Sync to upstream/release/672 (#1800)

# What's Changed?

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

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

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

# New Type Solver

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

# Internal Contributors

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

---------

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

Analysis/include/Luau/AutocompleteTypes.h

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

Analysis/include/Luau/ConstraintGenerator.h

@@ -3,6 +3,7 @@
 
 #include "Luau/Ast.h"
 #include "Luau/Constraint.h"
+#include "Luau/ConstraintSet.h"
 #include "Luau/ControlFlow.h"
 #include "Luau/DataFlowGraph.h"
 #include "Luau/EqSatSimplification.h"
@@ -91,9 +92,8 @@ struct ConstraintGenerator
     // Constraints that go straight to the solver.
     std::vector<ConstraintPtr> constraints;
 
-    // Constraints that do not go to the solver right away.  Other constraints
+    // The set of all free types introduced during constraint generation.
-    // will enqueue them during solving.
+    DenseHashSet<TypeId> freeTypes{nullptr};
-    std::vector<ConstraintPtr> unqueuedConstraints;
 
     // Map a function's signature scope back to its signature type.
     DenseHashMap<Scope*, TypeId> scopeToFunction{nullptr};
@@ -151,6 +151,9 @@ struct ConstraintGenerator
         std::vector<RequireCycle> requireCycles
     );
 
+    ConstraintSet run(AstStatBlock* block);
+    ConstraintSet runOnFragment(const ScopePtr& resumeScope, AstStatBlock* block);
+
     /**
      * The entry point to the ConstraintGenerator. This will construct a set
      * of scopes, constraints, and free types that can be solved later.
@@ -269,7 +272,7 @@ private:
     ControlFlow visit(const ScopePtr& scope, AstStatTypeAlias* alias);
     ControlFlow visit(const ScopePtr& scope, AstStatTypeFunction* function);
     ControlFlow visit(const ScopePtr& scope, AstStatDeclareGlobal* declareGlobal);
-    ControlFlow visit(const ScopePtr& scope, AstStatDeclareClass* declareClass);
+    ControlFlow visit(const ScopePtr& scope, AstStatDeclareExternType* declareExternType);
     ControlFlow visit(const ScopePtr& scope, AstStatDeclareFunction* declareFunction);
     ControlFlow visit(const ScopePtr& scope, AstStatError* error);
 
@@ -481,9 +484,4 @@ private:
     TypeId simplifyUnion(const ScopePtr& scope, Location location, TypeId left, TypeId right);
 };
 
-/** Borrow a vector of pointers from a vector of owning pointers to constraints.
- */
-std::vector<NotNull<Constraint>> borrowConstraints(const std::vector<ConstraintPtr>& constraints);
-
-
 } // namespace Luau

Analysis/include/Luau/ConstraintSet.h

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

Analysis/include/Luau/ConstraintSolver.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include "Luau/Constraint.h"
+#include "Luau/ConstraintSet.h"
 #include "Luau/DataFlowGraph.h"
 #include "Luau/DenseHash.h"
 #include "Luau/EqSatSimplification.h"
@@ -87,6 +88,7 @@ struct ConstraintSolver
     NotNull<Simplifier> simplifier;
     NotNull<TypeFunctionRuntime> typeFunctionRuntime;
     // The entire set of constraints that the solver is trying to resolve.
+    ConstraintSet constraintSet;
     std::vector<NotNull<Constraint>> constraints;
     NotNull<DenseHashMap<Scope*, TypeId>> scopeToFunction;
     NotNull<Scope> rootScope;
@@ -140,6 +142,19 @@ struct ConstraintSolver
 
     DenseHashMap<TypeId, const Constraint*> typeFunctionsToFinalize{nullptr};
 
+    explicit ConstraintSolver(
+        NotNull<Normalizer> normalizer,
+        NotNull<Simplifier> simplifier,
+        NotNull<TypeFunctionRuntime> typeFunctionRuntime,
+        ModuleName moduleName,
+        NotNull<ModuleResolver> moduleResolver,
+        std::vector<RequireCycle> requireCycles,
+        DcrLogger* logger,
+        NotNull<const DataFlowGraph> dfg,
+        TypeCheckLimits limits,
+        ConstraintSet constraintSet
+    );
+
     explicit ConstraintSolver(
         NotNull<Normalizer> normalizer,
         NotNull<Simplifier> simplifier,
@@ -174,6 +189,9 @@ struct ConstraintSolver
     bool isDone() const;
 
 private:
+    /// A helper that does most of the setup work that is shared between the two constructors.
+    void initFreeTypeTracking();
+
     void generalizeOneType(TypeId ty);
 
     /**
@@ -432,6 +450,10 @@ public:
     void fillInDiscriminantTypes(NotNull<const Constraint> constraint, const std::vector<std::optional<TypeId>>& discriminantTypes);
 };
 
+/** Borrow a vector of pointers from a vector of owning pointers to constraints.
+ */
+std::vector<NotNull<Constraint>> borrowConstraints(const std::vector<ConstraintPtr>& constraints);
+
 void dump(NotNull<Scope> rootScope, struct ToStringOptions& opts);
 
 } // namespace Luau

Analysis/include/Luau/DataFlowGraph.h

@@ -173,7 +173,7 @@ private:
     ControlFlow visit(AstStatTypeFunction* f);
     ControlFlow visit(AstStatDeclareGlobal* d);
     ControlFlow visit(AstStatDeclareFunction* d);
-    ControlFlow visit(AstStatDeclareClass* d);
+    ControlFlow visit(AstStatDeclareExternType* d);
     ControlFlow visit(AstStatError* error);
 
     DataFlowResult visitExpr(AstExpr* e);

Analysis/include/Luau/Error.h

@@ -332,11 +332,11 @@ struct TypePackMismatch
     bool operator==(const TypePackMismatch& rhs) const;
 };
 
-struct DynamicPropertyLookupOnClassesUnsafe
+struct DynamicPropertyLookupOnExternTypesUnsafe
 {
     TypeId ty;
 
-    bool operator==(const DynamicPropertyLookupOnClassesUnsafe& rhs) const;
+    bool operator==(const DynamicPropertyLookupOnExternTypesUnsafe& rhs) const;
 };
 
 struct UninhabitedTypeFunction
@@ -499,7 +499,7 @@ using TypeErrorData = Variant<
     TypesAreUnrelated,
     NormalizationTooComplex,
     TypePackMismatch,
-    DynamicPropertyLookupOnClassesUnsafe,
+    DynamicPropertyLookupOnExternTypesUnsafe,
     UninhabitedTypeFunction,
     UninhabitedTypePackFunction,
     WhereClauseNeeded,

Analysis/include/Luau/FileResolver.h

@@ -117,8 +117,7 @@ struct FileResolver
         return std::nullopt;
     }
 
-    // Make non-virtual when removing FFlagLuauImproveRequireByStringAutocomplete.
+    std::optional<RequireSuggestions> getRequireSuggestions(const ModuleName& requirer, const std::optional<std::string>& pathString) const;
-    virtual std::optional<RequireSuggestions> getRequireSuggestions(const ModuleName& requirer, const std::optional<std::string>& pathString) const;
 
     std::shared_ptr<RequireSuggester> requireSuggester;
 };

Analysis/include/Luau/Instantiation.h

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

Analysis/include/Luau/Normalize.h

@@ -181,7 +181,7 @@ struct NormalizedStringType
 
 bool isSubtype(const NormalizedStringType& subStr, const NormalizedStringType& superStr);
 
-struct NormalizedClassType
+struct NormalizedExternType
 {
     /** Has the following structure:
      *
@@ -192,7 +192,7 @@ struct NormalizedClassType
      *
      * Each TypeId is a class type.
      */
-    std::unordered_map<TypeId, TypeIds> classes;
+    std::unordered_map<TypeId, TypeIds> externTypes;
 
     /**
      * In order to maintain a consistent insertion order, we use this vector to
@@ -245,7 +245,7 @@ enum class NormalizationResult
 };
 
 // A normalized type is either any, unknown, or one of the form P | T | F | G where
-// * P is a union of primitive types (including singletons, classes and the error type)
+// * P is a union of primitive types (including singletons, extern types and the error type)
 // * T is a union of table types
 // * F is a union of an intersection of function types
 // * G is a union of generic/free/blocked types, intersected with a normalized type
@@ -260,7 +260,7 @@ struct NormalizedType
     // This type is either never, boolean type, or a boolean singleton.
     TypeId booleans;
 
-    NormalizedClassType classes;
+    NormalizedExternType externTypes;
 
     // The error part of the type.
     // This type is either never or the error type.
@@ -333,7 +333,7 @@ struct NormalizedType
     // Helpers that improve readability of the above (they just say if the component is present)
     bool hasTops() const;
     bool hasBooleans() const;
-    bool hasClasses() const;
+    bool hasExternTypes() const;
     bool hasErrors() const;
     bool hasNils() const;
     bool hasNumbers() const;
@@ -391,10 +391,10 @@ public:
     void unionTysWithTy(TypeIds& here, TypeId there);
     TypeId unionOfTops(TypeId here, TypeId there);
     TypeId unionOfBools(TypeId here, TypeId there);
-    void unionClassesWithClass(TypeIds& heres, TypeId there);
+    void unionExternTypesWithExternType(TypeIds& heres, TypeId there);
-    void unionClasses(TypeIds& heres, const TypeIds& theres);
+    void unionExternTypes(TypeIds& heres, const TypeIds& theres);
-    void unionClassesWithClass(NormalizedClassType& heres, TypeId there);
+    void unionExternTypesWithExternType(NormalizedExternType& heres, TypeId there);
-    void unionClasses(NormalizedClassType& heres, const NormalizedClassType& theres);
+    void unionExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres);
     void unionStrings(NormalizedStringType& here, const NormalizedStringType& there);
     std::optional<TypePackId> unionOfTypePacks(TypePackId here, TypePackId there);
     std::optional<TypeId> unionOfFunctions(TypeId here, TypeId there);
@@ -423,8 +423,8 @@ public:
     // ------- Normalizing intersections
     TypeId intersectionOfTops(TypeId here, TypeId there);
     TypeId intersectionOfBools(TypeId here, TypeId there);
-    void intersectClasses(NormalizedClassType& heres, const NormalizedClassType& theres);
+    void intersectExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres);
-    void intersectClassesWithClass(NormalizedClassType& heres, TypeId there);
+    void intersectExternTypesWithExternType(NormalizedExternType& heres, TypeId there);
     void intersectStrings(NormalizedStringType& here, const NormalizedStringType& there);
     std::optional<TypePackId> intersectionOfTypePacks(TypePackId here, TypePackId there);
     std::optional<TypeId> intersectionOfTables(TypeId here, TypeId there, SeenTablePropPairs& seenTablePropPairs, Set<TypeId>& seenSet);

Analysis/include/Luau/Quantify.h

@@ -16,7 +16,7 @@ struct Scope;
 
 void quantify(TypeId ty, TypeLevel level);
 
-// TODO: This is eerily similar to the pattern that NormalizedClassType
+// TODO: This is eerily similar to the pattern that NormalizedExternType
 // implements. We could, and perhaps should, merge them together.
 template<typename K, typename V>
 struct OrderedMap

Analysis/include/Luau/Subtyping.h

@@ -22,7 +22,7 @@ struct InternalErrorReporter;
 
 class TypeIds;
 class Normalizer;
-struct NormalizedClassType;
+struct NormalizedExternType;
 struct NormalizedFunctionType;
 struct NormalizedStringType;
 struct NormalizedType;
@@ -121,7 +121,7 @@ struct SubtypingEnvironment
     DenseHashMap<TypePackId, TypePackId> mappedGenericPacks{nullptr};
 
     /*
-     * See the test cyclic_tables_are_assumed_to_be_compatible_with_classes for
+     * See the test cyclic_tables_are_assumed_to_be_compatible_with_extern_types for
      * details.
      *
      * An empty value is equivalent to a nonexistent key.
@@ -229,9 +229,8 @@ private:
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const TableType* subTable, const TableType* superTable, NotNull<Scope> scope);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const MetatableType* subMt, const MetatableType* superMt, NotNull<Scope> scope);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const MetatableType* subMt, const TableType* superTable, NotNull<Scope> scope);
-    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const ClassType* subClass, const ClassType* superClass, NotNull<Scope> scope);
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const ExternType* subExternType, const ExternType* superExternType, NotNull<Scope> scope);
-    SubtypingResult
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, TypeId subTy, const ExternType* subExternType, TypeId superTy, const TableType* superTable, NotNull<Scope>);
-    isCovariantWith(SubtypingEnvironment& env, TypeId subTy, const ClassType* subClass, TypeId superTy, const TableType* superTable, NotNull<Scope>);
     SubtypingResult isCovariantWith(
         SubtypingEnvironment& env,
         const FunctionType* subFunction,
@@ -259,11 +258,11 @@ private:
     );
     SubtypingResult isCovariantWith(
         SubtypingEnvironment& env,
-        const NormalizedClassType& subClass,
+        const NormalizedExternType& subExternType,
-        const NormalizedClassType& superClass,
+        const NormalizedExternType& superExternType,
         NotNull<Scope> scope
     );
-    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const NormalizedClassType& subClass, const TypeIds& superTables, NotNull<Scope> scope);
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const NormalizedExternType& subExternType, const TypeIds& superTables, NotNull<Scope> scope);
     SubtypingResult isCovariantWith(
         SubtypingEnvironment& env,
         const NormalizedStringType& subString,

Analysis/include/Luau/ToString.h

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

Analysis/include/Luau/Type.h

@@ -74,10 +74,6 @@ struct FreeType
     // This one got promoted to explicit
     explicit FreeType(Scope* scope, TypeId lowerBound, TypeId upperBound, Polarity polarity = Polarity::Unknown);
     explicit FreeType(Scope* scope, TypeLevel level, TypeId lowerBound, TypeId upperBound);
-    // Old constructors
-    explicit FreeType(TypeLevel level);
-    explicit FreeType(Scope* scope);
-    FreeType(Scope* scope, TypeLevel level);
 
     int index;
     TypeLevel level;
@@ -291,7 +287,7 @@ struct MagicFunctionCallContext
 {
     NotNull<struct ConstraintSolver> solver;
     NotNull<const Constraint> constraint;
-    const class AstExprCall* callSite;
+    NotNull<const AstExprCall> callSite;
     TypePackId arguments;
     TypePackId result;
 };
@@ -536,15 +532,15 @@ struct ClassUserData
     virtual ~ClassUserData() {}
 };
 
-/** The type of a class.
+/** The type of an external userdata exposed to Luau.
  *
- * Classes behave like tables in many ways, but there are some important differences:
+ * Extern types behave like tables in many ways, but there are some important differences:
  *
  * The properties of a class are always exactly known.
- * Classes optionally have a parent class.
+ * Extern types optionally have a parent type.
- * Two different classes that share the same properties are nevertheless distinct and mutually incompatible.
+ * Two different extern types that share the same properties are nevertheless distinct and mutually incompatible.
  */
-struct ClassType
+struct ExternType
 {
     using Props = TableType::Props;
 
@@ -558,7 +554,7 @@ struct ClassType
     std::optional<Location> definitionLocation;
     std::optional<TableIndexer> indexer;
 
-    ClassType(
+    ExternType(
         Name name,
         Props props,
         std::optional<TypeId> parent,
@@ -579,7 +575,7 @@ struct ClassType
     {
     }
 
-    ClassType(
+    ExternType(
         Name name,
         Props props,
         std::optional<TypeId> parent,
@@ -779,7 +775,7 @@ using TypeVariant = Unifiable::Variant<
     FunctionType,
     TableType,
     MetatableType,
-    ClassType,
+    ExternType,
     AnyType,
     UnionType,
     IntersectionType,
@@ -990,7 +986,7 @@ public:
     const TypeId threadType;
     const TypeId bufferType;
     const TypeId functionType;
-    const TypeId classType;
+    const TypeId externType;
     const TypeId tableType;
     const TypeId emptyTableType;
     const TypeId trueType;
@@ -1002,6 +998,7 @@ public:
     const TypeId noRefineType;
     const TypeId falsyType;
     const TypeId truthyType;
+    const TypeId notNilType;
 
     const TypeId optionalNumberType;
     const TypeId optionalStringType;
@@ -1022,10 +1019,10 @@ TypeLevel* getMutableLevel(TypeId ty);
 
 std::optional<TypeLevel> getLevel(TypePackId tp);
 
-const Property* lookupClassProp(const ClassType* cls, const Name& name);
+const Property* lookupExternTypeProp(const ExternType* cls, const Name& name);
 
 // Whether `cls` is a subclass of `parent`
-bool isSubclass(const ClassType* cls, const ClassType* parent);
+bool isSubclass(const ExternType* cls, const ExternType* parent);
 
 Type* asMutable(TypeId ty);
 

Analysis/include/Luau/TypeArena.h

@@ -37,10 +37,6 @@ struct TypeArena
     TypeId freshType(NotNull<BuiltinTypes> builtins, Scope* scope);
     TypeId freshType(NotNull<BuiltinTypes> builtins, Scope* scope, TypeLevel level);
 
-    TypeId freshType_DEPRECATED(TypeLevel level);
-    TypeId freshType_DEPRECATED(Scope* scope);
-    TypeId freshType_DEPRECATED(Scope* scope, TypeLevel level);
-
     TypePackId freshTypePack(Scope* scope, Polarity polarity = Polarity::Unknown);
 
     TypePackId addTypePack(std::initializer_list<TypeId> types);

Analysis/include/Luau/TypeAttach.h

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

Analysis/include/Luau/TypeChecker2.h

@@ -160,7 +160,7 @@ private:
     void visit(AstTypeList types);
     void visit(AstStatDeclareFunction* stat);
     void visit(AstStatDeclareGlobal* stat);
-    void visit(AstStatDeclareClass* stat);
+    void visit(AstStatDeclareExternType* stat);
     void visit(AstStatError* stat);
     void visit(AstExpr* expr, ValueContext context);
     void visit(AstExprGroup* expr, ValueContext context);

Analysis/include/Luau/TypeFunctionRuntime.h

@@ -205,7 +205,7 @@ struct TypeFunctionTableType
     std::optional<TypeFunctionTypeId> metatable;
 };
 
-struct TypeFunctionClassType
+struct TypeFunctionExternType
 {
     using Name = std::string;
     using Props = std::map<Name, TypeFunctionProperty>;
@@ -222,7 +222,7 @@ struct TypeFunctionClassType
     std::optional<TypeFunctionTypeId> readParent;
     std::optional<TypeFunctionTypeId> writeParent;
 
-    TypeId classTy;
+    TypeId externTy;
 };
 
 struct TypeFunctionGenericType
@@ -244,7 +244,7 @@ using TypeFunctionTypeVariant = Luau::Variant<
     TypeFunctionNegationType,
     TypeFunctionFunctionType,
     TypeFunctionTableType,
-    TypeFunctionClassType,
+    TypeFunctionExternType,
     TypeFunctionGenericType>;
 
 struct TypeFunctionType

Analysis/include/Luau/TypeFwd.h

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

Analysis/include/Luau/TypeInfer.h

@@ -90,11 +90,11 @@ struct TypeChecker
     ControlFlow check(const ScopePtr& scope, TypeId ty, const ScopePtr& funScope, const AstStatLocalFunction& function);
     ControlFlow check(const ScopePtr& scope, const AstStatTypeAlias& typealias);
     ControlFlow check(const ScopePtr& scope, const AstStatTypeFunction& typefunction);
-    ControlFlow check(const ScopePtr& scope, const AstStatDeclareClass& declaredClass);
+    ControlFlow check(const ScopePtr& scope, const AstStatDeclareExternType& declaredExternType);
     ControlFlow check(const ScopePtr& scope, const AstStatDeclareFunction& declaredFunction);
 
     void prototype(const ScopePtr& scope, const AstStatTypeAlias& typealias, int subLevel = 0);
-    void prototype(const ScopePtr& scope, const AstStatDeclareClass& declaredClass);
+    void prototype(const ScopePtr& scope, const AstStatDeclareExternType& declaredExternType);
 
     ControlFlow checkBlock(const ScopePtr& scope, const AstStatBlock& statement);
     ControlFlow checkBlockWithoutRecursionCheck(const ScopePtr& scope, const AstStatBlock& statement);
@@ -487,7 +487,7 @@ private:
     /**
      * A set of incorrect class definitions which is used to avoid a second-pass analysis.
      */
-    DenseHashSet<const AstStatDeclareClass*> incorrectClassDefinitions{nullptr};
+    DenseHashSet<const AstStatDeclareExternType*> incorrectExternTypeDefinitions{nullptr};
 
     std::vector<std::pair<TypeId, ScopePtr>> deferredQuantification;
 };

Analysis/include/Luau/TypePack.h

@@ -185,6 +185,8 @@ TypePackIterator begin(TypePackId tp);
 TypePackIterator begin(TypePackId tp, const TxnLog* log);
 TypePackIterator end(TypePackId tp);
 
+TypePackId getTail(TypePackId tp);
+
 using SeenSet = std::set<std::pair<const void*, const void*>>;
 
 bool areEqual(SeenSet& seen, const TypePackVar& lhs, const TypePackVar& rhs);

Analysis/include/Luau/Unifier.h

@@ -140,7 +140,7 @@ private:
     void tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection = false, const LiteralProperties* aliasableMap = nullptr);
     void tryUnifyScalarShape(TypeId subTy, TypeId superTy, bool reversed);
     void tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed);
-    void tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed);
+    void tryUnifyWithExternType(TypeId subTy, TypeId superTy, bool reversed);
     void tryUnifyNegations(TypeId subTy, TypeId superTy);
 
     TypePackId tryApplyOverloadedFunction(TypeId function, const NormalizedFunctionType& overloads, TypePackId args);

Analysis/include/Luau/VisitType.h

@@ -126,7 +126,7 @@ struct GenericTypeVisitor
     {
         return visit(ty);
     }
-    virtual bool visit(TypeId ty, const ClassType& ctv)
+    virtual bool visit(TypeId ty, const ExternType& etv)
     {
         return visit(ty);
     }
@@ -313,11 +313,11 @@ struct GenericTypeVisitor
                 traverse(mtv->metatable);
             }
         }
-        else if (auto ctv = get<ClassType>(ty))
+        else if (auto etv = get<ExternType>(ty))
         {
-            if (visit(ty, *ctv))
+            if (visit(ty, *etv))
             {
-                for (const auto& [name, prop] : ctv->props)
+                for (const auto& [name, prop] : etv->props)
                 {
                     if (FFlag::LuauSolverV2)
                     {
@@ -335,16 +335,16 @@ struct GenericTypeVisitor
                         traverse(prop.type());
                 }
 
-                if (ctv->parent)
+                if (etv->parent)
-                    traverse(*ctv->parent);
+                    traverse(*etv->parent);
 
-                if (ctv->metatable)
+                if (etv->metatable)
-                    traverse(*ctv->metatable);
+                    traverse(*etv->metatable);
 
-                if (ctv->indexer)
+                if (etv->indexer)
                 {
-                    traverse(ctv->indexer->indexType);
+                    traverse(etv->indexer->indexType);
-                    traverse(ctv->indexer->indexResultType);
+                    traverse(etv->indexer->indexResultType);
                 }
             }
         }
@@ -396,7 +396,7 @@ struct GenericTypeVisitor
                 traverse(unwrapped);
 
             // Visiting into LazyType that hasn't been unwrapped may necessarily cause infinite expansion, so we don't do that on purpose.
-            // Asserting also makes no sense, because the type _will_ happen here, most likely as a property of some ClassType
+            // Asserting also makes no sense, because the type _will_ happen here, most likely as a property of some ExternType
             // that doesn't need to be expanded.
         }
         else if (auto stv = get<SingletonType>(ty))

Analysis/src/Anyification.cpp

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

Analysis/src/ApplyTypeFunction.cpp

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

Analysis/src/AstJsonEncoder.cpp

@@ -8,6 +8,8 @@
 
 #include <math.h>
 
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+
 namespace Luau
 {
 
@@ -431,8 +433,16 @@ struct AstJsonEncoder : public AstVisitor
                 if (node->self)
                     PROP(self);
                 PROP(args);
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                {
                     if (node->returnAnnotation)
                         PROP(returnAnnotation);
+                }
+                else
+                {
+                    if (node->returnAnnotation_DEPRECATED)
+                        write("returnAnnotation", node->returnAnnotation_DEPRECATED);
+                }
                 PROP(vararg);
                 PROP(varargLocation);
                 if (node->varargAnnotation)
@@ -465,26 +475,26 @@ struct AstJsonEncoder : public AstVisitor
         writeRaw("}");
     }
 
-    void write(const AstGenericType& genericType)
+    void write(class AstGenericType* genericType)
     {
         writeRaw("{");
         bool c = pushComma();
         writeType("AstGenericType");
-        write("name", genericType.name);
+        write("name", genericType->name);
-        if (genericType.defaultValue)
+        if (genericType->defaultValue)
-            write("luauType", genericType.defaultValue);
+            write("luauType", genericType->defaultValue);
         popComma(c);
         writeRaw("}");
     }
 
-    void write(const AstGenericTypePack& genericTypePack)
+    void write(class AstGenericTypePack* genericTypePack)
     {
         writeRaw("{");
         bool c = pushComma();
         writeType("AstGenericTypePack");
-        write("name", genericTypePack.name);
+        write("name", genericTypePack->name);
-        if (genericTypePack.defaultValue)
+        if (genericTypePack->defaultValue)
-            write("luauType", genericTypePack.defaultValue);
+            write("luauType", genericTypePack->defaultValue);
         popComma(c);
         writeRaw("}");
     }
@@ -902,7 +912,10 @@ struct AstJsonEncoder : public AstVisitor
                 PROP(paramNames);
                 PROP(vararg);
                 PROP(varargLocation);
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
                     PROP(retTypes);
+                else
+                    write("retTypes", node->retTypes_DEPRECATED);
                 PROP(generics);
                 PROP(genericPacks);
             }
@@ -923,7 +936,7 @@ struct AstJsonEncoder : public AstVisitor
         );
     }
 
-    void write(const AstDeclaredClassProp& prop)
+    void write(const AstDeclaredExternTypeProperty& prop)
     {
         writeRaw("{");
         bool c = pushComma();
@@ -936,7 +949,7 @@ struct AstJsonEncoder : public AstVisitor
         writeRaw("}");
     }
 
-    void write(class AstStatDeclareClass* node)
+    void write(class AstStatDeclareExternType* node)
     {
         writeNode(
             node,
@@ -1048,7 +1061,10 @@ struct AstJsonEncoder : public AstVisitor
                 PROP(genericPacks);
                 PROP(argTypes);
                 PROP(argNames);
+                if (FFlag::LuauStoreReturnTypesAsPackOnAst)
                     PROP(returnTypes);
+                else
+                    write("returnTypes", node->returnTypes_DEPRECATED);
             }
         );
     }
@@ -1429,7 +1445,7 @@ struct AstJsonEncoder : public AstVisitor
         return false;
     }
 
-    bool visit(class AstStatDeclareClass* node) override
+    bool visit(class AstStatDeclareExternType* node) override
     {
         write(node);
         return false;

Analysis/src/AstQuery.cpp

@@ -574,11 +574,11 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
                             return checkOverloadedDocumentationSymbol(module, propIt->second.type(), parentExpr, propIt->second.documentationSymbol);
                     }
                 }
-                else if (const ClassType* ctv = get<ClassType>(parentTy))
+                else if (const ExternType* etv = get<ExternType>(parentTy))
                 {
-                    while (ctv)
+                    while (etv)
                     {
-                        if (auto propIt = ctv->props.find(indexName->index.value); propIt != ctv->props.end())
+                        if (auto propIt = etv->props.find(indexName->index.value); propIt != etv->props.end())
                         {
                             if (FFlag::LuauSolverV2)
                             {
@@ -590,7 +590,7 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
                                     module, propIt->second.type(), parentExpr, propIt->second.documentationSymbol
                                 );
                         }
-                        ctv = ctv->parent ? Luau::get<Luau::ClassType>(*ctv->parent) : nullptr;
+                        etv = etv->parent ? Luau::get<Luau::ExternType>(*etv->parent) : nullptr;
                     }
                 }
                 else if (const PrimitiveType* ptv = get<PrimitiveType>(parentTy); ptv && ptv->metatable)

Analysis/src/AutocompleteCore.cpp

@@ -24,14 +24,10 @@ LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTINT(LuauTypeInferIterationLimit)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
 LUAU_FASTFLAGVARIABLE(DebugLuauMagicVariableNames)
-
-LUAU_FASTFLAG(LuauExposeRequireByStringAutocomplete)
-
-LUAU_FASTFLAGVARIABLE(LuauAutocompleteRefactorsForIncrementalAutocomplete)
-
 LUAU_FASTFLAGVARIABLE(LuauAutocompleteUsesModuleForTypeCompatibility)
 LUAU_FASTFLAGVARIABLE(LuauAutocompleteUnionCopyPreviousSeen)
 LUAU_FASTFLAGVARIABLE(LuauAutocompleteMissingFollows)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 static const std::unordered_set<std::string> kStatementStartingKeywords =
     {"while", "if", "local", "repeat", "function", "do", "for", "return", "break", "continue", "type", "export"};
@@ -311,7 +307,7 @@ static void autocompleteProps(
     const std::vector<AstNode*>& nodes,
     AutocompleteEntryMap& result,
     std::unordered_set<TypeId>& seen,
-    std::optional<const ClassType*> containingClass = std::nullopt
+    std::optional<const ExternType*> containingExternType = std::nullopt
 )
 {
     rootTy = follow(rootTy);
@@ -334,8 +330,8 @@ static void autocompleteProps(
             if (calledWithSelf == ftv->hasSelf)
                 return true;
 
-            // Calls on classes require strict match between how function is declared and how it's called
+            // Calls on extern types require strict match between how function is declared and how it's called
-            if (get<ClassType>(rootTy))
+            if (get<ExternType>(rootTy))
                 return false;
 
             // When called with ':', but declared without 'self', it is invalid if a function has incompatible first argument or no arguments at all
@@ -368,7 +364,7 @@ static void autocompleteProps(
         return calledWithSelf;
     };
 
-    auto fillProps = [&](const ClassType::Props& props)
+    auto fillProps = [&](const ExternType::Props& props)
     {
         for (const auto& [name, prop] : props)
         {
@@ -401,7 +397,7 @@ static void autocompleteProps(
                     prop.deprecated,
                     isWrongIndexer(type),
                     typeCorrect,
-                    containingClass,
+                    containingExternType,
                     &prop,
                     prop.documentationSymbol,
                     {},
@@ -432,12 +428,12 @@ static void autocompleteProps(
         }
     };
 
-    if (auto cls = get<ClassType>(ty))
+    if (auto cls = get<ExternType>(ty))
     {
-        containingClass = containingClass.value_or(cls);
+        containingExternType = containingExternType.value_or(cls);
         fillProps(cls->props);
         if (cls->parent)
-            autocompleteProps(module, typeArena, builtinTypes, rootTy, *cls->parent, indexType, nodes, result, seen, containingClass);
+            autocompleteProps(module, typeArena, builtinTypes, rootTy, *cls->parent, indexType, nodes, result, seen, containingExternType);
     }
     else if (auto tbl = get<TableType>(ty))
         fillProps(tbl->props);
@@ -491,7 +487,7 @@ static void autocompleteProps(
             // If we don't do this, and we have the misfortune of receiving a
             // recursive union like:
             //
-            //  t1 where t1 = t1 | Class
+            //  t1 where t1 = t1 | ExternType
             //
             // Then we are on a one way journey to a stack overflow.
             if (FFlag::LuauAutocompleteUnionCopyPreviousSeen)
@@ -591,7 +587,7 @@ AutocompleteEntryMap autocompleteProps(
 AutocompleteEntryMap autocompleteModuleTypes(const Module& module, const ScopePtr& scopeAtPosition, Position position, std::string_view moduleName)
 {
     AutocompleteEntryMap result;
-    ScopePtr startScope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position);
+    ScopePtr startScope = scopeAtPosition;
     for (ScopePtr& scope = startScope; scope; scope = scope->parent)
     {
         if (auto it = scope->importedTypeBindings.find(std::string(moduleName)); it != scope->importedTypeBindings.end())
@@ -703,6 +699,30 @@ static std::optional<TypeId> findTypeElementAt(const AstTypeList& astTypeList, T
     return {};
 }
 
+static std::optional<TypeId> findTypeElementAt(AstTypePack* astTypePack, TypePackId tp, Position position)
+{
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
+    if (const auto typePack = astTypePack->as<AstTypePackExplicit>())
+    {
+        return findTypeElementAt(typePack->typeList, tp, position);
+    }
+    else if (const auto variadic = astTypePack->as<AstTypePackVariadic>())
+    {
+        if (variadic->location.containsClosed(position))
+        {
+            auto [_, tail] = flatten(tp);
+
+            if (tail)
+            {
+                if (const VariadicTypePack* vtp = get<VariadicTypePack>(follow(*tail)))
+                    return findTypeElementAt(variadic->variadicType, vtp->ty, position);
+            }
+        }
+    }
+
+    return {};
+}
+
 static std::optional<TypeId> findTypeElementAt(AstType* astType, TypeId ty, Position position)
 {
     ty = follow(ty);
@@ -723,9 +743,17 @@ static std::optional<TypeId> findTypeElementAt(AstType* astType, TypeId ty, Posi
         if (auto element = findTypeElementAt(type->argTypes, ftv->argTypes, position))
             return element;
 
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        {
             if (auto element = findTypeElementAt(type->returnTypes, ftv->retTypes, position))
                 return element;
         }
+        else
+        {
+            if (auto element = findTypeElementAt(type->returnTypes_DEPRECATED, ftv->retTypes, position))
+                return element;
+        }
+    }
 
     // It's possible to walk through other types like intrsection and unions if we find value in doing that
     return {};
@@ -733,7 +761,7 @@ static std::optional<TypeId> findTypeElementAt(AstType* astType, TypeId ty, Posi
 
 std::optional<TypeId> getLocalTypeInScopeAt(const Module& module, const ScopePtr& scopeAtPosition, Position position, AstLocal* local)
 {
-    if (ScopePtr scope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position))
+    if (ScopePtr scope = scopeAtPosition)
     {
         for (const auto& [name, binding] : scope->bindings)
         {
@@ -875,7 +903,7 @@ AutocompleteEntryMap autocompleteTypeNames(
 {
     AutocompleteEntryMap result;
 
-    ScopePtr startScope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position);
+    ScopePtr startScope = scopeAtPosition;
 
     for (ScopePtr scope = startScope; scope; scope = scope->parent)
     {
@@ -1054,12 +1082,16 @@ AutocompleteEntryMap autocompleteTypeNames(
             }
         }
 
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        {
             if (!node->returnAnnotation)
                 return result;
 
-        for (size_t i = 0; i < node->returnAnnotation->types.size; i++)
+            if (const auto typePack = node->returnAnnotation->as<AstTypePackExplicit>())
             {
-            AstType* ret = node->returnAnnotation->types.data[i];
+                for (size_t i = 0; i < typePack->typeList.types.size; i++)
+                {
+                    AstType* ret = typePack->typeList.types.data[i];
 
                     if (ret->location.containsClosed(position))
                     {
@@ -1074,7 +1106,7 @@ AutocompleteEntryMap autocompleteTypeNames(
                     }
                 }
 
-        if (AstTypePack* retTp = node->returnAnnotation->tailType)
+                if (AstTypePack* retTp = typePack->typeList.tailType)
                 {
                     if (auto variadic = retTp->as<AstTypePackVariadic>())
                     {
@@ -1089,6 +1121,56 @@ AutocompleteEntryMap autocompleteTypeNames(
                     }
                 }
             }
+            else if (auto variadic = node->returnAnnotation->as<AstTypePackVariadic>())
+            {
+                if (variadic->location.containsClosed(position))
+                {
+                    if (const FunctionType* ftv = tryGetExpectedFunctionType(module, node))
+                    {
+                        if (auto ty = tryGetTypePackTypeAt(ftv->retTypes, ~0u))
+                            tryAddTypeCorrectSuggestion(result, startScope, topType, *ty, position);
+                    }
+                }
+            }
+        }
+        else
+        {
+            if (!node->returnAnnotation_DEPRECATED)
+                return result;
+
+            for (size_t i = 0; i < node->returnAnnotation_DEPRECATED->types.size; i++)
+            {
+                AstType* ret = node->returnAnnotation_DEPRECATED->types.data[i];
+
+                if (ret->location.containsClosed(position))
+                {
+                    if (const FunctionType* ftv = tryGetExpectedFunctionType(module, node))
+                    {
+                        if (auto ty = tryGetTypePackTypeAt(ftv->retTypes, i))
+                            tryAddTypeCorrectSuggestion(result, startScope, topType, *ty, position);
+                    }
+
+                    // TODO: with additional type information, we could suggest inferred return type here
+                    break;
+                }
+            }
+
+            if (AstTypePack* retTp = node->returnAnnotation_DEPRECATED->tailType)
+            {
+                if (auto variadic = retTp->as<AstTypePackVariadic>())
+                {
+                    if (variadic->location.containsClosed(position))
+                    {
+                        if (const FunctionType* ftv = tryGetExpectedFunctionType(module, node))
+                        {
+                            if (auto ty = tryGetTypePackTypeAt(ftv->retTypes, ~0u))
+                                tryAddTypeCorrectSuggestion(result, startScope, topType, *ty, position);
+                        }
+                    }
+                }
+            }
+        }
+    }
 
     return result;
 }
@@ -1208,7 +1290,7 @@ static AutocompleteEntryMap autocompleteStatement(
 )
 {
     // This is inefficient. :(
-    ScopePtr scope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position);
+    ScopePtr scope = scopeAtPosition;
 
     AutocompleteEntryMap result;
 
@@ -1386,7 +1468,7 @@ static AutocompleteContext autocompleteExpression(
     else
     {
         // This is inefficient. :(
-        ScopePtr scope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(module, position);
+        ScopePtr scope = scopeAtPosition;
 
         while (scope)
         {
@@ -1455,7 +1537,7 @@ static AutocompleteResult autocompleteExpression(
     return {result, ancestry, context};
 }
 
-static std::optional<const ClassType*> getMethodContainingClass(const ModulePtr& module, AstExpr* funcExpr)
+static std::optional<const ExternType*> getMethodContainingExternType(const ModulePtr& module, AstExpr* funcExpr)
 {
     AstExpr* parentExpr = nullptr;
     if (auto indexName = funcExpr->as<AstExprIndexName>())
@@ -1479,14 +1561,14 @@ static std::optional<const ClassType*> getMethodContainingClass(const ModulePtr&
 
     Luau::TypeId parentType = Luau::follow(*parentIt);
 
-    if (auto parentClass = Luau::get<ClassType>(parentType))
+    if (auto parentExternType = Luau::get<ExternType>(parentType))
     {
-        return parentClass;
+        return parentExternType;
     }
 
     if (auto parentUnion = Luau::get<UnionType>(parentType))
     {
-        return returnFirstNonnullOptionOfType<ClassType>(parentUnion);
+        return returnFirstNonnullOptionOfType<ExternType>(parentUnion);
     }
 
     return std::nullopt;
@@ -1544,10 +1626,7 @@ static std::optional<AutocompleteEntryMap> convertRequireSuggestionsToAutocomple
     {
         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;
@@ -1608,7 +1687,7 @@ static std::optional<AutocompleteEntryMap> autocompleteStringParams(
             {
                 return convertRequireSuggestionsToAutocompleteEntryMap(fileResolver->getRequireSuggestions(module->name, candidateString));
             }
-            if (std::optional<AutocompleteEntryMap> ret = callback(tag, getMethodContainingClass(module, candidate->func), candidateString))
+            if (std::optional<AutocompleteEntryMap> ret = callback(tag, getMethodContainingExternType(module, candidate->func), candidateString))
             {
                 return ret;
             }
@@ -1776,7 +1855,7 @@ static std::optional<AutocompleteEntry> makeAnonymousAutofilled(
     if (!type)
         return std::nullopt;
 
-    const ScopePtr scope = FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete ? scopeAtPosition : findScopeAtPosition(*module, position);
+    const ScopePtr scope = scopeAtPosition;
     if (!scope)
         return std::nullopt;
 

Analysis/src/BuiltinDefinitions.cpp

@@ -32,10 +32,9 @@
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauNonReentrantGeneralization2)
 LUAU_FASTFLAGVARIABLE(LuauTableCloneClonesType3)
-LUAU_FASTFLAG(LuauTrackInteriorFreeTypesOnScope)
-LUAU_FASTFLAGVARIABLE(LuauFollowTableFreeze)
 LUAU_FASTFLAGVARIABLE(LuauUserTypeFunTypecheck)
 LUAU_FASTFLAGVARIABLE(LuauMagicFreezeCheckBlocked)
+LUAU_FASTFLAGVARIABLE(LuauFormatUseLastPosition)
 
 namespace Luau
 {
@@ -344,7 +343,7 @@ void registerBuiltinGlobals(Frontend& frontend, GlobalTypes& globals, bool typeC
     if (auto it = globals.globalScope->exportedTypeBindings.find("vector"); it != globals.globalScope->exportedTypeBindings.end())
     {
         TypeId vectorTy = it->second.type;
-        ClassType* vectorCls = getMutable<ClassType>(vectorTy);
+        ExternType* vectorCls = getMutable<ExternType>(vectorTy);
 
         vectorCls->metatable = arena.addType(TableType{{}, std::nullopt, TypeLevel{}, TableState::Sealed});
         TableType* metatableTy = Luau::getMutable<TableType>(vectorCls->metatable);
@@ -705,6 +704,14 @@ bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
         return true;
     }
 
+    // CLI-150726: The block below effectively constructs a type pack and then type checks it by going parameter-by-parameter.
+    // This does _not_ handle cases like:
+    //
+    //  local foo : () -> (...string) = (nil :: any)
+    //  print(string.format("%s %d %s", foo()))
+    //
+    // ... which should be disallowed.
+
     std::vector<TypeId> expected = parseFormatString(context.builtinTypes, fmt->value.data, fmt->value.size);
     const auto& [params, tail] = flatten(context.arguments);
 
@@ -716,7 +723,9 @@ bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
     {
         TypeId actualTy = params[i + paramOffset];
         TypeId expectedTy = expected[i];
-        Location location = context.callSite->args.data[i + (calledWithSelf ? 0 : paramOffset)]->location;
+        Location location = FFlag::LuauFormatUseLastPosition
+            ? context.callSite->args.data[std::min(context.callSite->args.size - 1, i + (calledWithSelf ? 0 : paramOffset))]->location
+            : context.callSite->args.data[i + (calledWithSelf ? 0 : paramOffset)]->location;
         // use subtyping instead here
         SubtypingResult result = context.typechecker->subtyping->isSubtype(actualTy, expectedTy, context.checkScope);
 
@@ -1529,7 +1538,6 @@ bool MagicClone::infer(const MagicFunctionCallContext& context)
         tableType->scope = context.constraint->scope.get();
     }
 
-    if (FFlag::LuauTrackInteriorFreeTypesOnScope)
     trackInteriorFreeType(context.constraint->scope.get(), resultType);
 
     TypePackId clonedTypePack = arena->addTypePack({resultType});
@@ -1541,7 +1549,6 @@ bool MagicClone::infer(const MagicFunctionCallContext& context)
 static std::optional<TypeId> freezeTable(TypeId inputType, const MagicFunctionCallContext& context)
 {
     TypeArena* arena = context.solver->arena;
-    if (FFlag::LuauFollowTableFreeze)
     inputType = follow(inputType);
     if (auto mt = get<MetatableType>(inputType))
     {

Analysis/src/Clone.cpp

@@ -355,7 +355,7 @@ private:
         t->metatable = shallowClone(t->metatable);
     }
 
-    void cloneChildren(ClassType* t)
+    void cloneChildren(ExternType* t)
     {
         for (auto& [_, p] : t->props)
             p = shallowClone(p);

Analysis/src/Constraint.cpp

@@ -20,7 +20,7 @@ struct ReferenceCountInitializer : TypeOnceVisitor
 
     DenseHashSet<TypeId>* result;
 
-    ReferenceCountInitializer(DenseHashSet<TypeId>* result)
+    explicit ReferenceCountInitializer(DenseHashSet<TypeId>* result)
         : result(result)
     {
     }
@@ -43,24 +43,15 @@ struct ReferenceCountInitializer : TypeOnceVisitor
         return false;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
-        // ClassTypes never contain free types.
+        // ExternTypes never contain free types.
         return false;
     }
 
     bool visit(TypeId, const TypeFunctionInstanceType&) override
     {
-        // We do not consider reference counted types that are inside a type
+        return FFlag::DebugLuauGreedyGeneralization;
-        // function to be part of the reachable reference counted types.
-        // Otherwise, code can be constructed in just the right way such
-        // that two type functions both claim to mutate a free type, which
-        // prevents either type function from trying to generalize it, so
-        // we potentially get stuck.
-        //
-        // The default behavior here is `true` for "visit the child types"
-        // of this type, hence:
-        return false;
     }
 };
 
@@ -130,8 +121,10 @@ DenseHashSet<TypeId> Constraint::getMaybeMutatedFreeTypes() const
     }
     else if (auto hic = get<HasIndexerConstraint>(*this))
     {
+        if (FFlag::DebugLuauGreedyGeneralization)
+            rci.traverse(hic->subjectType);
         rci.traverse(hic->resultType);
-        // `HasIndexerConstraint` should not mutate `subjectType` or `indexType`.
+        // `HasIndexerConstraint` should not mutate `indexType`.
     }
     else if (auto apc = get<AssignPropConstraint>(*this))
     {
@@ -150,6 +143,10 @@ DenseHashSet<TypeId> Constraint::getMaybeMutatedFreeTypes() const
             rci.traverse(ty);
         // `UnpackConstraint` should not mutate `sourcePack`.
     }
+    else if (auto rpc = get<ReduceConstraint>(*this); FFlag::DebugLuauGreedyGeneralization && rpc)
+    {
+        rci.traverse(rpc->ty);
+    }
     else if (auto rpc = get<ReducePackConstraint>(*this))
     {
         rci.traverse(rpc->tp);

Analysis/src/ConstraintGenerator.cpp

@@ -34,15 +34,11 @@ LUAU_FASTINT(LuauCheckRecursionLimit)
 LUAU_FASTFLAG(DebugLuauLogSolverToJson)
 LUAU_FASTFLAG(DebugLuauMagicTypes)
 LUAU_FASTFLAG(LuauNonReentrantGeneralization2)
-LUAU_FASTFLAG(LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
 LUAU_FASTFLAGVARIABLE(LuauPropagateExpectedTypesForCalls)
 LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
 
-LUAU_FASTFLAGVARIABLE(LuauTrackInteriorFreeTypesOnScope)
 LUAU_FASTFLAGVARIABLE(LuauUngeneralizedTypesForRecursiveFunctions)
 
-LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
-LUAU_FASTFLAGVARIABLE(LuauDoNotLeakNilInRefinement)
 LUAU_FASTFLAG(LuauUserTypeFunTypecheck)
 LUAU_FASTFLAGVARIABLE(LuauRetainDefinitionAliasLocations)
 
@@ -50,9 +46,12 @@ LUAU_FASTFLAG(LuauDeprecatedAttribute)
 LUAU_FASTFLAGVARIABLE(LuauCacheInferencePerAstExpr)
 LUAU_FASTFLAGVARIABLE(LuauAlwaysResolveAstTypes)
 LUAU_FASTFLAGVARIABLE(LuauWeakNilRefinementType)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 LUAU_FASTFLAG(LuauGlobalVariableModuleIsolation)
 
 LUAU_FASTFLAGVARIABLE(LuauNoTypeFunctionsNamedTypeOf)
+LUAU_FASTFLAG(LuauAddCallConstraintForIterableFunctions)
+LUAU_FASTFLAG(LuauDoNotAddUpvalueTypesToLocalType)
 
 namespace Luau
 {
@@ -157,7 +156,7 @@ struct HasFreeType : TypeOnceVisitor
         return true;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -218,6 +217,32 @@ ConstraintGenerator::ConstraintGenerator(
     LUAU_ASSERT(module);
 }
 
+ConstraintSet ConstraintGenerator::run(AstStatBlock* block)
+{
+    visitModuleRoot(block);
+
+    return ConstraintSet{
+        NotNull{rootScope},
+        std::move(constraints),
+        std::move(freeTypes),
+        std::move(scopeToFunction),
+        std::move(errors)
+    };
+}
+
+ConstraintSet ConstraintGenerator::runOnFragment(const ScopePtr& resumeScope, AstStatBlock* block)
+{
+    visitFragmentRoot(resumeScope, block);
+
+    return ConstraintSet{
+        NotNull{rootScope},
+        std::move(constraints),
+        std::move(freeTypes),
+        std::move(scopeToFunction),
+        std::move(errors)
+    };
+}
+
 void ConstraintGenerator::visitModuleRoot(AstStatBlock* block)
 {
     LUAU_TIMETRACE_SCOPE("ConstraintGenerator::visitModuleRoot", "Typechecking");
@@ -263,8 +288,7 @@ void ConstraintGenerator::visitModuleRoot(AstStatBlock* block)
         GeneralizationConstraint{
             result,
             moduleFnTy,
-            (FFlag::LuauNonReentrantGeneralization2 || FFlag::LuauTrackInteriorFreeTypesOnScope) ? std::vector<TypeId>{}
+            std::vector<TypeId>{},
-                                                                                                 : std::move(DEPRECATED_interiorTypes.back())
         }
     );
 
@@ -273,7 +297,7 @@ void ConstraintGenerator::visitModuleRoot(AstStatBlock* block)
         scope->interiorFreeTypes = std::move(interiorFreeTypes.back().types);
         scope->interiorFreeTypePacks = std::move(interiorFreeTypes.back().typePacks);
     }
-    else if (FFlag::LuauTrackInteriorFreeTypesOnScope)
+    else
         scope->interiorFreeTypes = std::move(DEPRECATED_interiorTypes.back());
 
     getMutable<BlockedType>(result)->setOwner(genConstraint);
@@ -359,17 +383,17 @@ TypeId ConstraintGenerator::freshType(const ScopePtr& scope, Polarity polarity)
     {
         auto ft = Luau::freshType(arena, builtinTypes, scope.get(), polarity);
         interiorFreeTypes.back().types.push_back(ft);
-        return ft;
+
-    }
+        if (FFlag::DebugLuauGreedyGeneralization)
-    else if (FFlag::LuauTrackInteriorFreeTypesOnScope)
+            freeTypes.insert(ft);
-    {
+
-        auto ft = Luau::freshType(arena, builtinTypes, scope.get());
-        DEPRECATED_interiorTypes.back().push_back(ft);
         return ft;
     }
     else
     {
-        return Luau::freshType(arena, builtinTypes, scope.get());
+        auto ft = Luau::freshType(arena, builtinTypes, scope.get());
+        DEPRECATED_interiorTypes.back().push_back(ft);
+        return ft;
     }
 }
 
@@ -578,16 +602,9 @@ void ConstraintGenerator::computeRefinement(
 
         // When the top-level expression is `t[x]`, we want to refine it into `nil`, not `never`.
         LUAU_ASSERT(refis->get(proposition->key->def));
-        if (FFlag::LuauDoNotLeakNilInRefinement)
-        {
         refis->get(proposition->key->def)->shouldAppendNilType =
             (sense || !eq) && containsSubscriptedDefinition(proposition->key->def) && !proposition->implicitFromCall;
     }
-        else
-        {
-            refis->get(proposition->key->def)->shouldAppendNilType = (sense || !eq) && containsSubscriptedDefinition(proposition->key->def);
-        }
-    }
 }
 
 namespace
@@ -633,7 +650,7 @@ struct FindSimplificationBlockers : TypeOnceVisitor
         return false;
     }
 
-    bool visit(TypeId, const ClassType&) override
+    bool visit(TypeId, const ExternType&) override
     {
         return false;
     }
@@ -858,7 +875,7 @@ void ConstraintGenerator::checkAliases(const ScopePtr& scope, AstStatBlock* bloc
 
             aliasDefinitionLocations[function->name.value] = function->location;
         }
-        else if (auto classDeclaration = stat->as<AstStatDeclareClass>())
+        else if (auto classDeclaration = stat->as<AstStatDeclareExternType>())
         {
             if (scope->exportedTypeBindings.count(classDeclaration->name.value))
             {
@@ -1052,7 +1069,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStat* stat)
         return visit(scope, s);
     else if (auto s = stat->as<AstStatDeclareFunction>())
         return visit(scope, s);
-    else if (auto s = stat->as<AstStatDeclareClass>())
+    else if (auto s = stat->as<AstStatDeclareExternType>())
         return visit(scope, s);
     else if (auto s = stat->as<AstStatError>())
         return visit(scope, s);
@@ -1273,11 +1290,8 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatForIn* forI
 
     for (AstLocal* var : forIn->vars)
     {
-        TypeId assignee = arena->addType(BlockedType{});
-        variableTypes.push_back(assignee);
-
         TypeId loopVar = arena->addType(BlockedType{});
-        localTypes[loopVar].insert(assignee);
+        variableTypes.push_back(loopVar);
 
         if (var->annotation)
         {
@@ -1296,6 +1310,23 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatForIn* forI
         loopScope, getLocation(forIn->values), IterableConstraint{iterator, variableTypes, forIn->values.data[0], &module->astForInNextTypes}
     );
 
+    if (FFlag::LuauAddCallConstraintForIterableFunctions)
+    {
+        // Add an intersection ReduceConstraint for the key variable to denote that it can't be nil
+        AstLocal* keyVar = *forIn->vars.begin();
+        const DefId keyDef = dfg->getDef(keyVar);
+        const TypeId loopVar = loopScope->lvalueTypes[keyDef];
+
+        const TypeId intersectionTy =
+            createTypeFunctionInstance(builtinTypeFunctions().intersectFunc, {loopVar, builtinTypes->notNilType}, {}, loopScope, keyVar->location);
+
+        loopScope->bindings[keyVar] = Binding{intersectionTy, keyVar->location};
+        loopScope->lvalueTypes[keyDef] = intersectionTy;
+
+        auto c = addConstraint(loopScope, keyVar->location, ReduceConstraint{intersectionTy});
+        c->dependencies.push_back(iterable);
+    }
+
     for (TypeId var : variableTypes)
     {
         auto bt = getMutable<BlockedType>(var);
@@ -1378,7 +1409,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatLocalFuncti
     FunctionSignature sig = checkFunctionSignature(scope, function->func, /* expectedType */ std::nullopt, function->name->location);
     sig.bodyScope->bindings[function->name] = Binding{sig.signature, function->name->location};
 
-    bool sigFullyDefined = !hasFreeType(sig.signature);
+    bool sigFullyDefined = FFlag::DebugLuauGreedyGeneralization ? false : !hasFreeType(sig.signature);
     if (sigFullyDefined)
         emplaceType<BoundType>(asMutable(functionType), sig.signature);
 
@@ -1440,7 +1471,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatFunction* f
 
     Checkpoint start = checkpoint(this);
     FunctionSignature sig = checkFunctionSignature(scope, function->func, /* expectedType */ std::nullopt, function->name->location);
-    bool sigFullyDefined = !hasFreeType(sig.signature);
+    bool sigFullyDefined = FFlag::DebugLuauGreedyGeneralization ? false : !hasFreeType(sig.signature);
 
     DefId def = dfg->getDef(function->name);
 
@@ -1779,7 +1810,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatTypeFunctio
         GeneralizationConstraint{
             generalizedTy,
             sig.signature,
-            FFlag::LuauTrackInteriorFreeTypesOnScope ? std::vector<TypeId>{} : std::move(DEPRECATED_interiorTypes.back())
+            std::vector<TypeId>{},
         }
     );
 
@@ -1788,7 +1819,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatTypeFunctio
         sig.signatureScope->interiorFreeTypes = std::move(interiorFreeTypes.back().types);
         sig.signatureScope->interiorFreeTypePacks = std::move(interiorFreeTypes.back().typePacks);
     }
-    else if (FFlag::LuauTrackInteriorFreeTypesOnScope)
+    else
         sig.signatureScope->interiorFreeTypes = std::move(DEPRECATED_interiorTypes.back());
 
     getMutable<BlockedType>(generalizedTy)->setOwner(gc);
@@ -1852,71 +1883,71 @@ static bool isMetamethod(const Name& name)
            name == "__idiv";
 }
 
-ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatDeclareClass* declaredClass)
+ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatDeclareExternType* declaredExternType)
 {
     // If a class with the same name was already defined, we skip over
-    auto bindingIt = scope->exportedTypeBindings.find(declaredClass->name.value);
+    auto bindingIt = scope->exportedTypeBindings.find(declaredExternType->name.value);
     if (bindingIt == scope->exportedTypeBindings.end())
         return ControlFlow::None;
 
-    std::optional<TypeId> superTy = std::make_optional(builtinTypes->classType);
+    std::optional<TypeId> superTy = std::make_optional(builtinTypes->externType);
-    if (declaredClass->superName)
+    if (declaredExternType->superName)
     {
-        Name superName = Name(declaredClass->superName->value);
+        Name superName = Name(declaredExternType->superName->value);
         std::optional<TypeFun> lookupType = scope->lookupType(superName);
 
         if (!lookupType)
         {
-            reportError(declaredClass->location, UnknownSymbol{superName, UnknownSymbol::Type});
+            reportError(declaredExternType->location, UnknownSymbol{superName, UnknownSymbol::Type});
             return ControlFlow::None;
         }
 
-        // We don't have generic classes, so this assertion _should_ never be hit.
+        // We don't have generic extern types, so this assertion _should_ never be hit.
         LUAU_ASSERT(lookupType->typeParams.size() == 0 && lookupType->typePackParams.size() == 0);
         superTy = follow(lookupType->type);
 
-        if (!get<ClassType>(follow(*superTy)))
+        if (!get<ExternType>(follow(*superTy)))
         {
             reportError(
-                declaredClass->location,
+                declaredExternType->location,
-                GenericError{format("Cannot use non-class type '%s' as a superclass of class '%s'", superName.c_str(), declaredClass->name.value)}
+                GenericError{format("Cannot use non-class type '%s' as a superclass of class '%s'", superName.c_str(), declaredExternType->name.value)}
             );
 
             return ControlFlow::None;
         }
     }
 
-    Name className(declaredClass->name.value);
+    Name className(declaredExternType->name.value);
 
-    TypeId classTy = arena->addType(ClassType(className, {}, superTy, std::nullopt, {}, {}, module->name, declaredClass->location));
+    TypeId externTy = arena->addType(ExternType(className, {}, superTy, std::nullopt, {}, {}, module->name, declaredExternType->location));
-    ClassType* ctv = getMutable<ClassType>(classTy);
+    ExternType* etv = getMutable<ExternType>(externTy);
 
     TypeId metaTy = arena->addType(TableType{TableState::Sealed, scope->level, scope.get()});
     TableType* metatable = getMutable<TableType>(metaTy);
 
-    ctv->metatable = metaTy;
+    etv->metatable = metaTy;
 
     TypeId classBindTy = bindingIt->second.type;
-    emplaceType<BoundType>(asMutable(classBindTy), classTy);
+    emplaceType<BoundType>(asMutable(classBindTy), externTy);
 
-    if (declaredClass->indexer)
+    if (declaredExternType->indexer)
     {
         RecursionCounter counter{&recursionCount};
 
         if (recursionCount >= FInt::LuauCheckRecursionLimit)
         {
-            reportCodeTooComplex(declaredClass->indexer->location);
+            reportCodeTooComplex(declaredExternType->indexer->location);
         }
         else
         {
-            ctv->indexer = TableIndexer{
+            etv->indexer = TableIndexer{
-                resolveType(scope, declaredClass->indexer->indexType, /* inTypeArguments */ false),
+                resolveType(scope, declaredExternType->indexer->indexType, /* inTypeArguments */ false),
-                resolveType(scope, declaredClass->indexer->resultType, /* inTypeArguments */ false),
+                resolveType(scope, declaredExternType->indexer->resultType, /* inTypeArguments */ false),
             };
         }
     }
 
-    for (const AstDeclaredClassProp& prop : declaredClass->props)
+    for (const AstDeclaredExternTypeProperty& prop : declaredExternType->props)
     {
         Name propName(prop.name.value);
         TypeId propTy = resolveType(scope, prop.ty, /* inTypeArguments */ false);
@@ -1930,7 +1961,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatDeclareClas
             if (FunctionType* ftv = getMutable<FunctionType>(propTy))
             {
                 ftv->argNames.insert(ftv->argNames.begin(), FunctionArgument{"self", {}});
-                ftv->argTypes = addTypePack({classTy}, ftv->argTypes);
+                ftv->argTypes = addTypePack({externTy}, ftv->argTypes);
 
                 ftv->hasSelf = true;
 
@@ -1945,7 +1976,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatDeclareClas
             }
         }
 
-        TableType::Props& props = assignToMetatable ? metatable->props : ctv->props;
+        TableType::Props& props = assignToMetatable ? metatable->props : etv->props;
 
         if (props.count(propName) == 0)
         {
@@ -1976,7 +2007,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatDeclareClas
             }
             else
             {
-                reportError(declaredClass->location, GenericError{format("Cannot overload non-function class member '%s'", propName.c_str())});
+                reportError(declaredExternType->location, GenericError{format("Cannot overload non-function class member '%s'", propName.c_str())});
             }
         }
     }
@@ -2008,7 +2039,8 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatDeclareFunc
         funScope = childScope(global, scope);
 
     TypePackId paramPack = resolveTypePack(funScope, global->params, /* inTypeArguments */ false);
-    TypePackId retPack = resolveTypePack(funScope, global->retTypes, /* inTypeArguments */ false);
+    TypePackId retPack = FFlag::LuauStoreReturnTypesAsPackOnAst ? resolveTypePack(funScope, global->retTypes, /* inTypeArguments */ false)
+                                                                : resolveTypePack(funScope, global->retTypes_DEPRECATED, /* inTypeArguments */ false);
 
     FunctionDefinition defn;
 
@@ -2356,11 +2388,14 @@ InferencePack ConstraintGenerator::checkPack(const ScopePtr& scope, AstExprCall*
         argEndCheckpoint,
         this,
         [checkConstraint, callConstraint](const ConstraintPtr& constraint)
+        {
+            if (!(FFlag::DebugLuauGreedyGeneralization && get<PrimitiveTypeConstraint>(*constraint)))
             {
                 constraint->dependencies.emplace_back(checkConstraint);
 
                 callConstraint->dependencies.emplace_back(constraint.get());
             }
+        }
     );
 
     return InferencePack{rets, {refinementArena.variadic(returnRefinements)}};
@@ -2464,8 +2499,7 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprConstantStrin
     }
     else
     {
-        FreeType ft =
+        FreeType ft = FreeType{scope.get(), builtinTypes->neverType, builtinTypes->unknownType};
-            FFlag::LuauFreeTypesMustHaveBounds ? FreeType{scope.get(), builtinTypes->neverType, builtinTypes->unknownType} : FreeType{scope.get()};
         ft.lowerBound = arena->addType(SingletonType{StringSingleton{std::string{string->value.data, string->value.size}}});
         ft.upperBound = builtinTypes->stringType;
         freeTy = arena->addType(ft);
@@ -2492,8 +2526,7 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprConstantBool*
     }
     else
     {
-        FreeType ft =
+        FreeType ft = FreeType{scope.get(), builtinTypes->neverType, builtinTypes->unknownType};
-            FFlag::LuauFreeTypesMustHaveBounds ? FreeType{scope.get(), builtinTypes->neverType, builtinTypes->unknownType} : FreeType{scope.get()};
         ft.lowerBound = singletonType;
         ft.upperBound = builtinTypes->booleanType;
         freeTy = arena->addType(ft);
@@ -2658,8 +2691,7 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprFunction* fun
         GeneralizationConstraint{
             generalizedTy,
             sig.signature,
-            (FFlag::LuauNonReentrantGeneralization2 || FFlag::LuauTrackInteriorFreeTypesOnScope) ? std::vector<TypeId>{}
+            std::vector<TypeId>{},
-                                                                                                 : std::move(DEPRECATED_interiorTypes.back())
         }
     );
 
@@ -2673,9 +2705,7 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprFunction* fun
     }
     else
     {
-        if (FFlag::LuauTrackInteriorFreeTypesOnScope)
         sig.signatureScope->interiorFreeTypes = std::move(DEPRECATED_interiorTypes.back());
-
         getMutable<BlockedType>(generalizedTy)->setOwner(gc);
         DEPRECATED_interiorTypes.pop_back();
     }
@@ -2963,7 +2993,7 @@ std::tuple<TypeId, TypeId, RefinementId> ConstraintGenerator::checkBinary(
         else if (typeguard->type == "userdata")
         {
             // For now, we don't really care about being accurate with userdata if the typeguard was using typeof.
-            discriminantTy = builtinTypes->classType;
+            discriminantTy = builtinTypes->externType;
         }
         else if (!typeguard->isTypeof && typeguard->type == "vector")
             discriminantTy = builtinTypes->neverType; // TODO: figure out a way to deal with this quirky type
@@ -2973,8 +3003,8 @@ std::tuple<TypeId, TypeId, RefinementId> ConstraintGenerator::checkBinary(
         {
             TypeId ty = follow(typeFun->type);
 
-            // We're only interested in the root class of any classes.
+            // We're only interested in the root type of any extern type.
-            if (auto ctv = get<ClassType>(ty); ctv && (ctv->parent == builtinTypes->classType || hasTag(ty, kTypeofRootTag)))
+            if (auto etv = get<ExternType>(ty); etv && (etv->parent == builtinTypes->externType || hasTag(ty, kTypeofRootTag)))
                 discriminantTy = ty;
         }
 
@@ -3047,7 +3077,7 @@ void ConstraintGenerator::visitLValue(const ScopePtr& scope, AstExprLocal* local
     if (ty)
     {
         TypeIds* localDomain = localTypes.find(*ty);
-        if (localDomain)
+        if (localDomain && !(FFlag::LuauDoNotAddUpvalueTypesToLocalType && local->upvalue))
             localDomain->insert(rhsType);
     }
     else
@@ -3078,6 +3108,8 @@ void ConstraintGenerator::visitLValue(const ScopePtr& scope, AstExprLocal* local
     if (annotatedTy)
         addConstraint(scope, local->location, SubtypeConstraint{rhsType, *annotatedTy});
 
+    // This is vestigial.
+    if (!FFlag::LuauDoNotAddUpvalueTypesToLocalType)
         if (TypeIds* localDomain = localTypes.find(*ty))
             localDomain->insert(rhsType);
 }
@@ -3383,12 +3415,36 @@ ConstraintGenerator::FunctionSignature ConstraintGenerator::checkFunctionSignatu
 
     LUAU_ASSERT(nullptr != varargPack);
 
+    if (FFlag::DebugLuauGreedyGeneralization)
+    {
+        // Some of the types in argTypes will eventually be generics, and some
+        // will not. The ones that are not generic will be pruned when
+        // GeneralizationConstraint dispatches.
+        genericTypes.insert(genericTypes.begin(), argTypes.begin(), argTypes.end());
+        varargPack = follow(varargPack);
+        returnType = follow(returnType);
+        if (varargPack == returnType)
+            genericTypePacks = {varargPack};
+        else
+            genericTypePacks = {varargPack, returnType};
+    }
+
     // If there is both an annotation and an expected type, the annotation wins.
     // Type checking will sort out any discrepancies later.
-    if (fn->returnAnnotation)
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst && fn->returnAnnotation)
     {
         TypePackId annotatedRetType =
-            resolveTypePack(signatureScope, *fn->returnAnnotation, /* inTypeArguments */ false, /* replaceErrorWithFresh*/ true);
+            resolveTypePack(signatureScope, fn->returnAnnotation, /* inTypeArguments */ false, /* replaceErrorWithFresh*/ true);
+        // We bind the annotated type directly here so that, when we need to
+        // generate constraints for return types, we have a guarantee that we
+        // know the annotated return type already, if one was provided.
+        LUAU_ASSERT(get<FreeTypePack>(returnType));
+        emplaceTypePack<BoundTypePack>(asMutable(returnType), annotatedRetType);
+    }
+    else if (!FFlag::LuauStoreReturnTypesAsPackOnAst && fn->returnAnnotation_DEPRECATED)
+    {
+        TypePackId annotatedRetType =
+            resolveTypePack(signatureScope, *fn->returnAnnotation_DEPRECATED, /* inTypeArguments */ false, /* replaceErrorWithFresh*/ true);
         // We bind the annotated type directly here so that, when we need to
         // generate constraints for return types, we have a guarantee that we
         // know the annotated return type already, if one was provided.
@@ -3639,8 +3695,16 @@ TypeId ConstraintGenerator::resolveFunctionType(
     AstTypePackExplicit tempArgTypes{Location{}, fn->argTypes};
     TypePackId argTypes = resolveTypePack_(signatureScope, &tempArgTypes, inTypeArguments, replaceErrorWithFresh);
 
-    AstTypePackExplicit tempRetTypes{Location{}, fn->returnTypes};
+    TypePackId returnTypes;
-    TypePackId returnTypes = resolveTypePack_(signatureScope, &tempRetTypes, inTypeArguments, replaceErrorWithFresh);
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        returnTypes = resolveTypePack_(signatureScope, fn->returnTypes, inTypeArguments, replaceErrorWithFresh);
+    }
+    else
+    {
+        AstTypePackExplicit tempRetTypes{Location{}, fn->returnTypes_DEPRECATED};
+        returnTypes = resolveTypePack_(signatureScope, &tempRetTypes, inTypeArguments, replaceErrorWithFresh);
+    }
 
     // TODO: FunctionType needs a pointer to the scope so that we know
     // how to quantify/instantiate it.
@@ -3724,13 +3788,9 @@ TypeId ConstraintGenerator::resolveType_(const ScopePtr& scope, AstType* ty, boo
             }
         }
         else
-        {
-            if (FFlag::LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
         {
             if (unionAnnotation->types.size == 1)
                 return resolveType_(scope, unionAnnotation->types.data[0], inTypeArguments);
-            }
-
             std::vector<TypeId> parts;
             for (AstType* part : unionAnnotation->types)
             {
@@ -3758,13 +3818,9 @@ TypeId ConstraintGenerator::resolveType_(const ScopePtr& scope, AstType* ty, boo
             }
         }
         else
-        {
-            if (FFlag::LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
         {
             if (intersectionAnnotation->types.size == 1)
                 return resolveType_(scope, intersectionAnnotation->types.data[0], inTypeArguments);
-            }
-
             std::vector<TypeId> parts;
             for (AstType* part : intersectionAnnotation->types)
             {
@@ -4294,15 +4350,4 @@ TypeId ConstraintGenerator::simplifyUnion(const ScopePtr& scope, Location locati
     return ::Luau::simplifyUnion(builtinTypes, arena, left, right).result;
 }
 
-std::vector<NotNull<Constraint>> borrowConstraints(const std::vector<ConstraintPtr>& constraints)
-{
-    std::vector<NotNull<Constraint>> result;
-    result.reserve(constraints.size());
-
-    for (const auto& c : constraints)
-        result.emplace_back(c.get());
-
-    return result;
-}
-
 } // namespace Luau

Analysis/src/ConstraintSolver.cpp

@@ -11,7 +11,6 @@
 #include "Luau/Location.h"
 #include "Luau/ModuleResolver.h"
 #include "Luau/OverloadResolution.h"
-#include "Luau/Quantify.h"
 #include "Luau/RecursionCounter.h"
 #include "Luau/Simplify.h"
 #include "Luau/TableLiteralInference.h"
@@ -33,20 +32,20 @@ LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverIncludeDependencies)
 LUAU_FASTFLAGVARIABLE(DebugLuauLogBindings)
 LUAU_FASTINTVARIABLE(LuauSolverRecursionLimit, 500)
 LUAU_FASTFLAGVARIABLE(DebugLuauEqSatSimplification)
-LUAU_FASTFLAG(LuauTrackInteriorFreeTypesOnScope)
-LUAU_FASTFLAGVARIABLE(LuauTrackInteriorFreeTablesOnScope)
 LUAU_FASTFLAGVARIABLE(LuauHasPropProperBlock)
 LUAU_FASTFLAGVARIABLE(DebugLuauGreedyGeneralization)
-LUAU_FASTFLAG(LuauSearchForRefineableType)
 LUAU_FASTFLAG(LuauDeprecatedAttribute)
 LUAU_FASTFLAG(LuauNonReentrantGeneralization2)
 LUAU_FASTFLAG(LuauBidirectionalInferenceCollectIndexerTypes)
 LUAU_FASTFLAG(LuauNewTypeFunReductionChecks2)
 LUAU_FASTFLAGVARIABLE(LuauTrackInferredFunctionTypeFromCall)
+LUAU_FASTFLAGVARIABLE(LuauAddCallConstraintForIterableFunctions)
 
 namespace Luau
 {
 
+static void dump(ConstraintSolver* cs, ToStringOptions& opts);
+
 size_t HashBlockedConstraintId::operator()(const BlockedConstraintId& bci) const
 {
     size_t result = 0;
@@ -276,26 +275,6 @@ size_t HashInstantiationSignature::operator()(const InstantiationSignature& sign
     return hash;
 }
 
-void dump(ConstraintSolver* cs, ToStringOptions& opts)
-{
-    printf("constraints:\n");
-    for (NotNull<const Constraint> c : cs->unsolvedConstraints)
-    {
-        auto it = cs->blockedConstraints.find(c);
-        int blockCount = it == cs->blockedConstraints.end() ? 0 : int(it->second);
-        printf("\t%d\t%s\n", blockCount, toString(*c, opts).c_str());
-
-        if (FFlag::DebugLuauLogSolverIncludeDependencies)
-        {
-            for (NotNull<Constraint> dep : c->dependencies)
-            {
-                if (std::find(cs->unsolvedConstraints.begin(), cs->unsolvedConstraints.end(), dep) != cs->unsolvedConstraints.end())
-                    printf("\t\t|\t%s\n", toString(*dep, opts).c_str());
-            }
-        }
-    }
-}
-
 struct InstantiationQueuer : TypeOnceVisitor
 {
     ConstraintSolver* solver;
@@ -321,12 +300,44 @@ struct InstantiationQueuer : TypeOnceVisitor
         return true;
     }
 
-    bool visit(TypeId ty, const ClassType& ctv) override
+    bool visit(TypeId ty, const ExternType& etv) override
     {
         return false;
     }
 };
 
+ConstraintSolver::ConstraintSolver(
+    NotNull<Normalizer> normalizer,
+    NotNull<Simplifier> simplifier,
+    NotNull<TypeFunctionRuntime> typeFunctionRuntime,
+    ModuleName moduleName,
+    NotNull<ModuleResolver> moduleResolver,
+    std::vector<RequireCycle> requireCycles,
+    DcrLogger* logger,
+    NotNull<const DataFlowGraph> dfg,
+    TypeCheckLimits limits,
+    ConstraintSet constraintSet_
+)
+    : arena(normalizer->arena)
+    , builtinTypes(normalizer->builtinTypes)
+    , normalizer(normalizer)
+    , simplifier(simplifier)
+    , typeFunctionRuntime(typeFunctionRuntime)
+    , constraintSet(std::move(constraintSet_))
+    , constraints(borrowConstraints(constraintSet.constraints))
+    , scopeToFunction(&constraintSet.scopeToFunction)
+    , rootScope(constraintSet.rootScope)
+    , currentModuleName(std::move(moduleName))
+    , dfg(dfg)
+    , moduleResolver(moduleResolver)
+    , requireCycles(std::move(requireCycles))
+    , logger(logger)
+    , limits(std::move(limits))
+    , opts{/*exhaustive*/ true}
+{
+    initFreeTypeTracking();
+}
+
 ConstraintSolver::ConstraintSolver(
     NotNull<Normalizer> normalizer,
     NotNull<Simplifier> simplifier,
@@ -346,6 +357,7 @@ ConstraintSolver::ConstraintSolver(
     , normalizer(normalizer)
     , simplifier(simplifier)
     , typeFunctionRuntime(typeFunctionRuntime)
+    , constraintSet{rootScope}
     , constraints(std::move(constraints))
     , scopeToFunction(scopeToFunction)
     , rootScope(rootScope)
@@ -355,33 +367,9 @@ ConstraintSolver::ConstraintSolver(
     , requireCycles(std::move(requireCycles))
     , logger(logger)
     , limits(std::move(limits))
+    , opts{/*exhaustive*/ true}
 {
-    opts.exhaustive = true;
+    initFreeTypeTracking();
-
-    for (NotNull<Constraint> c : this->constraints)
-    {
-        unsolvedConstraints.emplace_back(c);
-
-        auto maybeMutatedTypesPerConstraint = c->getMaybeMutatedFreeTypes();
-        for (auto ty : maybeMutatedTypesPerConstraint)
-        {
-            auto [refCount, _] = unresolvedConstraints.try_insert(ty, 0);
-            refCount += 1;
-
-            if (FFlag::DebugLuauGreedyGeneralization)
-            {
-                auto [it, fresh] = mutatedFreeTypeToConstraint.try_emplace(ty, DenseHashSet<const Constraint*>{nullptr});
-                it->second.insert(c.get());
-            }
-        }
-        maybeMutatedFreeTypes.emplace(c, maybeMutatedTypesPerConstraint);
-
-
-        for (NotNull<const Constraint> dep : c->dependencies)
-        {
-            block(dep, c);
-        }
-    }
 }
 
 void ConstraintSolver::randomize(unsigned seed)
@@ -426,6 +414,18 @@ void ConstraintSolver::run()
         logger->captureInitialSolverState(rootScope, unsolvedConstraints);
     }
 
+    // Free types that have no constraints at all can be generalized right away.
+    if (FFlag::DebugLuauGreedyGeneralization)
+    {
+        for (TypeId ty : constraintSet.freeTypes)
+        {
+            if (auto it = mutatedFreeTypeToConstraint.find(ty); it == mutatedFreeTypeToConstraint.end() || it->second.empty())
+                generalizeOneType(ty);
+        }
+    }
+
+    constraintSet.freeTypes.clear();
+
     auto runSolverPass = [&](bool force)
     {
         bool progress = false;
@@ -655,12 +655,39 @@ struct TypeSearcher : TypeVisitor
 
     // }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
 };
 
+void ConstraintSolver::initFreeTypeTracking()
+{
+    for (NotNull<Constraint> c : this->constraints)
+    {
+        unsolvedConstraints.emplace_back(c);
+
+        auto maybeMutatedTypesPerConstraint = c->getMaybeMutatedFreeTypes();
+        for (auto ty : maybeMutatedTypesPerConstraint)
+        {
+            auto [refCount, _] = unresolvedConstraints.try_insert(ty, 0);
+            refCount += 1;
+
+            if (FFlag::DebugLuauGreedyGeneralization)
+            {
+                auto [it, fresh] = mutatedFreeTypeToConstraint.try_emplace(ty, nullptr);
+                it->second.insert(c.get());
+            }
+        }
+        maybeMutatedFreeTypes.emplace(c, maybeMutatedTypesPerConstraint);
+
+        for (NotNull<const Constraint> dep : c->dependencies)
+        {
+            block(dep, c);
+        }
+    }
+}
+
 void ConstraintSolver::generalizeOneType(TypeId ty)
 {
     ty = follow(ty);
@@ -858,8 +885,6 @@ bool ConstraintSolver::tryDispatch(const GeneralizationConstraint& c, NotNull<co
         bind(constraint, c.generalizedType, builtinTypes->errorRecoveryType());
     }
 
-    if (FFlag::LuauTrackInteriorFreeTypesOnScope)
-    {
     // We check if this member is initialized and then access it, but
     // clang-tidy doesn't understand this is safe.
     if (constraint->scope->interiorFreeTypes)
@@ -907,13 +932,6 @@ bool ConstraintSolver::tryDispatch(const GeneralizationConstraint& c, NotNull<co
             }
         }
     }
-    }
-    else
-    {
-        for (TypeId ty : c.interiorTypes)
-            generalize(NotNull{arena}, builtinTypes, constraint->scope, generalizedTypes, ty);
-    }
-
 
     return true;
 }
@@ -989,15 +1007,11 @@ bool ConstraintSolver::tryDispatch(const IterableConstraint& c, NotNull<const Co
     {
         TypeId keyTy = freshType(arena, builtinTypes, constraint->scope, Polarity::Mixed);
         TypeId valueTy = freshType(arena, builtinTypes, constraint->scope, Polarity::Mixed);
-        if (FFlag::LuauTrackInteriorFreeTypesOnScope)
-        {
         trackInteriorFreeType(constraint->scope, keyTy);
         trackInteriorFreeType(constraint->scope, valueTy);
-        }
         TypeId tableTy =
             arena->addType(TableType{TableType::Props{}, TableIndexer{keyTy, valueTy}, TypeLevel{}, constraint->scope, TableState::Free});
 
-        if (FFlag::LuauTrackInteriorFreeTypesOnScope && FFlag::LuauTrackInteriorFreeTablesOnScope)
         trackInteriorFreeType(constraint->scope, tableTy);
 
         unify(constraint, nextTy, tableTy);
@@ -1322,8 +1336,6 @@ void ConstraintSolver::fillInDiscriminantTypes(NotNull<const Constraint> constra
         if (!ty)
             continue;
 
-        if (FFlag::LuauSearchForRefineableType)
-        {
         if (isBlocked(*ty))
             // We bind any unused discriminants to the `*no-refine*` type indicating that it can be safely ignored.
             emplaceType<BoundType>(asMutable(follow(*ty)), builtinTypes->noRefineType);
@@ -1331,20 +1343,7 @@ void ConstraintSolver::fillInDiscriminantTypes(NotNull<const Constraint> constra
         // We also need to unconditionally unblock these types, otherwise
         // 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);
-        }
     }
 }
 
@@ -1457,9 +1456,9 @@ bool ConstraintSolver::tryDispatch(const FunctionCallConstraint& c, NotNull<cons
 
         if (ftv)
         {
-            if (ftv->magic)
+            if (ftv->magic && c.callSite)
             {
-                usedMagic = ftv->magic->infer(MagicFunctionCallContext{NotNull{this}, constraint, c.callSite, c.argsPack, result});
+                usedMagic = ftv->magic->infer(MagicFunctionCallContext{NotNull{this}, constraint, NotNull{c.callSite}, c.argsPack, result});
                 ftv->magic->refine(MagicRefinementContext{constraint->scope, c.callSite, c.discriminantTypes});
             }
         }
@@ -1534,7 +1533,7 @@ bool ConstraintSolver::tryDispatch(const FunctionCallConstraint& c, NotNull<cons
 
     // This can potentially contain free types if the return type of
     // `inferredTy` is never unified elsewhere.
-    if (FFlag::LuauTrackInteriorFreeTypesOnScope && FFlag::LuauTrackInferredFunctionTypeFromCall)
+    if (FFlag::LuauTrackInferredFunctionTypeFromCall)
         trackInteriorFreeType(constraint->scope, inferredTy);
 
     unblock(c.result, constraint->location);
@@ -1903,7 +1902,7 @@ bool ConstraintSolver::tryDispatchHasIndexer(
     }
     else if (auto mt = get<MetatableType>(subjectType))
         return tryDispatchHasIndexer(recursionDepth, constraint, mt->table, indexType, resultType, seen);
-    else if (auto ct = get<ClassType>(subjectType))
+    else if (auto ct = get<ExternType>(subjectType))
     {
         if (auto indexer = ct->indexer)
         {
@@ -2065,9 +2064,9 @@ bool ConstraintSolver::tryDispatch(const AssignPropConstraint& c, NotNull<const
     // Important: In every codepath through this function, the type `c.propType`
     // must be bound to something, even if it's just the errorType.
 
-    if (auto lhsClass = get<ClassType>(lhsType))
+    if (auto lhsExternType = get<ExternType>(lhsType))
     {
-        const Property* prop = lookupClassProp(lhsClass, propName);
+        const Property* prop = lookupExternTypeProp(lhsExternType, propName);
         if (!prop || !prop->writeTy.has_value())
         {
             bind(constraint, c.propType, builtinTypes->anyType);
@@ -2082,13 +2081,26 @@ bool ConstraintSolver::tryDispatch(const AssignPropConstraint& c, NotNull<const
     if (auto lhsFree = getMutable<FreeType>(lhsType))
     {
         auto lhsFreeUpperBound = follow(lhsFree->upperBound);
-        if (get<TableType>(lhsFreeUpperBound) || get<MetatableType>(lhsFreeUpperBound))
+
-            lhsType = lhsFreeUpperBound;
+        if (FFlag::DebugLuauGreedyGeneralization)
+        {
+            const auto [blocked, maybeTy, isIndex] = lookupTableProp(constraint, lhsType, propName, ValueContext::LValue);
+            if (!blocked.empty())
+            {
+                for (TypeId t : blocked)
+                    block(t, constraint);
+                return false;
+            }
+            else if (maybeTy)
+            {
+                bind(constraint, c.propType, isIndex ? arena->addType(UnionType{{*maybeTy, builtinTypes->nilType}}) : *maybeTy);
+                unify(constraint, rhsType, *maybeTy);
+                return true;
+            }
             else
             {
                 TypeId newUpperBound = arena->addType(TableType{TableState::Free, TypeLevel{}, constraint->scope});
 
-            if (FFlag::LuauTrackInteriorFreeTypesOnScope && FFlag::LuauTrackInteriorFreeTablesOnScope)
                 trackInteriorFreeType(constraint->scope, newUpperBound);
 
                 TableType* upperTable = getMutable<TableType>(newUpperBound);
@@ -2103,6 +2115,29 @@ bool ConstraintSolver::tryDispatch(const AssignPropConstraint& c, NotNull<const
                 return true;
             }
         }
+        else
+        {
+            if (get<TableType>(lhsFreeUpperBound) || get<MetatableType>(lhsFreeUpperBound))
+                lhsType = lhsFreeUpperBound;
+            else
+            {
+                TypeId newUpperBound = arena->addType(TableType{TableState::Free, TypeLevel{}, constraint->scope});
+
+                trackInteriorFreeType(constraint->scope, newUpperBound);
+
+                TableType* upperTable = getMutable<TableType>(newUpperBound);
+                LUAU_ASSERT(upperTable);
+
+                upperTable->props[c.propName] = rhsType;
+
+                // Food for thought: Could we block if simplification encounters a blocked type?
+                lhsFree->upperBound = simplifyIntersection(constraint->scope, constraint->location, lhsFreeUpperBound, newUpperBound);
+
+                bind(constraint, c.propType, rhsType);
+                return true;
+            }
+        }
+    }
 
     // Handle the case that lhsType is a table that already has the property or
     // a matching indexer. This also handles unions and intersections.
@@ -2252,20 +2287,20 @@ bool ConstraintSolver::tryDispatch(const AssignIndexConstraint& c, NotNull<const
             return *res;
     }
 
-    if (auto lhsClass = get<ClassType>(lhsType))
+    if (auto lhsExternType = get<ExternType>(lhsType))
     {
         while (true)
         {
-            if (lhsClass->indexer)
+            if (lhsExternType->indexer)
             {
-                unify(constraint, indexType, lhsClass->indexer->indexType);
+                unify(constraint, indexType, lhsExternType->indexer->indexType);
-                unify(constraint, rhsType, lhsClass->indexer->indexResultType);
+                unify(constraint, rhsType, lhsExternType->indexer->indexResultType);
-                bind(constraint, c.propType, arena->addType(UnionType{{lhsClass->indexer->indexResultType, builtinTypes->nilType}}));
+                bind(constraint, c.propType, arena->addType(UnionType{{lhsExternType->indexer->indexResultType, builtinTypes->nilType}}));
                 return true;
             }
 
-            if (lhsClass->parent)
+            if (lhsExternType->parent)
-                lhsClass = get<ClassType>(lhsClass->parent);
+                lhsExternType = get<ExternType>(lhsExternType->parent);
             else
                 break;
         }
@@ -2292,7 +2327,7 @@ bool ConstraintSolver::tryDispatch(const AssignIndexConstraint& c, NotNull<const
                     parts.insert(rhsType);
                 }
             }
-            else if (auto cls = get<ClassType>(follow(t)))
+            else if (auto cls = get<ExternType>(follow(t)))
             {
                 while (true)
                 {
@@ -2304,7 +2339,7 @@ bool ConstraintSolver::tryDispatch(const AssignIndexConstraint& c, NotNull<const
                     }
 
                     if (cls->parent)
-                        cls = get<ClassType>(cls->parent);
+                        cls = get<ExternType>(cls->parent);
                     else
                         break;
                 }
@@ -2355,7 +2390,6 @@ bool ConstraintSolver::tryDispatch(const UnpackConstraint& c, NotNull<const Cons
                 // constitute any meaningful constraint, so we replace it
                 // with a free type.
                 TypeId f = freshType(arena, builtinTypes, constraint->scope, Polarity::Positive); // FIXME?  Is this the right polarity?
-                if (FFlag::LuauTrackInteriorFreeTypesOnScope)
                 trackInteriorFreeType(constraint->scope, f);
                 shiftReferences(resultTy, f);
                 emplaceType<BoundType>(asMutable(resultTy), f);
@@ -2499,11 +2533,8 @@ bool ConstraintSolver::tryDispatchIterableTable(TypeId iteratorTy, const Iterabl
     {
         TypeId keyTy = freshType(arena, builtinTypes, constraint->scope, Polarity::Mixed);
         TypeId valueTy = freshType(arena, builtinTypes, constraint->scope, Polarity::Mixed);
-        if (FFlag::LuauTrackInteriorFreeTypesOnScope)
-        {
         trackInteriorFreeType(constraint->scope, keyTy);
         trackInteriorFreeType(constraint->scope, valueTy);
-        }
         TypeId tableTy = arena->addType(TableType{TableState::Sealed, {}, constraint->scope});
         getMutable<TableType>(tableTy)->indexer = TableIndexer{keyTy, valueTy};
 
@@ -2653,12 +2684,31 @@ bool ConstraintSolver::tryDispatchIterableFunction(TypeId nextTy, TypeId tableTy
     const FunctionType* nextFn = get<FunctionType>(nextTy);
     // If this does not hold, we should've never called `tryDispatchIterableFunction` in the first place.
     LUAU_ASSERT(nextFn);
-    const TypePackId nextRetPack = nextFn->retTypes;
 
     // the type of the `nextAstFragment` is the `nextTy`.
     (*c.astForInNextTypes)[c.nextAstFragment] = nextTy;
 
-    auto it = begin(nextRetPack);
+    if (FFlag::LuauAddCallConstraintForIterableFunctions)
+    {
+        // Construct a FunctionCallConstraint, to help us learn about the type of the loop variables being assigned to in this iterable
+        TypePackId tableTyPack = arena->addTypePack({tableTy});
+
+        TypePackId variablesPack = arena->addTypePack(BlockedTypePack{});
+
+        auto callConstraint = pushConstraint(constraint->scope, constraint->location, FunctionCallConstraint{nextTy, tableTyPack, variablesPack});
+
+        getMutable<BlockedTypePack>(variablesPack)->owner = callConstraint.get();
+
+        auto unpackConstraint = unpackAndAssign(c.variables, variablesPack, constraint);
+
+        inheritBlocks(constraint, callConstraint);
+
+        inheritBlocks(unpackConstraint, callConstraint);
+    }
+    else
+    {
+        const TypePackId nextRetPack = nextFn->retTypes;
+        TypePackIterator it = begin(nextRetPack);
         std::vector<TypeId> modifiedNextRetHead;
 
         // The first value is never nil in the context of the loop, even if it's nil
@@ -2680,6 +2730,7 @@ bool ConstraintSolver::tryDispatchIterableFunction(TypeId nextTy, TypeId tableTy
         auto unpackConstraint = unpackAndAssign(c.variables, modifiedNextRetPack, constraint);
 
         inheritBlocks(constraint, unpackConstraint);
+    }
 
     return true;
 }
@@ -2760,7 +2811,6 @@ TablePropLookupResult ConstraintSolver::lookupTableProp(
         if (ttv->state == TableState::Free)
         {
             TypeId result = freshType(arena, builtinTypes, ttv->scope, Polarity::Mixed);
-            if (FFlag::LuauTrackInteriorFreeTypesOnScope)
             trackInteriorFreeType(ttv->scope, result);
             switch (context)
             {
@@ -2835,9 +2885,9 @@ TablePropLookupResult ConstraintSolver::lookupTableProp(
         else if (get<MetatableType>(mtt))
             return lookupTableProp(constraint, mtt, propName, context, inConditional, suppressSimplification, seen);
     }
-    else if (auto ct = get<ClassType>(subjectType))
+    else if (auto ct = get<ExternType>(subjectType))
     {
-        if (auto p = lookupClassProp(ct, propName))
+        if (auto p = lookupExternTypeProp(ct, propName))
             return {{}, context == ValueContext::RValue ? p->readTy : p->writeTy};
         if (ct->indexer)
         {
@@ -2859,23 +2909,33 @@ TablePropLookupResult ConstraintSolver::lookupTableProp(
     {
         const TypeId upperBound = follow(ft->upperBound);
 
+        if (FFlag::DebugLuauGreedyGeneralization)
+        {
+            if (get<TableType>(upperBound) || get<PrimitiveType>(upperBound))
+            {
+                TablePropLookupResult res = lookupTableProp(constraint, upperBound, propName, context, inConditional, suppressSimplification, seen);
+                // If the upper bound is a table that already has the property, we don't need to extend its bounds.
+                if (res.propType || get<PrimitiveType>(upperBound))
+                    return res;
+            }
+        }
+        else
+        {
             if (get<TableType>(upperBound) || get<PrimitiveType>(upperBound))
                 return lookupTableProp(constraint, upperBound, propName, context, inConditional, suppressSimplification, seen);
+        }
 
-        // TODO: The upper bound could be an intersection that contains suitable tables or classes.
+        // TODO: The upper bound could be an intersection that contains suitable tables or extern types.
 
         NotNull<Scope> scope{ft->scope};
 
         const TypeId newUpperBound = arena->addType(TableType{TableState::Free, TypeLevel{}, scope});
 
-        if (FFlag::LuauTrackInteriorFreeTypesOnScope && FFlag::LuauTrackInteriorFreeTablesOnScope)
         trackInteriorFreeType(constraint->scope, newUpperBound);
 
         TableType* tt = getMutable<TableType>(newUpperBound);
         LUAU_ASSERT(tt);
         TypeId propType = freshType(arena, builtinTypes, scope, Polarity::Mixed);
-
-        if (FFlag::LuauTrackInteriorFreeTypesOnScope)
         trackInteriorFreeType(scope, propType);
 
         switch (context)
@@ -3095,7 +3155,7 @@ struct Blocker : TypeOnceVisitor
         return false;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -3471,4 +3531,35 @@ LUAU_NOINLINE void ConstraintSolver::throwUserCancelError() const
 template bool ConstraintSolver::unify(NotNull<const Constraint> constraint, TypeId subTy, TypeId superTy);
 template bool ConstraintSolver::unify(NotNull<const Constraint> constraint, TypePackId subTy, TypePackId superTy);
 
+std::vector<NotNull<Constraint>> borrowConstraints(const std::vector<ConstraintPtr>& constraints)
+{
+    std::vector<NotNull<Constraint>> result;
+    result.reserve(constraints.size());
+
+    for (const auto& c : constraints)
+        result.emplace_back(c.get());
+
+    return result;
+}
+
+void dump(ConstraintSolver* cs, ToStringOptions& opts)
+{
+    printf("constraints:\n");
+    for (NotNull<const Constraint> c : cs->unsolvedConstraints)
+    {
+        auto it = cs->blockedConstraints.find(c);
+        int blockCount = it == cs->blockedConstraints.end() ? 0 : int(it->second);
+        printf("\t%d\t%s\n", blockCount, toString(*c, opts).c_str());
+
+        if (FFlag::DebugLuauLogSolverIncludeDependencies)
+        {
+            for (NotNull<Constraint> dep : c->dependencies)
+            {
+                if (std::find(cs->unsolvedConstraints.begin(), cs->unsolvedConstraints.end(), dep) != cs->unsolvedConstraints.end())
+                    printf("\t\t|\t%s\n", toString(*dep, opts).c_str());
+            }
+        }
+    }
+}
+
 } // namespace Luau

Analysis/src/DataFlowGraph.cpp

@@ -16,6 +16,9 @@ LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAGVARIABLE(LuauPreprocessTypestatedArgument)
 LUAU_FASTFLAGVARIABLE(LuauDfgScopeStackTrueReset)
 LUAU_FASTFLAGVARIABLE(LuauDfgScopeStackNotNull)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+LUAU_FASTFLAGVARIABLE(LuauDoNotAddUpvalueTypesToLocalType)
+LUAU_FASTFLAGVARIABLE(LuauDfgIfBlocksShouldRespectControlFlow)
 namespace Luau
 {
 
@@ -470,7 +473,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStat* s)
         return visit(d);
     else if (auto d = s->as<AstStatDeclareFunction>())
         return visit(d);
-    else if (auto d = s->as<AstStatDeclareClass>())
+    else if (auto d = s->as<AstStatDeclareExternType>())
         return visit(d);
     else if (auto error = s->as<AstStatError>())
         return visit(error);
@@ -499,12 +502,26 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatIf* i)
     }
 
     DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
+    if (FFlag::LuauDfgIfBlocksShouldRespectControlFlow)
+    {
+        // If the control flow from the `if` or `else` block is non-linear,
+        // then we should assume that the _other_ branch is the one taken.
+        if (thencf != ControlFlow::None && elsecf == ControlFlow::None)
+            scope->inherit(elseScope);
+        else if (thencf == ControlFlow::None && elsecf != ControlFlow::None)
+            scope->inherit(thenScope);
+        else if ((thencf | elsecf) == ControlFlow::None)
+            join(scope, thenScope, elseScope);
+    }
+    else
+    {
         if (thencf != ControlFlow::None && elsecf == ControlFlow::None)
             join(scope, scope, elseScope);
         else if (thencf == ControlFlow::None && elsecf != ControlFlow::None)
             join(scope, thenScope, scope);
         else if ((thencf | elsecf) == ControlFlow::None)
             join(scope, thenScope, elseScope);
+    }
 
     if (thencf == elsecf)
         return thencf;
@@ -808,12 +825,15 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareFunction* d)
     visitGenerics(d->generics);
     visitGenericPacks(d->genericPacks);
     visitTypeList(d->params);
-    visitTypeList(d->retTypes);
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        visitTypePack(d->retTypes);
+    else
+        visitTypeList(d->retTypes_DEPRECATED);
 
     return ControlFlow::None;
 }
 
-ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareClass* d)
+ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareExternType* d)
 {
     // This declaration does not "introduce" any bindings in value namespace,
     // so there's no symbolic value to begin with. We'll traverse the properties
@@ -821,7 +841,7 @@ ControlFlow DataFlowGraphBuilder::visit(AstStatDeclareClass* d)
     DfgScope* unreachable = makeChildScope();
     PushScope ps{scopeStack, unreachable};
 
-    for (AstDeclaredClassProp prop : d->props)
+    for (AstDeclaredExternTypeProperty prop : d->props)
         visitType(prop.ty);
 
     return ControlFlow::None;
@@ -1032,8 +1052,16 @@ DataFlowResult DataFlowGraphBuilder::visitExpr(AstExprFunction* f)
     if (f->varargAnnotation)
         visitTypePack(f->varargAnnotation);
 
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
         if (f->returnAnnotation)
-        visitTypeList(*f->returnAnnotation);
+            visitTypePack(f->returnAnnotation);
+    }
+    else
+    {
+        if (f->returnAnnotation_DEPRECATED)
+            visitTypeList(*f->returnAnnotation_DEPRECATED);
+    }
 
     // TODO: function body can be re-entrant, as in mutations that occurs at the end of the function can also be
     // visible to the beginning of the function, so statically speaking, the body of the function has an exit point
@@ -1151,7 +1179,7 @@ DefId DataFlowGraphBuilder::visitLValue(AstExprLocal* l, DefId incomingDef)
     DfgScope* scope = FFlag::LuauDfgScopeStackNotNull ? currentScope() : currentScope_DEPRECATED();
 
     // In order to avoid alias tracking, we need to clip the reference to the parent def.
-    if (scope->canUpdateDefinition(l->local))
+    if (scope->canUpdateDefinition(l->local) && !(FFlag::LuauDoNotAddUpvalueTypesToLocalType && l->upvalue))
     {
         DefId updated = defArena->freshCell(l->local, l->location, containsSubscriptedDefinition(incomingDef));
         scope->bindings[l->local] = updated;
@@ -1275,7 +1303,10 @@ void DataFlowGraphBuilder::visitType(AstTypeFunction* f)
     visitGenerics(f->generics);
     visitGenericPacks(f->genericPacks);
     visitTypeList(f->argTypes);
-    visitTypeList(f->returnTypes);
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        visitTypePack(f->returnTypes);
+    else
+        visitTypeList(f->returnTypes_DEPRECATED);
 }
 
 void DataFlowGraphBuilder::visitType(AstTypeTypeof* t)

Analysis/src/Differ.cpp

@@ -277,7 +277,7 @@ static DifferResult diffSingleton(DifferEnvironment& env, TypeId left, TypeId ri
 static DifferResult diffFunction(DifferEnvironment& env, TypeId left, TypeId right);
 static DifferResult diffGeneric(DifferEnvironment& env, TypeId left, TypeId right);
 static DifferResult diffNegation(DifferEnvironment& env, TypeId left, TypeId right);
-static DifferResult diffClass(DifferEnvironment& env, TypeId left, TypeId right);
+static DifferResult diffExternType(DifferEnvironment& env, TypeId left, TypeId right);
 struct FindSeteqCounterexampleResult
 {
     // nullopt if no counterexample found
@@ -481,14 +481,14 @@ static DifferResult diffNegation(DifferEnvironment& env, TypeId left, TypeId rig
     return differResult;
 }
 
-static DifferResult diffClass(DifferEnvironment& env, TypeId left, TypeId right)
+static DifferResult diffExternType(DifferEnvironment& env, TypeId left, TypeId right)
 {
-    const ClassType* leftClass = get<ClassType>(left);
+    const ExternType* leftExternType = get<ExternType>(left);
-    const ClassType* rightClass = get<ClassType>(right);
+    const ExternType* rightExternType = get<ExternType>(right);
-    LUAU_ASSERT(leftClass);
+    LUAU_ASSERT(leftExternType);
-    LUAU_ASSERT(rightClass);
+    LUAU_ASSERT(rightExternType);
 
-    if (leftClass == rightClass)
+    if (leftExternType == rightExternType)
     {
         return DifferResult{};
     }
@@ -651,9 +651,9 @@ static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId rig
         {
             return diffNegation(env, left, right);
         }
-        else if (auto lc = get<ClassType>(left))
+        else if (auto lc = get<ExternType>(left))
         {
-            return diffClass(env, left, right);
+            return diffExternType(env, left, right);
         }
 
         throw InternalCompilerError{"Unimplemented Simple TypeId variant for diffing"};
@@ -960,7 +960,7 @@ bool isSimple(TypeId ty)
 {
     ty = follow(ty);
     // TODO: think about GenericType, etc.
-    return get<PrimitiveType>(ty) || get<SingletonType>(ty) || get<AnyType>(ty) || get<NegationType>(ty) || get<ClassType>(ty) ||
+    return get<PrimitiveType>(ty) || get<SingletonType>(ty) || get<AnyType>(ty) || get<NegationType>(ty) || get<ExternType>(ty) ||
            get<UnknownType>(ty) || get<NeverType>(ty);
 }
 

Analysis/src/EmbeddedBuiltinDefinitions.cpp

@@ -1,6 +1,9 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/BuiltinDefinitions.h"
 
+LUAU_FASTFLAG(LuauDeclareExternType)
+LUAU_FASTFLAG(LuauTypeFunOptional)
+
 namespace Luau
 {
 
@@ -259,7 +262,37 @@ declare buffer: {
 
 )BUILTIN_SRC";
 
-static const std::string kBuiltinDefinitionVectorSrc = R"BUILTIN_SRC(
+static const std::string kBuiltinDefinitionVectorSrc = (FFlag::LuauDeclareExternType)
+    ? R"BUILTIN_SRC(
+
+-- While vector would have been better represented as a built-in primitive type, type solver extern type handling covers most of the properties
+declare extern type vector with
+    x: number
+    y: number
+    z: number
+end
+
+declare vector: {
+    create: @checked (x: number, y: number, z: number?) -> vector,
+    magnitude: @checked (vec: vector) -> number,
+    normalize: @checked (vec: vector) -> vector,
+    cross: @checked (vec1: vector, vec2: vector) -> vector,
+    dot: @checked (vec1: vector, vec2: vector) -> number,
+    angle: @checked (vec1: vector, vec2: vector, axis: vector?) -> number,
+    floor: @checked (vec: vector) -> vector,
+    ceil: @checked (vec: vector) -> vector,
+    abs: @checked (vec: vector) -> vector,
+    sign: @checked (vec: vector) -> vector,
+    clamp: @checked (vec: vector, min: vector, max: vector) -> vector,
+    max: @checked (vector, ...vector) -> vector,
+    min: @checked (vector, ...vector) -> vector,
+
+    zero: vector,
+    one: vector,
+}
+
+)BUILTIN_SRC"
+    : R"BUILTIN_SRC(
 
 -- While vector would have been better represented as a built-in primitive type, type solver class handling covers most of the properties
 declare class vector
@@ -307,11 +340,11 @@ std::string getBuiltinDefinitionSource()
 }
 
 // TODO: split into separate tagged unions when the new solver can appropriately handle that.
-static const std::string kBuiltinDefinitionTypesSrc = R"BUILTIN_SRC(
+static const std::string kBuiltinDefinitionTypeMethodSrc = R"BUILTIN_SRC(
 
 export type type = {
     tag: "nil" | "unknown" | "never" | "any" | "boolean" | "number" | "string" | "buffer" | "thread" |
-         "singleton" | "negation" | "union" | "intesection" | "table" | "function" | "class" | "generic",
+         "singleton" | "negation" | "union" | "intersection" | "table" | "function" | "class" | "generic",
 
     is: (self: type, arg: string) -> boolean,
 
@@ -358,6 +391,10 @@ export type type = {
     ispack: (self: type) -> boolean,
 }
 
+)BUILTIN_SRC";
+
+static const std::string kBuiltinDefinitionTypesLibSrc = R"BUILTIN_SRC(
+
 declare types: {
     unknown: type,
     never: type,
@@ -377,12 +414,44 @@ declare types: {
     newfunction: @checked (parameters: { head: {type}?, tail: type? }?, returns: { head: {type}?, tail: type? }?, generics: {type}?) -> type,
     copy: @checked (arg: type) -> type,
 }
-
 )BUILTIN_SRC";
 
+static const std::string kBuiltinDefinitionTypesLibWithOptionalSrc = R"BUILTIN_SRC(
+
+declare types: {
+    unknown: type,
+    never: type,
+    any: type,
+    boolean: type,
+    number: type,
+    string: type,
+    thread: type,
+    buffer: type,
+
+    singleton: @checked (arg: string | boolean | nil) -> type,
+    optional: @checked (arg: type) -> type,
+    generic: @checked (name: string, ispack: boolean?) -> type,
+    negationof: @checked (arg: type) -> type,
+    unionof: @checked (...type) -> type,
+    intersectionof: @checked (...type) -> type,
+    newtable: @checked (props: {[type]: type} | {[type]: { read: type, write: type } } | nil, indexer: { index: type, readresult: type, writeresult: type }?, metatable: type?) -> type,
+    newfunction: @checked (parameters: { head: {type}?, tail: type? }?, returns: { head: {type}?, tail: type? }?, generics: {type}?) -> type,
+    copy: @checked (arg: type) -> type,
+}
+)BUILTIN_SRC";
+
+
 std::string getTypeFunctionDefinitionSource()
 {
-    return kBuiltinDefinitionTypesSrc;
+
+    std::string result = kBuiltinDefinitionTypeMethodSrc;
+
+    if (FFlag::LuauTypeFunOptional)
+        result += kBuiltinDefinitionTypesLibWithOptionalSrc;
+    else
+        result += kBuiltinDefinitionTypesLibSrc;
+
+    return result;
 }
 
 } // namespace Luau

Analysis/src/EqSatSimplification.cpp

@@ -330,9 +330,9 @@ Id toId(
         return egraph.add(TOpaque{ty});
     else if (get<FunctionType>(ty))
         return egraph.add(TFunction{ty});
-    else if (ty == builtinTypes->classType)
+    else if (ty == builtinTypes->externType)
         return egraph.add(TTopClass{});
-    else if (get<ClassType>(ty))
+    else if (get<ExternType>(ty))
         return egraph.add(TClass{ty});
     else if (get<AnyType>(ty))
         return egraph.add(TAny{});
@@ -752,7 +752,7 @@ TypeId fromId(
     else if (node.get<TTopTable>())
         return builtinTypes->tableType;
     else if (node.get<TTopClass>())
-        return builtinTypes->classType;
+        return builtinTypes->externType;
     else if (node.get<TBuffer>())
         return builtinTypes->bufferType;
     else if (auto opaque = node.get<TOpaque>())
@@ -1007,7 +1007,7 @@ static std::string getNodeName(const StringCache& strings, const EType& node)
         return "\xe2\x88\xa9";
     else if (auto cls = node.get<TClass>())
     {
-        const ClassType* ct = get<ClassType>(cls->value());
+        const ExternType* ct = get<ExternType>(cls->value());
         LUAU_ASSERT(ct);
         return ct->name;
     }
@@ -1177,12 +1177,12 @@ enum SubclassRelationship
 
 static SubclassRelationship relateClasses(const TClass* leftClass, const TClass* rightClass)
 {
-    const ClassType* leftClassType = Luau::get<ClassType>(leftClass->value());
+    const ExternType* leftExternType = Luau::get<ExternType>(leftClass->value());
-    const ClassType* rightClassType = Luau::get<ClassType>(rightClass->value());
+    const ExternType* rightExternType = Luau::get<ExternType>(rightClass->value());
 
-    if (isSubclass(leftClassType, rightClassType))
+    if (isSubclass(leftExternType, rightExternType))
         return RightSuper;
-    else if (isSubclass(rightClassType, leftClassType))
+    else if (isSubclass(rightExternType, leftExternType))
         return LeftSuper;
     else
         return Unrelated;

Analysis/src/Error.cpp

@@ -203,7 +203,7 @@ struct ErrorConverter
         TypeId t = follow(e.table);
         if (get<TableType>(t))
             return "Key '" + e.key + "' not found in table '" + Luau::toString(t) + "'";
-        else if (get<ClassType>(t))
+        else if (get<ExternType>(t))
             return "Key '" + e.key + "' not found in class '" + Luau::toString(t) + "'";
         else
             return "Type '" + Luau::toString(e.table) + "' does not have key '" + e.key + "'";
@@ -371,7 +371,7 @@ struct ErrorConverter
         std::string s = "Key '" + e.key + "' not found in ";
 
         TypeId t = follow(e.table);
-        if (get<ClassType>(t))
+        if (get<ExternType>(t))
             s += "class";
         else
             s += "table";
@@ -402,8 +402,8 @@ struct ErrorConverter
         std::optional<TypeId> metatable;
         if (const MetatableType* mtType = get<MetatableType>(type))
             metatable = mtType->metatable;
-        else if (const ClassType* classType = get<ClassType>(type))
+        else if (const ExternType* externType = get<ExternType>(type))
-            metatable = classType->metatable;
+            metatable = externType->metatable;
 
         if (!metatable)
             return std::nullopt;
@@ -611,7 +611,7 @@ struct ErrorConverter
         return ss;
     }
 
-    std::string operator()(const DynamicPropertyLookupOnClassesUnsafe& e) const
+    std::string operator()(const DynamicPropertyLookupOnExternTypesUnsafe& e) const
     {
         return "Attempting a dynamic property access on type '" + Luau::toString(e.ty) + "' is unsafe and may cause exceptions at runtime";
     }
@@ -1149,7 +1149,7 @@ bool TypePackMismatch::operator==(const TypePackMismatch& rhs) const
     return *wantedTp == *rhs.wantedTp && *givenTp == *rhs.givenTp;
 }
 
-bool DynamicPropertyLookupOnClassesUnsafe::operator==(const DynamicPropertyLookupOnClassesUnsafe& rhs) const
+bool DynamicPropertyLookupOnExternTypesUnsafe::operator==(const DynamicPropertyLookupOnExternTypesUnsafe& rhs) const
 {
     return ty == rhs.ty;
 }
@@ -1391,7 +1391,7 @@ void copyError(T& e, TypeArena& destArena, CloneState& cloneState)
         e.wantedTp = clone(e.wantedTp);
         e.givenTp = clone(e.givenTp);
     }
-    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnClassesUnsafe>)
+    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnExternTypesUnsafe>)
         e.ty = clone(e.ty);
     else if constexpr (std::is_same_v<T, UninhabitedTypeFunction>)
         e.ty = clone(e.ty);

Analysis/src/FileResolver.cpp

@@ -10,10 +10,6 @@
 #include <string_view>
 #include <utility>
 
-LUAU_FASTFLAGVARIABLE(LuauExposeRequireByStringAutocomplete)
-LUAU_FASTFLAGVARIABLE(LuauEscapeCharactersInRequireSuggestions)
-LUAU_FASTFLAGVARIABLE(LuauHideImpossibleRequireSuggestions)
-
 namespace Luau
 {
 
@@ -22,13 +18,10 @@ static std::optional<RequireSuggestions> processRequireSuggestions(std::optional
     if (!suggestions)
         return suggestions;
 
-    if (FFlag::LuauEscapeCharactersInRequireSuggestions)
-    {
     for (RequireSuggestion& suggestion : *suggestions)
     {
         suggestion.fullPath = escape(suggestion.fullPath);
     }
-    }
 
     return suggestions;
 }
@@ -112,13 +105,11 @@ static RequireSuggestions makeSuggestionsFromNode(std::unique_ptr<RequireNode> n
             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();
@@ -163,9 +154,6 @@ std::optional<RequireSuggestions> RequireSuggester::getRequireSuggestions(const
 
 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;
 }
 

Analysis/src/FragmentAutocomplete.cpp

@@ -27,10 +27,7 @@
 LUAU_FASTINT(LuauTypeInferRecursionLimit);
 LUAU_FASTINT(LuauTypeInferIterationLimit);
 LUAU_FASTINT(LuauTarjanChildLimit)
-LUAU_FASTFLAG(LuauAutocompleteRefactorsForIncrementalAutocomplete)
 
-LUAU_FASTFLAGVARIABLE(LuauMixedModeDefFinderTraversesTypeOf)
-LUAU_FASTFLAGVARIABLE(LuauCloneIncrementalModule)
 LUAU_FASTFLAGVARIABLE(DebugLogFragmentsFromAutocomplete)
 LUAU_FASTFLAGVARIABLE(LuauBetterCursorInCommentDetection)
 LUAU_FASTFLAGVARIABLE(LuauAllFreeTypesHaveScopes)
@@ -43,6 +40,7 @@ LUAU_FASTFLAGVARIABLE(LuauBetterScopeSelection)
 LUAU_FASTFLAGVARIABLE(LuauBlockDiffFragmentSelection)
 LUAU_FASTFLAGVARIABLE(LuauFragmentAcMemoryLeak)
 LUAU_FASTFLAGVARIABLE(LuauGlobalVariableModuleIsolation)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 namespace
 {
@@ -97,7 +95,11 @@ Location getFunctionDeclarationExtents(AstExprFunction* exprFn, AstExpr* exprNam
 {
     auto fnBegin = exprFn->location.begin;
     auto fnEnd = exprFn->location.end;
-    if (auto returnAnnot = exprFn->returnAnnotation)
+    if (auto returnAnnot = exprFn->returnAnnotation; FFlag::LuauStoreReturnTypesAsPackOnAst && returnAnnot)
+    {
+        fnEnd = returnAnnot->location.end;
+    }
+    else if (auto returnAnnot = exprFn->returnAnnotation_DEPRECATED; !FFlag::LuauStoreReturnTypesAsPackOnAst && returnAnnot)
     {
         if (returnAnnot->tailType)
             fnEnd = returnAnnot->tailType->location.end;
@@ -542,6 +544,11 @@ struct UsageFinder : public AstVisitor
         return true;
     }
 
+    bool visit(AstTypePack* node) override
+    {
+        return FFlag::LuauStoreReturnTypesAsPackOnAst;
+    }
+
     bool visit(AstStatTypeAlias* alias) override
     {
         declaredAliases.insert(std::string(alias->name.value));
@@ -728,7 +735,7 @@ struct MixedModeIncrementalTCDefFinder : public AstVisitor
         // requires that we find the local/global `m` and place it in the environment.
         // The default behaviour here is to return false, and have individual visitors override
         // the specific behaviour they need.
-        return FFlag::LuauMixedModeDefFinderTraversesTypeOf;
+        return true;
     }
 
     bool visit(AstStatTypeAlias* alias) override
@@ -1218,31 +1225,6 @@ ModulePtr cloneModule(CloneState& cloneState, const ModulePtr& source, std::uniq
     return incremental;
 }
 
-ModulePtr copyModule(const ModulePtr& result, std::unique_ptr<Allocator> alloc)
-{
-    ModulePtr incrementalModule = std::make_shared<Module>();
-    incrementalModule->name = result->name;
-    incrementalModule->humanReadableName = "Incremental$" + result->humanReadableName;
-    incrementalModule->internalTypes.owningModule = incrementalModule.get();
-    incrementalModule->interfaceTypes.owningModule = incrementalModule.get();
-    incrementalModule->allocator = std::move(alloc);
-    // Don't need to keep this alive (it's already on the source module)
-    copyModuleVec(incrementalModule->scopes, result->scopes);
-    copyModuleMap(incrementalModule->astTypes, result->astTypes);
-    copyModuleMap(incrementalModule->astTypePacks, result->astTypePacks);
-    copyModuleMap(incrementalModule->astExpectedTypes, result->astExpectedTypes);
-    // Don't need to clone astOriginalCallTypes
-    copyModuleMap(incrementalModule->astOverloadResolvedTypes, result->astOverloadResolvedTypes);
-    // Don't need to clone astForInNextTypes
-    copyModuleMap(incrementalModule->astForInNextTypes, result->astForInNextTypes);
-    // Don't need to clone astResolvedTypes
-    // Don't need to clone astResolvedTypePacks
-    // Don't need to clone upperBoundContributors
-    copyModuleMap(incrementalModule->astScopes, result->astScopes);
-    // Don't need to clone declared Globals;
-    return incrementalModule;
-}
-
 void mixedModeCompatibility(
     const ScopePtr& bottomScopeStale,
     const ScopePtr& myFakeScope,
@@ -1306,10 +1288,8 @@ FragmentTypeCheckResult typecheckFragmentHelper_DEPRECATED(
     ModulePtr incrementalModule = nullptr;
     if (FFlag::LuauAllFreeTypesHaveScopes)
         incrementalModule = cloneModule(cloneState, stale, std::move(astAllocator), freshChildOfNearestScope.get());
-    else if (FFlag::LuauCloneIncrementalModule)
-        incrementalModule = cloneModule_DEPRECATED(cloneState, stale, std::move(astAllocator));
     else
-        incrementalModule = copyModule(stale, std::move(astAllocator));
+        incrementalModule = cloneModule_DEPRECATED(cloneState, stale, std::move(astAllocator));
 
     reportWaypoint(reporter, FragmentAutocompleteWaypoint::CloneModuleEnd);
     incrementalModule->checkedInNewSolver = true;
@@ -1363,8 +1343,6 @@ FragmentTypeCheckResult typecheckFragmentHelper_DEPRECATED(
     };
 
     reportWaypoint(reporter, FragmentAutocompleteWaypoint::CloneAndSquashScopeStart);
-    if (FFlag::LuauCloneIncrementalModule)
-    {
     incrementalModule->scopes.emplace_back(root->location, freshChildOfNearestScope);
     cg.rootScope = freshChildOfNearestScope.get();
 
@@ -1385,22 +1363,7 @@ FragmentTypeCheckResult typecheckFragmentHelper_DEPRECATED(
         for (auto p : cg.scopes)
             incrementalModule->scopes.emplace_back(std::move(p));
     }
-    }
+
-    else
-    {
-        // Any additions to the scope must occur in a fresh scope
-        cg.rootScope = stale->getModuleScope().get();
-        incrementalModule->scopes.emplace_back(root->location, freshChildOfNearestScope);
-        mixedModeCompatibility(closestScope, freshChildOfNearestScope, stale, NotNull{&dfg}, root);
-        // closest Scope -> children = { ...., freshChildOfNearestScope}
-        // We need to trim nearestChild from the scope hierarchy
-        closestScope->children.emplace_back(freshChildOfNearestScope.get());
-        cg.visitFragmentRoot(freshChildOfNearestScope, root);
-        // Trim nearestChild from the closestScope
-        Scope* back = closestScope->children.back().get();
-        LUAU_ASSERT(back == freshChildOfNearestScope.get());
-        closestScope->children.pop_back();
-    }
     reportWaypoint(reporter, FragmentAutocompleteWaypoint::ConstraintSolverStart);
 
     if (FFlag::LuauAllFreeTypesHaveScopes)
@@ -1706,7 +1669,6 @@ FragmentAutocompleteResult fragmentAutocomplete(
     IFragmentAutocompleteReporter* reporter
 )
 {
-    LUAU_ASSERT(FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete);
     LUAU_TIMETRACE_SCOPE("Luau::fragmentAutocomplete", "FragmentAutocomplete");
     LUAU_TIMETRACE_ARGUMENT("name", moduleName.c_str());
 

Analysis/src/Frontend.cpp

@@ -40,6 +40,7 @@ LUAU_FASTFLAG(LuauInferInNoCheckMode)
 LUAU_FASTFLAGVARIABLE(LuauKnowsTheDataModel3)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauRethrowKnownExceptions, false)
+LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJson)
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJsonFile)
 LUAU_FASTFLAGVARIABLE(DebugLuauForbidInternalTypes)
@@ -128,9 +129,9 @@ static void generateDocumentationSymbols(TypeId ty, const std::string& rootName)
             prop.documentationSymbol = rootName + "." + name;
         }
     }
-    else if (ClassType* ctv = getMutable<ClassType>(ty))
+    else if (ExternType* etv = getMutable<ExternType>(ty))
     {
-        for (auto& [name, prop] : ctv->props)
+        for (auto& [name, prop] : etv->props)
         {
             prop.documentationSymbol = rootName + "." + name;
         }
@@ -1304,7 +1305,7 @@ ModulePtr check(
 
 struct InternalTypeFinder : TypeOnceVisitor
 {
-    bool visit(TypeId, const ClassType&) override
+    bool visit(TypeId, const ExternType&) override
     {
         return false;
     }
@@ -1419,10 +1420,36 @@ ModulePtr check(
         requireCycles
     };
 
+    // FIXME: Delete this flag when clipping FFlag::DebugLuauGreedyGeneralization.
+    //
+    // This optional<> only exists so that we can run one constructor when the flag
+    // is set, and another when it is unset.
+    std::optional<ConstraintSolver> cs;
+
+    if (FFlag::DebugLuauGreedyGeneralization)
+    {
+        ConstraintSet constraintSet = cg.run(sourceModule.root);
+        result->errors = std::move(constraintSet.errors);
+
+        cs.emplace(
+            NotNull{&normalizer},
+            NotNull{simplifier.get()},
+            NotNull{&typeFunctionRuntime},
+            result->name,
+            moduleResolver,
+            requireCycles,
+            logger.get(),
+            NotNull{&dfg},
+            limits,
+            std::move(constraintSet)
+        );
+    }
+    else
+    {
         cg.visitModuleRoot(sourceModule.root);
         result->errors = std::move(cg.errors);
 
-    ConstraintSolver cs{
+        cs.emplace(
             NotNull{&normalizer},
             NotNull{simplifier.get()},
             NotNull{&typeFunctionRuntime},
@@ -1435,14 +1462,17 @@ ModulePtr check(
             logger.get(),
             NotNull{&dfg},
             limits
-    };
+        );
+    }
+
+    LUAU_ASSERT(bool(cs));
 
     if (options.randomizeConstraintResolutionSeed)
-        cs.randomize(*options.randomizeConstraintResolutionSeed);
+        cs->randomize(*options.randomizeConstraintResolutionSeed);
 
     try
     {
-        cs.run();
+        cs->run();
     }
     catch (const TimeLimitError&)
     {
@@ -1462,12 +1492,12 @@ ModulePtr check(
             printf("%s\n", output.c_str());
     }
 
-    for (TypeError& e : cs.errors)
+    for (TypeError& e : cs->errors)
         result->errors.emplace_back(std::move(e));
 
     result->scopes = std::move(cg.scopes);
     result->type = sourceModule.type;
-    result->upperBoundContributors = std::move(cs.upperBoundContributors);
+    result->upperBoundContributors = std::move(cs->upperBoundContributors);
 
     if (result->timeout || result->cancelled)
     {

Analysis/src/Generalization.cpp

@@ -15,7 +15,6 @@
 #include "Luau/VisitType.h"
 
 LUAU_FASTFLAG(DebugLuauGreedyGeneralization)
-LUAU_FASTFLAG(LuauAutocompleteRefactorsForIncrementalAutocomplete)
 
 LUAU_FASTFLAGVARIABLE(LuauNonReentrantGeneralization2)
 
@@ -549,7 +548,7 @@ struct FreeTypeSearcher : TypeVisitor
                 traverse(*prop.readTy);
             else
             {
-                LUAU_ASSERT(prop.isShared() || FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete);
+                LUAU_ASSERT(prop.isShared());
 
                 Polarity p = polarity;
                 polarity = Polarity::Mixed;
@@ -605,7 +604,7 @@ struct FreeTypeSearcher : TypeVisitor
         return false;
     }
 
-    bool visit(TypeId, const ClassType&) override
+    bool visit(TypeId, const ExternType&) override
     {
         return false;
     }
@@ -897,7 +896,7 @@ struct TypeCacher : TypeOnceVisitor
         return false;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         cache(ty);
         return false;
@@ -1404,7 +1403,10 @@ std::optional<TypeId> generalize(
         }
 
         for (TypeId unsealedTableTy : fts.unsealedTables)
+        {
+            if (!generalizationTarget || unsealedTableTy == *generalizationTarget)
                 sealTable(scope, unsealedTableTy);
+        }
 
         for (const auto& [freePackId, params] : fts.typePacks)
         {
@@ -1464,29 +1466,93 @@ std::optional<TypeId> generalize(
 
 struct GenericCounter : TypeVisitor
 {
+    struct CounterState
+    {
+        size_t count = 0;
+        Polarity polarity = Polarity::None;
+    };
+
     NotNull<DenseHashSet<TypeId>> cachedTypes;
-    DenseHashMap<TypeId, size_t> generics{nullptr};
+    DenseHashMap<TypeId, CounterState> generics{nullptr};
-    DenseHashMap<TypePackId, size_t> genericPacks{nullptr};
+    DenseHashMap<TypePackId, CounterState> genericPacks{nullptr};
+
+    Polarity polarity = Polarity::Positive;
 
     explicit GenericCounter(NotNull<DenseHashSet<TypeId>> cachedTypes)
         : cachedTypes(cachedTypes)
     {
     }
 
+    bool visit(TypeId ty, const FunctionType& ft) override
+    {
+        if (ty->persistent)
+            return false;
+
+        polarity = invert(polarity);
+        traverse(ft.argTypes);
+        polarity = invert(polarity);
+        traverse(ft.retTypes);
+
+        return false;
+    }
+
+    bool visit(TypeId ty, const TableType& tt) override
+    {
+        if (ty->persistent)
+            return false;
+
+        const Polarity previous = polarity;
+
+        for (const auto& [_name, prop] : tt.props)
+        {
+            if (prop.isReadOnly())
+                traverse(*prop.readTy);
+            else
+            {
+                LUAU_ASSERT(prop.isShared());
+
+                polarity = Polarity::Mixed;
+                traverse(prop.type());
+                polarity = previous;
+            }
+        }
+
+        if (tt.indexer)
+        {
+            polarity = Polarity::Mixed;
+            traverse(tt.indexer->indexType);
+            traverse(tt.indexer->indexResultType);
+            polarity = previous;
+        }
+
+        return false;
+    }
+
+    bool visit(TypeId ty, const ExternType&) override
+    {
+        return false;
+    }
+
     bool visit(TypeId ty, const GenericType&) override
     {
-        size_t* count = generics.find(ty);
+        auto state = generics.find(ty);
-        if (count)
+        if (state)
-            ++*count;
+        {
+            ++state->count;
+            state->polarity |= polarity;
+        }
 
         return false;
     }
 
     bool visit(TypePackId tp, const GenericTypePack&) override
     {
-        size_t* count = genericPacks.find(tp);
+        auto state = genericPacks.find(tp);
-        if (count)
+        if (state)
-            ++*count;
+        {
+            ++state->count;
+            state->polarity |= polarity;
+        }
 
         return false;
     }
@@ -1513,66 +1579,78 @@ void pruneUnnecessaryGenerics(
     if (!functionTy)
         return;
 
-    // Types (and packs) to be removed from the generics list
+    // If a generic has no explicit name and is only referred to in one place in
-    DenseHashSet<TypeId> clipTypes{nullptr};
+    // the function's signature, it can be replaced with unknown.
-    DenseHashSet<TypePackId> clipTypePacks{nullptr};
 
     GenericCounter counter{cachedTypes};
     for (TypeId generic : functionTy->generics)
     {
+        generic = follow(generic);
         auto g = get<GenericType>(generic);
-        LUAU_ASSERT(g);
+        if (g && !g->explicitName)
-        if (!g)
+            counter.generics[generic] = {};
-            clipTypes.insert(generic);
-        else if (!g->explicitName)
-            counter.generics[generic] = 0;
     }
-    for (TypePackId genericPack : functionTy->genericPacks)
+
+    // It is sometimes the case that a pack in the generic list will become a
+    // pack that (transitively) has a generic tail.  If it does, we need to add
+    // that generic tail to the generic pack list.
+    for (size_t i = 0; i < functionTy->genericPacks.size(); ++i)
     {
-        auto g = get<GenericTypePack>(genericPack);
+        TypePackId genericPack = follow(functionTy->genericPacks[i]);
-        if (!g)
+
-            clipTypePacks.insert(genericPack);
+        TypePackId tail = getTail(genericPack);
-        else if (!g->explicitName)
+
-            counter.genericPacks[genericPack] = 0;
+        if (tail != genericPack)
+            functionTy->genericPacks.push_back(tail);
+
+        if (auto g = get<GenericTypePack>(tail); g && !g->explicitName)
+            counter.genericPacks[genericPack] = {};
     }
 
     counter.traverse(ty);
 
-    for (const auto& [generic, count] : counter.generics)
+    for (const auto& [generic, state] : counter.generics)
-    {
-        if (count == 1)
     {
+        if (state.count == 1 && state.polarity != Polarity::Mixed)
             emplaceType<BoundType>(asMutable(generic), builtinTypes->unknownType);
-            clipTypes.insert(generic);
-        }
     }
 
+    // Remove duplicates and types that aren't actually generics.
+    DenseHashSet<TypeId> seen{nullptr};
     auto it = std::remove_if(
         functionTy->generics.begin(),
         functionTy->generics.end(),
         [&](TypeId ty)
         {
-            return clipTypes.contains(ty);
+            ty = follow(ty);
+            if (seen.contains(ty))
+                return true;
+            seen.insert(ty);
+
+            return !get<GenericType>(ty);
         }
     );
 
     functionTy->generics.erase(it, functionTy->generics.end());
 
-    for (const auto& [genericPack, count] : counter.genericPacks)
+    for (const auto& [genericPack, state] : counter.genericPacks)
-    {
-        if (count == 1)
     {
+        if (state.count == 1)
             emplaceTypePack<BoundTypePack>(asMutable(genericPack), builtinTypes->unknownTypePack);
-            clipTypePacks.insert(genericPack);
-        }
     }
 
+    DenseHashSet<TypePackId> seen2{nullptr};
     auto it2 = std::remove_if(
         functionTy->genericPacks.begin(),
         functionTy->genericPacks.end(),
         [&](TypePackId tp)
         {
-            return clipTypePacks.contains(tp);
+            tp = follow(tp);
+            if (seen2.contains(tp))
+                return true;
+            seen2.insert(tp);
+
+            return !get<GenericTypePack>(tp);
         }
     );
 

Analysis/src/InferPolarity.cpp

@@ -95,16 +95,16 @@ struct InferPolarity : TypeVisitor
         // types.
         for (TypeId generic : ft.generics)
         {
+            generic = follow(generic);
             const auto gen = get<GenericType>(generic);
-            LUAU_ASSERT(gen);
+            if (gen && subsumes(scope, gen->scope))
-            if (subsumes(scope, gen->scope))
                 types[generic] = Polarity::None;
         }
         for (TypePackId genericPack : ft.genericPacks)
         {
+            genericPack = follow(genericPack);
             const auto gen = get<GenericTypePack>(genericPack);
-            LUAU_ASSERT(gen);
+            if (gen && subsumes(scope, gen->scope))
-            if (subsumes(scope, gen->scope))
                 packs[genericPack] = Polarity::None;
         }
 
@@ -118,7 +118,7 @@ struct InferPolarity : TypeVisitor
         return false;
     }
 
-    bool visit(TypeId, const ClassType&) override
+    bool visit(TypeId, const ExternType&) override
     {
         return false;
     }

Analysis/src/Instantiation.cpp

@@ -11,7 +11,6 @@
 #include <algorithm>
 
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
 
 namespace Luau
 {
@@ -50,7 +49,7 @@ bool Instantiation::ignoreChildren(TypeId ty)
 {
     if (log->getMutable<FunctionType>(ty))
         return true;
-    else if (get<ClassType>(ty))
+    else if (get<ExternType>(ty))
         return true;
     else
         return false;
@@ -120,7 +119,7 @@ bool ReplaceGenerics::ignoreChildren(TypeId ty)
         // whenever we quantify, so the vectors overlap if and only if they are equal.
         return (!generics.empty() || !genericPacks.empty()) && (ftv->generics == generics) && (ftv->genericPacks == genericPacks);
     }
-    else if (get<ClassType>(ty))
+    else if (get<ExternType>(ty))
         return true;
     else
     {
@@ -164,7 +163,7 @@ TypeId ReplaceGenerics::clean(TypeId ty)
     }
     else
     {
-        return FFlag::LuauFreeTypesMustHaveBounds ? arena->freshType(builtinTypes, scope, level) : addType(FreeType{scope, level});
+        return arena->freshType(builtinTypes, scope, level);
     }
 }
 

Analysis/src/Instantiation2.cpp

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

Analysis/src/IostreamHelpers.cpp

@@ -193,8 +193,8 @@ static void errorToString(std::ostream& stream, const T& err)
         stream << "NormalizationTooComplex { }";
     else if constexpr (std::is_same_v<T, TypePackMismatch>)
         stream << "TypePackMismatch { wanted = '" + toString(err.wantedTp) + "', given = '" + toString(err.givenTp) + "' }";
-    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnClassesUnsafe>)
+    else if constexpr (std::is_same_v<T, DynamicPropertyLookupOnExternTypesUnsafe>)
-        stream << "DynamicPropertyLookupOnClassesUnsafe { " << toString(err.ty) << " }";
+        stream << "DynamicPropertyLookupOnExternTypesUnsafe { " << toString(err.ty) << " }";
     else if constexpr (std::is_same_v<T, UninhabitedTypeFunction>)
         stream << "UninhabitedTypeFunction { " << toString(err.ty) << " }";
     else if constexpr (std::is_same_v<T, ExplicitFunctionAnnotationRecommended>)

Analysis/src/Linter.cpp

@@ -20,6 +20,7 @@ LUAU_FASTFLAG(LuauAttribute)
 LUAU_FASTFLAGVARIABLE(LintRedundantNativeAttribute)
 
 LUAU_FASTFLAG(LuauDeprecatedAttribute)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 namespace Luau
 {
@@ -908,6 +909,11 @@ private:
         return true;
     }
 
+    bool visit(AstTypePack* node) override
+    {
+        return FFlag::LuauStoreReturnTypesAsPackOnAst;
+    }
+
     bool visit(AstTypeReference* node) override
     {
         if (!node->prefix)
@@ -1970,6 +1976,11 @@ private:
         return true;
     }
 
+    bool visit(AstTypePack* node) override
+    {
+        return FFlag::LuauStoreReturnTypesAsPackOnAst;
+    }
+
     bool visit(AstTypeTable* node) override
     {
         if (FFlag::LuauSolverV2)
@@ -2372,9 +2383,9 @@ private:
 
     void check(AstExprIndexName* node, TypeId ty)
     {
-        if (const ClassType* cty = get<ClassType>(ty))
+        if (const ExternType* cty = get<ExternType>(ty))
         {
-            const Property* prop = lookupClassProp(cty, node->index.value);
+            const Property* prop = lookupExternTypeProp(cty, node->index.value);
 
             if (prop && prop->deprecated)
                 report(node->location, *prop, cty->name.c_str(), node->index.value);

Analysis/src/NonStrictTypeChecker.cpp

@@ -22,10 +22,10 @@
 
 LUAU_FASTFLAG(DebugLuauMagicTypes)
 
-LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
 LUAU_FASTFLAGVARIABLE(LuauNonStrictVisitorImprovements)
 LUAU_FASTFLAGVARIABLE(LuauNewNonStrictWarnOnUnknownGlobals)
-LUAU_FASTFLAGVARIABLE(LuauNewNonStrictVisitTypes)
+LUAU_FASTFLAGVARIABLE(LuauNewNonStrictVisitTypes2)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 namespace Luau
 {
@@ -217,7 +217,7 @@ struct NonStrictTypeChecker
             return *fst;
         else if (auto ftp = get<FreeTypePack>(pack))
         {
-            TypeId result = FFlag::LuauFreeTypesMustHaveBounds ? arena->freshType(builtinTypes, ftp->scope) : arena->addType(FreeType{ftp->scope});
+            TypeId result = arena->freshType(builtinTypes, ftp->scope);
             TypePackId freeTail = arena->addTypePack(FreeTypePack{ftp->scope});
 
             TypePack* resultPack = emplaceTypePack<TypePack>(asMutable(pack));
@@ -311,7 +311,7 @@ struct NonStrictTypeChecker
             return visit(s);
         else if (auto s = stat->as<AstStatDeclareGlobal>())
             return visit(s);
-        else if (auto s = stat->as<AstStatDeclareClass>())
+        else if (auto s = stat->as<AstStatDeclareExternType>())
             return visit(s);
         else if (auto s = stat->as<AstStatError>())
             return visit(s);
@@ -340,13 +340,10 @@ struct NonStrictTypeChecker
                 {
                     ctx.remove(dfg->getDef(local));
 
-                    if (FFlag::LuauNewNonStrictVisitTypes)
+                    if (FFlag::LuauNewNonStrictVisitTypes2)
-                    {
-                        if (local->annotation)
                         visit(local->annotation);
                 }
             }
-            }
             else
                 ctx = NonStrictContext::disjunction(builtinTypes, arena, visit(stat), ctx);
         }
@@ -430,8 +427,7 @@ struct NonStrictTypeChecker
 
     NonStrictContext visit(AstStatFor* forStatement)
     {
-        if (FFlag::LuauNewNonStrictVisitTypes)
+        if (FFlag::LuauNewNonStrictVisitTypes2)
-            if (forStatement->var->annotation)
             visit(forStatement->var->annotation);
 
         if (FFlag::LuauNonStrictVisitorImprovements)
@@ -453,14 +449,11 @@ struct NonStrictTypeChecker
 
     NonStrictContext visit(AstStatForIn* forInStatement)
     {
-        if (FFlag::LuauNewNonStrictVisitTypes)
+        if (FFlag::LuauNewNonStrictVisitTypes2)
         {
             for (auto var : forInStatement->vars)
-            {
-                if (var->annotation)
                 visit(var->annotation);
         }
-        }
 
         if (FFlag::LuauNonStrictVisitorImprovements)
         {
@@ -510,7 +503,7 @@ struct NonStrictTypeChecker
 
     NonStrictContext visit(AstStatTypeAlias* typeAlias)
     {
-        if (FFlag::LuauNewNonStrictVisitTypes)
+        if (FFlag::LuauNewNonStrictVisitTypes2)
         {
             visitGenerics(typeAlias->generics, typeAlias->genericPacks);
             visit(typeAlias->type);
@@ -526,7 +519,7 @@ struct NonStrictTypeChecker
 
     NonStrictContext visit(AstStatDeclareFunction* declFn)
     {
-        if (FFlag::LuauNewNonStrictVisitTypes)
+        if (FFlag::LuauNewNonStrictVisitTypes2)
         {
             visitGenerics(declFn->generics, declFn->genericPacks);
             visit(declFn->params);
@@ -538,15 +531,15 @@ struct NonStrictTypeChecker
 
     NonStrictContext visit(AstStatDeclareGlobal* declGlobal)
     {
-        if (FFlag::LuauNewNonStrictVisitTypes)
+        if (FFlag::LuauNewNonStrictVisitTypes2)
             visit(declGlobal->type);
 
         return {};
     }
 
-    NonStrictContext visit(AstStatDeclareClass* declClass)
+    NonStrictContext visit(AstStatDeclareExternType* declClass)
     {
-        if (FFlag::LuauNewNonStrictVisitTypes)
+        if (FFlag::LuauNewNonStrictVisitTypes2)
         {
             if (declClass->indexer)
             {
@@ -822,19 +815,21 @@ struct NonStrictTypeChecker
             }
             remainder.remove(dfg->getDef(local));
 
-            if (FFlag::LuauNewNonStrictVisitTypes)
+            if (FFlag::LuauNewNonStrictVisitTypes2)
-            {
-                if (local->annotation)
                 visit(local->annotation);
         }
-        }
 
-        if (FFlag::LuauNewNonStrictVisitTypes)
+        if (FFlag::LuauNewNonStrictVisitTypes2)
         {
             visitGenerics(exprFn->generics, exprFn->genericPacks);
 
-            if (exprFn->returnAnnotation)
+            if (FFlag::LuauStoreReturnTypesAsPackOnAst)
-                visit(*exprFn->returnAnnotation);
+                visit(exprFn->returnAnnotation);
+            else
+            {
+                if (exprFn->returnAnnotation_DEPRECATED)
+                    visit(*exprFn->returnAnnotation_DEPRECATED);
+            }
 
             if (exprFn->varargAnnotation)
                 visit(exprFn->varargAnnotation);
@@ -880,7 +875,7 @@ struct NonStrictTypeChecker
 
     NonStrictContext visit(AstExprTypeAssertion* typeAssertion)
     {
-        if (FFlag::LuauNewNonStrictVisitTypes)
+        if (FFlag::LuauNewNonStrictVisitTypes2)
             visit(typeAssertion->annotation);
 
         if (FFlag::LuauNonStrictVisitorImprovements)
@@ -921,7 +916,11 @@ struct NonStrictTypeChecker
 
     void visit(AstType* ty)
     {
-        LUAU_ASSERT(FFlag::LuauNewNonStrictVisitTypes);
+        LUAU_ASSERT(FFlag::LuauNewNonStrictVisitTypes2);
+
+        // If this node is `nullptr`, early exit.
+        if (!ty)
+            return;
 
         if (auto t = ty->as<AstTypeReference>())
             return visit(t);
@@ -1130,7 +1129,11 @@ struct NonStrictTypeChecker
 
     void visit(AstTypePack* pack)
     {
-        LUAU_ASSERT(FFlag::LuauNewNonStrictVisitTypes);
+        LUAU_ASSERT(FFlag::LuauNewNonStrictVisitTypes2);
+
+        // If there is no pack node, early exit.
+        if (!pack)
+            return;
 
         if (auto p = pack->as<AstTypePackExplicit>())
             return visit(p);

Analysis/src/Normalize.cpp

@@ -249,23 +249,23 @@ bool isSubtype(const NormalizedStringType& subStr, const NormalizedStringType& s
     return true;
 }
 
-void NormalizedClassType::pushPair(TypeId ty, TypeIds negations)
+void NormalizedExternType::pushPair(TypeId ty, TypeIds negations)
 {
-    auto result = classes.insert(std::make_pair(ty, std::move(negations)));
+    auto result = externTypes.insert(std::make_pair(ty, std::move(negations)));
     if (result.second)
         ordering.push_back(ty);
-    LUAU_ASSERT(ordering.size() == classes.size());
+    LUAU_ASSERT(ordering.size() == externTypes.size());
 }
 
-void NormalizedClassType::resetToNever()
+void NormalizedExternType::resetToNever()
 {
     ordering.clear();
-    classes.clear();
+    externTypes.clear();
 }
 
-bool NormalizedClassType::isNever() const
+bool NormalizedExternType::isNever() const
 {
-    return classes.empty();
+    return externTypes.empty();
 }
 
 void NormalizedFunctionType::resetToTop()
@@ -307,14 +307,14 @@ bool NormalizedType::isUnknown() const
                             strings.isString() && isThread(threads) && isBuffer(buffers);
 
     // Check is class
-    bool isTopClass = false;
+    bool isTopExternType = false;
-    for (auto [t, disj] : classes.classes)
+    for (const auto& [t, disj] : externTypes.externTypes)
     {
-        if (auto ct = get<ClassType>(t))
+        if (auto ct = get<ExternType>(t))
         {
             if (ct->name == "class" && disj.empty())
             {
-                isTopClass = true;
+                isTopExternType = true;
                 break;
             }
         }
@@ -330,24 +330,24 @@ bool NormalizedType::isUnknown() const
         }
     }
     // any = unknown or error ==> we need to make sure we have all the unknown components, but not errors
-    return get<NeverType>(errors) && hasAllPrimitives && isTopClass && isTopTable && functions.isTop;
+    return get<NeverType>(errors) && hasAllPrimitives && isTopExternType && isTopTable && functions.isTop;
 }
 
 bool NormalizedType::isExactlyNumber() const
 {
-    return hasNumbers() && !hasTops() && !hasBooleans() && !hasClasses() && !hasErrors() && !hasNils() && !hasStrings() && !hasThreads() &&
+    return hasNumbers() && !hasTops() && !hasBooleans() && !hasExternTypes() && !hasErrors() && !hasNils() && !hasStrings() && !hasThreads() &&
            !hasBuffers() && !hasTables() && !hasFunctions() && !hasTyvars();
 }
 
 bool NormalizedType::isSubtypeOfString() const
 {
-    return hasStrings() && !hasTops() && !hasBooleans() && !hasClasses() && !hasErrors() && !hasNils() && !hasNumbers() && !hasThreads() &&
+    return hasStrings() && !hasTops() && !hasBooleans() && !hasExternTypes() && !hasErrors() && !hasNils() && !hasNumbers() && !hasThreads() &&
            !hasBuffers() && !hasTables() && !hasFunctions() && !hasTyvars();
 }
 
 bool NormalizedType::isSubtypeOfBooleans() const
 {
-    return hasBooleans() && !hasTops() && !hasClasses() && !hasErrors() && !hasNils() && !hasNumbers() && !hasStrings() && !hasThreads() &&
+    return hasBooleans() && !hasTops() && !hasExternTypes() && !hasErrors() && !hasNils() && !hasNumbers() && !hasStrings() && !hasThreads() &&
            !hasBuffers() && !hasTables() && !hasFunctions() && !hasTyvars();
 }
 
@@ -380,9 +380,9 @@ bool NormalizedType::hasBooleans() const
     return !get<NeverType>(booleans);
 }
 
-bool NormalizedType::hasClasses() const
+bool NormalizedType::hasExternTypes() const
 {
-    return !classes.isNever();
+    return !externTypes.isNever();
 }
 
 bool NormalizedType::hasErrors() const
@@ -440,7 +440,7 @@ bool NormalizedType::isFalsy() const
             hasAFalse = !bs->value;
     }
 
-    return (hasAFalse || hasNils()) && (!hasTops() && !hasClasses() && !hasErrors() && !hasNumbers() && !hasStrings() && !hasThreads() &&
+    return (hasAFalse || hasNils()) && (!hasTops() && !hasExternTypes() && !hasErrors() && !hasNumbers() && !hasStrings() && !hasThreads() &&
                                         !hasBuffers() && !hasTables() && !hasFunctions() && !hasTyvars());
 }
 
@@ -452,7 +452,7 @@ bool NormalizedType::isTruthy() const
 static bool isShallowInhabited(const NormalizedType& norm)
 {
     // This test is just a shallow check, for example it returns `true` for `{ p : never }`
-    return !get<NeverType>(norm.tops) || !get<NeverType>(norm.booleans) || !norm.classes.isNever() || !get<NeverType>(norm.errors) ||
+    return !get<NeverType>(norm.tops) || !get<NeverType>(norm.booleans) || !norm.externTypes.isNever() || !get<NeverType>(norm.errors) ||
            !get<NeverType>(norm.nils) || !get<NeverType>(norm.numbers) || !norm.strings.isNever() || !get<NeverType>(norm.threads) ||
            !get<NeverType>(norm.buffers) || !norm.functions.isNever() || !norm.tables.empty() || !norm.tyvars.empty();
 }
@@ -471,7 +471,7 @@ NormalizationResult Normalizer::isInhabited(const NormalizedType* norm, Set<Type
         return NormalizationResult::HitLimits;
 
     if (!get<NeverType>(norm->tops) || !get<NeverType>(norm->booleans) || !get<NeverType>(norm->errors) || !get<NeverType>(norm->nils) ||
-        !get<NeverType>(norm->numbers) || !get<NeverType>(norm->threads) || !get<NeverType>(norm->buffers) || !norm->classes.isNever() ||
+        !get<NeverType>(norm->numbers) || !get<NeverType>(norm->threads) || !get<NeverType>(norm->buffers) || !norm->externTypes.isNever() ||
         !norm->strings.isNever() || !norm->functions.isNever())
         return NormalizationResult::True;
 
@@ -619,13 +619,13 @@ static int tyvarIndex(TypeId ty)
         return 0;
 }
 
-static bool isTop(NotNull<BuiltinTypes> builtinTypes, const NormalizedClassType& classes)
+static bool isTop(NotNull<BuiltinTypes> builtinTypes, const NormalizedExternType& externTypes)
 {
-    if (classes.classes.size() != 1)
+    if (externTypes.externTypes.size() != 1)
         return false;
 
-    auto first = classes.classes.begin();
+    auto first = externTypes.externTypes.begin();
-    if (first->first != builtinTypes->classType)
+    if (first->first != builtinTypes->externType)
         return false;
 
     if (!first->second.empty())
@@ -634,11 +634,11 @@ static bool isTop(NotNull<BuiltinTypes> builtinTypes, const NormalizedClassType&
     return true;
 }
 
-static void resetToTop(NotNull<BuiltinTypes> builtinTypes, NormalizedClassType& classes)
+static void resetToTop(NotNull<BuiltinTypes> builtinTypes, NormalizedExternType& externTypes)
 {
-    classes.ordering.clear();
+    externTypes.ordering.clear();
-    classes.classes.clear();
+    externTypes.externTypes.clear();
-    classes.pushPair(builtinTypes->classType, TypeIds{});
+    externTypes.pushPair(builtinTypes->externType, TypeIds{});
 }
 
 #ifdef LUAU_ASSERTENABLED
@@ -762,50 +762,50 @@ static bool areNormalizedTables(const TypeIds& tys)
     return true;
 }
 
-static bool areNormalizedClasses(const NormalizedClassType& tys)
+static bool areNormalizedExternTypes(const NormalizedExternType& tys)
 {
-    for (const auto& [ty, negations] : tys.classes)
+    for (const auto& [ty, negations] : tys.externTypes)
     {
-        const ClassType* ctv = get<ClassType>(ty);
+        const ExternType* etv = get<ExternType>(ty);
-        if (!ctv)
+        if (!etv)
         {
             return false;
         }
 
         for (TypeId negation : negations)
         {
-            const ClassType* nctv = get<ClassType>(negation);
+            const ExternType* nctv = get<ExternType>(negation);
             if (!nctv)
             {
                 return false;
             }
 
-            if (!isSubclass(nctv, ctv))
+            if (!isSubclass(nctv, etv))
             {
                 return false;
             }
         }
 
-        for (const auto& [otherTy, otherNegations] : tys.classes)
+        for (const auto& [otherTy, otherNegations] : tys.externTypes)
         {
             if (otherTy == ty)
                 continue;
 
-            const ClassType* octv = get<ClassType>(otherTy);
+            const ExternType* octv = get<ExternType>(otherTy);
             if (!octv)
             {
                 return false;
             }
 
-            if (isSubclass(ctv, octv))
+            if (isSubclass(etv, octv))
             {
-                auto iss = [ctv](TypeId t)
+                auto iss = [etv](TypeId t)
                 {
-                    const ClassType* c = get<ClassType>(t);
+                    const ExternType* c = get<ExternType>(t);
                     if (!c)
                         return false;
 
-                    return isSubclass(ctv, c);
+                    return isSubclass(etv, c);
                 };
 
                 if (!std::any_of(otherNegations.begin(), otherNegations.end(), iss))
@@ -847,7 +847,7 @@ static void assertInvariant(const NormalizedType& norm)
 
     LUAU_ASSERT(isNormalizedTop(norm.tops));
     LUAU_ASSERT(isNormalizedBoolean(norm.booleans));
-    LUAU_ASSERT(areNormalizedClasses(norm.classes));
+    LUAU_ASSERT(areNormalizedExternTypes(norm.externTypes));
     LUAU_ASSERT(isNormalizedError(norm.errors));
     LUAU_ASSERT(isNormalizedNil(norm.nils));
     LUAU_ASSERT(isNormalizedNumber(norm.numbers));
@@ -988,7 +988,7 @@ void Normalizer::clearNormal(NormalizedType& norm)
 {
     norm.tops = builtinTypes->neverType;
     norm.booleans = builtinTypes->neverType;
-    norm.classes.resetToNever();
+    norm.externTypes.resetToNever();
     norm.errors = builtinTypes->neverType;
     norm.nils = builtinTypes->neverType;
     norm.numbers = builtinTypes->neverType;
@@ -1138,17 +1138,17 @@ TypeId Normalizer::unionOfBools(TypeId here, TypeId there)
     return builtinTypes->booleanType;
 }
 
-void Normalizer::unionClassesWithClass(TypeIds& heres, TypeId there)
+void Normalizer::unionExternTypesWithExternType(TypeIds& heres, TypeId there)
 {
     if (heres.count(there))
         return;
 
-    const ClassType* tctv = get<ClassType>(there);
+    const ExternType* tctv = get<ExternType>(there);
 
     for (auto it = heres.begin(); it != heres.end();)
     {
         TypeId here = *it;
-        const ClassType* hctv = get<ClassType>(here);
+        const ExternType* hctv = get<ExternType>(here);
         if (isSubclass(tctv, hctv))
             return;
         else if (isSubclass(hctv, tctv))
@@ -1160,16 +1160,16 @@ void Normalizer::unionClassesWithClass(TypeIds& heres, TypeId there)
     heres.insert(there);
 }
 
-void Normalizer::unionClasses(TypeIds& heres, const TypeIds& theres)
+void Normalizer::unionExternTypes(TypeIds& heres, const TypeIds& theres)
 {
     for (TypeId there : theres)
-        unionClassesWithClass(heres, there);
+        unionExternTypesWithExternType(heres, there);
 }
 
 static bool isSubclass(TypeId test, TypeId parent)
 {
-    const ClassType* testCtv = get<ClassType>(test);
+    const ExternType* testCtv = get<ExternType>(test);
-    const ClassType* parentCtv = get<ClassType>(parent);
+    const ExternType* parentCtv = get<ExternType>(parent);
 
     LUAU_ASSERT(testCtv);
     LUAU_ASSERT(parentCtv);
@@ -1177,12 +1177,12 @@ static bool isSubclass(TypeId test, TypeId parent)
     return isSubclass(testCtv, parentCtv);
 }
 
-void Normalizer::unionClassesWithClass(NormalizedClassType& heres, TypeId there)
+void Normalizer::unionExternTypesWithExternType(NormalizedExternType& heres, TypeId there)
 {
     for (auto it = heres.ordering.begin(); it != heres.ordering.end();)
     {
         TypeId hereTy = *it;
-        TypeIds& hereNegations = heres.classes.at(hereTy);
+        TypeIds& hereNegations = heres.externTypes.at(hereTy);
 
         // If the incoming class is a subclass of another class in the map, we
         // must ensure that it is negated by one of the negations in the same
@@ -1204,7 +1204,7 @@ void Normalizer::unionClassesWithClass(NormalizedClassType& heres, TypeId there)
                 }
                 // If the incoming class is a superclass of one of the
                 // negations, then the negation no longer applies and must be
-                // removed. This is also true if they are equal. Since classes
+                // removed. This is also true if they are equal. Since extern types
                 // are, at this time, entirely persistent (we do not clone
                 // them), a pointer identity check is sufficient.
                 else if (isSubclass(hereNegation, there))
@@ -1231,7 +1231,7 @@ void Normalizer::unionClassesWithClass(NormalizedClassType& heres, TypeId there)
         {
             TypeIds negations = std::move(hereNegations);
             it = heres.ordering.erase(it);
-            heres.classes.erase(hereTy);
+            heres.externTypes.erase(hereTy);
 
             heres.pushPair(there, std::move(negations));
             return;
@@ -1248,10 +1248,10 @@ void Normalizer::unionClassesWithClass(NormalizedClassType& heres, TypeId there)
     heres.pushPair(there, TypeIds{});
 }
 
-void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassType& theres)
+void Normalizer::unionExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres)
 {
-    // This method bears much similarity with unionClassesWithClass, but is
+    // This method bears much similarity with unionExternTypesWithExternType, but is
-    // solving a more general problem. In unionClassesWithClass, we are dealing
+    // solving a more general problem. In unionExternTypesWithExternType, we are dealing
     // with a singular positive type. Since it's one type, we can use early
     // returns as control flow. Since it's guaranteed to be positive, we do not
     // have negations to worry about combining. The two aspects combine to make
@@ -1260,9 +1260,9 @@ void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassT
 
     for (const TypeId thereTy : theres.ordering)
     {
-        const TypeIds& thereNegations = theres.classes.at(thereTy);
+        const TypeIds& thereNegations = theres.externTypes.at(thereTy);
 
-        // If it happens that there are _no_ classes in the current map, or the
+        // If it happens that there are _no_ extern types in the current map, or the
         // incoming class is completely unrelated to any class in the current
         // map, we must insert the incoming pair as-is.
         bool insert = true;
@@ -1270,7 +1270,7 @@ void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassT
         for (auto it = heres.ordering.begin(); it != heres.ordering.end();)
         {
             TypeId hereTy = *it;
-            TypeIds& hereNegations = heres.classes.at(hereTy);
+            TypeIds& hereNegations = heres.externTypes.at(hereTy);
 
             if (isSubclass(thereTy, hereTy))
             {
@@ -1294,7 +1294,7 @@ void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassT
                     // If the incoming class is a superclass of one of the
                     // negations, then the negation no longer applies and must
                     // be removed. This is also true if they are equal. Since
-                    // classes are, at this time, entirely persistent (we do not
+                    // extern types are, at this time, entirely persistent (we do not
                     // clone them), a pointer identity check is sufficient.
                     else if (isSubclass(hereNegateTy, thereTy))
                     {
@@ -1319,17 +1319,17 @@ void Normalizer::unionClasses(NormalizedClassType& heres, const NormalizedClassT
             else if (isSubclass(hereTy, thereTy))
             {
                 TypeIds negations = std::move(hereNegations);
-                unionClasses(negations, thereNegations);
+                unionExternTypes(negations, thereNegations);
 
                 it = heres.ordering.erase(it);
-                heres.classes.erase(hereTy);
+                heres.externTypes.erase(hereTy);
                 heres.pushPair(thereTy, std::move(negations));
                 insert = false;
                 break;
             }
             else if (hereTy == thereTy)
             {
-                unionClasses(hereNegations, thereNegations);
+                unionExternTypes(hereNegations, thereNegations);
                 insert = false;
                 break;
             }
@@ -1690,7 +1690,7 @@ NormalizationResult Normalizer::unionNormals(NormalizedType& here, const Normali
         return NormalizationResult::HitLimits;
 
     here.booleans = unionOfBools(here.booleans, there.booleans);
-    unionClasses(here.classes, there.classes);
+    unionExternTypes(here.externTypes, there.externTypes);
 
     here.errors = (get<NeverType>(there.errors) ? here.errors : there.errors);
     here.nils = (get<NeverType>(there.nils) ? here.nils : there.nils);
@@ -1830,8 +1830,8 @@ NormalizationResult Normalizer::unionNormalWithTy(
         unionFunctionsWithFunction(here.functions, there);
     else if (get<TableType>(there) || get<MetatableType>(there))
         unionTablesWithTable(here.tables, there);
-    else if (get<ClassType>(there))
+    else if (get<ExternType>(there))
-        unionClassesWithClass(here.classes, there);
+        unionExternTypesWithExternType(here.externTypes, there);
     else if (get<ErrorType>(there))
         here.errors = there;
     else if (const PrimitiveType* ptv = get<PrimitiveType>(there))
@@ -1944,29 +1944,29 @@ std::optional<NormalizedType> Normalizer::negateNormal(const NormalizedType& her
             result.booleans = builtinTypes->trueType;
     }
 
-    if (here.classes.isNever())
+    if (here.externTypes.isNever())
     {
-        resetToTop(builtinTypes, result.classes);
+        resetToTop(builtinTypes, result.externTypes);
     }
-    else if (isTop(builtinTypes, result.classes))
+    else if (isTop(builtinTypes, result.externTypes))
     {
-        result.classes.resetToNever();
+        result.externTypes.resetToNever();
     }
     else
     {
         TypeIds rootNegations{};
 
-        for (const auto& [hereParent, hereNegations] : here.classes.classes)
+        for (const auto& [hereParent, hereNegations] : here.externTypes.externTypes)
         {
-            if (hereParent != builtinTypes->classType)
+            if (hereParent != builtinTypes->externType)
                 rootNegations.insert(hereParent);
 
             for (TypeId hereNegation : hereNegations)
-                unionClassesWithClass(result.classes, hereNegation);
+                unionExternTypesWithExternType(result.externTypes, hereNegation);
         }
 
         if (!rootNegations.empty())
-            result.classes.pushPair(builtinTypes->classType, rootNegations);
+            result.externTypes.pushPair(builtinTypes->externType, rootNegations);
     }
 
     result.nils = get<NeverType>(here.nils) ? builtinTypes->nilType : builtinTypes->neverType;
@@ -2144,7 +2144,7 @@ TypeId Normalizer::intersectionOfBools(TypeId here, TypeId there)
         return there;
 }
 
-void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedClassType& theres)
+void Normalizer::intersectExternTypes(NormalizedExternType& heres, const NormalizedExternType& theres)
 {
     if (theres.isNever())
     {
@@ -2178,12 +2178,12 @@ void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedCl
     //   declare the result of the intersection operation to be never.
     for (const TypeId thereTy : theres.ordering)
     {
-        const TypeIds& thereNegations = theres.classes.at(thereTy);
+        const TypeIds& thereNegations = theres.externTypes.at(thereTy);
 
         for (auto it = heres.ordering.begin(); it != heres.ordering.end();)
         {
             TypeId hereTy = *it;
-            TypeIds& hereNegations = heres.classes.at(hereTy);
+            TypeIds& hereNegations = heres.externTypes.at(hereTy);
 
             if (isSubclass(thereTy, hereTy))
             {
@@ -2206,10 +2206,10 @@ void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedCl
                     }
                 }
 
-                unionClasses(negations, thereNegations);
+                unionExternTypes(negations, thereNegations);
 
                 it = heres.ordering.erase(it);
-                heres.classes.erase(hereTy);
+                heres.externTypes.erase(hereTy);
                 heres.pushPair(thereTy, std::move(negations));
                 break;
             }
@@ -2234,15 +2234,15 @@ void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedCl
                 {
                     if (isSubclass(hereTy, *nIt))
                     {
-                        // eg SomeClass & (class & ~SomeClass)
+                        // eg SomeExternType & (class & ~SomeExternType)
-                        // or SomeClass & (class & ~ParentClass)
+                        // or SomeExternType & (class & ~ParentExternType)
-                        heres.classes.erase(hereTy);
+                        heres.externTypes.erase(hereTy);
                         it = heres.ordering.erase(it);
                         erasedHere = true;
                         break;
                     }
 
-                    // eg SomeClass & (class & ~Unrelated)
+                    // eg SomeExternType & (class & ~Unrelated)
                     if (!isSubclass(*nIt, hereTy))
                         nIt = negations.erase(nIt);
                     else
@@ -2251,30 +2251,30 @@ void Normalizer::intersectClasses(NormalizedClassType& heres, const NormalizedCl
 
                 if (!erasedHere)
                 {
-                    unionClasses(hereNegations, negations);
+                    unionExternTypes(hereNegations, negations);
                     ++it;
                 }
             }
             else if (hereTy == thereTy)
             {
-                unionClasses(hereNegations, thereNegations);
+                unionExternTypes(hereNegations, thereNegations);
                 break;
             }
             else
             {
                 it = heres.ordering.erase(it);
-                heres.classes.erase(hereTy);
+                heres.externTypes.erase(hereTy);
             }
         }
     }
 }
 
-void Normalizer::intersectClassesWithClass(NormalizedClassType& heres, TypeId there)
+void Normalizer::intersectExternTypesWithExternType(NormalizedExternType& heres, TypeId there)
 {
     for (auto it = heres.ordering.begin(); it != heres.ordering.end();)
     {
         TypeId hereTy = *it;
-        const TypeIds& hereNegations = heres.classes.at(hereTy);
+        const TypeIds& hereNegations = heres.externTypes.at(hereTy);
 
         // If the incoming class _is_ the current class, we skip it. Maybe
         // another entry will have a different story. We check for this first
@@ -2319,7 +2319,7 @@ void Normalizer::intersectClassesWithClass(NormalizedClassType& heres, TypeId th
             }
 
             it = heres.ordering.erase(it);
-            heres.classes.erase(hereTy);
+            heres.externTypes.erase(hereTy);
             if (!emptyIntersectWithNegation)
                 heres.pushPair(there, std::move(negations));
             break;
@@ -2335,7 +2335,7 @@ void Normalizer::intersectClassesWithClass(NormalizedClassType& heres, TypeId th
         else
         {
             it = heres.ordering.erase(it);
-            heres.classes.erase(hereTy);
+            heres.externTypes.erase(hereTy);
         }
     }
 }
@@ -3083,7 +3083,7 @@ NormalizationResult Normalizer::intersectNormals(NormalizedType& here, const Nor
 
     here.booleans = intersectionOfBools(here.booleans, there.booleans);
 
-    intersectClasses(here.classes, there.classes);
+    intersectExternTypes(here.externTypes, there.externTypes);
     here.errors = (get<NeverType>(there.errors) ? there.errors : here.errors);
     here.nils = (get<NeverType>(there.nils) ? there.nils : here.nils);
     here.numbers = (get<NeverType>(there.numbers) ? there.numbers : here.numbers);
@@ -3205,12 +3205,12 @@ NormalizationResult Normalizer::intersectNormalWithTy(
         intersectTablesWithTable(tables, there, seenTablePropPairs, seenSetTypes);
         here.tables = std::move(tables);
     }
-    else if (get<ClassType>(there))
+    else if (get<ExternType>(there))
     {
-        NormalizedClassType nct = std::move(here.classes);
+        NormalizedExternType nct = std::move(here.externTypes);
         clearNormal(here);
-        intersectClassesWithClass(nct, there);
+        intersectExternTypesWithExternType(nct, there);
-        here.classes = std::move(nct);
+        here.externTypes = std::move(nct);
     }
     else if (get<ErrorType>(there))
     {
@@ -3274,7 +3274,7 @@ NormalizationResult Normalizer::intersectNormalWithTy(
             subtractPrimitive(here, ntv->ty);
         else if (const SingletonType* stv = get<SingletonType>(t))
             subtractSingleton(here, follow(ntv->ty));
-        else if (get<ClassType>(t))
+        else if (get<ExternType>(t))
         {
             NormalizationResult res = intersectNormalWithNegationTy(t, here);
             if (shouldEarlyExit(res))
@@ -3334,7 +3334,7 @@ NormalizationResult Normalizer::intersectNormalWithTy(
     }
     else if (get<NeverType>(there))
     {
-        here.classes.resetToNever();
+        here.externTypes.resetToNever();
     }
     else if (get<NoRefineType>(there))
     {
@@ -3403,18 +3403,18 @@ TypeId Normalizer::typeFromNormal(const NormalizedType& norm)
     if (!get<NeverType>(norm.booleans))
         result.push_back(norm.booleans);
 
-    if (isTop(builtinTypes, norm.classes))
+    if (isTop(builtinTypes, norm.externTypes))
     {
-        result.push_back(builtinTypes->classType);
+        result.push_back(builtinTypes->externType);
     }
-    else if (!norm.classes.isNever())
+    else if (!norm.externTypes.isNever())
     {
         std::vector<TypeId> parts;
-        parts.reserve(norm.classes.classes.size());
+        parts.reserve(norm.externTypes.externTypes.size());
 
-        for (const TypeId normTy : norm.classes.ordering)
+        for (const TypeId normTy : norm.externTypes.ordering)
         {
-            const TypeIds& normNegations = norm.classes.classes.at(normTy);
+            const TypeIds& normNegations = norm.externTypes.externTypes.at(normTy);
 
             if (normNegations.empty())
             {

Analysis/src/RequireTracer.cpp

@@ -4,6 +4,8 @@
 #include "Luau/Ast.h"
 #include "Luau/Module.h"
 
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+
 namespace Luau
 {
 
@@ -65,6 +67,12 @@ struct RequireTracer : AstVisitor
         return true;
     }
 
+    bool visit(AstTypePack* node) override
+    {
+        // allow resolving require inside `typeof` annotations
+        return FFlag::LuauStoreReturnTypesAsPackOnAst;
+    }
+
     AstExpr* getDependent_DEPRECATED(AstExpr* node)
     {
         if (AstExprLocal* expr = node->as<AstExprLocal>())

Analysis/src/Simplify.cpp

@@ -6,6 +6,7 @@
 #include "Luau/DenseHash.h"
 #include "Luau/RecursionCounter.h"
 #include "Luau/Set.h"
+#include "Luau/Type.h"
 #include "Luau/TypeArena.h"
 #include "Luau/TypePairHash.h"
 #include "Luau/TypeUtils.h"
@@ -17,6 +18,7 @@ LUAU_FASTFLAG(LuauSolverV2)
 LUAU_DYNAMIC_FASTINTVARIABLE(LuauSimplificationComplexityLimit, 8)
 LUAU_FASTFLAGVARIABLE(LuauSimplificationRecheckAssumption)
 LUAU_FASTFLAGVARIABLE(LuauOptimizeFalsyAndTruthyIntersect)
+LUAU_FASTFLAGVARIABLE(LuauSimplificationTableExternType)
 
 namespace Luau
 {
@@ -316,11 +318,13 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     {
         if (get<AnyType>(right))
             return Relation::Subset;
-        else if (get<UnknownType>(right))
+
+        if (get<UnknownType>(right))
             return Relation::Coincident;
-        else if (get<ErrorType>(right))
+
+        if (get<ErrorType>(right))
             return Relation::Disjoint;
-        else
+
         return Relation::Superset;
     }
 
@@ -331,7 +335,7 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     {
         if (get<AnyType>(right))
             return Relation::Coincident;
-        else
+
         return Relation::Superset;
     }
 
@@ -356,7 +360,7 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     // * FunctionType
     // * TableType
     // * MetatableType
-    // * ClassType
+    // * ExternType
     // * UnionType
     // * IntersectionType
     // * NegationType
@@ -364,26 +368,33 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
     if (isTypeVariable(left) || isTypeVariable(right))
         return Relation::Intersects;
 
+    if (FFlag::LuauSimplificationTableExternType)
+    {
+        // if either type is a type function, we cannot know if they'll be related.
+        if (get<TypeFunctionInstanceType>(left) || get<TypeFunctionInstanceType>(right))
+            return Relation::Intersects;
+    }
+
     if (get<ErrorType>(left))
     {
         if (get<ErrorType>(right))
             return Relation::Coincident;
         else if (get<AnyType>(right))
             return Relation::Subset;
-        else
+
         return Relation::Disjoint;
     }
-    if (get<ErrorType>(right))
+    else if (get<ErrorType>(right))
         return flip(relate(right, left, seen));
 
     if (get<NeverType>(left))
     {
         if (get<NeverType>(right))
             return Relation::Coincident;
-        else
+
         return Relation::Subset;
     }
-    if (get<NeverType>(right))
+    else if (get<NeverType>(right))
         return flip(relate(right, left, seen));
 
     if (auto ut = get<IntersectionType>(left))
@@ -447,7 +458,7 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
         {
             if (lp->type == rp->type)
                 return Relation::Coincident;
-            else
+
             return Relation::Disjoint;
         }
 
@@ -455,9 +466,10 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
         {
             if (lp->type == PrimitiveType::String && rs->variant.get_if<StringSingleton>())
                 return Relation::Superset;
-            else if (lp->type == PrimitiveType::Boolean && rs->variant.get_if<BooleanSingleton>())
+
+            if (lp->type == PrimitiveType::Boolean && rs->variant.get_if<BooleanSingleton>())
                 return Relation::Superset;
-            else
+
             return Relation::Disjoint;
         }
 
@@ -465,33 +477,34 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
         {
             if (get<FunctionType>(right))
                 return Relation::Superset;
-            else
+
             return Relation::Disjoint;
         }
         if (lp->type == PrimitiveType::Table)
         {
             if (get<TableType>(right))
                 return Relation::Superset;
-            else
+
             return Relation::Disjoint;
         }
 
-        if (get<FunctionType>(right) || get<TableType>(right) || get<MetatableType>(right) || get<ClassType>(right))
+        if (get<FunctionType>(right) || get<TableType>(right) || get<MetatableType>(right) || get<ExternType>(right))
             return Relation::Disjoint;
     }
 
     if (auto ls = get<SingletonType>(left))
     {
-        if (get<FunctionType>(right) || get<TableType>(right) || get<MetatableType>(right) || get<ClassType>(right))
+        if (get<FunctionType>(right) || get<TableType>(right) || get<MetatableType>(right) || get<ExternType>(right))
             return Relation::Disjoint;
 
         if (get<PrimitiveType>(right))
             return flip(relate(right, left, seen));
+
         if (auto rs = get<SingletonType>(right))
         {
             if (ls->variant == rs->variant)
                 return Relation::Coincident;
-            else
+
             return Relation::Disjoint;
         }
     }
@@ -502,10 +515,10 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
         {
             if (rp->type == PrimitiveType::Function)
                 return Relation::Subset;
-            else
+
             return Relation::Disjoint;
         }
-        else
+
         return Relation::Intersects;
     }
 
@@ -515,10 +528,11 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
         {
             if (rp->type == PrimitiveType::Table)
                 return Relation::Subset;
-            else
+
             return Relation::Disjoint;
         }
-        else if (auto rt = get<TableType>(right))
+
+        if (auto rt = get<TableType>(right))
         {
             // TODO PROBABLY indexers and metatables.
             if (1 == rt->props.size())
@@ -538,28 +552,57 @@ Relation relate(TypeId left, TypeId right, SimplifierSeenSet& seen)
                  */
                 if (lt->props.size() > 1 && r == Relation::Superset)
                     return Relation::Intersects;
-                else
+
                 return r;
             }
-            else if (1 == lt->props.size())
+
+            if (1 == lt->props.size())
                 return flip(relate(right, left, seen));
-            else
+
             return Relation::Intersects;
         }
+
+        if (FFlag::LuauSimplificationTableExternType)
+        {
+            if (auto re = get<ExternType>(right))
+            {
+                Relation overall = Relation::Coincident;
+
+                for (auto& [name, prop] : lt->props)
+                {
+                    if (auto propInExternType = re->props.find(name); propInExternType != re->props.end())
+                    {
+                        Relation propRel = relate(prop.type(), propInExternType->second.type());
+
+                        if (propRel == Relation::Disjoint)
+                            return Relation::Disjoint;
+
+                        if (propRel == Relation::Coincident)
+                            continue;
+
+                        overall = Relation::Intersects;
+                    }
+                }
+
+                return overall;
+            }
+        }
+
         // TODO metatables
 
         return Relation::Disjoint;
     }
 
-    if (auto ct = get<ClassType>(left))
+    if (auto ct = get<ExternType>(left))
     {
-        if (auto rct = get<ClassType>(right))
+        if (auto rct = get<ExternType>(right))
         {
             if (isSubclass(ct, rct))
                 return Relation::Subset;
-            else if (isSubclass(rct, ct))
+
+            if (isSubclass(rct, ct))
                 return Relation::Superset;
-            else
+
             return Relation::Disjoint;
         }
 
@@ -873,7 +916,7 @@ std::optional<TypeId> TypeSimplifier::basicIntersectWithTruthy(TypeId target) co
     if (is<NeverType, ErrorType>(target))
         return target;
 
-    if (is<FunctionType, TableType, MetatableType, ClassType>(target))
+    if (is<FunctionType, TableType, MetatableType, ExternType>(target))
         return target;
 
     if (auto pt = get<PrimitiveType>(target))
@@ -909,7 +952,7 @@ std::optional<TypeId> TypeSimplifier::basicIntersectWithFalsy(TypeId target) con
     if (is<UnknownType>(target))
         return builtinTypes->falsyType;
 
-    if (is<FunctionType, TableType, MetatableType, ClassType>(target))
+    if (is<FunctionType, TableType, MetatableType, ExternType>(target))
         return builtinTypes->neverType;
 
     if (auto pt = get<PrimitiveType>(target))

Analysis/src/Substitution.cpp

@@ -136,9 +136,9 @@ static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log)
             clone.parts = a.parts;
             return dest.addType(std::move(clone));
         }
-        else if constexpr (std::is_same_v<T, ClassType>)
+        else if constexpr (std::is_same_v<T, ExternType>)
         {
-            ClassType clone{a.name, a.props, a.parent, a.metatable, a.tags, a.userData, a.definitionModuleName, a.definitionLocation, a.indexer};
+            ExternType clone{a.name, a.props, a.parent, a.metatable, a.tags, a.userData, a.definitionModuleName, a.definitionLocation, a.indexer};
             return dest.addType(std::move(clone));
         }
         else if constexpr (std::is_same_v<T, NegationType>)
@@ -252,21 +252,21 @@ void Tarjan::visitChildren(TypeId ty, int index)
         for (TypePackId a : tfit->packArguments)
             visitChild(a);
     }
-    else if (const ClassType* ctv = get<ClassType>(ty))
+    else if (const ExternType* etv = get<ExternType>(ty))
     {
-        for (const auto& [name, prop] : ctv->props)
+        for (const auto& [name, prop] : etv->props)
             visitChild(prop.type());
 
-        if (ctv->parent)
+        if (etv->parent)
-            visitChild(*ctv->parent);
+            visitChild(*etv->parent);
 
-        if (ctv->metatable)
+        if (etv->metatable)
-            visitChild(*ctv->metatable);
+            visitChild(*etv->metatable);
 
-        if (ctv->indexer)
+        if (etv->indexer)
         {
-            visitChild(ctv->indexer->indexType);
+            visitChild(etv->indexer->indexType);
-            visitChild(ctv->indexer->indexResultType);
+            visitChild(etv->indexer->indexResultType);
         }
     }
     else if (const NegationType* ntv = get<NegationType>(ty))
@@ -838,21 +838,21 @@ void Substitution::replaceChildren(TypeId ty)
         for (TypePackId& a : tfit->packArguments)
             a = replace(a);
     }
-    else if (ClassType* ctv = getMutable<ClassType>(ty))
+    else if (ExternType* etv = getMutable<ExternType>(ty))
     {
-        for (auto& [name, prop] : ctv->props)
+        for (auto& [name, prop] : etv->props)
             prop.setType(replace(prop.type()));
 
-        if (ctv->parent)
+        if (etv->parent)
-            ctv->parent = replace(*ctv->parent);
+            etv->parent = replace(*etv->parent);
 
-        if (ctv->metatable)
+        if (etv->metatable)
-            ctv->metatable = replace(*ctv->metatable);
+            etv->metatable = replace(*etv->metatable);
 
-        if (ctv->indexer)
+        if (etv->indexer)
         {
-            ctv->indexer->indexType = replace(ctv->indexer->indexType);
+            etv->indexer->indexType = replace(etv->indexer->indexType);
-            ctv->indexer->indexResultType = replace(ctv->indexer->indexResultType);
+            etv->indexer->indexResultType = replace(etv->indexer->indexResultType);
         }
     }
     else if (NegationType* ntv = getMutable<NegationType>(ty))

Analysis/src/Subtyping.cpp

@@ -7,13 +7,11 @@
 #include "Luau/Normalize.h"
 #include "Luau/RecursionCounter.h"
 #include "Luau/Scope.h"
-#include "Luau/StringUtils.h"
 #include "Luau/Substitution.h"
 #include "Luau/ToString.h"
 #include "Luau/TxnLog.h"
 #include "Luau/Type.h"
 #include "Luau/TypeArena.h"
-#include "Luau/TypeCheckLimits.h"
 #include "Luau/TypeFunction.h"
 #include "Luau/TypePack.h"
 #include "Luau/TypePath.h"
@@ -33,7 +31,7 @@ struct VarianceFlipper
     Subtyping::Variance* variance;
     Subtyping::Variance oldValue;
 
-    VarianceFlipper(Subtyping::Variance* v)
+    explicit VarianceFlipper(Subtyping::Variance* v)
         : variance(v)
         , oldValue(*v)
     {
@@ -315,7 +313,7 @@ struct ApplyMappedGenerics : Substitution
 
     bool ignoreChildren(TypeId ty) override
     {
-        if (get<ClassType>(ty))
+        if (get<ExternType>(ty))
             return true;
 
         return ty->persistent;
@@ -744,9 +742,9 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
         result = isCovariantWith(env, p, scope);
     else if (auto p = get2<MetatableType, TableType>(subTy, superTy))
         result = isCovariantWith(env, p, scope);
-    else if (auto p = get2<ClassType, ClassType>(subTy, superTy))
+    else if (auto p = get2<ExternType, ExternType>(subTy, superTy))
         result = isCovariantWith(env, p, scope);
-    else if (auto p = get2<ClassType, TableType>(subTy, superTy))
+    else if (auto p = get2<ExternType, TableType>(subTy, superTy))
         result = isCovariantWith(env, subTy, p.first, superTy, p.second, scope);
     else if (auto p = get2<TableType, PrimitiveType>(subTy, superTy))
         result = isCovariantWith(env, p, scope);
@@ -1336,7 +1334,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
     }
     // the top class type is not actually a primitive type, so the negation of
     // any one of them includes the top class type.
-    else if (auto p = get2<ClassType, PrimitiveType>(subTy, negatedTy))
+    else if (auto p = get2<ExternType, PrimitiveType>(subTy, negatedTy))
         result = {true};
     else if (auto p = get<PrimitiveType>(negatedTy); p && is<TableType, MetatableType>(subTy))
         result = {p->type != PrimitiveType::Table};
@@ -1344,9 +1342,9 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
         result = {p.second->type != PrimitiveType::Function};
     else if (auto p = get2<SingletonType, SingletonType>(subTy, negatedTy))
         result = {*p.first != *p.second};
-    else if (auto p = get2<ClassType, ClassType>(subTy, negatedTy))
+    else if (auto p = get2<ExternType, ExternType>(subTy, negatedTy))
         result = SubtypingResult::negate(isCovariantWith(env, p.first, p.second, scope));
-    else if (get2<FunctionType, ClassType>(subTy, negatedTy))
+    else if (get2<FunctionType, ExternType>(subTy, negatedTy))
         result = {true};
     else if (is<ErrorType, FunctionType, TableType, MetatableType>(negatedTy))
         iceReporter->ice("attempting to negate a non-testable type");
@@ -1471,15 +1469,15 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Meta
     }
 }
 
-SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const ClassType* subClass, const ClassType* superClass, NotNull<Scope> scope)
+SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const ExternType* subExternType, const ExternType* superExternType, NotNull<Scope> scope)
 {
-    return {isSubclass(subClass, superClass)};
+    return {isSubclass(subExternType, superExternType)};
 }
 
 SubtypingResult Subtyping::isCovariantWith(
     SubtypingEnvironment& env,
     TypeId subTy,
-    const ClassType* subClass,
+    const ExternType* subExternType,
     TypeId superTy,
     const TableType* superTable,
     NotNull<Scope> scope
@@ -1491,7 +1489,7 @@ SubtypingResult Subtyping::isCovariantWith(
 
     for (const auto& [name, prop] : superTable->props)
     {
-        if (auto classProp = lookupClassProp(subClass, name))
+        if (auto classProp = lookupExternTypeProp(subExternType, name))
         {
             result.andAlso(isCovariantWith(env, *classProp, prop, name, scope));
         }
@@ -1661,7 +1659,7 @@ SubtypingResult Subtyping::isCovariantWith(
     SubtypingResult result = isCovariantWith(env, subNorm->tops, superNorm->tops, scope);
     result.andAlso(isCovariantWith(env, subNorm->booleans, superNorm->booleans, scope));
     result.andAlso(
-        isCovariantWith(env, subNorm->classes, superNorm->classes, scope).orElse(isCovariantWith(env, subNorm->classes, superNorm->tables, scope))
+        isCovariantWith(env, subNorm->externTypes, superNorm->externTypes, scope).orElse(isCovariantWith(env, subNorm->externTypes, superNorm->tables, scope))
     );
     result.andAlso(isCovariantWith(env, subNorm->errors, superNorm->errors, scope));
     result.andAlso(isCovariantWith(env, subNorm->nils, superNorm->nils, scope));
@@ -1678,24 +1676,24 @@ SubtypingResult Subtyping::isCovariantWith(
 
 SubtypingResult Subtyping::isCovariantWith(
     SubtypingEnvironment& env,
-    const NormalizedClassType& subClass,
+    const NormalizedExternType& subExternType,
-    const NormalizedClassType& superClass,
+    const NormalizedExternType& superExternType,
     NotNull<Scope> scope
 )
 {
-    for (const auto& [subClassTy, _] : subClass.classes)
+    for (const auto& [subExternTypeTy, _] : subExternType.externTypes)
     {
         SubtypingResult result;
 
-        for (const auto& [superClassTy, superNegations] : superClass.classes)
+        for (const auto& [superExternTypeTy, superNegations] : superExternType.externTypes)
         {
-            result.orElse(isCovariantWith(env, subClassTy, superClassTy, scope));
+            result.orElse(isCovariantWith(env, subExternTypeTy, superExternTypeTy, scope));
             if (!result.isSubtype)
                 continue;
 
             for (TypeId negation : superNegations)
             {
-                result.andAlso(SubtypingResult::negate(isCovariantWith(env, subClassTy, negation, scope)));
+                result.andAlso(SubtypingResult::negate(isCovariantWith(env, subExternTypeTy, negation, scope)));
                 if (result.isSubtype)
                     break;
             }
@@ -1710,17 +1708,17 @@ SubtypingResult Subtyping::isCovariantWith(
 
 SubtypingResult Subtyping::isCovariantWith(
     SubtypingEnvironment& env,
-    const NormalizedClassType& subClass,
+    const NormalizedExternType& subExternType,
     const TypeIds& superTables,
     NotNull<Scope> scope
 )
 {
-    for (const auto& [subClassTy, _] : subClass.classes)
+    for (const auto& [subExternTypeTy, _] : subExternType.externTypes)
     {
         SubtypingResult result;
 
         for (TypeId superTableTy : superTables)
-            result.orElse(isCovariantWith(env, subClassTy, superTableTy, scope));
+            result.orElse(isCovariantWith(env, subExternTypeTy, superTableTy, scope));
 
         if (!result.isSubtype)
             return result;

Analysis/src/ToDot.cpp

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

Analysis/src/ToString.cpp

@@ -19,6 +19,8 @@
 #include <stdexcept>
 #include <string>
 
+LUAU_FASTFLAGVARIABLE(LuauEnableDenseTableAlias)
+
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAGVARIABLE(LuauSyntheticErrors)
 LUAU_FASTFLAGVARIABLE(LuauStringPartLengthLimit)
@@ -121,7 +123,7 @@ struct FindCyclicTypes final : TypeVisitor
         return true;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -720,7 +722,13 @@ struct TypeStringifier
         if (ttv.boundTo)
             return stringify(*ttv.boundTo);
 
-        if (!state.exhaustive)
+        bool showName = !state.exhaustive;
+        if (FFlag::LuauEnableDenseTableAlias)
+        {
+            // if hide table alias expansions are enabled and there is a name found for the table, use it
+            showName = !state.exhaustive || state.opts.hideTableAliasExpansions;
+        }
+        if (showName)
         {
             if (ttv.name)
             {
@@ -743,6 +751,10 @@ struct TypeStringifier
                 stringify(ttv.instantiatedTypeParams, ttv.instantiatedTypePackParams);
                 return;
             }
+        }
+
+        if (!state.exhaustive)
+        {
             if (ttv.syntheticName)
             {
                 state.result.invalid = true;
@@ -881,9 +893,9 @@ struct TypeStringifier
         state.emit(" }");
     }
 
-    void operator()(TypeId, const ClassType& ctv)
+    void operator()(TypeId, const ExternType& etv)
     {
-        state.emit(ctv.name);
+        state.emit(etv.name);
     }
 
     void operator()(TypeId, const AnyType&)

Analysis/src/TopoSortStatements.cpp

@@ -41,6 +41,8 @@
 #include <stdexcept>
 #include <optional>
 
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+
 namespace Luau
 {
 
@@ -297,6 +299,11 @@ struct ArcCollector : public AstVisitor
             add(*name);
         return true;
     }
+
+    bool visit(AstTypePack* node) override
+    {
+        return FFlag::LuauStoreReturnTypesAsPackOnAst;
+    }
 };
 
 struct ContainsFunctionCall : public AstVisitor

Analysis/src/Transpiler.cpp

@@ -12,9 +12,9 @@
 
 LUAU_FASTFLAG(LuauStoreCSTData2)
 LUAU_FASTFLAG(LuauAstTypeGroup3)
-LUAU_FASTFLAG(LuauFixDoBlockEndLocation)
 LUAU_FASTFLAG(LuauParseOptionalAsNode2)
 LUAU_FASTFLAG(LuauFixFunctionWithAttributesStartLocation)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 namespace
 {
@@ -331,7 +331,7 @@ struct Printer_DEPRECATED
         }
     }
 
-    void visualizeTypePackAnnotation(const AstTypePack& annotation, bool forVarArg)
+    void visualizeTypePackAnnotation(const AstTypePack& annotation, bool forVarArg, bool unconditionallyParenthesize = true)
     {
         advance(annotation.location.begin);
         if (const AstTypePackVariadic* variadicTp = annotation.as<AstTypePackVariadic>())
@@ -349,7 +349,7 @@ struct Printer_DEPRECATED
         else if (const AstTypePackExplicit* explicitTp = annotation.as<AstTypePackExplicit>())
         {
             LUAU_ASSERT(!forVarArg);
-            visualizeTypeList(explicitTp->typeList, true);
+            visualizeTypeList(explicitTp->typeList, unconditionallyParenthesize);
         }
         else
         {
@@ -705,8 +705,6 @@ struct Printer_DEPRECATED
             writer.keyword("do");
             for (const auto& s : block->body)
                 visualize(*s);
-            if (!FFlag::LuauFixDoBlockEndLocation)
-                writer.advance(block->location.end);
             writeEnd(program.location);
         }
         else if (const auto& a = program.as<AstStatIf>())
@@ -1065,12 +1063,15 @@ struct Printer_DEPRECATED
 
         writer.symbol(")");
 
-        if (writeTypes && func.returnAnnotation)
+        if (writeTypes && (FFlag::LuauStoreReturnTypesAsPackOnAst ? func.returnAnnotation != nullptr : func.returnAnnotation_DEPRECATED.has_value()))
         {
             writer.symbol(":");
             writer.space();
 
-            visualizeTypeList(*func.returnAnnotation, false);
+            if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                visualizeTypePackAnnotation(*func.returnAnnotation, false, false);
+            else
+                visualizeTypeList(*func.returnAnnotation_DEPRECATED, false);
         }
 
         visualizeBlock(*func.body);
@@ -1174,7 +1175,10 @@ struct Printer_DEPRECATED
             }
 
             writer.symbol("->");
-            visualizeTypeList(a->returnTypes, true);
+            if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                visualizeTypePackAnnotation(*a->returnTypes, false);
+            else
+                visualizeTypeList(a->returnTypes_DEPRECATED, true);
         }
         else if (const auto& a = typeAnnotation.as<AstTypeTable>())
         {
@@ -1368,7 +1372,7 @@ struct Printer
         }
     }
 
-    void visualizeTypePackAnnotation(AstTypePack& annotation, bool forVarArg)
+    void visualizeTypePackAnnotation(AstTypePack& annotation, bool forVarArg, bool unconditionallyParenthesize = true)
     {
         advance(annotation.location.begin);
         if (const AstTypePackVariadic* variadicTp = annotation.as<AstTypePackVariadic>())
@@ -1390,10 +1394,10 @@ struct Printer
             LUAU_ASSERT(!forVarArg);
             if (const auto cstNode = lookupCstNode<CstTypePackExplicit>(explicitTp))
                 visualizeTypeList(
-                    explicitTp->typeList, true, cstNode->openParenthesesPosition, cstNode->closeParenthesesPosition, cstNode->commaPositions
+                    explicitTp->typeList, FFlag::LuauStoreReturnTypesAsPackOnAst ? cstNode->hasParentheses : true, cstNode->openParenthesesPosition, cstNode->closeParenthesesPosition, cstNode->commaPositions
                 );
             else
-                visualizeTypeList(explicitTp->typeList, true);
+                visualizeTypeList(explicitTp->typeList, unconditionallyParenthesize);
         }
         else
         {
@@ -2316,8 +2320,6 @@ struct Printer
     {
         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, cstNode ? cstNode->genericsCommaPositions.begin() : nullptr);
@@ -2383,14 +2385,23 @@ struct Printer
             advanceBefore(func.argLocation->end, 1);
         writer.symbol(")");
 
-        if (writeTypes && func.returnAnnotation)
+        if (writeTypes && FFlag::LuauStoreReturnTypesAsPackOnAst ? func.returnAnnotation != nullptr : func.returnAnnotation_DEPRECATED.has_value())
         {
             if (cstNode)
                 advance(cstNode->returnSpecifierPosition);
             writer.symbol(":");
-            writer.space();
 
-            visualizeTypeList(*func.returnAnnotation, false);
+            if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+            {
+                if (!cstNode)
+                    writer.space();
+                visualizeTypePackAnnotation(*func.returnAnnotation, false, false);
+            }
+            else
+            {
+                writer.space();
+                visualizeTypeList(*func.returnAnnotation_DEPRECATED, false);
+            }
         }
 
         visualizeBlock(*func.body);
@@ -2573,7 +2584,10 @@ struct Printer
             if (cstNode)
                 advance(cstNode->returnArrowPosition);
             writer.symbol("->");
-            visualizeTypeList(a->returnTypes, true);
+            if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+                visualizeTypePackAnnotation(*a->returnTypes, false);
+            else
+                visualizeTypeList(a->returnTypes_DEPRECATED, true);
         }
         else if (const auto& a = typeAnnotation.as<AstTypeTable>())
         {

Analysis/src/Type.cpp

@@ -282,8 +282,8 @@ std::optional<TypeId> getMetatable(TypeId type, NotNull<BuiltinTypes> builtinTyp
 
     if (const MetatableType* mtType = get<MetatableType>(type))
         return mtType->metatable;
-    else if (const ClassType* classType = get<ClassType>(type))
+    else if (const ExternType* externType = get<ExternType>(type))
-        return classType->metatable;
+        return externType->metatable;
     else if (isString(type))
     {
         auto ptv = get<PrimitiveType>(builtinTypes->stringType);
@@ -346,10 +346,10 @@ std::optional<ModuleName> getDefinitionModuleName(TypeId type)
         if (ftv->definition)
             return ftv->definition->definitionModuleName;
     }
-    else if (auto ctv = get<ClassType>(type))
+    else if (auto etv = get<ExternType>(type))
     {
-        if (!ctv->definitionModuleName.empty())
+        if (!etv->definitionModuleName.empty())
-            return ctv->definitionModuleName;
+            return etv->definitionModuleName;
     }
 
     return std::nullopt;
@@ -506,31 +506,6 @@ FreeType::FreeType(Scope* scope, TypeLevel level, TypeId lowerBound, TypeId uppe
 {
 }
 
-// Old constructors
-FreeType::FreeType(TypeLevel level)
-    : index(Unifiable::freshIndex())
-    , level(level)
-    , scope(nullptr)
-{
-    LUAU_ASSERT(!FFlag::LuauFreeTypesMustHaveBounds);
-}
-
-FreeType::FreeType(Scope* scope)
-    : index(Unifiable::freshIndex())
-    , level{}
-    , scope(scope)
-{
-    LUAU_ASSERT(!FFlag::LuauFreeTypesMustHaveBounds);
-}
-
-FreeType::FreeType(Scope* scope, TypeLevel level)
-    : index(Unifiable::freshIndex())
-    , level(level)
-    , scope(scope)
-{
-    LUAU_ASSERT(!FFlag::LuauFreeTypesMustHaveBounds);
-}
-
 GenericType::GenericType()
     : index(Unifiable::freshIndex())
     , name("g" + std::to_string(index))
@@ -1014,7 +989,7 @@ BuiltinTypes::BuiltinTypes()
     , threadType(arena->addType(Type{PrimitiveType{PrimitiveType::Thread}, /*persistent*/ true}))
     , bufferType(arena->addType(Type{PrimitiveType{PrimitiveType::Buffer}, /*persistent*/ true}))
     , functionType(arena->addType(Type{PrimitiveType{PrimitiveType::Function}, /*persistent*/ true}))
-    , classType(arena->addType(Type{ClassType{"class", {}, std::nullopt, std::nullopt, {}, {}, {}, {}}, /*persistent*/ true}))
+    , externType(arena->addType(Type{ExternType{"class", {}, std::nullopt, std::nullopt, {}, {}, {}, {}}, /*persistent*/ true}))
     , tableType(arena->addType(Type{PrimitiveType{PrimitiveType::Table}, /*persistent*/ true}))
     , emptyTableType(arena->addType(Type{TableType{TableState::Sealed, TypeLevel{}, nullptr}, /*persistent*/ true}))
     , trueType(arena->addType(Type{SingletonType{BooleanSingleton{true}}, /*persistent*/ true}))
@@ -1026,6 +1001,7 @@ BuiltinTypes::BuiltinTypes()
     , noRefineType(arena->addType(Type{NoRefineType{}, /*persistent*/ true}))
     , falsyType(arena->addType(Type{UnionType{{falseType, nilType}}, /*persistent*/ true}))
     , truthyType(arena->addType(Type{NegationType{falsyType}, /*persistent*/ true}))
+    , notNilType(arena->addType(Type{NegationType{nilType}, /*persistent*/ true}))
     , optionalNumberType(arena->addType(Type{UnionType{{numberType, nilType}}, /*persistent*/ true}))
     , optionalStringType(arena->addType(Type{UnionType{{stringType, nilType}}, /*persistent*/ true}))
     , emptyTypePack(arena->addTypePack(TypePackVar{TypePack{{}}, /*persistent*/ true}))
@@ -1104,9 +1080,9 @@ void persist(TypeId ty)
                 queue.push_back(ttv->indexer->indexResultType);
             }
         }
-        else if (auto ctv = get<ClassType>(t))
+        else if (auto etv= get<ExternType>(t))
         {
-            for (const auto& [_name, prop] : ctv->props)
+            for (const auto& [_name, prop] : etv->props)
                 queue.push_back(prop.type());
         }
         else if (auto utv = get<UnionType>(t))
@@ -1206,7 +1182,7 @@ std::optional<TypeLevel> getLevel(TypePackId tp)
         return std::nullopt;
 }
 
-const Property* lookupClassProp(const ClassType* cls, const Name& name)
+const Property* lookupExternTypeProp(const ExternType* cls, const Name& name)
 {
     while (cls)
     {
@@ -1215,7 +1191,7 @@ const Property* lookupClassProp(const ClassType* cls, const Name& name)
             return &it->second;
 
         if (cls->parent)
-            cls = get<ClassType>(*cls->parent);
+            cls = get<ExternType>(*cls->parent);
         else
             return nullptr;
 
@@ -1225,7 +1201,7 @@ const Property* lookupClassProp(const ClassType* cls, const Name& name)
     return nullptr;
 }
 
-bool isSubclass(const ClassType* cls, const ClassType* parent)
+bool isSubclass(const ExternType* cls, const ExternType* parent)
 {
     while (cls)
     {
@@ -1234,7 +1210,7 @@ bool isSubclass(const ClassType* cls, const ClassType* parent)
         else if (!cls->parent)
             return false;
 
-        cls = get<ClassType>(*cls->parent);
+        cls = get<ExternType>(*cls->parent);
         LUAU_ASSERT(cls);
     }
 
@@ -1303,8 +1279,8 @@ static Tags* getTags(TypeId ty)
         return &ftv->tags;
     else if (auto ttv = getMutable<TableType>(ty))
         return &ttv->tags;
-    else if (auto ctv = getMutable<ClassType>(ty))
+    else if (auto etv = getMutable<ExternType>(ty))
-        return &ctv->tags;
+        return &etv->tags;
 
     return nullptr;
 }
@@ -1334,19 +1310,19 @@ bool hasTag(TypeId ty, const std::string& tagName)
 {
     ty = follow(ty);
 
-    // We special case classes because getTags only returns a pointer to one vector of tags.
+    // We special case extern types because getTags only returns a pointer to one vector of tags.
-    // But classes has multiple vector of tags, represented throughout the hierarchy.
+    // But extern types has multiple vector of tags, represented throughout the hierarchy.
-    if (auto ctv = get<ClassType>(ty))
+    if (auto etv = get<ExternType>(ty))
     {
-        while (ctv)
+        while (etv)
         {
-            if (hasTag(ctv->tags, tagName))
+            if (hasTag(etv->tags, tagName))
                 return true;
-            else if (!ctv->parent)
+            else if (!etv->parent)
                 return false;
 
-            ctv = get<ClassType>(*ctv->parent);
+            etv = get<ExternType>(*etv->parent);
-            LUAU_ASSERT(ctv);
+            LUAU_ASSERT(etv);
         }
     }
     else if (auto tags = getTags(ty))

Analysis/src/TypeArena.cpp

@@ -50,33 +50,6 @@ TypeId TypeArena::freshType(NotNull<BuiltinTypes> builtins, Scope* scope, TypeLe
     return allocated;
 }
 
-TypeId TypeArena::freshType_DEPRECATED(TypeLevel level)
-{
-    TypeId allocated = types.allocate(FreeType{level});
-
-    asMutable(allocated)->owningArena = this;
-
-    return allocated;
-}
-
-TypeId TypeArena::freshType_DEPRECATED(Scope* scope)
-{
-    TypeId allocated = types.allocate(FreeType{scope});
-
-    asMutable(allocated)->owningArena = this;
-
-    return allocated;
-}
-
-TypeId TypeArena::freshType_DEPRECATED(Scope* scope, TypeLevel level)
-{
-    TypeId allocated = types.allocate(FreeType{scope, level});
-
-    asMutable(allocated)->owningArena = this;
-
-    return allocated;
-}
-
 TypePackId TypeArena::freshTypePack(Scope* scope, Polarity polarity)
 {
     TypePackId allocated = typePacks.allocate(FreeTypePack{scope, polarity});

Analysis/src/TypeAttach.cpp

@@ -14,6 +14,7 @@
 #include <string>
 
 LUAU_FASTFLAG(LuauStoreCSTData2)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 static char* allocateString(Luau::Allocator& allocator, std::string_view contents)
 {
@@ -219,21 +220,21 @@ public:
         return Luau::visit(*this, mtv.table->ty);
     }
 
-    AstType* operator()(const ClassType& ctv)
+    AstType* operator()(const ExternType& etv)
     {
         RecursionCounter counter(&count);
 
-        char* name = allocateString(*allocator, ctv.name);
+        char* name = allocateString(*allocator, etv.name);
 
-        if (!options.expandClassProps || hasSeen(&ctv) || count > 1)
+        if (!options.expandExternTypeProps || hasSeen(&etv) || count > 1)
             return allocator->alloc<AstTypeReference>(Location(), std::nullopt, AstName{name}, std::nullopt, Location());
 
         AstArray<AstTableProp> props;
-        props.size = ctv.props.size();
+        props.size = etv.props.size();
         props.data = static_cast<AstTableProp*>(allocator->allocate(sizeof(AstTableProp) * props.size));
 
         int idx = 0;
-        for (const auto& [propName, prop] : ctv.props)
+        for (const auto& [propName, prop] : etv.props)
         {
             char* name = allocateString(*allocator, propName);
 
@@ -244,13 +245,13 @@ public:
         }
 
         AstTableIndexer* indexer = nullptr;
-        if (ctv.indexer)
+        if (etv.indexer)
         {
             RecursionCounter counter(&count);
 
             indexer = allocator->alloc<AstTableIndexer>();
-            indexer->indexType = Luau::visit(*this, ctv.indexer->indexType->ty);
+            indexer->indexType = Luau::visit(*this, etv.indexer->indexType->ty);
-            indexer->resultType = Luau::visit(*this, ctv.indexer->indexResultType->ty);
+            indexer->resultType = Luau::visit(*this, etv.indexer->indexResultType->ty);
         }
 
         return allocator->alloc<AstTypeTable>(Location(), props, indexer);
@@ -328,10 +329,20 @@ public:
         if (retTail)
             retTailAnnotation = rehydrate(*retTail);
 
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        {
+            auto returnAnnotation = allocator->alloc<AstTypePackExplicit>(Location(), AstTypeList{returnTypes, retTailAnnotation});
+            return allocator->alloc<AstTypeFunction>(
+                Location(), generics, genericPacks, AstTypeList{argTypes, argTailAnnotation}, argNames, returnAnnotation
+            );
+        }
+        else
+        {
             return allocator->alloc<AstTypeFunction>(
                 Location(), generics, genericPacks, AstTypeList{argTypes, argTailAnnotation}, argNames, AstTypeList{returnTypes, retTailAnnotation}
             );
         }
+    }
     AstType* operator()(const ErrorType&)
     {
         return allocator->alloc<AstTypeReference>(Location(), std::nullopt, AstName("Unifiable<Error>"), std::nullopt, Location());
@@ -585,6 +596,8 @@ public:
             visitLocal(arg);
         }
 
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        {
             if (!fn->returnAnnotation)
             {
                 if (auto result = getScope(fn->body->location))
@@ -597,7 +610,26 @@ public:
                     if (tail)
                         variadicAnnotation = TypeRehydrationVisitor(allocator, &syntheticNames).rehydrate(*tail);
 
-                fn->returnAnnotation = AstTypeList{typeAstPack(ret), variadicAnnotation};
+                    fn->returnAnnotation = allocator->alloc<AstTypePackExplicit>(Location(), AstTypeList{typeAstPack(ret), variadicAnnotation});
+                }
+            }
+        }
+        else
+        {
+            if (!fn->returnAnnotation_DEPRECATED)
+            {
+                if (auto result = getScope(fn->body->location))
+                {
+                    TypePackId ret = result->returnType;
+
+                    AstTypePack* variadicAnnotation = nullptr;
+                    const auto& [v, tail] = flatten(ret);
+
+                    if (tail)
+                        variadicAnnotation = TypeRehydrationVisitor(allocator, &syntheticNames).rehydrate(*tail);
+
+                    fn->returnAnnotation_DEPRECATED = AstTypeList{typeAstPack(ret), variadicAnnotation};
+                }
             }
         }
 

Analysis/src/TypeChecker2.cpp

@@ -30,10 +30,11 @@
 
 LUAU_FASTFLAG(DebugLuauMagicTypes)
 
-LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
 LUAU_FASTFLAGVARIABLE(LuauImproveTypePathsInErrors)
 LUAU_FASTFLAG(LuauUserTypeFunTypecheck)
 LUAU_FASTFLAGVARIABLE(LuauTypeCheckerAcceptNumberConcats)
+LUAU_FASTFLAGVARIABLE(LuauTypeCheckerStricterIndexCheck)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 namespace Luau
 {
@@ -661,7 +662,7 @@ void TypeChecker2::visit(AstStat* stat)
         return visit(s);
     else if (auto s = stat->as<AstStatDeclareGlobal>())
         return visit(s);
-    else if (auto s = stat->as<AstStatDeclareClass>())
+    else if (auto s = stat->as<AstStatDeclareExternType>())
         return visit(s);
     else if (auto s = stat->as<AstStatError>())
         return visit(s);
@@ -1221,7 +1222,10 @@ void TypeChecker2::visit(AstStatDeclareFunction* stat)
 {
     visitGenerics(stat->generics, stat->genericPacks);
     visit(stat->params);
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
         visit(stat->retTypes);
+    else
+        visit(stat->retTypes_DEPRECATED);
 }
 
 void TypeChecker2::visit(AstStatDeclareGlobal* stat)
@@ -1229,9 +1233,9 @@ void TypeChecker2::visit(AstStatDeclareGlobal* stat)
     visit(stat->type);
 }
 
-void TypeChecker2::visit(AstStatDeclareClass* stat)
+void TypeChecker2::visit(AstStatDeclareExternType* stat)
 {
-    for (const AstDeclaredClassProp& prop : stat->props)
+    for (const AstDeclaredExternTypeProperty& prop : stat->props)
         visit(prop.ty);
 }
 
@@ -1675,12 +1679,12 @@ void TypeChecker2::visit(AstExprIndexExpr* indexExpr, ValueContext context)
     {
         return indexExprMetatableHelper(indexExpr, mt, exprType, indexType);
     }
-    else if (auto cls = get<ClassType>(exprType))
+    else if (auto cls = get<ExternType>(exprType))
     {
         if (cls->indexer)
             testIsSubtype(indexType, cls->indexer->indexType, indexExpr->index->location);
         else
-            reportError(DynamicPropertyLookupOnClassesUnsafe{exprType}, indexExpr->location);
+            reportError(DynamicPropertyLookupOnExternTypesUnsafe{exprType}, indexExpr->location);
     }
     else if (get<UnionType>(exprType) && isOptional(exprType))
     {
@@ -1821,8 +1825,16 @@ void TypeChecker2::visit(AstExprFunction* fn)
     visit(fn->body);
 
     // we need to typecheck the return annotation itself, if it exists.
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
         if (fn->returnAnnotation)
-        visit(*fn->returnAnnotation);
+            visit(fn->returnAnnotation);
+    }
+    else
+    {
+        if (fn->returnAnnotation_DEPRECATED)
+            visit(*fn->returnAnnotation_DEPRECATED);
+    }
 
 
     // If the function type has a function annotation, we need to see if we can suggest an annotation
@@ -2036,7 +2048,7 @@ TypeId TypeChecker2::visit(AstExprBinary* expr, AstNode* overrideKey)
         // If we're working with things that are not tables, the metatable comparisons above are a little excessive
         // It's ok for one type to have a meta table and the other to not. In that case, we should fall back on
         // checking if the intersection of the types is inhabited. If `typesHaveIntersection` failed due to limits,
-        // TODO: Maybe add more checks here (e.g. for functions, classes, etc)
+        // TODO: Maybe add more checks here (e.g. for functions, extern types, etc)
         if (!(get<TableType>(leftType) || get<TableType>(rightType)))
             if (!leftMt.has_value() || !rightMt.has_value())
                 matches = matches || typesHaveIntersection != NormalizationResult::False;
@@ -2101,10 +2113,7 @@ TypeId TypeChecker2::visit(AstExprBinary* expr, AstNode* overrideKey)
                 }
                 else
                 {
-                    expectedRets = module->internalTypes.addTypePack(
+                    expectedRets = module->internalTypes.addTypePack({module->internalTypes.freshType(builtinTypes, scope, TypeLevel{})});
-                        {FFlag::LuauFreeTypesMustHaveBounds ? module->internalTypes.freshType(builtinTypes, scope, TypeLevel{})
-                                                            : module->internalTypes.freshType_DEPRECATED(scope, TypeLevel{})}
-                    );
                 }
 
                 TypeId expectedTy = module->internalTypes.addType(FunctionType(expectedArgs, expectedRets));
@@ -2367,8 +2376,7 @@ TypeId TypeChecker2::flattenPack(TypePackId pack)
         return *fst;
     else if (auto ftp = get<FreeTypePack>(pack))
     {
-        TypeId result = FFlag::LuauFreeTypesMustHaveBounds ? module->internalTypes.freshType(builtinTypes, ftp->scope)
+        TypeId result = module->internalTypes.freshType(builtinTypes, ftp->scope);
-                                                           : module->internalTypes.addType(FreeType{ftp->scope});
         TypePackId freeTail = module->internalTypes.addTypePack(FreeTypePack{ftp->scope});
 
         TypePack* resultPack = emplaceTypePack<TypePack>(asMutable(pack));
@@ -2613,7 +2621,10 @@ void TypeChecker2::visit(AstTypeFunction* ty)
 {
     visitGenerics(ty->generics, ty->genericPacks);
     visit(ty->argTypes);
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
         visit(ty->returnTypes);
+    else
+        visit(ty->returnTypes_DEPRECATED);
 }
 
 void TypeChecker2::visit(AstTypeTypeof* ty)
@@ -2937,7 +2948,7 @@ PropertyTypes TypeChecker2::lookupProp(
 
     if (normValid)
     {
-        for (const auto& [ty, _negations] : norm->classes.classes)
+        for (const auto& [ty, _negations] : norm->externTypes.externTypes)
         {
             fetch(ty);
 
@@ -3032,10 +3043,10 @@ void TypeChecker2::checkIndexTypeFromType(
         if (propTypes.foundOneProp())
             reportError(MissingUnionProperty{tableTy, propTypes.missingProp, prop}, location);
         // For class LValues, we don't want to report an extension error,
-        // because classes come into being with full knowledge of their
+        // because extern types come into being with full knowledge of their
         // shape. We instead want to report the unknown property error of
         // the `else` branch.
-        else if (context == ValueContext::LValue && !get<ClassType>(tableTy))
+        else if (context == ValueContext::LValue && !get<ExternType>(tableTy))
         {
             const auto lvPropTypes = lookupProp(norm.get(), prop, ValueContext::RValue, location, astIndexExprType, dummy);
             if (lvPropTypes.foundOneProp() && lvPropTypes.noneMissingProp())
@@ -3045,7 +3056,7 @@ void TypeChecker2::checkIndexTypeFromType(
             else
                 reportError(CannotExtendTable{tableTy, CannotExtendTable::Property, prop}, location);
         }
-        else if (context == ValueContext::RValue && !get<ClassType>(tableTy))
+        else if (context == ValueContext::RValue && !get<ExternType>(tableTy))
         {
             const auto rvPropTypes = lookupProp(norm.get(), prop, ValueContext::LValue, location, astIndexExprType, dummy);
             if (rvPropTypes.foundOneProp() && rvPropTypes.noneMissingProp())
@@ -3098,19 +3109,25 @@ PropertyType TypeChecker2::hasIndexTypeFromType(
                 return {NormalizationResult::True, {tt->indexer->indexResultType}};
         }
 
-
+        if (FFlag::LuauTypeCheckerStricterIndexCheck)
+        {
+            return {NormalizationResult::False, {builtinTypes->unknownType}};
+        }
+        else
+        {
             // if we are in a conditional context, we treat the property as present and `unknown` because
             // we may be _refining_ `tableTy` to include that property. we will want to revisit this a bit
             // in the future once luau has support for exact tables since this only applies when inexact.
             return {inConditional(typeContext) ? NormalizationResult::True : NormalizationResult::False, {builtinTypes->unknownType}};
         }
-    else if (const ClassType* cls = get<ClassType>(ty))
+    }
+    else if (const ExternType* cls = get<ExternType>(ty))
     {
         // If the property doesn't exist on the class, we consult the indexer
         // We need to check if the type of the index expression foo (x[foo])
         // is compatible with the indexer's indexType
         // Construct the intersection and test inhabitedness!
-        if (auto property = lookupClassProp(cls, prop))
+        if (auto property = lookupExternTypeProp(cls, prop))
             return {NormalizationResult::True, context == ValueContext::LValue ? property->writeTy : property->readTy};
         if (cls->indexer)
         {
@@ -3183,17 +3200,17 @@ void TypeChecker2::diagnoseMissingTableKey(UnknownProperty* utk, TypeErrorData&
 
     if (auto ttv = getTableType(utk->table))
         accumulate(ttv->props);
-    else if (auto ctv = get<ClassType>(follow(utk->table)))
+    else if (auto etv = get<ExternType>(follow(utk->table)))
     {
-        while (ctv)
+        while (etv)
         {
-            accumulate(ctv->props);
+            accumulate(etv->props);
 
-            if (!ctv->parent)
+            if (!etv->parent)
                 break;
 
-            ctv = get<ClassType>(*ctv->parent);
+            etv = get<ExternType>(*etv->parent);
-            LUAU_ASSERT(ctv);
+            LUAU_ASSERT(etv);
         }
     }
 

Analysis/src/TypeFunction.cpp

@@ -58,8 +58,6 @@ LUAU_FASTFLAGVARIABLE(LuauIndexTypeFunctionFunctionMetamethods)
 LUAU_FASTFLAGVARIABLE(LuauIntersectNotNil)
 LUAU_FASTFLAGVARIABLE(LuauSkipNoRefineDuringRefinement)
 LUAU_FASTFLAGVARIABLE(LuauMetatablesHaveLength)
-LUAU_FASTFLAGVARIABLE(LuauDontForgetToReduceUnionFunc)
-LUAU_FASTFLAGVARIABLE(LuauSearchForRefineableType)
 LUAU_FASTFLAGVARIABLE(LuauIndexAnyIsAny)
 LUAU_FASTFLAGVARIABLE(LuauFixCyclicIndexInIndexer)
 LUAU_FASTFLAGVARIABLE(LuauSimplyRefineNotNil)
@@ -68,6 +66,7 @@ LUAU_FASTFLAGVARIABLE(LuauNewTypeFunReductionChecks2)
 LUAU_FASTFLAGVARIABLE(LuauReduceUnionFollowUnionType)
 LUAU_FASTFLAG(LuauOptimizeFalsyAndTruthyIntersect)
 LUAU_FASTFLAGVARIABLE(LuauNarrowIntersectionNevers)
+LUAU_FASTFLAGVARIABLE(LuauRefineWaitForBlockedTypesInTarget)
 
 namespace Luau
 {
@@ -106,7 +105,7 @@ struct InstanceCollector_DEPRECATED : TypeOnceVisitor
             cyclicInstance.push_back(t);
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -182,7 +181,7 @@ struct InstanceCollector : TypeOnceVisitor
         }
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -270,7 +269,7 @@ struct UnscopedGenericFinder : TypeOnceVisitor
         return false;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -844,7 +843,7 @@ static std::optional<TypeFunctionReductionResult<TypeId>> tryDistributeTypeFunct
     {
         arguments[unionIndex] = option;
 
-        TypeFunctionReductionResult<TypeId> result = f(instance, arguments, packParams, ctx, args...);
+        TypeFunctionReductionResult<TypeId> result = f(instance, arguments, packParams, ctx, args...); // NOLINT
         blockedTypes.insert(blockedTypes.end(), result.blockedTypes.begin(), result.blockedTypes.end());
         if (result.reductionStatus != Reduction::MaybeOk)
             reductionStatus = result.reductionStatus;
@@ -869,7 +868,7 @@ static std::optional<TypeFunctionReductionResult<TypeId>> tryDistributeTypeFunct
             {},
         });
 
-        if (FFlag::LuauDontForgetToReduceUnionFunc && ctx->solver)
+        if (ctx->solver)
             ctx->pushConstraint(ReduceConstraint{resultTy});
 
         return {{resultTy, Reduction::MaybeOk, {}, {}}};
@@ -908,7 +907,7 @@ struct FindUserTypeFunctionBlockers : TypeOnceVisitor
         return true;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -1840,10 +1839,20 @@ TypeFunctionReductionResult<TypeId> orTypeFunction(
         return {rhsTy, Reduction::MaybeOk, {}, {}};
 
     // check to see if both operand types are resolved enough, and wait to reduce if not
+    if (FFlag::DebugLuauGreedyGeneralization)
+    {
+        if (is<BlockedType, PendingExpansionType, TypeFunctionInstanceType>(lhsTy))
+            return {std::nullopt, Reduction::MaybeOk, {lhsTy}, {}};
+        else if (is<BlockedType, PendingExpansionType, TypeFunctionInstanceType>(rhsTy))
+            return {std::nullopt, Reduction::MaybeOk, {rhsTy}, {}};
+    }
+    else
+    {
         if (isPending(lhsTy, ctx->solver))
             return {std::nullopt, Reduction::MaybeOk, {lhsTy}, {}};
         else if (isPending(rhsTy, ctx->solver))
             return {std::nullopt, Reduction::MaybeOk, {rhsTy}, {}};
+    }
 
     // Or evalutes to the LHS type if the LHS is truthy, and the RHS type if LHS is falsy.
     SimplifyResult filteredLhs = simplifyIntersection(ctx->builtins, ctx->arena, lhsTy, ctx->builtins->truthyType);
@@ -1877,10 +1886,20 @@ static TypeFunctionReductionResult<TypeId> comparisonTypeFunction(
     if (lhsTy == instance || rhsTy == instance)
         return {ctx->builtins->neverType, Reduction::MaybeOk, {}, {}};
 
+    if (FFlag::DebugLuauGreedyGeneralization)
+    {
+        if (is<BlockedType, PendingExpansionType, TypeFunctionInstanceType>(lhsTy))
+            return {std::nullopt, Reduction::MaybeOk, {lhsTy}, {}};
+        else if (is<BlockedType, PendingExpansionType, TypeFunctionInstanceType>(rhsTy))
+            return {std::nullopt, Reduction::MaybeOk, {rhsTy}, {}};
+    }
+    else
+    {
         if (isPending(lhsTy, ctx->solver))
             return {std::nullopt, Reduction::MaybeOk, {lhsTy}, {}};
         else if (isPending(rhsTy, ctx->solver))
             return {std::nullopt, Reduction::MaybeOk, {rhsTy}, {}};
+    }
 
     // Algebra Reduction Rules for comparison type functions
     // Note that comparing to never tells you nothing about the other operand
@@ -2130,7 +2149,7 @@ struct FindRefinementBlockers : TypeOnceVisitor
         return false;
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }
@@ -2241,8 +2260,12 @@ TypeFunctionReductionResult<TypeId> refineTypeFunction(
     for (size_t i = 1; i < typeParams.size(); i++)
         discriminantTypes.push_back(follow(typeParams.at(i)));
 
+    const bool targetIsPending = FFlag::DebugLuauGreedyGeneralization
+        ? is<BlockedType, PendingExpansionType, TypeFunctionInstanceType>(targetTy)
+        : isPending(targetTy, ctx->solver);
+
     // check to see if both operand types are resolved enough, and wait to reduce if not
-    if (isPending(targetTy, ctx->solver))
+    if (targetIsPending)
         return {std::nullopt, Reduction::MaybeOk, {targetTy}, {}};
     else
     {
@@ -2252,6 +2275,18 @@ TypeFunctionReductionResult<TypeId> refineTypeFunction(
                 return {std::nullopt, Reduction::MaybeOk, {t}, {}};
         }
     }
+
+    if (FFlag::LuauRefineWaitForBlockedTypesInTarget)
+    {
+        // If we have a blocked type in the target, we *could* potentially
+        // refine it, but more likely we end up with some type explosion in
+        // normalization.
+        FindRefinementBlockers frb;
+        frb.traverse(targetTy);
+        if (!frb.found.empty())
+            return {std::nullopt, Reduction::MaybeOk, {frb.found.begin(), frb.found.end()}, {}};
+    }
+
     // Refine a target type and a discriminant one at a time.
     // Returns result : TypeId, toBlockOn : vector<TypeId>
     auto stepRefine = [&ctx](TypeId target, TypeId discriminant) -> std::pair<TypeId, std::vector<TypeId>>
@@ -2281,8 +2316,6 @@ TypeFunctionReductionResult<TypeId> refineTypeFunction(
                 return {nullptr, {}};
         }
         else
-        {
-            if (FFlag::LuauSearchForRefineableType)
         {
             // If the discriminant type is only:
             // - The `*no-refine*` type or,
@@ -2292,18 +2325,6 @@ TypeFunctionReductionResult<TypeId> refineTypeFunction(
             crt.traverse(discriminant);
             if (!crt.found)
                 return {target, {}};
-            }
-            else
-            {
-                if (FFlag::LuauSkipNoRefineDuringRefinement)
-                    if (get<NoRefineType>(discriminant))
-                        return {target, {}};
-                if (auto nt = get<NegationType>(discriminant))
-                {
-                    if (get<NoRefineType>(follow(nt->ty)))
-                        return {target, {}};
-                }
-            }
 
             if (FFlag::LuauSimplyRefineNotNil)
             {
@@ -2329,8 +2350,32 @@ TypeFunctionReductionResult<TypeId> refineTypeFunction(
                 if (is<TableType>(target) || isSimpleDiscriminant(discriminant))
                 {
                     SimplifyResult result = simplifyIntersection(ctx->builtins, ctx->arena, target, discriminant);
+                    if (FFlag::DebugLuauGreedyGeneralization)
+                    {
+                        // Simplification considers free and generic types to be
+                        // 'blocking', but that's not suitable for refine<>.
+                        //
+                        // If we are only blocked on those types, we consider
+                        // the simplification a success and reduce.
+                        if (std::all_of(
+                                begin(result.blockedTypes),
+                                end(result.blockedTypes),
+                                [](auto&& v)
+                                {
+                                    return is<FreeType, GenericType>(follow(v));
+                                }
+                            ))
+                        {
+                            return {result.result, {}};
+                        }
+                        else
+                            return {nullptr, {result.blockedTypes.begin(), result.blockedTypes.end()}};
+                    }
+                    else
+                    {
                         if (!result.blockedTypes.empty())
                             return {nullptr, {result.blockedTypes.begin(), result.blockedTypes.end()}};
+                    }
                     return {result.result, {}};
                 }
             }
@@ -2684,7 +2729,7 @@ bool computeKeysOf(TypeId ty, Set<std::string>& result, DenseHashSet<TypeId>& se
         return res;
     }
 
-    if (auto classTy = get<ClassType>(ty))
+    if (auto classTy = get<ExternType>(ty))
     {
         for (auto [key, _] : classTy->props)
             result.insert(key);
@@ -2707,7 +2752,7 @@ bool computeKeysOf(TypeId ty, Set<std::string>& result, DenseHashSet<TypeId>& se
         return res;
     }
 
-    // this should not be reachable since the type should be a valid tables or classes part from normalization.
+    // this should not be reachable since the type should be a valid tables or extern types part from normalization.
     LUAU_ASSERT(false);
     return false;
 }
@@ -2733,9 +2778,9 @@ TypeFunctionReductionResult<TypeId> keyofFunctionImpl(
     if (!normTy)
         return {std::nullopt, Reduction::MaybeOk, {}, {}};
 
-    // if we don't have either just tables or just classes, we've got nothing to get keys of (at least until a future version perhaps adds classes
+    // if we don't have either just tables or just extern types, we've got nothing to get keys of (at least until a future version perhaps adds extern types
     // as well)
-    if (normTy->hasTables() == normTy->hasClasses())
+    if (normTy->hasTables() == normTy->hasExternTypes())
         return {std::nullopt, Reduction::Erroneous, {}, {}};
 
     // this is sort of atrocious, but we're trying to reject any type that has not normalized to a table or a union of tables.
@@ -2746,31 +2791,31 @@ TypeFunctionReductionResult<TypeId> keyofFunctionImpl(
     // we're going to collect the keys in here
     Set<std::string> keys{{}};
 
-    // computing the keys for classes
+    // computing the keys for extern types
-    if (normTy->hasClasses())
+    if (normTy->hasExternTypes())
     {
         LUAU_ASSERT(!normTy->hasTables());
 
-        // seen set for key computation for classes
+        // seen set for key computation for extern types
         DenseHashSet<TypeId> seen{{}};
 
-        auto classesIter = normTy->classes.ordering.begin();
+        auto externTypeIter = normTy->externTypes.ordering.begin();
-        auto classesIterEnd = normTy->classes.ordering.end();
+        auto externTypeIterEnd = normTy->externTypes.ordering.end();
-        LUAU_ASSERT(classesIter != classesIterEnd); // should be guaranteed by the `hasClasses` check earlier
+        LUAU_ASSERT(externTypeIter != externTypeIterEnd); // should be guaranteed by the `hasExternTypes` check earlier
 
         // collect all the properties from the first class type
-        if (!computeKeysOf(*classesIter, keys, seen, isRaw, ctx))
+        if (!computeKeysOf(*externTypeIter, keys, seen, isRaw, ctx))
             return {ctx->builtins->stringType, Reduction::MaybeOk, {}, {}}; // if it failed, we have a top type!
 
         // we need to look at each class to remove any keys that are not common amongst them all
-        while (++classesIter != classesIterEnd)
+        while (++externTypeIter != externTypeIterEnd)
         {
             seen.clear(); // we'll reuse the same seen set
 
             Set<std::string> localKeys{{}};
 
             // we can skip to the next class if this one is a top type
-            if (!computeKeysOf(*classesIter, localKeys, seen, isRaw, ctx))
+            if (!computeKeysOf(*externTypeIter, localKeys, seen, isRaw, ctx))
                 continue;
 
             for (auto& key : keys)
@@ -2785,7 +2830,7 @@ TypeFunctionReductionResult<TypeId> keyofFunctionImpl(
     // computing the keys for tables
     if (normTy->hasTables())
     {
-        LUAU_ASSERT(!normTy->hasClasses());
+        LUAU_ASSERT(!normTy->hasExternTypes());
 
         // seen set for key computation for tables
         DenseHashSet<TypeId> seen{{}};
@@ -2947,7 +2992,7 @@ bool searchPropsAndIndexer(
     return false;
 }
 
-/* Handles recursion / metamethods of tables/classes
+/* Handles recursion / metamethods of tables and extern types
    `isRaw` parameter indicates whether or not we should follow __index metamethods
    returns false if property of `ty` could not be found */
 bool tblIndexInto_DEPRECATED(TypeId indexer, TypeId indexee, DenseHashSet<TypeId>& result, NotNull<TypeFunctionContext> ctx, bool isRaw)
@@ -3122,11 +3167,11 @@ TypeFunctionReductionResult<TypeId> indexFunctionImpl(
             return {ctx->builtins->anyType, Reduction::MaybeOk, {}, {}};
     }
 
-    // if we don't have either just tables or just classes, we've got nothing to index into
+    // if we don't have either just tables or just extern types, we've got nothing to index into
-    if (indexeeNormTy->hasTables() == indexeeNormTy->hasClasses())
+    if (indexeeNormTy->hasTables() == indexeeNormTy->hasExternTypes())
         return {std::nullopt, Reduction::Erroneous, {}, {}};
 
-    // we're trying to reject any type that has not normalized to a table/class or a union of tables/classes.
+    // we're trying to reject any type that has not normalized to a table or extern type or a union of tables or extern types.
     if (indexeeNormTy->hasTops() || indexeeNormTy->hasBooleans() || indexeeNormTy->hasErrors() || indexeeNormTy->hasNils() ||
         indexeeNormTy->hasNumbers() || indexeeNormTy->hasStrings() || indexeeNormTy->hasThreads() || indexeeNormTy->hasBuffers() ||
         indexeeNormTy->hasFunctions() || indexeeNormTy->hasTyvars())
@@ -3157,18 +3202,18 @@ TypeFunctionReductionResult<TypeId> indexFunctionImpl(
 
     DenseHashSet<TypeId> properties{{}}; // vector of types that will be returned
 
-    if (indexeeNormTy->hasClasses())
+    if (indexeeNormTy->hasExternTypes())
     {
         LUAU_ASSERT(!indexeeNormTy->hasTables());
 
-        if (isRaw) // rawget should never reduce for classes (to match the behavior of the rawget global function)
+        if (isRaw) // rawget should never reduce for extern types (to match the behavior of the rawget global function)
             return {std::nullopt, Reduction::Erroneous, {}, {}};
 
-        // at least one class is guaranteed to be in the iterator by .hasClasses()
+        // at least one class is guaranteed to be in the iterator by .hasExternTypes()
-        for (auto classesIter = indexeeNormTy->classes.ordering.begin(); classesIter != indexeeNormTy->classes.ordering.end(); ++classesIter)
+        for (auto externTypeIter = indexeeNormTy->externTypes.ordering.begin(); externTypeIter != indexeeNormTy->externTypes.ordering.end(); ++externTypeIter)
         {
-            auto classTy = get<ClassType>(*classesIter);
+            auto externTy = get<ExternType>(*externTypeIter);
-            if (!classTy)
+            if (!externTy)
             {
                 LUAU_ASSERT(false); // this should not be possible according to normalization's spec
                 return {std::nullopt, Reduction::Erroneous, {}, {}};
@@ -3177,16 +3222,16 @@ TypeFunctionReductionResult<TypeId> indexFunctionImpl(
             for (TypeId ty : *typesToFind)
             {
                 // Search for all instances of indexer in class->props and class->indexer
-                if (searchPropsAndIndexer(ty, classTy->props, classTy->indexer, properties, ctx))
+                if (searchPropsAndIndexer(ty, externTy->props, externTy->indexer, properties, ctx))
                     continue; // Indexer was found in this class, so we can move on to the next
 
-                auto parent = classTy->parent;
+                auto parent = externTy->parent;
                 bool foundInParent = false;
                 while (parent && !foundInParent)
                 {
-                    auto parentClass = get<ClassType>(follow(*parent));
+                    auto parentExternType = get<ExternType>(follow(*parent));
-                    foundInParent = searchPropsAndIndexer(ty, parentClass->props, parentClass->indexer, properties, ctx);
+                    foundInParent = searchPropsAndIndexer(ty, parentExternType->props, parentExternType->indexer, properties, ctx);
-                    parent = parentClass->parent;
+                    parent = parentExternType->parent;
                 }
 
                 // we move on to the next type if any of the parents we went through had the property.
@@ -3198,7 +3243,7 @@ TypeFunctionReductionResult<TypeId> indexFunctionImpl(
                 // findMetatableEntry demands the ability to emit errors, so we must give it
                 // the necessary state to do that, even if we intend to just eat the errors.
                 ErrorVec dummy;
-                std::optional<TypeId> mmType = findMetatableEntry(ctx->builtins, dummy, *classesIter, "__index", Location{});
+                std::optional<TypeId> mmType = findMetatableEntry(ctx->builtins, dummy, *externTypeIter, "__index", Location{});
                 if (!mmType) // if a metatable does not exist, there is no where else to look
                     return {std::nullopt, Reduction::Erroneous, {}, {}};
 
@@ -3210,7 +3255,7 @@ TypeFunctionReductionResult<TypeId> indexFunctionImpl(
 
     if (indexeeNormTy->hasTables())
     {
-        LUAU_ASSERT(!indexeeNormTy->hasClasses());
+        LUAU_ASSERT(!indexeeNormTy->hasExternTypes());
 
         // at least one table is guaranteed to be in the iterator by .hasTables()
         for (auto tablesIter = indexeeNormTy->tables.begin(); tablesIter != indexeeNormTy->tables.end(); ++tablesIter)
@@ -3305,7 +3350,7 @@ TypeFunctionReductionResult<TypeId> setmetatableTypeFunction(
     // we're trying to reject any type that has not normalized to a table or a union/intersection of tables.
     if (targetNorm->hasTops() || targetNorm->hasBooleans() || targetNorm->hasErrors() || targetNorm->hasNils() || targetNorm->hasNumbers() ||
         targetNorm->hasStrings() || targetNorm->hasThreads() || targetNorm->hasBuffers() || targetNorm->hasFunctions() || targetNorm->hasTyvars() ||
-        targetNorm->hasClasses())
+        targetNorm->hasExternTypes())
         return {std::nullopt, Reduction::Erroneous, {}, {}};
 
     // if the supposed metatable is not a table, we will fail to reduce.
@@ -3379,7 +3424,7 @@ static TypeFunctionReductionResult<TypeId> getmetatableHelper(TypeId targetTy, c
         erroneous = false;
     }
 
-    if (auto clazz = get<ClassType>(targetTy))
+    if (auto clazz = get<ExternType>(targetTy))
     {
         metatable = clazz->metatable;
         erroneous = false;
@@ -3530,7 +3575,7 @@ BuiltinTypeFunctions::BuiltinTypeFunctions()
     , ltFunc{"lt", ltTypeFunction}
     , leFunc{"le", leTypeFunction}
     , eqFunc{"eq", eqTypeFunction}
-    , refineFunc{"refine", refineTypeFunction}
+    , refineFunc{"refine", refineTypeFunction, /*canReduceGenerics*/ FFlag::DebugLuauGreedyGeneralization}
     , singletonFunc{"singleton", singletonTypeFunction}
     , unionFunc{"union", unionTypeFunction}
     , intersectFunc{"intersect", intersectTypeFunction}

Analysis/src/TypeFunctionReductionGuesser.cpp

@@ -46,7 +46,7 @@ struct InstanceCollector2 : TypeOnceVisitor
             cyclicInstance.insert(t);
     }
 
-    bool visit(TypeId ty, const ClassType&) override
+    bool visit(TypeId ty, const ExternType&) override
     {
         return false;
     }

Analysis/src/TypeFunctionRuntime.cpp

@@ -15,6 +15,7 @@
 
 LUAU_DYNAMIC_FASTINT(LuauTypeFunctionSerdeIterationLimit)
 LUAU_FASTFLAGVARIABLE(LuauTypeFunReadWriteParents)
+LUAU_FASTFLAGVARIABLE(LuauTypeFunOptional)
 
 namespace Luau
 {
@@ -154,7 +155,7 @@ static std::string getTag(lua_State* L, TypeFunctionTypeId ty)
         return "table";
     else if (get<TypeFunctionFunctionType>(ty))
         return "function";
-    else if (get<TypeFunctionClassType>(ty))
+    else if (get<TypeFunctionExternType>(ty))
         return "class";
     else if (get<TypeFunctionGenericType>(ty))
         return "generic";
@@ -315,6 +316,38 @@ static int getSingletonValue(lua_State* L)
     luaL_error(L, "type.value: can't call `value` method on `%s` type", getTag(L, self).c_str());
 }
 
+// Luau: `types.optional(ty: type) -> type`
+// Returns the type instance representing an optional version of `ty`.
+// If `ty` is a union, this adds `nil` to the components of the union.
+// Otherwise, makes a union of the two things.
+static int createOptional(lua_State* L)
+{
+    LUAU_ASSERT(FFlag::LuauTypeFunOptional);
+
+    int argumentCount = lua_gettop(L);
+    if (argumentCount != 1)
+        luaL_error(L, "types.optional: expected 1 argument, but got %d", argumentCount);
+
+    TypeFunctionTypeId argument = getTypeUserData(L, 1);
+
+    std::vector<TypeFunctionTypeId> components;
+
+    if (auto unionTy = get<TypeFunctionUnionType>(argument))
+    {
+        components.reserve(unionTy->components.size() + 1);
+
+        components.insert(components.begin(), unionTy->components.begin(), unionTy->components.end());
+    }
+    else
+        components.emplace_back(argument);
+
+    components.emplace_back(allocateTypeFunctionType(L, TypeFunctionPrimitiveType(TypeFunctionPrimitiveType::NilType)));
+
+    allocTypeUserData(L, TypeFunctionUnionType{components});
+
+    return 1;
+}
+
 // Luau: `types.unionof(...: type) -> type`
 // Returns the type instance representing union
 static int createUnion(lua_State* L)
@@ -1114,7 +1147,7 @@ static int getClassParent_DEPRECATED(lua_State* L)
         luaL_error(L, "type.parent: expected 1 arguments, but got %d", argumentCount);
 
     TypeFunctionTypeId self = getTypeUserData(L, 1);
-    auto tfct = get<TypeFunctionClassType>(self);
+    auto tfct = get<TypeFunctionExternType>(self);
     if (!tfct)
         luaL_error(L, "type.parent: expected self to be a class, but got %s instead", getTag(L, self).c_str());
 
@@ -1136,7 +1169,7 @@ static int getReadParent(lua_State* L)
         luaL_error(L, "type.parent: expected 1 arguments, but got %d", argumentCount);
 
     TypeFunctionTypeId self = getTypeUserData(L, 1);
-    auto tfct = get<TypeFunctionClassType>(self);
+    auto tfct = get<TypeFunctionExternType>(self);
     if (!tfct)
         luaL_error(L, "type.parent: expected self to be a class, but got %s instead", getTag(L, self).c_str());
 
@@ -1158,7 +1191,7 @@ static int getWriteParent(lua_State* L)
         luaL_error(L, "type.parent: expected 1 arguments, but got %d", argumentCount);
 
     TypeFunctionTypeId self = getTypeUserData(L, 1);
-    auto tfct = get<TypeFunctionClassType>(self);
+    auto tfct = get<TypeFunctionExternType>(self);
     if (!tfct)
         luaL_error(L, "type.parent: expected self to be a class, but got %s instead", getTag(L, self).c_str());
 
@@ -1242,7 +1275,7 @@ static int getProps(lua_State* L)
         return 1;
     }
 
-    if (auto tfct = get<TypeFunctionClassType>(self))
+    if (auto tfct = get<TypeFunctionExternType>(self))
     {
         lua_createtable(L, int(tfct->props.size()), 0);
         for (auto& [name, prop] : tfct->props)
@@ -1305,7 +1338,7 @@ static int getIndexer(lua_State* L)
         return 1;
     }
 
-    if (auto tfct = get<TypeFunctionClassType>(self))
+    if (auto tfct = get<TypeFunctionExternType>(self))
     {
         // if the indexer does not exist, we should return nil
         if (!tfct->indexer.has_value())
@@ -1353,7 +1386,7 @@ static int getReadIndexer(lua_State* L)
         return 1;
     }
 
-    if (auto tfct = get<TypeFunctionClassType>(self))
+    if (auto tfct = get<TypeFunctionExternType>(self))
     {
         // if the indexer does not exist, we should return nil
         if (!tfct->indexer.has_value())
@@ -1399,7 +1432,7 @@ static int getWriteIndexer(lua_State* L)
         return 1;
     }
 
-    if (auto tfct = get<TypeFunctionClassType>(self))
+    if (auto tfct = get<TypeFunctionExternType>(self))
     {
         // if the indexer does not exist, we should return nil
         if (!tfct->indexer.has_value())
@@ -1439,7 +1472,7 @@ static int getMetatable(lua_State* L)
         return 1;
     }
 
-    if (auto tfct = get<TypeFunctionClassType>(self))
+    if (auto tfct = get<TypeFunctionExternType>(self))
     {
         // if the metatable does not exist, we should return nil
         if (!tfct->metatable.has_value())
@@ -1524,6 +1557,7 @@ void registerTypesLibrary(lua_State* L)
         {"copy", deepCopy},
         {"generic", createGeneric},
 
+        {(FFlag::LuauTypeFunOptional) ? "optional" : nullptr, (FFlag::LuauTypeFunOptional) ? createOptional : nullptr},
         {nullptr, nullptr}
     };
 
@@ -1593,7 +1627,7 @@ void registerTypeUserData(lua_State* L)
         // Union and Intersection type methods
         {"components", getComponents},
 
-        // Class type methods
+        //  Extern type methods
         {FFlag::LuauTypeFunReadWriteParents ? "readparent" : "parent", FFlag::LuauTypeFunReadWriteParents ? getReadParent : getClassParent_DEPRECATED},
 
         // Function type methods (cont.)
@@ -1604,7 +1638,7 @@ void registerTypeUserData(lua_State* L)
         {"name", getGenericName},
         {"ispack", getGenericIsPack},
 
-        // move this under Class type methods when removing FFlagLuauTypeFunReadWriteParents
+        // move this under extern type methods when removing FFlagLuauTypeFunReadWriteParents
         {FFlag::LuauTypeFunReadWriteParents ? "writeparent" : nullptr, FFlag::LuauTypeFunReadWriteParents ? getWriteParent : nullptr},
 
         {nullptr, nullptr}
@@ -1903,12 +1937,12 @@ bool areEqual(SeenSet& seen, const TypeFunctionFunctionType& lhs, const TypeFunc
     return true;
 }
 
-bool areEqual(SeenSet& seen, const TypeFunctionClassType& lhs, const TypeFunctionClassType& rhs)
+bool areEqual(SeenSet& seen, const TypeFunctionExternType& lhs, const TypeFunctionExternType& rhs)
 {
     if (seenSetContains(seen, &lhs, &rhs))
         return true;
 
-    return lhs.classTy == rhs.classTy;
+    return lhs.externTy == rhs.externTy;
 }
 
 bool areEqual(SeenSet& seen, const TypeFunctionType& lhs, const TypeFunctionType& rhs)
@@ -1976,8 +2010,8 @@ bool areEqual(SeenSet& seen, const TypeFunctionType& lhs, const TypeFunctionType
     }
 
     {
-        const TypeFunctionClassType* lf = get<TypeFunctionClassType>(&lhs);
+        const TypeFunctionExternType* lf = get<TypeFunctionExternType>(&lhs);
-        const TypeFunctionClassType* rf = get<TypeFunctionClassType>(&rhs);
+        const TypeFunctionExternType* rf = get<TypeFunctionExternType>(&rhs);
         if (lf && rf)
             return areEqual(seen, *lf, *rf);
     }
@@ -2266,7 +2300,7 @@ private:
             TypeFunctionTypePackId emptyTypePack = typeFunctionRuntime->typePackArena.allocate(TypeFunctionTypePack{});
             target = typeFunctionRuntime->typeArena.allocate(TypeFunctionFunctionType{{}, {}, emptyTypePack, emptyTypePack});
         }
-        else if (auto c = get<TypeFunctionClassType>(ty))
+        else if (auto c = get<TypeFunctionExternType>(ty))
             target = ty; // Don't copy a class since they are immutable
         else if (auto g = get<TypeFunctionGenericType>(ty))
             target = typeFunctionRuntime->typeArena.allocate(TypeFunctionGenericType{g->isNamed, g->isPack, g->name});
@@ -2321,7 +2355,7 @@ private:
             cloneChildren(t1, t2);
         else if (auto [f1, f2] = std::tuple{getMutable<TypeFunctionFunctionType>(ty), getMutable<TypeFunctionFunctionType>(tfti)}; f1 && f2)
             cloneChildren(f1, f2);
-        else if (auto [c1, c2] = std::tuple{getMutable<TypeFunctionClassType>(ty), getMutable<TypeFunctionClassType>(tfti)}; c1 && c2)
+        else if (auto [c1, c2] = std::tuple{getMutable<TypeFunctionExternType>(ty), getMutable<TypeFunctionExternType>(tfti)}; c1 && c2)
             cloneChildren(c1, c2);
         else if (auto [g1, g2] = std::tuple{getMutable<TypeFunctionGenericType>(ty), getMutable<TypeFunctionGenericType>(tfti)}; g1 && g2)
             cloneChildren(g1, g2);
@@ -2431,7 +2465,7 @@ private:
         f2->retTypes = shallowClone(f1->retTypes);
     }
 
-    void cloneChildren(TypeFunctionClassType* c1, TypeFunctionClassType* c2)
+    void cloneChildren(TypeFunctionExternType* c1, TypeFunctionExternType* c2)
     {
         // noop.
     }

Analysis/src/TypeFunctionRuntimeBuilder.cpp

@@ -206,12 +206,12 @@ private:
             TypeFunctionTypePackId emptyTypePack = typeFunctionRuntime->typePackArena.allocate(TypeFunctionTypePack{});
             target = typeFunctionRuntime->typeArena.allocate(TypeFunctionFunctionType{{}, {}, emptyTypePack, emptyTypePack});
         }
-        else if (auto c = get<ClassType>(ty))
+        else if (auto c = get<ExternType>(ty))
         {
             // 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
             target = typeFunctionRuntime->typeArena.allocate(
-                TypeFunctionClassType{{}, std::nullopt, std::nullopt, std::nullopt, std::nullopt, std::nullopt, ty}
+                TypeFunctionExternType{{}, std::nullopt, std::nullopt, std::nullopt, std::nullopt, std::nullopt, ty}
             );
         }
         else if (auto g = get<GenericType>(ty))
@@ -291,7 +291,7 @@ private:
             serializeChildren(m1, m2);
         else if (auto [f1, f2] = std::tuple{get<FunctionType>(ty), getMutable<TypeFunctionFunctionType>(tfti)}; f1 && f2)
             serializeChildren(f1, f2);
-        else if (auto [c1, c2] = std::tuple{get<ClassType>(ty), getMutable<TypeFunctionClassType>(tfti)}; c1 && c2)
+        else if (auto [c1, c2] = std::tuple{get<ExternType>(ty), getMutable<TypeFunctionExternType>(tfti)}; c1 && c2)
             serializeChildren(c1, c2);
         else if (auto [g1, g2] = std::tuple{get<GenericType>(ty), getMutable<TypeFunctionGenericType>(tfti)}; g1 && g2)
             serializeChildren(g1, g2);
@@ -411,7 +411,7 @@ private:
         f2->retTypes = shallowSerialize(f1->retTypes);
     }
 
-    void serializeChildren(const ClassType* c1, TypeFunctionClassType* c2)
+    void serializeChildren(const ExternType* c1, TypeFunctionExternType* c2)
     {
         for (const auto& [k, p] : c1->props)
         {
@@ -702,9 +702,9 @@ private:
             TypePackId emptyTypePack = state->ctx->arena->addTypePack(TypePack{});
             target = state->ctx->arena->addType(FunctionType{emptyTypePack, emptyTypePack, {}, false});
         }
-        else if (auto c = get<TypeFunctionClassType>(ty))
+        else if (auto c = get<TypeFunctionExternType>(ty))
         {
-            target = c->classTy;
+            target = c->externTy;
         }
         else if (auto g = get<TypeFunctionGenericType>(ty))
         {
@@ -811,7 +811,7 @@ private:
             deserializeChildren(m2, m1);
         else if (auto [f1, f2] = std::tuple{getMutable<FunctionType>(ty), getMutable<TypeFunctionFunctionType>(tfti)}; f1 && f2)
             deserializeChildren(f2, f1);
-        else if (auto [c1, c2] = std::tuple{getMutable<ClassType>(ty), getMutable<TypeFunctionClassType>(tfti)}; c1 && c2)
+        else if (auto [c1, c2] = std::tuple{getMutable<ExternType>(ty), getMutable<TypeFunctionExternType>(tfti)}; c1 && c2)
             deserializeChildren(c2, c1);
         else if (auto [g1, g2] = std::tuple{getMutable<GenericType>(ty), getMutable<TypeFunctionGenericType>(tfti)}; g1 && g2)
             deserializeChildren(g2, g1);
@@ -972,7 +972,7 @@ private:
             f1->retTypes = shallowDeserialize(f2->retTypes);
     }
 
-    void deserializeChildren(TypeFunctionClassType* c2, ClassType* c1)
+    void deserializeChildren(TypeFunctionExternType* c2, ExternType* c1)
     {
         // noop.
     }

Analysis/src/TypeInfer.cpp

@@ -32,8 +32,8 @@ LUAU_FASTINTVARIABLE(LuauVisitRecursionLimit, 500)
 LUAU_FASTFLAG(LuauKnowsTheDataModel3)
 LUAU_FASTFLAGVARIABLE(DebugLuauFreezeDuringUnification)
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
-LUAU_FASTFLAG(LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
-LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
+
 LUAU_FASTFLAG(LuauRetainDefinitionAliasLocations)
 LUAU_FASTFLAGVARIABLE(LuauStatForInFix)
 LUAU_FASTFLAGVARIABLE(LuauReduceCheckBinaryExprStackPressure)
@@ -44,7 +44,7 @@ namespace Luau
 
 static bool typeCouldHaveMetatable(TypeId ty)
 {
-    return get<TableType>(follow(ty)) || get<ClassType>(follow(ty)) || get<MetatableType>(follow(ty));
+    return get<TableType>(follow(ty)) || get<ExternType>(follow(ty)) || get<MetatableType>(follow(ty));
 }
 
 static void defaultLuauPrintLine(const std::string& s)
@@ -318,7 +318,7 @@ ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mo
     unifierState.skipCacheForType.clear();
 
     duplicateTypeAliases.clear();
-    incorrectClassDefinitions.clear();
+    incorrectExternTypeDefinitions.clear();
 
     return std::move(currentModule);
 }
@@ -383,7 +383,7 @@ ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStat& program)
     }
     else if (auto global = program.as<AstStatDeclareFunction>())
         return check(scope, *global);
-    else if (auto global = program.as<AstStatDeclareClass>())
+    else if (auto global = program.as<AstStatDeclareExternType>())
         return check(scope, *global);
     else if (auto errorStatement = program.as<AstStatError>())
     {
@@ -498,9 +498,9 @@ ControlFlow TypeChecker::checkBlockWithoutRecursionCheck(const ScopePtr& scope,
             prototype(scope, *typealias, subLevel);
             ++subLevel;
         }
-        else if (const auto& declaredClass = stat->as<AstStatDeclareClass>())
+        else if (const auto& declaredExternType = stat->as<AstStatDeclareExternType>())
         {
-            prototype(scope, *declaredClass);
+            prototype(scope, *declaredExternType);
         }
     }
 
@@ -788,7 +788,7 @@ struct Demoter : Substitution
 
     bool ignoreChildren(TypeId ty) override
     {
-        if (get<ClassType>(ty))
+        if (get<ExternType>(ty))
             return true;
 
         return false;
@@ -798,8 +798,7 @@ struct Demoter : Substitution
     {
         auto ftv = get<FreeType>(ty);
         LUAU_ASSERT(ftv);
-        return FFlag::LuauFreeTypesMustHaveBounds ? arena->freshType(builtins, demotedLevel(ftv->level))
+        return arena->freshType(builtins, demotedLevel(ftv->level));
-                                                  : addType(FreeType{demotedLevel(ftv->level)});
     }
 
     TypePackId clean(TypePackId tp) override
@@ -1686,82 +1685,82 @@ void TypeChecker::prototype(const ScopePtr& scope, const AstStatTypeAlias& typea
     }
 }
 
-void TypeChecker::prototype(const ScopePtr& scope, const AstStatDeclareClass& declaredClass)
+void TypeChecker::prototype(const ScopePtr& scope, const AstStatDeclareExternType& declaredExternType)
 {
-    std::optional<TypeId> superTy = std::make_optional(builtinTypes->classType);
+    std::optional<TypeId> superTy = std::make_optional(builtinTypes->externType);
-    if (declaredClass.superName)
+    if (declaredExternType.superName)
     {
-        Name superName = Name(declaredClass.superName->value);
+        Name superName = Name(declaredExternType.superName->value);
         std::optional<TypeFun> lookupType = scope->lookupType(superName);
 
         if (!lookupType)
         {
-            reportError(declaredClass.location, UnknownSymbol{superName, UnknownSymbol::Type});
+            reportError(declaredExternType.location, UnknownSymbol{superName, UnknownSymbol::Type});
-            incorrectClassDefinitions.insert(&declaredClass);
+            incorrectExternTypeDefinitions.insert(&declaredExternType);
             return;
         }
 
-        // We don't have generic classes, so this assertion _should_ never be hit.
+        // We don't have generic extern types, so this assertion _should_ never be hit.
         LUAU_ASSERT(lookupType->typeParams.size() == 0 && lookupType->typePackParams.size() == 0);
         superTy = lookupType->type;
 
-        if (!get<ClassType>(follow(*superTy)))
+        if (!get<ExternType>(follow(*superTy)))
         {
             reportError(
-                declaredClass.location,
+                declaredExternType.location,
-                GenericError{format("Cannot use non-class type '%s' as a superclass of class '%s'", superName.c_str(), declaredClass.name.value)}
+                GenericError{format("Cannot use non-class type '%s' as a superclass of class '%s'", superName.c_str(), declaredExternType.name.value)}
             );
-            incorrectClassDefinitions.insert(&declaredClass);
+            incorrectExternTypeDefinitions.insert(&declaredExternType);
             return;
         }
     }
 
-    Name className(declaredClass.name.value);
+    Name className(declaredExternType.name.value);
 
-    TypeId classTy = addType(ClassType(className, {}, superTy, std::nullopt, {}, {}, currentModule->name, declaredClass.location));
+    TypeId classTy = addType(ExternType(className, {}, superTy, std::nullopt, {}, {}, currentModule->name, declaredExternType.location));
-    ClassType* ctv = getMutable<ClassType>(classTy);
+    ExternType* etv = getMutable<ExternType>(classTy);
     TypeId metaTy = addType(TableType{TableState::Sealed, scope->level});
 
-    ctv->metatable = metaTy;
+    etv->metatable = metaTy;
     if (FFlag::LuauRetainDefinitionAliasLocations)
-        scope->exportedTypeBindings[className] = TypeFun{{}, classTy, declaredClass.location};
+        scope->exportedTypeBindings[className] = TypeFun{{}, classTy, declaredExternType.location};
     else
         scope->exportedTypeBindings[className] = TypeFun{{}, classTy};
 }
 
-ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStatDeclareClass& declaredClass)
+ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStatDeclareExternType& declaredExternType)
 {
-    Name className(declaredClass.name.value);
+    Name className(declaredExternType.name.value);
 
     // Don't bother checking if the class definition was incorrect
-    if (incorrectClassDefinitions.find(&declaredClass))
+    if (incorrectExternTypeDefinitions.find(&declaredExternType))
         return ControlFlow::None;
 
     std::optional<TypeFun> binding;
     if (auto it = scope->exportedTypeBindings.find(className); it != scope->exportedTypeBindings.end())
         binding = it->second;
 
-    // This class definition must have been `prototype()`d first.
+    // This extern type definition must have been `prototype()`d first.
     if (!binding)
-        ice("Class not predeclared");
+        ice("Extern type not predeclared");
 
-    TypeId classTy = binding->type;
+    TypeId externTy = binding->type;
-    ClassType* ctv = getMutable<ClassType>(classTy);
+    ExternType* etv = getMutable<ExternType>(externTy);
 
-    if (!ctv->metatable)
+    if (!etv->metatable)
-        ice("No metatable for declared class");
+        ice("No metatable for declared extern type");
 
-    if (const auto& indexer = declaredClass.indexer)
+    if (const auto& indexer = declaredExternType.indexer)
-        ctv->indexer = TableIndexer(resolveType(scope, *indexer->indexType), resolveType(scope, *indexer->resultType));
+        etv->indexer = TableIndexer(resolveType(scope, *indexer->indexType), resolveType(scope, *indexer->resultType));
 
-    TableType* metatable = getMutable<TableType>(*ctv->metatable);
+    TableType* metatable = getMutable<TableType>(*etv->metatable);
-    for (const AstDeclaredClassProp& prop : declaredClass.props)
+    for (const AstDeclaredExternTypeProperty& prop : declaredExternType.props)
     {
         Name propName(prop.name.value);
         TypeId propTy = resolveType(scope, *prop.ty);
 
         bool assignToMetatable = isMetamethod(propName);
-        Luau::ClassType::Props& assignTo = assignToMetatable ? metatable->props : ctv->props;
+        Luau::ExternType::Props& assignTo = assignToMetatable ? metatable->props : etv->props;
 
         // Function types always take 'self', but this isn't reflected in the
         // parsed annotation. Add it here.
@@ -1770,7 +1769,7 @@ ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStatDeclareClass&
             if (FunctionType* ftv = getMutable<FunctionType>(propTy))
             {
                 ftv->argNames.insert(ftv->argNames.begin(), FunctionArgument{"self", {}});
-                ftv->argTypes = addTypePack(TypePack{{classTy}, ftv->argTypes});
+                ftv->argTypes = addTypePack(TypePack{{externTy}, ftv->argTypes});
                 ftv->hasSelf = true;
 
                 FunctionDefinition defn;
@@ -1813,7 +1812,7 @@ ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStatDeclareClass&
             }
             else
             {
-                reportError(declaredClass.location, GenericError{format("Cannot overload non-function class member '%s'", propName.c_str())});
+                reportError(declaredExternType.location, GenericError{format("Cannot overload non-function class member '%s'", propName.c_str())});
             }
         }
     }
@@ -1852,7 +1851,8 @@ ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStatDeclareFuncti
     );
 
     TypePackId argPack = resolveTypePack(funScope, global.params);
-    TypePackId retPack = resolveTypePack(funScope, global.retTypes);
+    TypePackId retPack =
+        FFlag::LuauStoreReturnTypesAsPackOnAst ? resolveTypePack(funScope, *global.retTypes) : resolveTypePack(funScope, global.retTypes_DEPRECATED);
 
     FunctionDefinition defn;
 
@@ -2137,9 +2137,9 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromTypeImpl(
         if (auto found = findTablePropertyRespectingMeta(type, name, location, addErrors))
             return *found;
     }
-    else if (const ClassType* cls = get<ClassType>(type))
+    else if (const ExternType* cls = get<ExternType>(type))
     {
-        const Property* prop = lookupClassProp(cls, name);
+        const Property* prop = lookupExternTypeProp(cls, name);
         if (prop)
             return prop->type();
 
@@ -3462,14 +3462,14 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
             return errorRecoveryType(scope);
         }
     }
-    else if (const ClassType* lhsClass = get<ClassType>(lhs))
+    else if (const ExternType* lhsExternType = get<ExternType>(lhs))
     {
-        if (const Property* prop = lookupClassProp(lhsClass, name))
+        if (const Property* prop = lookupExternTypeProp(lhsExternType, name))
         {
             return prop->type();
         }
 
-        if (auto indexer = lhsClass->indexer)
+        if (auto indexer = lhsExternType->indexer)
         {
             Unifier state = mkUnifier(scope, expr.location);
             state.tryUnify(stringType, indexer->indexType);
@@ -3521,14 +3521,14 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
 
     if (value)
     {
-        if (const ClassType* exprClass = get<ClassType>(exprType))
+        if (const ExternType* exprExternType = get<ExternType>(exprType))
         {
-            if (const Property* prop = lookupClassProp(exprClass, value->value.data))
+            if (const Property* prop = lookupExternTypeProp(exprExternType, value->value.data))
             {
                 return prop->type();
             }
 
-            if (auto indexer = exprClass->indexer)
+            if (auto indexer = exprExternType->indexer)
             {
                 unify(stringType, indexer->indexType, scope, expr.index->location);
                 return indexer->indexResultType;
@@ -3554,20 +3554,20 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
     }
     else
     {
-        if (const ClassType* exprClass = get<ClassType>(exprType))
+        if (const ExternType* exprExternType = get<ExternType>(exprType))
         {
-            if (auto indexer = exprClass->indexer)
+            if (auto indexer = exprExternType->indexer)
             {
                 unify(indexType, indexer->indexType, scope, expr.index->location);
                 return indexer->indexResultType;
             }
         }
 
-        if (const ClassType* exprClass = get<ClassType>(exprType))
+        if (const ExternType* exprExternType = get<ExternType>(exprType))
         {
             if (isNonstrictMode())
                 return unknownType;
-            reportError(TypeError{expr.location, DynamicPropertyLookupOnClassesUnsafe{exprType}});
+            reportError(TypeError{expr.location, DynamicPropertyLookupOnExternTypesUnsafe{exprType}});
             return errorRecoveryType(scope);
         }
     }
@@ -3848,8 +3848,10 @@ std::pair<TypeId, ScopePtr> TypeChecker::checkFunctionSignature(
     auto [generics, genericPacks] = createGenericTypes(funScope, std::nullopt, expr, expr.generics, expr.genericPacks);
 
     TypePackId retPack;
-    if (expr.returnAnnotation)
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst && expr.returnAnnotation)
         retPack = resolveTypePack(funScope, *expr.returnAnnotation);
+    else if (!FFlag::LuauStoreReturnTypesAsPackOnAst && expr.returnAnnotation_DEPRECATED)
+        retPack = resolveTypePack(funScope, *expr.returnAnnotation_DEPRECATED);
     else if (isNonstrictMode())
         retPack = anyTypePack;
     else if (expectedFunctionType && expectedFunctionType->generics.empty() && expectedFunctionType->genericPacks.empty())
@@ -4056,7 +4058,8 @@ void TypeChecker::checkFunctionBody(const ScopePtr& scope, TypeId ty, const AstE
             // If we're in nonstrict mode we want to only report this missing return
             // statement if there are type annotations on the function. In strict mode
             // we report it regardless.
-            if (!isNonstrictMode() || function.returnAnnotation)
+            if (!isNonstrictMode() ||
+                (FFlag::LuauStoreReturnTypesAsPackOnAst ? function.returnAnnotation != nullptr : function.returnAnnotation_DEPRECATED.has_value()))
             {
                 reportError(getEndLocation(function), FunctionExitsWithoutReturning{funTy->retTypes});
             }
@@ -4611,9 +4614,9 @@ std::unique_ptr<WithPredicate<TypePackId>> TypeChecker::checkCallOverload(
     {
         callTy = getIndexTypeFromType(scope, mttv->metatable, "__call", expr.func->location, /* addErrors= */ false);
     }
-    else if (const ClassType* ctv = get<ClassType>(fn); ctv && ctv->metatable)
+    else if (const ExternType* etv = get<ExternType>(fn); etv && etv->metatable)
     {
-        callTy = getIndexTypeFromType(scope, *ctv->metatable, "__call", expr.func->location, /* addErrors= */ false);
+        callTy = getIndexTypeFromType(scope, *etv->metatable, "__call", expr.func->location, /* addErrors= */ false);
     }
 
     if (callTy)
@@ -5316,17 +5319,17 @@ void TypeChecker::diagnoseMissingTableKey(UnknownProperty* utk, TypeErrorData& d
 
     if (auto ttv = getTableType(utk->table))
         accumulate(ttv->props);
-    else if (auto ctv = get<ClassType>(follow(utk->table)))
+    else if (auto etv = get<ExternType>(follow(utk->table)))
     {
-        while (ctv)
+        while (etv)
         {
-            accumulate(ctv->props);
+            accumulate(etv->props);
 
-            if (!ctv->parent)
+            if (!etv->parent)
                 break;
 
-            ctv = get<ClassType>(*ctv->parent);
+            etv = get<ExternType>(*etv->parent);
-            LUAU_ASSERT(ctv);
+            LUAU_ASSERT(etv);
         }
     }
 
@@ -5405,8 +5408,7 @@ TypeId TypeChecker::freshType(const ScopePtr& scope)
 
 TypeId TypeChecker::freshType(TypeLevel level)
 {
-    return FFlag::LuauFreeTypesMustHaveBounds ? currentModule->internalTypes.freshType(builtinTypes, level)
+    return currentModule->internalTypes.freshType(builtinTypes, level);
-                                              : currentModule->internalTypes.addType(Type(FreeType(level)));
 }
 
 TypeId TypeChecker::singletonType(bool value)
@@ -5803,7 +5805,8 @@ TypeId TypeChecker::resolveTypeWorker(const ScopePtr& scope, const AstType& anno
         auto [generics, genericPacks] = createGenericTypes(funcScope, std::nullopt, annotation, func->generics, func->genericPacks);
 
         TypePackId argTypes = resolveTypePack(funcScope, func->argTypes);
-        TypePackId retTypes = resolveTypePack(funcScope, func->returnTypes);
+        TypePackId retTypes = FFlag::LuauStoreReturnTypesAsPackOnAst ? resolveTypePack(funcScope, *func->returnTypes)
+                                                                     : resolveTypePack(funcScope, func->returnTypes_DEPRECATED);
 
         std::vector<TypeId> genericTys;
         genericTys.reserve(generics.size());
@@ -5854,13 +5857,9 @@ TypeId TypeChecker::resolveTypeWorker(const ScopePtr& scope, const AstType& anno
         return builtinTypes->nilType;
     }
     else if (const auto& un = annotation.as<AstTypeUnion>())
-    {
-        if (FFlag::LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
     {
         if (un->types.size == 1)
             return resolveType(scope, *un->types.data[0]);
-        }
-
         std::vector<TypeId> types;
         for (AstType* ann : un->types)
             types.push_back(resolveType(scope, *ann));
@@ -5868,13 +5867,9 @@ TypeId TypeChecker::resolveTypeWorker(const ScopePtr& scope, const AstType& anno
         return addType(UnionType{types});
     }
     else if (const auto& un = annotation.as<AstTypeIntersection>())
-    {
-        if (FFlag::LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
     {
         if (un->types.size == 1)
             return resolveType(scope, *un->types.data[0]);
-        }
-
         std::vector<TypeId> types;
         for (AstType* ann : un->types)
             types.push_back(resolveType(scope, *ann));
@@ -6481,7 +6476,7 @@ void TypeChecker::resolve(const TypeGuardPredicate& typeguardP, RefinementMap& r
         return refine(
             [](TypeId ty) -> bool
             {
-                return get<ClassType>(ty);
+                return get<ExternType>(ty);
             }
         );
     }
@@ -6496,13 +6491,13 @@ void TypeChecker::resolve(const TypeGuardPredicate& typeguardP, RefinementMap& r
     TypeId type = follow(typeFun->type);
 
     // You cannot refine to the top class type.
-    if (type == builtinTypes->classType)
+    if (type == builtinTypes->externType)
     {
         return addRefinement(refis, typeguardP.lvalue, errorRecoveryType(scope));
     }
 
-    // We're only interested in the root class of any classes.
+    // We're only interested in the root type of any extern type.
-    if (auto ctv = get<ClassType>(type); !ctv || (ctv->parent != builtinTypes->classType && !hasTag(type, kTypeofRootTag)))
+    if (auto etv = get<ExternType>(type); !etv || (etv->parent != builtinTypes->externType && !hasTag(type, kTypeofRootTag)))
         return addRefinement(refis, typeguardP.lvalue, errorRecoveryType(scope));
 
     // This probably hints at breaking out type filtering functions from the predicate solver so that typeof is not tightly coupled with IsA.

Analysis/src/TypePack.cpp

@@ -208,6 +208,26 @@ TypePackIterator end(TypePackId tp)
     return TypePackIterator{};
 }
 
+TypePackId getTail(TypePackId tp)
+{
+    DenseHashSet<TypePackId> seen{nullptr};
+    while (tp)
+    {
+        tp = follow(tp);
+
+        if (seen.contains(tp))
+            break;
+        seen.insert(tp);
+
+        if (auto pack = get<TypePack>(tp); pack && pack->tail)
+            tp = *pack->tail;
+        else
+            break;
+    }
+
+    return follow(tp);
+}
+
 bool areEqual(SeenSet& seen, const TypePackVar& lhs, const TypePackVar& rhs)
 {
     TypePackId lhsId = const_cast<TypePackId>(&lhs);

Analysis/src/TypePath.cpp

@@ -307,9 +307,9 @@ struct TraversalState
                 prop = &it->second;
             }
         }
-        else if (auto c = get<ClassType>(*currentType))
+        else if (auto c = get<ExternType>(*currentType))
         {
-            prop = lookupClassProp(c, property.name);
+            prop = lookupExternTypeProp(c, property.name);
         }
         // For a metatable type, the table takes priority; check that before
         // falling through to the metatable entry below.
@@ -461,7 +461,7 @@ struct TraversalState
                     indexer = &(*mtMt->indexer);
             }
             // Note: we don't appear to walk the class hierarchy for indexers
-            else if (auto ct = get<ClassType>(current); ct && ct->indexer)
+            else if (auto ct = get<ExternType>(current); ct && ct->indexer)
                 indexer = &(*ct->indexer);
 
             if (indexer)

Analysis/src/TypeUtils.cpp

@@ -11,9 +11,6 @@
 #include <algorithm>
 
 LUAU_FASTFLAG(LuauSolverV2);
-LUAU_FASTFLAG(LuauAutocompleteRefactorsForIncrementalAutocomplete);
-LUAU_FASTFLAG(LuauTrackInteriorFreeTypesOnScope);
-LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
 LUAU_FASTFLAG(LuauNonReentrantGeneralization2)
 LUAU_FASTFLAG(LuauDisableNewSolverAssertsInMixedMode)
 
@@ -327,11 +324,10 @@ TypePack extendTypePack(
                     {
                         FreeType ft{ftp->scope, builtinTypes->neverType, builtinTypes->unknownType, ftp->polarity};
                         t = arena.addType(ft);
-                        if (FFlag::LuauTrackInteriorFreeTypesOnScope)
                         trackInteriorFreeType(ftp->scope, t);
                     }
                     else
-                        t = FFlag::LuauFreeTypesMustHaveBounds ? arena.freshType(builtinTypes, ftp->scope) : arena.freshType_DEPRECATED(ftp->scope);
+                        t = arena.freshType(builtinTypes, ftp->scope);
                 }
 
                 newPack.head.push_back(t);
@@ -438,7 +434,6 @@ TypeId stripNil(NotNull<BuiltinTypes> builtinTypes, TypeArena& arena, TypeId ty)
 
 ErrorSuppression shouldSuppressErrors(NotNull<Normalizer> normalizer, TypeId ty)
 {
-    LUAU_ASSERT(FFlag::LuauSolverV2 || FFlag::LuauAutocompleteRefactorsForIncrementalAutocomplete);
     std::shared_ptr<const NormalizedType> normType = normalizer->normalize(ty);
 
     if (!normType)
@@ -556,10 +551,8 @@ std::vector<TypeId> findBlockedArgTypesIn(AstExprCall* expr, NotNull<DenseHashMa
 
 void trackInteriorFreeType(Scope* scope, TypeId ty)
 {
-    if (FFlag::LuauDisableNewSolverAssertsInMixedMode)
+    if (!FFlag::LuauDisableNewSolverAssertsInMixedMode)
-        LUAU_ASSERT(FFlag::LuauTrackInteriorFreeTypesOnScope);
+        LUAU_ASSERT(FFlag::LuauSolverV2);
-    else
-        LUAU_ASSERT(FFlag::LuauSolverV2 && FFlag::LuauTrackInteriorFreeTypesOnScope);
     for (; scope; scope = scope->parent.get())
     {
         if (scope->interiorFreeTypes)

Analysis/src/Unifier.cpp

@@ -22,7 +22,6 @@ LUAU_FASTFLAGVARIABLE(LuauTransitiveSubtyping)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAGVARIABLE(LuauFixIndexerSubtypingOrdering)
 LUAU_FASTFLAGVARIABLE(LuauUnifierRecursionOnRestart)
-LUAU_FASTFLAG(LuauFreeTypesMustHaveBounds)
 
 namespace Luau
 {
@@ -292,7 +291,7 @@ TypePackId Widen::clean(TypePackId)
 
 bool Widen::ignoreChildren(TypeId ty)
 {
-    if (get<ClassType>(ty))
+    if (get<ExternType>(ty))
         return true;
 
     return !log->is<UnionType>(ty);
@@ -693,13 +692,13 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
     else if (log.getMutable<MetatableType>(subTy))
         tryUnifyWithMetatable(superTy, subTy, /*reversed*/ true);
 
-    else if (log.getMutable<ClassType>(superTy))
+    else if (log.getMutable<ExternType>(superTy))
-        tryUnifyWithClass(subTy, superTy, /*reversed*/ false);
+        tryUnifyWithExternType(subTy, superTy, /*reversed*/ false);
 
-    // Unification of nonclasses with classes is almost, but not quite symmetrical.
+    // Unification of Luau types with extern types is almost, but not quite symmetrical.
-    // The order in which we perform this test is significant in the case that both types are classes.
+    // The order in which we perform this test is significant in the case that both types are extern types.
-    else if (log.getMutable<ClassType>(subTy))
+    else if (log.getMutable<ExternType>(subTy))
-        tryUnifyWithClass(subTy, superTy, /*reversed*/ true);
+        tryUnifyWithExternType(subTy, superTy, /*reversed*/ true);
 
     else if (log.get<NegationType>(superTy) || log.get<NegationType>(subTy))
         tryUnifyNegations(subTy, superTy);
@@ -1107,15 +1106,15 @@ void Unifier::tryUnifyNormalizedTypes(
         if (!get<PrimitiveType>(superNorm.errors))
             return reportError(location, TypeMismatch{superTy, subTy, reason, error, mismatchContext()});
 
-    for (const auto& [subClass, _] : subNorm.classes.classes)
+    for (const auto& [subExternType, _] : subNorm.externTypes.externTypes)
     {
         bool found = false;
-        const ClassType* subCtv = get<ClassType>(subClass);
+        const ExternType* subCtv = get<ExternType>(subExternType);
         LUAU_ASSERT(subCtv);
 
-        for (const auto& [superClass, superNegations] : superNorm.classes.classes)
+        for (const auto& [superExternType, superNegations] : superNorm.externTypes.externTypes)
         {
-            const ClassType* superCtv = get<ClassType>(superClass);
+            const ExternType* superCtv = get<ExternType>(superExternType);
             LUAU_ASSERT(superCtv);
 
             if (isSubclass(subCtv, superCtv))
@@ -1124,7 +1123,7 @@ void Unifier::tryUnifyNormalizedTypes(
 
                 for (TypeId negation : superNegations)
                 {
-                    const ClassType* negationCtv = get<ClassType>(negation);
+                    const ExternType* negationCtv = get<ExternType>(negation);
                     LUAU_ASSERT(negationCtv);
 
                     if (isSubclass(subCtv, negationCtv))
@@ -1559,7 +1558,7 @@ void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCal
             if (FFlag::LuauSolverV2)
                 return freshType(NotNull{types}, builtinTypes, scope);
             else
-                return FFlag::LuauFreeTypesMustHaveBounds ? types->freshType(builtinTypes, scope, level) : types->freshType_DEPRECATED(scope, level);
+                return types->freshType(builtinTypes, scope, level);
         };
 
         const TypePackId emptyTp = types->addTypePack(TypePack{{}, std::nullopt});
@@ -2382,8 +2381,8 @@ void Unifier::tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed)
     }
 }
 
-// Class unification is almost, but not quite symmetrical.  We use the 'reversed' boolean to indicate which scenario we are evaluating.
+// Extern type unification is almost, but not quite symmetrical.  We use the 'reversed' boolean to indicate which scenario we are evaluating.
-void Unifier::tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed)
+void Unifier::tryUnifyWithExternType(TypeId subTy, TypeId superTy, bool reversed)
 {
     if (reversed)
         std::swap(superTy, subTy);
@@ -2396,20 +2395,20 @@ void Unifier::tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed)
             reportError(location, TypeMismatch{subTy, superTy, mismatchContext()});
     };
 
-    const ClassType* superClass = get<ClassType>(superTy);
+    const ExternType* superExternType = get<ExternType>(superTy);
-    if (!superClass)
+    if (!superExternType)
-        ice("tryUnifyClass invoked with non-class Type");
+        ice("tryUnifyExternType invoked with non-class Type");
 
-    if (const ClassType* subClass = get<ClassType>(subTy))
+    if (const ExternType* subExternType = get<ExternType>(subTy))
     {
         switch (variance)
         {
         case Covariant:
-            if (!isSubclass(subClass, superClass))
+            if (!isSubclass(subExternType, superExternType))
                 return fail();
             return;
         case Invariant:
-            if (subClass != superClass)
+            if (subExternType != superExternType)
                 return fail();
             return;
         }
@@ -2434,7 +2433,7 @@ void Unifier::tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed)
 
         for (const auto& [propName, prop] : subTable->props)
         {
-            const Property* classProp = lookupClassProp(superClass, propName);
+            const Property* classProp = lookupExternTypeProp(superExternType, propName);
             if (!classProp)
             {
                 ok = false;
@@ -2462,7 +2461,7 @@ void Unifier::tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed)
         if (subTable->indexer)
         {
             ok = false;
-            std::string msg = "Class " + superClass->name + " does not have an indexer";
+            std::string msg = "Extern type " + superExternType->name + " does not have an indexer";
             reportError(location, GenericError{msg});
         }
 
@@ -2635,9 +2634,9 @@ static void tryUnifyWithAny(
             queue.push_back(mt->table);
             queue.push_back(mt->metatable);
         }
-        else if (state.log.getMutable<ClassType>(ty))
+        else if (state.log.getMutable<ExternType>(ty))
         {
-            // ClassTypes never contain free types.
+            // ExternTypes never contain free types.
         }
         else if (auto union_ = state.log.getMutable<UnionType>(ty))
             queue.insert(queue.end(), union_->options.begin(), union_->options.end());
@@ -2654,7 +2653,7 @@ void Unifier::tryUnifyWithAny(TypeId subTy, TypeId anyTy)
     LUAU_ASSERT(get<AnyType>(anyTy) || get<ErrorType>(anyTy) || get<UnknownType>(anyTy) || get<NeverType>(anyTy));
 
     // These types are not visited in general loop below
-    if (log.get<PrimitiveType>(subTy) || log.get<AnyType>(subTy) || log.get<ClassType>(subTy))
+    if (log.get<PrimitiveType>(subTy) || log.get<AnyType>(subTy) || log.get<ExternType>(subTy))
         return;
 
     TypePackId anyTp = types->addTypePack(TypePackVar{VariadicTypePack{anyTy}});

Analysis/src/Unifier2.cpp

@@ -321,8 +321,8 @@ bool Unifier2::unify(TypeId subTy, const FunctionType* superFn)
     {
         for (TypeId generic : subFn->generics)
         {
-            const GenericType* gen = get<GenericType>(generic);
+            const GenericType* gen = get<GenericType>(follow(generic));
-            LUAU_ASSERT(gen);
+            if (gen)
                 genericSubstitutions[generic] = freshType(scope, gen->polarity);
         }
 
@@ -331,7 +331,7 @@ bool Unifier2::unify(TypeId subTy, const FunctionType* superFn)
             if (FFlag::LuauNonReentrantGeneralization2)
             {
                 const GenericTypePack* gen = get<GenericTypePack>(follow(genericPack));
-                LUAU_ASSERT(gen);
+                if (gen)
                     genericPackSubstitutions[genericPack] = freshTypePack(scope, gen->polarity);
             }
             else

Ast/include/Luau/Ast.h

@@ -446,7 +446,25 @@ public:
         AstStatBlock* body,
         size_t functionDepth,
         const AstName& debugname,
-        const std::optional<AstTypeList>& returnAnnotation = {},
+        AstTypePack* returnAnnotation,
+        AstTypePack* varargAnnotation = nullptr,
+        const std::optional<Location>& argLocation = std::nullopt
+    );
+
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+    AstExprFunction(
+        const Location& location,
+        const AstArray<AstAttr*>& attributes,
+        const AstArray<AstGenericType*>& generics,
+        const AstArray<AstGenericTypePack*>& genericPacks,
+        AstLocal* self,
+        const AstArray<AstLocal*>& args,
+        bool vararg,
+        const Location& varargLocation,
+        AstStatBlock* body,
+        size_t functionDepth,
+        const AstName& debugname,
+        const std::optional<AstTypeList>& returnAnnotation,
         AstTypePack* varargAnnotation = nullptr,
         const std::optional<Location>& argLocation = std::nullopt
     );
@@ -461,7 +479,9 @@ public:
     AstArray<AstGenericTypePack*> genericPacks;
     AstLocal* self;
     AstArray<AstLocal*> args;
-    std::optional<AstTypeList> returnAnnotation;
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+    std::optional<AstTypeList> returnAnnotation_DEPRECATED;
+    AstTypePack* returnAnnotation = nullptr;
     bool vararg = false;
     Location varargLocation;
     AstTypePack* varargAnnotation;
@@ -929,6 +949,36 @@ class AstStatDeclareFunction : public AstStat
 public:
     LUAU_RTTI(AstStatDeclareFunction)
 
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+    AstStatDeclareFunction(
+        const Location& location,
+        const AstName& name,
+        const Location& nameLocation,
+        const AstArray<AstGenericType*>& generics,
+        const AstArray<AstGenericTypePack*>& genericPacks,
+        const AstTypeList& params,
+        const AstArray<AstArgumentName>& paramNames,
+        bool vararg,
+        const Location& varargLocation,
+        AstTypePack* retTypes
+    );
+
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+    AstStatDeclareFunction(
+        const Location& location,
+        const AstArray<AstAttr*>& attributes,
+        const AstName& name,
+        const Location& nameLocation,
+        const AstArray<AstGenericType*>& generics,
+        const AstArray<AstGenericTypePack*>& genericPacks,
+        const AstTypeList& params,
+        const AstArray<AstArgumentName>& paramNames,
+        bool vararg,
+        const Location& varargLocation,
+        AstTypePack* retTypes
+    );
+
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
     AstStatDeclareFunction(
         const Location& location,
         const AstName& name,
@@ -942,6 +992,7 @@ public:
         const AstTypeList& retTypes
     );
 
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
     AstStatDeclareFunction(
         const Location& location,
         const AstArray<AstAttr*>& attributes,
@@ -971,10 +1022,12 @@ public:
     AstArray<AstArgumentName> paramNames;
     bool vararg = false;
     Location varargLocation;
-    AstTypeList retTypes;
+    AstTypePack* retTypes;
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+    AstTypeList retTypes_DEPRECATED;
 };
 
-struct AstDeclaredClassProp
+struct AstDeclaredExternTypeProperty
 {
     AstName name;
     Location nameLocation;
@@ -1000,16 +1053,16 @@ struct AstTableIndexer
     std::optional<Location> accessLocation;
 };
 
-class AstStatDeclareClass : public AstStat
+class AstStatDeclareExternType : public AstStat
 {
 public:
-    LUAU_RTTI(AstStatDeclareClass)
+    LUAU_RTTI(AstStatDeclareExternType)
 
-    AstStatDeclareClass(
+    AstStatDeclareExternType(
         const Location& location,
         const AstName& name,
         std::optional<AstName> superName,
-        const AstArray<AstDeclaredClassProp>& props,
+        const AstArray<AstDeclaredExternTypeProperty>& props,
         AstTableIndexer* indexer = nullptr
     );
 
@@ -1018,7 +1071,7 @@ public:
     AstName name;
     std::optional<AstName> superName;
 
-    AstArray<AstDeclaredClassProp> props;
+    AstArray<AstDeclaredExternTypeProperty> props;
     AstTableIndexer* indexer;
 };
 
@@ -1095,6 +1148,26 @@ class AstTypeFunction : public AstType
 public:
     LUAU_RTTI(AstTypeFunction)
 
+    AstTypeFunction(
+        const Location& location,
+        const AstArray<AstGenericType*>& generics,
+        const AstArray<AstGenericTypePack*>& genericPacks,
+        const AstTypeList& argTypes,
+        const AstArray<std::optional<AstArgumentName>>& argNames,
+        AstTypePack* returnTypes
+    );
+
+    AstTypeFunction(
+        const Location& location,
+        const AstArray<AstAttr*>& attributes,
+        const AstArray<AstGenericType*>& generics,
+        const AstArray<AstGenericTypePack*>& genericPacks,
+        const AstTypeList& argTypes,
+        const AstArray<std::optional<AstArgumentName>>& argNames,
+        AstTypePack* returnTypes
+    );
+
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
     AstTypeFunction(
         const Location& location,
         const AstArray<AstGenericType*>& generics,
@@ -1104,6 +1177,7 @@ public:
         const AstTypeList& returnTypes
     );
 
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
     AstTypeFunction(
         const Location& location,
         const AstArray<AstAttr*>& attributes,
@@ -1124,7 +1198,9 @@ public:
     AstArray<AstGenericTypePack*> genericPacks;
     AstTypeList argTypes;
     AstArray<std::optional<AstArgumentName>> argNames;
-    AstTypeList returnTypes;
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+    AstTypeList returnTypes_DEPRECATED;
+    AstTypePack* returnTypes;
 };
 
 class AstTypeTypeof : public AstType
@@ -1483,7 +1559,7 @@ public:
     {
         return visit(static_cast<AstStat*>(node));
     }
-    virtual bool visit(class AstStatDeclareClass* node)
+    virtual bool visit(class AstStatDeclareExternType* node)
     {
         return visit(static_cast<AstStat*>(node));
     }

Ast/include/Luau/Cst.h

@@ -473,8 +473,10 @@ class CstTypePackExplicit : public CstNode
 public:
     LUAU_CST_RTTI(CstTypePackExplicit)
 
-    CstTypePackExplicit(Position openParenthesesPosition, Position closeParenthesesPosition, AstArray<Position> commaPositions);
+    explicit CstTypePackExplicit();
+    explicit CstTypePackExplicit(Position openParenthesesPosition, Position closeParenthesesPosition, AstArray<Position> commaPositions);
 
+    bool hasParentheses;
     Position openParenthesesPosition;
     Position closeParenthesesPosition;
     AstArray<Position> commaPositions;

Ast/include/Luau/Parser.h

@@ -157,8 +157,8 @@ private:
     // type function Name ... end
     AstStat* parseTypeFunction(const Location& start, bool exported, Position typeKeywordPosition);
 
-    AstDeclaredClassProp parseDeclaredClassMethod(const AstArray<AstAttr*>& attributes);
+    AstDeclaredExternTypeProperty parseDeclaredExternTypeMethod(const AstArray<AstAttr*>& attributes);
-    AstDeclaredClassProp parseDeclaredClassMethod_DEPRECATED();
+    AstDeclaredExternTypeProperty parseDeclaredExternTypeMethod_DEPRECATED();
 
 
     // `declare global' Name: Type |
@@ -182,6 +182,14 @@ private:
         const Name* localName,
         const AstArray<AstAttr*>& attributes
     );
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+    std::pair<AstExprFunction*, AstLocal*> parseFunctionBody_DEPRECATED(
+        bool hasself,
+        const Lexeme& matchFunction,
+        const AstName& debugname,
+        const Name* localName,
+        const AstArray<AstAttr*>& attributes
+    );
 
     // explist ::= {exp `,'} exp
     void parseExprList(TempVector<AstExpr*>& result, TempVector<Position>* commaPositions = nullptr);
@@ -219,8 +227,12 @@ private:
         TempVector<std::optional<Position>>* nameColonPositions = nullptr
     );
 
-    std::optional<AstTypeList> parseOptionalReturnType(Position* returnSpecifierPosition = nullptr);
+    AstTypePack* parseOptionalReturnType(Position* returnSpecifierPosition = nullptr);
-    std::pair<Location, AstTypeList> parseReturnType();
+    AstTypePack* parseReturnType();
+
+    // Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+    std::optional<AstTypeList> parseOptionalReturnType_DEPRECATED(Position* returnSpecifierPosition = nullptr);
+    std::pair<Location, AstTypeList> parseReturnType_DEPRECATED();
 
     struct TableIndexerResult
     {
@@ -491,7 +503,7 @@ private:
     std::vector<CstTypeTable::Item> scratchCstTableTypeProps;
     std::vector<AstType*> scratchType;
     std::vector<AstTypeOrPack> scratchTypeOrPack;
-    std::vector<AstDeclaredClassProp> scratchDeclaredClassProps;
+    std::vector<AstDeclaredExternTypeProperty> scratchDeclaredClassProps;
     std::vector<AstExprTable::Item> scratchItem;
     std::vector<CstExprTable::Item> scratchCstItem;
     std::vector<AstArgumentName> scratchArgName;

Ast/src/Ast.cpp

@@ -4,6 +4,7 @@
 #include "Luau/Common.h"
 
 LUAU_FASTFLAG(LuauDeprecatedAttribute);
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 namespace Luau
 {
@@ -241,7 +242,7 @@ AstExprFunction::AstExprFunction(
     AstStatBlock* body,
     size_t functionDepth,
     const AstName& debugname,
-    const std::optional<AstTypeList>& returnAnnotation,
+    AstTypePack* returnAnnotation,
     AstTypePack* varargAnnotation,
     const std::optional<Location>& argLocation
 )
@@ -260,6 +261,41 @@ AstExprFunction::AstExprFunction(
     , debugname(debugname)
     , argLocation(argLocation)
 {
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
+}
+
+AstExprFunction::AstExprFunction(
+    const Location& location,
+    const AstArray<AstAttr*>& attributes,
+    const AstArray<AstGenericType*>& generics,
+    const AstArray<AstGenericTypePack*>& genericPacks,
+    AstLocal* self,
+    const AstArray<AstLocal*>& args,
+    bool vararg,
+    const Location& varargLocation,
+    AstStatBlock* body,
+    size_t functionDepth,
+    const AstName& debugname,
+    const std::optional<AstTypeList>& returnAnnotation,
+    AstTypePack* varargAnnotation,
+    const std::optional<Location>& argLocation
+)
+    : AstExpr(ClassIndex(), location)
+    , attributes(attributes)
+    , generics(generics)
+    , genericPacks(genericPacks)
+    , self(self)
+    , args(args)
+    , returnAnnotation_DEPRECATED(returnAnnotation)
+    , vararg(vararg)
+    , varargLocation(varargLocation)
+    , varargAnnotation(varargAnnotation)
+    , body(body)
+    , functionDepth(functionDepth)
+    , debugname(debugname)
+    , argLocation(argLocation)
+{
+    LUAU_ASSERT(!FFlag::LuauStoreReturnTypesAsPackOnAst);
 }
 
 void AstExprFunction::visit(AstVisitor* visitor)
@@ -275,8 +311,16 @@ void AstExprFunction::visit(AstVisitor* visitor)
         if (varargAnnotation)
             varargAnnotation->visit(visitor);
 
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        {
             if (returnAnnotation)
-            visitTypeList(visitor, *returnAnnotation);
+                returnAnnotation->visit(visitor);
+        }
+        else
+        {
+            if (returnAnnotation_DEPRECATED)
+                visitTypeList(visitor, *returnAnnotation_DEPRECATED);
+        }
 
         body->visit(visitor);
     }
@@ -855,7 +899,7 @@ AstStatDeclareFunction::AstStatDeclareFunction(
     const AstArray<AstArgumentName>& paramNames,
     bool vararg,
     const Location& varargLocation,
-    const AstTypeList& retTypes
+    AstTypePack* retTypes
 )
     : AstStat(ClassIndex(), location)
     , attributes()
@@ -869,8 +913,66 @@ AstStatDeclareFunction::AstStatDeclareFunction(
     , varargLocation(varargLocation)
     , retTypes(retTypes)
 {
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
 }
 
+AstStatDeclareFunction::AstStatDeclareFunction(
+    const Location& location,
+    const AstArray<AstAttr*>& attributes,
+    const AstName& name,
+    const Location& nameLocation,
+    const AstArray<AstGenericType*>& generics,
+    const AstArray<AstGenericTypePack*>& genericPacks,
+    const AstTypeList& params,
+    const AstArray<AstArgumentName>& paramNames,
+    bool vararg,
+    const Location& varargLocation,
+    AstTypePack* retTypes
+)
+    : AstStat(ClassIndex(), location)
+    , attributes(attributes)
+    , name(name)
+    , nameLocation(nameLocation)
+    , generics(generics)
+    , genericPacks(genericPacks)
+    , params(params)
+    , paramNames(paramNames)
+    , vararg(vararg)
+    , varargLocation(varargLocation)
+    , retTypes(retTypes)
+{
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
+}
+
+// Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+AstStatDeclareFunction::AstStatDeclareFunction(
+    const Location& location,
+    const AstName& name,
+    const Location& nameLocation,
+    const AstArray<AstGenericType*>& generics,
+    const AstArray<AstGenericTypePack*>& genericPacks,
+    const AstTypeList& params,
+    const AstArray<AstArgumentName>& paramNames,
+    bool vararg,
+    const Location& varargLocation,
+    const AstTypeList& retTypes
+)
+    : AstStat(ClassIndex(), location)
+    , attributes()
+    , name(name)
+    , nameLocation(nameLocation)
+    , generics(generics)
+    , genericPacks(genericPacks)
+    , params(params)
+    , paramNames(paramNames)
+    , vararg(vararg)
+    , varargLocation(varargLocation)
+    , retTypes_DEPRECATED(retTypes)
+{
+    LUAU_ASSERT(!FFlag::LuauStoreReturnTypesAsPackOnAst);
+}
+
+// Clip with FFlagLuauStoreReturnTypesAsPackOnAst
 AstStatDeclareFunction::AstStatDeclareFunction(
     const Location& location,
     const AstArray<AstAttr*>& attributes,
@@ -894,8 +996,9 @@ AstStatDeclareFunction::AstStatDeclareFunction(
     , paramNames(paramNames)
     , vararg(vararg)
     , varargLocation(varargLocation)
-    , retTypes(retTypes)
+    , retTypes_DEPRECATED(retTypes)
 {
+    LUAU_ASSERT(!FFlag::LuauStoreReturnTypesAsPackOnAst);
 }
 
 void AstStatDeclareFunction::visit(AstVisitor* visitor)
@@ -903,7 +1006,10 @@ void AstStatDeclareFunction::visit(AstVisitor* visitor)
     if (visitor->visit(this))
     {
         visitTypeList(visitor, params);
-        visitTypeList(visitor, retTypes);
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+            retTypes->visit(visitor);
+        else
+            visitTypeList(visitor, retTypes_DEPRECATED);
     }
 }
 
@@ -925,11 +1031,11 @@ bool AstStatDeclareFunction::hasAttribute(AstAttr::Type attributeType) const
     return hasAttributeInArray(attributes, attributeType);
 }
 
-AstStatDeclareClass::AstStatDeclareClass(
+AstStatDeclareExternType::AstStatDeclareExternType(
     const Location& location,
     const AstName& name,
     std::optional<AstName> superName,
-    const AstArray<AstDeclaredClassProp>& props,
+    const AstArray<AstDeclaredExternTypeProperty>& props,
     AstTableIndexer* indexer
 )
     : AstStat(ClassIndex(), location)
@@ -940,11 +1046,11 @@ AstStatDeclareClass::AstStatDeclareClass(
 {
 }
 
-void AstStatDeclareClass::visit(AstVisitor* visitor)
+void AstStatDeclareExternType::visit(AstVisitor* visitor)
 {
     if (visitor->visit(this))
     {
-        for (const AstDeclaredClassProp& prop : props)
+        for (const AstDeclaredExternTypeProperty& prop : props)
             prop.ty->visit(visitor);
     }
 }
@@ -1035,7 +1141,7 @@ AstTypeFunction::AstTypeFunction(
     const AstArray<AstGenericTypePack*>& genericPacks,
     const AstTypeList& argTypes,
     const AstArray<std::optional<AstArgumentName>>& argNames,
-    const AstTypeList& returnTypes
+    AstTypePack* returnTypes
 )
     : AstType(ClassIndex(), location)
     , attributes()
@@ -1045,9 +1151,53 @@ AstTypeFunction::AstTypeFunction(
     , argNames(argNames)
     , returnTypes(returnTypes)
 {
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
     LUAU_ASSERT(argNames.size == 0 || argNames.size == argTypes.types.size);
 }
 
+AstTypeFunction::AstTypeFunction(
+    const Location& location,
+    const AstArray<AstAttr*>& attributes,
+    const AstArray<AstGenericType*>& generics,
+    const AstArray<AstGenericTypePack*>& genericPacks,
+    const AstTypeList& argTypes,
+    const AstArray<std::optional<AstArgumentName>>& argNames,
+    AstTypePack* returnTypes
+)
+    : AstType(ClassIndex(), location)
+    , attributes(attributes)
+    , generics(generics)
+    , genericPacks(genericPacks)
+    , argTypes(argTypes)
+    , argNames(argNames)
+    , returnTypes(returnTypes)
+{
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
+    LUAU_ASSERT(argNames.size == 0 || argNames.size == argTypes.types.size);
+}
+
+// Clip with FFlagLuauStoreReturnTypesAsPackOnAst
+AstTypeFunction::AstTypeFunction(
+    const Location& location,
+    const AstArray<AstGenericType*>& generics,
+    const AstArray<AstGenericTypePack*>& genericPacks,
+    const AstTypeList& argTypes,
+    const AstArray<std::optional<AstArgumentName>>& argNames,
+    const AstTypeList& returnTypes
+)
+    : AstType(ClassIndex(), location)
+    , attributes()
+    , generics(generics)
+    , genericPacks(genericPacks)
+    , argTypes(argTypes)
+    , argNames(argNames)
+    , returnTypes_DEPRECATED(returnTypes)
+{
+    LUAU_ASSERT(!FFlag::LuauStoreReturnTypesAsPackOnAst);
+    LUAU_ASSERT(argNames.size == 0 || argNames.size == argTypes.types.size);
+}
+
+// Clip with FFlagLuauStoreReturnTypesAsPackOnAst
 AstTypeFunction::AstTypeFunction(
     const Location& location,
     const AstArray<AstAttr*>& attributes,
@@ -1063,8 +1213,9 @@ AstTypeFunction::AstTypeFunction(
     , genericPacks(genericPacks)
     , argTypes(argTypes)
     , argNames(argNames)
-    , returnTypes(returnTypes)
+    , returnTypes_DEPRECATED(returnTypes)
 {
+    LUAU_ASSERT(!FFlag::LuauStoreReturnTypesAsPackOnAst);
     LUAU_ASSERT(argNames.size == 0 || argNames.size == argTypes.types.size);
 }
 
@@ -1073,7 +1224,10 @@ void AstTypeFunction::visit(AstVisitor* visitor)
     if (visitor->visit(this))
     {
         visitTypeList(visitor, argTypes);
-        visitTypeList(visitor, returnTypes);
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+            returnTypes->visit(visitor);
+        else
+            visitTypeList(visitor, returnTypes_DEPRECATED);
     }
 }
 

Ast/src/Cst.cpp

@@ -252,8 +252,18 @@ CstTypeSingletonString::CstTypeSingletonString(AstArray<char> sourceString, CstE
     LUAU_ASSERT(quoteStyle != CstExprConstantString::QuotedInterp);
 }
 
+CstTypePackExplicit::CstTypePackExplicit()
+    : CstNode(CstClassIndex())
+    , hasParentheses(false)
+    , openParenthesesPosition(Position{0, 0})
+    , closeParenthesesPosition(Position{0, 0})
+    , commaPositions({})
+{
+}
+
 CstTypePackExplicit::CstTypePackExplicit(Position openParenthesesPosition, Position closeParenthesesPosition, AstArray<Position> commaPositions)
     : CstNode(CstClassIndex())
+    , hasParentheses(true)
     , openParenthesesPosition(openParenthesesPosition)
     , closeParenthesesPosition(closeParenthesesPosition)
     , commaPositions(commaPositions)

Ast/src/Parser.cpp

@@ -19,14 +19,13 @@ LUAU_FASTINTVARIABLE(LuauParseErrorLimit, 100)
 // See docs/SyntaxChanges.md for an explanation.
 LUAU_FASTFLAGVARIABLE(LuauSolverV2)
 LUAU_FASTFLAGVARIABLE(LuauStoreCSTData2)
-LUAU_FASTFLAGVARIABLE(LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
 LUAU_FASTFLAGVARIABLE(LuauAstTypeGroup3)
-LUAU_FASTFLAGVARIABLE(ParserNoErrorLimit)
-LUAU_FASTFLAGVARIABLE(LuauFixDoBlockEndLocation)
 LUAU_FASTFLAGVARIABLE(LuauParseOptionalAsNode2)
+LUAU_FASTFLAGVARIABLE(LuauDeclareExternType)
 LUAU_FASTFLAGVARIABLE(LuauParseStringIndexer)
 LUAU_FASTFLAGVARIABLE(LuauTypeFunResultInAutocomplete)
 LUAU_FASTFLAGVARIABLE(LuauDeprecatedAttribute)
+LUAU_FASTFLAGVARIABLE(LuauStoreReturnTypesAsPackOnAst)
 LUAU_FASTFLAGVARIABLE(LuauFixFunctionWithAttributesStartLocation)
 LUAU_DYNAMIC_FASTFLAGVARIABLE(DebugLuauReportReturnTypeVariadicWithTypeSuffix, false)
 
@@ -555,7 +554,7 @@ AstStat* Parser::parseDo()
 
     Location endLocation = lexer.current().location;
     body->hasEnd = expectMatchEndAndConsume(Lexeme::ReservedEnd, matchDo);
-    if (FFlag::LuauFixDoBlockEndLocation && body->hasEnd)
+    if (body->hasEnd)
         body->location.end = endLocation.end;
 
     if (FFlag::LuauStoreCSTData2 && options.storeCstData)
@@ -788,7 +787,9 @@ AstStat* Parser::parseFunctionStat(const AstArray<AstAttr*>& attributes)
 
     matchRecoveryStopOnToken[Lexeme::ReservedEnd]++;
 
-    AstExprFunction* body = parseFunctionBody(hasself, matchFunction, debugname, nullptr, attributes).first;
+    AstExprFunction* body = FFlag::LuauStoreReturnTypesAsPackOnAst
+                                ? parseFunctionBody(hasself, matchFunction, debugname, nullptr, attributes).first
+                                : parseFunctionBody_DEPRECATED(hasself, matchFunction, debugname, nullptr, attributes).first;
 
     matchRecoveryStopOnToken[Lexeme::ReservedEnd]--;
 
@@ -941,7 +942,8 @@ AstStat* Parser::parseLocal(const AstArray<AstAttr*>& attributes)
 
         matchRecoveryStopOnToken[Lexeme::ReservedEnd]++;
 
-        auto [body, var] = parseFunctionBody(false, matchFunction, name.name, &name, attributes);
+        auto [body, var] = FFlag::LuauStoreReturnTypesAsPackOnAst ? parseFunctionBody(false, matchFunction, name.name, &name, attributes)
+                                                                  : parseFunctionBody_DEPRECATED(false, matchFunction, name.name, &name, attributes);
 
         matchRecoveryStopOnToken[Lexeme::ReservedEnd]--;
 
@@ -1111,7 +1113,10 @@ AstStat* Parser::parseTypeFunction(const Location& start, bool exported, Positio
     size_t oldTypeFunctionDepth = typeFunctionDepth;
     typeFunctionDepth = functionStack.size();
 
-    AstExprFunction* body = parseFunctionBody(/* hasself */ false, matchFn, fnName->name, nullptr, AstArray<AstAttr*>({nullptr, 0})).first;
+    AstExprFunction* body =
+        FFlag::LuauStoreReturnTypesAsPackOnAst
+            ? parseFunctionBody(/* hasself */ false, matchFn, fnName->name, nullptr, AstArray<AstAttr*>({nullptr, 0})).first
+            : parseFunctionBody_DEPRECATED(/* hasself */ false, matchFn, fnName->name, nullptr, AstArray<AstAttr*>({nullptr, 0})).first;
 
     typeFunctionDepth = oldTypeFunctionDepth;
 
@@ -1133,7 +1138,7 @@ AstStat* Parser::parseTypeFunction(const Location& start, bool exported, Positio
     }
 }
 
-AstDeclaredClassProp Parser::parseDeclaredClassMethod(const AstArray<AstAttr*>& attributes)
+AstDeclaredExternTypeProperty Parser::parseDeclaredExternTypeMethod(const AstArray<AstAttr*>& attributes)
 {
     LUAU_ASSERT(FFlag::LuauDeprecatedAttribute);
 
@@ -1164,7 +1169,18 @@ AstDeclaredClassProp Parser::parseDeclaredClassMethod(const AstArray<AstAttr*>&
 
     expectMatchAndConsume(')', matchParen);
 
-    AstTypeList retTypes = parseOptionalReturnType().value_or(AstTypeList{copy<AstType*>(nullptr, 0), nullptr});
+    AstTypePack* retTypes;
+    AstTypeList retTypes_DEPRECATED;
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        retTypes = parseOptionalReturnType();
+        if (!retTypes)
+            retTypes = allocator.alloc<AstTypePackExplicit>(lexer.current().location, AstTypeList{copy<AstType*>(nullptr, 0), nullptr});
+    }
+    else
+    {
+        retTypes_DEPRECATED = parseOptionalReturnType_DEPRECATED().value_or(AstTypeList{copy<AstType*>(nullptr, 0), nullptr});
+    }
     Location end = lexer.previousLocation();
 
     TempVector<AstType*> vars(scratchType);
@@ -1172,7 +1188,7 @@ AstDeclaredClassProp Parser::parseDeclaredClassMethod(const AstArray<AstAttr*>&
 
     if (args.size() == 0 || args[0].name.name != "self" || args[0].annotation != nullptr)
     {
-        return AstDeclaredClassProp{
+        return AstDeclaredExternTypeProperty{
             fnName.name, fnName.location, reportTypeError(Location(start, end), {}, "'self' must be present as the unannotated first parameter"), true
         };
     }
@@ -1191,14 +1207,25 @@ AstDeclaredClassProp Parser::parseDeclaredClassMethod(const AstArray<AstAttr*>&
     if (vararg && !varargAnnotation)
         report(start, "All declaration parameters aside from 'self' must be annotated");
 
-    AstType* fnType = allocator.alloc<AstTypeFunction>(
+    AstType* fnType =
+        FFlag::LuauStoreReturnTypesAsPackOnAst
+            ? allocator.alloc<AstTypeFunction>(
                   Location(start, end), attributes, generics, genericPacks, AstTypeList{copy(vars), varargAnnotation}, copy(varNames), retTypes
+              )
+            : allocator.alloc<AstTypeFunction>(
+                  Location(start, end),
+                  attributes,
+                  generics,
+                  genericPacks,
+                  AstTypeList{copy(vars), varargAnnotation},
+                  copy(varNames),
+                  retTypes_DEPRECATED
               );
 
-    return AstDeclaredClassProp{fnName.name, fnName.location, fnType, true, Location(start, end)};
+    return AstDeclaredExternTypeProperty{fnName.name, fnName.location, fnType, true, Location(start, end)};
 }
 
-AstDeclaredClassProp Parser::parseDeclaredClassMethod_DEPRECATED()
+AstDeclaredExternTypeProperty Parser::parseDeclaredExternTypeMethod_DEPRECATED()
 {
     Location start = lexer.current().location;
 
@@ -1227,7 +1254,18 @@ AstDeclaredClassProp Parser::parseDeclaredClassMethod_DEPRECATED()
 
     expectMatchAndConsume(')', matchParen);
 
-    AstTypeList retTypes = parseOptionalReturnType().value_or(AstTypeList{copy<AstType*>(nullptr, 0), nullptr});
+    AstTypePack* retTypes;
+    AstTypeList retTypes_DEPRECATED;
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        retTypes = parseOptionalReturnType();
+        if (!retTypes)
+            retTypes = allocator.alloc<AstTypePackExplicit>(lexer.current().location, AstTypeList{copy<AstType*>(nullptr, 0), nullptr});
+    }
+    else
+    {
+        retTypes_DEPRECATED = parseOptionalReturnType_DEPRECATED().value_or(AstTypeList{copy<AstType*>(nullptr, 0), nullptr});
+    }
     Location end = lexer.previousLocation();
 
     TempVector<AstType*> vars(scratchType);
@@ -1235,7 +1273,7 @@ AstDeclaredClassProp Parser::parseDeclaredClassMethod_DEPRECATED()
 
     if (args.size() == 0 || args[0].name.name != "self" || args[0].annotation != nullptr)
     {
-        return AstDeclaredClassProp{
+        return AstDeclaredExternTypeProperty{
             fnName.name, fnName.location, reportTypeError(Location(start, end), {}, "'self' must be present as the unannotated first parameter"), true
         };
     }
@@ -1254,11 +1292,16 @@ AstDeclaredClassProp Parser::parseDeclaredClassMethod_DEPRECATED()
     if (vararg && !varargAnnotation)
         report(start, "All declaration parameters aside from 'self' must be annotated");
 
-    AstType* fnType = allocator.alloc<AstTypeFunction>(
+    AstType* fnType =
+        FFlag::LuauStoreReturnTypesAsPackOnAst
+            ? allocator.alloc<AstTypeFunction>(
                   Location(start, end), generics, genericPacks, AstTypeList{copy(vars), varargAnnotation}, copy(varNames), retTypes
+              )
+            : allocator.alloc<AstTypeFunction>(
+                  Location(start, end), generics, genericPacks, AstTypeList{copy(vars), varargAnnotation}, copy(varNames), retTypes_DEPRECATED
               );
 
-    return AstDeclaredClassProp{fnName.name, fnName.location, fnType, true, Location(start, end)};
+    return AstDeclaredExternTypeProperty{fnName.name, fnName.location, fnType, true, Location(start, end)};
 }
 
 AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*>& attributes)
@@ -1296,7 +1339,18 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
 
         expectMatchAndConsume(')', matchParen);
 
-        AstTypeList retTypes = parseOptionalReturnType().value_or(AstTypeList{copy<AstType*>(nullptr, 0)});
+        AstTypePack* retTypes;
+        AstTypeList retTypes_DEPRECATED;
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        {
+            retTypes = parseOptionalReturnType();
+            if (!retTypes)
+                retTypes = allocator.alloc<AstTypePackExplicit>(lexer.current().location, AstTypeList{copy<AstType*>(nullptr, 0), nullptr});
+        }
+        else
+        {
+            retTypes_DEPRECATED = parseOptionalReturnType_DEPRECATED().value_or(AstTypeList{copy<AstType*>(nullptr, 0)});
+        }
         Location end = lexer.current().location;
 
         TempVector<AstType*> vars(scratchType);
@@ -1314,6 +1368,8 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
         if (vararg && !varargAnnotation)
             return reportStatError(Location(start, end), {}, {}, "All declaration parameters must be annotated");
 
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+        {
             return allocator.alloc<AstStatDeclareFunction>(
                 Location(start, end),
                 attributes,
@@ -1328,20 +1384,61 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                 retTypes
             );
         }
-    else if (AstName(lexer.current().name) == "class")
+        else
         {
+            return allocator.alloc<AstStatDeclareFunction>(
+                Location(start, end),
+                attributes,
+                globalName.name,
+                globalName.location,
+                generics,
+                genericPacks,
+                AstTypeList{copy(vars), varargAnnotation},
+                copy(varNames),
+                vararg,
+                varargLocation,
+                retTypes_DEPRECATED
+            );
+        }
+    }
+    else if (AstName(lexer.current().name) == "class" || (FFlag::LuauDeclareExternType && AstName(lexer.current().name) == "extern"))
+    {
+        bool foundExtern = false;
+        if (FFlag::LuauDeclareExternType)
+        {
+            if (AstName(lexer.current().name) == "extern")
+            {
+                foundExtern = true;
                 nextLexeme();
+                if (AstName(lexer.current().name) != "type")
+                    return reportStatError(lexer.current().location, {}, {}, "Expected `type` keyword after `extern`, but got %s instead", lexer.current().name);
+            }
+        }
+
+        nextLexeme();
+
         Location classStart = lexer.current().location;
-        Name className = parseName("class name");
+        Name className = parseName(FFlag::LuauDeclareExternType ? "type name" : "class name");
         std::optional<AstName> superName = std::nullopt;
 
         if (AstName(lexer.current().name) == "extends")
         {
             nextLexeme();
-            superName = parseName("superclass name").name;
+            superName = parseName(FFlag::LuauDeclareExternType ? "supertype name" : "superclass name").name;
         }
 
-        TempVector<AstDeclaredClassProp> props(scratchDeclaredClassProps);
+        if (FFlag::LuauDeclareExternType)
+        {
+            if (foundExtern)
+            {
+                if (AstName(lexer.current().name) != "with")
+                    report(lexer.current().location, "Expected `with` keyword before listing properties of the external type, but got %s instead", lexer.current().name);
+                else
+                    nextLexeme();
+            }
+        }
+
+        TempVector<AstDeclaredExternTypeProperty> props(scratchDeclaredClassProps);
         AstTableIndexer* indexer = nullptr;
 
         while (lexer.current().type != Lexeme::ReservedEnd)
@@ -1368,9 +1465,9 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                 if (lexer.current().type == Lexeme::ReservedFunction)
                 {
                     if (FFlag::LuauDeprecatedAttribute)
-                        props.push_back(parseDeclaredClassMethod(attributes));
+                        props.push_back(parseDeclaredExternTypeMethod(attributes));
                     else
-                        props.push_back(parseDeclaredClassMethod_DEPRECATED());
+                        props.push_back(parseDeclaredExternTypeMethod_DEPRECATED());
                 }
                 else if (lexer.current().type == '[')
                 {
@@ -1393,7 +1490,7 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
 
                         if (chars && !containsNull)
                         {
-                            props.push_back(AstDeclaredClassProp{
+                            props.push_back(AstDeclaredExternTypeProperty{
                                 AstName(chars->data), Location(nameBegin, nameEnd), type, false, Location(begin.location, lexer.previousLocation())
                             });
                         }
@@ -1413,6 +1510,9 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                             badIndexer = parseTableIndexer_DEPRECATED(AstTableAccess::ReadWrite, std::nullopt, begin);
 
                         // we lose all additional indexer expressions from the AST after error recovery here
+                        if (FFlag::LuauDeclareExternType)
+                            report(badIndexer->location, "Cannot have more than one indexer on an extern type");
+                        else
                             report(badIndexer->location, "Cannot have more than one class indexer");
                     }
                     else
@@ -1434,7 +1534,7 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                     expectAndConsume(':', "property type annotation");
                     AstType* propType = parseType();
                     props.push_back(
-                        AstDeclaredClassProp{propName->name, propName->location, propType, false, Location(propStart, lexer.previousLocation())}
+                        AstDeclaredExternTypeProperty{propName->name, propName->location, propType, false, Location(propStart, lexer.previousLocation())}
                     );
                 }
             }
@@ -1444,9 +1544,9 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                 if (lexer.current().type == Lexeme::ReservedFunction)
                 {
                     if (FFlag::LuauDeprecatedAttribute)
-                        props.push_back(parseDeclaredClassMethod(attributes));
+                        props.push_back(parseDeclaredExternTypeMethod(attributes));
                     else
-                        props.push_back(parseDeclaredClassMethod_DEPRECATED());
+                        props.push_back(parseDeclaredExternTypeMethod_DEPRECATED());
                 }
                 else if (lexer.current().type == '[' &&
                          (lexer.lookahead().type == Lexeme::RawString || lexer.lookahead().type == Lexeme::QuotedString))
@@ -1468,7 +1568,7 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
 
                     if (chars && !containsNull)
                     {
-                        props.push_back(AstDeclaredClassProp{
+                        props.push_back(AstDeclaredExternTypeProperty{
                             AstName(chars->data), Location(nameBegin, nameEnd), type, false, Location(begin.location, lexer.previousLocation())
                         });
                     }
@@ -1492,6 +1592,9 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                             badIndexer = parseTableIndexer_DEPRECATED(AstTableAccess::ReadWrite, std::nullopt, lexer.current());
 
                         // we lose all additional indexer expressions from the AST after error recovery here
+                        if (FFlag::LuauDeclareExternType)
+                            report(badIndexer->location, "Cannot have more than one indexer on an extern type");
+                        else
                             report(badIndexer->location, "Cannot have more than one class indexer");
                     }
                     else
@@ -1515,7 +1618,7 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                     expectAndConsume(':', "property type annotation");
                     AstType* propType = parseType();
                     props.push_back(
-                        AstDeclaredClassProp{propName->name, propName->location, propType, false, Location(propStart, lexer.previousLocation())}
+                        AstDeclaredExternTypeProperty{propName->name, propName->location, propType, false, Location(propStart, lexer.previousLocation())}
                     );
                 }
             }
@@ -1524,7 +1627,7 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
         Location classEnd = lexer.current().location;
         nextLexeme(); // skip past `end`
 
-        return allocator.alloc<AstStatDeclareClass>(Location(classStart, classEnd), className.name, superName, copy(props), indexer);
+        return allocator.alloc<AstStatDeclareExternType>(Location(classStart, classEnd), className.name, superName, copy(props), indexer);
     }
     else if (std::optional<Name> globalName = parseNameOpt("global variable name"))
     {
@@ -1533,6 +1636,10 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
         AstType* type = parseType(/* in declaration context */ true);
         return allocator.alloc<AstStatDeclareGlobal>(Location(start, type->location), globalName->name, globalName->location, type);
     }
+    else if (FFlag::LuauDeclareExternType)
+    {
+        return reportStatError(start, {}, {}, "declare must be followed by an identifier, 'function', or 'extern type'");
+    }
     else
     {
         return reportStatError(start, {}, {}, "declare must be followed by an identifier, 'function', or 'class'");
@@ -1638,6 +1745,8 @@ std::pair<AstExprFunction*, AstLocal*> Parser::parseFunctionBody(
     const AstArray<AstAttr*>& attributes
 )
 {
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
+
     Location start = matchFunction.location;
 
     if (FFlag::LuauFixFunctionWithAttributesStartLocation)
@@ -1689,7 +1798,145 @@ std::pair<AstExprFunction*, AstLocal*> Parser::parseFunctionBody(
 
     matchRecoveryStopOnToken[')']--;
 
-    std::optional<AstTypeList> typelist = parseOptionalReturnType(cstNode ? &cstNode->returnSpecifierPosition : nullptr);
+    AstTypePack* typelist = parseOptionalReturnType(cstNode ? &cstNode->returnSpecifierPosition : nullptr);
+
+    AstLocal* funLocal = nullptr;
+
+    if (localName)
+        funLocal = pushLocal(Binding(*localName, nullptr));
+
+    unsigned int localsBegin = saveLocals();
+
+    Function fun;
+    fun.vararg = vararg;
+
+    functionStack.emplace_back(fun);
+
+    auto [self, vars] = prepareFunctionArguments(start, hasself, args);
+
+    AstStatBlock* body = parseBlock();
+
+    functionStack.pop_back();
+
+    restoreLocals(localsBegin);
+
+    Location end = lexer.current().location;
+
+    bool hasEnd = expectMatchEndAndConsume(Lexeme::ReservedEnd, matchFunction);
+    body->hasEnd = hasEnd;
+
+    if (FFlag::LuauStoreCSTData2)
+    {
+        AstExprFunction* node = allocator.alloc<AstExprFunction>(
+            Location(start, end),
+            attributes,
+            generics,
+            genericPacks,
+            self,
+            vars,
+            vararg,
+            varargLocation,
+            body,
+            functionStack.size(),
+            debugname,
+            typelist,
+            varargAnnotation,
+            argLocation
+        );
+        if (options.storeCstData)
+        {
+            cstNode->functionKeywordPosition = matchFunction.location.begin;
+            cstNodeMap[node] = cstNode;
+        }
+
+        return {node, funLocal};
+    }
+    else
+    {
+        return {
+            allocator.alloc<AstExprFunction>(
+                Location(start, end),
+                attributes,
+                generics,
+                genericPacks,
+                self,
+                vars,
+                vararg,
+                varargLocation,
+                body,
+                functionStack.size(),
+                debugname,
+                typelist,
+                varargAnnotation,
+                argLocation
+            ),
+            funLocal
+        };
+    }
+}
+
+std::pair<AstExprFunction*, AstLocal*> Parser::parseFunctionBody_DEPRECATED(
+    bool hasself,
+    const Lexeme& matchFunction,
+    const AstName& debugname,
+    const Name* localName,
+    const AstArray<AstAttr*>& attributes
+)
+{
+    LUAU_ASSERT(!FFlag::LuauStoreReturnTypesAsPackOnAst);
+
+    Location start = matchFunction.location;
+
+    if (FFlag::LuauFixFunctionWithAttributesStartLocation)
+    {
+        if (attributes.size > 0)
+            start = attributes.data[0]->location;
+    }
+
+    auto* cstNode = FFlag::LuauStoreCSTData2 && options.storeCstData ? allocator.alloc<CstExprFunction>() : nullptr;
+
+    auto [generics, genericPacks] =
+        FFlag::LuauStoreCSTData2 && cstNode
+            ? parseGenericTypeList(
+                  /* withDefaultValues= */ false, &cstNode->openGenericsPosition, &cstNode->genericsCommaPositions, &cstNode->closeGenericsPosition
+              )
+            : parseGenericTypeList(/* withDefaultValues= */ false);
+
+    MatchLexeme matchParen = lexer.current();
+    expectAndConsume('(', "function");
+
+    // NOTE: This was added in conjunction with passing `searchForMissing` to
+    // `expectMatchAndConsume` inside `parseTableType` so that the behavior of
+    // parsing code like below (note the missing `}`):
+    //
+    //  function (t: { a: number  ) end
+    //
+    // ... will still parse as (roughly):
+    //
+    //  function (t: { a: number }) end
+    //
+    matchRecoveryStopOnToken[')']++;
+
+    TempVector<Binding> args(scratchBinding);
+
+    bool vararg = false;
+    Location varargLocation;
+    AstTypePack* varargAnnotation = nullptr;
+
+    if (lexer.current().type != ')')
+        std::tie(vararg, varargLocation, varargAnnotation) =
+            parseBindingList(args, /* allowDot3= */ true, cstNode ? &cstNode->argsCommaPositions : nullptr);
+
+    std::optional<Location> argLocation;
+
+    if (matchParen.type == Lexeme::Type('(') && lexer.current().type == Lexeme::Type(')'))
+        argLocation = Location(matchParen.position, lexer.current().location.end);
+
+    expectMatchAndConsume(')', matchParen, true);
+
+    matchRecoveryStopOnToken[')']--;
+
+    std::optional<AstTypeList> typelist = parseOptionalReturnType_DEPRECATED(cstNode ? &cstNode->returnSpecifierPosition : nullptr);
 
     AstLocal* funLocal = nullptr;
 
@@ -1916,8 +2163,9 @@ AstTypePack* Parser::parseTypeList(
     return nullptr;
 }
 
-std::optional<AstTypeList> Parser::parseOptionalReturnType(Position* returnSpecifierPosition)
+AstTypePack* Parser::parseOptionalReturnType(Position* returnSpecifierPosition)
 {
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
     if (lexer.current().type == ':' || lexer.current().type == Lexeme::SkinnyArrow)
     {
         if (lexer.current().type == Lexeme::SkinnyArrow)
@@ -1929,7 +2177,41 @@ std::optional<AstTypeList> Parser::parseOptionalReturnType(Position* returnSpeci
 
         unsigned int oldRecursionCount = recursionCounter;
 
-        auto [_location, result] = parseReturnType();
+        auto result = parseReturnType();
+        LUAU_ASSERT(result);
+
+        // At this point, if we find a , character, it indicates that there are multiple return types
+        // in this type annotation, but the list wasn't wrapped in parentheses.
+        if (lexer.current().type == ',')
+        {
+            report(lexer.current().location, "Expected a statement, got ','; did you forget to wrap the list of return types in parentheses?");
+
+            nextLexeme();
+        }
+
+        recursionCounter = oldRecursionCount;
+
+        return result;
+    }
+
+    return nullptr;
+}
+
+std::optional<AstTypeList> Parser::parseOptionalReturnType_DEPRECATED(Luau::Position* returnSpecifierPosition)
+{
+    LUAU_ASSERT(!FFlag::LuauStoreReturnTypesAsPackOnAst);
+    if (lexer.current().type == ':' || lexer.current().type == Lexeme::SkinnyArrow)
+    {
+        if (lexer.current().type == Lexeme::SkinnyArrow)
+            report(lexer.current().location, "Function return type annotations are written after ':' instead of '->'");
+
+        if (FFlag::LuauStoreCSTData2 && returnSpecifierPosition)
+            *returnSpecifierPosition = lexer.current().location.begin;
+        nextLexeme();
+
+        unsigned int oldRecursionCount = recursionCounter;
+
+        auto [_location, result] = parseReturnType_DEPRECATED();
 
         // At this point, if we find a , character, it indicates that there are multiple return types
         // in this type annotation, but the list wasn't wrapped in parentheses.
@@ -1949,8 +2231,119 @@ std::optional<AstTypeList> Parser::parseOptionalReturnType(Position* returnSpeci
 }
 
 // ReturnType ::= Type | `(' TypeList `)'
-std::pair<Location, AstTypeList> Parser::parseReturnType()
+AstTypePack* Parser::parseReturnType()
 {
+    LUAU_ASSERT(FFlag::LuauStoreReturnTypesAsPackOnAst);
+    incrementRecursionCounter("type annotation");
+
+    Lexeme begin = lexer.current();
+
+    if (lexer.current().type != '(')
+    {
+        if (shouldParseTypePack(lexer))
+        {
+            return parseTypePack();
+        }
+        else
+        {
+            AstType* type = parseType();
+            AstTypePackExplicit* node = allocator.alloc<AstTypePackExplicit>(type->location, AstTypeList{copy(&type, 1), nullptr});
+            if (options.storeCstData)
+                cstNodeMap[node] = allocator.alloc<CstTypePackExplicit>();
+            return node;
+        }
+    }
+
+    nextLexeme();
+
+    Location innerBegin = lexer.current().location;
+
+    matchRecoveryStopOnToken[Lexeme::SkinnyArrow]++;
+
+    TempVector<AstType*> result(scratchType);
+    TempVector<std::optional<AstArgumentName>> resultNames(scratchOptArgName);
+    TempVector<Position> commaPositions(scratchPosition);
+    AstTypePack* varargAnnotation = nullptr;
+
+    // possibly () -> ReturnType
+    if (lexer.current().type != ')')
+    {
+        if (options.storeCstData)
+            varargAnnotation = parseTypeList(result, resultNames, &commaPositions);
+        else
+            varargAnnotation = parseTypeList(result, resultNames);
+    }
+
+    const Location location{begin.location, lexer.current().location};
+    Position closeParenthesesPosition = lexer.current().location.begin;
+    expectMatchAndConsume(')', begin, true);
+
+    matchRecoveryStopOnToken[Lexeme::SkinnyArrow]--;
+
+    if (lexer.current().type != Lexeme::SkinnyArrow && resultNames.empty())
+    {
+        // If it turns out that it's just '(A)', it's possible that there are unions/intersections to follow, so fold over it.
+        if (FFlag::LuauAstTypeGroup3)
+        {
+            if (result.size() == 1)
+            {
+                // TODO(CLI-140667): stop parsing type suffix when varargAnnotation != nullptr - this should be a parse error
+                AstType* inner = varargAnnotation == nullptr ? allocator.alloc<AstTypeGroup>(location, result[0]) : result[0];
+                AstType* returnType = parseTypeSuffix(inner, begin.location);
+
+                if (DFFlag::DebugLuauReportReturnTypeVariadicWithTypeSuffix && varargAnnotation != nullptr &&
+                    (returnType->is<AstTypeUnion>() || returnType->is<AstTypeIntersection>()))
+                    luau_telemetry_parsed_return_type_variadic_with_type_suffix = true;
+
+                // If parseType parses nothing, then returnType->location.end only points at the last non-type-pack
+                // type to successfully parse.  We need the span of the whole annotation.
+                Position endPos = result.size() == 1 ? location.end : returnType->location.end;
+
+                AstTypePackExplicit* node = allocator.alloc<AstTypePackExplicit>(Location{location.begin, endPos}, AstTypeList{copy(&returnType, 1), varargAnnotation});
+                if (options.storeCstData)
+                    cstNodeMap[node] = allocator.alloc<CstTypePackExplicit>();
+                return node;
+            }
+        }
+        else
+        {
+            if (result.size() == 1)
+            {
+                AstType* returnType = parseTypeSuffix(result[0], innerBegin);
+
+                if (DFFlag::DebugLuauReportReturnTypeVariadicWithTypeSuffix && varargAnnotation != nullptr &&
+                    (returnType->is<AstTypeUnion>() || returnType->is<AstTypeIntersection>()))
+                    luau_telemetry_parsed_return_type_variadic_with_type_suffix = true;
+
+                // If parseType parses nothing, then returnType->location.end only points at the last non-type-pack
+                // type to successfully parse.  We need the span of the whole annotation.
+                Position endPos = result.size() == 1 ? location.end : returnType->location.end;
+
+                AstTypePackExplicit* node = allocator.alloc<AstTypePackExplicit>(Location{location.begin, endPos}, AstTypeList{copy(&returnType, 1), varargAnnotation});
+                if (options.storeCstData)
+                    cstNodeMap[node] = allocator.alloc<CstTypePackExplicit>();
+                return node;
+            }
+        }
+
+        AstTypePackExplicit* node = allocator.alloc<AstTypePackExplicit>(location, AstTypeList{copy(result), varargAnnotation});
+        if (options.storeCstData)
+            cstNodeMap[node] = allocator.alloc<CstTypePackExplicit>(location.begin, closeParenthesesPosition, copy(commaPositions));
+        return node;
+    }
+
+    AstType* tail = parseFunctionTypeTail(begin, {nullptr, 0}, {}, {}, copy(result), copy(resultNames), varargAnnotation);
+
+    AstTypePackExplicit* node = allocator.alloc<AstTypePackExplicit>(Location{location, tail->location}, AstTypeList{copy(&tail, 1), nullptr});
+    if (options.storeCstData)
+        cstNodeMap[node] = allocator.alloc<CstTypePackExplicit>();
+    return node;
+}
+
+// ReturnType ::= Type | `(' TypeList `)'
+std::pair<Location, AstTypeList> Parser::parseReturnType_DEPRECATED()
+{
+    LUAU_ASSERT(!FFlag::LuauStoreReturnTypesAsPackOnAst);
     incrementRecursionCounter("type annotation");
 
     Lexeme begin = lexer.current();
@@ -2574,13 +2967,26 @@ AstType* Parser::parseFunctionTypeTail(
         expectAndConsume(Lexeme::SkinnyArrow, "function type");
     }
 
-    auto [endLocation, returnTypeList] = parseReturnType();
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        auto returnType = parseReturnType();
+        LUAU_ASSERT(returnType);
+
+        AstTypeList paramTypes = AstTypeList{params, varargAnnotation};
+        return allocator.alloc<AstTypeFunction>(
+            Location(begin.location, returnType->location), attributes, generics, genericPacks, paramTypes, paramNames, returnType
+        );
+    }
+    else
+    {
+        auto [endLocation, returnTypeList] = parseReturnType_DEPRECATED();
 
         AstTypeList paramTypes = AstTypeList{params, varargAnnotation};
         return allocator.alloc<AstTypeFunction>(
             Location(begin.location, endLocation), attributes, generics, genericPacks, paramTypes, paramNames, returnTypeList
         );
     }
+}
 
 static bool isTypeFollow(Lexeme::Type c)
 {
@@ -2693,17 +3099,8 @@ AstType* Parser::parseTypeSuffix(AstType* type, const Location& begin)
         }
     }
 
-    if (FFlag::LuauPreserveUnionIntersectionNodeForLeadingTokenSingleType)
-    {
     if (parts.size() == 1 && !isUnion && !isIntersection)
         return parts[0];
-    }
-    else
-    {
-        if (parts.size() == 1)
-            return parts[0];
-    }
-
     if (isUnion && isIntersection)
     {
         return reportTypeError(
@@ -3536,7 +3933,10 @@ AstExpr* Parser::parseSimpleExpr()
         Lexeme matchFunction = lexer.current();
         nextLexeme();
 
+        if (FFlag::LuauStoreReturnTypesAsPackOnAst)
             return parseFunctionBody(false, matchFunction, AstName(), nullptr, attributes).first;
+        else
+            return parseFunctionBody_DEPRECATED(false, matchFunction, AstName(), nullptr, attributes).first;
     }
     else if (lexer.current().type == Lexeme::Number)
     {
@@ -4666,7 +5066,7 @@ void Parser::report(const Location& location, const char* format, va_list args)
 
     parseErrors.emplace_back(location, message);
 
-    if (parseErrors.size() >= unsigned(FInt::LuauParseErrorLimit) && (!FFlag::ParserNoErrorLimit || !options.noErrorLimit))
+    if (parseErrors.size() >= unsigned(FInt::LuauParseErrorLimit) && !options.noErrorLimit)
         ParseError::raise(location, "Reached error limit (%d)", int(FInt::LuauParseErrorLimit));
 }
 

CLI/src/ReplRequirer.cpp

@@ -131,7 +131,7 @@ static luarequire_WriteResult get_config(lua_State* L, void* ctx, char* buffer,
     return write(getFileContents(req->absPath, "/.luaurc"), buffer, buffer_size, size_out);
 }
 
-static int load(lua_State* L, void* ctx, const char* chunkname, const char* contents)
+static int load(lua_State* L, void* ctx, const char* path, const char* chunkname, const char* contents)
 {
     ReplRequirer* req = static_cast<ReplRequirer*>(ctx);
 

Compiler/src/Compiler.cpp

@@ -28,6 +28,8 @@ LUAU_FASTINTVARIABLE(LuauCompileInlineDepth, 5)
 
 LUAU_FASTFLAGVARIABLE(LuauSeparateCompilerTypeInfo)
 
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
+
 namespace Luau
 {
 
@@ -4317,6 +4319,8 @@ void compileOrThrow(BytecodeBuilder& bytecode, const ParseResult& parseResult, c
             mainFlags |= LPF_NATIVE_FUNCTION;
     }
 
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
         AstExprFunction main(
             root->location,
             /* attributes= */ AstArray<AstAttr*>({nullptr, 0}),
@@ -4328,7 +4332,8 @@ void compileOrThrow(BytecodeBuilder& bytecode, const ParseResult& parseResult, c
             /* varargLocation= */ Luau::Location(),
             root,
             /* functionDepth= */ 0,
-        /* debugname= */ AstName()
+            /* debugname= */ AstName(),
+            /* returnAnnotation= */ nullptr
         );
         uint32_t mainid = compiler.compileFunction(&main, mainFlags);
 
@@ -4338,6 +4343,31 @@ void compileOrThrow(BytecodeBuilder& bytecode, const ParseResult& parseResult, c
         bytecode.setMainFunction(mainid);
         bytecode.finalize();
     }
+    else
+    {
+        AstExprFunction main(
+            root->location,
+            /* attributes= */ AstArray<AstAttr*>({nullptr, 0}),
+            /* generics= */ AstArray<AstGenericType*>(),
+            /* genericPacks= */ AstArray<AstGenericTypePack*>(),
+            /* self= */ nullptr,
+            AstArray<AstLocal*>(),
+            /* vararg= */ true,
+            /* varargLocation= */ Luau::Location(),
+            root,
+            /* functionDepth= */ 0,
+            /* debugname= */ AstName(),
+            /* returnAnnotation= */ std::nullopt
+        );
+        uint32_t mainid = compiler.compileFunction(&main, mainFlags);
+
+        const Compiler::Function* mainf = compiler.functions.find(&main);
+        LUAU_ASSERT(mainf && mainf->upvals.empty());
+
+        bytecode.setMainFunction(mainid);
+        bytecode.finalize();
+    }
+}
 
 void compileOrThrow(BytecodeBuilder& bytecode, const std::string& source, const CompileOptions& options, const ParseOptions& parseOptions)
 {

Require/Navigator/include/Luau/RequireNavigator.h

@@ -3,7 +3,6 @@
 
 #include "Luau/Config.h"
 
-#include <functional>
 #include <optional>
 #include <string>
 #include <string_view>
@@ -88,6 +87,11 @@ private:
     [[nodiscard]] Error navigateToAlias(const std::string& alias, const std::string& value);
     [[nodiscard]] Error navigateToAndPopulateConfig(const std::string& desiredAlias);
 
+    [[nodiscard]] Error resetToRequirer();
+    [[nodiscard]] Error jumpToAlias(const std::string& aliasPath);
+    [[nodiscard]] Error navigateToParent(std::optional<std::string> previousComponent);
+    [[nodiscard]] Error navigateToChild(const std::string& component);
+
     NavigationContext& navigationContext;
     ErrorHandler& errorHandler;
     Luau::Config config;

Require/Navigator/src/RequireNavigator.cpp

@@ -10,24 +10,11 @@
 #include <optional>
 #include <utility>
 
-static constexpr char kRequireErrorAmbiguous[] = "require path could not be resolved to a unique file";
-static constexpr char kRequireErrorGeneric[] = "error requiring module";
-
 namespace Luau::Require
 {
 
 using Error = std::optional<std::string>;
 
-static Error toError(NavigationContext::NavigateResult result)
-{
-    if (result == NavigationContext::NavigateResult::Success)
-        return std::nullopt;
-    if (result == NavigationContext::NavigateResult::Ambiguous)
-        return kRequireErrorAmbiguous;
-    else
-        return kRequireErrorGeneric;
-}
-
 static std::string extractAlias(std::string_view path)
 {
     // To ignore the '@' alias prefix when processing the alias
@@ -53,7 +40,7 @@ Navigator::Status Navigator::navigate(std::string path)
 {
     std::replace(path.begin(), path.end(), '\\', '/');
 
-    if (Error error = toError(navigationContext.reset(navigationContext.getRequirerIdentifier())))
+    if (Error error = resetToRequirer())
     {
         errorHandler.reportError(*error);
         return Status::ErrorReported;
@@ -98,7 +85,7 @@ Error Navigator::navigateImpl(std::string_view path)
 
             // If the alias is "@self", we reset to the requirer's context and
             // navigate directly from there.
-            if (Error error = toError(navigationContext.reset(navigationContext.getRequirerIdentifier())))
+            if (Error error = resetToRequirer())
                 return error;
             if (Error error = navigateThroughPath(path))
                 return error;
@@ -114,7 +101,7 @@ Error Navigator::navigateImpl(std::string_view path)
 
     if (pathType == PathType::RelativeToCurrent || pathType == PathType::RelativeToParent)
     {
-        if (Error error = toError(navigationContext.toParent()))
+        if (Error error = navigateToParent(std::nullopt))
             return error;
         if (Error error = navigateThroughPath(path))
             return error;
@@ -133,6 +120,7 @@ Error Navigator::navigateThroughPath(std::string_view path)
         components = splitPath(components.second);
     }
 
+    std::optional<std::string> previousComponent;
     while (!(components.first.empty() && components.second.empty()))
     {
         if (components.first == "." || components.first.empty())
@@ -142,14 +130,15 @@ Error Navigator::navigateThroughPath(std::string_view path)
         }
         else if (components.first == "..")
         {
-            if (Error error = toError(navigationContext.toParent()))
+            if (Error error = navigateToParent(previousComponent))
                 return error;
         }
         else
         {
-            if (Error error = toError(navigationContext.toChild(std::string{components.first})))
+            if (Error error = navigateToChild(std::string{components.first}))
                 return error;
         }
+        previousComponent = components.first;
         components = splitPath(components.second);
     }
 
@@ -167,11 +156,11 @@ Error Navigator::navigateToAlias(const std::string& alias, const std::string& va
     }
     else if (pathType == PathType::Aliased)
     {
-        return "@" + alias + " cannot point to other aliases";
+        return "alias \"@" + alias + "\" cannot point to an aliased path (\"" + value + "\")";
     }
     else
     {
-        if (Error error = toError(navigationContext.jumpToAlias(value)))
+        if (Error error = jumpToAlias(value))
             return error;
     }
 
@@ -189,7 +178,7 @@ Error Navigator::navigateToAndPopulateConfig(const std::string& desiredAlias)
         {
             std::optional<std::string> configContents = navigationContext.getConfig();
             if (!configContents)
-                return "could not get configuration file contents";
+                return "could not get configuration file contents to resolve alias \"" + desiredAlias + "\"";
 
             Luau::ConfigOptions opts;
             Luau::ConfigOptions::AliasOptions aliasOpts;
@@ -205,4 +194,56 @@ Error Navigator::navigateToAndPopulateConfig(const std::string& desiredAlias)
     return std::nullopt;
 }
 
+Error Navigator::resetToRequirer()
+{
+    NavigationContext::NavigateResult result = navigationContext.reset(navigationContext.getRequirerIdentifier());
+    if (result == NavigationContext::NavigateResult::Success)
+        return std::nullopt;
+
+    std::string errorMessage = "could not reset to requiring context";
+    if (result == NavigationContext::NavigateResult::Ambiguous)
+        errorMessage += " (ambiguous)";
+    return errorMessage;
+}
+
+Error Navigator::jumpToAlias(const std::string& aliasPath)
+{
+    NavigationContext::NavigateResult result = navigationContext.jumpToAlias(aliasPath);
+    if (result == NavigationContext::NavigateResult::Success)
+        return std::nullopt;
+
+    std::string errorMessage = "could not jump to alias \"" + aliasPath + "\"";
+    if (result == NavigationContext::NavigateResult::Ambiguous)
+        errorMessage += " (ambiguous)";
+    return errorMessage;
+}
+
+Error Navigator::navigateToParent(std::optional<std::string> previousComponent)
+{
+    NavigationContext::NavigateResult result = navigationContext.toParent();
+    if (result == NavigationContext::NavigateResult::Success)
+        return std::nullopt;
+
+    std::string errorMessage;
+    if (previousComponent)
+        errorMessage = "could not get parent of component \"" + *previousComponent + "\"";
+    else
+        errorMessage = "could not get parent of requiring context";
+    if (result == NavigationContext::NavigateResult::Ambiguous)
+        errorMessage += " (ambiguous)";
+    return errorMessage;
+}
+
+Error Navigator::navigateToChild(const std::string& component)
+{
+    NavigationContext::NavigateResult result = navigationContext.toChild(component);
+    if (result == NavigationContext::NavigateResult::Success)
+        return std::nullopt;
+
+    std::string errorMessage = "could not resolve child component \"" + component + "\"";
+    if (result == NavigationContext::NavigateResult::Ambiguous)
+        errorMessage += " (ambiguous)";
+    return errorMessage;
+}
+
 } // namespace Luau::Require

Require/Runtime/include/Luau/Require.h

@@ -106,8 +106,10 @@ struct luarequire_Configuration
     luarequire_WriteResult (*get_config)(lua_State* L, void* ctx, char* buffer, size_t buffer_size, size_t* size_out);
 
     // Executes the module and places the result on the stack. Returns the
-    // number of results placed on the stack.
+    // number of results placed on the stack. Returning -1 directs the requiring
-    int (*load)(lua_State* L, void* ctx, const char* chunkname, const char* contents);
+    // thread to yield. In this case, this thread should be resumed with the
+    // module result pushed onto its stack.
+    int (*load)(lua_State* L, void* ctx, const char* path, const char* chunkname, const char* contents);
 };
 
 // Populates function pointers in the given luarequire_Configuration.
@@ -115,7 +117,25 @@ typedef void (*luarequire_Configuration_init)(luarequire_Configuration* config);
 
 // Initializes and pushes the require closure onto the stack without
 // registration.
-LUALIB_API int lua_pushrequire(lua_State* L, luarequire_Configuration_init config_init, void* ctx);
+LUALIB_API int luarequire_pushrequire(lua_State* L, luarequire_Configuration_init config_init, void* ctx);
 
 // Initializes the require library and registers it globally.
 LUALIB_API void luaopen_require(lua_State* L, luarequire_Configuration_init config_init, void* ctx);
+
+// Initializes and pushes a "proxyrequire" closure onto the stack. This function
+// takes two parameters: the string path to resolve and the chunkname of an
+// existing module. The path is resolved as if it were being required from the
+// module that the chunkname represents.
+LUALIB_API int luarequire_pushproxyrequire(lua_State* L, luarequire_Configuration_init config_init, void* ctx);
+
+// Registers an aliased require path to a result. After registration, the given
+// result will always be immediately returned when the given path is required.
+// Expects the path and table to be passed as arguments on the stack.
+LUALIB_API int luarequire_registermodule(lua_State* L);
+
+// Clears the entry associated with the given cache key from the require cache.
+// Expects the cache key to be passed as an argument on the stack.
+LUALIB_API int luarequire_clearcacheentry(lua_State* L);
+
+// Clears all entries from the require cache.
+LUALIB_API int luarequire_clearcache(lua_State* L);

Require/Runtime/src/Navigation.cpp

@@ -6,6 +6,8 @@
 #include "lua.h"
 #include "lualib.h"
 
+#include <string>
+
 static constexpr size_t initalFileBufferSize = 1024;
 static constexpr size_t initalIdentifierBufferSize = 64;
 
@@ -111,14 +113,16 @@ std::optional<std::string> RuntimeNavigationContext::getStringFromCWriter(
 }
 
 
-RuntimeErrorHandler::RuntimeErrorHandler(lua_State* L)
+RuntimeErrorHandler::RuntimeErrorHandler(lua_State* L, std::string requiredPath)
     : L(L)
+    , errorPrefix("error requiring module \"" + std::move(requiredPath) + "\": ")
 {
 }
 
 void RuntimeErrorHandler::reportError(std::string message)
 {
-    luaL_errorL(L, "%s", message.c_str());
+    std::string fullError = errorPrefix + std::move(message);
+    luaL_errorL(L, "%s", fullError.c_str());
 }
 
 } // namespace Luau::Require

Require/Runtime/src/Navigation.h

@@ -4,6 +4,8 @@
 #include "Luau/RequireNavigator.h"
 #include "Luau/Require.h"
 
+#include <string>
+
 struct lua_State;
 struct luarequire_Configuration;
 
@@ -48,11 +50,12 @@ private:
 class RuntimeErrorHandler : public ErrorHandler
 {
 public:
-    RuntimeErrorHandler(lua_State* L);
+    RuntimeErrorHandler(lua_State* L, std::string requiredPath);
     void reportError(std::string message) override;
 
 private:
     lua_State* L;
+    std::string errorPrefix;
 };
 
 } // namespace Luau::Require

Require/Runtime/src/Require.cpp

@@ -35,7 +35,13 @@ static void validateConfig(lua_State* L, const luarequire_Configuration& config)
         luaL_error(L, "require configuration is missing required function pointer: load");
 }
 
-int lua_pushrequire(lua_State* L, luarequire_Configuration_init config_init, void* ctx)
+static int pushrequireclosureinternal(
+    lua_State* L,
+    luarequire_Configuration_init config_init,
+    void* ctx,
+    lua_CFunction requirelikefunc,
+    const char* debugname
+)
 {
     luarequire_Configuration* config = static_cast<luarequire_Configuration*>(lua_newuserdata(L, sizeof(luarequire_Configuration)));
     if (!config)
@@ -46,13 +52,38 @@ int lua_pushrequire(lua_State* L, luarequire_Configuration_init config_init, voi
 
     lua_pushlightuserdata(L, ctx);
 
-    // "require" captures config and ctx as upvalues
+    // require-like closure captures config and ctx as upvalues
-    lua_pushcclosure(L, Luau::Require::lua_require, "require", 2);
+    lua_pushcclosurek(L, requirelikefunc, debugname, 2, Luau::Require::lua_requirecont);
     return 1;
 }
 
+int luarequire_pushrequire(lua_State* L, luarequire_Configuration_init config_init, void* ctx)
+{
+    return pushrequireclosureinternal(L, config_init, ctx, Luau::Require::lua_require, "require");
+}
+
 void luaopen_require(lua_State* L, luarequire_Configuration_init config_init, void* ctx)
 {
-    lua_pushrequire(L, config_init, ctx);
+    luarequire_pushrequire(L, config_init, ctx);
     lua_setglobal(L, "require");
 }
+
+int luarequire_pushproxyrequire(lua_State* L, luarequire_Configuration_init config_init, void* ctx)
+{
+    return pushrequireclosureinternal(L, config_init, ctx, Luau::Require::lua_proxyrequire, "proxyrequire");
+}
+
+int luarequire_registermodule(lua_State* L)
+{
+    return Luau::Require::registerModuleImpl(L);
+}
+
+int luarequire_clearcacheentry(lua_State* L)
+{
+    return Luau::Require::clearCacheEntry(L);
+}
+
+int luarequire_clearcache(lua_State* L)
+{
+    return Luau::Require::clearCache(L);
+}

Require/Runtime/src/RequireImpl.cpp

@@ -13,7 +13,11 @@
 namespace Luau::Require
 {
 
-static const char* cacheTableKey = "_MODULES";
+// Stores explicitly registered modules.
+static const char* registeredCacheTableKey = "_REGISTEREDMODULES";
+
+// Stores the results of require calls.
+static const char* requiredCacheTableKey = "_MODULES";
 
 struct ResolvedRequire
 {
@@ -32,7 +36,7 @@ struct ResolvedRequire
 
 static bool isCached(lua_State* L, const std::string& key)
 {
-    luaL_findtable(L, LUA_REGISTRYINDEX, cacheTableKey, 1);
+    luaL_findtable(L, LUA_REGISTRYINDEX, requiredCacheTableKey, 1);
     lua_getfield(L, -1, key.c_str());
     bool cached = !lua_isnil(L, -1);
     lua_pop(L, 2);
@@ -40,16 +44,13 @@ static bool isCached(lua_State* L, const std::string& key)
     return cached;
 }
 
-static ResolvedRequire resolveRequire(luarequire_Configuration* lrc, lua_State* L, void* ctx, std::string path)
+static ResolvedRequire resolveRequire(luarequire_Configuration* lrc, lua_State* L, void* ctx, const char* requirerChunkname, std::string path)
 {
-    lua_Debug ar;
+    if (!lrc->is_require_allowed(L, ctx, requirerChunkname))
-    lua_getinfo(L, 1, "s", &ar);
-
-    if (!lrc->is_require_allowed(L, ctx, ar.source))
         luaL_error(L, "require is not supported in this context");
 
-    RuntimeNavigationContext navigationContext{lrc, L, ctx, ar.source};
+    RuntimeNavigationContext navigationContext{lrc, L, ctx, requirerChunkname};
-    RuntimeErrorHandler errorHandler{L}; // Errors reported directly to lua_State.
+    RuntimeErrorHandler errorHandler{L, path}; // Errors reported directly to lua_State.
 
     Navigator navigator(navigationContext, errorHandler);
 
@@ -60,7 +61,7 @@ static ResolvedRequire resolveRequire(luarequire_Configuration* lrc, lua_State*
 
     if (!navigationContext.isModulePresent())
     {
-        luaL_errorL(L, "no module present at resolved path");
+        errorHandler.reportError("no module present at resolved path");
         return ResolvedRequire{ResolvedRequire::Status::ErrorReported};
     }
 
@@ -74,7 +75,7 @@ static ResolvedRequire resolveRequire(luarequire_Configuration* lrc, lua_State*
     if (isCached(L, *cacheKey))
     {
         // Put cached result on top of stack before returning.
-        lua_getfield(L, LUA_REGISTRYINDEX, cacheTableKey);
+        lua_getfield(L, LUA_REGISTRYINDEX, requiredCacheTableKey);
         lua_getfield(L, -1, cacheKey->c_str());
         lua_remove(L, -2);
 
@@ -103,21 +104,27 @@ static ResolvedRequire resolveRequire(luarequire_Configuration* lrc, lua_State*
     };
 }
 
-int lua_require(lua_State* L)
+static int checkRegisteredModules(lua_State* L, const char* path)
 {
-    luarequire_Configuration* lrc = static_cast<luarequire_Configuration*>(lua_touserdata(L, lua_upvalueindex(1)));
+    luaL_findtable(L, LUA_REGISTRYINDEX, registeredCacheTableKey, 1);
-    if (!lrc)
+    lua_getfield(L, -1, path);
-        luaL_error(L, "unable to find require configuration");
+    if (lua_isnil(L, -1))
+    {
+        lua_pop(L, 2);
+        return 0;
+    }
 
-    void* ctx = lua_tolightuserdata(L, lua_upvalueindex(2));
+    lua_remove(L, -2);
-
-    const char* path = luaL_checkstring(L, 1);
-
-    ResolvedRequire resolvedRequire = resolveRequire(lrc, L, ctx, path);
-    if (resolvedRequire.status == ResolvedRequire::Status::Cached)
     return 1;
+}
+
+int lua_requirecont(lua_State* L, int status)
+{
+    // Number of stack arguments present before this continuation is called.
+    const int numStackArgs = 2;
+    const int numResults = lua_gettop(L) - numStackArgs;
+    const char* cacheKey = luaL_checkstring(L, 2);
 
-    int numResults = lrc->load(L, ctx, resolvedRequire.chunkname.c_str(), resolvedRequire.contents.c_str());
     if (numResults > 1)
         luaL_error(L, "module must return a single value");
 
@@ -127,13 +134,13 @@ int lua_require(lua_State* L)
         // Initial stack state
         // (-1) result
 
-        lua_getfield(L, LUA_REGISTRYINDEX, cacheTableKey);
+        lua_getfield(L, LUA_REGISTRYINDEX, requiredCacheTableKey);
         // (-2) result, (-1) cache table
 
         lua_pushvalue(L, -2);
         // (-3) result, (-2) cache table, (-1) result
 
-        lua_setfield(L, -2, resolvedRequire.cacheKey.c_str());
+        lua_setfield(L, -2, cacheKey);
         // (-2) result, (-1) cache table
 
         lua_pop(L, 1);
@@ -143,4 +150,103 @@ int lua_require(lua_State* L)
     return numResults;
 }
 
+int lua_requireinternal(lua_State* L, const char* requirerChunkname)
+{
+    // If modifying the state of the stack, please update numStackArgs in the
+    // lua_requirecont continuation function.
+
+    luarequire_Configuration* lrc = static_cast<luarequire_Configuration*>(lua_touserdata(L, lua_upvalueindex(1)));
+    if (!lrc)
+        luaL_error(L, "unable to find require configuration");
+
+    void* ctx = lua_tolightuserdata(L, lua_upvalueindex(2));
+
+    // (1) path
+    const char* path = luaL_checkstring(L, 1);
+
+    if (checkRegisteredModules(L, path) == 1)
+        return 1;
+
+    ResolvedRequire resolvedRequire = resolveRequire(lrc, L, ctx, requirerChunkname, path);
+    if (resolvedRequire.status == ResolvedRequire::Status::Cached)
+        return 1;
+
+    // (1) path, (2) cacheKey
+    lua_pushstring(L, resolvedRequire.cacheKey.c_str());
+
+    int numArgsBeforeLoad = lua_gettop(L);
+    int numResults = lrc->load(L, ctx, path, resolvedRequire.chunkname.c_str(), resolvedRequire.contents.c_str());
+    if (numResults == -1)
+    {
+        if (lua_gettop(L) != numArgsBeforeLoad)
+            luaL_error(L, "stack cannot be modified when require yields");
+
+        return lua_yield(L, 0);
+    }
+
+    return lua_requirecont(L, LUA_OK);
+}
+
+int lua_proxyrequire(lua_State* L)
+{
+    const char* requirerChunkname = luaL_checkstring(L, 2);
+    return lua_requireinternal(L, requirerChunkname);
+}
+
+int lua_require(lua_State* L)
+{
+    lua_Debug ar;
+    int level = 1;
+
+    do
+    {
+        if (!lua_getinfo(L, level++, "s", &ar))
+            luaL_error(L, "require is not supported in this context");
+    } while (ar.what[0] == 'C');
+
+    return lua_requireinternal(L, ar.source);
+}
+
+int registerModuleImpl(lua_State* L)
+{
+    if (lua_gettop(L) != 2)
+        luaL_error(L, "expected 2 arguments: aliased require path and desired result");
+
+    size_t len;
+    const char* path = luaL_checklstring(L, 1, &len);
+    std::string_view pathView(path, len);
+    if (pathView.empty() || pathView[0] != '@')
+        luaL_argerrorL(L, 1, "path must begin with '@'");
+
+    luaL_findtable(L, LUA_REGISTRYINDEX, registeredCacheTableKey, 1);
+    // (1) path, (2) result, (3) cache table
+
+    lua_insert(L, 1);
+    // (1) cache table, (2) path, (3) result
+
+    lua_settable(L, 1);
+    // (1) cache table
+
+    lua_pop(L, 1);
+
+    return 0;
+}
+
+int clearCacheEntry(lua_State* L)
+{
+    const char* cacheKey = luaL_checkstring(L, 1);
+    luaL_findtable(L, LUA_REGISTRYINDEX, requiredCacheTableKey, 1);
+    lua_pushnil(L);
+    lua_setfield(L, -2, cacheKey);
+    lua_pop(L, 1);
+    return 0;
+}
+
+int clearCache(lua_State* L)
+{
+    lua_newtable(L);
+    lua_setfield(L, LUA_REGISTRYINDEX, requiredCacheTableKey);
+    return 0;
+}
+
 } // namespace Luau::Require

Require/Runtime/src/RequireImpl.h

@@ -7,5 +7,12 @@ namespace Luau::Require
 {
 
 int lua_require(lua_State* L);
+int lua_proxyrequire(lua_State* L);
+int lua_requirecont(lua_State* L, int status);
+
+int registerModuleImpl(lua_State* L);
+
+int clearCacheEntry(lua_State* L);
+int clearCache(lua_State* L);
 
 } // namespace Luau::Require

Sources.cmake

@@ -179,6 +179,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/include/Luau/Clone.h
     Analysis/include/Luau/Constraint.h
     Analysis/include/Luau/ConstraintGenerator.h
+    Analysis/include/Luau/ConstraintSet.h
     Analysis/include/Luau/ConstraintSolver.h
     Analysis/include/Luau/ControlFlow.h
     Analysis/include/Luau/DataFlowGraph.h

VM/include/lualib.h

@@ -58,6 +58,9 @@ LUALIB_API const char* luaL_findtable(lua_State* L, int idx, const char* fname,
 
 LUALIB_API const char* luaL_typename(lua_State* L, int idx);
 
+// wrapper for making calls from yieldable C functions
+LUALIB_API int luaL_callyieldable(lua_State* L, int nargs, int nresults);
+
 /*
 ** ===============================================================
 ** some useful macros

VM/src/laux.cpp

@@ -12,6 +12,7 @@
 #include <string.h>
 
 LUAU_FASTFLAGVARIABLE(LuauLibWhereErrorAutoreserve)
+LUAU_FASTFLAG(LuauYieldableContinuations)
 
 // convert a stack index to positive
 #define abs_index(L, i) ((i) > 0 || (i) <= LUA_REGISTRYINDEX ? (i) : lua_gettop(L) + (i) + 1)
@@ -355,6 +356,22 @@ const char* luaL_typename(lua_State* L, int idx)
     return obj ? luaT_objtypename(L, obj) : "no value";
 }
 
+int luaL_callyieldable(lua_State* L, int nargs, int nresults)
+{
+    LUAU_ASSERT(FFlag::LuauYieldableContinuations);
+
+    api_check(L, iscfunction(L->ci->func));
+    Closure* cl = clvalue(L->ci->func);
+    api_check(L, cl->c.cont);
+
+    lua_call(L, nargs, nresults);
+
+    if (L->status == LUA_YIELD || L->status == LUA_BREAK)
+        return -1; // -1 is a marker for yielding from C
+
+    return cl->c.cont(L, LUA_OK);
+}
+
 /*
 ** {======================================================
 ** Generic Buffer manipulation

VM/src/lbaselib.cpp

@@ -11,6 +11,8 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+LUAU_FASTFLAG(LuauYieldableContinuations)
+
 static void writestring(const char* s, size_t l)
 {
     fwrite(s, 1, l, stdout);
@@ -294,10 +296,18 @@ static int luaB_pcally(lua_State* L)
     // any errors from this point on are handled by continuation
     L->ci->flags |= LUA_CALLINFO_HANDLE;
 
+    if (!FFlag::LuauYieldableContinuations)
+    {
         // maintain yieldable invariant (baseCcalls <= nCcalls)
         L->baseCcalls++;
+    }
+
     int status = luaD_pcall(L, luaB_pcallrun, func, savestack(L, func), 0);
+
+    if (!FFlag::LuauYieldableContinuations)
+    {
         L->baseCcalls--;
+    }
 
     // necessary to accomodate functions that return lots of values
     expandstacklimit(L, L->top);
@@ -348,12 +358,20 @@ static int luaB_xpcally(lua_State* L)
     StkId errf = L->base;
     StkId func = L->base + 1;
 
+    if (!FFlag::LuauYieldableContinuations)
+    {
         // maintain yieldable invariant (baseCcalls <= nCcalls)
         L->baseCcalls++;
-    int status = luaD_pcall(L, luaB_pcallrun, func, savestack(L, func), savestack(L, errf));
+    }
-    L->baseCcalls--;
 
-    // necessary to accomodate functions that return lots of values
+    int status = luaD_pcall(L, luaB_pcallrun, func, savestack(L, func), savestack(L, errf));
+
+    if (!FFlag::LuauYieldableContinuations)
+    {
+        L->baseCcalls--;
+    }
+
+    // necessary to accommodate functions that return lots of values
     expandstacklimit(L, L->top);
 
     // yielding means we need to propagate yield; resume will call continuation function later

VM/src/ldo.cpp

@@ -17,6 +17,8 @@
 
 #include <string.h>
 
+LUAU_FASTFLAGVARIABLE(LuauYieldableContinuations)
+
 // keep max stack allocation request under 1GB
 #define MAX_STACK_SIZE (int(1024 / sizeof(TValue)) * 1024 * 1024)
 
@@ -260,6 +262,60 @@ void luaD_call(lua_State* L, StkId func, int nresults)
     if (++L->nCcalls >= LUAI_MAXCCALLS)
         luaD_checkCstack(L);
 
+    if (FFlag::LuauYieldableContinuations)
+    {
+        // when called from a yieldable C function, maintain yieldable invariant (baseCcalls <= nCcalls)
+        bool fromyieldableccall = false;
+
+        if (L->ci != L->base_ci)
+        {
+            Closure* ccl = clvalue(L->ci->func);
+
+            if (ccl->isC && ccl->c.cont)
+            {
+                fromyieldableccall = true;
+                L->baseCcalls++;
+            }
+        }
+
+        ptrdiff_t funcoffset = savestack(L, func);
+        ptrdiff_t cioffset = saveci(L, L->ci);
+
+        if (luau_precall(L, func, nresults) == PCRLUA)
+        {                                        // is a Lua function?
+            L->ci->flags |= LUA_CALLINFO_RETURN; // luau_execute will stop after returning from the stack frame
+
+            bool oldactive = L->isactive;
+            L->isactive = true;
+            luaC_threadbarrier(L);
+
+            luau_execute(L); // call it
+
+            if (!oldactive)
+                L->isactive = false;
+        }
+
+        bool yielded = L->status == LUA_YIELD || L->status == LUA_BREAK;
+
+        if (fromyieldableccall)
+        {
+            // restore original yieldable invariant
+            // in case of an error, this would either be restored by luaD_pcall or the thread would no longer be resumable
+            L->baseCcalls--;
+
+            // on yield, we have to set the CallInfo top of the C function including slots for expected results, to restore later
+            if (yielded)
+            {
+                CallInfo* callerci = restoreci(L, cioffset);
+                callerci->top = restorestack(L, funcoffset) + (nresults != LUA_MULTRET ? nresults : 0);
+            }
+        }
+
+        if (nresults != LUA_MULTRET && !yielded)
+            L->top = restorestack(L, funcoffset) + nresults;
+    }
+    else
+    {
         ptrdiff_t old_func = savestack(L, func);
 
         if (luau_precall(L, func, nresults) == PCRLUA)
@@ -278,6 +334,7 @@ void luaD_call(lua_State* L, StkId func, int nresults)
 
         if (nresults != LUA_MULTRET)
             L->top = restorestack(L, old_func) + nresults;
+    }
 
     L->nCcalls--;
     luaC_checkGC(L);
@@ -323,9 +380,18 @@ static void resume_continue(lua_State* L)
             // C continuation; we expect this to be followed by Lua continuations
             int n = cl->c.cont(L, 0);
 
+            if (FFlag::LuauYieldableContinuations)
+            {
+                // continuation can break or yield again
+                if (L->status == LUA_BREAK || L->status == LUA_YIELD)
+                    break;
+            }
+            else
+            {
                 // Continuation can break again
                 if (L->status == LUA_BREAK)
                     break;
+            }
 
             luau_poscall(L, L->top - n);
         }
@@ -370,6 +436,11 @@ static void resume(lua_State* L, void* ud)
                 // finish interrupted execution of `OP_CALL'
                 luau_poscall(L, firstArg);
             }
+            else if (FFlag::LuauYieldableContinuations)
+            {
+                // restore arguments we have protected for C continuation
+                L->base = L->ci->base;
+            }
         }
         else
         {
@@ -576,6 +647,7 @@ static void restore_stack_limit(lua_State* L)
 int luaD_pcall(lua_State* L, Pfunc func, void* u, ptrdiff_t old_top, ptrdiff_t ef)
 {
     unsigned short oldnCcalls = L->nCcalls;
+    unsigned short oldbaseCcalls = FFlag::LuauYieldableContinuations ? L->baseCcalls : 0;
     ptrdiff_t old_ci = saveci(L, L->ci);
     bool oldactive = L->isactive;
     int status = luaD_rawrunprotected(L, func, u);
@@ -612,6 +684,9 @@ int luaD_pcall(lua_State* L, Pfunc func, void* u, ptrdiff_t old_top, ptrdiff_t e
         // restore nCcalls before calling the debugprotectederror callback which may rely on the proper value to have been restored.
         L->nCcalls = oldnCcalls;
 
+        if (FFlag::LuauYieldableContinuations)
+            L->baseCcalls = oldbaseCcalls;
+
         // an error occurred, check if we have a protected error callback
         if (yieldable && L->global->cb.debugprotectederror)
         {

fuzz/proto.cpp

@@ -124,8 +124,8 @@ int registerTypes(Luau::Frontend& frontend, Luau::GlobalTypes& globals, bool for
     // Vector3 stub
     TypeId vector3MetaType = arena.addType(TableType{});
 
-    TypeId vector3InstanceType = arena.addType(ClassType{"Vector3", {}, nullopt, vector3MetaType, {}, {}, "Test", {}});
+    TypeId vector3InstanceType = arena.addType(ExternType{"Vector3", {}, nullopt, vector3MetaType, {}, {}, "Test", {}});
-    getMutable<ClassType>(vector3InstanceType)->props = {
+    getMutable<ExternType>(vector3InstanceType)->props = {
         {"X", {builtinTypes.numberType}},
         {"Y", {builtinTypes.numberType}},
         {"Z", {builtinTypes.numberType}},
@@ -139,16 +139,16 @@ int registerTypes(Luau::Frontend& frontend, Luau::GlobalTypes& globals, bool for
     globals.globalScope->exportedTypeBindings["Vector3"] = TypeFun{{}, vector3InstanceType};
 
     // Instance stub
-    TypeId instanceType = arena.addType(ClassType{"Instance", {}, nullopt, nullopt, {}, {}, "Test", {}});
+    TypeId instanceType = arena.addType(ExternType{"Instance", {}, nullopt, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(instanceType)->props = {
+    getMutable<ExternType>(instanceType)->props = {
         {"Name", {builtinTypes.stringType}},
     };
 
     globals.globalScope->exportedTypeBindings["Instance"] = TypeFun{{}, instanceType};
 
     // Part stub
-    TypeId partType = arena.addType(ClassType{"Part", {}, instanceType, nullopt, {}, {}, "Test", {}});
+    TypeId partType = arena.addType(ExternType{"Part", {}, instanceType, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(partType)->props = {
+    getMutable<ExternType>(partType)->props = {
         {"Position", {vector3InstanceType}},
     };
 

fuzz/protoprint.cpp

@@ -36,7 +36,7 @@ static const std::string kTypes[] = {
     "vector",
 };
 
-static const std::string kClasses[] = {
+static const std::string kExternTypes[] = {
     "Vector3",
     "Instance",
     "Part",
@@ -902,8 +902,8 @@ struct ProtoToLuau
 
     void print(const luau::TypeClass& type)
     {
-        size_t index = size_t(type.kind()) % std::size(kClasses);
+        size_t index = size_t(type.kind()) % std::size(kExternTypes);
-        source += kClasses[index];
+        source += kExternTypes[index];
     }
 
     void print(const luau::TypeRef& type)

tests/AstJsonEncoder.test.cpp

@@ -13,6 +13,7 @@ using namespace Luau;
 
 LUAU_FASTFLAG(LuauAstTypeGroup3)
 LUAU_FASTFLAG(LuauFixFunctionWithAttributesStartLocation)
+LUAU_FASTFLAG(LuauStoreReturnTypesAsPackOnAst)
 
 struct JsonEncoderFixture
 {
@@ -420,21 +421,40 @@ TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstStatDeclareFunction")
 {
     AstStat* statement = expectParseStatement("declare function foo(x: number): string");
 
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        std::string_view expected =
+            R"({"type":"AstStatDeclareFunction","location":"0,0 - 0,39","attributes":[],"name":"foo","nameLocation":"0,17 - 0,20","params":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,24 - 0,30","name":"number","nameLocation":"0,24 - 0,30","parameters":[]}]},"paramNames":[{"type":"AstArgumentName","name":"x","location":"0,21 - 0,22"}],"vararg":false,"varargLocation":"0,0 - 0,0","retTypes":{"type":"AstTypePackExplicit","location":"0,33 - 0,39","typeList":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,33 - 0,39","name":"string","nameLocation":"0,33 - 0,39","parameters":[]}]}},"generics":[],"genericPacks":[]})";
+        CHECK(toJson(statement) == expected);
+    }
+    else
+    {
         std::string_view expected =
             R"({"type":"AstStatDeclareFunction","location":"0,0 - 0,39","attributes":[],"name":"foo","nameLocation":"0,17 - 0,20","params":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,24 - 0,30","name":"number","nameLocation":"0,24 - 0,30","parameters":[]}]},"paramNames":[{"type":"AstArgumentName","name":"x","location":"0,21 - 0,22"}],"vararg":false,"varargLocation":"0,0 - 0,0","retTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,33 - 0,39","name":"string","nameLocation":"0,33 - 0,39","parameters":[]}]},"generics":[],"genericPacks":[]})";
 
         CHECK(toJson(statement) == expected);
     }
+}
 
 TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstStatDeclareFunction2")
 {
     AstStat* statement = expectParseStatement("declare function foo(x: number, ...: string): string");
 
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        std::string_view expected =
+            R"({"type":"AstStatDeclareFunction","location":"0,0 - 0,52","attributes":[],"name":"foo","nameLocation":"0,17 - 0,20","params":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,24 - 0,30","name":"number","nameLocation":"0,24 - 0,30","parameters":[]}],"tailType":{"type":"AstTypePackVariadic","location":"0,37 - 0,43","variadicType":{"type":"AstTypeReference","location":"0,37 - 0,43","name":"string","nameLocation":"0,37 - 0,43","parameters":[]}}},"paramNames":[{"type":"AstArgumentName","name":"x","location":"0,21 - 0,22"}],"vararg":true,"varargLocation":"0,32 - 0,35","retTypes":{"type":"AstTypePackExplicit","location":"0,46 - 0,52","typeList":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,46 - 0,52","name":"string","nameLocation":"0,46 - 0,52","parameters":[]}]}},"generics":[],"genericPacks":[]})";
+
+        CHECK(toJson(statement) == expected);
+    }
+    else
+    {
         std::string_view expected =
             R"({"type":"AstStatDeclareFunction","location":"0,0 - 0,52","attributes":[],"name":"foo","nameLocation":"0,17 - 0,20","params":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,24 - 0,30","name":"number","nameLocation":"0,24 - 0,30","parameters":[]}],"tailType":{"type":"AstTypePackVariadic","location":"0,37 - 0,43","variadicType":{"type":"AstTypeReference","location":"0,37 - 0,43","name":"string","nameLocation":"0,37 - 0,43","parameters":[]}}},"paramNames":[{"type":"AstArgumentName","name":"x","location":"0,21 - 0,22"}],"vararg":true,"varargLocation":"0,32 - 0,35","retTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,46 - 0,52","name":"string","nameLocation":"0,46 - 0,52","parameters":[]}]},"generics":[],"genericPacks":[]})";
 
         CHECK(toJson(statement) == expected);
     }
+}
 
 TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstAttr")
 {
@@ -463,9 +483,18 @@ TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstStatDeclareClass")
 
     REQUIRE(2 == root->body.size);
 
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        std::string_view expected1 =
+            R"({"type":"AstStatDeclareClass","location":"1,22 - 4,11","name":"Foo","props":[{"name":"prop","nameLocation":"2,12 - 2,16","type":"AstDeclaredClassProp","luauType":{"type":"AstTypeReference","location":"2,18 - 2,24","name":"number","nameLocation":"2,18 - 2,24","parameters":[]},"location":"2,12 - 2,24"},{"name":"method","nameLocation":"3,21 - 3,27","type":"AstDeclaredClassProp","luauType":{"type":"AstTypeFunction","location":"3,12 - 3,54","attributes":[],"generics":[],"genericPacks":[],"argTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"3,39 - 3,45","name":"number","nameLocation":"3,39 - 3,45","parameters":[]}]},"argNames":[{"type":"AstArgumentName","name":"foo","location":"3,34 - 3,37"}],"returnTypes":{"type":"AstTypePackExplicit","location":"3,48 - 3,54","typeList":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"3,48 - 3,54","name":"string","nameLocation":"3,48 - 3,54","parameters":[]}]}}},"location":"3,12 - 3,54"}],"indexer":null})";
+        CHECK(toJson(root->body.data[0]) == expected1);
+    }
+    else
+    {
         std::string_view expected1 =
             R"({"type":"AstStatDeclareClass","location":"1,22 - 4,11","name":"Foo","props":[{"name":"prop","nameLocation":"2,12 - 2,16","type":"AstDeclaredClassProp","luauType":{"type":"AstTypeReference","location":"2,18 - 2,24","name":"number","nameLocation":"2,18 - 2,24","parameters":[]},"location":"2,12 - 2,24"},{"name":"method","nameLocation":"3,21 - 3,27","type":"AstDeclaredClassProp","luauType":{"type":"AstTypeFunction","location":"3,12 - 3,54","attributes":[],"generics":[],"genericPacks":[],"argTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"3,39 - 3,45","name":"number","nameLocation":"3,39 - 3,45","parameters":[]}]},"argNames":[{"type":"AstArgumentName","name":"foo","location":"3,34 - 3,37"}],"returnTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"3,48 - 3,54","name":"string","nameLocation":"3,48 - 3,54","parameters":[]}]}},"location":"3,12 - 3,54"}],"indexer":null})";
         CHECK(toJson(root->body.data[0]) == expected1);
+    }
 
     std::string_view expected2 =
         R"({"type":"AstStatDeclareClass","location":"6,22 - 8,11","name":"Bar","superName":"Foo","props":[{"name":"prop2","nameLocation":"7,12 - 7,17","type":"AstDeclaredClassProp","luauType":{"type":"AstTypeReference","location":"7,19 - 7,25","name":"string","nameLocation":"7,19 - 7,25","parameters":[]},"location":"7,12 - 7,25"}],"indexer":null})";
@@ -476,7 +505,19 @@ TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_annotation")
 {
     AstStat* statement = expectParseStatement("type T = ((number) -> (string | nil)) & ((string) -> ())");
 
-    if (FFlag::LuauAstTypeGroup3)
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst && 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":"AstTypePackExplicit","location":"0,22 - 0,36","typeList":{"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":"AstTypePackExplicit","location":"0,53 - 0,55","typeList":{"type":"AstTypeList","types":[]}}}}]},"exported":false})";
+        CHECK(toJson(statement) == expected);
+    }
+    else if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        std::string_view expected =
+            R"({"type":"AstStatTypeAlias","location":"0,0 - 0,55","name":"T","generics":[],"genericPacks":[],"value":{"type":"AstTypeIntersection","location":"0,9 - 0,55","types":[{"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":"AstTypePackExplicit","location":"0,22 - 0,36","typeList":{"type":"AstTypeList","types":[{"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":"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":"AstTypePackExplicit","location":"0,53 - 0,55","typeList":{"type":"AstTypeList","types":[]}}}]},"exported":false})";
+        CHECK(toJson(statement) == expected);
+    }
+    else 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})";
@@ -516,11 +557,19 @@ TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstTypeFunction")
 {
     AstStat* statement = expectParseStatement(R"(type fun = (string, bool, named: number) -> ())");
 
+    if (FFlag::LuauStoreReturnTypesAsPackOnAst)
+    {
+        std::string_view expected =
+            R"({"type":"AstStatTypeAlias","location":"0,0 - 0,46","name":"fun","generics":[],"genericPacks":[],"value":{"type":"AstTypeFunction","location":"0,11 - 0,46","attributes":[],"generics":[],"genericPacks":[],"argTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,12 - 0,18","name":"string","nameLocation":"0,12 - 0,18","parameters":[]},{"type":"AstTypeReference","location":"0,20 - 0,24","name":"bool","nameLocation":"0,20 - 0,24","parameters":[]},{"type":"AstTypeReference","location":"0,33 - 0,39","name":"number","nameLocation":"0,33 - 0,39","parameters":[]}]},"argNames":[null,null,{"type":"AstArgumentName","name":"named","location":"0,26 - 0,31"}],"returnTypes":{"type":"AstTypePackExplicit","location":"0,44 - 0,46","typeList":{"type":"AstTypeList","types":[]}}},"exported":false})";
+        CHECK(toJson(statement) == expected);
+    }
+    else
+    {
         std::string_view expected =
             R"({"type":"AstStatTypeAlias","location":"0,0 - 0,46","name":"fun","generics":[],"genericPacks":[],"value":{"type":"AstTypeFunction","location":"0,11 - 0,46","attributes":[],"generics":[],"genericPacks":[],"argTypes":{"type":"AstTypeList","types":[{"type":"AstTypeReference","location":"0,12 - 0,18","name":"string","nameLocation":"0,12 - 0,18","parameters":[]},{"type":"AstTypeReference","location":"0,20 - 0,24","name":"bool","nameLocation":"0,20 - 0,24","parameters":[]},{"type":"AstTypeReference","location":"0,33 - 0,39","name":"number","nameLocation":"0,33 - 0,39","parameters":[]}]},"argNames":[null,null,{"type":"AstArgumentName","name":"named","location":"0,26 - 0,31"}],"returnTypes":{"type":"AstTypeList","types":[]}},"exported":false})";
-
         CHECK(toJson(statement) == expected);
     }
+}
 
 TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstTypeError")
 {
@@ -550,4 +599,63 @@ TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstTypePackExplicit")
     CHECK(toJson(root->body.data[1]) == expected);
 }
 
+TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstGenericType")
+{
+    AstStatBlock* root = expectParse(R"(
+        a = function<b, c>()
+        end
+    )");
+
+    CHECK(1 == root->body.size);
+
+    std::string_view expected =
+        R"({"type":"AstStatAssign","location":"1,8 - 2,11","vars":[{"type":"AstExprGlobal","location":"1,8 - 1,9","global":"a"}],"values":[{"type":"AstExprFunction","location":"1,12 - 2,11","attributes":[],"generics":[{"type":"AstGenericType","name":"b"},{"type":"AstGenericType","name":"c"}],"genericPacks":[],"args":[],"vararg":false,"varargLocation":"0,0 - 0,0","body":{"type":"AstStatBlock","location":"1,28 - 2,8","hasEnd":true,"body":[]},"functionDepth":1,"debugname":""}]})";
+
+    CHECK(toJson(root->body.data[0]) == expected);
+}
+
+TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstGenericTypeWithDefault")
+{
+    AstStatBlock* root = expectParse(R"(
+        type Foo<X = string> = X
+    )");
+
+    CHECK(1 == root->body.size);
+
+    std::string_view expected =
+        R"({"type":"AstStatTypeAlias","location":"1,8 - 1,32","name":"Foo","generics":[{"type":"AstGenericType","name":"X","luauType":{"type":"AstTypeReference","location":"1,21 - 1,27","name":"string","nameLocation":"1,21 - 1,27","parameters":[]}}],"genericPacks":[],"value":{"type":"AstTypeReference","location":"1,31 - 1,32","name":"X","nameLocation":"1,31 - 1,32","parameters":[]},"exported":false})";
+
+    CHECK(toJson(root->body.data[0]) == expected);
+}
+
+TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstGenericTypePack")
+{
+    AstStatBlock* root = expectParse(R"(
+        a = function<b..., c...>()
+        end
+    )");
+
+    CHECK(1 == root->body.size);
+
+    std::string_view expected =
+        R"({"type":"AstStatAssign","location":"1,8 - 2,11","vars":[{"type":"AstExprGlobal","location":"1,8 - 1,9","global":"a"}],"values":[{"type":"AstExprFunction","location":"1,12 - 2,11","attributes":[],"generics":[],"genericPacks":[{"type":"AstGenericTypePack","name":"b"},{"type":"AstGenericTypePack","name":"c"}],"args":[],"vararg":false,"varargLocation":"0,0 - 0,0","body":{"type":"AstStatBlock","location":"1,34 - 2,8","hasEnd":true,"body":[]},"functionDepth":1,"debugname":""}]})";
+
+    CHECK(toJson(root->body.data[0]) == expected);
+}
+
+TEST_CASE_FIXTURE(JsonEncoderFixture, "encode_AstGenericTypePackWithDefault")
+{
+    AstStatBlock* root = expectParse(R"(
+        type Foo<X... = ...string> = any
+    )");
+
+    CHECK(1 == root->body.size);
+
+    std::string_view expected =
+        R"({"type":"AstStatTypeAlias","location":"1,8 - 1,40","name":"Foo","generics":[],"genericPacks":[{"type":"AstGenericTypePack","name":"X","luauType":{"type":"AstTypePackVariadic","location":"1,24 - 1,33","variadicType":{"type":"AstTypeReference","location":"1,27 - 1,33","name":"string","nameLocation":"1,27 - 1,33","parameters":[]}}}],"value":{"type":"AstTypeReference","location":"1,37 - 1,40","name":"any","nameLocation":"1,37 - 1,40","parameters":[]},"exported":false})";
+
+    CHECK(toJson(root->body.data[0]) == expected);
+}
+
 TEST_SUITE_END();
+

tests/Autocomplete.test.cpp

@@ -20,14 +20,13 @@ 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)
+static std::optional<AutocompleteEntryMap> nullCallback(std::string tag, std::optional<const ExternType*> ptr, std::optional<std::string> contents)
 {
     return std::nullopt;
 }
@@ -159,7 +158,7 @@ struct ACBuiltinsFixture : ACFixtureImpl<BuiltinsFixture>
 {
 };
 
-struct ACClassFixture : ACFixtureImpl<ClassFixture>
+struct ACExternTypeFixture : ACFixtureImpl<ExternTypeFixture>
 {
 };
 
@@ -3754,7 +3753,7 @@ TEST_CASE_FIXTURE(ACFixture, "string_contents_is_available_to_callback")
     bool isCorrect = false;
     auto ac1 = autocomplete(
         '1',
-        [&isCorrect](std::string, std::optional<const ClassType*>, std::optional<std::string> contents) -> std::optional<AutocompleteEntryMap>
+        [&isCorrect](std::string, std::optional<const ExternType*>, std::optional<std::string> contents) -> std::optional<AutocompleteEntryMap>
         {
             isCorrect = contents && *contents == "testing/";
             return std::nullopt;
@@ -3766,8 +3765,6 @@ TEST_CASE_FIXTURE(ACFixture, "string_contents_is_available_to_callback")
 
 TEST_CASE_FIXTURE(ACBuiltinsFixture, "require_by_string")
 {
-    ScopedFastFlag sff{FFlag::LuauExposeRequireByStringAutocomplete, true};
-
     fileResolver.source["MainModule"] = R"(
         local info = "MainModule serves as the root directory"
     )";
@@ -3960,7 +3957,7 @@ TEST_CASE_FIXTURE(ACFixture, "string_completion_outside_quotes")
         local x = require(@1"@2"@3)
     )");
 
-    StringCompletionCallback callback = [](std::string, std::optional<const ClassType*>, std::optional<std::string> contents
+    StringCompletionCallback callback = [](std::string, std::optional<const ExternType*>, std::optional<std::string> contents
                                         ) -> std::optional<AutocompleteEntryMap>
     {
         Luau::AutocompleteEntryMap results = {{"test", Luau::AutocompleteEntry{Luau::AutocompleteEntryKind::String, std::nullopt, false, false}}};
@@ -4432,7 +4429,7 @@ local x = 1 + result.
     CHECK(ac.entryMap.count("x"));
 }
 
-TEST_CASE_FIXTURE(ACClassFixture, "ac_dont_overflow_on_recursive_union")
+TEST_CASE_FIXTURE(ACExternTypeFixture, "ac_dont_overflow_on_recursive_union")
 {
     ScopedFastFlag _{FFlag::LuauAutocompleteUnionCopyPreviousSeen, true};
     check(R"(

tests/BuiltinDefinitions.test.cpp

@@ -28,9 +28,9 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "lib_documentation_symbols")
         {
             props = &ttv->props;
         }
-        else if (const ClassType* ctv = get<ClassType>(binding.typeId))
+        else if (const ExternType* etv = get<ExternType>(binding.typeId))
         {
-            props = &ctv->props;
+            props = &etv->props;
         }
 
         if (props)

tests/ClassFixture.cpp

@@ -9,7 +9,7 @@ using std::nullopt;
 namespace Luau
 {
 
-ClassFixture::ClassFixture(bool prepareAutocomplete)
+ExternTypeFixture::ExternTypeFixture(bool prepareAutocomplete)
     : BuiltinsFixture(prepareAutocomplete)
 {
     GlobalTypes& globals = frontend.globals;
@@ -19,22 +19,22 @@ ClassFixture::ClassFixture(bool prepareAutocomplete)
 
     unfreeze(arena);
 
-    TypeId connectionType = arena.addType(ClassType{"Connection", {}, nullopt, nullopt, {}, {}, "Connection", {}});
+    TypeId connectionType = arena.addType(ExternType{"Connection", {}, nullopt, nullopt, {}, {}, "Connection", {}});
 
-    TypeId baseClassInstanceType = arena.addType(ClassType{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
+    TypeId baseClassInstanceType = arena.addType(ExternType{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(baseClassInstanceType)->props = {
+    getMutable<ExternType>(baseClassInstanceType)->props = {
         {"BaseMethod", Property::readonly(makeFunction(arena, baseClassInstanceType, {numberType}, {}))},
         {"BaseField", {numberType}},
 
         {"Touched", Property::readonly(connectionType)},
     };
 
-    getMutable<ClassType>(connectionType)->props = {
+    getMutable<ExternType>(connectionType)->props = {
         {"Connect", {makeFunction(arena, connectionType, {makeFunction(arena, nullopt, {baseClassInstanceType}, {})}, {})}}
     };
 
-    TypeId baseClassType = arena.addType(ClassType{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
+    TypeId baseClassType = arena.addType(ExternType{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(baseClassType)->props = {
+    getMutable<ExternType>(baseClassType)->props = {
         {"StaticMethod", {makeFunction(arena, nullopt, {}, {numberType})}},
         {"Clone", {makeFunction(arena, nullopt, {baseClassInstanceType}, {baseClassInstanceType})}},
         {"New", {makeFunction(arena, nullopt, {}, {baseClassInstanceType})}},
@@ -42,49 +42,49 @@ ClassFixture::ClassFixture(bool prepareAutocomplete)
     globals.globalScope->exportedTypeBindings["BaseClass"] = TypeFun{{}, baseClassInstanceType};
     addGlobalBinding(globals, "BaseClass", baseClassType, "@test");
 
-    TypeId childClassInstanceType = arena.addType(ClassType{"ChildClass", {}, baseClassInstanceType, nullopt, {}, {}, "Test", {}});
+    TypeId childClassInstanceType = arena.addType(ExternType{"ChildClass", {}, baseClassInstanceType, nullopt, {}, {}, "Test", {}});
 
-    getMutable<ClassType>(childClassInstanceType)->props = {
+    getMutable<ExternType>(childClassInstanceType)->props = {
         {"Method", {makeFunction(arena, childClassInstanceType, {}, {stringType})}},
     };
 
-    TypeId childClassType = arena.addType(ClassType{"ChildClass", {}, baseClassType, nullopt, {}, {}, "Test", {}});
+    TypeId childClassType = arena.addType(ExternType{"ChildClass", {}, baseClassType, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(childClassType)->props = {
+    getMutable<ExternType>(childClassType)->props = {
         {"New", {makeFunction(arena, nullopt, {}, {childClassInstanceType})}},
     };
     globals.globalScope->exportedTypeBindings["ChildClass"] = TypeFun{{}, childClassInstanceType};
     addGlobalBinding(globals, "ChildClass", childClassType, "@test");
 
-    TypeId grandChildInstanceType = arena.addType(ClassType{"GrandChild", {}, childClassInstanceType, nullopt, {}, {}, "Test", {}});
+    TypeId grandChildInstanceType = arena.addType(ExternType{"GrandChild", {}, childClassInstanceType, nullopt, {}, {}, "Test", {}});
 
-    getMutable<ClassType>(grandChildInstanceType)->props = {
+    getMutable<ExternType>(grandChildInstanceType)->props = {
         {"Method", {makeFunction(arena, grandChildInstanceType, {}, {stringType})}},
     };
 
-    TypeId grandChildType = arena.addType(ClassType{"GrandChild", {}, baseClassType, nullopt, {}, {}, "Test", {}});
+    TypeId grandChildType = arena.addType(ExternType{"GrandChild", {}, baseClassType, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(grandChildType)->props = {
+    getMutable<ExternType>(grandChildType)->props = {
         {"New", {makeFunction(arena, nullopt, {}, {grandChildInstanceType})}},
     };
     globals.globalScope->exportedTypeBindings["GrandChild"] = TypeFun{{}, grandChildInstanceType};
     addGlobalBinding(globals, "GrandChild", childClassType, "@test");
 
-    TypeId anotherChildInstanceType = arena.addType(ClassType{"AnotherChild", {}, baseClassInstanceType, nullopt, {}, {}, "Test", {}});
+    TypeId anotherChildInstanceType = arena.addType(ExternType{"AnotherChild", {}, baseClassInstanceType, nullopt, {}, {}, "Test", {}});
 
-    getMutable<ClassType>(anotherChildInstanceType)->props = {
+    getMutable<ExternType>(anotherChildInstanceType)->props = {
         {"Method", {makeFunction(arena, anotherChildInstanceType, {}, {stringType})}},
     };
 
-    TypeId anotherChildType = arena.addType(ClassType{"AnotherChild", {}, baseClassType, nullopt, {}, {}, "Test", {}});
+    TypeId anotherChildType = arena.addType(ExternType{"AnotherChild", {}, baseClassType, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(anotherChildType)->props = {
+    getMutable<ExternType>(anotherChildType)->props = {
         {"New", {makeFunction(arena, nullopt, {}, {anotherChildInstanceType})}},
     };
     globals.globalScope->exportedTypeBindings["AnotherChild"] = TypeFun{{}, anotherChildInstanceType};
     addGlobalBinding(globals, "AnotherChild", childClassType, "@test");
 
-    TypeId unrelatedClassInstanceType = arena.addType(ClassType{"UnrelatedClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
+    TypeId unrelatedClassInstanceType = arena.addType(ExternType{"UnrelatedClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
 
-    TypeId unrelatedClassType = arena.addType(ClassType{"UnrelatedClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
+    TypeId unrelatedClassType = arena.addType(ExternType{"UnrelatedClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(unrelatedClassType)->props = {
+    getMutable<ExternType>(unrelatedClassType)->props = {
         {"New", {makeFunction(arena, nullopt, {}, {unrelatedClassInstanceType})}},
     };
     globals.globalScope->exportedTypeBindings["UnrelatedClass"] = TypeFun{{}, unrelatedClassInstanceType};
@@ -92,14 +92,14 @@ ClassFixture::ClassFixture(bool prepareAutocomplete)
 
     TypeId vector2MetaType = arena.addType(TableType{});
 
-    vector2InstanceType = arena.addType(ClassType{"Vector2", {}, nullopt, vector2MetaType, {}, {}, "Test", {}});
+    vector2InstanceType = arena.addType(ExternType{"Vector2", {}, nullopt, vector2MetaType, {}, {}, "Test", {}});
-    getMutable<ClassType>(vector2InstanceType)->props = {
+    getMutable<ExternType>(vector2InstanceType)->props = {
         {"X", {numberType}},
         {"Y", {numberType}},
     };
 
-    vector2Type = arena.addType(ClassType{"Vector2", {}, nullopt, nullopt, {}, {}, "Test", {}});
+    vector2Type = arena.addType(ExternType{"Vector2", {}, nullopt, nullopt, {}, {}, "Test", {}});
-    getMutable<ClassType>(vector2Type)->props = {
+    getMutable<ExternType>(vector2Type)->props = {
         {"New", {makeFunction(arena, nullopt, {numberType, numberType}, {vector2InstanceType})}},
     };
     getMutable<TableType>(vector2MetaType)->props = {
@@ -114,7 +114,7 @@ ClassFixture::ClassFixture(bool prepareAutocomplete)
     addGlobalBinding(globals, "Vector2", vector2Type, "@test");
 
     TypeId callableClassMetaType = arena.addType(TableType{});
-    TypeId callableClassType = arena.addType(ClassType{"CallableClass", {}, nullopt, callableClassMetaType, {}, {}, "Test", {}});
+    TypeId callableClassType = arena.addType(ExternType{"CallableClass", {}, nullopt, callableClassMetaType, {}, {}, "Test", {}});
     getMutable<TableType>(callableClassMetaType)->props = {
         {"__call", {makeFunction(arena, nullopt, {callableClassType, stringType}, {numberType})}},
     };
@@ -124,7 +124,7 @@ ClassFixture::ClassFixture(bool prepareAutocomplete)
     {
         TypeId indexableClassMetaType = arena.addType(TableType{});
         TypeId indexableClassType =
-            arena.addType(ClassType{className, {}, nullopt, indexableClassMetaType, {}, {}, "Test", {}, TableIndexer{keyType, returnType}});
+            arena.addType(ExternType{className, {}, nullopt, indexableClassMetaType, {}, {}, "Test", {}, TableIndexer{keyType, returnType}});
         globals.globalScope->exportedTypeBindings[className] = TypeFun{{}, indexableClassType};
     };
 
@@ -134,9 +134,9 @@ ClassFixture::ClassFixture(bool prepareAutocomplete)
     addIndexableClass("IndexableNumericKeyClass", numberType, numberType);
 
     // Add a confusing derived class which shares the same name internally, but has a unique alias
-    TypeId duplicateBaseClassInstanceType = arena.addType(ClassType{"BaseClass", {}, baseClassInstanceType, nullopt, {}, {}, "Test", {}});
+    TypeId duplicateBaseClassInstanceType = arena.addType(ExternType{"BaseClass", {}, baseClassInstanceType, nullopt, {}, {}, "Test", {}});
 
-    getMutable<ClassType>(duplicateBaseClassInstanceType)->props = {
+    getMutable<ExternType>(duplicateBaseClassInstanceType)->props = {
         {"Method", {makeFunction(arena, duplicateBaseClassInstanceType, {}, {stringType})}},
     };
 

tests/ClassFixture.h

@@ -6,9 +6,9 @@
 namespace Luau
 {
 
-struct ClassFixture : BuiltinsFixture
+struct ExternTypeFixture : BuiltinsFixture
 {
-    explicit ClassFixture(bool prepareAutocomplete = false);
+    explicit ExternTypeFixture(bool prepareAutocomplete = false);
 
     TypeId vector2Type;
     TypeId vector2InstanceType;

tests/Conformance.test.cpp

@@ -35,6 +35,7 @@ LUAU_FASTFLAG(LuauLibWhereErrorAutoreserve)
 LUAU_FASTFLAG(DebugLuauAbortingChecks)
 LUAU_FASTINT(CodegenHeuristicsInstructionLimit)
 LUAU_DYNAMIC_FASTFLAG(LuauStringFormatFixC)
+LUAU_FASTFLAG(LuauYieldableContinuations)
 
 static lua_CompileOptions defaultOptions()
 {
@@ -823,6 +824,236 @@ TEST_CASE("Pack")
     runConformance("tpack.luau");
 }
 
+int singleYield(lua_State* L)
+{
+    lua_pushnumber(L, 2);
+
+    return lua_yield(L, 1);
+}
+
+int singleYieldContinuation(lua_State* L, int status)
+{
+    lua_pushnumber(L, 4);
+    return 1;
+}
+
+int multipleYields(lua_State* L)
+{
+    lua_settop(L, 1); // Only 1 argument expected
+    int base = luaL_checkinteger(L, 1);
+
+    luaL_checkstack(L, 2, "cmultiyield");
+
+    // current state
+    int pos = 1;
+    lua_pushinteger(L, pos);
+
+    // return value
+    lua_pushinteger(L, base + pos);
+    return lua_yield(L, 1);
+}
+
+int multipleYieldsContinuation(lua_State* L, int status)
+{
+    // function arguments are still alive
+    int base = luaL_checkinteger(L, 1);
+
+    // function state is still alive
+    int pos = luaL_checkinteger(L, 2) + 1;
+    luaL_checkstack(L, 1, "cmultiyieldcont");
+    lua_pushinteger(L, pos);
+    lua_replace(L, 2);
+
+    luaL_checkstack(L, 1, "cmultiyieldcont");
+
+    if (pos < 4)
+    {
+        lua_pushinteger(L, base + pos);
+        return lua_yield(L, 1);
+    }
+    else
+    {
+        lua_pushinteger(L, base + pos);
+        return 1;
+    }
+}
+
+int nestedMultipleYieldHelper(lua_State* L)
+{
+    int context = luaL_checkinteger(L, lua_upvalueindex(1));
+
+    lua_pushinteger(L, 100 + context);
+    return lua_yield(L, 1);
+}
+
+int nestedMultipleYieldHelperContinuation(lua_State* L, int status)
+{
+    int context = luaL_checkinteger(L, lua_upvalueindex(1));
+    lua_pushinteger(L, 110 + context);
+    return 1;
+}
+
+int nestedMultipleYieldHelperNonYielding(lua_State* L)
+{
+    int context = luaL_checkinteger(L, lua_upvalueindex(1));
+    lua_pushinteger(L, 105 + context);
+    return 1;
+}
+
+int multipleYieldsWithNestedCall(lua_State* L)
+{
+    lua_settop(L, 2); // Only 2 arguments expected
+    bool nestedShouldYield = luaL_checkboolean(L, 2);
+
+    lua_pushinteger(L, 0); // state
+
+    lua_pushnumber(L, 5);
+    if (nestedShouldYield)
+        lua_pushcclosurek(L, nestedMultipleYieldHelper, nullptr, 1, nestedMultipleYieldHelperContinuation);
+    else
+        lua_pushcclosurek(L, nestedMultipleYieldHelperNonYielding, nullptr, 1, nullptr);
+
+    return luaL_callyieldable(L, 0, 1);
+}
+
+int multipleYieldsWithNestedCallContinuation(lua_State* L, int status)
+{
+    int state = luaL_checkinteger(L, 3);
+    luaL_checkstack(L, 1, "cnestedmultiyieldcont");
+    lua_pushinteger(L, state + 1);
+    lua_replace(L, 3);
+
+    if (state == 0)
+    {
+        return lua_yield(L, lua_gettop(L) - 3);
+    }
+    else if (state == 1)
+    {
+        lua_pushnumber(L, luaL_checkinteger(L, 1) + 200);
+        return lua_yield(L, 1);
+    }
+    else
+    {
+        lua_pushnumber(L, luaL_checkinteger(L, 1) + 210);
+        return 1;
+    }
+}
+
+int passthroughCall(lua_State* L)
+{
+    luaL_checkstack(L, 3, "cpass");
+    lua_pushvalue(L, 1);
+    lua_pushvalue(L, 2);
+    lua_pushvalue(L, 3);
+    return luaL_callyieldable(L, 2, 1);
+}
+
+int passthroughCallContinuation(lua_State* L, int status)
+{
+    LUAU_ASSERT(lua_gettop(L) == 4); // 3 original arguments and the return value
+    LUAU_ASSERT(lua_tonumber(L, -1) == 0.5);
+    return 1;
+}
+
+int passthroughCallMoreResults(lua_State* L)
+{
+    luaL_checkstack(L, 3, "cpass");
+    lua_pushvalue(L, 1);
+    lua_pushvalue(L, 2);
+    lua_pushvalue(L, 3);
+    return luaL_callyieldable(L, 2, 10);
+}
+
+int passthroughCallMoreResultsContinuation(lua_State* L, int status)
+{
+    LUAU_ASSERT(lua_gettop(L) == 13); // 3 original arguments and 10 requested return values
+
+    for (int i = 0; i < 9; i++)
+    {
+        LUAU_ASSERT(lua_isnil(L, -1));
+        lua_pop(L, 1);
+    }
+
+    LUAU_ASSERT(lua_tonumber(L, -1) == 0.5);
+    return 1;
+}
+
+int passthroughCallArgReuse(lua_State* L)
+{
+    return luaL_callyieldable(L, 2, 1);
+}
+
+int passthroughCallArgReuseContinuation(lua_State* L, int status)
+{
+    LUAU_ASSERT(lua_gettop(L) == 1); // Original arguments were consumed, only return remains
+    LUAU_ASSERT(lua_tonumber(L, -1) == 0.5);
+    return 1;
+}
+
+int passthroughCallVaradic(lua_State* L)
+{
+    luaL_checkany(L, 1);
+    return luaL_callyieldable(L, lua_gettop(L) - 1, LUA_MULTRET);
+}
+
+int passthroughCallVaradicContinuation(lua_State* L, int status)
+{
+    return lua_gettop(L);
+}
+
+int passthroughCallWithState(lua_State* L)
+{
+    luaL_checkany(L, 1);
+    int args = lua_gettop(L) - 1;
+
+    lua_pushnumber(L, 42);
+    lua_insert(L, 1);
+
+    return luaL_callyieldable(L, args, LUA_MULTRET);
+}
+
+int passthroughCallWithStateContinuation(lua_State* L, int status)
+{
+    LUAU_ASSERT(luaL_checkinteger(L, 1) == 42);
+
+    return lua_gettop(L) - 1;
+}
+
+TEST_CASE("CYield")
+{
+    ScopedFastFlag luauYieldableContinuations{FFlag::LuauYieldableContinuations, true};
+
+    runConformance(
+        "cyield.luau",
+        [](lua_State* L)
+        {
+            lua_pushcclosurek(L, singleYield, "singleYield", 0, singleYieldContinuation);
+            lua_setglobal(L, "singleYield");
+
+            lua_pushcclosurek(L, multipleYields, "multipleYields", 0, multipleYieldsContinuation);
+            lua_setglobal(L, "multipleYields");
+
+            lua_pushcclosurek(L, multipleYieldsWithNestedCall, "multipleYieldsWithNestedCall", 0, multipleYieldsWithNestedCallContinuation);
+            lua_setglobal(L, "multipleYieldsWithNestedCall");
+
+            lua_pushcclosurek(L, passthroughCall, "passthroughCall", 0, passthroughCallContinuation);
+            lua_setglobal(L, "passthroughCall");
+
+            lua_pushcclosurek(L, passthroughCallMoreResults, "passthroughCallMoreResults", 0, passthroughCallMoreResultsContinuation);
+            lua_setglobal(L, "passthroughCallMoreResults");
+
+            lua_pushcclosurek(L, passthroughCallArgReuse, "passthroughCallArgReuse", 0, passthroughCallArgReuseContinuation);
+            lua_setglobal(L, "passthroughCallArgReuse");
+
+            lua_pushcclosurek(L, passthroughCallVaradic, "passthroughCallVaradic", 0, passthroughCallVaradicContinuation);
+            lua_setglobal(L, "passthroughCallVaradic");
+
+            lua_pushcclosurek(L, passthroughCallWithState, "passthroughCallWithState", 0, passthroughCallWithStateContinuation);
+            lua_setglobal(L, "passthroughCallWithState");
+        }
+    );
+}
+
 TEST_CASE("Vector")
 {
     lua_CompileOptions copts = defaultOptions();
@@ -957,7 +1188,7 @@ static void populateRTTI(lua_State* L, Luau::TypeId type)
 
         lua_pushstring(L, "function");
     }
-    else if (auto c = Luau::get<Luau::ClassType>(type))
+    else if (auto c = Luau::get<Luau::ExternType>(type))
     {
         lua_pushstring(L, c->name.c_str());
     }

tests/DataFlowGraph.test.cpp

@@ -13,6 +13,7 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(LuauSolverV2);
+LUAU_FASTFLAG(LuauDoNotAddUpvalueTypesToLocalType)
 
 struct DataFlowGraphFixture
 {
@@ -421,6 +422,8 @@ TEST_CASE_FIXTURE(DataFlowGraphFixture, "property_lookup_on_a_phi_node_3")
 
 TEST_CASE_FIXTURE(DataFlowGraphFixture, "function_captures_are_phi_nodes_of_all_versions")
 {
+    ScopedFastFlag _{FFlag::LuauDoNotAddUpvalueTypesToLocalType, true};
+
     dfg(R"(
         local x = 5
 
@@ -439,15 +442,14 @@ TEST_CASE_FIXTURE(DataFlowGraphFixture, "function_captures_are_phi_nodes_of_all_
     DefId x4 = getDef<AstExprLocal, 3>(); // x = "five"
 
     CHECK(x1 != x2);
-    CHECK(x2 != x3);
+    CHECK(x2 == x3);
     CHECK(x3 != x4);
 
     const Phi* phi = get<Phi>(x2);
     REQUIRE(phi);
-    REQUIRE(phi->operands.size() == 3);
+    REQUIRE(phi->operands.size() == 2);
     CHECK(phi->operands.at(0) == x1);
-    CHECK(phi->operands.at(1) == x3);
+    CHECK(phi->operands.at(1) == x4);
-    CHECK(phi->operands.at(2) == x4);
 }
 
 TEST_CASE_FIXTURE(DataFlowGraphFixture, "function_captures_are_phi_nodes_of_all_versions_properties")