Sync to upstream/release/667 (#1754)

After a very auspicious release last week, we have a new bevy of changes
for you!

## What's Changed

### Deprecated Attribute

This release includes an implementation of the `@deprecated` attribute
proposed in [this
RFC](https://rfcs.luau.org/syntax-attribute-functions-deprecated.html).
It relies on the new type solver to propagate deprecation information
from function and method AST nodes to the corresponding type objects.
These objects are queried by a linter pass when it encounters local,
global, or indexed variables, to issue deprecation warnings. Uses of
deprecated functions and methods in recursion are ignored. To support
deprecation of class methods, the parser has been extended to allow
attribute declarations on class methods. The implementation does not
support parameters, so it is not currently possible for users to
customize deprecation messages.

### General

- Add a limit for normalization of function types.

### New Type Solver

- Fix type checker to accept numbers as concat operands (Fixes #1671).
- Fix user-defined type functions failing when used inside type
aliases/nested calls (Fixes #1738, Fixes #1679).
- Improve constraint generation for overloaded functions (in part thanks
to @vvatheus in #1694).
- Improve type inference for indexers on table literals, especially when
passing table literals directly as a function call argument.
- Equate regular error type and intersection with a negation of an error
type.
- Avoid swapping types in 2-part union when RHS is optional.
- Use simplification when doing `~nil` refinements.
- `len<>` now works on metatables without `__len` function.

### AST

- Retain source information for `AstTypeUnion` and
`AstTypeIntersection`.

### Transpiler

- Print attributes on functions.

### Parser

- Allow types in indexers to begin with string literals by @jackdotink
in #1750.

### Autocomplete

- Evaluate user-defined type functions in ill-formed source code to
provide autocomplete.
- Fix the start location of functions that have attributes.
- Implement better fragment selection.

### Internal Contributors

Co-authored-by: Andy Friesen <afriesen@roblox.com>
Co-authored-by: Ariel Weiss <aaronweiss@roblox.com>
Co-authored-by: Aviral Goel <agoel@roblox.com>
Co-authored-by: Hunter Goldstein <hgoldstein@roblox.com>
Co-authored-by: Sora Kanosue <skanosue@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: Vyacheslav Egorov <vegorov@roblox.com>

**Full Changelog**:
https://github.com/luau-lang/luau/compare/0.666...0.667

---------

Co-authored-by: Hunter Goldstein <hgoldstein@roblox.com>
Co-authored-by: Varun Saini <61795485+vrn-sn@users.noreply.github.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: Ariel Weiss <aaronweiss@roblox.com>

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/BuiltinDefinitions.h

@@ -70,6 +70,7 @@ Property makeProperty(TypeId ty, std::optional<std::string> documentationSymbol
 void assignPropDocumentationSymbols(TableType::Props& props, const std::string& baseName);
 
 std::string getBuiltinDefinitionSource();
+std::string getTypeFunctionDefinitionSource();
 
 void addGlobalBinding(GlobalTypes& globals, const std::string& name, TypeId ty, const std::string& packageName);
 void addGlobalBinding(GlobalTypes& globals, const std::string& name, Binding binding);

Analysis/include/Luau/Constraint.h

@@ -50,6 +50,7 @@ struct GeneralizationConstraint
     TypeId sourceType;
 
     std::vector<TypeId> interiorTypes;
+    bool hasDeprecatedAttribute = false;
 };
 
 // variables ~ iterate iterator

Analysis/include/Luau/ConstraintGenerator.h

@@ -117,12 +117,15 @@ struct ConstraintGenerator
 
     // Needed to register all available type functions for execution at later stages.
     NotNull<TypeFunctionRuntime> typeFunctionRuntime;
+    DenseHashMap<const AstStatTypeFunction*, ScopePtr> astTypeFunctionEnvironmentScopes{nullptr};
+
     // Needed to resolve modules to make 'require' import types properly.
     NotNull<ModuleResolver> moduleResolver;
     // Occasionally constraint generation needs to produce an ICE.
     const NotNull<InternalErrorReporter> ice;
 
     ScopePtr globalScope;
+    ScopePtr typeFunctionScope;
 
     std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope;
     std::vector<RequireCycle> requireCycles;
@@ -140,6 +143,7 @@ struct ConstraintGenerator
         NotNull<BuiltinTypes> builtinTypes,
         NotNull<InternalErrorReporter> ice,
         const ScopePtr& globalScope,
+        const ScopePtr& typeFunctionScope,
         std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope,
         DcrLogger* logger,
         NotNull<DataFlowGraph> dfg,

Analysis/include/Luau/ConstraintSolver.h

@@ -365,7 +365,7 @@ 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

Analysis/include/Luau/DataFlowGraph.h

@@ -38,8 +38,6 @@ struct DataFlowGraph
     DefId getDef(const AstExpr* expr) const;
     // Look up the definition optionally, knowing it may not be present.
     std::optional<DefId> getDefOptional(const AstExpr* expr) const;
-    // Look up for the rvalue def for a compound assignment.
-    std::optional<DefId> getRValueDefForCompoundAssign(const AstExpr* expr) const;
 
     DefId getDef(const AstLocal* local) const;
 
@@ -66,10 +64,6 @@ private:
     // All keys in this maps are really only statements that ambiently declares a symbol.
     DenseHashMap<const AstStat*, const Def*> declaredDefs{nullptr};
 
-    // Compound assignments are in a weird situation where the local being assigned to is also being used at its
-    // previous type implicitly in an rvalue position. This map provides the previous binding.
-    DenseHashMap<const AstExpr*, const Def*> compoundAssignDefs{nullptr};
-
     DenseHashMap<const AstExpr*, const RefinementKey*> astRefinementKeys{nullptr};
     friend struct DataFlowGraphBuilder;
 };

Analysis/include/Luau/FileResolver.h

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

Analysis/include/Luau/FragmentAutocomplete.h

@@ -15,6 +15,28 @@ 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,
@@ -27,6 +49,8 @@ struct FragmentAutocompleteAncestryResult
     std::vector<AstLocal*> localStack;
     std::vector<AstNode*> ancestry;
     AstStat* nearestStatement = nullptr;
+    AstStatBlock* parentBlock = nullptr;
+    Location fragmentSelectionRegion;
 };
 
 struct FragmentParseResult
@@ -37,6 +61,7 @@ struct FragmentParseResult
     AstStat* nearestStatement = nullptr;
     std::vector<Comment> commentLocations;
     std::unique_ptr<Allocator> alloc = std::make_unique<Allocator>();
+    Position scopePos{0, 0};
 };
 
 struct FragmentTypeCheckResult
@@ -54,10 +79,28 @@ struct FragmentAutocompleteResult
     AutocompleteResult acResults;
 };
 
-FragmentAutocompleteAncestryResult findAncestryForFragmentParse(AstStatBlock* root, const Position& cursorPos);
+struct FragmentRegion
+{
+    Location fragmentLocation;
+    AstStat* nearestStatement = nullptr; // used for tests
+    AstStatBlock* parentBlock = nullptr; // used for scope detection
+};
+
+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* root,
+    AstStatBlock* stale,
+    AstStatBlock* mostRecentParse,
     AstNameTable* names,
     std::string_view src,
     const Position& cursorPos,
@@ -70,7 +113,9 @@ std::pair<FragmentTypeCheckStatus, FragmentTypeCheckResult> typecheckFragment(
     const Position& cursorPos,
     std::optional<FrontendOptions> opts,
     std::string_view src,
-    std::optional<Position> fragmentEndPosition
+    std::optional<Position> fragmentEndPosition,
+    AstStatBlock* recentParse = nullptr,
+    IFragmentAutocompleteReporter* reporter = nullptr
 );
 
 FragmentAutocompleteResult fragmentAutocomplete(
@@ -80,7 +125,9 @@ FragmentAutocompleteResult fragmentAutocomplete(
     Position cursorPosition,
     std::optional<FrontendOptions> opts,
     StringCompletionCallback callback,
-    std::optional<Position> fragmentEndPosition = std::nullopt
+    std::optional<Position> fragmentEndPosition = std::nullopt,
+    AstStatBlock* recentParse = nullptr,
+    IFragmentAutocompleteReporter* reporter = nullptr
 );
 
 enum class FragmentAutocompleteStatus
@@ -102,6 +149,7 @@ struct FragmentContext
     const ParseResult& freshParse;
     std::optional<FrontendOptions> opts;
     std::optional<Position> DEPRECATED_fragmentEndPosition;
+    IFragmentAutocompleteReporter* reporter = nullptr;
 };
 
 /**

Analysis/include/Luau/Frontend.h

@@ -10,7 +10,6 @@
 #include "Luau/Set.h"
 #include "Luau/TypeCheckLimits.h"
 #include "Luau/Variant.h"
-#include "Luau/AnyTypeSummary.h"
 
 #include <mutex>
 #include <string>
@@ -34,7 +33,6 @@ struct HotComment;
 struct BuildQueueItem;
 struct BuildQueueWorkState;
 struct FrontendCancellationToken;
-struct AnyTypeSummary;
 
 struct LoadDefinitionFileResult
 {
@@ -305,6 +303,7 @@ 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
@@ -319,6 +318,7 @@ 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

@@ -12,8 +12,8 @@ std::optional<TypeId> generalize(
     NotNull<TypeArena> arena,
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<Scope> scope,
-    NotNull<DenseHashSet<TypeId>> bakedTypes,
+    NotNull<DenseHashSet<TypeId>> cachedTypes,
-    TypeId ty,
+    TypeId ty
-    /* avoid sealing tables*/ bool avoidSealingTables = false
 );
+
 }

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/Module.h

@@ -8,7 +8,6 @@
 #include "Luau/ParseResult.h"
 #include "Luau/Scope.h"
 #include "Luau/TypeArena.h"
-#include "Luau/AnyTypeSummary.h"
 #include "Luau/DataFlowGraph.h"
 
 #include <memory>
@@ -21,14 +20,13 @@ LUAU_FASTFLAG(LuauIncrementalAutocompleteCommentDetection)
 namespace Luau
 {
 
-using LogLuauProc = void (*)(std::string_view);
+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>;
@@ -86,10 +84,6 @@ struct Module
     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;

Analysis/include/Luau/NonStrictTypeChecker.h

@@ -1,9 +1,10 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/DataFlowGraph.h"
+#include "Luau/EqSatSimplification.h"
 #include "Luau/Module.h"
 #include "Luau/NotNull.h"
-#include "Luau/DataFlowGraph.h"
 
 namespace Luau
 {

Analysis/include/Luau/Quantify.h

@@ -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/Scope.h

@@ -35,7 +35,7 @@ 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;
@@ -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;
 

Analysis/include/Luau/Type.h

@@ -19,7 +19,6 @@
 #include <optional>
 #include <set>
 #include <string>
-#include <unordered_map>
 #include <vector>
 
 LUAU_FASTINT(LuauTableTypeMaximumStringifierLength)
@@ -38,6 +37,15 @@ struct Constraint;
 struct Subtyping;
 struct TypeChecker2;
 
+enum struct Polarity : uint8_t
+{
+    None = 0b000,
+    Positive = 0b001,
+    Negative = 0b010,
+    Mixed = 0b011,
+    Unknown = 0b100,
+};
+
 /**
  * There are three kinds of type variables:
  * - `Free` variables are metavariables, which stand for unconstrained types.
@@ -396,6 +404,7 @@ struct FunctionType
     // 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
@@ -622,7 +631,6 @@ struct UserDefinedFunctionData
     AstStatTypeFunction* definition = nullptr;
 
     DenseHashMap<Name, std::pair<AstStatTypeFunction*, size_t>> environment{""};
-    DenseHashMap<Name, AstStatTypeFunction*> environment_DEPRECATED{""};
 };
 
 /**

Analysis/include/Luau/TypeChecker2.h

@@ -13,6 +13,8 @@
 #include "Luau/TypeOrPack.h"
 #include "Luau/TypeUtils.h"
 
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
+
 namespace Luau
 {
 
@@ -38,18 +40,29 @@ struct Reasonings
 
     std::string toString()
     {
+        if (FFlag::LuauImproveTypePathsInErrors && reasons.empty())
+            return "";
+
         // DenseHashSet ordering is entirely undefined, so we want to
         // sort the reasons here to achieve a stable error
         // stringification.
         std::sort(reasons.begin(), reasons.end());
-        std::string allReasons;
+        std::string allReasons = FFlag::LuauImproveTypePathsInErrors ? "\nthis is because " : "";
         bool first = true;
         for (const std::string& reason : reasons)
         {
-            if (first)
+            if (FFlag::LuauImproveTypePathsInErrors)
-                first = false;
+            {
+                if (reasons.size() > 1)
+                    allReasons += "\n\t * ";
+            }
             else
-                allReasons += "\n\t";
+            {
+                if (first)
+                    first = false;
+                else
+                    allReasons += "\n\t";
+            }
 
             allReasons += reason;
         }

Analysis/include/Luau/TypeFunction.h

@@ -48,6 +48,9 @@ struct TypeFunctionRuntime
     // 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;
 
@@ -174,6 +177,7 @@ struct FunctionGraphReductionResult
     DenseHashSet<TypePackId> blockedPacks{nullptr};
     DenseHashSet<TypeId> reducedTypes{nullptr};
     DenseHashSet<TypePackId> reducedPacks{nullptr};
+    DenseHashSet<TypeId> irreducibleTypes{nullptr};
 };
 
 /**

Analysis/include/Luau/TypeFunctionRuntime.h

@@ -223,8 +223,6 @@ struct TypeFunctionClassType
     std::optional<TypeFunctionTypeId> writeParent;
 
     TypeId classTy;
-
-    std::string name_DEPRECATED;
 };
 
 struct TypeFunctionGenericType

Analysis/include/Luau/TypeFunctionRuntimeBuilder.h

@@ -28,14 +28,8 @@ struct TypeFunctionRuntimeBuilderState
 {
     NotNull<TypeFunctionContext> ctx;
 
-    // Mapping of class name to ClassType
-    // Invariant: users can not create a new class types -> any class types that get deserialized must have been an argument to the type function
-    // Using this invariant, whenever a ClassType is serialized, we can put it into this map
-    // whenever a ClassType is deserialized, we can use this map to return the corresponding value
-    DenseHashMap<std::string, TypeId> classesSerialized_DEPRECATED{{}};
-
     // List of errors that occur during serialization/deserialization
-    // At every iteration of serialization/deserialzation, if this list.size() != 0, we halt the process
+    // At every iteration of serialization/deserialization, if this list.size() != 0, we halt the process
     std::vector<std::string> errors{};
 
     TypeFunctionRuntimeBuilderState(NotNull<TypeFunctionContext> ctx)

Analysis/include/Luau/TypePath.h

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

Analysis/src/AnyTypeSummary.cpp

@@ -1,902 +0,0 @@
-// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
-#include "Luau/AnyTypeSummary.h"
-
-#include "Luau/BuiltinDefinitions.h"
-#include "Luau/Clone.h"
-#include "Luau/Common.h"
-#include "Luau/Config.h"
-#include "Luau/ConstraintGenerator.h"
-#include "Luau/ConstraintSolver.h"
-#include "Luau/DataFlowGraph.h"
-#include "Luau/DcrLogger.h"
-#include "Luau/Module.h"
-#include "Luau/Parser.h"
-#include "Luau/Scope.h"
-#include "Luau/StringUtils.h"
-#include "Luau/TimeTrace.h"
-#include "Luau/ToString.h"
-#include "Luau/Transpiler.h"
-#include "Luau/TypeArena.h"
-#include "Luau/TypeChecker2.h"
-#include "Luau/NonStrictTypeChecker.h"
-#include "Luau/TypeInfer.h"
-#include "Luau/Variant.h"
-#include "Luau/VisitType.h"
-#include "Luau/TypePack.h"
-#include "Luau/TypeOrPack.h"
-
-#include <algorithm>
-#include <memory>
-#include <chrono>
-#include <condition_variable>
-#include <exception>
-#include <mutex>
-#include <stdexcept>
-#include <string>
-#include <iostream>
-
-
-#include <stdio.h>
-
-LUAU_FASTFLAGVARIABLE(StudioReportLuauAny2);
-LUAU_FASTINTVARIABLE(LuauAnySummaryRecursionLimit, 300);
-
-LUAU_FASTFLAG(DebugLuauMagicTypes);
-
-namespace Luau
-{
-
-void AnyTypeSummary::traverse(const Module* module, AstStat* src, NotNull<BuiltinTypes> builtinTypes)
-{
-    visit(findInnerMostScope(src->location, module), src, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStat* stat, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    RecursionLimiter limiter{&recursionCount, FInt::LuauAnySummaryRecursionLimit};
-
-    if (auto s = stat->as<AstStatBlock>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto i = stat->as<AstStatIf>())
-        return visit(scope, i, module, builtinTypes);
-    else if (auto s = stat->as<AstStatWhile>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatRepeat>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto r = stat->as<AstStatReturn>())
-        return visit(scope, r, module, builtinTypes);
-    else if (auto e = stat->as<AstStatExpr>())
-        return visit(scope, e, module, builtinTypes);
-    else if (auto s = stat->as<AstStatLocal>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatFor>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatForIn>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto a = stat->as<AstStatAssign>())
-        return visit(scope, a, module, builtinTypes);
-    else if (auto a = stat->as<AstStatCompoundAssign>())
-        return visit(scope, a, module, builtinTypes);
-    else if (auto f = stat->as<AstStatFunction>())
-        return visit(scope, f, module, builtinTypes);
-    else if (auto f = stat->as<AstStatLocalFunction>())
-        return visit(scope, f, module, builtinTypes);
-    else if (auto a = stat->as<AstStatTypeAlias>())
-        return visit(scope, a, module, builtinTypes);
-    else if (auto s = stat->as<AstStatDeclareGlobal>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatDeclareFunction>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatDeclareClass>())
-        return visit(scope, s, module, builtinTypes);
-    else if (auto s = stat->as<AstStatError>())
-        return visit(scope, s, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatBlock* block, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    RecursionCounter counter{&recursionCount};
-
-    if (recursionCount >= FInt::LuauAnySummaryRecursionLimit)
-        return; // don't report
-
-    for (AstStat* stat : block->body)
-        visit(scope, stat, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatIf* ifStatement, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (ifStatement->thenbody)
-    {
-        const Scope* thenScope = findInnerMostScope(ifStatement->thenbody->location, module);
-        visit(thenScope, ifStatement->thenbody, module, builtinTypes);
-    }
-
-    if (ifStatement->elsebody)
-    {
-        const Scope* elseScope = findInnerMostScope(ifStatement->elsebody->location, module);
-        visit(elseScope, ifStatement->elsebody, module, builtinTypes);
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatWhile* while_, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* whileScope = findInnerMostScope(while_->location, module);
-    visit(whileScope, while_->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatRepeat* repeat, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* repeatScope = findInnerMostScope(repeat->location, module);
-    visit(repeatScope, repeat->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatReturn* ret, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* retScope = findInnerMostScope(ret->location, module);
-
-    auto ctxNode = getNode(rootSrc, ret);
-    bool seenTP = false;
-
-    for (auto val : ret->list)
-    {
-        if (isAnyCall(retScope, val, module, builtinTypes))
-        {
-            TelemetryTypePair types;
-            types.inferredType = toString(lookupType(val, module, builtinTypes));
-            TypeInfo ti{Pattern::FuncApp, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-
-        if (isAnyCast(retScope, val, module, builtinTypes))
-        {
-            if (auto cast = val->as<AstExprTypeAssertion>())
-            {
-                TelemetryTypePair types;
-
-                types.annotatedType = toString(lookupAnnotation(cast->annotation, module, builtinTypes));
-                types.inferredType = toString(lookupType(cast->expr, module, builtinTypes));
-
-                TypeInfo ti{Pattern::Casts, toString(ctxNode), types};
-                typeInfo.push_back(ti);
-            }
-        }
-
-        if (ret->list.size > 1 && !seenTP)
-        {
-            if (containsAny(retScope->returnType))
-            {
-                seenTP = true;
-
-                TelemetryTypePair types;
-
-                types.inferredType = toString(retScope->returnType);
-
-                TypeInfo ti{Pattern::TypePk, toString(ctxNode), types};
-                typeInfo.push_back(ti);
-            }
-        }
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatLocal* local, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, local);
-
-    TypePackId values = reconstructTypePack(local->values, module, builtinTypes);
-    auto [head, tail] = flatten(values);
-
-    size_t posn = 0;
-    for (AstLocal* loc : local->vars)
-    {
-        if (local->vars.data[0] == loc && posn < local->values.size)
-        {
-            if (loc->annotation)
-            {
-                auto annot = lookupAnnotation(loc->annotation, module, builtinTypes);
-                if (containsAny(annot))
-                {
-                    TelemetryTypePair types;
-
-                    types.annotatedType = toString(annot);
-                    types.inferredType = toString(lookupType(local->values.data[posn], module, builtinTypes));
-
-                    TypeInfo ti{Pattern::VarAnnot, toString(ctxNode), types};
-                    typeInfo.push_back(ti);
-                }
-            }
-
-            const AstExprTypeAssertion* maybeRequire = local->values.data[posn]->as<AstExprTypeAssertion>();
-            if (!maybeRequire)
-                continue;
-
-            if (std::min(local->values.size - 1, posn) < head.size())
-            {
-                if (isAnyCast(scope, local->values.data[posn], module, builtinTypes))
-                {
-                    TelemetryTypePair types;
-
-                    types.inferredType = toString(head[std::min(local->values.size - 1, posn)]);
-
-                    TypeInfo ti{Pattern::Casts, toString(ctxNode), types};
-                    typeInfo.push_back(ti);
-                }
-            }
-        }
-        else
-        {
-
-            if (std::min(local->values.size - 1, posn) < head.size())
-            {
-                if (loc->annotation)
-                {
-                    auto annot = lookupAnnotation(loc->annotation, module, builtinTypes);
-                    if (containsAny(annot))
-                    {
-                        TelemetryTypePair types;
-
-                        types.annotatedType = toString(annot);
-                        types.inferredType = toString(head[std::min(local->values.size - 1, posn)]);
-
-                        TypeInfo ti{Pattern::VarAnnot, toString(ctxNode), types};
-                        typeInfo.push_back(ti);
-                    }
-                }
-            }
-            else
-            {
-                if (tail)
-                {
-                    if (containsAny(*tail))
-                    {
-                        TelemetryTypePair types;
-
-                        types.inferredType = toString(*tail);
-
-                        TypeInfo ti{Pattern::VarAny, toString(ctxNode), types};
-                        typeInfo.push_back(ti);
-                    }
-                }
-            }
-        }
-
-        ++posn;
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatFor* for_, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* forScope = findInnerMostScope(for_->location, module);
-    visit(forScope, for_->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatForIn* forIn, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const Scope* loopScope = findInnerMostScope(forIn->location, module);
-    visit(loopScope, forIn->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatAssign* assign, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, assign);
-
-    TypePackId values = reconstructTypePack(assign->values, module, builtinTypes);
-    auto [head, tail] = flatten(values);
-
-    size_t posn = 0;
-    for (AstExpr* var : assign->vars)
-    {
-        TypeId tp = lookupType(var, module, builtinTypes);
-        if (containsAny(tp))
-        {
-            TelemetryTypePair types;
-
-            types.annotatedType = toString(tp);
-
-            auto loc = std::min(assign->vars.size - 1, posn);
-            if (head.size() >= assign->vars.size && posn < head.size())
-            {
-                types.inferredType = toString(head[posn]);
-            }
-            else if (loc < head.size())
-                types.inferredType = toString(head[loc]);
-            else
-                types.inferredType = toString(builtinTypes->nilType);
-
-            TypeInfo ti{Pattern::Assign, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-        ++posn;
-    }
-
-    for (AstExpr* val : assign->values)
-    {
-        if (isAnyCall(scope, val, module, builtinTypes))
-        {
-            TelemetryTypePair types;
-
-            types.inferredType = toString(lookupType(val, module, builtinTypes));
-
-            TypeInfo ti{Pattern::FuncApp, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-
-        if (isAnyCast(scope, val, module, builtinTypes))
-        {
-            if (auto cast = val->as<AstExprTypeAssertion>())
-            {
-                TelemetryTypePair types;
-
-                types.annotatedType = toString(lookupAnnotation(cast->annotation, module, builtinTypes));
-                types.inferredType = toString(lookupType(val, module, builtinTypes));
-
-                TypeInfo ti{Pattern::Casts, toString(ctxNode), types};
-                typeInfo.push_back(ti);
-            }
-        }
-    }
-
-    if (tail)
-    {
-        if (containsAny(*tail))
-        {
-            TelemetryTypePair types;
-
-            types.inferredType = toString(*tail);
-
-            TypeInfo ti{Pattern::Assign, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatCompoundAssign* assign, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, assign);
-
-    TelemetryTypePair types;
-
-    types.inferredType = toString(lookupType(assign->value, module, builtinTypes));
-    types.annotatedType = toString(lookupType(assign->var, module, builtinTypes));
-
-    if (module->astTypes.contains(assign->var))
-    {
-        if (containsAny(*module->astTypes.find(assign->var)))
-        {
-            TypeInfo ti{Pattern::Assign, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-    }
-    else if (module->astTypePacks.contains(assign->var))
-    {
-        if (containsAny(*module->astTypePacks.find(assign->var)))
-        {
-            TypeInfo ti{Pattern::Assign, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-    }
-
-    if (isAnyCall(scope, assign->value, module, builtinTypes))
-    {
-        TypeInfo ti{Pattern::FuncApp, toString(ctxNode), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (isAnyCast(scope, assign->value, module, builtinTypes))
-    {
-        if (auto cast = assign->value->as<AstExprTypeAssertion>())
-        {
-            types.annotatedType = toString(lookupAnnotation(cast->annotation, module, builtinTypes));
-            types.inferredType = toString(lookupType(cast->expr, module, builtinTypes));
-
-            TypeInfo ti{Pattern::Casts, toString(ctxNode), types};
-            typeInfo.push_back(ti);
-        }
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatFunction* function, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    TelemetryTypePair types;
-    types.inferredType = toString(lookupType(function->func, module, builtinTypes));
-
-    if (hasVariadicAnys(scope, function->func, module, builtinTypes))
-    {
-        TypeInfo ti{Pattern::VarAny, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (hasArgAnys(scope, function->func, module, builtinTypes))
-    {
-        TypeInfo ti{Pattern::FuncArg, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (hasAnyReturns(scope, function->func, module, builtinTypes))
-    {
-        TypeInfo ti{Pattern::FuncRet, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (function->func->body->body.size > 0)
-        visit(scope, function->func->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatLocalFunction* function, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    TelemetryTypePair types;
-
-    if (hasVariadicAnys(scope, function->func, module, builtinTypes))
-    {
-        types.inferredType = toString(lookupType(function->func, module, builtinTypes));
-        TypeInfo ti{Pattern::VarAny, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (hasArgAnys(scope, function->func, module, builtinTypes))
-    {
-        types.inferredType = toString(lookupType(function->func, module, builtinTypes));
-        TypeInfo ti{Pattern::FuncArg, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (hasAnyReturns(scope, function->func, module, builtinTypes))
-    {
-        types.inferredType = toString(lookupType(function->func, module, builtinTypes));
-        TypeInfo ti{Pattern::FuncRet, toString(function), types};
-        typeInfo.push_back(ti);
-    }
-
-    if (function->func->body->body.size > 0)
-        visit(scope, function->func->body, module, builtinTypes);
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatTypeAlias* alias, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, alias);
-
-    auto annot = lookupAnnotation(alias->type, module, builtinTypes);
-    if (containsAny(annot))
-    {
-        // no expr => no inference for aliases
-        TelemetryTypePair types;
-
-        types.annotatedType = toString(annot);
-        TypeInfo ti{Pattern::Alias, toString(ctxNode), types};
-        typeInfo.push_back(ti);
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    auto ctxNode = getNode(rootSrc, expr);
-
-    if (isAnyCall(scope, expr->expr, module, builtinTypes))
-    {
-        TelemetryTypePair types;
-        types.inferredType = toString(lookupType(expr->expr, module, builtinTypes));
-
-        TypeInfo ti{Pattern::FuncApp, toString(ctxNode), types};
-        typeInfo.push_back(ti);
-    }
-}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatDeclareGlobal* declareGlobal, const Module* module, NotNull<BuiltinTypes> builtinTypes) {}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatDeclareClass* declareClass, const Module* module, NotNull<BuiltinTypes> builtinTypes) {}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatDeclareFunction* declareFunction, const Module* module, NotNull<BuiltinTypes> builtinTypes) {}
-
-void AnyTypeSummary::visit(const Scope* scope, AstStatError* error, const Module* module, NotNull<BuiltinTypes> builtinTypes) {}
-
-TypeId AnyTypeSummary::checkForFamilyInhabitance(const TypeId instance, const Location location)
-{
-    if (seenTypeFamilyInstances.find(instance))
-        return instance;
-
-    seenTypeFamilyInstances.insert(instance);
-    return instance;
-}
-
-TypeId AnyTypeSummary::lookupType(const AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    const TypeId* ty = module->astTypes.find(expr);
-    if (ty)
-        return checkForFamilyInhabitance(follow(*ty), expr->location);
-
-    const TypePackId* tp = module->astTypePacks.find(expr);
-    if (tp)
-    {
-        if (auto fst = first(*tp, /*ignoreHiddenVariadics*/ false))
-            return checkForFamilyInhabitance(*fst, expr->location);
-        else if (finite(*tp) && size(*tp) == 0)
-            return checkForFamilyInhabitance(builtinTypes->nilType, expr->location);
-    }
-
-    return builtinTypes->errorRecoveryType();
-}
-
-TypePackId AnyTypeSummary::reconstructTypePack(AstArray<AstExpr*> exprs, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (exprs.size == 0)
-        return arena.addTypePack(TypePack{{}, std::nullopt});
-
-    std::vector<TypeId> head;
-
-    for (size_t i = 0; i < exprs.size - 1; ++i)
-    {
-        head.push_back(lookupType(exprs.data[i], module, builtinTypes));
-    }
-
-    const TypePackId* tail = module->astTypePacks.find(exprs.data[exprs.size - 1]);
-    if (tail)
-        return arena.addTypePack(TypePack{std::move(head), follow(*tail)});
-    else
-        return arena.addTypePack(TypePack{std::move(head), builtinTypes->errorRecoveryTypePack()});
-}
-
-bool AnyTypeSummary::isAnyCall(const Scope* scope, AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (auto call = expr->as<AstExprCall>())
-    {
-        TypePackId args = reconstructTypePack(call->args, module, builtinTypes);
-        if (containsAny(args))
-            return true;
-
-        TypeId func = lookupType(call->func, module, builtinTypes);
-        if (containsAny(func))
-            return true;
-    }
-    return false;
-}
-
-bool AnyTypeSummary::hasVariadicAnys(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (expr->vararg && expr->varargAnnotation)
-    {
-        auto annot = lookupPackAnnotation(expr->varargAnnotation, module);
-        if (annot && containsAny(*annot))
-        {
-            return true;
-        }
-    }
-    return false;
-}
-
-bool AnyTypeSummary::hasArgAnys(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (expr->args.size > 0)
-    {
-        for (const AstLocal* arg : expr->args)
-        {
-            if (arg->annotation)
-            {
-                auto annot = lookupAnnotation(arg->annotation, module, builtinTypes);
-                if (containsAny(annot))
-                {
-                    return true;
-                }
-            }
-        }
-    }
-    return false;
-}
-
-bool AnyTypeSummary::hasAnyReturns(const Scope* scope, AstExprFunction* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (!expr->returnAnnotation)
-    {
-        return false;
-    }
-
-    for (AstType* ret : expr->returnAnnotation->types)
-    {
-        if (containsAny(lookupAnnotation(ret, module, builtinTypes)))
-        {
-            return true;
-        }
-    }
-
-    if (expr->returnAnnotation->tailType)
-    {
-        auto annot = lookupPackAnnotation(expr->returnAnnotation->tailType, module);
-        if (annot && containsAny(*annot))
-        {
-            return true;
-        }
-    }
-
-    return false;
-}
-
-bool AnyTypeSummary::isAnyCast(const Scope* scope, AstExpr* expr, const Module* module, NotNull<BuiltinTypes> builtinTypes)
-{
-    if (auto cast = expr->as<AstExprTypeAssertion>())
-    {
-        auto annot = lookupAnnotation(cast->annotation, module, builtinTypes);
-        if (containsAny(annot))
-        {
-            return true;
-        }
-    }
-    return false;
-}
-
-TypeId AnyTypeSummary::lookupAnnotation(AstType* annotation, const Module* module, NotNull<BuiltinTypes> builtintypes)
-{
-    if (FFlag::DebugLuauMagicTypes)
-    {
-        if (auto ref = annotation->as<AstTypeReference>(); ref && ref->parameters.size > 0)
-        {
-            if (auto ann = ref->parameters.data[0].type)
-            {
-                TypeId argTy = lookupAnnotation(ref->parameters.data[0].type, module, builtintypes);
-                return follow(argTy);
-            }
-        }
-    }
-
-    const TypeId* ty = module->astResolvedTypes.find(annotation);
-    if (ty)
-        return checkForTypeFunctionInhabitance(follow(*ty), annotation->location);
-    else
-        return checkForTypeFunctionInhabitance(builtintypes->errorRecoveryType(), annotation->location);
-}
-
-TypeId AnyTypeSummary::checkForTypeFunctionInhabitance(const TypeId instance, const Location location)
-{
-    if (seenTypeFunctionInstances.find(instance))
-        return instance;
-    seenTypeFunctionInstances.insert(instance);
-
-    return instance;
-}
-
-std::optional<TypePackId> AnyTypeSummary::lookupPackAnnotation(AstTypePack* annotation, const Module* module)
-{
-    const TypePackId* tp = module->astResolvedTypePacks.find(annotation);
-    if (tp != nullptr)
-        return {follow(*tp)};
-    return {};
-}
-
-bool AnyTypeSummary::containsAny(TypeId typ)
-{
-    typ = follow(typ);
-
-    if (auto t = seen.find(typ); t && !*t)
-    {
-        return false;
-    }
-
-    seen[typ] = false;
-
-    RecursionCounter counter{&recursionCount};
-    if (recursionCount >= FInt::LuauAnySummaryRecursionLimit)
-    {
-        return false;
-    }
-
-    bool found = false;
-
-    if (auto ty = get<AnyType>(typ))
-    {
-        found = true;
-    }
-    else if (auto ty = get<UnknownType>(typ))
-    {
-        found = true;
-    }
-    else if (auto ty = get<TableType>(typ))
-    {
-        for (auto& [_name, prop] : ty->props)
-        {
-            if (FFlag::LuauSolverV2)
-            {
-                if (auto newT = follow(prop.readTy))
-                {
-                    if (containsAny(*newT))
-                        found = true;
-                }
-                else if (auto newT = follow(prop.writeTy))
-                {
-                    if (containsAny(*newT))
-                        found = true;
-                }
-            }
-            else
-            {
-                if (containsAny(prop.type()))
-                    found = true;
-            }
-        }
-    }
-    else if (auto ty = get<IntersectionType>(typ))
-    {
-        for (auto part : ty->parts)
-        {
-            if (containsAny(part))
-            {
-                found = true;
-            }
-        }
-    }
-    else if (auto ty = get<UnionType>(typ))
-    {
-        for (auto option : ty->options)
-        {
-            if (containsAny(option))
-            {
-                found = true;
-            }
-        }
-    }
-    else if (auto ty = get<FunctionType>(typ))
-    {
-        if (containsAny(ty->argTypes))
-            found = true;
-        else if (containsAny(ty->retTypes))
-            found = true;
-    }
-
-    seen[typ] = found;
-
-    return found;
-}
-
-bool AnyTypeSummary::containsAny(TypePackId typ)
-{
-    typ = follow(typ);
-
-    if (auto t = seen.find(typ); t && !*t)
-    {
-        return false;
-    }
-
-    seen[typ] = false;
-
-    auto [head, tail] = flatten(typ);
-    bool found = false;
-
-    for (auto tp : head)
-    {
-        if (containsAny(tp))
-            found = true;
-    }
-
-    if (tail)
-    {
-        if (auto vtp = get<VariadicTypePack>(tail))
-        {
-            if (auto ty = get<AnyType>(follow(vtp->ty)))
-            {
-                found = true;
-            }
-        }
-        else if (auto tftp = get<TypeFunctionInstanceTypePack>(tail))
-        {
-
-            for (TypePackId tp : tftp->packArguments)
-            {
-                if (containsAny(tp))
-                {
-                    found = true;
-                }
-            }
-
-            for (TypeId t : tftp->typeArguments)
-            {
-                if (containsAny(t))
-                {
-                    found = true;
-                }
-            }
-        }
-    }
-
-    seen[typ] = found;
-
-    return found;
-}
-
-const Scope* AnyTypeSummary::findInnerMostScope(const Location location, const Module* module)
-{
-    const Scope* bestScope = module->getModuleScope().get();
-
-    bool didNarrow = false;
-    do
-    {
-        didNarrow = false;
-        for (auto scope : bestScope->children)
-        {
-            if (scope->location.encloses(location))
-            {
-                bestScope = scope.get();
-                didNarrow = true;
-                break;
-            }
-        }
-    } while (didNarrow && bestScope->children.size() > 0);
-
-    return bestScope;
-}
-
-std::optional<AstExpr*> AnyTypeSummary::matchRequire(const AstExprCall& call)
-{
-    const char* require = "require";
-
-    if (call.args.size != 1)
-        return std::nullopt;
-
-    const AstExprGlobal* funcAsGlobal = call.func->as<AstExprGlobal>();
-    if (!funcAsGlobal || funcAsGlobal->name != require)
-        return std::nullopt;
-
-    if (call.args.size != 1)
-        return std::nullopt;
-
-    return call.args.data[0];
-}
-
-AstNode* AnyTypeSummary::getNode(AstStatBlock* root, AstNode* node)
-{
-    FindReturnAncestry finder(node, root->location.end);
-    root->visit(&finder);
-
-    if (!finder.currNode)
-        finder.currNode = node;
-
-    LUAU_ASSERT(finder.found && finder.currNode);
-    return finder.currNode;
-}
-
-bool AnyTypeSummary::FindReturnAncestry::visit(AstStatLocalFunction* node)
-{
-    currNode = node;
-    return !found;
-}
-
-bool AnyTypeSummary::FindReturnAncestry::visit(AstStatFunction* node)
-{
-    currNode = node;
-    return !found;
-}
-
-bool AnyTypeSummary::FindReturnAncestry::visit(AstType* node)
-{
-    return !found;
-}
-
-bool AnyTypeSummary::FindReturnAncestry::visit(AstNode* node)
-{
-    if (node == stat)
-    {
-        found = true;
-    }
-
-    if (node->location.end == rootEnd && stat->location.end >= rootEnd)
-    {
-        currNode = node;
-        found = true;
-    }
-
-    return !found;
-}
-
-
-AnyTypeSummary::TypeInfo::TypeInfo(Pattern code, std::string node, TelemetryTypePair type)
-    : code(code)
-    , node(node)
-    , type(type)
-{
-}
-
-AnyTypeSummary::FindReturnAncestry::FindReturnAncestry(AstNode* stat, Position rootEnd)
-    : stat(stat)
-    , rootEnd(rootEnd)
-{
-}
-
-AnyTypeSummary::AnyTypeSummary() {}
-
-} // namespace Luau

Analysis/src/AstJsonEncoder.cpp

@@ -1065,6 +1065,11 @@ struct AstJsonEncoder : public AstVisitor
         );
     }
 
+    void write(class AstTypeOptional* node)
+    {
+        writeNode(node, "AstTypeOptional", [&]() {});
+    }
+
     void write(class AstTypeUnion* node)
     {
         writeNode(
@@ -1146,6 +1151,8 @@ struct AstJsonEncoder : public AstVisitor
             return writeString("checked");
         case AstAttr::Type::Native:
             return writeString("native");
+        case AstAttr::Type::Deprecated:
+            return writeString("deprecated");
         }
     }
 

Analysis/src/AutocompleteCore.cpp

@@ -25,9 +25,12 @@ LUAU_FASTINT(LuauTypeInferIterationLimit)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
 LUAU_FASTFLAGVARIABLE(DebugLuauMagicVariableNames)
 
+LUAU_FASTFLAG(LuauExposeRequireByStringAutocomplete)
+
 LUAU_FASTFLAGVARIABLE(LuauAutocompleteRefactorsForIncrementalAutocomplete)
 
 LUAU_FASTFLAGVARIABLE(LuauAutocompleteUsesModuleForTypeCompatibility)
+LUAU_FASTFLAGVARIABLE(LuauAutocompleteUnionCopyPreviousSeen)
 
 static const std::unordered_set<std::string> kStatementStartingKeywords =
     {"while", "if", "local", "repeat", "function", "do", "for", "return", "break", "continue", "type", "export"};
@@ -482,6 +485,21 @@ static void autocompleteProps(
             AutocompleteEntryMap inner;
             std::unordered_set<TypeId> innerSeen;
 
+            // If we don't do this, and we have the misfortune of receiving a
+            // recursive union like:
+            //
+            //  t1 where t1 = t1 | Class
+            //
+            // Then we are on a one way journey to a stack overflow.
+            if (FFlag::LuauAutocompleteUnionCopyPreviousSeen)
+            {
+                for (auto ty: seen)
+                {
+                    if (is<UnionType, IntersectionType>(ty))
+                        innerSeen.insert(ty);
+                }
+            }
+
             if (isNil(*iter))
             {
                 ++iter;
@@ -1519,10 +1537,14 @@ static std::optional<AutocompleteEntryMap> convertRequireSuggestionsToAutocomple
         return std::nullopt;
 
     AutocompleteEntryMap result;
-    for (const RequireSuggestion& suggestion : *suggestions)
+    for (RequireSuggestion& suggestion : *suggestions)
     {
         AutocompleteEntry entry = {AutocompleteEntryKind::RequirePath};
         entry.insertText = std::move(suggestion.fullPath);
+        if (FFlag::LuauExposeRequireByStringAutocomplete)
+        {
+            entry.tags = std::move(suggestion.tags);
+        }
         result[std::move(suggestion.label)] = std::move(entry);
     }
     return result;

Analysis/src/BuiltinDefinitions.cpp

@@ -32,8 +32,8 @@ LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAGVARIABLE(LuauStringFormatErrorSuppression)
 LUAU_FASTFLAGVARIABLE(LuauTableCloneClonesType3)
 LUAU_FASTFLAG(LuauTrackInteriorFreeTypesOnScope)
-LUAU_FASTFLAGVARIABLE(LuauFreezeIgnorePersistent)
 LUAU_FASTFLAGVARIABLE(LuauFollowTableFreeze)
+LUAU_FASTFLAGVARIABLE(LuauUserTypeFunTypecheck)
 
 namespace Luau
 {
@@ -288,6 +288,22 @@ 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());
@@ -399,14 +415,21 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
         // clang-format on
     }
 
-    for (const auto& pair : globals.globalScope->bindings)
+    if (FFlag::LuauUserTypeFunTypecheck)
     {
-        persist(pair.second.typeId);
+        finalizeGlobalBindings(globals.globalScope);
-
+    }
-        if (TableType* ttv = getMutable<TableType>(pair.second.typeId))
+    else
+    {
+        for (const auto& pair : globals.globalScope->bindings)
         {
-            if (!ttv->name)
+            persist(pair.second.typeId);
-                ttv->name = "typeof(" + toString(pair.first) + ")";
+
+            if (TableType* ttv = getMutable<TableType>(pair.second.typeId))
+            {
+                if (!ttv->name)
+                    ttv->name = "typeof(" + toString(pair.first) + ")";
+            }
         }
     }
 
@@ -467,6 +490,59 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
     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)
@@ -1444,7 +1520,7 @@ bool MagicClone::infer(const MagicFunctionCallContext& context)
         return false;
 
     CloneState cloneState{context.solver->builtinTypes};
-    TypeId resultType = shallowClone(inputType, *arena, cloneState, /* ignorePersistent */ FFlag::LuauFreezeIgnorePersistent);
+    TypeId resultType = shallowClone(inputType, *arena, cloneState, /* ignorePersistent */ true);
 
     if (auto tableType = getMutable<TableType>(resultType))
     {
@@ -1481,7 +1557,7 @@ static std::optional<TypeId> freezeTable(TypeId inputType, const MagicFunctionCa
     {
         // 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 */ FFlag::LuauFreezeIgnorePersistent);
+        TypeId resultType = shallowClone(inputType, *arena, cloneState, /* ignorePersistent */ true);
         auto tableTy = getMutable<TableType>(resultType);
         // `clone` should not break this.
         LUAU_ASSERT(tableTy);

Analysis/src/Clone.cpp

@@ -1,6 +1,7 @@
 // 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"
@@ -8,11 +9,12 @@
 #include "Luau/VisitType.h"
 
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAG(LuauFreezeIgnorePersistent)
 
 // 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
 {
 
@@ -131,7 +133,7 @@ protected:
         ty = follow(ty, FollowOption::DisableLazyTypeThunks);
         if (auto it = types->find(ty); it != types->end())
             return it->second;
-        else if (ty->persistent && (!FFlag::LuauFreezeIgnorePersistent || ty != forceTy))
+        else if (ty->persistent && ty != forceTy)
             return ty;
         return std::nullopt;
     }
@@ -141,7 +143,7 @@ protected:
         tp = follow(tp);
         if (auto it = packs->find(tp); it != packs->end())
             return it->second;
-        else if (tp->persistent && (!FFlag::LuauFreezeIgnorePersistent || tp != forceTp))
+        else if (tp->persistent && tp != forceTp)
             return tp;
         return std::nullopt;
     }
@@ -167,7 +169,7 @@ public:
 
         if (auto clone = find(ty))
             return *clone;
-        else if (ty->persistent && (!FFlag::LuauFreezeIgnorePersistent || ty != forceTy))
+        else if (ty->persistent && ty != forceTy)
             return ty;
 
         TypeId target = arena->addType(ty->ty);
@@ -193,7 +195,7 @@ public:
 
         if (auto clone = find(tp))
             return *clone;
-        else if (tp->persistent && (!FFlag::LuauFreezeIgnorePersistent || tp != forceTp))
+        else if (tp->persistent && tp != forceTp)
             return tp;
 
         TypePackId target = arena->addTypePack(tp->ty);
@@ -395,7 +397,7 @@ private:
             ty = shallowClone(ty);
     }
 
-    void cloneChildren(LazyType* t)
+    virtual void cloneChildren(LazyType* t)
     {
         if (auto unwrapped = t->unwrapped.load())
             t->unwrapped.store(shallowClone(unwrapped));
@@ -477,7 +479,7 @@ private:
 
 class FragmentAutocompleteTypeCloner final : public TypeCloner
 {
-    Scope* freeTypeReplacementScope = nullptr;
+    Scope* replacementForNullScope = nullptr;
 
 public:
     FragmentAutocompleteTypeCloner(
@@ -487,12 +489,12 @@ public:
         NotNull<SeenTypePacks> packs,
         TypeId forceTy,
         TypePackId forceTp,
-        Scope* freeTypeReplacementScope
+        Scope* replacementForNullScope
     )
         : TypeCloner(arena, builtinTypes, types, packs, forceTy, forceTp)
-        , freeTypeReplacementScope(freeTypeReplacementScope)
+        , replacementForNullScope(replacementForNullScope)
     {
-        LUAU_ASSERT(freeTypeReplacementScope);
+        LUAU_ASSERT(replacementForNullScope);
     }
 
     TypeId shallowClone(TypeId ty) override
@@ -502,7 +504,7 @@ public:
 
         if (auto clone = find(ty))
             return *clone;
-        else if (ty->persistent && (!FFlag::LuauFreezeIgnorePersistent || ty != forceTy))
+        else if (ty->persistent && ty != forceTy)
             return ty;
 
         TypeId target = arena->addType(ty->ty);
@@ -512,12 +514,18 @@ public:
             generic->scope = nullptr;
         else if (auto free = getMutable<FreeType>(target))
         {
-            free->scope = freeTypeReplacementScope;
+            free->scope = replacementForNullScope;
+        }
+        else if (auto tt = getMutable<TableType>(target))
+        {
+            if (FFlag::LuauClonedTableAndFunctionTypesMustHaveScopes)
+                tt->scope = replacementForNullScope;
         }
         else if (auto fn = getMutable<FunctionType>(target))
-            fn->scope = nullptr;
+        {
-        else if (auto table = getMutable<TableType>(target))
+            if (FFlag::LuauClonedTableAndFunctionTypesMustHaveScopes)
-            table->scope = nullptr;
+                fn->scope = replacementForNullScope;
+        }
 
         (*types)[ty] = target;
         queue.emplace_back(target);
@@ -530,7 +538,7 @@ public:
 
         if (auto clone = find(tp))
             return *clone;
-        else if (tp->persistent && (!FFlag::LuauFreezeIgnorePersistent || tp != forceTp))
+        else if (tp->persistent && tp != forceTp)
             return tp;
 
         TypePackId target = arena->addTypePack(tp->ty);
@@ -538,12 +546,22 @@ public:
         if (auto generic = getMutable<GenericTypePack>(target))
             generic->scope = nullptr;
         else if (auto free = getMutable<FreeTypePack>(target))
-            free->scope = freeTypeReplacementScope;
+            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));
+        }
+    }
 };
 
 
@@ -551,7 +569,7 @@ public:
 
 TypePackId shallowClone(TypePackId tp, TypeArena& dest, CloneState& cloneState, bool ignorePersistent)
 {
-    if (tp->persistent && (!FFlag::LuauFreezeIgnorePersistent || !ignorePersistent))
+    if (tp->persistent && !ignorePersistent)
         return tp;
 
     TypeCloner cloner{
@@ -560,7 +578,7 @@ TypePackId shallowClone(TypePackId tp, TypeArena& dest, CloneState& cloneState,
         NotNull{&cloneState.seenTypes},
         NotNull{&cloneState.seenTypePacks},
         nullptr,
-        FFlag::LuauFreezeIgnorePersistent && ignorePersistent ? tp : nullptr
+        ignorePersistent ? tp : nullptr
     };
 
     return cloner.shallowClone(tp);
@@ -568,7 +586,7 @@ TypePackId shallowClone(TypePackId tp, TypeArena& dest, CloneState& cloneState,
 
 TypeId shallowClone(TypeId typeId, TypeArena& dest, CloneState& cloneState, bool ignorePersistent)
 {
-    if (typeId->persistent && (!FFlag::LuauFreezeIgnorePersistent || !ignorePersistent))
+    if (typeId->persistent && !ignorePersistent)
         return typeId;
 
     TypeCloner cloner{
@@ -576,7 +594,7 @@ TypeId shallowClone(TypeId typeId, TypeArena& dest, CloneState& cloneState, bool
         cloneState.builtinTypes,
         NotNull{&cloneState.seenTypes},
         NotNull{&cloneState.seenTypePacks},
-        FFlag::LuauFreezeIgnorePersistent && ignorePersistent ? typeId : nullptr,
+        ignorePersistent ? typeId : nullptr,
         nullptr
     };
 
@@ -728,7 +746,7 @@ Binding cloneIncremental(const Binding& binding, TypeArena& dest, CloneState& cl
     b.deprecatedSuggestion = binding.deprecatedSuggestion;
     b.documentationSymbol = binding.documentationSymbol;
     b.location = binding.location;
-    b.typeId = cloner.clone(binding.typeId);
+    b.typeId = FFlag::LuauDoNotClonePersistentBindings && binding.typeId->persistent ? binding.typeId : cloner.clone(binding.typeId);
 
     return b;
 }

Analysis/src/ConstraintGenerator.cpp

@@ -33,15 +33,21 @@ LUAU_FASTINT(LuauCheckRecursionLimit)
 LUAU_FASTFLAG(DebugLuauLogSolverToJson)
 LUAU_FASTFLAG(DebugLuauMagicTypes)
 LUAU_FASTFLAG(LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
+LUAU_FASTFLAGVARIABLE(LuauPropagateExpectedTypesForCalls)
 LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
 
 LUAU_FASTFLAGVARIABLE(LuauTrackInteriorFreeTypesOnScope)
 LUAU_FASTFLAGVARIABLE(LuauDeferBidirectionalInferenceForTableAssignment)
 LUAU_FASTFLAGVARIABLE(LuauUngeneralizedTypesForRecursiveFunctions)
+LUAU_FASTFLAGVARIABLE(LuauGlobalSelfAssignmentCycle)
 
 LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
 LUAU_FASTFLAGVARIABLE(LuauInferLocalTypesInMultipleAssignments)
 LUAU_FASTFLAGVARIABLE(LuauDoNotLeakNilInRefinement)
+LUAU_FASTFLAGVARIABLE(LuauExtraFollows)
+LUAU_FASTFLAG(LuauUserTypeFunTypecheck)
+
+LUAU_FASTFLAG(LuauDeprecatedAttribute)
 
 namespace Luau
 {
@@ -182,6 +188,7 @@ ConstraintGenerator::ConstraintGenerator(
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<InternalErrorReporter> ice,
     const ScopePtr& globalScope,
+    const ScopePtr& typeFunctionScope,
     std::function<void(const ModuleName&, const ScopePtr&)> prepareModuleScope,
     DcrLogger* logger,
     NotNull<DataFlowGraph> dfg,
@@ -198,6 +205,7 @@ ConstraintGenerator::ConstraintGenerator(
     , moduleResolver(moduleResolver)
     , ice(ice)
     , globalScope(globalScope)
+    , typeFunctionScope(typeFunctionScope)
     , prepareModuleScope(std::move(prepareModuleScope))
     , requireCycles(std::move(requireCycles))
     , logger(logger)
@@ -219,6 +227,14 @@ void ConstraintGenerator::visitModuleRoot(AstStatBlock* block)
 
     rootScope->returnType = freshTypePack(scope);
 
+    if (FFlag::LuauUserTypeFunTypecheck)
+    {
+        // Create module-local scope for the type function environment
+        ScopePtr localTypeFunctionScope = std::make_shared<Scope>(typeFunctionScope);
+        localTypeFunctionScope->location = block->location;
+        typeFunctionRuntime->rootScope = localTypeFunctionScope;
+    }
+
     TypeId moduleFnTy = arena->addType(FunctionType{TypeLevel{}, rootScope, builtinTypes->anyTypePack, rootScope->returnType});
     interiorTypes.emplace_back();
 
@@ -534,7 +550,7 @@ void ConstraintGenerator::computeRefinement(
             refis->get(proposition->key->def)->shouldAppendNilType =
                 (sense || !eq) && containsSubscriptedDefinition(proposition->key->def) && !proposition->implicitFromCall;
         }
-        else 
+        else
         {
             refis->get(proposition->key->def)->shouldAppendNilType = (sense || !eq) && containsSubscriptedDefinition(proposition->key->def);
         }
@@ -697,6 +713,9 @@ void ConstraintGenerator::checkAliases(const ScopePtr& scope, AstStatBlock* bloc
     std::unordered_map<Name, Location> aliasDefinitionLocations;
     std::unordered_map<Name, Location> classDefinitionLocations;
 
+    bool hasTypeFunction = false;
+    ScopePtr typeFunctionEnvScope;
+
     // In order to enable mutually-recursive type aliases, we need to
     // populate the type bindings before we actually check any of the
     // alias statements.
@@ -742,6 +761,9 @@ void ConstraintGenerator::checkAliases(const ScopePtr& scope, AstStatBlock* bloc
         }
         else if (auto function = stat->as<AstStatTypeFunction>())
         {
+            if (FFlag::LuauUserTypeFunTypecheck)
+                hasTypeFunction = true;
+
             // If a type function w/ same name has already been defined, error for having duplicates
             if (scope->exportedTypeBindings.count(function->name.value) || scope->privateTypeBindings.count(function->name.value))
             {
@@ -751,7 +773,8 @@ void ConstraintGenerator::checkAliases(const ScopePtr& scope, AstStatBlock* bloc
                 continue;
             }
 
-            ScopePtr defnScope = childScope(function, scope);
+            // Variable becomes unused with the removal of FFlag::LuauUserTypeFunTypecheck
+            ScopePtr defnScope = FFlag::LuauUserTypeFunTypecheck ? nullptr : childScope(function, scope);
 
             // Create TypeFunctionInstanceType
 
@@ -818,11 +841,22 @@ void ConstraintGenerator::checkAliases(const ScopePtr& scope, AstStatBlock* bloc
         }
     }
 
+    if (FFlag::LuauUserTypeFunTypecheck && hasTypeFunction)
+        typeFunctionEnvScope = std::make_shared<Scope>(typeFunctionRuntime->rootScope);
+
     // Additional pass for user-defined type functions to fill in their environments completely
     for (AstStat* stat : block->body)
     {
         if (auto function = stat->as<AstStatTypeFunction>())
         {
+            if (FFlag::LuauUserTypeFunTypecheck)
+            {
+                // Similar to global pre-population, create a binding for each type function in the scope upfront
+                TypeId bt = arena->addType(BlockedType{});
+                typeFunctionEnvScope->bindings[function->name] = Binding{bt, function->location};
+                astTypeFunctionEnvironmentScopes[function] = typeFunctionEnvScope;
+            }
+
             // Find the type function we have already created
             TypeFunctionInstanceType* mainTypeFun = nullptr;
 
@@ -841,51 +875,60 @@ void ConstraintGenerator::checkAliases(const ScopePtr& scope, AstStatBlock* bloc
                 UserDefinedFunctionData& userFuncData = mainTypeFun->userFuncData;
                 size_t level = 0;
 
-                for (Scope* curr = scope.get(); curr; curr = curr->parent.get())
+                if (FFlag::LuauUserTypeFunTypecheck)
                 {
-                    for (auto& [name, tf] : curr->privateTypeBindings)
+                    auto addToEnvironment = [this](UserDefinedFunctionData& userFuncData, ScopePtr scope, const Name& name, TypeId type, size_t level)
                     {
                         if (userFuncData.environment.find(name))
-                            continue;
+                            return;
 
-                        if (auto ty = get<TypeFunctionInstanceType>(tf.type); ty && ty->userFuncData.definition)
+                        if (auto ty = get<TypeFunctionInstanceType>(type); ty && ty->userFuncData.definition)
+                        {
                             userFuncData.environment[name] = std::make_pair(ty->userFuncData.definition, level);
-                    }
 
-                    for (auto& [name, tf] : curr->exportedTypeBindings)
+                            if (auto it = astTypeFunctionEnvironmentScopes.find(ty->userFuncData.definition))
+                            {
+                                if (auto existing = (*it)->linearSearchForBinding(name, /* traverseScopeChain */ false))
+                                    scope->bindings[ty->userFuncData.definition->name] =
+                                        Binding{existing->typeId, ty->userFuncData.definition->location};
+                            }
+                        }
+                    };
+
+                    for (Scope* curr = scope.get(); curr; curr = curr->parent.get())
                     {
-                        if (userFuncData.environment.find(name))
+                        for (auto& [name, tf] : curr->privateTypeBindings)
-                            continue;
+                            addToEnvironment(userFuncData, typeFunctionEnvScope, name, tf.type, level);
 
-                        if (auto ty = get<TypeFunctionInstanceType>(tf.type); ty && ty->userFuncData.definition)
+                        for (auto& [name, tf] : curr->exportedTypeBindings)
-                            userFuncData.environment[name] = std::make_pair(ty->userFuncData.definition, level);
+                            addToEnvironment(userFuncData, typeFunctionEnvScope, name, tf.type, level);
+
+                        level++;
                     }
-
-                    level++;
                 }
-            }
+                else
-            else if (mainTypeFun)
-            {
-                UserDefinedFunctionData& userFuncData = mainTypeFun->userFuncData;
-
-                for (Scope* curr = scope.get(); curr; curr = curr->parent.get())
                 {
-                    for (auto& [name, tf] : curr->privateTypeBindings)
+                    for (Scope* curr = scope.get(); curr; curr = curr->parent.get())
                     {
-                        if (userFuncData.environment_DEPRECATED.find(name))
+                        for (auto& [name, tf] : curr->privateTypeBindings)
-                            continue;
+                        {
+                            if (userFuncData.environment.find(name))
+                                continue;
 
-                        if (auto ty = get<TypeFunctionInstanceType>(tf.type); ty && ty->userFuncData.definition)
+                            if (auto ty = get<TypeFunctionInstanceType>(tf.type); ty && ty->userFuncData.definition)
-                            userFuncData.environment_DEPRECATED[name] = ty->userFuncData.definition;
+                                userFuncData.environment[name] = std::make_pair(ty->userFuncData.definition, level);
-                    }
+                        }
 
-                    for (auto& [name, tf] : curr->exportedTypeBindings)
+                        for (auto& [name, tf] : curr->exportedTypeBindings)
-                    {
+                        {
-                        if (userFuncData.environment_DEPRECATED.find(name))
+                            if (userFuncData.environment.find(name))
-                            continue;
+                                continue;
 
-                        if (auto ty = get<TypeFunctionInstanceType>(tf.type); ty && ty->userFuncData.definition)
+                            if (auto ty = get<TypeFunctionInstanceType>(tf.type); ty && ty->userFuncData.definition)
-                            userFuncData.environment_DEPRECATED[name] = ty->userFuncData.definition;
+                                userFuncData.environment[name] = std::make_pair(ty->userFuncData.definition, level);
+                        }
+
+                        level++;
                     }
                 }
             }
@@ -1317,6 +1360,23 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatRepeat* rep
     return ControlFlow::None;
 }
 
+static void propagateDeprecatedAttributeToConstraint(ConstraintV& c, const AstExprFunction* func)
+{
+    LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+    if (GeneralizationConstraint* genConstraint = c.get_if<GeneralizationConstraint>())
+    {
+        genConstraint->hasDeprecatedAttribute = func->hasAttribute(AstAttr::Type::Deprecated);
+    }
+}
+
+static void propagateDeprecatedAttributeToType(TypeId signature, const AstExprFunction* func)
+{
+    LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+    FunctionType* fty = getMutable<FunctionType>(signature);
+    LUAU_ASSERT(fty);
+    fty->isDeprecatedFunction = func->hasAttribute(AstAttr::Type::Deprecated);
+}
+
 ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatLocalFunction* function)
 {
     // Local
@@ -1354,6 +1414,9 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatLocalFuncti
         std::unique_ptr<Constraint> c =
             std::make_unique<Constraint>(constraintScope, function->name->location, GeneralizationConstraint{functionType, sig.signature});
 
+        if (FFlag::LuauDeprecatedAttribute)
+            propagateDeprecatedAttributeToConstraint(c->c, function->func);
+
         Constraint* previous = nullptr;
         forEachConstraint(
             start,
@@ -1377,7 +1440,11 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatLocalFuncti
         module->astTypes[function->func] = functionType;
     }
     else
+    {
         module->astTypes[function->func] = sig.signature;
+        if (FFlag::LuauDeprecatedAttribute)
+            propagateDeprecatedAttributeToType(sig.signature, function->func);
+    }
 
     return ControlFlow::None;
 }
@@ -1418,7 +1485,11 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatFunction* f
 
     TypeId generalizedType = arena->addType(BlockedType{});
     if (sigFullyDefined)
+    {
         emplaceType<BoundType>(asMutable(generalizedType), sig.signature);
+        if (FFlag::LuauDeprecatedAttribute)
+            propagateDeprecatedAttributeToType(sig.signature, function->func);
+    }
     else
     {
         const ScopePtr& constraintScope = sig.signatureScope ? sig.signatureScope : sig.bodyScope;
@@ -1426,6 +1497,9 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatFunction* f
         NotNull<Constraint> c = addConstraint(constraintScope, function->name->location, GeneralizationConstraint{generalizedType, sig.signature});
         getMutable<BlockedType>(generalizedType)->setOwner(c);
 
+        if (FFlag::LuauDeprecatedAttribute)
+            propagateDeprecatedAttributeToConstraint(c->c, function->func);
+
         Constraint* previous = nullptr;
         forEachConstraint(
             start,
@@ -1687,6 +1761,64 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatTypeAlias*
 
 ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatTypeFunction* function)
 {
+    if (!FFlag::LuauUserTypeFunTypecheck)
+        return ControlFlow::None;
+
+    auto scopePtr = astTypeFunctionEnvironmentScopes.find(function);
+    LUAU_ASSERT(scopePtr);
+
+    Checkpoint startCheckpoint = checkpoint(this);
+    FunctionSignature sig = checkFunctionSignature(*scopePtr, function->body, /* expectedType */ std::nullopt);
+
+    // Place this function as a child of the non-type function scope
+    scope->children.push_back(NotNull{sig.signatureScope.get()});
+
+    interiorTypes.push_back(std::vector<TypeId>{});
+    checkFunctionBody(sig.bodyScope, function->body);
+    Checkpoint endCheckpoint = checkpoint(this);
+
+    TypeId generalizedTy = arena->addType(BlockedType{});
+    NotNull<Constraint> gc = addConstraint(
+        sig.signatureScope,
+        function->location,
+        GeneralizationConstraint{
+            generalizedTy, sig.signature, FFlag::LuauTrackInteriorFreeTypesOnScope ? std::vector<TypeId>{} : std::move(interiorTypes.back())
+        }
+    );
+
+    if (FFlag::LuauTrackInteriorFreeTypesOnScope)
+        sig.signatureScope->interiorFreeTypes = std::move(interiorTypes.back());
+
+    getMutable<BlockedType>(generalizedTy)->setOwner(gc);
+    interiorTypes.pop_back();
+
+    Constraint* previous = nullptr;
+    forEachConstraint(
+        startCheckpoint,
+        endCheckpoint,
+        this,
+        [gc, &previous](const ConstraintPtr& constraint)
+        {
+            gc->dependencies.emplace_back(constraint.get());
+
+            if (auto psc = get<PackSubtypeConstraint>(*constraint); psc && psc->returns)
+            {
+                if (previous)
+                    constraint->dependencies.push_back(NotNull{previous});
+
+                previous = constraint.get();
+            }
+        }
+    );
+
+    std::optional<TypeId> existingFunctionTy = (*scopePtr)->lookup(function->name);
+
+    if (!existingFunctionTy)
+        ice->ice("checkAliases did not populate type function name", function->nameLocation);
+
+    if (auto bt = get<BlockedType>(*existingFunctionTy); bt && nullptr == bt->getOwner())
+        emplaceType<BoundType>(asMutable(*existingFunctionTy), generalizedTy);
+
     return ControlFlow::None;
 }
 
@@ -1883,6 +2015,8 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatDeclareFunc
     TypeId fnType = arena->addType(FunctionType{TypeLevel{}, funScope.get(), std::move(genericTys), std::move(genericTps), paramPack, retPack, defn});
     FunctionType* ftv = getMutable<FunctionType>(fnType);
     ftv->isCheckedFunction = global->isCheckedFunction();
+    if (FFlag::LuauDeprecatedAttribute)
+        ftv->isDeprecatedFunction = global->hasAttribute(AstAttr::Type::Deprecated);
 
     ftv->argNames.reserve(global->paramNames.size);
     for (const auto& el : global->paramNames)
@@ -2050,13 +2184,23 @@ InferencePack ConstraintGenerator::checkPack(const ScopePtr& scope, AstExprCall*
         }
         else if (i < exprArgs.size() - 1 || !(arg->is<AstExprCall>() || arg->is<AstExprVarargs>()))
         {
-            auto [ty, refinement] = check(scope, arg, /*expectedType*/ std::nullopt, /*forceSingleton*/ false, /*generalize*/ false);
+            std::optional<TypeId> expectedType = std::nullopt;
+            if (FFlag::LuauPropagateExpectedTypesForCalls && i < expectedTypesForCall.size())
+            {
+                expectedType = expectedTypesForCall[i];
+            }
+            auto [ty, refinement] = check(scope, arg, expectedType, /*forceSingleton*/ false, /*generalize*/ false);
             args.push_back(ty);
             argumentRefinements.push_back(refinement);
         }
         else
         {
-            auto [tp, refis] = checkPack(scope, arg, {});
+            std::vector<std::optional<Luau::TypeId>> expectedTypes = {};
+            if (FFlag::LuauPropagateExpectedTypesForCalls && i < expectedTypesForCall.size())
+            {
+                expectedTypes.insert(expectedTypes.end(), expectedTypesForCall.begin() + int(i), expectedTypesForCall.end());
+            }
+            auto [tp, refis] = checkPack(scope, arg, expectedTypes);
             argTail = tp;
             argumentRefinements.insert(argumentRefinements.end(), refis.begin(), refis.end());
         }
@@ -2082,7 +2226,7 @@ InferencePack ConstraintGenerator::checkPack(const ScopePtr& scope, AstExprCall*
         {
             std::vector<TypeId> unpackedTypes;
             if (args.size() > 0)
-                target = args[0];
+                target = FFlag::LuauExtraFollows ? follow(args[0]) : args[0];
             else
             {
                 target = arena->addType(BlockedType{});
@@ -2316,8 +2460,7 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprConstantBool*
 Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprLocal* local)
 {
     const RefinementKey* key = dfg->getRefinementKey(local);
-    std::optional<DefId> rvalueDef = dfg->getRValueDefForCompoundAssign(local);
+    LUAU_ASSERT(key);
-    LUAU_ASSERT(key || rvalueDef);
 
     std::optional<TypeId> maybeTy;
 
@@ -2325,11 +2468,6 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprLocal* local)
     if (key)
         maybeTy = lookup(scope, local->location, key->def);
 
-    // if the current def doesn't have a type, we might be doing a compound assignment
-    // and therefore might need to look at the rvalue def instead.
-    if (!maybeTy && rvalueDef)
-        maybeTy = lookup(scope, local->location, *rvalueDef);
-
     if (maybeTy)
     {
         TypeId ty = follow(*maybeTy);
@@ -2345,11 +2483,9 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprLocal* local)
 Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprGlobal* global)
 {
     const RefinementKey* key = dfg->getRefinementKey(global);
-    std::optional<DefId> rvalueDef = dfg->getRValueDefForCompoundAssign(global);
+    LUAU_ASSERT(key);
-    LUAU_ASSERT(key || rvalueDef);
 
-    // we'll use whichever of the two definitions we have here.
+    DefId def = key->def;
-    DefId def = key ? key->def : *rvalueDef;
 
     /* prepopulateGlobalScope() has already added all global functions to the environment by this point, so any
      * global that is not already in-scope is definitely an unknown symbol.
@@ -2891,6 +3027,13 @@ void ConstraintGenerator::visitLValue(const ScopePtr& scope, AstExprGlobal* glob
         DefId def = dfg->getDef(global);
         rootScope->lvalueTypes[def] = rhsType;
 
+        if (FFlag::LuauGlobalSelfAssignmentCycle)
+        {
+            // Ignore possible self-assignment, it doesn't create a new constraint
+            if (annotatedTy == follow(rhsType))
+                return;
+        }
+
         // Sketchy: We're specifically looking for BlockedTypes that were
         // initially created by ConstraintGenerator::prepopulateGlobalScope.
         if (auto bt = get<BlockedType>(follow(*annotatedTy)); bt && !bt->getOwner())
@@ -3085,7 +3228,7 @@ ConstraintGenerator::FunctionSignature ConstraintGenerator::checkFunctionSignatu
     signatureScope = childScope(fn, parent);
 
     // We need to assign returnType before creating bodyScope so that the
-    // return type gets propogated to bodyScope.
+    // return type gets propagated to bodyScope.
     returnType = freshTypePack(signatureScope);
     signatureScope->returnType = returnType;
 
@@ -3467,6 +3610,8 @@ TypeId ConstraintGenerator::resolveFunctionType(
     // how to quantify/instantiate it.
     FunctionType ftv{TypeLevel{}, scope.get(), {}, {}, argTypes, returnTypes};
     ftv.isCheckedFunction = fn->isCheckedFunction();
+    if (FFlag::LuauDeprecatedAttribute)
+        ftv.isDeprecatedFunction = fn->hasAttribute(AstAttr::Type::Deprecated);
 
     // This replicates the behavior of the appropriate FunctionType
     // constructors.
@@ -3511,6 +3656,10 @@ TypeId ConstraintGenerator::resolveType(const ScopePtr& scope, AstType* ty, bool
         TypeId exprType = check(scope, tof->expr).ty;
         result = exprType;
     }
+    else if (ty->is<AstTypeOptional>())
+    {
+        return builtinTypes->nilType;
+    }
     else if (auto unionAnnotation = ty->as<AstTypeUnion>())
     {
         if (FFlag::LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
@@ -3873,9 +4022,18 @@ struct GlobalPrepopulator : AstVisitor
 void ConstraintGenerator::prepopulateGlobalScopeForFragmentTypecheck(const ScopePtr& globalScope, const ScopePtr& resumeScope, AstStatBlock* program)
 {
     FragmentTypeCheckGlobalPrepopulator gp{NotNull{globalScope.get()}, NotNull{resumeScope.get()}, dfg, arena};
+
     if (prepareModuleScope)
         prepareModuleScope(module->name, resumeScope);
+
     program->visit(&gp);
+
+    if (FFlag::LuauUserTypeFunTypecheck)
+    {
+        // Handle type function globals as well, without preparing a module scope since they have a separate environment
+        GlobalPrepopulator tfgp{NotNull{typeFunctionRuntime->rootScope.get()}, arena, dfg};
+        program->visit(&tfgp);
+    }
 }
 
 void ConstraintGenerator::prepopulateGlobalScope(const ScopePtr& globalScope, AstStatBlock* program)
@@ -3886,6 +4044,13 @@ void ConstraintGenerator::prepopulateGlobalScope(const ScopePtr& globalScope, As
         prepareModuleScope(module->name, globalScope);
 
     program->visit(&gp);
+
+    if (FFlag::LuauUserTypeFunTypecheck)
+    {
+        // Handle type function globals as well, without preparing a module scope since they have a separate environment
+        GlobalPrepopulator tfgp{NotNull{typeFunctionRuntime->rootScope.get()}, arena, dfg};
+        program->visit(&tfgp);
+    }
 }
 
 bool ConstraintGenerator::recordPropertyAssignment(TypeId ty)

Analysis/src/ConstraintSolver.cpp

@@ -37,6 +37,10 @@ LUAU_FASTFLAG(LuauTrackInteriorFreeTypesOnScope)
 LUAU_FASTFLAGVARIABLE(LuauTrackInteriorFreeTablesOnScope)
 LUAU_FASTFLAGVARIABLE(LuauPrecalculateMutatedFreeTypes2)
 LUAU_FASTFLAGVARIABLE(DebugLuauGreedyGeneralization)
+LUAU_FASTFLAG(LuauSearchForRefineableType)
+LUAU_FASTFLAG(LuauDeprecatedAttribute)
+LUAU_FASTFLAG(LuauBidirectionalInferenceCollectIndexerTypes)
+LUAU_FASTFLAG(LuauNewTypeFunReductionChecks2)
 
 namespace Luau
 {
@@ -624,14 +628,6 @@ bool ConstraintSolver::isDone() const
 
 struct TypeSearcher : TypeVisitor
 {
-    enum struct Polarity: uint8_t
-    {
-        None = 0b00,
-        Positive = 0b01,
-        Negative = 0b10,
-        Mixed = 0b11,
-    };
-
     TypeId needle;
     Polarity current = Polarity::Positive;
 
@@ -747,12 +743,12 @@ void ConstraintSolver::generalizeOneType(TypeId ty)
 
         switch (ts.result)
         {
-            case TypeSearcher::Polarity::None:
+            case Polarity::None:
                 asMutable(ty)->reassign(Type{BoundType{upperBound}});
                 break;
 
-            case TypeSearcher::Polarity::Negative:
+            case Polarity::Negative:
-            case TypeSearcher::Polarity::Mixed:
+            case Polarity::Mixed:
                 if (get<UnknownType>(upperBound) && ts.count > 1)
                 {
                     asMutable(ty)->reassign(Type{GenericType{tyScope}});
@@ -762,15 +758,17 @@ void ConstraintSolver::generalizeOneType(TypeId ty)
                     asMutable(ty)->reassign(Type{BoundType{upperBound}});
                 break;
 
-            case TypeSearcher::Polarity::Positive:
+            case Polarity::Positive:
-            if (get<UnknownType>(lowerBound) && ts.count > 1)
+                if (get<UnknownType>(lowerBound) && ts.count > 1)
-            {
+                {
-                asMutable(ty)->reassign(Type{GenericType{tyScope}});
+                    asMutable(ty)->reassign(Type{GenericType{tyScope}});
-                function->generics.emplace_back(ty);
+                    function->generics.emplace_back(ty);
-            }
+                }
-            else
+                else
-                asMutable(ty)->reassign(Type{BoundType{lowerBound}});
+                    asMutable(ty)->reassign(Type{BoundType{lowerBound}});
-            break;
+                break;
+            default:
+                LUAU_ASSERT(!"Unreachable");
         }
     }
 }
@@ -907,26 +905,25 @@ bool ConstraintSolver::tryDispatch(const GeneralizationConstraint& c, NotNull<co
     else if (get<PendingExpansionType>(generalizedType))
         return block(generalizedType, constraint);
 
-    std::optional<QuantifierResult> generalized;
-
     std::optional<TypeId> generalizedTy = generalize(NotNull{arena}, builtinTypes, constraint->scope, generalizedTypes, c.sourceType);
-    if (generalizedTy)
+    if (!generalizedTy)
-        generalized = QuantifierResult{*generalizedTy}; // FIXME insertedGenerics and insertedGenericPacks
-    else
         reportError(CodeTooComplex{}, constraint->location);
 
-    if (generalized)
+    if (generalizedTy)
     {
         if (get<BlockedType>(generalizedType))
-            bind(constraint, generalizedType, generalized->result);
+            bind(constraint, generalizedType, *generalizedTy);
         else
-            unify(constraint, generalizedType, generalized->result);
+            unify(constraint, generalizedType, *generalizedTy);
 
-        for (auto [free, gen] : generalized->insertedGenerics.pairings)
+        if (FFlag::LuauDeprecatedAttribute)
-            unify(constraint, free, gen);
+        {
-
+            if (FunctionType* fty = getMutable<FunctionType>(follow(generalizedType)))
-        for (auto [free, gen] : generalized->insertedGenericPacks.pairings)
+            {
-            unify(constraint, free, gen);
+                if (c.hasDeprecatedAttribute)
+                    fty->isDeprecatedFunction = true;
+            }
+        }
     }
     else
     {
@@ -940,12 +937,12 @@ bool ConstraintSolver::tryDispatch(const GeneralizationConstraint& c, NotNull<co
         // clang-tidy doesn't understand this is safe.
         if (constraint->scope->interiorFreeTypes)
             for (TypeId ty : *constraint->scope->interiorFreeTypes) // NOLINT(bugprone-unchecked-optional-access)
-                generalize(NotNull{arena}, builtinTypes, constraint->scope, generalizedTypes, ty, /* avoidSealingTables */ false);
+                generalize(NotNull{arena}, builtinTypes, constraint->scope, generalizedTypes, ty);
     }
     else
     {
         for (TypeId ty : c.interiorTypes)
-            generalize(NotNull{arena}, builtinTypes, constraint->scope, generalizedTypes, ty, /* avoidSealingTables */ false);
+            generalize(NotNull{arena}, builtinTypes, constraint->scope, generalizedTypes, ty);
     }
 
 
@@ -1356,15 +1353,29 @@ void ConstraintSolver::fillInDiscriminantTypes(NotNull<const Constraint> constra
         if (!ty)
             continue;
 
-        // If the discriminant type has been transmuted, we need to unblock them.
+        if (FFlag::LuauSearchForRefineableType)
-        if (!isBlocked(*ty))
         {
-            unblock(*ty, constraint->location);
+            if (isBlocked(*ty))
-            continue;
+                // We bind any unused discriminants to the `*no-refine*` type indicating that it can be safely ignored.
-        }
+                emplaceType<BoundType>(asMutable(follow(*ty)), builtinTypes->noRefineType);
 
-        // We bind any unused discriminants to the `*no-refine*` type indicating that it can be safely ignored.
+            // We also need to unconditionally unblock these types, otherwise
-        emplaceType<BoundType>(asMutable(follow(*ty)), builtinTypes->noRefineType);
+            // you end up with funky looking "Blocked on *no-refine*."
+            unblock(*ty, constraint->location);
+        }
+        else
+        {
+
+            // If the discriminant type has been transmuted, we need to unblock them.
+            if (!isBlocked(*ty))
+            {
+                unblock(*ty, constraint->location);
+                continue;
+            }
+
+            // We bind any unused discriminants to the `*no-refine*` type indicating that it can be safely ignored.
+            emplaceType<BoundType>(asMutable(follow(*ty)), builtinTypes->noRefineType);
+        }
     }
 }
 
@@ -1553,6 +1564,43 @@ static AstExpr* unwrapGroup(AstExpr* expr)
     return expr;
 }
 
+struct ContainsGenerics : public TypeOnceVisitor
+{
+    DenseHashSet<const void*> generics{nullptr};
+
+    bool found = false;
+
+    bool visit(TypeId ty) override
+    {
+        return !found;
+    }
+
+    bool visit(TypeId ty, const GenericType&) override
+    {
+        found |= generics.contains(ty);
+        return true;
+    }
+
+    bool visit(TypeId ty, const TypeFunctionInstanceType&) override
+    {
+        return !found;
+    }
+
+    bool visit(TypePackId tp, const GenericTypePack&) override
+    {
+        found |= generics.contains(tp);
+        return !found;
+    }
+
+    bool hasGeneric(TypeId ty)
+    {
+        traverse(ty);
+        auto ret = found;
+        found = false;
+        return ret;
+    }
+};
+
 bool ConstraintSolver::tryDispatch(const FunctionCheckConstraint& c, NotNull<const Constraint> constraint)
 {
     TypeId fn = follow(c.fn);
@@ -1595,36 +1643,49 @@ bool ConstraintSolver::tryDispatch(const FunctionCheckConstraint& c, NotNull<con
     DenseHashMap<TypeId, TypeId> replacements{nullptr};
     DenseHashMap<TypePackId, TypePackId> replacementPacks{nullptr};
 
+    ContainsGenerics containsGenerics;
+
     for (auto generic : ftv->generics)
+    {
         replacements[generic] = builtinTypes->unknownType;
+        if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
+            containsGenerics.generics.insert(generic);
+    }
 
     for (auto genericPack : ftv->genericPacks)
+    {
         replacementPacks[genericPack] = builtinTypes->unknownTypePack;
+        if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
+            containsGenerics.generics.insert(genericPack);
+    }
 
     // If the type of the function has generics, we don't actually want to push any of the generics themselves
     // into the argument types as expected types because this creates an unnecessary loop. Instead, we want to
     // replace these types with `unknown` (and `...unknown`) to keep any structure but not create the cycle.
-    if (!replacements.empty() || !replacementPacks.empty())
+    if (!FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
     {
-        Replacer replacer{arena, std::move(replacements), std::move(replacementPacks)};
+        if (!replacements.empty() || !replacementPacks.empty())
-
-        std::optional<TypeId> res = replacer.substitute(fn);
-        if (res)
         {
-            if (*res != fn)
+            Replacer replacer{arena, std::move(replacements), std::move(replacementPacks)};
+
+            std::optional<TypeId> res = replacer.substitute(fn);
+            if (res)
             {
-                FunctionType* ftvMut = getMutable<FunctionType>(*res);
+                if (*res != fn)
-                LUAU_ASSERT(ftvMut);
+                {
-                ftvMut->generics.clear();
+                    FunctionType* ftvMut = getMutable<FunctionType>(*res);
-                ftvMut->genericPacks.clear();
+                    LUAU_ASSERT(ftvMut);
+                    ftvMut->generics.clear();
+                    ftvMut->genericPacks.clear();
+                }
+
+                fn = *res;
+                ftv = get<FunctionType>(*res);
+                LUAU_ASSERT(ftv);
+
+                // we've potentially copied type functions here, so we need to reproduce their reduce constraint.
+                reproduceConstraints(constraint->scope, constraint->location, replacer);
             }
-
-            fn = *res;
-            ftv = get<FunctionType>(*res);
-            LUAU_ASSERT(ftv);
-
-            // we've potentially copied type functions here, so we need to reproduce their reduce constraint.
-            reproduceConstraints(constraint->scope, constraint->location, replacer);
         }
     }
 
@@ -1643,6 +1704,10 @@ bool ConstraintSolver::tryDispatch(const FunctionCheckConstraint& c, NotNull<con
 
         (*c.astExpectedTypes)[expr] = expectedArgTy;
 
+        // Generic types are skipped over entirely, for now.
+        if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes && containsGenerics.hasGeneric(expectedArgTy))
+            continue;
+
         const FunctionType* expectedLambdaTy = get<FunctionType>(expectedArgTy);
         const FunctionType* lambdaTy = get<FunctionType>(actualArgTy);
         const AstExprFunction* lambdaExpr = expr->as<AstExprFunction>();
@@ -2354,11 +2419,18 @@ bool ConstraintSolver::tryDispatch(const ReduceConstraint& c, NotNull<const Cons
     for (TypePackId r : result.reducedPacks)
         unblock(r, constraint->location);
 
+    if (FFlag::LuauNewTypeFunReductionChecks2)
+    {
+        for (TypeId ity : result.irreducibleTypes)
+            uninhabitedTypeFunctions.insert(ity);
+    }
+
     bool reductionFinished = result.blockedTypes.empty() && result.blockedPacks.empty();
 
     ty = follow(ty);
+
     // If we couldn't reduce this type function, stick it in the set!
-    if (get<TypeFunctionInstanceType>(ty))
+    if (get<TypeFunctionInstanceType>(ty) && (!FFlag::LuauNewTypeFunReductionChecks2 || !result.irreducibleTypes.find(ty)))
         typeFunctionsToFinalize[ty] = constraint;
 
     if (force || reductionFinished)
@@ -3278,7 +3350,7 @@ void ConstraintSolver::shiftReferences(TypeId source, TypeId target)
     }
 }
 
-std::optional<TypeId> ConstraintSolver::generalizeFreeType(NotNull<Scope> scope, TypeId type, bool avoidSealingTables)
+std::optional<TypeId> ConstraintSolver::generalizeFreeType(NotNull<Scope> scope, TypeId type)
 {
     TypeId t = follow(type);
     if (get<FreeType>(t))
@@ -3293,7 +3365,7 @@ std::optional<TypeId> ConstraintSolver::generalizeFreeType(NotNull<Scope> scope,
         // that until all constraint generation is complete.
     }
 
-    return generalize(NotNull{arena}, builtinTypes, scope, generalizedTypes, type, avoidSealingTables);
+    return generalize(NotNull{arena}, builtinTypes, scope, generalizedTypes, type);
 }
 
 bool ConstraintSolver::hasUnresolvedConstraints(TypeId ty)

Analysis/src/DataFlowGraph.cpp

@@ -82,12 +82,6 @@ std::optional<DefId> DataFlowGraph::getDefOptional(const AstExpr* expr) const
     return NotNull{*def};
 }
 
-std::optional<DefId> DataFlowGraph::getRValueDefForCompoundAssign(const AstExpr* expr) const
-{
-    auto def = compoundAssignDefs.find(expr);
-    return def ? std::optional<DefId>(*def) : std::nullopt;
-}
-
 DefId DataFlowGraph::getDef(const AstLocal* local) const
 {
     auto def = localDefs.find(local);
@@ -1168,6 +1162,8 @@ void DataFlowGraphBuilder::visitType(AstType* t)
         return visitType(f);
     else if (auto tyof = t->as<AstTypeTypeof>())
         return visitType(tyof);
+    else if (auto o = t->as<AstTypeOptional>())
+        return;
     else if (auto u = t->as<AstTypeUnion>())
         return visitType(u);
     else if (auto i = t->as<AstTypeIntersection>())

Analysis/src/EmbeddedBuiltinDefinitions.cpp

@@ -1,8 +1,6 @@
 // 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_FASTFLAGVARIABLE(LuauDebugInfoDefn)
-
 namespace Luau
 {
 
@@ -215,15 +213,6 @@ declare debug: {
 
 )BUILTIN_SRC";
 
-static const std::string kBuiltinDefinitionDebugSrc_DEPRECATED = 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...),
-    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: {
@@ -309,7 +298,7 @@ std::string getBuiltinDefinitionSource()
     result += kBuiltinDefinitionOsSrc;
     result += kBuiltinDefinitionCoroutineSrc;
     result += kBuiltinDefinitionTableSrc;
-    result += FFlag::LuauDebugInfoDefn ? kBuiltinDefinitionDebugSrc : kBuiltinDefinitionDebugSrc_DEPRECATED;
+    result += kBuiltinDefinitionDebugSrc;
     result += kBuiltinDefinitionUtf8Src;
     result += kBuiltinDefinitionBufferSrc;
     result += kBuiltinDefinitionVectorSrc;
@@ -317,4 +306,83 @@ std::string getBuiltinDefinitionSource()
     return result;
 }
 
+// TODO: split into separate tagged unions when the new solver can appropriately handle that.
+static const std::string kBuiltinDefinitionTypesSrc = R"BUILTIN_SRC(
+
+export type type = {
+    tag: "nil" | "unknown" | "never" | "any" | "boolean" | "number" | "string" | "buffer" | "thread" |
+         "singleton" | "negation" | "union" | "intesection" | "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,
+}
+
+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";
+
+std::string getTypeFunctionDefinitionSource()
+{
+    return kBuiltinDefinitionTypesSrc;
+}
+
 } // namespace Luau

Analysis/src/Error.cpp

@@ -8,6 +8,7 @@
 #include "Luau/StringUtils.h"
 #include "Luau/ToString.h"
 #include "Luau/Type.h"
+#include "Luau/TypeChecker2.h"
 #include "Luau/TypeFunction.h"
 
 #include <optional>
@@ -17,6 +18,7 @@
 #include <unordered_set>
 
 LUAU_FASTINTVARIABLE(LuauIndentTypeMismatchMaxTypeLength, 10)
+LUAU_FASTFLAG(LuauNonStrictFuncDefErrorFix)
 
 static std::string wrongNumberOfArgsString(
     size_t expectedCount,
@@ -116,7 +118,10 @@ 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)
@@ -751,8 +756,15 @@ struct ErrorConverter
 
     std::string operator()(const NonStrictFunctionDefinitionError& e) const
     {
-        return "Argument " + e.argument + " with type '" + toString(e.argumentType) + "' in function '" + e.functionName +
+        if (FFlag::LuauNonStrictFuncDefErrorFix && e.functionName.empty())
-               "' is used in a way that will run time error";
+        {
+            return "Argument " + e.argument + " with type '" + toString(e.argumentType) + "' is used in a way that will run time error";
+        }
+        else
+        {
+            return "Argument " + e.argument + " with type '" + toString(e.argumentType) + "' in function '" + e.functionName +
+                   "' is used in a way that will run time error";
+        }
     }
 
     std::string operator()(const PropertyAccessViolation& e) const

Analysis/src/FileResolver.cpp

@@ -0,0 +1,172 @@
+// 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>
+
+LUAU_FASTFLAGVARIABLE(LuauExposeRequireByStringAutocomplete)
+LUAU_FASTFLAGVARIABLE(LuauEscapeCharactersInRequireSuggestions)
+LUAU_FASTFLAGVARIABLE(LuauHideImpossibleRequireSuggestions)
+
+namespace Luau
+{
+
+static std::optional<RequireSuggestions> processRequireSuggestions(std::optional<RequireSuggestions> suggestions)
+{
+    if (!suggestions)
+        return suggestions;
+
+    if (FFlag::LuauEscapeCharactersInRequireSuggestions)
+    {
+        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 (FFlag::LuauHideImpossibleRequireSuggestions)
+        {
+            // 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
+{
+    if (!FFlag::LuauExposeRequireByStringAutocomplete)
+        return std::nullopt;
+
+    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"
@@ -49,12 +48,10 @@ LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauRunCustomModuleChecks, false)
 
 LUAU_FASTFLAGVARIABLE(LuauModuleHoldsAstRoot)
 
-LUAU_FASTFLAGVARIABLE(LuauBetterReverseDependencyTracking)
 LUAU_FASTFLAGVARIABLE(LuauFixMultithreadTypecheck)
 
-LUAU_FASTFLAG(StudioReportLuauAny2)
-
 LUAU_FASTFLAGVARIABLE(LuauSelectivelyRetainDFGArena)
+LUAU_FASTFLAG(LuauTypeFunResultInAutocomplete)
 
 namespace Luau
 {
@@ -462,20 +459,6 @@ 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;
@@ -1035,14 +1018,11 @@ bool Frontend::parseGraph(
 
             buildQueue.push_back(top->name);
 
-            if (FFlag::LuauBetterReverseDependencyTracking)
+            // at this point we know all valid dependencies are processed into SourceNodes
+            for (const ModuleName& dep : top->requireSet)
             {
-                // at this point we know all valid dependencies are processed into SourceNodes
+                if (auto it = sourceNodes.find(dep); it != sourceNodes.end())
-                for (const ModuleName& dep : top->requireSet)
+                    it->second->dependents.insert(top->name);
-                {
-                    if (auto it = sourceNodes.find(dep); it != sourceNodes.end())
-                        it->second->dependents.insert(top->name);
-                }
             }
         }
         else
@@ -1331,51 +1311,35 @@ void Frontend::recordItemResult(const BuildQueueItem& item)
     if (item.exception)
         std::rethrow_exception(item.exception);
 
-    if (FFlag::LuauBetterReverseDependencyTracking)
+    bool replacedModule = false;
+    if (item.options.forAutocomplete)
     {
-        bool replacedModule = false;
+        replacedModule = moduleResolverForAutocomplete.setModule(item.name, item.module);
-        if (item.options.forAutocomplete)
+        item.sourceNode->dirtyModuleForAutocomplete = false;
-        {
-            replacedModule = moduleResolverForAutocomplete.setModule(item.name, item.module);
-            item.sourceNode->dirtyModuleForAutocomplete = false;
-        }
-        else
-        {
-            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);
     }
     else
     {
-        if (item.options.forAutocomplete)
+        replacedModule = moduleResolver.setModule(item.name, item.module);
-        {
+        item.sourceNode->dirtyModule = false;
-            moduleResolverForAutocomplete.setModule(item.name, item.module);
-            item.sourceNode->dirtyModuleForAutocomplete = false;
-        }
-        else
-        {
-            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;
 
@@ -1464,7 +1428,6 @@ ScopePtr Frontend::getModuleEnvironment(const SourceModule& module, const Config
 
 bool Frontend::allModuleDependenciesValid(const ModuleName& name, bool forAutocomplete) const
 {
-    LUAU_ASSERT(FFlag::LuauBetterReverseDependencyTracking);
     auto it = sourceNodes.find(name);
     return it != sourceNodes.end() && !it->second->hasInvalidModuleDependency(forAutocomplete);
 }
@@ -1486,72 +1449,27 @@ void Frontend::markDirty(const ModuleName& name, std::vector<ModuleName>* marked
     LUAU_TIMETRACE_SCOPE("Frontend::markDirty", "Frontend");
     LUAU_TIMETRACE_ARGUMENT("name", name.c_str());
 
-    if (FFlag::LuauBetterReverseDependencyTracking)
+    traverseDependents(
-    {
+        name,
-        traverseDependents(
+        [markedDirty](SourceNode& sourceNode)
-            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;
-            }
-        );
-    }
-    else
-    {
-        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())
-        {
-            ModuleName next = std::move(queue.back());
-            queue.pop_back();
-
-            LUAU_ASSERT(sourceNodes.count(next) > 0);
-            SourceNode& sourceNode = *sourceNodes[next];
-
             if (markedDirty)
-                markedDirty->push_back(next);
+                markedDirty->push_back(sourceNode.name);
 
             if (sourceNode.dirtySourceModule && sourceNode.dirtyModule && sourceNode.dirtyModuleForAutocomplete)
-                continue;
+                return false;
 
             sourceNode.dirtySourceModule = true;
             sourceNode.dirtyModule = true;
             sourceNode.dirtyModuleForAutocomplete = true;
 
-            if (0 == reverseDeps.count(next))
+            return true;
-                continue;
-
-            sourceModules.erase(next);
-
-            const std::vector<ModuleName>& dependents = reverseDeps[next];
-            queue.insert(queue.end(), dependents.begin(), dependents.end());
         }
-    }
+    );
 }
 
 void Frontend::traverseDependents(const ModuleName& name, std::function<bool(SourceNode&)> processSubtree)
 {
-    LUAU_ASSERT(FFlag::LuauBetterReverseDependencyTracking);
     LUAU_TIMETRACE_SCOPE("Frontend::traverseDependents", "Frontend");
 
     if (sourceNodes.count(name) == 0)
@@ -1598,6 +1516,7 @@ 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,
@@ -1614,6 +1533,7 @@ ModulePtr check(
         moduleResolver,
         fileResolver,
         parentScope,
+        typeFunctionScope,
         std::move(prepareModuleScope),
         options,
         limits,
@@ -1675,6 +1595,7 @@ 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,
@@ -1721,7 +1642,7 @@ ModulePtr check(
     SimplifierPtr simplifier = newSimplifier(NotNull{&result->internalTypes}, builtinTypes);
     TypeFunctionRuntime typeFunctionRuntime{iceHandler, NotNull{&limits}};
 
-    typeFunctionRuntime.allowEvaluation = sourceModule.parseErrors.empty();
+    typeFunctionRuntime.allowEvaluation = FFlag::LuauTypeFunResultInAutocomplete || sourceModule.parseErrors.empty();
 
     ConstraintGenerator cg{
         result,
@@ -1732,6 +1653,7 @@ ModulePtr check(
         builtinTypes,
         iceHandler,
         parentScope,
+        typeFunctionScope,
         std::move(prepareModuleScope),
         logger.get(),
         NotNull{&dfg},
@@ -1914,6 +1836,7 @@ ModulePtr Frontend::check(
                 NotNull{forAutocomplete ? &moduleResolverForAutocomplete : &moduleResolver},
                 NotNull{fileResolver},
                 environmentScope ? *environmentScope : globals.globalScope,
+                globals.globalTypeFunctionScope,
                 prepareModuleScopeWrap,
                 options,
                 typeCheckLimits,
@@ -2012,14 +1935,11 @@ std::pair<SourceNode*, SourceModule*> Frontend::getSourceNode(const ModuleName&
     sourceNode->name = sourceModule->name;
     sourceNode->humanReadableName = sourceModule->humanReadableName;
 
-    if (FFlag::LuauBetterReverseDependencyTracking)
+    // clear all prior dependents. we will re-add them after parsing the rest of the graph
+    for (const auto& [moduleName, _] : sourceNode->requireLocations)
     {
-        // clear all prior dependents. we will re-add them after parsing the rest of the graph
+        if (auto depIt = sourceNodes.find(moduleName); depIt != sourceNodes.end())
-        for (const auto& [moduleName, _] : sourceNode->requireLocations)
+            depIt->second->dependents.erase(sourceNode->name);
-        {
-            if (auto depIt = sourceNodes.find(moduleName); depIt != sourceNodes.end())
-                depIt->second->dependents.erase(sourceNode->name);
-        }
     }
 
     sourceNode->requireSet.clear();
@@ -2147,17 +2067,9 @@ bool FrontendModuleResolver::setModule(const ModuleName& moduleName, ModulePtr m
 {
     std::scoped_lock lock(moduleMutex);
 
-    if (FFlag::LuauBetterReverseDependencyTracking)
+    bool replaced = modules.count(moduleName) > 0;
-    {
+    modules[moduleName] = std::move(module);
-        bool replaced = modules.count(moduleName) > 0;
+    return replaced;
-        modules[moduleName] = std::move(module);
-        return replaced;
-    }
-    else
-    {
-        modules[moduleName] = std::move(module);
-        return false;
-    }
 }
 
 void FrontendModuleResolver::clearModules()

Analysis/src/Generalization.cpp

@@ -30,7 +30,6 @@ struct MutatingGeneralizer : TypeOnceVisitor
     std::vector<TypePackId> genericPacks;
 
     bool isWithinFunction = false;
-    bool avoidSealingTables = false;
 
     MutatingGeneralizer(
         NotNull<TypeArena> arena,
@@ -38,8 +37,7 @@ struct MutatingGeneralizer : TypeOnceVisitor
         NotNull<Scope> scope,
         NotNull<DenseHashSet<TypeId>> cachedTypes,
         DenseHashMap<const void*, size_t> positiveTypes,
-        DenseHashMap<const void*, size_t> negativeTypes,
+        DenseHashMap<const void*, size_t> negativeTypes
-        bool avoidSealingTables
     )
         : TypeOnceVisitor(/* skipBoundTypes */ true)
         , arena(arena)
@@ -48,7 +46,6 @@ struct MutatingGeneralizer : TypeOnceVisitor
         , cachedTypes(cachedTypes)
         , positiveTypes(std::move(positiveTypes))
         , negativeTypes(std::move(negativeTypes))
-        , avoidSealingTables(avoidSealingTables)
     {
     }
 
@@ -145,7 +142,7 @@ struct MutatingGeneralizer : TypeOnceVisitor
                 TypeId onlyType = it->parts[0];
                 LUAU_ASSERT(onlyType != needle);
                 emplaceType<BoundType>(asMutable(needle), onlyType);
-            } 
+            }
             else if (FFlag::LuauGeneralizationRemoveRecursiveUpperBound2 && it->parts.empty())
             {
                 emplaceType<BoundType>(asMutable(needle), builtinTypes->unknownType);
@@ -292,8 +289,7 @@ struct MutatingGeneralizer : TypeOnceVisitor
         TableType* tt = getMutable<TableType>(ty);
         LUAU_ASSERT(tt);
 
-        if (!avoidSealingTables)
+        tt->state = TableState::Sealed;
-            tt->state = TableState::Sealed;
 
         return true;
     }
@@ -332,26 +328,19 @@ struct FreeTypeSearcher : TypeVisitor
     {
     }
 
-    enum Polarity
+    Polarity polarity = Polarity::Positive;
-    {
-        Positive,
-        Negative,
-        Both,
-    };
-
-    Polarity polarity = Positive;
 
     void flip()
     {
         switch (polarity)
         {
-        case Positive:
+        case Polarity::Positive:
-            polarity = Negative;
+            polarity = Polarity::Negative;
             break;
-        case Negative:
+        case Polarity::Negative:
-            polarity = Positive;
+            polarity = Polarity::Positive;
             break;
-        case Both:
+        default:
             break;
         }
     }
@@ -359,11 +348,11 @@ struct FreeTypeSearcher : TypeVisitor
     DenseHashSet<const void*> seenPositive{nullptr};
     DenseHashSet<const void*> seenNegative{nullptr};
 
-    bool seenWithPolarity(const void* ty)
+    bool seenWithCurrentPolarity(const void* ty)
     {
         switch (polarity)
         {
-        case Positive:
+        case Polarity::Positive:
         {
             if (seenPositive.contains(ty))
                 return true;
@@ -371,7 +360,7 @@ struct FreeTypeSearcher : TypeVisitor
             seenPositive.insert(ty);
             return false;
         }
-        case Negative:
+        case Polarity::Negative:
         {
             if (seenNegative.contains(ty))
                 return true;
@@ -379,7 +368,7 @@ struct FreeTypeSearcher : TypeVisitor
             seenNegative.insert(ty);
             return false;
         }
-        case Both:
+        case Polarity::Mixed:
         {
             if (seenPositive.contains(ty) && seenNegative.contains(ty))
                 return true;
@@ -388,6 +377,8 @@ struct FreeTypeSearcher : TypeVisitor
             seenNegative.insert(ty);
             return false;
         }
+        default:
+            LUAU_ASSERT(!"Unreachable");
         }
 
         return false;
@@ -401,7 +392,7 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypeId ty) override
     {
-        if (cachedTypes->contains(ty) || seenWithPolarity(ty))
+        if (cachedTypes->contains(ty) || seenWithCurrentPolarity(ty))
             return false;
 
         LUAU_ASSERT(ty);
@@ -410,7 +401,7 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypeId ty, const FreeType& ft) override
     {
-        if (cachedTypes->contains(ty) || seenWithPolarity(ty))
+        if (cachedTypes->contains(ty) || seenWithCurrentPolarity(ty))
             return false;
 
         if (!subsumes(scope, ft.scope))
@@ -418,16 +409,18 @@ struct FreeTypeSearcher : TypeVisitor
 
         switch (polarity)
         {
-        case Positive:
+        case Polarity::Positive:
             positiveTypes[ty]++;
             break;
-        case Negative:
+        case Polarity::Negative:
             negativeTypes[ty]++;
             break;
-        case Both:
+        case Polarity::Mixed:
             positiveTypes[ty]++;
             negativeTypes[ty]++;
             break;
+        default:
+            LUAU_ASSERT(!"Unreachable");
         }
 
         return true;
@@ -435,23 +428,25 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypeId ty, const TableType& tt) override
     {
-        if (cachedTypes->contains(ty) || seenWithPolarity(ty))
+        if (cachedTypes->contains(ty) || seenWithCurrentPolarity(ty))
             return false;
 
         if ((tt.state == TableState::Free || tt.state == TableState::Unsealed) && subsumes(scope, tt.scope))
         {
             switch (polarity)
             {
-            case Positive:
+            case Polarity::Positive:
                 positiveTypes[ty]++;
                 break;
-            case Negative:
+            case Polarity::Negative:
                 negativeTypes[ty]++;
                 break;
-            case Both:
+            case Polarity::Mixed:
                 positiveTypes[ty]++;
                 negativeTypes[ty]++;
                 break;
+            default:
+                LUAU_ASSERT(!"Unreachable");
             }
         }
 
@@ -464,7 +459,7 @@ struct FreeTypeSearcher : TypeVisitor
                 LUAU_ASSERT(prop.isShared() || FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete);
 
                 Polarity p = polarity;
-                polarity = Both;
+                polarity = Polarity::Mixed;
                 traverse(prop.type());
                 polarity = p;
             }
@@ -481,7 +476,7 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypeId ty, const FunctionType& ft) override
     {
-        if (cachedTypes->contains(ty) || seenWithPolarity(ty))
+        if (cachedTypes->contains(ty) || seenWithCurrentPolarity(ty))
             return false;
 
         flip();
@@ -500,7 +495,7 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypePackId tp, const FreeTypePack& ftp) override
     {
-        if (seenWithPolarity(tp))
+        if (seenWithCurrentPolarity(tp))
             return false;
 
         if (!subsumes(scope, ftp.scope))
@@ -508,16 +503,18 @@ struct FreeTypeSearcher : TypeVisitor
 
         switch (polarity)
         {
-        case Positive:
+        case Polarity::Positive:
             positiveTypes[tp]++;
             break;
-        case Negative:
+        case Polarity::Negative:
             negativeTypes[tp]++;
             break;
-        case Both:
+        case Polarity::Mixed:
             positiveTypes[tp]++;
             negativeTypes[tp]++;
             break;
+        default:
+            LUAU_ASSERT(!"Unreachable");
         }
 
         return true;
@@ -547,7 +544,7 @@ struct TypeCacher : TypeOnceVisitor
     {
     }
 
-    void cache(TypeId ty)
+    void cache(TypeId ty) const
     {
         cachedTypes->insert(ty);
     }
@@ -972,8 +969,7 @@ std::optional<TypeId> generalize(
     NotNull<BuiltinTypes> builtinTypes,
     NotNull<Scope> scope,
     NotNull<DenseHashSet<TypeId>> cachedTypes,
-    TypeId ty,
+    TypeId ty
-    bool avoidSealingTables
 )
 {
     ty = follow(ty);
@@ -984,7 +980,7 @@ std::optional<TypeId> generalize(
     FreeTypeSearcher fts{scope, cachedTypes};
     fts.traverse(ty);
 
-    MutatingGeneralizer gen{arena, builtinTypes, scope, cachedTypes, std::move(fts.positiveTypes), std::move(fts.negativeTypes), avoidSealingTables};
+    MutatingGeneralizer gen{arena, builtinTypes, scope, cachedTypes, std::move(fts.positiveTypes), std::move(fts.negativeTypes)};
 
     gen.traverse(ty);
 

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/Linter.cpp

@@ -19,6 +19,8 @@ LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauAttribute)
 LUAU_FASTFLAGVARIABLE(LintRedundantNativeAttribute)
 
+LUAU_FASTFLAG(LuauDeprecatedAttribute)
+
 namespace Luau
 {
 
@@ -2280,6 +2282,57 @@ 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))
@@ -2325,18 +2378,59 @@ private:
 
             if (prop && prop->deprecated)
                 report(node->location, *prop, cty->name.c_str(), node->index.value);
+            else if (FFlag::LuauDeprecatedAttribute && prop)
+            {
+                if (std::optional<TypeId> ty = prop->readTy)
+                {
+                    const FunctionType* fty = get<FunctionType>(follow(ty));
+                    bool shouldReport = fty && fty->isDeprecatedFunction && !inScope(fty);
+
+                    if (shouldReport)
+                    {
+                        const char* className = nullptr;
+                        if (AstExprGlobal* global = node->expr->as<AstExprGlobal>())
+                            className = global->name.value;
+
+                        const char* functionName = node->index.value;
+
+                        report(node->location, className, functionName);
+                    }
+                }
+            }
         }
         else if (const TableType* tty = get<TableType>(ty))
         {
             auto prop = tty->props.find(node->index.value);
 
-            if (prop != tty->props.end() && prop->second.deprecated)
+            if (prop != tty->props.end())
             {
-                // strip synthetic typeof() for builtin tables
+                if (prop->second.deprecated)
-                if (tty->name && tty->name->compare(0, 7, "typeof(") == 0 && tty->name->back() == ')')
+                {
-                    report(node->location, prop->second, tty->name->substr(7, tty->name->length() - 8).c_str(), node->index.value);
+                    // strip synthetic typeof() for builtin tables
-                else
+                    if (tty->name && tty->name->compare(0, 7, "typeof(") == 0 && tty->name->back() == ')')
-                    report(node->location, prop->second, tty->name ? tty->name->c_str() : nullptr, node->index.value);
+                        report(node->location, prop->second, tty->name->substr(7, tty->name->length() - 8).c_str(), node->index.value);
+                    else
+                        report(node->location, prop->second, tty->name ? tty->name->c_str() : nullptr, node->index.value);
+                }
+                else if (FFlag::LuauDeprecatedAttribute)
+                {
+                    if (std::optional<TypeId> ty = prop->second.readTy)
+                    {
+                        const FunctionType* fty = get<FunctionType>(follow(ty));
+                        bool shouldReport = fty && fty->isDeprecatedFunction && !inScope(fty);
+
+                        if (shouldReport)
+                        {
+                            const char* className = nullptr;
+                            if (AstExprGlobal* global = node->expr->as<AstExprGlobal>())
+                                className = global->name.value;
+
+                            const char* functionName = node->index.value;
+
+                            report(node->location, className, functionName);
+                        }
+                    }
+                }
             }
         }
     }
@@ -2355,6 +2449,26 @@ 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());
@@ -2364,6 +2478,63 @@ 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

Analysis/src/Module.cpp

@@ -20,7 +20,7 @@ LUAU_FASTFLAGVARIABLE(LuauIncrementalAutocompleteCommentDetection)
 namespace Luau
 {
 
-static void defaultLogLuau(std::string_view input)
+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.

Analysis/src/NonStrictTypeChecker.cpp

@@ -2,6 +2,7 @@
 #include "Luau/NonStrictTypeChecker.h"
 
 #include "Luau/Ast.h"
+#include "Luau/AstQuery.h"
 #include "Luau/Common.h"
 #include "Luau/Simplify.h"
 #include "Luau/Type.h"
@@ -22,6 +23,7 @@
 LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
 LUAU_FASTFLAGVARIABLE(LuauNonStrictVisitorImprovements)
 LUAU_FASTFLAGVARIABLE(LuauNewNonStrictWarnOnUnknownGlobals)
+LUAU_FASTFLAGVARIABLE(LuauNonStrictFuncDefErrorFix)
 
 namespace Luau
 {
@@ -763,7 +765,17 @@ struct NonStrictTypeChecker
         for (AstLocal* local : exprFn->args)
         {
             if (std::optional<TypeId> ty = willRunTimeErrorFunctionDefinition(local, remainder))
-                reportError(NonStrictFunctionDefinitionError{exprFn->debugname.value, local->name.value, *ty}, local->location);
+            {
+                if (FFlag::LuauNonStrictFuncDefErrorFix)
+                {
+                    const char* debugname = exprFn->debugname.value;
+                    reportError(NonStrictFunctionDefinitionError{debugname ? debugname : "", local->name.value, *ty}, local->location);
+                }
+                else
+                {
+                    reportError(NonStrictFunctionDefinitionError{exprFn->debugname.value, local->name.value, *ty}, local->location);
+                }
+            }
             remainder.remove(dfg->getDef(local));
         }
         return remainder;

Analysis/src/Normalize.cpp

@@ -17,12 +17,15 @@
 
 LUAU_FASTFLAGVARIABLE(DebugLuauCheckNormalizeInvariant)
 
+LUAU_FASTFLAGVARIABLE(LuauNormalizeNegatedErrorToAnError)
+LUAU_FASTFLAGVARIABLE(LuauNormalizeIntersectErrorToAnError)
 LUAU_FASTINTVARIABLE(LuauNormalizeCacheLimit, 100000)
 LUAU_FASTINTVARIABLE(LuauNormalizeIntersectionLimit, 200)
+LUAU_FASTINTVARIABLE(LuauNormalizeUnionLimit, 100)
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAGVARIABLE(LuauNormalizeNegationFix)
 LUAU_FASTFLAGVARIABLE(LuauFixInfiniteRecursionInNormalization)
-LUAU_FASTFLAGVARIABLE(LuauFixNormalizedIntersectionOfNegatedClass)
+LUAU_FASTFLAGVARIABLE(LuauNormalizedBufferIsNotUnknown)
+LUAU_FASTFLAGVARIABLE(LuauNormalizeLimitFunctionSet)
 
 namespace Luau
 {
@@ -304,7 +307,9 @@ bool NormalizedType::isUnknown() const
 
     // Otherwise, we can still be unknown!
     bool hasAllPrimitives = isPrim(booleans, PrimitiveType::Boolean) && isPrim(nils, PrimitiveType::NilType) && isNumber(numbers) &&
-                            strings.isString() && isPrim(threads, PrimitiveType::Thread) && isThread(threads);
+                            strings.isString() &&
+                            (FFlag::LuauNormalizedBufferIsNotUnknown ? isThread(threads) && isBuffer(buffers)
+                                                                     : isPrim(threads, PrimitiveType::Thread) && isThread(threads));
 
     // Check is class
     bool isTopClass = false;
@@ -579,7 +584,7 @@ NormalizationResult Normalizer::isIntersectionInhabited(TypeId left, TypeId righ
 {
     left = follow(left);
     right = follow(right);
-    // We're asking if intersection is inahbited between left and right but we've already seen them ....
+    // We're asking if intersection is inhabited between left and right but we've already seen them ....
 
     if (cacheInhabitance)
     {
@@ -1685,6 +1690,13 @@ NormalizationResult Normalizer::unionNormals(NormalizedType& here, const Normali
             return res;
     }
 
+    if (FFlag::LuauNormalizeLimitFunctionSet)
+    {
+        // Limit based on worst-case expansion of the function unions
+        if (here.functions.parts.size() * there.functions.parts.size() >= size_t(FInt::LuauNormalizeUnionLimit))
+            return NormalizationResult::HitLimits;
+    }
+
     here.booleans = unionOfBools(here.booleans, there.booleans);
     unionClasses(here.classes, there.classes);
 
@@ -1696,6 +1708,7 @@ NormalizationResult Normalizer::unionNormals(NormalizedType& here, const Normali
     here.buffers = (get<NeverType>(there.buffers) ? here.buffers : there.buffers);
     unionFunctions(here.functions, there.functions);
     unionTables(here.tables, there.tables);
+
     return NormalizationResult::True;
 }
 
@@ -1735,7 +1748,7 @@ NormalizationResult Normalizer::intersectNormalWithNegationTy(TypeId toNegate, N
     return NormalizationResult::True;
 }
 
-// See above for an explaination of `ignoreSmallerTyvars`.
+// See above for an explanation of `ignoreSmallerTyvars`.
 NormalizationResult Normalizer::unionNormalWithTy(
     NormalizedType& here,
     TypeId there,
@@ -2289,7 +2302,7 @@ void Normalizer::intersectClassesWithClass(NormalizedClassType& heres, TypeId th
 
             for (auto nIt = negations.begin(); nIt != negations.end();)
             {
-                if (FFlag::LuauFixNormalizedIntersectionOfNegatedClass && isSubclass(there, *nIt))
+                if (isSubclass(there, *nIt))
                 {
                     // Hitting this block means that the incoming class is a
                     // subclass of this type, _and_ one of its negations is a
@@ -3050,7 +3063,7 @@ NormalizationResult Normalizer::intersectTyvarsWithTy(
     return NormalizationResult::True;
 }
 
-// See above for an explaination of `ignoreSmallerTyvars`.
+// See above for an explanation of `ignoreSmallerTyvars`.
 NormalizationResult Normalizer::intersectNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars)
 {
     RecursionCounter _rc(&sharedState->counters.recursionCount);
@@ -3068,11 +3081,17 @@ NormalizationResult Normalizer::intersectNormals(NormalizedType& here, const Nor
         return unionNormals(here, there, ignoreSmallerTyvars);
     }
 
-    // Limit based on worst-case expansion of the table intersection
+    // Limit based on worst-case expansion of the table/function intersections
     // This restriction can be relaxed when table intersection simplification is improved
     if (here.tables.size() * there.tables.size() >= size_t(FInt::LuauNormalizeIntersectionLimit))
         return NormalizationResult::HitLimits;
 
+    if (FFlag::LuauNormalizeLimitFunctionSet)
+    {
+        if (here.functions.parts.size() * there.functions.parts.size() >= size_t(FInt::LuauNormalizeIntersectionLimit))
+            return NormalizationResult::HitLimits;
+    }
+
     here.booleans = intersectionOfBools(here.booleans, there.booleans);
 
     intersectClasses(here.classes, there.classes);
@@ -3208,7 +3227,7 @@ NormalizationResult Normalizer::intersectNormalWithTy(
     {
         TypeId errors = here.errors;
         clearNormal(here);
-        here.errors = errors;
+        here.errors = FFlag::LuauNormalizeIntersectErrorToAnError && get<ErrorType>(errors) ? errors : there;
     }
     else if (const PrimitiveType* ptv = get<PrimitiveType>(there))
     {
@@ -3305,11 +3324,16 @@ NormalizationResult Normalizer::intersectNormalWithTy(
             clearNormal(here);
             return NormalizationResult::True;
         }
+        else if (FFlag::LuauNormalizeNegatedErrorToAnError && get<ErrorType>(t))
+        {
+            // ~error is still an error, so intersecting with the negation is the same as intersecting with a type
+            TypeId errors = here.errors;
+            clearNormal(here);
+            here.errors = FFlag::LuauNormalizeIntersectErrorToAnError && get<ErrorType>(errors) ? errors : t;
+        }
         else if (auto nt = get<NegationType>(t))
         {
-            if (FFlag::LuauNormalizeNegationFix)
+            here.tyvars = std::move(tyvars);
-                here.tyvars = std::move(tyvars);
-
             return intersectNormalWithTy(here, nt->ty, seenTablePropPairs, seenSetTypes);
         }
         else

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/RequireTracer.cpp

@@ -4,8 +4,6 @@
 #include "Luau/Ast.h"
 #include "Luau/Module.h"
 
-LUAU_FASTFLAGVARIABLE(LuauExtendedSimpleRequire)
-
 namespace Luau
 {
 
@@ -106,96 +104,50 @@ struct RequireTracer : AstVisitor
     {
         ModuleInfo moduleContext{currentModuleName};
 
-        if (FFlag::LuauExtendedSimpleRequire)
+        // seed worklist with require arguments
+        work.reserve(requireCalls.size());
+
+        for (AstExprCall* require : requireCalls)
+            work.push_back(require->args.data[0]);
+
+        // 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)
         {
-            // seed worklist with require arguments
+            if (AstNode* dep = getDependent(work[i]))
-            work.reserve(requireCalls.size());
+                work.push_back(dep);
-
-            for (AstExprCall* require : requireCalls)
-                work.push_back(require->args.data[0]);
-
-            // 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 (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)
-            {
-                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))
-                    continue;
-
-                std::optional<ModuleInfo> info;
-
-                if (AstNode* dep = getDependent(expr))
-                {
-                    const ModuleInfo* context = result.exprs.find(dep);
-
-                    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 if (AstExpr* asExpr = expr->asExpr())
-                {
-                    info = fileResolver->resolveModule(&moduleContext, asExpr);
-                }
-
-                if (info)
-                    result.exprs[expr] = std::move(*info);
-            }
         }
-        else
+
+        // resolve all expressions to a module info
+        for (size_t i = work.size(); i > 0; --i)
         {
-            // seed worklist with require arguments
+            AstNode* expr = work[i - 1];
-            work_DEPRECATED.reserve(requireCalls.size());
 
-            for (AstExprCall* require : requireCalls)
+            // when multiple expressions depend on the same one we push it to work queue multiple times
-                work_DEPRECATED.push_back(require->args.data[0]);
+            if (result.exprs.contains(expr))
+                continue;
 
-            // push all dependent expressions to the work stack; note that the vector is modified during traversal
+            std::optional<ModuleInfo> info;
-            for (size_t i = 0; i < work_DEPRECATED.size(); ++i)
-                if (AstExpr* dep = getDependent_DEPRECATED(work_DEPRECATED[i]))
-                    work_DEPRECATED.push_back(dep);
 
-            // resolve all expressions to a module info
+            if (AstNode* dep = getDependent(expr))
-            for (size_t i = work_DEPRECATED.size(); i > 0; --i)
             {
-                AstExpr* expr = work_DEPRECATED[i - 1];
+                const ModuleInfo* context = result.exprs.find(dep);
 
-                // when multiple expressions depend on the same one we push it to work queue multiple times
+                if (context && expr->is<AstExprLocal>())
-                if (result.exprs.contains(expr))
+                    info = *context; // locals just inherit their dependent context, no resolution required
-                    continue;
+                else if (context && (expr->is<AstExprGroup>() || expr->is<AstTypeGroup>()))
-
+                    info = *context; // simple group nodes propagate their value
-                std::optional<ModuleInfo> info;
+                else if (context && (expr->is<AstTypeTypeof>() || expr->is<AstExprTypeAssertion>()))
-
+                    info = *context; // typeof type annotations will resolve to the typeof content
-                if (AstExpr* dep = getDependent_DEPRECATED(expr))
+                else if (AstExpr* asExpr = expr->asExpr())
-                {
+                    info = fileResolver->resolveModule(context, asExpr);
-                    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);
-                }
-                else
-                {
-                    info = fileResolver->resolveModule(&moduleContext, expr);
-                }
-
-                if (info)
-                    result.exprs[expr] = std::move(*info);
             }
+            else if (AstExpr* asExpr = expr->asExpr())
+            {
+                info = fileResolver->resolveModule(&moduleContext, asExpr);
+            }
+
+            if (info)
+                result.exprs[expr] = std::move(*info);
         }
 
         // resolve all requires according to their argument
@@ -224,7 +176,6 @@ struct RequireTracer : AstVisitor
     ModuleName currentModuleName;
 
     DenseHashMap<AstLocal*, AstExpr*> locals;
-    std::vector<AstExpr*> work_DEPRECATED;
     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)
 {

Analysis/src/Substitution.cpp

@@ -13,6 +13,7 @@ LUAU_FASTINTVARIABLE(LuauTarjanChildLimit, 10000)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTINTVARIABLE(LuauTarjanPreallocationSize, 256)
 LUAU_FASTFLAG(LuauSyntheticErrors)
+LUAU_FASTFLAG(LuauDeprecatedAttribute)
 
 namespace Luau
 {
@@ -102,6 +103,8 @@ static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool a
             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>)

Analysis/src/Subtyping.cpp

@@ -22,7 +22,7 @@
 #include <algorithm>
 
 LUAU_FASTFLAGVARIABLE(DebugLuauSubtypingCheckPathValidity)
-LUAU_FASTFLAGVARIABLE(LuauSubtypingFixTailPack)
+LUAU_FASTFLAGVARIABLE(LuauSubtypingStopAtNormFail)
 
 namespace Luau
 {
@@ -416,6 +416,14 @@ SubtypingResult Subtyping::isSubtype(TypeId subTy, TypeId superTy, NotNull<Scope
 
     SubtypingResult result = isCovariantWith(env, subTy, superTy, scope);
 
+    if (FFlag::LuauSubtypingStopAtNormFail && result.normalizationTooComplex)
+    {
+        if (result.isCacheable)
+            resultCache[{subTy, superTy}] = result;
+
+        return result;
+    }
+
     for (const auto& [subTy, bounds] : env.mappedGenerics)
     {
         const auto& lb = bounds.lowerBound;
@@ -593,7 +601,12 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
         if (!result.isSubtype && !result.normalizationTooComplex)
         {
             SubtypingResult semantic = isCovariantWith(env, normalizer->normalize(subTy), normalizer->normalize(superTy), scope);
-            if (semantic.isSubtype)
+
+            if (FFlag::LuauSubtypingStopAtNormFail && semantic.normalizationTooComplex)
+            {
+                result = semantic;
+            }
+            else if (semantic.isSubtype)
             {
                 semantic.reasoning.clear();
                 result = semantic;
@@ -608,7 +621,12 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
         if (!result.isSubtype && !result.normalizationTooComplex)
         {
             SubtypingResult semantic = isCovariantWith(env, normalizer->normalize(subTy), normalizer->normalize(superTy), scope);
-            if (semantic.isSubtype)
+
+            if (FFlag::LuauSubtypingStopAtNormFail && semantic.normalizationTooComplex)
+            {
+                result = semantic;
+            }
+            else if (semantic.isSubtype)
             {
                 // Clear the semantic reasoning, as any reasonings within
                 // potentially contain invalid paths.
@@ -754,7 +772,8 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
     // Match head types pairwise
 
     for (size_t i = 0; i < headSize; ++i)
-        results.push_back(isCovariantWith(env, subHead[i], superHead[i], scope).withBothComponent(TypePath::Index{i}));
+        results.push_back(isCovariantWith(env, subHead[i], superHead[i], scope).withBothComponent(TypePath::Index{i, TypePath::Index::Variant::Pack})
+        );
 
     // Handle mismatched head sizes
 
@@ -767,7 +786,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
                 for (size_t i = headSize; i < superHead.size(); ++i)
                     results.push_back(isCovariantWith(env, vt->ty, superHead[i], scope)
                                           .withSubPath(TypePath::PathBuilder().tail().variadic().build())
-                                          .withSuperComponent(TypePath::Index{i}));
+                                          .withSuperComponent(TypePath::Index{i, TypePath::Index::Variant::Pack}));
             }
             else if (auto gt = get<GenericTypePack>(*subTail))
             {
@@ -821,7 +840,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
             {
                 for (size_t i = headSize; i < subHead.size(); ++i)
                     results.push_back(isCovariantWith(env, subHead[i], vt->ty, scope)
-                                          .withSubComponent(TypePath::Index{i})
+                                          .withSubComponent(TypePath::Index{i, TypePath::Index::Variant::Pack})
                                           .withSuperPath(TypePath::PathBuilder().tail().variadic().build()));
             }
             else if (auto gt = get<GenericTypePack>(*superTail))
@@ -859,7 +878,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
             else
                 return SubtypingResult{false}
                     .withSuperComponent(TypePath::PackField::Tail)
-                    .withError({scope->location, UnexpectedTypePackInSubtyping{FFlag::LuauSubtypingFixTailPack ? *superTail : *subTail}});
+                    .withError({scope->location, UnexpectedTypePackInSubtyping{*superTail}});
         }
         else
             return {false};
@@ -1082,6 +1101,10 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     for (TypeId ty : superUnion)
     {
         SubtypingResult next = isCovariantWith(env, subTy, ty, scope);
+
+        if (FFlag::LuauSubtypingStopAtNormFail && next.normalizationTooComplex)
+            return SubtypingResult{false, /* normalizationTooComplex */ true};
+
         if (next.isSubtype)
             return SubtypingResult{true};
     }
@@ -1100,7 +1123,13 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Unio
     std::vector<SubtypingResult> subtypings;
     size_t i = 0;
     for (TypeId ty : subUnion)
-        subtypings.push_back(isCovariantWith(env, ty, superTy, scope).withSubComponent(TypePath::Index{i++}));
+    {
+        subtypings.push_back(isCovariantWith(env, ty, superTy, scope).withSubComponent(TypePath::Index{i++, TypePath::Index::Variant::Union}));
+
+        if (FFlag::LuauSubtypingStopAtNormFail && subtypings.back().normalizationTooComplex)
+            return SubtypingResult{false, /* normalizationTooComplex */ true};
+    }
+
     return SubtypingResult::all(subtypings);
 }
 
@@ -1110,7 +1139,13 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     std::vector<SubtypingResult> subtypings;
     size_t i = 0;
     for (TypeId ty : superIntersection)
-        subtypings.push_back(isCovariantWith(env, subTy, ty, scope).withSuperComponent(TypePath::Index{i++}));
+    {
+        subtypings.push_back(isCovariantWith(env, subTy, ty, scope).withSuperComponent(TypePath::Index{i++, TypePath::Index::Variant::Intersection}));
+
+        if (FFlag::LuauSubtypingStopAtNormFail && subtypings.back().normalizationTooComplex)
+            return SubtypingResult{false, /* normalizationTooComplex */ true};
+    }
+
     return SubtypingResult::all(subtypings);
 }
 
@@ -1120,7 +1155,13 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Inte
     std::vector<SubtypingResult> subtypings;
     size_t i = 0;
     for (TypeId ty : subIntersection)
-        subtypings.push_back(isCovariantWith(env, ty, superTy, scope).withSubComponent(TypePath::Index{i++}));
+    {
+        subtypings.push_back(isCovariantWith(env, ty, superTy, scope).withSubComponent(TypePath::Index{i++, TypePath::Index::Variant::Intersection}));
+
+        if (FFlag::LuauSubtypingStopAtNormFail && subtypings.back().normalizationTooComplex)
+            return SubtypingResult{false, /* normalizationTooComplex */ true};
+    }
+
     return SubtypingResult::any(subtypings);
 }
 
@@ -1410,7 +1451,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Meta
         // of the supertype table.
         //
         // There's a flaw here in that if the __index metamethod contributes a new
-        // field that would satisfy the subtyping relationship, we'll erronously say
+        // field that would satisfy the subtyping relationship, we'll erroneously say
         // that the metatable isn't a subtype of the table, even though they have
         // compatible properties/shapes. We'll revisit this later when we have a
         // better understanding of how important this is.
@@ -1760,7 +1801,12 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
     {
         results.emplace_back();
         for (TypeId superTy : superTypes)
+        {
             results.back().orElse(isCovariantWith(env, subTy, superTy, scope));
+
+            if (FFlag::LuauSubtypingStopAtNormFail && results.back().normalizationTooComplex)
+                return SubtypingResult{false, /* normalizationTooComplex */ true};
+        }
     }
 
     return SubtypingResult::all(results);

Analysis/src/TableLiteralInference.cpp

@@ -13,9 +13,9 @@
 #include "Luau/TypeUtils.h"
 #include "Luau/Unifier2.h"
 
-LUAU_FASTFLAGVARIABLE(LuauDontInPlaceMutateTableType)
-LUAU_FASTFLAGVARIABLE(LuauAllowNonSharedTableTypesInLiteral)
 LUAU_FASTFLAGVARIABLE(LuauBidirectionalInferenceUpcast)
+LUAU_FASTFLAGVARIABLE(LuauBidirectionalInferenceCollectIndexerTypes)
+LUAU_FASTFLAGVARIABLE(LuauBidirectionalFailsafe)
 
 namespace Luau
 {
@@ -138,14 +138,13 @@ TypeId matchLiteralType(
      * things like replace explicit named properties with indexers as required
      * by the expected type.
      */
+
     if (!isLiteral(expr))
     {
         if (FFlag::LuauBidirectionalInferenceUpcast)
         {
             auto result = subtyping->isSubtype(/*subTy=*/exprType, /*superTy=*/expectedType, unifier->scope);
-            return result.isSubtype
+            return result.isSubtype ? expectedType : exprType;
-                ? expectedType
-                : exprType;
         }
         else
             return exprType;
@@ -154,11 +153,23 @@ TypeId matchLiteralType(
     expectedType = follow(expectedType);
     exprType = follow(exprType);
 
-    if (get<AnyType>(expectedType) || get<UnknownType>(expectedType))
+    if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
     {
-        // "Narrowing" to unknown or any is not going to do anything useful.
+        // The intent of `matchLiteralType` is to upcast values when it's safe
-        return exprType;
+        // to do so. it's always safe to upcast to `any` or `unknown`, so we
+        // can unconditionally do so here.
+        if (is<AnyType, UnknownType>(expectedType))
+            return expectedType;
     }
+    else
+    {
+        if (get<AnyType>(expectedType) || get<UnknownType>(expectedType))
+        {
+            // "Narrowing" to unknown or any is not going to do anything useful.
+            return exprType;
+        }
+    }
+
 
     if (expr->is<AstExprConstantString>())
     {
@@ -240,6 +251,15 @@ TypeId matchLiteralType(
     if (auto exprTable = expr->as<AstExprTable>())
     {
         TableType* const tableTy = getMutable<TableType>(exprType);
+
+        // This can occur if we have an expression like:
+        //
+        //  { x = {}, x = 42 }
+        //
+        // The type of this will be `{ x: number }`
+        if (FFlag::LuauBidirectionalFailsafe && !tableTy)
+            return exprType;
+
         LUAU_ASSERT(tableTy);
 
         const TableType* expectedTableTy = get<TableType>(expectedType);
@@ -266,6 +286,9 @@ TypeId matchLiteralType(
 
         DenseHashSet<AstExprConstantString*> keysToDelete{nullptr};
 
+        DenseHashSet<TypeId> indexerKeyTypes{nullptr};
+        DenseHashSet<TypeId> indexerValueTypes{nullptr};
+
         for (const AstExprTable::Item& item : exprTable->items)
         {
             if (isRecord(item))
@@ -273,23 +296,20 @@ TypeId matchLiteralType(
                 const AstArray<char>& s = item.key->as<AstExprConstantString>()->value;
                 std::string keyStr{s.data, s.data + s.size};
                 auto it = tableTy->props.find(keyStr);
+
+                // This can occur, potentially, if we are re-entrant.
+                if (FFlag::LuauBidirectionalFailsafe && it == tableTy->props.end())
+                    continue;
+
                 LUAU_ASSERT(it != tableTy->props.end());
 
                 Property& prop = it->second;
 
-                if (FFlag::LuauAllowNonSharedTableTypesInLiteral)
+                // If we encounter a duplcate property, we may have already
-                {
+                // set it to be read-only. If that's the case, the only thing
-                    // If we encounter a duplcate property, we may have already
+                // that will definitely crash is trying to access a write
-                    // set it to be read-only. If that's the case, the only thing
+                // only property.
-                    // that will definitely crash is trying to access a write
+                LUAU_ASSERT(!prop.isWriteOnly());
-                    // only property.
-                    LUAU_ASSERT(!prop.isWriteOnly());
-                }
-                else
-                {
-                    // Table literals always initially result in shared read-write types
-                    LUAU_ASSERT(prop.isShared());
-                }
                 TypeId propTy = *prop.readTy;
 
                 auto it2 = expectedTableTy->props.find(keyStr);
@@ -317,15 +337,20 @@ TypeId matchLiteralType(
                             toBlock
                         );
 
-                        if (tableTy->indexer)
+                        if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
-                            unifier->unify(matchedType, tableTy->indexer->indexResultType);
+                        {
+                            indexerKeyTypes.insert(arena->addType(SingletonType{StringSingleton{keyStr}}));
+                            indexerValueTypes.insert(matchedType);
+                        }
                         else
-                            tableTy->indexer = TableIndexer{expectedTableTy->indexer->indexType, matchedType};
+                        {
+                            if (tableTy->indexer)
+                                unifier->unify(matchedType, tableTy->indexer->indexResultType);
+                            else
+                                tableTy->indexer = TableIndexer{expectedTableTy->indexer->indexType, matchedType};
+                        }
 
-                        if (FFlag::LuauDontInPlaceMutateTableType)
+                        keysToDelete.insert(item.key->as<AstExprConstantString>());
-                            keysToDelete.insert(item.key->as<AstExprConstantString>());
-                        else
-                            tableTy->props.erase(keyStr);
 
                     }
 
@@ -381,6 +406,11 @@ TypeId matchLiteralType(
                 LUAU_ASSERT(matchedType);
 
                 (*astExpectedTypes)[item.value] = matchedType;
+                // NOTE: We do *not* add to the potential indexer types here.
+                // I think this is correct to support something like:
+                //
+                //  { [string]: number, foo: boolean }
+                //
             }
             else if (item.kind == AstExprTable::Item::List)
             {
@@ -405,9 +435,18 @@ TypeId matchLiteralType(
                         toBlock
                     );
 
-                    // if the index result type is the prop type, we can replace it with the matched type here.
+                    if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
-                    if (tableTy->indexer->indexResultType == *propTy)
+                    {
-                        tableTy->indexer->indexResultType = matchedType;
+                        indexerKeyTypes.insert(builtinTypes->numberType);
+                        indexerValueTypes.insert(matchedType);
+                    }
+                    else
+                    {
+                        // if the index result type is the prop type, we can replace it with the matched type here.
+                        if (tableTy->indexer->indexResultType == *propTy)
+                            tableTy->indexer->indexResultType = matchedType;
+                    }
+
                 }
             }
             else if (item.kind == AstExprTable::Item::General)
@@ -429,19 +468,23 @@ TypeId matchLiteralType(
                 // Populate expected types for non-string keys declared with [] (the code below will handle the case where they are strings)
                 if (!item.key->as<AstExprConstantString>() && expectedTableTy->indexer)
                     (*astExpectedTypes)[item.key] = expectedTableTy->indexer->indexType;
+
+                if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes)
+                {
+                    indexerKeyTypes.insert(tKey);
+                    indexerValueTypes.insert(tProp);
+                }
+
             }
             else
                 LUAU_ASSERT(!"Unexpected");
         }
 
-        if (FFlag::LuauDontInPlaceMutateTableType)
+        for (const auto& key : keysToDelete)
         {
-            for (const auto& key : keysToDelete)
+            const AstArray<char>& s = key->value;
-            {
+            std::string keyStr{s.data, s.data + s.size};
-                const AstArray<char>& s = key->value;
+            tableTy->props.erase(keyStr);
-                std::string keyStr{s.data, s.data + s.size};
-                tableTy->props.erase(keyStr);
-            }
         }
 
         // Keys that the expectedType says we should have, but that aren't
@@ -493,9 +536,39 @@ TypeId matchLiteralType(
         // have one too.
         // TODO: If the expected table also has an indexer, we might want to
         // push the expected indexer's types into it.
-        if (expectedTableTy->indexer && !tableTy->indexer)
+        if (FFlag::LuauBidirectionalInferenceCollectIndexerTypes && expectedTableTy->indexer)
         {
-            tableTy->indexer = expectedTableTy->indexer;
+            if (indexerValueTypes.size() > 0 && indexerKeyTypes.size() > 0)
+            {
+                TypeId inferredKeyType = builtinTypes->neverType;
+                TypeId inferredValueType = builtinTypes->neverType;
+                for (auto kt: indexerKeyTypes)
+                {
+                    auto simplified = simplifyUnion(builtinTypes, arena, inferredKeyType, kt);
+                    inferredKeyType = simplified.result;
+                }
+                for (auto vt: indexerValueTypes)
+                {
+                    auto simplified = simplifyUnion(builtinTypes, arena, inferredValueType, vt);
+                    inferredValueType = simplified.result;
+                }
+                tableTy->indexer = TableIndexer{inferredKeyType, inferredValueType};
+                auto keyCheck = subtyping->isSubtype(inferredKeyType, expectedTableTy->indexer->indexType, unifier->scope);
+                if (keyCheck.isSubtype)
+                    tableTy->indexer->indexType = expectedTableTy->indexer->indexType;
+                auto valueCheck = subtyping->isSubtype(inferredValueType, expectedTableTy->indexer->indexResultType, unifier->scope);
+                if (valueCheck.isSubtype)
+                    tableTy->indexer->indexResultType = expectedTableTy->indexer->indexResultType;
+            }
+            else
+                LUAU_ASSERT(indexerKeyTypes.empty() && indexerValueTypes.empty());
+        }
+        else
+        {
+            if (expectedTableTy->indexer && !tableTy->indexer)
+            {
+                tableTy->indexer = expectedTableTy->indexer;
+            }
         }
     }
 

Analysis/src/Transpiler.cpp

@@ -10,10 +10,12 @@
 #include <limits>
 #include <math.h>
 
-LUAU_FASTFLAG(LuauStoreCSTData)
+LUAU_FASTFLAG(LuauStoreCSTData2)
 LUAU_FASTFLAG(LuauExtendStatEndPosWithSemicolon)
-LUAU_FASTFLAG(LuauAstTypeGroup2)
+LUAU_FASTFLAG(LuauAstTypeGroup3)
 LUAU_FASTFLAG(LuauFixDoBlockEndLocation)
+LUAU_FASTFLAG(LuauParseOptionalAsNode2)
+LUAU_FASTFLAG(LuauFixFunctionWithAttributesStartLocation)
 
 namespace
 {
@@ -166,7 +168,7 @@ struct StringWriter : Writer
 
     void symbol(std::string_view s) override
     {
-        if (FFlag::LuauStoreCSTData)
+        if (FFlag::LuauStoreCSTData2)
         {
             write(s);
         }
@@ -256,7 +258,7 @@ public:
             first = !first;
         else
         {
-            if (FFlag::LuauStoreCSTData && commaPosition)
+            if (FFlag::LuauStoreCSTData2 && commaPosition)
             {
                 writer.advance(*commaPosition);
                 commaPosition++;
@@ -271,6 +273,43 @@ private:
     const Position* commaPosition;
 };
 
+class ArgNameInserter
+{
+public:
+    ArgNameInserter(Writer& w, AstArray<std::optional<AstArgumentName>> names, AstArray<std::optional<Position>> colonPositions)
+        : writer(w)
+        , names(names)
+        , colonPositions(colonPositions)
+    {
+    }
+
+    void operator()()
+    {
+        if (idx < names.size)
+        {
+            const auto name = names.data[idx];
+            if (name.has_value())
+            {
+                writer.advance(name->second.begin);
+                writer.identifier(name->first.value);
+                if (idx < colonPositions.size)
+                {
+                    LUAU_ASSERT(colonPositions.data[idx].has_value());
+                    writer.advance(*colonPositions.data[idx]);
+                }
+                writer.symbol(":");
+            }
+        }
+        idx++;
+    }
+
+private:
+    Writer& writer;
+    AstArray<std::optional<AstArgumentName>> names;
+    AstArray<std::optional<Position>> colonPositions;
+    size_t idx = 0;
+};
+
 struct Printer_DEPRECATED
 {
     explicit Printer_DEPRECATED(Writer& writer)
@@ -330,7 +369,7 @@ struct Printer_DEPRECATED
         else if (typeCount == 1)
         {
             bool shouldParenthesize = unconditionallyParenthesize && (list.types.size == 0 || !list.types.data[0]->is<AstTypeGroup>());
-            if (FFlag::LuauAstTypeGroup2 ? shouldParenthesize : unconditionallyParenthesize)
+            if (FFlag::LuauAstTypeGroup3 ? shouldParenthesize : unconditionallyParenthesize)
                 writer.symbol("(");
 
             // Only variadic tail
@@ -343,7 +382,7 @@ struct Printer_DEPRECATED
                 visualizeTypeAnnotation(*list.types.data[0]);
             }
 
-            if (FFlag::LuauAstTypeGroup2 ? shouldParenthesize : unconditionallyParenthesize)
+            if (FFlag::LuauAstTypeGroup3 ? shouldParenthesize : unconditionallyParenthesize)
                 writer.symbol(")");
         }
         else
@@ -1191,9 +1230,18 @@ struct Printer_DEPRECATED
                 AstType* l = a->types.data[0];
                 AstType* r = a->types.data[1];
 
-                auto lta = l->as<AstTypeReference>();
+                if (FFlag::LuauParseOptionalAsNode2)
-                if (lta && lta->name == "nil")
+                {
-                    std::swap(l, r);
+                    auto lta = l->as<AstTypeReference>();
+                    if (lta && lta->name == "nil" && !r->is<AstTypeOptional>())
+                        std::swap(l, r);
+                }
+                else
+                {
+                    auto lta = l->as<AstTypeReference>();
+                    if (lta && lta->name == "nil")
+                        std::swap(l, r);
+                }
 
                 // it's still possible that we had a (T | U) or (T | nil) and not (nil | T)
                 auto rta = r->as<AstTypeReference>();
@@ -1216,6 +1264,15 @@ struct Printer_DEPRECATED
 
             for (size_t i = 0; i < a->types.size; ++i)
             {
+                if (FFlag::LuauParseOptionalAsNode2)
+                {
+                    if (a->types.data[i]->is<AstTypeOptional>())
+                    {
+                        writer.symbol("?");
+                        continue;
+                    }
+                }
+
                 if (i > 0)
                 {
                     writer.maybeSpace(a->types.data[i]->location.begin, 2);
@@ -1312,7 +1369,7 @@ struct Printer
         }
     }
 
-    void visualizeTypePackAnnotation(const AstTypePack& annotation, bool forVarArg)
+    void visualizeTypePackAnnotation(AstTypePack& annotation, bool forVarArg)
     {
         advance(annotation.location.begin);
         if (const AstTypePackVariadic* variadicTp = annotation.as<AstTypePackVariadic>())
@@ -1322,15 +1379,22 @@ struct Printer
 
             visualizeTypeAnnotation(*variadicTp->variadicType);
         }
-        else if (const AstTypePackGeneric* genericTp = annotation.as<AstTypePackGeneric>())
+        else if (AstTypePackGeneric* genericTp = annotation.as<AstTypePackGeneric>())
         {
             writer.symbol(genericTp->genericName.value);
+            if (const auto cstNode = lookupCstNode<CstTypePackGeneric>(genericTp))
+                advance(cstNode->ellipsisPosition);
             writer.symbol("...");
         }
-        else if (const AstTypePackExplicit* explicitTp = annotation.as<AstTypePackExplicit>())
+        else if (AstTypePackExplicit* explicitTp = annotation.as<AstTypePackExplicit>())
         {
             LUAU_ASSERT(!forVarArg);
-            visualizeTypeList(explicitTp->typeList, true);
+            if (const auto cstNode = lookupCstNode<CstTypePackExplicit>(explicitTp))
+                visualizeTypeList(
+                    explicitTp->typeList, true, cstNode->openParenthesesPosition, cstNode->closeParenthesesPosition, cstNode->commaPositions
+                );
+            else
+                visualizeTypeList(explicitTp->typeList, true);
         }
         else
         {
@@ -1338,19 +1402,37 @@ struct Printer
         }
     }
 
-    void visualizeTypeList(const AstTypeList& list, bool unconditionallyParenthesize)
+    void visualizeNamedTypeList(
+        const AstTypeList& list,
+        bool unconditionallyParenthesize,
+        std::optional<Position> openParenthesesPosition,
+        std::optional<Position> closeParenthesesPosition,
+        AstArray<Position> commaPositions,
+        AstArray<std::optional<AstArgumentName>> argNames,
+        AstArray<std::optional<Position>> argNamesColonPositions
+    )
     {
         size_t typeCount = list.types.size + (list.tailType != nullptr ? 1 : 0);
         if (typeCount == 0)
         {
+            if (openParenthesesPosition)
+                advance(*openParenthesesPosition);
             writer.symbol("(");
+            if (closeParenthesesPosition)
+                advance(*closeParenthesesPosition);
             writer.symbol(")");
         }
         else if (typeCount == 1)
         {
             bool shouldParenthesize = unconditionallyParenthesize && (list.types.size == 0 || !list.types.data[0]->is<AstTypeGroup>());
-            if (FFlag::LuauAstTypeGroup2 ? shouldParenthesize : unconditionallyParenthesize)
+            if (FFlag::LuauAstTypeGroup3 ? shouldParenthesize : unconditionallyParenthesize)
+            {
+                if (openParenthesesPosition)
+                    advance(*openParenthesesPosition);
                 writer.symbol("(");
+            }
+
+            ArgNameInserter(writer, argNames, argNamesColonPositions)();
 
             // Only variadic tail
             if (list.types.size == 0)
@@ -1362,34 +1444,51 @@ struct Printer
                 visualizeTypeAnnotation(*list.types.data[0]);
             }
 
-            if (FFlag::LuauAstTypeGroup2 ? shouldParenthesize : unconditionallyParenthesize)
+            if (FFlag::LuauAstTypeGroup3 ? shouldParenthesize : unconditionallyParenthesize)
+            {
+                if (closeParenthesesPosition)
+                    advance(*closeParenthesesPosition);
                 writer.symbol(")");
+            }
         }
         else
         {
+            if (openParenthesesPosition)
+                advance(*openParenthesesPosition);
             writer.symbol("(");
 
-            bool first = true;
+            CommaSeparatorInserter comma(writer, commaPositions.size > 0 ? commaPositions.begin() : nullptr);
+            ArgNameInserter argName(writer, argNames, argNamesColonPositions);
             for (const auto& el : list.types)
             {
-                if (first)
+                comma();
-                    first = false;
+                argName();
-                else
-                    writer.symbol(",");
-
                 visualizeTypeAnnotation(*el);
             }
 
             if (list.tailType)
             {
-                writer.symbol(",");
+                comma();
                 visualizeTypePackAnnotation(*list.tailType, false);
             }
 
+            if (closeParenthesesPosition)
+                advance(*closeParenthesesPosition);
             writer.symbol(")");
         }
     }
 
+    void visualizeTypeList(
+        const AstTypeList& list,
+        bool unconditionallyParenthesize,
+        std::optional<Position> openParenthesesPosition = std::nullopt,
+        std::optional<Position> closeParenthesesPosition = std::nullopt,
+        AstArray<Position> commaPositions = {}
+    )
+    {
+        visualizeNamedTypeList(list, unconditionallyParenthesize, openParenthesesPosition, closeParenthesesPosition, commaPositions, {}, {});
+    }
+
     bool isIntegerish(double d)
     {
         if (d <= std::numeric_limits<int>::max() && d >= std::numeric_limits<int>::min())
@@ -1400,13 +1499,14 @@ struct Printer
 
     void visualize(AstExpr& expr)
     {
-        advance(expr.location.begin);
+        if (!expr.is<AstExprFunction>() || FFlag::LuauFixFunctionWithAttributesStartLocation)
+            advance(expr.location.begin);
 
         if (const auto& a = expr.as<AstExprGroup>())
         {
             writer.symbol("(");
             visualize(*a->expr);
-            advance(Position{a->location.end.line, a->location.end.column - 1});
+            advanceBefore(a->location.end, 1);
             writer.symbol(")");
         }
         else if (expr.is<AstExprConstantNil>())
@@ -1534,6 +1634,17 @@ struct Printer
         }
         else if (const auto& a = expr.as<AstExprFunction>())
         {
+            for (const auto& attribute : a->attributes)
+                visualizeAttribute(*attribute);
+            if (FFlag::LuauFixFunctionWithAttributesStartLocation)
+            {
+                if (const auto cstNode = lookupCstNode<CstExprFunction>(a))
+                    advance(cstNode->functionKeywordPosition);
+            }
+            else
+            {
+                advance(a->location.begin);
+            }
             writer.keyword("function");
             visualizeFunctionBody(*a);
         }
@@ -1775,9 +1886,18 @@ struct Printer
         writer.advance(newPos);
     }
 
+    void advanceBefore(const Position& newPos, unsigned int tokenLength)
+    {
+        if (newPos.column >= tokenLength)
+            advance(Position{newPos.line, newPos.column - tokenLength});
+        else
+            advance(newPos);
+    }
+
     void visualize(AstStat& program)
     {
-        advance(program.location.begin);
+        if ((!program.is<AstStatLocalFunction>() && !program.is<AstStatFunction>()) || FFlag::LuauFixFunctionWithAttributesStartLocation)
+            advance(program.location.begin);
 
         if (const auto& block = program.as<AstStatBlock>())
         {
@@ -1817,8 +1937,8 @@ struct Printer
             visualizeBlock(*a->body);
             if (const auto cstNode = lookupCstNode<CstStatRepeat>(a))
                 writer.advance(cstNode->untilPosition);
-            else if (a->condition->location.begin.column > 5)
+            else
-                writer.advance(Position{a->condition->location.begin.line, a->condition->location.begin.column - 6});
+                advanceBefore(a->condition->location.begin, 6);
             writer.keyword("until");
             visualize(*a->condition);
         }
@@ -2014,13 +2134,36 @@ struct Printer
         }
         else if (const auto& a = program.as<AstStatFunction>())
         {
+            for (const auto& attribute : a->func->attributes)
+                visualizeAttribute(*attribute);
+            if (FFlag::LuauFixFunctionWithAttributesStartLocation)
+            {
+                if (const auto cstNode = lookupCstNode<CstStatFunction>(a))
+                    advance(cstNode->functionKeywordPosition);
+            }
+            else
+            {
+                advance(a->location.begin);
+            }
             writer.keyword("function");
             visualize(*a->name);
             visualizeFunctionBody(*a->func);
         }
         else if (const auto& a = program.as<AstStatLocalFunction>())
         {
+            for (const auto& attribute : a->func->attributes)
+                visualizeAttribute(*attribute);
+
             const auto cstNode = lookupCstNode<CstStatLocalFunction>(a);
+            if (FFlag::LuauFixFunctionWithAttributesStartLocation)
+            {
+                if (cstNode)
+                    advance(cstNode->localKeywordPosition);
+            }
+            else
+            {
+                advance(a->location.begin);
+            }
 
             writer.keyword("local");
 
@@ -2121,7 +2264,20 @@ struct Printer
         {
             if (writeTypes)
             {
-                writer.keyword("type function");
+                const auto cstNode = lookupCstNode<CstStatTypeFunction>(t);
+                if (t->exported)
+                    writer.keyword("export");
+                if (cstNode)
+                    advance(cstNode->typeKeywordPosition);
+                else
+                    writer.space();
+                writer.keyword("type");
+                if (cstNode)
+                    advance(cstNode->functionKeywordPosition);
+                else
+                    writer.space();
+                writer.keyword("function");
+                advance(t->nameLocation.begin);
                 writer.identifier(t->name.value);
                 visualizeFunctionBody(*t->body);
             }
@@ -2151,17 +2307,23 @@ struct Printer
 
         if (program.hasSemicolon)
         {
-            if (FFlag::LuauStoreCSTData)
+            if (FFlag::LuauStoreCSTData2)
-                advance(Position{program.location.end.line, program.location.end.column - 1});
+                advanceBefore(program.location.end, 1);
             writer.symbol(";");
         }
     }
 
     void visualizeFunctionBody(AstExprFunction& func)
     {
+        const auto cstNode = lookupCstNode<CstExprFunction>(&func);
+
+        // TODO(CLI-139347): need to handle return type (incl. parentheses of return type)
+
         if (func.generics.size > 0 || func.genericPacks.size > 0)
         {
-            CommaSeparatorInserter comma(writer);
+            CommaSeparatorInserter comma(writer, cstNode ? cstNode->genericsCommaPositions.begin() : nullptr);
+            if (cstNode)
+                advance(cstNode->openGenericsPosition);
             writer.symbol("<");
             for (const auto& o : func.generics)
             {
@@ -2176,13 +2338,19 @@ struct Printer
 
                 writer.advance(o->location.begin);
                 writer.identifier(o->name.value);
+                if (const auto* genericTypePackCstNode = lookupCstNode<CstGenericTypePack>(o))
+                    advance(genericTypePackCstNode->ellipsisPosition);
                 writer.symbol("...");
             }
+            if (cstNode)
+                advance(cstNode->closeGenericsPosition);
             writer.symbol(">");
         }
 
+        if (func.argLocation)
+            advance(func.argLocation->begin);
         writer.symbol("(");
-        CommaSeparatorInserter comma(writer);
+        CommaSeparatorInserter comma(writer, cstNode ? cstNode->argsCommaPositions.begin() : nullptr);
 
         for (size_t i = 0; i < func.args.size; ++i)
         {
@@ -2212,10 +2380,14 @@ struct Printer
             }
         }
 
+        if (func.argLocation)
+            advanceBefore(func.argLocation->end, 1);
         writer.symbol(")");
 
         if (writeTypes && func.returnAnnotation)
         {
+            if (cstNode)
+                advance(cstNode->returnSpecifierPosition);
             writer.symbol(":");
             writer.space();
 
@@ -2301,6 +2473,23 @@ struct Printer
         }
     }
 
+    void visualizeAttribute(AstAttr& attribute)
+    {
+        advance(attribute.location.begin);
+        switch (attribute.type)
+        {
+        case AstAttr::Checked:
+            writer.keyword("@checked");
+            break;
+        case AstAttr::Native:
+            writer.keyword("@native");
+            break;
+        case AstAttr::Deprecated:
+            writer.keyword("@deprecated");
+            break;
+        }
+    }
+
     void visualizeTypeAnnotation(AstType& typeAnnotation)
     {
         advance(typeAnnotation.location.begin);
@@ -2340,9 +2529,13 @@ struct Printer
         }
         else if (const auto& a = typeAnnotation.as<AstTypeFunction>())
         {
+            const auto cstNode = lookupCstNode<CstTypeFunction>(a);
+
             if (a->generics.size > 0 || a->genericPacks.size > 0)
             {
-                CommaSeparatorInserter comma(writer);
+                CommaSeparatorInserter comma(writer, cstNode ? cstNode->genericsCommaPositions.begin() : nullptr);
+                if (cstNode)
+                    advance(cstNode->openGenericsPosition);
                 writer.symbol("<");
                 for (const auto& o : a->generics)
                 {
@@ -2357,15 +2550,29 @@ struct Printer
 
                     writer.advance(o->location.begin);
                     writer.identifier(o->name.value);
+                    if (const auto* genericTypePackCstNode = lookupCstNode<CstGenericTypePack>(o))
+                        advance(genericTypePackCstNode->ellipsisPosition);
                     writer.symbol("...");
                 }
+                if (cstNode)
+                    advance(cstNode->closeGenericsPosition);
                 writer.symbol(">");
             }
 
             {
-                visualizeTypeList(a->argTypes, true);
+                visualizeNamedTypeList(
+                    a->argTypes,
+                    true,
+                    cstNode ? std::make_optional(cstNode->openArgsPosition) : std::nullopt,
+                    cstNode ? std::make_optional(cstNode->closeArgsPosition) : std::nullopt,
+                    cstNode ? cstNode->argumentsCommaPositions : Luau::AstArray<Position>{},
+                    a->argNames,
+                    cstNode ? cstNode->argumentNameColonPositions : Luau::AstArray<std::optional<Position>>{}
+                );
             }
 
+            if (cstNode)
+                advance(cstNode->returnArrowPosition);
             writer.symbol("->");
             visualizeTypeList(a->returnTypes, true);
         }
@@ -2527,14 +2734,25 @@ struct Printer
         }
         else if (const auto& a = typeAnnotation.as<AstTypeUnion>())
         {
-            if (a->types.size == 2)
+            const auto cstNode = lookupCstNode<CstTypeUnion>(a);
+
+            if (!cstNode && a->types.size == 2)
             {
                 AstType* l = a->types.data[0];
                 AstType* r = a->types.data[1];
 
-                auto lta = l->as<AstTypeReference>();
+                if (FFlag::LuauParseOptionalAsNode2)
-                if (lta && lta->name == "nil")
+                {
-                    std::swap(l, r);
+                    auto lta = l->as<AstTypeReference>();
+                    if (lta && lta->name == "nil" && !r->is<AstTypeOptional>())
+                        std::swap(l, r);
+                }
+                else
+                {
+                    auto lta = l->as<AstTypeReference>();
+                    if (lta && lta->name == "nil")
+                        std::swap(l, r);
+                }
 
                 // it's still possible that we had a (T | U) or (T | nil) and not (nil | T)
                 auto rta = r->as<AstTypeReference>();
@@ -2555,15 +2773,39 @@ struct Printer
                 }
             }
 
+            if (cstNode && cstNode->leadingPosition)
+            {
+                advance(*cstNode->leadingPosition);
+                writer.symbol("|");
+            }
+
+            size_t separatorIndex = 0;
             for (size_t i = 0; i < a->types.size; ++i)
             {
+                if (FFlag::LuauParseOptionalAsNode2)
+                {
+                    if (const auto optional = a->types.data[i]->as<AstTypeOptional>())
+                    {
+                        advance(optional->location.begin);
+                        writer.symbol("?");
+                        continue;
+                    }
+                }
+
                 if (i > 0)
                 {
-                    writer.maybeSpace(a->types.data[i]->location.begin, 2);
+                    if (cstNode && FFlag::LuauParseOptionalAsNode2)
+                    {
+                        // separatorIndex is only valid if `?` is handled as an AstTypeOptional
+                        advance(cstNode->separatorPositions.data[separatorIndex]);
+                        separatorIndex++;
+                    }
+                    else
+                        writer.maybeSpace(a->types.data[i]->location.begin, 2);
                     writer.symbol("|");
                 }
 
-                bool wrap = a->types.data[i]->as<AstTypeIntersection>() || a->types.data[i]->as<AstTypeFunction>();
+                bool wrap = !cstNode && (a->types.data[i]->as<AstTypeIntersection>() || a->types.data[i]->as<AstTypeFunction>());
 
                 if (wrap)
                     writer.symbol("(");
@@ -2576,15 +2818,27 @@ struct Printer
         }
         else if (const auto& a = typeAnnotation.as<AstTypeIntersection>())
         {
+            const auto cstNode = lookupCstNode<CstTypeIntersection>(a);
+
+            // If the sizes are equal, we know there is a leading & token
+            if (cstNode && cstNode->leadingPosition)
+            {
+                advance(*cstNode->leadingPosition);
+                writer.symbol("&");
+            }
+
             for (size_t i = 0; i < a->types.size; ++i)
             {
                 if (i > 0)
                 {
-                    writer.maybeSpace(a->types.data[i]->location.begin, 2);
+                    if (cstNode)
+                        advance(cstNode->separatorPositions.data[i - 1]);
+                    else
+                        writer.maybeSpace(a->types.data[i]->location.begin, 2);
                     writer.symbol("&");
                 }
 
-                bool wrap = a->types.data[i]->as<AstTypeUnion>() || a->types.data[i]->as<AstTypeFunction>();
+                bool wrap = !cstNode && (a->types.data[i]->as<AstTypeUnion>() || a->types.data[i]->as<AstTypeFunction>());
 
                 if (wrap)
                     writer.symbol("(");
@@ -2599,7 +2853,7 @@ struct Printer
         {
             writer.symbol("(");
             visualizeTypeAnnotation(*a->type);
-            advance(Position{a->location.end.line, a->location.end.column - 1});
+            advanceBefore(a->location.end, 1);
             writer.symbol(")");
         }
         else if (const auto& a = typeAnnotation.as<AstTypeSingletonBool>())
@@ -2633,7 +2887,7 @@ std::string toString(AstNode* node)
     StringWriter writer;
     writer.pos = node->location.begin;
 
-    if (FFlag::LuauStoreCSTData)
+    if (FFlag::LuauStoreCSTData2)
     {
         Printer printer(writer, CstNodeMap{nullptr});
         printer.writeTypes = true;
@@ -2669,7 +2923,7 @@ void dump(AstNode* node)
 std::string transpile(AstStatBlock& block, const CstNodeMap& cstNodeMap)
 {
     StringWriter writer;
-    if (FFlag::LuauStoreCSTData)
+    if (FFlag::LuauStoreCSTData2)
     {
         Printer(writer, cstNodeMap).visualizeBlock(block);
     }
@@ -2683,7 +2937,7 @@ std::string transpile(AstStatBlock& block, const CstNodeMap& cstNodeMap)
 std::string transpileWithTypes(AstStatBlock& block, const CstNodeMap& cstNodeMap)
 {
     StringWriter writer;
-    if (FFlag::LuauStoreCSTData)
+    if (FFlag::LuauStoreCSTData2)
     {
         Printer printer(writer, cstNodeMap);
         printer.writeTypes = true;

Analysis/src/TypeAttach.cpp

@@ -13,6 +13,8 @@
 
 #include <string>
 
+LUAU_FASTFLAG(LuauStoreCSTData2)
+
 static char* allocateString(Luau::Allocator& allocator, std::string_view contents)
 {
     char* result = (char*)allocator.allocate(contents.size() + 1);
@@ -305,7 +307,8 @@ public:
             std::optional<AstArgumentName>* arg = &argNames.data[i++];
 
             if (el)
-                new (arg) std::optional<AstArgumentName>(AstArgumentName(AstName(el->name.c_str()), el->location));
+                new (arg)
+                    std::optional<AstArgumentName>(AstArgumentName(AstName(el->name.c_str()), FFlag::LuauStoreCSTData2 ? Location() : el->location));
             else
                 new (arg) std::optional<AstArgumentName>();
         }

Analysis/src/TypeChecker2.cpp

@@ -26,10 +26,14 @@
 #include "Luau/VisitType.h"
 
 #include <algorithm>
+#include <sstream>
 
 LUAU_FASTFLAG(DebugLuauMagicTypes)
 
 LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
+LUAU_FASTFLAGVARIABLE(LuauImproveTypePathsInErrors)
+LUAU_FASTFLAG(LuauUserTypeFunTypecheck)
+LUAU_FASTFLAGVARIABLE(LuauTypeCheckerAcceptNumberConcats)
 
 namespace Luau
 {
@@ -1201,7 +1205,8 @@ void TypeChecker2::visit(AstStatTypeAlias* stat)
 
 void TypeChecker2::visit(AstStatTypeFunction* stat)
 {
-    // TODO: add type checking for user-defined type functions
+    if (FFlag::LuauUserTypeFunTypecheck)
+        visit(stat->body);
 }
 
 void TypeChecker2::visit(AstTypeList types)
@@ -2225,10 +2230,21 @@ TypeId TypeChecker2::visit(AstExprBinary* expr, AstNode* overrideKey)
 
         return builtinTypes->numberType;
     case AstExprBinary::Op::Concat:
-        testIsSubtype(leftType, builtinTypes->stringType, expr->left->location);
+    {
-        testIsSubtype(rightType, builtinTypes->stringType, expr->right->location);
+        if (FFlag::LuauTypeCheckerAcceptNumberConcats)
+        {
+            const TypeId numberOrString = module->internalTypes.addType(UnionType{{builtinTypes->numberType, builtinTypes->stringType}});
+            testIsSubtype(leftType, numberOrString, expr->left->location);
+            testIsSubtype(rightType, numberOrString, expr->right->location);
+        }
+        else
+        {
+            testIsSubtype(leftType, builtinTypes->stringType, expr->left->location);
+            testIsSubtype(rightType, builtinTypes->stringType, expr->right->location);
+        }
 
         return builtinTypes->stringType;
+    }
     case AstExprBinary::Op::CompareGe:
     case AstExprBinary::Op::CompareGt:
     case AstExprBinary::Op::CompareLe:
@@ -2701,20 +2717,61 @@ Reasonings TypeChecker2::explainReasonings_(TID subTy, TID superTy, Location loc
         if (!subLeafTy && !superLeafTy && !subLeafTp && !superLeafTp)
             ice->ice("Subtyping test returned a reasoning where one path ends at a type and the other ends at a pack.", location);
 
-        std::string relation = "a subtype of";
+        if (FFlag::LuauImproveTypePathsInErrors)
-        if (reasoning.variance == SubtypingVariance::Invariant)
+        {
-            relation = "exactly";
+            std::string relation = "a subtype of";
-        else if (reasoning.variance == SubtypingVariance::Contravariant)
+            if (reasoning.variance == SubtypingVariance::Invariant)
-            relation = "a supertype of";
+                relation = "exactly";
+            else if (reasoning.variance == SubtypingVariance::Contravariant)
+                relation = "a supertype of";
 
-        std::string reason;
+            std::string subLeafAsString = toString(subLeaf);
-        if (reasoning.subPath == reasoning.superPath)
+            // if the string is empty, it must be an empty type pack
-            reason = "at " + toString(reasoning.subPath) + ", " + toString(subLeaf) + " is not " + relation + " " + toString(superLeaf);
+            if (subLeafAsString.empty())
+                subLeafAsString = "()";
+
+            std::string superLeafAsString = toString(superLeaf);
+            // if the string is empty, it must be an empty type pack
+            if (superLeafAsString.empty())
+                superLeafAsString = "()";
+
+            std::stringstream baseReasonBuilder;
+            baseReasonBuilder << "`" << subLeafAsString << "` is not " << relation << " `" << superLeafAsString << "`";
+            std::string baseReason = baseReasonBuilder.str();
+
+            std::stringstream reason;
+
+            if (reasoning.subPath == reasoning.superPath)
+                reason << toStringHuman(reasoning.subPath) << "`" << subLeafAsString << "` in the former type and `" << superLeafAsString
+                       << "` in the latter type, and " << baseReason;
+            else if (!reasoning.subPath.empty() && !reasoning.superPath.empty())
+                reason << toStringHuman(reasoning.subPath) << "`" << subLeafAsString << "` and " << toStringHuman(reasoning.superPath) << "`"
+                       << superLeafAsString << "`, and " << baseReason;
+            else if (!reasoning.subPath.empty())
+                reason << toStringHuman(reasoning.subPath) << "`" << subLeafAsString << "`, which is not " << relation << " `" << superLeafAsString
+                       << "`";
+            else
+                reason << toStringHuman(reasoning.superPath) << "`" << superLeafAsString << "`, and " << baseReason;
+
+            reasons.push_back(reason.str());
+        }
         else
-            reason = "type " + toString(subTy) + toString(reasoning.subPath, /* prefixDot */ true) + " (" + toString(subLeaf) + ") is not " +
+        {
-                     relation + " " + toString(superTy) + toString(reasoning.superPath, /* prefixDot */ true) + " (" + toString(superLeaf) + ")";
+            std::string relation = "a subtype of";
+            if (reasoning.variance == SubtypingVariance::Invariant)
+                relation = "exactly";
+            else if (reasoning.variance == SubtypingVariance::Contravariant)
+                relation = "a supertype of";
 
-        reasons.push_back(reason);
+            std::string reason;
+            if (reasoning.subPath == reasoning.superPath)
+                reason = "at " + toString(reasoning.subPath) + ", " + toString(subLeaf) + " is not " + relation + " " + toString(superLeaf);
+            else
+                reason = "type " + toString(subTy) + toString(reasoning.subPath, /* prefixDot */ true) + " (" + toString(subLeaf) + ") is not " +
+                         relation + " " + toString(superTy) + toString(reasoning.superPath, /* prefixDot */ true) + " (" + toString(superLeaf) + ")";
+
+            reasons.push_back(reason);
+        }
 
         // if we haven't already proved this isn't suppressing, we have to keep checking.
         if (suppressed)

Analysis/src/TypeFunctionRuntime.cpp

@@ -13,11 +13,7 @@
 #include <set>
 #include <vector>
 
-LUAU_FASTFLAGVARIABLE(LuauTypeFunFixHydratedClasses)
 LUAU_DYNAMIC_FASTINT(LuauTypeFunctionSerdeIterationLimit)
-LUAU_FASTFLAGVARIABLE(LuauTypeFunSingletonEquality)
-LUAU_FASTFLAGVARIABLE(LuauUserTypeFunTypeofReturnsType)
-LUAU_FASTFLAGVARIABLE(LuauTypeFunPrintFix)
 LUAU_FASTFLAGVARIABLE(LuauTypeFunReadWriteParents)
 
 namespace Luau
@@ -1617,11 +1613,8 @@ void registerTypeUserData(lua_State* L)
     // Create and register metatable for type userdata
     luaL_newmetatable(L, "type");
 
-    if (FFlag::LuauUserTypeFunTypeofReturnsType)
+    lua_pushstring(L, "type");
-    {
+    lua_setfield(L, -2, "__type");
-        lua_pushstring(L, "type");
-        lua_setfield(L, -2, "__type");
-    }
 
     // Protect metatable from being changed
     lua_pushstring(L, "The metatable is locked");
@@ -1662,10 +1655,7 @@ static int print(lua_State* L)
         const char* s = luaL_tolstring(L, i, &l); // convert to string using __tostring et al
         if (i > 1)
         {
-            if (FFlag::LuauTypeFunPrintFix)
+            result.append(1, '\t');
-                result.append(1, '\t');
-            else
-                result.append('\t', 1);
         }
         result.append(s, l);
         lua_pop(L, 1);
@@ -1758,14 +1748,14 @@ bool areEqual(SeenSet& seen, const TypeFunctionSingletonType& lhs, const TypeFun
 
     {
         const TypeFunctionBooleanSingleton* lp = get<TypeFunctionBooleanSingleton>(&lhs);
-        const TypeFunctionBooleanSingleton* rp = get<TypeFunctionBooleanSingleton>(FFlag::LuauTypeFunSingletonEquality ? &rhs : &lhs);
+        const TypeFunctionBooleanSingleton* rp = get<TypeFunctionBooleanSingleton>(&rhs);
         if (lp && rp)
             return lp->value == rp->value;
     }
 
     {
         const TypeFunctionStringSingleton* lp = get<TypeFunctionStringSingleton>(&lhs);
-        const TypeFunctionStringSingleton* rp = get<TypeFunctionStringSingleton>(FFlag::LuauTypeFunSingletonEquality ? &rhs : &lhs);
+        const TypeFunctionStringSingleton* rp = get<TypeFunctionStringSingleton>(&rhs);
         if (lp && rp)
             return lp->value == rp->value;
     }
@@ -1918,10 +1908,7 @@ bool areEqual(SeenSet& seen, const TypeFunctionClassType& lhs, const TypeFunctio
     if (seenSetContains(seen, &lhs, &rhs))
         return true;
 
-    if (FFlag::LuauTypeFunFixHydratedClasses)
+    return lhs.classTy == rhs.classTy;
-        return lhs.classTy == rhs.classTy;
-    else
-        return lhs.name_DEPRECATED == rhs.name_DEPRECATED;
 }
 
 bool areEqual(SeenSet& seen, const TypeFunctionType& lhs, const TypeFunctionType& rhs)

Analysis/src/TypeFunctionRuntimeBuilder.cpp

@@ -19,7 +19,6 @@
 // used to control the recursion limit of any operations done by user-defined type functions
 // currently, controls serialization, deserialization, and `type.copy`
 LUAU_DYNAMIC_FASTINTVARIABLE(LuauTypeFunctionSerdeIterationLimit, 100'000);
-LUAU_FASTFLAG(LuauTypeFunFixHydratedClasses)
 LUAU_FASTFLAG(LuauTypeFunReadWriteParents)
 
 namespace Luau
@@ -209,19 +208,11 @@ private:
         }
         else if (auto c = get<ClassType>(ty))
         {
-            if (FFlag::LuauTypeFunFixHydratedClasses)
+            // Since there aren't any new class types being created in type functions, we will deserialize by using a direct reference to the original
-            {
+            // class
-                // Since there aren't any new class types being created in type functions, we will deserialize by using a direct reference to the
+            target = typeFunctionRuntime->typeArena.allocate(
-                // original class
+                TypeFunctionClassType{{}, std::nullopt, std::nullopt, std::nullopt, std::nullopt, std::nullopt, ty}
-                target = typeFunctionRuntime->typeArena.allocate(TypeFunctionClassType{{}, std::nullopt, std::nullopt, std::nullopt, std::nullopt, std::nullopt, ty});
+            );
-            }
-            else
-            {
-                state->classesSerialized_DEPRECATED[c->name] = ty;
-                target = typeFunctionRuntime->typeArena.allocate(
-                    TypeFunctionClassType{{}, std::nullopt, std::nullopt, std::nullopt, std::nullopt, std::nullopt, /* classTy */ nullptr, c->name}
-                );
-            }
         }
         else if (auto g = get<GenericType>(ty))
         {
@@ -713,17 +704,7 @@ private:
         }
         else if (auto c = get<TypeFunctionClassType>(ty))
         {
-            if (FFlag::LuauTypeFunFixHydratedClasses)
+            target = c->classTy;
-            {
-                target = c->classTy;
-            }
-            else
-            {
-                if (auto result = state->classesSerialized_DEPRECATED.find(c->name_DEPRECATED))
-                    target = *result;
-                else
-                    state->ctx->ice->ice("Deserializing user defined type function arguments: mysterious class type is being deserialized");
-            }
         }
         else if (auto g = get<TypeFunctionGenericType>(ty))
         {

Analysis/src/TypeInfer.cpp

@@ -5721,6 +5721,10 @@ TypeId TypeChecker::resolveTypeWorker(const ScopePtr& scope, const AstType& anno
         TypeId ty = checkExpr(scope, *typeOf->expr).type;
         return ty;
     }
+    else if (annotation.is<AstTypeOptional>())
+    {
+        return builtinTypes->nilType;
+    }
     else if (const auto& un = annotation.as<AstTypeUnion>())
     {
         if (FFlag::LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)

Analysis/src/TypePath.cpp

@@ -14,7 +14,8 @@
 #include <type_traits>
 
 LUAU_FASTFLAG(LuauSolverV2);
-LUAU_FASTFLAGVARIABLE(LuauDisableNewSolverAssertsInMixedMode);
+LUAU_FASTFLAGVARIABLE(LuauDisableNewSolverAssertsInMixedMode)
+
 // Maximum number of steps to follow when traversing a path. May not always
 // equate to the number of components in a path, depending on the traversal
 // logic.
@@ -638,6 +639,247 @@ std::string toString(const TypePath::Path& path, bool prefixDot)
     return result.str();
 }
 
+std::string toStringHuman(const TypePath::Path& path)
+{
+    LUAU_ASSERT(FFlag::LuauSolverV2);
+
+    enum class State
+    {
+        Initial,
+        Normal,
+        Property,
+        PendingIs,
+        PendingAs,
+        PendingWhich,
+    };
+
+    std::stringstream result;
+    State state = State::Initial;
+    bool last = false;
+
+    auto strComponent = [&](auto&& c)
+    {
+        using T = std::decay_t<decltype(c)>;
+        if constexpr (std::is_same_v<T, TypePath::Property>)
+        {
+            if (state == State::PendingIs)
+                result << ", ";
+
+            switch (state)
+            {
+            case State::Initial:
+            case State::PendingIs:
+                if (c.isRead)
+                    result << "accessing `";
+                else
+                    result << "writing to `";
+                break;
+            case State::Property:
+                // if the previous state was a property, then we're doing a sequence of indexing
+                result << '.';
+                break;
+            default:
+                break;
+            }
+
+            result << c.name;
+
+            state = State::Property;
+        }
+        else if constexpr (std::is_same_v<T, TypePath::Index>)
+        {
+            size_t humanIndex = c.index + 1;
+
+            if (state == State::Initial && !last)
+                result << "in" << ' ';
+            else if (state == State::PendingIs)
+                result << ' ' << "has" << ' ';
+            else if (state == State::Property)
+                result << '`' << ' ' << "has" << ' ';
+
+            result << "the " << humanIndex;
+            switch (humanIndex)
+            {
+            case 1:
+                result << "st";
+                break;
+            case 2:
+                result << "nd";
+                break;
+            case 3:
+                result << "rd";
+                break;
+            default:
+                result << "th";
+            }
+
+            switch (c.variant)
+            {
+            case TypePath::Index::Variant::Pack:
+                result << ' ' << "entry in the type pack";
+                break;
+            case TypePath::Index::Variant::Union:
+                result << ' ' << "component of the union";
+                break;
+            case TypePath::Index::Variant::Intersection:
+                result << ' ' << "component of the intersection";
+                break;
+            }
+
+            if (state == State::PendingWhich)
+                result << ' ' << "which";
+
+            if (state == State::PendingIs || state == State::Property)
+                state = State::PendingAs;
+            else
+                state = State::PendingIs;
+        }
+        else if constexpr (std::is_same_v<T, TypePath::TypeField>)
+        {
+            if (state == State::Initial && !last)
+                result << "in" << ' ';
+            else if (state == State::PendingIs)
+                result << ", ";
+            else if (state == State::Property)
+                result << '`' << ' ' << "has" << ' ';
+
+            switch (c)
+            {
+            case TypePath::TypeField::Table:
+                result << "the table portion";
+                if (state == State::Property)
+                    state = State::PendingAs;
+                else
+                    state = State::PendingIs;
+                break;
+            case TypePath::TypeField::Metatable:
+                result << "the metatable portion";
+                if (state == State::Property)
+                    state = State::PendingAs;
+                else
+                    state = State::PendingIs;
+                break;
+            case TypePath::TypeField::LowerBound:
+                result << "the lower bound of" << ' ';
+                state = State::Normal;
+                break;
+            case TypePath::TypeField::UpperBound:
+                result << "the upper bound of" << ' ';
+                state = State::Normal;
+                break;
+            case TypePath::TypeField::IndexLookup:
+                result << "the index type";
+                if (state == State::Property)
+                    state = State::PendingAs;
+                else
+                    state = State::PendingIs;
+                break;
+            case TypePath::TypeField::IndexResult:
+                result << "the result of indexing";
+                if (state == State::Property)
+                    state = State::PendingAs;
+                else
+                    state = State::PendingIs;
+                break;
+            case TypePath::TypeField::Negated:
+                result << "the negation" << ' ';
+                state = State::Normal;
+                break;
+            case TypePath::TypeField::Variadic:
+                result << "the variadic" << ' ';
+                state = State::Normal;
+                break;
+            }
+        }
+        else if constexpr (std::is_same_v<T, TypePath::PackField>)
+        {
+            if (state == State::PendingIs)
+                result << ", ";
+            else if (state == State::Property)
+                result << "`, ";
+
+            switch (c)
+            {
+            case TypePath::PackField::Arguments:
+                if (state == State::Initial)
+                    result << "it" << ' ';
+                else if (state == State::PendingIs)
+                    result << "the function" << ' ';
+
+                result << "takes";
+                break;
+            case TypePath::PackField::Returns:
+                if (state == State::Initial)
+                    result << "it" << ' ';
+                else if (state == State::PendingIs)
+                    result << "the function" << ' ';
+
+                result << "returns";
+                break;
+            case TypePath::PackField::Tail:
+                if (state == State::Initial)
+                    result << "it has" << ' ';
+                result << "a tail of";
+                break;
+            }
+
+            if (state == State::PendingIs)
+            {
+                result << ' ';
+                state = State::PendingWhich;
+            }
+            else
+            {
+                result << ' ';
+                state = State::Normal;
+            }
+        }
+        else if constexpr (std::is_same_v<T, TypePath::Reduction>)
+        {
+            if (state == State::Initial)
+                result << "it" << ' ';
+            result << "reduces to" << ' ';
+            state = State::Normal;
+        }
+        else
+        {
+            static_assert(always_false_v<T>, "Unhandled Component variant");
+        }
+    };
+
+    size_t count = 0;
+
+    for (const TypePath::Component& component : path.components)
+    {
+        count++;
+        if (count == path.components.size())
+            last = true;
+
+        Luau::visit(strComponent, component);
+    }
+
+    switch (state)
+    {
+    case State::Property:
+        result << "` results in ";
+        break;
+    case State::PendingWhich:
+        // pending `which` becomes `is` if it's at the end
+        result << "is" << ' ';
+        break;
+    case State::PendingIs:
+        result << ' ' << "is" << ' ';
+        break;
+    case State::PendingAs:
+        result << ' ' << "as" << ' ';
+        break;
+    default:
+        break;
+    }
+
+    return result.str();
+}
+
 static bool traverse(TraversalState& state, const Path& path)
 {
     auto step = [&state](auto&& c)

Analysis/src/TypedAllocator.cpp

@@ -24,6 +24,7 @@ const size_t kPageSize = sysconf(_SC_PAGESIZE);
 #endif
 #endif
 
+#include <stdint.h>
 #include <stdlib.h>
 
 LUAU_FASTFLAG(DebugLuauFreezeArena)

Analysis/src/Unifier2.cpp

@@ -19,6 +19,7 @@
 
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
 LUAU_FASTFLAGVARIABLE(LuauUnifyMetatableWithAny)
+LUAU_FASTFLAG(LuauExtraFollows)
 
 namespace Luau
 {
@@ -282,7 +283,7 @@ bool Unifier2::unifyFreeWithType(TypeId subTy, TypeId superTy)
     if (superArgTail)
         return doDefault();
 
-    const IntersectionType* upperBoundIntersection = get<IntersectionType>(subFree->upperBound);
+    const IntersectionType* upperBoundIntersection = get<IntersectionType>(FFlag::LuauExtraFollows ? upperBound : subFree->upperBound);
     if (!upperBoundIntersection)
         return doDefault();
 
@@ -649,38 +650,33 @@ struct FreeTypeSearcher : TypeVisitor
     {
     }
 
-    enum Polarity
+    Polarity polarity = Polarity::Positive;
-    {
-        Positive,
-        Negative,
-        Both,
-    };
-
-    Polarity polarity = Positive;
 
     void flip()
     {
         switch (polarity)
         {
-        case Positive:
+        case Polarity::Positive:
-            polarity = Negative;
+            polarity = Polarity::Negative;
             break;
-        case Negative:
+        case Polarity::Negative:
-            polarity = Positive;
+            polarity = Polarity::Positive;
             break;
-        case Both:
+        case Polarity::Mixed:
             break;
+        default:
+            LUAU_ASSERT(!"Unreachable");
         }
     }
 
     DenseHashSet<const void*> seenPositive{nullptr};
     DenseHashSet<const void*> seenNegative{nullptr};
 
-    bool seenWithPolarity(const void* ty)
+    bool seenWithCurrentPolarity(const void* ty)
     {
         switch (polarity)
         {
-        case Positive:
+        case Polarity::Positive:
         {
             if (seenPositive.contains(ty))
                 return true;
@@ -688,7 +684,7 @@ struct FreeTypeSearcher : TypeVisitor
             seenPositive.insert(ty);
             return false;
         }
-        case Negative:
+        case Polarity::Negative:
         {
             if (seenNegative.contains(ty))
                 return true;
@@ -696,7 +692,7 @@ struct FreeTypeSearcher : TypeVisitor
             seenNegative.insert(ty);
             return false;
         }
-        case Both:
+        case Polarity::Mixed:
         {
             if (seenPositive.contains(ty) && seenNegative.contains(ty))
                 return true;
@@ -705,6 +701,8 @@ struct FreeTypeSearcher : TypeVisitor
             seenNegative.insert(ty);
             return false;
         }
+        default:
+            LUAU_ASSERT(!"Unreachable");
         }
 
         return false;
@@ -718,7 +716,7 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypeId ty) override
     {
-        if (seenWithPolarity(ty))
+        if (seenWithCurrentPolarity(ty))
             return false;
 
         LUAU_ASSERT(ty);
@@ -727,7 +725,7 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypeId ty, const FreeType& ft) override
     {
-        if (seenWithPolarity(ty))
+        if (seenWithCurrentPolarity(ty))
             return false;
 
         if (!subsumes(scope, ft.scope))
@@ -735,16 +733,18 @@ struct FreeTypeSearcher : TypeVisitor
 
         switch (polarity)
         {
-        case Positive:
+        case Polarity::Positive:
             positiveTypes[ty]++;
             break;
-        case Negative:
+        case Polarity::Negative:
             negativeTypes[ty]++;
             break;
-        case Both:
+        case Polarity::Mixed:
             positiveTypes[ty]++;
             negativeTypes[ty]++;
             break;
+        default:
+            LUAU_ASSERT(!"Unreachable");
         }
 
         return true;
@@ -752,23 +752,25 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypeId ty, const TableType& tt) override
     {
-        if (seenWithPolarity(ty))
+        if (seenWithCurrentPolarity(ty))
             return false;
 
         if ((tt.state == TableState::Free || tt.state == TableState::Unsealed) && subsumes(scope, tt.scope))
         {
             switch (polarity)
             {
-            case Positive:
+            case Polarity::Positive:
                 positiveTypes[ty]++;
                 break;
-            case Negative:
+            case Polarity::Negative:
                 negativeTypes[ty]++;
                 break;
-            case Both:
+            case Polarity::Mixed:
                 positiveTypes[ty]++;
                 negativeTypes[ty]++;
                 break;
+            default:
+                LUAU_ASSERT(!"Unreachable");
             }
         }
 
@@ -781,7 +783,7 @@ struct FreeTypeSearcher : TypeVisitor
                 LUAU_ASSERT(prop.isShared());
 
                 Polarity p = polarity;
-                polarity = Both;
+                polarity = Polarity::Mixed;
                 traverse(prop.type());
                 polarity = p;
             }
@@ -798,7 +800,7 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypeId ty, const FunctionType& ft) override
     {
-        if (seenWithPolarity(ty))
+        if (seenWithCurrentPolarity(ty))
             return false;
 
         flip();
@@ -817,7 +819,7 @@ struct FreeTypeSearcher : TypeVisitor
 
     bool visit(TypePackId tp, const FreeTypePack& ftp) override
     {
-        if (seenWithPolarity(tp))
+        if (seenWithCurrentPolarity(tp))
             return false;
 
         if (!subsumes(scope, ftp.scope))
@@ -825,16 +827,18 @@ struct FreeTypeSearcher : TypeVisitor
 
         switch (polarity)
         {
-        case Positive:
+        case Polarity::Positive:
             positiveTypes[tp]++;
             break;
-        case Negative:
+        case Polarity::Negative:
             negativeTypes[tp]++;
             break;
-        case Both:
+        case Polarity::Mixed:
             positiveTypes[tp]++;
             negativeTypes[tp]++;
             break;
+        default:
+            LUAU_ASSERT(!"Unreachable");
         }
 
         return true;

Ast/include/Luau/Ast.h

@@ -194,6 +194,7 @@ public:
     {
         Checked,
         Native,
+        Deprecated,
     };
 
     AstAttr(const Location& location, Type type);
@@ -453,6 +454,7 @@ public:
     void visit(AstVisitor* visitor) override;
 
     bool hasNativeAttribute() const;
+    bool hasAttribute(AstAttr::Type attributeType) const;
 
     AstArray<AstAttr*> attributes;
     AstArray<AstGenericType*> generics;
@@ -890,14 +892,22 @@ class AstStatTypeFunction : public AstStat
 public:
     LUAU_RTTI(AstStatTypeFunction);
 
-    AstStatTypeFunction(const Location& location, const AstName& name, const Location& nameLocation, AstExprFunction* body, bool exported);
+    AstStatTypeFunction(
+        const Location& location,
+        const AstName& name,
+        const Location& nameLocation,
+        AstExprFunction* body,
+        bool exported,
+        bool hasErrors
+    );
 
     void visit(AstVisitor* visitor) override;
 
     AstName name;
     Location nameLocation;
-    AstExprFunction* body;
+    AstExprFunction* body = nullptr;
-    bool exported;
+    bool exported = false;
+    bool hasErrors = false;
 };
 
 class AstStatDeclareGlobal : public AstStat
@@ -950,6 +960,7 @@ public:
     void visit(AstVisitor* visitor) override;
 
     bool isCheckedFunction() const;
+    bool hasAttribute(AstAttr::Type attributeType) const;
 
     AstArray<AstAttr*> attributes;
     AstName name;
@@ -1106,6 +1117,7 @@ public:
     void visit(AstVisitor* visitor) override;
 
     bool isCheckedFunction() const;
+    bool hasAttribute(AstAttr::Type attributeType) const;
 
     AstArray<AstAttr*> attributes;
     AstArray<AstGenericType*> generics;
@@ -1127,6 +1139,16 @@ public:
     AstExpr* expr;
 };
 
+class AstTypeOptional : public AstType
+{
+public:
+    LUAU_RTTI(AstTypeOptional)
+
+    AstTypeOptional(const Location& location);
+
+    void visit(AstVisitor* visitor) override;
+};
+
 class AstTypeUnion : public AstType
 {
 public:
@@ -1449,6 +1471,10 @@ public:
     {
         return visit(static_cast<AstStat*>(node));
     }
+    virtual bool visit(class AstStatTypeFunction* node)
+    {
+        return visit(static_cast<AstStat*>(node));
+    }
     virtual bool visit(class AstStatDeclareFunction* node)
     {
         return visit(static_cast<AstStat*>(node));
@@ -1488,6 +1514,10 @@ public:
     {
         return visit(static_cast<AstType*>(node));
     }
+    virtual bool visit(class AstTypeOptional* node)
+    {
+        return visit(static_cast<AstType*>(node));
+    }
     virtual bool visit(class AstTypeUnion* node)
     {
         return visit(static_cast<AstType*>(node));

Ast/include/Luau/Cst.h

@@ -105,6 +105,21 @@ public:
     Position closeBracketPosition;
 };
 
+class CstExprFunction : public CstNode
+{
+public:
+    LUAU_CST_RTTI(CstExprFunction)
+
+    CstExprFunction();
+
+    Position functionKeywordPosition{0, 0};
+    Position openGenericsPosition{0,0};
+    AstArray<Position> genericsCommaPositions;
+    Position closeGenericsPosition{0,0};
+    AstArray<Position> argsCommaPositions;
+    Position returnSpecifierPosition{0,0};
+};
+
 class CstExprTable : public CstNode
 {
 public:
@@ -260,13 +275,24 @@ public:
     Position opPosition;
 };
 
+class CstStatFunction : public CstNode
+{
+public:
+    LUAU_CST_RTTI(CstStatFunction)
+
+    explicit CstStatFunction(Position functionKeywordPosition);
+
+    Position functionKeywordPosition;
+};
+
 class CstStatLocalFunction : public CstNode
 {
 public:
     LUAU_CST_RTTI(CstStatLocalFunction)
 
-    explicit CstStatLocalFunction(Position functionKeywordPosition);
+    explicit CstStatLocalFunction(Position localKeywordPosition, Position functionKeywordPosition);
 
+    Position localKeywordPosition;
     Position functionKeywordPosition;
 };
 
@@ -311,6 +337,17 @@ public:
     Position equalsPosition;
 };
 
+class CstStatTypeFunction : public CstNode
+{
+public:
+    LUAU_CST_RTTI(CstStatTypeFunction)
+
+    CstStatTypeFunction(Position typeKeywordPosition, Position functionKeywordPosition);
+
+    Position typeKeywordPosition;
+    Position functionKeywordPosition;
+};
+
 class CstTypeReference : public CstNode
 {
 public:
@@ -359,6 +396,32 @@ public:
     bool isArray = false;
 };
 
+class CstTypeFunction : public CstNode
+{
+public:
+    LUAU_CST_RTTI(CstTypeFunction)
+
+    CstTypeFunction(
+        Position openGenericsPosition,
+        AstArray<Position> genericsCommaPositions,
+        Position closeGenericsPosition,
+        Position openArgsPosition,
+        AstArray<std::optional<Position>> argumentNameColonPositions,
+        AstArray<Position> argumentsCommaPositions,
+        Position closeArgsPosition,
+        Position returnArrowPosition
+    );
+
+    Position openGenericsPosition;
+    AstArray<Position> genericsCommaPositions;
+    Position closeGenericsPosition;
+    Position openArgsPosition;
+    AstArray<std::optional<Position>> argumentNameColonPositions;
+    AstArray<Position> argumentsCommaPositions;
+    Position closeArgsPosition;
+    Position returnArrowPosition;
+};
+
 class CstTypeTypeof : public CstNode
 {
 public:
@@ -370,6 +433,28 @@ public:
     Position closePosition;
 };
 
+class CstTypeUnion : public CstNode
+{
+public:
+    LUAU_CST_RTTI(CstTypeUnion)
+
+    CstTypeUnion(std::optional<Position> leadingPosition, AstArray<Position> separatorPositions);
+
+    std::optional<Position> leadingPosition;
+    AstArray<Position> separatorPositions;
+};
+
+class CstTypeIntersection : public CstNode
+{
+public:
+    LUAU_CST_RTTI(CstTypeIntersection)
+
+    explicit CstTypeIntersection(std::optional<Position> leadingPosition, AstArray<Position> separatorPositions);
+
+    std::optional<Position> leadingPosition;
+    AstArray<Position> separatorPositions;
+};
+
 class CstTypeSingletonString : public CstNode
 {
 public:
@@ -382,4 +467,26 @@ public:
     unsigned int blockDepth;
 };
 
+class CstTypePackExplicit : public CstNode
+{
+public:
+    LUAU_CST_RTTI(CstTypePackExplicit)
+
+    CstTypePackExplicit(Position openParenthesesPosition, Position closeParenthesesPosition, AstArray<Position> commaPositions);
+
+    Position openParenthesesPosition;
+    Position closeParenthesesPosition;
+    AstArray<Position> commaPositions;
+};
+
+class CstTypePackGeneric : public CstNode
+{
+public:
+    LUAU_CST_RTTI(CstTypePackGeneric)
+
+    explicit CstTypePackGeneric(Position ellipsisPosition);
+
+    Position ellipsisPosition;
+};
+
 } // namespace Luau

Ast/include/Luau/Parser.h

@@ -125,7 +125,7 @@ private:
     AstStat* parseFor();
 
     // funcname ::= Name {`.' Name} [`:' Name]
-    AstExpr* parseFunctionName(Location start_DEPRECATED, bool& hasself, AstName& debugname);
+    AstExpr* parseFunctionName(bool& hasself, AstName& debugname);
 
     // function funcname funcbody
     LUAU_FORCEINLINE AstStat* parseFunctionStat(const AstArray<AstAttr*>& attributes = {nullptr, 0});
@@ -155,9 +155,11 @@ private:
     AstStat* parseTypeAlias(const Location& start, bool exported, Position typeKeywordPosition);
 
     // type function Name ... end
-    AstStat* parseTypeFunction(const Location& start, bool exported);
+    AstStat* parseTypeFunction(const Location& start, bool exported, Position typeKeywordPosition);
+
+    AstDeclaredClassProp parseDeclaredClassMethod(const AstArray<AstAttr*>& attributes);
+    AstDeclaredClassProp parseDeclaredClassMethod_DEPRECATED();
 
-    AstDeclaredClassProp parseDeclaredClassMethod();
 
     // `declare global' Name: Type |
     // `declare function' Name`(' [parlist] `)' [`:` Type]
@@ -192,7 +194,8 @@ private:
     std::tuple<bool, Location, AstTypePack*> parseBindingList(
         TempVector<Binding>& result,
         bool allowDot3 = false,
-        TempVector<Position>* commaPositions = nullptr
+        AstArray<Position>* commaPositions = nullptr,
+        std::optional<Position> initialCommaPosition = std::nullopt
     );
 
     AstType* parseOptionalType();
@@ -209,9 +212,14 @@ private:
     //      |   `(' [TypeList] `)' `->` ReturnType
 
     // Returns the variadic annotation, if it exists.
-    AstTypePack* parseTypeList(TempVector<AstType*>& result, TempVector<std::optional<AstArgumentName>>& resultNames);
+    AstTypePack* parseTypeList(
+        TempVector<AstType*>& result,
+        TempVector<std::optional<AstArgumentName>>& resultNames,
+        TempVector<Position>* commaPositions = nullptr,
+        TempVector<std::optional<Position>>* nameColonPositions = nullptr
+    );
 
-    std::optional<AstTypeList> parseOptionalReturnType();
+    std::optional<AstTypeList> parseOptionalReturnType(Position* returnSpecifierPosition = nullptr);
     std::pair<Location, AstTypeList> parseReturnType();
 
     struct TableIndexerResult
@@ -222,9 +230,9 @@ private:
         Position colonPosition;
     };
 
-    TableIndexerResult parseTableIndexer(AstTableAccess access, std::optional<Location> accessLocation);
+    TableIndexerResult parseTableIndexer(AstTableAccess access, std::optional<Location> accessLocation, Lexeme begin);
-    // Remove with FFlagLuauStoreCSTData
+    // Remove with FFlagLuauStoreCSTData2
-    AstTableIndexer* parseTableIndexer_DEPRECATED(AstTableAccess access, std::optional<Location> accessLocation);
+    AstTableIndexer* parseTableIndexer_DEPRECATED(AstTableAccess access, std::optional<Location> accessLocation, Lexeme begin);
 
     AstTypeOrPack parseFunctionType(bool allowPack, const AstArray<AstAttr*>& attributes);
     AstType* parseFunctionTypeTail(
@@ -305,7 +313,7 @@ private:
     std::pair<AstArray<AstGenericType*>, AstArray<AstGenericTypePack*>> parseGenericTypeList(
         bool withDefaultValues,
         Position* openPosition = nullptr,
-        TempVector<Position>* commaPositions = nullptr,
+        AstArray<Position>* commaPositions = nullptr,
         Position* closePosition = nullptr
     );
 
@@ -491,6 +499,7 @@ private:
     std::vector<AstGenericTypePack*> scratchGenericTypePacks;
     std::vector<std::optional<AstArgumentName>> scratchOptArgName;
     std::vector<Position> scratchPosition;
+    std::vector<std::optional<Position>> scratchOptPosition;
     std::string scratchData;
 
     CstNodeMap cstNodeMap;

Ast/src/Ast.cpp

@@ -3,9 +3,24 @@
 
 #include "Luau/Common.h"
 
+LUAU_FASTFLAG(LuauDeprecatedAttribute);
+
 namespace Luau
 {
 
+static bool hasAttributeInArray(const AstArray<AstAttr*> attributes, AstAttr::Type attributeType)
+{
+    LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+
+    for (const auto attribute : attributes)
+    {
+        if (attribute->type == attributeType)
+            return true;
+    }
+
+    return false;
+}
+
 static void visitTypeList(AstVisitor* visitor, const AstTypeList& list)
 {
     for (AstType* ty : list.types)
@@ -277,6 +292,13 @@ bool AstExprFunction::hasNativeAttribute() const
     return false;
 }
 
+bool AstExprFunction::hasAttribute(const AstAttr::Type attributeType) const
+{
+    LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+
+    return hasAttributeInArray(attributes, attributeType);
+}
+
 AstExprTable::AstExprTable(const Location& location, const AstArray<Item>& items)
     : AstExpr(ClassIndex(), location)
     , items(items)
@@ -791,13 +813,15 @@ AstStatTypeFunction::AstStatTypeFunction(
     const AstName& name,
     const Location& nameLocation,
     AstExprFunction* body,
-    bool exported
+    bool exported,
+    bool hasErrors
 )
     : AstStat(ClassIndex(), location)
     , name(name)
     , nameLocation(nameLocation)
     , body(body)
     , exported(exported)
+    , hasErrors(hasErrors)
 {
 }
 
@@ -894,6 +918,13 @@ bool AstStatDeclareFunction::isCheckedFunction() const
     return false;
 }
 
+bool AstStatDeclareFunction::hasAttribute(AstAttr::Type attributeType) const
+{
+    LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+
+    return hasAttributeInArray(attributes, attributeType);
+}
+
 AstStatDeclareClass::AstStatDeclareClass(
     const Location& location,
     const AstName& name,
@@ -1057,6 +1088,13 @@ bool AstTypeFunction::isCheckedFunction() const
     return false;
 }
 
+bool AstTypeFunction::hasAttribute(AstAttr::Type attributeType) const
+{
+    LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
+
+    return hasAttributeInArray(attributes, attributeType);
+}
+
 AstTypeTypeof::AstTypeTypeof(const Location& location, AstExpr* expr)
     : AstType(ClassIndex(), location)
     , expr(expr)
@@ -1069,6 +1107,16 @@ void AstTypeTypeof::visit(AstVisitor* visitor)
         expr->visit(visitor);
 }
 
+AstTypeOptional::AstTypeOptional(const Location& location)
+    : AstType(ClassIndex(), location)
+{
+}
+
+void AstTypeOptional::visit(AstVisitor* visitor)
+{
+    visitor->visit(this);
+}
+
 AstTypeUnion::AstTypeUnion(const Location& location, const AstArray<AstType*>& types)
     : AstType(ClassIndex(), location)
     , types(types)

Ast/src/Cst.cpp

@@ -38,6 +38,10 @@ CstExprIndexExpr::CstExprIndexExpr(Position openBracketPosition, Position closeB
 {
 }
 
+CstExprFunction::CstExprFunction() : CstNode(CstClassIndex())
+{
+}
+
 CstExprTable::CstExprTable(const AstArray<Item>& items)
     : CstNode(CstClassIndex())
     , items(items)
@@ -125,12 +129,19 @@ CstStatCompoundAssign::CstStatCompoundAssign(Position opPosition)
 {
 }
 
-CstStatLocalFunction::CstStatLocalFunction(Position functionKeywordPosition)
+CstStatFunction::CstStatFunction(Position functionKeywordPosition)
     : CstNode(CstClassIndex())
     , functionKeywordPosition(functionKeywordPosition)
 {
 }
 
+CstStatLocalFunction::CstStatLocalFunction(Position localKeywordPosition, Position functionKeywordPosition)
+    : CstNode(CstClassIndex())
+    , localKeywordPosition(localKeywordPosition)
+    , functionKeywordPosition(functionKeywordPosition)
+{
+}
+
 CstGenericType::CstGenericType(std::optional<Position> defaultEqualsPosition)
     : CstNode(CstClassIndex())
     , defaultEqualsPosition(defaultEqualsPosition)
@@ -160,6 +171,13 @@ CstStatTypeAlias::CstStatTypeAlias(
 {
 }
 
+CstStatTypeFunction::CstStatTypeFunction(Position typeKeywordPosition, Position functionKeywordPosition)
+    : CstNode(CstClassIndex())
+    , typeKeywordPosition(typeKeywordPosition)
+    , functionKeywordPosition(functionKeywordPosition)
+{
+}
+
 CstTypeReference::CstTypeReference(
     std::optional<Position> prefixPointPosition,
     Position openParametersPosition,
@@ -181,6 +199,28 @@ CstTypeTable::CstTypeTable(AstArray<Item> items, bool isArray)
 {
 }
 
+CstTypeFunction::CstTypeFunction(
+    Position openGenericsPosition,
+    AstArray<Position> genericsCommaPositions,
+    Position closeGenericsPosition,
+    Position openArgsPosition,
+    AstArray<std::optional<Position>> argumentNameColonPositions,
+    AstArray<Position> argumentsCommaPositions,
+    Position closeArgsPosition,
+    Position returnArrowPosition
+)
+    : CstNode(CstClassIndex())
+    , openGenericsPosition(openGenericsPosition)
+    , genericsCommaPositions(genericsCommaPositions)
+    , closeGenericsPosition(closeGenericsPosition)
+    , openArgsPosition(openArgsPosition)
+    , argumentNameColonPositions(argumentNameColonPositions)
+    , argumentsCommaPositions(argumentsCommaPositions)
+    , closeArgsPosition(closeArgsPosition)
+    , returnArrowPosition(returnArrowPosition)
+{
+}
+
 CstTypeTypeof::CstTypeTypeof(Position openPosition, Position closePosition)
     : CstNode(CstClassIndex())
     , openPosition(openPosition)
@@ -188,6 +228,20 @@ CstTypeTypeof::CstTypeTypeof(Position openPosition, Position closePosition)
 {
 }
 
+CstTypeUnion::CstTypeUnion(std::optional<Position> leadingPosition, AstArray<Position> separatorPositions)
+    : CstNode(CstClassIndex())
+    , leadingPosition(leadingPosition)
+    , separatorPositions(separatorPositions)
+{
+}
+
+CstTypeIntersection::CstTypeIntersection(std::optional<Position> leadingPosition, AstArray<Position> separatorPositions)
+    : CstNode(CstClassIndex())
+    , leadingPosition(leadingPosition)
+    , separatorPositions(separatorPositions)
+{
+}
+
 CstTypeSingletonString::CstTypeSingletonString(AstArray<char> sourceString, CstExprConstantString::QuoteStyle quoteStyle, unsigned int blockDepth)
     : CstNode(CstClassIndex())
     , sourceString(sourceString)
@@ -197,4 +251,18 @@ CstTypeSingletonString::CstTypeSingletonString(AstArray<char> sourceString, CstE
     LUAU_ASSERT(quoteStyle != CstExprConstantString::QuotedInterp);
 }
 
+CstTypePackExplicit::CstTypePackExplicit(Position openParenthesesPosition, Position closeParenthesesPosition, AstArray<Position> commaPositions)
+    : CstNode(CstClassIndex())
+    , openParenthesesPosition(openParenthesesPosition)
+    , closeParenthesesPosition(closeParenthesesPosition)
+    , commaPositions(commaPositions)
+{
+}
+
+CstTypePackGeneric::CstTypePackGeneric(Position ellipsisPosition)
+    : CstNode(CstClassIndex())
+    , ellipsisPosition(ellipsisPosition)
+{
+}
+
 } // namespace Luau

Ast/src/Lexer.cpp

@@ -8,8 +8,6 @@
 
 #include <limits.h>
 
-LUAU_FASTFLAGVARIABLE(LexerFixInterpStringStart)
-
 namespace Luau
 {
 
@@ -789,7 +787,7 @@ Lexeme Lexer::readNext()
             return Lexeme(Location(start, 1), '}');
         }
 
-        return readInterpolatedStringSection(FFlag::LexerFixInterpStringStart ? start : position(), Lexeme::InterpStringMid, Lexeme::InterpStringEnd);
+        return readInterpolatedStringSection(start, Lexeme::InterpStringMid, Lexeme::InterpStringEnd);
     }
 
     case '=':

Compiler/src/Compiler.cpp

@@ -26,6 +26,8 @@ LUAU_FASTINTVARIABLE(LuauCompileInlineThreshold, 25)
 LUAU_FASTINTVARIABLE(LuauCompileInlineThresholdMaxBoost, 300)
 LUAU_FASTINTVARIABLE(LuauCompileInlineDepth, 5)
 
+LUAU_FASTFLAGVARIABLE(LuauSeparateCompilerTypeInfo)
+
 namespace Luau
 {
 
@@ -4269,20 +4271,40 @@ void compileOrThrow(BytecodeBuilder& bytecode, const ParseResult& parseResult, c
     }
 
     // computes type information for all functions based on type annotations
-    if (options.typeInfoLevel >= 1)
+    if (FFlag::LuauSeparateCompilerTypeInfo)
-        buildTypeMap(
+    {
-            compiler.functionTypes,
+        if (options.typeInfoLevel >= 1 || options.optimizationLevel >= 2)
-            compiler.localTypes,
+            buildTypeMap(
-            compiler.exprTypes,
+                compiler.functionTypes,
-            root,
+                compiler.localTypes,
-            options.vectorType,
+                compiler.exprTypes,
-            compiler.userdataTypes,
+                root,
-            compiler.builtinTypes,
+                options.vectorType,
-            compiler.builtins,
+                compiler.userdataTypes,
-            compiler.globals,
+                compiler.builtinTypes,
-            options.libraryMemberTypeCb,
+                compiler.builtins,
-            bytecode
+                compiler.globals,
-        );
+                options.libraryMemberTypeCb,
+                bytecode
+            );
+    }
+    else
+    {
+        if (options.typeInfoLevel >= 1)
+            buildTypeMap(
+                compiler.functionTypes,
+                compiler.localTypes,
+                compiler.exprTypes,
+                root,
+                options.vectorType,
+                compiler.userdataTypes,
+                compiler.builtinTypes,
+                compiler.builtins,
+                compiler.globals,
+                options.libraryMemberTypeCb,
+                bytecode
+            );
+    }
 
     for (AstExprFunction* expr : functions)
     {

Compiler/src/Types.cpp

@@ -125,6 +125,10 @@ static LuauBytecodeType getType(
     {
         return getType(group->type, generics, typeAliases, resolveAliases, hostVectorType, userdataTypes, bytecode);
     }
+    else if (const AstTypeOptional* optional = ty->as<AstTypeOptional>())
+    {
+        return LBC_TYPE_NIL;
+    }
 
     return LBC_TYPE_ANY;
 }

Sources.cmake

@@ -169,7 +169,6 @@ target_sources(Luau.CodeGen PRIVATE
 # Luau.Analysis Sources
 target_sources(Luau.Analysis PRIVATE
     Analysis/include/Luau/Anyification.h
-    Analysis/include/Luau/AnyTypeSummary.h
     Analysis/include/Luau/ApplyTypeFunction.h
     Analysis/include/Luau/AstJsonEncoder.h
     Analysis/include/Luau/AstQuery.h
@@ -248,7 +247,6 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/include/Luau/VisitType.h
 
     Analysis/src/Anyification.cpp
-    Analysis/src/AnyTypeSummary.cpp
     Analysis/src/ApplyTypeFunction.cpp
     Analysis/src/AstJsonEncoder.cpp
     Analysis/src/AstQuery.cpp
@@ -266,6 +264,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/src/EmbeddedBuiltinDefinitions.cpp
     Analysis/src/Error.cpp
     Analysis/src/EqSatSimplification.cpp
+    Analysis/src/FileResolver.cpp
     Analysis/src/FragmentAutocomplete.cpp
     Analysis/src/Frontend.cpp
     Analysis/src/Generalization.cpp
@@ -432,7 +431,6 @@ endif()
 if(TARGET Luau.UnitTest)
     # Luau.UnitTest Sources
     target_sources(Luau.UnitTest PRIVATE
-        tests/AnyTypeSummary.test.cpp
         tests/AssemblyBuilderA64.test.cpp
         tests/AssemblyBuilderX64.test.cpp
         tests/AstJsonEncoder.test.cpp

VM/include/lua.h

@@ -327,9 +327,12 @@ LUA_API void lua_setuserdatadtor(lua_State* L, int tag, lua_Destructor dtor);
 LUA_API lua_Destructor lua_getuserdatadtor(lua_State* L, int tag);
 
 // alternative access for metatables already registered with luaL_newmetatable
-LUA_API void lua_setuserdatametatable(lua_State* L, int tag, int idx);
+// used by lua_newuserdatataggedwithmetatable to create tagged userdata with the associated metatable assigned
+LUA_API void lua_setuserdatametatable(lua_State* L, int tag);
 LUA_API void lua_getuserdatametatable(lua_State* L, int tag);
 
+LUA_API void lua_setuserdatametatable_DEPRECATED(lua_State* L, int tag, int idx); // Deprecated for incorrect behavior with 'idx != -1'
+
 LUA_API void lua_setlightuserdataname(lua_State* L, int tag, const char* name);
 LUA_API const char* lua_getlightuserdataname(lua_State* L, int tag);
 

VM/src/lapi.cpp

@@ -1470,7 +1470,16 @@ lua_Destructor lua_getuserdatadtor(lua_State* L, int tag)
     return L->global->udatagc[tag];
 }
 
-void lua_setuserdatametatable(lua_State* L, int tag, int idx)
+void lua_setuserdatametatable(lua_State* L, int tag)
+{
+    api_check(L, unsigned(tag) < LUA_UTAG_LIMIT);
+    api_check(L, !L->global->udatamt[tag]); // reassignment not supported
+    api_check(L, ttistable(L->top - 1));
+    L->global->udatamt[tag] = hvalue(L->top - 1);
+    L->top--;
+}
+
+void lua_setuserdatametatable_DEPRECATED(lua_State* L, int tag, int idx)
 {
     api_check(L, unsigned(tag) < LUA_UTAG_LIMIT);
     api_check(L, !L->global->udatamt[tag]); // reassignment not supported

fuzz/proto.cpp

@@ -134,6 +134,7 @@ int registerTypes(Luau::Frontend& frontend, Luau::GlobalTypes& globals, bool for
     getMutable<TableType>(vector3MetaType)->props = {
         {"__add", {makeFunction(arena, nullopt, {vector3InstanceType, vector3InstanceType}, {vector3InstanceType})}},
     };
+    getMutable<TableType>(vector3MetaType)->state = TableState::Sealed;
 
     globals.globalScope->exportedTypeBindings["Vector3"] = TypeFun{{}, vector3InstanceType};
 

tests/AstJsonEncoder.test.cpp

@@ -11,7 +11,8 @@
 
 using namespace Luau;
 
-LUAU_FASTFLAG(LuauAstTypeGroup2)
+LUAU_FASTFLAG(LuauAstTypeGroup3)
+LUAU_FASTFLAG(LuauFixFunctionWithAttributesStartLocation)
 
 struct JsonEncoderFixture
 {
@@ -440,7 +441,9 @@ TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstAttr")
     AstStat* expr = expectParseStatement("@checked function a(b) return c end");
 
     std::string_view expected =
-        R"({"type":"AstStatFunction","location":"0,9 - 0,35","name":{"type":"AstExprGlobal","location":"0,18 - 0,19","global":"a"},"func":{"type":"AstExprFunction","location":"0,9 - 0,35","attributes":[{"type":"AstAttr","location":"0,0 - 0,8","name":"checked"}],"generics":[],"genericPacks":[],"args":[{"luauType":null,"name":"b","type":"AstLocal","location":"0,20 - 0,21"}],"vararg":false,"varargLocation":"0,0 - 0,0","body":{"type":"AstStatBlock","location":"0,22 - 0,32","hasEnd":true,"body":[{"type":"AstStatReturn","location":"0,23 - 0,31","list":[{"type":"AstExprGlobal","location":"0,30 - 0,31","global":"c"}]}]},"functionDepth":1,"debugname":"a"}})";
+        FFlag::LuauFixFunctionWithAttributesStartLocation
+            ? R"({"type":"AstStatFunction","location":"0,0 - 0,35","name":{"type":"AstExprGlobal","location":"0,18 - 0,19","global":"a"},"func":{"type":"AstExprFunction","location":"0,0 - 0,35","attributes":[{"type":"AstAttr","location":"0,0 - 0,8","name":"checked"}],"generics":[],"genericPacks":[],"args":[{"luauType":null,"name":"b","type":"AstLocal","location":"0,20 - 0,21"}],"vararg":false,"varargLocation":"0,0 - 0,0","body":{"type":"AstStatBlock","location":"0,22 - 0,32","hasEnd":true,"body":[{"type":"AstStatReturn","location":"0,23 - 0,31","list":[{"type":"AstExprGlobal","location":"0,30 - 0,31","global":"c"}]}]},"functionDepth":1,"debugname":"a"}})"
+            : R"({"type":"AstStatFunction","location":"0,9 - 0,35","name":{"type":"AstExprGlobal","location":"0,18 - 0,19","global":"a"},"func":{"type":"AstExprFunction","location":"0,9 - 0,35","attributes":[{"type":"AstAttr","location":"0,0 - 0,8","name":"checked"}],"generics":[],"genericPacks":[],"args":[{"luauType":null,"name":"b","type":"AstLocal","location":"0,20 - 0,21"}],"vararg":false,"varargLocation":"0,0 - 0,0","body":{"type":"AstStatBlock","location":"0,22 - 0,32","hasEnd":true,"body":[{"type":"AstStatReturn","location":"0,23 - 0,31","list":[{"type":"AstExprGlobal","location":"0,30 - 0,31","global":"c"}]}]},"functionDepth":1,"debugname":"a"}})";
 
     CHECK(toJson(expr) == expected);
 }
@@ -473,7 +476,7 @@ TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_annotation")
 {
     AstStat* statement = expectParseStatement("type T = ((number) -> (string | nil)) & ((string) -> ())");
 
-    if (FFlag::LuauAstTypeGroup2)
+    if (FFlag::LuauAstTypeGroup3)
     {
         std::string_view expected =
             R"({"type":"AstStatTypeAlias","location":"0,0 - 0,56","name":"T","generics":[],"genericPacks":[],"value":{"type":"AstTypeIntersection","location":"0,9 - 0,56","types":[{"type":"AstTypeGroup","location":"0,9 - 0,37","inner":{"type":"AstTypeFunction","location":"0,10 - 0,36","attributes":[],"generics":[],"genericPacks":[],"argTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,11 - 0,17","name":"number","nameLocation":"0,11 - 0,17","parameters":[]}]},"argNames":[],"returnTypes":{"type":"AstTypeList","types":[{"type":"AstTypeGroup","location":"0,22 - 0,36","inner":{"type":"AstTypeUnion","location":"0,23 - 0,35","types":[{"type":"AstTypeReference","location":"0,23 - 0,29","name":"string","nameLocation":"0,23 - 0,29","parameters":[]},{"type":"AstTypeReference","location":"0,32 - 0,35","name":"nil","nameLocation":"0,32 - 0,35","parameters":[]}]}}]}}},{"type":"AstTypeGroup","location":"0,40 - 0,56","inner":{"type":"AstTypeFunction","location":"0,41 - 0,55","attributes":[],"generics":[],"genericPacks":[],"argTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,42 - 0,48","name":"string","nameLocation":"0,42 - 0,48","parameters":[]}]},"argNames":[],"returnTypes":{"type":"AstTypeList","types":[]}}}]},"exported":false})";

tests/Autocomplete.test.cpp

@@ -1,11 +1,14 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Autocomplete.h"
+#include "Luau/AutocompleteTypes.h"
 #include "Luau/BuiltinDefinitions.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/Type.h"
 #include "Luau/VisitType.h"
 #include "Luau/StringUtils.h"
 
+
+#include "ClassFixture.h"
 #include "Fixture.h"
 #include "ScopedFlags.h"
 
@@ -17,6 +20,11 @@ LUAU_FASTFLAG(LuauTraceTypesInNonstrictMode2)
 LUAU_FASTFLAG(LuauSetMetatableDoesNotTimeTravel)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
 
+LUAU_FASTFLAG(LuauExposeRequireByStringAutocomplete)
+LUAU_FASTFLAG(LuauAutocompleteUnionCopyPreviousSeen)
+LUAU_FASTFLAG(LuauUserTypeFunTypecheck)
+LUAU_FASTFLAG(LuauTypeFunResultInAutocomplete)
+
 using namespace Luau;
 
 static std::optional<AutocompleteEntryMap> nullCallback(std::string tag, std::optional<const ClassType*> ptr, std::optional<std::string> contents)
@@ -151,6 +159,10 @@ struct ACBuiltinsFixture : ACFixtureImpl<BuiltinsFixture>
 {
 };
 
+struct ACClassFixture : ACFixtureImpl<ClassFixture>
+{
+};
+
 TEST_SUITE_BEGIN("AutocompleteTest");
 
 TEST_CASE_FIXTURE(ACFixture, "empty_program")
@@ -3752,6 +3764,73 @@ TEST_CASE_FIXTURE(ACFixture, "string_contents_is_available_to_callback")
     CHECK(isCorrect);
 }
 
+TEST_CASE_FIXTURE(ACBuiltinsFixture, "require_by_string")
+{
+    ScopedFastFlag sff{FFlag::LuauExposeRequireByStringAutocomplete, true};
+
+    fileResolver.source["MainModule"] = R"(
+        local info = "MainModule serves as the root directory"
+    )";
+
+    fileResolver.source["MainModule/Folder"] = R"(
+        local info = "MainModule/Folder serves as a subdirectory"
+    )";
+
+    fileResolver.source["MainModule/Folder/Requirer"] = R"(
+        local res0 = require("@")
+
+        local res1 = require(".")
+        local res2 = require("./")
+        local res3 = require("./Sib")
+
+        local res4 = require("..")
+        local res5 = require("../")
+        local res6 = require("../Sib")
+    )";
+
+    fileResolver.source["MainModule/Folder/SiblingDependency"] = R"(
+        return {"result"}
+    )";
+
+    fileResolver.source["MainModule/ParentDependency"] = R"(
+        return {"result"}
+    )";
+
+    struct RequireCompletion
+    {
+        std::string label;
+        std::string insertText;
+    };
+
+    auto checkEntries = [](const AutocompleteEntryMap& entryMap, const std::vector<RequireCompletion>& completions)
+    {
+        CHECK(completions.size() == entryMap.size());
+        for (const auto& completion : completions)
+        {
+            CHECK(entryMap.count(completion.label));
+            CHECK(entryMap.at(completion.label).insertText == completion.insertText);
+        }
+    };
+
+    AutocompleteResult acResult;
+    acResult = autocomplete("MainModule/Folder/Requirer", Position{1, 31});
+    checkEntries(acResult.entryMap, {{"@defaultalias", "@defaultalias"}, {"./", "./"}, {"../", "../"}});
+
+    acResult = autocomplete("MainModule/Folder/Requirer", Position{3, 31});
+    checkEntries(acResult.entryMap, {{"@defaultalias", "@defaultalias"}, {"./", "./"}, {"../", "../"}});
+    acResult = autocomplete("MainModule/Folder/Requirer", Position{4, 32});
+    checkEntries(acResult.entryMap, {{"..", "."}, {"Requirer", "./Requirer"}, {"SiblingDependency", "./SiblingDependency"}});
+    acResult = autocomplete("MainModule/Folder/Requirer", Position{5, 35});
+    checkEntries(acResult.entryMap, {{"..", "."}, {"Requirer", "./Requirer"}, {"SiblingDependency", "./SiblingDependency"}});
+
+    acResult = autocomplete("MainModule/Folder/Requirer", Position{7, 32});
+    checkEntries(acResult.entryMap, {{"@defaultalias", "@defaultalias"}, {"./", "./"}, {"../", "../"}});
+    acResult = autocomplete("MainModule/Folder/Requirer", Position{8, 33});
+    checkEntries(acResult.entryMap, {{"..", "../.."}, {"Folder", "../Folder"}, {"ParentDependency", "../ParentDependency"}});
+    acResult = autocomplete("MainModule/Folder/Requirer", Position{9, 36});
+    checkEntries(acResult.entryMap, {{"..", "../.."}, {"Folder", "../Folder"}, {"ParentDependency", "../ParentDependency"}});
+}
+
 TEST_CASE_FIXTURE(ACFixture, "autocomplete_response_perf1" * doctest::timeout(0.5))
 {
     if (FFlag::LuauSolverV2)
@@ -4346,4 +4425,99 @@ local x = 1 + result.
     CHECK(ac.entryMap.count("x"));
 }
 
+TEST_CASE_FIXTURE(ACClassFixture, "ac_dont_overflow_on_recursive_union")
+{
+    ScopedFastFlag _{FFlag::LuauAutocompleteUnionCopyPreviousSeen, true};
+    check(R"(
+        local table1: {ChildClass} = {}
+        local table2 = {}
+
+        for index, value in table2[1] do
+            table.insert(table1, value)
+            value.@1
+        end
+    )");
+
+    auto ac = autocomplete('1');
+    // RIDE-11517: This should *really* be the members of `ChildClass`, but
+    // would previously stack overflow.
+    CHECK(ac.entryMap.empty());
+}
+
+TEST_CASE_FIXTURE(ACBuiltinsFixture, "type_function_has_types_definitions")
+{
+    // Needs new global initialization in the Fixture, but can't place the flag inside the base Fixture
+    if (!FFlag::LuauUserTypeFunTypecheck)
+        return;
+
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+
+    check(R"(
+type function foo()
+    types.@1
+end
+    )");
+
+    auto ac = autocomplete('1');
+    CHECK_EQ(ac.entryMap.count("singleton"), 1);
+}
+
+TEST_CASE_FIXTURE(ACBuiltinsFixture, "type_function_private_scope")
+{
+    // Needs new global initialization in the Fixture, but can't place the flag inside the base Fixture
+    if (!FFlag::LuauUserTypeFunTypecheck)
+        return;
+
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+
+    // Global scope polution by the embedder has no effect
+    addGlobalBinding(frontend.globals, "thisAlsoShouldNotBeThere", Binding{builtinTypes->anyType});
+    addGlobalBinding(frontend.globalsForAutocomplete, "thisAlsoShouldNotBeThere", Binding{builtinTypes->anyType});
+
+    check(R"(
+local function thisShouldNotBeThere() end
+
+type function thisShouldBeThere() end
+
+type function foo()
+    this@1
+end
+
+this@2
+    )");
+
+    auto ac = autocomplete('1');
+    CHECK_EQ(ac.entryMap.count("thisShouldNotBeThere"), 0);
+    CHECK_EQ(ac.entryMap.count("thisAlsoShouldNotBeThere"), 0);
+    CHECK_EQ(ac.entryMap.count("thisShouldBeThere"), 1);
+
+    ac = autocomplete('2');
+    CHECK_EQ(ac.entryMap.count("thisShouldNotBeThere"), 1);
+    CHECK_EQ(ac.entryMap.count("thisAlsoShouldNotBeThere"), 1);
+    CHECK_EQ(ac.entryMap.count("thisShouldBeThere"), 0);
+}
+
+TEST_CASE_FIXTURE(ACBuiltinsFixture, "type_function_eval_in_autocomplete")
+{
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+    ScopedFastFlag luauTypeFunResultInAutocomplete{FFlag::LuauTypeFunResultInAutocomplete, true};
+
+    check(R"(
+type function foo(x)
+    local tbl = types.newtable(nil, nil, nil)
+    tbl:setproperty(types.singleton("boolean"), x)
+    tbl:setproperty(types.singleton("number"), types.number)
+    return tbl
+end
+
+local function test(a: foo<string>)
+    return a.@1
+end
+    )");
+
+    auto ac = autocomplete('1');
+    CHECK_EQ(ac.entryMap.count("boolean"), 1);
+    CHECK_EQ(ac.entryMap.count("number"), 1);
+}
+
 TEST_SUITE_END();

tests/ClassFixture.cpp

@@ -9,7 +9,8 @@ using std::nullopt;
 namespace Luau
 {
 
-ClassFixture::ClassFixture()
+ClassFixture::ClassFixture(bool prepareAutocomplete)
+    : BuiltinsFixture(prepareAutocomplete)
 {
     GlobalTypes& globals = frontend.globals;
     TypeArena& arena = globals.globalTypes;

tests/ClassFixture.h

@@ -8,7 +8,7 @@ namespace Luau
 
 struct ClassFixture : BuiltinsFixture
 {
-    ClassFixture();
+    explicit ClassFixture(bool prepareAutocomplete = false);
 
     TypeId vector2Type;
     TypeId vector2InstanceType;

tests/Conformance.test.cpp

@@ -477,9 +477,8 @@ void setupUserdataHelpers(lua_State* L)
 {
     // create metatable with all the metamethods
     luaL_newmetatable(L, "vec2");
-    luaL_getmetatable(L, "vec2");
     lua_pushvalue(L, -1);
-    lua_setuserdatametatable(L, kTagVec2, -1);
+    lua_setuserdatametatable(L, kTagVec2);
 
     lua_pushcfunction(L, lua_vec2_index, nullptr);
     lua_setfield(L, -2, "__index");
@@ -2255,12 +2254,12 @@ TEST_CASE("UserdataApi")
 
     // tagged user data with fast metatable access
     luaL_newmetatable(L, "udata3");
-    luaL_getmetatable(L, "udata3");
+    lua_pushvalue(L, -1);
-    lua_setuserdatametatable(L, 50, -1);
+    lua_setuserdatametatable(L, 50);
 
     luaL_newmetatable(L, "udata4");
-    luaL_getmetatable(L, "udata4");
+    lua_pushvalue(L, -1);
-    lua_setuserdatametatable(L, 51, -1);
+    lua_setuserdatametatable(L, 51);
 
     void* ud7 = lua_newuserdatatagged(L, 16, 50);
     lua_getuserdatametatable(L, 50);

tests/ConstraintGeneratorFixture.cpp

@@ -34,6 +34,7 @@ void ConstraintGeneratorFixture::generateConstraints(const std::string& code)
         builtinTypes,
         NotNull(&ice),
         frontend.globals.globalScope,
+        frontend.globals.globalTypeFunctionScope,
         /*prepareModuleScope*/ nullptr,
         &logger,
         NotNull{dfg.get()},

tests/Fixture.cpp

@@ -5,6 +5,7 @@
 #include "Luau/BuiltinDefinitions.h"
 #include "Luau/Common.h"
 #include "Luau/Constraint.h"
+#include "Luau/FileResolver.h"
 #include "Luau/ModuleResolver.h"
 #include "Luau/NotNull.h"
 #include "Luau/Parser.h"
@@ -34,6 +35,110 @@ extern std::optional<unsigned> randomSeed; // tests/main.cpp
 namespace Luau
 {
 
+static std::string getNodeName(const TestRequireNode* node)
+{
+    std::string name;
+    size_t lastSlash = node->moduleName.find_last_of('/');
+    if (lastSlash != std::string::npos)
+        name = node->moduleName.substr(lastSlash + 1);
+    else
+        name = node->moduleName;
+
+    return name;
+}
+
+std::string TestRequireNode::getLabel() const
+{
+    return getNodeName(this);
+}
+
+std::string TestRequireNode::getPathComponent() const
+{
+    return getNodeName(this);
+}
+
+static std::vector<std::string_view> splitStringBySlashes(std::string_view str)
+{
+    std::vector<std::string_view> components;
+    size_t pos = 0;
+    size_t nextPos = str.find_first_of('/', pos);
+    if (nextPos == std::string::npos)
+    {
+        components.push_back(str);
+        return components;
+    }
+    while (nextPos != std::string::npos)
+    {
+        components.push_back(str.substr(pos, nextPos - pos));
+        pos = nextPos + 1;
+        nextPos = str.find_first_of('/', pos);
+    }
+    components.push_back(str.substr(pos));
+    return components;
+}
+
+std::unique_ptr<RequireNode> TestRequireNode::resolvePathToNode(const std::string& path) const
+{
+    std::vector<std::string_view> components = splitStringBySlashes(path);
+    LUAU_ASSERT((components.empty() || components[0] == "." || components[0] == "..") && "Path must begin with ./ or ../ in test");
+
+    std::vector<std::string_view> normalizedComponents = splitStringBySlashes(moduleName);
+    normalizedComponents.pop_back();
+    LUAU_ASSERT(!normalizedComponents.empty() && "Must have a root module");
+
+    for (std::string_view component : components)
+    {
+        if (component == "..")
+        {
+            if (normalizedComponents.empty())
+                LUAU_ASSERT(!"Cannot go above root module in test");
+            else
+                normalizedComponents.pop_back();
+        }
+        else if (!component.empty() && component != ".")
+        {
+            normalizedComponents.emplace_back(component);
+        }
+    }
+
+    std::string moduleName;
+    for (size_t i = 0; i < normalizedComponents.size(); i++)
+    {
+        if (i > 0)
+            moduleName += '/';
+        moduleName += normalizedComponents[i];
+    }
+
+    if (allSources->count(moduleName) == 0)
+        return nullptr;
+
+    return std::make_unique<TestRequireNode>(moduleName, allSources);
+}
+
+std::vector<std::unique_ptr<RequireNode>> TestRequireNode::getChildren() const
+{
+    std::vector<std::unique_ptr<RequireNode>> result;
+    for (const auto& entry : *allSources)
+    {
+        if (std::string_view(entry.first).substr(0, moduleName.size()) == moduleName && entry.first.size() > moduleName.size() &&
+            entry.first[moduleName.size()] == '/' && entry.first.find('/', moduleName.size() + 1) == std::string::npos)
+        {
+            result.push_back(std::make_unique<TestRequireNode>(entry.first, allSources));
+        }
+    }
+    return result;
+}
+
+std::vector<RequireAlias> TestRequireNode::getAvailableAliases() const
+{
+    return {{"defaultalias"}};
+}
+
+std::unique_ptr<RequireNode> TestRequireSuggester::getNode(const ModuleName& name) const
+{
+    return std::make_unique<TestRequireNode>(name, &resolver->source);
+}
+
 std::optional<ModuleInfo> TestFileResolver::resolveModuleInfo(const ModuleName& currentModuleName, const AstExpr& pathExpr)
 {
     if (auto name = pathExprToModuleName(currentModuleName, pathExpr))
@@ -218,6 +323,7 @@ AstStatBlock* Fixture::parse(const std::string& source, const ParseOptions& pars
                     NotNull{&moduleResolver},
                     NotNull{&fileResolver},
                     frontend.globals.globalScope,
+                    frontend.globals.globalTypeFunctionScope,
                     /*prepareModuleScope*/ nullptr,
                     frontend.options,
                     {},
@@ -266,7 +372,7 @@ LintResult Fixture::lint(const std::string& source, const std::optional<LintOpti
     fileResolver.source[mm] = std::move(source);
     frontend.markDirty(mm);
 
-    return lintModule(mm);
+    return lintModule(mm, lintOptions);
 }
 
 LintResult Fixture::lintModule(const ModuleName& moduleName, const std::optional<LintOptions>& lintOptions)

tests/Fixture.h

@@ -37,10 +37,45 @@ namespace Luau
 
 struct TypeChecker;
 
+struct TestRequireNode : RequireNode
+{
+    TestRequireNode(ModuleName moduleName, std::unordered_map<ModuleName, std::string>* allSources)
+        : moduleName(std::move(moduleName))
+        , allSources(allSources)
+    {
+    }
+
+    std::string getLabel() const override;
+    std::string getPathComponent() const override;
+    std::unique_ptr<RequireNode> resolvePathToNode(const std::string& path) const override;
+    std::vector<std::unique_ptr<RequireNode>> getChildren() const override;
+    std::vector<RequireAlias> getAvailableAliases() const override;
+
+    ModuleName moduleName;
+    std::unordered_map<ModuleName, std::string>* allSources;
+};
+
+struct TestFileResolver;
+struct TestRequireSuggester : RequireSuggester
+{
+    TestRequireSuggester(TestFileResolver* resolver)
+        : resolver(resolver)
+    {
+    }
+
+    std::unique_ptr<RequireNode> getNode(const ModuleName& name) const override;
+    TestFileResolver* resolver;
+};
+
 struct TestFileResolver
     : FileResolver
     , ModuleResolver
 {
+    TestFileResolver()
+        : FileResolver(std::make_shared<TestRequireSuggester>(this))
+    {
+    }
+
     std::optional<ModuleInfo> resolveModuleInfo(const ModuleName& currentModuleName, const AstExpr& pathExpr) override;
 
     const ModulePtr getModule(const ModuleName& moduleName) const override;

tests/Frontend.test.cpp

@@ -17,8 +17,8 @@ LUAU_FASTFLAG(LuauSolverV2);
 LUAU_FASTFLAG(DebugLuauFreezeArena)
 LUAU_FASTFLAG(DebugLuauMagicTypes)
 LUAU_FASTFLAG(LuauSelectivelyRetainDFGArena)
-LUAU_FASTFLAG(LuauBetterReverseDependencyTracking)
 LUAU_FASTFLAG(LuauModuleHoldsAstRoot)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
 
 namespace
 {
@@ -921,7 +921,17 @@ TEST_CASE_FIXTURE(FrontendFixture, "it_should_be_safe_to_stringify_errors_when_f
     // When this test fails, it is because the TypeIds needed by the error have been deallocated.
     // It is thus basically impossible to predict what will happen when this assert is evaluated.
     // It could segfault, or you could see weird type names like the empty string or <VALUELESS BY EXCEPTION>
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        REQUIRE_EQ(
+            "Type\n\t"
+            "'{ count: string }'"
+            "\ncould not be converted into\n\t"
+            "'{ Count: number }'",
+            toString(result.errors[0])
+        );
+    }
+    else if (FFlag::LuauSolverV2)
         REQUIRE_EQ(
             R"(Type
     '{ count: string }'
@@ -1589,8 +1599,6 @@ return {x = a, y = b, z = c}
 
 TEST_CASE_FIXTURE(FrontendFixture, "test_traverse_dependents")
 {
-    ScopedFastFlag dependencyTracking{FFlag::LuauBetterReverseDependencyTracking, true};
-
     fileResolver.source["game/Gui/Modules/A"] = "return {hello=5, world=true}";
     fileResolver.source["game/Gui/Modules/B"] = R"(
         return require(game:GetService('Gui').Modules.A)
@@ -1623,8 +1631,6 @@ TEST_CASE_FIXTURE(FrontendFixture, "test_traverse_dependents")
 
 TEST_CASE_FIXTURE(FrontendFixture, "test_traverse_dependents_early_exit")
 {
-    ScopedFastFlag dependencyTracking{FFlag::LuauBetterReverseDependencyTracking, true};
-
     fileResolver.source["game/Gui/Modules/A"] = "return {hello=5, world=true}";
     fileResolver.source["game/Gui/Modules/B"] = R"(
         return require(game:GetService('Gui').Modules.A)
@@ -1652,8 +1658,6 @@ TEST_CASE_FIXTURE(FrontendFixture, "test_traverse_dependents_early_exit")
 
 TEST_CASE_FIXTURE(FrontendFixture, "test_dependents_stored_on_node_as_graph_updates")
 {
-    ScopedFastFlag dependencyTracking{FFlag::LuauBetterReverseDependencyTracking, true};
-
     auto updateSource = [&](const std::string& name, const std::string& source)
     {
         fileResolver.source[name] = source;
@@ -1768,7 +1772,6 @@ TEST_CASE_FIXTURE(FrontendFixture, "test_dependents_stored_on_node_as_graph_upda
 
 TEST_CASE_FIXTURE(FrontendFixture, "test_invalid_dependency_tracking_per_module_resolver")
 {
-    ScopedFastFlag dependencyTracking{FFlag::LuauBetterReverseDependencyTracking, true};
     ScopedFastFlag newSolver{FFlag::LuauSolverV2, false};
 
     fileResolver.source["game/Gui/Modules/A"] = "return {hello=5, world=true}";

tests/Lexer.test.cpp

@@ -8,8 +8,6 @@
 
 using namespace Luau;
 
-LUAU_FASTFLAG(LexerFixInterpStringStart)
-
 TEST_SUITE_BEGIN("LexerTests");
 
 TEST_CASE("broken_string_works")
@@ -156,7 +154,7 @@ TEST_CASE("string_interpolation_basic")
     Lexeme interpEnd = lexer.next();
     CHECK_EQ(interpEnd.type, Lexeme::InterpStringEnd);
     // The InterpStringEnd should start with }, not `.
-    CHECK_EQ(interpEnd.location.begin.column, FFlag::LexerFixInterpStringStart ? 11 : 12);
+    CHECK_EQ(interpEnd.location.begin.column, 11);
 }
 
 TEST_CASE("string_interpolation_full")
@@ -177,7 +175,7 @@ TEST_CASE("string_interpolation_full")
     Lexeme interpMid = lexer.next();
     CHECK_EQ(interpMid.type, Lexeme::InterpStringMid);
     CHECK_EQ(interpMid.toString(), "} {");
-    CHECK_EQ(interpMid.location.begin.column, FFlag::LexerFixInterpStringStart ? 11 : 12);
+    CHECK_EQ(interpMid.location.begin.column, 11);
 
     Lexeme quote2 = lexer.next();
     CHECK_EQ(quote2.type, Lexeme::QuotedString);
@@ -186,7 +184,7 @@ TEST_CASE("string_interpolation_full")
     Lexeme interpEnd = lexer.next();
     CHECK_EQ(interpEnd.type, Lexeme::InterpStringEnd);
     CHECK_EQ(interpEnd.toString(), "} end`");
-    CHECK_EQ(interpEnd.location.begin.column, FFlag::LexerFixInterpStringStart ? 19 : 20);
+    CHECK_EQ(interpEnd.location.begin.column, 19);
 }
 
 TEST_CASE("string_interpolation_double_brace")

tests/Linter.test.cpp

@@ -9,6 +9,7 @@
 
 LUAU_FASTFLAG(LuauSolverV2);
 LUAU_FASTFLAG(LintRedundantNativeAttribute);
+LUAU_FASTFLAG(LuauDeprecatedAttribute);
 
 using namespace Luau;
 
@@ -1600,6 +1601,326 @@ setfenv(h :: any, {})
     CHECK_EQ(result.warnings[3].location.begin.line + 1, 11);
 }
 
+static void checkDeprecatedWarning(const Luau::LintWarning& warning, const Luau::Position& begin, const Luau::Position& end, const char* msg)
+{
+    CHECK_EQ(warning.code, LintWarning::Code_DeprecatedApi);
+    CHECK_EQ(warning.location, Location(begin, end));
+    CHECK_EQ(warning.text, msg);
+}
+
+TEST_CASE_FIXTURE(Fixture, "DeprecatedAttribute")
+{
+    ScopedFastFlag sff[] = {{FFlag::LuauDeprecatedAttribute, true}, {FFlag::LuauSolverV2, true}};
+
+    // @deprecated works on local functions
+    {
+        LintResult result = lint(R"(
+@deprecated
+local function testfun(x)
+    return x + 1
+end
+
+testfun(1)
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(6, 0), Position(6, 7), "Function 'testfun' is deprecated");
+    }
+
+    // @deprecated works on globals functions
+    {
+        LintResult result = lint(R"(
+@deprecated
+function testfun(x)
+    return x + 1
+end
+
+testfun(1)
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(6, 0), Position(6, 7), "Function 'testfun' is deprecated");
+    }
+
+    // @deprecated works on fully typed functions
+    {
+        LintResult result = lint(R"(
+@deprecated
+local function testfun(x:number):number
+    return x + 1
+end
+
+if math.random(2) == 2 then
+    testfun(1)
+end
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(7, 4), Position(7, 11), "Function 'testfun' is deprecated");
+    }
+
+    // @deprecated works on functions without an explicit return type
+    {
+        LintResult result = lint(R"(
+@deprecated
+local function testfun(x:number)
+    return x + 1
+end
+
+g(testfun)
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(6, 2), Position(6, 9), "Function 'testfun' is deprecated");
+    }
+
+    // @deprecated works on functions without an explicit argument type
+    {
+        LintResult result = lint(R"(
+@deprecated
+local function testfun(x):number
+    if x == 1 then
+        return x
+    else
+        return 1 + testfun(x - 1)
+    end
+end
+
+testfun(1)
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(10, 0), Position(10, 7), "Function 'testfun' is deprecated");
+    }
+
+    // @deprecated works on inner functions
+    {
+        LintResult result = lint(R"(
+function flipFlop()
+    local state = false
+
+    @deprecated
+    local function invert()
+        state = !state
+        return state
+    end
+
+    return invert
+end
+
+f = flipFlop()
+assert(f() == true)
+)");
+
+        REQUIRE(2 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(10, 11), Position(10, 17), "Function 'invert' is deprecated");
+        checkDeprecatedWarning(result.warnings[1], Position(14, 7), Position(14, 8), "Function 'f' is deprecated");
+    }
+
+    // @deprecated does not automatically apply to inner functions
+    {
+        LintResult result = lint(R"(
+@deprecated
+function flipFlop()
+    local state = false
+
+    local function invert()
+        state = !state
+        return state
+    end
+
+    return invert
+end
+
+f = flipFlop()
+assert(f() == true)
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(13, 4), Position(13, 12), "Function 'flipFlop' is deprecated");
+    }
+
+    // @deprecated works correctly if deprecated function is shadowed
+    {
+        LintResult result = lint(R"(
+@deprecated
+local function doTheThing()
+    print("doing")
+end
+
+doTheThing()
+
+local function shadow()
+    local function doTheThing()
+        print("doing!")
+    end
+
+    doTheThing()
+end
+
+shadow()
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(6, 0), Position(6, 10), "Function 'doTheThing' is deprecated");
+    }
+
+    // @deprecated does not issue warnings if a deprecated function uses itself
+    {
+        LintResult result = lint(R"(
+@deprecated
+function fibonacci(n)
+    if n == 0 then
+        return 0
+    elseif n == 1 then
+        return 1
+    else
+        return fibonacci(n - 1) + fibonacci(n - 2)
+    end
+end
+
+fibonacci(5)
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(12, 0), Position(12, 9), "Function 'fibonacci' is deprecated");
+    }
+
+    // @deprecated works for mutually recursive functions
+    {
+        LintResult result = lint(R"(
+@deprecated
+function odd(x)
+    if x == 0 then
+        return false
+    else
+        return even(x - 1)
+    end
+end
+
+@deprecated
+function even(x)
+    if x == 0 then
+        return true
+    else
+        return odd(x - 1)
+    end
+end
+
+assert(odd(1) == true)
+assert(even(0) == true)
+)");
+
+        REQUIRE(4 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(6, 15), Position(6, 19), "Function 'even' is deprecated");
+        checkDeprecatedWarning(result.warnings[1], Position(15, 15), Position(15, 18), "Function 'odd' is deprecated");
+        checkDeprecatedWarning(result.warnings[2], Position(19, 7), Position(19, 10), "Function 'odd' is deprecated");
+        checkDeprecatedWarning(result.warnings[3], Position(20, 7), Position(20, 11), "Function 'even' is deprecated");
+    }
+
+    // @deprecated works for methods with a literal class name
+    {
+        LintResult result = lint(R"(
+Account = { balance=0 }
+
+@deprecated
+function Account:deposit(v)
+    self.balance = self.balance + v
+end
+    
+Account:deposit(200.00)
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(8, 0), Position(8, 15), "Member 'Account.deposit' is deprecated");
+    }
+
+    // @deprecated works for methods with a compound expression class name
+    {
+        LintResult result = lint(R"(
+Account = { balance=0 }
+
+function getAccount()
+    return Account
+end
+
+@deprecated
+function Account:deposit (v)
+    self.balance = self.balance + v
+end
+    
+(getAccount()):deposit(200.00)
+)");
+
+        REQUIRE(1 == result.warnings.size());
+        checkDeprecatedWarning(result.warnings[0], Position(12, 0), Position(12, 22), "Member 'deposit' is deprecated");
+    }
+}
+
+TEST_CASE_FIXTURE(Fixture, "DeprecatedAttributeFunctionDeclaration")
+{
+    ScopedFastFlag sff[] = {{FFlag::LuauDeprecatedAttribute, true}, {FFlag::LuauSolverV2, true}};
+
+    // @deprecated works on function type declarations
+
+    loadDefinition(R"(
+@deprecated declare function bar(x: number): string
+)");
+
+    LintResult result = lint(R"(
+bar(2)
+)");
+
+    REQUIRE(1 == result.warnings.size());
+    checkDeprecatedWarning(result.warnings[0], Position(1, 0), Position(1, 3), "Function 'bar' is deprecated");
+}
+
+TEST_CASE_FIXTURE(Fixture, "DeprecatedAttributeTableDeclaration")
+{
+    ScopedFastFlag sff[] = {{FFlag::LuauDeprecatedAttribute, true}, {FFlag::LuauSolverV2, true}};
+
+    // @deprecated works on table type declarations
+
+    loadDefinition(R"(
+declare Hooty : {
+    tooty : @deprecated @checked (number) -> number
+}
+)");
+
+    LintResult result = lint(R"(
+print(Hooty:tooty(2.0))
+)");
+
+    REQUIRE(1 == result.warnings.size());
+    checkDeprecatedWarning(result.warnings[0], Position(1, 6), Position(1, 17), "Member 'Hooty.tooty' is deprecated");
+}
+
+TEST_CASE_FIXTURE(Fixture, "DeprecatedAttributeMethodDeclaration")
+{
+    ScopedFastFlag sff[] = {{FFlag::LuauDeprecatedAttribute, true}, {FFlag::LuauSolverV2, true}};
+
+    // @deprecated works on table type declarations
+
+    loadDefinition(R"(
+declare class Foo
+   @deprecated
+   function bar(self, value: number) : number
+end
+
+declare Foo: {
+   new: () -> Foo
+}
+)");
+
+    LintResult result = lint(R"(
+local foo = Foo.new()
+print(foo:bar(2.0))
+)");
+
+    REQUIRE(1 == result.warnings.size());
+    checkDeprecatedWarning(result.warnings[0], Position(2, 6), Position(2, 13), "Member 'bar' is deprecated");
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "TableOperations")
 {
     LintResult result = lint(R"(

tests/NonStrictTypeChecker.test.cpp

@@ -17,6 +17,8 @@
 
 LUAU_FASTFLAG(LuauNewNonStrictWarnOnUnknownGlobals)
 LUAU_FASTFLAG(LuauNonStrictVisitorImprovements)
+LUAU_FASTFLAG(LuauNonStrictFuncDefErrorFix)
+LUAU_FASTFLAG(LuauNormalizedBufferIsNotUnknown)
 
 using namespace Luau;
 
@@ -359,6 +361,23 @@ end
     NONSTRICT_REQUIRE_FUNC_DEFINITION_ERR(Position(1, 11), "x", result);
 }
 
+TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "function_def_sequencing_errors_2")
+{
+    ScopedFastFlag luauNonStrictFuncDefErrorFix{FFlag::LuauNonStrictFuncDefErrorFix, true};
+    ScopedFastFlag luauNonStrictVisitorImprovements{FFlag::LuauNonStrictVisitorImprovements, true};
+
+    CheckResult result = checkNonStrict(R"(
+local t = {function(x)
+    abs(x)
+    lower(x)
+end}
+)");
+    LUAU_REQUIRE_ERROR_COUNT(3, result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(2, 8), "abs", result);
+    NONSTRICT_REQUIRE_CHECKED_ERR(Position(3, 10), "lower", result);
+    CHECK(toString(result.errors[2]) == "Argument x with type 'unknown' is used in a way that will run time error");
+}
+
 TEST_CASE_FIXTURE(NonStrictTypeCheckerFixture, "local_fn_produces_error")
 {
     CheckResult result = checkNonStrict(R"(
@@ -649,4 +668,17 @@ TEST_CASE_FIXTURE(Fixture, "unknown_globals_in_non_strict")
     LUAU_REQUIRE_ERROR_COUNT(2, result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "buffer_is_not_unknown")
+{
+    ScopedFastFlag luauNormalizedBufferIsNotUnknown{FFlag::LuauNormalizedBufferIsNotUnknown, true};
+
+    CheckResult result = check(Mode::Nonstrict, R"(
+local function wrap(b: buffer, i: number, v: number)
+    buffer.writeu32(b, i * 4, v)
+end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/Normalize.test.cpp

@@ -10,10 +10,15 @@
 #include "Luau/Normalize.h"
 #include "Luau/BuiltinDefinitions.h"
 
+LUAU_FASTFLAG(LuauNormalizeNegatedErrorToAnError)
+LUAU_FASTFLAG(LuauNormalizeIntersectErrorToAnError)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
-LUAU_FASTFLAG(LuauFixNormalizedIntersectionOfNegatedClass)
+LUAU_FASTINT(LuauNormalizeIntersectionLimit)
-LUAU_FASTFLAG(LuauNormalizeNegationFix)
+LUAU_FASTINT(LuauNormalizeUnionLimit)
+LUAU_FASTFLAG(LuauNormalizeLimitFunctionSet)
+LUAU_FASTFLAG(LuauSubtypingStopAtNormFail)
+
 using namespace Luau;
 
 namespace
@@ -594,6 +599,25 @@ TEST_CASE_FIXTURE(NormalizeFixture, "intersect_truthy_expressed_as_intersection"
     )")));
 }
 
+TEST_CASE_FIXTURE(NormalizeFixture, "intersect_error")
+{
+    ScopedFastFlag luauNormalizeIntersectErrorToAnError{FFlag::LuauNormalizeIntersectErrorToAnError, true};
+
+    std::shared_ptr<const NormalizedType> norm = toNormalizedType(R"(string & AAA)", 1);
+    REQUIRE(norm);
+    CHECK("*error-type*" == toString(normalizer.typeFromNormal(*norm)));
+}
+
+TEST_CASE_FIXTURE(NormalizeFixture, "intersect_not_error")
+{
+    ScopedFastFlag luauNormalizeIntersectErrorToAnError{FFlag::LuauNormalizeIntersectErrorToAnError, true};
+    ScopedFastFlag luauNormalizeNegatedErrorToAnError{FFlag::LuauNormalizeNegatedErrorToAnError, true};
+
+    std::shared_ptr<const NormalizedType> norm = toNormalizedType(R"(string & Not<)", 1);
+    REQUIRE(norm);
+    CHECK("*error-type*" == toString(normalizer.typeFromNormal(*norm)));
+}
+
 TEST_CASE_FIXTURE(NormalizeFixture, "union_of_union")
 {
     CHECK(R"("alpha" | "beta" | "gamma")" == toString(normal(R"(
@@ -852,7 +876,6 @@ TEST_CASE_FIXTURE(NormalizeFixture, "crazy_metatable")
 
 TEST_CASE_FIXTURE(NormalizeFixture, "negations_of_classes")
 {
-    ScopedFastFlag _{FFlag::LuauFixNormalizedIntersectionOfNegatedClass, true};
     createSomeClasses(&frontend);
     CHECK("(Parent & ~Child) | Unrelated" == toString(normal("(Parent & Not<Child>) | Unrelated")));
     CHECK("((class & ~Child) | boolean | buffer | function | number | string | table | thread)?" == toString(normal("Not<Child>")));
@@ -1034,7 +1057,6 @@ TEST_CASE_FIXTURE(NormalizeFixture, "free_type_and_not_truthy")
 {
     ScopedFastFlag sff[] = {
         {FFlag::LuauSolverV2, true}, // Only because it affects the stringification of free types
-        {FFlag::LuauNormalizeNegationFix, true},
     };
 
     TypeId freeTy = arena.freshType(builtinTypes, &globalScope);
@@ -1155,4 +1177,38 @@ end
 )");
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_limit_function_intersection_complexity")
+{
+    ScopedFastInt luauNormalizeIntersectionLimit{FInt::LuauNormalizeIntersectionLimit, 50};
+    ScopedFastInt luauNormalizeUnionLimit{FInt::LuauNormalizeUnionLimit, 20};
+    ScopedFastFlag luauNormalizeLimitFunctionSet{FFlag::LuauNormalizeLimitFunctionSet, true};
+    ScopedFastFlag luauSubtypingStopAtNormFail{FFlag::LuauSubtypingStopAtNormFail, true};
+
+    CheckResult result = check(R"(
+function _(_).readu32(l0)
+return ({[_(_(_))]=_,[_(if _ then _)]=_,n0=_,})[_],nil
+end
+_(_)[_(n32)] %= _(_(_))
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_propagate_normalization_failures")
+{
+    ScopedFastInt luauNormalizeIntersectionLimit{FInt::LuauNormalizeIntersectionLimit, 50};
+    ScopedFastInt luauNormalizeUnionLimit{FInt::LuauNormalizeUnionLimit, 20};
+    ScopedFastFlag luauNormalizeLimitFunctionSet{FFlag::LuauNormalizeLimitFunctionSet, true};
+    ScopedFastFlag luauSubtypingStopAtNormFail{FFlag::LuauSubtypingStopAtNormFail, true};
+
+    CheckResult result = check(R"(
+function _(_,"").readu32(l0)
+return ({[_(_(_))]=_,[_(if _ then _,_())]=_,[""]=_,})[_],nil
+end
+_().readu32 %= _(_(_(_),_))
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/Parser.test.cpp

@@ -18,12 +18,17 @@ LUAU_FASTINT(LuauParseErrorLimit)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauAllowComplexTypesInGenericParams)
 LUAU_FASTFLAG(LuauErrorRecoveryForTableTypes)
-LUAU_FASTFLAG(LuauErrorRecoveryForClassNames)
-LUAU_FASTFLAG(LuauFixFunctionNameStartPosition)
 LUAU_FASTFLAG(LuauExtendStatEndPosWithSemicolon)
 LUAU_FASTFLAG(LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
-LUAU_FASTFLAG(LuauAstTypeGroup2)
+LUAU_FASTFLAG(LuauAstTypeGroup3)
 LUAU_FASTFLAG(LuauFixDoBlockEndLocation)
+LUAU_FASTFLAG(LuauParseOptionalAsNode2)
+LUAU_FASTFLAG(LuauParseStringIndexer)
+LUAU_FASTFLAG(LuauFixFunctionWithAttributesStartLocation)
+LUAU_DYNAMIC_FASTFLAG(DebugLuauReportReturnTypeVariadicWithTypeSuffix)
+
+// Clip with DebugLuauReportReturnTypeVariadicWithTypeSuffix
+extern bool luau_telemetry_parsed_return_type_variadic_with_type_suffix;
 
 namespace
 {
@@ -372,7 +377,7 @@ TEST_CASE_FIXTURE(Fixture, "return_type_is_an_intersection_type_if_led_with_one_
 
     AstTypeIntersection* returnAnnotation = annotation->returnTypes.types.data[0]->as<AstTypeIntersection>();
     REQUIRE(returnAnnotation != nullptr);
-    if (FFlag::LuauAstTypeGroup2)
+    if (FFlag::LuauAstTypeGroup3)
         CHECK(returnAnnotation->types.data[0]->as<AstTypeGroup>());
     else
         CHECK(returnAnnotation->types.data[0]->as<AstTypeReference>());
@@ -2127,8 +2132,6 @@ TEST_CASE_FIXTURE(Fixture, "variadic_definition_parsing")
 
 TEST_CASE_FIXTURE(Fixture, "missing_declaration_prop")
 {
-    ScopedFastFlag luauErrorRecoveryForClassNames{FFlag::LuauErrorRecoveryForClassNames, true};
-
     matchParseError(
         R"(
         declare class Foo
@@ -2451,7 +2454,7 @@ TEST_CASE_FIXTURE(Fixture, "leading_union_intersection_with_single_type_preserve
 
 TEST_CASE_FIXTURE(Fixture, "parse_simple_ast_type_group")
 {
-    ScopedFastFlag _{FFlag::LuauAstTypeGroup2, true};
+    ScopedFastFlag _{FFlag::LuauAstTypeGroup3, true};
 
     AstStatBlock* stat = parse(R"(
         type Foo = (string)
@@ -2469,7 +2472,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_simple_ast_type_group")
 
 TEST_CASE_FIXTURE(Fixture, "parse_nested_ast_type_group")
 {
-    ScopedFastFlag _{FFlag::LuauAstTypeGroup2, true};
+    ScopedFastFlag _{FFlag::LuauAstTypeGroup3, true};
 
     AstStatBlock* stat = parse(R"(
         type Foo = ((string))
@@ -2490,7 +2493,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_nested_ast_type_group")
 
 TEST_CASE_FIXTURE(Fixture, "parse_return_type_ast_type_group")
 {
-    ScopedFastFlag _{FFlag::LuauAstTypeGroup2, true};
+    ScopedFastFlag _{FFlag::LuauAstTypeGroup3, true};
 
     AstStatBlock* stat = parse(R"(
         type Foo = () -> (string)
@@ -2543,6 +2546,40 @@ TEST_CASE_FIXTURE(Fixture, "do_block_end_location_is_after_end_token")
     CHECK_EQ(block->location, Location{{1, 8}, {3, 11}});
 }
 
+TEST_CASE_FIXTURE(Fixture, "function_start_locations_are_before_attributes")
+{
+    ScopedFastFlag _{FFlag::LuauFixFunctionWithAttributesStartLocation, true};
+
+    AstStatBlock* stat = parse(R"(
+        @native
+        function globalFunction()
+        end
+
+        @native
+        local function localFunction()
+        end
+
+        local _ = @native function()
+        end
+    )");
+    REQUIRE(stat);
+    REQUIRE_EQ(3, stat->body.size);
+
+    auto globalFunction = stat->body.data[0]->as<AstStatFunction>();
+    REQUIRE(globalFunction);
+    CHECK_EQ(globalFunction->location, Location({1, 8}, {3, 11}));
+
+    auto localFunction = stat->body.data[1]->as<AstStatLocalFunction>();
+    REQUIRE(localFunction);
+    CHECK_EQ(localFunction->location, Location({5, 8}, {7, 11}));
+
+    auto localVariable = stat->body.data[2]->as<AstStatLocal>();
+    REQUIRE(localVariable);
+    REQUIRE_EQ(localVariable->values.size, 1);
+    auto anonymousFunction = localVariable->values.data[0]->as<AstExprFunction>();
+    CHECK_EQ(anonymousFunction->location, Location({9, 18}, {10, 11}));
+}
+
 TEST_SUITE_END();
 
 TEST_SUITE_BEGIN("ParseErrorRecovery");
@@ -3813,7 +3850,7 @@ TEST_CASE_FIXTURE(Fixture, "grouped_function_type")
     auto unionTy = paramTy.type->as<AstTypeUnion>();
     LUAU_ASSERT(unionTy);
     CHECK_EQ(unionTy->types.size, 2);
-    if (FFlag::LuauAstTypeGroup2)
+    if (FFlag::LuauAstTypeGroup3)
     {
         auto groupTy = unionTy->types.data[0]->as<AstTypeGroup>(); // (() -> ())
         REQUIRE(groupTy);
@@ -3821,7 +3858,10 @@ TEST_CASE_FIXTURE(Fixture, "grouped_function_type")
     }
     else
         CHECK(unionTy->types.data[0]->is<AstTypeFunction>()); // () -> ()
-    CHECK(unionTy->types.data[1]->is<AstTypeReference>());    // nil
+    if (FFlag::LuauParseOptionalAsNode2)
+        CHECK(unionTy->types.data[1]->is<AstTypeOptional>()); // ?
+    else
+        CHECK(unionTy->types.data[1]->is<AstTypeReference>()); // nil
 }
 
 TEST_CASE_FIXTURE(Fixture, "complex_union_in_generic_ty")
@@ -3879,7 +3919,6 @@ TEST_CASE_FIXTURE(Fixture, "recover_from_bad_table_type")
 
 TEST_CASE_FIXTURE(Fixture, "function_name_has_correct_start_location")
 {
-    ScopedFastFlag _{FFlag::LuauFixFunctionNameStartPosition, true};
     AstStatBlock* block = parse(R"(
         function simple()
         end
@@ -3926,5 +3965,24 @@ TEST_CASE_FIXTURE(Fixture, "stat_end_includes_semicolon_position")
     CHECK_EQ(Position{3, 22}, stat3->location.end);
 }
 
+TEST_CASE_FIXTURE(Fixture, "parsing_type_suffix_for_return_type_with_variadic")
+{
+    ScopedFastFlag sff{DFFlag::DebugLuauReportReturnTypeVariadicWithTypeSuffix, true};
+
+    ParseResult result = tryParse(R"(
+        function foo(): (string, ...number) | boolean
+        end
+    )");
+
+    // TODO(CLI-140667): this should produce a ParseError in future when we fix the invalid syntax
+    CHECK(result.errors.size() == 0);
+    CHECK_EQ(luau_telemetry_parsed_return_type_variadic_with_type_suffix, true);
+}
+
+TEST_CASE_FIXTURE(Fixture, "parsing_string_union_indexers")
+{
+    ScopedFastFlag _{FFlag::LuauParseStringIndexer, true};
+    parse(R"(type foo = { ["bar" | "baz"]: number })");
+}
 
 TEST_SUITE_END();

tests/RequireTracer.test.cpp

@@ -6,8 +6,6 @@
 
 #include "doctest.h"
 
-LUAU_FASTFLAG(LuauExtendedSimpleRequire)
-
 using namespace Luau;
 
 namespace
@@ -182,8 +180,6 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "follow_string_indexexpr")
 
 TEST_CASE_FIXTURE(RequireTracerFixture, "follow_group")
 {
-    ScopedFastFlag luauExtendedSimpleRequire{FFlag::LuauExtendedSimpleRequire, true};
-
     AstStatBlock* block = parse(R"(
         local R = (((game).Test))
         require(R)
@@ -200,8 +196,6 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "follow_group")
 
 TEST_CASE_FIXTURE(RequireTracerFixture, "follow_type_annotation")
 {
-    ScopedFastFlag luauExtendedSimpleRequire{FFlag::LuauExtendedSimpleRequire, true};
-
     AstStatBlock* block = parse(R"(
         local R = game.Test :: (typeof(game.Redirect))
         require(R)
@@ -218,8 +212,6 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "follow_type_annotation")
 
 TEST_CASE_FIXTURE(RequireTracerFixture, "follow_type_annotation_2")
 {
-    ScopedFastFlag luauExtendedSimpleRequire{FFlag::LuauExtendedSimpleRequire, true};
-
     AstStatBlock* block = parse(R"(
         local R = game.Test :: (typeof(game.Redirect))
         local N = R.Nested

tests/ScopedFlags.h

@@ -3,7 +3,7 @@
 
 #include "Luau/Common.h"
 
-#include <string.h>
+#include <vector>
 
 template<typename T>
 struct [[nodiscard]] ScopedFValue
@@ -49,4 +49,4 @@ public:
 };
 
 using ScopedFastFlag = ScopedFValue<bool>;
-using ScopedFastInt = ScopedFValue<int>;
+using ScopedFastInt = ScopedFValue<int>;

tests/Subtyping.test.cpp

@@ -15,7 +15,8 @@
 
 #include <initializer_list>
 
-LUAU_FASTFLAG(LuauSolverV2);
+LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAG(LuauNormalizedBufferIsNotUnknown)
 
 using namespace Luau;
 
@@ -961,6 +962,20 @@ TEST_IS_NOT_SUBTYPE(childClass, negate(rootClass));
 TEST_IS_NOT_SUBTYPE(childClass, meet(builtinTypes->classType, negate(rootClass)));
 TEST_IS_SUBTYPE(anotherChildClass, meet(builtinTypes->classType, negate(childClass)));
 
+// Negated primitives against unknown
+TEST_IS_NOT_SUBTYPE(builtinTypes->unknownType, negate(builtinTypes->booleanType));
+TEST_IS_NOT_SUBTYPE(builtinTypes->unknownType, negate(builtinTypes->numberType));
+TEST_IS_NOT_SUBTYPE(builtinTypes->unknownType, negate(builtinTypes->stringType));
+TEST_IS_NOT_SUBTYPE(builtinTypes->unknownType, negate(builtinTypes->threadType));
+
+TEST_CASE_FIXTURE(SubtypeFixture, "unknown <!: ~buffer")
+{
+    // TODO: replace with TEST_IS_NOT_SUBTYPE on flag removal
+    ScopedFastFlag luauNormalizedBufferIsNotUnknown{FFlag::LuauNormalizedBufferIsNotUnknown, true};
+
+    CHECK_IS_NOT_SUBTYPE(builtinTypes->unknownType, negate(builtinTypes->bufferType));
+}
+
 TEST_CASE_FIXTURE(SubtypeFixture, "Root <: class")
 {
     CHECK_IS_SUBTYPE(rootClass, builtinTypes->classType);

tests/ToString.test.cpp

@@ -5,14 +5,16 @@
 
 #include "Fixture.h"
 
+#include "Luau/TypeChecker2.h"
 #include "ScopedFlags.h"
 #include "doctest.h"
 
 using namespace Luau;
 
-LUAU_FASTFLAG(LuauRecursiveTypeParameterRestriction);
+LUAU_FASTFLAG(LuauRecursiveTypeParameterRestriction)
-LUAU_FASTFLAG(LuauSolverV2);
+LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAG(LuauAttributeSyntax);
+LUAU_FASTFLAG(LuauAttributeSyntax)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
 
 TEST_SUITE_BEGIN("ToString");
 
@@ -871,9 +873,28 @@ TEST_CASE_FIXTURE(Fixture, "tostring_error_mismatch")
     )");
 
     std::string expected;
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+        expected =
+            "Type pack '{ a: number, b: string, c: { d: string } }' could not be converted into '{ a: number, b: string, c: { d: number } }'; \n"
+            "this is because in the 1st entry in the type pack, accessing `c.d` results in `string` in the former type and `number` in the latter "
+            "type, and `string` is not exactly `number`";
+    else if (FFlag::LuauSolverV2)
         expected =
             R"(Type pack '{ a: number, b: string, c: { d: string } }' could not be converted into '{ a: number, b: string, c: { d: number } }'; at [0][read "c"][read "d"], string is not exactly number)";
+    else if (FFlag::LuauImproveTypePathsInErrors)
+        expected = R"(Type
+	'{ a: number, b: string, c: { d: string } }'
+could not be converted into
+	'{| a: number, b: string, c: {| d: number |} |}'
+caused by:
+  Property 'c' is not compatible.
+Type
+	'{ d: string }'
+could not be converted into
+	'{| d: number |}'
+caused by:
+  Property 'd' is not compatible.
+Type 'string' could not be converted into 'number' in an invariant context)";
     else
         expected = R"(Type
     '{ a: number, b: string, c: { d: string } }'

tests/TypeFunction.test.cpp

@@ -13,8 +13,13 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAG(LuauIndexTypeFunctionImprovements)
 LUAU_DYNAMIC_FASTINT(LuauTypeFamilyApplicationCartesianProductLimit)
+LUAU_FASTFLAG(LuauIndexTypeFunctionFunctionMetamethods)
 LUAU_FASTFLAG(LuauMetatableTypeFunctions)
+LUAU_FASTFLAG(LuauMetatablesHaveLength)
+LUAU_FASTFLAG(LuauIndexAnyIsAny)
+LUAU_FASTFLAG(LuauNewTypeFunReductionChecks2)
 
 struct TypeFunctionFixture : Fixture
 {
@@ -142,19 +147,17 @@ TEST_CASE_FIXTURE(TypeFunctionFixture, "unsolvable_function")
     if (!FFlag::LuauSolverV2)
         return;
 
+    ScopedFastFlag luauNewTypeFunReductionChecks2{FFlag::LuauNewTypeFunReductionChecks2, true};
+
     CheckResult result = check(R"(
         local impossible: <T>(Swap<T>) -> Swap<Swap<T>>
         local a = impossible(123)
         local b = impossible(true)
     )");
 
-    LUAU_REQUIRE_ERROR_COUNT(6, result);
+    LUAU_REQUIRE_ERROR_COUNT(2, result);
-    CHECK(toString(result.errors[0]) == "Type function instance Swap<Swap<T>> is uninhabited");
+    CHECK(toString(result.errors[0]) == "Type 'number' could not be converted into 'never'");
-    CHECK(toString(result.errors[1]) == "Type function instance Swap<T> is uninhabited");
+    CHECK(toString(result.errors[1]) == "Type 'boolean' could not be converted into 'never'");
-    CHECK(toString(result.errors[2]) == "Type function instance Swap<Swap<T>> is uninhabited");
-    CHECK(toString(result.errors[3]) == "Type function instance Swap<T> is uninhabited");
-    CHECK(toString(result.errors[4]) == "Type function instance Swap<Swap<T>> is uninhabited");
-    CHECK(toString(result.errors[5]) == "Type function instance Swap<T> is uninhabited");
 }
 
 TEST_CASE_FIXTURE(TypeFunctionFixture, "table_internal_functions")
@@ -904,6 +907,21 @@ end
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "index_of_any_is_any")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    ScopedFastFlag sff{FFlag::LuauIndexAnyIsAny, true};
+
+    CheckResult result = check(R"(
+        type T = index<any, "a">
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+    CHECK(toString(requireTypeAlias("T")) == "any");
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "index_type_function_works")
 {
     if (!FFlag::LuauSolverV2)
@@ -965,6 +983,31 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "index_type_function_works_w_array")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "cyclic_metatable_should_not_crash_index")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    ScopedFastFlag sff{FFlag::LuauIndexTypeFunctionImprovements, true};
+
+    // t :: t1 where t1 = {metatable {__index: t1, __tostring: (t1) -> string}}
+    CheckResult result = check(R"(
+        local mt = {}
+        local t = setmetatable({}, mt)
+        mt.__index = t
+
+        function mt:__tostring()
+            return t.p
+        end
+
+        type IndexFromT = index<typeof(t), "p">
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(2, result);
+    CHECK_EQ("Type 't' does not have key 'p'", toString(result.errors[0]));
+    CHECK_EQ("Property '\"p\"' does not exist on type 't'", toString(result.errors[1]));
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "index_type_function_works_w_generic_types")
 {
     if (!FFlag::LuauSolverV2)
@@ -1003,6 +1046,61 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "index_type_function_errors_w_bad_indexer")
     CHECK(toString(result.errors[1]) == "Property 'boolean' does not exist on type 'MyObject'");
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "index_type_function_works_on_function_metamethods")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    ScopedFastFlag sff[]
+    {
+        {FFlag::LuauIndexTypeFunctionFunctionMetamethods, true},
+        {FFlag::LuauIndexTypeFunctionImprovements, true},
+    };
+
+    CheckResult result = check(R"(
+        type Foo = {x: string}
+        local t = {}
+        setmetatable(t, {
+            __index = function(x: string): Foo
+                return {x = x}
+            end
+        })
+
+        type Bar = index<typeof(t), "bar">
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+
+    CHECK_EQ(toString(requireTypeAlias("Bar"), {true}), "{ x: string }");
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "index_type_function_works_on_function_metamethods2")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    ScopedFastFlag sff[]
+    {
+        {FFlag::LuauIndexTypeFunctionFunctionMetamethods, true},
+        {FFlag::LuauIndexTypeFunctionImprovements, true},
+    };
+
+    CheckResult result = check(R"(
+        type Foo = {x: string}
+        local t = {}
+        setmetatable(t, {
+            __index = function(x: string): Foo
+                return {x = x}
+            end
+        })
+
+        type Bar = index<typeof(t), number>
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "index_type_function_errors_w_var_indexer")
 {
     if (!FFlag::LuauSolverV2)
@@ -1454,4 +1552,35 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "getmetatable_respects_metatable_metamethod")
     CHECK_EQ(toString(requireTypeAlias("Metatable")), "string");
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "type_function_correct_cycle_check")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    ScopedFastFlag luauNewTypeFunReductionChecks2{FFlag::LuauNewTypeFunReductionChecks2, true};
+
+    CheckResult result = check(R"(
+type foo<T> = { a: add<T, T>, b : add<T, T> }
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "len_typefun_on_metatable")
+{
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+    ScopedFastFlag luauMetatablesHaveLength{FFlag::LuauMetatablesHaveLength, true};
+
+    CheckResult result = check(R"(
+local t = setmetatable({}, { __mode = "v" })
+
+local function f()
+    table.insert(t, {})
+    print(#t * 100)
+end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeFunction.user.test.cpp

@@ -7,13 +7,12 @@
 
 using namespace Luau;
 
-LUAU_FASTFLAG(LuauTypeFunFixHydratedClasses)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(DebugLuauEqSatSimplification)
-LUAU_FASTFLAG(LuauTypeFunSingletonEquality)
-LUAU_FASTFLAG(LuauUserTypeFunTypeofReturnsType)
 LUAU_FASTFLAG(LuauTypeFunReadWriteParents)
-LUAU_FASTFLAG(LuauTypeFunPrintFix)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
+LUAU_FASTFLAG(LuauUserTypeFunTypecheck)
+LUAU_FASTFLAG(LuauNewTypeFunReductionChecks2)
 
 TEST_SUITE_BEGIN("UserDefinedTypeFunctionTests");
 
@@ -613,9 +612,12 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_function_methods_work")
             ty:setreturns(nil, types.boolean) -- (string, number) -> (...boolean)
             if ty:is("function") then
                 -- creating a copy of `ty` parameters
-                local arr = {}
+                local arr: {type} = {}
-                for index, val in ty:parameters().head do
+                local args = ty:parameters().head
-                    table.insert(arr, val)
+                if args then
+                    for index, val in args do
+                        table.insert(arr, val)
+                    end
                 end
                 return types.newfunction({head = arr}, ty:returns()) -- (string, number) -> (...boolean)
             end
@@ -648,7 +650,6 @@ TEST_CASE_FIXTURE(ClassFixture, "udtf_class_serialization_works")
 TEST_CASE_FIXTURE(ClassFixture, "udtf_class_serialization_works2")
 {
     ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
-    ScopedFastFlag luauTypeFunFixHydratedClasses{FFlag::LuauTypeFunFixHydratedClasses, true};
 
     CheckResult result = check(R"(
         type function serialize_class(arg)
@@ -719,7 +720,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_check_mutability")
                 readresult = types.boolean,
                 writeresult = types.boolean,
             }
-            local ty = types.newtable(props, indexer, nil) -- {[number]: boolean}
+            local ty = types.newtable(nil, indexer, nil) -- {[number]: boolean}
             ty:setproperty(types.singleton("string"), types.number) -- {string: number, [number]: boolean}
             local metatbl = types.newtable(nil, nil, ty) -- { {  }, @metatable { [number]: boolean, string: number } }
             -- mutate the table
@@ -894,6 +895,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_type_overrides_eq_metamethod")
             if p1 == p2 and t1 == t2 then
                 return types.number
             end
+            return types.unknown
         end
         local function ok(idx: hello<>): number return idx end
     )");
@@ -988,8 +990,37 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_calling_each_other_3")
         end
     )");
 
-    LUAU_REQUIRE_ERROR_COUNT(4, result);
+    if (FFlag::LuauUserTypeFunTypecheck)
-    CHECK(toString(result.errors[0]) == R"('third' type function errored at runtime: [string "first"]:4: attempt to call a nil value)");
+    {
+        LUAU_REQUIRE_ERROR_COUNT(5, result);
+        CHECK(toString(result.errors[0]) == R"(Unknown global 'fourth')");
+        CHECK(toString(result.errors[1]) == R"('third' type function errored at runtime: [string "first"]:4: attempt to call a nil value)");
+    }
+    else
+    {
+        LUAU_REQUIRE_ERROR_COUNT(4, result);
+        CHECK(toString(result.errors[0]) == R"('third' type function errored at runtime: [string "first"]:4: attempt to call a nil value)");
+    }
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_calling_each_other_unordered")
+{
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+
+    CheckResult result = check(R"(
+        type function bar()
+            return types.singleton(foo())
+        end
+        type function foo()
+            return "hi"
+        end
+        local function ok(idx: bar<>): nil return idx end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    TypePackMismatch* tpm = get<TypePackMismatch>(result.errors[0]);
+    REQUIRE(tpm);
+    CHECK(toString(tpm->givenTp) == "\"hi\"");
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_no_shared_state")
@@ -1013,10 +1044,21 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_no_shared_state")
         local function ok2(idx: bar<'y'>): nil return idx end
     )");
 
-    // We are only checking first errors, others are mostly duplicates
+    if (FFlag::LuauUserTypeFunTypecheck)
-    LUAU_REQUIRE_ERROR_COUNT(8, result);
+    {
-    CHECK(toString(result.errors[0]) == R"('bar' type function errored at runtime: [string "foo"]:4: attempt to modify a readonly table)");
+        // We are only checking first errors, others are mostly duplicates
-    CHECK(toString(result.errors[1]) == R"(Type function instance bar<"x"> is uninhabited)");
+        LUAU_REQUIRE_ERROR_COUNT(9, result);
+        CHECK(toString(result.errors[0]) == R"(Unknown global 'glob')");
+        CHECK(toString(result.errors[1]) == R"('bar' type function errored at runtime: [string "foo"]:4: attempt to modify a readonly table)");
+        CHECK(toString(result.errors[2]) == R"(Type function instance bar<"x"> is uninhabited)");
+    }
+    else
+    {
+        // We are only checking first errors, others are mostly duplicates
+        LUAU_REQUIRE_ERROR_COUNT(8, result);
+        CHECK(toString(result.errors[0]) == R"('bar' type function errored at runtime: [string "foo"]:4: attempt to modify a readonly table)");
+        CHECK(toString(result.errors[1]) == R"(Type function instance bar<"x"> is uninhabited)");
+    }
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_math_reset")
@@ -1075,10 +1117,23 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_calling_illegal_global")
         local function ok(idx: illegal<number>): nil return idx end
     )");
 
-    LUAU_REQUIRE_ERROR_COUNT(4, result); // There are 2 type function uninhabited error, 2 user defined type function error
+    if (FFlag::LuauUserTypeFunTypecheck)
-    UserDefinedTypeFunctionError* e = get<UserDefinedTypeFunctionError>(result.errors[0]);
+    {
-    REQUIRE(e);
+        // We are only checking first errors, others are mostly duplicates
-    CHECK(e->message == "'illegal' type function errored at runtime: [string \"illegal\"]:3: this function is not supported in type functions");
+        LUAU_REQUIRE_ERROR_COUNT(5, result);
+        CHECK(toString(result.errors[0]) == R"(Unknown global 'gcinfo')");
+        CHECK(
+            toString(result.errors[1]) ==
+            R"('illegal' type function errored at runtime: [string "illegal"]:3: this function is not supported in type functions)"
+        );
+    }
+    else
+    {
+        LUAU_REQUIRE_ERROR_COUNT(4, result); // There are 2 type function uninhabited error, 2 user defined type function error
+        UserDefinedTypeFunctionError* e = get<UserDefinedTypeFunctionError>(result.errors[0]);
+        REQUIRE(e);
+        CHECK(e->message == "'illegal' type function errored at runtime: [string \"illegal\"]:3: this function is not supported in type functions");
+    }
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_recursion_and_gc")
@@ -1172,7 +1227,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "no_type_methods_on_types")
 
     CheckResult result = check(R"(
         type function test(x)
-            return if types.is(x, "number") then types.string else types.boolean
+            return if (types :: any).is(x, "number") then types.string else types.boolean
         end
         local function ok(tbl: test<number>): never return tbl end
     )");
@@ -1243,9 +1298,36 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "tag_field")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(3, result);
-    CHECK(toString(result.errors[0]) == R"(Type pack '"number"' could not be converted into 'never'; at [0], "number" is not a subtype of never)");
+
-    CHECK(toString(result.errors[1]) == R"(Type pack '"string"' could not be converted into 'never'; at [0], "string" is not a subtype of never)");
+    if (FFlag::LuauImproveTypePathsInErrors)
-    CHECK(toString(result.errors[2]) == R"(Type pack '"table"' could not be converted into 'never'; at [0], "table" is not a subtype of never)");
+    {
+
+        CHECK(
+            toString(result.errors[0]) ==
+            "Type pack '\"number\"' could not be converted into 'never'; \n"
+            R"(this is because the 1st entry in the type pack is `"number"` in the former type and `never` in the latter type, and `"number"` is not a subtype of `never`)"
+        );
+        CHECK(
+            toString(result.errors[1]) ==
+            "Type pack '\"string\"' could not be converted into 'never'; \n"
+            R"(this is because the 1st entry in the type pack is `"string"` in the former type and `never` in the latter type, and `"string"` is not a subtype of `never`)"
+        );
+        CHECK(
+            toString(result.errors[2]) ==
+            "Type pack '\"table\"' could not be converted into 'never'; \n"
+            R"(this is because the 1st entry in the type pack is `"table"` in the former type and `never` in the latter type, and `"table"` is not a subtype of `never`)"
+        );
+    }
+    else
+    {
+        CHECK(
+            toString(result.errors[0]) == R"(Type pack '"number"' could not be converted into 'never'; at [0], "number" is not a subtype of never)"
+        );
+        CHECK(
+            toString(result.errors[1]) == R"(Type pack '"string"' could not be converted into 'never'; at [0], "string" is not a subtype of never)"
+        );
+        CHECK(toString(result.errors[2]) == R"(Type pack '"table"' could not be converted into 'never'; at [0], "table" is not a subtype of never)");
+    }
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "metatable_serialization")
@@ -1293,8 +1375,12 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "implicit_export")
     ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
 
     fileResolver.source["game/A"] = R"(
-type function concat(a, b)
+type function concat(a: type, b: type)
-    return types.singleton(a:value() .. b:value())
+    local as = a:value()
+    local bs = b:value()
+    assert(typeof(as) == "string")
+    assert(typeof(bs) == "string")
+    return types.singleton(as .. bs)
 end
 export type Concat<T, U> = concat<T, U>
 local a: concat<'first', 'second'>
@@ -1342,8 +1428,12 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "explicit_export")
     ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
 
     fileResolver.source["game/A"] = R"(
-export type function concat(a, b)
+export type function concat(a: type, b: type)
-    return types.singleton(a:value() .. b:value())
+    local as = a:value()
+    local bs = b:value()
+    assert(typeof(as) == "string")
+    assert(typeof(bs) == "string")
+    return types.singleton(as .. bs)
 end
 local a: concat<'first', 'second'>
 return {}
@@ -1892,7 +1982,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_eqsat_opaque")
 TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_singleton_equality_bool")
 {
     ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
-    ScopedFastFlag luauTypeFunSingletonEquality{FFlag::LuauTypeFunSingletonEquality, true};
 
     CheckResult result = check(R"(
 type function compare(arg)
@@ -1909,7 +1998,6 @@ local function ok(idx: compare<true>): false return idx end
 TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_singleton_equality_string")
 {
     ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
-    ScopedFastFlag luauTypeFunSingletonEquality{FFlag::LuauTypeFunSingletonEquality, true};
 
     CheckResult result = check(R"(
 type function compare(arg)
@@ -1926,7 +2014,6 @@ local function ok(idx: compare<"a">): false return idx end
 TEST_CASE_FIXTURE(BuiltinsFixture, "typeof_type_userdata_returns_type")
 {
     ScopedFastFlag solverV2{FFlag::LuauSolverV2, true};
-    ScopedFastFlag luauUserTypeFunTypeofReturnsType{FFlag::LuauUserTypeFunTypeofReturnsType, true};
 
     CheckResult result = check(R"(
 type function test(t)
@@ -1943,7 +2030,7 @@ local _:test<number>
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "udtf_print_tab_char_fix")
 {
-    ScopedFastFlag sffs[] = {{FFlag::LuauSolverV2, true}, {FFlag::LuauTypeFunPrintFix, true}};
+    ScopedFastFlag solverV2{FFlag::LuauSolverV2, true};
 
     CheckResult result = check(R"(
         type function test(t)
@@ -1982,4 +2069,139 @@ TEST_CASE_FIXTURE(ClassFixture, "udtf_class_parent_ops")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "typecheck_success")
+{
+    // Needs new global initialization in the Fixture, but can't place the flag inside the base Fixture
+    if (!FFlag::LuauUserTypeFunTypecheck)
+        return;
+
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+
+    CheckResult result = check(R"(
+type function foo(x: type)
+    return types.singleton(x.tag)
+end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "typecheck_failure")
+{
+    // Needs new global initialization in the Fixture, but can't place the flag inside the base Fixture
+    if (!FFlag::LuauUserTypeFunTypecheck)
+        return;
+
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+
+    CheckResult result = check(R"(
+type function foo()
+    return types.singleton({1})
+end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "outer_generics_irreducible")
+{
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+    ScopedFastFlag luauNewTypeFunReductionChecks2{FFlag::LuauNewTypeFunReductionChecks2, true};
+
+    CheckResult result = check(R"(
+type function func(t)
+    return t
+end
+
+type wrap<T> = { a: func<T?> }
+
+local x: wrap<string> = nil :: any
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK(toString(requireType("x"), ToStringOptions{true}) == "{ a: string? }");
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "inner_generics_reducible")
+{
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+
+    CheckResult result = check(R"(
+type function func(t)
+    return t
+end
+
+type wrap<T> = { a: func<<T>(T) -> number>, b: T }
+
+local x: wrap<string> = nil :: any
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK(toString(requireType("x"), ToStringOptions{true}) == "{ a: <T>(T) -> number, b: string }");
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "blocking_nested_pending_expansions")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    CheckResult result = check(R"(
+type function func(t)
+    return t
+end
+
+type test<T> = { x: T, y: T? }
+type wrap<T> = { a: func<(string, keyof<test<T>>) -> number>, b: T }
+local x: wrap<string>
+local y: keyof<typeof(x)>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK(toString(requireType("x"), ToStringOptions{true}) == R"({ a: (string, "x" | "y") -> number, b: string })");
+    CHECK(toString(requireType("y"), ToStringOptions{true}) == R"("a" | "b")");
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "blocking_nested_pending_expansions_2")
+{
+    ScopedFastFlag newSolver{FFlag::LuauSolverV2, true};
+
+    CheckResult result = check(R"(
+type function foo(t)
+    return types.unionof(t, types.singleton(nil))
+end
+
+local x: foo<{a: foo<string>, b: foo<number>}> = nil
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK(toString(requireType("x"), ToStringOptions{true}) == "{ a: string?, b: number? }?");
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "irreducible_pending_expansions")
+{
+    if (!FFlag::LuauSolverV2)
+        return;
+
+    ScopedFastFlag luauNewTypeFunReductionChecks2{FFlag::LuauNewTypeFunReductionChecks2, true};
+
+    CheckResult result = check(R"(
+type function foo(t)
+    return types.unionof(t, types.singleton(nil))
+end
+
+type table<T> = { a: index<T, "a"> }
+type wrap<T> = foo<table<T>>
+
+local x: wrap<{a: number}> = { a = 2 }
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK(toString(requireType("x"), ToStringOptions{true}) == "{ a: number }?");
+}
+
 TEST_SUITE_END();

tests/TypeInfer.aliases.test.cpp

@@ -11,6 +11,11 @@ using namespace Luau;
 
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauFixInfiniteRecursionInNormalization)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
+LUAU_FASTFLAG(LuauPrecalculateMutatedFreeTypes2)
+LUAU_FASTFLAG(LuauDeferBidirectionalInferenceForTableAssignment)
+LUAU_FASTFLAG(LuauBidirectionalInferenceUpcast)
+LUAU_FASTFLAG(LuauBidirectionalInferenceCollectIndexerTypes)
 
 TEST_SUITE_BEGIN("TypeAliases");
 
@@ -216,7 +221,11 @@ TEST_CASE_FIXTURE(Fixture, "generic_aliases")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type '{ v: string }' could not be converted into 'T<number>'; at [read "v"], string is not exactly number)";
+    const std::string expected = (FFlag::LuauImproveTypePathsInErrors)
+                                     ? "Type '{ v: string }' could not be converted into 'T<number>'; \n"
+                                       "this is because accessing `v` results in `string` in the former type and `number` in the latter type, and "
+                                       "`string` is not exactly `number`"
+                                     : R"(Type '{ v: string }' could not be converted into 'T<number>'; at [read "v"], string is not exactly number)";
     CHECK(result.errors[0].location == Location{{4, 31}, {4, 44}});
     CHECK_EQ(expected, toString(result.errors[0]));
 }
@@ -236,7 +245,11 @@ TEST_CASE_FIXTURE(Fixture, "dependent_generic_aliases")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
     const std::string expected =
-        R"(Type '{ t: { v: string } }' could not be converted into 'U<number>'; at [read "t"][read "v"], string is not exactly number)";
+        (FFlag::LuauImproveTypePathsInErrors)
+            ? "Type '{ t: { v: string } }' could not be converted into 'U<number>'; \n"
+              "this is because accessing `t.v` results in `string` in the former type and `number` in the latter type, and `string` is not exactly "
+              "`number`"
+            : R"(Type '{ t: { v: string } }' could not be converted into 'U<number>'; at [read "t"][read "v"], string is not exactly number)";
 
     CHECK(result.errors[0].location == Location{{4, 31}, {4, 52}});
     CHECK_EQ(expected, toString(result.errors[0]));
@@ -244,8 +257,12 @@ TEST_CASE_FIXTURE(Fixture, "dependent_generic_aliases")
 
 TEST_CASE_FIXTURE(Fixture, "mutually_recursive_generic_aliases")
 {
-    // CLI-116108
+    ScopedFastFlag sffs[] = {
-    DOES_NOT_PASS_NEW_SOLVER_GUARD();
+        {FFlag::LuauPrecalculateMutatedFreeTypes2, true},
+        {FFlag::LuauDeferBidirectionalInferenceForTableAssignment, true},
+        {FFlag::LuauBidirectionalInferenceUpcast, true},
+        {FFlag::LuauBidirectionalInferenceCollectIndexerTypes, true},
+    };
 
     CheckResult result = check(R"(
         --!strict

tests/TypeInfer.builtins.test.cpp

@@ -12,7 +12,7 @@ using namespace Luau;
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauTableCloneClonesType3)
 LUAU_FASTFLAG(LuauStringFormatErrorSuppression)
-LUAU_FASTFLAG(LuauFreezeIgnorePersistent)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
 
 TEST_SUITE_BEGIN("BuiltinTests");
 
@@ -146,7 +146,20 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "sort_with_bad_predicate")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+    const std::string expected = (FFlag::LuauImproveTypePathsInErrors) ? "Type\n\t"
+                                                                         "'(number, number) -> boolean'"
+                                                                         "\ncould not be converted into\n\t"
+                                                                         "'((string, string) -> boolean)?'"
+                                                                         "\ncaused by:\n"
+                                                                         "  None of the union options are compatible. For example:\n"
+                                                                         "Type\n\t"
+                                                                         "'(number, number) -> boolean'"
+                                                                         "\ncould not be converted into\n\t"
+                                                                         "'(string, string) -> boolean'"
+                                                                         "\ncaused by:\n"
+                                                                         "  Argument #1 type is not compatible.\n"
+                                                                         "Type 'string' could not be converted into 'number'"
+                                                                       : R"(Type
     '(number, number) -> boolean'
 could not be converted into
     '((string, string) -> boolean)?'
@@ -985,7 +998,14 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "tonumber_returns_optional_number_type")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    if (FFlag::LuauSolverV2)
+
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+        CHECK_EQ(
+            "Type 'number?' could not be converted into 'number'; \n"
+            "this is because the 2nd component of the union is `nil`, which is not a subtype of `number`",
+            toString(result.errors[0])
+        );
+    else if (FFlag::LuauSolverV2)
         CHECK_EQ(
             "Type 'number?' could not be converted into 'number'; type number?[1] (nil) is not a subtype of number (number)",
             toString(result.errors[0])
@@ -1256,8 +1276,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "table_freeze_errors_on_non_tables")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "table_freeze_persistent_skip")
 {
-    ScopedFastFlag luauFreezeIgnorePersistent{FFlag::LuauFreezeIgnorePersistent, true};
-
     CheckResult result = check(R"(
         table.freeze(table)
     )");
@@ -1267,8 +1285,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "table_freeze_persistent_skip")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "table_clone_persistent_skip")
 {
-    ScopedFastFlag luauFreezeIgnorePersistent{FFlag::LuauFreezeIgnorePersistent, true};
-
     CheckResult result = check(R"(
         table.clone(table)
     )");

tests/TypeInfer.classes.test.cpp

@@ -13,7 +13,8 @@
 using namespace Luau;
 using std::nullopt;
 
-LUAU_FASTFLAG(LuauSolverV2);
+LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
 
 TEST_SUITE_BEGIN("TypeInferClasses");
 
@@ -545,7 +546,13 @@ local b: B = a
 
     LUAU_REQUIRE_ERRORS(result);
 
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+        CHECK(
+            "Type 'A' could not be converted into 'B'; \n"
+            "this is because accessing `x` results in `ChildClass` in the former type and `BaseClass` in the latter type, and `ChildClass` is not "
+            "exactly `BaseClass`" == toString(result.errors.at(0))
+        );
+    else if (FFlag::LuauSolverV2)
         CHECK(toString(result.errors.at(0)) == "Type 'A' could not be converted into 'B'; at [read \"x\"], ChildClass is not exactly BaseClass");
     else
     {

tests/TypeInfer.definitions.test.cpp

@@ -9,9 +9,8 @@
 
 using namespace Luau;
 
-LUAU_FASTFLAG(LuauClipNestedAndRecursiveUnion)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
-LUAU_FASTFLAG(LuauPreventReentrantTypeFunctionReduction)
+LUAU_FASTFLAG(LuauDontForgetToReduceUnionFunc)
 
 TEST_SUITE_BEGIN("DefinitionTests");
 
@@ -544,8 +543,6 @@ TEST_CASE_FIXTURE(Fixture, "definition_file_has_source_module_name_set")
 
 TEST_CASE_FIXTURE(Fixture, "recursive_redefinition_reduces_rightfully")
 {
-    ScopedFastFlag _{FFlag::LuauClipNestedAndRecursiveUnion, true};
-
     LUAU_REQUIRE_NO_ERRORS(check(R"(
         local t: {[string]: string} = {}
 
@@ -557,9 +554,40 @@ TEST_CASE_FIXTURE(Fixture, "recursive_redefinition_reduces_rightfully")
     )"));
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "cli_142285_reduce_minted_union_func")
+{
+    ScopedFastFlag sffs[] = {
+        {FFlag::LuauSolverV2, true},
+        {FFlag::LuauDontForgetToReduceUnionFunc, true}
+    };
+
+    CheckResult result = check(R"(
+        local function middle(a: number, b: number): number
+            return math.ceil((a + b) / 2 - 0.5)
+        end
+
+        local function find<T>(array: {T}, item: T): number?
+            local l, m, r = 1, middle(1, #array), #array
+            while l <= r do
+                if item <= array[m] then
+                    if item == array[m] then return m end
+                    m, r = middle(l, m-1), m-1
+                else
+                    l, m = middle(m+1, r), m+1
+                end
+            end
+        return nil
+        end
+    )");
+    LUAU_REQUIRE_ERROR_COUNT(3, result);
+    // There are three errors in the above snippet, but they should all be where
+    // clause needed errors.
+    for (const auto& e: result.errors)
+        CHECK(get<WhereClauseNeeded>(e));
+}
+
 TEST_CASE_FIXTURE(Fixture, "vector3_overflow")
 {
-    ScopedFastFlag _{FFlag::LuauPreventReentrantTypeFunctionReduction, true};
     // We set this to zero to ensure that we either run to completion or stack overflow here.
     ScopedFastInt sfi{FInt::LuauTypeInferRecursionLimit, 0};
 

tests/TypeInfer.functions.test.cpp

@@ -22,8 +22,9 @@ LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTINT(LuauTarjanChildLimit)
 LUAU_FASTFLAG(DebugLuauEqSatSimplification)
-LUAU_FASTFLAG(LuauSubtypingFixTailPack)
 LUAU_FASTFLAG(LuauUngeneralizedTypesForRecursiveFunctions)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
+LUAU_FASTFLAG(LuauReduceUnionFollowUnionType)
 
 TEST_SUITE_BEGIN("TypeInferFunctions");
 
@@ -1306,7 +1307,16 @@ f(function(a, b, c, ...) return a + b end)
     LUAU_REQUIRE_ERRORS(result);
 
     std::string expected;
-    if (FFlag::LuauInstantiateInSubtyping)
+    if (FFlag::LuauInstantiateInSubtyping && FFlag::LuauImproveTypePathsInErrors)
+    {
+        expected = "Type\n\t"
+                   "'<a>(number, number, a) -> number'"
+                   "\ncould not be converted into\n\t"
+                   "'(number, number) -> number'"
+                   "\ncaused by:\n"
+                   "  Argument count mismatch. Function expects 3 arguments, but only 2 are specified";
+    }
+    else if (FFlag::LuauInstantiateInSubtyping)
     {
         expected = R"(Type
     '<a>(number, number, a) -> number'
@@ -1315,6 +1325,15 @@ could not be converted into
 caused by:
   Argument count mismatch. Function expects 3 arguments, but only 2 are specified)";
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        expected = "Type\n\t"
+                   "'(number, number, *error-type*) -> number'"
+                   "\ncould not be converted into\n\t"
+                   "'(number, number) -> number'"
+                   "\ncaused by:\n"
+                   "  Argument count mismatch. Function expects 3 arguments, but only 2 are specified";
+    }
     else
     {
         expected = R"(Type
@@ -1519,7 +1538,14 @@ local b: B = a
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+    const std::string expected = (FFlag::LuauImproveTypePathsInErrors)
+                                     ? "Type\n\t"
+                                       "'(number, number) -> string'"
+                                       "\ncould not be converted into\n\t"
+                                       "'(number) -> string'"
+                                       "\ncaused by:\n"
+                                       "  Argument count mismatch. Function expects 2 arguments, but only 1 is specified"
+                                     : R"(Type
     '(number, number) -> string'
 could not be converted into
     '(number) -> string'
@@ -1542,7 +1568,14 @@ local b: B = a
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+    const std::string expected = (FFlag::LuauImproveTypePathsInErrors) ? "Type\n\t"
+                                                                         "'(number, number) -> string'"
+                                                                         "\ncould not be converted into\n\t"
+                                                                         "'(number, string) -> string'"
+                                                                         "\ncaused by:\n"
+                                                                         "  Argument #2 type is not compatible.\n"
+                                                                         "Type 'string' could not be converted into 'number'"
+                                                                       : R"(Type
     '(number, number) -> string'
 could not be converted into
     '(number, string) -> string'
@@ -1566,7 +1599,13 @@ local b: B = a
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+    const std::string expected = (FFlag::LuauImproveTypePathsInErrors) ? "Type\n\t"
+                                                                         "'(number, number) -> number'"
+                                                                         "\ncould not be converted into\n\t"
+                                                                         "'(number, number) -> (number, boolean)'"
+                                                                         "\ncaused by:\n"
+                                                                         "  Function only returns 1 value, but 2 are required here"
+                                                                       : R"(Type
     '(number, number) -> number'
 could not be converted into
     '(number, number) -> (number, boolean)'
@@ -1589,7 +1628,14 @@ local b: B = a
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+    const std::string expected = (FFlag::LuauImproveTypePathsInErrors) ? "Type\n\t"
+                                                                         "'(number, number) -> string'"
+                                                                         "\ncould not be converted into\n\t"
+                                                                         "'(number, number) -> number'"
+                                                                         "\ncaused by:\n"
+                                                                         "  Return type is not compatible.\n"
+                                                                         "Type 'string' could not be converted into 'number'"
+                                                                       : R"(Type
     '(number, number) -> string'
 could not be converted into
     '(number, number) -> number'
@@ -1613,7 +1659,14 @@ local b: B = a
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+    const std::string expected = (FFlag::LuauImproveTypePathsInErrors) ? "Type\n\t"
+                                                                         "'(number, number) -> (number, string)'"
+                                                                         "\ncould not be converted into\n\t"
+                                                                         "'(number, number) -> (number, boolean)'"
+                                                                         "\ncaused by:\n"
+                                                                         "  Return #2 type is not compatible.\n"
+                                                                         "Type 'string' could not be converted into 'boolean'"
+                                                                       : R"(Type
     '(number, number) -> (number, string)'
 could not be converted into
     '(number, number) -> (number, boolean)'
@@ -1769,6 +1822,24 @@ end
             R"(Type function instance add<a, number> depends on generic function parameters but does not appear in the function signature; this construct cannot be type-checked at this time)"
         );
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(2, result);
+        CHECK_EQ(toString(result.errors[0]), R"(Type
+	'(string) -> string'
+could not be converted into
+	'((number) -> number)?'
+caused by:
+  None of the union options are compatible. For example:
+Type
+	'(string) -> string'
+could not be converted into
+	'(number) -> number'
+caused by:
+  Argument #1 type is not compatible.
+Type 'number' could not be converted into 'string')");
+        CHECK_EQ(toString(result.errors[1]), R"(Type 'string' could not be converted into 'number')");
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(2, result);
@@ -1812,15 +1883,31 @@ function t:b() return 2 end -- not OK
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    CHECK_EQ(
+
-        R"(Type
+    if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        CHECK_EQ(
+            "Type\n\t"
+            "'(*error-type*) -> number'"
+            "\ncould not be converted into\n\t"
+            "'() -> number'\n"
+            "caused by:\n"
+            "  Argument count mismatch. Function expects 1 argument, but none are specified",
+            toString(result.errors[0])
+        );
+    }
+    else
+    {
+        CHECK_EQ(
+            R"(Type
     '(*error-type*) -> number'
 could not be converted into
     '() -> number'
 caused by:
   Argument count mismatch. Function expects 1 argument, but none are specified)",
-        toString(result.errors[0])
+            toString(result.errors[0])
-    );
+        );
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "too_few_arguments_variadic")
@@ -2078,7 +2165,13 @@ z = y -- Not OK, so the line is colorable
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+    const std::string expected =
+        (FFlag::LuauImproveTypePathsInErrors)
+            ? "Type\n\t"
+              R"('(("blue" | "red") -> ("blue" | "red") -> ("blue" | "red") -> boolean) & (("blue" | "red") -> ("blue") -> ("blue") -> false) & (("blue" | "red") -> ("red") -> ("red") -> false) & (("blue") -> ("blue") -> ("blue" | "red") -> false) & (("red") -> ("red") -> ("blue" | "red") -> false)')"
+              "\ncould not be converted into\n\t"
+              R"('("blue" | "red") -> ("blue" | "red") -> ("blue" | "red") -> false'; none of the intersection parts are compatible)"
+            : R"(Type
     '(("blue" | "red") -> ("blue" | "red") -> ("blue" | "red") -> boolean) & (("blue" | "red") -> ("blue") -> ("blue") -> false) & (("blue" | "red") -> ("red") -> ("red") -> false) & (("blue") -> ("blue") -> ("blue" | "red") -> false) & (("red") -> ("red") -> ("blue" | "red") -> false)'
 could not be converted into
     '("blue" | "red") -> ("blue" | "red") -> ("blue" | "red") -> false'; none of the intersection parts are compatible)";
@@ -2412,7 +2505,14 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "num_is_solved_before_num_or_str")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    if (FFlag::LuauSolverV2)
+
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+        CHECK(
+            "Type pack 'string' could not be converted into 'number'; \n"
+            "this is because the 1st entry in the type pack is `string` in the former type and `number` in the latter type, and `string` is not a "
+            "subtype of `number`" == toString(result.errors.at(0))
+        );
+    else if (FFlag::LuauSolverV2)
         CHECK(toString(result.errors.at(0)) == "Type pack 'string' could not be converted into 'number'; at [0], string is not a subtype of number");
     else
         CHECK_EQ("Type 'string' could not be converted into 'number'", toString(result.errors[0]));
@@ -2437,7 +2537,13 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "num_is_solved_after_num_or_str")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+        CHECK(
+            "Type pack 'string' could not be converted into 'number'; \n"
+            "this is because the 1st entry in the type pack is `string` in the former type and `number` in the latter type, and `string` is not a "
+            "subtype of `number`" == toString(result.errors.at(0))
+        );
+    else if (FFlag::LuauSolverV2)
         CHECK(toString(result.errors.at(0)) == "Type pack 'string' could not be converted into 'number'; at [0], string is not a subtype of number");
     else
         CHECK_EQ("Type 'string' could not be converted into 'number'", toString(result.errors[0]));
@@ -3033,8 +3139,6 @@ TEST_CASE_FIXTURE(Fixture, "hidden_variadics_should_not_break_subtyping")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "coroutine_wrap_result_call")
 {
-    ScopedFastFlag luauSubtypingFixTailPack{FFlag::LuauSubtypingFixTailPack, true};
-
     CheckResult result = check(R"(
         function foo(a, b)
             coroutine.wrap(a)(b)
@@ -3088,4 +3192,30 @@ TEST_CASE_FIXTURE(Fixture, "recursive_function_calls_should_not_use_the_generali
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "fuzz_unwind_mutually_recursive_union_type_func")
+{
+    ScopedFastFlag sffs[] = {
+        {FFlag::LuauSolverV2, true},
+        {FFlag::LuauReduceUnionFollowUnionType, true}
+    };
+
+    // This block ends up minting a type like:
+    //
+    //  t2 where t1 = union<t2, t1> | union<t2, t1> | union<t2, t1> ; t2 = union<t2, t1>
+    //
+    CheckResult result = check(R"(
+        local _ = ...
+        function _()
+            _ = _
+        end
+        _[function(...) repeat until _(_[l100]) _ = _ end] += _
+    )");
+    LUAU_REQUIRE_ERROR_COUNT(2, result);
+    auto err0 = get<UnknownSymbol>(result.errors[0]);
+    CHECK(err0);
+    CHECK_EQ(err0->name, "l100");
+    auto err1 = get<NotATable>(result.errors[1]);
+    CHECK(err1);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.generics.test.cpp

@@ -10,9 +10,10 @@
 #include "ScopedFlags.h"
 #include "doctest.h"
 
-LUAU_FASTFLAG(LuauInstantiateInSubtyping);
+LUAU_FASTFLAG(LuauInstantiateInSubtyping)
-LUAU_FASTFLAG(LuauSolverV2);
+LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauDeferBidirectionalInferenceForTableAssignment)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
 
 using namespace Luau;
 
@@ -875,7 +876,13 @@ y.a.c = y
         CHECK(mismatch);
         CHECK_EQ(toString(mismatch->givenType), "{ a: { c: T<string>?, d: number }, b: number }");
         CHECK_EQ(toString(mismatch->wantedType), "T<string>");
-        std::string reason = "at [read \"a\"][read \"d\"], number is not exactly string\n\tat [read \"b\"], number is not exactly string";
+        std::string reason =
+            (FFlag::LuauImproveTypePathsInErrors)
+                ? "\nthis is because \n\t"
+                  " * accessing `a.d` results in `number` in the former type and `string` in the latter type, and `number` is not exactly "
+                  "`string`\n\t"
+                  " * accessing `b` results in `number` in the former type and `string` in the latter type, and `number` is not exactly `string`"
+                : "at [read \"a\"][read \"d\"], number is not exactly string\n\tat [read \"b\"], number is not exactly string";
         CHECK_EQ(mismatch->reason, reason);
     }
     else

tests/TypeInfer.intersectionTypes.test.cpp

@@ -9,7 +9,8 @@
 
 using namespace Luau;
 
-LUAU_FASTFLAG(LuauSolverV2);
+LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
 
 TEST_SUITE_BEGIN("IntersectionTypes");
 
@@ -357,12 +358,21 @@ TEST_CASE_FIXTURE(Fixture, "table_intersection_write_sealed_indirect")
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(4, result);
-        const std::string expected = R"(Type
+
+        const std::string expected = (FFlag::LuauImproveTypePathsInErrors)
+                                         ? "Type\n\t"
+                                           "'(string, number) -> string'"
+                                           "\ncould not be converted into\n\t"
+                                           "'(string) -> string'\n"
+                                           "caused by:\n"
+                                           "  Argument count mismatch. Function expects 2 arguments, but only 1 is specified"
+                                         : R"(Type
     '(string, number) -> string'
 could not be converted into
     '(string) -> string'
 caused by:
   Argument count mismatch. Function expects 2 arguments, but only 1 is specified)";
+
         CHECK_EQ(expected, toString(result.errors[0]));
         CHECK_EQ(toString(result.errors[1]), "Cannot add property 'z' to table 'X & Y'");
         CHECK_EQ(toString(result.errors[2]), "Type 'number' could not be converted into 'string'");
@@ -387,7 +397,14 @@ TEST_CASE_FIXTURE(Fixture, "table_write_sealed_indirect")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(4, result);
-    const std::string expected = R"(Type
+    const std::string expected = (FFlag::LuauImproveTypePathsInErrors)
+                                     ? "Type\n\t"
+                                       "'(string, number) -> string'"
+                                       "\ncould not be converted into\n\t"
+                                       "'(string) -> string'\n"
+                                       "caused by:\n"
+                                       "  Argument count mismatch. Function expects 2 arguments, but only 1 is specified"
+                                     : R"(Type
     '(string, number) -> string'
 could not be converted into
     '(string) -> string'
@@ -430,7 +447,20 @@ Type 'number' could not be converted into 'X')";
         R"(Type 'number' could not be converted into 'X & Y & Z'; type number (number) is not a subtype of X & Y & Z[0] (X)
 	type number (number) is not a subtype of X & Y & Z[1] (Y)
 	type number (number) is not a subtype of X & Y & Z[2] (Z))";
-    if (FFlag::LuauSolverV2)
+
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type "
+                                     "'number'"
+                                     " could not be converted into "
+                                     "'X & Y & Z'; \n"
+                                     "this is because \n\t"
+                                     " * the 1st component of the intersection is `X`, and `number` is not a subtype of `X`\n\t"
+                                     " * the 2nd component of the intersection is `Y`, and `number` is not a subtype of `Y`\n\t"
+                                     " * the 3rd component of the intersection is `Z`, and `number` is not a subtype of `Z`";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else if (FFlag::LuauSolverV2)
         CHECK_EQ(dcrExprected, toString(result.errors[0]));
     else
         CHECK_EQ(expected, toString(result.errors[0]));
@@ -450,7 +480,23 @@ end
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    if (FFlag::LuauSolverV2)
+
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type pack "
+                                     "'X & Y & Z'"
+                                     " could not be converted into "
+                                     "'number'; \n"
+                                     "this is because \n\t"
+                                     " * in the 1st entry in the type pack has the 1st component of the intersection as `X` and the 1st entry in the "
+                                     "type pack is `number`, and `X` is not a subtype of `number`\n\t"
+                                     " * in the 1st entry in the type pack has the 2nd component of the intersection as `Y` and the 1st entry in the "
+                                     "type pack is `number`, and `Y` is not a subtype of `number`\n\t"
+                                     " * in the 1st entry in the type pack has the 3rd component of the intersection as `Z` and the 1st entry in the "
+                                     "type pack is `number`, and `Z` is not a subtype of `number`";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         CHECK_EQ(
             R"(Type pack 'X & Y & Z' could not be converted into 'number'; type X & Y & Z[0][0] (X) is not a subtype of number[0] (number)
@@ -503,7 +549,19 @@ TEST_CASE_FIXTURE(Fixture, "intersect_bool_and_false")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    if (FFlag::LuauSolverV2)
+
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type "
+                                     "'boolean & false'"
+                                     " could not be converted into "
+                                     "'true'; \n"
+                                     "this is because \n\t"
+                                     " * the 1st component of the intersection is `boolean`, which is not a subtype of `true`\n\t"
+                                     " * the 2nd component of the intersection is `false`, which is not a subtype of `true`";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         CHECK_EQ(
             R"(Type 'boolean & false' could not be converted into 'true'; type boolean & false[0] (boolean) is not a subtype of true (true)
@@ -527,8 +585,21 @@ TEST_CASE_FIXTURE(Fixture, "intersect_false_and_bool_and_false")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
+
     // TODO: odd stringification of `false & (boolean & false)`.)
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type "
+                                     "'boolean & false & false'"
+                                     " could not be converted into "
+                                     "'true'; \n"
+                                     "this is because \n\t"
+                                     " * the 1st component of the intersection is `false`, which is not a subtype of `true`\n\t"
+                                     " * the 2nd component of the intersection is `boolean`, which is not a subtype of `true`\n\t"
+                                     " * the 3rd component of the intersection is `false`, which is not a subtype of `true`";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else if (FFlag::LuauSolverV2)
         CHECK_EQ(
             R"(Type 'boolean & false & false' could not be converted into 'true'; type boolean & false & false[0] (false) is not a subtype of true (true)
 	type boolean & false & false[1] (boolean) is not a subtype of true (true)
@@ -550,7 +621,39 @@ TEST_CASE_FIXTURE(Fixture, "intersect_saturate_overloaded_functions")
             local z : (number) -> number = x -- Not OK
         end
     )");
-    if (FFlag::LuauSolverV2)
+
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected1 =
+            "Type\n\t"
+            "'((number?) -> number?) & ((string?) -> string?)'"
+            "\ncould not be converted into\n\t"
+            "'(nil) -> nil'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `number` and it returns the 1st entry in the type pack is `nil`, and `number` is not a subtype of `nil`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `string` and it returns the 1st entry in the type pack is `nil`, and `string` is not a subtype of `nil`";
+
+        const std::string expected2 =
+            "Type\n\t"
+            "'((number?) -> number?) & ((string?) -> string?)'"
+            "\ncould not be converted into\n\t"
+            "'(number) -> number'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 2nd component of the "
+            "union as `nil` and it returns the 1st entry in the type pack is `number`, and `nil` is not a subtype of `number`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `string` and it returns the 1st entry in the type pack is `number`, and `string` is not a subtype of `number`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 2nd component of the "
+            "union as `nil` and it returns the 1st entry in the type pack is `number`, and `nil` is not a subtype of `number`\n\t"
+            " * in the 2nd component of the intersection, the function takes the 1st entry in the type pack which is `string?` and it takes the 1st "
+            "entry in the type pack is `number`, and `string?` is not a supertype of `number`";
+
+        CHECK_EQ(expected1, toString(result.errors[0]));
+        CHECK_EQ(expected2, toString(result.errors[1]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         LUAU_REQUIRE_ERROR_COUNT(2, result);
         const std::string expected1 = R"(Type
@@ -568,6 +671,15 @@ could not be converted into
         CHECK_EQ(expected1, toString(result.errors[0]));
         CHECK_EQ(expected2, toString(result.errors[1]));
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        const std::string expected = R"(Type
+	'((number?) -> number?) & ((string?) -> string?)'
+could not be converted into
+	'(number) -> number'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -592,11 +704,23 @@ TEST_CASE_FIXTURE(Fixture, "union_saturate_overloaded_functions")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+
+    if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type\n\t"
+                                     "'((number) -> number) & ((string) -> string)'"
+                                     "\ncould not be converted into\n\t"
+                                     "'(boolean | number) -> boolean | number'; none of the intersection parts are compatible";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else
+    {
+        const std::string expected = R"(Type
     '((number) -> number) & ((string) -> string)'
 could not be converted into
     '(boolean | number) -> boolean | number'; none of the intersection parts are compatible)";
-    CHECK_EQ(expected, toString(result.errors[0]));
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "intersection_of_tables")
@@ -609,16 +733,42 @@ TEST_CASE_FIXTURE(Fixture, "intersection_of_tables")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected =
+
-        (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
-            ? R"(Type '{ p: number?, q: number?, r: number? } & { p: number?, q: string? }' could not be converted into '{ p: nil }'; type { p: number?, q: number?, r: number? } & { p: number?, q: string? }[0][read "p"][0] (number) is not exactly { p: nil }[read "p"] (nil)
+    {
-	type { p: number?, q: number?, r: number? } & { p: number?, q: string? }[1][read "p"][0] (number) is not exactly { p: nil }[read "p"] (nil))"
+        const std::string expected = "Type "
-            :
+                                     "'{ p: number?, q: number?, r: number? } & { p: number?, q: string? }'"
+                                     " could not be converted into "
+                                     "'{ p: nil }'; \n"
+                                     "this is because \n\t"
+                                     " * in the 1st component of the intersection, accessing `p` has the 1st component of the union as `number` and "
+                                     "accessing `p` results in `nil`, and `number` is not exactly `nil`\n\t"
+                                     " * in the 2nd component of the intersection, accessing `p` has the 1st component of the union as `number` and "
+                                     "accessing `p` results in `nil`, and `number` is not exactly `nil`";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected =
             R"(Type
+	'{| p: number?, q: number?, r: number? |} & {| p: number?, q: string? |}'
+could not be converted into
+	'{| p: nil |}'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else
+    {
+        const std::string expected =
+            (FFlag::LuauSolverV2)
+                ? R"(Type '{ p: number?, q: number?, r: number? } & { p: number?, q: string? }' could not be converted into '{ p: nil }'; type { p: number?, q: number?, r: number? } & { p: number?, q: string? }[0][read "p"][0] (number) is not exactly { p: nil }[read "p"] (nil)
+	type { p: number?, q: number?, r: number? } & { p: number?, q: string? }[1][read "p"][0] (number) is not exactly { p: nil }[read "p"] (nil))"
+                :
+                R"(Type
     '{| p: number?, q: number?, r: number? |} & {| p: number?, q: string? |}'
 could not be converted into
     '{| p: nil |}'; none of the intersection parts are compatible)";
-    CHECK_EQ(expected, toString(result.errors[0]));
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "intersection_of_tables_with_top_properties")
@@ -630,7 +780,28 @@ TEST_CASE_FIXTURE(Fixture, "intersection_of_tables_with_top_properties")
         end
     )");
 
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type\n\t"
+                                     "'{ p: number?, q: any } & { p: unknown, q: string? }'"
+                                     "\ncould not be converted into\n\t"
+                                     "'{ p: string?, q: number? }'; \n"
+                                     "this is because \n\t"
+                                     " * in the 1st component of the intersection, accessing `p` has the 1st component of the union as `number` and "
+                                     "accessing `p` results in `string?`, and `number` is not exactly `string?`\n\t"
+                                     " * in the 1st component of the intersection, accessing `p` results in `number?` and accessing `p` has the 1st "
+                                     "component of the union as `string`, and `number?` is not exactly `string`\n\t"
+                                     " * in the 1st component of the intersection, accessing `q` results in `any` and accessing `q` results in "
+                                     "`number?`, and `any` is not exactly `number?`\n\t"
+                                     " * in the 2nd component of the intersection, accessing `p` results in `unknown` and accessing `p` results in "
+                                     "`string?`, and `unknown` is not exactly `string?`\n\t"
+                                     " * in the 2nd component of the intersection, accessing `q` has the 1st component of the union as `string` and "
+                                     "accessing `q` results in `number?`, and `string` is not exactly `number?`\n\t"
+                                     " * in the 2nd component of the intersection, accessing `q` results in `string?` and accessing `q` has the 1st "
+                                     "component of the union as `number`, and `string?` is not exactly `number`";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
         CHECK_EQ(
@@ -646,6 +817,15 @@ could not be converted into
             toString(result.errors[0])
         );
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        const std::string expected = R"(Type
+	'{| p: number?, q: any |} & {| p: unknown, q: string? |}'
+could not be converted into
+	'{| p: string?, q: number? |}'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -678,7 +858,52 @@ TEST_CASE_FIXTURE(Fixture, "overloaded_functions_returning_intersections")
         end
     )");
 
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected1 =
+            "Type\n\t"
+            "'((number?) -> { p: number } & { q: number }) & ((string?) -> { p: number } & { r: number })'"
+            "\ncould not be converted into\n\t"
+            "'(nil) -> { p: number, q: number, r: number }'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "intersection as `{ p: number }` and it returns the 1st entry in the type pack is `{ p: number, q: number, r: number }`, and `{ p: "
+            "number }` is not a subtype of `{ p: number, q: number, r: number }`\n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 2nd component of the "
+            "intersection as `{ q: number }` and it returns the 1st entry in the type pack is `{ p: number, q: number, r: number }`, and `{ q: "
+            "number }` is not a subtype of `{ p: number, q: number, r: number }`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "intersection as `{ p: number }` and it returns the 1st entry in the type pack is `{ p: number, q: number, r: number }`, and `{ p: "
+            "number }` is not a subtype of `{ p: number, q: number, r: number }`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 2nd component of the "
+            "intersection as `{ r: number }` and it returns the 1st entry in the type pack is `{ p: number, q: number, r: number }`, and `{ r: "
+            "number }` is not a subtype of `{ p: number, q: number, r: number }`";
+
+        const std::string expected2 =
+            "Type\n\t"
+            "'((number?) -> { p: number } & { q: number }) & ((string?) -> { p: number } & { r: number })'"
+            "\ncould not be converted into\n\t"
+            "'(number?) -> { p: number, q: number, r: number }'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "intersection as `{ p: number }` and it returns the 1st entry in the type pack is `{ p: number, q: number, r: number }`, and `{ p: "
+            "number }` is not a subtype of `{ p: number, q: number, r: number }`\n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 2nd component of the "
+            "intersection as `{ q: number }` and it returns the 1st entry in the type pack is `{ p: number, q: number, r: number }`, and `{ q: "
+            "number }` is not a subtype of `{ p: number, q: number, r: number }`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "intersection as `{ p: number }` and it returns the 1st entry in the type pack is `{ p: number, q: number, r: number }`, and `{ p: "
+            "number }` is not a subtype of `{ p: number, q: number, r: number }`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 2nd component of the "
+            "intersection as `{ r: number }` and it returns the 1st entry in the type pack is `{ p: number, q: number, r: number }`, and `{ r: "
+            "number }` is not a subtype of `{ p: number, q: number, r: number }`\n\t"
+            " * in the 2nd component of the intersection, the function takes the 1st entry in the type pack which is `string?` and it takes the 1st "
+            "entry in the type pack has the 1st component of the union as `number`, and `string?` is not a supertype of `number`";
+
+        CHECK_EQ(expected1, toString(result.errors[0]));
+        CHECK_EQ(expected2, toString(result.errors[1]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         LUAU_REQUIRE_ERROR_COUNT(2, result);
         CHECK_EQ(
@@ -703,6 +928,17 @@ could not be converted into
             toString(result.errors[1])
         );
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        CHECK_EQ(
+            R"(Type
+	'((number?) -> {| p: number |} & {| q: number |}) & ((string?) -> {| p: number |} & {| r: number |})'
+could not be converted into
+	'(number?) -> {| p: number, q: number, r: number |}'; none of the intersection parts are compatible)",
+            toString(result.errors[0])
+        );
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -730,6 +966,15 @@ TEST_CASE_FIXTURE(Fixture, "overloaded_functions_mentioning_generic")
     {
         LUAU_REQUIRE_ERROR_COUNT(0, result);
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        const std::string expected = R"(Type
+	'((number?) -> a | number) & ((string?) -> a | string)'
+could not be converted into
+	'(number?) -> a'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -757,6 +1002,15 @@ TEST_CASE_FIXTURE(Fixture, "overloaded_functions_mentioning_generics")
     {
         LUAU_REQUIRE_NO_ERRORS(result);
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        const std::string expected = R"(Type
+	'((a?) -> a | b) & ((c?) -> b | c)'
+could not be converted into
+	'(a?) -> (a & c) | b'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -778,7 +1032,35 @@ TEST_CASE_FIXTURE(Fixture, "overloaded_functions_mentioning_generic_packs")
             end
         end
     )");
-    if (FFlag::LuauSolverV2)
+
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected1 =
+            "Type\n\t"
+            "'((number?, a...) -> (number?, b...)) & ((string?, a...) -> (string?, b...))'"
+            "\ncould not be converted into\n\t"
+            "'(nil, a...) -> (nil, b...)'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `number` and it returns the 1st entry in the type pack is `nil`, and `number` is not a subtype of `nil`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `string` and it returns the 1st entry in the type pack is `nil`, and `string` is not a subtype of `nil`";
+
+        const std::string expected2 =
+            "Type\n\t"
+            "'((number?, a...) -> (number?, b...)) & ((string?, a...) -> (string?, b...))'"
+            "\ncould not be converted into\n\t"
+            "'(nil, b...) -> (nil, a...)'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `number` and it returns the 1st entry in the type pack is `nil`, and `number` is not a subtype of `nil`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `string` and it returns the 1st entry in the type pack is `nil`, and `string` is not a subtype of `nil`";
+
+        CHECK_EQ(expected1, toString(result.errors[0]));
+        CHECK_EQ(expected2, toString(result.errors[1]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         LUAU_REQUIRE_ERROR_COUNT(2, result);
         CHECK_EQ(
@@ -798,6 +1080,15 @@ could not be converted into
             toString(result.errors[1])
         );
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        const std::string expected = R"(Type
+	'((number?, a...) -> (number?, b...)) & ((string?, a...) -> (string?, b...))'
+could not be converted into
+	'(nil, b...) -> (nil, a...)'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -824,11 +1115,23 @@ TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_unknown_result")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+
+    if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type\n\t"
+                                     "'((nil) -> unknown) & ((number) -> number)'"
+                                     "\ncould not be converted into\n\t"
+                                     "'(number?) -> number?'; none of the intersection parts are compatible";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else
+    {
+        const std::string expected = R"(Type
     '((nil) -> unknown) & ((number) -> number)'
 could not be converted into
     '(number?) -> number?'; none of the intersection parts are compatible)";
-    CHECK_EQ(expected, toString(result.errors[0]));
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_unknown_arguments")
@@ -846,11 +1149,23 @@ TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_unknown_arguments")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+
+    if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type\n\t"
+                                     "'((number) -> number?) & ((unknown) -> string?)'"
+                                     "\ncould not be converted into\n\t"
+                                     "'(number?) -> nil'; none of the intersection parts are compatible";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
+    else
+    {
+        const std::string expected = R"(Type
     '((number) -> number?) & ((unknown) -> string?)'
 could not be converted into
     '(number?) -> nil'; none of the intersection parts are compatible)";
-    CHECK_EQ(expected, toString(result.errors[0]));
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_never_result")
@@ -864,7 +1179,36 @@ TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_never_result")
     end
     )");
 
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected1 =
+            "Type\n\t"
+            "'((nil) -> never) & ((number) -> number)'"
+            "\ncould not be converted into\n\t"
+            "'(number?) -> number'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function takes the 1st entry in the type pack which is `number` and it takes the 1st "
+            "entry in the type pack has the 2nd component of the union as `nil`, and `number` is not a supertype of `nil`\n\t"
+            " * in the 2nd component of the intersection, the function takes the 1st entry in the type pack which is `nil` and it takes the 1st "
+            "entry in the type pack has the 1st component of the union as `number`, and `nil` is not a supertype of `number`";
+
+        const std::string expected2 =
+            "Type\n\t"
+            "'((nil) -> never) & ((number) -> number)'"
+            "\ncould not be converted into\n\t"
+            "'(number?) -> never'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which is `number` and it returns the "
+            "1st entry in the type pack is `never`, and `number` is not a subtype of `never`\n\t"
+            " * in the 1st component of the intersection, the function takes the 1st entry in the type pack which is `number` and it takes the 1st "
+            "entry in the type pack has the 2nd component of the union as `nil`, and `number` is not a supertype of `nil`\n\t"
+            " * in the 2nd component of the intersection, the function takes the 1st entry in the type pack which is `nil` and it takes the 1st "
+            "entry in the type pack has the 1st component of the union as `number`, and `nil` is not a supertype of `number`";
+
+        CHECK_EQ(expected1, toString(result.errors[0]));
+        CHECK_EQ(expected2, toString(result.errors[1]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         LUAU_REQUIRE_ERROR_COUNT(2, result);
         CHECK_EQ(
@@ -885,6 +1229,15 @@ could not be converted into
             toString(result.errors[1])
         );
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        const std::string expected = R"(Type
+	'((nil) -> never) & ((number) -> number)'
+could not be converted into
+	'(number?) -> never'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -907,7 +1260,40 @@ TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_never_arguments")
         end
     )");
 
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected1 =
+            "Type\n\t"
+            "'((never) -> string?) & ((number) -> number?)'"
+            "\ncould not be converted into\n\t"
+            "'(never) -> nil'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `number` and it returns the 1st entry in the type pack is `nil`, and `number` is not a subtype of `nil`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `string` and it returns the 1st entry in the type pack is `nil`, and `string` is not a subtype of `nil`";
+
+        const std::string expected2 =
+            "Type\n\t"
+            "'((never) -> string?) & ((number) -> number?)'"
+            "\ncould not be converted into\n\t"
+            "'(number?) -> nil'; \n"
+            "this is because \n\t"
+            " * in the 1st component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `number` and it returns the 1st entry in the type pack is `nil`, and `number` is not a subtype of `nil`\n\t"
+            " * in the 1st component of the intersection, the function takes the 1st entry in the type pack which is `number` and it takes the 1st "
+            "entry in the type pack has the 2nd component of the union as `nil`, and `number` is not a supertype of `nil`\n\t"
+            " * in the 2nd component of the intersection, the function returns the 1st entry in the type pack which has the 1st component of the "
+            "union as `string` and it returns the 1st entry in the type pack is `nil`, and `string` is not a subtype of `nil`\n\t"
+            " * in the 2nd component of the intersection, the function takes the 1st entry in the type pack which is `never` and it takes the 1st "
+            "entry in the type pack has the 1st component of the union as `number`, and `never` is not a supertype of `number`\n\t"
+            " * in the 2nd component of the intersection, the function takes the 1st entry in the type pack which is `never` and it takes the 1st "
+            "entry in the type pack has the 2nd component of the union as `nil`, and `never` is not a supertype of `nil`";
+
+        CHECK_EQ(expected1, toString(result.errors[0]));
+        CHECK_EQ(expected2, toString(result.errors[1]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         LUAU_REQUIRE_ERROR_COUNT(2, result);
         const std::string expected1 = R"(Type
@@ -926,6 +1312,15 @@ could not be converted into
         CHECK_EQ(expected1, toString(result.errors[0]));
         CHECK_EQ(expected2, toString(result.errors[1]));
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        const std::string expected = R"(Type
+	'((never) -> string?) & ((number) -> number?)'
+could not be converted into
+	'(number?) -> nil'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -950,11 +1345,23 @@ TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_overlapping_results_and_
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type
+
+    if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type\n\t"
+                                     "'((number?) -> (...number)) & ((string?) -> number | string)'"
+                                     "\ncould not be converted into\n\t"
+                                     "'(number | string) -> (number, number?)'; none of the intersection parts are compatible";
+        CHECK(expected == toString(result.errors[0]));
+    }
+    else
+    {
+        const std::string expected = R"(Type
     '((number?) -> (...number)) & ((string?) -> number | string)'
 could not be converted into
     '(number | string) -> (number, number?)'; none of the intersection parts are compatible)";
-    CHECK_EQ(expected, toString(result.errors[0]));
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_weird_typepacks_1")
@@ -1022,6 +1429,15 @@ TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_weird_typepacks_3")
     {
         LUAU_REQUIRE_NO_ERRORS(result);
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+        const std::string expected = R"(Type
+	'(() -> (a...)) & (() -> (number?, a...))'
+could not be converted into
+	'() -> number'; none of the intersection parts are compatible)";
+        CHECK_EQ(expected, toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(1, result);
@@ -1045,7 +1461,21 @@ TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_weird_typepacks_4")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    if (FFlag::LuauSolverV2)
+
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type\n\t"
+                                     "'((a...) -> ()) & ((number, a...) -> number)'"
+                                     "\ncould not be converted into\n\t"
+                                     "'((a...) -> ()) & ((number, a...) -> number)'; \n"
+                                     "this is because \n\t"
+                                     " * in the 1st component of the intersection, the function returns is `()` in the former type and `number` in "
+                                     "the latter type, and `()` is not a subtype of `number`\n\t"
+                                     " * in the 2nd component of the intersection, the function takes a tail of `a...` and in the 1st component of "
+                                     "the intersection, the function takes a tail of `a...`, and `a...` is not a supertype of `a...`";
+        CHECK(expected == toString(result.errors[0]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         CHECK_EQ(
             R"(Type
@@ -1056,6 +1486,16 @@ could not be converted into
             toString(result.errors[0])
         );
     }
+    else if (FFlag::LuauImproveTypePathsInErrors)
+    {
+        CHECK_EQ(
+            R"(Type
+	'((a...) -> ()) & ((number, a...) -> number)'
+could not be converted into
+	'(number?) -> ()'; none of the intersection parts are compatible)",
+            toString(result.errors[0])
+        );
+    }
     else
     {
         CHECK_EQ(

tests/TypeInfer.modules.test.cpp

@@ -12,6 +12,7 @@
 
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAG(LuauImproveTypePathsInErrors)
 
 using namespace Luau;
 
@@ -461,7 +462,14 @@ local b: B.T = a
     CheckResult result = frontend.check("game/C");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type 'T' from 'game/A' could not be converted into 'T' from 'game/B'; \n"
+                                     "this is because accessing `x` results in `number` in the former type and `string` in the latter type, and "
+                                     "`number` is not exactly `string`";
+        CHECK(expected == toString(result.errors[0]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         CHECK(
             toString(result.errors.at(0)) ==
@@ -507,7 +515,14 @@ local b: B.T = a
     CheckResult result = frontend.check("game/D");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    if (FFlag::LuauSolverV2)
+    if (FFlag::LuauSolverV2 && FFlag::LuauImproveTypePathsInErrors)
+    {
+        const std::string expected = "Type 'T' from 'game/B' could not be converted into 'T' from 'game/C'; \n"
+                                     "this is because accessing `x` results in `number` in the former type and `string` in the latter type, and "
+                                     "`number` is not exactly `string`";
+        CHECK(expected == toString(result.errors[0]));
+    }
+    else if (FFlag::LuauSolverV2)
     {
         CHECK(
             toString(result.errors.at(0)) ==