Sync to upstream/release/533 (#560)

Analysis/include/Luau/Constraint.h

@@ -1,10 +1,10 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
-#include "Luau/Location.h"
 #include "Luau/NotNull.h"
 #include "Luau/Variant.h"
 
+#include <string>
 #include <memory>
 #include <vector>
 
@@ -47,18 +47,24 @@ struct InstantiationConstraint
     TypeId superType;
 };
 
-using ConstraintV = Variant<SubtypeConstraint, PackSubtypeConstraint, GeneralizationConstraint, InstantiationConstraint>;
+// name(namedType) = name
+struct NameConstraint
+{
+    TypeId namedType;
+    std::string name;
+};
+
+using ConstraintV = Variant<SubtypeConstraint, PackSubtypeConstraint, GeneralizationConstraint, InstantiationConstraint, NameConstraint>;
 using ConstraintPtr = std::unique_ptr<struct Constraint>;
 
 struct Constraint
 {
-    Constraint(ConstraintV&& c, Location location);
+    explicit Constraint(ConstraintV&& c);
 
     Constraint(const Constraint&) = delete;
     Constraint& operator=(const Constraint&) = delete;
 
     ConstraintV c;
-    Location location;
     std::vector<NotNull<Constraint>> dependencies;
 };
 

Analysis/include/Luau/ConstraintGraphBuilder.h

@@ -17,20 +17,7 @@
 namespace Luau
 {
 
-struct Scope2
-{
-    // The parent scope of this scope. Null if there is no parent (i.e. this
-    // is the module-level scope).
-    Scope2* parent = nullptr;
-    // All the children of this scope.
-    std::vector<Scope2*> children;
-    std::unordered_map<Symbol, TypeId> bindings; // TODO: I think this can be a DenseHashMap
-    TypePackId returnType;
-    // All constraints belonging to this scope.
-    std::vector<ConstraintPtr> constraints;
-
-    std::optional<TypeId> lookup(Symbol sym);
-};
+struct Scope2;
 
 struct ConstraintGraphBuilder
 {
@@ -47,6 +34,10 @@ struct ConstraintGraphBuilder
     // A mapping of AST node to TypePackId.
     DenseHashMap<const AstExpr*, TypePackId> astTypePacks{nullptr};
     DenseHashMap<const AstExpr*, TypeId> astOriginalCallTypes{nullptr};
+    // Types resolved from type annotations. Analogous to astTypes.
+    DenseHashMap<const AstType*, TypeId> astResolvedTypes{nullptr};
+    // Type packs resolved from type annotations. Analogous to astTypePacks.
+    DenseHashMap<const AstTypePack*, TypePackId> astResolvedTypePacks{nullptr};
 
     explicit ConstraintGraphBuilder(TypeArena* arena);
 
@@ -73,9 +64,8 @@ struct ConstraintGraphBuilder
      * Adds a new constraint with no dependencies to a given scope.
      * @param scope the scope to add the constraint to. Must not be null.
      * @param cv the constraint variant to add.
-     * @param location the location to attribute to the constraint.
      */
-    void addConstraint(Scope2* scope, ConstraintV cv, Location location);
+    void addConstraint(Scope2* scope, ConstraintV cv);
 
     /**
      * Adds a constraint to a given scope.
@@ -99,6 +89,7 @@ struct ConstraintGraphBuilder
     void visit(Scope2* scope, AstStatReturn* ret);
     void visit(Scope2* scope, AstStatAssign* assign);
     void visit(Scope2* scope, AstStatIf* ifStatement);
+    void visit(Scope2* scope, AstStatTypeAlias* alias);
 
     TypePackId checkExprList(Scope2* scope, const AstArray<AstExpr*>& exprs);
 
@@ -124,6 +115,24 @@ struct ConstraintGraphBuilder
      * @param fn the function expression to check.
      */
     void checkFunctionBody(Scope2* scope, AstExprFunction* fn);
+
+    /**
+     * Resolves a type from its AST annotation.
+     * @param scope the scope that the type annotation appears within.
+     * @param ty the AST annotation to resolve.
+     * @return the type of the AST annotation.
+     **/
+    TypeId resolveType(Scope2* scope, AstType* ty);
+
+    /**
+     * Resolves a type pack from its AST annotation.
+     * @param scope the scope that the type annotation appears within.
+     * @param tp the AST annotation to resolve.
+     * @return the type pack of the AST annotation.
+     **/
+    TypePackId resolveTypePack(Scope2* scope, AstTypePack* tp);
+
+    TypePackId resolveTypePack(Scope2* scope, const AstTypeList& list);
 };
 
 /**

Analysis/include/Luau/ConstraintSolver.h

@@ -55,6 +55,7 @@ struct ConstraintSolver
     bool tryDispatch(const PackSubtypeConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const GeneralizationConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const InstantiationConstraint& c, NotNull<const Constraint> constraint, bool force);
+    bool tryDispatch(const NameConstraint& c, NotNull<const Constraint> constraint);
 
     void block(NotNull<const Constraint> target, NotNull<const Constraint> constraint);
     /**
@@ -85,7 +86,7 @@ struct ConstraintSolver
      * @param subType the sub-type to unify.
      * @param superType the super-type to unify.
      */
-    void unify(TypeId subType, TypeId superType, Location location);
+    void unify(TypeId subType, TypeId superType);
 
     /**
      * Creates a new Unifier and performs a single unification operation. Commits
@@ -93,7 +94,7 @@ struct ConstraintSolver
      * @param subPack the sub-type pack to unify.
      * @param superPack the super-type pack to unify.
      */
-    void unify(TypePackId subPack, TypePackId superPack, Location location);
+    void unify(TypePackId subPack, TypePackId superPack);
 
 private:
     /**

Analysis/include/Luau/ConstraintSolverLogger.h

@@ -1,6 +1,8 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 
-#include "Luau/ConstraintGraphBuilder.h"
+#include "Luau/Constraint.h"
+#include "Luau/NotNull.h"
+#include "Luau/Scope.h"
 #include "Luau/ToString.h"
 
 #include <optional>

Analysis/include/Luau/Error.h

@@ -169,6 +169,13 @@ struct GenericError
     bool operator==(const GenericError& rhs) const;
 };
 
+struct InternalError
+{
+    std::string message;
+
+    bool operator==(const InternalError& rhs) const;
+};
+
 struct CannotCallNonFunction
 {
     TypeId ty;
@@ -293,12 +300,12 @@ struct NormalizationTooComplex
     }
 };
 
-using TypeErrorData =
-    Variant<TypeMismatch, UnknownSymbol, UnknownProperty, NotATable, CannotExtendTable, OnlyTablesCanHaveMethods, DuplicateTypeDefinition,
-        CountMismatch, FunctionDoesNotTakeSelf, FunctionRequiresSelf, OccursCheckFailed, UnknownRequire, IncorrectGenericParameterCount, SyntaxError,
-        CodeTooComplex, UnificationTooComplex, UnknownPropButFoundLikeProp, GenericError, CannotCallNonFunction, ExtraInformation, DeprecatedApiUsed,
-        ModuleHasCyclicDependency, IllegalRequire, FunctionExitsWithoutReturning, DuplicateGenericParameter, CannotInferBinaryOperation,
-        MissingProperties, SwappedGenericTypeParameter, OptionalValueAccess, MissingUnionProperty, TypesAreUnrelated, NormalizationTooComplex>;
+using TypeErrorData = Variant<TypeMismatch, UnknownSymbol, UnknownProperty, NotATable, CannotExtendTable, OnlyTablesCanHaveMethods,
+    DuplicateTypeDefinition, CountMismatch, FunctionDoesNotTakeSelf, FunctionRequiresSelf, OccursCheckFailed, UnknownRequire,
+    IncorrectGenericParameterCount, SyntaxError, CodeTooComplex, UnificationTooComplex, UnknownPropButFoundLikeProp, GenericError, InternalError,
+    CannotCallNonFunction, ExtraInformation, DeprecatedApiUsed, ModuleHasCyclicDependency, IllegalRequire, FunctionExitsWithoutReturning,
+    DuplicateGenericParameter, CannotInferBinaryOperation, MissingProperties, SwappedGenericTypeParameter, OptionalValueAccess, MissingUnionProperty,
+    TypesAreUnrelated, NormalizationTooComplex>;
 
 struct TypeError
 {
@@ -339,7 +346,13 @@ T* get(TypeError& e)
 
 using ErrorVec = std::vector<TypeError>;
 
+struct TypeErrorToStringOptions
+{
+    FileResolver* fileResolver = nullptr;
+};
+
 std::string toString(const TypeError& error);
+std::string toString(const TypeError& error, TypeErrorToStringOptions options);
 
 bool containsParseErrorName(const TypeError& error);
 
@@ -356,4 +369,24 @@ struct InternalErrorReporter
     [[noreturn]] void ice(const std::string& message);
 };
 
+class InternalCompilerError : public std::exception {
+public:
+  explicit InternalCompilerError(const std::string& message, const std::string& moduleName)
+  : message(message)
+  , moduleName(moduleName)
+  {
+  }
+  explicit InternalCompilerError(const std::string& message, const std::string& moduleName, const Location& location)
+  : message(message)
+  , moduleName(moduleName)
+  , location(location)
+  {
+  }
+  virtual const char* what() const throw();
+
+  const std::string message;
+  const std::string moduleName;
+  const std::optional<Location> location;
+};
+
 } // namespace Luau

Analysis/include/Luau/IostreamHelpers.h

@@ -30,6 +30,7 @@ std::ostream& operator<<(std::ostream& lhs, const OccursCheckFailed& error);
 std::ostream& operator<<(std::ostream& lhs, const UnknownRequire& error);
 std::ostream& operator<<(std::ostream& lhs, const UnknownPropButFoundLikeProp& e);
 std::ostream& operator<<(std::ostream& lhs, const GenericError& error);
+std::ostream& operator<<(std::ostream& lhs, const InternalError& error);
 std::ostream& operator<<(std::ostream& lhs, const FunctionExitsWithoutReturning& error);
 std::ostream& operator<<(std::ostream& lhs, const MissingProperties& error);
 std::ostream& operator<<(std::ostream& lhs, const IllegalRequire& error);

Analysis/include/Luau/Module.h

@@ -1,10 +1,11 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/Error.h"
 #include "Luau/FileResolver.h"
 #include "Luau/ParseOptions.h"
-#include "Luau/Error.h"
 #include "Luau/ParseResult.h"
+#include "Luau/Scope.h"
 #include "Luau/TypeArena.h"
 
 #include <memory>
@@ -19,7 +20,9 @@ struct Module;
 
 using ScopePtr = std::shared_ptr<struct Scope>;
 using ModulePtr = std::shared_ptr<Module>;
-struct Scope2;
+
+class AstType;
+class AstTypePack;
 
 /// Root of the AST of a parsed source file
 struct SourceModule
@@ -73,6 +76,8 @@ struct Module
     DenseHashMap<const AstExpr*, TypeId> astExpectedTypes{nullptr};
     DenseHashMap<const AstExpr*, TypeId> astOriginalCallTypes{nullptr};
     DenseHashMap<const AstExpr*, TypeId> astOverloadResolvedTypes{nullptr};
+    DenseHashMap<const AstType*, TypeId> astResolvedTypes{nullptr};
+    DenseHashMap<const AstTypePack*, TypePackId> astResolvedTypePacks{nullptr};
 
     std::unordered_map<Name, TypeId> declaredGlobals;
     ErrorVec errors;

Analysis/include/Luau/Normalize.h

@@ -9,8 +9,8 @@ namespace Luau
 
 struct InternalErrorReporter;
 
-bool isSubtype(TypeId superTy, TypeId subTy, InternalErrorReporter& ice);
-bool isSubtype(TypePackId superTy, TypePackId subTy, InternalErrorReporter& ice);
+bool isSubtype(TypeId subTy, TypeId superTy, InternalErrorReporter& ice);
+bool isSubtype(TypePackId subTy, TypePackId superTy, InternalErrorReporter& ice);
 
 std::pair<TypeId, bool> normalize(TypeId ty, TypeArena& arena, InternalErrorReporter& ice);
 std::pair<TypeId, bool> normalize(TypeId ty, const ModulePtr& module, InternalErrorReporter& ice);

Analysis/include/Luau/RecursionCounter.h

@@ -6,8 +6,6 @@
 #include <stdexcept>
 #include <exception>
 
-LUAU_FASTFLAG(LuauRecursionLimitException);
-
 namespace Luau
 {
 
@@ -39,21 +37,12 @@ private:
 
 struct RecursionLimiter : RecursionCounter
 {
-    // TODO: remove ctx after LuauRecursionLimitException is removed
-    RecursionLimiter(int* count, int limit, const char* ctx)
+    RecursionLimiter(int* count, int limit)
         : RecursionCounter(count)
     {
-        LUAU_ASSERT(ctx);
         if (limit > 0 && *count > limit)
         {
-            if (FFlag::LuauRecursionLimitException)
-                throw RecursionLimitException();
-            else
-            {
-                std::string m = "Internal recursion counter limit exceeded: ";
-                m += ctx;
-                throw std::runtime_error(m);
-            }
+            throw RecursionLimitException();
         }
     }
 };

Analysis/include/Luau/Scope.h

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/Constraint.h"
 #include "Luau/Location.h"
 #include "Luau/TypeVar.h"
 
@@ -64,4 +65,21 @@ struct Scope
     std::unordered_map<Name, TypePackId> typeAliasTypePackParameters;
 };
 
+struct Scope2
+{
+    // The parent scope of this scope. Null if there is no parent (i.e. this
+    // is the module-level scope).
+    Scope2* parent = nullptr;
+    // All the children of this scope.
+    std::vector<Scope2*> children;
+    std::unordered_map<Symbol, TypeId> bindings; // TODO: I think this can be a DenseHashMap
+    std::unordered_map<Name, TypeId> typeBindings;
+    TypePackId returnType;
+    // All constraints belonging to this scope.
+    std::vector<ConstraintPtr> constraints;
+
+    std::optional<TypeId> lookup(Symbol sym);
+    std::optional<TypeId> lookupTypeBinding(const Name& name);
+};
+
 } // namespace Luau

Analysis/include/Luau/TypeVar.h

@@ -287,7 +287,6 @@ struct FunctionTypeVar
     bool hasSelf;
     Tags tags;
     bool hasNoGenerics = false;
-    bool generalized = false;
 };
 
 enum class TableState

Analysis/include/Luau/Unifiable.h

@@ -117,6 +117,7 @@ struct Generic
     explicit Generic(const Name& name);
     explicit Generic(Scope2* scope);
     Generic(TypeLevel level, const Name& name);
+    Generic(Scope2* scope, const Name& name);
 
     int index;
     TypeLevel level;

Analysis/include/Luau/Unifier.h

@@ -79,12 +79,8 @@ private:
     void tryUnifySingletons(TypeId subTy, TypeId superTy);
     void tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCall = false);
     void tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection = false);
-    void DEPRECATED_tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection = false);
-    void tryUnifyFreeTable(TypeId subTy, TypeId superTy);
-    void tryUnifySealedTables(TypeId subTy, TypeId superTy, bool isIntersection);
     void tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed);
     void tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed);
-    void tryUnifyIndexer(const TableIndexer& subIndexer, const TableIndexer& superIndexer);
 
     TypeId widen(TypeId ty);
     TypePackId widen(TypePackId tp);

Analysis/include/Luau/VisitTypeVar.h

@@ -169,7 +169,7 @@ struct GenericTypeVarVisitor
 
     void traverse(TypeId ty)
     {
-        RecursionLimiter limiter{&recursionCounter, FInt::LuauVisitRecursionLimit, "TypeVarVisitor"};
+        RecursionLimiter limiter{&recursionCounter, FInt::LuauVisitRecursionLimit};
 
         if (visit_detail::hasSeen(seen, ty))
         {

Analysis/src/Clone.cpp

@@ -317,7 +317,7 @@ TypePackId clone(TypePackId tp, TypeArena& dest, CloneState& cloneState)
     if (tp->persistent)
         return tp;
 
-    RecursionLimiter _ra(&cloneState.recursionCount, FInt::LuauTypeCloneRecursionLimit, "cloning TypePackId");
+    RecursionLimiter _ra(&cloneState.recursionCount, FInt::LuauTypeCloneRecursionLimit);
 
     TypePackId& res = cloneState.seenTypePacks[tp];
 
@@ -335,7 +335,7 @@ TypeId clone(TypeId typeId, TypeArena& dest, CloneState& cloneState)
     if (typeId->persistent)
         return typeId;
 
-    RecursionLimiter _ra(&cloneState.recursionCount, FInt::LuauTypeCloneRecursionLimit, "cloning TypeId");
+    RecursionLimiter _ra(&cloneState.recursionCount, FInt::LuauTypeCloneRecursionLimit);
 
     TypeId& res = cloneState.seenTypes[typeId];
 

Analysis/src/Constraint.cpp

@@ -5,9 +5,8 @@
 namespace Luau
 {
 
-Constraint::Constraint(ConstraintV&& c, Location location)
+Constraint::Constraint(ConstraintV&& c)
     : c(std::move(c))
-    , location(location)
 {
 }
 

Analysis/src/ConstraintGraphBuilder.cpp

@@ -2,28 +2,13 @@
 
 #include "Luau/ConstraintGraphBuilder.h"
 
+#include "Luau/Scope.h"
+
 namespace Luau
 {
 
 const AstStat* getFallthrough(const AstStat* node); // TypeInfer.cpp
 
-std::optional<TypeId> Scope2::lookup(Symbol sym)
-{
-    Scope2* s = this;
-
-    while (true)
-    {
-        auto it = s->bindings.find(sym);
-        if (it != s->bindings.end())
-            return it->second;
-
-        if (s->parent)
-            s = s->parent;
-        else
-            return std::nullopt;
-    }
-}
-
 ConstraintGraphBuilder::ConstraintGraphBuilder(TypeArena* arena)
     : singletonTypes(getSingletonTypes())
     , arena(arena)
@@ -59,10 +44,10 @@ Scope2* ConstraintGraphBuilder::childScope(Location location, Scope2* parent)
     return borrow;
 }
 
-void ConstraintGraphBuilder::addConstraint(Scope2* scope, ConstraintV cv, Location location)
+void ConstraintGraphBuilder::addConstraint(Scope2* scope, ConstraintV cv)
 {
     LUAU_ASSERT(scope);
-    scope->constraints.emplace_back(new Constraint{std::move(cv), location});
+    scope->constraints.emplace_back(new Constraint{std::move(cv)});
 }
 
 void ConstraintGraphBuilder::addConstraint(Scope2* scope, std::unique_ptr<Constraint> c)
@@ -79,6 +64,13 @@ void ConstraintGraphBuilder::visit(AstStatBlock* block)
     rootScope = scopes.back().second.get();
     rootScope->returnType = freshTypePack(rootScope);
 
+    // TODO: We should share the global scope.
+    rootScope->typeBindings["nil"] = singletonTypes.nilType;
+    rootScope->typeBindings["number"] = singletonTypes.numberType;
+    rootScope->typeBindings["string"] = singletonTypes.stringType;
+    rootScope->typeBindings["boolean"] = singletonTypes.booleanType;
+    rootScope->typeBindings["thread"] = singletonTypes.threadType;
+
     visit(rootScope, block);
 }
 
@@ -102,6 +94,8 @@ void ConstraintGraphBuilder::visit(Scope2* scope, AstStat* stat)
         checkPack(scope, e->expr);
     else if (auto i = stat->as<AstStatIf>())
         visit(scope, i);
+    else if (auto a = stat->as<AstStatTypeAlias>())
+        visit(scope, a);
     else
         LUAU_ASSERT(0);
 }
@@ -114,8 +108,14 @@ void ConstraintGraphBuilder::visit(Scope2* scope, AstStatLocal* local)
 
     for (AstLocal* local : local->vars)
     {
-        // TODO annotations
         TypeId ty = freshType(scope);
+
+        if (local->annotation)
+        {
+            TypeId annotation = resolveType(scope, local->annotation);
+            addConstraint(scope, SubtypeConstraint{ty, annotation});
+        }
+
         varTypes.push_back(ty);
         scope->bindings[local] = ty;
     }
@@ -136,14 +136,14 @@ void ConstraintGraphBuilder::visit(Scope2* scope, AstStatLocal* local)
             {
                 std::vector<TypeId> tailValues{varTypes.begin() + i, varTypes.end()};
                 TypePackId tailPack = arena->addTypePack(std::move(tailValues));
-                addConstraint(scope, PackSubtypeConstraint{exprPack, tailPack}, local->location);
+                addConstraint(scope, PackSubtypeConstraint{exprPack, tailPack});
             }
         }
         else
         {
             TypeId exprType = check(scope, local->values.data[i]);
             if (i < varTypes.size())
-                addConstraint(scope, SubtypeConstraint{varTypes[i], exprType}, local->vars.data[i]->location);
+                addConstraint(scope, SubtypeConstraint{varTypes[i], exprType});
         }
     }
 }
@@ -188,7 +188,7 @@ void ConstraintGraphBuilder::visit(Scope2* scope, AstStatLocalFunction* function
 
     checkFunctionBody(innerScope, function->func);
 
-    std::unique_ptr<Constraint> c{new Constraint{GeneralizationConstraint{functionType, actualFunctionType, innerScope}, function->location}};
+    std::unique_ptr<Constraint> c{new Constraint{GeneralizationConstraint{functionType, actualFunctionType, innerScope}}};
     addConstraints(c.get(), innerScope);
 
     addConstraint(scope, std::move(c));
@@ -240,7 +240,7 @@ void ConstraintGraphBuilder::visit(Scope2* scope, AstStatFunction* function)
 
     checkFunctionBody(innerScope, function->func);
 
-    std::unique_ptr<Constraint> c{new Constraint{GeneralizationConstraint{functionType, actualFunctionType, innerScope}, function->location}};
+    std::unique_ptr<Constraint> c{new Constraint{GeneralizationConstraint{functionType, actualFunctionType, innerScope}}};
     addConstraints(c.get(), innerScope);
 
     addConstraint(scope, std::move(c));
@@ -251,13 +251,26 @@ void ConstraintGraphBuilder::visit(Scope2* scope, AstStatReturn* ret)
     LUAU_ASSERT(scope);
 
     TypePackId exprTypes = checkPack(scope, ret->list);
-    addConstraint(scope, PackSubtypeConstraint{exprTypes, scope->returnType}, ret->location);
+    addConstraint(scope, PackSubtypeConstraint{exprTypes, scope->returnType});
 }
 
 void ConstraintGraphBuilder::visit(Scope2* scope, AstStatBlock* block)
 {
     LUAU_ASSERT(scope);
 
+    // In order to enable mutually-recursive type aliases, we need to
+    // populate the type bindings before we actually check any of the
+    // alias statements. Since we're not ready to actually resolve
+    // any of the annotations, we just use a fresh type for now.
+    for (AstStat* stat : block->body)
+    {
+        if (auto alias = stat->as<AstStatTypeAlias>())
+        {
+            TypeId initialType = freshType(scope);
+            scope->typeBindings[alias->name.value] = initialType;
+        }
+    }
+
     for (AstStat* stat : block->body)
         visit(scope, stat);
 }
@@ -267,7 +280,7 @@ void ConstraintGraphBuilder::visit(Scope2* scope, AstStatAssign* assign)
     TypePackId varPackId = checkExprList(scope, assign->vars);
     TypePackId valuePack = checkPack(scope, assign->values);
 
-    addConstraint(scope, PackSubtypeConstraint{valuePack, varPackId}, assign->location);
+    addConstraint(scope, PackSubtypeConstraint{valuePack, varPackId});
 }
 
 void ConstraintGraphBuilder::visit(Scope2* scope, AstStatIf* ifStatement)
@@ -284,6 +297,28 @@ void ConstraintGraphBuilder::visit(Scope2* scope, AstStatIf* ifStatement)
     }
 }
 
+void ConstraintGraphBuilder::visit(Scope2* scope, AstStatTypeAlias* alias)
+{
+    // TODO: Exported type aliases
+    // TODO: Generic type aliases
+
+    auto it = scope->typeBindings.find(alias->name.value);
+    // This should always be here since we do a separate pass over the
+    // AST to set up typeBindings. If it's not, we've somehow skipped
+    // this alias in that first pass.
+    LUAU_ASSERT(it != scope->typeBindings.end());
+
+    TypeId ty = resolveType(scope, alias->type);
+
+    // Rather than using a subtype constraint, we instead directly bind
+    // the free type we generated in the first pass to the resolved type.
+    // This prevents a case where you could cause another constraint to
+    // bind the free alias type to an unrelated type, causing havoc.
+    asMutable(it->second)->ty.emplace<BoundTypeVar>(ty);
+
+    addConstraint(scope, NameConstraint{ty, alias->name.value});
+}
+
 TypePackId ConstraintGraphBuilder::checkPack(Scope2* scope, AstArray<AstExpr*> exprs)
 {
     LUAU_ASSERT(scope);
@@ -350,13 +385,13 @@ TypePackId ConstraintGraphBuilder::checkPack(Scope2* scope, AstExpr* expr)
         astOriginalCallTypes[call->func] = fnType;
 
         TypeId instantiatedType = freshType(scope);
-        addConstraint(scope, InstantiationConstraint{instantiatedType, fnType}, expr->location);
+        addConstraint(scope, InstantiationConstraint{instantiatedType, fnType});
 
         TypePackId rets = freshTypePack(scope);
         FunctionTypeVar ftv(arena->addTypePack(TypePack{args, {}}), rets);
         TypeId inferredFnType = arena->addType(ftv);
 
-        addConstraint(scope, SubtypeConstraint{inferredFnType, instantiatedType}, expr->location);
+        addConstraint(scope, SubtypeConstraint{inferredFnType, instantiatedType});
         result = rets;
     }
     else
@@ -413,7 +448,7 @@ TypeId ConstraintGraphBuilder::check(Scope2* scope, AstExpr* expr)
             TypePack onePack{{typeResult}, freshTypePack(scope)};
             TypePackId oneTypePack = arena->addTypePack(std::move(onePack));
 
-            addConstraint(scope, PackSubtypeConstraint{packResult, oneTypePack}, expr->location);
+            addConstraint(scope, PackSubtypeConstraint{packResult, oneTypePack});
 
             return typeResult;
         }
@@ -454,7 +489,7 @@ TypeId ConstraintGraphBuilder::check(Scope2* scope, AstExprIndexName* indexName)
 
     TypeId expectedTableType = arena->addType(std::move(ttv));
 
-    addConstraint(scope, SubtypeConstraint{obj, expectedTableType}, indexName->location);
+    addConstraint(scope, SubtypeConstraint{obj, expectedTableType});
 
     return result;
 }
@@ -465,8 +500,7 @@ TypeId ConstraintGraphBuilder::checkExprTable(Scope2* scope, AstExprTable* expr)
     TableTypeVar* ttv = getMutable<TableTypeVar>(ty);
     LUAU_ASSERT(ttv);
 
-    auto createIndexer = [this, scope, ttv](
-                             TypeId currentIndexType, TypeId currentResultType, Location itemLocation, std::optional<Location> keyLocation) {
+    auto createIndexer = [this, scope, ttv](TypeId currentIndexType, TypeId currentResultType) {
         if (!ttv->indexer)
         {
             TypeId indexType = this->freshType(scope);
@@ -474,8 +508,8 @@ TypeId ConstraintGraphBuilder::checkExprTable(Scope2* scope, AstExprTable* expr)
             ttv->indexer = TableIndexer{indexType, resultType};
         }
 
-        addConstraint(scope, SubtypeConstraint{ttv->indexer->indexType, currentIndexType}, keyLocation ? *keyLocation : itemLocation);
-        addConstraint(scope, SubtypeConstraint{ttv->indexer->indexResultType, currentResultType}, itemLocation);
+        addConstraint(scope, SubtypeConstraint{ttv->indexer->indexType, currentIndexType});
+        addConstraint(scope, SubtypeConstraint{ttv->indexer->indexResultType, currentResultType});
     };
 
     for (const AstExprTable::Item& item : expr->items)
@@ -495,13 +529,13 @@ TypeId ConstraintGraphBuilder::checkExprTable(Scope2* scope, AstExprTable* expr)
             }
             else
             {
-                createIndexer(keyTy, itemTy, item.value->location, item.key->location);
+                createIndexer(keyTy, itemTy);
             }
         }
         else
         {
             TypeId numberType = singletonTypes.numberType;
-            createIndexer(numberType, itemTy, item.value->location, std::nullopt);
+            createIndexer(numberType, itemTy);
         }
     }
 
@@ -514,15 +548,29 @@ std::pair<TypeId, Scope2*> ConstraintGraphBuilder::checkFunctionSignature(Scope2
     TypePackId returnType = freshTypePack(innerScope);
     innerScope->returnType = returnType;
 
+    if (fn->returnAnnotation)
+    {
+        TypePackId annotatedRetType = resolveTypePack(innerScope, *fn->returnAnnotation);
+        addConstraint(innerScope, PackSubtypeConstraint{returnType, annotatedRetType});
+    }
+
     std::vector<TypeId> argTypes;
 
     for (AstLocal* local : fn->args)
     {
         TypeId t = freshType(innerScope);
         argTypes.push_back(t);
-        innerScope->bindings[local] = t; // TODO annotations
+        innerScope->bindings[local] = t;
+
+        if (local->annotation)
+        {
+            TypeId argAnnotation = resolveType(innerScope, local->annotation);
+            addConstraint(innerScope, SubtypeConstraint{t, argAnnotation});
+        }
     }
 
+    // TODO: Vararg annotation.
+
     FunctionTypeVar actualFunction{arena->addTypePack(argTypes), returnType};
     TypeId actualFunctionType = arena->addType(std::move(actualFunction));
     LUAU_ASSERT(actualFunctionType);
@@ -541,10 +589,171 @@ void ConstraintGraphBuilder::checkFunctionBody(Scope2* scope, AstExprFunction* f
     if (nullptr != getFallthrough(fn->body))
     {
         TypePackId empty = arena->addTypePack({}); // TODO we could have CSG retain one of these forever
-        addConstraint(scope, PackSubtypeConstraint{scope->returnType, empty}, fn->body->location);
+        addConstraint(scope, PackSubtypeConstraint{scope->returnType, empty});
     }
 }
 
+TypeId ConstraintGraphBuilder::resolveType(Scope2* scope, AstType* ty)
+{
+    TypeId result = nullptr;
+
+    if (auto ref = ty->as<AstTypeReference>())
+    {
+        // TODO: Support imported types w/ require tracing.
+        // TODO: Support generic type references.
+        LUAU_ASSERT(!ref->prefix);
+        LUAU_ASSERT(!ref->hasParameterList);
+
+        // TODO: If it doesn't exist, should we introduce a free binding?
+        // This is probably important for handling type aliases.
+        result = scope->lookupTypeBinding(ref->name.value).value_or(singletonTypes.errorRecoveryType());
+    }
+    else if (auto tab = ty->as<AstTypeTable>())
+    {
+        TableTypeVar::Props props;
+        std::optional<TableIndexer> indexer;
+
+        for (const AstTableProp& prop : tab->props)
+        {
+            std::string name = prop.name.value;
+            // TODO: Recursion limit.
+            TypeId propTy = resolveType(scope, prop.type);
+            // TODO: Fill in location.
+            props[name] = {propTy};
+        }
+
+        if (tab->indexer)
+        {
+            // TODO: Recursion limit.
+            indexer = TableIndexer{
+                resolveType(scope, tab->indexer->indexType),
+                resolveType(scope, tab->indexer->resultType),
+            };
+        }
+
+        // TODO: Remove TypeLevel{} here, we don't need it.
+        result = arena->addType(TableTypeVar{props, indexer, TypeLevel{}, TableState::Sealed});
+    }
+    else if (auto fn = ty->as<AstTypeFunction>())
+    {
+        // TODO: Generic functions.
+        // TODO: Scope (though it may not be needed).
+        // TODO: Recursion limit.
+        TypePackId argTypes = resolveTypePack(scope, fn->argTypes);
+        TypePackId returnTypes = resolveTypePack(scope, fn->returnTypes);
+
+        // TODO: Is this the right constructor to use?
+        result = arena->addType(FunctionTypeVar{argTypes, returnTypes});
+
+        FunctionTypeVar* ftv = getMutable<FunctionTypeVar>(result);
+        ftv->argNames.reserve(fn->argNames.size);
+        for (const auto& el : fn->argNames)
+        {
+            if (el)
+            {
+                const auto& [name, location] = *el;
+                ftv->argNames.push_back(FunctionArgument{name.value, location});
+            }
+            else
+            {
+                ftv->argNames.push_back(std::nullopt);
+            }
+        }
+    }
+    else if (auto tof = ty->as<AstTypeTypeof>())
+    {
+        // TODO: Recursion limit.
+        TypeId exprType = check(scope, tof->expr);
+        result = exprType;
+    }
+    else if (auto unionAnnotation = ty->as<AstTypeUnion>())
+    {
+        std::vector<TypeId> parts;
+        for (AstType* part : unionAnnotation->types)
+        {
+            // TODO: Recursion limit.
+            parts.push_back(resolveType(scope, part));
+        }
+
+        result = arena->addType(UnionTypeVar{parts});
+    }
+    else if (auto intersectionAnnotation = ty->as<AstTypeIntersection>())
+    {
+        std::vector<TypeId> parts;
+        for (AstType* part : intersectionAnnotation->types)
+        {
+            // TODO: Recursion limit.
+            parts.push_back(resolveType(scope, part));
+        }
+
+        result = arena->addType(IntersectionTypeVar{parts});
+    }
+    else if (auto boolAnnotation = ty->as<AstTypeSingletonBool>())
+    {
+        result = arena->addType(SingletonTypeVar(BooleanSingleton{boolAnnotation->value}));
+    }
+    else if (auto stringAnnotation = ty->as<AstTypeSingletonString>())
+    {
+        result = arena->addType(SingletonTypeVar(StringSingleton{std::string(stringAnnotation->value.data, stringAnnotation->value.size)}));
+    }
+    else if (ty->is<AstTypeError>())
+    {
+        result = singletonTypes.errorRecoveryType();
+    }
+    else
+    {
+        LUAU_ASSERT(0);
+        result = singletonTypes.errorRecoveryType();
+    }
+
+    astResolvedTypes[ty] = result;
+    return result;
+}
+
+TypePackId ConstraintGraphBuilder::resolveTypePack(Scope2* scope, AstTypePack* tp)
+{
+    TypePackId result;
+    if (auto expl = tp->as<AstTypePackExplicit>())
+    {
+        result = resolveTypePack(scope, expl->typeList);
+    }
+    else if (auto var = tp->as<AstTypePackVariadic>())
+    {
+        TypeId ty = resolveType(scope, var->variadicType);
+        result = arena->addTypePack(TypePackVar{VariadicTypePack{ty}});
+    }
+    else if (auto gen = tp->as<AstTypePackGeneric>())
+    {
+        result = arena->addTypePack(TypePackVar{GenericTypePack{scope, gen->genericName.value}});
+    }
+    else
+    {
+        LUAU_ASSERT(0);
+        result = singletonTypes.errorRecoveryTypePack();
+    }
+
+    astResolvedTypePacks[tp] = result;
+    return result;
+}
+
+TypePackId ConstraintGraphBuilder::resolveTypePack(Scope2* scope, const AstTypeList& list)
+{
+    std::vector<TypeId> head;
+
+    for (AstType* headTy : list.types)
+    {
+        head.push_back(resolveType(scope, headTy));
+    }
+
+    std::optional<TypePackId> tail = std::nullopt;
+    if (list.tailType)
+    {
+        tail = resolveTypePack(scope, list.tailType);
+    }
+
+    return arena->addTypePack(TypePack{head, tail});
+}
+
 void collectConstraints(std::vector<NotNull<Constraint>>& result, Scope2* scope)
 {
     for (const auto& c : scope->constraints)

Analysis/src/ConstraintSolver.cpp

@@ -2,6 +2,7 @@
 
 #include "Luau/ConstraintSolver.h"
 #include "Luau/Instantiation.h"
+#include "Luau/Location.h"
 #include "Luau/Quantify.h"
 #include "Luau/ToString.h"
 #include "Luau/Unifier.h"
@@ -179,6 +180,8 @@ bool ConstraintSolver::tryDispatch(NotNull<const Constraint> constraint, bool fo
         success = tryDispatch(*gc, constraint, force);
     else if (auto ic = get<InstantiationConstraint>(*constraint))
         success = tryDispatch(*ic, constraint, force);
+    else if (auto nc = get<NameConstraint>(*constraint))
+        success = tryDispatch(*nc, constraint);
     else
         LUAU_ASSERT(0);
 
@@ -197,7 +200,7 @@ bool ConstraintSolver::tryDispatch(const SubtypeConstraint& c, NotNull<const Con
     else if (isBlocked(c.superType))
         return block(c.superType, constraint);
 
-    unify(c.subType, c.superType, constraint->location);
+    unify(c.subType, c.superType);
 
     unblock(c.subType);
     unblock(c.superType);
@@ -207,7 +210,7 @@ bool ConstraintSolver::tryDispatch(const SubtypeConstraint& c, NotNull<const Con
 
 bool ConstraintSolver::tryDispatch(const PackSubtypeConstraint& c, NotNull<const Constraint> constraint, bool force)
 {
-    unify(c.subPack, c.superPack, constraint->location);
+    unify(c.subPack, c.superPack);
     unblock(c.subPack);
     unblock(c.superPack);
 
@@ -222,7 +225,7 @@ bool ConstraintSolver::tryDispatch(const GeneralizationConstraint& c, NotNull<co
     if (isBlocked(c.generalizedType))
         asMutable(c.generalizedType)->ty.emplace<BoundTypeVar>(c.sourceType);
     else
-        unify(c.generalizedType, c.sourceType, constraint->location);
+        unify(c.generalizedType, c.sourceType);
 
     TypeId generalized = quantify(arena, c.sourceType, c.scope);
     *asMutable(c.sourceType) = *generalized;
@@ -243,12 +246,28 @@ bool ConstraintSolver::tryDispatch(const InstantiationConstraint& c, NotNull<con
     std::optional<TypeId> instantiated = inst.substitute(c.superType);
     LUAU_ASSERT(instantiated); // TODO FIXME HANDLE THIS
 
-    unify(c.subType, *instantiated, constraint->location);
+    unify(c.subType, *instantiated);
     unblock(c.subType);
 
     return true;
 }
 
+bool ConstraintSolver::tryDispatch(const NameConstraint& c, NotNull<const Constraint> constraint)
+{
+    if (isBlocked(c.namedType))
+        return block(c.namedType, constraint);
+
+    TypeId target = follow(c.namedType);
+    if (TableTypeVar* ttv = getMutable<TableTypeVar>(target))
+        ttv->name = c.name;
+    else if (MetatableTypeVar* mtv = getMutable<MetatableTypeVar>(target))
+        mtv->syntheticName = c.name;
+    else
+        return block(c.namedType, constraint);
+
+    return true;
+}
+
 void ConstraintSolver::block_(BlockedConstraintId target, NotNull<const Constraint> constraint)
 {
     blocked[target].push_back(constraint);
@@ -321,19 +340,19 @@ bool ConstraintSolver::isBlocked(NotNull<const Constraint> constraint)
     return blockedIt != blockedConstraints.end() && blockedIt->second > 0;
 }
 
-void ConstraintSolver::unify(TypeId subType, TypeId superType, Location location)
+void ConstraintSolver::unify(TypeId subType, TypeId superType)
 {
     UnifierSharedState sharedState{&iceReporter};
-    Unifier u{arena, Mode::Strict, location, Covariant, sharedState};
+    Unifier u{arena, Mode::Strict, Location{}, Covariant, sharedState};
 
     u.tryUnify(subType, superType);
     u.log.commit();
 }
 
-void ConstraintSolver::unify(TypePackId subPack, TypePackId superPack, Location location)
+void ConstraintSolver::unify(TypePackId subPack, TypePackId superPack)
 {
     UnifierSharedState sharedState{&iceReporter};
-    Unifier u{arena, Mode::Strict, location, Covariant, sharedState};
+    Unifier u{arena, Mode::Strict, Location{}, Covariant, sharedState};
 
     u.tryUnify(subPack, superPack);
     u.log.commit();

Analysis/src/Error.cpp

@@ -7,6 +7,9 @@
 
 #include <stdexcept>
 
+LUAU_FASTFLAGVARIABLE(LuauTypeMismatchModuleNameResolution, false)
+LUAU_FASTFLAGVARIABLE(LuauUseInternalCompilerErrorException, false)
+
 static std::string wrongNumberOfArgsString(size_t expectedCount, size_t actualCount, const char* argPrefix = nullptr, bool isVariadic = false)
 {
     std::string s = "expects ";
@@ -49,6 +52,8 @@ namespace Luau
 
 struct ErrorConverter
 {
+    FileResolver* fileResolver = nullptr;
+
     std::string operator()(const Luau::TypeMismatch& tm) const
     {
         std::string givenTypeName = Luau::toString(tm.givenType);
@@ -62,8 +67,18 @@ struct ErrorConverter
             {
                 if (auto wantedDefinitionModule = getDefinitionModuleName(tm.wantedType))
                 {
-                    result = "Type '" + givenTypeName + "' from '" + *givenDefinitionModule + "' could not be converted into '" + wantedTypeName +
-                             "' from '" + *wantedDefinitionModule + "'";
+                    if (FFlag::LuauTypeMismatchModuleNameResolution && fileResolver != nullptr)
+                    {
+                        std::string givenModuleName = fileResolver->getHumanReadableModuleName(*givenDefinitionModule);
+                        std::string wantedModuleName = fileResolver->getHumanReadableModuleName(*wantedDefinitionModule);
+                        result = "Type '" + givenTypeName + "' from '" + givenModuleName + "' could not be converted into '" + wantedTypeName +
+                                 "' from '" + wantedModuleName + "'";
+                    }
+                    else
+                    {
+                        result = "Type '" + givenTypeName + "' from '" + *givenDefinitionModule + "' could not be converted into '" + wantedTypeName +
+                                 "' from '" + *wantedDefinitionModule + "'";
+                    }
                 }
             }
         }
@@ -78,7 +93,14 @@ struct ErrorConverter
             if (!tm.reason.empty())
                 result += tm.reason + " ";
 
-            result += Luau::toString(*tm.error);
+            if (FFlag::LuauTypeMismatchModuleNameResolution)
+            {
+                result += Luau::toString(*tm.error, TypeErrorToStringOptions{fileResolver});
+            }
+            else
+            {
+                result += Luau::toString(*tm.error);
+            }
         }
         else if (!tm.reason.empty())
         {
@@ -280,6 +302,11 @@ struct ErrorConverter
         return e.message;
     }
 
+    std::string operator()(const Luau::InternalError& e) const
+    {
+        return e.message;
+    }
+
     std::string operator()(const Luau::CannotCallNonFunction& e) const
     {
         return "Cannot call non-function " + toString(e.ty);
@@ -598,6 +625,11 @@ bool GenericError::operator==(const GenericError& rhs) const
     return message == rhs.message;
 }
 
+bool InternalError::operator==(const InternalError& rhs) const
+{
+    return message == rhs.message;
+}
+
 bool CannotCallNonFunction::operator==(const CannotCallNonFunction& rhs) const
 {
     return ty == rhs.ty;
@@ -685,7 +717,12 @@ bool TypesAreUnrelated::operator==(const TypesAreUnrelated& rhs) const
 
 std::string toString(const TypeError& error)
 {
-    ErrorConverter converter;
+    return toString(error, TypeErrorToStringOptions{});
+}
+
+std::string toString(const TypeError& error, TypeErrorToStringOptions options)
+{
+    ErrorConverter converter{options.fileResolver};
     return Luau::visit(converter, error.data);
 }
 
@@ -773,6 +810,9 @@ void copyError(T& e, TypeArena& destArena, CloneState cloneState)
     else if constexpr (std::is_same_v<T, GenericError>)
     {
     }
+    else if constexpr (std::is_same_v<T, InternalError>)
+    {
+    }
     else if constexpr (std::is_same_v<T, CannotCallNonFunction>)
     {
         e.ty = clone(e.ty);
@@ -847,22 +887,51 @@ void copyErrors(ErrorVec& errors, TypeArena& destArena)
 
 void InternalErrorReporter::ice(const std::string& message, const Location& location)
 {
-    std::runtime_error error("Internal error in " + moduleName + " at " + toString(location) + ": " + message);
+    if (FFlag::LuauUseInternalCompilerErrorException)
+    {
+        InternalCompilerError error(message, moduleName, location);
 
-    if (onInternalError)
-        onInternalError(error.what());
+        if (onInternalError)
+            onInternalError(error.what());
 
-    throw error;
+        throw error;
+    }
+    else
+    {
+        std::runtime_error error("Internal error in " + moduleName + " at " + toString(location) + ": " + message);
+
+        if (onInternalError)
+            onInternalError(error.what());
+
+        throw error;
+    }
 }
 
 void InternalErrorReporter::ice(const std::string& message)
 {
-    std::runtime_error error("Internal error in " + moduleName + ": " + message);
+    if (FFlag::LuauUseInternalCompilerErrorException)
+    {
+        InternalCompilerError error(message, moduleName);
 
-    if (onInternalError)
-        onInternalError(error.what());
+        if (onInternalError)
+            onInternalError(error.what());
 
-    throw error;
+        throw error;
+    }
+    else
+    {
+        std::runtime_error error("Internal error in " + moduleName + ": " + message);
+
+        if (onInternalError)
+            onInternalError(error.what());
+
+        throw error;
+    }
+}
+
+const char* InternalCompilerError::what() const throw()
+{
+    return this->message.data();
 }
 
 } // namespace Luau

Analysis/src/Frontend.cpp

@@ -801,6 +801,8 @@ ModulePtr Frontend::check(const SourceModule& sourceModule, Mode mode, const Sco
     result->astTypes = std::move(cgb.astTypes);
     result->astTypePacks = std::move(cgb.astTypePacks);
     result->astOriginalCallTypes = std::move(cgb.astOriginalCallTypes);
+    result->astResolvedTypes = std::move(cgb.astResolvedTypes);
+    result->astResolvedTypePacks = std::move(cgb.astResolvedTypePacks);
 
     result->clonePublicInterface(iceHandler);
 

Analysis/src/IostreamHelpers.cpp

@@ -111,6 +111,8 @@ static void errorToString(std::ostream& stream, const T& err)
     }
     else if constexpr (std::is_same_v<T, GenericError>)
         stream << "GenericError { " << err.message << " }";
+    else if constexpr (std::is_same_v<T, InternalError>)
+        stream << "InternalError { " << err.message << " }";
     else if constexpr (std::is_same_v<T, CannotCallNonFunction>)
         stream << "CannotCallNonFunction { " << toString(err.ty) << " }";
     else if constexpr (std::is_same_v<T, ExtraInformation>)

Analysis/src/Module.cpp

@@ -11,7 +11,6 @@
 #include "Luau/TypePack.h"
 #include "Luau/TypeVar.h"
 #include "Luau/VisitTypeVar.h"
-#include "Luau/ConstraintGraphBuilder.h" // FIXME: For Scope2 TODO pull out into its own header
 
 #include <algorithm>
 

Analysis/src/Quantify.cpp

@@ -2,11 +2,10 @@
 
 #include "Luau/Quantify.h"
 
-#include "Luau/ConstraintGraphBuilder.h" // TODO for Scope2; move to separate header
-#include "Luau/TxnLog.h"
+#include "Luau/Scope.h"
 #include "Luau/Substitution.h"
+#include "Luau/TxnLog.h"
 #include "Luau/VisitTypeVar.h"
-#include "Luau/ConstraintGraphBuilder.h" // TODO for Scope2; move to separate header
 
 LUAU_FASTFLAG(LuauAlwaysQuantify);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
@@ -177,8 +176,6 @@ void quantify(TypeId ty, TypeLevel level)
 
     if (ftv->generics.empty() && ftv->genericPacks.empty() && !q.seenMutableType && !q.seenGenericType)
         ftv->hasNoGenerics = true;
-
-    ftv->generalized = true;
 }
 
 void quantify(TypeId ty, Scope2* scope)
@@ -201,8 +198,6 @@ void quantify(TypeId ty, Scope2* scope)
 
     if (ftv->generics.empty() && ftv->genericPacks.empty() && !q.seenMutableType && !q.seenGenericType)
         ftv->hasNoGenerics = true;
-
-    ftv->generalized = true;
 }
 
 struct PureQuantifier : Substitution

Analysis/src/Scope.cpp

@@ -121,4 +121,36 @@ std::optional<Binding> Scope::linearSearchForBinding(const std::string& name, bo
     return std::nullopt;
 }
 
+std::optional<TypeId> Scope2::lookup(Symbol sym)
+{
+    Scope2* s = this;
+
+    while (true)
+    {
+        auto it = s->bindings.find(sym);
+        if (it != s->bindings.end())
+            return it->second;
+
+        if (s->parent)
+            s = s->parent;
+        else
+            return std::nullopt;
+    }
+}
+
+std::optional<TypeId> Scope2::lookupTypeBinding(const Name& name)
+{
+    Scope2* s = this;
+    while (s)
+    {
+        auto it = s->typeBindings.find(name);
+        if (it != s->typeBindings.end())
+            return it->second;
+
+        s = s->parent;
+    }
+
+    return std::nullopt;
+}
+
 } // namespace Luau

Analysis/src/ToString.cpp

@@ -1411,6 +1411,12 @@ std::string toString(const Constraint& c, ToStringOptions& opts)
         opts.nameMap = std::move(superStr.nameMap);
         return subStr.name + " ~ inst " + superStr.name;
     }
+    else if (const NameConstraint* nc = Luau::get<NameConstraint>(c))
+    {
+        ToStringResult namedStr = toStringDetailed(nc->namedType, opts);
+        opts.nameMap = std::move(namedStr.nameMap);
+        return "@name(" + namedStr.name + ") = " + nc->name;
+    }
     else
     {
         LUAU_ASSERT(false);

Analysis/src/TypeChecker2.cpp

@@ -7,6 +7,9 @@
 #include "Luau/AstQuery.h"
 #include "Luau/Clone.h"
 #include "Luau/Normalize.h"
+#include "Luau/ConstraintGraphBuilder.h" // FIXME move Scope2 into its own header
+#include "Luau/Unifier.h"
+#include "Luau/ToString.h"
 
 namespace Luau
 {
@@ -39,6 +42,104 @@ struct TypeChecker2 : public AstVisitor
         return follow(*ty);
     }
 
+    TypeId lookupAnnotation(AstType* annotation)
+    {
+        TypeId* ty = module->astResolvedTypes.find(annotation);
+        LUAU_ASSERT(ty);
+        return follow(*ty);
+    }
+
+    TypePackId reconstructPack(AstArray<AstExpr*> exprs, TypeArena& arena)
+    {
+        std::vector<TypeId> head;
+
+        for (size_t i = 0; i < exprs.size - 1; ++i)
+        {
+            head.push_back(lookupType(exprs.data[i]));
+        }
+
+        TypePackId tail = lookupPack(exprs.data[exprs.size - 1]);
+        return arena.addTypePack(TypePack{head, tail});
+    }
+
+    Scope2* findInnermostScope(Location location)
+    {
+        Scope2* bestScope = module->getModuleScope2();
+        Location bestLocation = module->scope2s[0].first;
+
+        for (size_t i = 0; i < module->scope2s.size(); ++i)
+        {
+            auto& [scopeBounds, scope] = module->scope2s[i];
+            if (scopeBounds.encloses(location))
+            {
+                if (scopeBounds.begin > bestLocation.begin || scopeBounds.end < bestLocation.end)
+                {
+                    bestScope = scope.get();
+                    bestLocation = scopeBounds;
+                }
+            }
+            else
+            {
+                // TODO: Is this sound? This relies on the fact that scopes are inserted
+                // into the scope list in the order that they appear in the AST.
+                break;
+            }
+        }
+
+        return bestScope;
+    }
+
+    bool visit(AstStatLocal* local) override
+    {
+        for (size_t i = 0; i < local->values.size; ++i)
+        {
+            AstExpr* value = local->values.data[i];
+            if (i == local->values.size - 1)
+            {
+                if (i < local->values.size)
+                {
+                    TypePackId valueTypes = lookupPack(value);
+                    auto it = begin(valueTypes);
+                    for (size_t j = i; j < local->vars.size; ++j)
+                    {
+                        if (it == end(valueTypes))
+                        {
+                            break;
+                        }
+
+                        AstLocal* var = local->vars.data[i];
+                        if (var->annotation)
+                        {
+                            TypeId varType = lookupAnnotation(var->annotation);
+                            if (!isSubtype(*it, varType, ice))
+                            {
+                                reportError(TypeMismatch{varType, *it}, value->location);
+                            }
+                        }
+
+                        ++it;
+                    }
+                }
+            }
+            else
+            {
+                TypeId valueType = lookupType(value);
+                AstLocal* var = local->vars.data[i];
+
+                if (var->annotation)
+                {
+                    TypeId varType = lookupAnnotation(var->annotation);
+                    if (!isSubtype(varType, valueType, ice))
+                    {
+                        reportError(TypeMismatch{varType, valueType}, value->location);
+                    }
+                }
+            }
+        }
+
+        return true;
+    }
+
     bool visit(AstStatAssign* assign) override
     {
         size_t count = std::min(assign->vars.size, assign->values.size);
@@ -62,6 +163,30 @@ struct TypeChecker2 : public AstVisitor
         return true;
     }
 
+    bool visit(AstStatReturn* ret) override
+    {
+        Scope2* scope = findInnermostScope(ret->location);
+        TypePackId expectedRetType = scope->returnType;
+
+        TypeArena arena;
+        TypePackId actualRetType = reconstructPack(ret->list, arena);
+
+        UnifierSharedState sharedState{&ice};
+        Unifier u{&arena, Mode::Strict, ret->location, Covariant, sharedState};
+        u.anyIsTop = true;
+
+        u.tryUnify(actualRetType, expectedRetType);
+        const bool ok = u.errors.empty() && u.log.empty();
+
+        if (!ok)
+        {
+            for (const TypeError& e : u.errors)
+                module->errors.push_back(e);
+        }
+
+        return true;
+    }
+
     bool visit(AstExprCall* call) override
     {
         TypePackId expectedRetType = lookupPack(call);
@@ -91,6 +216,35 @@ struct TypeChecker2 : public AstVisitor
         return true;
     }
 
+    bool visit(AstExprFunction* fn) override
+    {
+        TypeId inferredFnTy = lookupType(fn);
+        const FunctionTypeVar* inferredFtv = get<FunctionTypeVar>(inferredFnTy);
+        LUAU_ASSERT(inferredFtv);
+
+        auto argIt = begin(inferredFtv->argTypes);
+        for (const auto& arg : fn->args)
+        {
+            if (argIt == end(inferredFtv->argTypes))
+                break;
+
+            if (arg->annotation)
+            {
+                TypeId inferredArgTy = *argIt;
+                TypeId annotatedArgTy = lookupAnnotation(arg->annotation);
+
+                if (!isSubtype(annotatedArgTy, inferredArgTy, ice))
+                {
+                    reportError(TypeMismatch{annotatedArgTy, inferredArgTy}, arg->location);
+                }
+            }
+
+            ++argIt;
+        }
+
+        return true;
+    }
+
     bool visit(AstExprIndexName* indexName) override
     {
         TypeId leftType = lookupType(indexName->expr);
@@ -144,6 +298,25 @@ struct TypeChecker2 : public AstVisitor
         return true;
     }
 
+    bool visit(AstType* ty) override
+    {
+        return true;
+    }
+
+    bool visit(AstTypeReference* ty) override
+    {
+        Scope2* scope = findInnermostScope(ty->location);
+
+        // TODO: Imported types
+        // TODO: Generic types
+        if (!scope->lookupTypeBinding(ty->name.value))
+        {
+            reportError(UnknownSymbol{ty->name.value, UnknownSymbol::Context::Type}, ty->location);
+        }
+
+        return true;
+    }
+
     void reportError(TypeErrorData&& data, const Location& location)
     {
         module->errors.emplace_back(location, sourceModule->name, std::move(data));

Analysis/src/TypeInfer.cpp

@@ -35,13 +35,9 @@ LUAU_FASTFLAGVARIABLE(LuauLowerBoundsCalculation, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauFreezeDuringUnification, false)
 LUAU_FASTFLAGVARIABLE(LuauSelfCallAutocompleteFix2, false)
 LUAU_FASTFLAGVARIABLE(LuauReduceUnionRecursion, false)
-LUAU_FASTFLAGVARIABLE(LuauOnlyMutateInstantiatedTables, false)
-LUAU_FASTFLAGVARIABLE(LuauUnsealedTableLiteral, false)
 LUAU_FASTFLAGVARIABLE(LuauReturnAnyInsteadOfICE, false) // Eventually removed as false.
 LUAU_FASTFLAG(LuauNormalizeFlagIsConservative)
 LUAU_FASTFLAGVARIABLE(LuauReturnTypeInferenceInNonstrict, false)
-LUAU_FASTFLAGVARIABLE(LuauRecursionLimitException, false);
-LUAU_FASTFLAGVARIABLE(LuauApplyTypeFunctionFix, false);
 LUAU_FASTFLAGVARIABLE(LuauAlwaysQuantify, false);
 LUAU_FASTFLAGVARIABLE(LuauReportErrorsOnIndexerKeyMismatch, false)
 LUAU_FASTFLAG(LuauQuantifyConstrained)
@@ -275,22 +271,15 @@ TypeChecker::TypeChecker(ModuleResolver* resolver, InternalErrorReporter* iceHan
 
 ModulePtr TypeChecker::check(const SourceModule& module, Mode mode, std::optional<ScopePtr> environmentScope)
 {
-    if (FFlag::LuauRecursionLimitException)
-    {
-        try
-        {
-            return checkWithoutRecursionCheck(module, mode, environmentScope);
-        }
-        catch (const RecursionLimitException&)
-        {
-            reportErrorCodeTooComplex(module.root->location);
-            return std::move(currentModule);
-        }
-    }
-    else
+    try
     {
         return checkWithoutRecursionCheck(module, mode, environmentScope);
     }
+    catch (const RecursionLimitException&)
+    {
+        reportErrorCodeTooComplex(module.root->location);
+        return std::move(currentModule);
+    }
 }
 
 ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mode mode, std::optional<ScopePtr> environmentScope)
@@ -445,22 +434,15 @@ void TypeChecker::checkBlock(const ScopePtr& scope, const AstStatBlock& block)
         reportErrorCodeTooComplex(block.location);
         return;
     }
-    if (FFlag::LuauRecursionLimitException)
-    {
-        try
-        {
-            checkBlockWithoutRecursionCheck(scope, block);
-        }
-        catch (const RecursionLimitException&)
-        {
-            reportErrorCodeTooComplex(block.location);
-            return;
-        }
-    }
-    else
+    try
     {
         checkBlockWithoutRecursionCheck(scope, block);
     }
+    catch (const RecursionLimitException&)
+    {
+        reportErrorCodeTooComplex(block.location);
+        return;
+    }
 }
 
 void TypeChecker::checkBlockWithoutRecursionCheck(const ScopePtr& scope, const AstStatBlock& block)
@@ -1917,7 +1899,7 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromType(
 
         for (TypeId t : utv)
         {
-            RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit, "getIndexTypeForType unions");
+            RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit);
 
             // Not needed when we normalize types.
             if (get<AnyTypeVar>(follow(t)))
@@ -1967,7 +1949,7 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromType(
 
         for (TypeId t : itv->parts)
         {
-            RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit, "getIndexTypeFromType intersections");
+            RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit);
 
             if (std::optional<TypeId> ty = getIndexTypeFromType(scope, t, name, location, false))
                 parts.push_back(*ty);
@@ -2190,7 +2172,7 @@ TypeId TypeChecker::checkExprTable(
         }
     }
 
-    TableState state = (expr.items.size == 0 || isNonstrictMode() || FFlag::LuauUnsealedTableLiteral) ? TableState::Unsealed : TableState::Sealed;
+    TableState state = TableState::Unsealed;
     TableTypeVar table = TableTypeVar{std::move(props), indexer, scope->level, state};
     table.definitionModuleName = currentModuleName;
     return addType(table);
@@ -5175,9 +5157,7 @@ TypePackId TypeChecker::resolveTypePack(const ScopePtr& scope, const AstTypePack
 
 bool ApplyTypeFunction::isDirty(TypeId ty)
 {
-    if (FFlag::LuauApplyTypeFunctionFix && typeArguments.count(ty))
-        return true;
-    else if (!FFlag::LuauApplyTypeFunctionFix && get<GenericTypeVar>(ty))
+    if (typeArguments.count(ty))
         return true;
     else if (const FreeTypeVar* ftv = get<FreeTypeVar>(ty))
     {
@@ -5191,9 +5171,7 @@ bool ApplyTypeFunction::isDirty(TypeId ty)
 
 bool ApplyTypeFunction::isDirty(TypePackId tp)
 {
-    if (FFlag::LuauApplyTypeFunctionFix && typePackArguments.count(tp))
-        return true;
-    else if (!FFlag::LuauApplyTypeFunctionFix && get<GenericTypePack>(tp))
+    if (typePackArguments.count(tp))
         return true;
     else
         return false;
@@ -5218,29 +5196,15 @@ bool ApplyTypeFunction::ignoreChildren(TypePackId tp)
 TypeId ApplyTypeFunction::clean(TypeId ty)
 {
     TypeId& arg = typeArguments[ty];
-    if (FFlag::LuauApplyTypeFunctionFix)
-    {
-        LUAU_ASSERT(arg);
-        return arg;
-    }
-    else if (arg)
-        return arg;
-    else
-        return addType(FreeTypeVar{level});
+    LUAU_ASSERT(arg);
+    return arg;
 }
 
 TypePackId ApplyTypeFunction::clean(TypePackId tp)
 {
     TypePackId& arg = typePackArguments[tp];
-    if (FFlag::LuauApplyTypeFunctionFix)
-    {
-        LUAU_ASSERT(arg);
-        return arg;
-    }
-    else if (arg)
-        return arg;
-    else
-        return addTypePack(FreeTypePack{level});
+    LUAU_ASSERT(arg);
+    return arg;
 }
 
 TypeId TypeChecker::instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf, const std::vector<TypeId>& typeParams,
@@ -5273,7 +5237,7 @@ TypeId TypeChecker::instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf,
 
     TypeId target = follow(instantiated);
     bool needsClone = follow(tf.type) == target;
-    bool shouldMutate = (!FFlag::LuauOnlyMutateInstantiatedTables || getTableType(tf.type));
+    bool shouldMutate = getTableType(tf.type);
     TableTypeVar* ttv = getMutableTableType(target);
 
     if (shouldMutate && ttv && needsClone)

Analysis/src/TypeVar.cpp

@@ -23,7 +23,6 @@ LUAU_FASTFLAG(DebugLuauFreezeArena)
 LUAU_FASTINTVARIABLE(LuauTypeMaximumStringifierLength, 500)
 LUAU_FASTINTVARIABLE(LuauTableTypeMaximumStringifierLength, 0)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
-LUAU_FASTFLAG(LuauSubtypingAddOptPropsToUnsealedTables)
 LUAU_FASTFLAG(LuauNonCopyableTypeVarFields)
 
 namespace Luau
@@ -172,22 +171,15 @@ bool isString(TypeId ty)
 // Returns true when ty is a supertype of string
 bool maybeString(TypeId ty)
 {
-    if (FFlag::LuauSubtypingAddOptPropsToUnsealedTables)
-    {
-        ty = follow(ty);
+    ty = follow(ty);
 
-        if (isPrim(ty, PrimitiveTypeVar::String) || get<AnyTypeVar>(ty))
-            return true;
+    if (isPrim(ty, PrimitiveTypeVar::String) || get<AnyTypeVar>(ty))
+        return true;
 
-        if (auto utv = get<UnionTypeVar>(ty))
-            return std::any_of(begin(utv), end(utv), maybeString);
+    if (auto utv = get<UnionTypeVar>(ty))
+        return std::any_of(begin(utv), end(utv), maybeString);
 
-        return false;
-    }
-    else
-    {
-        return isString(ty);
-    }
+    return false;
 }
 
 bool isThread(TypeId ty)
@@ -369,7 +361,7 @@ bool maybeSingleton(TypeId ty)
 
 bool hasLength(TypeId ty, DenseHashSet<TypeId>& seen, int* recursionCount)
 {
-    RecursionLimiter _rl(recursionCount, FInt::LuauTypeInferRecursionLimit, "hasLength");
+    RecursionLimiter _rl(recursionCount, FInt::LuauTypeInferRecursionLimit);
 
     ty = follow(ty);
 

Analysis/src/Unifiable.cpp

@@ -53,6 +53,14 @@ Generic::Generic(TypeLevel level, const Name& name)
 {
 }
 
+Generic::Generic(Scope2* scope, const Name& name)
+    : index(++nextIndex)
+    , scope(scope)
+    , name(name)
+    , explicitName(true)
+{
+}
+
 int Generic::nextIndex = 0;
 
 Error::Error()

Analysis/src/Unifier.cpp

@@ -17,11 +17,8 @@ LUAU_FASTINT(LuauTypeInferTypePackLoopLimit);
 LUAU_FASTINT(LuauTypeInferIterationLimit);
 LUAU_FASTFLAG(LuauAutocompleteDynamicLimits)
 LUAU_FASTINTVARIABLE(LuauTypeInferLowerBoundsIterationLimit, 2000);
-LUAU_FASTFLAGVARIABLE(LuauTableSubtypingVariance2, false);
 LUAU_FASTFLAG(LuauLowerBoundsCalculation);
 LUAU_FASTFLAG(LuauErrorRecoveryType);
-LUAU_FASTFLAGVARIABLE(LuauSubtypingAddOptPropsToUnsealedTables, false)
-LUAU_FASTFLAGVARIABLE(LuauTxnLogRefreshFunctionPointers, false)
 LUAU_FASTFLAG(LuauQuantifyConstrained)
 
 namespace Luau
@@ -354,7 +351,7 @@ void Unifier::tryUnify(TypeId subTy, TypeId superTy, bool isFunctionCall, bool i
 void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool isIntersection)
 {
     RecursionLimiter _ra(&sharedState.counters.recursionCount,
-        FFlag::LuauAutocompleteDynamicLimits ? sharedState.counters.recursionLimit : FInt::LuauTypeInferRecursionLimit, "TypeId tryUnify_");
+        FFlag::LuauAutocompleteDynamicLimits ? sharedState.counters.recursionLimit : FInt::LuauTypeInferRecursionLimit);
 
     ++sharedState.counters.iterationCount;
 
@@ -983,7 +980,7 @@ void Unifier::tryUnify(TypePackId subTp, TypePackId superTp, bool isFunctionCall
 void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCall)
 {
     RecursionLimiter _ra(&sharedState.counters.recursionCount,
-        FFlag::LuauAutocompleteDynamicLimits ? sharedState.counters.recursionLimit : FInt::LuauTypeInferRecursionLimit, "TypePackId tryUnify_");
+        FFlag::LuauAutocompleteDynamicLimits ? sharedState.counters.recursionLimit : FInt::LuauTypeInferRecursionLimit);
 
     ++sharedState.counters.iterationCount;
 
@@ -1316,12 +1313,9 @@ void Unifier::tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCal
         tryUnify_(subFunction->retTypes, superFunction->retTypes);
     }
 
-    if (FFlag::LuauTxnLogRefreshFunctionPointers)
-    {
-        // Updating the log may have invalidated the function pointers
-        superFunction = log.getMutable<FunctionTypeVar>(superTy);
-        subFunction = log.getMutable<FunctionTypeVar>(subTy);
-    }
+    // Updating the log may have invalidated the function pointers
+    superFunction = log.getMutable<FunctionTypeVar>(superTy);
+    subFunction = log.getMutable<FunctionTypeVar>(subTy);
 
     ctx = context;
 
@@ -1360,9 +1354,6 @@ struct Resetter
 
 void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
 {
-    if (!FFlag::LuauTableSubtypingVariance2)
-        return DEPRECATED_tryUnifyTables(subTy, superTy, isIntersection);
-
     TableTypeVar* superTable = log.getMutable<TableTypeVar>(superTy);
     TableTypeVar* subTable = log.getMutable<TableTypeVar>(subTy);
 
@@ -1379,8 +1370,7 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
         {
             auto subIter = subTable->props.find(propName);
 
-            if (subIter == subTable->props.end() && (!FFlag::LuauSubtypingAddOptPropsToUnsealedTables || subTable->state == TableState::Unsealed) &&
-                !isOptional(superProp.type))
+            if (subIter == subTable->props.end() && subTable->state == TableState::Unsealed && !isOptional(superProp.type))
                 missingProperties.push_back(propName);
         }
 
@@ -1398,7 +1388,7 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
         {
             auto superIter = superTable->props.find(propName);
 
-            if (superIter == superTable->props.end() && (FFlag::LuauSubtypingAddOptPropsToUnsealedTables || !isOptional(subProp.type)))
+            if (superIter == superTable->props.end())
                 extraProperties.push_back(propName);
         }
 
@@ -1443,7 +1433,7 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
             if (innerState.errors.empty())
                 log.concat(std::move(innerState.log));
         }
-        else if ((!FFlag::LuauSubtypingAddOptPropsToUnsealedTables || subTable->state == TableState::Unsealed) && isOptional(prop.type))
+        else if (subTable->state == TableState::Unsealed && isOptional(prop.type))
         // This is sound because unsealed table types are precise, so `{ p : T } <: { p : T, q : U? }`
         // since if `t : { p : T }` then we are guaranteed that `t.q` is `nil`.
         // TODO: if the supertype is written to, the subtype may no longer be precise (alias analysis?)
@@ -1512,9 +1502,6 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
         else if (variance == Covariant)
         {
         }
-        else if (!FFlag::LuauSubtypingAddOptPropsToUnsealedTables && isOptional(prop.type))
-        {
-        }
         else if (superTable->state == TableState::Free)
         {
             PendingType* pendingSuper = log.queue(superTy);
@@ -1639,296 +1626,6 @@ TypeId Unifier::deeplyOptional(TypeId ty, std::unordered_map<TypeId, TypeId> see
         return types->addType(UnionTypeVar{{getSingletonTypes().nilType, ty}});
 }
 
-void Unifier::DEPRECATED_tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
-{
-    LUAU_ASSERT(!FFlag::LuauTableSubtypingVariance2);
-    Resetter resetter{&variance};
-    variance = Invariant;
-
-    TableTypeVar* superTable = log.getMutable<TableTypeVar>(superTy);
-    TableTypeVar* subTable = log.getMutable<TableTypeVar>(subTy);
-
-    if (!superTable || !subTable)
-        ice("passed non-table types to unifyTables");
-
-    if (superTable->state == TableState::Sealed && subTable->state == TableState::Sealed)
-        return tryUnifySealedTables(subTy, superTy, isIntersection);
-    else if ((superTable->state == TableState::Sealed && subTable->state == TableState::Unsealed) ||
-             (superTable->state == TableState::Unsealed && subTable->state == TableState::Sealed))
-        return tryUnifySealedTables(subTy, superTy, isIntersection);
-    else if ((superTable->state == TableState::Sealed && subTable->state == TableState::Generic) ||
-             (superTable->state == TableState::Generic && subTable->state == TableState::Sealed))
-        reportError(TypeError{location, TypeMismatch{superTy, subTy}});
-    else if ((superTable->state == TableState::Free) != (subTable->state == TableState::Free)) // one table is free and the other is not
-    {
-        TypeId freeTypeId = subTable->state == TableState::Free ? subTy : superTy;
-        TypeId otherTypeId = subTable->state == TableState::Free ? superTy : subTy;
-
-        return tryUnifyFreeTable(otherTypeId, freeTypeId);
-    }
-    else if (superTable->state == TableState::Free && subTable->state == TableState::Free)
-    {
-        tryUnifyFreeTable(subTy, superTy);
-
-        // avoid creating a cycle when the types are already pointing at each other
-        if (follow(superTy) != follow(subTy))
-        {
-            log.bindTable(superTy, subTy);
-        }
-        return;
-    }
-    else if (superTable->state != TableState::Sealed && subTable->state != TableState::Sealed)
-    {
-        // All free tables are checked in one of the branches above
-        LUAU_ASSERT(superTable->state != TableState::Free);
-        LUAU_ASSERT(subTable->state != TableState::Free);
-
-        // Tables must have exactly the same props and their types must all unify
-        // I honestly have no idea if this is remotely close to reasonable.
-        for (const auto& [name, prop] : superTable->props)
-        {
-            const auto& r = subTable->props.find(name);
-            if (r == subTable->props.end())
-                reportError(TypeError{location, UnknownProperty{subTy, name}});
-            else
-                tryUnify_(r->second.type, prop.type);
-        }
-
-        if (superTable->indexer && subTable->indexer)
-            tryUnifyIndexer(*subTable->indexer, *superTable->indexer);
-        else if (superTable->indexer)
-        {
-            // passing/assigning a table without an indexer to something that has one
-            // e.g. table.insert(t, 1) where t is a non-sealed table and doesn't have an indexer.
-            if (subTable->state == TableState::Unsealed)
-            {
-                log.changeIndexer(subTy, superTable->indexer);
-            }
-            else
-                reportError(TypeError{location, CannotExtendTable{subTy, CannotExtendTable::Indexer}});
-        }
-    }
-    else if (superTable->state == TableState::Sealed)
-    {
-        // lt is sealed and so it must be possible for rt to have precisely the same shape
-        // Verify that this is the case, then bind rt to lt.
-        ice("unsealed tables are not working yet", location);
-    }
-    else if (subTable->state == TableState::Sealed)
-        return tryUnifyTables(superTy, subTy, isIntersection);
-    else
-        ice("tryUnifyTables");
-}
-
-void Unifier::tryUnifyFreeTable(TypeId subTy, TypeId superTy)
-{
-    LUAU_ASSERT(!FFlag::LuauTableSubtypingVariance2);
-    TableTypeVar* freeTable = log.getMutable<TableTypeVar>(superTy);
-    TableTypeVar* subTable = log.getMutable<TableTypeVar>(subTy);
-
-    if (!freeTable || !subTable)
-        ice("passed non-table types to tryUnifyFreeTable");
-
-    // Any properties in freeTable must unify with those in otherTable.
-    // Then bind freeTable to otherTable.
-    for (const auto& [freeName, freeProp] : freeTable->props)
-    {
-        if (auto subProp = findTablePropertyRespectingMeta(subTy, freeName))
-        {
-            tryUnify_(*subProp, freeProp.type);
-
-            /*
-             * TypeVars are commonly cyclic, so it is entirely possible
-             * for unifying a property of a table to change the table itself!
-             * We need to check for this and start over if we notice this occurring.
-             *
-             * I believe this is guaranteed to terminate eventually because this will
-             * only happen when a free table is bound to another table.
-             */
-            if (!log.getMutable<TableTypeVar>(superTy) || !log.getMutable<TableTypeVar>(subTy))
-                return tryUnify_(subTy, superTy);
-
-            if (TableTypeVar* pendingFreeTtv = log.getMutable<TableTypeVar>(superTy); pendingFreeTtv && pendingFreeTtv->boundTo)
-                return tryUnify_(subTy, superTy);
-        }
-        else
-        {
-            // If the other table is also free, then we are learning that it has more
-            // properties than we previously thought.  Else, it is an error.
-            if (subTable->state == TableState::Free)
-            {
-                PendingType* pendingSub = log.queue(subTy);
-                TableTypeVar* pendingSubTtv = getMutable<TableTypeVar>(pendingSub);
-                LUAU_ASSERT(pendingSubTtv);
-                pendingSubTtv->props.insert({freeName, freeProp});
-            }
-            else
-                reportError(TypeError{location, UnknownProperty{subTy, freeName}});
-        }
-    }
-
-    if (freeTable->indexer && subTable->indexer)
-    {
-        Unifier innerState = makeChildUnifier();
-        innerState.tryUnifyIndexer(*subTable->indexer, *freeTable->indexer);
-
-        checkChildUnifierTypeMismatch(innerState.errors, superTy, subTy);
-
-        log.concat(std::move(innerState.log));
-    }
-    else if (subTable->state == TableState::Free && freeTable->indexer)
-    {
-        log.changeIndexer(superTy, subTable->indexer);
-    }
-
-    if (!freeTable->boundTo && subTable->state != TableState::Free)
-    {
-        log.bindTable(superTy, subTy);
-    }
-}
-
-void Unifier::tryUnifySealedTables(TypeId subTy, TypeId superTy, bool isIntersection)
-{
-    LUAU_ASSERT(!FFlag::LuauTableSubtypingVariance2);
-    TableTypeVar* superTable = log.getMutable<TableTypeVar>(superTy);
-    TableTypeVar* subTable = log.getMutable<TableTypeVar>(subTy);
-
-    if (!superTable || !subTable)
-        ice("passed non-table types to unifySealedTables");
-
-    std::vector<std::string> missingPropertiesInSuper;
-    bool isUnnamedTable = subTable->name == std::nullopt && subTable->syntheticName == std::nullopt;
-    bool errorReported = false;
-
-    // Optimization: First test that the property sets are compatible without doing any recursive unification
-    if (!subTable->indexer)
-    {
-        for (const auto& [propName, superProp] : superTable->props)
-        {
-            auto subIter = subTable->props.find(propName);
-            if (subIter == subTable->props.end() && !isOptional(superProp.type))
-                missingPropertiesInSuper.push_back(propName);
-        }
-
-        if (!missingPropertiesInSuper.empty())
-        {
-            reportError(TypeError{location, MissingProperties{superTy, subTy, std::move(missingPropertiesInSuper)}});
-            return;
-        }
-    }
-
-    Unifier innerState = makeChildUnifier();
-
-    // Tables must have exactly the same props and their types must all unify
-    for (const auto& it : superTable->props)
-    {
-        const auto& r = subTable->props.find(it.first);
-        if (r == subTable->props.end())
-        {
-            if (isOptional(it.second.type))
-                continue;
-
-            missingPropertiesInSuper.push_back(it.first);
-
-            innerState.reportError(TypeError{location, TypeMismatch{superTy, subTy}});
-        }
-        else
-        {
-            if (isUnnamedTable && r->second.location)
-            {
-                size_t oldErrorSize = innerState.errors.size();
-                Location old = innerState.location;
-                innerState.location = *r->second.location;
-                innerState.tryUnify_(r->second.type, it.second.type);
-                innerState.location = old;
-
-                if (oldErrorSize != innerState.errors.size() && !errorReported)
-                {
-                    errorReported = true;
-                    reportError(innerState.errors.back());
-                }
-            }
-            else
-            {
-                innerState.tryUnify_(r->second.type, it.second.type);
-            }
-        }
-    }
-
-    if (superTable->indexer || subTable->indexer)
-    {
-        if (superTable->indexer && subTable->indexer)
-            innerState.tryUnifyIndexer(*subTable->indexer, *superTable->indexer);
-        else if (subTable->state == TableState::Unsealed)
-        {
-            if (superTable->indexer && !subTable->indexer)
-            {
-                log.changeIndexer(subTy, superTable->indexer);
-            }
-        }
-        else if (superTable->state == TableState::Unsealed)
-        {
-            if (subTable->indexer && !superTable->indexer)
-            {
-                log.changeIndexer(superTy, subTable->indexer);
-            }
-        }
-        else if (superTable->indexer)
-        {
-            innerState.tryUnify_(getSingletonTypes().stringType, superTable->indexer->indexType);
-            for (const auto& [name, type] : subTable->props)
-            {
-                const auto& it = superTable->props.find(name);
-                if (it == superTable->props.end())
-                    innerState.tryUnify_(type.type, superTable->indexer->indexResultType);
-            }
-        }
-        else
-            innerState.reportError(TypeError{location, TypeMismatch{superTy, subTy}});
-    }
-
-    if (!errorReported)
-        log.concat(std::move(innerState.log));
-    else
-        return;
-
-    if (!missingPropertiesInSuper.empty())
-    {
-        reportError(TypeError{location, MissingProperties{superTy, subTy, std::move(missingPropertiesInSuper)}});
-        return;
-    }
-
-    // If the superTy is an immediate part of an intersection type, do not do extra-property check.
-    // Otherwise, we would falsely generate an extra-property-error for 's' in this code:
-    // local a: {n: number} & {s: string} = {n=1, s=""}
-    // When checking against the table '{n: number}'.
-    if (!isIntersection && superTable->state != TableState::Unsealed && !superTable->indexer)
-    {
-        // Check for extra properties in the subTy
-        std::vector<std::string> extraPropertiesInSub;
-
-        for (const auto& [subKey, subProp] : subTable->props)
-        {
-            const auto& superIt = superTable->props.find(subKey);
-            if (superIt == superTable->props.end())
-            {
-                if (isOptional(subProp.type))
-                    continue;
-
-                extraPropertiesInSub.push_back(subKey);
-            }
-        }
-
-        if (!extraPropertiesInSub.empty())
-        {
-            reportError(TypeError{location, MissingProperties{superTy, subTy, std::move(extraPropertiesInSub), MissingProperties::Extra}});
-            return;
-        }
-    }
-
-    checkChildUnifierTypeMismatch(innerState.errors, superTy, subTy);
-}
-
 void Unifier::tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed)
 {
     const MetatableTypeVar* superMetatable = get<MetatableTypeVar>(superTy);
@@ -2068,14 +1765,6 @@ void Unifier::tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed)
         return fail();
 }
 
-void Unifier::tryUnifyIndexer(const TableIndexer& subIndexer, const TableIndexer& superIndexer)
-{
-    LUAU_ASSERT(!FFlag::LuauTableSubtypingVariance2);
-
-    tryUnify_(subIndexer.indexType, superIndexer.indexType);
-    tryUnify_(subIndexer.indexResultType, superIndexer.indexResultType);
-}
-
 static void queueTypePack(std::vector<TypeId>& queue, DenseHashSet<TypePackId>& seenTypePacks, Unifier& state, TypePackId a, TypePackId anyTypePack)
 {
     while (true)
@@ -2435,7 +2124,7 @@ void Unifier::occursCheck(TypeId needle, TypeId haystack)
 void Unifier::occursCheck(DenseHashSet<TypeId>& seen, TypeId needle, TypeId haystack)
 {
     RecursionLimiter _ra(&sharedState.counters.recursionCount,
-        FFlag::LuauAutocompleteDynamicLimits ? sharedState.counters.recursionLimit : FInt::LuauTypeInferRecursionLimit, "occursCheck for TypeId");
+        FFlag::LuauAutocompleteDynamicLimits ? sharedState.counters.recursionLimit : FInt::LuauTypeInferRecursionLimit);
 
     auto check = [&](TypeId tv) {
         occursCheck(seen, needle, tv);
@@ -2506,7 +2195,7 @@ void Unifier::occursCheck(DenseHashSet<TypePackId>& seen, TypePackId needle, Typ
         ice("Expected needle pack to be free");
 
     RecursionLimiter _ra(&sharedState.counters.recursionCount,
-        FFlag::LuauAutocompleteDynamicLimits ? sharedState.counters.recursionLimit : FInt::LuauTypeInferRecursionLimit, "occursCheck for TypePackId");
+        FFlag::LuauAutocompleteDynamicLimits ? sharedState.counters.recursionLimit : FInt::LuauTypeInferRecursionLimit);
 
     while (!log.getMutable<ErrorTypeVar>(haystack))
     {

CLI/Analyze.cpp

@@ -9,6 +9,7 @@
 #include "FileUtils.h"
 
 LUAU_FASTFLAG(DebugLuauTimeTracing)
+LUAU_FASTFLAG(LuauTypeMismatchModuleNameResolution)
 
 enum class ReportFormat
 {
@@ -49,6 +50,9 @@ static void reportError(const Luau::Frontend& frontend, ReportFormat format, con
 
     if (const Luau::SyntaxError* syntaxError = Luau::get_if<Luau::SyntaxError>(&error.data))
         report(format, humanReadableName.c_str(), error.location, "SyntaxError", syntaxError->message.c_str());
+    else if (FFlag::LuauTypeMismatchModuleNameResolution)
+        report(format, humanReadableName.c_str(), error.location, "TypeError",
+            Luau::toString(error, Luau::TypeErrorToStringOptions{frontend.fileResolver}).c_str());
     else
         report(format, humanReadableName.c_str(), error.location, "TypeError", Luau::toString(error).c_str());
 }

CMakeLists.txt

@@ -11,6 +11,7 @@ option(LUAU_BUILD_TESTS "Build tests" ON)
 option(LUAU_BUILD_WEB "Build Web module" OFF)
 option(LUAU_WERROR "Warnings as errors" OFF)
 option(LUAU_STATIC_CRT "Link with the static CRT (/MT)" OFF)
+option(LUAU_EXTERN_C "Use extern C for all APIs" OFF)
 
 if(LUAU_STATIC_CRT)
     cmake_minimum_required(VERSION 3.15)
@@ -115,6 +116,14 @@ target_compile_options(Luau.CodeGen PRIVATE ${LUAU_OPTIONS})
 target_compile_options(Luau.VM PRIVATE ${LUAU_OPTIONS})
 target_compile_options(isocline PRIVATE ${LUAU_OPTIONS} ${ISOCLINE_OPTIONS})
 
+if(LUAU_EXTERN_C)
+    # enable extern "C" for VM (lua.h, lualib.h) and Compiler (luacode.h) to make Luau friendlier to use from non-C++ languages
+    # note that we enable LUA_USE_LONGJMP=1 as well; otherwise functions like luaL_error will throw C++ exceptions, which can't be done from extern "C" functions
+    target_compile_definitions(Luau.VM PUBLIC LUA_USE_LONGJMP=1)
+    target_compile_definitions(Luau.VM PUBLIC LUA_API=extern\"C\")
+    target_compile_definitions(Luau.Compiler PUBLIC LUACODE_API=extern\"C\")
+endif()
+
 if (MSVC AND MSVC_VERSION GREATER_EQUAL 1924)
     # disable partial redundancy elimination which regresses interpreter codegen substantially in VS2022:
     # https://developercommunity.visualstudio.com/t/performance-regression-on-a-complex-interpreter-lo/1631863

Common/include/Luau/Bytecode.h

@@ -7,7 +7,7 @@
 // Creating the bytecode is outside the scope of this file and is handled by bytecode builder (BytecodeBuilder.h) and bytecode compiler (Compiler.h)
 // Note that ALL enums declared in this file are order-sensitive since the values are baked into bytecode that needs to be processed by legacy clients.
 
-// Bytecode definitions
+// # Bytecode definitions
 // Bytecode instructions are using "word code" - each instruction is one or many 32-bit words.
 // The first word in the instruction is always the instruction header, and *must* contain the opcode (enum below) in the least significant byte.
 //
@@ -19,7 +19,7 @@
 // Instruction word is sometimes followed by one extra word, indicated as AUX - this is just a 32-bit word and is decoded according to the specification for each opcode.
 // For each opcode the encoding is *static* - that is, based on the opcode you know a-priory how large the instruction is, with the exception of NEWCLOSURE
 
-// Bytecode indices
+// # Bytecode indices
 // Bytecode instructions commonly refer to integer values that define offsets or indices for various entities. For each type, there's a maximum encodable value.
 // Note that in some cases, the compiler will set a lower limit than the maximum encodable value is to prevent fragile code into bumping against the limits whenever we change the compilation details.
 // Additionally, in some specific instructions such as ANDK, the limit on the encoded value is smaller; this means that if a value is larger, a different instruction must be selected.
@@ -29,6 +29,15 @@
 // Constants: 0-2^23-1. Constants are stored in a table allocated with each proto; to allow for future bytecode tweaks the encodable value is limited to 23 bits.
 // Closures: 0-2^15-1. Closures are created from child protos via a child index; the limit is for the number of closures immediately referenced in each function.
 // Jumps: -2^23..2^23. Jump offsets are specified in word increments, so jumping over an instruction may sometimes require an offset of 2 or more.
+
+// # Bytecode versions
+// Bytecode serialized format embeds a version number, that dictates both the serialized form as well as the allowed instructions. As long as the bytecode version falls into supported
+// range (indicated by LBC_BYTECODE_MIN / LBC_BYTECODE_MAX) and was produced by Luau compiler, it should load and execute correctly.
+//
+// Note that Luau runtime doesn't provide indefinite bytecode compatibility: support for older versions gets removed over time. As such, bytecode isn't a durable storage format and it's expected
+// that Luau users can recompile bytecode from source on Luau version upgrades if necessary.
+
+// Bytecode opcode, part of the instruction header
 enum LuauOpcode
 {
     // NOP: noop
@@ -380,8 +389,10 @@ enum LuauOpcode
 // Bytecode tags, used internally for bytecode encoded as a string
 enum LuauBytecodeTag
 {
-    // Bytecode version
-    LBC_VERSION = 2,
+    // Bytecode version; runtime supports [MIN, MAX], compiler emits TARGET by default but may emit a higher version when flags are enabled
+    LBC_VERSION_MIN = 2,
+    LBC_VERSION_MAX = 2,
+    LBC_VERSION_TARGET = 2,
     // Types of constant table entries
     LBC_CONSTANT_NIL = 0,
     LBC_CONSTANT_BOOLEAN,

Compiler/include/Luau/BytecodeBuilder.h

@@ -119,6 +119,8 @@ public:
 
     static std::string getError(const std::string& message);
 
+    static uint8_t getVersion();
+
 private:
     struct Constant
     {

Compiler/src/BytecodeBuilder.cpp

@@ -9,6 +9,9 @@
 namespace Luau
 {
 
+static_assert(LBC_VERSION_TARGET >= LBC_VERSION_MIN && LBC_VERSION_TARGET <= LBC_VERSION_MAX, "Invalid bytecode version setup");
+static_assert(LBC_VERSION_MAX <= 127, "Bytecode version should be 7-bit so that we can extend the serialization to use varint transparently");
+
 static const uint32_t kMaxConstantCount = 1 << 23;
 static const uint32_t kMaxClosureCount = 1 << 15;
 
@@ -572,7 +575,10 @@ void BytecodeBuilder::finalize()
     bytecode.reserve(capacity);
 
     // assemble final bytecode blob
-    bytecode = char(LBC_VERSION);
+    uint8_t version = getVersion();
+    LUAU_ASSERT(version >= LBC_VERSION_MIN && version <= LBC_VERSION_MAX);
+
+    bytecode = char(version);
 
     writeStringTable(bytecode);
 
@@ -1040,7 +1046,7 @@ void BytecodeBuilder::expandJumps()
 
 std::string BytecodeBuilder::getError(const std::string& message)
 {
-    // 0 acts as a special marker for error bytecode (it's equal to LBC_VERSION for valid bytecode blobs)
+    // 0 acts as a special marker for error bytecode (it's equal to LBC_VERSION_TARGET for valid bytecode blobs)
     std::string result;
     result += char(0);
     result += message;
@@ -1048,6 +1054,12 @@ std::string BytecodeBuilder::getError(const std::string& message)
     return result;
 }
 
+uint8_t BytecodeBuilder::getVersion()
+{
+    // This function usually returns LBC_VERSION_TARGET but may sometimes return a higher number (within LBC_VERSION_MIN/MAX) under fast flags
+    return LBC_VERSION_TARGET;
+}
+
 #ifdef LUAU_ASSERTENABLED
 void BytecodeBuilder::validate() const
 {

Compiler/src/Compiler.cpp

@@ -16,8 +16,6 @@
 #include <bitset>
 #include <math.h>
 
-LUAU_FASTFLAGVARIABLE(LuauCompileIterNoPairs, false)
-
 LUAU_FASTINTVARIABLE(LuauCompileLoopUnrollThreshold, 25)
 LUAU_FASTINTVARIABLE(LuauCompileLoopUnrollThresholdMaxBoost, 300)
 
@@ -2672,7 +2670,7 @@ struct Compiler
                 else if (builtin.isGlobal("pairs")) // for .. in pairs(t)
                 {
                     skipOp = LOP_FORGPREP_NEXT;
-                    loopOp = FFlag::LuauCompileIterNoPairs ? LOP_FORGLOOP : LOP_FORGLOOP_NEXT;
+                    loopOp = LOP_FORGLOOP;
                 }
             }
             else if (stat->values.size == 2)
@@ -2682,7 +2680,7 @@ struct Compiler
                 if (builtin.isGlobal("next")) // for .. in next,t
                 {
                     skipOp = LOP_FORGPREP_NEXT;
-                    loopOp = FFlag::LuauCompileIterNoPairs ? LOP_FORGLOOP : LOP_FORGLOOP_NEXT;
+                    loopOp = LOP_FORGLOOP;
                 }
             }
         }

VM/src/ludata.cpp

@@ -26,6 +26,8 @@ void luaU_freeudata(lua_State* L, Udata* u, lua_Page* page)
     {
         void (*dtor)(lua_State*, void*) = nullptr;
         dtor = L->global->udatagc[u->tag];
+        // TODO: access to L here is highly unsafe since this is called during internal GC traversal
+        // certain operations such as lua_getthreaddata are okay, but by and large this risks crashes on improper use
         if (dtor)
             dtor(L, u->data);
     }

VM/src/lvmload.cpp

@@ -154,11 +154,11 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
         return 1;
     }
 
-    if (version != LBC_VERSION)
+    if (version < LBC_VERSION_MIN || version > LBC_VERSION_MAX)
     {
         char chunkid[LUA_IDSIZE];
         luaO_chunkid(chunkid, chunkname, LUA_IDSIZE);
-        lua_pushfstring(L, "%s: bytecode version mismatch (expected %d, got %d)", chunkid, LBC_VERSION, version);
+        lua_pushfstring(L, "%s: bytecode version mismatch (expected [%d..%d], got %d)", chunkid, LBC_VERSION_MIN, LBC_VERSION_MAX, version);
         return 1;
     }
 

tests/Compiler.test.cpp

@@ -261,8 +261,6 @@ L1: RETURN R0 0
 
 TEST_CASE("ForBytecode")
 {
-    ScopedFastFlag sff2("LuauCompileIterNoPairs", false);
-
     // basic for loop: variable directly refers to internal iteration index (R2)
     CHECK_EQ("\n" + compileFunction0("for i=1,5 do print(i) end"), R"(
 LOADN R2 1
@@ -329,7 +327,7 @@ L0: GETIMPORT R5 3
 MOVE R6 R3
 MOVE R7 R4
 CALL R5 2 0
-L1: FORGLOOP_NEXT R0 L0
+L1: FORGLOOP R0 L0 2
 RETURN R0 0
 )");
 
@@ -342,7 +340,7 @@ L0: GETIMPORT R5 3
 MOVE R6 R3
 MOVE R7 R4
 CALL R5 2 0
-L1: FORGLOOP_NEXT R0 L0
+L1: FORGLOOP R0 L0 2
 RETURN R0 0
 )");
 }
@@ -2262,8 +2260,6 @@ TEST_CASE("TypeAliasing")
 
 TEST_CASE("DebugLineInfo")
 {
-    ScopedFastFlag sff("LuauCompileIterNoPairs", false);
-
     Luau::BytecodeBuilder bcb;
     bcb.setDumpFlags(Luau::BytecodeBuilder::Dump_Code | Luau::BytecodeBuilder::Dump_Lines);
     Luau::compileOrThrow(bcb, R"(
@@ -2313,7 +2309,7 @@ return result
 15: L0: MOVE R7 R1
 15: MOVE R8 R5
 15: CONCAT R1 R7 R8
-14: L1: FORGLOOP_NEXT R2 L0
+14: L1: FORGLOOP R2 L0 1
 17: RETURN R1 1
 )");
 }
@@ -2545,8 +2541,6 @@ a
 
 TEST_CASE("DebugSource")
 {
-    ScopedFastFlag sff("LuauCompileIterNoPairs", false);
-
     const char* source = R"(
 local kSelectedBiomes = {
     ['Mountains'] = true,
@@ -2614,7 +2608,7 @@ L0: MOVE R7 R1
 MOVE R8 R5
 CONCAT R1 R7 R8
    14: for k in pairs(kSelectedBiomes) do
-L1: FORGLOOP_NEXT R2 L0
+L1: FORGLOOP R2 L0 1
    17: return result
 RETURN R1 1
 )");
@@ -2622,8 +2616,6 @@ RETURN R1 1
 
 TEST_CASE("DebugLocals")
 {
-    ScopedFastFlag sff("LuauCompileIterNoPairs", false);
-
     const char* source = R"(
 function foo(e, f)
     local a = 1
@@ -2661,12 +2653,12 @@ end
 local 0: reg 5, start pc 5 line 5, end pc 8 line 5
 local 1: reg 6, start pc 14 line 8, end pc 18 line 8
 local 2: reg 7, start pc 14 line 8, end pc 18 line 8
-local 3: reg 3, start pc 21 line 12, end pc 24 line 12
-local 4: reg 3, start pc 26 line 16, end pc 30 line 16
-local 5: reg 0, start pc 0 line 3, end pc 34 line 21
-local 6: reg 1, start pc 0 line 3, end pc 34 line 21
-local 7: reg 2, start pc 1 line 4, end pc 34 line 21
-local 8: reg 3, start pc 34 line 21, end pc 34 line 21
+local 3: reg 3, start pc 22 line 12, end pc 25 line 12
+local 4: reg 3, start pc 27 line 16, end pc 31 line 16
+local 5: reg 0, start pc 0 line 3, end pc 35 line 21
+local 6: reg 1, start pc 0 line 3, end pc 35 line 21
+local 7: reg 2, start pc 1 line 4, end pc 35 line 21
+local 8: reg 3, start pc 35 line 21, end pc 35 line 21
 3: LOADN R2 1
 4: LOADN R5 1
 4: LOADN R3 3
@@ -2683,7 +2675,7 @@ local 8: reg 3, start pc 34 line 21, end pc 34 line 21
 8: MOVE R9 R6
 8: MOVE R10 R7
 8: CALL R8 2 0
-7: L3: FORGLOOP_NEXT R3 L2
+7: L3: FORGLOOP R3 L2 2
 11: LOADN R3 2
 12: GETIMPORT R4 1
 12: LOADN R5 2
@@ -3795,8 +3787,6 @@ RETURN R0 1
 
 TEST_CASE("SharedClosure")
 {
-    ScopedFastFlag sff("LuauCompileIterNoPairs", false);
-
     // closures can be shared even if functions refer to upvalues, as long as upvalues are top-level
     CHECK_EQ("\n" + compileFunction(R"(
 local val = ...
@@ -3939,7 +3929,7 @@ L2: GETIMPORT R5 1
 NEWCLOSURE R6 P1
 CAPTURE VAL R3
 CALL R5 1 0
-L3: FORGLOOP_NEXT R0 L2
+L3: FORGLOOP R0 L2 2
 LOADN R2 1
 LOADN R0 10
 LOADN R1 1

tests/Fixture.h

@@ -2,13 +2,13 @@
 #pragma once
 
 #include "Luau/Config.h"
-#include "Luau/ConstraintGraphBuilder.h"
 #include "Luau/FileResolver.h"
 #include "Luau/Frontend.h"
 #include "Luau/IostreamHelpers.h"
 #include "Luau/Linter.h"
 #include "Luau/Location.h"
 #include "Luau/ModuleResolver.h"
+#include "Luau/Scope.h"
 #include "Luau/ToString.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypeVar.h"

tests/Module.test.cpp

@@ -279,7 +279,6 @@ TEST_CASE_FIXTURE(Fixture, "clone_recursion_limit")
     int limit = 400;
 #endif
     ScopedFastInt luauTypeCloneRecursionLimit{"LuauTypeCloneRecursionLimit", limit};
-    ScopedFastFlag sff{"LuauRecursionLimitException", true};
 
     TypeArena src;
 

tests/Normalize.test.cpp

@@ -12,7 +12,6 @@ using namespace Luau;
 struct NormalizeFixture : Fixture
 {
     ScopedFastFlag sff1{"LuauLowerBoundsCalculation", true};
-    ScopedFastFlag sff2{"LuauTableSubtypingVariance2", true};
 };
 
 void createSomeClasses(TypeChecker& typeChecker)

tests/RuntimeLimits.test.cpp

@@ -264,10 +264,13 @@ TEST_CASE_FIXTURE(LimitFixture, "typescript_port_of_Result_type")
         }
     )LUA";
 
+    CheckResult result = check(src);
+    CodeTooComplex ctc;
+
     if (FFlag::LuauLowerBoundsCalculation)
-        (void)check(src);
+        LUAU_REQUIRE_ERRORS(result);
     else
-        CHECK_THROWS_AS(check(src), std::exception);
+        CHECK(hasError(result, &ctc));
 }
 
 TEST_SUITE_END();

tests/ToString.test.cpp

@@ -409,8 +409,6 @@ TEST_CASE_FIXTURE(Fixture, "toStringDetailed")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "toStringDetailed2")
 {
-    ScopedFastFlag sff{"LuauUnsealedTableLiteral", true};
-
     CheckResult result = check(R"(
         local base = {}
         function base:one() return 1 end

tests/TypeInfer.aliases.test.cpp

@@ -7,8 +7,21 @@
 
 using namespace Luau;
 
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+
 TEST_SUITE_BEGIN("TypeAliases");
 
+TEST_CASE_FIXTURE(Fixture, "basic_alias")
+{
+    CheckResult result = check(R"(
+        type T = number
+        local x: T = 1
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+    CHECK_EQ("number", toString(requireType("x")));
+}
+
 TEST_CASE_FIXTURE(Fixture, "cyclic_function_type_in_type_alias")
 {
     CheckResult result = check(R"(
@@ -24,6 +37,63 @@ TEST_CASE_FIXTURE(Fixture, "cyclic_function_type_in_type_alias")
     CHECK_EQ("t1 where t1 = () -> t1?", toString(requireType("g")));
 }
 
+TEST_CASE_FIXTURE(Fixture, "names_are_ascribed")
+{
+    CheckResult result = check(R"(
+        type T = { x: number }
+        local x: T
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+    CHECK_EQ("T", toString(requireType("x")));
+}
+
+TEST_CASE_FIXTURE(Fixture, "cannot_steal_hoisted_type_alias")
+{
+    // This is a tricky case. In order to support recursive type aliases,
+    // we first walk the block and generate free types as placeholders.
+    // We then walk the AST as normal. If we declare a type alias as below,
+    // we generate a free type. We then begin our normal walk, examining
+    // local x: T = "foo", which establishes two constraints:
+    // a <: b
+    // string <: a
+    // We then visit the type alias, and establish that
+    // b <: number
+    // Then, when solving these constraints, we dispatch them in the order
+    // they appear above. This means that a ~ b, and a ~ string, thus
+    // b ~ string. This means the b <: number constraint has no effect.
+    // Essentially we've "stolen" the alias's type out from under it.
+    // This test ensures that we don't actually do this.
+    CheckResult result = check(R"(
+        local x: T = "foo"
+        type T = number
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+    {
+        CHECK(result.errors[0] == TypeError{
+            Location{{1, 21}, {1, 26}},
+            getMainSourceModule()->name,
+            TypeMismatch{
+                getSingletonTypes().numberType,
+                getSingletonTypes().stringType,
+            },
+        });
+    }
+    else
+    {
+        CHECK(result.errors[0] == TypeError{
+            Location{{1, 8}, {1, 26}},
+            getMainSourceModule()->name,
+            TypeMismatch{
+                getSingletonTypes().numberType,
+                getSingletonTypes().stringType,
+            },
+        });
+    }
+}
+
 TEST_CASE_FIXTURE(Fixture, "cyclic_types_of_named_table_fields_do_not_expand_when_stringified")
 {
     CheckResult result = check(R"(
@@ -41,7 +111,22 @@ TEST_CASE_FIXTURE(Fixture, "cyclic_types_of_named_table_fields_do_not_expand_whe
     CHECK_EQ(typeChecker.numberType, tm->givenType);
 }
 
-TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types")
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_aliases")
+{
+    CheckResult result = check(R"(
+        --!strict
+        type T = { f: number, g: U }
+        type U = { h: number, i: T? }
+        local x: T = { f = 37, g = { h = 5, i = nil } }
+        x.g.i = x
+        local y: T = { f = 3, g = { h = 5, i = nil } }
+        y.g.i = y
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_generic_aliases")
 {
     CheckResult result = check(R"(
         --!strict

tests/TypeInfer.annotations.test.cpp

@@ -30,11 +30,21 @@ TEST_CASE_FIXTURE(Fixture, "successful_check")
     dumpErrors(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "variable_type_is_supertype")
+{
+    CheckResult result = check(R"(
+        local x: number = 1
+        local y: number? = x
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_CASE_FIXTURE(Fixture, "function_parameters_can_have_annotations")
 {
     CheckResult result = check(R"(
         function double(x: number)
-            return x * 2
+            return 2
         end
 
         local four = double(2)
@@ -47,7 +57,7 @@ TEST_CASE_FIXTURE(Fixture, "function_parameter_annotations_are_checked")
 {
     CheckResult result = check(R"(
         function double(x: number)
-            return x * 2
+            return 2
         end
 
         local four = double("two")
@@ -70,13 +80,13 @@ TEST_CASE_FIXTURE(Fixture, "function_return_annotations_are_checked")
     const FunctionTypeVar* ftv = get<FunctionTypeVar>(fiftyType);
     REQUIRE(ftv != nullptr);
 
-    TypePackId retPack = ftv->retTypes;
+    TypePackId retPack = follow(ftv->retTypes);
     const TypePack* tp = get<TypePack>(retPack);
     REQUIRE(tp != nullptr);
 
     REQUIRE_EQ(1, tp->head.size());
 
-    REQUIRE_EQ(typeChecker.anyType, tp->head[0]);
+    REQUIRE_EQ(typeChecker.anyType, follow(tp->head[0]));
 }
 
 TEST_CASE_FIXTURE(Fixture, "function_return_multret_annotations_are_checked")
@@ -116,6 +126,23 @@ TEST_CASE_FIXTURE(Fixture, "function_return_annotation_should_continuously_parse
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "unknown_type_reference_generates_error")
+{
+    CheckResult result = check(R"(
+        local x: IDoNotExist
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK(result.errors[0] == TypeError{
+        Location{{1, 17}, {1, 28}},
+        getMainSourceModule()->name,
+        UnknownSymbol{
+            "IDoNotExist",
+            UnknownSymbol::Context::Type,
+        },
+    });
+}
+
 TEST_CASE_FIXTURE(Fixture, "typeof_variable_type_annotation_should_return_its_type")
 {
     CheckResult result = check(R"(
@@ -632,7 +659,10 @@ int AssertionCatcher::tripped;
 
 TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice")
 {
-    ScopedFastFlag sffs{"DebugLuauMagicTypes", true};
+    ScopedFastFlag sffs[] = {
+        {"DebugLuauMagicTypes", true},
+        {"LuauUseInternalCompilerErrorException", false},
+    };
 
     AssertionCatcher ac;
 
@@ -646,9 +676,10 @@ TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice")
 
 TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice_handler")
 {
-    ScopedFastFlag sffs{"DebugLuauMagicTypes", true};
-
-    AssertionCatcher ac;
+    ScopedFastFlag sffs[] = {
+        {"DebugLuauMagicTypes", true},
+        {"LuauUseInternalCompilerErrorException", false},
+    };
 
     bool caught = false;
 
@@ -662,8 +693,44 @@ TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice_handler")
         std::runtime_error);
 
     CHECK_EQ(true, caught);
+}
 
-    frontend.iceHandler.onInternalError = {};
+TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice_exception_with_flag")
+{
+    ScopedFastFlag sffs[] = {
+        {"DebugLuauMagicTypes", true},
+        {"LuauUseInternalCompilerErrorException", true},
+    };
+
+    AssertionCatcher ac;
+
+    CHECK_THROWS_AS(check(R"(
+            local a: _luau_ice = 55
+        )"),
+        InternalCompilerError);
+
+    LUAU_ASSERT(1 == AssertionCatcher::tripped);
+}
+
+TEST_CASE_FIXTURE(Fixture, "luau_ice_triggers_an_ice_exception_with_flag_handler")
+{
+    ScopedFastFlag sffs[] = {
+        {"DebugLuauMagicTypes", true},
+        {"LuauUseInternalCompilerErrorException", true},
+    };
+
+    bool caught = false;
+
+    frontend.iceHandler.onInternalError = [&](const char*) {
+        caught = true;
+    };
+
+    CHECK_THROWS_AS(check(R"(
+            local a: _luau_ice = 55
+        )"),
+        InternalCompilerError);
+
+    CHECK_EQ(true, caught);
 }
 
 TEST_CASE_FIXTURE(Fixture, "luau_ice_is_not_special_without_the_flag")

tests/TypeInfer.generics.test.cpp

@@ -700,11 +700,6 @@ end
 
 TEST_CASE_FIXTURE(Fixture, "generic_functions_should_be_memory_safe")
 {
-    ScopedFastFlag sffs[] = {
-        {"LuauTableSubtypingVariance2", true},
-        {"LuauUnsealedTableLiteral", true},
-    };
-
     CheckResult result = check(R"(
 --!strict
 -- At one point this produced a UAF
@@ -979,8 +974,6 @@ TEST_CASE_FIXTURE(Fixture, "instantiate_generic_function_in_assignments2")
 
 TEST_CASE_FIXTURE(Fixture, "self_recursive_instantiated_param")
 {
-    ScopedFastFlag sff{"LuauOnlyMutateInstantiatedTables", true};
-
     // Mutability in type function application right now can create strange recursive types
     CheckResult result = check(R"(
 type Table = { a: number }
@@ -1015,8 +1008,6 @@ TEST_CASE_FIXTURE(Fixture, "no_stack_overflow_from_quantifying")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "infer_generic_function_function_argument")
 {
-    ScopedFastFlag sff{"LuauUnsealedTableLiteral", true};
-
     CheckResult result = check(R"(
         local function sum<a>(x: a, y: a, f: (a, a) -> a)
             return f(x, y)
@@ -1123,8 +1114,6 @@ TEST_CASE_FIXTURE(Fixture, "substitution_with_bound_table")
 
 TEST_CASE_FIXTURE(Fixture, "apply_type_function_nested_generics1")
 {
-    ScopedFastFlag sff{"LuauApplyTypeFunctionFix", true};
-
     // https://github.com/Roblox/luau/issues/484
     CheckResult result = check(R"(
 --!strict
@@ -1153,8 +1142,6 @@ local complex: ComplexObject<string> = {
 
 TEST_CASE_FIXTURE(Fixture, "apply_type_function_nested_generics2")
 {
-    ScopedFastFlag sff{"LuauApplyTypeFunctionFix", true};
-
     // https://github.com/Roblox/luau/issues/484
     CheckResult result = check(R"(
 --!strict

tests/TypeInfer.modules.test.cpp

@@ -12,8 +12,6 @@
 
 using namespace Luau;
 
-LUAU_FASTFLAG(LuauTableSubtypingVariance2)
-
 TEST_SUITE_BEGIN("TypeInferModules");
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "require")
@@ -326,16 +324,9 @@ local b: B.T = a
     CheckResult result = frontend.check("game/C");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    if (FFlag::LuauTableSubtypingVariance2)
-    {
-        CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/A' could not be converted into 'T' from 'game/B'
+    CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/A' could not be converted into 'T' from 'game/B'
 caused by:
   Property 'x' is not compatible. Type 'number' could not be converted into 'string')");
-    }
-    else
-    {
-        CHECK_EQ(toString(result.errors[0]), "Type 'T' from 'game/A' could not be converted into 'T' from 'game/B'");
-    }
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "module_type_conflict_instantiated")
@@ -367,16 +358,9 @@ local b: B.T = a
     CheckResult result = frontend.check("game/D");
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    if (FFlag::LuauTableSubtypingVariance2)
-    {
-        CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/B' could not be converted into 'T' from 'game/C'
+    CHECK_EQ(toString(result.errors[0]), R"(Type 'T' from 'game/B' could not be converted into 'T' from 'game/C'
 caused by:
   Property 'x' is not compatible. Type 'number' could not be converted into 'string')");
-    }
-    else
-    {
-        CHECK_EQ(toString(result.errors[0]), "Type 'T' from 'game/B' could not be converted into 'T' from 'game/C'");
-    }
 }
 
 TEST_SUITE_END();

tests/TypeInfer.refinements.test.cpp

@@ -353,8 +353,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "assert_non_binary_expressions_actually_resol
 
 TEST_CASE_FIXTURE(Fixture, "assign_table_with_refined_property_with_a_similar_type_is_illegal")
 {
-    ScopedFastFlag LuauTableSubtypingVariance2{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         local t: {x: number?} = {x = nil}
 

tests/TypeInfer.singletons.test.cpp

@@ -260,10 +260,6 @@ TEST_CASE_FIXTURE(Fixture, "table_properties_alias_or_parens_is_indexer")
 
 TEST_CASE_FIXTURE(Fixture, "table_properties_type_error_escapes")
 {
-    ScopedFastFlag sffs[]{
-        {"LuauUnsealedTableLiteral", true},
-    };
-
     CheckResult result = check(R"(
         --!strict
         local x: { ["<>"] : number } 

tests/TypeInfer.tables.test.cpp

@@ -276,8 +276,6 @@ TEST_CASE_FIXTURE(Fixture, "open_table_unification")
 
 TEST_CASE_FIXTURE(Fixture, "open_table_unification_2")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         local a = {}
         a.x = 99
@@ -347,8 +345,6 @@ TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_1")
 
 TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_2")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         --!strict
         function foo(o)
@@ -370,8 +366,6 @@ TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_2")
 
 TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_3")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         local T = {}
         T.bar = 'hello'
@@ -477,8 +471,6 @@ TEST_CASE_FIXTURE(Fixture, "ok_to_add_property_to_free_table")
 
 TEST_CASE_FIXTURE(Fixture, "okay_to_add_property_to_unsealed_tables_by_assignment")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         --!strict
         local t = { u = {} }
@@ -512,8 +504,6 @@ TEST_CASE_FIXTURE(Fixture, "okay_to_add_property_to_unsealed_tables_by_function_
 
 TEST_CASE_FIXTURE(Fixture, "width_subtyping")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         --!strict
         function f(x : { q : number })
@@ -772,8 +762,6 @@ TEST_CASE_FIXTURE(Fixture, "infer_indexer_for_left_unsealed_table_from_right_han
 
 TEST_CASE_FIXTURE(Fixture, "sealed_table_value_can_infer_an_indexer")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         local t: { a: string, [number]: string } = { a = "foo" }
     )");
@@ -783,8 +771,6 @@ TEST_CASE_FIXTURE(Fixture, "sealed_table_value_can_infer_an_indexer")
 
 TEST_CASE_FIXTURE(Fixture, "array_factory_function")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         function empty() return {} end
         local array: {string} = empty()
@@ -1175,8 +1161,6 @@ TEST_CASE_FIXTURE(Fixture, "defining_a_self_method_for_a_local_sealed_table_must
 
 TEST_CASE_FIXTURE(Fixture, "defining_a_method_for_a_local_unsealed_table_is_ok")
 {
-    ScopedFastFlag sff{"LuauUnsealedTableLiteral", true};
-
     CheckResult result = check(R"(
         local t = {x = 1}
         function t.m() end
@@ -1187,8 +1171,6 @@ TEST_CASE_FIXTURE(Fixture, "defining_a_method_for_a_local_unsealed_table_is_ok")
 
 TEST_CASE_FIXTURE(Fixture, "defining_a_self_method_for_a_local_unsealed_table_is_ok")
 {
-    ScopedFastFlag sff{"LuauUnsealedTableLiteral", true};
-
     CheckResult result = check(R"(
         local t = {x = 1}
         function t:m() end
@@ -1468,11 +1450,6 @@ TEST_CASE_FIXTURE(Fixture, "right_table_missing_key2")
 
 TEST_CASE_FIXTURE(Fixture, "casting_unsealed_tables_with_props_into_table_with_indexer")
 {
-    ScopedFastFlag sff[]{
-        {"LuauTableSubtypingVariance2", true},
-        {"LuauUnsealedTableLiteral", true},
-    };
-
     CheckResult result = check(R"(
         type StringToStringMap = { [string]: string }
         local rt: StringToStringMap = { ["foo"] = 1 }
@@ -1518,11 +1495,6 @@ TEST_CASE_FIXTURE(Fixture, "casting_tables_with_props_into_table_with_indexer2")
 
 TEST_CASE_FIXTURE(Fixture, "casting_tables_with_props_into_table_with_indexer3")
 {
-    ScopedFastFlag sff[]{
-        {"LuauTableSubtypingVariance2", true},
-        {"LuauUnsealedTableLiteral", true},
-    };
-
     CheckResult result = check(R"(
         local function foo(a: {[string]: number, a: string}) end
         foo({ a = 1 })
@@ -1609,8 +1581,6 @@ TEST_CASE_FIXTURE(Fixture, "table_subtyping_with_extra_props_dont_report_multipl
 
 TEST_CASE_FIXTURE(Fixture, "table_subtyping_with_extra_props_is_ok")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         local vec3 = {x = 1, y = 2, z = 3}
         local vec1 = {x = 1}
@@ -1998,8 +1968,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "table_insert_should_cope_with_optional_prope
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "table_insert_should_cope_with_optional_properties_in_strict")
 {
-    ScopedFastFlag sff{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         --!strict
         local buttons = {}
@@ -2013,8 +1981,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "table_insert_should_cope_with_optional_prope
 
 TEST_CASE_FIXTURE(Fixture, "error_detailed_prop")
 {
-    ScopedFastFlag LuauTableSubtypingVariance2{"LuauTableSubtypingVariance2", true}; // Only for new path
-
     CheckResult result = check(R"(
 type A = { x: number, y: number }
 type B = { x: number, y: string }
@@ -2031,8 +1997,6 @@ caused by:
 
 TEST_CASE_FIXTURE(Fixture, "error_detailed_prop_nested")
 {
-    ScopedFastFlag LuauTableSubtypingVariance2{"LuauTableSubtypingVariance2", true}; // Only for new path
-
     CheckResult result = check(R"(
 type AS = { x: number, y: number }
 type BS = { x: number, y: string }
@@ -2054,11 +2018,6 @@ caused by:
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "error_detailed_metatable_prop")
 {
-    ScopedFastFlag sff[]{
-        {"LuauTableSubtypingVariance2", true},
-        {"LuauUnsealedTableLiteral", true},
-    };
-
     CheckResult result = check(R"(
 local a1 = setmetatable({ x = 2, y = 3 }, { __call = function(s) end });
 local b1 = setmetatable({ x = 2, y = "hello" }, { __call = function(s) end });
@@ -2085,8 +2044,6 @@ caused by:
 
 TEST_CASE_FIXTURE(Fixture, "error_detailed_indexer_key")
 {
-    ScopedFastFlag luauTableSubtypingVariance2{"LuauTableSubtypingVariance2", true}; // Only for new path
-
     CheckResult result = check(R"(
         type A = { [number]: string }
         type B = { [string]: string }
@@ -2103,8 +2060,6 @@ caused by:
 
 TEST_CASE_FIXTURE(Fixture, "error_detailed_indexer_value")
 {
-    ScopedFastFlag luauTableSubtypingVariance2{"LuauTableSubtypingVariance2", true}; // Only for new path
-
     CheckResult result = check(R"(
         type A = { [number]: number }
         type B = { [number]: string }
@@ -2121,10 +2076,6 @@ caused by:
 
 TEST_CASE_FIXTURE(Fixture, "explicitly_typed_table")
 {
-    ScopedFastFlag sffs[]{
-        {"LuauTableSubtypingVariance2", true},
-    };
-
     CheckResult result = check(R"(
 --!strict
 type Super = { x : number }
@@ -2140,11 +2091,6 @@ a.p = { x = 9 }
 
 TEST_CASE_FIXTURE(Fixture, "explicitly_typed_table_error")
 {
-    ScopedFastFlag sffs[]{
-        {"LuauTableSubtypingVariance2", true},
-        {"LuauUnsealedTableLiteral", true},
-    };
-
     CheckResult result = check(R"(
 --!strict
 type Super = { x : number }
@@ -2166,10 +2112,6 @@ caused by:
 
 TEST_CASE_FIXTURE(Fixture, "explicitly_typed_table_with_indexer")
 {
-    ScopedFastFlag sffs[]{
-        {"LuauTableSubtypingVariance2", true},
-    };
-
     CheckResult result = check(R"(
 --!strict
 type Super = { x : number }
@@ -2185,10 +2127,6 @@ a.p = { x = 9 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "recursive_metatable_type_call")
 {
-    ScopedFastFlag sff[]{
-        {"LuauUnsealedTableLiteral", true},
-    };
-
     CheckResult result = check(R"(
 local b
 b = setmetatable({}, {__call = b})
@@ -2201,11 +2139,6 @@ b()
 
 TEST_CASE_FIXTURE(Fixture, "table_subtyping_shouldn't_add_optional_properties_to_sealed_tables")
 {
-    ScopedFastFlag sffs[] = {
-        {"LuauTableSubtypingVariance2", true},
-        {"LuauSubtypingAddOptPropsToUnsealedTables", true},
-    };
-
     CheckResult result = check(R"(
         --!strict
         local function setNumber(t: { p: number? }, x:number) t.p = x end
@@ -2706,8 +2639,6 @@ type t0<t32> = any
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "instantiate_table_cloning_2")
 {
-    ScopedFastFlag sff{"LuauOnlyMutateInstantiatedTables", true};
-
     CheckResult result = check(R"(
 type X<T> = T
 type K = X<typeof(math)>
@@ -2725,8 +2656,6 @@ type K = X<typeof(math)>
 
 TEST_CASE_FIXTURE(Fixture, "instantiate_table_cloning_3")
 {
-    ScopedFastFlag sff{"LuauOnlyMutateInstantiatedTables", true};
-
     CheckResult result = check(R"(
 type X<T> = T
 local a = {}
@@ -2977,8 +2906,6 @@ TEST_CASE_FIXTURE(Fixture, "mixed_tables_with_implicit_numbered_keys")
 
 TEST_CASE_FIXTURE(Fixture, "expected_indexer_value_type_extra")
 {
-    ScopedFastFlag luauSubtypingAddOptPropsToUnsealedTables{"LuauSubtypingAddOptPropsToUnsealedTables", true};
-
     CheckResult result = check(R"(
         type X = { { x: boolean?, y: boolean? } }
 

tests/TypeInfer.test.cpp

@@ -887,8 +887,6 @@ end
 
 TEST_CASE_FIXTURE(Fixture, "cli_50041_committing_txnlog_in_apollo_client_error")
 {
-    ScopedFastFlag subtypingVariance{"LuauTableSubtypingVariance2", true};
-
     CheckResult result = check(R"(
         --!strict
         --!nolint
@@ -928,7 +926,6 @@ TEST_CASE_FIXTURE(Fixture, "cli_50041_committing_txnlog_in_apollo_client_error")
 TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_no_ice")
 {
     ScopedFastInt sfi("LuauTypeInferRecursionLimit", 2);
-    ScopedFastFlag sff{"LuauRecursionLimitException", true};
 
     CheckResult result = check(R"(
         function complex()

tests/TypeInfer.unionTypes.test.cpp

@@ -428,12 +428,6 @@ y = x
 
 TEST_CASE_FIXTURE(Fixture, "unify_sealed_table_union_check")
 {
-    ScopedFastFlag sffs[] = {
-        {"LuauTableSubtypingVariance2", true},
-        {"LuauUnsealedTableLiteral", true},
-        {"LuauSubtypingAddOptPropsToUnsealedTables", true},
-    };
-
     CheckResult result = check(R"(
  -- the difference between this and unify_unsealed_table_union_check is the type annotation on x
 local t = { x = 3, y = true }

tests/VisitTypeVar.test.cpp

@@ -10,14 +10,9 @@ using namespace Luau;
 
 LUAU_FASTINT(LuauVisitRecursionLimit)
 
-struct VisitTypeVarFixture : Fixture
-{
-    ScopedFastFlag flag2 = {"LuauRecursionLimitException", true};
-};
-
 TEST_SUITE_BEGIN("VisitTypeVar");
 
-TEST_CASE_FIXTURE(VisitTypeVarFixture, "throw_when_limit_is_exceeded")
+TEST_CASE_FIXTURE(Fixture, "throw_when_limit_is_exceeded")
 {
     ScopedFastInt sfi{"LuauVisitRecursionLimit", 3};
 
@@ -30,7 +25,7 @@ TEST_CASE_FIXTURE(VisitTypeVarFixture, "throw_when_limit_is_exceeded")
     CHECK_THROWS_AS(toString(tType), RecursionLimitException);
 }
 
-TEST_CASE_FIXTURE(VisitTypeVarFixture, "dont_throw_when_limit_is_high_enough")
+TEST_CASE_FIXTURE(Fixture, "dont_throw_when_limit_is_high_enough")
 {
     ScopedFastInt sfi{"LuauVisitRecursionLimit", 8};