Sync to upstream/release/684 (#1930)

## General
- Support AstStatDeclareGlobal output as a source string (via
@karl-police in #1889)
- Luau heap dump correctly reports the size of a string, now including
overhead for the string type
- Prevent yields from Luau `xpcall` error handling function.
 
## Analysis
- Avoid exponential blowup when normalizing union of normalized free
variables.
- Fix type pack-related bugs that caused infinite recursion when:
  - A generic type pack was bound to itself during subtyping.
- In type pack flattening, when that same generic type pack was now
being bound another generic type pack which contained it.
- Properly simplify `any & (*error-type* | string)` to `*error-type* |
*error-type* | string` instead of hanging due to creating a huge union
type.

---

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

---------

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

Analysis/include/Luau/BuiltinTypeFunctions.h

@@ -53,4 +53,4 @@ struct BuiltinTypeFunctions
 
 const BuiltinTypeFunctions& builtinTypeFunctions();
 
-}
+} // namespace Luau

Analysis/include/Luau/Constraint.h

@@ -341,7 +341,6 @@ struct Constraint
     DenseHashSet<TypeId> getMaybeMutatedFreeTypes_DEPRECATED() const;
 
     TypeIds getMaybeMutatedFreeTypes() const;
-
 };
 
 using ConstraintPtr = std::unique_ptr<Constraint>;

Analysis/include/Luau/Instantiation.h

@@ -92,6 +92,11 @@ struct GenericTypeFinder : TypeOnceVisitor
 {
     bool found = false;
 
+    GenericTypeFinder()
+        : TypeOnceVisitor("GenericTypeFinder")
+    {
+    }
+
     bool visit(TypeId ty) override
     {
         return !found;

Analysis/include/Luau/OrderedSet.h

@@ -65,4 +65,4 @@ private:
     DenseHashSet<T> elementSet{nullptr};
 };
 
-}
+} // namespace Luau

Analysis/include/Luau/RecursionCounter.h

@@ -12,8 +12,8 @@ namespace Luau
 
 struct RecursionLimitException : public InternalCompilerError
 {
-    RecursionLimitException()
+    RecursionLimitException(const std::string system)
-        : InternalCompilerError("Internal recursion counter limit exceeded")
+        : InternalCompilerError("Internal recursion counter limit exceeded in " + system)
     {
     }
 };
@@ -38,12 +38,12 @@ protected:
 
 struct RecursionLimiter : RecursionCounter
 {
-    RecursionLimiter(int* count, int limit)
+    RecursionLimiter(const std::string system, int* count, int limit)
         : RecursionCounter(count)
     {
         if (limit > 0 && *count > limit)
         {
-            throw RecursionLimitException();
+            throw RecursionLimitException(system);
         }
     }
 };

Analysis/include/Luau/Subtyping.h

@@ -157,8 +157,10 @@ struct Subtyping
     Variance variance = Variance::Covariant;
 
     using SeenSet = Set<std::pair<TypeId, TypeId>, TypePairHash>;
+    using SeenTypePackSet = Set<std::pair<TypePackId, TypePackId>, TypePairHash>;
 
     SeenSet seenTypes{{}};
+    SeenTypePackSet seenPacks{{}};
 
     Subtyping(
         NotNull<BuiltinTypes> builtinTypes,

Analysis/include/Luau/ToString.h

@@ -2,6 +2,7 @@
 #pragma once
 
 #include "Luau/Common.h"
+#include "Luau/DenseHash.h"
 #include "Luau/TypeFwd.h"
 
 #include <memory>
@@ -134,6 +135,10 @@ std::string dump(TypeId ty);
 std::string dump(const std::optional<TypeId>& ty);
 std::string dump(TypePackId ty);
 std::string dump(const std::optional<TypePackId>& ty);
+std::string dump(const std::vector<TypeId>& types);
+std::string dump(DenseHashMap<TypeId, TypeId>& types);
+std::string dump(DenseHashMap<TypePackId, TypePackId>& types);
+
 std::string dump(const Constraint& c);
 
 std::string dump(const std::shared_ptr<Scope>& scope, const char* name);
@@ -153,4 +158,5 @@ inline std::string toString(const TypeOrPack& tyOrTp)
 
 std::string dump(const TypeOrPack& tyOrTp);
 
+std::string toStringVector(const std::vector<TypeId>& types, ToStringOptions& opts);
 } // namespace Luau

Analysis/include/Luau/TypeIds.h

@@ -32,8 +32,8 @@ public:
     TypeIds(const TypeIds&) = default;
     TypeIds& operator=(const TypeIds&) = default;
 
-    TypeIds(TypeIds&&) = default;
+    TypeIds(TypeIds&&) noexcept = default;
-    TypeIds& operator=(TypeIds&&) = default;
+    TypeIds& operator=(TypeIds&&) noexcept = default;
 
     void insert(TypeId ty);
     /// Erase every element that does not also occur in tys

Analysis/include/Luau/TypePath.h

@@ -231,7 +231,7 @@ std::string toString(const TypePath::Path& path, bool prefixDot = false);
 /// Converts a Path to a human readable string for error reporting.
 std::string toStringHuman(const TypePath::Path& path);
 
-// TODO: clip traverse_DEPRECATED along with `LuauReturnMappedGenericPacksFromSubtyping`
+// TODO: clip traverse_DEPRECATED along with `LuauReturnMappedGenericPacksFromSubtyping2`
 std::optional<TypeOrPack> traverse_DEPRECATED(TypeId root, const Path& path, NotNull<BuiltinTypes> builtinTypes);
 std::optional<TypeOrPack> traverse_DEPRECATED(TypePackId root, const Path& path, NotNull<BuiltinTypes> builtinTypes);
 std::optional<TypeOrPack> traverse(

Analysis/include/Luau/VisitType.h

@@ -73,6 +73,8 @@ struct GenericTypeVisitor
 {
     using Set = S;
 
+    const std::string visitorName;
+
     Set seen;
     bool skipBoundTypes = false;
     int recursionCounter = 0;
@@ -80,8 +82,9 @@ struct GenericTypeVisitor
 
     GenericTypeVisitor() = default;
 
-    explicit GenericTypeVisitor(Set seen, bool skipBoundTypes = false)
+    explicit GenericTypeVisitor(const std::string visitorName, Set seen, bool skipBoundTypes = false)
-        : seen(std::move(seen))
+        : visitorName(visitorName)
+        , seen(std::move(seen))
         , skipBoundTypes(skipBoundTypes)
     {
     }
@@ -215,7 +218,7 @@ struct GenericTypeVisitor
 
     void traverse(TypeId ty)
     {
-        RecursionLimiter limiter{&recursionCounter, FInt::LuauVisitRecursionLimit};
+        RecursionLimiter limiter{visitorName, &recursionCounter, FInt::LuauVisitRecursionLimit};
 
         if (visit_detail::hasSeen(seen, ty))
         {
@@ -527,8 +530,8 @@ struct GenericTypeVisitor
  */
 struct TypeVisitor : GenericTypeVisitor<std::unordered_set<void*>>
 {
-    explicit TypeVisitor(bool skipBoundTypes = false)
+    explicit TypeVisitor(const std::string visitorName, bool skipBoundTypes = false)
-        : GenericTypeVisitor{{}, skipBoundTypes}
+        : GenericTypeVisitor{visitorName, {}, skipBoundTypes}
     {
     }
 };
@@ -536,8 +539,8 @@ struct TypeVisitor : GenericTypeVisitor<std::unordered_set<void*>>
 /// Visit each type under a given type.  Each type will only be checked once even if there are multiple paths to it.
 struct TypeOnceVisitor : GenericTypeVisitor<DenseHashSet<void*>>
 {
-    explicit TypeOnceVisitor(bool skipBoundTypes = false)
+    explicit TypeOnceVisitor(const std::string visitorName, bool skipBoundTypes = false)
-        : GenericTypeVisitor{DenseHashSet<void*>{nullptr}, skipBoundTypes}
+        : GenericTypeVisitor{visitorName, DenseHashSet<void*>{nullptr}, skipBoundTypes}
     {
     }
 };

Analysis/src/AstQuery.cpp

@@ -583,7 +583,9 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
                                 return checkOverloadedDocumentationSymbol(module, *ty, parentExpr, propIt->second.documentationSymbol);
                         }
                         else
-                            return checkOverloadedDocumentationSymbol(module, propIt->second.type_DEPRECATED(), parentExpr, propIt->second.documentationSymbol);
+                            return checkOverloadedDocumentationSymbol(
+                                module, propIt->second.type_DEPRECATED(), parentExpr, propIt->second.documentationSymbol
+                            );
                     }
                 }
                 else if (const ExternType* etv = get<ExternType>(parentTy))

Analysis/src/BuiltinDefinitions.cpp

@@ -771,7 +771,9 @@ bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
 
         if (iter == end(context.arguments))
         {
-            context.typechecker->reportError(CountMismatch{1, std::nullopt, 0, CountMismatch::Arg, true, "string.format"}, context.callSite->location);
+            context.typechecker->reportError(
+                CountMismatch{1, std::nullopt, 0, CountMismatch::Arg, true, "string.format"}, context.callSite->location
+            );
             return true;
         }
 
@@ -823,7 +825,8 @@ bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
         {
             TypeId actualTy = params[i + paramOffset];
             TypeId expectedTy = expected[i];
-            Location location = context.callSite->args.data[std::min(context.callSite->args.size - 1, i + (calledWithSelf ? 0 : paramOffset))]->location;
+            Location location =
+                context.callSite->args.data[std::min(context.callSite->args.size - 1, i + (calledWithSelf ? 0 : paramOffset))]->location;
             // use subtyping instead here
             SubtypingResult result = context.typechecker->subtyping->isSubtype(actualTy, expectedTy, context.checkScope);
 
@@ -845,7 +848,6 @@ bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
         }
 
         return true;
-
     }
     else
     {
@@ -863,7 +865,9 @@ bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
 
         if (!fmt)
         {
-            context.typechecker->reportError(CountMismatch{1, std::nullopt, 0, CountMismatch::Arg, true, "string.format"}, context.callSite->location);
+            context.typechecker->reportError(
+                CountMismatch{1, std::nullopt, 0, CountMismatch::Arg, true, "string.format"}, context.callSite->location
+            );
             return true;
         }
 
@@ -887,7 +891,8 @@ bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
         {
             TypeId actualTy = params[i + paramOffset];
             TypeId expectedTy = expected[i];
-            Location location = context.callSite->args.data[std::min(context.callSite->args.size - 1, i + (calledWithSelf ? 0 : paramOffset))]->location;
+            Location location =
+                context.callSite->args.data[std::min(context.callSite->args.size - 1, i + (calledWithSelf ? 0 : paramOffset))]->location;
             // use subtyping instead here
             SubtypingResult result = context.typechecker->subtyping->isSubtype(actualTy, expectedTy, context.checkScope);
 
@@ -895,15 +900,15 @@ bool MagicFormat::typeCheck(const MagicFunctionTypeCheckContext& context)
             {
                 switch (shouldSuppressErrors(NotNull{&context.typechecker->normalizer}, actualTy))
                 {
-                    case ErrorSuppression::Suppress:
+                case ErrorSuppression::Suppress:
-                        break;
+                    break;
-                    case ErrorSuppression::NormalizationFailed:
+                case ErrorSuppression::NormalizationFailed:
-                        break;
+                    break;
-                    case ErrorSuppression::DoNotSuppress:
+                case ErrorSuppression::DoNotSuppress:
-                        Reasonings reasonings = context.typechecker->explainReasonings(actualTy, expectedTy, location, result);
+                    Reasonings reasonings = context.typechecker->explainReasonings(actualTy, expectedTy, location, result);
 
-                        if (!reasonings.suppressed)
+                    if (!reasonings.suppressed)
-                            context.typechecker->reportError(TypeMismatch{expectedTy, actualTy, reasonings.toString()}, location);
+                        context.typechecker->reportError(TypeMismatch{expectedTy, actualTy, reasonings.toString()}, location);
                 }
             }
         }

Analysis/src/BuiltinTypeFunctions.cpp

@@ -124,7 +124,7 @@ std::optional<TypeFunctionReductionResult<TypeId>> tryDistributeTypeFunctionApp(
     return std::nullopt;
 }
 
-}
+} // namespace
 
 TypeFunctionReductionResult<TypeId> notTypeFunction(
     TypeId instance,
@@ -1034,6 +1034,12 @@ TypeFunctionReductionResult<TypeId> eqTypeFunction(
 struct FindRefinementBlockers : TypeOnceVisitor
 {
     DenseHashSet<TypeId> found{nullptr};
+
+    FindRefinementBlockers()
+        : TypeOnceVisitor("FindRefinementBlockers")
+    {
+    }
+
     bool visit(TypeId ty, const BlockedType&) override
     {
         found.insert(ty);
@@ -1056,7 +1062,7 @@ struct ContainsRefinableType : TypeOnceVisitor
 {
     bool found = false;
     ContainsRefinableType()
-        : TypeOnceVisitor(/* skipBoundTypes */ true)
+        : TypeOnceVisitor("ContainsRefinableType", /* skipBoundTypes */ true)
     {
     }
 
@@ -1163,7 +1169,7 @@ struct RefineTypeScrubber : public Substitution
         return !is<UnionType, IntersectionType>(ty);
     }
 
-    TypeId clean(TypeId ty) override 
+    TypeId clean(TypeId ty) override
     {
         // NOTE: this feels pretty similar to other places where we try to
         // filter over a set type, may be worth combining those in the future.
@@ -1199,7 +1205,6 @@ struct RefineTypeScrubber : public Substitution
         }
         return ty;
     }
-
 };
 
 bool occurs(TypeId haystack, TypeId needle, DenseHashSet<TypeId>& seen)
@@ -1431,7 +1436,6 @@ TypeFunctionReductionResult<TypeId> refineTypeFunction(
 
             return {resultTy, {}};
         }
-
     };
 
     // refine target with each discriminant type in sequence (reverse of insertion order)
@@ -1494,7 +1498,7 @@ struct CollectUnionTypeOptions : TypeOnceVisitor
     DenseHashSet<TypeId> blockingTypes{nullptr};
 
     explicit CollectUnionTypeOptions(NotNull<TypeFunctionContext> ctx)
-        : TypeOnceVisitor(/* skipBoundTypes */ true)
+        : TypeOnceVisitor("CollectUnionTypeOptions", /* skipBoundTypes */ true)
         , ctx(ctx)
     {
     }
@@ -1764,7 +1768,8 @@ bool computeKeysOf_DEPRECATED(TypeId ty, Set<std::string>& result, DenseHashSet<
     return false;
 }
 
-namespace {
+namespace
+{
 
 /**
  * Computes the keys of `ty` into `result`
@@ -1847,7 +1852,7 @@ bool computeKeysOf(TypeId ty, Set<std::optional<std::string>>& result, DenseHash
     return false;
 }
 
-}
+} // namespace
 
 TypeFunctionReductionResult<TypeId> keyofFunctionImpl(
     const std::vector<TypeId>& typeParams,
@@ -2824,4 +2829,4 @@ const BuiltinTypeFunctions& builtinTypeFunctions()
     return *result;
 }
 
-}
+} // namespace Luau

Analysis/src/Constraint.cpp

@@ -24,7 +24,8 @@ struct ReferenceCountInitializer_DEPRECATED : TypeOnceVisitor
     bool traverseIntoTypeFunctions = true;
 
     explicit ReferenceCountInitializer_DEPRECATED(DenseHashSet<TypeId>* result)
-        : result(result)
+        : TypeOnceVisitor("ReferenceCountInitializer_DEPRECATED")
+        , result(result)
     {
     }
 
@@ -78,7 +79,8 @@ struct ReferenceCountInitializer : TypeOnceVisitor
     bool traverseIntoTypeFunctions = true;
 
     explicit ReferenceCountInitializer(NotNull<TypeIds> result)
-        : result(result)
+        : TypeOnceVisitor("ReferenceCountInitializer")
+        , result(result)
     {
     }
 

Analysis/src/ConstraintGenerator.cpp

@@ -139,7 +139,10 @@ struct HasFreeType : TypeOnceVisitor
 {
     bool result = false;
 
-    HasFreeType() {}
+    HasFreeType()
+        : TypeOnceVisitor("TypeOnceVisitor")
+    {
+    }
 
     bool visit(TypeId ty) override
     {
@@ -640,6 +643,11 @@ struct FindSimplificationBlockers : TypeOnceVisitor
 {
     bool found = false;
 
+    FindSimplificationBlockers()
+        : TypeOnceVisitor("FindSimplificationBlockers")
+    {
+    }
+
     bool visit(TypeId) override
     {
         return !found;
@@ -1026,7 +1034,7 @@ ControlFlow ConstraintGenerator::visitBlockWithoutChildScope(const ScopePtr& sco
 
 ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStat* stat)
 {
-    RecursionLimiter limiter{&recursionCount, FInt::LuauCheckRecursionLimit};
+    RecursionLimiter limiter{"ConstraintGenerator", &recursionCount, FInt::LuauCheckRecursionLimit};
 
     if (auto s = stat->as<AstStatBlock>())
         return visit(scope, s);

Analysis/src/ConstraintSolver.cpp

@@ -34,7 +34,6 @@ LUAU_FASTINTVARIABLE(LuauSolverRecursionLimit, 500)
 LUAU_FASTFLAGVARIABLE(DebugLuauEqSatSimplification)
 LUAU_FASTFLAG(LuauEagerGeneralization4)
 LUAU_FASTFLAG(LuauStuckTypeFunctionsStillDispatch)
-LUAU_FASTFLAGVARIABLE(LuauGuardAgainstMalformedTypeAliasExpansion2)
 LUAU_FASTFLAGVARIABLE(LuauAvoidGenericsLeakingDuringFunctionCallCheck)
 LUAU_FASTFLAGVARIABLE(LuauMissingFollowInAssignIndexConstraint)
 LUAU_FASTFLAGVARIABLE(LuauRemoveTypeCallsForReadWriteProps)
@@ -43,6 +42,7 @@ LUAU_FASTFLAGVARIABLE(LuauUseOrderedTypeSetsInConstraints)
 LUAU_FASTFLAG(LuauPushFunctionTypesInFunctionStatement)
 LUAU_FASTFLAG(LuauAvoidExcessiveTypeCopying)
 LUAU_FASTFLAGVARIABLE(LuauForceSimplifyConstraint)
+LUAU_FASTFLAGVARIABLE(LuauContainsAnyGenericFollowBeforeChecking)
 
 namespace Luau
 {
@@ -285,7 +285,8 @@ struct InstantiationQueuer : TypeOnceVisitor
     Location location;
 
     explicit InstantiationQueuer(NotNull<Scope> scope, const Location& location, ConstraintSolver* solver)
-        : solver(solver)
+        : TypeOnceVisitor("InstantiationQueuer")
+        , solver(solver)
         , scope(scope)
         , location(location)
     {
@@ -432,7 +433,8 @@ void ConstraintSolver::run()
         {
             for (TypeId ty : constraintSet.freeTypes)
             {
-                if (auto it = mutatedFreeTypeToConstraint_DEPRECATED.find(ty); it == mutatedFreeTypeToConstraint_DEPRECATED.end() || it->second.empty())
+                if (auto it = mutatedFreeTypeToConstraint_DEPRECATED.find(ty);
+                    it == mutatedFreeTypeToConstraint_DEPRECATED.end() || it->second.empty())
                     generalizeOneType(ty);
             }
         }
@@ -633,8 +635,7 @@ void ConstraintSolver::finalizeTypeFunctions()
         if (get<TypeFunctionInstanceType>(ty))
         {
             TypeFunctionContext context{NotNull{this}, constraint->scope, NotNull{constraint}};
-            FunctionGraphReductionResult result =
+            FunctionGraphReductionResult result = reduceTypeFunctions(t, constraint->location, NotNull{&context}, true);
-                reduceTypeFunctions(t, constraint->location, NotNull{&context}, true);
 
             for (TypeId r : result.reducedTypes)
                 unblock(r, constraint->location);
@@ -663,7 +664,8 @@ struct TypeSearcher : TypeVisitor
     }
 
     explicit TypeSearcher(TypeId needle, Polarity initialPolarity)
-        : needle(needle)
+        : TypeVisitor("TypeSearcher")
+        , needle(needle)
         , current(initialPolarity)
     {
     }
@@ -1195,7 +1197,8 @@ struct InfiniteTypeFinder : TypeOnceVisitor
     bool foundInfiniteType = false;
 
     explicit InfiniteTypeFinder(ConstraintSolver* solver, const InstantiationSignature& signature, NotNull<Scope> scope)
-        : solver(solver)
+        : TypeOnceVisitor("InfiniteTypeFinder")
+        , solver(solver)
         , signature(signature)
         , scope(scope)
     {
@@ -1235,7 +1238,7 @@ bool ConstraintSolver::tryDispatch(const TypeAliasExpansionConstraint& c, NotNul
         auto cTarget = follow(c.target);
         LUAU_ASSERT(get<PendingExpansionType>(cTarget));
         // We do this check here to ensure that we don't bind an alias to itself
-        if (FFlag::LuauGuardAgainstMalformedTypeAliasExpansion2 && occursCheck(cTarget, result))
+        if (occursCheck(cTarget, result))
         {
             reportError(OccursCheckFailed{}, constraint->location);
             bind(constraint, cTarget, builtinTypes->errorType);
@@ -1656,6 +1659,11 @@ struct ContainsGenerics_DEPRECATED : public TypeOnceVisitor
 
     bool found = false;
 
+    ContainsGenerics_DEPRECATED()
+        : TypeOnceVisitor("ContainsGenerics_DEPRECATED")
+    {
+    }
+
     bool visit(TypeId ty) override
     {
         return !found;
@@ -1736,7 +1744,8 @@ struct ContainsGenerics : public TypeOnceVisitor
     NotNull<DenseHashSet<const void*>> generics;
 
     explicit ContainsGenerics(NotNull<DenseHashSet<const void*>> generics)
-        : generics{generics}
+        : TypeOnceVisitor("ContainsGenerics")
+        , generics{generics}
     {
     }
 
@@ -2139,7 +2148,7 @@ bool ConstraintSolver::tryDispatchHasIndexer(
     Set<TypeId>& seen
 )
 {
-    RecursionLimiter _rl{&recursionDepth, FInt::LuauSolverRecursionLimit};
+    RecursionLimiter _rl{"ConstraintSolver::tryDispatchHasIndexer", &recursionDepth, FInt::LuauSolverRecursionLimit};
 
     subjectType = follow(subjectType);
     indexType = follow(indexType);
@@ -2315,6 +2324,11 @@ struct BlockedTypeFinder : TypeOnceVisitor
 {
     std::optional<TypeId> blocked;
 
+    BlockedTypeFinder()
+        : TypeOnceVisitor("ContainsGenerics_DEPRECATED")
+    {
+    }
+
     bool visit(TypeId ty) override
     {
         // If we've already found one, stop traversing.
@@ -2873,7 +2887,7 @@ struct FindAllUnionMembers : TypeOnceVisitor
     TypeIds blockedTys;
 
     FindAllUnionMembers()
-        : TypeOnceVisitor(/* skipBoundTypes */ true)
+        : TypeOnceVisitor("FindAllUnionMembers", /* skipBoundTypes */ true)
     {
     }
 
@@ -2959,7 +2973,7 @@ struct ContainsAnyGeneric final : public TypeOnceVisitor
     bool found = false;
 
     explicit ContainsAnyGeneric()
-        : TypeOnceVisitor(true)
+        : TypeOnceVisitor("ContainsAnyGeneric", /* skipBoundTypes */ true)
     {
     }
 
@@ -2971,7 +2985,10 @@ struct ContainsAnyGeneric final : public TypeOnceVisitor
 
     bool visit(TypePackId ty) override
     {
-        found = found || is<GenericTypePack>(ty);
+        if (FFlag::LuauContainsAnyGenericFollowBeforeChecking)
+            found = found || is<GenericTypePack>(follow(ty));
+        else
+            found = found || is<GenericTypePack>(ty);
         return !found;
     }
 
@@ -3367,7 +3384,8 @@ TablePropLookupResult ConstraintSolver::lookupTableProp(
                     return {{}, builtinTypes->errorType};
             }
 
-            TypeId indexType = FFlag::LuauRemoveTypeCallsForReadWriteProps ? follow(*indexProp->second.readTy) : follow(indexProp->second.type_DEPRECATED());
+            TypeId indexType =
+                FFlag::LuauRemoveTypeCallsForReadWriteProps ? follow(*indexProp->second.readTy) : follow(indexProp->second.type_DEPRECATED());
 
             if (auto ft = get<FunctionType>(indexType))
             {
@@ -3654,7 +3672,8 @@ struct Blocker : TypeOnceVisitor
     bool blocked = false;
 
     explicit Blocker(NotNull<ConstraintSolver> solver, NotNull<const Constraint> constraint)
-        : solver(solver)
+        : TypeOnceVisitor("Blocker")
+        , solver(solver)
         , constraint(constraint)
     {
     }

Analysis/src/EmbeddedBuiltinDefinitions.cpp

@@ -1,7 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/BuiltinDefinitions.h"
 
-LUAU_FASTFLAG(LuauDeclareExternType)
 LUAU_FASTFLAG(LuauTypeFunOptional)
 
 namespace Luau
@@ -262,8 +261,7 @@ declare buffer: {
 
 )BUILTIN_SRC";
 
-static const char* const kBuiltinDefinitionVectorSrc = (FFlag::LuauDeclareExternType)
+static const char* const kBuiltinDefinitionVectorSrc = R"BUILTIN_SRC(
-    ? R"BUILTIN_SRC(
 
 -- While vector would have been better represented as a built-in primitive type, type solver extern type handling covers most of the properties
 declare extern type vector with
@@ -291,35 +289,6 @@ declare vector: {
     one: vector,
 }
 
-)BUILTIN_SRC"
-    : R"BUILTIN_SRC(
-
--- While vector would have been better represented as a built-in primitive type, type solver class handling covers most of the properties
-declare class vector
-    x: number
-    y: number
-    z: number
-end
-
-declare vector: {
-    create: @checked (x: number, y: number, z: number?) -> vector,
-    magnitude: @checked (vec: vector) -> number,
-    normalize: @checked (vec: vector) -> vector,
-    cross: @checked (vec1: vector, vec2: vector) -> vector,
-    dot: @checked (vec1: vector, vec2: vector) -> number,
-    angle: @checked (vec1: vector, vec2: vector, axis: vector?) -> number,
-    floor: @checked (vec: vector) -> vector,
-    ceil: @checked (vec: vector) -> vector,
-    abs: @checked (vec: vector) -> vector,
-    sign: @checked (vec: vector) -> vector,
-    clamp: @checked (vec: vector, min: vector, max: vector) -> vector,
-    max: @checked (vector, ...vector) -> vector,
-    min: @checked (vector, ...vector) -> vector,
-
-    zero: vector,
-    one: vector,
-}
-
 )BUILTIN_SRC";
 
 std::string getBuiltinDefinitionSource()

Analysis/src/Error.cpp

@@ -870,7 +870,7 @@ struct ErrorConverter
     std::string operator()(const CannotCheckDynamicStringFormatCalls& e) const
     {
         return "We cannot statically check the type of `string.format` when called with a format string that is not statically known.\n"
-            "If you'd like to use an unchecked `string.format` call, you can cast the format string to `any` using `:: any`.";
+               "If you'd like to use an unchecked `string.format` call, you can cast the format string to `any` using `:: any`.";
     }
 
 

Analysis/src/ExpectedTypeVisitor.cpp

@@ -81,7 +81,9 @@ struct IndexerIndexCollector : public TypeOnceVisitor
 {
     NotNull<TypeIds> indexes;
 
-    explicit IndexerIndexCollector(NotNull<TypeIds> indexes) : TypeOnceVisitor(/* skipBoundTypes */ true), indexes(indexes)
+    explicit IndexerIndexCollector(NotNull<TypeIds> indexes)
+        : TypeOnceVisitor("IndexerIndexCollector", /* skipBoundTypes */ true)
+        , indexes(indexes)
     {
     }
 
@@ -100,7 +102,6 @@ struct IndexerIndexCollector : public TypeOnceVisitor
     {
         return true;
     }
-
 };
 
 struct IndexCollector : public TypeOnceVisitor
@@ -108,7 +109,9 @@ struct IndexCollector : public TypeOnceVisitor
     NotNull<TypeArena> arena;
     TypeIds indexes;
 
-    explicit IndexCollector(NotNull<TypeArena> arena) : TypeOnceVisitor(/* skipBoundTypes */ true), arena(arena)
+    explicit IndexCollector(NotNull<TypeArena> arena)
+        : TypeOnceVisitor("IndexCollector", /* skipBoundTypes */ true)
+        , arena(arena)
     {
     }
 
@@ -140,10 +143,9 @@ struct IndexCollector : public TypeOnceVisitor
 
         return false;
     }
-
 };
 
-}
+} // namespace
 
 bool ExpectedTypeVisitor::visit(AstExprIndexExpr* expr)
 {
@@ -156,17 +158,11 @@ bool ExpectedTypeVisitor::visit(AstExprIndexExpr* expr)
         ic.traverse(*ty);
         if (ic.indexes.size() > 1)
         {
-            applyExpectedType(
+            applyExpectedType(arena->addType(UnionType{ic.indexes.take()}), expr->index);
-                arena->addType(UnionType{ic.indexes.take()}),
-                expr->index
-            );
         }
         else if (ic.indexes.size() == 1)
         {
-            applyExpectedType(
+            applyExpectedType(*ic.indexes.begin(), expr->index);
-                *ic.indexes.begin(),
-                expr->index
-            );
         }
     }
 
@@ -314,4 +310,4 @@ void ExpectedTypeVisitor::applyExpectedType(TypeId expectedType, const AstExpr*
     }
 }
 
-} // namespace Luau
+} // namespace Luau

Analysis/src/FragmentAutocomplete.cpp

@@ -619,11 +619,10 @@ struct UsageFinder : public AstVisitor
             {
                 auto def = dfg->getDef(local);
                 localBindingsReferenced.emplace_back(def, local->local);
-                symbolsToRefine.emplace_back(def, Symbol(local->local));                
+                symbolsToRefine.emplace_back(def, Symbol(local->local));
             }
             else
                 localBindingsReferenced.emplace_back(dfg->getDef(local), local->local);
-
         }
         return true;
     }
@@ -635,7 +634,7 @@ struct UsageFinder : public AstVisitor
         if (FFlag::LuauFragmentAutocompleteTracksRValueRefinements)
         {
             auto def = dfg->getDef(global);
-            symbolsToRefine.emplace_back(def, Symbol(global->name));            
+            symbolsToRefine.emplace_back(def, Symbol(global->name));
         }
         return true;
     }

Analysis/src/Frontend.cpp

@@ -1016,7 +1016,8 @@ void Frontend::checkBuildQueueItem(BuildQueueItem& item)
         return;
     }
 
-    ModulePtr module = check(sourceModule, mode, requireCycles, environmentScope, /*forAutocomplete*/ false, item.recordJsonLog, std::move(typeCheckLimits));
+    ModulePtr module =
+        check(sourceModule, mode, requireCycles, environmentScope, /*forAutocomplete*/ false, item.recordJsonLog, std::move(typeCheckLimits));
 
     double duration = getTimestamp() - timestamp;
 
@@ -1368,6 +1369,11 @@ ModulePtr check(
 
 struct InternalTypeFinder : TypeOnceVisitor
 {
+    InternalTypeFinder()
+        : TypeOnceVisitor("InternalTypeFinder")
+    {
+    }
+
     bool visit(TypeId, const ExternType&) override
     {
         return false;

Analysis/src/Generalization.cpp

@@ -46,7 +46,7 @@ struct MutatingGeneralizer : TypeOnceVisitor
         DenseHashMap<const void*, size_t> positiveTypes,
         DenseHashMap<const void*, size_t> negativeTypes
     )
-        : TypeOnceVisitor(/* skipBoundTypes */ true)
+        : TypeOnceVisitor("MutatingGeneralizer", /* skipBoundTypes */ true)
         , arena(arena)
         , builtinTypes(builtinTypes)
         , scope(scope)
@@ -338,7 +338,7 @@ struct FreeTypeSearcher : TypeVisitor
     NotNull<DenseHashSet<TypeId>> cachedTypes;
 
     explicit FreeTypeSearcher(NotNull<Scope> scope, NotNull<DenseHashSet<TypeId>> cachedTypes)
-        : TypeVisitor(/*skipBoundTypes*/ true)
+        : TypeVisitor("FreeTypeSearcher", /*skipBoundTypes*/ true)
         , scope(scope)
         , cachedTypes(cachedTypes)
     {
@@ -649,7 +649,7 @@ struct TypeCacher : TypeOnceVisitor
     DenseHashSet<TypePackId> uncacheablePacks{nullptr};
 
     explicit TypeCacher(NotNull<DenseHashSet<TypeId>> cachedTypes)
-        : TypeOnceVisitor(/* skipBoundTypes */ false)
+        : TypeOnceVisitor("TypeCacher", /* skipBoundTypes */ false)
         , cachedTypes(cachedTypes)
     {
     }
@@ -1136,7 +1136,6 @@ struct TypeRemover
             }
         }
     }
-
 };
 
 void removeType(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, TypeId haystack, TypeId needle)
@@ -1145,7 +1144,7 @@ void removeType(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, Ty
     tr.process(haystack);
 }
 
-}
+} // namespace
 
 GeneralizationResult<TypeId> generalizeType(
     NotNull<TypeArena> arena,
@@ -1410,7 +1409,8 @@ struct GenericCounter : TypeVisitor
     Polarity polarity = Polarity::Positive;
 
     explicit GenericCounter(NotNull<DenseHashSet<TypeId>> cachedTypes)
-        : cachedTypes(cachedTypes)
+        : TypeVisitor("GenericCounter")
+        , cachedTypes(cachedTypes)
     {
     }
 

Analysis/src/InferPolarity.cpp

@@ -23,7 +23,8 @@ struct InferPolarity : TypeVisitor
     Polarity polarity = Polarity::Positive;
 
     explicit InferPolarity(NotNull<TypeArena> arena, NotNull<Scope> scope)
-        : arena(arena)
+        : TypeVisitor("InferPolarity")
+        , arena(arena)
         , scope(scope)
     {
     }

Analysis/src/Normalize.cpp

@@ -25,6 +25,7 @@ LUAU_FASTFLAGVARIABLE(LuauNormalizationIntersectTablesPreservesExternTypes)
 LUAU_FASTFLAGVARIABLE(LuauNormalizationReorderFreeTypeIntersect)
 LUAU_FASTFLAG(LuauRefineTablesWithReadType)
 LUAU_FASTFLAG(LuauUseWorkspacePropToChooseSolver)
+LUAU_FASTFLAGVARIABLE(LuauNormalizationLimitTyvarUnionSize)
 
 namespace Luau
 {
@@ -1530,6 +1531,12 @@ NormalizationResult Normalizer::unionNormals(NormalizedType& here, const Normali
         return NormalizationResult::True;
     }
 
+    if (FFlag::LuauNormalizationLimitTyvarUnionSize)
+    {
+        if (here.tyvars.size() * there.tyvars.size() >= size_t(FInt::LuauNormalizeUnionLimit))
+            return NormalizationResult::HitLimits;
+    }
+
     for (auto it = there.tyvars.begin(); it != there.tyvars.end(); it++)
     {
         TypeId tyvar = it->first;

Analysis/src/OverloadResolution.cpp

@@ -11,7 +11,7 @@
 #include "Luau/Unifier2.h"
 
 LUAU_FASTFLAGVARIABLE(LuauArityMismatchOnUndersaturatedUnknownArguments)
-LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 
 namespace Luau
 {
@@ -247,9 +247,7 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
 )
 {
     TypeFunctionContext context{arena, builtinTypes, scope, simplifier, normalizer, typeFunctionRuntime, ice, limits};
-    FunctionGraphReductionResult result = reduceTypeFunctions(
+    FunctionGraphReductionResult result = reduceTypeFunctions(fnTy, callLoc, NotNull{&context}, /*force=*/true);
-        fnTy, callLoc, NotNull{&context}, /*force=*/true
-    );
     if (!result.errors.empty())
         return {OverloadIsNonviable, result.errors};
 
@@ -330,7 +328,7 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
             return {Analysis::Ok, {}};
         }
 
-        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
         {
             // If we have an arity mismatch with generic type pack parameters, then subPath matches Args :: Tail :: ...
             // and superPath matches Args :: ...
@@ -405,15 +403,15 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
                           : argExprs->size() != 0        ? argExprs->back()->location
                                                          : fnExpr->location;
 
-            std::optional<TypeId> failedSubTy = FFlag::LuauReturnMappedGenericPacksFromSubtyping
+            std::optional<TypeId> failedSubTy = FFlag::LuauReturnMappedGenericPacksFromSubtyping2
                                                     ? traverseForType(fnTy, reason.subPath, builtinTypes, NotNull{&sr.mappedGenericPacks}, arena)
                                                     : traverseForType_DEPRECATED(fnTy, reason.subPath, builtinTypes);
             std::optional<TypeId> failedSuperTy =
-                FFlag::LuauReturnMappedGenericPacksFromSubtyping
+                FFlag::LuauReturnMappedGenericPacksFromSubtyping2
                     ? traverseForType(prospectiveFunction, reason.superPath, builtinTypes, NotNull{&sr.mappedGenericPacks}, arena)
                     : traverseForType_DEPRECATED(prospectiveFunction, reason.superPath, builtinTypes);
 
-            if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+            if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
                 maybeEmplaceError(&errors, argLocation, &reason, failedSubTy, failedSuperTy);
             else if (failedSubTy && failedSuperTy)
             {
@@ -443,7 +441,7 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
                 }
             }
         }
-        else if (FFlag::LuauReturnMappedGenericPacksFromSubtyping && reason.superPath.components.size() > 1)
+        else if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2 && reason.superPath.components.size() > 1)
         {
             // traverseForIndex only has a value if path is of form [...PackSlice, Index]
             if (const auto index =
@@ -466,11 +464,11 @@ std::pair<OverloadResolver::Analysis, ErrorVec> OverloadResolver::checkOverload_
             }
         }
 
-        std::optional<TypePackId> failedSubPack = FFlag::LuauReturnMappedGenericPacksFromSubtyping
+        std::optional<TypePackId> failedSubPack = FFlag::LuauReturnMappedGenericPacksFromSubtyping2
                                                       ? traverseForPack(fnTy, reason.subPath, builtinTypes, NotNull{&sr.mappedGenericPacks}, arena)
                                                       : traverseForPack_DEPRECATED(fnTy, reason.subPath, builtinTypes);
         std::optional<TypePackId> failedSuperPack =
-            FFlag::LuauReturnMappedGenericPacksFromSubtyping
+            FFlag::LuauReturnMappedGenericPacksFromSubtyping2
                 ? traverseForPack(prospectiveFunction, reason.superPath, builtinTypes, NotNull{&sr.mappedGenericPacks}, arena)
                 : traverseForPack_DEPRECATED(prospectiveFunction, reason.superPath, builtinTypes);
 

Analysis/src/Quantify.cpp

@@ -21,7 +21,8 @@ struct Quantifier final : TypeOnceVisitor
     bool seenMutableType = false;
 
     explicit Quantifier(TypeLevel level)
-        : level(level)
+        : TypeOnceVisitor("Quantifier")
+        , level(level)
     {
     }
 

Analysis/src/Scope.cpp

@@ -229,9 +229,9 @@ void Scope::inheritAssignments(const ScopePtr& childScope)
     {
         if (!FFlag::LuauSolverV2)
             return;
-        
+
         for (const auto& [k, a] : childScope->lvalueTypes)
-            lvalueTypes[k] = a;   
+            lvalueTypes[k] = a;
     }
 }
 

Analysis/src/Simplify.cpp

@@ -23,6 +23,7 @@ LUAU_FASTFLAG(LuauRemoveTypeCallsForReadWriteProps)
 LUAU_FASTFLAGVARIABLE(LuauRelateTablesAreNeverDisjoint)
 LUAU_FASTFLAG(LuauRefineTablesWithReadType)
 LUAU_FASTFLAGVARIABLE(LuauMissingSeenSetRelate)
+LUAU_FASTFLAGVARIABLE(LuauSimplifyAnyAndUnion)
 
 namespace Luau
 {
@@ -1426,7 +1427,7 @@ std::optional<TypeId> TypeSimplifier::basicIntersect(TypeId left, TypeId right)
 
 TypeId TypeSimplifier::intersect(TypeId left, TypeId right)
 {
-    RecursionLimiter rl(&recursionDepth, 15);
+    RecursionLimiter rl("TypeSimplifier::intersect", &recursionDepth, 15);
 
     left = simplify(left);
     right = simplify(right);
@@ -1442,6 +1443,10 @@ TypeId TypeSimplifier::intersect(TypeId left, TypeId right)
         return right;
     if (get<UnknownType>(right) && !get<ErrorType>(left))
         return left;
+    if (FFlag::LuauSimplifyAnyAndUnion && get<AnyType>(left) && get<UnionType>(right))
+        return union_(builtinTypes->errorType, right);
+    if (FFlag::LuauSimplifyAnyAndUnion && get<UnionType>(left) && get<AnyType>(right))
+        return union_(builtinTypes->errorType, left);
     if (get<AnyType>(left))
         return arena->addType(UnionType{{right, builtinTypes->errorType}});
     if (get<AnyType>(right))
@@ -1514,7 +1519,7 @@ TypeId TypeSimplifier::intersect(TypeId left, TypeId right)
 
 TypeId TypeSimplifier::union_(TypeId left, TypeId right)
 {
-    RecursionLimiter rl(&recursionDepth, 15);
+    RecursionLimiter rl("TypeSimplifier::union", &recursionDepth, 15);
 
     left = simplify(left);
     right = simplify(right);
@@ -1602,7 +1607,7 @@ TypeId TypeSimplifier::simplify(TypeId ty)
 
 TypeId TypeSimplifier::simplify(TypeId ty, DenseHashSet<TypeId>& seen)
 {
-    RecursionLimiter limiter(&recursionDepth, 60);
+    RecursionLimiter limiter("TypeSimplifier::simplify", &recursionDepth, 60);
 
     ty = follow(ty);
 
@@ -1843,7 +1848,7 @@ std::optional<TypeId> TypeSimplifier::intersectWithSimpleDiscriminant(TypeId tar
                     return builtinTypes->neverType;
                 if (property->writeTy && is<NeverType>(follow(property->writeTy)))
                     return builtinTypes->neverType;
-                
+
                 // If the property we get back is pointer identical to the
                 // original property, return the underlying property as an
                 // optimization.

Analysis/src/Subtyping.cpp

@@ -2,6 +2,7 @@
 
 #include "Luau/Subtyping.h"
 
+#include "iostream"
 #include "Luau/Common.h"
 #include "Luau/Error.h"
 #include "Luau/Normalize.h"
@@ -21,7 +22,7 @@ LUAU_FASTINTVARIABLE(LuauSubtypingReasoningLimit, 100)
 LUAU_FASTFLAGVARIABLE(LuauSubtypingCheckFunctionGenericCounts)
 LUAU_FASTFLAG(LuauEagerGeneralization4)
 LUAU_FASTFLAG(LuauRemoveTypeCallsForReadWriteProps)
-LUAU_FASTFLAGVARIABLE(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAGVARIABLE(LuauReturnMappedGenericPacksFromSubtyping2)
 
 namespace Luau
 {
@@ -78,7 +79,7 @@ static void assertReasoningValid_DEPRECATED(TID subTy, TID superTy, const Subtyp
 template<typename TID>
 static void assertReasoningValid(TID subTy, TID superTy, const SubtypingResult& result, NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena)
 {
-    LUAU_ASSERT(FFlag::LuauReturnMappedGenericPacksFromSubtyping);
+    LUAU_ASSERT(FFlag::LuauReturnMappedGenericPacksFromSubtyping2);
 
     if (!FFlag::DebugLuauSubtypingCheckPathValidity)
         return;
@@ -513,7 +514,7 @@ SubtypingResult Subtyping::isSubtype(TypeId subTy, TypeId superTy, NotNull<Scope
      * cacheable.
      */
 
-    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
     {
         result.mappedGenericPacks = std::move(env.mappedGenericPacks);
     }
@@ -530,7 +531,7 @@ SubtypingResult Subtyping::isSubtype(TypePackId subTp, TypePackId superTp, NotNu
 
     SubtypingResult result = isCovariantWith(env, subTp, superTp, scope);
 
-    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
     {
         if (!env.mappedGenericPacks.empty())
             result.mappedGenericPacks = std::move(env.mappedGenericPacks);
@@ -543,7 +544,7 @@ SubtypingResult Subtyping::cache(SubtypingEnvironment& env, SubtypingResult resu
 {
     const std::pair<TypeId, TypeId> p{subTy, superTy};
 
-    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping && !env.mappedGenericPacks.empty())
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2 && !env.mappedGenericPacks.empty())
         result.mappedGenericPacks = env.mappedGenericPacks;
 
     if (result.isCacheable)
@@ -572,6 +573,30 @@ struct SeenSetPopper
         seenTypes->erase(pair);
     }
 };
+
+struct SeenTypePackSetPopper
+{
+    Subtyping::SeenTypePackSet* seenTypes;
+    std::pair<TypePackId, TypePackId> pair;
+
+    SeenTypePackSetPopper(Subtyping::SeenTypePackSet* seenTypes, std::pair<TypePackId, TypePackId> pair)
+        : seenTypes(seenTypes)
+          , pair(std::move(pair))
+    {
+        LUAU_ASSERT(FFlag::LuauReturnMappedGenericPacksFromSubtyping2);
+    }
+
+    SeenTypePackSetPopper(const SeenTypePackSetPopper&) = delete;
+    SeenTypePackSetPopper& operator=(const SeenTypePackSetPopper&) = delete;
+    SeenTypePackSetPopper(SeenTypePackSetPopper&&) = delete;
+    SeenTypePackSetPopper& operator=(SeenTypePackSetPopper&&) = delete;
+
+    ~SeenTypePackSetPopper()
+    {
+        LUAU_ASSERT(FFlag::LuauReturnMappedGenericPacksFromSubtyping2);
+        seenTypes->erase(pair);
+    }
+};
 } // namespace
 
 SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId subTy, TypeId superTy, NotNull<Scope> scope)
@@ -598,7 +623,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     const SubtypingResult* cachedResult = resultCache.find({subTy, superTy});
     if (cachedResult)
     {
-        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
         {
             for (const auto& [genericTp, boundTp] : cachedResult->mappedGenericPacks)
                 env.mappedGenericPacks.try_insert(genericTp, boundTp);
@@ -610,7 +635,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     cachedResult = env.tryFindSubtypingResult({subTy, superTy});
     if (cachedResult)
     {
-        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
         {
             for (const auto& [genericTp, boundTp] : cachedResult->mappedGenericPacks)
                 env.mappedGenericPacks.try_insert(genericTp, boundTp);
@@ -857,7 +882,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId sub
     else if (auto p = get2<SingletonType, TableType>(subTy, superTy))
         result = isCovariantWith(env, p, scope);
 
-    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
         assertReasoningValid(subTy, superTy, result, builtinTypes, arena);
     else
         assertReasoningValid_DEPRECATED(subTy, superTy, result, builtinTypes);
@@ -870,6 +895,20 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
     subTp = follow(subTp);
     superTp = follow(superTp);
 
+    std::optional<SeenTypePackSetPopper> popper = std::nullopt;
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
+    {
+        std::pair<TypePackId, TypePackId> typePair = {subTp, superTp};
+        if (!seenPacks.insert(typePair))
+        {
+            SubtypingResult res;
+            res.isSubtype = true;
+            res.isCacheable = false;
+            return res;
+        }
+        popper.emplace(&seenPacks, std::move(typePair));
+    }
+
     auto [subHead, subTail] = flatten(subTp);
     auto [superHead, superTail] = flatten(superTp);
 
@@ -908,15 +947,32 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
                     //
                     // <X>(X) -> () <: (T) -> ()
 
-                    // Possible optimization: If headSize == 0 then we can just use subTp as-is.
+                    TypePackId superTailPack;
-                    std::vector<TypeId> headSlice = FFlag::LuauReturnMappedGenericPacksFromSubtyping
+                    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
-                                                        ? std::vector<TypeId>(begin(superHead) + headSize, end(superHead))
+                    {
-                                                        : std::vector<TypeId>(begin(superHead), begin(superHead) + headSize);
+                        if (headSize == 0)
-                    TypePackId superTailPack = arena->addTypePack(std::move(headSlice), superTail);
+                            superTailPack = superTp;
+                        else if (headSize == superHead.size())
+                            superTailPack = superTail ? *superTail : builtinTypes->emptyTypePack;
+                        else
+                        {
+                            auto superHeadIter = begin(superHead);
+                            for (size_t i = 0; i < headSize; ++i)
+                                ++superHeadIter;
+                            std::vector<TypeId> headSlice(std::move(superHeadIter), end(superHead));
+                            superTailPack = arena->addTypePack(std::move(headSlice), superTail);
+                        }
+                    }
+                    else
+                    {
+                        // Possible optimization: If headSize == 0 then we can just use subTp as-is.
+                        std::vector<TypeId> headSlice = std::vector<TypeId>(begin(superHead), begin(superHead) + headSize);
+                        superTailPack = arena->addTypePack(std::move(headSlice), superTail);
+                    }
 
                     if (TypePackId* other = env.getMappedPackBounds(*subTail))
                     {
-                        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+                        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
                         {
                             const TypePack* tp = get<TypePack>(*other);
                             if (const VariadicTypePack* vtp = tp ? get<VariadicTypePack>(tp->tail) : nullptr; vtp && vtp->hidden)
@@ -982,15 +1038,32 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
                     //
                     // <X...>(X...) -> () <: (T) -> ()
 
-                    // Possible optimization: If headSize == 0 then we can just use subTp as-is.
+                    TypePackId subTailPack;
-                    std::vector<TypeId> headSlice = FFlag::LuauReturnMappedGenericPacksFromSubtyping
+                    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
-                                                        ? std::vector<TypeId>(begin(subHead) + headSize, end(subHead))
+                    {
-                                                        : std::vector<TypeId>(begin(subHead), begin(subHead) + headSize);
+                        if (headSize == 0)
-                    TypePackId subTailPack = arena->addTypePack(std::move(headSlice), subTail);
+                            subTailPack = subTp;
+                        else if (headSize == subHead.size())
+                            subTailPack = subTail ? *subTail : builtinTypes->emptyTypePack;
+                        else
+                        {
+                            auto subHeadIter = begin(subHead);
+                            for (size_t i = 0; i < headSize; ++i)
+                                ++subHeadIter;
+                            std::vector<TypeId> headSlice(std::move(subHeadIter), end(subHead));
+                            subTailPack = arena->addTypePack(std::move(headSlice), subTail);
+                        }
+                    }
+                    else
+                    {
+                        // Possible optimization: If headSize == 0 then we can just use subTp as-is.
+                        std::vector<TypeId> headSlice = std::vector<TypeId>(begin(subHead), begin(subHead) + headSize);
+                        subTailPack = arena->addTypePack(std::move(headSlice), subTail);
+                    }
 
                     if (TypePackId* other = env.getMappedPackBounds(*superTail))
                     {
-                        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+                        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
                         {
                             const TypePack* tp = get<TypePack>(*other);
                             if (const VariadicTypePack* vtp = tp ? get<VariadicTypePack>(tp->tail) : nullptr; vtp && vtp->hidden)
@@ -1142,7 +1215,7 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypePackId
 
     SubtypingResult result = SubtypingResult::all(results);
 
-    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
         assertReasoningValid(subTp, superTp, result, builtinTypes, arena);
     else
         assertReasoningValid_DEPRECATED(subTp, superTp, result, builtinTypes);
@@ -1177,7 +1250,7 @@ SubtypingResult Subtyping::isContravariantWith(SubtypingEnvironment& env, SubTy&
         }
     }
 
-    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
         assertReasoningValid(subTy, superTy, result, builtinTypes, arena);
     else
         assertReasoningValid_DEPRECATED(subTy, superTy, result, builtinTypes);
@@ -1198,7 +1271,7 @@ SubtypingResult Subtyping::isInvariantWith(SubtypingEnvironment& env, SubTy&& su
             reasoning.variance = SubtypingVariance::Invariant;
     }
 
-    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
         assertReasoningValid(subTy, superTy, result, builtinTypes, arena);
     else
         assertReasoningValid_DEPRECATED(subTy, superTy, result, builtinTypes);
@@ -1862,7 +1935,9 @@ SubtypingResult Subtyping::isCovariantWith(
         if (FFlag::LuauRemoveTypeCallsForReadWriteProps)
             res.andAlso(isInvariantWith(env, *subProp.readTy, *superProp.readTy, scope).withBothComponent(TypePath::Property::read(name)));
         else
-            res.andAlso(isInvariantWith(env, subProp.type_DEPRECATED(), superProp.type_DEPRECATED(), scope).withBothComponent(TypePath::Property::read(name)));
+            res.andAlso(
+                isInvariantWith(env, subProp.type_DEPRECATED(), superProp.type_DEPRECATED(), scope).withBothComponent(TypePath::Property::read(name))
+            );
     }
     else
     {
@@ -2131,6 +2206,13 @@ bool Subtyping::bindGeneric(SubtypingEnvironment& env, TypePackId subTp, TypePac
     if (TypePackId* m = env.getMappedPackBounds(subTp))
         return *m == superTp;
 
+    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
+    {
+        // We shouldn't bind generic type packs to themselves
+        if (subTp == superTp)
+            return true;
+    }
+
     env.mappedGenericPacks[subTp] = superTp;
 
     return true;

Analysis/src/ToString.cpp

@@ -52,7 +52,11 @@ namespace
 
 struct FindCyclicTypes final : TypeVisitor
 {
-    FindCyclicTypes() = default;
+    FindCyclicTypes()
+        : TypeVisitor("FindCyclicTypes")
+    {
+    }
+
     FindCyclicTypes(const FindCyclicTypes&) = delete;
     FindCyclicTypes& operator=(const FindCyclicTypes&) = delete;
 
@@ -589,7 +593,7 @@ struct TypeStringifier
         if (FFlag::LuauSolverAgnosticStringification && FInt::DebugLuauVerboseTypeNames >= 1)
             state.emit(ftv.polarity);
         else if (FFlag::LuauSolverV2 && FInt::DebugLuauVerboseTypeNames >= 1)
-            state.emit(ftv.polarity);            
+            state.emit(ftv.polarity);
 
 
         if (FInt::DebugLuauVerboseTypeNames >= 2)
@@ -827,7 +831,9 @@ struct TypeStringifier
 
         std::string openbrace = "@@@";
         std::string closedbrace = "@@@?!";
-        switch (state.opts.hideTableKind ? ((FFlag::LuauSolverV2 || FFlag::LuauSolverAgnosticStringification) ? TableState::Sealed : TableState::Unsealed) : ttv.state)
+        switch (state.opts.hideTableKind
+                    ? ((FFlag::LuauSolverV2 || FFlag::LuauSolverAgnosticStringification) ? TableState::Sealed : TableState::Unsealed)
+                    : ttv.state)
         {
         case TableState::Sealed:
             if (FFlag::LuauSolverV2 || FFlag::LuauSolverAgnosticStringification)
@@ -1899,6 +1905,39 @@ std::string dump(const std::optional<TypePackId>& ty)
     return "nullopt";
 }
 
+std::string dump(const std::vector<TypeId>& types)
+{
+    return toStringVector(types, dumpOptions());
+}
+
+std::string dump(DenseHashMap<TypeId, TypeId>& types)
+{
+    std::string s = "{";
+    ToStringOptions& opts = dumpOptions();
+    for (const auto& [key, value] : types)
+    {
+        if (s.length() == 1)
+            s += ", ";
+        s += toString(key, opts) + " : " + toString(value, opts);
+    }
+    s += "}";
+    return s;
+}
+
+std::string dump(DenseHashMap<TypePackId, TypePackId>& types)
+{
+    std::string s = "{";
+    ToStringOptions& opts = dumpOptions();
+    for (const auto& [key, value] : types)
+    {
+        if (s.length() == 1)
+            s += ", ";
+        s += toString(key, opts) + " : " + toString(value, opts);
+    }
+    s += "}";
+    return s;
+}
+
 std::string dump(const ScopePtr& scope, const char* name)
 {
     auto binding = scope->linearSearchForBinding(name);
@@ -2005,7 +2044,7 @@ std::string toString(const Constraint& constraint, ToStringOptions& opts)
             return tos(c.resultType) + " ~ hasIndexer " + tos(c.subjectType) + " " + tos(c.indexType);
         }
         else if constexpr (std::is_same_v<T, AssignPropConstraint>)
-            return tos(c.propType) +  " ~ assignProp " + tos(c.lhsType) + " " + c.propName + " " + tos(c.rhsType);
+            return tos(c.propType) + " ~ assignProp " + tos(c.lhsType) + " " + c.propName + " " + tos(c.rhsType);
         else if constexpr (std::is_same_v<T, AssignIndexConstraint>)
             return "assignIndex " + tos(c.lhsType) + " " + tos(c.indexType) + " " + tos(c.rhsType);
         else if constexpr (std::is_same_v<T, UnpackConstraint>)

Analysis/src/Type.cpp

@@ -446,7 +446,7 @@ bool maybeSingleton(TypeId ty)
 
 bool hasLength(TypeId ty, DenseHashSet<TypeId>& seen, int* recursionCount)
 {
-    RecursionLimiter _rl(recursionCount, FInt::LuauTypeInferRecursionLimit);
+    RecursionLimiter _rl("Type::hasLength", recursionCount, FInt::LuauTypeInferRecursionLimit);
 
     ty = follow(ty);
 

Analysis/src/TypeChecker2.cpp

@@ -37,7 +37,7 @@ LUAU_FASTFLAG(LuauStuckTypeFunctionsStillDispatch)
 LUAU_FASTFLAG(LuauSubtypingCheckFunctionGenericCounts)
 LUAU_FASTFLAG(LuauTableLiteralSubtypeCheckFunctionCalls)
 LUAU_FASTFLAGVARIABLE(LuauSuppressErrorsForMultipleNonviableOverloads)
-LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 LUAU_FASTFLAG(LuauInferActualIfElseExprType)
 LUAU_FASTFLAG(LuauNewNonStrictSuppressSoloConstraintSolvingIncomplete)
 
@@ -161,6 +161,11 @@ struct TypeFunctionFinder : TypeOnceVisitor
     DenseHashSet<TypeId> mentionedFunctions{nullptr};
     DenseHashSet<TypePackId> mentionedFunctionPacks{nullptr};
 
+    TypeFunctionFinder()
+        : TypeOnceVisitor("TypeFunctionFinder")
+    {
+    }
+
     bool visit(TypeId ty, const TypeFunctionInstanceType&) override
     {
         mentionedFunctions.insert(ty);
@@ -182,6 +187,7 @@ struct InternalTypeFunctionFinder : TypeOnceVisitor
     DenseHashSet<TypePackId> mentionedFunctionPacks{nullptr};
 
     explicit InternalTypeFunctionFinder(std::vector<TypeId>& declStack)
+        : TypeOnceVisitor("InternalTypeFunctionFinder")
     {
         TypeFunctionFinder f;
         for (TypeId fn : declStack)
@@ -2052,7 +2058,8 @@ void TypeChecker2::visit(AstExprFunction* fn)
                     TypeFunctionReductionGuessResult result = guesser.guessTypeFunctionReductionForFunctionExpr(*fn, inferredFtv, retTy);
                     if (result.shouldRecommendAnnotation && !get<UnknownType>(result.guessedReturnType))
                         reportError(
-                            ExplicitFunctionAnnotationRecommended{std::move(result.guessedFunctionAnnotations), result.guessedReturnType}, fn->location
+                            ExplicitFunctionAnnotationRecommended{std::move(result.guessedFunctionAnnotations), result.guessedReturnType},
+                            fn->location
                         );
                 }
             }
@@ -2207,7 +2214,9 @@ TypeId TypeChecker2::visit(AstExprBinary* expr, AstNode* overrideKey)
         auto name = getIdentifierOfBaseVar(expr->left);
         reportError(
             CannotInferBinaryOperation{
-                expr->op, std::move(name), isComparison ? CannotInferBinaryOperation::OpKind::Comparison : CannotInferBinaryOperation::OpKind::Operation
+                expr->op,
+                std::move(name),
+                isComparison ? CannotInferBinaryOperation::OpKind::Comparison : CannotInferBinaryOperation::OpKind::Operation
             },
             expr->location
         );
@@ -2920,11 +2929,11 @@ Reasonings TypeChecker2::explainReasonings_(TID subTy, TID superTy, Location loc
             continue;
 
         std::optional<TypeOrPack> optSubLeaf =
-            FFlag::LuauReturnMappedGenericPacksFromSubtyping
+            FFlag::LuauReturnMappedGenericPacksFromSubtyping2
                 ? traverse(subTy, reasoning.subPath, builtinTypes, NotNull{&r.mappedGenericPacks}, subtyping->arena)
                 : traverse_DEPRECATED(subTy, reasoning.subPath, builtinTypes);
         std::optional<TypeOrPack> optSuperLeaf =
-            FFlag::LuauReturnMappedGenericPacksFromSubtyping
+            FFlag::LuauReturnMappedGenericPacksFromSubtyping2
                 ? traverse(superTy, reasoning.superPath, builtinTypes, NotNull{&r.mappedGenericPacks}, subtyping->arena)
                 : traverse_DEPRECATED(superTy, reasoning.superPath, builtinTypes);
 
@@ -3071,7 +3080,7 @@ bool TypeChecker2::testPotentialLiteralIsSubtype(AstExpr* expr, TypeId expectedT
         else if (auto binExpr = expr->as<AstExprBinary>(); binExpr && binExpr->op == AstExprBinary::Or)
         {
             // In this case: `{ ... } or { ... }` is literal _enough_ that
-            // we should do this covariant check. 
+            // we should do this covariant check.
             auto relaxedExpectedLhs = module->internalTypes.addType(UnionType{{builtinTypes->falsyType, expectedType}});
             bool passes = testPotentialLiteralIsSubtype(binExpr->left, relaxedExpectedLhs);
             passes &= testPotentialLiteralIsSubtype(binExpr->right, expectedType);

Analysis/src/TypeFunction.cpp

@@ -60,6 +60,12 @@ struct InstanceCollector : TypeOnceVisitor
     std::vector<const void*> typeFunctionInstanceStack;
     std::vector<TypeId> cyclicInstance;
 
+
+    InstanceCollector()
+        : TypeOnceVisitor("InstanceCollector")
+    {
+    }
+
     bool visit(TypeId ty, const TypeFunctionInstanceType& tfit) override
     {
         // TypeVisitor performs a depth-first traversal in the absence of
@@ -146,6 +152,11 @@ struct UnscopedGenericFinder : TypeOnceVisitor
     std::vector<TypePackId> scopeGenTps;
     bool foundUnscoped = false;
 
+    UnscopedGenericFinder()
+        : TypeOnceVisitor("UnscopedGenericFinder")
+    {
+    }
+
     bool visit(TypeId ty) override
     {
         // Once we have found an unscoped generic, we will stop the traversal
@@ -660,8 +671,7 @@ struct TypeFunctionReducer
             if (tryGuessing(subject))
                 return;
 
-            TypeFunctionReductionResult<TypePackId> result =
+            TypeFunctionReductionResult<TypePackId> result = tfit->function->reducer(subject, tfit->typeArguments, tfit->packArguments, ctx);
-                tfit->function->reducer(subject, tfit->typeArguments, tfit->packArguments, ctx);
             handleTypeFunctionReduction(subject, std::move(result));
         }
     }

Analysis/src/TypeFunctionReductionGuesser.cpp

@@ -24,6 +24,11 @@ struct InstanceCollector2 : TypeOnceVisitor
     DenseHashSet<TypeId> cyclicInstance{nullptr};
     DenseHashSet<TypeId> instanceArguments{nullptr};
 
+    InstanceCollector2()
+        : TypeOnceVisitor("InstanceCollector2")
+    {
+    }
+
     bool visit(TypeId ty, const TypeFunctionInstanceType& it) override
     {
         // TypeOnceVisitor performs a depth-first traversal in the absence of

Analysis/src/TypeIds.cpp

@@ -157,4 +157,4 @@ std::vector<TypeId> TypeIds::take()
     return std::move(order);
 }
 
-}
+} // namespace Luau

Analysis/src/TypeInfer.cpp

@@ -442,7 +442,7 @@ struct InplaceDemoter : TypeOnceVisitor
     TypeArena* arena;
 
     InplaceDemoter(TypeLevel level, TypeArena* arena)
-        : TypeOnceVisitor(/* skipBoundTypes= */ true)
+        : TypeOnceVisitor("InplaceDemoter", /* skipBoundTypes= */ true)
         , newLevel(level)
         , arena(arena)
     {
@@ -2150,7 +2150,7 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromTypeImpl(
 
         for (TypeId t : utv)
         {
-            RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit);
+            RecursionLimiter _rl("TypeInfer::UnionType", &recursionCount, FInt::LuauTypeInferRecursionLimit);
 
             // Not needed when we normalize types.
             if (get<AnyType>(follow(t)))
@@ -2189,7 +2189,7 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromTypeImpl(
 
         for (TypeId t : itv->parts)
         {
-            RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit);
+            RecursionLimiter _rl("TypeInfer::IntersectionType", &recursionCount, FInt::LuauTypeInferRecursionLimit);
 
             if (std::optional<TypeId> ty = getIndexTypeFromType(scope, t, name, location, /* addErrors= */ false))
                 parts.push_back(*ty);
@@ -4129,7 +4129,9 @@ void TypeChecker::checkArgumentList(
         auto [minParams, optMaxParams] = getParameterExtents(&state.log, paramPack);
         state.reportError(TypeError{
             location,
-            CountMismatch{minParams, optMaxParams, std::distance(begin(argPack), end(argPack)), CountMismatch::Context::Arg, false, std::move(namePath)}
+            CountMismatch{
+                minParams, optMaxParams, std::distance(begin(argPack), end(argPack)), CountMismatch::Context::Arg, false, std::move(namePath)
+            }
         });
     };
 
@@ -4248,7 +4250,8 @@ void TypeChecker::checkArgumentList(
                         namePath = *path;
 
                     state.reportError(TypeError{
-                        funName.location, CountMismatch{minParams, optMaxParams, paramIndex, CountMismatch::Context::Arg, isVariadic, std::move(namePath)}
+                        funName.location,
+                        CountMismatch{minParams, optMaxParams, paramIndex, CountMismatch::Context::Arg, isVariadic, std::move(namePath)}
                     });
                     return;
                 }

Analysis/src/TypePack.cpp

@@ -4,7 +4,7 @@
 #include "Luau/Error.h"
 #include "Luau/TxnLog.h"
 
-#include <stdexcept>
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 
 namespace Luau
 {
@@ -455,10 +455,13 @@ std::pair<std::vector<TypeId>, std::optional<TypePackId>> flatten(TypePackId tp,
 
 std::pair<std::vector<TypeId>, std::optional<TypePackId>> flatten(TypePackId tp, const DenseHashMap<TypePackId, TypePackId>& mappedGenericPacks)
 {
+    LUAU_ASSERT(FFlag::LuauReturnMappedGenericPacksFromSubtyping2);
+
     tp = mappedGenericPacks.contains(tp) ? *mappedGenericPacks.find(tp) : tp;
 
     std::vector<TypeId> flattened;
     std::optional<TypePackId> tail = std::nullopt;
+    DenseHashSet<TypePackId> seenGenericPacks{nullptr};
 
     while (tp)
     {
@@ -467,9 +470,10 @@ std::pair<std::vector<TypeId>, std::optional<TypePackId>> flatten(TypePackId tp,
         for (; it != end(tp); ++it)
             flattened.push_back(*it);
 
-        if (const auto tpTail = it.tail(); tpTail && mappedGenericPacks.contains(*tpTail))
+        if (const auto tpTail = it.tail(); tpTail && !seenGenericPacks.contains(*tpTail) && mappedGenericPacks.contains(*tpTail))
         {
             tp = *mappedGenericPacks.find(*tpTail);
+            seenGenericPacks.insert(*tpTail);
             continue;
         }
 

Analysis/src/TypePath.cpp

@@ -16,7 +16,7 @@
 #include <sstream>
 
 LUAU_FASTFLAG(LuauSolverV2);
-LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 
 // Maximum number of steps to follow when traversing a path. May not always
 // equate to the number of components in a path, depending on the traversal
@@ -285,7 +285,7 @@ struct TraversalState
 
     TypeOrPack current;
     NotNull<BuiltinTypes> builtinTypes;
-    // TODO: make these NotNull when LuauReturnMappedGenericPacksFromSubtyping is clipped
+    // TODO: make these NotNull when LuauReturnMappedGenericPacksFromSubtyping2 is clipped
     const DenseHashMap<TypePackId, TypePackId>* mappedGenericPacks;
     TypeArena* arena;
     int steps = 0;
@@ -417,7 +417,7 @@ struct TraversalState
         {
             auto currentPack = get<TypePackId>(current);
             LUAU_ASSERT(currentPack);
-            if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+            if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
             {
                 if (const auto tp = get<TypePack>(*currentPack))
                 {
@@ -576,7 +576,7 @@ struct TraversalState
 
                 if (auto tail = it.tail())
                 {
-                    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping && mappedGenericPacks && mappedGenericPacks->contains(*tail))
+                    if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2 && mappedGenericPacks && mappedGenericPacks->contains(*tail))
                         updateCurrent(*mappedGenericPacks->find(*tail));
                     else
                         updateCurrent(*tail);
@@ -595,9 +595,9 @@ struct TraversalState
         if (checkInvariants())
             return false;
 
-        // TODO: clip this check once LuauReturnMappedGenericPacksFromSubtyping is clipped
+        // TODO: clip this check once LuauReturnMappedGenericPacksFromSubtyping2 is clipped
         // arena and mappedGenericPacks should be NonNull once that happens
-        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping)
+        if (FFlag::LuauReturnMappedGenericPacksFromSubtyping2)
             LUAU_ASSERT(arena && mappedGenericPacks);
         else if (!arena || !mappedGenericPacks)
             return false;

Analysis/src/Unifier.cpp

@@ -33,7 +33,8 @@ struct PromoteTypeLevels final : TypeOnceVisitor
     TypeLevel minLevel;
 
     PromoteTypeLevels(TxnLog& log, const TypeArena* typeArena, TypeLevel minLevel)
-        : log(log)
+        : TypeOnceVisitor("PromoteTypeLevels")
+        , log(log)
         , typeArena(typeArena)
         , minLevel(minLevel)
     {
@@ -145,7 +146,8 @@ void promoteTypeLevels(TxnLog& log, const TypeArena* typeArena, TypeLevel minLev
 struct SkipCacheForType final : TypeOnceVisitor
 {
     SkipCacheForType(const DenseHashMap<TypeId, bool>& skipCacheForType, const TypeArena* typeArena)
-        : skipCacheForType(skipCacheForType)
+        : TypeOnceVisitor("SkipCacheForType")
+        , skipCacheForType(skipCacheForType)
         , typeArena(typeArena)
     {
     }
@@ -404,7 +406,7 @@ static bool isBlocked(const TxnLog& log, TypePackId tp)
 
 void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool isIntersection, const LiteralProperties* literalProperties)
 {
-    RecursionLimiter _ra(&sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
+    RecursionLimiter _ra("Unifier::tryUnify_", &sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
 
     ++sharedState.counters.iterationCount;
 
@@ -1448,7 +1450,7 @@ void Unifier::tryUnify(TypePackId subTp, TypePackId superTp, bool isFunctionCall
  */
 void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCall)
 {
-    RecursionLimiter _ra(&sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
+    RecursionLimiter _ra("Unifier::tryUnify_", &sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
 
     ++sharedState.counters.iterationCount;
 
@@ -2030,7 +2032,7 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection,
         {
             if (FFlag::LuauUnifierRecursionOnRestart)
             {
-                RecursionLimiter _ra(&sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
+                RecursionLimiter _ra("Unifier::tryUnifyTables", &sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
                 tryUnify(subTy, superTy, false, isIntersection);
                 return;
             }
@@ -2048,7 +2050,7 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection,
         {
             if (errors.empty())
             {
-                RecursionLimiter _ra(&sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
+                RecursionLimiter _ra("Unifier::tryUnifyTables", &sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
                 tryUnifyTables(subTy, superTy, isIntersection);
             }
 
@@ -2120,7 +2122,7 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection,
         {
             if (FFlag::LuauUnifierRecursionOnRestart)
             {
-                RecursionLimiter _ra(&sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
+                RecursionLimiter _ra("Unifier::tryUnifyTables", &sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
                 tryUnify(subTy, superTy, false, isIntersection);
                 return;
             }
@@ -2140,7 +2142,7 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection,
         {
             if (errors.empty())
             {
-                RecursionLimiter _ra(&sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
+                RecursionLimiter _ra("Unifier::tryUnifyTables", &sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
                 tryUnifyTables(subTy, superTy, isIntersection);
             }
 
@@ -2732,7 +2734,7 @@ bool Unifier::occursCheck(TypeId needle, TypeId haystack, bool reversed)
 
 bool Unifier::occursCheck(DenseHashSet<TypeId>& seen, TypeId needle, TypeId haystack)
 {
-    RecursionLimiter _ra(&sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
+    RecursionLimiter _ra("Unifier::occursCheck", &sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
 
     bool occurrence = false;
 
@@ -2806,7 +2808,7 @@ bool Unifier::occursCheck(DenseHashSet<TypePackId>& seen, TypePackId needle, Typ
     if (!log.getMutable<FreeTypePack>(needle) && !(hideousFixMeGenericsAreActuallyFree && log.is<GenericTypePack>(needle)))
         ice("Expected needle pack to be free");
 
-    RecursionLimiter _ra(&sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
+    RecursionLimiter _ra("Unifier::occursCheck", &sharedState.counters.recursionCount, sharedState.counters.recursionLimit);
 
     while (!log.getMutable<ErrorTypePack>(haystack))
     {

Analysis/src/Unifier2.cpp

@@ -722,7 +722,7 @@ TypeId Unifier2::mkIntersection(TypeId left, TypeId right)
 
 OccursCheckResult Unifier2::occursCheck(DenseHashSet<TypeId>& seen, TypeId needle, TypeId haystack)
 {
-    RecursionLimiter _ra(&recursionCount, recursionLimit);
+    RecursionLimiter _ra("Unifier2::occursCheck", &recursionCount, recursionLimit);
 
     OccursCheckResult occurrence = OccursCheckResult::Pass;
 
@@ -784,7 +784,7 @@ OccursCheckResult Unifier2::occursCheck(DenseHashSet<TypePackId>& seen, TypePack
     if (!getMutable<FreeTypePack>(needle))
         ice->ice("Expected needle pack to be free");
 
-    RecursionLimiter _ra(&recursionCount, recursionLimit);
+    RecursionLimiter _ra("Unifier2::occursCheck", &recursionCount, recursionLimit);
 
     while (!getMutable<ErrorTypePack>(haystack))
     {

Analysis/src/UserDefinedTypeFunction.cpp

@@ -39,7 +39,7 @@ private:
     T oldValue;
 };
 
-}
+} // namespace
 
 struct FindUserTypeFunctionBlockers : TypeOnceVisitor
 {
@@ -48,7 +48,7 @@ struct FindUserTypeFunctionBlockers : TypeOnceVisitor
     std::vector<TypeId> blockingTypes;
 
     explicit FindUserTypeFunctionBlockers(NotNull<TypeFunctionContext> ctx)
-        : TypeOnceVisitor(/* skipBoundTypes */ true)
+        : TypeOnceVisitor("FindUserTypeFunctionBlockers", /* skipBoundTypes */ true)
         , ctx(ctx)
     {
     }

Ast/src/Parser.cpp

@@ -18,7 +18,6 @@ LUAU_FASTINTVARIABLE(LuauParseErrorLimit, 100)
 // flag so that we don't break production games by reverting syntax changes.
 // See docs/SyntaxChanges.md for an explanation.
 LUAU_FASTFLAGVARIABLE(LuauSolverV2)
-LUAU_FASTFLAGVARIABLE(LuauDeclareExternType)
 LUAU_FASTFLAGVARIABLE(LuauParseStringIndexer)
 LUAU_FASTFLAGVARIABLE(LuauParseAttributeFixUninit)
 LUAU_DYNAMIC_FASTFLAGVARIABLE(DebugLuauReportReturnTypeVariadicWithTypeSuffix, false)
@@ -1249,49 +1248,45 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
             retTypes
         );
     }
-    else if (AstName(lexer.current().name) == "class" || (FFlag::LuauDeclareExternType && AstName(lexer.current().name) == "extern"))
+    else if (AstName(lexer.current().name) == "class" || AstName(lexer.current().name) == "extern")
     {
         bool foundExtern = false;
-        if (FFlag::LuauDeclareExternType)
+        if (AstName(lexer.current().name) == "extern")
         {
-            if (AstName(lexer.current().name) == "extern")
+            foundExtern = true;
-            {
+            nextLexeme();
-                foundExtern = true;
+            if (AstName(lexer.current().name) != "type")
-                nextLexeme();
+                return reportStatError(
-                if (AstName(lexer.current().name) != "type")
+                    lexer.current().location, {}, {}, "Expected `type` keyword after `extern`, but got %s instead", lexer.current().name
-                    return reportStatError(
-                        lexer.current().location, {}, {}, "Expected `type` keyword after `extern`, but got %s instead", lexer.current().name
                     );
             }
-        }
+
 
         nextLexeme();
 
         Location classStart = lexer.current().location;
-        Name className = parseName(FFlag::LuauDeclareExternType ? "type name" : "class name");
+        Name className = parseName("type name");
         std::optional<AstName> superName = std::nullopt;
 
         if (AstName(lexer.current().name) == "extends")
         {
             nextLexeme();
-            superName = parseName(FFlag::LuauDeclareExternType ? "supertype name" : "superclass name").name;
+            superName = parseName("supertype name").name;
         }
 
-        if (FFlag::LuauDeclareExternType)
+        if (foundExtern)
         {
-            if (foundExtern)
+            if (AstName(lexer.current().name) != "with")
-            {
+                report(
-                if (AstName(lexer.current().name) != "with")
+                    lexer.current().location,
-                    report(
+                    "Expected `with` keyword before listing properties of the external type, but got %s instead",
-                        lexer.current().location,
+                    lexer.current().name
-                        "Expected `with` keyword before listing properties of the external type, but got %s instead",
+                );
-                        lexer.current().name
+            else
-                    );
+                nextLexeme();
-                else
-                    nextLexeme();
-            }
         }
 
+
         TempVector<AstDeclaredExternTypeProperty> props(scratchDeclaredClassProps);
         AstTableIndexer* indexer = nullptr;
 
@@ -1357,10 +1352,7 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                         AstTableIndexer* badIndexer = parseTableIndexer(AstTableAccess::ReadWrite, std::nullopt, begin).node;
 
                         // we lose all additional indexer expressions from the AST after error recovery here
-                        if (FFlag::LuauDeclareExternType)
+                        report(badIndexer->location, "Cannot have more than one indexer on an extern type");
-                            report(badIndexer->location, "Cannot have more than one indexer on an extern type");
-                        else
-                            report(badIndexer->location, "Cannot have more than one class indexer");
                     }
                     else
                     {
@@ -1427,10 +1419,7 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
                         AstTableIndexer* badIndexer = parseTableIndexer(AstTableAccess::ReadWrite, std::nullopt, lexer.current()).node;
 
                         // we lose all additional indexer expressions from the AST after error recovery here
-                        if (FFlag::LuauDeclareExternType)
+                        report(badIndexer->location, "Cannot have more than one indexer on an extern type");
-                            report(badIndexer->location, "Cannot have more than one indexer on an extern type");
-                        else
-                            report(badIndexer->location, "Cannot have more than one class indexer");
                     }
                     else
                     {
@@ -1466,13 +1455,9 @@ AstStat* Parser::parseDeclaration(const Location& start, const AstArray<AstAttr*
         AstType* type = parseType(/* in declaration context */ true);
         return allocator.alloc<AstStatDeclareGlobal>(Location(start, type->location), globalName->name, globalName->location, type);
     }
-    else if (FFlag::LuauDeclareExternType)
-    {
-        return reportStatError(start, {}, {}, "declare must be followed by an identifier, 'function', or 'extern type'");
-    }
     else
     {
-        return reportStatError(start, {}, {}, "declare must be followed by an identifier, 'function', or 'class'");
+        return reportStatError(start, {}, {}, "declare must be followed by an identifier, 'function', or 'extern type'");
     }
 }
 

Common/include/Luau/ExperimentalFlags.h

@@ -12,13 +12,14 @@ inline bool isAnalysisFlagExperimental(const char* flag)
     // or critical bugs that are found after the code has been submitted. This list is intended _only_ for flags that affect
     // Luau's type checking. Flags that may change runtime behavior (e.g.: parser or VM flags) are not appropriate for this list.
     static const char* const kList[] = {
-        "LuauInstantiateInSubtyping",                   // requires some fixes to lua-apps code
+        "LuauInstantiateInSubtyping",                // requires some fixes to lua-apps code
-        "LuauFixIndexerSubtypingOrdering",              // requires some small fixes to lua-apps code since this fixes a false negative
+        "LuauFixIndexerSubtypingOrdering",           // requires some small fixes to lua-apps code since this fixes a false negative
-        "StudioReportLuauAny2",                         // takes telemetry data for usage of any types
+        "StudioReportLuauAny2",                      // takes telemetry data for usage of any types
-        "LuauTableCloneClonesType3",                    // requires fixes in lua-apps code, terrifyingly
+        "LuauTableCloneClonesType3",                 // requires fixes in lua-apps code, terrifyingly
-        "LuauNormalizationReorderFreeTypeIntersect",    // requires fixes in lua-apps code, also terrifyingly
+        "LuauNormalizationReorderFreeTypeIntersect", // requires fixes in lua-apps code, also terrifyingly
         "LuauSolverV2",
-        "UseNewLuauTypeSolverDefaultEnabled",           // This can change the default solver used in cli applications, so it also needs to be disabled. Will require fixes in lua-apps code
+        "UseNewLuauTypeSolverDefaultEnabled", // This can change the default solver used in cli applications, so it also needs to be disabled. Will
+                                              // require fixes in lua-apps code
         // makes sure we always have at least one entry
         nullptr,
     };

Compiler/src/Compiler.cpp

@@ -26,10 +26,8 @@ LUAU_FASTINTVARIABLE(LuauCompileInlineThreshold, 25)
 LUAU_FASTINTVARIABLE(LuauCompileInlineThresholdMaxBoost, 300)
 LUAU_FASTINTVARIABLE(LuauCompileInlineDepth, 5)
 
-LUAU_FASTFLAGVARIABLE(LuauCompileInlineNonConstInit)
 LUAU_FASTFLAGVARIABLE(LuauSeparateCompilerTypeInfo)
 
-LUAU_FASTFLAGVARIABLE(LuauCompileFixTypeFunctionSkip)
 
 namespace Luau
 {
@@ -696,10 +694,7 @@ struct Compiler
                 // if the argument is a local that isn't mutated, we will simply reuse the existing register
                 if (int reg = le ? getExprLocalReg(le) : -1; reg >= 0 && (!lv || !lv->written))
                 {
-                    if (FFlag::LuauCompileInlineNonConstInit)
+                    args.push_back({var, uint8_t(reg), {Constant::Type_Unknown}, kDefaultAllocPc, lv ? lv->init : nullptr});
-                        args.push_back({var, uint8_t(reg), {Constant::Type_Unknown}, kDefaultAllocPc, lv ? lv->init : nullptr});
-                    else
-                        args.push_back({var, uint8_t(reg), {Constant::Type_Unknown}, kDefaultAllocPc});
                 }
                 else
                 {
@@ -725,7 +720,7 @@ struct Compiler
             {
                 pushLocal(arg.local, arg.reg, arg.allocpc);
 
-                if (FFlag::LuauCompileInlineNonConstInit && arg.init)
+                if (arg.init)
                 {
                     if (Variable* lv = variables.find(arg.local))
                         lv->init = arg.init;
@@ -785,11 +780,8 @@ struct Compiler
             if (Constant* var = locstants.find(local))
                 var->type = Constant::Type_Unknown;
 
-            if (FFlag::LuauCompileInlineNonConstInit)
+            if (Variable* lv = variables.find(local))
-            {
+                lv->init = nullptr;
-                if (Variable* lv = variables.find(local))
-                    lv->init = nullptr;
-            }
         }
 
         foldConstants(constants, variables, locstants, builtinsFold, builtinsFoldLibraryK, options.libraryMemberConstantCb, func->body);
@@ -3956,7 +3948,7 @@ struct Compiler
 
         bool visit(AstStatTypeFunction* node) override
         {
-            return !FFlag::LuauCompileFixTypeFunctionSkip;
+            return false;
         }
     };
 

Compiler/src/CostModel.cpp

@@ -8,8 +8,6 @@
 
 #include <limits.h>
 
-LUAU_FASTFLAGVARIABLE(LuauCompileCostModelConstants)
-
 namespace Luau
 {
 namespace Compile
@@ -43,25 +41,6 @@ static uint64_t parallelMulSat(uint64_t a, int b)
     return r | (s - (s >> 7));
 }
 
-inline bool getNumber_DEPRECATED(AstExpr* node, double& result)
-{
-    // since constant model doesn't use constant folding atm, we perform the basic extraction that's sufficient to handle positive/negative literals
-    if (AstExprConstantNumber* ne = node->as<AstExprConstantNumber>())
-    {
-        result = ne->value;
-        return true;
-    }
-
-    if (AstExprUnary* ue = node->as<AstExprUnary>(); ue && ue->op == AstExprUnary::Minus)
-        if (AstExprConstantNumber* ne = ue->expr->as<AstExprConstantNumber>())
-        {
-            result = -ne->value;
-            return true;
-        }
-
-    return false;
-}
-
 struct Cost
 {
     static const uint64_t kLiteral = ~0ull;
@@ -132,7 +111,7 @@ struct CostVisitor : AstVisitor
 
     Cost model(AstExpr* node)
     {
-        if (FFlag::LuauCompileCostModelConstants && constants.contains(node))
+        if (constants.contains(node))
             return Cost(0, Cost::kLiteral);
 
         if (AstExprGroup* expr = node->as<AstExprGroup>())
@@ -280,17 +259,8 @@ struct CostVisitor : AstVisitor
         int tripCount = -1;
         double from, to, step = 1;
 
-        if (FFlag::LuauCompileCostModelConstants)
+        if (getNumber(node->from, from) && getNumber(node->to, to) && (!node->step || getNumber(node->step, step)))
-        {
+            tripCount = getTripCount(from, to, step);
-            if (getNumber(node->from, from) && getNumber(node->to, to) && (!node->step || getNumber(node->step, step)))
-                tripCount = getTripCount(from, to, step);
-        }
-        else
-        {
-            if (getNumber_DEPRECATED(node->from, from) && getNumber_DEPRECATED(node->to, to) &&
-                (!node->step || getNumber_DEPRECATED(node->step, step)))
-                tripCount = getTripCount(from, to, step);
-        }
 
         loop(node->body, 1, tripCount < 0 ? 3 : tripCount);
         return false;

Compiler/src/ValueTracking.cpp

@@ -3,8 +3,6 @@
 
 #include "Luau/Lexer.h"
 
-LUAU_FASTFLAG(LuauCompileInlineNonConstInit)
-
 namespace Luau
 {
 namespace Compile
@@ -85,11 +83,8 @@ struct ValueVisitor : AstVisitor
 
     bool visit(AstExprFunction* node) override
     {
-        if (FFlag::LuauCompileInlineNonConstInit)
+        for (AstLocal* arg : node->args)
-        {
+            variables[arg].init = nullptr;
-            for (AstLocal* arg : node->args)
-                variables[arg].init = nullptr;
-        }
 
         return true;
     }

VM/src/lapi.cpp

@@ -15,6 +15,8 @@
 
 #include <string.h>
 
+LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauSafeStackCheck, false)
+
 /*
  * This file contains most implementations of core Lua APIs from lua.h.
  *
@@ -139,7 +141,36 @@ int lua_checkstack(lua_State* L, int size)
         res = 0; // stack overflow
     else if (size > 0)
     {
-        luaD_checkstack(L, size);
+        if (DFFlag::LuauSafeStackCheck)
+        {
+            if (stacklimitreached(L, size))
+            {
+                struct CallContext
+                {
+                    int size;
+
+                    static void run(lua_State* L, void* ud)
+                    {
+                        CallContext* ctx = (CallContext*)ud;
+
+                        luaD_growstack(L, ctx->size);
+                    }
+                } ctx = {size};
+
+                // there could be no memory to extend the stack
+                if (luaD_rawrunprotected(L, &CallContext::run, &ctx) != LUA_OK)
+                    return 0;
+            }
+            else
+            {
+                condhardstacktests(luaD_reallocstack(L, L->stacksize - EXTRA_STACK, 0));
+            }
+        }
+        else
+        {
+            luaD_checkstack(L, size);
+        }
+
         expandstacklimit(L, L->top + size);
     }
     return res;

VM/src/ldo.cpp

@@ -17,6 +17,8 @@
 
 #include <string.h>
 
+LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauErrorYield, false)
+
 // keep max stack allocation request under 1GB
 #define MAX_STACK_SIZE (int(1024 / sizeof(TValue)) * 1024 * 1024)
 
@@ -249,6 +251,23 @@ void luaD_checkCstack(lua_State* L)
         luaD_throw(L, LUA_ERRERR); // error while handling stack error
 }
 
+static void performcall(lua_State* L, StkId func, int nresults)
+{
+    if (luau_precall(L, func, nresults) == PCRLUA)
+    {                                        // is a Lua function?
+        L->ci->flags |= LUA_CALLINFO_RETURN; // luau_execute will stop after returning from the stack frame
+
+        bool oldactive = L->isactive;
+        L->isactive = true;
+        luaC_threadbarrier(L);
+
+        luau_execute(L); // call it
+
+        if (!oldactive)
+            L->isactive = false;
+    }
+}
+
 /*
 ** Call a function (C or Lua). The function to be called is at *func.
 ** The arguments are on the stack, right after the function.
@@ -277,18 +296,25 @@ void luaD_call(lua_State* L, StkId func, int nresults)
     ptrdiff_t funcoffset = savestack(L, func);
     ptrdiff_t cioffset = saveci(L, L->ci);
 
-    if (luau_precall(L, func, nresults) == PCRLUA)
+    if (DFFlag::LuauErrorYield)
-    {                                        // is a Lua function?
+    {
-        L->ci->flags |= LUA_CALLINFO_RETURN; // luau_execute will stop after returning from the stack frame
+        performcall(L, func, nresults);
+    }
+    else
+    {
+        if (luau_precall(L, func, nresults) == PCRLUA)
+        {                                        // is a Lua function?
+            L->ci->flags |= LUA_CALLINFO_RETURN; // luau_execute will stop after returning from the stack frame
 
-        bool oldactive = L->isactive;
+            bool oldactive = L->isactive;
-        L->isactive = true;
+            L->isactive = true;
-        luaC_threadbarrier(L);
+            luaC_threadbarrier(L);
 
-        luau_execute(L); // call it
+            luau_execute(L); // call it
 
-        if (!oldactive)
+            if (!oldactive)
-            L->isactive = false;
+                L->isactive = false;
+        }
     }
 
     bool yielded = L->status == LUA_YIELD || L->status == LUA_BREAK;
@@ -314,6 +340,27 @@ void luaD_call(lua_State* L, StkId func, int nresults)
     luaC_checkGC(L);
 }
 
+// Non-yieldable version of luaD_call, used primarily to call an error handler which cannot yield
+void luaD_callny(lua_State* L, StkId func, int nresults)
+{
+    if (++L->nCcalls >= LUAI_MAXCCALLS)
+        luaD_checkCstack(L);
+
+    LUAU_ASSERT(L->nCcalls > L->baseCcalls);
+
+    ptrdiff_t funcoffset = savestack(L, func);
+
+    performcall(L, func, nresults);
+
+    LUAU_ASSERT(L->status != LUA_YIELD && L->status != LUA_BREAK);
+
+    if (nresults != LUA_MULTRET)
+        L->top = restorestack(L, funcoffset) + nresults;
+
+    L->nCcalls--;
+    luaC_checkGC(L);
+}
+
 static void seterrorobj(lua_State* L, int errcode, StkId oldtop)
 {
     switch (errcode)
@@ -595,7 +642,11 @@ static void callerrfunc(lua_State* L, void* ud)
     setobj2s(L, L->top, L->top - 1);
     setobj2s(L, L->top - 1, errfunc);
     incr_top(L);
-    luaD_call(L, L->top - 2, 1);
+
+    if (DFFlag::LuauErrorYield)
+        luaD_callny(L, L->top - 2, 1);
+    else
+        luaD_call(L, L->top - 2, 1);
 }
 
 static void restore_stack_limit(lua_State* L)

VM/src/ldo.h

@@ -10,15 +10,16 @@
 // returns target stack for 'n' extra elements to reallocate
 // if possible, stack size growth factor is 2x
 #define getgrownstacksize(L, n) ((n) <= L->stacksize ? 2 * L->stacksize : L->stacksize + (n))
+#define stacklimitreached(L, n) ((char*)L->stack_last - (char*)L->top <= (n) * (int)sizeof(TValue))
 
 #define luaD_checkstackfornewci(L, n) \
-    if ((char*)L->stack_last - (char*)L->top <= (n) * (int)sizeof(TValue)) \
+    if (stacklimitreached(L, (n))) \
         luaD_reallocstack(L, getgrownstacksize(L, (n)), 1); \
     else \
         condhardstacktests(luaD_reallocstack(L, L->stacksize - EXTRA_STACK, 1));
 
 #define luaD_checkstack(L, n) \
-    if ((char*)L->stack_last - (char*)L->top <= (n) * (int)sizeof(TValue)) \
+    if (stacklimitreached(L, (n))) \
         luaD_growstack(L, n); \
     else \
         condhardstacktests(luaD_reallocstack(L, L->stacksize - EXTRA_STACK, 0));
@@ -55,6 +56,7 @@ typedef void (*Pfunc)(lua_State* L, void* ud);
 LUAI_FUNC CallInfo* luaD_growCI(lua_State* L);
 
 LUAI_FUNC void luaD_call(lua_State* L, StkId func, int nresults);
+LUAI_FUNC void luaD_callny(lua_State* L, StkId func, int nresults);
 LUAI_FUNC int luaD_pcall(lua_State* L, Pfunc func, void* u, ptrdiff_t oldtop, ptrdiff_t ef);
 LUAI_FUNC void luaD_reallocCI(lua_State* L, int newsize);
 LUAI_FUNC void luaD_reallocstack(lua_State* L, int newsize, int fornewci);

VM/src/lgcdebug.cpp

@@ -14,6 +14,8 @@
 #include <string.h>
 #include <stdio.h>
 
+LUAU_FASTFLAGVARIABLE(LuauHeapDumpStringSizeOverhead)
+
 static void validateobjref(global_State* g, GCObject* f, GCObject* t)
 {
     LUAU_ASSERT(!isdead(g, t));
@@ -651,7 +653,10 @@ static void enumedges(EnumContext* ctx, GCObject* from, TValue* data, size_t siz
 
 static void enumstring(EnumContext* ctx, TString* ts)
 {
-    enumnode(ctx, obj2gco(ts), ts->len, NULL);
+    if (FFlag::LuauHeapDumpStringSizeOverhead)
+        enumnode(ctx, obj2gco(ts), sizestring(ts->len), NULL);
+    else
+        enumnode(ctx, obj2gco(ts), ts->len, NULL);
 }
 
 static void enumtable(EnumContext* ctx, LuaTable* h)

fuzz/protoprint.cpp

@@ -2,28 +2,200 @@
 #include "luau.pb.h"
 
 static const std::string kNames[] = {
-    "_G",           "_VERSION",   "__add",      "__call",         "__concat",    "__div",        "__eq",      "__idiv",     "__index",
+    "_G",
-    "__iter",       "__le",       "__len",      "__lt",           "__mod",       "__mode",       "__mul",     "__namecall", "__newindex",
+    "_VERSION",
-    "__pow",        "__sub",      "__type",     "__unm",          "abs",         "acos",         "arshift",   "asin",       "assert",
+    "__add",
-    "atan",         "atan2",      "band",       "bit32",          "bnot",        "boolean",      "bor",       "btest",      "buffer",
+    "__call",
-    "bxor",         "byte",       "ceil",       "char",           "charpattern", "clamp",        "clear",     "clock",      "clone",
+    "__concat",
-    "close",        "codepoint",  "codes",      "collectgarbage", "concat",      "copy",         "coroutine", "cos",        "cosh",
+    "__div",
-    "countlz",      "countrz",    "create",     "date",           "debug",       "deg",          "difftime",  "error",      "exp",
+    "__eq",
-    "extract",      "fill",       "find",       "floor",          "fmod",        "foreach",      "foreachi",  "format",     "freeze",
+    "__idiv",
-    "frexp",        "fromstring", "function",   "gcinfo",         "getfenv",     "getmetatable", "getn",      "gmatch",     "gsub",
+    "__index",
-    "huge",         "info",       "insert",     "ipairs",         "isfrozen",    "isyieldable",  "ldexp",     "len",        "loadstring",
+    "__iter",
-    "log",          "log10",      "lower",      "lrotate",        "lshift",      "match",        "math",      "max",        "maxn",
+    "__le",
-    "min",          "modf",       "move",       "newproxy",       "next",        "nil",          "noise",     "number",     "offset",
+    "__len",
-    "os",           "pack",       "packsize",   "pairs",          "pcall",       "pi",           "pow",       "print",      "rad",
+    "__lt",
-    "random",       "randomseed", "rawequal",   "rawget",         "rawlen",      "rawset",       "readf32",   "readf64",    "readi16",
+    "__mod",
-    "readi32",      "readi8",     "readstring", "readu16",        "readu32",     "readu8",       "remove",    "rep",        "replace",
+    "__mode",
-    "require",      "resume",     "reverse",    "round",          "rrotate",     "rshift",       "running",   "select",     "setfenv",
+    "__mul",
-    "setmetatable", "sign",       "sin",        "sinh",           "sort",        "split",        "sqrt",      "status",     "string",
+    "__namecall",
-    "sub",          "table",      "tan",        "tanh",           "thread",      "time",         "tonumber",  "tostring",   "tostring",
+    "__newindex",
-    "traceback",    "type",       "typeof",     "unpack",         "upper",       "userdata",     "utf8",      "vector",     "wrap",
+    "__pow",
-    "writef32",     "writef64",   "writei16",   "writei32",       "writei8",     "writestring",  "writeu16",  "writeu32",   "writeu8",
+    "__sub",
-    "xpcall",       "yield",      "types",      "unknown",        "never",       "any",          "singleton", "optional",   "generic",
+    "__type",
-    "negationof",   "unionof",    "intersectionof", "newtable",   "newfunction",
+    "__unm",
+    "abs",
+    "acos",
+    "arshift",
+    "asin",
+    "assert",
+    "atan",
+    "atan2",
+    "band",
+    "bit32",
+    "bnot",
+    "boolean",
+    "bor",
+    "btest",
+    "buffer",
+    "bxor",
+    "byte",
+    "ceil",
+    "char",
+    "charpattern",
+    "clamp",
+    "clear",
+    "clock",
+    "clone",
+    "close",
+    "codepoint",
+    "codes",
+    "collectgarbage",
+    "concat",
+    "copy",
+    "coroutine",
+    "cos",
+    "cosh",
+    "countlz",
+    "countrz",
+    "create",
+    "date",
+    "debug",
+    "deg",
+    "difftime",
+    "error",
+    "exp",
+    "extract",
+    "fill",
+    "find",
+    "floor",
+    "fmod",
+    "foreach",
+    "foreachi",
+    "format",
+    "freeze",
+    "frexp",
+    "fromstring",
+    "function",
+    "gcinfo",
+    "getfenv",
+    "getmetatable",
+    "getn",
+    "gmatch",
+    "gsub",
+    "huge",
+    "info",
+    "insert",
+    "ipairs",
+    "isfrozen",
+    "isyieldable",
+    "ldexp",
+    "len",
+    "loadstring",
+    "log",
+    "log10",
+    "lower",
+    "lrotate",
+    "lshift",
+    "match",
+    "math",
+    "max",
+    "maxn",
+    "min",
+    "modf",
+    "move",
+    "newproxy",
+    "next",
+    "nil",
+    "noise",
+    "number",
+    "offset",
+    "os",
+    "pack",
+    "packsize",
+    "pairs",
+    "pcall",
+    "pi",
+    "pow",
+    "print",
+    "rad",
+    "random",
+    "randomseed",
+    "rawequal",
+    "rawget",
+    "rawlen",
+    "rawset",
+    "readf32",
+    "readf64",
+    "readi16",
+    "readi32",
+    "readi8",
+    "readstring",
+    "readu16",
+    "readu32",
+    "readu8",
+    "remove",
+    "rep",
+    "replace",
+    "require",
+    "resume",
+    "reverse",
+    "round",
+    "rrotate",
+    "rshift",
+    "running",
+    "select",
+    "setfenv",
+    "setmetatable",
+    "sign",
+    "sin",
+    "sinh",
+    "sort",
+    "split",
+    "sqrt",
+    "status",
+    "string",
+    "sub",
+    "table",
+    "tan",
+    "tanh",
+    "thread",
+    "time",
+    "tonumber",
+    "tostring",
+    "tostring",
+    "traceback",
+    "type",
+    "typeof",
+    "unpack",
+    "upper",
+    "userdata",
+    "utf8",
+    "vector",
+    "wrap",
+    "writef32",
+    "writef64",
+    "writei16",
+    "writei32",
+    "writei8",
+    "writestring",
+    "writeu16",
+    "writeu32",
+    "writeu8",
+    "xpcall",
+    "yield",
+    "types",
+    "unknown",
+    "never",
+    "any",
+    "singleton",
+    "optional",
+    "generic",
+    "negationof",
+    "unionof",
+    "intersectionof",
+    "newtable",
+    "newfunction",
 };
 
 static const std::string kTypes[] = {
@@ -46,25 +218,8 @@ static const std::string kExternTypes[] = {
 };
 
 static const std::string kBuiltinTypes[] = {
-    "len",
+    "len", "unm", "add", "sub",   "mul",      "div",   "idiv",   "pow",          "mod",          "concat",
-    "unm",
+    "lt",  "le",  "eq",  "keyof", "rawkeyof", "index", "rawget", "setmetatable", "getmetatable",
-    "add",
-    "sub",
-    "mul",
-    "div",
-    "idiv",
-    "pow",
-    "mod",
-    "concat",
-    "lt",
-    "le",
-    "eq",
-    "keyof",
-    "rawkeyof",
-    "index",
-    "rawget",
-    "setmetatable",
-    "getmetatable",
 };
 
 struct ProtoToLuau

tests/ClassFixture.cpp

@@ -12,7 +12,6 @@ namespace Luau
 ExternTypeFixture::ExternTypeFixture(bool prepareAutocomplete)
     : BuiltinsFixture(prepareAutocomplete)
 {
-
 }
 
 Frontend& ExternTypeFixture::getFrontend()
@@ -37,7 +36,8 @@ Frontend& ExternTypeFixture::getFrontend()
     };
 
     getMutable<ExternType>(connectionType)->props = {
-        {"Connect", {makeFunction(arena, connectionType, {makeFunction(arena, nullopt, {baseClassInstanceType}, {})}, {})}}};
+        {"Connect", {makeFunction(arena, connectionType, {makeFunction(arena, nullopt, {baseClassInstanceType}, {})}, {})}}
+    };
 
     TypeId baseClassType = arena.addType(ExternType{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test", {}});
     getMutable<ExternType>(baseClassType)->props = {
@@ -114,7 +114,8 @@ Frontend& ExternTypeFixture::getFrontend()
          {arena.addType(IntersectionType{{
              makeFunction(arena, vector2InstanceType, {vector2InstanceType}, {vector2InstanceType}),
              makeFunction(arena, vector2InstanceType, {getBuiltins()->numberType}, {vector2InstanceType}),
-         }})}}};
+         }})}}
+    };
     globals.globalScope->exportedTypeBindings["Vector2"] = TypeFun{{}, vector2InstanceType};
     addGlobalBinding(globals, "Vector2", vector2Type, "@test");
 

tests/Compiler.test.cpp

@@ -17,15 +17,12 @@ namespace Luau
 std::string rep(const std::string& s, size_t n);
 }
 
-LUAU_FASTFLAG(LuauCompileInlineNonConstInit)
 LUAU_FASTINT(LuauCompileInlineDepth)
 LUAU_FASTINT(LuauCompileInlineThreshold)
 LUAU_FASTINT(LuauCompileInlineThresholdMaxBoost)
 LUAU_FASTINT(LuauCompileLoopUnrollThreshold)
 LUAU_FASTINT(LuauCompileLoopUnrollThresholdMaxBoost)
 LUAU_FASTINT(LuauRecursionLimit)
-LUAU_FASTFLAG(LuauCompileFixTypeFunctionSkip)
-LUAU_FASTFLAG(LuauCompileCostModelConstants)
 
 using namespace Luau;
 
@@ -2990,8 +2987,6 @@ TEST_CASE("TypeFunction")
 
 TEST_CASE("NoTypeFunctionsInBytecode")
 {
-    ScopedFastFlag luauCompileFixTypeFunctionSkip{FFlag::LuauCompileFixTypeFunctionSkip, true};
-
     Luau::BytecodeBuilder bcb;
     bcb.setDumpFlags(Luau::BytecodeBuilder::Dump_Code);
     Luau::compileOrThrow(bcb, R"(
@@ -3616,8 +3611,6 @@ RETURN R4 1
 
 TEST_CASE("CostModelRemarks")
 {
-    ScopedFastFlag luauCompileCostModelConstants{FFlag::LuauCompileCostModelConstants, true};
-
     CHECK_EQ(
         compileWithRemarks(R"(
 local a, b = ...
@@ -7624,8 +7617,6 @@ RETURN R1 1
 
 TEST_CASE("InlineNonConstInitializers")
 {
-    ScopedFastFlag luauCompileInlineNonConstInit{FFlag::LuauCompileInlineNonConstInit, true};
-
     CHECK_EQ(
         "\n" + compileFunction(
                    R"(
@@ -7655,8 +7646,6 @@ RETURN R0 0
 
 TEST_CASE("InlineNonConstInitializers2")
 {
-    ScopedFastFlag luauCompileInlineNonConstInit{FFlag::LuauCompileInlineNonConstInit, true};
-
     CHECK_EQ(
         "\n" + compileFunction(
                    R"(

tests/Conformance.test.cpp

@@ -34,9 +34,13 @@ void luaC_validate(lua_State* L);
 // internal functions, declared in lvm.h - not exposed via lua.h
 void luau_callhook(lua_State* L, lua_Hook hook, void* userdata);
 
+LUAU_FASTFLAG(LuauHeapDumpStringSizeOverhead)
 LUAU_FASTFLAG(DebugLuauAbortingChecks)
 LUAU_FASTINT(CodegenHeuristicsInstructionLimit)
 LUAU_FASTFLAG(LuauRemoveTypeCallsForReadWriteProps)
+LUAU_DYNAMIC_FASTFLAG(LuauErrorYield)
+LUAU_DYNAMIC_FASTFLAG(LuauSafeStackCheck)
+
 
 static lua_CompileOptions defaultOptions()
 {
@@ -754,6 +758,8 @@ TEST_CASE("Closure")
 
 TEST_CASE("Calls")
 {
+    ScopedFastFlag luauSafeStackCheck{DFFlag::LuauSafeStackCheck, true};
+
     runConformance("calls.luau");
 }
 
@@ -816,6 +822,8 @@ TEST_CASE("UTF8")
 
 TEST_CASE("Coroutine")
 {
+    ScopedFastFlag luauErrorYield{DFFlag::LuauErrorYield, true};
+
     runConformance("coroutine.luau");
 }
 
@@ -2094,13 +2102,33 @@ int slowlyOverflowStack(lua_State* L)
 
 TEST_CASE("ApiStack")
 {
-    StateRef globalState(luaL_newstate(), lua_close);
+    ScopedFastFlag luauSafeStackCheck{DFFlag::LuauSafeStackCheck, true};
-    lua_State* L = globalState.get();
 
-    lua_pushcfunction(L, slowlyOverflowStack, "foo");
+    StateRef globalState(lua_newstate(blockableRealloc, nullptr), lua_close);
-    int result = lua_pcall(L, 0, 0, 0);
+    lua_State* GL = globalState.get();
-    REQUIRE(result == LUA_ERRRUN);
+
-    CHECK(strcmp(luaL_checkstring(L, -1), "stack overflow (test)") == 0);
+    {
+        lua_State* L = lua_newthread(GL);
+
+        lua_pushcfunction(L, slowlyOverflowStack, "foo");
+        int result = lua_pcall(L, 0, 0, 0);
+        REQUIRE(result == LUA_ERRRUN);
+        CHECK(strcmp(luaL_checkstring(L, -1), "stack overflow (test)") == 0);
+    }
+
+    {
+        lua_State* L = lua_newthread(GL);
+
+        REQUIRE(lua_checkstack(L, 100) == 1);
+
+        blockableReallocAllowed = false;
+        REQUIRE(lua_checkstack(L, 1000) == 0);
+        blockableReallocAllowed = true;
+
+        REQUIRE(lua_checkstack(L, 1000) == 1);
+
+        REQUIRE(lua_checkstack(L, LUAI_MAXCSTACK * 2) == 0);
+    }
 }
 
 TEST_CASE("ApiAlloc")
@@ -2315,6 +2343,8 @@ TEST_CASE("StringConversion")
 
 TEST_CASE("GCDump")
 {
+    ScopedFastFlag luauHeapDumpStringSizeOverhead{FFlag::LuauHeapDumpStringSizeOverhead, true};
+
     // internal function, declared in lgc.h - not exposed via lua.h
     extern void luaC_dump(lua_State * L, void* file, const char* (*categoryName)(lua_State* L, uint8_t memcat));
     extern void luaC_enumheap(
@@ -2362,14 +2392,15 @@ local function f()
     x[1] = math.abs(42)
 end
 function foo()
-    coroutine.yield()
+    x[2] = ''
+    for i = 1, 10000 do x[2] ..= '1234567890' end
 end
 foo()
 return f
 )");
     lua_pushstring(CL, "=GCDump");
-    lua_loadstring(CL);
+    REQUIRE(lua_loadstring(CL) == 1);
-    lua_resume(CL, nullptr, 0);
+    REQUIRE(lua_resume(CL, nullptr, 0) == LUA_OK);
 
 #ifdef _WIN32
     const char* path = "NUL";
@@ -2380,6 +2411,7 @@ return f
     FILE* f = fopen(path, "w");
     REQUIRE(f);
 
+    luaC_fullgc(L);
     luaC_dump(L, f, nullptr);
 
     fclose(f);
@@ -2395,14 +2427,10 @@ return f
 
     struct EnumContext
     {
-        EnumContext()
+        Luau::DenseHashMap<void*, Node> nodes{nullptr};
-            : nodes{nullptr}
+        Luau::DenseHashMap<void*, void*> edges{nullptr};
-            , edges{nullptr}
-        {
-        }
 
-        Luau::DenseHashMap<void*, Node> nodes;
+        bool seenTargetString = false;
-        Luau::DenseHashMap<void*, void*> edges;
     } ctx;
 
     luaC_enumheap(
@@ -2425,6 +2453,14 @@ return f
                 else if (tt == LUA_TTHREAD)
                     CHECK(sv == "thread at unnamed:1 =GCDump");
             }
+            else if (tt == LUA_TSTRING && size >= 100000)
+            {
+                CHECK(!context.seenTargetString);
+                context.seenTargetString = true;
+
+                // The only string we have in this test that is 100000 characters long should include string data overhead
+                CHECK(size > 100000);
+            }
 
             context.nodes[gco] = {gco, tt, memcat, size, name ? name : ""};
         },
@@ -2437,6 +2473,7 @@ return f
 
     CHECK(!ctx.nodes.empty());
     CHECK(!ctx.edges.empty());
+    CHECK(ctx.seenTargetString);
 }
 
 TEST_CASE("Interrupt")
@@ -3296,6 +3333,7 @@ TEST_CASE("HugeFunctionLoadFailure")
     REQUIRE_EQ(largeAllocationToFail, expectedTotalLargeAllocations);
 }
 
+
 TEST_CASE("IrInstructionLimit")
 {
     if (!codegen || !luau_codegen_supported())

tests/ConstraintGeneratorFixture.cpp

@@ -61,7 +61,8 @@ void ConstraintGeneratorFixture::solve(const std::string& code)
         {},
         &logger,
         NotNull{dfg.get()},
-        {}};
+        {}
+    };
 
     cs.run();
 }

tests/CostModel.test.cpp

@@ -5,8 +5,6 @@
 
 #include "doctest.h"
 
-LUAU_FASTFLAG(LuauCompileCostModelConstants)
-
 using namespace Luau;
 
 namespace Luau
@@ -133,37 +131,6 @@ end
     CHECK_EQ(5, Luau::Compile::computeCost(model, args2, 1));
 }
 
-TEST_CASE("ControlFlow")
-{
-    ScopedFastFlag luauCompileCostModelConstants{FFlag::LuauCompileCostModelConstants, false};
-
-    uint64_t model = modelFunction(R"(
-function test(a)
-    while a < 0 do
-        a += 1
-    end
-    for i=10,1,-1 do
-        a += 1
-    end
-    for i in pairs({}) do
-        a += 1
-        if a % 2 == 0 then continue end
-    end
-    repeat
-        a += 1
-        if a % 2 == 0 then break end
-    until a > 10
-    return a
-end
-)");
-
-    const bool args1[] = {false};
-    const bool args2[] = {true};
-
-    CHECK_EQ(76, Luau::Compile::computeCost(model, args1, 1));
-    CHECK_EQ(73, Luau::Compile::computeCost(model, args2, 1));
-}
-
 TEST_CASE("Conditional")
 {
     uint64_t model = modelFunction(R"(

tests/EqSatSimplification.test.cpp

@@ -135,7 +135,9 @@ TEST_CASE_FIXTURE(ESFixture, "string | never")
 
 TEST_CASE_FIXTURE(ESFixture, "string | never | number")
 {
-    CHECK("number | string" == simplifyStr(arena->addType(UnionType{{getBuiltins()->stringType, getBuiltins()->neverType, getBuiltins()->numberType}})));
+    CHECK(
+        "number | string" == simplifyStr(arena->addType(UnionType{{getBuiltins()->stringType, getBuiltins()->neverType, getBuiltins()->numberType}}))
+    );
 }
 
 TEST_CASE_FIXTURE(ESFixture, "string & string")
@@ -161,9 +163,9 @@ TEST_CASE_FIXTURE(ESFixture, "never & string")
 TEST_CASE_FIXTURE(ESFixture, "string & (unknown | never)")
 {
     CHECK(
-        "string" == simplifyStr(arena->addType(
+        "string" == simplifyStr(arena->addType(IntersectionType{
-                        IntersectionType{{getBuiltins()->stringType, arena->addType(UnionType{{getBuiltins()->unknownType, getBuiltins()->neverType}})}}
+                        {getBuiltins()->stringType, arena->addType(UnionType{{getBuiltins()->unknownType, getBuiltins()->neverType}})}
-                    ))
+                    }))
     );
 }
 
@@ -386,7 +388,8 @@ TEST_CASE_FIXTURE(ESFixture, "union<number, number>")
 {
     CHECK(
         "number" ==
-        simplifyStr(arena->addType(TypeFunctionInstanceType{builtinTypeFunctions().unionFunc, {getBuiltins()->numberType, getBuiltins()->numberType}}))
+        simplifyStr(arena->addType(TypeFunctionInstanceType{builtinTypeFunctions().unionFunc, {getBuiltins()->numberType, getBuiltins()->numberType}})
+        )
     );
 }
 
@@ -418,9 +421,9 @@ TEST_CASE_FIXTURE(ESFixture, "blocked & ~number & function")
 
 TEST_CASE_FIXTURE(ESFixture, "(number | boolean | string | nil | table) & (false | nil)")
 {
-    const TypeId t1 = arena->addType(
+    const TypeId t1 = arena->addType(UnionType{
-        UnionType{{getBuiltins()->numberType, getBuiltins()->booleanType, getBuiltins()->stringType, getBuiltins()->nilType, getBuiltins()->tableType}}
+        {getBuiltins()->numberType, getBuiltins()->booleanType, getBuiltins()->stringType, getBuiltins()->nilType, getBuiltins()->tableType}
-    );
+    });
 
     CHECK("false?" == simplifyStr(arena->addType(IntersectionType{{t1, getBuiltins()->falsyType}})));
 }
@@ -689,7 +692,8 @@ TEST_CASE_FIXTURE(ESFixture, "lt<number, _> == boolean")
 TEST_CASE_FIXTURE(ESFixture, "unknown & ~string")
 {
     CHECK_EQ(
-        "~string", simplifyStr(arena->addType(IntersectionType{{getBuiltins()->unknownType, arena->addType(NegationType{getBuiltins()->stringType})}}))
+        "~string",
+        simplifyStr(arena->addType(IntersectionType{{getBuiltins()->unknownType, arena->addType(NegationType{getBuiltins()->stringType})}}))
     );
 }
 

tests/Fixture.cpp

@@ -696,9 +696,10 @@ Frontend& Fixture::getFrontend()
         &fileResolver,
         &configResolver,
         FrontendOptions{
-            /* retainFullTypeGraphs= */ true, /* forAutocomplete */ false, /* runLintChecks */ false, /* randomConstraintResolutionSeed */ randomSeed}
+            /* retainFullTypeGraphs= */ true, /* forAutocomplete */ false, /* runLintChecks */ false, /* randomConstraintResolutionSeed */ randomSeed
+        }
     );
-    
+
     builtinTypes = f.builtinTypes;
     // Fixture::Fixture begins here
     configResolver.defaultConfig.mode = Mode::Strict;
@@ -732,7 +733,6 @@ Frontend& Fixture::getFrontend()
 BuiltinsFixture::BuiltinsFixture(bool prepareAutocomplete)
     : Fixture(prepareAutocomplete)
 {
-   
 }
 
 Frontend& BuiltinsFixture::getFrontend()

tests/Fixture.h

@@ -165,7 +165,7 @@ struct Fixture
     NullModuleResolver moduleResolver;
     std::unique_ptr<SourceModule> sourceModule;
     InternalErrorReporter ice;
-    
+
 
     std::string decorateWithTypes(const std::string& code);
 
@@ -185,8 +185,10 @@ struct Fixture
     // TODO: test theory about dynamic dispatch
     NotNull<BuiltinTypes> getBuiltins();
     virtual Frontend& getFrontend();
+
 private:
     bool hasDumpedErrors = false;
+
 protected:
     bool forAutocomplete = false;
     std::optional<Frontend> frontend;

tests/FragmentAutocomplete.test.cpp

@@ -162,7 +162,7 @@ struct FragmentAutocompleteFixtureImpl : BaseType
         Position cursorPos,
         std::function<void(FragmentAutocompleteStatusResult& result)> assertions,
         std::optional<Position> fragmentEndPosition = std::nullopt
-        )
+    )
     {
         ScopedFastFlag sff{FFlag::LuauSolverV2, true};
         this->getFrontend().setLuauSolverSelectionFromWorkspace(SolverMode::New);
@@ -179,7 +179,7 @@ struct FragmentAutocompleteFixtureImpl : BaseType
         Position cursorPos,
         std::function<void(FragmentAutocompleteStatusResult& result)> assertions,
         std::optional<Position> fragmentEndPosition = std::nullopt
-        )
+    )
     {
         ScopedFastFlag sff{FFlag::LuauSolverV2, false};
         this->getFrontend().setLuauSolverSelectionFromWorkspace(SolverMode::Old);
@@ -238,7 +238,7 @@ struct FragmentAutocompleteFixtureImpl : BaseType
         ParseResult parseResult = parseHelper(document);
         FrontendOptions options;
         FragmentContext context{document, parseResult, options, fragmentEndPosition};
-        return Luau::tryFragmentAutocomplete(this->getFrontend(). module, cursorPos, context, nullCallback);
+        return Luau::tryFragmentAutocomplete(this->getFrontend().module, cursorPos, context, nullCallback);
     }
 
     SourceModule& getSource()
@@ -3792,11 +3792,17 @@ if result.type == "ok" then
     result.
 end
 )";
-    autocompleteFragmentInOldSolver(source, dest, Position{8, 11}, [](auto& result){
+    autocompleteFragmentInOldSolver(
-        REQUIRE(result.result);
+        source,
-        CHECK_EQ(result.result->acResults.entryMap.count("type"), 1);
+        dest,
-        CHECK_EQ(result.result->acResults.entryMap.count("value"), 1);
+        Position{8, 11},
-    });
+        [](auto& result)
+        {
+            REQUIRE(result.result);
+            CHECK_EQ(result.result->acResults.entryMap.count("type"), 1);
+            CHECK_EQ(result.result->acResults.entryMap.count("value"), 1);
+        }
+    );
 }
 
 TEST_CASE_FIXTURE(FragmentAutocompleteFixture, "tagged_union_completion_second_branch_of_union_old_solver")
@@ -3825,11 +3831,17 @@ if result.type == "err" then
 end
 )";
 
-    autocompleteFragmentInOldSolver(source, dest, Position{8, 11}, [](auto& result){
+    autocompleteFragmentInOldSolver(
-        REQUIRE(result.result);
+        source,
-        CHECK_EQ(result.result->acResults.entryMap.count("type"), 1);
+        dest,
-        CHECK_EQ(result.result->acResults.entryMap.count("error"), 1);
+        Position{8, 11},
-    });
+        [](auto& result)
+        {
+            REQUIRE(result.result);
+            CHECK_EQ(result.result->acResults.entryMap.count("type"), 1);
+            CHECK_EQ(result.result->acResults.entryMap.count("error"), 1);
+        }
+    );
 }
 
 TEST_CASE_FIXTURE(FragmentAutocompleteFixture, "tagged_union_completion_first_branch_of_union_new_solver")
@@ -3858,11 +3870,17 @@ if result.type == "ok" then
     result.
 end
 )";
-    autocompleteFragmentInNewSolver(source, dest, Position{8, 11}, [](auto& result){
+    autocompleteFragmentInNewSolver(
-        REQUIRE(result.result);
+        source,
-        CHECK_EQ(result.result->acResults.entryMap.count("type"), 1);
+        dest,
-        CHECK_EQ(result.result->acResults.entryMap.count("value"), 1);
+        Position{8, 11},
-    });
+        [](auto& result)
+        {
+            REQUIRE(result.result);
+            CHECK_EQ(result.result->acResults.entryMap.count("type"), 1);
+            CHECK_EQ(result.result->acResults.entryMap.count("value"), 1);
+        }
+    );
 }
 
 TEST_CASE_FIXTURE(FragmentAutocompleteFixture, "tagged_union_completion_second_branch_of_union_new_solver")
@@ -3891,11 +3909,17 @@ if result.type == "err" then
 end
 )";
 
-    autocompleteFragmentInNewSolver(source, dest, Position{8, 11}, [](auto& result){
+    autocompleteFragmentInNewSolver(
-        REQUIRE(result.result);
+        source,
-        CHECK_EQ(result.result->acResults.entryMap.count("type"), 1);
+        dest,
-        CHECK_EQ(result.result->acResults.entryMap.count("error"), 1);
+        Position{8, 11},
-    });
+        [](auto& result)
+        {
+            REQUIRE(result.result);
+            CHECK_EQ(result.result->acResults.entryMap.count("type"), 1);
+            CHECK_EQ(result.result->acResults.entryMap.count("error"), 1);
+        }
+    );
 }
 
 TEST_CASE_FIXTURE(FragmentAutocompleteBuiltinsFixture, "inline_prop_read_on_requires_provides_results")

tests/Frontend.test.cpp

@@ -623,7 +623,8 @@ TEST_CASE_FIXTURE(FrontendFixture, "produce_errors_for_unchanged_file_with_error
 
     getFrontend().check("Modules/A");
 
-    fileResolver.source["Modules/A"] = "local p = 4 -- We have fixed the problem, but we didn't tell the getFrontend(). so it will not recheck this file!";
+    fileResolver.source["Modules/A"] =
+        "local p = 4 -- We have fixed the problem, but we didn't tell the getFrontend(). so it will not recheck this file!";
     CheckResult secondResult = getFrontend().check("Modules/A");
 
     CHECK_EQ(1, secondResult.errors.size());

tests/Module.test.cpp

@@ -201,7 +201,8 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "builtin_types_point_into_globalTypes_arena")
     TableType* exportsTable = getMutable<TableType>(*exports);
     REQUIRE(exportsTable != nullptr);
 
-    TypeId signType = FFlag::LuauRemoveTypeCallsForReadWriteProps ? *exportsTable->props["sign"].readTy : exportsTable->props["sign"].type_DEPRECATED();
+    TypeId signType =
+        FFlag::LuauRemoveTypeCallsForReadWriteProps ? *exportsTable->props["sign"].readTy : exportsTable->props["sign"].type_DEPRECATED();
     REQUIRE(signType != nullptr);
 
     CHECK(!isInArena(signType, module->interfaceTypes));

tests/NonstrictMode.test.cpp

@@ -206,7 +206,9 @@ TEST_CASE_FIXTURE(Fixture, "inline_table_props_are_also_any")
 
     CHECK_EQ(*getBuiltins()->anyType, *ttv->props["one"].type_DEPRECATED());
     CHECK_EQ(*getBuiltins()->anyType, *ttv->props["two"].type_DEPRECATED());
-    CHECK_MESSAGE(get<FunctionType>(follow(ttv->props["three"].type_DEPRECATED())), "Should be a function: " << *ttv->props["three"].type_DEPRECATED());
+    CHECK_MESSAGE(
+        get<FunctionType>(follow(ttv->props["three"].type_DEPRECATED())), "Should be a function: " << *ttv->props["three"].type_DEPRECATED()
+    );
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "for_in_iterator_variables_are_any")

tests/Normalize.test.cpp

@@ -16,7 +16,7 @@ LUAU_FASTINT(LuauNormalizeIntersectionLimit)
 LUAU_FASTINT(LuauNormalizeUnionLimit)
 LUAU_FASTFLAG(LuauSimplifyOutOfLine2)
 LUAU_FASTFLAG(LuauNormalizationReorderFreeTypeIntersect)
-LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 using namespace Luau;
 
 namespace
@@ -1223,7 +1223,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_union_type_pack_cycle")
     ScopedFastFlag sff[] = {
         {FFlag::LuauSolverV2, true},
         {FFlag::LuauSimplifyOutOfLine2, true},
-        {FFlag::LuauReturnMappedGenericPacksFromSubtyping, true},
+        {FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true},
     };
     ScopedFastInt sfi{FInt::LuauTypeInferRecursionLimit, 0};
 

tests/Parser.test.cpp

@@ -18,7 +18,6 @@ LUAU_FASTINT(LuauTypeLengthLimit)
 LUAU_FASTINT(LuauParseErrorLimit)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauParseStringIndexer)
-LUAU_FASTFLAG(LuauDeclareExternType)
 LUAU_DYNAMIC_FASTFLAG(DebugLuauReportReturnTypeVariadicWithTypeSuffix)
 
 // Clip with DebugLuauReportReturnTypeVariadicWithTypeSuffix
@@ -1999,8 +1998,6 @@ TEST_CASE_FIXTURE(Fixture, "parse_class_declarations")
 
 TEST_CASE_FIXTURE(Fixture, "parse_extern_type_declarations")
 {
-    ScopedFastFlag sff{FFlag::LuauDeclareExternType, true};
-
     AstStatBlock* stat = parseEx(R"(
         declare extern type Foo with
             prop: number
@@ -2051,8 +2048,6 @@ TEST_CASE_FIXTURE(Fixture, "parse_extern_type_declarations")
 
 TEST_CASE_FIXTURE(Fixture, "parse_extern_type_declarations_missing_with")
 {
-    ScopedFastFlag sff{FFlag::LuauDeclareExternType, true};
-
     ParseResult result = tryParse(R"(
         declare extern type Foo
             prop: number
@@ -2108,8 +2103,6 @@ TEST_CASE_FIXTURE(Fixture, "parse_extern_type_declarations_missing_with")
 
 TEST_CASE_FIXTURE(Fixture, "parse_extern_type_declarations")
 {
-    ScopedFastFlag sff{FFlag::LuauDeclareExternType, true};
-
     AstStatBlock* stat = parseEx(R"(
         declare extern type Foo with
             prop: number
@@ -2160,8 +2153,6 @@ TEST_CASE_FIXTURE(Fixture, "parse_extern_type_declarations")
 
 TEST_CASE_FIXTURE(Fixture, "parse_extern_type_declarations_missing_with")
 {
-    ScopedFastFlag sff{FFlag::LuauDeclareExternType, true};
-
     ParseResult result = tryParse(R"(
         declare extern type Foo
             prop: number
@@ -2281,7 +2272,7 @@ TEST_CASE_FIXTURE(Fixture, "class_indexer")
             [number]: number
         end
         )",
-        (FFlag::LuauDeclareExternType) ? "Cannot have more than one indexer on an extern type" : "Cannot have more than one class indexer"
+        "Cannot have more than one indexer on an extern type"
     );
 
     REQUIRE_EQ(1, p1.root->body.size);

tests/RuntimeLimits.test.cpp

@@ -19,6 +19,9 @@ using namespace Luau;
 
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
 LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAG(LuauEagerGeneralization4)
+LUAU_FASTFLAG(LuauPushFunctionTypesInFunctionStatement)
+LUAU_FASTFLAG(LuauSimplifyAnyAndUnion)
 
 struct LimitFixture : BuiltinsFixture
 {
@@ -47,7 +50,7 @@ TEST_CASE_FIXTURE(LimitFixture, "typescript_port_of_Result_type")
 {
     DOES_NOT_PASS_NEW_SOLVER_GUARD();
 
-    constexpr const char* src = R"LUA(
+    constexpr const char* src = R"LUAU(
         --!strict
 
         -- Big thanks to Dionysusnu by letting us use this code as part of our test suite!
@@ -272,11 +275,62 @@ TEST_CASE_FIXTURE(LimitFixture, "typescript_port_of_Result_type")
         return {
             Result = Result,
         }
-    )LUA";
+    )LUAU";
 
     CheckResult result = check(src);
 
     CHECK(hasError<CodeTooComplex>(result));
 }
 
+TEST_CASE_FIXTURE(LimitFixture, "Signal_exerpt" * doctest::timeout(0.5))
+{
+    ScopedFastFlag sff[] = {
+        // These flags are required to surface the problem.
+        {FFlag::LuauSolverV2, true},
+        {FFlag::LuauEagerGeneralization4, true},
+        {FFlag::LuauPushFunctionTypesInFunctionStatement, true},
+
+        // And this flag is the one that fixes it.
+        {FFlag::LuauSimplifyAnyAndUnion, true},
+    };
+
+    constexpr const char* src = R"LUAU(
+        local Signal = {}
+        Signal.ClassName = "Signal"
+        export type Signal<T...> = typeof(setmetatable(
+            {} :: {},
+            {} :: typeof({ __index = Signal })
+        ))
+        function Signal.new<T...>(): Signal<T...>
+            return nil :: any
+        end
+
+        function Signal.Connect<T...>(self: Signal<T...>)
+        end
+
+        function Signal.DisconnectAll<T...>(self: Signal<T...>): ()
+            self._handlerListHead = false
+        end
+
+        function Signal.Fire<T...>(self: Signal<T...>): ()
+            local connection
+            rawget(connection, "_signal")
+        end
+
+        function Signal.Wait<T...>(self: Signal<T...>)
+            connection = self:Connect(function()
+                connection:Disconnect()
+            end)
+        end
+
+        function Signal.Once<T...>(self: Signal<T...>, fn: SignalHandler<T...>): Connection<T...>
+            connection = self:Connect(function() end)
+        end
+    )LUAU";
+
+    CheckResult result = check(src);
+
+    (void)result;
+}
+
 TEST_SUITE_END();

tests/Simplify.test.cpp

@@ -9,6 +9,7 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(LuauSolverV2)
+LUAU_FASTFLAG(LuauSimplifyAnyAndUnion)
 LUAU_DYNAMIC_FASTINT(LuauSimplificationComplexityLimit)
 
 namespace
@@ -62,6 +63,7 @@ struct SimplifyFixture : Fixture
     TypeId anotherChildClassTy = nullptr;
     TypeId unrelatedClassTy = nullptr;
 
+    // This only affects type stringification.
     ScopedFastFlag sff{FFlag::LuauSolverV2, true};
 
     SimplifyFixture()
@@ -619,4 +621,26 @@ TEST_CASE_FIXTURE(SimplifyFixture, "cyclic_never_union_and_string")
     CHECK(getBuiltins()->stringType == union_(leftType, getBuiltins()->stringType));
 }
 
+TEST_CASE_FIXTURE(SimplifyFixture, "any & (error | string)")
+{
+    ScopedFastFlag sff{FFlag::LuauSimplifyAnyAndUnion, true};
+
+    TypeId errStringTy = arena->addType(UnionType{{getBuiltins()->errorType, getBuiltins()->stringType}});
+
+    auto res = intersect(builtinTypes->anyType, errStringTy);
+
+    CHECK("*error-type* | string" == toString(res));
+}
+
+TEST_CASE_FIXTURE(SimplifyFixture, "(error | string) & any")
+{
+    ScopedFastFlag sff{FFlag::LuauSimplifyAnyAndUnion, true};
+
+    TypeId errStringTy = arena->addType(UnionType{{getBuiltins()->errorType, getBuiltins()->stringType}});
+
+    auto res = intersect(errStringTy, builtinTypes->anyType);
+
+    CHECK("*error-type* | string" == toString(res));
+}
+
 TEST_SUITE_END();

tests/Subtyping.test.cpp

@@ -17,7 +17,7 @@
 
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauEagerGeneralization4)
-LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 
 using namespace Luau;
 
@@ -1240,11 +1240,19 @@ TEST_CASE_FIXTURE(SubtypeFixture, "(...unknown) -> () <: <T>(T...) -> ()")
 TEST_CASE_FIXTURE(SubtypeFixture, "bill")
 {
     TypeId a = arena.addType(TableType{
-        {{"a", getBuiltins()->stringType}}, TableIndexer{getBuiltins()->stringType, getBuiltins()->numberType}, TypeLevel{}, nullptr, TableState::Sealed
+        {{"a", getBuiltins()->stringType}},
+        TableIndexer{getBuiltins()->stringType, getBuiltins()->numberType},
+        TypeLevel{},
+        nullptr,
+        TableState::Sealed
     });
 
     TypeId b = arena.addType(TableType{
-        {{"a", getBuiltins()->stringType}}, TableIndexer{getBuiltins()->stringType, getBuiltins()->numberType}, TypeLevel{}, nullptr, TableState::Sealed
+        {{"a", getBuiltins()->stringType}},
+        TableIndexer{getBuiltins()->stringType, getBuiltins()->numberType},
+        TypeLevel{},
+        nullptr,
+        TableState::Sealed
     });
 
     CHECK(isSubtype(a, b).isSubtype);
@@ -1387,7 +1395,7 @@ TEST_CASE_FIXTURE(SubtypeFixture, "<T>({ x: T }) -> T <: ({ method: <T>({ x: T }
 
 TEST_CASE_FIXTURE(SubtypeFixture, "subtyping_reasonings_to_follow_a_reduced_type_function_instance")
 {
-    ScopedFastFlag sff{FFlag::LuauReturnMappedGenericPacksFromSubtyping, true};
+    ScopedFastFlag sff{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
 
     TypeId longTy = arena.addType(UnionType{
         {getBuiltins()->booleanType,
@@ -1631,9 +1639,9 @@ TEST_CASE_FIXTURE(SubtypeFixture, "substitute_a_generic_for_a_negation")
     TypeId bTy = arena.addType(GenericType{"B"});
     getMutable<GenericType>(bTy)->scope = moduleScope.get();
 
-    TypeId genericFunctionTy =
+    TypeId genericFunctionTy = arena.addType(
-        arena.addType(FunctionType{{aTy, bTy}, {}, arena.addTypePack({aTy, bTy}), arena.addTypePack({join(meet(aTy, getBuiltins()->truthyType), bTy)})}
+        FunctionType{{aTy, bTy}, {}, arena.addTypePack({aTy, bTy}), arena.addTypePack({join(meet(aTy, getBuiltins()->truthyType), bTy)})}
-        );
+    );
 
     const TypeId truthyTy = getBuiltins()->truthyType;
 

tests/ToString.test.cpp

@@ -61,7 +61,8 @@ TEST_CASE_FIXTURE(Fixture, "free_types_stringify_the_same_regardless_of_solver")
 {
     ScopedFastFlag sff{FFlag::LuauSolverAgnosticStringification, true};
     TypeArena a;
-    TypeId t = a.addType(FreeType{getFrontend().globals.globalScope.get(), getFrontend().builtinTypes->neverType, getFrontend().builtinTypes->unknownType});
+    TypeId t =
+        a.addType(FreeType{getFrontend().globals.globalScope.get(), getFrontend().builtinTypes->neverType, getFrontend().builtinTypes->unknownType});
 
     CHECK_EQ("'a", toString(t));
 }

tests/TypeFunction.test.cpp

@@ -744,10 +744,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "keyof_oss_crash_gh1161")
     if (!FFlag::LuauSolverV2)
         return;
 
-    ScopedFastFlag sff[] = {
+    ScopedFastFlag sff[] = {{FFlag::LuauEagerGeneralization4, true}, {FFlag::LuauStuckTypeFunctionsStillDispatch, true}};
-        {FFlag::LuauEagerGeneralization4, true},
-        {FFlag::LuauStuckTypeFunctionsStillDispatch, true}
-    };
 
     CheckResult result = check(R"(
         local EnumVariants = {
@@ -1787,7 +1784,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "keyof_should_not_assert_on_empty_string_prop
     LUAU_REQUIRE_NO_ERRORS(results);
     CHECK_EQ(R"("" | "one")", toString(requireTypeAlias("FoobarKeys")));
     CHECK_EQ(R"("" | "two")", toString(requireTypeAlias("TableKeys")));
-
 }
 
 struct TFFixture
@@ -1796,7 +1792,10 @@ struct TFFixture
     NotNull<TypeArena> arena{&arena_};
 
     BuiltinTypes builtinTypes_;
-    NotNull<BuiltinTypes> getBuiltins(){ return NotNull{&builtinTypes_};}
+    NotNull<BuiltinTypes> getBuiltins()
+    {
+        return NotNull{&builtinTypes_};
+    }
 
     ScopePtr globalScope = std::make_shared<Scope>(getBuiltins()->anyTypePack);
 

tests/TypeFunction.user.test.cpp

@@ -2417,10 +2417,7 @@ local function ok(idx: get<>): number return idx end
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(4, result);
-    CHECK(
+    CHECK(toString(result.errors[1]) == R"(Type function instance get<> is uninhabited)");
-        toString(result.errors[1]) ==
-        R"(Type function instance get<> is uninhabited)"
-    );
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "type_alias_unreferenced_do_not_block")

tests/TypeInfer.aliases.test.cpp

@@ -10,7 +10,6 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAG(LuauGuardAgainstMalformedTypeAliasExpansion2)
 LUAU_FASTFLAG(LuauTableLiteralSubtypeSpecificCheck2)
 
 TEST_SUITE_BEGIN("TypeAliases");
@@ -1244,8 +1243,6 @@ TEST_CASE_FIXTURE(Fixture, "exported_type_function_location_is_accessible_on_mod
 
 TEST_CASE_FIXTURE(Fixture, "fuzzer_cursed_type_aliases")
 {
-    ScopedFastFlag _{FFlag::LuauGuardAgainstMalformedTypeAliasExpansion2, true};
-
     // This used to crash under the new solver: we would like this to continue
     // to not crash.
     LUAU_REQUIRE_ERRORS(check(R"(
@@ -1282,8 +1279,6 @@ TEST_CASE_FIXTURE(Fixture, "type_alias_dont_crash_on_duplicate_with_typeof")
 
 TEST_CASE_FIXTURE(Fixture, "fuzzer_more_cursed_aliases")
 {
-    ScopedFastFlag _{FFlag::LuauGuardAgainstMalformedTypeAliasExpansion2, true};
-
     LUAU_REQUIRE_ERRORS(check(R"(
 export type t138 = t0<t138>
 export type t0<t0,t10,t10,t109> = t0

tests/TypeInfer.annotations.test.cpp

@@ -272,7 +272,8 @@ TEST_CASE_FIXTURE(Fixture, "infer_type_of_value_a_via_typeof_with_assignment")
 
         LUAU_REQUIRE_ERROR_COUNT(1, result);
         CHECK(
-            result.errors[0] == (TypeError{Location{Position{2, 29}, Position{2, 30}}, TypeMismatch{getBuiltins()->nilType, getBuiltins()->numberType}})
+            result.errors[0] ==
+            (TypeError{Location{Position{2, 29}, Position{2, 30}}, TypeMismatch{getBuiltins()->nilType, getBuiltins()->numberType}})
         );
     }
     else
@@ -447,7 +448,8 @@ TEST_CASE_FIXTURE(Fixture, "self_referential_type_alias")
     if (FFlag::LuauRemoveTypeCallsForReadWriteProps)
         REQUIRE(incr->readTy);
 
-    const FunctionType* incrFunc = FFlag::LuauRemoveTypeCallsForReadWriteProps ? get<FunctionType>(*incr->readTy) : get<FunctionType>(incr->type_DEPRECATED());
+    const FunctionType* incrFunc =
+        FFlag::LuauRemoveTypeCallsForReadWriteProps ? get<FunctionType>(*incr->readTy) : get<FunctionType>(incr->type_DEPRECATED());
     REQUIRE(incrFunc);
 
     std::optional<TypeId> firstArg = first(incrFunc->argTypes);

tests/TypeInfer.generics.test.cpp

@@ -9,7 +9,7 @@
 
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 LUAU_FASTFLAG(LuauTableLiteralSubtypeSpecificCheck2)
 LUAU_FASTFLAG(LuauIntersectNotNil)
 LUAU_FASTFLAG(LuauSubtypingCheckFunctionGenericCounts)
@@ -18,6 +18,7 @@ LUAU_FASTFLAG(LuauStuckTypeFunctionsStillDispatch)
 LUAU_FASTFLAG(LuauRemoveTypeCallsForReadWriteProps)
 LUAU_FASTFLAG(DebugLuauAssertOnForcedConstraint)
 LUAU_FASTFLAG(LuauPushFunctionTypesInFunctionStatement)
+LUAU_FASTFLAG(LuauContainsAnyGenericFollowBeforeChecking)
 
 using namespace Luau;
 
@@ -1004,7 +1005,7 @@ local TheDispatcher: Dispatcher = {
 
 TEST_CASE_FIXTURE(Fixture, "generic_argument_count_too_few")
 {
-    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping, true};
+    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
 
     CheckResult result = check(R"(
 function test(a: number)
@@ -1032,7 +1033,7 @@ wrapper(test)
 
 TEST_CASE_FIXTURE(Fixture, "generic_argument_count_too_many")
 {
-    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping, true};
+    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
 
     CheckResult result = check(R"(
 function test2(a: number, b: string)
@@ -1076,7 +1077,7 @@ wrapper(test2, 1, "")
 
 TEST_CASE_FIXTURE(Fixture, "generic_argument_pack_type_inferred_from_return")
 {
-    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping, true};
+    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
 
     CheckResult result = check(R"(
 function test2(a: number)
@@ -1106,7 +1107,7 @@ wrapper(test2, 1)
 
 TEST_CASE_FIXTURE(Fixture, "generic_argument_pack_type_inferred_from_return_no_error")
 {
-    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping, true};
+    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
 
     CheckResult result = check(R"(
 function test2(a: number)
@@ -1124,7 +1125,7 @@ wrapper(test2, "hello")
 
 TEST_CASE_FIXTURE(Fixture, "nested_generic_argument_type_packs")
 {
-    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping, true};
+    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
 
     CheckResult result = check(R"(
 function test2(a: number)
@@ -1851,4 +1852,63 @@ end
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "generic_type_packs_shouldnt_be_bound_to_themselves")
+{
+    ScopedFastFlag flags[] = {
+        {FFlag::LuauSolverV2, true},
+        {FFlag::LuauSubtypingCheckFunctionGenericCounts, true},
+        {FFlag::LuauEagerGeneralization4, true}
+    };
+
+    CheckResult result = check(R"(
+export type t1<T...> = {
+    foo: (self: t1<T...>, bar: (T...) -> ()) -> ()
+}
+
+export type t2<T...> = {
+    baz: (self: t2<T...>) -> t1<T...>,
+}
+
+export type t3<T...> = {
+    f: (self: t3<T...>, T...)->  (),
+    g: t1<T...>,
+    h: t1<(Player, T...)>
+}
+
+local t2 = {}
+
+function t2.new<T...>(): t2<T...>
+end
+
+local function create_t3<T...>(): t3<T...>
+    local t2_1 = t2.new()
+    local t2_2 = t2.new()
+    local my_t3 = {
+        f = function(_self: t3<T...>, ...: T...) end,
+        g = t2_1:baz(),
+        h = t2_2:baz()
+    }
+    return my_t3
+end
+    )");
+
+    // Note: we just need this test not to crash
+    LUAU_REQUIRE_ERROR_COUNT(5, result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "follow_bound_type_packs_in_generic_type_visitor")
+{
+    ScopedFastFlag _{FFlag::LuauContainsAnyGenericFollowBeforeChecking, true};
+    // Note: we just need this test not to crash
+    check(R"(
+function (_(_,_,nil))
+(if l0 then typeof else `{_:_()}`,typeof).n0<A...,A...>(l0)
+function _:_():typeof<A...>()
+end
+function _:_().typeof<A...>()
+end
+end
+    )");
+}
+
 TEST_SUITE_END();

tests/TypeInfer.intersectionTypes.test.cpp

@@ -12,7 +12,7 @@ using namespace Luau;
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauTableLiteralSubtypeSpecificCheck2)
 LUAU_FASTFLAG(LuauRefineTablesWithReadType)
-LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 LUAU_FASTFLAG(LuauPushFunctionTypesInFunctionStatement)
 LUAU_FASTFLAG(LuauTableLiteralSubtypeSpecificCheck2)
 
@@ -1162,7 +1162,7 @@ could not be converted into
 
 TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_weird_typepacks_4")
 {
-    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping, true};
+    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
 
     CheckResult result = check(R"(
         function f<a...>()

tests/TypeInfer.modules.test.cpp

@@ -13,7 +13,7 @@
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTFLAG(LuauEagerGeneralization4)
-LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping)
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2)
 
 using namespace Luau;
 
@@ -823,7 +823,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "cycles_dont_make_everything_any")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "cross_module_function_mutation")
 {
-    ScopedFastFlag _[] = {{FFlag::LuauSolverV2, true}, {FFlag::LuauReturnMappedGenericPacksFromSubtyping, true}};
+    ScopedFastFlag _[] = {{FFlag::LuauSolverV2, true}, {FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true}};
 
     fileResolver.source["game/A"] = R"(
 function test2(a: number, b: string)

tests/TypeInfer.oop.test.cpp

@@ -559,7 +559,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "textbook_class_pattern")
     if (!FFlag::LuauSolverV2)
         return;
 
-    ScopedFastFlag sff[] ={
+    ScopedFastFlag sff[] = {
         {FFlag::LuauEagerGeneralization4, true},
     };
 
@@ -591,7 +591,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "textbook_class_pattern_2")
     if (!FFlag::LuauSolverV2)
         return;
 
-    ScopedFastFlag sff[] ={
+    ScopedFastFlag sff[] = {
         {FFlag::LuauEagerGeneralization4, true},
     };
 

tests/TypeInfer.refinements.test.cpp

@@ -127,7 +127,8 @@ struct RefinementExternTypeFixture : BuiltinsFixture
         };
 
         TypeId optionalPart = arena.addType(UnionType{{part, getBuiltins()->nilType}});
-        TypeId weldConstraint = getFrontend().globals.globalTypes.addType(ExternType{"WeldConstraint", {}, inst, std::nullopt, {}, nullptr, "Test", {}});
+        TypeId weldConstraint =
+            getFrontend().globals.globalTypes.addType(ExternType{"WeldConstraint", {}, inst, std::nullopt, {}, nullptr, "Test", {}});
         getMutable<ExternType>(weldConstraint)->props = {
             {"Part0", Property{optionalPart}},
             {"Part1", Property{optionalPart}},
@@ -2453,7 +2454,7 @@ end)
 )"));
 }
 
-TEST_CASE_FIXTURE(Fixture, "refinements_table_intersection_limits" * doctest::timeout(1.0))
+TEST_CASE_FIXTURE(Fixture, "refinements_table_intersection_limits" * doctest::timeout(1.5))
 {
     CheckResult result = check(R"(
 --!strict

tests/TypeInfer.tables.test.cpp

@@ -40,6 +40,7 @@ LUAU_FASTFLAG(LuauDfgForwardNilFromAndOr)
 LUAU_FASTFLAG(LuauInferActualIfElseExprType)
 LUAU_FASTFLAG(LuauDoNotPrototypeTableIndex)
 LUAU_FASTFLAG(LuauPushFunctionTypesInFunctionStatement)
+LUAU_FASTFLAG(LuauNormalizationLimitTyvarUnionSize)
 
 TEST_SUITE_BEGIN("TableTests");
 
@@ -6129,7 +6130,7 @@ TEST_CASE_FIXTURE(Fixture, "cli_119126_regression")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(2, results);
-    for (const auto& err: results.errors)
+    for (const auto& err : results.errors)
     {
         auto e = get<TypeMismatch>(err);
         REQUIRE(e);
@@ -6173,5 +6174,23 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "oss_1914_access_after_assignment_with_assert
     CHECK_EQ("number", toString(requireType("myAge")));
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "cli_162179_avoid_exponential_blowup_in_normalization" * doctest::timeout(1.0))
+{
+    ScopedFastFlag sffs[] = {
+        {FFlag::LuauSimplifyOutOfLine2, true},
+        {FFlag::LuauNormalizationLimitTyvarUnionSize, true},
+    };
+
+    const std::string source =
+        "local res = {\n" + rep("\"foo\",\n", 100) + "}\n"
+        + "local function check(index: number)\n"
+        + "  if res[index] == \"foo\" then\n"
+        + "    print(\"found a foo!\")\n"
+        + "  end\n"
+        + "end";
+
+    LUAU_REQUIRE_NO_ERRORS(check(source));
+}
+
 
 TEST_SUITE_END();

tests/TypeInfer.test.cpp

@@ -1984,7 +1984,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "assert_table_freeze_constraint_solving")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "fuzz_assert_table_freeze_constraint_solving")
 {
-    ScopedFastFlag _ {FFlag::LuauSolverV2, true};
+    ScopedFastFlag _{FFlag::LuauSolverV2, true};
     // This is the original fuzzer version of the above issue.
     CheckResult results = check(R"(
         local function l0()
@@ -2383,7 +2383,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_remover_heap_use_after_free")
         local l249 = require(module0)
         _,_ = {[`{_}`]=_,[_._G._]=(_)(),[_["" + _]._G]={_=_,_=_,[_._G[_]._]=_G,},},_,(_)()
     )"));
-
 }
 
 TEST_CASE_FIXTURE(Fixture, "fuzzer_missing_follow_in_assign_index_constraint")
@@ -2449,7 +2448,7 @@ TEST_CASE_FIXTURE(Fixture, "oss_1815_verbatim")
         {FFlag::LuauInferActualIfElseExprType, true},
         // This is needed so that we don't hide the string literal free types
         // behind a `union<_, _>`
-        {FFlag::LuauSimplifyOutOfLine2, true}, 
+        {FFlag::LuauSimplifyOutOfLine2, true},
         {FFlag::LuauTableLiteralSubtypeSpecificCheck2, true},
     };
 
@@ -2476,7 +2475,6 @@ TEST_CASE_FIXTURE(Fixture, "oss_1815_verbatim")
     REQUIRE(err3);
     CHECK_EQ("\"foo\"", toString(err3->wantedType));
     CHECK_EQ("\"doge2\"", toString(err3->givenType));
-
 }
 
 TEST_CASE_FIXTURE(Fixture, "if_then_else_bidirectional_inference")

tests/TypeInfer.tryUnify.test.cpp

@@ -47,7 +47,8 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "compatible_functions_are_unified")
     }};
 
     Type functionTwo{TypeVariant{FunctionType(
-        arena.addTypePack({arena.freshType(getBuiltins(), globalScope->level)}), arena.addTypePack({arena.freshType(getBuiltins(), globalScope->level)})
+        arena.addTypePack({arena.freshType(getBuiltins(), globalScope->level)}),
+        arena.addTypePack({arena.freshType(getBuiltins(), globalScope->level)})
     )}};
 
     state.tryUnify(&functionTwo, &functionOne);
@@ -291,7 +292,8 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "free_tail_is_grown_properly")
 {
     TypePackId threeNumbers =
         arena.addTypePack(TypePack{{getBuiltins()->numberType, getBuiltins()->numberType, getBuiltins()->numberType}, std::nullopt});
-    TypePackId numberAndFreeTail = arena.addTypePack(TypePack{{getBuiltins()->numberType}, arena.addTypePack(TypePackVar{FreeTypePack{TypeLevel{}}})});
+    TypePackId numberAndFreeTail =
+        arena.addTypePack(TypePack{{getBuiltins()->numberType}, arena.addTypePack(TypePackVar{FreeTypePack{TypeLevel{}}})});
 
     CHECK(state.canUnify(numberAndFreeTail, threeNumbers).empty());
 }

tests/TypeInfer.typestates.test.cpp

@@ -710,9 +710,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "refinement_through_erroring")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "refinement_through_erroring_in_loop")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sffs[] = {{FFlag::LuauSolverV2, true}, {FFlag::LuauDfgAllowUpdatesInLoops, true}};
-        {FFlag::LuauSolverV2, true}, {FFlag::LuauDfgAllowUpdatesInLoops, true}
-    };
 
     CheckResult result = check(R"(
         --!strict

tests/TypeInfer.unionTypes.test.cpp

@@ -633,7 +633,11 @@ TEST_CASE_FIXTURE(Fixture, "indexing_into_a_cyclic_union_doesnt_crash")
 
     u.options.push_back(badCyclicUnionTy);
     u.options.push_back(arena.addType(TableType{
-        {}, TableIndexer{getBuiltins()->numberType, getBuiltins()->numberType}, TypeLevel{}, getFrontend().globals.globalScope.get(), TableState::Sealed
+        {},
+        TableIndexer{getBuiltins()->numberType, getBuiltins()->numberType},
+        TypeLevel{},
+        getFrontend().globals.globalScope.get(),
+        TableState::Sealed
     }));
 
     asMutable(badCyclicUnionTy)->ty.emplace<UnionType>(std::move(u));

tests/TypePath.test.cpp

@@ -18,6 +18,8 @@ using namespace Luau::TypePath;
 LUAU_FASTFLAG(LuauSolverV2);
 LUAU_DYNAMIC_FASTINT(LuauTypePathMaximumTraverseSteps);
 
+LUAU_FASTFLAG(LuauReturnMappedGenericPacksFromSubtyping2);
+
 struct TypePathFixture : Fixture
 {
     ScopedFastFlag sff1{FFlag::LuauSolverV2, true};
@@ -494,6 +496,8 @@ TEST_CASE_FIXTURE(TypePathFixture, "tail")
 
 TEST_CASE_FIXTURE(TypePathFixture, "pack_slice_has_tail")
 {
+    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
+
     TypeArena& arena = getFrontend().globals.globalTypes;
     unfreeze(arena);
 
@@ -510,6 +514,8 @@ TEST_CASE_FIXTURE(TypePathFixture, "pack_slice_has_tail")
 
 TEST_CASE_FIXTURE(TypePathFixture, "pack_slice_finite_pack")
 {
+    ScopedFastFlag _{FFlag::LuauReturnMappedGenericPacksFromSubtyping2, true};
+
     TypeArena& arena = getFrontend().globals.globalTypes;
     unfreeze(arena);
 

tests/TypeVar.test.cpp

@@ -365,6 +365,12 @@ struct VisitCountTracker final : TypeOnceVisitor
     std::unordered_map<TypeId, unsigned> tyVisits;
     std::unordered_map<TypePackId, unsigned> tpVisits;
 
+    VisitCountTracker()
+        : TypeOnceVisitor("VisitCountTracker")
+    {
+    }
+
+
     void cycle(TypeId) override {}
     void cycle(TypePackId) override {}
 

tests/conformance/calls.luau

@@ -241,7 +241,7 @@ if not limitedstack then
   function recurse(n, ...) return n <= 1 and (1 + #{...}) or recurse(n-1, table.unpack(table.create(4000, 1))) + 1 end
 
   local ok, msg = pcall(recurse, 19000)
-  assert(not ok and string.find(msg, "not enough memory"))
+  assert(not ok and string.find(msg, "too many results to unpack"))
 end
 
 return('OK')

tests/conformance/coroutine.luau

@@ -382,4 +382,13 @@ do
   assert(st and msg == nil)
 end
 
+do
+  local co = coroutine.wrap(xpcall)
+
+  co(0, coroutine.yield, 0)
+  local status, err = pcall(co, 0, 0, 0)
+  assert(status == false)
+  assert(err == "cannot resume dead coroutine")
+end
+
 return 'OK'