Sync to upstream/release/548 (#699)

- Fix rare type checking bugs with invalid generic types escaping the
module scope
- Fix type checking of variadic type packs in certain cases
- Implement type normalization, which resolves a large set of various
issues with unions/intersections in type checker
- Improve parse errors for trailing commas in function calls and type
lists
- Reduce profiling skew when using --profile with very high frequencies
- Improve performance of `lua_getinfo` (`debug.info`, `debug.traceback`
and profiling overhead are now 20% faster/smaller)
- Improve performance of polymorphic comparisons (1-2% lift on some
benchmarks)
- Improve performance of closure creation (1-2% lift on some benchmarks)
- Improve string comparison performance (4% lift on string sorting)

Analysis/include/Luau/ConstraintSolver.h

@@ -7,6 +7,7 @@
 #include "Luau/Constraint.h"
 #include "Luau/TypeVar.h"
 #include "Luau/ToString.h"
+#include "Luau/Normalize.h"
 
 #include <vector>
 
@@ -44,6 +45,7 @@ struct ConstraintSolver
     TypeArena* arena;
     NotNull<SingletonTypes> singletonTypes;
     InternalErrorReporter iceReporter;
+    NotNull<Normalizer> normalizer;
     // The entire set of constraints that the solver is trying to resolve.
     std::vector<NotNull<Constraint>> constraints;
     NotNull<Scope> rootScope;
@@ -74,9 +76,12 @@ struct ConstraintSolver
 
     DcrLogger* logger;
 
-    explicit ConstraintSolver(TypeArena* arena, NotNull<SingletonTypes> singletonTypes, NotNull<Scope> rootScope, ModuleName moduleName,
+    explicit ConstraintSolver(NotNull<Normalizer> normalizer, NotNull<Scope> rootScope, ModuleName moduleName,
         NotNull<ModuleResolver> moduleResolver, std::vector<RequireCycle> requireCycles, DcrLogger* logger);
 
+    // Randomize the order in which to dispatch constraints
+    void randomize(unsigned seed);
+
     /**
      * Attempts to dispatch all pending constraints and reach a type solution
      * that satisfies all of the constraints.
@@ -85,8 +90,9 @@ struct ConstraintSolver
 
     bool done();
 
-    /** Attempt to dispatch a constraint.  Returns true if it was successful.
+    /** Attempt to dispatch a constraint.  Returns true if it was successful. If
-     * If tryDispatch() returns false, the constraint remains in the unsolved set and will be retried later.
+     * tryDispatch() returns false, the constraint remains in the unsolved set
+     * and will be retried later.
      */
     bool tryDispatch(NotNull<const Constraint> c, bool force);
 

Analysis/include/Luau/Error.h

@@ -16,7 +16,7 @@ struct TypeMismatch
     TypeMismatch() = default;
     TypeMismatch(TypeId wantedType, TypeId givenType);
     TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason);
-    TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, TypeError error);
+    TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, std::optional<TypeError> error);
 
     TypeId wantedType = nullptr;
     TypeId givenType = nullptr;

Analysis/include/Luau/Frontend.h

@@ -83,8 +83,13 @@ struct FrontendOptions
     // is complete.
     bool retainFullTypeGraphs = false;
 
-    // Run typechecking only in mode required for autocomplete (strict mode in order to get more precise type information)
+    // Run typechecking only in mode required for autocomplete (strict mode in
+    // order to get more precise type information)
     bool forAutocomplete = false;
+
+    // If not empty, randomly shuffle the constraint set before attempting to
+    // solve.  Use this value to seed the random number generator.
+    std::optional<unsigned> randomizeConstraintResolutionSeed;
 };
 
 struct CheckResult

Analysis/include/Luau/Normalize.h

@@ -1,9 +1,9 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
-#include "Luau/Module.h"
 #include "Luau/NotNull.h"
 #include "Luau/TypeVar.h"
+#include "Luau/UnifierSharedState.h"
 
 #include <memory>
 
@@ -29,4 +29,231 @@ std::pair<TypePackId, bool> normalize(
 std::pair<TypePackId, bool> normalize(TypePackId ty, NotNull<Module> module, NotNull<SingletonTypes> singletonTypes, InternalErrorReporter& ice);
 std::pair<TypePackId, bool> normalize(TypePackId ty, const ModulePtr& module, NotNull<SingletonTypes> singletonTypes, InternalErrorReporter& ice);
 
+class TypeIds
+{
+private:
+    std::unordered_set<TypeId> types;
+    std::vector<TypeId> order;
+    std::size_t hash = 0;
+
+public:
+    using iterator = std::vector<TypeId>::iterator;
+    using const_iterator = std::vector<TypeId>::const_iterator;
+
+    TypeIds(const TypeIds&) = delete;
+    TypeIds(TypeIds&&) = default;
+    TypeIds() = default;
+    ~TypeIds() = default;
+    TypeIds& operator=(TypeIds&&) = default;
+
+    void insert(TypeId ty);
+    /// Erase every element that does not also occur in tys
+    void retain(const TypeIds& tys);
+    void clear();
+
+    iterator begin();
+    iterator end();
+    const_iterator begin() const;
+    const_iterator end() const;
+    iterator erase(const_iterator it);
+
+    size_t size() const;
+    bool empty() const;
+    size_t count(TypeId ty) const;
+
+    template<class Iterator>
+    void insert(Iterator begin, Iterator end)
+    {
+        for (Iterator it = begin; it != end; ++it)
+            insert(*it);
+    }
+
+    bool operator ==(const TypeIds& there) const;
+    size_t getHash() const;
+};
+
+} // namespace Luau
+
+template<> struct std::hash<Luau::TypeIds>
+{
+    std::size_t operator()(const Luau::TypeIds& tys) const
+    {
+        return tys.getHash();
+    }
+};
+
+template<> struct std::hash<const Luau::TypeIds*>
+{
+    std::size_t operator()(const Luau::TypeIds* tys) const
+    {
+        return tys->getHash();
+    }
+};
+
+template<> struct std::equal_to<Luau::TypeIds>
+{
+    bool operator()(const Luau::TypeIds& here, const Luau::TypeIds& there) const
+    {
+        return here == there;
+    }
+};
+
+template<> struct std::equal_to<const Luau::TypeIds*>
+{
+    bool operator()(const Luau::TypeIds* here, const Luau::TypeIds* there) const
+    {
+        return *here == *there;
+    }
+};
+
+namespace Luau
+{
+
+// A normalized string type is either `string` (represented by `nullopt`)
+// or a union of string singletons.
+using NormalizedStringType = std::optional<std::map<std::string, TypeId>>;
+
+// A normalized function type is either `never` (represented by `nullopt`)
+// or an intersection of function types.
+// NOTE: type normalization can fail on function types with generics
+// (e.g. because we do not support unions and intersections of generic type packs),
+// so this type may contain `error`.
+using NormalizedFunctionType = std::optional<TypeIds>;
+
+// A normalized generic/free type is a union, where each option is of the form (X & T) where
+// * X is either a free type or a generic
+// * T is a normalized type.
+struct NormalizedType;
+using NormalizedTyvars = std::unordered_map<TypeId, std::unique_ptr<NormalizedType>>;
+
+// A normalized type is either any, unknown, or one of the form P | T | F | G where
+// * P is a union of primitive types (including singletons, classes and the error type)
+// * T is a union of table types
+// * F is a union of an intersection of function types
+// * G is a union of generic/free normalized types, intersected with a normalized type
+struct NormalizedType
+{
+    // The top part of the type.
+    // This type is either never, unknown, or any.
+    // If this type is not never, all the other fields are null.
+    TypeId tops;
+
+    // The boolean part of the type.
+    // This type is either never, boolean type, or a boolean singleton.
+    TypeId booleans;
+
+    // The class part of the type.
+    // Each element of this set is a class, and none of the classes are subclasses of each other.
+    TypeIds classes;
+
+    // The error part of the type.
+    // This type is either never or the error type.
+    TypeId errors;
+
+    // The nil part of the type.
+    // This type is either never or nil.
+    TypeId nils;
+
+    // The number part of the type.
+    // This type is either never or number.
+    TypeId numbers;
+
+    // The string part of the type.
+    // This may be the `string` type, or a union of singletons.
+    NormalizedStringType strings = std::map<std::string,TypeId>{};
+
+    // The thread part of the type.
+    // This type is either never or thread.
+    TypeId threads;
+
+    // The (meta)table part of the type.
+    // Each element of this set is a (meta)table type.
+    TypeIds tables;
+
+    // The function part of the type.
+    NormalizedFunctionType functions;
+
+    // The generic/free part of the type.
+    NormalizedTyvars tyvars;
+
+    NormalizedType(NotNull<SingletonTypes> singletonTypes);
+
+    NormalizedType(const NormalizedType&) = delete;
+    NormalizedType(NormalizedType&&) = default;
+    NormalizedType() = delete;
+    ~NormalizedType() = default;
+    NormalizedType& operator=(NormalizedType&&) = default;
+    NormalizedType& operator=(NormalizedType&) = delete;
+};
+
+class Normalizer
+{
+    std::unordered_map<TypeId, std::unique_ptr<NormalizedType>> cachedNormals;
+    std::unordered_map<const TypeIds*, TypeId> cachedIntersections;
+    std::unordered_map<const TypeIds*, TypeId> cachedUnions;
+    std::unordered_map<const TypeIds*, std::unique_ptr<TypeIds>> cachedTypeIds;
+    bool withinResourceLimits();
+
+public:
+    TypeArena* arena;
+    NotNull<SingletonTypes> singletonTypes;
+    NotNull<UnifierSharedState> sharedState;
+
+    Normalizer(TypeArena* arena, NotNull<SingletonTypes> singletonTypes, NotNull<UnifierSharedState> sharedState);
+    Normalizer(const Normalizer&) = delete;
+    Normalizer(Normalizer&&) = delete;
+    Normalizer() = delete;
+    ~Normalizer() = default;
+    Normalizer& operator=(Normalizer&&) = delete;
+    Normalizer& operator=(Normalizer&) = delete;
+
+    // If this returns null, the typechecker should emit a "too complex" error
+    const NormalizedType* normalize(TypeId ty);
+    void clearNormal(NormalizedType& norm);
+
+    // ------- Cached TypeIds
+    TypeId unionType(TypeId here, TypeId there);
+    TypeId intersectionType(TypeId here, TypeId there);
+    const TypeIds* cacheTypeIds(TypeIds tys);
+    void clearCaches();
+
+    // ------- Normalizing unions
+    void unionTysWithTy(TypeIds& here, TypeId there);
+    TypeId unionOfTops(TypeId here, TypeId there);
+    TypeId unionOfBools(TypeId here, TypeId there);
+    void unionClassesWithClass(TypeIds& heres, TypeId there);
+    void unionClasses(TypeIds& heres, const TypeIds& theres);
+    void unionStrings(NormalizedStringType& here, const NormalizedStringType& there);
+    std::optional<TypePackId> unionOfTypePacks(TypePackId here, TypePackId there);
+    std::optional<TypeId> unionOfFunctions(TypeId here, TypeId there);
+    std::optional<TypeId> unionSaturatedFunctions(TypeId here, TypeId there);
+    void unionFunctionsWithFunction(NormalizedFunctionType& heress, TypeId there);
+    void unionFunctions(NormalizedFunctionType& heress, const NormalizedFunctionType& theress);
+    void unionTablesWithTable(TypeIds& heres, TypeId there);
+    void unionTables(TypeIds& heres, const TypeIds& theres);
+    bool unionNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
+    bool unionNormalWithTy(NormalizedType& here, TypeId there, int ignoreSmallerTyvars = -1);
+
+    // ------- Normalizing intersections
+    void intersectTysWithTy(TypeIds& here, TypeId there);
+    TypeId intersectionOfTops(TypeId here, TypeId there);
+    TypeId intersectionOfBools(TypeId here, TypeId there);
+    void intersectClasses(TypeIds& heres, const TypeIds& theres);
+    void intersectClassesWithClass(TypeIds& heres, TypeId there);
+    void intersectStrings(NormalizedStringType& here, const NormalizedStringType& there);
+    std::optional<TypePackId> intersectionOfTypePacks(TypePackId here, TypePackId there);
+    std::optional<TypeId> intersectionOfTables(TypeId here, TypeId there);
+    void intersectTablesWithTable(TypeIds& heres, TypeId there);
+    void intersectTables(TypeIds& heres, const TypeIds& theres);
+    std::optional<TypeId> intersectionOfFunctions(TypeId here, TypeId there);
+    void intersectFunctionsWithFunction(NormalizedFunctionType& heress, TypeId there);
+    void intersectFunctions(NormalizedFunctionType& heress, const NormalizedFunctionType& theress);
+    bool intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there);
+    bool intersectNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
+    bool intersectNormalWithTy(NormalizedType& here, TypeId there);
+
+    // -------- Convert back from a normalized type to a type
+    TypeId typeFromNormal(const NormalizedType& norm);
+};
+
 } // namespace Luau

Analysis/include/Luau/TypeInfer.h

@@ -234,6 +234,8 @@ public:
     TypeId anyify(const ScopePtr& scope, TypeId ty, Location location);
     TypePackId anyify(const ScopePtr& scope, TypePackId ty, Location location);
 
+    TypePackId anyifyModuleReturnTypePackGenerics(TypePackId ty);
+
     void reportError(const TypeError& error);
     void reportError(const Location& location, TypeErrorData error);
     void reportErrors(const ErrorVec& errors);
@@ -359,6 +361,7 @@ public:
     InternalErrorReporter* iceHandler;
 
     UnifierSharedState unifierState;
+    Normalizer normalizer;
 
     std::vector<RequireCycle> requireCycles;
 

Analysis/include/Luau/Unifiable.h

@@ -96,7 +96,7 @@ struct Free
     bool forwardedTypeAlias = false;
 
 private:
-    static int nextIndex;
+    static int DEPRECATED_nextIndex;
 };
 
 template<typename Id>
@@ -127,7 +127,7 @@ struct Generic
     bool explicitName = false;
 
 private:
-    static int nextIndex;
+    static int DEPRECATED_nextIndex;
 };
 
 struct Error

Analysis/include/Luau/Unifier.h

@@ -9,6 +9,7 @@
 #include "Luau/TxnLog.h"
 #include "Luau/TypeArena.h"
 #include "Luau/UnifierSharedState.h"
+#include "Normalize.h"
 
 #include <unordered_set>
 
@@ -52,6 +53,7 @@ struct Unifier
 {
     TypeArena* const types;
     NotNull<SingletonTypes> singletonTypes;
+    NotNull<Normalizer> normalizer;
     Mode mode;
 
     NotNull<Scope> scope; // const Scope maybe
@@ -60,13 +62,14 @@ struct Unifier
     Location location;
     Variance variance = Covariant;
     bool anyIsTop = false; // If true, we consider any to be a top type.  If false, it is a familiar but weird mix of top and bottom all at once.
+    bool normalize; // Normalize unions and intersections if necessary
     bool useScopes = false; // If true, we use the scope hierarchy rather than TypeLevels
     CountMismatch::Context ctx = CountMismatch::Arg;
 
     UnifierSharedState& sharedState;
 
-    Unifier(TypeArena* types, NotNull<SingletonTypes> singletonTypes, Mode mode, NotNull<Scope> scope, const Location& location, Variance variance,
+    Unifier(NotNull<Normalizer> normalizer, Mode mode, NotNull<Scope> scope, const Location& location, Variance variance,
-        UnifierSharedState& sharedState, TxnLog* parentLog = nullptr);
+        TxnLog* parentLog = nullptr);
 
     // Test whether the two type vars unify.  Never commits the result.
     ErrorVec canUnify(TypeId subTy, TypeId superTy);
@@ -84,6 +87,7 @@ private:
     void tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTypeVar* uv, bool cacheEnabled, bool isFunctionCall);
     void tryUnifyTypeWithIntersection(TypeId subTy, TypeId superTy, const IntersectionTypeVar* uv);
     void tryUnifyIntersectionWithType(TypeId subTy, const IntersectionTypeVar* uv, TypeId superTy, bool cacheEnabled, bool isFunctionCall);
+    void tryUnifyNormalizedTypes(TypeId subTy, TypeId superTy, const NormalizedType& subNorm, const NormalizedType& superNorm, std::string reason, std::optional<TypeError> error = std::nullopt);
     void tryUnifyPrimitives(TypeId subTy, TypeId superTy);
     void tryUnifySingletons(TypeId subTy, TypeId superTy);
     void tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCall = false);
@@ -92,6 +96,8 @@ private:
     void tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed);
     void tryUnifyWithClass(TypeId subTy, TypeId superTy, bool reversed);
 
+    TypePackId tryApplyOverloadedFunction(TypeId function, const NormalizedFunctionType& overloads, TypePackId args);
+
     TypeId widen(TypeId ty);
     TypePackId widen(TypePackId tp);
 

Analysis/src/Autocomplete.cpp

@@ -12,8 +12,6 @@
 #include <unordered_set>
 #include <utility>
 
-LUAU_FASTFLAG(LuauSelfCallAutocompleteFix3)
-
 static const std::unordered_set<std::string> kStatementStartingKeywords = {
     "while", "if", "local", "repeat", "function", "do", "for", "return", "break", "continue", "type", "export"};
 
@@ -139,7 +137,8 @@ static bool checkTypeMatch(TypeId subTy, TypeId superTy, NotNull<Scope> scope, T
 {
     InternalErrorReporter iceReporter;
     UnifierSharedState unifierState(&iceReporter);
-    Unifier unifier(typeArena, singletonTypes, Mode::Strict, scope, Location(), Variance::Covariant, unifierState);
+    Normalizer normalizer{typeArena, singletonTypes, NotNull{&unifierState}};
+    Unifier unifier(NotNull<Normalizer>{&normalizer}, Mode::Strict, scope, Location(), Variance::Covariant);
 
     return unifier.canUnify(subTy, superTy).empty();
 }
@@ -151,18 +150,6 @@ static TypeCorrectKind checkTypeCorrectKind(
 
     NotNull<Scope> moduleScope{module.getModuleScope().get()};
 
-    auto canUnify = [&typeArena, singletonTypes, moduleScope](TypeId subTy, TypeId superTy) {
-        LUAU_ASSERT(!FFlag::LuauSelfCallAutocompleteFix3);
-
-        InternalErrorReporter iceReporter;
-        UnifierSharedState unifierState(&iceReporter);
-        Unifier unifier(typeArena, singletonTypes, Mode::Strict, moduleScope, Location(), Variance::Covariant, unifierState);
-
-        unifier.tryUnify(subTy, superTy);
-        bool ok = unifier.errors.empty();
-        return ok;
-    };
-
     auto typeAtPosition = findExpectedTypeAt(module, node, position);
 
     if (!typeAtPosition)
@@ -170,30 +157,11 @@ static TypeCorrectKind checkTypeCorrectKind(
 
     TypeId expectedType = follow(*typeAtPosition);
 
-    auto checkFunctionType = [typeArena, singletonTypes, moduleScope, &canUnify, &expectedType](const FunctionTypeVar* ftv) {
+    auto checkFunctionType = [typeArena, singletonTypes, moduleScope, &expectedType](const FunctionTypeVar* ftv) {
-        if (FFlag::LuauSelfCallAutocompleteFix3)
+        if (std::optional<TypeId> firstRetTy = first(ftv->retTypes))
-        {
+            return checkTypeMatch(*firstRetTy, expectedType, moduleScope, typeArena, singletonTypes);
-            if (std::optional<TypeId> firstRetTy = first(ftv->retTypes))
-                return checkTypeMatch(*firstRetTy, expectedType, moduleScope, typeArena, singletonTypes);
 
-            return false;
+        return false;
-        }
-        else
-        {
-            auto [retHead, retTail] = flatten(ftv->retTypes);
-
-            if (!retHead.empty() && canUnify(retHead.front(), expectedType))
-                return true;
-
-            // We might only have a variadic tail pack, check if the element is compatible
-            if (retTail)
-            {
-                if (const VariadicTypePack* vtp = get<VariadicTypePack>(follow(*retTail)); vtp && canUnify(vtp->ty, expectedType))
-                    return true;
-            }
-
-            return false;
-        }
     };
 
     // We also want to suggest functions that return compatible result
@@ -212,11 +180,8 @@ static TypeCorrectKind checkTypeCorrectKind(
         }
     }
 
-    if (FFlag::LuauSelfCallAutocompleteFix3)
+    return checkTypeMatch(ty, expectedType, NotNull{module.getModuleScope().get()}, typeArena, singletonTypes) ? TypeCorrectKind::Correct
-        return checkTypeMatch(ty, expectedType, NotNull{module.getModuleScope().get()}, typeArena, singletonTypes) ? TypeCorrectKind::Correct
+                                                                                                               : TypeCorrectKind::None;
-                                                                                                                   : TypeCorrectKind::None;
-    else
-        return canUnify(ty, expectedType) ? TypeCorrectKind::Correct : TypeCorrectKind::None;
 }
 
 enum class PropIndexType
@@ -230,51 +195,14 @@ static void autocompleteProps(const Module& module, TypeArena* typeArena, NotNul
     PropIndexType indexType, const std::vector<AstNode*>& nodes, AutocompleteEntryMap& result, std::unordered_set<TypeId>& seen,
     std::optional<const ClassTypeVar*> containingClass = std::nullopt)
 {
-    if (FFlag::LuauSelfCallAutocompleteFix3)
+    rootTy = follow(rootTy);
-        rootTy = follow(rootTy);
-
     ty = follow(ty);
 
     if (seen.count(ty))
         return;
     seen.insert(ty);
 
-    auto isWrongIndexer_DEPRECATED = [indexType, useStrictFunctionIndexers = !!get<ClassTypeVar>(ty)](Luau::TypeId type) {
-        LUAU_ASSERT(!FFlag::LuauSelfCallAutocompleteFix3);
-
-        if (indexType == PropIndexType::Key)
-            return false;
-
-        bool colonIndex = indexType == PropIndexType::Colon;
-
-        if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(type))
-        {
-            return useStrictFunctionIndexers ? colonIndex != ftv->hasSelf : false;
-        }
-        else if (const IntersectionTypeVar* itv = get<IntersectionTypeVar>(type))
-        {
-            bool allHaveSelf = true;
-            for (auto subType : itv->parts)
-            {
-                if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(Luau::follow(subType)))
-                {
-                    allHaveSelf &= ftv->hasSelf;
-                }
-                else
-                {
-                    return colonIndex;
-                }
-            }
-            return useStrictFunctionIndexers ? colonIndex != allHaveSelf : false;
-        }
-        else
-        {
-            return colonIndex;
-        }
-    };
     auto isWrongIndexer = [typeArena, singletonTypes, &module, rootTy, indexType](Luau::TypeId type) {
-        LUAU_ASSERT(FFlag::LuauSelfCallAutocompleteFix3);
-
         if (indexType == PropIndexType::Key)
             return false;
 
@@ -337,7 +265,7 @@ static void autocompleteProps(const Module& module, TypeArena* typeArena, NotNul
                     AutocompleteEntryKind::Property,
                     type,
                     prop.deprecated,
-                    FFlag::LuauSelfCallAutocompleteFix3 ? isWrongIndexer(type) : isWrongIndexer_DEPRECATED(type),
+                    isWrongIndexer(type),
                     typeCorrect,
                     containingClass,
                     &prop,
@@ -380,31 +308,8 @@ static void autocompleteProps(const Module& module, TypeArena* typeArena, NotNul
     {
         autocompleteProps(module, typeArena, singletonTypes, rootTy, mt->table, indexType, nodes, result, seen);
 
-        if (FFlag::LuauSelfCallAutocompleteFix3)
+        if (auto mtable = get<TableTypeVar>(mt->metatable))
-        {
+            fillMetatableProps(mtable);
-            if (auto mtable = get<TableTypeVar>(mt->metatable))
-                fillMetatableProps(mtable);
-        }
-        else
-        {
-            auto mtable = get<TableTypeVar>(mt->metatable);
-            if (!mtable)
-                return;
-
-            auto indexIt = mtable->props.find("__index");
-            if (indexIt != mtable->props.end())
-            {
-                TypeId followed = follow(indexIt->second.type);
-                if (get<TableTypeVar>(followed) || get<MetatableTypeVar>(followed))
-                    autocompleteProps(module, typeArena, singletonTypes, rootTy, followed, indexType, nodes, result, seen);
-                else if (auto indexFunction = get<FunctionTypeVar>(followed))
-                {
-                    std::optional<TypeId> indexFunctionResult = first(indexFunction->retTypes);
-                    if (indexFunctionResult)
-                        autocompleteProps(module, typeArena, singletonTypes, rootTy, *indexFunctionResult, indexType, nodes, result, seen);
-                }
-            }
-        }
     }
     else if (auto i = get<IntersectionTypeVar>(ty))
     {
@@ -446,9 +351,6 @@ static void autocompleteProps(const Module& module, TypeArena* typeArena, NotNul
             AutocompleteEntryMap inner;
             std::unordered_set<TypeId> innerSeen;
 
-            if (!FFlag::LuauSelfCallAutocompleteFix3)
-                innerSeen = seen;
-
             if (isNil(*iter))
             {
                 ++iter;
@@ -472,7 +374,7 @@ static void autocompleteProps(const Module& module, TypeArena* typeArena, NotNul
             ++iter;
         }
     }
-    else if (auto pt = get<PrimitiveTypeVar>(ty); pt && FFlag::LuauSelfCallAutocompleteFix3)
+    else if (auto pt = get<PrimitiveTypeVar>(ty))
     {
         if (pt->metatable)
         {
@@ -480,7 +382,7 @@ static void autocompleteProps(const Module& module, TypeArena* typeArena, NotNul
                 fillMetatableProps(mtable);
         }
     }
-    else if (FFlag::LuauSelfCallAutocompleteFix3 && get<StringSingleton>(get<SingletonTypeVar>(ty)))
+    else if (get<StringSingleton>(get<SingletonTypeVar>(ty)))
     {
         autocompleteProps(module, typeArena, singletonTypes, rootTy, singletonTypes->stringType, indexType, nodes, result, seen);
     }
@@ -1416,11 +1318,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
         TypeId ty = follow(*it);
         PropIndexType indexType = indexName->op == ':' ? PropIndexType::Colon : PropIndexType::Point;
 
-        if (!FFlag::LuauSelfCallAutocompleteFix3 && isString(ty))
+        return {autocompleteProps(*module, &typeArena, singletonTypes, ty, indexType, ancestry), ancestry, AutocompleteContext::Property};
-            return {autocompleteProps(*module, &typeArena, singletonTypes, globalScope->bindings[AstName{"string"}].typeId, indexType, ancestry),
-                ancestry, AutocompleteContext::Property};
-        else
-            return {autocompleteProps(*module, &typeArena, singletonTypes, ty, indexType, ancestry), ancestry, AutocompleteContext::Property};
     }
     else if (auto typeReference = node->as<AstTypeReference>())
     {

Analysis/src/ConstraintSolver.cpp

@@ -14,6 +14,8 @@
 #include "Luau/VisitTypeVar.h"
 #include "Luau/TypeUtils.h"
 
+#include <random>
+
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolver, false);
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJson, false);
 LUAU_FASTFLAG(LuauFixNameMaps)
@@ -251,10 +253,11 @@ void dump(ConstraintSolver* cs, ToStringOptions& opts)
     }
 }
 
-ConstraintSolver::ConstraintSolver(TypeArena* arena, NotNull<SingletonTypes> singletonTypes, NotNull<Scope> rootScope, ModuleName moduleName,
+ConstraintSolver::ConstraintSolver(NotNull<Normalizer> normalizer, NotNull<Scope> rootScope, ModuleName moduleName,
     NotNull<ModuleResolver> moduleResolver, std::vector<RequireCycle> requireCycles, DcrLogger* logger)
-    : arena(arena)
+    : arena(normalizer->arena)
-    , singletonTypes(singletonTypes)
+    , singletonTypes(normalizer->singletonTypes)
+    , normalizer(normalizer)
     , constraints(collectConstraints(rootScope))
     , rootScope(rootScope)
     , currentModuleName(std::move(moduleName))
@@ -278,6 +281,12 @@ ConstraintSolver::ConstraintSolver(TypeArena* arena, NotNull<SingletonTypes> sin
         LUAU_ASSERT(logger);
 }
 
+void ConstraintSolver::randomize(unsigned seed)
+{
+    std::mt19937 g(seed);
+    std::shuffle(begin(unsolvedConstraints), end(unsolvedConstraints), g);
+}
+
 void ConstraintSolver::run()
 {
     if (done())
@@ -1355,8 +1364,7 @@ bool ConstraintSolver::isBlocked(NotNull<const Constraint> constraint)
 
 void ConstraintSolver::unify(TypeId subType, TypeId superType, NotNull<Scope> scope)
 {
-    UnifierSharedState sharedState{&iceReporter};
+    Unifier u{normalizer, Mode::Strict, scope, Location{}, Covariant};
-    Unifier u{arena, singletonTypes, Mode::Strict, scope, Location{}, Covariant, sharedState};
     u.useScopes = true;
 
     u.tryUnify(subType, superType);
@@ -1379,7 +1387,7 @@ void ConstraintSolver::unify(TypeId subType, TypeId superType, NotNull<Scope> sc
 void ConstraintSolver::unify(TypePackId subPack, TypePackId superPack, NotNull<Scope> scope)
 {
     UnifierSharedState sharedState{&iceReporter};
-    Unifier u{arena, singletonTypes, Mode::Strict, scope, Location{}, Covariant, sharedState};
+    Unifier u{normalizer, Mode::Strict, scope, Location{}, Covariant};
     u.useScopes = true;
 
     u.tryUnify(subPack, superPack);

Analysis/src/Error.cpp

@@ -511,11 +511,11 @@ TypeMismatch::TypeMismatch(TypeId wantedType, TypeId givenType, std::string reas
 {
 }
 
-TypeMismatch::TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, TypeError error)
+TypeMismatch::TypeMismatch(TypeId wantedType, TypeId givenType, std::string reason, std::optional<TypeError> error)
     : wantedType(wantedType)
     , givenType(givenType)
     , reason(reason)
-    , error(std::make_shared<TypeError>(std::move(error)))
+    , error(error ? std::make_shared<TypeError>(std::move(*error)) : nullptr)
 {
 }
 

Analysis/src/Frontend.cpp

@@ -860,12 +860,18 @@ ModulePtr Frontend::check(
     const NotNull<ModuleResolver> mr{forAutocomplete ? &moduleResolverForAutocomplete : &moduleResolver};
     const ScopePtr& globalScope{forAutocomplete ? typeCheckerForAutocomplete.globalScope : typeChecker.globalScope};
 
+    Normalizer normalizer{&result->internalTypes, singletonTypes, NotNull{&typeChecker.unifierState}};
+
     ConstraintGraphBuilder cgb{
         sourceModule.name, result, &result->internalTypes, mr, singletonTypes, NotNull(&iceHandler), globalScope, logger.get()};
     cgb.visit(sourceModule.root);
     result->errors = std::move(cgb.errors);
 
-    ConstraintSolver cs{&result->internalTypes, singletonTypes, NotNull(cgb.rootScope), sourceModule.name, NotNull(&moduleResolver), requireCycles, logger.get()};
+    ConstraintSolver cs{NotNull{&normalizer}, NotNull(cgb.rootScope), sourceModule.name, NotNull(&moduleResolver), requireCycles, logger.get()};
+
+    if (options.randomizeConstraintResolutionSeed)
+        cs.randomize(*options.randomizeConstraintResolutionSeed);
+
     cs.run();
 
     for (TypeError& e : cs.errors)

Analysis/src/Module.cpp

@@ -14,6 +14,7 @@
 
 #include <algorithm>
 
+LUAU_FASTFLAG(LuauAnyifyModuleReturnGenerics)
 LUAU_FASTFLAG(LuauLowerBoundsCalculation);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 LUAU_FASTFLAGVARIABLE(LuauForceExportSurfacesToBeNormal, false);
@@ -285,13 +286,16 @@ void Module::clonePublicInterface(NotNull<SingletonTypes> singletonTypes, Intern
         }
     }
 
-    for (TypeId ty : returnType)
+    if (!FFlag::LuauAnyifyModuleReturnGenerics)
     {
-        if (get<GenericTypeVar>(follow(ty)))
+        for (TypeId ty : returnType)
         {
-            auto t = asMutable(ty);
+            if (get<GenericTypeVar>(follow(ty)))
-            t->ty = AnyTypeVar{};
+            {
-            t->normal = true;
+                auto t = asMutable(ty);
+                t->ty = AnyTypeVar{};
+                t->normal = true;
+            }
         }
     }
 

Analysis/src/TypeChecker2.cpp

@@ -280,7 +280,8 @@ struct TypeChecker2
         TypePackId actualRetType = reconstructPack(ret->list, arena);
 
         UnifierSharedState sharedState{&ice};
-        Unifier u{&arena, singletonTypes, Mode::Strict, stack.back(), ret->location, Covariant, sharedState};
+        Normalizer normalizer{&arena, singletonTypes, NotNull{&sharedState}};
+        Unifier u{NotNull{&normalizer}, Mode::Strict, stack.back(), ret->location, Covariant};
         u.anyIsTop = true;
 
         u.tryUnify(actualRetType, expectedRetType);
@@ -1206,7 +1207,8 @@ struct TypeChecker2
     ErrorVec tryUnify(NotNull<Scope> scope, const Location& location, TID subTy, TID superTy)
     {
         UnifierSharedState sharedState{&ice};
-        Unifier u{&module->internalTypes, singletonTypes, Mode::Strict, scope, location, Covariant, sharedState};
+        Normalizer normalizer{&module->internalTypes, singletonTypes, NotNull{&sharedState}};
+        Unifier u{NotNull{&normalizer}, Mode::Strict, scope, location, Covariant};
         u.anyIsTop = true;
         u.tryUnify(subTy, superTy);
 

Analysis/src/TypeInfer.cpp

@@ -32,19 +32,21 @@ LUAU_FASTINTVARIABLE(LuauCheckRecursionLimit, 300)
 LUAU_FASTINTVARIABLE(LuauVisitRecursionLimit, 500)
 LUAU_FASTFLAG(LuauKnowsTheDataModel3)
 LUAU_FASTFLAG(LuauAutocompleteDynamicLimits)
+LUAU_FASTFLAG(LuauTypeNormalization2)
 LUAU_FASTFLAGVARIABLE(LuauFunctionArgMismatchDetails, false)
-LUAU_FASTFLAGVARIABLE(LuauInplaceDemoteSkipAllBound, false)
 LUAU_FASTFLAGVARIABLE(LuauLowerBoundsCalculation, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauFreezeDuringUnification, false)
-LUAU_FASTFLAGVARIABLE(LuauSelfCallAutocompleteFix3, false)
 LUAU_FASTFLAGVARIABLE(LuauReturnAnyInsteadOfICE, false) // Eventually removed as false.
 LUAU_FASTFLAGVARIABLE(DebugLuauSharedSelf, false)
+LUAU_FASTFLAGVARIABLE(LuauAnyifyModuleReturnGenerics, false)
 LUAU_FASTFLAGVARIABLE(LuauUnknownAndNeverType, false)
 LUAU_FASTFLAGVARIABLE(LuauCallUnifyPackTails, false)
 LUAU_FASTFLAGVARIABLE(LuauCheckGenericHOFTypes, false)
 LUAU_FASTFLAGVARIABLE(LuauBinaryNeedsExpectedTypesToo, false)
+LUAU_FASTFLAGVARIABLE(LuauFixVarargExprHeadType, false)
 LUAU_FASTFLAGVARIABLE(LuauNeverTypesAndOperatorsInference, false)
 LUAU_FASTFLAGVARIABLE(LuauReturnsFromCallsitesAreNotWidened, false)
+LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 LUAU_FASTFLAGVARIABLE(LuauCompleteVisitor, false)
 LUAU_FASTFLAGVARIABLE(LuauUnionOfTypesFollow, false)
 LUAU_FASTFLAGVARIABLE(LuauReportShadowedTypeAlias, false)
@@ -255,6 +257,7 @@ TypeChecker::TypeChecker(ModuleResolver* resolver, NotNull<SingletonTypes> singl
     , singletonTypes(singletonTypes)
     , iceHandler(iceHandler)
     , unifierState(iceHandler)
+    , normalizer(nullptr, singletonTypes, NotNull{&unifierState})
     , nilType(singletonTypes->nilType)
     , numberType(singletonTypes->numberType)
     , stringType(singletonTypes->stringType)
@@ -301,12 +304,13 @@ ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mo
     LUAU_TIMETRACE_SCOPE("TypeChecker::check", "TypeChecker");
     LUAU_TIMETRACE_ARGUMENT("module", module.name.c_str());
 
-    currentModule.reset(new Module());
+    currentModule.reset(new Module);
     currentModule->type = module.type;
     currentModule->allocator = module.allocator;
     currentModule->names = module.names;
 
     iceHandler->moduleName = module.name;
+    normalizer.arena = &currentModule->internalTypes;
 
     if (FFlag::LuauAutocompleteDynamicLimits)
     {
@@ -351,15 +355,23 @@ ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mo
     if (get<FreeTypePack>(follow(moduleScope->returnType)))
         moduleScope->returnType = addTypePack(TypePack{{}, std::nullopt});
     else
-    {
         moduleScope->returnType = anyify(moduleScope, moduleScope->returnType, Location{});
-    }
+
+    if (FFlag::LuauAnyifyModuleReturnGenerics)
+        moduleScope->returnType = anyifyModuleReturnTypePackGenerics(moduleScope->returnType);
 
     for (auto& [_, typeFun] : moduleScope->exportedTypeBindings)
         typeFun.type = anyify(moduleScope, typeFun.type, Location{});
 
     prepareErrorsForDisplay(currentModule->errors);
 
+    if (FFlag::LuauTypeNormalization2)
+    {
+        // Clear the normalizer caches, since they contain types from the internal type surface
+        normalizer.clearCaches();
+        normalizer.arena = nullptr;
+    }
+
     currentModule->clonePublicInterface(singletonTypes, *iceHandler);
 
     // Clear unifier cache since it's keyed off internal types that get deallocated
@@ -474,7 +486,7 @@ struct InplaceDemoter : TypeVarOnceVisitor
     TypeArena* arena;
 
     InplaceDemoter(TypeLevel level, TypeArena* arena)
-        : TypeVarOnceVisitor(/* skipBoundTypes= */ FFlag::LuauInplaceDemoteSkipAllBound)
+        : TypeVarOnceVisitor(/* skipBoundTypes= */ true)
         , newLevel(level)
         , arena(arena)
     {
@@ -494,12 +506,6 @@ struct InplaceDemoter : TypeVarOnceVisitor
         return false;
     }
 
-    bool visit(TypeId ty, const BoundTypeVar& btyRef) override
-    {
-        LUAU_ASSERT(!FFlag::LuauInplaceDemoteSkipAllBound);
-        return true;
-    }
-
     bool visit(TypeId ty) override
     {
         if (ty->owningArena != arena)
@@ -1029,8 +1035,11 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatAssign& assign)
 
         if (right)
         {
-            if (!maybeGeneric(left) && isGeneric(right))
+            if (!FFlag::LuauInstantiateInSubtyping)
-                right = instantiate(scope, right, loc);
+            {
+                if (!maybeGeneric(left) && isGeneric(right))
+                    right = instantiate(scope, right, loc);
+            }
 
             // Setting a table entry to nil doesn't mean nil is the type of the indexer, it is just deleting the entry
             const TableTypeVar* destTableTypeReceivingNil = nullptr;
@@ -1104,7 +1113,9 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatLocal& local)
         variableTypes.push_back(ty);
         expectedTypes.push_back(ty);
 
-        instantiateGenerics.push_back(annotation != nullptr && !maybeGeneric(ty));
+        // with FFlag::LuauInstantiateInSubtyping enabled, we shouldn't need to produce instantiateGenerics at all.
+        if (!FFlag::LuauInstantiateInSubtyping)
+            instantiateGenerics.push_back(annotation != nullptr && !maybeGeneric(ty));
     }
 
     if (local.values.size > 0)
@@ -1729,9 +1740,7 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatDeclareClass& declar
             {
                 ftv->argNames.insert(ftv->argNames.begin(), FunctionArgument{"self", {}});
                 ftv->argTypes = addTypePack(TypePack{{classTy}, ftv->argTypes});
-
+                ftv->hasSelf = true;
-                if (FFlag::LuauSelfCallAutocompleteFix3)
-                    ftv->hasSelf = true;
             }
         }
 
@@ -1905,8 +1914,18 @@ WithPredicate<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExp
 
     if (get<TypePack>(varargPack))
     {
-        std::vector<TypeId> types = flatten(varargPack).first;
+        if (FFlag::LuauFixVarargExprHeadType)
-        return {!types.empty() ? types[0] : nilType};
+        {
+            if (std::optional<TypeId> ty = first(varargPack))
+                return {*ty};
+
+            return {nilType};
+        }
+        else
+        {
+            std::vector<TypeId> types = flatten(varargPack).first;
+            return {!types.empty() ? types[0] : nilType};
+        }
     }
     else if (get<FreeTypePack>(varargPack))
     {
@@ -3967,7 +3986,10 @@ void TypeChecker::checkArgumentList(const ScopePtr& scope, const AstExpr& funNam
         }
         else
         {
-            unifyWithInstantiationIfNeeded(*argIter, *paramIter, scope, state);
+            if (FFlag::LuauInstantiateInSubtyping)
+                state.tryUnify(*argIter, *paramIter, /*isFunctionCall*/ false);
+            else
+                unifyWithInstantiationIfNeeded(*argIter, *paramIter, scope, state);
             ++argIter;
             ++paramIter;
         }
@@ -4523,8 +4545,11 @@ WithPredicate<TypePackId> TypeChecker::checkExprList(const ScopePtr& scope, cons
 
             TypeId actualType = substituteFreeForNil && expr->is<AstExprConstantNil>() ? freshType(scope) : type;
 
-            if (instantiateGenerics.size() > i && instantiateGenerics[i])
+            if (!FFlag::LuauInstantiateInSubtyping)
-                actualType = instantiate(scope, actualType, expr->location);
+            {
+                if (instantiateGenerics.size() > i && instantiateGenerics[i])
+                    actualType = instantiate(scope, actualType, expr->location);
+            }
 
             if (expectedType)
             {
@@ -4686,6 +4711,8 @@ bool TypeChecker::unifyWithInstantiationIfNeeded(TypeId subTy, TypeId superTy, c
 
 void TypeChecker::unifyWithInstantiationIfNeeded(TypeId subTy, TypeId superTy, const ScopePtr& scope, Unifier& state)
 {
+    LUAU_ASSERT(!FFlag::LuauInstantiateInSubtyping);
+
     if (!maybeGeneric(subTy))
         // Quick check to see if we definitely can't instantiate
         state.tryUnify(subTy, superTy, /*isFunctionCall*/ false);
@@ -4828,6 +4855,33 @@ TypePackId TypeChecker::anyify(const ScopePtr& scope, TypePackId ty, Location lo
     }
 }
 
+TypePackId TypeChecker::anyifyModuleReturnTypePackGenerics(TypePackId tp)
+{
+    tp = follow(tp);
+
+    if (const VariadicTypePack* vtp = get<VariadicTypePack>(tp))
+        return get<GenericTypeVar>(vtp->ty) ? anyTypePack : tp;
+
+    if (!get<TypePack>(follow(tp)))
+        return tp;
+
+    std::vector<TypeId> resultTypes;
+    std::optional<TypePackId> resultTail;
+
+    TypePackIterator it = begin(tp);
+
+    for (TypePackIterator e = end(tp); it != e; ++it)
+    {
+        TypeId ty = follow(*it);
+        resultTypes.push_back(get<GenericTypeVar>(ty) ? anyType : ty);
+    }
+
+    if (std::optional<TypePackId> tail = it.tail())
+        resultTail = anyifyModuleReturnTypePackGenerics(*tail);
+
+    return addTypePack(resultTypes, resultTail);
+}
+
 void TypeChecker::reportError(const TypeError& error)
 {
     if (currentModule->mode == Mode::NoCheck)
@@ -4955,8 +5009,7 @@ void TypeChecker::merge(RefinementMap& l, const RefinementMap& r)
 
 Unifier TypeChecker::mkUnifier(const ScopePtr& scope, const Location& location)
 {
-    return Unifier{
+    return Unifier{NotNull{&normalizer}, currentModule->mode, NotNull{scope.get()}, location, Variance::Covariant};
-        &currentModule->internalTypes, singletonTypes, currentModule->mode, NotNull{scope.get()}, location, Variance::Covariant, unifierState};
 }
 
 TypeId TypeChecker::freshType(const ScopePtr& scope)

Analysis/src/TypeVar.cpp

@@ -27,6 +27,7 @@ LUAU_FASTFLAG(LuauUnknownAndNeverType)
 LUAU_FASTFLAGVARIABLE(LuauMaybeGenericIntersectionTypes, false)
 LUAU_FASTFLAGVARIABLE(LuauStringFormatArgumentErrorFix, false)
 LUAU_FASTFLAGVARIABLE(LuauNoMoreGlobalSingletonTypes, false)
+LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 
 namespace Luau
 {
@@ -339,6 +340,8 @@ bool isSubset(const UnionTypeVar& super, const UnionTypeVar& sub)
 // then instantiate U if `isGeneric(U)` is true, and `maybeGeneric(T)` is false.
 bool isGeneric(TypeId ty)
 {
+    LUAU_ASSERT(!FFlag::LuauInstantiateInSubtyping);
+
     ty = follow(ty);
     if (auto ftv = get<FunctionTypeVar>(ty))
         return ftv->generics.size() > 0 || ftv->genericPacks.size() > 0;
@@ -350,6 +353,8 @@ bool isGeneric(TypeId ty)
 
 bool maybeGeneric(TypeId ty)
 {
+    LUAU_ASSERT(!FFlag::LuauInstantiateInSubtyping);
+
     if (FFlag::LuauMaybeGenericIntersectionTypes)
     {
         ty = follow(ty);

Analysis/src/Unifiable.cpp

@@ -1,60 +1,64 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Unifiable.h"
 
+LUAU_FASTFLAG(LuauTypeNormalization2);
+
 namespace Luau
 {
 namespace Unifiable
 {
 
+static int nextIndex = 0;
+
 Free::Free(TypeLevel level)
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , level(level)
 {
 }
 
 Free::Free(Scope* scope)
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , scope(scope)
 {
 }
 
 Free::Free(Scope* scope, TypeLevel level)
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , level(level)
     , scope(scope)
 {
 }
 
-int Free::nextIndex = 0;
+int Free::DEPRECATED_nextIndex = 0;
 
 Generic::Generic()
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , name("g" + std::to_string(index))
 {
 }
 
 Generic::Generic(TypeLevel level)
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , level(level)
     , name("g" + std::to_string(index))
 {
 }
 
 Generic::Generic(const Name& name)
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , name(name)
     , explicitName(true)
 {
 }
 
 Generic::Generic(Scope* scope)
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , scope(scope)
 {
 }
 
 Generic::Generic(TypeLevel level, const Name& name)
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , level(level)
     , name(name)
     , explicitName(true)
@@ -62,14 +66,14 @@ Generic::Generic(TypeLevel level, const Name& name)
 }
 
 Generic::Generic(Scope* scope, const Name& name)
-    : index(++nextIndex)
+    : index(FFlag::LuauTypeNormalization2 ? ++nextIndex : ++DEPRECATED_nextIndex)
     , scope(scope)
     , name(name)
     , explicitName(true)
 {
 }
 
-int Generic::nextIndex = 0;
+int Generic::DEPRECATED_nextIndex = 0;
 
 Error::Error()
     : index(++nextIndex)

Analysis/src/Unifier.cpp

@@ -2,6 +2,7 @@
 #include "Luau/Unifier.h"
 
 #include "Luau/Common.h"
+#include "Luau/Instantiation.h"
 #include "Luau/RecursionCounter.h"
 #include "Luau/Scope.h"
 #include "Luau/TypePack.h"
@@ -20,7 +21,9 @@ LUAU_FASTINTVARIABLE(LuauTypeInferLowerBoundsIterationLimit, 2000);
 LUAU_FASTFLAG(LuauLowerBoundsCalculation);
 LUAU_FASTFLAG(LuauErrorRecoveryType);
 LUAU_FASTFLAG(LuauUnknownAndNeverType)
+LUAU_FASTFLAGVARIABLE(LuauSubtypeNormalizer, false);
 LUAU_FASTFLAGVARIABLE(LuauScalarShapeSubtyping, false)
+LUAU_FASTFLAGVARIABLE(LuauInstantiateInSubtyping, false)
 LUAU_FASTFLAG(LuauClassTypeVarsInSubstitution)
 LUAU_FASTFLAG(LuauCallUnifyPackTails)
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
@@ -343,17 +346,19 @@ static bool subsumes(bool useScopes, TY_A* left, TY_B* right)
         return left->level.subsumes(right->level);
 }
 
-Unifier::Unifier(TypeArena* types, NotNull<SingletonTypes> singletonTypes, Mode mode, NotNull<Scope> scope, const Location& location,
+Unifier::Unifier(NotNull<Normalizer> normalizer, Mode mode, NotNull<Scope> scope, const Location& location,
-    Variance variance, UnifierSharedState& sharedState, TxnLog* parentLog)
+    Variance variance, TxnLog* parentLog)
-    : types(types)
+    : types(normalizer->arena)
-    , singletonTypes(singletonTypes)
+    , singletonTypes(normalizer->singletonTypes)
+    , normalizer(normalizer)
     , mode(mode)
     , scope(scope)
     , log(parentLog)
     , location(location)
     , variance(variance)
-    , sharedState(sharedState)
+    , sharedState(*normalizer->sharedState)
 {
+    normalize = FFlag::LuauSubtypeNormalizer;
     LUAU_ASSERT(sharedState.iceHandler);
 }
 
@@ -524,7 +529,7 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
     {
         tryUnifyUnionWithType(subTy, subUnion, superTy);
     }
-    else if (const UnionTypeVar* uv = log.getMutable<UnionTypeVar>(superTy))
+    else if (const UnionTypeVar* uv = (FFlag::LuauSubtypeNormalizer? nullptr: log.getMutable<UnionTypeVar>(superTy)))
     {
         tryUnifyTypeWithUnion(subTy, superTy, uv, cacheEnabled, isFunctionCall);
     }
@@ -532,6 +537,10 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
     {
         tryUnifyTypeWithIntersection(subTy, superTy, uv);
     }
+    else if (const UnionTypeVar* uv = log.getMutable<UnionTypeVar>(superTy))
+    {
+        tryUnifyTypeWithUnion(subTy, superTy, uv, cacheEnabled, isFunctionCall);
+    }
     else if (const IntersectionTypeVar* uv = log.getMutable<IntersectionTypeVar>(subTy))
     {
         tryUnifyIntersectionWithType(subTy, uv, superTy, cacheEnabled, isFunctionCall);
@@ -585,7 +594,7 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
 
 void Unifier::tryUnifyUnionWithType(TypeId subTy, const UnionTypeVar* subUnion, TypeId superTy)
 {
-    // A | B <: T if A <: T and B <: T
+    // A | B <: T if and only if A <: T and B <: T
     bool failed = false;
     std::optional<TypeError> unificationTooComplex;
     std::optional<TypeError> firstFailedOption;
@@ -715,6 +724,7 @@ void Unifier::tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTyp
     {
         TypeId type = uv->options[(i + startIndex) % uv->options.size()];
         Unifier innerState = makeChildUnifier();
+        innerState.normalize = false;
         innerState.tryUnify_(subTy, type, isFunctionCall);
 
         if (innerState.errors.empty())
@@ -741,6 +751,20 @@ void Unifier::tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTyp
     {
         reportError(*unificationTooComplex);
     }
+    else if (!found && normalize)
+    {
+        // It is possible that T <: A | B even though T </: A and T </:B
+        // for example boolean <: true | false.
+        // We deal with this by type normalization.
+        const NormalizedType* subNorm = normalizer->normalize(subTy);
+        const NormalizedType* superNorm = normalizer->normalize(superTy);
+        if (!subNorm || !superNorm)
+            reportError(TypeError{location, UnificationTooComplex{}});
+        else if ((failedOptionCount == 1 || foundHeuristic) && failedOption)
+            tryUnifyNormalizedTypes(subTy, superTy, *subNorm, *superNorm, "None of the union options are compatible. For example:", *failedOption);
+        else
+            tryUnifyNormalizedTypes(subTy, superTy, *subNorm, *superNorm, "none of the union options are compatible");
+    }
     else if (!found)
     {
         if ((failedOptionCount == 1 || foundHeuristic) && failedOption)
@@ -755,7 +779,7 @@ void Unifier::tryUnifyTypeWithIntersection(TypeId subTy, TypeId superTy, const I
     std::optional<TypeError> unificationTooComplex;
     std::optional<TypeError> firstFailedOption;
 
-    // T <: A & B if T <: A and T <: B
+    // T <: A & B if and only if  T <: A and T <: B
     for (TypeId type : uv->parts)
     {
         Unifier innerState = makeChildUnifier();
@@ -806,6 +830,7 @@ void Unifier::tryUnifyIntersectionWithType(TypeId subTy, const IntersectionTypeV
     {
         TypeId type = uv->parts[(i + startIndex) % uv->parts.size()];
         Unifier innerState = makeChildUnifier();
+        innerState.normalize = false;
         innerState.tryUnify_(type, superTy, isFunctionCall);
 
         if (innerState.errors.empty())
@@ -822,12 +847,207 @@ void Unifier::tryUnifyIntersectionWithType(TypeId subTy, const IntersectionTypeV
 
     if (unificationTooComplex)
         reportError(*unificationTooComplex);
+    else if (!found && normalize)
+    {
+        // It is possible that A & B <: T even though A </: T and B </: T
+        // for example string? & number? <: nil.
+        // We deal with this by type normalization.
+        const NormalizedType* subNorm = normalizer->normalize(subTy);
+        const NormalizedType* superNorm = normalizer->normalize(superTy);
+        if (subNorm && superNorm)
+            tryUnifyNormalizedTypes(subTy, superTy, *subNorm, *superNorm, "none of the intersection parts are compatible");
+        else
+            reportError(TypeError{location, UnificationTooComplex{}});
+    }
     else if (!found)
     {
         reportError(TypeError{location, TypeMismatch{superTy, subTy, "none of the intersection parts are compatible"}});
     }
 }
 
+void Unifier::tryUnifyNormalizedTypes(TypeId subTy, TypeId superTy, const NormalizedType& subNorm, const NormalizedType& superNorm, std::string reason, std::optional<TypeError> error)
+{
+    LUAU_ASSERT(FFlag::LuauSubtypeNormalizer);
+
+    if (get<UnknownTypeVar>(superNorm.tops) || get<AnyTypeVar>(superNorm.tops) || get<AnyTypeVar>(subNorm.tops))
+        return;
+    else if (get<UnknownTypeVar>(subNorm.tops))
+        return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+
+    if (get<ErrorTypeVar>(subNorm.errors))
+        if (!get<ErrorTypeVar>(superNorm.errors))
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+
+    if (get<PrimitiveTypeVar>(subNorm.booleans))
+    {
+        if (!get<PrimitiveTypeVar>(superNorm.booleans))
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+    }
+    else if (const SingletonTypeVar* stv = get<SingletonTypeVar>(subNorm.booleans))
+    {
+        if (!get<PrimitiveTypeVar>(superNorm.booleans) && stv != get<SingletonTypeVar>(superNorm.booleans))
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+    }
+
+    if (get<PrimitiveTypeVar>(subNorm.nils))
+        if (!get<PrimitiveTypeVar>(superNorm.nils))
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+
+    if (get<PrimitiveTypeVar>(subNorm.numbers))
+        if (!get<PrimitiveTypeVar>(superNorm.numbers))
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+
+    if (subNorm.strings && superNorm.strings)
+    {
+        for (auto [name, ty] : *subNorm.strings)
+            if (!superNorm.strings->count(name))
+                return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+    }
+    else if (!subNorm.strings && superNorm.strings)
+        return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+
+    if (get<PrimitiveTypeVar>(subNorm.threads))
+        if (!get<PrimitiveTypeVar>(superNorm.errors))
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+
+    for (TypeId subClass : subNorm.classes)
+    {
+        bool found = false;
+        const ClassTypeVar* subCtv = get<ClassTypeVar>(subClass);
+        for (TypeId superClass : superNorm.classes)
+        {
+            const ClassTypeVar* superCtv = get<ClassTypeVar>(superClass);
+            if (isSubclass(subCtv, superCtv))
+            {
+                found = true;
+                break;
+            }
+        }
+        if (!found)
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+    }
+
+    for (TypeId subTable : subNorm.tables)
+    {
+        bool found = false;
+        for (TypeId superTable : superNorm.tables)
+        {
+            Unifier innerState = makeChildUnifier();
+            if (get<MetatableTypeVar>(superTable))
+                innerState.tryUnifyWithMetatable(subTable, superTable, /* reversed */ false);
+            else if (get<MetatableTypeVar>(subTable))
+                innerState.tryUnifyWithMetatable(superTable, subTable, /* reversed */ true);
+            else
+                innerState.tryUnifyTables(subTable, superTable);
+            if (innerState.errors.empty())
+            {
+                found = true;
+                log.concat(std::move(innerState.log));
+                break;
+            }
+            else if (auto e = hasUnificationTooComplex(innerState.errors))
+                return reportError(*e);
+        }
+        if (!found)
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+    }
+
+    if (subNorm.functions)
+    {
+        if (!superNorm.functions)
+            return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+        if (superNorm.functions->empty())
+            return;
+        for (TypeId superFun : *superNorm.functions)
+        {
+            Unifier innerState = makeChildUnifier();
+            const FunctionTypeVar* superFtv = get<FunctionTypeVar>(superFun);
+            if (!superFtv)
+                return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+            TypePackId tgt = innerState.tryApplyOverloadedFunction(subTy, subNorm.functions, superFtv->argTypes);
+            innerState.tryUnify_(tgt, superFtv->retTypes);
+            if (innerState.errors.empty())
+                log.concat(std::move(innerState.log));
+            else if (auto e = hasUnificationTooComplex(innerState.errors))
+                return reportError(*e);
+            else
+                return reportError(TypeError{location, TypeMismatch{superTy, subTy, reason, error}});
+        }
+    }
+
+    for (auto& [tyvar, subIntersect] : subNorm.tyvars)
+    {
+        auto found = superNorm.tyvars.find(tyvar);
+        if (found == superNorm.tyvars.end())
+            tryUnifyNormalizedTypes(subTy, superTy, *subIntersect, superNorm, reason, error);
+        else
+            tryUnifyNormalizedTypes(subTy, superTy, *subIntersect, *found->second, reason, error);
+        if (!errors.empty())
+            return;
+    }
+}
+
+TypePackId Unifier::tryApplyOverloadedFunction(TypeId function, const NormalizedFunctionType& overloads, TypePackId args)
+{
+    if (!overloads || overloads->empty())
+    {
+        reportError(TypeError{location, CannotCallNonFunction{function}});
+        return singletonTypes->errorRecoveryTypePack();
+    }
+
+    std::optional<TypePackId> result;
+    const FunctionTypeVar* firstFun = nullptr;
+    for (TypeId overload : *overloads)
+    {
+        if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(overload))
+        {
+            // TODO: instantiate generics?
+            if (ftv->generics.empty() && ftv->genericPacks.empty())
+            {
+                if (!firstFun)
+                    firstFun = ftv;
+                Unifier innerState = makeChildUnifier();
+                innerState.tryUnify_(args, ftv->argTypes);
+                if (innerState.errors.empty())
+                {
+                    log.concat(std::move(innerState.log));
+                    if (result)
+                    {
+                        // Annoyingly, since we don't support intersection of generic type packs,
+                        // the intersection may fail. We rather arbitrarily use the first matching overload
+                        // in that case.
+                        if (std::optional<TypePackId> intersect = normalizer->intersectionOfTypePacks(*result, ftv->retTypes))
+                            result = intersect;
+                    }
+                    else
+                        result = ftv->retTypes;
+                }
+                else if (auto e = hasUnificationTooComplex(innerState.errors))
+                {
+                    reportError(*e);
+                    return singletonTypes->errorRecoveryTypePack(args);
+                }
+            }
+        }
+    }
+
+    if (result)
+        return *result;
+    else if (firstFun)
+    {
+        // TODO: better error reporting?
+        // The logic for error reporting overload resolution
+        // is currently over in TypeInfer.cpp, should we move it?
+        reportError(TypeError{location, GenericError{"No matching overload."}});
+        return singletonTypes->errorRecoveryTypePack(firstFun->retTypes);
+    }
+    else
+    {
+        reportError(TypeError{location, CannotCallNonFunction{function}});
+        return singletonTypes->errorRecoveryTypePack();
+    }
+}
+
 bool Unifier::canCacheResult(TypeId subTy, TypeId superTy)
 {
     bool* superTyInfo = sharedState.skipCacheForType.find(superTy);
@@ -1253,14 +1473,38 @@ void Unifier::tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCal
         ice("passed non-function types to unifyFunction");
 
     size_t numGenerics = superFunction->generics.size();
-    if (numGenerics != subFunction->generics.size())
+    size_t numGenericPacks = superFunction->genericPacks.size();
+
+    bool shouldInstantiate = (numGenerics == 0 && subFunction->generics.size() > 0) || (numGenericPacks == 0 && subFunction->genericPacks.size() > 0);
+
+    if (FFlag::LuauInstantiateInSubtyping && variance == Covariant && shouldInstantiate)
+    {
+        Instantiation instantiation{&log, types, scope->level, scope};
+
+        std::optional<TypeId> instantiated = instantiation.substitute(subTy);
+        if (instantiated.has_value())
+        {
+            subFunction = log.getMutable<FunctionTypeVar>(*instantiated);
+
+            if (!subFunction)
+                ice("instantiation made a function type into a non-function type in unifyFunction");
+
+            numGenerics = std::min(superFunction->generics.size(), subFunction->generics.size());
+            numGenericPacks = std::min(superFunction->genericPacks.size(), subFunction->genericPacks.size());
+
+        }
+        else
+        {
+            reportError(TypeError{location, UnificationTooComplex{}});
+        }
+    }
+    else if (numGenerics != subFunction->generics.size())
     {
         numGenerics = std::min(superFunction->generics.size(), subFunction->generics.size());
 
         reportError(TypeError{location, TypeMismatch{superTy, subTy, "different number of generic type parameters"}});
     }
 
-    size_t numGenericPacks = superFunction->genericPacks.size();
     if (numGenericPacks != subFunction->genericPacks.size())
     {
         numGenericPacks = std::min(superFunction->genericPacks.size(), subFunction->genericPacks.size());
@@ -1376,6 +1620,27 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
     std::vector<std::string> missingProperties;
     std::vector<std::string> extraProperties;
 
+    if (FFlag::LuauInstantiateInSubtyping)
+    {
+        if (variance == Covariant && subTable->state == TableState::Generic && superTable->state != TableState::Generic)
+        {
+            Instantiation instantiation{&log, types, subTable->level, scope};
+
+            std::optional<TypeId> instantiated = instantiation.substitute(subTy);
+            if (instantiated.has_value())
+            {
+                subTable = log.getMutable<TableTypeVar>(*instantiated);
+
+                if (!subTable)
+                    ice("instantiation made a table type into a non-table type in tryUnifyTables");
+            }
+            else
+            {
+                reportError(TypeError{location, UnificationTooComplex{}});
+            }
+        }
+    }
+
     // Optimization: First test that the property sets are compatible without doing any recursive unification
     if (!subTable->indexer && subTable->state != TableState::Free)
     {
@@ -2344,8 +2609,9 @@ bool Unifier::occursCheck(DenseHashSet<TypePackId>& seen, TypePackId needle, Typ
 
 Unifier Unifier::makeChildUnifier()
 {
-    Unifier u = Unifier{types, singletonTypes, mode, scope, location, variance, sharedState, &log};
+    Unifier u = Unifier{normalizer, mode, scope, location, variance, &log};
     u.anyIsTop = anyIsTop;
+    u.normalize = normalize;
     return u;
 }
 

Ast/src/Parser.cpp

@@ -25,6 +25,8 @@ LUAU_DYNAMIC_FASTFLAGVARIABLE(LuaReportParseIntegerIssues, false)
 LUAU_FASTFLAGVARIABLE(LuauInterpolatedStringBaseSupport, false)
 LUAU_FASTFLAGVARIABLE(LuauTypeAnnotationLocationChange, false)
 
+LUAU_FASTFLAGVARIABLE(LuauCommaParenWarnings, false)
+
 bool lua_telemetry_parsed_out_of_range_bin_integer = false;
 bool lua_telemetry_parsed_out_of_range_hex_integer = false;
 bool lua_telemetry_parsed_double_prefix_hex_integer = false;
@@ -1062,6 +1064,12 @@ void Parser::parseExprList(TempVector<AstExpr*>& result)
     {
         nextLexeme();
 
+        if (FFlag::LuauCommaParenWarnings && lexer.current().type == ')')
+        {
+            report(lexer.current().location, "Expected expression after ',' but got ')' instead");
+            break;
+        }
+
         result.push_back(parseExpr());
     }
 }
@@ -1148,7 +1156,14 @@ AstTypePack* Parser::parseTypeList(TempVector<AstType*>& result, TempVector<std:
         result.push_back(parseTypeAnnotation());
         if (lexer.current().type != ',')
             break;
+
         nextLexeme();
+
+        if (FFlag::LuauCommaParenWarnings && lexer.current().type == ')')
+        {
+            report(lexer.current().location, "Expected type after ',' but got ')' instead");
+            break;
+        }
     }
 
     return nullptr;
@@ -2514,7 +2529,15 @@ std::pair<AstArray<AstGenericType>, AstArray<AstGenericTypePack>> Parser::parseG
             }
 
             if (lexer.current().type == ',')
+            {
                 nextLexeme();
+
+                if (FFlag::LuauCommaParenWarnings && lexer.current().type == '>')
+                {
+                    report(lexer.current().location, "Expected type after ',' but got '>' instead");
+                    break;
+                }
+            }
             else
                 break;
         }

CLI/Profiler.cpp

@@ -82,11 +82,13 @@ static void profilerLoop()
 
         if (now - last >= 1.0 / double(gProfiler.frequency))
         {
-            gProfiler.ticks += uint64_t((now - last) * 1e6);
+            int64_t ticks = int64_t((now - last) * 1e6);
+
+            gProfiler.ticks += ticks;
             gProfiler.samples++;
             gProfiler.callbacks->interrupt = profilerTrigger;
 
-            last = now;
+            last += ticks * 1e-6;
         }
         else
         {

CodeGen/include/Luau/AssemblyBuilderX64.h

@@ -152,6 +152,7 @@ private:
     void placeModRegMem(OperandX64 rhs, uint8_t regop);
     void placeRex(RegisterX64 op);
     void placeRex(OperandX64 op);
+    void placeRexNoW(OperandX64 op);
     void placeRex(RegisterX64 lhs, OperandX64 rhs);
     void placeVex(OperandX64 dst, OperandX64 src1, OperandX64 src2, bool setW, uint8_t mode, uint8_t prefix);
     void placeImm8Or32(int32_t imm);

CodeGen/include/Luau/CodeAllocator.h

@@ -24,13 +24,15 @@ struct CodeAllocator
     void* context = nullptr;
 
     // Called when new block is created to create and setup the unwinding information for all the code in the block
-    // If data is placed inside the block itself (some platforms require this), we also return 'unwindDataSizeInBlock'
+    // 'startOffset' reserves space for data at the beginning of the page
-    void* (*createBlockUnwindInfo)(void* context, uint8_t* block, size_t blockSize, size_t& unwindDataSizeInBlock) = nullptr;
+    void* (*createBlockUnwindInfo)(void* context, uint8_t* block, size_t blockSize, size_t& startOffset) = nullptr;
 
     // Called to destroy unwinding information returned by 'createBlockUnwindInfo'
     void (*destroyBlockUnwindInfo)(void* context, void* unwindData) = nullptr;
 
-    static const size_t kMaxUnwindDataSize = 128;
+    // Unwind information can be placed inside the block with some implementation-specific reservations at the beginning
+    // But to simplify block space checks, we limit the max size of all that data
+    static const size_t kMaxReservedDataSize = 256;
 
     bool allocateNewBlock(size_t& unwindInfoSize);
 

CodeGen/include/Luau/CodeBlockUnwind.h

@@ -10,7 +10,7 @@ namespace CodeGen
 {
 
 // context must be an UnwindBuilder
-void* createBlockUnwindInfo(void* context, uint8_t* block, size_t blockSize, size_t& unwindDataSizeInBlock);
+void* createBlockUnwindInfo(void* context, uint8_t* block, size_t blockSize, size_t& startOffset);
 void destroyBlockUnwindInfo(void* context, void* unwindData);
 
 } // namespace CodeGen

CodeGen/include/Luau/UnwindBuilder.h

@@ -14,7 +14,10 @@ namespace CodeGen
 class UnwindBuilder
 {
 public:
-    virtual ~UnwindBuilder() {}
+    virtual ~UnwindBuilder() = default;
+
+    virtual void setBeginOffset(size_t beginOffset) = 0;
+    virtual size_t getBeginOffset() const = 0;
 
     virtual void start() = 0;
 

CodeGen/include/Luau/UnwindBuilderDwarf2.h

@@ -12,6 +12,9 @@ namespace CodeGen
 class UnwindBuilderDwarf2 : public UnwindBuilder
 {
 public:
+    void setBeginOffset(size_t beginOffset) override;
+    size_t getBeginOffset() const override;
+
     void start() override;
 
     void spill(int espOffset, RegisterX64 reg) override;
@@ -26,6 +29,8 @@ public:
     void finalize(char* target, void* funcAddress, size_t funcSize) const override;
 
 private:
+    size_t beginOffset = 0;
+
     static const unsigned kRawDataLimit = 128;
     uint8_t rawData[kRawDataLimit];
     uint8_t* pos = rawData;

CodeGen/include/Luau/UnwindBuilderWin.h

@@ -22,6 +22,9 @@ struct UnwindCodeWin
 class UnwindBuilderWin : public UnwindBuilder
 {
 public:
+    void setBeginOffset(size_t beginOffset) override;
+    size_t getBeginOffset() const override;
+
     void start() override;
 
     void spill(int espOffset, RegisterX64 reg) override;
@@ -36,6 +39,8 @@ public:
     void finalize(char* target, void* funcAddress, size_t funcSize) const override;
 
 private:
+    size_t beginOffset = 0;
+
     // Windows unwind codes are written in reverse, so we have to collect them all first
     std::vector<UnwindCodeWin> unwindCodes;
 

CodeGen/src/AssemblyBuilderX64.cpp

@@ -354,10 +354,15 @@ void AssemblyBuilderX64::jmp(Label& label)
 
 void AssemblyBuilderX64::jmp(OperandX64 op)
 {
+    LUAU_ASSERT((op.cat == CategoryX64::reg ? op.base.size : op.memSize) == SizeX64::qword);
+
     if (logText)
         log("jmp", op);
 
-    placeRex(op);
+    // Indirect absolute calls always work in 64 bit width mode, so REX.W is optional
+    // While we could keep an optional prefix, in Windows x64 ABI it signals a tail call return statement to the unwinder
+    placeRexNoW(op);
+
     place(0xff);
     placeModRegMem(op, 4);
     commit();
@@ -376,10 +381,14 @@ void AssemblyBuilderX64::call(Label& label)
 
 void AssemblyBuilderX64::call(OperandX64 op)
 {
+    LUAU_ASSERT((op.cat == CategoryX64::reg ? op.base.size : op.memSize) == SizeX64::qword);
+
     if (logText)
         log("call", op);
 
-    placeRex(op);
+    // Indirect absolute calls always work in 64 bit width mode, so REX.W is optional
+    placeRexNoW(op);
+
     place(0xff);
     placeModRegMem(op, 2);
     commit();
@@ -838,6 +847,21 @@ void AssemblyBuilderX64::placeRex(OperandX64 op)
         place(code | 0x40);
 }
 
+void AssemblyBuilderX64::placeRexNoW(OperandX64 op)
+{
+    uint8_t code = 0;
+
+    if (op.cat == CategoryX64::reg)
+        code = REX_B(op.base);
+    else if (op.cat == CategoryX64::mem)
+        code = REX_X(op.index) | REX_B(op.base);
+    else
+        LUAU_ASSERT(!"No encoding for left operand of this category");
+
+    if (code != 0)
+        place(code | 0x40);
+}
+
 void AssemblyBuilderX64::placeRex(RegisterX64 lhs, OperandX64 rhs)
 {
     uint8_t code = REX_W(lhs.size == SizeX64::qword);

CodeGen/src/CodeAllocator.cpp

@@ -91,7 +91,7 @@ CodeAllocator::CodeAllocator(size_t blockSize, size_t maxTotalSize)
     : blockSize(blockSize)
     , maxTotalSize(maxTotalSize)
 {
-    LUAU_ASSERT(blockSize > kMaxUnwindDataSize);
+    LUAU_ASSERT(blockSize > kMaxReservedDataSize);
     LUAU_ASSERT(maxTotalSize >= blockSize);
 }
 
@@ -116,15 +116,15 @@ bool CodeAllocator::allocate(
     size_t totalSize = alignedDataSize + codeSize;
 
     // Function has to fit into a single block with unwinding information
-    if (totalSize > blockSize - kMaxUnwindDataSize)
+    if (totalSize > blockSize - kMaxReservedDataSize)
         return false;
 
-    size_t unwindInfoSize = 0;
+    size_t startOffset = 0;
 
     // We might need a new block
     if (totalSize > size_t(blockEnd - blockPos))
     {
-        if (!allocateNewBlock(unwindInfoSize))
+        if (!allocateNewBlock(startOffset))
             return false;
 
         LUAU_ASSERT(totalSize <= size_t(blockEnd - blockPos));
@@ -132,20 +132,20 @@ bool CodeAllocator::allocate(
 
     LUAU_ASSERT((uintptr_t(blockPos) & (kPageSize - 1)) == 0); // Allocation starts on page boundary
 
-    size_t dataOffset = unwindInfoSize + alignedDataSize - dataSize;
+    size_t dataOffset = startOffset + alignedDataSize - dataSize;
-    size_t codeOffset = unwindInfoSize + alignedDataSize;
+    size_t codeOffset = startOffset + alignedDataSize;
 
     if (dataSize)
         memcpy(blockPos + dataOffset, data, dataSize);
     if (codeSize)
         memcpy(blockPos + codeOffset, code, codeSize);
 
-    size_t pageAlignedSize = alignToPageSize(unwindInfoSize + totalSize);
+    size_t pageAlignedSize = alignToPageSize(startOffset + totalSize);
 
     makePagesExecutable(blockPos, pageAlignedSize);
     flushInstructionCache(blockPos + codeOffset, codeSize);
 
-    result = blockPos + unwindInfoSize;
+    result = blockPos + startOffset;
     resultSize = totalSize;
     resultCodeStart = blockPos + codeOffset;
 
@@ -190,7 +190,7 @@ bool CodeAllocator::allocateNewBlock(size_t& unwindInfoSize)
         // 'Round up' to preserve 16 byte alignment of the following data and code
         unwindInfoSize = (unwindInfoSize + 15) & ~15;
 
-        LUAU_ASSERT(unwindInfoSize <= kMaxUnwindDataSize);
+        LUAU_ASSERT(unwindInfoSize <= kMaxReservedDataSize);
 
         if (!unwindInfo)
             return false;

CodeGen/src/CodeBlockUnwind.cpp

@@ -51,7 +51,7 @@ namespace Luau
 namespace CodeGen
 {
 
-void* createBlockUnwindInfo(void* context, uint8_t* block, size_t blockSize, size_t& unwindDataSizeInBlock)
+void* createBlockUnwindInfo(void* context, uint8_t* block, size_t blockSize, size_t& beginOffset)
 {
 #if defined(_WIN32) && defined(_M_X64)
     UnwindBuilder* unwind = (UnwindBuilder*)context;
@@ -75,7 +75,7 @@ void* createBlockUnwindInfo(void* context, uint8_t* block, size_t blockSize, siz
         return nullptr;
     }
 
-    unwindDataSizeInBlock = unwindSize;
+    beginOffset = unwindSize + unwind->getBeginOffset();
     return block;
 #elif !defined(_WIN32)
     UnwindBuilder* unwind = (UnwindBuilder*)context;
@@ -94,7 +94,7 @@ void* createBlockUnwindInfo(void* context, uint8_t* block, size_t blockSize, siz
     __register_frame(unwindData);
 #endif
 
-    unwindDataSizeInBlock = unwindSize;
+    beginOffset = unwindSize + unwind->getBeginOffset();
     return block;
 #endif
 

CodeGen/src/UnwindBuilderDwarf2.cpp

@@ -129,6 +129,16 @@ namespace Luau
 namespace CodeGen
 {
 
+void UnwindBuilderDwarf2::setBeginOffset(size_t beginOffset)
+{
+    this->beginOffset = beginOffset;
+}
+
+size_t UnwindBuilderDwarf2::getBeginOffset() const
+{
+    return beginOffset;
+}
+
 void UnwindBuilderDwarf2::start()
 {
     uint8_t* cieLength = pos;

CodeGen/src/UnwindBuilderWin.cpp

@@ -32,6 +32,16 @@ struct UnwindInfoWin
     uint8_t frameregoff : 4;
 };
 
+void UnwindBuilderWin::setBeginOffset(size_t beginOffset)
+{
+    this->beginOffset = beginOffset;
+}
+
+size_t UnwindBuilderWin::getBeginOffset() const
+{
+    return beginOffset;
+}
+
 void UnwindBuilderWin::start()
 {
     stackOffset = 8; // Return address was pushed by calling the function

Common/include/Luau/ExperimentalFlags.h

@@ -13,6 +13,7 @@ inline bool isFlagExperimental(const char* flag)
     static const char* kList[] = {
         "LuauLowerBoundsCalculation",
         "LuauInterpolatedStringBaseSupport",
+        "LuauInstantiateInSubtyping", // requires some fixes to lua-apps code
         // makes sure we always have at least one entry
         nullptr,
     };

Makefile

@@ -4,6 +4,7 @@ MAKEFLAGS+=-r -j8
 COMMA=,
 
 config=debug
+protobuf=system
 
 BUILD=build/$(config)
 
@@ -95,12 +96,22 @@ ifeq ($(config),fuzz)
 	CXX=clang++ # our fuzzing infra relies on llvm fuzzer
 	CXXFLAGS+=-fsanitize=address,fuzzer -Ibuild/libprotobuf-mutator -O2
 	LDFLAGS+=-fsanitize=address,fuzzer
+	LPROTOBUF=-lprotobuf
+	DPROTOBUF=-D CMAKE_BUILD_TYPE=Release -D LIB_PROTO_MUTATOR_TESTING=OFF
+	EPROTOC=protoc
 endif
 
 ifeq ($(config),profile)
 	CXXFLAGS+=-O2 -DNDEBUG -gdwarf-4 -DCALLGRIND=1
 endif
 
+ifeq ($(protobuf),download)
+	CXXFLAGS+=-Ibuild/libprotobuf-mutator/external.protobuf/include
+	LPROTOBUF=build/libprotobuf-mutator/external.protobuf/lib/libprotobuf.a
+	DPROTOBUF+=-D LIB_PROTO_MUTATOR_DOWNLOAD_PROTOBUF=ON
+	EPROTOC=../build/libprotobuf-mutator/external.protobuf/bin/protoc
+endif
+
 # target-specific flags
 $(AST_OBJECTS): CXXFLAGS+=-std=c++17 -ICommon/include -IAst/include
 $(COMPILER_OBJECTS): CXXFLAGS+=-std=c++17 -ICompiler/include -ICommon/include -IAst/include
@@ -115,7 +126,7 @@ $(FUZZ_OBJECTS): CXXFLAGS+=-std=c++17 -ICommon/include -IAst/include -ICompiler/
 
 $(TESTS_TARGET): LDFLAGS+=-lpthread
 $(REPL_CLI_TARGET): LDFLAGS+=-lpthread
-fuzz-proto fuzz-prototest: LDFLAGS+=build/libprotobuf-mutator/src/libfuzzer/libprotobuf-mutator-libfuzzer.a build/libprotobuf-mutator/src/libprotobuf-mutator.a -lprotobuf
+fuzz-proto fuzz-prototest: LDFLAGS+=build/libprotobuf-mutator/src/libfuzzer/libprotobuf-mutator-libfuzzer.a build/libprotobuf-mutator/src/libprotobuf-mutator.a $(LPROTOBUF)
 
 # pseudo targets
 .PHONY: all test clean coverage format luau-size aliases
@@ -199,7 +210,7 @@ $(BUILD)/%.c.o: %.c
 
 # protobuf fuzzer setup
 fuzz/luau.pb.cpp: fuzz/luau.proto build/libprotobuf-mutator
-	cd fuzz && protoc luau.proto --cpp_out=.
+	cd fuzz && $(EPROTOC) luau.proto --cpp_out=.
 	mv fuzz/luau.pb.cc fuzz/luau.pb.cpp
 
 $(BUILD)/fuzz/proto.cpp.o: fuzz/luau.pb.cpp
@@ -207,7 +218,7 @@ $(BUILD)/fuzz/protoprint.cpp.o: fuzz/luau.pb.cpp
 
 build/libprotobuf-mutator:
 	git clone https://github.com/google/libprotobuf-mutator build/libprotobuf-mutator
-	CXX= cmake -S build/libprotobuf-mutator -B build/libprotobuf-mutator -D CMAKE_BUILD_TYPE=Release -D LIB_PROTO_MUTATOR_TESTING=OFF
+	CXX= cmake -S build/libprotobuf-mutator -B build/libprotobuf-mutator $(DPROTOBUF)
 	make -C build/libprotobuf-mutator -j8
 
 # picks up include dependencies for all object files

VM/include/lua.h

@@ -401,13 +401,15 @@ struct lua_Debug
     const char* name;           // (n)
     const char* what;           // (s) `Lua', `C', `main', `tail'
     const char* source;         // (s)
+    const char* short_src;      // (s)
     int linedefined;            // (s)
     int currentline;            // (l)
     unsigned char nupvals;      // (u) number of upvalues
     unsigned char nparams;      // (a) number of parameters
     char isvararg;              // (a)
-    char short_src[LUA_IDSIZE]; // (s)
     void* userdata;             // only valid in luau_callhook
+
+    char ssbuf[LUA_IDSIZE];
 };
 
 // }======================================================================

VM/src/ldebug.cpp

@@ -12,6 +12,8 @@
 #include <string.h>
 #include <stdio.h>
 
+LUAU_FASTFLAGVARIABLE(LuauFasterGetInfo, false)
+
 static const char* getfuncname(Closure* f);
 
 static int currentpc(lua_State* L, CallInfo* ci)
@@ -89,9 +91,9 @@ const char* lua_setlocal(lua_State* L, int level, int n)
     return name;
 }
 
-static int auxgetinfo(lua_State* L, const char* what, lua_Debug* ar, Closure* f, CallInfo* ci)
+static Closure* auxgetinfo(lua_State* L, const char* what, lua_Debug* ar, Closure* f, CallInfo* ci)
 {
-    int status = 1;
+    Closure* cl = NULL;
     for (; *what; what++)
     {
         switch (*what)
@@ -103,14 +105,23 @@ static int auxgetinfo(lua_State* L, const char* what, lua_Debug* ar, Closure* f,
                 ar->source = "=[C]";
                 ar->what = "C";
                 ar->linedefined = -1;
+                if (FFlag::LuauFasterGetInfo)
+                    ar->short_src = "[C]";
             }
             else
             {
-                ar->source = getstr(f->l.p->source);
+                TString* source = f->l.p->source;
+                ar->source = getstr(source);
                 ar->what = "Lua";
                 ar->linedefined = f->l.p->linedefined;
+                if (FFlag::LuauFasterGetInfo)
+                    ar->short_src = luaO_chunkid(ar->ssbuf, sizeof(ar->ssbuf), getstr(source), source->len);
+            }
+            if (!FFlag::LuauFasterGetInfo)
+            {
+                luaO_chunkid(ar->ssbuf, LUA_IDSIZE, ar->source, 0);
+                ar->short_src = ar->ssbuf;
             }
-            luaO_chunkid(ar->short_src, ar->source, LUA_IDSIZE);
             break;
         }
         case 'l':
@@ -150,10 +161,15 @@ static int auxgetinfo(lua_State* L, const char* what, lua_Debug* ar, Closure* f,
             ar->name = ci ? getfuncname(ci_func(ci)) : getfuncname(f);
             break;
         }
+        case 'f':
+        {
+            cl = f;
+            break;
+        }
         default:;
         }
     }
-    return status;
+    return cl;
 }
 
 int lua_stackdepth(lua_State* L)
@@ -163,7 +179,6 @@ int lua_stackdepth(lua_State* L)
 
 int lua_getinfo(lua_State* L, int level, const char* what, lua_Debug* ar)
 {
-    int status = 0;
     Closure* f = NULL;
     CallInfo* ci = NULL;
     if (level < 0)
@@ -180,15 +195,28 @@ int lua_getinfo(lua_State* L, int level, const char* what, lua_Debug* ar)
     }
     if (f)
     {
-        status = auxgetinfo(L, what, ar, f, ci);
+        if (FFlag::LuauFasterGetInfo)
-        if (strchr(what, 'f'))
         {
-            luaC_threadbarrier(L);
+            // auxgetinfo fills ar and optionally requests to put closure on stack
-            setclvalue(L, L->top, f);
+            if (Closure* fcl = auxgetinfo(L, what, ar, f, ci))
-            incr_top(L);
+            {
+                luaC_threadbarrier(L);
+                setclvalue(L, L->top, fcl);
+                incr_top(L);
+            }
+        }
+        else
+        {
+            auxgetinfo(L, what, ar, f, ci);
+            if (strchr(what, 'f'))
+            {
+                luaC_threadbarrier(L);
+                setclvalue(L, L->top, f);
+                incr_top(L);
+            }
         }
     }
-    return status;
+    return f ? 1 : 0;
 }
 
 static const char* getfuncname(Closure* cl)
@@ -284,10 +312,11 @@ static void pusherror(lua_State* L, const char* msg)
     CallInfo* ci = L->ci;
     if (isLua(ci))
     {
-        char buff[LUA_IDSIZE]; // add file:line information
+        TString* source = getluaproto(ci)->source;
-        luaO_chunkid(buff, getstr(getluaproto(ci)->source), LUA_IDSIZE);
+        char chunkbuf[LUA_IDSIZE]; // add file:line information
+        const char* chunkid = luaO_chunkid(chunkbuf, sizeof(chunkbuf), getstr(source), source->len);
         int line = currentline(L, ci);
-        luaO_pushfstring(L, "%s:%d: %s", buff, line, msg);
+        luaO_pushfstring(L, "%s:%d: %s", chunkid, line, msg);
     }
     else
     {

VM/src/lgc.cpp

@@ -13,8 +13,6 @@
 
 #include <string.h>
 
-LUAU_FASTFLAGVARIABLE(LuauBetterThreadMark, false)
-
 /*
  * Luau uses an incremental non-generational non-moving mark&sweep garbage collector.
  *
@@ -473,54 +471,25 @@ static size_t propagatemark(global_State* g)
 
         bool active = th->isactive || th == th->global->mainthread;
 
-        if (FFlag::LuauBetterThreadMark)
+        traversestack(g, th);
+
+        // active threads will need to be rescanned later to mark new stack writes so we mark them gray again
+        if (active)
         {
-            traversestack(g, th);
+            th->gclist = g->grayagain;
+            g->grayagain = o;
 
-            // active threads will need to be rescanned later to mark new stack writes so we mark them gray again
+            black2gray(o);
-            if (active)
-            {
-                th->gclist = g->grayagain;
-                g->grayagain = o;
-
-                black2gray(o);
-            }
-
-            // the stack needs to be cleared after the last modification of the thread state before sweep begins
-            // if the thread is inactive, we might not see the thread in this cycle so we must clear it now
-            if (!active || g->gcstate == GCSatomic)
-                clearstack(th);
-
-            // we could shrink stack at any time but we opt to do it during initial mark to do that just once per cycle
-            if (g->gcstate == GCSpropagate)
-                shrinkstack(th);
         }
-        else
-        {
-            // TODO: Refactor this logic!
-            if (!active && g->gcstate == GCSpropagate)
-            {
-                traversestack(g, th);
-                clearstack(th);
-            }
-            else
-            {
-                th->gclist = g->grayagain;
-                g->grayagain = o;
 
-                black2gray(o);
+        // the stack needs to be cleared after the last modification of the thread state before sweep begins
+        // if the thread is inactive, we might not see the thread in this cycle so we must clear it now
+        if (!active || g->gcstate == GCSatomic)
+            clearstack(th);
 
-                traversestack(g, th);
+        // we could shrink stack at any time but we opt to do it during initial mark to do that just once per cycle
-
+        if (g->gcstate == GCSpropagate)
-                // final traversal?
+            shrinkstack(th);
-                if (g->gcstate == GCSatomic)
-                    clearstack(th);
-            }
-
-            // we could shrink stack at any time but we opt to skip it during atomic since it's redundant to do that more than once per cycle
-            if (g->gcstate != GCSatomic)
-                shrinkstack(th);
-        }
 
         return sizeof(lua_State) + sizeof(TValue) * th->stacksize + sizeof(CallInfo) * th->size_ci;
     }

VM/src/lobject.cpp

@@ -15,6 +15,8 @@
 
 
 
+LUAU_FASTFLAG(LuauFasterGetInfo)
+
 const TValue luaO_nilobject_ = {{NULL}, {0}, LUA_TNIL};
 
 int luaO_log2(unsigned int x)
@@ -117,44 +119,68 @@ const char* luaO_pushfstring(lua_State* L, const char* fmt, ...)
     return msg;
 }
 
-void luaO_chunkid(char* out, const char* source, size_t bufflen)
+const char* luaO_chunkid(char* buf, size_t buflen, const char* source, size_t srclen)
 {
     if (*source == '=')
     {
-        source++; // skip the `='
+        if (FFlag::LuauFasterGetInfo)
-        size_t srclen = strlen(source);
+        {
-        size_t dstlen = srclen < bufflen ? srclen : bufflen - 1;
+            if (srclen <= buflen)
-        memcpy(out, source, dstlen);
+                return source + 1;
-        out[dstlen] = '\0';
+            // truncate the part after =
+            memcpy(buf, source + 1, buflen - 1);
+            buf[buflen - 1] = '\0';
+        }
+        else
+        {
+            source++; // skip the `='
+            size_t len = strlen(source);
+            size_t dstlen = len < buflen ? len : buflen - 1;
+            memcpy(buf, source, dstlen);
+            buf[dstlen] = '\0';
+        }
     }
     else if (*source == '@')
     {
-        size_t l;
+        if (FFlag::LuauFasterGetInfo)
-        source++; // skip the `@'
-        bufflen -= sizeof("...");
-        l = strlen(source);
-        strcpy(out, "");
-        if (l > bufflen)
         {
-            source += (l - bufflen); // get last part of file name
+            if (srclen <= buflen)
-            strcat(out, "...");
+                return source + 1;
-        }
+            // truncate the part after @
-        strcat(out, source);
+            memcpy(buf, "...", 3);
-    }
+            memcpy(buf + 3, source + srclen - (buflen - 4), buflen - 4);
-    else
+            buf[buflen - 1] = '\0';
-    {                                         // out = [string "string"]
-        size_t len = strcspn(source, "\n\r"); // stop at first newline
-        bufflen -= sizeof("[string \"...\"]");
-        if (len > bufflen)
-            len = bufflen;
-        strcpy(out, "[string \"");
-        if (source[len] != '\0')
-        { // must truncate?
-            strncat(out, source, len);
-            strcat(out, "...");
         }
         else
-            strcat(out, source);
+        {
-        strcat(out, "\"]");
+            size_t l;
+            source++; // skip the `@'
+            buflen -= sizeof("...");
+            l = strlen(source);
+            strcpy(buf, "");
+            if (l > buflen)
+            {
+                source += (l - buflen); // get last part of file name
+                strcat(buf, "...");
+            }
+            strcat(buf, source);
+        }
     }
+    else
+    {                                         // buf = [string "string"]
+        size_t len = strcspn(source, "\n\r"); // stop at first newline
+        buflen -= sizeof("[string \"...\"]");
+        if (len > buflen)
+            len = buflen;
+        strcpy(buf, "[string \"");
+        if (source[len] != '\0')
+        { // must truncate?
+            strncat(buf, source, len);
+            strcat(buf, "...");
+        }
+        else
+            strcat(buf, source);
+        strcat(buf, "\"]");
+    }
+    return buf;
 }

VM/src/lobject.h

@@ -460,4 +460,4 @@ LUAI_FUNC int luaO_rawequalKey(const TKey* t1, const TValue* t2);
 LUAI_FUNC int luaO_str2d(const char* s, double* result);
 LUAI_FUNC const char* luaO_pushvfstring(lua_State* L, const char* fmt, va_list argp);
 LUAI_FUNC const char* luaO_pushfstring(lua_State* L, const char* fmt, ...);
-LUAI_FUNC void luaO_chunkid(char* out, const char* source, size_t len);
+LUAI_FUNC const char* luaO_chunkid(char* buf, size_t buflen, const char* source, size_t srclen);

VM/src/lvmexecute.cpp

@@ -781,6 +781,7 @@ reentry:
 
                     default:
                         LUAU_ASSERT(!"Unknown upvalue capture type");
+                        LUAU_UNREACHABLE(); // improves switch() codegen by eliding opcode bounds checks
                     }
                 }
 
@@ -1184,7 +1185,9 @@ reentry:
                         // slow path after switch()
                         break;
 
-                    default:;
+                    default:
+                        LUAU_ASSERT(!"Unknown value type");
+                        LUAU_UNREACHABLE(); // improves switch() codegen by eliding opcode bounds checks
                     }
 
                     // slow-path: tables with metatables and userdata values
@@ -1296,7 +1299,9 @@ reentry:
                         // slow path after switch()
                         break;
 
-                    default:;
+                    default:
+                        LUAU_ASSERT(!"Unknown value type");
+                        LUAU_UNREACHABLE(); // improves switch() codegen by eliding opcode bounds checks
                     }
 
                     // slow-path: tables with metatables and userdata values

VM/src/lvmload.cpp

@@ -148,16 +148,16 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
     // 0 means the rest of the bytecode is the error message
     if (version == 0)
     {
-        char chunkid[LUA_IDSIZE];
+        char chunkbuf[LUA_IDSIZE];
-        luaO_chunkid(chunkid, chunkname, LUA_IDSIZE);
+        const char* chunkid = luaO_chunkid(chunkbuf, sizeof(chunkbuf), chunkname, strlen(chunkname));
         lua_pushfstring(L, "%s%.*s", chunkid, int(size - offset), data + offset);
         return 1;
     }
 
     if (version < LBC_VERSION_MIN || version > LBC_VERSION_MAX)
     {
-        char chunkid[LUA_IDSIZE];
+        char chunkbuf[LUA_IDSIZE];
-        luaO_chunkid(chunkid, chunkname, LUA_IDSIZE);
+        const char* chunkid = luaO_chunkid(chunkbuf, sizeof(chunkbuf), chunkname, strlen(chunkname));
         lua_pushfstring(L, "%s: bytecode version mismatch (expected [%d..%d], got %d)", chunkid, LBC_VERSION_MIN, LBC_VERSION_MAX, version);
         return 1;
     }

VM/src/lvmutils.cpp

@@ -220,8 +220,13 @@ int luaV_strcmp(const TString* ls, const TString* rs)
         return 0;
 
     const char* l = getstr(ls);
-    size_t ll = ls->len;
     const char* r = getstr(rs);
+
+    // always safe to read one character because even empty strings are nul terminated
+    if (*l != *r)
+        return uint8_t(*l) - uint8_t(*r);
+
+    size_t ll = ls->len;
     size_t lr = rs->len;
     size_t lmin = ll < lr ? ll : lr;
 

tests/AssemblyBuilderX64.test.cpp

@@ -240,12 +240,12 @@ TEST_CASE_FIXTURE(AssemblyBuilderX64Fixture, "FormsOfLea")
 
 TEST_CASE_FIXTURE(AssemblyBuilderX64Fixture, "FormsOfAbsoluteJumps")
 {
-    SINGLE_COMPARE(jmp(rax), 0x48, 0xff, 0xe0);
+    SINGLE_COMPARE(jmp(rax), 0xff, 0xe0);
-    SINGLE_COMPARE(jmp(r14), 0x49, 0xff, 0xe6);
+    SINGLE_COMPARE(jmp(r14), 0x41, 0xff, 0xe6);
-    SINGLE_COMPARE(jmp(qword[r14 + rdx * 4]), 0x49, 0xff, 0x24, 0x96);
+    SINGLE_COMPARE(jmp(qword[r14 + rdx * 4]), 0x41, 0xff, 0x24, 0x96);
-    SINGLE_COMPARE(call(rax), 0x48, 0xff, 0xd0);
+    SINGLE_COMPARE(call(rax), 0xff, 0xd0);
-    SINGLE_COMPARE(call(r14), 0x49, 0xff, 0xd6);
+    SINGLE_COMPARE(call(r14), 0x41, 0xff, 0xd6);
-    SINGLE_COMPARE(call(qword[r14 + rdx * 4]), 0x49, 0xff, 0x14, 0x96);
+    SINGLE_COMPARE(call(qword[r14 + rdx * 4]), 0x41, 0xff, 0x14, 0x96);
 }
 
 TEST_CASE_FIXTURE(AssemblyBuilderX64Fixture, "FormsOfImul")

tests/Autocomplete.test.cpp

@@ -2955,8 +2955,6 @@ local abc = b@1
 
 TEST_CASE_FIXTURE(ACFixture, "no_incompatible_self_calls_on_class")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     loadDefinition(R"(
 declare class Foo
     function one(self): number
@@ -2995,8 +2993,6 @@ t.@1
 
 TEST_CASE_FIXTURE(ACFixture, "do_compatible_self_calls")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     check(R"(
 local t = {}
 function t:m() end
@@ -3011,8 +3007,6 @@ t:@1
 
 TEST_CASE_FIXTURE(ACFixture, "no_incompatible_self_calls")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     check(R"(
 local t = {}
 function t.m() end
@@ -3027,8 +3021,6 @@ t:@1
 
 TEST_CASE_FIXTURE(ACFixture, "no_incompatible_self_calls_2")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     check(R"(
 local f: (() -> number) & ((number) -> number) = function(x: number?) return 2 end
 local t = {}
@@ -3059,8 +3051,6 @@ t:@1
 
 TEST_CASE_FIXTURE(ACFixture, "no_wrong_compatible_self_calls_with_generics")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     check(R"(
 local t = {}
 function t.m<T>(a: T) end
@@ -3076,8 +3066,6 @@ t:@1
 
 TEST_CASE_FIXTURE(ACFixture, "string_prim_self_calls_are_fine")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     check(R"(
 local s = "hello"
 s:@1
@@ -3095,8 +3083,6 @@ s:@1
 
 TEST_CASE_FIXTURE(ACFixture, "string_prim_non_self_calls_are_avoided")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     check(R"(
 local s = "hello"
 s.@1
@@ -3112,8 +3098,6 @@ s.@1
 
 TEST_CASE_FIXTURE(ACBuiltinsFixture, "library_non_self_calls_are_fine")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     check(R"(
 string.@1
     )");
@@ -3143,8 +3127,6 @@ table.@1
 
 TEST_CASE_FIXTURE(ACBuiltinsFixture, "library_self_calls_are_invalid")
 {
-    ScopedFastFlag selfCallAutocompleteFix3{"LuauSelfCallAutocompleteFix3", true};
-
     check(R"(
 string:@1
     )");

tests/CodeAllocator.test.cpp

@@ -96,12 +96,12 @@ TEST_CASE("CodeAllocationWithUnwindCallbacks")
         data.resize(8);
 
         allocator.context = &info;
-        allocator.createBlockUnwindInfo = [](void* context, uint8_t* block, size_t blockSize, size_t& unwindDataSizeInBlock) -> void* {
+        allocator.createBlockUnwindInfo = [](void* context, uint8_t* block, size_t blockSize, size_t& beginOffset) -> void* {
             Info& info = *(Info*)context;
 
             CHECK(info.unwind.size() == 8);
             memcpy(block, info.unwind.data(), info.unwind.size());
-            unwindDataSizeInBlock = 8;
+            beginOffset = 8;
 
             info.block = block;
 
@@ -194,10 +194,12 @@ TEST_CASE("Dwarf2UnwindCodesX64")
 // Windows x64 ABI
 constexpr RegisterX64 rArg1 = rcx;
 constexpr RegisterX64 rArg2 = rdx;
+constexpr RegisterX64 rArg3 = r8;
 #else
 // System V AMD64 ABI
 constexpr RegisterX64 rArg1 = rdi;
 constexpr RegisterX64 rArg2 = rsi;
+constexpr RegisterX64 rArg3 = rdx;
 #endif
 
 constexpr RegisterX64 rNonVol1 = r12;
@@ -313,6 +315,119 @@ TEST_CASE("GeneratedCodeExecutionWithThrow")
     }
 }
 
+TEST_CASE("GeneratedCodeExecutionWithThrowOutsideTheGate")
+{
+    AssemblyBuilderX64 build(/* logText= */ false);
+
+#if defined(_WIN32)
+    std::unique_ptr<UnwindBuilder> unwind = std::make_unique<UnwindBuilderWin>();
+#else
+    std::unique_ptr<UnwindBuilder> unwind = std::make_unique<UnwindBuilderDwarf2>();
+#endif
+
+    unwind->start();
+
+    // Prologue (some of these registers don't have to be saved, but we want to have a big prologue)
+    build.push(r10);
+    unwind->save(r10);
+    build.push(r11);
+    unwind->save(r11);
+    build.push(r12);
+    unwind->save(r12);
+    build.push(r13);
+    unwind->save(r13);
+    build.push(r14);
+    unwind->save(r14);
+    build.push(r15);
+    unwind->save(r15);
+    build.push(rbp);
+    unwind->save(rbp);
+
+    int stackSize = 64;
+    int localsSize = 16;
+
+    build.sub(rsp, stackSize + localsSize);
+    unwind->allocStack(stackSize + localsSize);
+
+    build.lea(rbp, qword[rsp + stackSize]);
+    unwind->setupFrameReg(rbp, stackSize);
+
+    unwind->finish();
+
+    size_t prologueSize = build.setLabel().location;
+
+    // Body
+    build.mov(rax, rArg1);
+    build.mov(rArg1, 25);
+    build.jmp(rax);
+
+    Label returnOffset = build.setLabel();
+
+    // Epilogue
+    build.lea(rsp, qword[rbp + localsSize]);
+    build.pop(rbp);
+    build.pop(r15);
+    build.pop(r14);
+    build.pop(r13);
+    build.pop(r12);
+    build.pop(r11);
+    build.pop(r10);
+    build.ret();
+
+    build.finalize();
+
+    size_t blockSize = 4096; // Force allocate to create a new block each time
+    size_t maxTotalSize = 1024 * 1024;
+    CodeAllocator allocator(blockSize, maxTotalSize);
+
+    allocator.context = unwind.get();
+    allocator.createBlockUnwindInfo = createBlockUnwindInfo;
+    allocator.destroyBlockUnwindInfo = destroyBlockUnwindInfo;
+
+    uint8_t* nativeData1;
+    size_t sizeNativeData1;
+    uint8_t* nativeEntry1;
+    REQUIRE(
+        allocator.allocate(build.data.data(), build.data.size(), build.code.data(), build.code.size(), nativeData1, sizeNativeData1, nativeEntry1));
+    REQUIRE(nativeEntry1);
+
+    // Now we set the offset at the begining so that functions in new blocks will not overlay the locations
+    // specified by the unwind information of the entry function
+    unwind->setBeginOffset(prologueSize);
+
+    using FunctionType = int64_t(void*, void (*)(int64_t), void*);
+    FunctionType* f = (FunctionType*)nativeEntry1;
+
+    uint8_t* nativeExit = nativeEntry1 + returnOffset.location;
+
+    AssemblyBuilderX64 build2(/* logText= */ false);
+
+    build2.mov(r12, rArg3);
+    build2.call(rArg2);
+    build2.jmp(r12);
+
+    build2.finalize();
+
+    uint8_t* nativeData2;
+    size_t sizeNativeData2;
+    uint8_t* nativeEntry2;
+    REQUIRE(allocator.allocate(
+        build2.data.data(), build2.data.size(), build2.code.data(), build2.code.size(), nativeData2, sizeNativeData2, nativeEntry2));
+    REQUIRE(nativeEntry2);
+
+    // To simplify debugging, CHECK_THROWS_WITH_AS is not used here
+    try
+    {
+        f(nativeEntry2, throwing, nativeExit);
+    }
+    catch (const std::runtime_error& error)
+    {
+        CHECK(strcmp(error.what(), "testing") == 0);
+    }
+
+    REQUIRE(nativeEntry2);
+}
+
 #endif
 
 TEST_SUITE_END();

tests/ConstraintSolver.test.cpp

@@ -28,8 +28,11 @@ TEST_CASE_FIXTURE(ConstraintGraphBuilderFixture, "hello")
     cgb.visit(block);
     NotNull<Scope> rootScope{cgb.rootScope};
 
+    InternalErrorReporter iceHandler;
+    UnifierSharedState sharedState{&iceHandler};
+    Normalizer normalizer{&arena, singletonTypes, NotNull{&sharedState}};
     NullModuleResolver resolver;
-    ConstraintSolver cs{&arena, singletonTypes, rootScope, "MainModule", NotNull(&resolver), {}, &logger};
+    ConstraintSolver cs{NotNull{&normalizer}, rootScope, "MainModule", NotNull(&resolver), {}, &logger};
 
     cs.run();
 
@@ -49,9 +52,11 @@ TEST_CASE_FIXTURE(ConstraintGraphBuilderFixture, "generic_function")
     cgb.visit(block);
     NotNull<Scope> rootScope{cgb.rootScope};
 
+    InternalErrorReporter iceHandler;
+    UnifierSharedState sharedState{&iceHandler};
+    Normalizer normalizer{&arena, singletonTypes, NotNull{&sharedState}};
     NullModuleResolver resolver;
-    ConstraintSolver cs{&arena, singletonTypes, rootScope, "MainModule", NotNull(&resolver), {}, &logger};
+    ConstraintSolver cs{NotNull{&normalizer}, rootScope, "MainModule", NotNull(&resolver), {}, &logger};
-
     cs.run();
 
     TypeId idType = requireBinding(rootScope, "id");
@@ -79,7 +84,10 @@ TEST_CASE_FIXTURE(ConstraintGraphBuilderFixture, "proper_let_generalization")
     ToStringOptions opts;
 
     NullModuleResolver resolver;
-    ConstraintSolver cs{&arena, singletonTypes, rootScope, "MainModule", NotNull(&resolver), {}, &logger};
+    InternalErrorReporter iceHandler;
+    UnifierSharedState sharedState{&iceHandler};
+    Normalizer normalizer{&arena, singletonTypes, NotNull{&sharedState}};
+    ConstraintSolver cs{NotNull{&normalizer}, rootScope, "MainModule", NotNull(&resolver), {}, &logger};
 
     cs.run();
 

tests/Fixture.cpp

@@ -22,6 +22,8 @@ LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 LUAU_FASTFLAG(LuauUnknownAndNeverType)
 LUAU_FASTFLAG(LuauReportShadowedTypeAlias)
 
+extern std::optional<unsigned> randomSeed; // tests/main.cpp
+
 namespace Luau
 {
 
@@ -90,7 +92,7 @@ std::optional<std::string> TestFileResolver::getEnvironmentForModule(const Modul
 
 Fixture::Fixture(bool freeze, bool prepareAutocomplete)
     : sff_DebugLuauFreezeArena("DebugLuauFreezeArena", freeze)
-    , frontend(&fileResolver, &configResolver, {/* retainFullTypeGraphs= */ true})
+    , frontend(&fileResolver, &configResolver, {/* retainFullTypeGraphs= */ true, /* forAutocomplete */ false, /* randomConstraintResolutionSeed */ randomSeed})
     , typeChecker(frontend.typeChecker)
     , singletonTypes(frontend.singletonTypes)
 {

tests/Linter.test.cpp

@@ -21,14 +21,14 @@ end
 return math.max(fib(5), 1)
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "UnknownGlobal")
 {
     LintResult result = lint("--!nocheck\nreturn foo");
 
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Unknown global 'foo'");
 }
 
@@ -39,7 +39,7 @@ TEST_CASE_FIXTURE(Fixture, "DeprecatedGlobal")
 
     LintResult result = lintTyped("Wait(5)");
 
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Global 'Wait' is deprecated, use 'wait' instead");
 }
 
@@ -53,7 +53,7 @@ TEST_CASE_FIXTURE(Fixture, "DeprecatedGlobalNoReplacement")
 
     LintResult result = lintTyped("Version()");
 
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Global 'Version' is deprecated");
 }
 
@@ -64,7 +64,7 @@ local _ = 5
 return _
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Placeholder value '_' is read here; consider using a named variable");
 }
 
@@ -75,7 +75,7 @@ _ = 5
 print(_)
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Placeholder value '_' is read here; consider using a named variable");
 }
 
@@ -86,7 +86,7 @@ local _ = 5
 _ = 6
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "BuiltinGlobalWrite")
@@ -100,7 +100,7 @@ end
 assert(5)
 )");
 
-    CHECK_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Built-in global 'math' is overwritten here; consider using a local or changing the name");
     CHECK_EQ(result.warnings[1].text, "Built-in global 'assert' is overwritten here; consider using a local or changing the name");
 }
@@ -111,7 +111,7 @@ TEST_CASE_FIXTURE(Fixture, "MultilineBlock")
 if true then print(1) print(2) print(3) end
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "A new statement is on the same line; add semi-colon on previous statement to silence");
 }
 
@@ -121,7 +121,7 @@ TEST_CASE_FIXTURE(Fixture, "MultilineBlockSemicolonsWhitelisted")
 print(1); print(2); print(3)
 )");
 
-    CHECK(result.warnings.empty());
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "MultilineBlockMissedSemicolon")
@@ -130,7 +130,7 @@ TEST_CASE_FIXTURE(Fixture, "MultilineBlockMissedSemicolon")
 print(1); print(2) print(3)
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "A new statement is on the same line; add semi-colon on previous statement to silence");
 }
 
@@ -142,7 +142,7 @@ local _x do
 end
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "ConfusingIndentation")
@@ -152,7 +152,7 @@ print(math.max(1,
 2))
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Statement spans multiple lines; use indentation to silence");
 }
 
@@ -167,7 +167,7 @@ end
 return bar()
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Global 'foo' is only used in the enclosing function 'bar'; consider changing it to local");
 }
 
@@ -188,7 +188,7 @@ end
 return bar() + baz()
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Global 'foo' is never read before being written. Consider changing it to local");
 }
 
@@ -213,7 +213,7 @@ end
 return bar() + baz() + read()
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "GlobalAsLocalWithConditional")
@@ -233,7 +233,7 @@ end
 return bar() + baz()
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "GlobalAsLocal3WithConditionalRead")
@@ -257,7 +257,7 @@ end
 return bar() + baz() + read()
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "GlobalAsLocalInnerRead")
@@ -275,7 +275,7 @@ function baz() bar = 0 end
 return foo() + baz()
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "GlobalAsLocalMulti")
@@ -304,7 +304,7 @@ fnA() -- prints "true", "nil"
 fnB() -- prints "false", "nil"
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text,
         "Global 'moreInternalLogic' is only used in the enclosing function defined at line 2; consider changing it to local");
 }
@@ -319,7 +319,7 @@ local arg = 5
 print(arg)
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Variable 'arg' shadows previous declaration at line 2");
 }
 
@@ -337,7 +337,7 @@ end
 return bar()
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Variable 'global' shadows a global variable used at line 3");
 }
 
@@ -352,7 +352,7 @@ end
 return bar()
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Variable 'a' shadows previous declaration at line 2");
 }
 
@@ -372,7 +372,7 @@ end
 return bar()
 )");
 
-    CHECK_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Variable 'arg' is never used; prefix with '_' to silence");
     CHECK_EQ(result.warnings[1].text, "Variable 'blarg' is never used; prefix with '_' to silence");
 }
@@ -387,7 +387,7 @@ local Roact = require(game.Packages.Roact)
 local _Roact = require(game.Packages.Roact)
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Import 'Roact' is never used; prefix with '_' to silence");
 }
 
@@ -412,7 +412,7 @@ end
 return foo()
 )");
 
-    CHECK_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Function 'bar' is never used; prefix with '_' to silence");
     CHECK_EQ(result.warnings[1].text, "Function 'qux' is never used; prefix with '_' to silence");
 }
@@ -427,7 +427,7 @@ end
 print("hi!")
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 5);
     CHECK_EQ(result.warnings[0].text, "Unreachable code (previous statement always returns)");
 }
@@ -443,7 +443,7 @@ end
 print("hi!")
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 3);
     CHECK_EQ(result.warnings[0].text, "Unreachable code (previous statement always breaks)");
 }
@@ -459,7 +459,7 @@ end
 print("hi!")
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 3);
     CHECK_EQ(result.warnings[0].text, "Unreachable code (previous statement always continues)");
 }
@@ -495,7 +495,7 @@ end
 return { foo1, foo2, foo3 }
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 7);
     CHECK_EQ(result.warnings[0].text, "Unreachable code (previous statement always returns)");
 }
@@ -515,7 +515,7 @@ end
 return foo1
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "UnreachableCodeAssertFalseReturnSilent")
@@ -532,7 +532,7 @@ end
 return foo1
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "UnreachableCodeErrorReturnNonSilentBranchy")
@@ -550,7 +550,7 @@ end
 return foo1
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 7);
     CHECK_EQ(result.warnings[0].text, "Unreachable code (previous statement always errors)");
 }
@@ -571,7 +571,7 @@ end
 return foo1
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 8);
     CHECK_EQ(result.warnings[0].text, "Unreachable code (previous statement always errors)");
 }
@@ -589,7 +589,7 @@ end
 return foo1
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "UnreachableCodeLoopRepeat")
@@ -605,8 +605,8 @@ end
 return foo1
 )");
 
-    CHECK_EQ(result.warnings.size(),
+    // this is technically a bug, since the repeat body always returns; fixing this bug is a bit more involved than I'd like
-        0); // this is technically a bug, since the repeat body always returns; fixing this bug is a bit more involved than I'd like
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "UnknownType")
@@ -633,7 +633,7 @@ local _o02 = type(game) == "vector"
 local _o03 = typeof(game) == "Part"
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 3);
+    REQUIRE(3 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 2);
     CHECK_EQ(result.warnings[0].text, "Unknown type 'Part' (expected primitive type)");
     CHECK_EQ(result.warnings[1].location.begin.line, 3);
@@ -654,7 +654,7 @@ for i=#t,1,-1 do
 end
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 3);
     CHECK_EQ(result.warnings[0].text, "For loop should iterate backwards; did you forget to specify -1 as step?");
 }
@@ -669,7 +669,7 @@ for i=8,1,-1 do
 end
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 1);
     CHECK_EQ(result.warnings[0].text, "For loop should iterate backwards; did you forget to specify -1 as step?");
 }
@@ -684,7 +684,7 @@ for i=1.3,7.5,1 do
 end
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 1);
     CHECK_EQ(result.warnings[0].text, "For loop ends at 7.3 instead of 7.5; did you forget to specify step?");
 }
@@ -702,7 +702,7 @@ for i=#t,0 do
 end
 )");
 
-    CHECK_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 1);
     CHECK_EQ(result.warnings[0].text, "For loop starts at 0, but arrays start at 1");
     CHECK_EQ(result.warnings[1].location.begin.line, 7);
@@ -730,7 +730,7 @@ local _a,_b,_c = pcall(), nil
 end
 )");
 
-    CHECK_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 5);
     CHECK_EQ(result.warnings[0].text, "Assigning 2 values to 3 variables initializes extra variables with nil; add 'nil' to value list to silence");
     CHECK_EQ(result.warnings[1].location.begin.line, 11);
@@ -795,7 +795,7 @@ end
 return f1,f2,f3,f4,f5,f6,f7
 )");
 
-    CHECK_EQ(result.warnings.size(), 3);
+    REQUIRE(3 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 4);
     CHECK_EQ(result.warnings[0].text,
         "Function 'f1' can implicitly return no values even though there's an explicit return at line 4; add explicit return to silence");
@@ -851,7 +851,7 @@ end
 return f1,f2,f3,f4
 )");
 
-    CHECK_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].location.begin.line, 25);
     CHECK_EQ(result.warnings[0].text,
         "Function 'f3' can implicitly return no values even though there's an explicit return at line 21; add explicit return to silence");
@@ -874,7 +874,7 @@ type InputData = {
 }
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "BreakFromInfiniteLoopMakesStatementReachable")
@@ -893,7 +893,7 @@ until true
 return 1
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "IgnoreLintAll")
@@ -903,7 +903,7 @@ TEST_CASE_FIXTURE(Fixture, "IgnoreLintAll")
 return foo
 )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "IgnoreLintSpecific")
@@ -914,7 +914,7 @@ local x = 1
 return foo
 )");
 
-    CHECK_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Variable 'x' is never used; prefix with '_' to silence");
 }
 
@@ -933,7 +933,7 @@ local _ = ("%"):format()
 string.format("hello %+10d %.02f %%", 4, 5)
 )");
 
-    CHECK_EQ(result.warnings.size(), 4);
+    REQUIRE(4 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid format string: unfinished format specifier");
     CHECK_EQ(result.warnings[1].text, "Invalid format string: invalid format specifier: must be a string format specifier or %");
     CHECK_EQ(result.warnings[2].text, "Invalid format string: invalid format specifier: must be a string format specifier or %");
@@ -973,7 +973,7 @@ string.packsize("c99999999999999999999")
 string.packsize("=!1bbbI3c42")
 )");
 
-    CHECK_EQ(result.warnings.size(), 11);
+    REQUIRE(11 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid pack format: unexpected character; must be a pack specifier or space");
     CHECK_EQ(result.warnings[1].text, "Invalid pack format: unexpected character; must be a pack specifier or space");
     CHECK_EQ(result.warnings[2].text, "Invalid pack format: unexpected character; must be a pack specifier or space");
@@ -1017,7 +1017,7 @@ local _ = s:match("%q")
 string.match(s, "[A-Z]+(%d)%1")
 )");
 
-    CHECK_EQ(result.warnings.size(), 14);
+    REQUIRE(14 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid match pattern: invalid character class, must refer to a defined class or its inverse");
     CHECK_EQ(result.warnings[1].text, "Invalid match pattern: invalid character class, must refer to a defined class or its inverse");
     CHECK_EQ(result.warnings[2].text, "Invalid match pattern: invalid character class, must refer to a defined class or its inverse");
@@ -1049,7 +1049,7 @@ string.match(s, "((a)%1)")
 string.match(s, "((a)%3)")
 )~");
 
-    CHECK_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid match pattern: invalid capture reference, must refer to a closed capture");
     CHECK_EQ(result.warnings[0].location.begin.line, 7);
     CHECK_EQ(result.warnings[1].text, "Invalid match pattern: invalid capture reference, must refer to a valid capture");
@@ -1087,7 +1087,7 @@ string.match(s, "[]|'[]")
 string.match(s, "[^]|'[]")
 )~");
 
-    CHECK_EQ(result.warnings.size(), 7);
+    REQUIRE(7 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid match pattern: expected ] at the end of the string to close a set");
     CHECK_EQ(result.warnings[1].text, "Invalid match pattern: expected ] at the end of the string to close a set");
     CHECK_EQ(result.warnings[2].text, "Invalid match pattern: character range can't include character sets");
@@ -1118,7 +1118,7 @@ string.find("foo");
 ("foo"):find()
 )");
 
-    CHECK_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid match pattern: invalid character class, must refer to a defined class or its inverse");
     CHECK_EQ(result.warnings[0].location.begin.line, 4);
     CHECK_EQ(result.warnings[1].text, "Invalid match pattern: invalid character class, must refer to a defined class or its inverse");
@@ -1141,7 +1141,7 @@ string.gsub(s, '[A-Z]+(%d)', "%0%1")
 string.gsub(s, 'foo', "%0")
 )");
 
-    CHECK_EQ(result.warnings.size(), 4);
+    REQUIRE(4 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid match replacement: unfinished replacement");
     CHECK_EQ(result.warnings[1].text, "Invalid match replacement: unexpected replacement character; must be a digit or %");
     CHECK_EQ(result.warnings[2].text, "Invalid match replacement: invalid capture index, must refer to pattern capture");
@@ -1162,7 +1162,7 @@ os.date("it's %c now")
 os.date("!*t")
 )");
 
-    CHECK_EQ(result.warnings.size(), 4);
+    REQUIRE(4 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid date format: unfinished replacement");
     CHECK_EQ(result.warnings[1].text, "Invalid date format: unexpected replacement character; must be a date format specifier or %");
     CHECK_EQ(result.warnings[2].text, "Invalid date format: unexpected replacement character; must be a date format specifier or %");
@@ -1181,7 +1181,7 @@ s:match("[]")
 nons:match("[]")
 )~");
 
-    REQUIRE_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Invalid match pattern: expected ] at the end of the string to close a set");
     CHECK_EQ(result.warnings[0].location.begin.line, 3);
     CHECK_EQ(result.warnings[1].text, "Invalid match pattern: expected ] at the end of the string to close a set");
@@ -1231,7 +1231,7 @@ _ = {
 }
 )");
 
-    CHECK_EQ(result.warnings.size(), 6);
+    REQUIRE(6 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Table field 'first' is a duplicate; previously defined at line 3");
     CHECK_EQ(result.warnings[1].text, "Table field 'first' is a duplicate; previously defined at line 9");
     CHECK_EQ(result.warnings[2].text, "Table index 1 is a duplicate; previously defined as a list entry");
@@ -1248,7 +1248,7 @@ TEST_CASE_FIXTURE(Fixture, "ImportOnlyUsedInTypeAnnotation")
         local x: Foo.Y = 1
     )");
 
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Variable 'x' is never used; prefix with '_' to silence");
 }
 
@@ -1259,7 +1259,7 @@ TEST_CASE_FIXTURE(Fixture, "DisableUnknownGlobalWithTypeChecking")
         unknownGlobal()
     )");
 
-    REQUIRE_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "no_spurious_warning_after_a_function_type_alias")
@@ -1271,7 +1271,7 @@ TEST_CASE_FIXTURE(Fixture, "no_spurious_warning_after_a_function_type_alias")
         return exports
     )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "use_all_parent_scopes_for_globals")
@@ -1294,7 +1294,7 @@ TEST_CASE_FIXTURE(Fixture, "use_all_parent_scopes_for_globals")
 
     LintResult result = frontend.lint("A");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "DeadLocalsUsed")
@@ -1320,7 +1320,7 @@ do
 end
     )");
 
-    CHECK_EQ(result.warnings.size(), 3);
+    REQUIRE(3 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Variable 'x' defined at line 4 is never initialized or assigned; initialize with 'nil' to silence");
     CHECK_EQ(result.warnings[1].text, "Assigning 2 values to 3 variables initializes extra variables with nil; add 'nil' to value list to silence");
     CHECK_EQ(result.warnings[2].text, "Variable 'c' defined at line 12 is never initialized or assigned; initialize with 'nil' to silence");
@@ -1333,7 +1333,7 @@ local foo
 function foo() end
     )");
 
-    CHECK_EQ(result.warnings.size(), 0);
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "DuplicateGlobalFunction")
@@ -1408,7 +1408,7 @@ TEST_CASE_FIXTURE(Fixture, "DontTriggerTheWarningIfTheFunctionsAreInDifferentSco
         return c
     )");
 
-    CHECK(result.warnings.empty());
+    REQUIRE(0 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "LintHygieneUAF")
@@ -1444,7 +1444,7 @@ TEST_CASE_FIXTURE(Fixture, "LintHygieneUAF")
         local h: Hooty.Pt
     )");
 
-    CHECK_EQ(result.warnings.size(), 12);
+    REQUIRE(12 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "DeprecatedApi")
@@ -1478,7 +1478,7 @@ return function (i: Instance)
 end
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 3);
+    REQUIRE(3 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Member 'Instance.Wait' is deprecated");
     CHECK_EQ(result.warnings[1].text, "Member 'toHSV' is deprecated, use 'Color3:ToHSV' instead");
     CHECK_EQ(result.warnings[2].text, "Member 'Instance.DataCost' is deprecated");
@@ -1511,7 +1511,7 @@ table.create(42, {})
 table.create(42, {} :: {})
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 10);
+    REQUIRE(10 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "table.insert will insert the value before the last element, which is likely a bug; consider removing the "
                                       "second argument or wrap it in parentheses to silence");
     CHECK_EQ(result.warnings[1].text, "table.insert will append the value to the table; consider removing the second argument for efficiency");
@@ -1556,7 +1556,7 @@ _ = true and true or false -- no warning since this is is a common pattern used
 _ = if true then 1 elseif true then 2 else 3
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 8);
+    REQUIRE(8 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Condition has already been checked on line 2");
     CHECK_EQ(result.warnings[0].location.begin.line + 1, 4);
     CHECK_EQ(result.warnings[1].text, "Condition has already been checked on column 5");
@@ -1580,7 +1580,7 @@ elseif correct({a = 1, b = 2 * (-2), c = opaque.path['with']("calls", false)}) t
 end
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Condition has already been checked on line 4");
     CHECK_EQ(result.warnings[0].location.begin.line + 1, 5);
 }
@@ -1601,7 +1601,7 @@ end
 return foo, moo, a1, a2
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 4);
+    REQUIRE(4 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Function parameter 'a1' already defined on column 14");
     CHECK_EQ(result.warnings[1].text, "Variable 'a1' is never used; prefix with '_' to silence");
     CHECK_EQ(result.warnings[2].text, "Variable 'a1' already defined on column 7");
@@ -1618,7 +1618,7 @@ _ = math.random() < 0.5 and 0 or 42
 _ = (math.random() < 0.5 and false) or 42 -- currently ignored
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "The and-or expression always evaluates to the second alternative because the first alternative is false; "
                                       "consider using if-then-else expression instead");
     CHECK_EQ(result.warnings[1].text, "The and-or expression always evaluates to the second alternative because the first alternative is nil; "
@@ -1640,7 +1640,7 @@ do end
 --!nolint
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 6);
+    REQUIRE(6 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Unknown comment directive 'struct'; did you mean 'strict'?");
     CHECK_EQ(result.warnings[1].text, "Unknown comment directive 'nolintGlobal'");
     CHECK_EQ(result.warnings[2].text, "nolint directive refers to unknown lint rule 'Global'");
@@ -1656,7 +1656,7 @@ TEST_CASE_FIXTURE(Fixture, "WrongCommentMuteSelf")
 --!struct
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 0); // --!nolint disables WrongComment lint :)
+    REQUIRE(0 == result.warnings.size()); // --!nolint disables WrongComment lint :)
 }
 
 TEST_CASE_FIXTURE(Fixture, "DuplicateConditionsIfStatAndExpr")
@@ -1668,7 +1668,7 @@ elseif if 0 then 5 else 4 then
 end
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Condition has already been checked on line 2");
 }
 
@@ -1681,13 +1681,13 @@ TEST_CASE_FIXTURE(Fixture, "WrongCommentOptimize")
 --!optimize 2
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 3);
+    REQUIRE(3 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "optimize directive requires an optimization level");
     CHECK_EQ(result.warnings[1].text, "optimize directive uses unknown optimization level 'me', 0..2 expected");
     CHECK_EQ(result.warnings[2].text, "optimize directive uses unknown optimization level '100500', 0..2 expected");
 
     result = lint("--!optimize   ");
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "optimize directive requires an optimization level");
 }
 
@@ -1700,7 +1700,7 @@ TEST_CASE_FIXTURE(Fixture, "TestStringInterpolation")
         local _ = `unknown {foo}`
     )");
 
-    REQUIRE_EQ(result.warnings.size(), 1);
+    REQUIRE(1 == result.warnings.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "IntegerParsing")
@@ -1710,7 +1710,7 @@ local _ = 0b10000000000000000000000000000000000000000000000000000000000000000
 local _ = 0x10000000000000000
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "Binary number literal exceeded available precision and has been truncated to 2^64");
     CHECK_EQ(result.warnings[1].text, "Hexadecimal number literal exceeded available precision and has been truncated to 2^64");
 }
@@ -1725,7 +1725,7 @@ local _ = 0x0x123
 local _ = 0x0xffffffffffffffffffffffffffffffffff
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 2);
+    REQUIRE(2 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text,
         "Hexadecimal number literal has a double prefix, which will fail to parse in the future; remove the extra 0x to fix");
     CHECK_EQ(result.warnings[1].text,
@@ -1756,7 +1756,7 @@ local _ = (a <= b) == 0
 local _ = a <= (b == 0)
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 5);
+    REQUIRE(5 == result.warnings.size());
     CHECK_EQ(result.warnings[0].text, "not X == Y is equivalent to (not X) == Y; consider using X ~= Y, or add parentheses to silence");
     CHECK_EQ(result.warnings[1].text, "not X ~= Y is equivalent to (not X) ~= Y; consider using X == Y, or add parentheses to silence");
     CHECK_EQ(result.warnings[2].text, "not X <= Y is equivalent to (not X) <= Y; add parentheses to silence");

tests/Normalize.test.cpp

@@ -356,6 +356,11 @@ TEST_CASE_FIXTURE(NormalizeFixture, "table_with_any_prop")
 
 TEST_CASE_FIXTURE(NormalizeFixture, "intersection")
 {
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
     check(R"(
         local a: number & string
         local b: number
@@ -374,8 +379,9 @@ TEST_CASE_FIXTURE(NormalizeFixture, "intersection")
     CHECK(!isSubtype(c, a));
     CHECK(isSubtype(a, c));
 
-    CHECK(!isSubtype(d, a));
+    // These types are both equivalent to never
-    CHECK(!isSubtype(a, d));
+    CHECK(isSubtype(d, a));
+    CHECK(isSubtype(a, d));
 }
 
 TEST_CASE_FIXTURE(NormalizeFixture, "union_and_intersection")

tests/Parser.test.cpp

@@ -2722,4 +2722,59 @@ TEST_CASE_FIXTURE(Fixture, "error_message_for_using_function_as_type_annotation"
         result.errors[0].getMessage());
 }
 
+TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the_end_of_a_function_argument_list")
+{
+    ScopedFastFlag sff{"LuauCommaParenWarnings", true};
+
+    ParseResult result = tryParse(R"(
+        foo(a, b, c,)
+    )");
+
+    REQUIRE(1 == result.errors.size());
+
+    CHECK(Location({1, 20}, {1, 21}) == result.errors[0].getLocation());
+    CHECK("Expected expression after ',' but got ')' instead" == result.errors[0].getMessage());
+}
+
+TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the_end_of_a_function_parameter_list")
+{
+    ScopedFastFlag sff{"LuauCommaParenWarnings", true};
+
+    ParseResult result = tryParse(R"(
+        export type VisitFn = (
+            any,
+            Array<TAnyNode | Array<TAnyNode>>, -- extra comma here
+        ) -> any
+    )");
+
+    REQUIRE(1 == result.errors.size());
+
+    CHECK(Location({4, 8}, {4, 9}) == result.errors[0].getLocation());
+    CHECK("Expected type after ',' but got ')' instead" == result.errors[0].getMessage());
+}
+
+TEST_CASE_FIXTURE(Fixture, "get_a_nice_error_when_there_is_an_extra_comma_at_the_end_of_a_generic_parameter_list")
+{
+    ScopedFastFlag sff{"LuauCommaParenWarnings", true};
+
+    ParseResult result = tryParse(R"(
+        export type VisitFn = <A, B,>(a: A, b: B) -> ()
+    )");
+
+    REQUIRE(1 == result.errors.size());
+
+    CHECK(Location({1, 36}, {1, 37}) == result.errors[0].getLocation());
+    CHECK("Expected type after ',' but got '>' instead" == result.errors[0].getMessage());
+
+    REQUIRE(1 == result.root->body.size);
+
+    AstStatTypeAlias* t = result.root->body.data[0]->as<AstStatTypeAlias>();
+    REQUIRE(t != nullptr);
+
+    AstTypeFunction* f = t->type->as<AstTypeFunction>();
+    REQUIRE(f != nullptr);
+
+    CHECK(2 == f->generics.size);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.classes.test.cpp

@@ -480,4 +480,38 @@ local a: ChildClass = i
     CHECK_EQ("Type 'ChildClass' from 'Test' could not be converted into 'ChildClass' from 'MainModule'", toString(result.errors[0]));
 }
 
+TEST_CASE_FIXTURE(ClassFixture, "intersections_of_unions_of_classes")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : (BaseClass | Vector2) & (ChildClass | AnotherChild)
+        local y : (ChildClass | AnotherChild)
+        x = y
+        y = x
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(ClassFixture, "unions_of_intersections_of_classes")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : (BaseClass & ChildClass) | (BaseClass & AnotherChild) | (BaseClass & Vector2)
+        local y : (ChildClass | AnotherChild)
+        x = y
+        y = x
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.functions.test.cpp

@@ -2,6 +2,7 @@
 
 #include "Luau/AstQuery.h"
 #include "Luau/BuiltinDefinitions.h"
+#include "Luau/Error.h"
 #include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypeVar.h"
@@ -14,6 +15,7 @@
 using namespace Luau;
 
 LUAU_FASTFLAG(LuauLowerBoundsCalculation);
+LUAU_FASTFLAG(LuauInstantiateInSubtyping);
 LUAU_FASTFLAG(LuauSpecialTypesAsterisked);
 
 TEST_SUITE_BEGIN("TypeInferFunctions");
@@ -1087,10 +1089,20 @@ f(function(a, b, c, ...) return a + b end)
 
     LUAU_REQUIRE_ERRORS(result);
 
-    CHECK_EQ(R"(Type '(number, number, a) -> number' could not be converted into '(number, number) -> number'
+    if (FFlag::LuauInstantiateInSubtyping)
+    {
+        CHECK_EQ(R"(Type '<a>(number, number, a) -> number' could not be converted into '(number, number) -> number'
 caused by:
   Argument count mismatch. Function expects 3 arguments, but only 2 are specified)",
-        toString(result.errors[0]));
+            toString(result.errors[0]));
+    }
+    else
+    {
+        CHECK_EQ(R"(Type '(number, number, a) -> number' could not be converted into '(number, number) -> number'
+caused by:
+  Argument count mismatch. Function expects 3 arguments, but only 2 are specified)",
+            toString(result.errors[0]));
+    }
 
     // Infer from variadic packs into elements
     result = check(R"(
@@ -1189,10 +1201,20 @@ f(function(a, b, c, ...) return a + b end)
 
     LUAU_REQUIRE_ERRORS(result);
 
-    CHECK_EQ(R"(Type '(number, number, a) -> number' could not be converted into '(number, number) -> number'
+    if (FFlag::LuauInstantiateInSubtyping)
+    {
+        CHECK_EQ(R"(Type '<a>(number, number, a) -> number' could not be converted into '(number, number) -> number'
 caused by:
   Argument count mismatch. Function expects 3 arguments, but only 2 are specified)",
-        toString(result.errors[0]));
+            toString(result.errors[0]));
+    }
+    else
+    {
+        CHECK_EQ(R"(Type '(number, number, a) -> number' could not be converted into '(number, number) -> number'
+caused by:
+  Argument count mismatch. Function expects 3 arguments, but only 2 are specified)",
+            toString(result.errors[0]));
+    }
 
     // Infer from variadic packs into elements
     result = check(R"(

tests/TypeInfer.generics.test.cpp

@@ -10,6 +10,7 @@
 #include "doctest.h"
 
 LUAU_FASTFLAG(LuauCheckGenericHOFTypes)
+LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 LUAU_FASTFLAG(LuauSpecialTypesAsterisked)
 
 using namespace Luau;
@@ -960,7 +961,11 @@ TEST_CASE_FIXTURE(Fixture, "instantiate_generic_function_in_assignments")
     TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
     REQUIRE(tm);
     CHECK_EQ("((number) -> number, string) -> number", toString(tm->wantedType));
-    CHECK_EQ("((number) -> number, number) -> number", toString(tm->givenType));
+    if (FFlag::LuauInstantiateInSubtyping)
+        CHECK_EQ("<a, b...>((a) -> (b...), a) -> (b...)", toString(tm->givenType));
+    else
+        CHECK_EQ("((number) -> number, number) -> number", toString(tm->givenType));
+
 }
 
 TEST_CASE_FIXTURE(Fixture, "instantiate_generic_function_in_assignments2")
@@ -980,7 +985,10 @@ TEST_CASE_FIXTURE(Fixture, "instantiate_generic_function_in_assignments2")
     TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
     REQUIRE(tm);
     CHECK_EQ("(string, string) -> number", toString(tm->wantedType));
-    CHECK_EQ("((string) -> number, string) -> number", toString(*tm->givenType));
+    if (FFlag::LuauInstantiateInSubtyping)
+        CHECK_EQ("<a, b...>((a) -> (b...), a) -> (b...)", toString(tm->givenType));
+    else
+        CHECK_EQ("((string) -> number, string) -> number", toString(*tm->givenType));
 }
 
 TEST_CASE_FIXTURE(Fixture, "self_recursive_instantiated_param")
@@ -1110,6 +1118,15 @@ local c = sumrec(function(x, y, f) return f(x, y) end) -- type binders are not i
     {
         LUAU_REQUIRE_NO_ERRORS(result);
     }
+    else if (FFlag::LuauInstantiateInSubtyping)
+    {
+        LUAU_REQUIRE_ERRORS(result);
+        CHECK_EQ(
+            R"(Type '<a, b, c...>(a, b, (a, b) -> (c...)) -> (c...)' could not be converted into '<a>(a, a, (a, a) -> a) -> a'
+caused by:
+  Argument #1 type is not compatible. Generic subtype escaping scope)",
+            toString(result.errors[0]));
+    }
     else
     {
         LUAU_REQUIRE_ERRORS(result);
@@ -1219,4 +1236,48 @@ TEST_CASE_FIXTURE(Fixture, "do_not_always_instantiate_generic_intersection_types
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "hof_subtype_instantiation_regression")
+{
+    CheckResult result = check(R"(
+--!strict
+
+local function defaultSort<T>(a: T, b: T)
+    return true
+end
+type A = any
+return function<T>(array: {T}): {T}
+    table.sort(array, defaultSort)
+    return array
+end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "higher_rank_polymorphism_should_not_accept_instantiated_arguments")
+{
+    ScopedFastFlag sffs[] = {
+        {"LuauInstantiateInSubtyping", true},
+        {"LuauCheckGenericHOFTypes", true}, // necessary because of interactions with the test
+    };
+
+    CheckResult result = check(R"(
+--!strict
+
+local function instantiate(f: <a>(a) -> a): (number) -> number
+    return f
+end
+
+instantiate(function(x: string) return "foo" end)
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    auto tm1 = get<TypeMismatch>(result.errors[0]);
+    REQUIRE(tm1);
+
+    CHECK_EQ("<a>(a) -> a", toString(tm1->wantedType));
+    CHECK_EQ("<a>(string) -> string", toString(tm1->givenType));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.intersectionTypes.test.cpp

@@ -446,4 +446,459 @@ TEST_CASE_FIXTURE(Fixture, "no_stack_overflow_from_flattenintersection")
     LUAU_REQUIRE_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "intersect_bool_and_false")
+{
+    CheckResult result = check(R"(
+        local x : (boolean & false)
+        local y : false = x -- OK
+        local z : true = x  -- Not OK
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type 'boolean & false' could not be converted into 'true'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "intersect_false_and_bool_and_false")
+{
+    CheckResult result = check(R"(
+        local x : false & (boolean & false)
+        local y : false = x -- OK
+        local z : true = x  -- Not OK
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    // TODO: odd stringification of `false & (boolean & false)`.)
+    CHECK_EQ(toString(result.errors[0]), "Type 'boolean & false & false' could not be converted into 'true'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "intersect_saturate_overloaded_functions")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : ((number?) -> number?) & ((string?) -> string?)
+        local y : (nil) -> nil = x -- OK
+        local z : (number) -> number = x -- Not OK
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((number?) -> number?) & ((string?) -> string?)' could not be converted into '(number) -> number'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_saturate_overloaded_functions")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : ((number) -> number) & ((string) -> string)
+        local y : ((number | string) -> (number | string)) = x -- OK
+        local z : ((number | boolean) -> (number | boolean)) = x -- Not OK
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((number) -> number) & ((string) -> string)' could not be converted into '(boolean | number) -> boolean | number'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "intersection_of_tables")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : { p : number?, q : string? } & { p : number?, q : number?, r : number? }
+        local y : { p : number?, q : nil, r : number? } = x -- OK
+        local z : { p : nil } = x -- Not OK
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '{| p: number?, q: number?, r: number? |} & {| p: number?, q: string? |}' could not be converted into '{| p: nil |}'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "intersection_of_tables_with_top_properties")
+{
+    CheckResult result = check(R"(
+        local x : { p : number?, q : any } & { p : unknown, q : string? }
+        local y : { p : number?, q : string? } = x -- OK
+        local z : { p : string?, q : number? } = x -- Not OK
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '{| p: number?, q: any |} & {| p: unknown, q: string? |}' could not be converted into '{| p: string?, q: number? |}'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "intersection_of_tables_with_never_properties")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : { p : number?, q : never } & { p : never, q : string? }
+        local y : { p : never, q : never } = x -- OK
+        local z : never = x -- OK
+    )");
+
+    // TODO: this should not produce type errors, since never <: { p : never }
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '{| p: never, q: string? |} & {| p: number?, q: never |}' could not be converted into 'never'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloaded_functions_returning_intersections")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : ((number?) -> ({ p : number } & { q : number })) & ((string?) -> ({ p : number } & { r : number }))
+        local y : (nil) -> { p : number, q : number, r : number} = x -- OK
+        local z : (number?) -> { p : number, q : number, r : number} = x -- Not OK
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((number?) -> {| p: number |} & {| q: number |}) & ((string?) -> {| p: number |} & {| r: number |})' could not be converted into '(number?) -> {| p: number, q: number, r: number |}'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloaded_functions_mentioning_generic")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a>()
+        local x : ((number?) -> (a | number)) & ((string?) -> (a | string))
+        local y : (nil) -> a = x -- OK
+        local z : (number?) -> a = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((number?) -> a | number) & ((string?) -> a | string)' could not be converted into '(number?) -> a'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloaded_functions_mentioning_generics")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a,b,c>()
+        local x : ((a?) -> (a | b)) & ((c?) -> (b | c))
+        local y : (nil) -> ((a & c) | b) = x -- OK
+        local z : (a?) -> ((a & c) | b) = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((a?) -> a | b) & ((c?) -> b | c)' could not be converted into '(a?) -> (a & c) | b'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloaded_functions_mentioning_generic_packs")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a...,b...>()
+        local x : ((number?, a...) -> (number?, b...)) & ((string?, a...) -> (string?, b...))
+        local y : ((nil, a...) -> (nil, b...)) = x -- OK
+        local z : ((nil, b...) -> (nil, a...)) = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((number?, a...) -> (number?, b...)) & ((string?, a...) -> (string?, b...))' could not be converted into '(nil, b...) -> (nil, a...)'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_unknown_result")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a...,b...>()
+        local x : ((number) -> number) & ((nil) -> unknown)
+        local y : (number?) -> unknown = x -- OK
+        local z : (number?) -> number? = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((nil) -> unknown) & ((number) -> number)' could not be converted into '(number?) -> number?'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_unknown_arguments")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a...,b...>()
+        local x : ((number) -> number?) & ((unknown) -> string?)
+        local y : (number) -> nil = x -- OK
+        local z : (number?) -> nil = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((number) -> number?) & ((unknown) -> string?)' could not be converted into '(number?) -> nil'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_never_result")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a...,b...>()
+        local x : ((number) -> number) & ((nil) -> never)
+        local y : (number?) -> number = x -- OK
+        local z : (number?) -> never = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((nil) -> never) & ((number) -> number)' could not be converted into '(number?) -> never'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_never_arguments")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a...,b...>()
+        local x : ((number) -> number?) & ((never) -> string?)
+        local y : (never) -> nil = x -- OK
+        local z : (number?) -> nil = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((never) -> string?) & ((number) -> number?)' could not be converted into '(number?) -> nil'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_overlapping_results_and_variadics")
+{
+    CheckResult result = check(R"(
+        local x : ((string?) -> (string | number)) & ((number?) -> ...number)
+        local y : ((nil) -> (number, number?)) = x -- OK
+        local z : ((string | number) -> (number, number?)) = x -- Not OK
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((number?) -> (...number)) & ((string?) -> number | string)' could not be converted into '(number | string) -> (number, number?)'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_weird_typepacks_1")
+{
+    CheckResult result = check(R"(
+      function f<a...,b...>()
+        local x : (() -> a...) & (() -> b...)
+        local y : (() -> b...) & (() -> a...) = x -- OK
+        local z : () -> () = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '(() -> (a...)) & (() -> (b...))' could not be converted into '() -> ()'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_weird_typepacks_2")
+{
+    CheckResult result = check(R"(
+      function f<a...,b...>()
+        local x : ((a...) -> ()) & ((b...) -> ())
+        local y : ((b...) -> ()) & ((a...) -> ()) = x -- OK
+        local z : () -> () = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((a...) -> ()) & ((b...) -> ())' could not be converted into '() -> ()'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_weird_typepacks_3")
+{
+    CheckResult result = check(R"(
+      function f<a...>()
+        local x : (() -> a...) & (() -> (number?,a...))
+        local y : (() -> (number?,a...)) & (() -> a...) = x -- OK
+        local z : () -> (number) = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '(() -> (a...)) & (() -> (number?, a...))' could not be converted into '() -> number'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "overloadeded_functions_with_weird_typepacks_4")
+{
+    CheckResult result = check(R"(
+      function f<a...>()
+        local x : ((a...) -> ()) & ((number,a...) -> number)
+        local y : ((number,a...) -> number) & ((a...) -> ()) = x -- OK
+        local z : (number?) -> () = x -- Not OK
+      end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '((a...) -> ()) & ((number, a...) -> number)' could not be converted into '(number?) -> ()'; none of the intersection parts are compatible");
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "intersect_metatables")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local a : string? = nil
+        local b : number? = nil
+    
+        local x = setmetatable({}, { p = 5, q = a });
+        local y = setmetatable({}, { q = b, r = "hi" });
+        local z = setmetatable({}, { p = 5, q = nil, r = "hi" });
+
+        type X = typeof(x)
+        type Y = typeof(y)
+        type Z = typeof(z)
+
+        local xy : X&Y = z;
+        local yx : Y&X = z;
+        z = xy;
+        z = yx;
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "intersect_metatable_subtypes")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x = setmetatable({ a = 5 }, { p = 5 });
+        local y = setmetatable({ b = "hi" }, { p = 5, q = "hi" });
+        local z = setmetatable({ a = 5, b = "hi" }, { p = 5, q = "hi" });
+
+        type X = typeof(x)
+        type Y = typeof(y)
+        type Z = typeof(z)
+
+        local xy : X&Y = z;
+        local yx : Y&X = z;
+        z = xy;
+        z = yx;
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "intersect_metatables_with_properties")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x = setmetatable({ a = 5 }, { p = 5 });
+        local y = setmetatable({ b = "hi" }, { q = "hi" });
+        local z = setmetatable({ a = 5, b = "hi" }, { p = 5, q = "hi" });
+
+        type X = typeof(x)
+        type Y = typeof(y)
+        type Z = typeof(z)
+
+        local xy : X&Y = z;
+        z = xy;
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "intersect_metatable_with table")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x = setmetatable({ a = 5 }, { p = 5 });
+        local z = setmetatable({ a = 5, b = "hi" }, { p = 5 });
+
+        type X = typeof(x)
+        type Y = { b : string }
+        type Z = typeof(z)
+
+        -- TODO: once we have shape types, we should be able to initialize these with z
+        local xy : X&Y;
+        local yx : Y&X;
+        z = xy;
+        z = yx;
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "CLI-44817")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        type X = {x: number}
+        type Y = {y: number}
+        type Z = {z: number}
+
+        type XY = {x: number, y: number}
+        type XYZ = {x:number, y: number, z: number}
+
+        local xy: XY = {x = 0, y = 0}
+        local xyz: XYZ = {x = 0, y = 0, z = 0}
+
+        local xNy: X&Y = xy
+        local xNyNz: X&Y&Z = xyz
+
+        local t1: XY = xNy -- Type 'X & Y' could not be converted into 'XY'
+        local t2: XY = xNyNz -- Type 'X & Y & Z' could not be converted into 'XY'
+        local t3: XYZ = xNyNz -- Type 'X & Y & Z' could not be converted into 'XYZ'
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.modules.test.cpp

@@ -10,6 +10,8 @@
 
 #include "doctest.h"
 
+LUAU_FASTFLAG(LuauInstantiateInSubtyping)
+
 using namespace Luau;
 
 LUAU_FASTFLAG(LuauSpecialTypesAsterisked)
@@ -248,7 +250,24 @@ end
 
 return m
 )");
-    LUAU_REQUIRE_NO_ERRORS(result);
+
+    if (FFlag::LuauInstantiateInSubtyping)
+    {
+        // though this didn't error before the flag, it seems as though it should error since fields of a table are invariant.
+        // the user's intent would likely be that these "method" fields would be read-only, but without an annotation, accepting this should be unsound.
+
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+        CHECK_EQ(R"(Type 'n' could not be converted into 't1 where t1 = {- Clone: (t1) -> (a...) -}'
+caused by:
+  Property 'Clone' is not compatible. Type '<a>(a) -> ()' could not be converted into 't1 where t1 = ({- Clone: t1 -}) -> (a...)'; different number of generic type parameters)",
+                 toString(result.errors[0]));
+    }
+    else
+    {
+        LUAU_REQUIRE_NO_ERRORS(result);
+    }
+
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "custom_require_global")
@@ -367,8 +386,6 @@ type Table = typeof(tbl)
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "do_not_modify_imported_types_5")
 {
-    ScopedFastFlag luauInplaceDemoteSkipAllBound{"LuauInplaceDemoteSkipAllBound", true};
-
     fileResolver.source["game/A"] = R"(
 export type Type = {x: number, y: number}
 local arrayops = {}

tests/TypeInfer.provisional.test.cpp

@@ -271,30 +271,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "bail_early_if_unification_is_too_complicated
     }
 }
 
-// Should be in TypeInfer.tables.test.cpp
-// It's unsound to instantiate tables containing generic methods,
-// since mutating properties means table properties should be invariant.
-// We currently allow this but we shouldn't!
-TEST_CASE_FIXTURE(Fixture, "invariant_table_properties_means_instantiating_tables_in_call_is_unsound")
-{
-    CheckResult result = check(R"(
-        --!strict
-        local t = {}
-        function t.m(x) return x end
-        local a : string = t.m("hi")
-        local b : number = t.m(5)
-        function f(x : { m : (number)->number })
-            x.m = function(x) return 1+x end
-        end
-        f(t) -- This shouldn't typecheck
-        local c : string = t.m("hi")
-    )");
-
-    // TODO: this should error!
-    // This should be fixed by replacing generic tables by generics with type bounds.
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
 // FIXME: Move this test to another source file when removing FFlag::LuauLowerBoundsCalculation
 TEST_CASE_FIXTURE(Fixture, "do_not_ice_when_trying_to_pick_first_of_generic_type_pack")
 {
@@ -608,7 +584,8 @@ TEST_CASE_FIXTURE(Fixture, "free_options_cannot_be_unified_together")
 
     InternalErrorReporter iceHandler;
     UnifierSharedState sharedState{&iceHandler};
-    Unifier u{&arena, singletonTypes, Mode::Strict, NotNull{scope.get()}, Location{}, Variance::Covariant, sharedState};
+    Normalizer normalizer{&arena, singletonTypes, NotNull{&sharedState}};
+    Unifier u{NotNull{&normalizer}, Mode::Strict, NotNull{scope.get()}, Location{}, Variance::Covariant};
 
     u.tryUnify(option1, option2);
 
@@ -635,4 +612,87 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "for_in_loop_with_zero_iterators")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+// Ideally, we would not try to export a function type with generic types from incorrect scope
+TEST_CASE_FIXTURE(BuiltinsFixture, "generic_type_leak_to_module_interface")
+{
+    ScopedFastFlag LuauAnyifyModuleReturnGenerics{"LuauAnyifyModuleReturnGenerics", true};
+
+    fileResolver.source["game/A"] = R"(
+local wrapStrictTable
+
+local metatable = {
+    __index = function(self, key)
+        local value = self.__tbl[key]
+        if type(value) == "table" then
+            -- unification of the free 'wrapStrictTable' with this function type causes generics of this function to leak out of scope
+            return wrapStrictTable(value, self.__name .. "." .. key)
+        end
+        return value
+    end,
+}
+
+return wrapStrictTable
+    )";
+
+    frontend.check("game/A");
+
+    fileResolver.source["game/B"] = R"(
+local wrapStrictTable = require(game.A)
+
+local Constants = {}
+
+return wrapStrictTable(Constants, "Constants")
+    )";
+
+    frontend.check("game/B");
+
+    ModulePtr m = frontend.moduleResolver.modules["game/B"];
+    REQUIRE(m);
+
+    std::optional<TypeId> result = first(m->getModuleScope()->returnType);
+    REQUIRE(result);
+    CHECK(get<AnyTypeVar>(*result));
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "generic_type_leak_to_module_interface_variadic")
+{
+    ScopedFastFlag LuauAnyifyModuleReturnGenerics{"LuauAnyifyModuleReturnGenerics", true};
+
+    fileResolver.source["game/A"] = R"(
+local wrapStrictTable
+
+local metatable = {
+    __index = function<T>(self, key, ...: T)
+        local value = self.__tbl[key]
+        if type(value) == "table" then
+            -- unification of the free 'wrapStrictTable' with this function type causes generics of this function to leak out of scope
+            return wrapStrictTable(value, self.__name .. "." .. key)
+        end
+        return ...
+    end,
+}
+
+return wrapStrictTable
+    )";
+
+    frontend.check("game/A");
+
+    fileResolver.source["game/B"] = R"(
+local wrapStrictTable = require(game.A)
+
+local Constants = {}
+
+return wrapStrictTable(Constants, "Constants")
+    )";
+
+    frontend.check("game/B");
+
+    ModulePtr m = frontend.moduleResolver.modules["game/B"];
+    REQUIRE(m);
+
+    std::optional<TypeId> result = first(m->getModuleScope()->returnType);
+    REQUIRE(result);
+    CHECK(get<AnyTypeVar>(*result));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.tables.test.cpp

@@ -11,7 +11,8 @@
 
 using namespace Luau;
 
-LUAU_FASTFLAG(LuauLowerBoundsCalculation);
+LUAU_FASTFLAG(LuauLowerBoundsCalculation)
+LUAU_FASTFLAG(LuauInstantiateInSubtyping)
 
 TEST_SUITE_BEGIN("TableTests");
 
@@ -2038,11 +2039,22 @@ caused by:
 caused by:
   Property 'y' is not compatible. Type 'string' could not be converted into 'number')");
 
-    CHECK_EQ(toString(result.errors[1]), R"(Type 'b2' could not be converted into 'a2'
+    if (FFlag::LuauInstantiateInSubtyping)
+    {
+        CHECK_EQ(toString(result.errors[1]), R"(Type 'b2' could not be converted into 'a2'
+caused by:
+  Type '{ __call: <a, b>(a, b) -> () }' could not be converted into '{ __call: <a>(a) -> () }'
+caused by:
+  Property '__call' is not compatible. Type '<a, b>(a, b) -> ()' could not be converted into '<a>(a) -> ()'; different number of generic type parameters)");
+    }
+    else
+    {
+        CHECK_EQ(toString(result.errors[1]), R"(Type 'b2' could not be converted into 'a2'
 caused by:
   Type '{ __call: (a, b) -> () }' could not be converted into '{ __call: <a>(a) -> () }'
 caused by:
   Property '__call' is not compatible. Type '(a, b) -> ()' could not be converted into '<a>(a) -> ()'; different number of generic type parameters)");
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "error_detailed_indexer_key")
@@ -3173,4 +3185,53 @@ caused by:
     CHECK_EQ("<a, b...>(t1) -> string where t1 = {+ absolutely_no_scalar_has_this_method: (t1) -> (a, b...) +}", toString(requireType("f")));
 }
 
+TEST_CASE_FIXTURE(Fixture, "invariant_table_properties_means_instantiating_tables_in_call_is_unsound")
+{
+    ScopedFastFlag sff[]{
+        {"LuauInstantiateInSubtyping", true},
+    };
+
+    CheckResult result = check(R"(
+        --!strict
+        local t = {}
+        function t.m(x) return x end
+        local a : string = t.m("hi")
+        local b : number = t.m(5)
+        function f(x : { m : (number)->number })
+            x.m = function(x) return 1+x end
+        end
+        f(t) -- This shouldn't typecheck
+        local c : string = t.m("hi")
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+    CHECK_EQ(toString(result.errors[0]), R"(Type 't' could not be converted into '{| m: (number) -> number |}'
+caused by:
+  Property 'm' is not compatible. Type '<a>(a) -> a' could not be converted into '(number) -> number'; different number of generic type parameters)");
+    // this error message is not great since the underlying issue is that the context is invariant,
+    // and `(number) -> number` cannot be a subtype of `<a>(a) -> a`.
+}
+
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "generic_table_instantiation_potential_regression")
+{
+    CheckResult result = check(R"(
+--!strict
+
+function f(x)
+  x.p = 5
+  return x
+end
+local g : ({ p : number, q : string }) -> ({ p : number, r : boolean }) = f
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    MissingProperties* error = get<MissingProperties>(result.errors[0]);
+    REQUIRE(error != nullptr);
+    REQUIRE(error->properties.size() == 1);
+
+    CHECK_EQ("r", error->properties[0]);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.test.cpp

@@ -17,7 +17,9 @@
 LUAU_FASTFLAG(LuauLowerBoundsCalculation);
 LUAU_FASTFLAG(LuauFixLocationSpanTableIndexExpr);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauInstantiateInSubtyping);
 LUAU_FASTFLAG(LuauSpecialTypesAsterisked);
+LUAU_FASTFLAG(LuauCheckGenericHOFTypes);
 
 using namespace Luau;
 
@@ -999,7 +1001,26 @@ TEST_CASE_FIXTURE(Fixture, "cli_50041_committing_txnlog_in_apollo_client_error")
         end
     )");
 
-    LUAU_REQUIRE_NO_ERRORS(result);
+    if (FFlag::LuauInstantiateInSubtyping && !FFlag::LuauCheckGenericHOFTypes)
+    {
+        // though this didn't error before the flag, it seems as though it should error since fields of a table are invariant.
+        // the user's intent would likely be that these "method" fields would be read-only, but without an annotation, accepting this should be unsound.
+
+        LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+        CHECK_EQ(R"(Type 't1 where t1 = {+ getStoreFieldName: (t1, {| fieldName: string |} & {| from: number? |}) -> (a, b...) +}' could not be converted into 'Policies'
+caused by:
+  Property 'getStoreFieldName' is not compatible. Type 't1 where t1 = ({+ getStoreFieldName: t1 +}, {| fieldName: string |} & {| from: number? |}) -> (a, b...)' could not be converted into '(Policies, FieldSpecifier) -> string'
+caused by:
+  Argument #2 type is not compatible. Type 'FieldSpecifier' could not be converted into 'FieldSpecifier & {| from: number? |}'
+caused by:
+  Not all intersection parts are compatible. Table type 'FieldSpecifier' not compatible with type '{| from: number? |}' because the former has extra field 'fieldName')",
+                 toString(result.errors[0]));
+    }
+    else
+    {
+        LUAU_REQUIRE_NO_ERRORS(result);
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_no_ice")
@@ -1020,6 +1041,43 @@ TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_no_ice")
     CHECK_EQ("Code is too complex to typecheck! Consider simplifying the code around this area", toString(result.errors[0]));
 }
 
+TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_normalizer")
+{
+    ScopedFastInt sfi("LuauTypeInferRecursionLimit", 10);
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+        {"LuauAutocompleteDynamicLimits", true},
+    };
+
+    CheckResult result = check(R"(
+        function f<a,b,c,d,e,f,g,h,i,j>()
+            local x : a&b&c&d&e&f&g&h&(i?)
+            local y : (a&b&c&d&e&f&g&h&i)? = x
+        end
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+    CHECK_EQ("Internal error: Code is too complex to typecheck! Consider adding type annotations around this area", toString(result.errors[0]));
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_infer_cache_limit_normalizer")
+{
+    ScopedFastInt sfi("LuauNormalizeCacheLimit", 10);
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : ((number) -> number) & ((string) -> string) & ((nil) -> nil) & (({}) -> {})
+        local y : (number | string | nil | {}) -> (number | string | nil | {}) = x
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+    CHECK_EQ("Internal error: Code is too complex to typecheck! Consider adding type annotations around this area", toString(result.errors[0]));
+}
+
 TEST_CASE_FIXTURE(Fixture, "follow_on_new_types_in_substitution")
 {
     CheckResult result = check(R"(

tests/TypeInfer.tryUnify.test.cpp

@@ -17,8 +17,8 @@ struct TryUnifyFixture : Fixture
     ScopePtr globalScope{new Scope{arena.addTypePack({TypeId{}})}};
     InternalErrorReporter iceHandler;
     UnifierSharedState unifierState{&iceHandler};
-
+    Normalizer normalizer{&arena, singletonTypes, NotNull{&unifierState}};
-    Unifier state{&arena, singletonTypes, Mode::Strict, NotNull{globalScope.get()}, Location{}, Variance::Covariant, unifierState};
+    Unifier state{NotNull{&normalizer}, Mode::Strict, NotNull{globalScope.get()}, Location{}, Variance::Covariant};
 };
 
 TEST_SUITE_BEGIN("TryUnifyTests");

tests/TypeInfer.typePacks.cpp

@@ -1000,4 +1000,23 @@ TEST_CASE_FIXTURE(Fixture, "unify_variadic_tails_in_arguments_free")
     CHECK_EQ(toString(result.errors[0]), "Type 'number' could not be converted into 'boolean'");
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "type_packs_with_tails_in_vararg_adjustment")
+{
+    ScopedFastFlag luauFixVarargExprHeadType{"LuauFixVarargExprHeadType", true};
+
+    CheckResult result = check(R"(
+        local function wrapReject<TArg, TResult>(fn: (self: any, ...TArg) -> ...TResult): (self: any, ...TArg) -> ...TResult
+            return function(self, ...)
+                local arguments = { ... }
+                local ok, result = pcall(function()
+                    return fn(self, table.unpack(arguments))
+                end)
+                return result
+            end
+        end 
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.unionTypes.test.cpp

@@ -541,5 +541,182 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "table_union_write_indirect")
             R"(Type '(string) -> number' could not be converted into '((number) -> string) | ((number) -> string)'; none of the union options are compatible)");
 }
 
+TEST_CASE_FIXTURE(Fixture, "union_true_and_false")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : boolean
+        local y1 : (true | false) = x -- OK
+        local y2 : (true | false | (string & number)) = x -- OK
+        local y3 : (true | (string & number) | false) = x -- OK
+        local y4 : (true | (boolean & true) | false) = x -- OK
+     )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_functions")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : (number) -> number?
+        local y : ((number?) -> number?) | ((number) -> number) = x -- OK
+     )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_generic_functions")
+{
+    CheckResult result = check(R"(
+        local x : <a>(a) -> a?
+        local y : (<a>(a?) -> a?) | (<b>(b) -> b) = x -- Not OK
+     )");
+
+    // TODO: should this example typecheck?
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_generic_typepack_functions")
+{
+    CheckResult result = check(R"(
+        local x : <a...>(number, a...) -> (number?, a...)
+        local y : (<a...>(number?, a...) -> (number?, a...)) | (<b...>(number, b...) -> (number, b...)) = x -- Not OK
+     )");
+
+    // TODO: should this example typecheck?
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_functions_mentioning_generics")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a,b>()
+        local x : (a) -> a?
+        local y : ((a?) -> nil) | ((a) -> a) = x -- OK
+        local z : ((b?) -> nil) | ((b) -> b) = x -- Not OK
+      end
+     )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '(a) -> a?' could not be converted into '((b) -> b) | ((b?) -> nil)'; none of the union options are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_functions_mentioning_generic_typepacks")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+      function f<a...>()
+        local x : (number, a...) -> (number?, a...)
+        local y : ((number | string, a...) -> (number, a...)) | ((number?, a...) -> (nil, a...)) = x -- OK
+        local z : ((number) -> number) | ((number?, a...) -> (number?, a...)) = x -- Not OK
+      end
+     )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '(number, a...) -> (number?, a...)' could not be converted into '((number) -> number) | ((number?, a...) -> (number?, a...))'; none of the union options are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_functions_with_mismatching_arg_arities")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : (number) -> number?
+        local y : ((number?) -> number) | ((number | string) -> nil) = x -- OK
+        local z : ((number, string?) -> number) | ((number) -> nil) = x -- Not OK
+     )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '(number) -> number?' could not be converted into '((number) -> nil) | ((number, string?) -> number)'; none of the union options are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_functions_with_mismatching_result_arities")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : () -> (number | string)
+        local y : (() -> number) | (() -> string) = x -- OK
+        local z : (() -> number) | (() -> (string, string)) = x -- Not OK
+     )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '() -> number | string' could not be converted into '(() -> (string, string)) | (() -> number)'; none of the union options are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_functions_with_variadics")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : (...nil) -> (...number?)
+        local y : ((...string?) -> (...number)) | ((...number?) -> nil) = x -- OK
+        local z : ((...string?) -> (...number)) | ((...string?) -> nil) = x -- OK
+     )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '(...nil) -> (...number?)' could not be converted into '((...string?) -> (...number)) | ((...string?) -> nil)'; none of the union options are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_functions_with_mismatching_arg_variadics")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : (number) -> ()
+        local y : ((number?) -> ()) | ((...number) -> ()) = x -- OK
+        local z : ((number?) -> ()) | ((...number?) -> ()) = x -- Not OK
+     )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '(number) -> ()' could not be converted into '((...number?) -> ()) | ((number?) -> ())'; none of the union options are compatible");
+}
+
+TEST_CASE_FIXTURE(Fixture, "union_of_functions_with_mismatching_result_variadics")
+{
+    ScopedFastFlag sffs[] {
+        {"LuauSubtypeNormalizer", true},
+        {"LuauTypeNormalization2", true},
+    };
+
+    CheckResult result = check(R"(
+        local x : () -> (number?, ...number)
+        local y : (() -> (...number)) | (() -> nil) = x -- OK
+        local z : (() -> (...number)) | (() -> number) = x -- OK
+     )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type '() -> (number?, ...number)' could not be converted into '(() -> (...number)) | (() -> number)'; none of the union options are compatible");
+}
 
 TEST_SUITE_END();

tests/conformance/basic.lua

@@ -508,6 +508,9 @@ assert((function() function cmp(a,b) return a<b,a<=b,a>b,a>=b end return concat(
 assert((function() function cmp(a,b) return a<b,a<=b,a>b,a>=b end return concat(cmp('abc', 'abd')) end)() == "true,true,false,false")
 assert((function() function cmp(a,b) return a<b,a<=b,a>b,a>=b end return concat(cmp('ab\\0c', 'ab\\0d')) end)() == "true,true,false,false")
 assert((function() function cmp(a,b) return a<b,a<=b,a>b,a>=b end return concat(cmp('ab\\0c', 'ab\\0')) end)() == "false,false,true,true")
+assert((function() function cmp(a,b) return a<b,a<=b,a>b,a>=b end return concat(cmp('\\0a', '\\0b')) end)() == "true,true,false,false")
+assert((function() function cmp(a,b) return a<b,a<=b,a>b,a>=b end return concat(cmp('a', 'a\\0')) end)() == "true,true,false,false")
+assert((function() function cmp(a,b) return a<b,a<=b,a>b,a>=b end return concat(cmp('a', '\200')) end)() == "true,true,false,false")
 
 -- array access
 assert((function() local a = {4,5,6} return a[3] end)() == 6)

tests/main.cpp

@@ -21,6 +21,7 @@
 #include <sys/sysctl.h>
 #endif
 
+#include <random>
 #include <optional>
 
 // Indicates if verbose output is enabled; can be overridden via --verbose
@@ -30,6 +31,10 @@ bool verbose = false;
 // Default optimization level for conformance test; can be overridden via -On
 int optimizationLevel = 1;
 
+// Something to seed a pseudorandom number generator with.  Defaults to
+// something from std::random_device.
+std::optional<unsigned> randomSeed;
+
 static bool skipFastFlag(const char* flagName)
 {
     if (strncmp(flagName, "Test", 4) == 0)
@@ -261,6 +266,16 @@ int main(int argc, char** argv)
             optimizationLevel = level;
     }
 
+    int rseed = -1;
+    if (doctest::parseIntOption(argc, argv, "--random-seed=", doctest::option_int, rseed))
+        randomSeed = unsigned(rseed);
+
+    if (doctest::parseOption(argc, argv, "--randomize") && !randomSeed)
+    {
+        randomSeed = std::random_device()();
+        printf("Using RNG seed %u\n", *randomSeed);
+    }
+
     if (std::vector<doctest::String> flags; doctest::parseCommaSepArgs(argc, argv, "--fflags=", flags))
         setFastFlags(flags);
 
@@ -295,6 +310,8 @@ int main(int argc, char** argv)
         printf(" --verbose                             Enables verbose output (e.g. lua 'print' statements)\n");
         printf(" --fflags=                             Sets specified fast flags\n");
         printf(" --list-fflags                         List all fast flags\n");
+        printf(" --randomize                           Use a random RNG seed\n");
+        printf(" --random-seed=n                       Use a particular RNG seed\n");
     }
     return result;
 }

tools/lldb_formatters.lldb

@@ -5,3 +5,6 @@ type synthetic add -x "^Luau::Variant<.+>$" -l lldb_formatters.LuauVariantSynthe
 type summary add -x "^Luau::Variant<.+>$" -F lldb_formatters.luau_variant_summary
 
 type synthetic add -x "^Luau::AstArray<.+>$" -l lldb_formatters.AstArraySyntheticChildrenProvider
+
+type summary add --summary-string "${var.line}:${var.column}" Luau::Position
+type summary add --summary-string "${var.begin}-${var.end}" Luau::Location

tools/natvis/Ast.natvis

@@ -22,4 +22,25 @@
     </Expand>
   </Type>
 
+  <Type Name="Luau::AstName">
+    <DisplayString>{value,na}</DisplayString>
+  </Type>
+
+  <Type Name="Luau::AstLocal">
+    <DisplayString>{name.value,na}</DisplayString>
+  </Type>
+
+  <Type Name="Luau::Symbol">
+    <DisplayString Condition="local">local {local->name.value,na}</DisplayString>
+    <DisplayString>global {global.value,na}</DisplayString>
+  </Type>
+
+  <Type Name="Luau::Position">
+    <DisplayString>{line}:{column}</DisplayString>
+  </Type>
+
+  <Type Name="Luau::Location">
+    <DisplayString>{begin}-{end}</DisplayString>
+  </Type>
+
 </AutoVisualizer>

tools/test_dcr.py

@@ -22,6 +22,10 @@ def safeParseInt(i, default=0):
         return default
 
 
+def makeDottedName(path):
+    return ".".join(path)
+
+
 class Handler(x.ContentHandler):
     def __init__(self, failList):
         self.currentTest = []
@@ -41,7 +45,7 @@ class Handler(x.ContentHandler):
             if self.currentTest:
                 passed = attrs["test_case_success"] == "true"
 
-                dottedName = ".".join(self.currentTest)
+                dottedName = makeDottedName(self.currentTest)
 
                 # Sometimes we get multiple XML trees for the same test. All of
                 # them must report a pass in order for us to consider the test
@@ -60,6 +64,10 @@ class Handler(x.ContentHandler):
             self.currentTest.pop()
 
 
+def print_stderr(*args, **kw):
+    print(*args, **kw, file=sys.stderr)
+
+
 def main():
     parser = argparse.ArgumentParser(
         description="Run Luau.UnitTest with deferred constraint resolution enabled"
@@ -80,6 +88,16 @@ def main():
         help="Write a new faillist.txt after running tests.",
     )
 
+    parser.add_argument("--randomize", action="store_true", help="Pick a random seed")
+
+    parser.add_argument(
+        "--random-seed",
+        action="store",
+        dest="random_seed",
+        type=int,
+        help="Accept a specific RNG seed",
+    )
+
     args = parser.parse_args()
 
     failList = loadFailList()
@@ -90,7 +108,12 @@ def main():
         "--fflags=true,DebugLuauDeferredConstraintResolution=true",
     ]
 
-    print('>', ' '.join(commandLine), file=sys.stderr)
+    if args.random_seed:
+        commandLine.append("--random-seed=" + str(args.random_seed))
+    elif args.randomize:
+        commandLine.append("--randomize")
+
+    print_stderr(">", " ".join(commandLine))
 
     p = sp.Popen(
         commandLine,
@@ -104,15 +127,21 @@ def main():
             sys.stdout.buffer.write(line)
         return
     else:
-        x.parse(p.stdout, handler)
+        try:
+            x.parse(p.stdout, handler)
+        except x.SAXParseException as e:
+            print_stderr(
+                f"XML parsing failed during test {makeDottedName(handler.currentTest)}.  That probably means that the test crashed"
+            )
+            sys.exit(1)
 
     p.wait()
 
     for testName, passed in handler.results.items():
         if passed and testName in failList:
-            print("UNEXPECTED: {} should have failed".format(testName))
+            print_stderr(f"UNEXPECTED: {testName} should have failed")
         elif not passed and testName not in failList:
-            print("UNEXPECTED: {} should have passed".format(testName))
+            print_stderr(f"UNEXPECTED: {testName} should have passed")
 
     if args.write:
         newFailList = sorted(
@@ -126,14 +155,11 @@ def main():
         with open(FAIL_LIST_PATH, "w", newline="\n") as f:
             for name in newFailList:
                 print(name, file=f)
-        print("Updated faillist.txt", file=sys.stderr)
+        print_stderr("Updated faillist.txt")
 
     if handler.numSkippedTests > 0:
-        print(
+        print_stderr(
-            "{} test(s) were skipped!  That probably means that a test segfaulted!".format(
+            f"{handler.numSkippedTests} test(s) were skipped!  That probably means that a test segfaulted!"
-                handler.numSkippedTests
-            ),
-            file=sys.stderr,
         )
         sys.exit(1)
 
@@ -143,7 +169,7 @@ def main():
     )
 
     if ok:
-        print("Everything in order!", file=sys.stderr)
+        print_stderr("Everything in order!")
 
     sys.exit(0 if ok else 1)