::DebugLuauToStringNoLexicalSort)
+        if (FFlag::LuauStringPartLengthLimit)
-            std::sort(results.begin(), results.end());
+        {
+            if (!lengthLimitHit && !FFlag::DebugLuauToStringNoLexicalSort)
+                std::sort(results.begin(), results.end());
+        }
+        else
+        {
+            if (!FFlag::DebugLuauToStringNoLexicalSort)
+                std::sort(results.begin(), results.end());
+        }
 
         if (optional && results.size() > 1)
             state.emit("(");
@@ -953,6 +1023,9 @@ struct TypeStringifier
         }
 
         std::vector<std::string> results = {};
+        size_t resultsLength = 0;
+        bool lengthLimitHit = false;
+
         for (auto el : uv.parts)
         {
             el = follow(el);
@@ -969,14 +1042,34 @@ struct TypeStringifier
             if (needParens)
                 state.emit(")");
 
+            if (FFlag::LuauStringPartLengthLimit)
+                resultsLength += state.result.name.length();
+
             results.push_back(std::move(state.result.name));
+
             state.result.name = std::move(saved);
+
+            if (FFlag::LuauStringPartLengthLimit)
+            {
+                lengthLimitHit = state.opts.maxTypeLength > 0 && resultsLength > state.opts.maxTypeLength;
+
+                if (lengthLimitHit)
+                    break;
+            }
         }
 
         state.unsee(&uv);
 
-        if (!FFlag::DebugLuauToStringNoLexicalSort)
+        if (FFlag::LuauStringPartLengthLimit)
-            std::sort(results.begin(), results.end());
+        {
+            if (!lengthLimitHit && !FFlag::DebugLuauToStringNoLexicalSort)
+                std::sort(results.begin(), results.end());
+        }
+        else
+        {
+            if (!FFlag::DebugLuauToStringNoLexicalSort)
+                std::sort(results.begin(), results.end());
+        }
 
         bool first = true;
         bool shouldPlaceOnNewlines = results.size() > state.opts.compositeTypesSingleLineLimit || isOverloadedFunction(ty);
@@ -998,7 +1091,15 @@ struct TypeStringifier
     void operator()(TypeId, const ErrorType& tv)
     {
         state.result.error = true;
-        state.emit("*error-type*");
+
+        if (FFlag::LuauSyntheticErrors && tv.synthetic)
+        {
+            state.emit("*error-type<");
+            stringify(*tv.synthetic);
+            state.emit(">*");
+        }
+        else
+            state.emit("*error-type*");
     }
 
     void operator()(TypeId, const LazyType& ltv)
@@ -1173,10 +1274,18 @@ struct TypePackStringifier
         state.unsee(&tp);
     }
 
-    void operator()(TypePackId, const Unifiable::Error& error)
+    void operator()(TypePackId, const ErrorTypePack& error)
     {
         state.result.error = true;
-        state.emit("*error-type*");
+
+        if (FFlag::LuauSyntheticErrors && error.synthetic)
+        {
+            state.emit("*");
+            stringify(*error.synthetic);
+            state.emit("*");
+        }
+        else
+            state.emit("*error-type*");
     }
 
     void operator()(TypePackId, const VariadicTypePack& pack)
@@ -1205,6 +1314,9 @@ struct TypePackStringifier
             state.emit(state.getName(tp));
         }
 
+        if (FInt::DebugLuauVerboseTypeNames >= 1)
+            state.emit(pack.polarity);
+
         if (FInt::DebugLuauVerboseTypeNames >= 2)
         {
             state.emit("-");
@@ -1224,6 +1336,9 @@ struct TypePackStringifier
             state.emit("free-");
         state.emit(state.getName(tp));
 
+        if (FInt::DebugLuauVerboseTypeNames >= 1)
+            state.emit(pack.polarity);
+
         if (FInt::DebugLuauVerboseTypeNames >= 2)
         {
             state.emit("-");
@@ -1848,6 +1963,8 @@ std::string toString(const Constraint& constraint, ToStringOptions& opts)
         }
         else if constexpr (std::is_same_v<T, EqualityConstraint>)
             return "equality: " + tos(c.resultType) + " ~ " + tos(c.assignmentType);
+        else if constexpr (std::is_same_v<T, TableCheckConstraint>)
+            return "table_check " + tos(c.expectedType) + " :> " + tos(c.exprType);
         else
             static_assert(always_false_v<T>, "Non-exhaustive constraint switch");
     };