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/benchmark.yml

@@ -63,10 +63,10 @@ jobs:
           }
           valgrind --tool=callgrind ./luau-analyze --mode=nonstrict bench/other/LuauPolyfillMap.lua 2>&1 | filter map-nonstrict | tee -a analyze-output.txt
           valgrind --tool=callgrind ./luau-analyze --mode=strict bench/other/LuauPolyfillMap.lua 2>&1 | filter map-strict | tee -a analyze-output.txt
-          valgrind --tool=callgrind ./luau-analyze --mode=strict --fflags=DebugLuauDeferredConstraintResolution bench/other/LuauPolyfillMap.lua 2>&1 | filter map-dcr | tee -a analyze-output.txt
+          valgrind --tool=callgrind ./luau-analyze --mode=strict --fflags=LuauSolverV2 bench/other/LuauPolyfillMap.lua 2>&1 | filter map-dcr | tee -a analyze-output.txt
           valgrind --tool=callgrind ./luau-analyze --mode=nonstrict bench/other/regex.lua 2>&1 | filter regex-nonstrict | tee -a analyze-output.txt
           valgrind --tool=callgrind ./luau-analyze --mode=strict bench/other/regex.lua 2>&1 | filter regex-strict | tee -a analyze-output.txt
-          valgrind --tool=callgrind ./luau-analyze --mode=strict --fflags=DebugLuauDeferredConstraintResolution bench/other/regex.lua 2>&1 | filter regex-dcr | tee -a analyze-output.txt
+          valgrind --tool=callgrind ./luau-analyze --mode=strict --fflags=LuauSolverV2 bench/other/regex.lua 2>&1 | filter regex-dcr | tee -a analyze-output.txt
 
       - name: Run benchmark (compile)
         run: |

.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-analyze tests/conformance/assert.lua
-         ./luau-compile tests/conformance/assert.lua
+         ./luau tests/conformance/assert.luau
+         ./luau-analyze tests/conformance/assert.luau
+         ./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-analyze tests/conformance/assert.lua
-        Debug/luau-compile tests/conformance/assert.lua
+        Debug/luau tests/conformance/assert.luau
+        Debug/luau-analyze tests/conformance/assert.luau
+        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
-        os: [{name: ubuntu, version: ubuntu-20.04}, {name: macos, version: macos-latest}, {name: windows, version: windows-latest}]
+      matrix: # not using ubuntu-latest to improve compatibility
+        os: [{name: ubuntu, version: ubuntu-22.04}, {name: macos, version: macos-latest}, {name: windows, version: windows-latest}]
     name: ${{matrix.os.name}}
     runs-on: ${{matrix.os.version}}
     steps:
@@ -38,7 +38,7 @@ jobs:
     - name: configure
       run: cmake . -DCMAKE_BUILD_TYPE=Release
     - name: build
-      run: cmake --build . --target Luau.Repl.CLI Luau.Analyze.CLI Luau.Compile.CLI --config Release -j 2
+      run: cmake --build . --target Luau.Repl.CLI Luau.Analyze.CLI Luau.Compile.CLI Luau.Ast.CLI --config Release -j 2
     - name: pack
       if: matrix.os.name != 'windows'
       run: zip luau-${{matrix.os.name}}.zip luau*

.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
-        os: [{name: ubuntu, version: ubuntu-20.04}, {name: macos, version: macos-latest}, {name: windows, version: windows-latest}]
+      matrix: # not using ubuntu-latest to improve compatibility
+        os: [{name: ubuntu, version: ubuntu-22.04}, {name: macos, version: macos-latest}, {name: windows, version: windows-latest}]
     name: ${{matrix.os.name}}
     runs-on: ${{matrix.os.version}}
     steps:
@@ -23,17 +23,18 @@ jobs:
       run: cmake . -DCMAKE_BUILD_TYPE=Release
     - name: build
       run: cmake --build . --target Luau.Repl.CLI Luau.Analyze.CLI Luau.Compile.CLI --config Release -j 2
-    - uses: actions/upload-artifact@v2
+    - uses: actions/upload-artifact@v4
       if: matrix.os.name != 'windows'
       with:
         name: luau-${{matrix.os.name}}
         path: luau*
-    - uses: actions/upload-artifact@v2
+        overwrite: true
+    - uses: actions/upload-artifact@v4
       if: matrix.os.name == 'windows'
       with:
         name: luau-${{matrix.os.name}}
         path: Release\luau*.exe
-
+        overwrite: true
   web:
     runs-on: ubuntu-latest
     steps:
@@ -52,7 +53,8 @@ jobs:
         source emsdk/emsdk_env.sh
         emcmake cmake . -DLUAU_BUILD_WEB=ON -DCMAKE_BUILD_TYPE=Release
         make -j2 Luau.Web
-    - uses: actions/upload-artifact@v2
+    - uses: actions/upload-artifact@v4
       with:
         name: Luau.Web.js
         path: Luau.Web.js
+        overwrite: true

.gitignore

@@ -1,5 +1,6 @@
 /build/
 /build[.-]*/
+/out
 /cmake/
 /cmake[.-]*/
 /coverage/
@@ -12,6 +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/Autocomplete.h

@@ -1,10 +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/AutocompleteTypes.h"
 #include "Luau/Location.h"
 #include "Luau/Type.h"
 
-#include <unordered_map>
 #include <string>
 #include <memory>
 #include <optional>
@@ -16,89 +16,8 @@ struct Frontend;
 struct SourceModule;
 struct Module;
 struct TypeChecker;
-
-using ModulePtr = std::shared_ptr<Module>;
-
-enum class AutocompleteContext
-{
-    Unknown,
-    Expression,
-    Statement,
-    Property,
-    Type,
-    Keyword,
-    String,
-};
-
-enum class AutocompleteEntryKind
-{
-    Property,
-    Binding,
-    Keyword,
-    String,
-    Type,
-    Module,
-    GeneratedFunction,
-};
-
-enum class ParenthesesRecommendation
-{
-    None,
-    CursorAfter,
-    CursorInside,
-};
-
-enum class TypeCorrectKind
-{
-    None,
-    Correct,
-    CorrectFunctionResult,
-};
-
-struct AutocompleteEntry
-{
-    AutocompleteEntryKind kind = AutocompleteEntryKind::Property;
-    // Nullopt if kind is Keyword
-    std::optional<TypeId> type = std::nullopt;
-    bool deprecated = false;
-    // Only meaningful if kind is Property.
-    bool wrongIndexType = false;
-    // 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 Property*> prop = std::nullopt;
-    std::optional<std::string> documentationSymbol = std::nullopt;
-    Tags tags;
-    ParenthesesRecommendation parens = ParenthesesRecommendation::None;
-    std::optional<std::string> insertText;
-
-    // Only meaningful if kind is Property.
-    bool indexedWithSelf = false;
-};
-
-using AutocompleteEntryMap = std::unordered_map<std::string, AutocompleteEntry>;
-struct AutocompleteResult
-{
-    AutocompleteEntryMap entryMap;
-    std::vector<AstNode*> ancestry;
-    AutocompleteContext context = AutocompleteContext::Unknown;
-
-    AutocompleteResult() = default;
-    AutocompleteResult(AutocompleteEntryMap entryMap, std::vector<AstNode*> ancestry, AutocompleteContext context)
-        : entryMap(std::move(entryMap))
-        , ancestry(std::move(ancestry))
-        , context(context)
-    {
-    }
-};
-
-using ModuleName = std::string;
-using StringCompletionCallback =
-    std::function<std::optional<AutocompleteEntryMap>(std::string tag, std::optional<const ClassType*> ctx, std::optional<std::string> contents)>;
+struct FileResolver;
 
 AutocompleteResult autocomplete(Frontend& frontend, const ModuleName& moduleName, Position position, StringCompletionCallback callback);
 
-constexpr char kGeneratedAnonymousFunctionEntryName[] = "function (anonymous autofilled)";
-
 } // namespace Luau

Analysis/include/Luau/AutocompleteTypes.h

@@ -0,0 +1,92 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/Ast.h"
+#include "Luau/Type.h"
+
+#include <unordered_map>
+
+namespace Luau
+{
+
+enum class AutocompleteContext
+{
+    Unknown,
+    Expression,
+    Statement,
+    Property,
+    Type,
+    Keyword,
+    String,
+};
+
+enum class AutocompleteEntryKind
+{
+    Property,
+    Binding,
+    Keyword,
+    String,
+    Type,
+    Module,
+    GeneratedFunction,
+    RequirePath,
+};
+
+enum class ParenthesesRecommendation
+{
+    None,
+    CursorAfter,
+    CursorInside,
+};
+
+enum class TypeCorrectKind
+{
+    None,
+    Correct,
+    CorrectFunctionResult,
+};
+
+struct AutocompleteEntry
+{
+    AutocompleteEntryKind kind = AutocompleteEntryKind::Property;
+    // Nullopt if kind is Keyword
+    std::optional<TypeId> type = std::nullopt;
+    bool deprecated = false;
+    // Only meaningful if kind is Property.
+    bool wrongIndexType = false;
+    // Set if this suggestion matches the type expected in the context
+    TypeCorrectKind typeCorrect = TypeCorrectKind::None;
+
+    std::optional<const ExternType*> containingExternType = std::nullopt;
+    std::optional<const Property*> prop = std::nullopt;
+    std::optional<std::string> documentationSymbol = std::nullopt;
+    Tags tags;
+    ParenthesesRecommendation parens = ParenthesesRecommendation::None;
+    std::optional<std::string> insertText;
+
+    // Only meaningful if kind is Property.
+    bool indexedWithSelf = false;
+};
+
+using AutocompleteEntryMap = std::unordered_map<std::string, AutocompleteEntry>;
+struct AutocompleteResult
+{
+    AutocompleteEntryMap entryMap;
+    std::vector<AstNode*> ancestry;
+    AutocompleteContext context = AutocompleteContext::Unknown;
+
+    AutocompleteResult() = default;
+    AutocompleteResult(AutocompleteEntryMap entryMap, std::vector<AstNode*> ancestry, AutocompleteContext context)
+        : entryMap(std::move(entryMap))
+        , ancestry(std::move(ancestry))
+        , context(context)
+    {
+    }
+};
+
+using StringCompletionCallback =
+    std::function<std::optional<AutocompleteEntryMap>(std::string tag, std::optional<const ExternType*> ctx, std::optional<std::string> contents)>;
+
+constexpr char kGeneratedAnonymousFunctionEntryName[] = "function (anonymous autofilled)";
+
+} // namespace Luau

Analysis/include/Luau/BuiltinDefinitions.h

@@ -9,6 +9,8 @@
 namespace Luau
 {
 
+static constexpr char kRequireTagName[] = "require";
+
 struct Frontend;
 struct GlobalTypes;
 struct TypeChecker;
@@ -63,14 +65,12 @@ TypeId makeFunction( // Polymorphic
     bool checked = false
 );
 
-void attachMagicFunction(TypeId ty, MagicFunction fn);
-void attachDcrMagicFunction(TypeId ty, DcrMagicFunction fn);
-void attachDcrMagicRefinement(TypeId ty, DcrMagicRefinement fn);
-void attachDcrMagicFunctionTypeCheck(TypeId ty, DcrMagicFunctionTypeCheck fn);
+void attachMagicFunction(TypeId ty, std::shared_ptr<MagicFunction> 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);
@@ -80,4 +80,16 @@ std::optional<Binding> tryGetGlobalBinding(GlobalTypes& globals, const std::stri
 Binding* tryGetGlobalBindingRef(GlobalTypes& globals, const std::string& name);
 TypeId getGlobalBinding(GlobalTypes& globals, const std::string& name);
 
+
+/** A number of built-in functions are magical enough that we need to match on them specifically by
+ * name when they are called. These are listed here to be used whenever necessary, instead of duplicating this logic repeatedly.
+ */
+
+bool matchSetMetatable(const AstExprCall& call);
+bool matchTableFreeze(const AstExprCall& call);
+bool matchAssert(const AstExprCall& call);
+
+// Returns `true` if the function should introduce typestate for its first argument.
+bool shouldTypestateForFirstArgument(const AstExprCall& call);
+
 } // namespace Luau

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>
 
@@ -22,8 +23,26 @@ struct CloneState
     SeenTypePacks seenTypePacks;
 };
 
+/** `shallowClone` will make a copy of only the _top level_ constructor of the type,
+ * 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, bool ignorePersistent = false);
+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

@@ -3,23 +3,23 @@
 
 #include "Luau/Ast.h"
 #include "Luau/Constraint.h"
+#include "Luau/ConstraintSet.h"
 #include "Luau/ControlFlow.h"
 #include "Luau/DataFlowGraph.h"
+#include "Luau/EqSatSimplification.h"
 #include "Luau/InsertionOrderedMap.h"
 #include "Luau/Module.h"
 #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 "Luau/Normalize.h"
 
 #include <memory>
 #include <vector>
-#include <unordered_map>
 
 namespace Luau
 {
@@ -28,6 +28,7 @@ struct Scope;
 using ScopePtr = std::shared_ptr<Scope>;
 
 struct DcrLogger;
+struct TypeFunctionRuntime;
 
 struct Inference
 {
@@ -91,9 +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
-    // will enqueue them during solving.
-    std::vector<ConstraintPtr> unqueuedConstraints;
+    // The set of all free types introduced during constraint generation.
+    DenseHashSet<TypeId> freeTypes{nullptr};
+
+    // 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};
@@ -108,33 +111,49 @@ struct ConstraintGenerator
 
     // Needed to be able to enable error-suppression preservation for immediate refinements.
     NotNull<Normalizer> normalizer;
+
+    NotNull<Simplifier> simplifier;
+
+    // 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(
         ModulePtr module,
         NotNull<Normalizer> normalizer,
+        NotNull<Simplifier> simplifier,
+        NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<ModuleResolver> moduleResolver,
         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.
@@ -142,20 +161,29 @@ struct ConstraintGenerator
      */
     void visitModuleRoot(AstStatBlock* block);
 
+    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.
@@ -223,7 +251,10 @@ private:
     );
     void applyRefinements(const ScopePtr& scope, Location location, RefinementId refinement);
 
+    LUAU_NOINLINE void checkAliases(const ScopePtr& scope, AstStatBlock* block);
+
     ControlFlow visitBlockWithoutChildScope(const ScopePtr& scope, AstStatBlock* block);
+    ControlFlow visitBlockWithoutChildScope_DEPRECATED(const ScopePtr& scope, AstStatBlock* block);
 
     ControlFlow visit(const ScopePtr& scope, AstStat* stat);
     ControlFlow visit(const ScopePtr& scope, AstStatBlock* block);
@@ -241,7 +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);
 
@@ -273,7 +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);
@@ -282,11 +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);
@@ -321,6 +366,11 @@ private:
      */
     void checkFunctionBody(const ScopePtr& scope, AstExprFunction* fn);
 
+    // Specializations of 'resolveType' below
+    TypeId resolveReferenceType(const ScopePtr& scope, AstType* ty, AstTypeReference* ref, bool inTypeArguments, bool replaceErrorWithFresh);
+    TypeId resolveTableType(const ScopePtr& scope, AstType* ty, AstTypeTable* tab, bool inTypeArguments, bool replaceErrorWithFresh);
+    TypeId resolveFunctionType(const ScopePtr& scope, AstType* ty, AstTypeFunction* fn, bool inTypeArguments, bool replaceErrorWithFresh);
+
     /**
      * Resolves a type from its AST annotation.
      * @param scope the scope that the type annotation appears within.
@@ -330,6 +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.
@@ -339,6 +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.
@@ -360,7 +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
     );
@@ -377,7 +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
     );
@@ -391,6 +449,7 @@ private:
     TypeId makeUnion(const ScopePtr& scope, Location location, TypeId lhs, TypeId rhs);
     // make an intersect type function of these two types
     TypeId makeIntersect(const ScopePtr& scope, Location location, TypeId lhs, TypeId rhs);
+    void prepopulateGlobalScopeForFragmentTypecheck(const ScopePtr& globalScope, const ScopePtr& resumeScope, AstStatBlock* program);
 
     /** Scan the program for global definitions.
      *
@@ -421,11 +480,8 @@ private:
         const ScopePtr& scope,
         Location location
     );
+
+    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

@@ -3,7 +3,10 @@
 #pragma once
 
 #include "Luau/Constraint.h"
+#include "Luau/ConstraintSet.h"
+#include "Luau/DataFlowGraph.h"
 #include "Luau/DenseHash.h"
+#include "Luau/EqSatSimplification.h"
 #include "Luau/Error.h"
 #include "Luau/Location.h"
 #include "Luau/Module.h"
@@ -12,6 +15,7 @@
 #include "Luau/ToString.h"
 #include "Luau/Type.h"
 #include "Luau/TypeCheckLimits.h"
+#include "Luau/TypeFunction.h"
 #include "Luau/TypeFwd.h"
 #include "Luau/Variant.h"
 
@@ -56,17 +60,43 @@ 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;
     NotNull<BuiltinTypes> builtinTypes;
     InternalErrorReporter iceReporter;
     NotNull<Normalizer> normalizer;
+    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;
 
+    // The dataflow graph of the program, used in constraint generation and for magic functions.
+    NotNull<const DataFlowGraph> dfg;
+
     // Constraints that the solver has generated, rather than sourcing from the
     // scope tree.
     std::vector<std::unique_ptr<Constraint>> solverConstraints;
@@ -91,6 +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{{}};
 
@@ -111,12 +144,29 @@ struct ConstraintSolver
 
     explicit ConstraintSolver(
         NotNull<Normalizer> normalizer,
-        NotNull<Scope> rootScope,
-        std::vector<NotNull<Constraint>> constraints,
+        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,
+        DcrLogger* logger,
+        NotNull<const DataFlowGraph> dfg,
         TypeCheckLimits limits
     );
 
@@ -136,9 +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.
      *
@@ -164,13 +219,14 @@ public:
      */
     bool tryDispatch(NotNull<const Constraint> c, bool force);
 
-    bool tryDispatch(const SubtypeConstraint& c, NotNull<const Constraint> constraint, bool force);
-    bool tryDispatch(const PackSubtypeConstraint& c, NotNull<const Constraint> constraint, bool force);
-    bool tryDispatch(const GeneralizationConstraint& c, NotNull<const Constraint> constraint, bool force);
+    bool tryDispatch(const SubtypeConstraint& c, NotNull<const Constraint> constraint);
+    bool tryDispatch(const PackSubtypeConstraint& c, NotNull<const Constraint> constraint);
+    bool tryDispatch(const GeneralizationConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const IterableConstraint& c, NotNull<const Constraint> constraint, bool force);
     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);
@@ -191,16 +247,16 @@ public:
     bool tryDispatch(const UnpackConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const ReduceConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const ReducePackConstraint& c, NotNull<const Constraint> constraint, bool force);
-    bool tryDispatch(const EqualityConstraint& c, NotNull<const Constraint> constraint, bool force);
+    bool tryDispatch(const EqualityConstraint& c, NotNull<const Constraint> constraint);
 
     // for a, ... in some_table do
     // also handles __iter metamethod
     bool tryDispatchIterableTable(TypeId iteratorTy, const IterableConstraint& c, NotNull<const Constraint> constraint, bool force);
 
     // for a, ... in next_function, t, ... do
-    bool tryDispatchIterableFunction(TypeId nextTy, TypeId tableTy, const IterableConstraint& c, NotNull<const Constraint> constraint, bool force);
+    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,
@@ -208,7 +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,
@@ -267,10 +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);
@@ -278,18 +335,18 @@ public:
     /**
      * @returns true if the TypeId is in a blocked state.
      */
-    bool isBlocked(TypeId ty);
+    bool isBlocked(TypeId ty) const;
 
     /**
      * @returns true if the TypePackId is in a blocked state.
      */
-    bool isBlocked(TypePackId tp);
+    bool isBlocked(TypePackId tp) const;
 
     /**
      * Returns whether the constraint is blocked on anything.
      * @param constraint the constraint to check.
      */
-    bool isBlocked(NotNull<const Constraint> constraint);
+    bool isBlocked(NotNull<const Constraint> constraint) const;
 
     /** Pushes a new solver constraint to the solver.
      * @param cv the body of the constraint.
@@ -305,7 +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);
@@ -326,7 +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
@@ -376,17 +433,27 @@ public:
      **/
     void reproduceConstraints(NotNull<Scope> scope, const Location& location, const Substitution& subst);
 
+    TypeId simplifyIntersection(NotNull<Scope> scope, Location location, TypeId left, TypeId right);
+    TypeId simplifyIntersection(NotNull<Scope> scope, Location location, std::set<TypeId> parts);
+    TypeId simplifyUnion(NotNull<Scope> scope, Location location, TypeId left, TypeId right);
+
     TypeId errorRecoveryType() const;
     TypePackId errorRecoveryTypePack() const;
 
     TypePackId anyifyModuleReturnTypePackGenerics(TypePackId tp);
 
-    void throwTimeLimitError();
-    void throwUserCancelError();
+    void throwTimeLimitError() const;
+    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"
 
@@ -35,8 +36,8 @@ struct DataFlowGraph
     DataFlowGraph& operator=(DataFlowGraph&&) = default;
 
     DefId getDef(const AstExpr* expr) const;
-    // Look up for the rvalue def for a compound assignment.
-    std::optional<DefId> getRValueDefForCompoundAssign(const AstExpr* expr) const;
+    // Look up the definition optionally, knowing it may not be present.
+    std::optional<DefId> getDefOptional(const AstExpr* expr) const;
 
     DefId getDef(const AstLocal* local) const;
 
@@ -46,13 +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;
-    RefinementKeyArena keyArena;
+    NotNull<DefArena> defArena;
+    NotNull<RefinementKeyArena> keyArena;
 
     DenseHashMap<const AstExpr*, const Def*> astDefs{nullptr};
 
@@ -63,12 +64,7 @@ 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;
 };
 
@@ -105,25 +101,37 @@ struct DataFlowResult
     const RefinementKey* parent = nullptr;
 };
 
+using ScopeStack = std::vector<DfgScope*>;
+
 struct DataFlowGraphBuilder
 {
-    static DataFlowGraph build(AstStatBlock* root, NotNull<struct InternalErrorReporter> handle);
+    static DataFlowGraph build(
+        AstStatBlock* block,
+        NotNull<DefArena> defArena,
+        NotNull<RefinementKeyArena> keyArena,
+        NotNull<struct 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<RefinementKeyArena> keyArena{&graph.keyArena};
+    NotNull<DefArena> defArena;
+    NotNull<RefinementKeyArena> keyArena;
 
     struct InternalErrorReporter* handle = nullptr;
-    DfgScope* moduleScope = nullptr;
 
+    /// The arena owning all of the scope allocations for the dataflow graph being built.
     std::vector<std::unique_ptr<DfgScope>> scopes;
 
+    /// A stack of scopes used by the visitor to see where we are.
+    ScopeStack scopeStack;
+    NotNull<DfgScope> currentScope();
+    DfgScope* currentScope_DEPRECATED();
+
     struct FunctionCapture
     {
         std::vector<DefId> captureDefs;
@@ -134,81 +142,81 @@ private:
     DenseHashMap<Symbol, FunctionCapture> captures{Symbol{}};
     void resolveCaptures();
 
-    DfgScope* childScope(DfgScope* scope, 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(DfgScope* scope, Symbol symbol);
-    DefId lookup(DfgScope* scope, DefId def, const std::string& key);
+    DefId lookup(Symbol symbol, Location location);
+    DefId lookup(DefId def, const std::string& key, Location location);
 
-    ControlFlow visit(DfgScope* scope, AstStatBlock* b);
-    ControlFlow visitBlockWithoutChildScope(DfgScope* scope, AstStatBlock* b);
+    ControlFlow visit(AstStatBlock* b);
+    ControlFlow visitBlockWithoutChildScope(AstStatBlock* b);
 
-    ControlFlow visit(DfgScope* scope, AstStat* s);
-    ControlFlow visit(DfgScope* scope, AstStatIf* i);
-    ControlFlow visit(DfgScope* scope, AstStatWhile* w);
-    ControlFlow visit(DfgScope* scope, AstStatRepeat* r);
-    ControlFlow visit(DfgScope* scope, AstStatBreak* b);
-    ControlFlow visit(DfgScope* scope, AstStatContinue* c);
-    ControlFlow visit(DfgScope* scope, AstStatReturn* r);
-    ControlFlow visit(DfgScope* scope, AstStatExpr* e);
-    ControlFlow visit(DfgScope* scope, AstStatLocal* l);
-    ControlFlow visit(DfgScope* scope, AstStatFor* f);
-    ControlFlow visit(DfgScope* scope, AstStatForIn* f);
-    ControlFlow visit(DfgScope* scope, AstStatAssign* a);
-    ControlFlow visit(DfgScope* scope, AstStatCompoundAssign* c);
-    ControlFlow visit(DfgScope* scope, AstStatFunction* f);
-    ControlFlow visit(DfgScope* scope, AstStatLocalFunction* l);
-    ControlFlow visit(DfgScope* scope, AstStatTypeAlias* t);
-    ControlFlow visit(DfgScope* scope, AstStatTypeFunction* f);
-    ControlFlow visit(DfgScope* scope, AstStatDeclareGlobal* d);
-    ControlFlow visit(DfgScope* scope, AstStatDeclareFunction* d);
-    ControlFlow visit(DfgScope* scope, AstStatDeclareClass* d);
-    ControlFlow visit(DfgScope* scope, AstStatError* error);
+    ControlFlow visit(AstStat* s);
+    ControlFlow visit(AstStatIf* i);
+    ControlFlow visit(AstStatWhile* w);
+    ControlFlow visit(AstStatRepeat* r);
+    ControlFlow visit(AstStatBreak* b);
+    ControlFlow visit(AstStatContinue* c);
+    ControlFlow visit(AstStatReturn* r);
+    ControlFlow visit(AstStatExpr* e);
+    ControlFlow visit(AstStatLocal* l);
+    ControlFlow visit(AstStatFor* f);
+    ControlFlow visit(AstStatForIn* f);
+    ControlFlow visit(AstStatAssign* a);
+    ControlFlow visit(AstStatCompoundAssign* c);
+    ControlFlow visit(AstStatFunction* f);
+    ControlFlow visit(AstStatLocalFunction* l);
+    ControlFlow visit(AstStatTypeAlias* t);
+    ControlFlow visit(AstStatTypeFunction* f);
+    ControlFlow visit(AstStatDeclareGlobal* d);
+    ControlFlow visit(AstStatDeclareFunction* d);
+    ControlFlow visit(AstStatDeclareExternType* d);
+    ControlFlow visit(AstStatError* error);
 
-    DataFlowResult visitExpr(DfgScope* scope, AstExpr* e);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprGroup* group);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprLocal* l);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprGlobal* g);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprCall* c);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprIndexName* i);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprIndexExpr* i);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprFunction* f);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprTable* t);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprUnary* u);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprBinary* b);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprTypeAssertion* t);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprIfElse* i);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprInterpString* i);
-    DataFlowResult visitExpr(DfgScope* scope, AstExprError* error);
+    DataFlowResult visitExpr(AstExpr* e);
+    DataFlowResult visitExpr(AstExprGroup* group);
+    DataFlowResult visitExpr(AstExprLocal* l);
+    DataFlowResult visitExpr(AstExprGlobal* g);
+    DataFlowResult visitExpr(AstExprCall* c);
+    DataFlowResult visitExpr(AstExprIndexName* i);
+    DataFlowResult visitExpr(AstExprIndexExpr* i);
+    DataFlowResult visitExpr(AstExprFunction* f);
+    DataFlowResult visitExpr(AstExprTable* t);
+    DataFlowResult visitExpr(AstExprUnary* u);
+    DataFlowResult visitExpr(AstExprBinary* b);
+    DataFlowResult visitExpr(AstExprTypeAssertion* t);
+    DataFlowResult visitExpr(AstExprIfElse* i);
+    DataFlowResult visitExpr(AstExprInterpString* i);
+    DataFlowResult visitExpr(AstExprError* error);
 
-    void visitLValue(DfgScope* scope, AstExpr* e, DefId incomingDef);
-    DefId visitLValue(DfgScope* scope, AstExprLocal* l, DefId incomingDef);
-    DefId visitLValue(DfgScope* scope, AstExprGlobal* g, DefId incomingDef);
-    DefId visitLValue(DfgScope* scope, AstExprIndexName* i, DefId incomingDef);
-    DefId visitLValue(DfgScope* scope, AstExprIndexExpr* i, DefId incomingDef);
-    DefId visitLValue(DfgScope* scope, AstExprError* e, DefId incomingDef);
+    void visitLValue(AstExpr* e, DefId incomingDef);
+    DefId visitLValue(AstExprLocal* l, DefId incomingDef);
+    DefId visitLValue(AstExprGlobal* g, DefId incomingDef);
+    DefId visitLValue(AstExprIndexName* i, DefId incomingDef);
+    DefId visitLValue(AstExprIndexExpr* i, DefId incomingDef);
+    DefId visitLValue(AstExprError* e, DefId incomingDef);
 
-    void visitType(DfgScope* scope, AstType* t);
-    void visitType(DfgScope* scope, AstTypeReference* r);
-    void visitType(DfgScope* scope, AstTypeTable* t);
-    void visitType(DfgScope* scope, AstTypeFunction* f);
-    void visitType(DfgScope* scope, AstTypeTypeof* t);
-    void visitType(DfgScope* scope, AstTypeUnion* u);
-    void visitType(DfgScope* scope, AstTypeIntersection* i);
-    void visitType(DfgScope* scope, AstTypeError* error);
+    void visitType(AstType* t);
+    void visitType(AstTypeReference* r);
+    void visitType(AstTypeTable* t);
+    void visitType(AstTypeFunction* f);
+    void visitType(AstTypeTypeof* t);
+    void visitType(AstTypeUnion* u);
+    void visitType(AstTypeIntersection* i);
+    void visitType(AstTypeError* error);
 
-    void visitTypePack(DfgScope* scope, AstTypePack* p);
-    void visitTypePack(DfgScope* scope, AstTypePackExplicit* e);
-    void visitTypePack(DfgScope* scope, AstTypePackVariadic* v);
-    void visitTypePack(DfgScope* scope, AstTypePackGeneric* g);
+    void visitTypePack(AstTypePack* p);
+    void visitTypePack(AstTypePackExplicit* e);
+    void visitTypePack(AstTypePackVariadic* v);
+    void visitTypePack(AstTypePackGeneric* g);
 
-    void visitTypeList(DfgScope* scope, AstTypeList l);
+    void visitTypeList(AstTypeList l);
 
-    void visitGenerics(DfgScope* scope, AstArray<AstGenericType> g);
-    void visitGenericPacks(DfgScope* scope, AstArray<AstGenericTypePack> g);
+    void visitGenerics(AstArray<AstGenericType*> 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/EqSatSimplification.h

@@ -0,0 +1,50 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#pragma once
+
+#include "Luau/TypeFwd.h"
+#include "Luau/NotNull.h"
+#include "Luau/DenseHash.h"
+
+#include <memory>
+#include <optional>
+#include <vector>
+
+namespace Luau
+{
+struct TypeArena;
+}
+
+// The EqSat stuff is pretty template heavy, so we go to some lengths to prevent
+// the complexity from leaking outside its implementation sources.
+namespace Luau::EqSatSimplification
+{
+
+struct Simplifier;
+
+using SimplifierPtr = std::unique_ptr<Simplifier, void (*)(Simplifier*)>;
+
+SimplifierPtr newSimplifier(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes);
+
+} // namespace Luau::EqSatSimplification
+
+namespace Luau
+{
+
+struct EqSatSimplificationResult
+{
+    TypeId result;
+
+    // New type function applications that were created by the reduction phase.
+    // We return these so that the ConstraintSolver can know to try to reduce
+    // them.
+    std::vector<TypeId> newTypeFunctions;
+};
+
+using EqSatSimplification::newSimplifier;    // NOLINT: clang-tidy thinks these are unused.  It is incorrect.
+using Luau::EqSatSimplification::Simplifier; // NOLINT
+using Luau::EqSatSimplification::SimplifierPtr;
+
+std::optional<EqSatSimplificationResult> eqSatSimplify(NotNull<Simplifier> simplifier, TypeId ty);
+
+} // namespace Luau

Analysis/include/Luau/EqSatSimplificationImpl.h

@@ -0,0 +1,376 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#pragma once
+
+#include "Luau/EGraph.h"
+#include "Luau/Id.h"
+#include "Luau/Language.h"
+#include "Luau/Lexer.h" // For Allocator
+#include "Luau/NotNull.h"
+#include "Luau/TypeArena.h"
+#include "Luau/TypeFwd.h"
+
+namespace Luau
+{
+struct TypeFunction;
+}
+
+namespace Luau::EqSatSimplification
+{
+
+using StringId = uint32_t;
+using Id = Luau::EqSat::Id;
+
+LUAU_EQSAT_UNIT(TNil);
+LUAU_EQSAT_UNIT(TBoolean);
+LUAU_EQSAT_UNIT(TNumber);
+LUAU_EQSAT_UNIT(TString);
+LUAU_EQSAT_UNIT(TThread);
+LUAU_EQSAT_UNIT(TTopFunction);
+LUAU_EQSAT_UNIT(TTopTable);
+LUAU_EQSAT_UNIT(TTopClass);
+LUAU_EQSAT_UNIT(TBuffer);
+
+// Used for any type that eqsat can't do anything interesting with.
+LUAU_EQSAT_ATOM(TOpaque, TypeId);
+
+LUAU_EQSAT_ATOM(SBoolean, bool);
+LUAU_EQSAT_ATOM(SString, StringId);
+
+LUAU_EQSAT_ATOM(TFunction, TypeId);
+
+LUAU_EQSAT_ATOM(TImportedTable, TypeId);
+
+LUAU_EQSAT_ATOM(TClass, TypeId);
+
+LUAU_EQSAT_UNIT(TAny);
+LUAU_EQSAT_UNIT(TError);
+LUAU_EQSAT_UNIT(TUnknown);
+LUAU_EQSAT_UNIT(TNever);
+
+LUAU_EQSAT_NODE_SET(Union);
+LUAU_EQSAT_NODE_SET(Intersection);
+
+LUAU_EQSAT_NODE_ARRAY(Negation, 1);
+
+LUAU_EQSAT_NODE_ATOM_WITH_VECTOR(TTypeFun, std::shared_ptr<const TypeFunctionInstanceType>);
+
+LUAU_EQSAT_UNIT(TNoRefine);
+LUAU_EQSAT_UNIT(Invalid);
+
+// enodes are immutable, but types are cyclic.  We need a way to tie the knot.
+// We handle this by generating TBound nodes at points where we encounter cycles.
+// Each TBound has an ordinal that we later map onto the type.
+// We use a substitution rule to replace all TBound nodes with their referrent.
+LUAU_EQSAT_ATOM(TBound, size_t);
+
+// Tables are sufficiently unlike other enodes that the Language.h macros won't cut it.
+struct TTable
+{
+    explicit TTable(Id basis);
+    TTable(Id basis, std::vector<StringId> propNames_, std::vector<Id> propTypes_);
+
+    // All TTables extend some other table.  This may be TTopTable.
+    //
+    // It will frequently be a TImportedTable, in which case we can reuse things
+    // like source location and documentation info.
+    Id getBasis() const;
+    EqSat::Slice<const Id> propTypes() const;
+    // TODO: Also support read-only table props
+    // TODO: Indexer type, index result type.
+
+    std::vector<StringId> propNames;
+
+    // The enode interface
+    EqSat::Slice<Id> mutableOperands();
+    EqSat::Slice<const Id> operands() const;
+    bool operator==(const TTable& rhs) const;
+    bool operator!=(const TTable& rhs) const
+    {
+        return !(*this == rhs);
+    }
+
+    struct Hash
+    {
+        size_t operator()(const TTable& value) const;
+    };
+
+private:
+    // The first element of this vector is the basis.  Subsequent elements are
+    // property types. As we add other things like read-only properties and
+    // indexers, the structure of this array is likely to change.
+    //
+    // We encode our data in this way so that the operands() method can properly
+    // return a Slice<Id>.
+    std::vector<Id> storage;
+};
+
+template<typename L>
+using Node = EqSat::Node<L>;
+
+using EType = EqSat::Language<
+    TNil,
+    TBoolean,
+    TNumber,
+    TString,
+    TThread,
+    TTopFunction,
+    TTopTable,
+    TTopClass,
+    TBuffer,
+
+    TOpaque,
+
+    SBoolean,
+    SString,
+
+    TFunction,
+    TTable,
+    TImportedTable,
+    TClass,
+
+    TAny,
+    TError,
+    TUnknown,
+    TNever,
+
+    Union,
+    Intersection,
+
+    Negation,
+
+    TTypeFun,
+
+    Invalid,
+    TNoRefine,
+    TBound>;
+
+
+struct StringCache
+{
+    Allocator allocator;
+    DenseHashMap<std::string_view, StringId> strings{{}};
+    std::vector<std::string_view> views;
+
+    StringId add(std::string_view s);
+    std::string_view asStringView(StringId id) const;
+    std::string asString(StringId id) const;
+};
+
+using EGraph = Luau::EqSat::EGraph<EType, struct Simplify>;
+
+struct Simplify
+{
+    using Data = bool;
+
+    template<typename T>
+    Data make(const EGraph&, const T&) const;
+
+    void join(Data& left, const Data& right) const;
+};
+
+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 = "");
+};
+
+struct Simplifier
+{
+    NotNull<TypeArena> arena;
+    NotNull<BuiltinTypes> builtinTypes;
+    EGraph egraph;
+    StringCache stringCache;
+
+    // enodes are immutable but types can be cyclic, so we need some way to
+    // encode the cycle. This map is used to connect TBound nodes to the right
+    // eclass.
+    //
+    // The cyclicIntersection rewrite rule uses this to sense when a cycle can
+    // be deleted from an intersection or union.
+    std::unordered_map<size_t, Id> mappingIdToClass;
+
+    std::vector<Subst> substs;
+
+    using RewriteRuleFn = void (Simplifier::*)(Id id);
+
+    Simplifier(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes);
+
+    // Utilities
+    const EqSat::EClass<EType, Simplify::Data>& get(Id id) const;
+    Id find(Id id) const;
+    Id add(EType enode);
+
+    template<typename Tag>
+    const Tag* isTag(Id id) const;
+
+    template<typename Tag>
+    const Tag* isTag(const EType& enode) const;
+
+    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);
+
+    // Rewrite rules
+    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);
+    void expandNegation(Id id);
+    void intersectionOfUnion(Id id);
+    void intersectTableProperty(Id id);
+    void uninhabitedTable(Id id);
+    void unneededTableModification(Id id);
+    void builtinTypeFunctions(Id id);
+    void iffyTypeFunctions(Id id);
+    void strictMetamethods(Id id);
+};
+
+template<typename Tag>
+struct QueryIterator
+{
+    QueryIterator();
+    QueryIterator(EGraph* egraph, Id eclass);
+
+    bool operator==(const QueryIterator& other) const;
+    bool operator!=(const QueryIterator& other) const;
+
+    std::pair<const Tag*, size_t> operator*() const;
+
+    QueryIterator& operator++();
+    QueryIterator& operator++(int);
+
+private:
+    EGraph* egraph = nullptr;
+    Id eclass;
+    size_t index = 0;
+};
+
+template<typename Tag>
+struct Query
+{
+    EGraph* egraph;
+    Id eclass;
+
+    Query(EGraph* egraph, Id eclass)
+        : egraph(egraph)
+        , eclass(eclass)
+    {
+    }
+
+    QueryIterator<Tag> begin()
+    {
+        return QueryIterator<Tag>{egraph, eclass};
+    }
+
+    QueryIterator<Tag> end()
+    {
+        return QueryIterator<Tag>{};
+    }
+};
+
+template<typename Tag>
+QueryIterator<Tag>::QueryIterator()
+    : egraph(nullptr)
+    , eclass(Id{0})
+    , index(0)
+{
+}
+
+template<typename Tag>
+QueryIterator<Tag>::QueryIterator(EGraph* egraph_, Id eclass)
+    : egraph(egraph_)
+    , eclass(eclass)
+    , index(0)
+{
+    const auto& ecl = (*egraph)[eclass];
+
+    static constexpr const int idx = EType::VariantTy::getTypeId<Tag>();
+
+    for (const auto& enode : ecl.nodes)
+    {
+        if (enode.node.index() < idx)
+            ++index;
+        else
+            break;
+    }
+
+    if (index >= ecl.nodes.size() || ecl.nodes[index].node.index() != idx)
+    {
+        egraph = nullptr;
+        index = 0;
+    }
+}
+
+template<typename Tag>
+bool QueryIterator<Tag>::operator==(const QueryIterator<Tag>& rhs) const
+{
+    if (egraph == nullptr && rhs.egraph == nullptr)
+        return true;
+
+    return egraph == rhs.egraph && eclass == rhs.eclass && index == rhs.index;
+}
+
+template<typename Tag>
+bool QueryIterator<Tag>::operator!=(const QueryIterator<Tag>& rhs) const
+{
+    return !(*this == rhs);
+}
+
+template<typename Tag>
+std::pair<const Tag*, size_t> QueryIterator<Tag>::operator*() const
+{
+    LUAU_ASSERT(egraph != nullptr);
+
+    EGraph::EClassT& ecl = (*egraph)[eclass];
+
+    LUAU_ASSERT(index < ecl.nodes.size());
+    auto& enode = ecl.nodes[index].node;
+    Tag* result = enode.template get<Tag>();
+    LUAU_ASSERT(result);
+    return {result, index};
+}
+
+// pre-increment
+template<typename Tag>
+QueryIterator<Tag>& QueryIterator<Tag>::operator++()
+{
+    const auto& ecl = (*egraph)[eclass];
+
+    do
+    {
+        ++index;
+        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;
+}
+
+// post-increment
+template<typename Tag>
+QueryIterator<Tag>& QueryIterator<Tag>::operator++(int)
+{
+    QueryIterator<Tag> res = *this;
+    ++res;
+    return res;
+}
+
+} // namespace Luau::EqSatSimplification

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
@@ -448,6 +448,20 @@ struct UnexpectedTypePackInSubtyping
     bool operator==(const UnexpectedTypePackInSubtyping& rhs) const;
 };
 
+struct UserDefinedTypeFunctionError
+{
+    std::string message;
+
+    bool operator==(const UserDefinedTypeFunctionError& rhs) const;
+};
+
+struct ReservedIdentifier
+{
+    std::string name;
+
+    bool operator==(const ReservedIdentifier& rhs) const;
+};
+
 using TypeErrorData = Variant<
     TypeMismatch,
     UnknownSymbol,
@@ -485,7 +499,7 @@ using TypeErrorData = Variant<
     TypesAreUnrelated,
     NormalizationTooComplex,
     TypePackMismatch,
-    DynamicPropertyLookupOnClassesUnsafe,
+    DynamicPropertyLookupOnExternTypesUnsafe,
     UninhabitedTypeFunction,
     UninhabitedTypePackFunction,
     WhereClauseNeeded,
@@ -496,7 +510,9 @@ using TypeErrorData = Variant<
     CheckedFunctionIncorrectArgs,
     UnexpectedTypeInSubtyping,
     UnexpectedTypePackInSubtyping,
-    ExplicitFunctionAnnotationRecommended>;
+    ExplicitFunctionAnnotationRecommended,
+    UserDefinedTypeFunctionError,
+    ReservedIdentifier>;
 
 struct TypeErrorSummary
 {

Analysis/include/Luau/FileResolver.h

@@ -1,8 +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 <string>
+#include <memory>
 #include <optional>
+#include <string>
+#include <vector>
 
 namespace Luau
 {
@@ -18,7 +20,7 @@ struct SourceCode
         None,
         Module,
         Script,
-        Local
+        Local_DEPRECATED
     };
 
     std::string source;
@@ -31,8 +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;
@@ -51,6 +116,10 @@ struct FileResolver
     {
         return std::nullopt;
     }
+
+    std::optional<RequireSuggestions> getRequireSuggestions(const ModuleName& requirer, const std::optional<std::string>& pathString) const;
+
+    std::shared_ptr<RequireSuggester> requireSuggester;
 };
 
 struct NullFileResolver : FileResolver

Analysis/include/Luau/FragmentAutocomplete.h

@@ -0,0 +1,196 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/Ast.h"
+#include "Luau/Parser.h"
+#include "Luau/AutocompleteTypes.h"
+#include "Luau/DenseHash.h"
+#include "Luau/Module.h"
+#include "Luau/Frontend.h"
+
+#include <memory>
+#include <vector>
+
+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
+{
+    std::string fragmentToParse;
+    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
+{
+    ModulePtr incrementalModule = nullptr;
+    ScopePtr freshScope;
+    std::vector<AstNode*> ancestry;
+};
+
+struct FragmentAutocompleteResult
+{
+    ModulePtr incrementalModule;
+    Scope* freshScope;
+    TypeArena arenaForAutocomplete_DEPRECATED;
+    AutocompleteResult acResults;
+};
+
+struct FragmentRegion
+{
+    Location fragmentLocation;
+    AstStat* nearestStatement = nullptr; // used for tests
+    AstStatBlock* parentBlock = nullptr; // used for scope detection
+};
+
+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);
+
+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::optional<Position> fragmentEndPosition,
+    AstStatBlock* recentParse = nullptr,
+    IFragmentAutocompleteReporter* reporter = nullptr
+);
+
+FragmentAutocompleteResult fragmentAutocomplete(
+    Frontend& frontend,
+    std::string_view src,
+    const ModuleName& moduleName,
+    Position cursorPosition,
+    std::optional<FrontendOptions> opts,
+    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
 {
@@ -44,21 +44,6 @@ struct LoadDefinitionFileResult
 
 std::optional<Mode> parseMode(const std::vector<HotComment>& hotcomments);
 
-std::vector<std::string_view> parsePathExpr(const AstExpr& pathExpr);
-
-// Exported only for convenient testing.
-std::optional<ModuleName> pathExprToModuleName(const ModuleName& currentModuleName, const std::vector<std::string_view>& expr);
-
-/** Try to convert an AST fragment into a ModuleName.
- * Returns std::nullopt if the expression cannot be resolved.  This will most likely happen in cases where
- * the import path involves some dynamic computation that we cannot see into at typechecking time.
- *
- * Unintuitively, weirdly-formulated modules (like game.Parent.Parent.Parent.Foo) will successfully produce a ModuleName
- * as long as it falls within the permitted syntax.  This is ok because we will fail to find the module and produce an
- * error when we try during typechecking.
- */
-std::optional<ModuleName> pathExprToModuleName(const ModuleName& currentModuleName, const AstExpr& expr);
-
 struct SourceNode
 {
     bool hasDirtySourceModule() const
@@ -71,13 +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;
 };
 
@@ -132,7 +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:
@@ -166,9 +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
@@ -209,6 +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(
@@ -241,6 +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);
 
@@ -286,6 +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
@@ -300,6 +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

@@ -60,7 +60,7 @@ struct ReplaceGenerics : Substitution
 };
 
 // A substitution which replaces generic functions by monomorphic functions
-struct Instantiation : Substitution
+struct Instantiation final : Substitution
 {
     Instantiation(const TxnLog* log, TypeArena* arena, NotNull<BuiltinTypes> builtinTypes, TypeLevel level, Scope* scope)
         : Substitution(log, arena)
@@ -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 +8,7 @@
 #include "Luau/ParseResult.h"
 #include "Luau/Scope.h"
 #include "Luau/TypeArena.h"
-#include "Luau/AnyTypeSummary.h"
+#include "Luau/DataFlowGraph.h"
 
 #include <memory>
 #include <vector>
@@ -18,8 +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>;
@@ -54,6 +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);
 
@@ -67,19 +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
 
@@ -132,6 +138,11 @@ struct Module
     TypePackId returnType = nullptr;
     std::unordered_map<Name, TypeFun> exportedTypeBindings;
 
+    // Arenas related to the DFG must persist after the DFG no longer exists, as
+    // Module objects maintain raw pointers to objects in these arenas.
+    DefArena defArena;
+    RefinementKeyArena keyArena;
+
     bool hasModuleScope() const;
     ScopePtr getModuleScope() const;
 

Analysis/include/Luau/ModuleResolver.h

@@ -20,8 +20,6 @@ struct ModuleResolver
     virtual ~ModuleResolver() {}
 
     /** Compute a ModuleName from an AST fragment.  This AST fragment is generally the argument to the require() function.
-     *
-     * You probably want to implement this with some variation of pathExprToModuleName.
      *
      * @returns The ModuleInfo if the expression is a syntactically legal path.
      * @returns std::nullopt if we are unable to determine whether or not the expression is a valid path.  Type inference will

Analysis/include/Luau/NonStrictTypeChecker.h

@@ -1,19 +1,23 @@
 // 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
 {
 
 struct BuiltinTypes;
+struct TypeFunctionRuntime;
 struct UnifierSharedState;
 struct TypeCheckLimits;
 
 void checkNonStrict(
     NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<InternalErrorReporter> ice,
     NotNull<UnifierSharedState> unifierState,
     NotNull<const DataFlowGraph> dfg,

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"
@@ -21,10 +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(TypePackId subTy, TypePackId superTy, NotNull<Scope> scope, NotNull<BuiltinTypes> builtinTypes, InternalErrorReporter& ice);
-bool isConsistentSubtype(TypeId subTy, TypeId superTy, NotNull<Scope> scope, NotNull<BuiltinTypes> builtinTypes, InternalErrorReporter& ice);
-bool isConsistentSubtype(TypePackId subTy, TypePackId 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
+);
+bool isSubtype(
+    TypePackId subPack,
+    TypePackId superPack,
+    NotNull<Scope> scope,
+    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
+    InternalErrorReporter& ice
+);
 
 class TypeIds
 {
@@ -168,7 +181,7 @@ struct NormalizedStringType
 
 bool isSubtype(const NormalizedStringType& subStr, const NormalizedStringType& superStr);
 
-struct NormalizedClassType
+struct NormalizedExternType
 {
     /** Has the following structure:
      *
@@ -179,7 +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
@@ -232,7 +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
@@ -247,7 +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.
@@ -320,7 +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;
@@ -336,6 +349,7 @@ struct NormalizedType
 };
 
 
+using SeenTablePropPairs = Set<std::pair<TypeId, TypeId>, TypeIdPairHash>;
 
 class Normalizer
 {
@@ -377,10 +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 unionClasses(TypeIds& heres, const TypeIds& theres);
-    void unionClassesWithClass(NormalizedClassType& heres, TypeId there);
-    void unionClasses(NormalizedClassType& heres, const NormalizedClassType& theres);
+    void unionExternTypesWithExternType(TypeIds& heres, TypeId there);
+    void unionExternTypes(TypeIds& heres, const TypeIds& theres);
+    void unionExternTypesWithExternType(NormalizedExternType& heres, TypeId there);
+    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);
@@ -390,7 +404,13 @@ public:
     void unionTablesWithTable(TypeIds& heres, TypeId there);
     void unionTables(TypeIds& heres, const TypeIds& theres);
     NormalizationResult unionNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
-    NormalizationResult unionNormalWithTy(NormalizedType& here, TypeId there, Set<TypeId>& seenSetTypes, int ignoreSmallerTyvars = -1);
+    NormalizationResult unionNormalWithTy(
+        NormalizedType& here,
+        TypeId there,
+        SeenTablePropPairs& seenTablePropPairs,
+        Set<TypeId>& seenSetTypes,
+        int ignoreSmallerTyvars = -1
+    );
 
     // ------- Negations
     std::optional<NormalizedType> negateNormal(const NormalizedType& here);
@@ -403,20 +423,30 @@ public:
     // ------- Normalizing intersections
     TypeId intersectionOfTops(TypeId here, TypeId there);
     TypeId intersectionOfBools(TypeId here, TypeId there);
-    void intersectClasses(NormalizedClassType& heres, const NormalizedClassType& theres);
-    void intersectClassesWithClass(NormalizedClassType& heres, TypeId there);
+    void intersectExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres);
+    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, Set<TypeId>& seenSet);
-    void intersectTablesWithTable(TypeIds& heres, TypeId there, Set<TypeId>& seenSetTypes);
+    std::optional<TypeId> intersectionOfTables(TypeId here, TypeId there, SeenTablePropPairs& seenTablePropPairs, Set<TypeId>& seenSet);
+    void intersectTablesWithTable(TypeIds& heres, TypeId there, SeenTablePropPairs& seenTablePropPairs, Set<TypeId>& seenSetTypes);
     void intersectTables(TypeIds& heres, const TypeIds& theres);
     std::optional<TypeId> intersectionOfFunctions(TypeId here, TypeId there);
     void intersectFunctionsWithFunction(NormalizedFunctionType& heress, TypeId there);
     void intersectFunctions(NormalizedFunctionType& heress, const NormalizedFunctionType& theress);
-    NormalizationResult intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there, Set<TypeId>& seenSetTypes);
+    NormalizationResult intersectTyvarsWithTy(
+        NormalizedTyvars& here,
+        TypeId there,
+        SeenTablePropPairs& seenTablePropPairs,
+        Set<TypeId>& seenSetTypes
+    );
     NormalizationResult intersectNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
-    NormalizationResult intersectNormalWithTy(NormalizedType& here, TypeId there, Set<TypeId>& seenSetTypes);
-    NormalizationResult normalizeIntersections(const std::vector<TypeId>& intersections, NormalizedType& outType, Set<TypeId>& seenSet);
+    NormalizationResult intersectNormalWithTy(NormalizedType& here, TypeId there, SeenTablePropPairs& seenTablePropPairs, Set<TypeId>& seenSetTypes);
+    NormalizationResult normalizeIntersections(
+        const std::vector<TypeId>& intersections,
+        NormalizedType& outType,
+        SeenTablePropPairs& seenTablePropPairs,
+        Set<TypeId>& seenSet
+    );
 
     // Check for inhabitance
     NormalizationResult isInhabited(TypeId ty);
@@ -426,7 +456,7 @@ public:
 
     // Check for intersections being inhabited
     NormalizationResult isIntersectionInhabited(TypeId left, TypeId right);
-    NormalizationResult isIntersectionInhabited(TypeId left, TypeId right, Set<TypeId>& seenSet);
+    NormalizationResult isIntersectionInhabited(TypeId left, TypeId right, SeenTablePropPairs& seenTablePropPairs, Set<TypeId>& seenSet);
 
     // -------- Convert back from a normalized type to a type
     TypeId typeFromNormal(const NormalizedType& norm);

Analysis/include/Luau/OverloadResolution.h

@@ -2,12 +2,13 @@
 #pragma once
 
 #include "Luau/Ast.h"
-#include "Luau/InsertionOrderedMap.h"
-#include "Luau/NotNull.h"
-#include "Luau/TypeFwd.h"
-#include "Luau/Location.h"
+#include "Luau/EqSatSimplification.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
 {
@@ -34,7 +35,9 @@ struct OverloadResolver
     OverloadResolver(
         NotNull<BuiltinTypes> builtinTypes,
         NotNull<TypeArena> arena,
+        NotNull<Simplifier> simplifier,
         NotNull<Normalizer> normalizer,
+        NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<Scope> scope,
         NotNull<InternalErrorReporter> reporter,
         NotNull<TypeCheckLimits> limits,
@@ -43,7 +46,9 @@ struct OverloadResolver
 
     NotNull<BuiltinTypes> builtinTypes;
     NotNull<TypeArena> arena;
+    NotNull<Simplifier> simplifier;
     NotNull<Normalizer> normalizer;
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     NotNull<Scope> scope;
     NotNull<InternalErrorReporter> ice;
     NotNull<TypeCheckLimits> limits;
@@ -108,7 +113,9 @@ struct SolveResult
 SolveResult solveFunctionCall(
     NotNull<TypeArena> arena,
     NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
     NotNull<Normalizer> normalizer,
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<InternalErrorReporter> iceReporter,
     NotNull<TypeCheckLimits> limits,
     NotNull<Scope> scope,

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 AstExpr;
+class AstNode;
 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)
-    {
-        return false;
-    }
-
-    virtual bool ignoreChildren(TypePackId ty)
-    {
-        return false;
-    }
+    virtual bool ignoreChildren(TypeId ty);
+    virtual bool ignoreChildren(TypePackId ty);
 
     // Some subclasses might ignore children visit, but not other actions like replacing the children
-    virtual bool ignoreChildrenVisit(TypeId ty)
-    {
-        return ignoreChildren(ty);
-    }
-
-    virtual bool ignoreChildrenVisit(TypePackId ty)
-    {
-        return ignoreChildren(ty);
-    }
+    virtual bool ignoreChildrenVisit(TypeId ty);
+    virtual bool ignoreChildrenVisit(TypePackId 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)
-    {
-        if (ty)
-            return replace(*ty);
-        else
-            return std::nullopt;
-    }
+    std::optional<Ty> replace(std::optional<Ty> ty);
 };
 
 } // 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;
@@ -96,6 +97,22 @@ struct SubtypingEnvironment
         DenseHashSet<TypeId> upperBound{nullptr};
     };
 
+    /* For nested subtyping relationship tests of mapped generic bounds, we keep the outer environment immutable */
+    SubtypingEnvironment* parent = nullptr;
+
+    /// Applies `mappedGenerics` to the given type.
+    /// This is used specifically to substitute for generics in type function instances.
+    std::optional<TypeId> applyMappedGenerics(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId ty);
+
+    const TypeId* tryFindSubstitution(TypeId ty) const;
+    const SubtypingResult* tryFindSubtypingResult(std::pair<TypeId, TypeId> subAndSuper) const;
+
+    bool containsMappedType(TypeId ty) const;
+    bool containsMappedPack(TypePackId tp) const;
+
+    GenericBounds& getMappedTypeBounds(TypeId ty);
+    TypePackId* getMappedPackBounds(TypePackId tp);
+
     /*
      * When we encounter a generic over the course of a subtyping test, we need
      * to tentatively map that generic onto a type on the other side.
@@ -104,7 +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.
@@ -112,17 +129,15 @@ struct SubtypingEnvironment
     DenseHashMap<TypeId, TypeId> substitutions{nullptr};
 
     DenseHashMap<std::pair<TypeId, TypeId>, SubtypingResult, TypePairHash> ephemeralCache{{}};
-
-    /// Applies `mappedGenerics` to the given type.
-    /// This is used specifically to substitute for generics in type function instances.
-    std::optional<TypeId> applyMappedGenerics(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, TypeId ty);
 };
 
 struct Subtyping
 {
     NotNull<BuiltinTypes> builtinTypes;
     NotNull<TypeArena> arena;
+    NotNull<Simplifier> simplifier;
     NotNull<Normalizer> normalizer;
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     NotNull<InternalErrorReporter> iceReporter;
 
     TypeCheckLimits limits;
@@ -142,7 +157,9 @@ struct Subtyping
     Subtyping(
         NotNull<BuiltinTypes> builtinTypes,
         NotNull<TypeArena> typeArena,
+        NotNull<Simplifier> simplifier,
         NotNull<Normalizer> normalizer,
+        NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<InternalErrorReporter> iceReporter
     );
 
@@ -212,9 +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, TypeId subTy, const ClassType* subClass, TypeId superTy, const TableType* superTable, NotNull<Scope>);
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const ExternType* subExternType, const ExternType* superExternType, NotNull<Scope> scope);
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, TypeId subTy, const ExternType* subExternType, TypeId superTy, const TableType* superTable, NotNull<Scope>);
     SubtypingResult isCovariantWith(
         SubtypingEnvironment& env,
         const FunctionType* subFunction,
@@ -242,11 +258,11 @@ private:
     );
     SubtypingResult isCovariantWith(
         SubtypingEnvironment& env,
-        const NormalizedClassType& subClass,
-        const NormalizedClassType& superClass,
+        const NormalizedExternType& subExternType,
+        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 +44,8 @@ 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);
     size_t compositeTypesSingleLineLimit = 5; // The number of type elements permitted on a single line when printing type unions/intersections

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)
@@ -31,6 +31,7 @@ namespace Luau
 struct TypeArena;
 struct Scope;
 using ScopePtr = std::shared_ptr<Scope>;
+struct Module;
 
 struct TypeFunction;
 struct Constraint;
@@ -68,11 +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);
-    explicit FreeType(Scope* scope);
-    FreeType(Scope* scope, TypeLevel level);
-
-    FreeType(Scope* scope, TypeId lowerBound, TypeId upperBound);
+    // New constructors
+    explicit FreeType(TypeLevel level, TypeId lowerBound, TypeId upperBound);
+    // This one got promoted to explicit
+    explicit FreeType(Scope* scope, TypeId lowerBound, TypeId upperBound, Polarity polarity = Polarity::Unknown);
+    explicit FreeType(Scope* scope, TypeLevel level, TypeId lowerBound, TypeId upperBound);
 
     int index;
     TypeLevel level;
@@ -86,6 +87,8 @@ struct FreeType
     // Only used under local type inference
     TypeId lowerBound = nullptr;
     TypeId upperBound = nullptr;
+
+    Polarity polarity = Polarity::Unknown;
 };
 
 struct GenericType
@@ -94,8 +97,8 @@ struct GenericType
     GenericType();
 
     explicit GenericType(TypeLevel level);
-    explicit GenericType(const Name& name);
-    explicit GenericType(Scope* scope);
+    explicit GenericType(const Name& name, Polarity polarity = Polarity::Unknown);
+    explicit GenericType(Scope* scope, Polarity polarity = Polarity::Unknown);
 
     GenericType(TypeLevel level, const Name& name);
     GenericType(Scope* scope, const Name& name);
@@ -105,6 +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,
@@ -130,14 +135,14 @@ struct BlockedType
     BlockedType();
     int index;
 
-    Constraint* getOwner() const;
-    void setOwner(Constraint* newOwner);
-    void replaceOwner(Constraint* newOwner);
+    const Constraint* getOwner() const;
+    void setOwner(const 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
@@ -278,19 +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;
@@ -307,8 +308,30 @@ struct MagicFunctionTypeCheckContext
     NotNull<Scope> checkScope;
 };
 
-using DcrMagicRefinement = void (*)(const MagicRefinementContext&);
-using DcrMagicFunctionTypeCheck = std::function<void(const MagicFunctionTypeCheckContext&)>;
+struct MagicFunction
+{
+    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
@@ -325,10 +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 = {},
@@ -345,16 +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
@@ -363,25 +374,16 @@ struct FunctionType
     std::vector<std::optional<FunctionArgument>> argNames;
     Tags tags;
     TypeLevel level;
-    Scope* scope = nullptr;
     TypePackId argTypes;
     TypePackId retTypes;
-    MagicFunction magicFunction = nullptr;
-    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;
+    std::shared_ptr<MagicFunction> magic = 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
@@ -458,7 +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;
@@ -503,9 +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.
@@ -531,15 +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.
- * Two different classes that share the same properties are nevertheless distinct and mutually incompatible.
+ * Extern types optionally have a parent type.
+ * Two different extern types that share the same properties are nevertheless distinct and mutually incompatible.
  */
-struct ClassType
+struct ExternType
 {
     using Props = TableType::Props;
 
@@ -553,7 +554,7 @@ struct ClassType
     std::optional<Location> definitionLocation;
     std::optional<TableIndexer> indexer;
 
-    ClassType(
+    ExternType(
         Name name,
         Props props,
         std::optional<TypeId> parent,
@@ -574,7 +575,7 @@ struct ClassType
     {
     }
 
-    ClassType(
+    ExternType(
         Name name,
         Props props,
         std::optional<TypeId> parent,
@@ -598,6 +599,18 @@ struct ClassType
     }
 };
 
+// Data required to initialize a user-defined function and its environment
+struct UserDefinedFunctionData
+{
+    // Store a weak module reference to ensure the lifetime requirements are preserved
+    std::weak_ptr<Module> owner;
+
+    // References to AST elements are owned by the Module allocator which also stores this type
+    AstStatTypeFunction* definition = nullptr;
+
+    DenseHashMap<Name, std::pair<AstStatTypeFunction*, size_t>> environment{""};
+};
+
 /**
  * An instance of a type function that has not yet been reduced to a more concrete
  * type. The constraint solver receives a constraint to reduce each
@@ -612,21 +625,21 @@ 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<AstExprFunction*> userFuncBody; // Body 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(
         NotNull<const TypeFunction> function,
         std::vector<TypeId> typeArguments,
         std::vector<TypePackId> packArguments,
-        std::optional<AstName> userFuncName = std::nullopt,
-        std::optional<AstExprFunction*> userFuncBody = std::nullopt
+        std::optional<AstName> userFuncName,
+        UserDefinedFunctionData userFuncData
     )
         : function(function)
         , typeArguments(typeArguments)
         , packArguments(packArguments)
         , userFuncName(userFuncName)
-        , userFuncBody(userFuncBody)
+        , userFuncData(userFuncData)
     {
     }
 
@@ -643,6 +656,13 @@ struct TypeFunctionInstanceType
         , packArguments(packArguments)
     {
     }
+
+    TypeFunctionInstanceType(NotNull<const TypeFunction> function, std::vector<TypeId> typeArguments, std::vector<TypePackId> packArguments)
+        : function{function}
+        , typeArguments(typeArguments)
+        , packArguments(packArguments)
+    {
+    }
 };
 
 /** Represents a pending type alias instantiation.
@@ -670,6 +690,11 @@ struct AnyType
 {
 };
 
+// A special, trivial type for the refinement system that is always eliminated from intersections.
+struct NoRefineType
+{
+};
+
 // `T | U`
 struct UnionType
 {
@@ -737,7 +762,7 @@ struct NegationType
     TypeId ty;
 };
 
-using ErrorType = Unifiable::Error;
+using ErrorType = Unifiable::Error<TypeId>;
 
 using TypeVariant = Unifiable::Variant<
     TypeId,
@@ -750,7 +775,7 @@ using TypeVariant = Unifiable::Variant<
     FunctionType,
     TableType,
     MetatableType,
-    ClassType,
+    ExternType,
     AnyType,
     UnionType,
     IntersectionType,
@@ -758,6 +783,7 @@ using TypeVariant = Unifiable::Variant<
     UnknownType,
     NeverType,
     NegationType,
+    NoRefineType,
     TypeFunctionInstanceType>;
 
 struct Type final
@@ -803,6 +829,13 @@ struct Type final
     Type& operator=(const TypeVariant& rhs);
     Type& operator=(TypeVariant&& rhs);
 
+    Type(Type&&) = default;
+    Type& operator=(Type&&) = default;
+
+    Type clone() const;
+
+private:
+    Type(const Type&) = default;
     Type& operator=(const Type& rhs);
 };
 
@@ -835,6 +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)
@@ -842,16 +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)
     {
     }
 
@@ -943,7 +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;
@@ -952,8 +995,10 @@ public:
     const TypeId unknownType;
     const TypeId neverType;
     const TypeId errorType;
+    const TypeId noRefineType;
     const TypeId falsyType;
     const TypeId truthyType;
+    const TypeId notNilType;
 
     const TypeId optionalNumberType;
     const TypeId optionalStringType;
@@ -974,10 +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);
 
@@ -1154,11 +1199,15 @@ 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);
 
+// A tag to mark a type which doesn't derive directly from the root type as overriding the return of `typeof`.
+// Any classes which derive from this type will have typeof return this type.
+static constexpr char kTypeofRootTag[] = "typeofRoot";
+
 void attachTag(TypeId ty, const std::string& tagName);
 void attachTag(Property& prop, const std::string& tagName);
 

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(Scope* scope);
-    TypeId freshType(Scope* scope, TypeLevel level);
+    TypeId freshType(NotNull<BuiltinTypes> builtins, TypeLevel level);
+    TypeId freshType(NotNull<BuiltinTypes> builtins, Scope* scope);
+    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/Subtyping.h"
+#include "Luau/TypeUtils.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)
-                first = false;
+            if (FFlag::LuauImproveTypePathsInErrors)
+            {
+                if (reasons.size() > 1)
+                    allReasons += "\n\t * ";
+            }
             else
-                allReasons += "\n\t";
+            {
+                if (first)
+                    first = false;
+                else
+                    allReasons += "\n\t";
+            }
 
             allReasons += reason;
         }
@@ -60,7 +74,9 @@ struct Reasonings
 
 void check(
     NotNull<BuiltinTypes> builtinTypes,
-    NotNull<UnifierSharedState> sharedState,
+    NotNull<Simplifier> simplifier,
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime,
+    NotNull<UnifierSharedState> unifierState,
     NotNull<TypeCheckLimits> limits,
     DcrLogger* logger,
     const SourceModule& sourceModule,
@@ -70,6 +86,8 @@ void check(
 struct TypeChecker2
 {
     NotNull<BuiltinTypes> builtinTypes;
+    NotNull<Simplifier> simplifier;
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     DcrLogger* logger;
     const NotNull<TypeCheckLimits> limits;
     const NotNull<InternalErrorReporter> ice;
@@ -88,6 +106,8 @@ struct TypeChecker2
 
     TypeChecker2(
         NotNull<BuiltinTypes> builtinTypes,
+        NotNull<Simplifier> simplifier,
+        NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<UnifierSharedState> unifierState,
         NotNull<TypeCheckLimits> limits,
         DcrLogger* logger,
@@ -109,14 +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);
-    TypeId lookupExpectedType(AstExpr* expr);
-    TypePackId lookupExpectedPack(AstExpr* expr, TypeArena& arena);
+    std::optional<TypePackId> lookupPackAnnotation(AstTypePack* annotation) const;
+    TypeId lookupExpectedType(AstExpr* expr) const;
+    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);
@@ -140,7 +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);
@@ -153,7 +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);
@@ -168,7 +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);
@@ -210,6 +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

@@ -1,29 +1,71 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
-#include "Luau/ConstraintSolver.h"
+#include "Luau/Constraint.h"
+#include "Luau/EqSatSimplification.h"
 #include "Luau/Error.h"
 #include "Luau/NotNull.h"
 #include "Luau/TypeCheckLimits.h"
+#include "Luau/TypeFunctionRuntime.h"
 #include "Luau/TypeFwd.h"
 
 #include <functional>
 #include <string>
 #include <optional>
 
+struct lua_State;
+
 namespace Luau
 {
 
 struct TypeArena;
 struct TxnLog;
+struct ConstraintSolver;
 class Normalizer;
 
+using StateRef = std::unique_ptr<lua_State, void (*)(lua_State*)>;
+
+struct TypeFunctionRuntime
+{
+    TypeFunctionRuntime(NotNull<InternalErrorReporter> ice, NotNull<TypeCheckLimits> limits);
+    ~TypeFunctionRuntime();
+
+    // Return value is an error message if registration failed
+    std::optional<std::string> registerFunction(AstStatTypeFunction* function);
+
+    // For user-defined type functions, we store all generated types and packs for the duration of the typecheck
+    TypedAllocator<TypeFunctionType> typeArena;
+    TypedAllocator<TypeFunctionTypePackVar> typePackArena;
+
+    NotNull<InternalErrorReporter> ice;
+    NotNull<TypeCheckLimits> limits;
+
+    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();
+};
+
 struct TypeFunctionContext
 {
     NotNull<TypeArena> arena;
     NotNull<BuiltinTypes> builtins;
     NotNull<Scope> scope;
+    NotNull<Simplifier> simplifier;
     NotNull<Normalizer> normalizer;
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     NotNull<InternalErrorReporter> ice;
     NotNull<TypeCheckLimits> limits;
 
@@ -32,33 +74,26 @@ 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<AstExprFunction*> userFuncBody; // Body 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)
-        : arena(cs->arena)
-        , builtins(cs->builtinTypes)
-        , scope(scope)
-        , normalizer(cs->normalizer)
-        , ice(NotNull{&cs->iceReporter})
-        , limits(NotNull{&cs->limits})
-        , solver(cs.get())
-        , constraint(constraint.get())
-    {
-    }
+    TypeFunctionContext(NotNull<ConstraintSolver> cs, NotNull<Scope> scope, NotNull<const Constraint> constraint);
 
     TypeFunctionContext(
         NotNull<TypeArena> arena,
         NotNull<BuiltinTypes> builtins,
         NotNull<Scope> scope,
+        NotNull<Simplifier> simplifier,
         NotNull<Normalizer> normalizer,
+        NotNull<TypeFunctionRuntime> typeFunctionRuntime,
         NotNull<InternalErrorReporter> ice,
         NotNull<TypeCheckLimits> limits
     )
         : arena(arena)
         , builtins(builtins)
         , scope(scope)
+        , simplifier(simplifier)
         , normalizer(normalizer)
+        , typeFunctionRuntime(typeFunctionRuntime)
         , ice(ice)
         , limits(limits)
         , solver(nullptr)
@@ -66,7 +101,17 @@ struct TypeFunctionContext
     {
     }
 
-    NotNull<Constraint> pushConstraint(ConstraintV&& c);
+    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,
@@ -75,19 +120,25 @@ struct TypeFunctionContext
 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
-    /// permanently, whether this type function reduction results in an
-    /// uninhabitable type. This will trigger an error to be reported.
-    bool uninhabited;
+    /// Indicates the status of this reduction: is `Reduction::Irreducible` if
+    /// the this result indicates the type function is irreducible, and
+    /// `Reduction::Erroneous` if this result indicates the type function is
+    /// erroneous. `Reduction::MaybeOk` otherwise.
+    Reduction reductionStatus;
     /// Any types that need to be progressed or mutated before the reduction may
     /// proceed.
     std::vector<TypeId> blockedTypes;
     /// Any type packs that need to be progressed or mutated before the
     /// reduction may proceed.
     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>
@@ -104,6 +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
@@ -116,15 +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};
 };
 
 /**
@@ -192,6 +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

@@ -0,0 +1,296 @@
+// 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/Variant.h"
+#include "Luau/TypeFwd.h"
+
+#include <optional>
+#include <string>
+#include <map>
+#include <vector>
+
+using lua_State = struct lua_State;
+
+namespace Luau
+{
+
+void* typeFunctionAlloc(void* ud, void* ptr, size_t osize, size_t nsize);
+
+// Replica of types from Type.h
+struct TypeFunctionType;
+using TypeFunctionTypeId = const TypeFunctionType*;
+
+struct TypeFunctionTypePackVar;
+using TypeFunctionTypePackId = const TypeFunctionTypePackVar*;
+
+struct TypeFunctionPrimitiveType
+{
+    enum Type
+    {
+        NilType,
+        Boolean,
+        Number,
+        String,
+        Thread,
+        Buffer,
+    };
+
+    Type type;
+
+    TypeFunctionPrimitiveType(Type type)
+        : type(type)
+    {
+    }
+};
+
+struct TypeFunctionBooleanSingleton
+{
+    bool value = false;
+};
+
+struct TypeFunctionStringSingleton
+{
+    std::string value;
+};
+
+using TypeFunctionSingletonVariant = Variant<TypeFunctionBooleanSingleton, TypeFunctionStringSingleton>;
+
+struct TypeFunctionSingletonType
+{
+    TypeFunctionSingletonVariant variant;
+
+    explicit TypeFunctionSingletonType(TypeFunctionSingletonVariant variant)
+        : variant(std::move(variant))
+    {
+    }
+};
+
+template<typename T>
+const T* get(const TypeFunctionSingletonType* tv)
+{
+    LUAU_ASSERT(tv);
+
+    return tv ? get_if<T>(&tv->variant) : nullptr;
+}
+
+template<typename T>
+T* getMutable(const TypeFunctionSingletonType* tv)
+{
+    LUAU_ASSERT(tv);
+
+    return tv ? get_if<T>(&const_cast<TypeFunctionSingletonType*>(tv)->variant) : nullptr;
+}
+
+struct TypeFunctionUnionType
+{
+    std::vector<TypeFunctionTypeId> components;
+};
+
+struct TypeFunctionIntersectionType
+{
+    std::vector<TypeFunctionTypeId> components;
+};
+
+struct TypeFunctionAnyType
+{
+};
+
+struct TypeFunctionUnknownType
+{
+};
+
+struct TypeFunctionNeverType
+{
+};
+
+struct TypeFunctionNegationType
+{
+    TypeFunctionTypeId type;
+};
+
+struct TypeFunctionTypePack
+{
+    std::vector<TypeFunctionTypeId> head;
+    std::optional<TypeFunctionTypePackId> tail;
+};
+
+struct TypeFunctionVariadicTypePack
+{
+    TypeFunctionTypeId type;
+};
+
+struct TypeFunctionGenericTypePack
+{
+    bool isNamed = false;
+
+    std::string name;
+};
+
+using TypeFunctionTypePackVariant = Variant<TypeFunctionTypePack, TypeFunctionVariadicTypePack, TypeFunctionGenericTypePack>;
+
+struct TypeFunctionTypePackVar
+{
+    TypeFunctionTypePackVariant type;
+
+    TypeFunctionTypePackVar(TypeFunctionTypePackVariant type)
+        : type(std::move(type))
+    {
+    }
+
+    bool operator==(const TypeFunctionTypePackVar& rhs) const;
+};
+
+struct TypeFunctionFunctionType
+{
+    std::vector<TypeFunctionTypeId> generics;
+    std::vector<TypeFunctionTypePackId> genericPacks;
+
+    TypeFunctionTypePackId argTypes;
+    TypeFunctionTypePackId retTypes;
+};
+
+template<typename T>
+const T* get(TypeFunctionTypePackId tv)
+{
+    LUAU_ASSERT(tv);
+
+    return tv ? get_if<T>(&tv->type) : nullptr;
+}
+
+template<typename T>
+T* getMutable(TypeFunctionTypePackId tv)
+{
+    LUAU_ASSERT(tv);
+
+    return tv ? get_if<T>(&const_cast<TypeFunctionTypePackVar*>(tv)->type) : nullptr;
+}
+
+struct TypeFunctionTableIndexer
+{
+    TypeFunctionTableIndexer(TypeFunctionTypeId keyType, TypeFunctionTypeId valueType)
+        : keyType(keyType)
+        , valueType(valueType)
+    {
+    }
+
+    TypeFunctionTypeId keyType;
+    TypeFunctionTypeId valueType;
+};
+
+struct TypeFunctionProperty
+{
+    static TypeFunctionProperty readonly(TypeFunctionTypeId ty);
+    static TypeFunctionProperty writeonly(TypeFunctionTypeId ty);
+    static TypeFunctionProperty rw(TypeFunctionTypeId ty);                             // Shared read-write type.
+    static TypeFunctionProperty rw(TypeFunctionTypeId read, TypeFunctionTypeId write); // Separate read-write type.
+
+    bool isReadOnly() const;
+    bool isWriteOnly() const;
+
+    std::optional<TypeFunctionTypeId> readTy;
+    std::optional<TypeFunctionTypeId> writeTy;
+};
+
+struct TypeFunctionTableType
+{
+    using Name = std::string;
+    using Props = std::map<Name, TypeFunctionProperty>;
+
+    Props props;
+
+    std::optional<TypeFunctionTableIndexer> indexer;
+
+    // Should always be a TypeFunctionTableType
+    std::optional<TypeFunctionTypeId> metatable;
+};
+
+struct TypeFunctionExternType
+{
+    using Name = std::string;
+    using Props = std::map<Name, TypeFunctionProperty>;
+
+    Props props;
+
+    std::optional<TypeFunctionTableIndexer> indexer;
+
+    std::optional<TypeFunctionTypeId> metatable; // metaclass?
+
+    // 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;
+};
+
+using TypeFunctionTypeVariant = Luau::Variant<
+    TypeFunctionPrimitiveType,
+    TypeFunctionAnyType,
+    TypeFunctionUnknownType,
+    TypeFunctionNeverType,
+    TypeFunctionSingletonType,
+    TypeFunctionUnionType,
+    TypeFunctionIntersectionType,
+    TypeFunctionNegationType,
+    TypeFunctionFunctionType,
+    TypeFunctionTableType,
+    TypeFunctionExternType,
+    TypeFunctionGenericType>;
+
+struct TypeFunctionType
+{
+    TypeFunctionTypeVariant type;
+
+    TypeFunctionType(TypeFunctionTypeVariant type)
+        : type(std::move(type))
+    {
+    }
+
+    bool operator==(const TypeFunctionType& rhs) const;
+};
+
+template<typename T>
+const T* get(TypeFunctionTypeId tv)
+{
+    LUAU_ASSERT(tv);
+
+    return tv ? Luau::get_if<T>(&tv->type) : nullptr;
+}
+
+template<typename T>
+T* getMutable(TypeFunctionTypeId tv)
+{
+    LUAU_ASSERT(tv);
+
+    return tv ? Luau::get_if<T>(&const_cast<TypeFunctionType*>(tv)->type) : nullptr;
+}
+
+std::optional<std::string> checkResultForError(lua_State* L, const char* typeFunctionName, int luaResult);
+
+TypeFunctionType* allocateTypeFunctionType(lua_State* L, TypeFunctionTypeVariant type);
+TypeFunctionTypePackVar* allocateTypeFunctionTypePack(lua_State* L, TypeFunctionTypePackVariant type);
+
+void allocTypeUserData(lua_State* L, TypeFunctionTypeVariant type);
+
+bool isTypeUserData(lua_State* L, int idx);
+TypeFunctionTypeId getTypeUserData(lua_State* L, int idx);
+std::optional<TypeFunctionTypeId> optionalTypeUserData(lua_State* L, int idx);
+
+void registerTypesLibrary(lua_State* L);
+void registerTypeUserData(lua_State* L);
+
+void setTypeFunctionEnvironment(lua_State* L);
+
+void resetTypeFunctionState(lua_State* L);
+
+} // namespace Luau

Analysis/include/Luau/TypeFunctionRuntimeBuilder.h

@@ -0,0 +1,44 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/Type.h"
+#include "Luau/TypeFunction.h"
+#include "Luau/TypeFunctionRuntime.h"
+
+namespace Luau
+{
+
+using Kind = Variant<TypeId, TypePackId>;
+
+template<typename T>
+const T* get(const Kind& kind)
+{
+    return get_if<T>(&kind);
+}
+
+using TypeFunctionKind = Variant<TypeFunctionTypeId, TypeFunctionTypePackId>;
+
+template<typename T>
+const T* get(const TypeFunctionKind& tfkind)
+{
+    return get_if<T>(&tfkind);
+}
+
+struct TypeFunctionRuntimeBuilderState
+{
+    NotNull<TypeFunctionContext> ctx;
+
+    // List of errors that occur during serialization/deserialization
+    // 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)
+    {
+    }
+};
+
+TypeFunctionTypeId serialize(TypeId ty, TypeFunctionRuntimeBuilderState* state);
+TypeId deserialize(TypeFunctionTypeId ty, TypeFunctionRuntimeBuilderState* state);
+
+} // namespace Luau

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<AstGenericTypePack>& genericPackNames,
+        const AstArray<AstGenericType*>& genericNames,
+        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(TypePackVariant&& ty);
-    TypePackVar(TypePackVariant&& ty, bool persistent);
+    explicit TypePackVar(const TypePackVariant& tp);
+    explicit TypePackVar(TypePackVariant&& tp);
+    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

@@ -42,15 +42,27 @@ 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;
 };
 
 /// Represents fields of a type or pack that contain a type.
 enum class TypeField
 {
+    /// The table of a metatable type.
+    Table,
     /// The metatable of a type. This could be a metatable type, a primitive
     /// type, a class type, or perhaps even a string singleton type.
     Metatable,
@@ -203,6 +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)
     {
@@ -248,4 +248,47 @@ std::optional<Ty> follow(std::optional<Ty> ty)
         return std::nullopt;
 }
 
+/**
+ * Returns whether or not expr is a literal expression, for example:
+ * - Scalar literals (numbers, booleans, strings, nil)
+ * - Table literals
+ * - Lambdas (a "function literal")
+ */
+bool isLiteral(const AstExpr* expr);
+
+/**
+ * Given a table literal and a mapping from expression to type, determine
+ * whether any literal expression in this table depends on any 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.
+ * @param expr Expression to search
+ * @param astTypes Mapping from AST node to TypeID
+ * @returns A vector of blocked types
+ */
+std::vector<TypeId> findBlockedTypesIn(AstExprTable* expr, NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes);
+
+/**
+ * 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.
+ * 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.
+ * @param expr Expression to search
+ * @param astTypes Mapping from AST node to TypeID
+ * @returns A vector of blocked types
+ */
+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:
@@ -179,7 +174,7 @@ public:
     bool occursCheck(TypePackId needle, TypePackId haystack, bool reversed);
     bool occursCheck(DenseHashSet<TypePackId>& seen, TypePackId needle, TypePackId haystack);
 
-    Unifier makeChildUnifier();
+    std::unique_ptr<Unifier> makeChildUnifier();
 
     void reportError(TypeError err);
     LUAU_NOINLINE void reportError(Location location, TypeErrorData data);
@@ -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);
     }
@@ -133,6 +134,10 @@ struct GenericTypeVisitor
     {
         return visit(ty);
     }
+    virtual bool visit(TypeId ty, const NoRefineType& nrt)
+    {
+        return visit(ty);
+    }
     virtual bool visit(TypeId ty, const UnknownType& utv)
     {
         return visit(ty);
@@ -186,7 +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);
     }
@@ -308,11 +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)
                     {
@@ -330,21 +335,23 @@ struct GenericTypeVisitor
                         traverse(prop.type());
                 }
 
-                if (ctv->parent)
-                    traverse(*ctv->parent);
+                if (etv->parent)
+                    traverse(*etv->parent);
 
-                if (ctv->metatable)
-                    traverse(*ctv->metatable);
+                if (etv->metatable)
+                    traverse(*etv->metatable);
 
-                if (ctv->indexer)
+                if (etv->indexer)
                 {
-                    traverse(ctv->indexer->indexType);
-                    traverse(ctv->indexer->indexResultType);
+                    traverse(etv->indexer->indexType);
+                    traverse(etv->indexer->indexResultType);
                 }
             }
         }
         else if (auto atv = get<AnyType>(ty))
             visit(ty, *atv);
+        else if (auto nrt = get<NoRefineType>(ty))
+            visit(ty, *nrt);
         else if (auto utv = get<UnionType>(ty))
         {
             if (visit(ty, *utv))
@@ -389,7 +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))
@@ -455,7 +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, false);
-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
 {
 
@@ -425,13 +427,22 @@ struct AstJsonEncoder : public AstVisitor
             "AstExprFunction",
             [&]()
             {
+                PROP(attributes);
                 PROP(generics);
                 PROP(genericPacks);
                 if (node->self)
                     PROP(self);
                 PROP(args);
-                if (node->returnAnnotation)
-                    PROP(returnAnnotation);
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                {
+                    if (node->returnAnnotation)
+                        PROP(returnAnnotation);
+                }
+                else
+                {
+                    if (node->returnAnnotation_DEPRECATED)
+                        write("returnAnnotation", node->returnAnnotation_DEPRECATED);
+                }
                 PROP(vararg);
                 PROP(varargLocation);
                 if (node->varargAnnotation)
@@ -464,26 +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);
-        if (genericType.defaultValue)
-            write("luauType", genericType.defaultValue);
+        write("name", genericType->name);
+        if (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);
-        if (genericTypePack.defaultValue)
-            write("luauType", genericTypePack.defaultValue);
+        write("name", genericTypePack->name);
+        if (genericTypePack->defaultValue)
+            write("luauType", genericTypePack->defaultValue);
         popComma(c);
         writeRaw("}");
     }
@@ -881,7 +892,7 @@ struct AstJsonEncoder : public AstVisitor
                 PROP(name);
                 PROP(generics);
                 PROP(genericPacks);
-                PROP(type);
+                write("value", node->type);
                 PROP(exported);
             }
         );
@@ -894,14 +905,17 @@ struct AstJsonEncoder : public AstVisitor
             "AstStatDeclareFunction",
             [&]()
             {
-                // TODO: attributes
+                PROP(attributes);
                 PROP(name);
                 PROP(nameLocation);
                 PROP(params);
                 PROP(paramNames);
                 PROP(vararg);
                 PROP(varargLocation);
-                PROP(retTypes);
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                    PROP(retTypes);
+                else
+                    write("retTypes", node->retTypes_DEPRECATED);
                 PROP(generics);
                 PROP(genericPacks);
             }
@@ -922,7 +936,7 @@ struct AstJsonEncoder : public AstVisitor
         );
     }
 
-    void write(const AstDeclaredClassProp& prop)
+    void write(const AstDeclaredExternTypeProperty& prop)
     {
         writeRaw("{");
         bool c = pushComma();
@@ -935,7 +949,7 @@ struct AstJsonEncoder : public AstVisitor
         writeRaw("}");
     }
 
-    void write(class AstStatDeclareClass* node)
+    void write(class AstStatDeclareExternType* node)
     {
         writeNode(
             node,
@@ -1042,11 +1056,15 @@ struct AstJsonEncoder : public AstVisitor
             "AstTypeFunction",
             [&]()
             {
+                PROP(attributes);
                 PROP(generics);
                 PROP(genericPacks);
                 PROP(argTypes);
                 PROP(argNames);
-                PROP(returnTypes);
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                    PROP(returnTypes);
+                else
+                    write("returnTypes", node->returnTypes_DEPRECATED);
             }
         );
     }
@@ -1063,6 +1081,11 @@ struct AstJsonEncoder : public AstVisitor
         );
     }
 
+    void write(class AstTypeOptional* node)
+    {
+        writeNode(node, "AstTypeOptional", [&]() {});
+    }
+
     void write(class AstTypeUnion* node)
     {
         writeNode(
@@ -1136,6 +1159,44 @@ struct AstJsonEncoder : public AstVisitor
         );
     }
 
+    void write(AstAttr::Type type)
+    {
+        switch (type)
+        {
+        case AstAttr::Type::Checked:
+            return writeString("checked");
+        case AstAttr::Type::Native:
+            return writeString("native");
+        case AstAttr::Type::Deprecated:
+            return writeString("deprecated");
+        }
+    }
+
+    void write(class AstAttr* node)
+    {
+        writeNode(
+            node,
+            "AstAttr",
+            [&]()
+            {
+                write("name", node->type);
+            }
+        );
+    }
+
+    bool visit(class AstTypeGroup* node) override
+    {
+        writeNode(
+            node,
+            "AstTypeGroup",
+            [&]()
+            {
+                write("inner", node->type);
+            }
+        );
+        return false;
+    }
+
     bool visit(class AstTypeSingletonBool* node) override
     {
         writeNode(
@@ -1384,7 +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

@@ -41,11 +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;
     }
 
@@ -509,6 +513,37 @@ static std::optional<DocumentationSymbol> checkOverloadedDocumentationSymbol(
     return documentationSymbol;
 }
 
+static std::optional<DocumentationSymbol> getMetatableDocumentation(
+    const Module& module,
+    AstExpr* parentExpr,
+    const TableType* mtable,
+    const AstName& index
+)
+{
+    auto indexIt = mtable->props.find("__index");
+    if (indexIt == mtable->props.end())
+        return std::nullopt;
+
+    TypeId followed = follow(indexIt->second.type());
+    const TableType* ttv = get<TableType>(followed);
+    if (!ttv)
+        return std::nullopt;
+
+    auto propIt = ttv->props.find(index.value);
+    if (propIt == ttv->props.end())
+        return std::nullopt;
+
+    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);
+
+    return std::nullopt;
+}
+
 std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const SourceModule& source, const Module& module, Position position)
 {
     std::vector<AstNode*> ancestry = findAstAncestryOfPosition(source, position);
@@ -539,17 +574,31 @@ 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 (auto propIt = ctv->props.find(indexName->index.value); propIt != ctv->props.end())
+                    while (etv)
                     {
-                        if (FFlag::LuauSolverV2)
+                        if (auto propIt = etv->props.find(indexName->index.value); propIt != etv->props.end())
                         {
-                            if (auto ty = propIt->second.readTy)
-                                return checkOverloadedDocumentationSymbol(module, *ty, parentExpr, propIt->second.documentationSymbol);
+                            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
+                                );
                         }
-                        else
-                            return checkOverloadedDocumentationSymbol(module, propIt->second.type(), parentExpr, propIt->second.documentationSymbol);
+                        etv = etv->parent ? Luau::get<Luau::ExternType>(*etv->parent) : nullptr;
+                    }
+                }
+                else if (const PrimitiveType* ptv = get<PrimitiveType>(parentTy); ptv && ptv->metatable)
+                {
+                    if (auto mtable = get<TableType>(*ptv->metatable))
+                    {
+                        if (std::optional<std::string> docSymbol = getMetatableDocumentation(module, parentExpr, mtable, indexName->index))
+                            return docSymbol;
                     }
                 }
             }

Analysis/src/AutocompleteCore.h

@@ -0,0 +1,27 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/AutocompleteTypes.h"
+
+namespace Luau
+{
+struct Module;
+struct FileResolver;
+
+using ModulePtr = std::shared_ptr<Module>;
+using ModuleName = std::string;
+
+
+AutocompleteResult autocomplete_(
+    const ModulePtr& module,
+    NotNull<BuiltinTypes> builtinTypes,
+    TypeArena* typeArena,
+    std::vector<AstNode*>& ancestry,
+    Scope* globalScope,
+    const ScopePtr& scopeAtPosition,
+    Position position,
+    FileResolver* fileResolver,
+    StringCompletionCallback callback
+);
+
+} // namespace Luau

Analysis/src/BuiltinDefinitions.cpp

@@ -2,20 +2,24 @@
 #include "Luau/BuiltinDefinitions.h"
 
 #include "Luau/Ast.h"
-#include "Luau/Frontend.h"
-#include "Luau/Symbol.h"
+#include "Luau/Clone.h"
 #include "Luau/Common.h"
-#include "Luau/ToString.h"
-#include "Luau/ConstraintSolver.h"
 #include "Luau/ConstraintGenerator.h"
+#include "Luau/ConstraintSolver.h"
+#include "Luau/DenseHash.h"
+#include "Luau/Error.h"
+#include "Luau/Frontend.h"
+#include "Luau/InferPolarity.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>
 
@@ -25,47 +29,93 @@
  * about a function that takes any number of values, but where each value must have some specific type.
  */
 
-LUAU_FASTFLAG(LuauSolverV2);
-LUAU_FASTFLAGVARIABLE(LuauDCRMagicFunctionTypeChecker, false);
+LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAG(LuauNonReentrantGeneralization2)
+LUAU_FASTFLAGVARIABLE(LuauTableCloneClonesType3)
+LUAU_FASTFLAGVARIABLE(LuauUserTypeFunTypecheck)
+LUAU_FASTFLAGVARIABLE(LuauMagicFreezeCheckBlocked)
+LUAU_FASTFLAGVARIABLE(LuauFormatUseLastPosition)
 
 namespace Luau
 {
 
-static std::optional<WithPredicate<TypePackId>> magicFunctionSelect(
-    TypeChecker& typechecker,
-    const ScopePtr& scope,
-    const AstExprCall& expr,
-    WithPredicate<TypePackId> withPredicate
-);
-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 MagicSelect 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 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);
-static bool dcrMagicFunctionRequire(MagicFunctionCallContext context);
-static bool dcrMagicFunctionPack(MagicFunctionCallContext context);
+struct MagicAssert 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 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)
 {
@@ -160,34 +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;
-    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;
+        ftv->magic = std::move(magic);
     else
         LUAU_ASSERT(!"Got a non functional type");
 }
@@ -222,6 +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;
 }
 
@@ -263,6 +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());
@@ -270,6 +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()});
@@ -279,8 +325,8 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
     );
     LUAU_ASSERT(loadResult.success);
 
-    TypeId genericK = arena.addType(GenericType{"K"});
-    TypeId genericV = arena.addType(GenericType{"V"});
+    TypeId genericK = arena.addType(GenericType{globalScope, "K"});
+    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);
@@ -293,6 +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}});
@@ -306,7 +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);
@@ -318,7 +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
@@ -352,23 +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);
-
-        if (TableType* ttv = getMutable<TableType>(pair.second.typeId))
+        finalizeGlobalBindings(globals.globalScope);
+    }
+    else
+    {
+        for (const auto& pair : globals.globalScope->bindings)
         {
-            if (!ttv->name)
-                ttv->name = "typeof(" + toString(pair.first) + ")";
+            persist(pair.second.typeId);
+
+            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})}, {}
         });
@@ -379,9 +454,8 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
         addGlobalBinding(globals, "assert", assertTy, "@luau");
     }
 
-    attachMagicFunction(getGlobalBinding(globals, "setmetatable"), magicFunctionSetMetaTable);
-    attachMagicFunction(getGlobalBinding(globals, "select"), magicFunctionSelect);
-    attachDcrMagicFunction(getGlobalBinding(globals, "select"), dcrMagicFunctionSelect);
+    attachMagicFunction(getGlobalBinding(globals, "setmetatable"), std::make_shared<MagicSetMetatable>());
+    attachMagicFunction(getGlobalBinding(globals, "select"), std::make_shared<MagicSelect>());
 
     if (TableType* ttv = getMutable<TableType>(getGlobalBinding(globals, "table")))
     {
@@ -392,10 +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});
-            ttv->props["freeze"] = makeProperty(idTy, "@luau/global/table.freeze");
+            if (globalScope)
+                inferGenericPolarities(NotNull{&globals.globalTypes}, NotNull{globalScope}, idTy);
             ttv->props["clone"] = makeProperty(idTy, "@luau/global/table.clone");
         }
         else
@@ -410,12 +490,68 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
         ttv->props["foreach"].deprecated = true;
         ttv->props["foreachi"].deprecated = true;
 
-        attachMagicFunction(ttv->props["pack"].type(), magicFunctionPack);
-        attachDcrMagicFunction(ttv->props["pack"].type(), dcrMagicFunctionPack);
+        attachMagicFunction(ttv->props["pack"].type(), std::make_shared<MagicPack>());
+        if (FFlag::LuauTableCloneClonesType3)
+            attachMagicFunction(ttv->props["clone"].type(), std::make_shared<MagicClone>());
+        attachMagicFunction(ttv->props["freeze"].type(), std::make_shared<MagicFreeze>());
     }
 
-    attachMagicFunction(getGlobalBinding(globals, "require"), magicFunctionRequire);
-    attachDcrMagicFunction(getGlobalBinding(globals, "require"), dcrMagicFunctionRequire);
+    TypeId requireTy = getGlobalBinding(globals, "require");
+    attachTag(requireTy, kRequireTagName);
+    attachMagicFunction(requireTy, std::make_shared<MagicRequire>());
+
+    if (FFlag::LuauUserTypeFunTypecheck)
+    {
+        // Global scope cannot be the parent of the type checking environment because it can be changed by the embedder
+        globals.globalTypeFunctionScope->exportedTypeBindings = globals.globalScope->exportedTypeBindings;
+        globals.globalTypeFunctionScope->builtinTypeNames = globals.globalScope->builtinTypeNames;
+
+        // Type function runtime also removes a few standard libraries and globals, so we will take only the ones that are defined
+        static const char* typeFunctionRuntimeBindings[] = {
+            // Libraries
+            "math",
+            "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);
+    }
 }
 
 static std::vector<TypeId> parseFormatString(NotNull<BuiltinTypes> builtinTypes, const char* data, size_t size)
@@ -454,7 +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,
@@ -504,7 +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;
 
@@ -548,7 +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)
@@ -563,7 +699,18 @@ static void dcrMagicFunctionTypeCheckFormat(MagicFunctionTypeCheckContext contex
         fmt = context.callSite->args.data[0]->as<AstExprConstantString>();
 
     if (!fmt)
-        return;
+    {
+        context.typechecker->reportError(CountMismatch{1, std::nullopt, 0, CountMismatch::Arg, true, "string.format"}, context.callSite->location);
+        return true;
+    }
+
+    // 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);
@@ -576,15 +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);
-            context.typechecker->reportError(TypeMismatch{expectedTy, actualTy, reasonings.toString()}, location);
+            switch (shouldSuppressErrors(NotNull{&context.typechecker->normalizer}, actualTy))
+            {
+            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)
@@ -647,7 +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,
@@ -683,7 +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);
 
@@ -716,7 +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,
@@ -756,7 +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);
 
@@ -792,7 +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,
@@ -850,7 +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);
 
@@ -927,12 +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);
-    if (FFlag::LuauDCRMagicFunctionTypeChecker)
-        attachDcrMagicFunctionTypeCheck(formatFn, dcrMagicFunctionTypeCheckFormat);
+    attachMagicFunction(formatFn, std::make_shared<MagicFormat>());
 
 
     const TypeId stringToStringType = makeFunction(*arena, std::nullopt, {}, {}, {stringType}, {}, {stringType}, /* checked */ true);
@@ -946,16 +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);
-    attachDcrMagicFunction(gmatchFunc, dcrMagicFunctionGmatch);
+    attachMagicFunction(gmatchFunc, std::make_shared<MagicGmatch>());
 
     FunctionType matchFuncTy{
         arena->addTypePack({stringType, stringType, optionalNumber}), arena->addTypePack(TypePackVar{VariadicTypePack{stringType}})
     };
     matchFuncTy.isCheckedFunction = true;
     const TypeId matchFunc = arena->addType(matchFuncTy);
-    attachMagicFunction(matchFunc, magicFunctionMatch);
-    attachDcrMagicFunction(matchFunc, dcrMagicFunctionMatch);
+    attachMagicFunction(matchFunc, std::make_shared<MagicMatch>());
 
     FunctionType findFuncTy{
         arena->addTypePack({stringType, stringType, optionalNumber, optionalBoolean}),
@@ -963,8 +1120,7 @@ TypeId makeStringMetatable(NotNull<BuiltinTypes> builtinTypes)
     };
     findFuncTy.isCheckedFunction = true;
     const TypeId findFunc = arena->addType(findFuncTy);
-    attachMagicFunction(findFunc, magicFunctionFind);
-    attachDcrMagicFunction(findFunc, dcrMagicFunctionFind);
+    attachMagicFunction(findFunc, std::make_shared<MagicFind>());
 
     // string.byte : string -> number? -> number? -> ...number
     FunctionType stringDotByte{arena->addTypePack({stringType, optionalNumber, optionalNumber}), numberVariadicList};
@@ -1025,7 +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,
@@ -1070,7 +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)
     {
@@ -1115,7 +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,
@@ -1197,7 +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,
@@ -1231,7 +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,
@@ -1274,7 +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;
@@ -1314,6 +1480,171 @@ static bool dcrMagicFunctionPack(MagicFunctionCallContext context)
     return true;
 }
 
+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);
+
+        if (!frozenTable)
+            return std::nullopt;
+
+        TypeId resultType = arena->addType(MetatableType{*frozenTable, mt->metatable, mt->syntheticName});
+
+        return resultType;
+    }
+
+    if (get<TableType>(inputType))
+    {
+        // 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, /* ignorePersistent */ true);
+        auto tableTy = getMutable<TableType>(resultType);
+        // `clone` should not break this.
+        LUAU_ASSERT(tableTy);
+        tableTy->state = TableState::Sealed;
+
+        // We'll mutate the table to make every property type read-only.
+        for (auto iter = tableTy->props.begin(); iter != tableTy->props.end();)
+        {
+            if (iter->second.isWriteOnly())
+                iter = tableTy->props.erase(iter);
+            else
+            {
+                iter->second.writeTy = std::nullopt;
+                iter++;
+            }
+        }
+
+        return resultType;
+    }
+
+    context.solver->reportError(TypeMismatch{context.solver->builtinTypes->tableType, inputType}, context.callSite->argLocation);
+    return std::nullopt;
+}
+
+std::optional<WithPredicate<TypePackId>> MagicFreeze::
+    handleOldSolver(struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>)
+{
+    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();
+
+    const auto& [paramTypes, paramTail] = extendTypePack(*arena, context.solver->builtinTypes, context.arguments, 1);
+    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]);
+
+    AstExpr* targetExpr = context.callSite->args.data[0];
+    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)
+    {
+        if (resultTy)
+            asMutable(*resultTy)->ty.emplace<BoundType>(context.solver->builtinTypes->errorType);
+        asMutable(context.result)->ty.emplace<BoundTypePack>(context.solver->builtinTypes->errorTypePack);
+
+        return true;
+    }
+
+    if (resultTy)
+        asMutable(*resultTy)->ty.emplace<BoundType>(*frozenType);
+    asMutable(context.result)->ty.emplace<BoundTypePack>(arena->addTypePack({*frozenType}));
+
+    return true;
+}
+
 static bool checkRequirePath(TypeChecker& typechecker, AstExpr* expr)
 {
     // require(foo.parent.bar) will technically work, but it depends on legacy goop that
@@ -1336,7 +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,
@@ -1382,7 +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)
     {
@@ -1405,4 +1736,52 @@ static bool dcrMagicFunctionRequire(MagicFunctionCallContext context)
     return false;
 }
 
+bool matchSetMetatable(const AstExprCall& call)
+{
+    const char* smt = "setmetatable";
+
+    if (call.args.size != 2)
+        return false;
+
+    const AstExprGlobal* funcAsGlobal = call.func->as<AstExprGlobal>();
+    if (!funcAsGlobal || funcAsGlobal->name != smt)
+        return false;
+
+    return true;
+}
+
+bool matchTableFreeze(const AstExprCall& call)
+{
+    if (call.args.size < 1)
+        return false;
+
+    const AstExprIndexName* index = call.func->as<AstExprIndexName>();
+    if (!index || index->index != "freeze")
+        return false;
+
+    const AstExprGlobal* global = index->expr->as<AstExprGlobal>();
+    if (!global || global->name != "table")
+        return false;
+
+    return true;
+}
+
+bool matchAssert(const AstExprCall& call)
+{
+    if (call.args.size < 1)
+        return false;
+
+    const AstExprGlobal* funcAsGlobal = call.func->as<AstExprGlobal>();
+    if (!funcAsGlobal || funcAsGlobal->name != "assert")
+        return false;
+
+    return true;
+}
+
+bool shouldTypestateForFirstArgument(const AstExprCall& call)
+{
+    // TODO: magic function for setmetatable and assert and then add them
+    return matchTableFreeze(call);
+}
+
 } // namespace Luau

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;
     }
@@ -140,15 +161,15 @@ private:
         }
     }
 
-private:
-    TypeId shallowClone(TypeId ty)
+public:
+    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 @@ private:
             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 @@ private:
         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);
@@ -189,6 +208,7 @@ private:
         return target;
     }
 
+private:
     Property shallowClone(const Property& p)
     {
         if (FFlag::LuauSolverV2)
@@ -256,8 +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(Unifiable::Error* t)
+    void cloneChildren(ErrorType* t)
     {
         // noop.
     }
@@ -336,7 +355,7 @@ private:
         t->metatable = shallowClone(t->metatable);
     }
 
-    void cloneChildren(ClassType* t)
+    void cloneChildren(ExternType* t)
     {
         for (auto& [_, p] : t->props)
             p = shallowClone(p);
@@ -359,6 +378,11 @@ private:
         // noop.
     }
 
+    void cloneChildren(NoRefineType* t)
+    {
+        // noop.
+    }
+
     void cloneChildren(UnionType* t)
     {
         for (TypeId& ty : t->options)
@@ -371,7 +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));
@@ -422,6 +446,11 @@ private:
         t->boundTo = shallowClone(t->boundTo);
     }
 
+    void cloneChildren(ErrorTypePack* t)
+    {
+        // noop.
+    }
+
     void cloneChildren(VariadicTypePack* t)
     {
         t->ty = shallowClone(t->ty);
@@ -446,14 +475,131 @@ 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, bool ignorePersistent)
+{
+    if (tp->persistent && !ignorePersistent)
+        return tp;
+
+    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, bool ignorePersistent)
+{
+    if (typeId->persistent && !ignorePersistent)
+        return typeId;
+
+    TypeCloner cloner{
+        NotNull{&dest},
+        cloneState.builtinTypes,
+        NotNull{&cloneState.seenTypes},
+        NotNull{&cloneState.seenTypePacks},
+        ignorePersistent ? typeId : nullptr,
+        nullptr
+    };
+
+    return cloner.shallowClone(typeId);
+}
+
 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);
 }
 
@@ -462,13 +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;
 
@@ -493,4 +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

@@ -3,6 +3,8 @@
 #include "Luau/Constraint.h"
 #include "Luau/VisitType.h"
 
+LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
+
 namespace Luau
 {
 
@@ -18,7 +20,7 @@ struct ReferenceCountInitializer : TypeOnceVisitor
 
     DenseHashSet<TypeId>* result;
 
-    ReferenceCountInitializer(DenseHashSet<TypeId>* result)
+    explicit ReferenceCountInitializer(DenseHashSet<TypeId>* result)
         : result(result)
     {
     }
@@ -41,11 +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
+    {
+        return FFlag::DebugLuauGreedyGeneralization;
+    }
 };
 
 bool isReferenceCountedType(const TypeId typ)
@@ -97,6 +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);
@@ -104,12 +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))
     {
@@ -128,10 +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/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

@@ -277,7 +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
@@ -481,14 +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 ClassType* rightClass = get<ClassType>(right);
-    LUAU_ASSERT(leftClass);
-    LUAU_ASSERT(rightClass);
+    const ExternType* leftExternType = get<ExternType>(left);
+    const ExternType* rightExternType = get<ExternType>(right);
+    LUAU_ASSERT(leftExternType);
+    LUAU_ASSERT(rightExternType);
 
-    if (leftClass == rightClass)
+    if (leftExternType == rightExternType)
     {
         return DifferResult{};
     }
@@ -651,9 +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"};
@@ -718,7 +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();
@@ -960,7 +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

@@ -1,102 +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(LuauDeclareExternType)
+LUAU_FASTFLAG(LuauTypeFunOptional)
+
 namespace Luau
 {
 
-static const std::string kBuiltinDefinitionLuaSrcChecked = 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,
-}
+static const std::string kBuiltinDefinitionBaseSrc = R"BUILTIN_SRC(
 
 @checked declare function require(target: any): any
 
@@ -144,6 +55,119 @@ declare function loadstring<A...>(src: string, chunkname: string?): (((A...) ->
 
 @checked declare function newproxy(mt: boolean?): any
 
+-- 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
+
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionBit32Src = 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,
+}
+
+)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,
+    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,
+    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,
+    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,
+}
+
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionCoroutineSrc = R"BUILTIN_SRC(
+
 declare coroutine: {
     create: <A..., R...>(f: (A...) -> R...) -> thread,
     resume: <A..., R...>(co: thread, A...) -> (boolean, R...),
@@ -155,6 +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) -> ()),
@@ -177,11 +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,
@@ -191,10 +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.
-declare function unpack<V>(tab: {V}, i: number?, j: number?): ...V
-
+)BUILTIN_SRC";
 
+static const std::string kBuiltinDefinitionBufferSrc = R"BUILTIN_SRC(
 --- Buffer API
 declare buffer: {
     create: @checked (size: number) -> buffer,
@@ -221,13 +256,201 @@ 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 = (FFlag::LuauDeclareExternType)
+    ? R"BUILTIN_SRC(
+
+-- While vector would have been better represented as a built-in primitive type, type solver extern type handling covers most of the properties
+declare extern type vector with
+    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,
+    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,
+    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";
 
 std::string getBuiltinDefinitionSource()
 {
-    std::string result = kBuiltinDefinitionLuaSrcChecked;
+    std::string result = kBuiltinDefinitionBaseSrc;
+
+    result += kBuiltinDefinitionBit32Src;
+    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/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>
@@ -17,8 +18,7 @@
 #include <unordered_set>
 
 LUAU_FASTINTVARIABLE(LuauIndentTypeMismatchMaxTypeLength, 10)
-
-LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauImproveNonFunctionCallError, false)
+LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
 
 static std::string wrongNumberOfArgsString(
     size_t expectedCount,
@@ -70,7 +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", "*"},
@@ -86,12 +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
 {
@@ -118,7 +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)
@@ -185,7 +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 + "'";
@@ -353,7 +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";
@@ -384,8 +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))
-            metatable = classType->metatable;
+        else if (const ExternType* externType = get<ExternType>(type))
+            metatable = externType->metatable;
 
         if (!metatable)
             return std::nullopt;
@@ -408,35 +426,30 @@ struct ErrorConverter
 
     std::string operator()(const Luau::CannotCallNonFunction& e) const
     {
-        if (DFFlag::LuauImproveNonFunctionCallError)
+        if (auto unionTy = get<UnionType>(follow(e.ty)))
         {
-            if (auto unionTy = get<UnionType>(follow(e.ty)))
+            std::string err = "Cannot call a value of the union type:";
+
+            for (auto option : unionTy)
             {
-                std::string err = "Cannot call a value of the union type:";
+                option = follow(option);
 
-                for (auto option : unionTy)
+                if (get<FunctionType>(option) || findCallMetamethod(option))
                 {
-                    option = follow(option);
-
-                    if (get<FunctionType>(option) || findCallMetamethod(option))
-                    {
-                        err += "\n  | " + toString(option);
-                        continue;
-                    }
-
-                    // early-exit if we find something that isn't callable in the union.
-                    return "Cannot call a value of type " + toString(option) + " in union:\n  " + toString(e.ty);
+                    err += "\n  | " + toString(option);
+                    continue;
                 }
 
-                err += "\nWe are unable to determine the appropriate result type for such a call.";
-
-                return err;
+                // early-exit if we find something that isn't callable in the union.
+                return "Cannot call a value of type " + toString(option) + " in union:\n  " + toString(e.ty);
             }
 
-            return "Cannot call a value of type " + toString(e.ty);
+            err += "\nWe are unable to determine the appropriate result type for such a call.";
+
+            return err;
         }
 
-        return "Cannot call non-function " + toString(e.ty);
+        return "Cannot call a value of type " + toString(e.ty);
     }
     std::string operator()(const Luau::ExtraInformation& e) const
     {
@@ -598,7 +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";
     }
@@ -608,7 +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())
@@ -645,7 +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 ";
 
@@ -699,10 +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.
@@ -758,8 +772,15 @@ struct ErrorConverter
 
     std::string operator()(const NonStrictFunctionDefinitionError& e) const
     {
-        return "Argument " + e.argument + " with type '" + toString(e.argumentType) + "' in function '" + e.functionName +
-               "' is used in a way that will run time error";
+        if (e.functionName.empty())
+        {
+            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
@@ -793,6 +814,16 @@ struct ErrorConverter
         return "Encountered an unexpected type pack in subtyping: " + toString(e.tp);
     }
 
+    std::string operator()(const UserDefinedTypeFunctionError& e) const
+    {
+        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";
@@ -1118,7 +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;
 }
@@ -1175,6 +1206,16 @@ bool UnexpectedTypePackInSubtyping::operator==(const UnexpectedTypePackInSubtypi
     return tp == rhs.tp;
 }
 
+bool UserDefinedTypeFunctionError::operator==(const UserDefinedTypeFunctionError& rhs) const
+{
+    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())
@@ -1350,7 +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);
@@ -1384,6 +1425,9 @@ void copyError(T& e, TypeArena& destArena, CloneState& cloneState)
         e.ty = clone(e.ty);
     else if constexpr (std::is_same_v<T, UnexpectedTypePackInSubtyping>)
         e.tp = clone(e.tp);
+    else if constexpr (std::is_same_v<T, UserDefinedTypeFunctionError>)
+    {
+    }
     else if constexpr (std::is_same_v<T, CannotAssignToNever>)
     {
         e.rhsType = clone(e.rhsType);
@@ -1391,6 +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"
@@ -10,8 +9,10 @@
 #include "Luau/ConstraintSolver.h"
 #include "Luau/DataFlowGraph.h"
 #include "Luau/DcrLogger.h"
+#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"
@@ -36,18 +37,17 @@ LUAU_FASTINT(LuauTypeInferIterationLimit)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
 LUAU_FASTINT(LuauTarjanChildLimit)
 LUAU_FASTFLAG(LuauInferInNoCheckMode)
-LUAU_FASTFLAGVARIABLE(LuauKnowsTheDataModel3, false)
-LUAU_FASTFLAGVARIABLE(LuauStoreCommentsForDefinitionFiles, false)
+LUAU_FASTFLAGVARIABLE(LuauKnowsTheDataModel3)
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJson, false)
-LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJsonFile, false)
-LUAU_FASTFLAGVARIABLE(DebugLuauForbidInternalTypes, false)
-LUAU_FASTFLAGVARIABLE(DebugLuauForceStrictMode, false)
-LUAU_FASTFLAGVARIABLE(DebugLuauForceNonStrictMode, false)
-LUAU_FASTFLAGVARIABLE(LuauSourceModuleUpdatedWithSelectedMode, false)
-LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauRunCustomModuleChecks, false)
+LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauRethrowKnownExceptions, false)
+LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
+LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJson)
+LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJsonFile)
+LUAU_FASTFLAGVARIABLE(DebugLuauForbidInternalTypes)
+LUAU_FASTFLAGVARIABLE(DebugLuauForceStrictMode)
+LUAU_FASTFLAGVARIABLE(DebugLuauForceNonStrictMode)
 
-LUAU_FASTFLAG(StudioReportLuauAny2)
+LUAU_FASTFLAG(LuauTypeFunResultInAutocomplete)
 
 namespace Luau
 {
@@ -77,6 +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)
@@ -115,9 +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;
         }
@@ -134,7 +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;
@@ -205,72 +219,6 @@ LoadDefinitionFileResult Frontend::loadDefinitionFile(
     return LoadDefinitionFileResult{true, parseResult, sourceModule, checkedModule};
 }
 
-std::vector<std::string_view> parsePathExpr(const AstExpr& pathExpr)
-{
-    const AstExprIndexName* indexName = pathExpr.as<AstExprIndexName>();
-    if (!indexName)
-        return {};
-
-    std::vector<std::string_view> segments{indexName->index.value};
-
-    while (true)
-    {
-        if (AstExprIndexName* in = indexName->expr->as<AstExprIndexName>())
-        {
-            segments.push_back(in->index.value);
-            indexName = in;
-            continue;
-        }
-        else if (AstExprGlobal* indexNameAsGlobal = indexName->expr->as<AstExprGlobal>())
-        {
-            segments.push_back(indexNameAsGlobal->name.value);
-            break;
-        }
-        else if (AstExprLocal* indexNameAsLocal = indexName->expr->as<AstExprLocal>())
-        {
-            segments.push_back(indexNameAsLocal->local->name.value);
-            break;
-        }
-        else
-            return {};
-    }
-
-    std::reverse(segments.begin(), segments.end());
-    return segments;
-}
-
-std::optional<std::string> pathExprToModuleName(const ModuleName& currentModuleName, const std::vector<std::string_view>& segments)
-{
-    if (segments.empty())
-        return std::nullopt;
-
-    std::vector<std::string_view> result;
-
-    auto it = segments.begin();
-
-    if (*it == "script" && !currentModuleName.empty())
-    {
-        result = split(currentModuleName, '/');
-        ++it;
-    }
-
-    for (; it != segments.end(); ++it)
-    {
-        if (result.size() > 1 && *it == "Parent")
-            result.pop_back();
-        else
-            result.push_back(*it);
-    }
-
-    return join(result, "/");
-}
-
-std::optional<std::string> pathExprToModuleName(const ModuleName& currentModuleName, const AstExpr& pathExpr)
-{
-    std::vector<std::string_view> segments = parsePathExpr(pathExpr);
-    return pathExprToModuleName(currentModuleName, segments);
-}
-
 namespace
 {
 
@@ -351,8 +299,7 @@ static void filterLintOptions(LintOptions& lintOptions, const std::vector<HotCom
 std::vector<RequireCycle> getRequireCycles(
     const FileResolver* resolver,
     const std::unordered_map<ModuleName, std::shared_ptr<SourceNode>>& sourceNodes,
-    const SourceNode* start,
-    bool stopAtFirst = false
+    const SourceNode* start
 )
 {
     std::vector<RequireCycle> result;
@@ -422,9 +369,6 @@ std::vector<RequireCycle> getRequireCycles(
         {
             result.push_back({depLocation, std::move(cycle)});
 
-            if (stopAtFirst)
-                return result;
-
             // note: if we didn't find a cycle, all nodes that we've seen don't depend [transitively] on start
             // so it's safe to *only* clear seen vector when we find a cycle
             // if we don't do it, we will not have correct reporting for some cycles
@@ -511,20 +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;
@@ -555,7 +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)
     {
@@ -579,18 +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;
     }
 
@@ -603,67 +534,13 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
         };
     }
 
-    std::mutex mtx;
-    std::condition_variable cv;
-    std::vector<size_t> readyQueueItems;
+    state->executeTask = executeTask;
+    state->remaining = state->buildQueueItems.size();
 
-    size_t processing = 0;
-    size_t remaining = buildQueueItems.size();
-
-    auto itemTask = [&](size_t i)
+    // Record dependencies between modules
+    for (size_t i = 0; i < state->buildQueueItems.size(); i++)
     {
-        BuildQueueItem& item = 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];
+        BuildQueueItem& item = state->buildQueueItems[i];
 
         for (const ModuleName& dep : item.sourceNode->requireSet)
         {
@@ -673,41 +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
-    if (processing == 0)
-        sendCycleItemTask();
+    // In the first pass, check all modules with no pending dependencies
+    for (size_t i = 0; i < state->buildQueueItems.size(); i++)
+    {
+        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)
@@ -724,7 +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--;
@@ -735,26 +616,26 @@ std::vector<ModuleName> Frontend::checkQueuedModules(
                 }
             }
 
-            LUAU_ASSERT(processing >= readyQueueItems.size());
-            processing -= readyQueueItems.size();
+            LUAU_ASSERT(state->processing >= state->readyQueueItems.size());
+            state->processing -= state->readyQueueItems.size();
 
-            LUAU_ASSERT(remaining >= readyQueueItems.size());
-            remaining -= readyQueueItems.size();
-            readyQueueItems.clear();
+            LUAU_ASSERT(state->remaining >= state->readyQueueItems.size());
+            state->remaining -= state->readyQueueItems.size();
+            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)
@@ -762,19 +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)
-            sendCycleItemTask();
+        if (state->remaining != 0 && state->processing == 0)
+            sendQueueCycleItemTask(state);
     }
 
     std::vector<ModuleName> checkedModules;
-    checkedModules.reserve(buildQueueItems.size());
+    checkedModules.reserve(state->buildQueueItems.size());
 
-    for (size_t i = 0; i < buildQueueItems.size(); i++)
-        checkedModules.push_back(std::move(buildQueueItems[i].name));
+    for (size_t i = 0; i < state->buildQueueItems.size(); i++)
+        checkedModules.push_back(std::move(state->buildQueueItems[i].name));
 
     return checkedModules;
 }
@@ -812,6 +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,
@@ -860,6 +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
         {
@@ -948,14 +862,11 @@ void Frontend::addBuildQueueItems(
         data.environmentScope = getModuleEnvironment(*sourceModule, data.config, frontendOptions.forAutocomplete);
         data.recordJsonLog = FFlag::DebugLuauLogSolverToJson;
 
-        Mode mode = sourceModule->mode.value_or(data.config.mode);
-
-        // in NoCheck mode we only need to compute the value of .cyclic for typeck
         // in the future we could replace toposort with an algorithm that can flag cyclic nodes by itself
         // however, for now getRequireCycles isn't expensive in practice on the cases we care about, and long term
         // all correct programs must be acyclic so this code triggers rarely
         if (cycleDetected)
-            data.requireCycles = getRequireCycles(fileResolver, sourceNodes, sourceNode.get(), mode == Mode::NoCheck);
+            data.requireCycles = getRequireCycles(fileResolver, sourceNodes, sourceNode.get());
 
         data.options = frontendOptions;
 
@@ -987,8 +898,7 @@ void Frontend::checkBuildQueueItem(BuildQueueItem& item)
     else
         mode = sourceModule.mode.value_or(config.mode);
 
-    if (FFlag::LuauSourceModuleUpdatedWithSelectedMode)
-        item.sourceModule->mode = {mode};
+    item.sourceModule->mode = {mode};
     ScopePtr environmentScope = item.environmentScope;
     double timestamp = getTimestamp();
     const std::vector<RequireCycle>& requireCycles = item.requireCycles;
@@ -1041,7 +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;
@@ -1061,7 +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)
@@ -1093,6 +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();
@@ -1146,17 +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;
 
@@ -1164,6 +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;
@@ -1191,6 +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);
@@ -1205,16 +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())
@@ -1225,22 +1246,10 @@ void Frontend::markDirty(const ModuleName& name, std::vector<ModuleName>* marked
         LUAU_ASSERT(sourceNodes.count(next) > 0);
         SourceNode& sourceNode = *sourceNodes[next];
 
-        if (markedDirty)
-            markedDirty->push_back(next);
-
-        if (sourceNode.dirtySourceModule && sourceNode.dirtyModule && sourceNode.dirtyModuleForAutocomplete)
+        if (!processSubtree(sourceNode))
             continue;
 
-        sourceNode.dirtySourceModule = true;
-        sourceNode.dirtyModule = true;
-        sourceNode.dirtyModuleForAutocomplete = true;
-
-        if (0 == reverseDeps.count(next))
-            continue;
-
-        sourceModules.erase(next);
-
-        const std::vector<ModuleName>& dependents = reverseDeps[next];
+        const Set<ModuleName>& dependents = sourceNode.dependents;
         queue.insert(queue.end(), dependents.begin(), dependents.end());
     }
 }
@@ -1268,6 +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,
@@ -1284,6 +1294,7 @@ ModulePtr check(
         moduleResolver,
         fileResolver,
         parentScope,
+        typeFunctionScope,
         std::move(prepareModuleScope),
         options,
         limits,
@@ -1294,7 +1305,7 @@ ModulePtr check(
 
 struct InternalTypeFinder : TypeOnceVisitor
 {
-    bool visit(TypeId, const ClassType&) override
+    bool visit(TypeId, const ExternType&) override
     {
         return false;
     }
@@ -1345,6 +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,
@@ -1357,11 +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;
 
@@ -1376,47 +1392,87 @@ ModulePtr check(
         }
     }
 
-    DataFlowGraph dfg = DataFlowGraphBuilder::build(sourceModule.root, iceHandler);
+    DataFlowGraph dfg = DataFlowGraphBuilder::build(sourceModule.root, NotNull{&result->defArena}, NotNull{&result->keyArena}, iceHandler);
 
     UnifierSharedState unifierState{iceHandler};
     unifierState.counters.recursionLimit = FInt::LuauTypeInferRecursionLimit;
     unifierState.counters.iterationLimit = limits.unifierIterationLimit.value_or(FInt::LuauTypeInferIterationLimit);
 
     Normalizer normalizer{&result->internalTypes, builtinTypes, NotNull{&unifierState}};
+    SimplifierPtr simplifier = newSimplifier(NotNull{&result->internalTypes}, builtinTypes);
+    TypeFunctionRuntime typeFunctionRuntime{iceHandler, NotNull{&limits}};
+
+    typeFunctionRuntime.allowEvaluation = FFlag::LuauTypeFunResultInAutocomplete || sourceModule.parseErrors.empty();
 
     ConstraintGenerator cg{
         result,
         NotNull{&normalizer},
+        NotNull{simplifier.get()},
+        NotNull{&typeFunctionRuntime},
         moduleResolver,
         builtinTypes,
         iceHandler,
         parentScope,
+        typeFunctionScope,
         std::move(prepareModuleScope),
         logger.get(),
         NotNull{&dfg},
         requireCycles
     };
 
-    cg.visitModuleRoot(sourceModule.root);
-    result->errors = std::move(cg.errors);
+    // FIXME: Delete this flag when clipping FFlag::DebugLuauGreedyGeneralization.
+    //
+    // 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{
-        NotNull{&normalizer},
-        NotNull(cg.rootScope),
-        borrowConstraints(cg.constraints),
-        result->name,
-        moduleResolver,
-        requireCycles,
-        logger.get(),
-        limits
-    };
+    if (FFlag::DebugLuauGreedyGeneralization)
+    {
+        ConstraintSet constraintSet = cg.run(sourceModule.root);
+        result->errors = std::move(constraintSet.errors);
+
+        cs.emplace(
+            NotNull{&normalizer},
+            NotNull{simplifier.get()},
+            NotNull{&typeFunctionRuntime},
+            result->name,
+            moduleResolver,
+            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&)
     {
@@ -1436,12 +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)
     {
@@ -1461,12 +1517,31 @@ ModulePtr check(
         switch (mode)
         {
         case Mode::Nonstrict:
-            Luau::checkNonStrict(builtinTypes, iceHandler, NotNull{&unifierState}, NotNull{&dfg}, NotNull{&limits}, sourceModule, result.get());
+            Luau::checkNonStrict(
+                builtinTypes,
+                NotNull{simplifier.get()},
+                NotNull{&typeFunctionRuntime},
+                iceHandler,
+                NotNull{&unifierState},
+                NotNull{&dfg},
+                NotNull{&limits},
+                sourceModule,
+                result.get()
+            );
             break;
         case Mode::Definition:
             // fallthrough intentional
         case Mode::Strict:
-            Luau::check(builtinTypes, NotNull{&unifierState}, NotNull{&limits}, logger.get(), sourceModule, result.get());
+            Luau::check(
+                builtinTypes,
+                NotNull{simplifier.get()},
+                NotNull{&typeFunctionRuntime},
+                NotNull{&unifierState},
+                NotNull{&limits},
+                logger.get(),
+                sourceModule,
+                result.get()
+            );
             break;
         case Mode::NoCheck:
             break;
@@ -1550,6 +1625,7 @@ ModulePtr Frontend::check(
                 NotNull{forAutocomplete ? &moduleResolverForAutocomplete : &moduleResolver},
                 NotNull{fileResolver},
                 environmentScope ? *environmentScope : globals.globalScope,
+                globals.globalTypeFunctionScope,
                 prepareModuleScopeWrap,
                 options,
                 typeCheckLimits,
@@ -1647,6 +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;
@@ -1768,11 +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};
-    clone.magicFunction = ftv->magicFunction;
-    clone.dcrMagicFunction = ftv->dcrMagicFunction;
-    clone.dcrMagicRefinement = ftv->dcrMagicRefinement;
+    FunctionType clone = FunctionType{level, ftv->argTypes, ftv->retTypes, ftv->definition, ftv->hasSelf};
+    clone.magic = ftv->magic;
     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>)
-        stream << "DynamicPropertyLookupOnClassesUnsafe { " << toString(err.ty) << " }";
+    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnExternTypesUnsafe>)
+        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>)
@@ -227,6 +227,10 @@ static void errorToString(std::ostream& stream, const T& err)
         stream << "UnexpectedTypeInSubtyping {  ty = '" + toString(err.ty) + "' }";
     else if constexpr (std::is_same_v<T, UnexpectedTypePackInSubtyping>)
         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

@@ -17,8 +17,10 @@ LUAU_FASTINTVARIABLE(LuauSuggestionDistance, 4)
 LUAU_FASTFLAG(LuauSolverV2)
 
 LUAU_FASTFLAG(LuauAttribute)
-LUAU_FASTFLAG(LuauNativeAttribute)
-LUAU_FASTFLAGVARIABLE(LintRedundantNativeAttribute, false)
+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 (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);
-                else
-                    report(node->location, prop->second, tty->name ? tty->name->c_str() : nullptr, node->index.value);
+                if (prop->second.deprecated)
+                {
+                    // strip synthetic typeof() for builtin tables
+                    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);
+                    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_FASTFLAGVARIABLE(LuauSkipEmptyInstantiations, false);
+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;
         }
     );
@@ -122,7 +144,7 @@ struct ClonePublicInterface : Substitution
 
         if (FunctionType* ftv = getMutable<FunctionType>(result))
         {
-            if (FFlag::LuauSkipEmptyInstantiations && ftv->generics.empty() && ftv->genericPacks.empty())
+            if (ftv->generics.empty() && ftv->genericPacks.empty())
             {
                 GenericTypeFinder marker;
                 marker.traverse(result);
@@ -136,6 +158,26 @@ struct ClonePublicInterface : Substitution
         else if (TableType* ttv = getMutable<TableType>(result))
         {
             ttv->level = TypeLevel{0, 0};
+            if (FFlag::LuauSolverV2)
+                ttv->scope = nullptr;
+        }
+
+        if (FFlag::LuauSolverV2)
+        {
+            if (auto freety = getMutable<FreeType>(result))
+            {
+                module->errors.emplace_back(
+                    freety->scope->location,
+                    module->name,
+                    InternalError{"Free type is escaping its module; please report this bug at "
+                                  "https://github.com/luau-lang/luau/issues"}
+                );
+                result = builtinTypes->errorRecoveryType();
+            }
+            else if (auto genericty = getMutable<GenericType>(result))
+            {
+                genericty->scope = nullptr;
+            }
         }
 
         return result;
@@ -143,7 +185,27 @@ struct ClonePublicInterface : Substitution
 
     TypePackId clean(TypePackId tp) override
     {
-        return clone(tp);
+        if (FFlag::LuauSolverV2)
+        {
+            auto clonedTp = clone(tp);
+            if (auto ftp = getMutable<FreeTypePack>(clonedTp))
+            {
+                module->errors.emplace_back(
+                    ftp->scope->location,
+                    module->name,
+                    InternalError{"Free type pack is escaping its module; please report this bug at "
+                                  "https://github.com/luau-lang/luau/issues"}
+                );
+                clonedTp = builtinTypes->errorRecoveryTypePack();
+            }
+            else if (auto gtp = getMutable<GenericTypePack>(clonedTp))
+                gtp->scope = nullptr;
+            return clonedTp;
+        }
+        else
+        {
+            return clone(tp);
+        }
     }
 
     TypeId cloneType(TypeId ty)
@@ -203,7 +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/OverloadResolution.cpp

@@ -10,13 +10,17 @@
 #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,
     NotNull<InternalErrorReporter> reporter,
     NotNull<TypeCheckLimits> limits,
@@ -24,11 +28,13 @@ OverloadResolver::OverloadResolver(
 )
     : builtinTypes(builtinTypes)
     , arena(arena)
+    , simplifier(simplifier)
     , normalizer(normalizer)
+    , typeFunctionRuntime(typeFunctionRuntime)
     , scope(scope)
     , ice(reporter)
     , limits(limits)
-    , subtyping({builtinTypes, arena, normalizer, ice})
+    , subtyping({builtinTypes, arena, simplifier, normalizer, typeFunctionRuntime, ice})
     , callLoc(callLocation)
 {
 }
@@ -107,6 +113,7 @@ std::optional<ErrorVec> OverloadResolver::testIsSubtype(const Location& location
         case ErrorSuppression::NormalizationFailed:
             errors.emplace_back(location, NormalizationTooComplex{});
             // intentionally fallthrough here since we couldn't prove this was error-suppressing
+            [[fallthrough]];
         case ErrorSuppression::DoNotSuppress:
             errors.emplace_back(location, TypeMismatch{superTy, subTy});
             break;
@@ -136,6 +143,7 @@ std::optional<ErrorVec> OverloadResolver::testIsSubtype(const Location& location
         case ErrorSuppression::NormalizationFailed:
             errors.emplace_back(location, NormalizationTooComplex{});
             // intentionally fallthrough here since we couldn't prove this was error-suppressing
+            [[fallthrough]];
         case ErrorSuppression::DoNotSuppress:
             errors.emplace_back(location, TypePackMismatch{superTy, subTy});
             break;
@@ -197,8 +205,9 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
     const std::vector<AstExpr*>* argExprs
 )
 {
-    FunctionGraphReductionResult result =
-        reduceTypeFunctions(fnTy, callLoc, TypeFunctionContext{arena, builtinTypes, scope, normalizer, ice, limits}, /*force=*/true);
+    FunctionGraphReductionResult result = reduceTypeFunctions(
+        fnTy, callLoc, TypeFunctionContext{arena, builtinTypes, scope, simplifier, normalizer, typeFunctionRuntime, ice, limits}, /*force=*/true
+    );
     if (!result.errors.empty())
         return {OverloadIsNonviable, result.errors};
 
@@ -247,15 +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);
-                    TypeError error{fnExpr->location, CountMismatch{minParams, optMaxParams, args->head.size(), CountMismatch::Arg, isVariadic}};
+                    if (get<UnknownType>(follow(requiredHead[i])) || !subtyping.isSubtype(builtinTypes->nilType, requiredHead[i], scope).isSubtype)
+                    {
+                        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}};
+                    }
                 }
             }
 
@@ -301,6 +327,7 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
                 case ErrorSuppression::NormalizationFailed:
                     errors.emplace_back(argLocation, NormalizationTooComplex{});
                     // intentionally fallthrough here since we couldn't prove this was error-suppressing
+                    [[fallthrough]];
                 case ErrorSuppression::DoNotSuppress:
                     // TODO extract location from the SubtypingResult path and argExprs
                     switch (reason.variance)
@@ -398,10 +425,12 @@ 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,
     NotNull<InternalErrorReporter> iceReporter,
     NotNull<TypeCheckLimits> limits,
@@ -410,8 +439,9 @@ std::optional<TypeId> selectOverload(
     TypePackId argsPack
 )
 {
-    OverloadResolver resolver{builtinTypes, arena, normalizer, scope, iceReporter, limits, location};
-    auto [status, overload] = resolver.selectOverload(fn, argsPack);
+    auto resolver =
+        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;
@@ -425,7 +455,9 @@ std::optional<TypeId> selectOverload(
 SolveResult solveFunctionCall(
     NotNull<TypeArena> arena,
     NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Simplifier> simplifier,
     NotNull<Normalizer> normalizer,
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime,
     NotNull<InternalErrorReporter> iceReporter,
     NotNull<TypeCheckLimits> limits,
     NotNull<Scope> scope,
@@ -434,22 +466,23 @@ SolveResult solveFunctionCall(
     TypePackId argsPack
 )
 {
-    std::optional<TypeId> overloadToUse = selectOverload(builtinTypes, arena, normalizer, scope, iceReporter, limits, location, fn, argsPack);
+    std::optional<TypeId> overloadToUse =
+        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 (expr->is<AstExprLocal>())
-                    info = context ? std::optional<ModuleInfo>(*context) : std::nullopt;
-                else
-                    info = fileResolver->resolveModule(context, expr);
+                if (context && expr->is<AstExprLocal>())
+                    info = *context; // locals just inherit their dependent context, no resolution required
+                else if (context && (expr->is<AstExprGroup>() || expr->is<AstTypeGroup>()))
+                    info = *context; // simple group nodes propagate their value
+                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

@@ -2,9 +2,11 @@
 
 #include "Luau/Simplify.h"
 
+#include "Luau/Common.h"
 #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"
@@ -13,7 +15,10 @@
 
 LUAU_FASTINT(LuauTypeReductionRecursionLimit)
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_DYNAMIC_FASTINTVARIABLE(LuauSimplificationComplexityLimit, 8);
+LUAU_DYNAMIC_FASTINTVARIABLE(LuauSimplificationComplexityLimit, 8)
+LUAU_FASTFLAGVARIABLE(LuauSimplificationRecheckAssumption)
+LUAU_FASTFLAGVARIABLE(LuauOptimizeFalsyAndTruthyIntersect)
+LUAU_FASTFLAGVARIABLE(LuauSimplificationTableExternType)
 
 namespace Luau
 {
@@ -29,25 +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 intersectNegations(TypeId a, TypeId b);
+    TypeId intersectTypeWithNegation(TypeId left, TypeId right);
+    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 union_(TypeId ty, TypeId discriminant);
+    TypeId intersect(TypeId left, TypeId right);
+    TypeId union_(TypeId left, TypeId right);
 
     TypeId simplify(TypeId ty);
     TypeId simplify(TypeId ty, DenseHashSet<TypeId>& seen);
@@ -141,6 +148,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Intersects;
         }
+        break;
     case Relation::Coincident:
         switch (b)
         {
@@ -155,6 +163,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Intersects;
         }
+        break;
     case Relation::Superset:
         switch (b)
         {
@@ -169,6 +178,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Superset;
         }
+        break;
     case Relation::Subset:
         switch (b)
         {
@@ -183,6 +193,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Intersects;
         }
+        break;
     case Relation::Intersects:
         switch (b)
         {
@@ -197,6 +208,7 @@ Relation combine(Relation a, Relation b)
         case Relation::Superset:
             return Relation::Intersects;
         }
+        break;
     }
 
     LUAU_UNREACHABLE();
@@ -306,12 +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))
@@ -321,8 +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))
@@ -346,7 +360,7 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     // * FunctionType
     // * TableType
     // * MetatableType
-    // * ClassType
+    // * ExternType
     // * UnionType
     // * IntersectionType
     // * NegationType
@@ -354,26 +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))
@@ -437,52 +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;
         }
     }
 
@@ -492,11 +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))
@@ -505,10 +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())
@@ -528,29 +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;
@@ -566,7 +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;
 
@@ -700,7 +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)
@@ -715,6 +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)
@@ -755,6 +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}});
+            }
         }
     }
 
@@ -833,6 +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);
@@ -1059,6 +1200,9 @@ TypeId TypeSimplifier::intersectIntersectionWithType(TypeId left, TypeId right)
 
 std::optional<TypeId> TypeSimplifier::basicIntersect(TypeId left, TypeId right)
 {
+    left = follow(left);
+    right = follow(right);
+
     if (get<AnyType>(left) && get<ErrorType>(right))
         return right;
     if (get<AnyType>(right) && get<ErrorType>(left))
@@ -1166,6 +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;
@@ -1398,8 +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());
@@ -1413,8 +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));
@@ -1424,8 +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_FASTINTVARIABLE(LuauTarjanPreallocationSize, 256);
+LUAU_FASTFLAG(LuauSolverV2)
+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)>;
 
@@ -50,11 +51,33 @@ static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool a
             LUAU_ASSERT(ty->persistent);
             return ty;
         }
-        else if constexpr (std::is_same_v<T, ErrorType>)
+        else if constexpr (std::is_same_v<T, NoRefineType>)
         {
             LUAU_ASSERT(ty->persistent);
             return ty;
         }
+        else if constexpr (std::is_same_v<T, ErrorType>)
+        {
+            if (FFlag::LuauSyntheticErrors)
+            {
+                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>)
         {
             LUAU_ASSERT(ty->persistent);
@@ -71,15 +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.dcrMagicFunction = a.dcrMagicFunction;
-            clone.dcrMagicRefinement = a.dcrMagicRefinement;
+            clone.magic = a.magic;
             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>)
@@ -113,21 +136,16 @@ 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)
-            {
-                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;
+            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));
         }
         else if constexpr (std::is_same_v<T, NegationType>)
             return dest.addType(NegationType{a.ty});
         else if constexpr (std::is_same_v<T, TypeFunctionInstanceType>)
         {
-            TypeFunctionInstanceType clone{a.function, a.typeArguments, a.packArguments, a.userFuncName, a.userFuncBody};
+            TypeFunctionInstanceType clone{a.function, a.typeArguments, a.packArguments, a.userFuncName, a.userFuncData};
             return dest.addType(std::move(clone));
         }
         else
@@ -234,21 +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)
-            visitChild(*ctv->parent);
+        if (etv->parent)
+            visitChild(*etv->parent);
 
-        if (ctv->metatable)
-            visitChild(*ctv->metatable);
+        if (etv->metatable)
+            visitChild(*etv->metatable);
 
-        if (ctv->indexer)
+        if (etv->indexer)
         {
-            visitChild(ctv->indexer->indexType);
-            visitChild(ctv->indexer->indexResultType);
+            visitChild(etv->indexer->indexType);
+            visitChild(etv->indexer->indexResultType);
         }
     }
     else if (const NegationType* ntv = get<NegationType>(ty))
@@ -522,6 +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);
@@ -532,6 +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)
 {
@@ -632,7 +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)
@@ -794,21 +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)
-            ctv->parent = replace(*ctv->parent);
+        if (etv->parent)
+            etv->parent = replace(*etv->parent);
 
-        if (ctv->metatable)
-            ctv->metatable = replace(*ctv->metatable);
+        if (etv->metatable)
+            etv->metatable = replace(*etv->metatable);
 
-        if (ctv->indexer)
+        if (etv->indexer)
         {
-            ctv->indexer->indexType = replace(ctv->indexer->indexType);
-            ctv->indexer->indexResultType = replace(ctv->indexer->indexResultType);
+            etv->indexer->indexType = replace(etv->indexer->indexType);
+            etv->indexer->indexResultType = replace(etv->indexer->indexResultType);
         }
     }
     else if (NegationType* ntv = getMutable<NegationType>(ty))
@@ -848,4 +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