Sync to upstream/release/584 (#977)

* Added support for async typechecking cancellation using a token passed
through frontend options
* Added luaC_enumheap for building debug tools that need a graph of Luau
heap

In our new typechecker:
* Errors or now suppressed when checking property lookup of
error-suppressing unions

In our native code generation (jit):
* Fixed unhandled value type in NOT_ANY lowering
* Fast-call tag checks will exit to VM on failure, instead of relying on
a native fallback
* Added vector type to the type information
* Eliminated redundant direct jumps across dead blocks
* Debugger APIs are now disabled for call frames executing natively
* Implemented support for unwind registration on macOS 14

Analysis/include/Luau/Cancellation.h

@@ -0,0 +1,24 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include <atomic>
+
+namespace Luau
+{
+
+struct FrontendCancellationToken
+{
+    void cancel()
+    {
+        cancelled.store(true);
+    }
+
+    bool requested()
+    {
+        return cancelled.load();
+    }
+
+    std::atomic<bool> cancelled;
+};
+
+} // namespace Luau

Analysis/include/Luau/Differ.h

@@ -21,8 +21,8 @@ struct DiffPathNode
     Kind kind;
     // non-null when TableProperty
     std::optional<Name> tableProperty;
-    // non-null when FunctionArgument, FunctionReturn, Union, or Intersection (i.e. anonymous fields)
+    // non-null when FunctionArgument (unless variadic arg), FunctionReturn (unless variadic arg), Union, or Intersection (i.e. anonymous fields)
-    std::optional<int> index;
+    std::optional<size_t> index;
 
     /**
      * Do not use for leaf nodes
@@ -32,7 +32,7 @@ struct DiffPathNode
     {
     }
 
-    DiffPathNode(Kind kind, std::optional<Name> tableProperty, std::optional<int> index)
+    DiffPathNode(Kind kind, std::optional<Name> tableProperty, std::optional<size_t> index)
         : kind(kind)
         , tableProperty(tableProperty)
         , index(index)
@@ -42,19 +42,35 @@ struct DiffPathNode
     std::string toString() const;
 
     static DiffPathNode constructWithTableProperty(Name tableProperty);
+
+    static DiffPathNode constructWithKindAndIndex(Kind kind, size_t index);
+
+    static DiffPathNode constructWithKind(Kind kind);
 };
+
 struct DiffPathNodeLeaf
 {
     std::optional<TypeId> ty;
     std::optional<Name> tableProperty;
-    DiffPathNodeLeaf(std::optional<TypeId> ty, std::optional<Name> tableProperty)
+    std::optional<int> minLength;
+    bool isVariadic;
+    DiffPathNodeLeaf(std::optional<TypeId> ty, std::optional<Name> tableProperty, std::optional<int> minLength, bool isVariadic)
         : ty(ty)
         , tableProperty(tableProperty)
+        , minLength(minLength)
+        , isVariadic(isVariadic)
     {
     }
 
+    static DiffPathNodeLeaf detailsNormal(TypeId ty);
+
+    static DiffPathNodeLeaf detailsTableProperty(TypeId ty, Name tableProperty);
+
+    static DiffPathNodeLeaf detailsLength(int minLength, bool isVariadic);
+
     static DiffPathNodeLeaf nullopts();
 };
+
 struct DiffPath
 {
     std::vector<DiffPathNode> path;

Analysis/include/Luau/Error.h

@@ -357,13 +357,13 @@ struct PackWhereClauseNeeded
     bool operator==(const PackWhereClauseNeeded& rhs) const;
 };
 
-using TypeErrorData =
+using TypeErrorData = Variant<TypeMismatch, UnknownSymbol, UnknownProperty, NotATable, CannotExtendTable, OnlyTablesCanHaveMethods,
-    Variant<TypeMismatch, UnknownSymbol, UnknownProperty, NotATable, CannotExtendTable, OnlyTablesCanHaveMethods, DuplicateTypeDefinition,
+    DuplicateTypeDefinition, CountMismatch, FunctionDoesNotTakeSelf, FunctionRequiresSelf, OccursCheckFailed, UnknownRequire,
-        CountMismatch, FunctionDoesNotTakeSelf, FunctionRequiresSelf, OccursCheckFailed, UnknownRequire, IncorrectGenericParameterCount, SyntaxError,
+    IncorrectGenericParameterCount, SyntaxError, CodeTooComplex, UnificationTooComplex, UnknownPropButFoundLikeProp, GenericError, InternalError,
-        CodeTooComplex, UnificationTooComplex, UnknownPropButFoundLikeProp, GenericError, InternalError, CannotCallNonFunction, ExtraInformation,
+    CannotCallNonFunction, ExtraInformation, DeprecatedApiUsed, ModuleHasCyclicDependency, IllegalRequire, FunctionExitsWithoutReturning,
-        DeprecatedApiUsed, ModuleHasCyclicDependency, IllegalRequire, FunctionExitsWithoutReturning, DuplicateGenericParameter,
+    DuplicateGenericParameter, CannotInferBinaryOperation, MissingProperties, SwappedGenericTypeParameter, OptionalValueAccess, MissingUnionProperty,
-        CannotInferBinaryOperation, MissingProperties, SwappedGenericTypeParameter, OptionalValueAccess, MissingUnionProperty, TypesAreUnrelated,
+    TypesAreUnrelated, NormalizationTooComplex, TypePackMismatch, DynamicPropertyLookupOnClassesUnsafe, UninhabitedTypeFamily,
-        NormalizationTooComplex, TypePackMismatch, DynamicPropertyLookupOnClassesUnsafe, UninhabitedTypeFamily, UninhabitedTypePackFamily, WhereClauseNeeded, PackWhereClauseNeeded>;
+    UninhabitedTypePackFamily, WhereClauseNeeded, PackWhereClauseNeeded>;
 
 struct TypeErrorSummary
 {

Analysis/include/Luau/Frontend.h

@@ -29,6 +29,7 @@ struct ModuleResolver;
 struct ParseResult;
 struct HotComment;
 struct BuildQueueItem;
+struct FrontendCancellationToken;
 
 struct LoadDefinitionFileResult
 {
@@ -96,6 +97,8 @@ struct FrontendOptions
     std::optional<unsigned> randomizeConstraintResolutionSeed;
 
     std::optional<LintOptions> enabledLintWarnings;
+
+    std::shared_ptr<FrontendCancellationToken> cancellationToken;
 };
 
 struct CheckResult
@@ -191,6 +194,7 @@ private:
         std::optional<double> finishTime;
         std::optional<int> instantiationChildLimit;
         std::optional<int> unifierIterationLimit;
+        std::shared_ptr<FrontendCancellationToken> cancellationToken;
     };
 
     ModulePtr check(const SourceModule& sourceModule, Mode mode, std::vector<RequireCycle> requireCycles, std::optional<ScopePtr> environmentScope,

Analysis/include/Luau/InsertionOrderedMap.h

@@ -16,10 +16,10 @@ struct InsertionOrderedMap
 {
     static_assert(std::is_trivially_copyable_v<K>, "key must be trivially copyable");
 
-    private:
+private:
     using vec = std::vector<std::pair<K, V>>;
 
-    public:
+public:
     using iterator = typename vec::iterator;
     using const_iterator = typename vec::const_iterator;
 
@@ -131,4 +131,4 @@ private:
     std::unordered_map<K, size_t> indices;
 };
 
-}
+} // namespace Luau

Analysis/include/Luau/Module.h

@@ -112,6 +112,7 @@ struct Module
     Mode mode;
     SourceCode::Type type;
     bool timeout = false;
+    bool cancelled = false;
 
     TypePackId returnType = nullptr;
     std::unordered_map<Name, TypeFun> exportedTypeBindings;

Analysis/include/Luau/ToString.h

@@ -139,6 +139,6 @@ std::string dump(const std::shared_ptr<Scope>& scope, const char* name);
 std::string generateName(size_t n);
 
 std::string toString(const Position& position);
-std::string toString(const Location& location);
+std::string toString(const Location& location, int offset = 0, bool useBegin = true);
 
 } // namespace Luau

Analysis/include/Luau/TypeChecker2.h

@@ -12,6 +12,7 @@ namespace Luau
 struct DcrLogger;
 struct BuiltinTypes;
 
-void check(NotNull<BuiltinTypes> builtinTypes, NotNull<struct UnifierSharedState> sharedState, DcrLogger* logger, const SourceModule& sourceModule, Module* module);
+void check(NotNull<BuiltinTypes> builtinTypes, NotNull<struct UnifierSharedState> sharedState, DcrLogger* logger, const SourceModule& sourceModule,
+    Module* module);
 
 } // namespace Luau

Analysis/include/Luau/TypeInfer.h

@@ -25,6 +25,7 @@ namespace Luau
 struct Scope;
 struct TypeChecker;
 struct ModuleResolver;
+struct FrontendCancellationToken;
 
 using Name = std::string;
 using ScopePtr = std::shared_ptr<Scope>;
@@ -64,6 +65,15 @@ public:
     }
 };
 
+class UserCancelError : public InternalCompilerError
+{
+public:
+    explicit UserCancelError(const std::string& moduleName)
+        : InternalCompilerError("Analysis has been cancelled by user", moduleName)
+    {
+    }
+};
+
 struct GlobalTypes
 {
     GlobalTypes(NotNull<BuiltinTypes> builtinTypes);
@@ -262,6 +272,7 @@ public:
     [[noreturn]] void ice(const std::string& message, const Location& location);
     [[noreturn]] void ice(const std::string& message);
     [[noreturn]] void throwTimeLimitError();
+    [[noreturn]] void throwUserCancelError();
 
     ScopePtr childFunctionScope(const ScopePtr& parent, const Location& location, int subLevel = 0);
     ScopePtr childScope(const ScopePtr& parent, const Location& location);
@@ -387,6 +398,8 @@ public:
     std::optional<int> instantiationChildLimit;
     std::optional<int> unifierIterationLimit;
 
+    std::shared_ptr<FrontendCancellationToken> cancellationToken;
+
 public:
     const TypeId nilType;
     const TypeId numberType;

Analysis/include/Luau/Unifier.h

@@ -76,8 +76,7 @@ struct Unifier
     std::vector<TypeId> blockedTypes;
     std::vector<TypePackId> blockedTypePacks;
 
-    Unifier(
+    Unifier(NotNull<Normalizer> normalizer, NotNull<Scope> scope, const Location& location, Variance variance, TxnLog* parentLog = nullptr);
-        NotNull<Normalizer> normalizer, NotNull<Scope> scope, const Location& location, Variance variance, TxnLog* parentLog = nullptr);
 
     // Configure the Unifier to test for scope subsumption via embedded Scope
     // pointers rather than TypeLevels.

Analysis/src/Clone.cpp

@@ -7,7 +7,6 @@
 #include "Luau/Unifiable.h"
 
 LUAU_FASTFLAG(DebugLuauCopyBeforeNormalizing)
-LUAU_FASTFLAG(LuauClonePublicInterfaceLess2)
 LUAU_FASTFLAG(DebugLuauReadWriteProperties)
 
 LUAU_FASTINTVARIABLE(LuauTypeCloneRecursionLimit, 300)

Analysis/src/Differ.cpp

@@ -3,7 +3,9 @@
 #include "Luau/Error.h"
 #include "Luau/ToString.h"
 #include "Luau/Type.h"
+#include "Luau/TypePack.h"
 #include <optional>
+#include <string>
 
 namespace Luau
 {
@@ -18,6 +20,20 @@ std::string DiffPathNode::toString() const
         return *tableProperty;
         break;
     }
+    case DiffPathNode::Kind::FunctionArgument:
+    {
+        if (!index.has_value())
+            return "Arg[Variadic]";
+        // Add 1 because Lua is 1-indexed
+        return "Arg[" + std::to_string(*index + 1) + "]";
+    }
+    case DiffPathNode::Kind::FunctionReturn:
+    {
+        if (!index.has_value())
+            return "Ret[Variadic]";
+        // Add 1 because Lua is 1-indexed
+        return "Ret[" + std::to_string(*index + 1) + "]";
+    }
     default:
     {
         throw InternalCompilerError{"DiffPathNode::toString is not exhaustive"};
@@ -30,9 +46,34 @@ DiffPathNode DiffPathNode::constructWithTableProperty(Name tableProperty)
     return DiffPathNode{DiffPathNode::Kind::TableProperty, tableProperty, std::nullopt};
 }
 
+DiffPathNode DiffPathNode::constructWithKindAndIndex(Kind kind, size_t index)
+{
+    return DiffPathNode{kind, std::nullopt, index};
+}
+
+DiffPathNode DiffPathNode::constructWithKind(Kind kind)
+{
+    return DiffPathNode{kind, std::nullopt, std::nullopt};
+}
+
+DiffPathNodeLeaf DiffPathNodeLeaf::detailsNormal(TypeId ty)
+{
+    return DiffPathNodeLeaf{ty, std::nullopt, std::nullopt, false};
+}
+
+DiffPathNodeLeaf DiffPathNodeLeaf::detailsTableProperty(TypeId ty, Name tableProperty)
+{
+    return DiffPathNodeLeaf{ty, tableProperty, std::nullopt, false};
+}
+
+DiffPathNodeLeaf DiffPathNodeLeaf::detailsLength(int minLength, bool isVariadic)
+{
+    return DiffPathNodeLeaf{std::nullopt, std::nullopt, minLength, isVariadic};
+}
+
 DiffPathNodeLeaf DiffPathNodeLeaf::nullopts()
 {
-    return DiffPathNodeLeaf{std::nullopt, std::nullopt};
+    return DiffPathNodeLeaf{std::nullopt, std::nullopt, std::nullopt, false};
 }
 
 std::string DiffPath::toString(bool prependDot) const
@@ -79,9 +120,21 @@ std::string DiffError::toStringALeaf(std::string rootName, const DiffPathNodeLea
         }
         throw InternalCompilerError{"Both leaf.ty and otherLeaf.ty is nullopt"};
     }
+    case DiffError::Kind::LengthMismatchInFnArgs:
+    {
+        if (!leaf.minLength.has_value())
+            throw InternalCompilerError{"leaf.minLength is nullopt"};
+        return pathStr + " takes " + std::to_string(*leaf.minLength) + (leaf.isVariadic ? " or more" : "") + " arguments";
+    }
+    case DiffError::Kind::LengthMismatchInFnRets:
+    {
+        if (!leaf.minLength.has_value())
+            throw InternalCompilerError{"leaf.minLength is nullopt"};
+        return pathStr + " returns " + std::to_string(*leaf.minLength) + (leaf.isVariadic ? " or more" : "") + " values";
+    }
     default:
     {
-        throw InternalCompilerError{"DiffPath::toStringWithLeaf is not exhaustive"};
+        throw InternalCompilerError{"DiffPath::toStringALeaf is not exhaustive"};
     }
     }
 }
@@ -139,6 +192,14 @@ static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId rig
 static DifferResult diffTable(DifferEnvironment& env, TypeId left, TypeId right);
 static DifferResult diffPrimitive(DifferEnvironment& env, TypeId left, TypeId right);
 static DifferResult diffSingleton(DifferEnvironment& env, TypeId left, TypeId right);
+static DifferResult diffFunction(DifferEnvironment& env, TypeId left, TypeId right);
+/**
+ * The last argument gives context info on which complex type contained the TypePack.
+ */
+static DifferResult diffTpi(DifferEnvironment& env, DiffError::Kind possibleNonNormalErrorKind, TypePackId left, TypePackId right);
+static DifferResult diffCanonicalTpShape(DifferEnvironment& env, DiffError::Kind possibleNonNormalErrorKind,
+    const std::pair<std::vector<TypeId>, std::optional<TypePackId>>& left, const std::pair<std::vector<TypeId>, std::optional<TypePackId>>& right);
+static DifferResult diffHandleFlattenedTail(DifferEnvironment& env, DiffError::Kind possibleNonNormalErrorKind, TypePackId left, TypePackId right);
 
 static DifferResult diffTable(DifferEnvironment& env, TypeId left, TypeId right)
 {
@@ -152,7 +213,7 @@ static DifferResult diffTable(DifferEnvironment& env, TypeId left, TypeId right)
             // left has a field the right doesn't
             return DifferResult{DiffError{
                 DiffError::Kind::MissingProperty,
-                DiffPathNodeLeaf{value.type(), field},
+                DiffPathNodeLeaf::detailsTableProperty(value.type(), field),
                 DiffPathNodeLeaf::nullopts(),
                 getDevFixFriendlyName(env.rootLeft),
                 getDevFixFriendlyName(env.rootRight),
@@ -164,8 +225,9 @@ static DifferResult diffTable(DifferEnvironment& env, TypeId left, TypeId right)
         if (leftTable->props.find(field) == leftTable->props.end())
         {
             // right has a field the left doesn't
-            return DifferResult{DiffError{DiffError::Kind::MissingProperty, DiffPathNodeLeaf::nullopts(), DiffPathNodeLeaf{value.type(), field},
+            return DifferResult{
-                getDevFixFriendlyName(env.rootLeft), getDevFixFriendlyName(env.rootRight)}};
+                DiffError{DiffError::Kind::MissingProperty, DiffPathNodeLeaf::nullopts(), DiffPathNodeLeaf::detailsTableProperty(value.type(), field),
+                    getDevFixFriendlyName(env.rootLeft), getDevFixFriendlyName(env.rootRight)}};
         }
     }
     // left and right have the same set of keys
@@ -191,8 +253,8 @@ static DifferResult diffPrimitive(DifferEnvironment& env, TypeId left, TypeId ri
     {
         return DifferResult{DiffError{
             DiffError::Kind::Normal,
-            DiffPathNodeLeaf{left, std::nullopt},
+            DiffPathNodeLeaf::detailsNormal(left),
-            DiffPathNodeLeaf{right, std::nullopt},
+            DiffPathNodeLeaf::detailsNormal(right),
             getDevFixFriendlyName(env.rootLeft),
             getDevFixFriendlyName(env.rootRight),
         }};
@@ -209,8 +271,8 @@ static DifferResult diffSingleton(DifferEnvironment& env, TypeId left, TypeId ri
     {
         return DifferResult{DiffError{
             DiffError::Kind::Normal,
-            DiffPathNodeLeaf{left, std::nullopt},
+            DiffPathNodeLeaf::detailsNormal(left),
-            DiffPathNodeLeaf{right, std::nullopt},
+            DiffPathNodeLeaf::detailsNormal(right),
             getDevFixFriendlyName(env.rootLeft),
             getDevFixFriendlyName(env.rootRight),
         }};
@@ -218,6 +280,17 @@ static DifferResult diffSingleton(DifferEnvironment& env, TypeId left, TypeId ri
     return DifferResult{};
 }
 
+static DifferResult diffFunction(DifferEnvironment& env, TypeId left, TypeId right)
+{
+    const FunctionType* leftFunction = get<FunctionType>(left);
+    const FunctionType* rightFunction = get<FunctionType>(right);
+
+    DifferResult differResult = diffTpi(env, DiffError::Kind::LengthMismatchInFnArgs, leftFunction->argTypes, rightFunction->argTypes);
+    if (differResult.diffError.has_value())
+        return differResult;
+    return diffTpi(env, DiffError::Kind::LengthMismatchInFnRets, leftFunction->retTypes, rightFunction->retTypes);
+}
+
 static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId right)
 {
     left = follow(left);
@@ -227,8 +300,8 @@ static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId rig
     {
         return DifferResult{DiffError{
             DiffError::Kind::Normal,
-            DiffPathNodeLeaf{left, std::nullopt},
+            DiffPathNodeLeaf::detailsNormal(left),
-            DiffPathNodeLeaf{right, std::nullopt},
+            DiffPathNodeLeaf::detailsNormal(right),
             getDevFixFriendlyName(env.rootLeft),
             getDevFixFriendlyName(env.rootRight),
         }};
@@ -244,6 +317,11 @@ static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId rig
         {
             return diffSingleton(env, left, right);
         }
+        else if (auto la = get<AnyType>(left))
+        {
+            // Both left and right must be Any if either is Any for them to be equal!
+            return DifferResult{};
+        }
 
         throw InternalCompilerError{"Unimplemented Simple TypeId variant for diffing"};
     }
@@ -254,9 +332,116 @@ static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId rig
     {
         return diffTable(env, left, right);
     }
+    if (auto lf = get<FunctionType>(left))
+    {
+        return diffFunction(env, left, right);
+    }
     throw InternalCompilerError{"Unimplemented non-simple TypeId variant for diffing"};
 }
 
+static DifferResult diffTpi(DifferEnvironment& env, DiffError::Kind possibleNonNormalErrorKind, TypePackId left, TypePackId right)
+{
+    left = follow(left);
+    right = follow(right);
+
+    // Canonicalize
+    std::pair<std::vector<TypeId>, std::optional<TypePackId>> leftFlatTpi = flatten(left);
+    std::pair<std::vector<TypeId>, std::optional<TypePackId>> rightFlatTpi = flatten(right);
+
+    // Check for shape equality
+    DifferResult diffResult = diffCanonicalTpShape(env, possibleNonNormalErrorKind, leftFlatTpi, rightFlatTpi);
+    if (diffResult.diffError.has_value())
+    {
+        return diffResult;
+    }
+
+    // Left and Right have the same shape
+    for (size_t i = 0; i < leftFlatTpi.first.size(); i++)
+    {
+        DifferResult differResult = diffUsingEnv(env, leftFlatTpi.first[i], rightFlatTpi.first[i]);
+        if (!differResult.diffError.has_value())
+            continue;
+
+        switch (possibleNonNormalErrorKind)
+        {
+        case DiffError::Kind::LengthMismatchInFnArgs:
+        {
+            differResult.wrapDiffPath(DiffPathNode::constructWithKindAndIndex(DiffPathNode::Kind::FunctionArgument, i));
+            return differResult;
+        }
+        case DiffError::Kind::LengthMismatchInFnRets:
+        {
+            differResult.wrapDiffPath(DiffPathNode::constructWithKindAndIndex(DiffPathNode::Kind::FunctionReturn, i));
+            return differResult;
+        }
+        default:
+        {
+            throw InternalCompilerError{"Unhandled Tpi diffing case with same shape"};
+        }
+        }
+    }
+    if (!leftFlatTpi.second.has_value())
+        return DifferResult{};
+
+    return diffHandleFlattenedTail(env, possibleNonNormalErrorKind, *leftFlatTpi.second, *rightFlatTpi.second);
+}
+
+static DifferResult diffCanonicalTpShape(DifferEnvironment& env, DiffError::Kind possibleNonNormalErrorKind,
+    const std::pair<std::vector<TypeId>, std::optional<TypePackId>>& left, const std::pair<std::vector<TypeId>, std::optional<TypePackId>>& right)
+{
+    if (left.first.size() == right.first.size() && left.second.has_value() == right.second.has_value())
+        return DifferResult{};
+
+    return DifferResult{DiffError{
+        possibleNonNormalErrorKind,
+        DiffPathNodeLeaf::detailsLength(int(left.first.size()), left.second.has_value()),
+        DiffPathNodeLeaf::detailsLength(int(right.first.size()), right.second.has_value()),
+        getDevFixFriendlyName(env.rootLeft),
+        getDevFixFriendlyName(env.rootRight),
+    }};
+}
+
+static DifferResult diffHandleFlattenedTail(DifferEnvironment& env, DiffError::Kind possibleNonNormalErrorKind, TypePackId left, TypePackId right)
+{
+    left = follow(left);
+    right = follow(right);
+
+    if (left->ty.index() != right->ty.index())
+    {
+        throw InternalCompilerError{"Unhandled case where the tail of 2 normalized typepacks have different variants"};
+    }
+
+    // Both left and right are the same variant
+
+    if (auto lv = get<VariadicTypePack>(left))
+    {
+        auto rv = get<VariadicTypePack>(right);
+        DifferResult differResult = diffUsingEnv(env, lv->ty, rv->ty);
+        if (!differResult.diffError.has_value())
+            return DifferResult{};
+
+        switch (possibleNonNormalErrorKind)
+        {
+        case DiffError::Kind::LengthMismatchInFnArgs:
+        {
+            differResult.wrapDiffPath(DiffPathNode::constructWithKind(DiffPathNode::Kind::FunctionArgument));
+            return differResult;
+        }
+        case DiffError::Kind::LengthMismatchInFnRets:
+        {
+            differResult.wrapDiffPath(DiffPathNode::constructWithKind(DiffPathNode::Kind::FunctionReturn));
+            return differResult;
+        }
+        default:
+        {
+            throw InternalCompilerError{"Unhandled flattened tail case for VariadicTypePack"};
+        }
+        }
+    }
+
+    throw InternalCompilerError{"Unhandled tail type pack variant for flattened tails"};
+}
+
 DifferResult diff(TypeId ty1, TypeId ty2)
 {
     DifferEnvironment differEnv{ty1, ty2};
@@ -267,7 +452,7 @@ bool isSimple(TypeId ty)
 {
     ty = follow(ty);
     // TODO: think about GenericType, etc.
-    return get<PrimitiveType>(ty) || get<SingletonType>(ty);
+    return get<PrimitiveType>(ty) || get<SingletonType>(ty) || get<AnyType>(ty);
 }
 
 } // namespace Luau

Analysis/src/Error.cpp

@@ -495,12 +495,16 @@ struct ErrorConverter
 
     std::string operator()(const WhereClauseNeeded& e) const
     {
-        return "Type family instance " + Luau::toString(e.ty) + " depends on generic function parameters but does not appear in the function signature; this construct cannot be type-checked at this time";
+        return "Type family instance " + Luau::toString(e.ty) +
+               " depends on generic function parameters but does not appear in the function signature; this construct cannot be type-checked at this "
+               "time";
     }
 
     std::string operator()(const PackWhereClauseNeeded& e) const
     {
-        return "Type pack family instance " + Luau::toString(e.tp) + " depends on generic function parameters but does not appear in the function signature; this construct cannot be type-checked at this time";
+        return "Type pack family instance " + Luau::toString(e.tp) +
+               " depends on generic function parameters but does not appear in the function signature; this construct cannot be type-checked at this "
+               "time";
     }
 };
 

Analysis/src/Frontend.cpp

@@ -35,7 +35,7 @@ LUAU_FASTINTVARIABLE(LuauAutocompleteCheckTimeoutMs, 100)
 LUAU_FASTFLAGVARIABLE(DebugLuauDeferredConstraintResolution, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJson, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauReadWriteProperties, false)
-LUAU_FASTFLAGVARIABLE(LuauFixBuildQueueExceptionUnwrap, false)
+LUAU_FASTFLAGVARIABLE(LuauTypecheckCancellation, false)
 
 namespace Luau
 {
@@ -461,6 +461,10 @@ CheckResult Frontend::check(const ModuleName& name, std::optional<FrontendOption
         if (item.module->timeout)
             checkResult.timeoutHits.push_back(item.name);
 
+        // If check was manually cancelled, do not return partial results
+        if (FFlag::LuauTypecheckCancellation && item.module->cancelled)
+            return {};
+
         checkResult.errors.insert(checkResult.errors.end(), item.module->errors.begin(), item.module->errors.end());
 
         if (item.name == name)
@@ -610,6 +614,7 @@ std::vector<ModuleName> Frontend::checkQueuedModules(std::optional<FrontendOptio
 
     std::vector<size_t> nextItems;
     std::optional<size_t> itemWithException;
+    bool cancelled = false;
 
     while (remaining != 0)
     {
@@ -626,15 +631,15 @@ std::vector<ModuleName> Frontend::checkQueuedModules(std::optional<FrontendOptio
             {
                 const BuildQueueItem& item = buildQueueItems[i];
 
-                if (FFlag::LuauFixBuildQueueExceptionUnwrap)
+                // If exception was thrown, stop adding new items and wait for processing items to complete
-                {
+                if (item.exception)
-                    // If exception was thrown, stop adding new items and wait for processing items to complete
+                    itemWithException = i;
-                    if (item.exception)
-                        itemWithException = i;
 
-                    if (itemWithException)
+                if (FFlag::LuauTypecheckCancellation && item.module && item.module->cancelled)
-                        break;
+                    cancelled = true;
-                }
+
+                if (itemWithException || cancelled)
+                    break;
 
                 recordItemResult(item);
 
@@ -671,8 +676,12 @@ std::vector<ModuleName> Frontend::checkQueuedModules(std::optional<FrontendOptio
         // If we aren't done, but don't have anything processing, we hit a cycle
         if (remaining != 0 && processing == 0)
         {
+            // Typechecking might have been cancelled by user, don't return partial results
+            if (FFlag::LuauTypecheckCancellation && cancelled)
+                return {};
+
             // We might have stopped because of a pending exception
-            if (FFlag::LuauFixBuildQueueExceptionUnwrap && itemWithException)
+            if (itemWithException)
             {
                 recordItemResult(buildQueueItems[*itemWithException]);
                 break;
@@ -901,6 +910,9 @@ void Frontend::checkBuildQueueItem(BuildQueueItem& item)
         else
             typeCheckLimits.unifierIterationLimit = std::nullopt;
 
+        if (FFlag::LuauTypecheckCancellation)
+            typeCheckLimits.cancellationToken = item.options.cancellationToken;
+
         ModulePtr moduleForAutocomplete = check(sourceModule, Mode::Strict, requireCycles, environmentScope, /*forAutocomplete*/ true,
             /*recordJsonLog*/ false, typeCheckLimits);
 
@@ -918,7 +930,12 @@ void Frontend::checkBuildQueueItem(BuildQueueItem& item)
         return;
     }
 
-    ModulePtr module = check(sourceModule, mode, requireCycles, environmentScope, /*forAutocomplete*/ false, item.recordJsonLog, {});
+    TypeCheckLimits typeCheckLimits;
+
+    if (FFlag::LuauTypecheckCancellation)
+        typeCheckLimits.cancellationToken = item.options.cancellationToken;
+
+    ModulePtr module = check(sourceModule, mode, requireCycles, environmentScope, /*forAutocomplete*/ false, item.recordJsonLog, typeCheckLimits);
 
     item.stats.timeCheck += getTimestamp() - timestamp;
     item.stats.filesStrict += mode == Mode::Strict;
@@ -996,6 +1013,10 @@ void Frontend::checkBuildQueueItems(std::vector<BuildQueueItem>& items)
     for (BuildQueueItem& item : items)
     {
         checkBuildQueueItem(item);
+
+        if (FFlag::LuauTypecheckCancellation && item.module && item.module->cancelled)
+            break;
+
         recordItemResult(item);
     }
 }
@@ -1232,8 +1253,8 @@ ModulePtr Frontend::check(const SourceModule& sourceModule, Mode mode, std::vect
         catch (const InternalCompilerError& err)
         {
             InternalCompilerError augmented = err.location.has_value()
-                ? InternalCompilerError{err.message, sourceModule.humanReadableName, *err.location}
+                                                  ? InternalCompilerError{err.message, sourceModule.humanReadableName, *err.location}
-                : InternalCompilerError{err.message, sourceModule.humanReadableName};
+                                                  : InternalCompilerError{err.message, sourceModule.humanReadableName};
             throw augmented;
         }
     }
@@ -1254,6 +1275,9 @@ ModulePtr Frontend::check(const SourceModule& sourceModule, Mode mode, std::vect
         typeChecker.instantiationChildLimit = typeCheckLimits.instantiationChildLimit;
         typeChecker.unifierIterationLimit = typeCheckLimits.unifierIterationLimit;
 
+        if (FFlag::LuauTypecheckCancellation)
+            typeChecker.cancellationToken = typeCheckLimits.cancellationToken;
+
         return typeChecker.check(sourceModule, mode, environmentScope);
     }
 }

Analysis/src/Module.cpp

@@ -15,8 +15,6 @@
 #include <algorithm>
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
-LUAU_FASTFLAGVARIABLE(LuauClonePublicInterfaceLess2, false);
-LUAU_FASTFLAGVARIABLE(LuauCloneSkipNonInternalVisit, false);
 
 namespace Luau
 {
@@ -98,7 +96,7 @@ struct ClonePublicInterface : Substitution
 
     bool ignoreChildrenVisit(TypeId ty) override
     {
-        if (FFlag::LuauCloneSkipNonInternalVisit && ty->owningArena != &module->internalTypes)
+        if (ty->owningArena != &module->internalTypes)
             return true;
 
         return false;
@@ -106,7 +104,7 @@ struct ClonePublicInterface : Substitution
 
     bool ignoreChildrenVisit(TypePackId tp) override
     {
-        if (FFlag::LuauCloneSkipNonInternalVisit && tp->owningArena != &module->internalTypes)
+        if (tp->owningArena != &module->internalTypes)
             return true;
 
         return false;
@@ -211,35 +209,23 @@ void Module::clonePublicInterface(NotNull<BuiltinTypes> builtinTypes, InternalEr
     TxnLog log;
     ClonePublicInterface clonePublicInterface{&log, builtinTypes, this};
 
-    if (FFlag::LuauClonePublicInterfaceLess2)
+    returnType = clonePublicInterface.cloneTypePack(returnType);
-        returnType = clonePublicInterface.cloneTypePack(returnType);
-    else
-        returnType = clone(returnType, interfaceTypes, cloneState);
 
     moduleScope->returnType = returnType;
     if (varargPack)
     {
-        if (FFlag::LuauClonePublicInterfaceLess2)
+        varargPack = clonePublicInterface.cloneTypePack(*varargPack);
-            varargPack = clonePublicInterface.cloneTypePack(*varargPack);
-        else
-            varargPack = clone(*varargPack, interfaceTypes, cloneState);
         moduleScope->varargPack = varargPack;
     }
 
     for (auto& [name, tf] : moduleScope->exportedTypeBindings)
     {
-        if (FFlag::LuauClonePublicInterfaceLess2)
+        tf = clonePublicInterface.cloneTypeFun(tf);
-            tf = clonePublicInterface.cloneTypeFun(tf);
-        else
-            tf = clone(tf, interfaceTypes, cloneState);
     }
 
     for (auto& [name, ty] : declaredGlobals)
     {
-        if (FFlag::LuauClonePublicInterfaceLess2)
+        ty = clonePublicInterface.cloneType(ty);
-            ty = clonePublicInterface.cloneType(ty);
-        else
-            ty = clone(ty, interfaceTypes, cloneState);
     }
 
     // Copy external stuff over to Module itself

Analysis/src/Substitution.cpp

@@ -8,93 +8,15 @@
 #include <algorithm>
 #include <stdexcept>
 
-LUAU_FASTFLAG(LuauClonePublicInterfaceLess2)
 LUAU_FASTINTVARIABLE(LuauTarjanChildLimit, 10000)
 LUAU_FASTFLAG(DebugLuauReadWriteProperties)
-LUAU_FASTFLAG(LuauCloneSkipNonInternalVisit)
 LUAU_FASTFLAGVARIABLE(LuauTarjanSingleArr, false)
 
 namespace Luau
 {
 
-static TypeId DEPRECATED_shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool alwaysClone)
-{
-    ty = log->follow(ty);
-
-    TypeId result = ty;
-
-    if (auto pty = log->pending(ty))
-        ty = &pty->pending;
-
-    if (const FunctionType* ftv = get<FunctionType>(ty))
-    {
-        FunctionType clone = FunctionType{ftv->level, ftv->scope, ftv->argTypes, ftv->retTypes, ftv->definition, ftv->hasSelf};
-        clone.generics = ftv->generics;
-        clone.genericPacks = ftv->genericPacks;
-        clone.magicFunction = ftv->magicFunction;
-        clone.dcrMagicFunction = ftv->dcrMagicFunction;
-        clone.dcrMagicRefinement = ftv->dcrMagicRefinement;
-        clone.tags = ftv->tags;
-        clone.argNames = ftv->argNames;
-        result = dest.addType(std::move(clone));
-    }
-    else if (const TableType* ttv = get<TableType>(ty))
-    {
-        LUAU_ASSERT(!ttv->boundTo);
-        TableType clone = TableType{ttv->props, ttv->indexer, ttv->level, ttv->scope, ttv->state};
-        clone.definitionModuleName = ttv->definitionModuleName;
-        clone.definitionLocation = ttv->definitionLocation;
-        clone.name = ttv->name;
-        clone.syntheticName = ttv->syntheticName;
-        clone.instantiatedTypeParams = ttv->instantiatedTypeParams;
-        clone.instantiatedTypePackParams = ttv->instantiatedTypePackParams;
-        clone.tags = ttv->tags;
-        result = dest.addType(std::move(clone));
-    }
-    else if (const MetatableType* mtv = get<MetatableType>(ty))
-    {
-        MetatableType clone = MetatableType{mtv->table, mtv->metatable};
-        clone.syntheticName = mtv->syntheticName;
-        result = dest.addType(std::move(clone));
-    }
-    else if (const UnionType* utv = get<UnionType>(ty))
-    {
-        UnionType clone;
-        clone.options = utv->options;
-        result = dest.addType(std::move(clone));
-    }
-    else if (const IntersectionType* itv = get<IntersectionType>(ty))
-    {
-        IntersectionType clone;
-        clone.parts = itv->parts;
-        result = dest.addType(std::move(clone));
-    }
-    else if (const PendingExpansionType* petv = get<PendingExpansionType>(ty))
-    {
-        PendingExpansionType clone{petv->prefix, petv->name, petv->typeArguments, petv->packArguments};
-        result = dest.addType(std::move(clone));
-    }
-    else if (const NegationType* ntv = get<NegationType>(ty))
-    {
-        result = dest.addType(NegationType{ntv->ty});
-    }
-    else if (const TypeFamilyInstanceType* tfit = get<TypeFamilyInstanceType>(ty))
-    {
-        TypeFamilyInstanceType clone{tfit->family, tfit->typeArguments, tfit->packArguments};
-        result = dest.addType(std::move(clone));
-    }
-    else
-        return result;
-
-    asMutable(result)->documentationSymbol = ty->documentationSymbol;
-    return result;
-}
-
 static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool alwaysClone)
 {
-    if (!FFlag::LuauClonePublicInterfaceLess2)
-        return DEPRECATED_shallowClone(ty, dest, log, alwaysClone);
-
     auto go = [ty, &dest, alwaysClone](auto&& a) {
         using T = std::decay_t<decltype(a)>;
 
@@ -224,7 +146,7 @@ void Tarjan::visitChildren(TypeId ty, int index)
 {
     LUAU_ASSERT(ty == log->follow(ty));
 
-    if (FFlag::LuauCloneSkipNonInternalVisit ? ignoreChildrenVisit(ty) : ignoreChildren(ty))
+    if (ignoreChildrenVisit(ty))
         return;
 
     if (auto pty = log->pending(ty))
@@ -324,7 +246,7 @@ void Tarjan::visitChildren(TypePackId tp, int index)
 {
     LUAU_ASSERT(tp == log->follow(tp));
 
-    if (FFlag::LuauCloneSkipNonInternalVisit ? ignoreChildrenVisit(tp) : ignoreChildren(tp))
+    if (ignoreChildrenVisit(tp))
         return;
 
     if (auto ptp = log->pending(tp))
@@ -856,7 +778,7 @@ std::optional<TypePackId> Substitution::substitute(TypePackId tp)
 
 TypeId Substitution::clone(TypeId ty)
 {
-    return shallowClone(ty, *arena, log, /* alwaysClone */ FFlag::LuauClonePublicInterfaceLess2);
+    return shallowClone(ty, *arena, log, /* alwaysClone */ true);
 }
 
 TypePackId Substitution::clone(TypePackId tp)
@@ -888,12 +810,8 @@ TypePackId Substitution::clone(TypePackId tp)
         clone.packArguments.assign(tfitp->packArguments.begin(), tfitp->packArguments.end());
         return addTypePack(std::move(clone));
     }
-    else if (FFlag::LuauClonePublicInterfaceLess2)
-    {
-        return addTypePack(*tp);
-    }
     else
-        return tp;
+        return addTypePack(*tp);
 }
 
 void Substitution::foundDirty(TypeId ty)

Analysis/src/ToString.cpp

@@ -13,8 +13,10 @@
 
 #include <algorithm>
 #include <stdexcept>
+#include <string>
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+LUAU_FASTFLAGVARIABLE(LuauToStringPrettifyLocation, false)
 
 /*
  * Enables increasing levels of verbosity for Luau type names when stringifying.
@@ -1739,9 +1741,17 @@ std::string toString(const Position& position)
     return "{ line = " + std::to_string(position.line) + ", col = " + std::to_string(position.column) + " }";
 }
 
-std::string toString(const Location& location)
+std::string toString(const Location& location, int offset, bool useBegin)
 {
-    return "Location { " + toString(location.begin) + ", " + toString(location.end) + " }";
+    if (FFlag::LuauToStringPrettifyLocation)
+    {
+        return "(" + std::to_string(location.begin.line + offset) + ", " + std::to_string(location.begin.column + offset) + ") - (" +
+               std::to_string(location.end.line + offset) + ", " + std::to_string(location.end.column + offset) + ")";
+    }
+    else
+    {
+        return "Location { " + toString(location.begin) + ", " + toString(location.end) + " }";
+    }
 }
 
 } // namespace Luau

Analysis/src/TypeChecker2.cpp

@@ -1239,7 +1239,8 @@ struct TypeChecker2
             return std::move(u.errors);
         }
 
-        std::pair<Analysis, ErrorVec> checkOverload(TypeId fnTy, const TypePack* args, Location fnLoc, const std::vector<Location>* argLocs, bool callMetamethodOk = true)
+        std::pair<Analysis, ErrorVec> checkOverload(
+            TypeId fnTy, const TypePack* args, Location fnLoc, const std::vector<Location>* argLocs, bool callMetamethodOk = true)
         {
             fnTy = follow(fnTy);
 
@@ -1257,17 +1258,18 @@ struct TypeChecker2
                 std::vector<Location> withSelfLocs = *argLocs;
                 withSelfLocs.insert(withSelfLocs.begin(), fnLoc);
 
-                return checkOverload(*callMm, &withSelf, fnLoc, &withSelfLocs, /*callMetamethodOk=*/ false);
+                return checkOverload(*callMm, &withSelf, fnLoc, &withSelfLocs, /*callMetamethodOk=*/false);
             }
             else
                 return {TypeIsNotAFunction, {}}; // Intentionally empty. We can just fabricate the type error later on.
         }
 
         LUAU_NOINLINE
-        std::pair<Analysis, ErrorVec> checkOverload_(TypeId fnTy, const FunctionType* fn, const TypePack* args, Location fnLoc, const std::vector<Location>* argLocs)
+        std::pair<Analysis, ErrorVec> checkOverload_(
+            TypeId fnTy, const FunctionType* fn, const TypePack* args, Location fnLoc, const std::vector<Location>* argLocs)
         {
             TxnLog fake;
-            FamilyGraphReductionResult result = reduceFamilies(fnTy, callLoc, arena, builtinTypes, scope, normalizer, &fake, /*force=*/ true);
+            FamilyGraphReductionResult result = reduceFamilies(fnTy, callLoc, arena, builtinTypes, scope, normalizer, &fake, /*force=*/true);
             if (!result.errors.empty())
                 return {OverloadIsNonviable, result.errors};
 
@@ -2374,6 +2376,9 @@ struct TypeChecker2
             return;
         }
 
+        if (norm->shouldSuppressErrors())
+            return;
+
         bool foundOneProp = false;
         std::vector<TypeId> typesMissingTheProp;
 
@@ -2539,7 +2544,8 @@ struct TypeChecker2
     }
 };
 
-void check(NotNull<BuiltinTypes> builtinTypes, NotNull<UnifierSharedState> unifierState, DcrLogger* logger, const SourceModule& sourceModule, Module* module)
+void check(
+    NotNull<BuiltinTypes> builtinTypes, NotNull<UnifierSharedState> unifierState, DcrLogger* logger, const SourceModule& sourceModule, Module* module)
 {
     TypeChecker2 typeChecker{builtinTypes, unifierState, logger, &sourceModule, module};
 

Analysis/src/TypeInfer.cpp

@@ -2,6 +2,7 @@
 #include "Luau/TypeInfer.h"
 
 #include "Luau/ApplyTypeFunction.h"
+#include "Luau/Cancellation.h"
 #include "Luau/Clone.h"
 #include "Luau/Common.h"
 #include "Luau/Instantiation.h"
@@ -302,6 +303,10 @@ ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mo
     {
         currentModule->timeout = true;
     }
+    catch (const UserCancelError&)
+    {
+        currentModule->cancelled = true;
+    }
 
     if (FFlag::DebugLuauSharedSelf)
     {
@@ -345,7 +350,9 @@ ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mo
 ControlFlow TypeChecker::check(const ScopePtr& scope, const AstStat& program)
 {
     if (finishTime && TimeTrace::getClock() > *finishTime)
-        throw TimeLimitError(iceHandler->moduleName);
+        throwTimeLimitError();
+    if (cancellationToken && cancellationToken->requested())
+        throwUserCancelError();
 
     if (auto block = program.as<AstStatBlock>())
         return check(scope, *block);
@@ -4929,16 +4936,26 @@ void TypeChecker::reportErrors(const ErrorVec& errors)
         reportError(err);
 }
 
-void TypeChecker::ice(const std::string& message, const Location& location)
+LUAU_NOINLINE void TypeChecker::ice(const std::string& message, const Location& location)
 {
     iceHandler->ice(message, location);
 }
 
-void TypeChecker::ice(const std::string& message)
+LUAU_NOINLINE void TypeChecker::ice(const std::string& message)
 {
     iceHandler->ice(message);
 }
 
+LUAU_NOINLINE void TypeChecker::throwTimeLimitError()
+{
+    throw TimeLimitError(iceHandler->moduleName);
+}
+
+LUAU_NOINLINE void TypeChecker::throwUserCancelError()
+{
+    throw UserCancelError(iceHandler->moduleName);
+}
+
 void TypeChecker::prepareErrorsForDisplay(ErrorVec& errVec)
 {
     // Remove errors with names that were generated by recovery from a parse error

Analysis/src/Unifier.cpp

@@ -19,7 +19,6 @@
 LUAU_FASTINT(LuauTypeInferTypePackLoopLimit)
 LUAU_FASTFLAG(LuauErrorRecoveryType)
 LUAU_FASTFLAGVARIABLE(LuauInstantiateInSubtyping, false)
-LUAU_FASTFLAGVARIABLE(LuauVariadicAnyCanBeGeneric, false)
 LUAU_FASTFLAGVARIABLE(LuauMaintainScopesInUnifier, false)
 LUAU_FASTFLAGVARIABLE(LuauTransitiveSubtyping, false)
 LUAU_FASTFLAGVARIABLE(LuauOccursIsntAlwaysFailure, false)

Ast/include/Luau/Location.h

@@ -39,11 +39,6 @@ struct Location
     bool containsClosed(const Position& p) const;
     void extend(const Location& other);
     void shift(const Position& start, const Position& oldEnd, const Position& newEnd);
-
-    /**
-     * Use offset=1 when displaying for the user.
-     */
-    std::string toString(int offset = 0, bool useBegin = true) const;
 };
 
 } // namespace Luau

Ast/src/Location.cpp

@@ -129,12 +129,4 @@ void Location::shift(const Position& start, const Position& oldEnd, const Positi
     end.shift(start, oldEnd, newEnd);
 }
 
-std::string Location::toString(int offset, bool useBegin) const
-{
-    const Position& pos = useBegin ? this->begin : this->end;
-    std::string line{std::to_string(pos.line + offset)};
-    std::string column{std::to_string(pos.column + offset)};
-    return "(" + line + ", " + column + ")";
-}
-
 } // namespace Luau

Ast/src/TimeTrace.cpp

@@ -92,14 +92,6 @@ struct GlobalContext
 {
     ~GlobalContext()
     {
-        // Ideally we would want all ThreadContext destructors to run
-        // But in VS, not all thread_local object instances are destroyed
-        for (ThreadContext* context : threads)
-        {
-            if (!context->events.empty())
-                context->flushEvents();
-        }
-
         if (traceFile)
             fclose(traceFile);
     }

CLI/Reduce.cpp

@@ -429,8 +429,7 @@ struct Reducer
         }
     }
 
-    void run(const std::string scriptName, const std::string command, std::string_view source,
+    void run(const std::string scriptName, const std::string command, std::string_view source, std::string_view searchText)
-        std::string_view searchText)
     {
         this->scriptName = scriptName;
 

CodeGen/include/Luau/IrBuilder.h

@@ -26,6 +26,7 @@ struct IrBuilder
 
     void rebuildBytecodeBasicBlocks(Proto* proto);
     void translateInst(LuauOpcode op, const Instruction* pc, int i);
+    void handleFastcallFallback(IrOp fallbackOrUndef, const Instruction* pc, int i);
 
     bool isInternalBlock(IrOp block);
     void beginBlock(IrOp block);
@@ -61,10 +62,13 @@ struct IrBuilder
     IrOp vmConst(uint32_t index);
     IrOp vmUpvalue(uint8_t index);
 
+    IrOp vmExit(uint32_t pcpos);
+
     bool inTerminatedBlock = false;
 
     bool activeFastcallFallback = false;
     IrOp fastcallFallbackReturn;
+    int fastcallSkipTarget = -1;
 
     IrFunction function;
 

CodeGen/include/Luau/IrData.h

@@ -165,7 +165,7 @@ enum class IrCmd : uint8_t
     NOT_ANY, // TODO: boolean specialization will be useful
 
     // Unconditional jump
-    // A: block
+    // A: block/vmexit
     JUMP,
 
     // Jump if TValue is truthy
@@ -364,7 +364,7 @@ enum class IrCmd : uint8_t
 
     // Guard against tag mismatch
     // A, B: tag
-    // C: block/undef
+    // C: block/vmexit/undef
     // D: bool (finish execution in VM on failure)
     // In final x64 lowering, A can also be Rn
     // When undef is specified instead of a block, execution is aborted on check failure; if D is true, execution is continued in VM interpreter
@@ -384,7 +384,7 @@ enum class IrCmd : uint8_t
     CHECK_NO_METATABLE,
 
     // Guard against executing in unsafe environment, exits to VM on check failure
-    // A: unsigned int (pcpos)/undef
+    // A: vmexit/undef
     // When undef is specified, execution is aborted on check failure
     CHECK_SAFE_ENV,
 
@@ -670,6 +670,9 @@ enum class IrOpKind : uint32_t
 
     // To reference a VM upvalue
     VmUpvalue,
+
+    // To reference an exit to VM at specific PC pos
+    VmExit,
 };
 
 struct IrOp

CodeGen/src/CodeBlockUnwind.cpp

@@ -24,11 +24,23 @@ extern "C" void __register_frame(const void*);
 extern "C" void __deregister_frame(const void*);
 
 extern "C" void __unw_add_dynamic_fde() __attribute__((weak));
-
 #endif
 
 #if defined(__APPLE__) && defined(__aarch64__)
 #include <sys/sysctl.h>
+#include <mach-o/loader.h>
+#include <dlfcn.h>
+
+struct unw_dynamic_unwind_sections_t
+{
+    uintptr_t dso_base;
+    uintptr_t dwarf_section;
+    size_t dwarf_section_length;
+    uintptr_t compact_unwind_section;
+    size_t compact_unwind_section_length;
+};
+
+typedef int (*unw_add_find_dynamic_unwind_sections_t)(int (*)(uintptr_t addr, unw_dynamic_unwind_sections_t* info));
 #endif
 
 namespace Luau
@@ -36,6 +48,26 @@ namespace Luau
 namespace CodeGen
 {
 
+#if defined(__APPLE__) && defined(__aarch64__)
+static int findDynamicUnwindSections(uintptr_t addr, unw_dynamic_unwind_sections_t* info)
+{
+    // Define a minimal mach header for JIT'd code.
+    static const mach_header_64 kFakeMachHeader = {
+        MH_MAGIC_64,
+        CPU_TYPE_ARM64,
+        CPU_SUBTYPE_ARM64_ALL,
+        MH_DYLIB,
+    };
+
+    info->dso_base = (uintptr_t)&kFakeMachHeader;
+    info->dwarf_section = 0;
+    info->dwarf_section_length = 0;
+    info->compact_unwind_section = 0;
+    info->compact_unwind_section_length = 0;
+    return 1;
+}
+#endif
+
 #if defined(__linux__) || defined(__APPLE__)
 static void visitFdeEntries(char* pos, void (*cb)(const void*))
 {
@@ -87,6 +119,15 @@ void* createBlockUnwindInfo(void* context, uint8_t* block, size_t blockSize, siz
     visitFdeEntries(unwindData, __register_frame);
 #endif
 
+#if defined(__APPLE__) && defined(__aarch64__)
+    // Starting from macOS 14, we need to register unwind section callback to state that our ABI doesn't require pointer authentication
+    // This might conflict with other JITs that do the same; unfortunately this is the best we can do for now.
+    static unw_add_find_dynamic_unwind_sections_t unw_add_find_dynamic_unwind_sections =
+        unw_add_find_dynamic_unwind_sections_t(dlsym(RTLD_DEFAULT, "__unw_add_find_dynamic_unwind_sections"));
+    static int regonce = unw_add_find_dynamic_unwind_sections ? unw_add_find_dynamic_unwind_sections(findDynamicUnwindSections) : 0;
+    LUAU_ASSERT(regonce == 0);
+#endif
+
     beginOffset = unwindSize + unwind->getBeginOffset();
     return block;
 }

CodeGen/src/CodeGen.cpp

@@ -141,14 +141,6 @@ static int onEnter(lua_State* L, Proto* proto)
     return GateFn(data->context.gateEntry)(L, proto, target, &data->context);
 }
 
-static void onSetBreakpoint(lua_State* L, Proto* proto, int instruction)
-{
-    if (!proto->execdata)
-        return;
-
-    LUAU_ASSERT(!"Native breakpoints are not implemented");
-}
-
 #if defined(__aarch64__)
 unsigned int getCpuFeaturesA64()
 {
@@ -245,7 +237,6 @@ void create(lua_State* L)
     ecb->close = onCloseState;
     ecb->destroy = onDestroyFunction;
     ecb->enter = onEnter;
-    ecb->setbreakpoint = onSetBreakpoint;
 }
 
 void compile(lua_State* L, int idx)
@@ -259,7 +250,8 @@ void compile(lua_State* L, int idx)
         return;
 
 #if defined(__aarch64__)
-    A64::AssemblyBuilderA64 build(/* logText= */ false, getCpuFeaturesA64());
+    static unsigned int cpuFeatures = getCpuFeaturesA64();
+    A64::AssemblyBuilderA64 build(/* logText= */ false, cpuFeatures);
 #else
     X64::AssemblyBuilderX64 build(/* logText= */ false);
 #endif

CodeGen/src/CodeGenAssembly.cpp

@@ -100,7 +100,8 @@ std::string getAssembly(lua_State* L, int idx, AssemblyOptions options)
     case AssemblyOptions::Host:
     {
 #if defined(__aarch64__)
-        A64::AssemblyBuilderA64 build(/* logText= */ options.includeAssembly, getCpuFeaturesA64());
+        static unsigned int cpuFeatures = getCpuFeaturesA64();
+        A64::AssemblyBuilderA64 build(/* logText= */ options.includeAssembly, cpuFeatures);
 #else
         X64::AssemblyBuilderX64 build(/* logText= */ options.includeAssembly);
 #endif

CodeGen/src/CodeGenLower.h

@@ -44,6 +44,18 @@ inline void gatherFunctions(std::vector<Proto*>& results, Proto* proto)
         gatherFunctions(results, proto->p[i]);
 }
 
+inline IrBlock& getNextBlock(IrFunction& function, std::vector<uint32_t>& sortedBlocks, IrBlock& dummy, size_t i)
+{
+    for (size_t j = i + 1; j < sortedBlocks.size(); ++j)
+    {
+        IrBlock& block = function.blocks[sortedBlocks[j]];
+        if (block.kind != IrBlockKind::Dead)
+            return block;
+    }
+
+    return dummy;
+}
+
 template<typename AssemblyBuilder, typename IrLowering>
 inline bool lowerImpl(AssemblyBuilder& build, IrLowering& lowering, IrFunction& function, int bytecodeid, AssemblyOptions options)
 {
@@ -118,6 +130,8 @@ inline bool lowerImpl(AssemblyBuilder& build, IrLowering& lowering, IrFunction&
 
         build.setLabel(block.label);
 
+        IrBlock& nextBlock = getNextBlock(function, sortedBlocks, dummy, i);
+
         for (uint32_t index = block.start; index <= block.finish; index++)
         {
             LUAU_ASSERT(index < function.instructions.size());
@@ -156,9 +170,7 @@ inline bool lowerImpl(AssemblyBuilder& build, IrLowering& lowering, IrFunction&
                 toStringDetailed(ctx, block, blockIndex, inst, index, /* includeUseInfo */ true);
             }
 
-            IrBlock& next = i + 1 < sortedBlocks.size() ? function.blocks[sortedBlocks[i + 1]] : dummy;
+            lowering.lowerInst(inst, index, nextBlock);
-
-            lowering.lowerInst(inst, index, next);
 
             if (lowering.hasError())
             {

CodeGen/src/EmitCommon.h

@@ -12,7 +12,7 @@ constexpr unsigned kTValueSizeLog2 = 4;
 constexpr unsigned kLuaNodeSizeLog2 = 5;
 
 // TKey.tt and TKey.next are packed together in a bitfield
-constexpr unsigned kOffsetOfTKeyTagNext = 12;  // offsetof cannot be used on a bit field
+constexpr unsigned kOffsetOfTKeyTagNext = 12; // offsetof cannot be used on a bit field
 constexpr unsigned kTKeyTagBits = 4;
 constexpr unsigned kTKeyTagMask = (1 << kTKeyTagBits) - 1;
 
@@ -33,7 +33,7 @@ struct ModuleHelpers
     Label continueCallInVm;
 
     // A64
-    Label reentry;   // x0: closure
+    Label reentry; // x0: closure
 };
 
 } // namespace CodeGen

CodeGen/src/EmitCommonX64.cpp

@@ -268,7 +268,6 @@ void callStepGc(IrRegAllocX64& regs, AssemblyBuilderX64& build)
     build.setLabel(skip);
 }
 
-
 void emitClearNativeFlag(AssemblyBuilderX64& build)
 {
     build.mov(rax, qword[rState + offsetof(lua_State, ci)]);

CodeGen/src/IrBuilder.cpp

@@ -128,8 +128,16 @@ void IrBuilder::buildFunctionIr(Proto* proto)
 
         // We skip dead bytecode instructions when they appear after block was already terminated
         if (!inTerminatedBlock)
+        {
             translateInst(op, pc, i);
 
+            if (fastcallSkipTarget != -1)
+            {
+                nexti = fastcallSkipTarget;
+                fastcallSkipTarget = -1;
+            }
+        }
+
         i = nexti;
         LUAU_ASSERT(i <= proto->sizecode);
 
@@ -357,49 +365,17 @@ void IrBuilder::translateInst(LuauOpcode op, const Instruction* pc, int i)
         translateInstCloseUpvals(*this, pc);
         break;
     case LOP_FASTCALL:
-    {
+        handleFastcallFallback(translateFastCallN(*this, pc, i, false, 0, {}), pc, i);
-        int skip = LUAU_INSN_C(*pc);
-        IrOp next = blockAtInst(i + skip + 2);
-
-        translateFastCallN(*this, pc, i, false, 0, {}, next);
-
-        activeFastcallFallback = true;
-        fastcallFallbackReturn = next;
         break;
-    }
     case LOP_FASTCALL1:
-    {
+        handleFastcallFallback(translateFastCallN(*this, pc, i, true, 1, undef()), pc, i);
-        int skip = LUAU_INSN_C(*pc);
-        IrOp next = blockAtInst(i + skip + 2);
-
-        translateFastCallN(*this, pc, i, true, 1, undef(), next);
-
-        activeFastcallFallback = true;
-        fastcallFallbackReturn = next;
         break;
-    }
     case LOP_FASTCALL2:
-    {
+        handleFastcallFallback(translateFastCallN(*this, pc, i, true, 2, vmReg(pc[1])), pc, i);
-        int skip = LUAU_INSN_C(*pc);
-        IrOp next = blockAtInst(i + skip + 2);
-
-        translateFastCallN(*this, pc, i, true, 2, vmReg(pc[1]), next);
-
-        activeFastcallFallback = true;
-        fastcallFallbackReturn = next;
         break;
-    }
     case LOP_FASTCALL2K:
-    {
+        handleFastcallFallback(translateFastCallN(*this, pc, i, true, 2, vmConst(pc[1])), pc, i);
-        int skip = LUAU_INSN_C(*pc);
-        IrOp next = blockAtInst(i + skip + 2);
-
-        translateFastCallN(*this, pc, i, true, 2, vmConst(pc[1]), next);
-
-        activeFastcallFallback = true;
-        fastcallFallbackReturn = next;
         break;
-    }
     case LOP_FORNPREP:
         translateInstForNPrep(*this, pc, i);
         break;
@@ -493,6 +469,25 @@ void IrBuilder::translateInst(LuauOpcode op, const Instruction* pc, int i)
     }
 }
 
+void IrBuilder::handleFastcallFallback(IrOp fallbackOrUndef, const Instruction* pc, int i)
+{
+    int skip = LUAU_INSN_C(*pc);
+
+    if (fallbackOrUndef.kind != IrOpKind::Undef)
+    {
+        IrOp next = blockAtInst(i + skip + 2);
+        inst(IrCmd::JUMP, next);
+        beginBlock(fallbackOrUndef);
+
+        activeFastcallFallback = true;
+        fastcallFallbackReturn = next;
+    }
+    else
+    {
+        fastcallSkipTarget = i + skip + 2;
+    }
+}
+
 bool IrBuilder::isInternalBlock(IrOp block)
 {
     IrBlock& target = function.blocks[block.index];
@@ -718,5 +713,10 @@ IrOp IrBuilder::vmUpvalue(uint8_t index)
     return {IrOpKind::VmUpvalue, index};
 }
 
+IrOp IrBuilder::vmExit(uint32_t pcpos)
+{
+    return {IrOpKind::VmExit, pcpos};
+}
+
 } // namespace CodeGen
 } // namespace Luau

CodeGen/src/IrDump.cpp

@@ -389,6 +389,9 @@ void toString(IrToStringContext& ctx, IrOp op)
     case IrOpKind::VmUpvalue:
         append(ctx.result, "U%d", vmUpvalueOp(op));
         break;
+    case IrOpKind::VmExit:
+        append(ctx.result, "exit(%d)", op.index);
+        break;
     }
 }
 

CodeGen/src/IrLoweringA64.cpp

@@ -178,6 +178,7 @@ IrLoweringA64::IrLoweringA64(AssemblyBuilderA64& build, ModuleHelpers& helpers,
     , function(function)
     , regs(function, {{x0, x15}, {x16, x17}, {q0, q7}, {q16, q31}})
     , valueTracker(function)
+    , exitHandlerMap(~0u)
 {
     // In order to allocate registers during lowering, we need to know where instruction results are last used
     updateLastUseLocations(function);
@@ -514,8 +515,11 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
             build.cmp(regOp(inst.a), LUA_TBOOLEAN);
             build.b(ConditionA64::NotEqual, notbool);
 
-            // boolean => invert value
+            if (inst.b.kind == IrOpKind::Constant)
-            build.eor(inst.regA64, regOp(inst.b), 1);
+                build.mov(inst.regA64, intOp(inst.b) == 0 ? 1 : 0);
+            else
+                build.eor(inst.regA64, regOp(inst.b), 1); // boolean => invert value
+
             build.b(exit);
 
             // not boolean => result is true iff tag was nil
@@ -527,7 +531,16 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         break;
     }
     case IrCmd::JUMP:
-        jumpOrFallthrough(blockOp(inst.a), next);
+        if (inst.a.kind == IrOpKind::VmExit)
+        {
+            Label fresh;
+            build.b(getTargetLabel(inst.a, fresh));
+            finalizeTargetLabel(inst.a, fresh);
+        }
+        else
+        {
+            jumpOrFallthrough(blockOp(inst.a), next);
+        }
         break;
     case IrCmd::JUMP_IF_TRUTHY:
     {
@@ -1029,8 +1042,8 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     case IrCmd::CHECK_TAG:
     {
         bool continueInVm = (inst.d.kind == IrOpKind::Constant && intOp(inst.d));
-        Label abort; // used when guard aborts execution
+        Label fresh; // used when guard aborts execution or jumps to a VM exit
-        Label& fail = inst.c.kind == IrOpKind::Undef ? (continueInVm ? helpers.exitContinueVmClearNativeFlag : abort) : labelOp(inst.c);
+        Label& fail = continueInVm ? helpers.exitContinueVmClearNativeFlag : getTargetLabel(inst.c, fresh);
         if (tagOp(inst.b) == 0)
         {
             build.cbnz(regOp(inst.a), fail);
@@ -1040,55 +1053,43 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
             build.cmp(regOp(inst.a), tagOp(inst.b));
             build.b(ConditionA64::NotEqual, fail);
         }
-        if (abort.id && !continueInVm)
+        if (!continueInVm)
-            emitAbort(build, abort);
+            finalizeTargetLabel(inst.c, fresh);
         break;
     }
     case IrCmd::CHECK_READONLY:
     {
-        Label abort; // used when guard aborts execution
+        Label fresh; // used when guard aborts execution or jumps to a VM exit
         RegisterA64 temp = regs.allocTemp(KindA64::w);
         build.ldrb(temp, mem(regOp(inst.a), offsetof(Table, readonly)));
-        build.cbnz(temp, inst.b.kind == IrOpKind::Undef ? abort : labelOp(inst.b));
+        build.cbnz(temp, getTargetLabel(inst.b, fresh));
-        if (abort.id)
+        finalizeTargetLabel(inst.b, fresh);
-            emitAbort(build, abort);
         break;
     }
     case IrCmd::CHECK_NO_METATABLE:
     {
-        Label abort; // used when guard aborts execution
+        Label fresh; // used when guard aborts execution or jumps to a VM exit
         RegisterA64 temp = regs.allocTemp(KindA64::x);
         build.ldr(temp, mem(regOp(inst.a), offsetof(Table, metatable)));
-        build.cbnz(temp, inst.b.kind == IrOpKind::Undef ? abort : labelOp(inst.b));
+        build.cbnz(temp, getTargetLabel(inst.b, fresh));
-        if (abort.id)
+        finalizeTargetLabel(inst.b, fresh);
-            emitAbort(build, abort);
         break;
     }
     case IrCmd::CHECK_SAFE_ENV:
     {
-        Label abort; // used when guard aborts execution
+        Label fresh; // used when guard aborts execution or jumps to a VM exit
         RegisterA64 temp = regs.allocTemp(KindA64::x);
         RegisterA64 tempw = castReg(KindA64::w, temp);
         build.ldr(temp, mem(rClosure, offsetof(Closure, env)));
         build.ldrb(tempw, mem(temp, offsetof(Table, safeenv)));
-
+        build.cbz(tempw, getTargetLabel(inst.a, fresh));
-        if (inst.a.kind == IrOpKind::Undef)
+        finalizeTargetLabel(inst.a, fresh);
-        {
-            build.cbz(tempw, abort);
-            emitAbort(build, abort);
-        }
-        else
-        {
-            Label self;
-            build.cbz(tempw, self);
-            exitHandlers.push_back({self, uintOp(inst.a)});
-        }
         break;
     }
     case IrCmd::CHECK_ARRAY_SIZE:
     {
-        Label abort; // used when guard aborts execution
+        Label fresh; // used when guard aborts execution or jumps to a VM exit
-        Label& fail = inst.c.kind == IrOpKind::Undef ? abort : labelOp(inst.c);
+        Label& fail = getTargetLabel(inst.c, fresh);
 
         RegisterA64 temp = regs.allocTemp(KindA64::w);
         build.ldr(temp, mem(regOp(inst.a), offsetof(Table, sizearray)));
@@ -1120,8 +1121,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         else
             LUAU_ASSERT(!"Unsupported instruction form");
 
-        if (abort.id)
+        finalizeTargetLabel(inst.c, fresh);
-            emitAbort(build, abort);
         break;
     }
     case IrCmd::JUMP_SLOT_MATCH:
@@ -1158,15 +1158,13 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     }
     case IrCmd::CHECK_NODE_NO_NEXT:
     {
-        Label abort; // used when guard aborts execution
+        Label fresh; // used when guard aborts execution or jumps to a VM exit
         RegisterA64 temp = regs.allocTemp(KindA64::w);
 
         build.ldr(temp, mem(regOp(inst.a), offsetof(LuaNode, key) + kOffsetOfTKeyTagNext));
         build.lsr(temp, temp, kTKeyTagBits);
-        build.cbnz(temp, inst.b.kind == IrOpKind::Undef ? abort : labelOp(inst.b));
+        build.cbnz(temp, getTargetLabel(inst.b, fresh));
-
+        finalizeTargetLabel(inst.b, fresh);
-        if (abort.id)
-            emitAbort(build, abort);
         break;
     }
     case IrCmd::INTERRUPT:
@@ -1799,6 +1797,35 @@ void IrLoweringA64::jumpOrFallthrough(IrBlock& target, IrBlock& next)
         build.b(target.label);
 }
 
+Label& IrLoweringA64::getTargetLabel(IrOp op, Label& fresh)
+{
+    if (op.kind == IrOpKind::Undef)
+        return fresh;
+
+    if (op.kind == IrOpKind::VmExit)
+    {
+        if (uint32_t* index = exitHandlerMap.find(op.index))
+            return exitHandlers[*index].self;
+
+        return fresh;
+    }
+
+    return labelOp(op);
+}
+
+void IrLoweringA64::finalizeTargetLabel(IrOp op, Label& fresh)
+{
+    if (op.kind == IrOpKind::Undef)
+    {
+        emitAbort(build, fresh);
+    }
+    else if (op.kind == IrOpKind::VmExit && fresh.id != 0)
+    {
+        exitHandlerMap[op.index] = uint32_t(exitHandlers.size());
+        exitHandlers.push_back({fresh, op.index});
+    }
+}
+
 RegisterA64 IrLoweringA64::tempDouble(IrOp op)
 {
     if (op.kind == IrOpKind::Inst)

CodeGen/src/IrLoweringA64.h

@@ -2,6 +2,7 @@
 #pragma once
 
 #include "Luau/AssemblyBuilderA64.h"
+#include "Luau/DenseHash.h"
 #include "Luau/IrData.h"
 
 #include "IrRegAllocA64.h"
@@ -33,6 +34,9 @@ struct IrLoweringA64
     bool isFallthroughBlock(IrBlock target, IrBlock next);
     void jumpOrFallthrough(IrBlock& target, IrBlock& next);
 
+    Label& getTargetLabel(IrOp op, Label& fresh);
+    void finalizeTargetLabel(IrOp op, Label& fresh);
+
     // Operand data build helpers
     // May emit data/address synthesis instructions
     RegisterA64 tempDouble(IrOp op);
@@ -77,6 +81,7 @@ struct IrLoweringA64
 
     std::vector<InterruptHandler> interruptHandlers;
     std::vector<ExitHandler> exitHandlers;
+    DenseHashMap<uint32_t, uint32_t> exitHandlerMap;
 
     bool error = false;
 };

CodeGen/src/IrLoweringX64.cpp

@@ -28,6 +28,7 @@ IrLoweringX64::IrLoweringX64(AssemblyBuilderX64& build, ModuleHelpers& helpers,
     , function(function)
     , regs(build, function)
     , valueTracker(function)
+    , exitHandlerMap(~0u)
 {
     // In order to allocate registers during lowering, we need to know where instruction results are last used
     updateLastUseLocations(function);
@@ -492,8 +493,17 @@ void IrLoweringX64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
             build.jcc(ConditionX64::NotEqual, savezero);
         }
 
-        build.cmp(regOp(inst.b), 0);
+        if (inst.b.kind == IrOpKind::Constant)
-        build.jcc(ConditionX64::Equal, saveone);
+        {
+            // If value is 1, we fallthrough to storing 0
+            if (intOp(inst.b) == 0)
+                build.jmp(saveone);
+        }
+        else
+        {
+            build.cmp(regOp(inst.b), 0);
+            build.jcc(ConditionX64::Equal, saveone);
+        }
 
         build.setLabel(savezero);
         build.mov(inst.regX64, 0);
@@ -506,7 +516,24 @@ void IrLoweringX64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         break;
     }
     case IrCmd::JUMP:
-        jumpOrFallthrough(blockOp(inst.a), next);
+        if (inst.a.kind == IrOpKind::VmExit)
+        {
+            if (uint32_t* index = exitHandlerMap.find(inst.a.index))
+            {
+                build.jmp(exitHandlers[*index].self);
+            }
+            else
+            {
+                Label self;
+                build.jmp(self);
+                exitHandlerMap[inst.a.index] = uint32_t(exitHandlers.size());
+                exitHandlers.push_back({self, inst.a.index});
+            }
+        }
+        else
+        {
+            jumpOrFallthrough(blockOp(inst.a), next);
+        }
         break;
     case IrCmd::JUMP_IF_TRUTHY:
         jumpIfTruthy(build, vmRegOp(inst.a), labelOp(inst.b), labelOp(inst.c));
@@ -907,19 +934,7 @@ void IrLoweringX64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         build.mov(tmp.reg, qword[tmp.reg + offsetof(Closure, env)]);
         build.cmp(byte[tmp.reg + offsetof(Table, safeenv)], 0);
 
-        if (inst.a.kind == IrOpKind::Undef)
+        jumpOrAbortOnUndef(ConditionX64::Equal, ConditionX64::NotEqual, inst.a);
-        {
-            Label skip;
-            build.jcc(ConditionX64::NotEqual, skip);
-            build.ud2();
-            build.setLabel(skip);
-        }
-        else
-        {
-            Label self;
-            build.jcc(ConditionX64::Equal, self);
-            exitHandlers.push_back({self, uintOp(inst.a)});
-        }
         break;
     }
     case IrCmd::CHECK_ARRAY_SIZE:
@@ -1473,6 +1488,20 @@ void IrLoweringX64::jumpOrAbortOnUndef(ConditionX64 cond, ConditionX64 condInver
         build.ud2();
         build.setLabel(skip);
     }
+    else if (targetOrUndef.kind == IrOpKind::VmExit)
+    {
+        if (uint32_t* index = exitHandlerMap.find(targetOrUndef.index))
+        {
+            build.jcc(cond, exitHandlers[*index].self);
+        }
+        else
+        {
+            Label self;
+            build.jcc(cond, self);
+            exitHandlerMap[targetOrUndef.index] = uint32_t(exitHandlers.size());
+            exitHandlers.push_back({self, targetOrUndef.index});
+        }
+    }
     else
     {
         build.jcc(cond, labelOp(targetOrUndef));

CodeGen/src/IrLoweringX64.h

@@ -2,6 +2,7 @@
 #pragma once
 
 #include "Luau/AssemblyBuilderX64.h"
+#include "Luau/DenseHash.h"
 #include "Luau/IrData.h"
 #include "Luau/IrRegAllocX64.h"
 
@@ -77,6 +78,7 @@ struct IrLoweringX64
 
     std::vector<InterruptHandler> interruptHandlers;
     std::vector<ExitHandler> exitHandlers;
+    DenseHashMap<uint32_t, uint32_t> exitHandlerMap;
 };
 
 } // namespace X64

CodeGen/src/IrTranslateBuiltins.cpp

@@ -18,12 +18,12 @@ namespace Luau
 namespace CodeGen
 {
 
-static void builtinCheckDouble(IrBuilder& build, IrOp arg, IrOp fallback)
+static void builtinCheckDouble(IrBuilder& build, IrOp arg, int pcpos)
 {
     if (arg.kind == IrOpKind::Constant)
         LUAU_ASSERT(build.function.constOp(arg).kind == IrConstKind::Double);
     else
-        build.loadAndCheckTag(arg, LUA_TNUMBER, fallback);
+        build.loadAndCheckTag(arg, LUA_TNUMBER, build.vmExit(pcpos));
 }
 
 static IrOp builtinLoadDouble(IrBuilder& build, IrOp arg)
@@ -38,27 +38,27 @@ static IrOp builtinLoadDouble(IrBuilder& build, IrOp arg)
 
 // (number, ...) -> number
 static BuiltinImplResult translateBuiltinNumberToNumber(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
     build.inst(IrCmd::FASTCALL, build.constUint(bfid), build.vmReg(ra), build.vmReg(arg), args, build.constInt(1), build.constInt(1));
 
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinNumberToNumberLibm(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
 
     IrOp res = build.inst(IrCmd::INVOKE_LIBM, build.constUint(bfid), va);
@@ -68,17 +68,17 @@ static BuiltinImplResult translateBuiltinNumberToNumberLibm(
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltin2NumberToNumberLibm(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 2 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
     IrOp vb = builtinLoadDouble(build, args);
@@ -90,17 +90,17 @@ static BuiltinImplResult translateBuiltin2NumberToNumberLibm(
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinMathLdexp(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 2 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
     IrOp vb = builtinLoadDouble(build, args);
@@ -114,17 +114,17 @@ static BuiltinImplResult translateBuiltinMathLdexp(
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 // (number, ...) -> (number, number)
 static BuiltinImplResult translateBuiltinNumberTo2Number(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 2)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
     build.inst(
         IrCmd::FASTCALL, build.constUint(bfid), build.vmReg(ra), build.vmReg(arg), args, build.constInt(1), build.constInt(nresults == 1 ? 1 : 2));
 
@@ -134,7 +134,7 @@ static BuiltinImplResult translateBuiltinNumberTo2Number(
     if (nresults != 1)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra + 1), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 2};
+    return {BuiltinImplType::Full, 2};
 }
 
 static BuiltinImplResult translateBuiltinAssert(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
@@ -151,12 +151,12 @@ static BuiltinImplResult translateBuiltinAssert(IrBuilder& build, int nparams, i
     return {BuiltinImplType::UsesFallback, 0};
 }
 
-static BuiltinImplResult translateBuiltinMathDeg(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinMathDeg(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
 
     const double rpd = (3.14159265358979323846 / 180.0);
 
@@ -167,15 +167,15 @@ static BuiltinImplResult translateBuiltinMathDeg(IrBuilder& build, int nparams,
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
-static BuiltinImplResult translateBuiltinMathRad(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinMathRad(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
 
     const double rpd = (3.14159265358979323846 / 180.0);
 
@@ -186,11 +186,11 @@ static BuiltinImplResult translateBuiltinMathRad(IrBuilder& build, int nparams,
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinMathLog(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
@@ -213,7 +213,7 @@ static BuiltinImplResult translateBuiltinMathLog(
             denom = log(*y);
     }
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
 
@@ -227,19 +227,19 @@ static BuiltinImplResult translateBuiltinMathLog(
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
-static BuiltinImplResult translateBuiltinMathMin(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinMathMin(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 2 || nparams > kMinMaxUnrolledParams || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
 
     for (int i = 3; i <= nparams; ++i)
-        builtinCheckDouble(build, build.vmReg(vmRegOp(args) + (i - 2)), fallback);
+        builtinCheckDouble(build, build.vmReg(vmRegOp(args) + (i - 2)), pcpos);
 
     IrOp varg1 = builtinLoadDouble(build, build.vmReg(arg));
     IrOp varg2 = builtinLoadDouble(build, args);
@@ -257,19 +257,19 @@ static BuiltinImplResult translateBuiltinMathMin(IrBuilder& build, int nparams,
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
-static BuiltinImplResult translateBuiltinMathMax(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinMathMax(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 2 || nparams > kMinMaxUnrolledParams || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
 
     for (int i = 3; i <= nparams; ++i)
-        builtinCheckDouble(build, build.vmReg(vmRegOp(args) + (i - 2)), fallback);
+        builtinCheckDouble(build, build.vmReg(vmRegOp(args) + (i - 2)), pcpos);
 
     IrOp varg1 = builtinLoadDouble(build, build.vmReg(arg));
     IrOp varg2 = builtinLoadDouble(build, args);
@@ -287,10 +287,10 @@ static BuiltinImplResult translateBuiltinMathMax(IrBuilder& build, int nparams,
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
-static BuiltinImplResult translateBuiltinMathClamp(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinMathClamp(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback, int pcpos)
 {
     if (nparams < 3 || nresults > 1)
         return {BuiltinImplType::None, -1};
@@ -299,9 +299,9 @@ static BuiltinImplResult translateBuiltinMathClamp(IrBuilder& build, int nparams
 
     LUAU_ASSERT(args.kind == IrOpKind::VmReg);
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
-    builtinCheckDouble(build, build.vmReg(vmRegOp(args) + 1), fallback);
+    builtinCheckDouble(build, build.vmReg(vmRegOp(args) + 1), pcpos);
 
     IrOp min = builtinLoadDouble(build, args);
     IrOp max = builtinLoadDouble(build, build.vmReg(vmRegOp(args) + 1));
@@ -321,12 +321,12 @@ static BuiltinImplResult translateBuiltinMathClamp(IrBuilder& build, int nparams
     return {BuiltinImplType::UsesFallback, 1};
 }
 
-static BuiltinImplResult translateBuiltinMathUnary(IrBuilder& build, IrCmd cmd, int nparams, int ra, int arg, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinMathUnary(IrBuilder& build, IrCmd cmd, int nparams, int ra, int arg, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
 
     IrOp varg = builtinLoadDouble(build, build.vmReg(arg));
     IrOp result = build.inst(cmd, varg);
@@ -336,10 +336,10 @@ static BuiltinImplResult translateBuiltinMathUnary(IrBuilder& build, IrCmd cmd,
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
-static BuiltinImplResult translateBuiltinType(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinType(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
@@ -350,10 +350,10 @@ static BuiltinImplResult translateBuiltinType(IrBuilder& build, int nparams, int
     build.inst(IrCmd::STORE_POINTER, build.vmReg(ra), name);
     build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TSTRING));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
-static BuiltinImplResult translateBuiltinTypeof(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinTypeof(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
@@ -363,20 +363,20 @@ static BuiltinImplResult translateBuiltinTypeof(IrBuilder& build, int nparams, i
     build.inst(IrCmd::STORE_POINTER, build.vmReg(ra), name);
     build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TSTRING));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinBit32BinaryOp(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 2 || nparams > kBit32BinaryOpUnrolledParams || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
 
     for (int i = 3; i <= nparams; ++i)
-        builtinCheckDouble(build, build.vmReg(vmRegOp(args) + (i - 2)), fallback);
+        builtinCheckDouble(build, build.vmReg(vmRegOp(args) + (i - 2)), pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
     IrOp vb = builtinLoadDouble(build, args);
@@ -433,16 +433,16 @@ static BuiltinImplResult translateBuiltinBit32BinaryOp(
             build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
     }
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinBit32Bnot(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
 
     IrOp vaui = build.inst(IrCmd::NUM_TO_UINT, va);
@@ -454,19 +454,19 @@ static BuiltinImplResult translateBuiltinBit32Bnot(
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinBit32Shift(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback, int pcpos)
 {
     if (nparams < 2 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
     IrOp block = build.block(IrBlockKind::Internal);
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
     IrOp vb = builtinLoadDouble(build, args);
@@ -499,13 +499,13 @@ static BuiltinImplResult translateBuiltinBit32Shift(
 }
 
 static BuiltinImplResult translateBuiltinBit32Rotate(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 2 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
     IrOp vb = builtinLoadDouble(build, args);
@@ -522,17 +522,17 @@ static BuiltinImplResult translateBuiltinBit32Rotate(
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinBit32Extract(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback, int pcpos)
 {
     if (nparams < 2 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
     IrOp vb = builtinLoadDouble(build, args);
@@ -553,7 +553,7 @@ static BuiltinImplResult translateBuiltinBit32Extract(
     }
     else
     {
-        builtinCheckDouble(build, build.vmReg(args.index + 1), fallback);
+        builtinCheckDouble(build, build.vmReg(args.index + 1), pcpos);
         IrOp vc = builtinLoadDouble(build, build.vmReg(args.index + 1));
         IrOp w = build.inst(IrCmd::NUM_TO_INT, vc);
 
@@ -586,12 +586,12 @@ static BuiltinImplResult translateBuiltinBit32Extract(
 }
 
 static BuiltinImplResult translateBuiltinBit32ExtractK(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 2 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
     IrOp n = build.inst(IrCmd::NUM_TO_UINT, va);
@@ -613,16 +613,16 @@ static BuiltinImplResult translateBuiltinBit32ExtractK(
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinBit32Countz(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
 
     IrOp vaui = build.inst(IrCmd::NUM_TO_UINT, va);
@@ -637,18 +637,18 @@ static BuiltinImplResult translateBuiltinBit32Countz(
     if (ra != arg)
         build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
 static BuiltinImplResult translateBuiltinBit32Replace(
-    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+    IrBuilder& build, LuauBuiltinFunction bfid, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback, int pcpos)
 {
     if (nparams < 3 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
-    builtinCheckDouble(build, build.vmReg(args.index + 1), fallback);
+    builtinCheckDouble(build, build.vmReg(args.index + 1), pcpos);
 
     IrOp va = builtinLoadDouble(build, build.vmReg(arg));
     IrOp vb = builtinLoadDouble(build, args);
@@ -678,7 +678,7 @@ static BuiltinImplResult translateBuiltinBit32Replace(
     }
     else
     {
-        builtinCheckDouble(build, build.vmReg(args.index + 2), fallback);
+        builtinCheckDouble(build, build.vmReg(args.index + 2), pcpos);
         IrOp vd = builtinLoadDouble(build, build.vmReg(args.index + 2));
         IrOp w = build.inst(IrCmd::NUM_TO_INT, vd);
 
@@ -716,16 +716,16 @@ static BuiltinImplResult translateBuiltinBit32Replace(
     return {BuiltinImplType::UsesFallback, 1};
 }
 
-static BuiltinImplResult translateBuiltinVector(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinVector(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 3 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
     LUAU_ASSERT(LUA_VECTOR_SIZE == 3);
 
-    builtinCheckDouble(build, build.vmReg(arg), fallback);
+    builtinCheckDouble(build, build.vmReg(arg), pcpos);
-    builtinCheckDouble(build, args, fallback);
+    builtinCheckDouble(build, args, pcpos);
-    builtinCheckDouble(build, build.vmReg(vmRegOp(args) + 1), fallback);
+    builtinCheckDouble(build, build.vmReg(vmRegOp(args) + 1), pcpos);
 
     IrOp x = builtinLoadDouble(build, build.vmReg(arg));
     IrOp y = builtinLoadDouble(build, args);
@@ -734,15 +734,15 @@ static BuiltinImplResult translateBuiltinVector(IrBuilder& build, int nparams, i
     build.inst(IrCmd::STORE_VECTOR, build.vmReg(ra), x, y, z);
     build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TVECTOR));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
-static BuiltinImplResult translateBuiltinStringLen(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+static BuiltinImplResult translateBuiltinStringLen(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, int pcpos)
 {
     if (nparams < 1 || nresults > 1)
         return {BuiltinImplType::None, -1};
 
-    build.loadAndCheckTag(build.vmReg(arg), LUA_TSTRING, fallback);
+    build.loadAndCheckTag(build.vmReg(arg), LUA_TSTRING, build.vmExit(pcpos));
 
     IrOp ts = build.inst(IrCmd::LOAD_POINTER, build.vmReg(arg));
 
@@ -751,10 +751,10 @@ static BuiltinImplResult translateBuiltinStringLen(IrBuilder& build, int nparams
     build.inst(IrCmd::STORE_DOUBLE, build.vmReg(ra), build.inst(IrCmd::INT_TO_NUM, len));
     build.inst(IrCmd::STORE_TAG, build.vmReg(ra), build.constTag(LUA_TNUMBER));
 
-    return {BuiltinImplType::UsesFallback, 1};
+    return {BuiltinImplType::Full, 1};
 }
 
-BuiltinImplResult translateBuiltin(IrBuilder& build, int bfid, int ra, int arg, IrOp args, int nparams, int nresults, IrOp fallback)
+BuiltinImplResult translateBuiltin(IrBuilder& build, int bfid, int ra, int arg, IrOp args, int nparams, int nresults, IrOp fallback, int pcpos)
 {
     // Builtins are not allowed to handle variadic arguments
     if (nparams == LUA_MULTRET)
@@ -765,27 +765,27 @@ BuiltinImplResult translateBuiltin(IrBuilder& build, int bfid, int ra, int arg,
     case LBF_ASSERT:
         return translateBuiltinAssert(build, nparams, ra, arg, args, nresults, fallback);
     case LBF_MATH_DEG:
-        return translateBuiltinMathDeg(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinMathDeg(build, nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_RAD:
-        return translateBuiltinMathRad(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinMathRad(build, nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_LOG:
-        return translateBuiltinMathLog(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinMathLog(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_MIN:
-        return translateBuiltinMathMin(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinMathMin(build, nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_MAX:
-        return translateBuiltinMathMax(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinMathMax(build, nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_CLAMP:
-        return translateBuiltinMathClamp(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinMathClamp(build, nparams, ra, arg, args, nresults, fallback, pcpos);
     case LBF_MATH_FLOOR:
-        return translateBuiltinMathUnary(build, IrCmd::FLOOR_NUM, nparams, ra, arg, nresults, fallback);
+        return translateBuiltinMathUnary(build, IrCmd::FLOOR_NUM, nparams, ra, arg, nresults, pcpos);
     case LBF_MATH_CEIL:
-        return translateBuiltinMathUnary(build, IrCmd::CEIL_NUM, nparams, ra, arg, nresults, fallback);
+        return translateBuiltinMathUnary(build, IrCmd::CEIL_NUM, nparams, ra, arg, nresults, pcpos);
     case LBF_MATH_SQRT:
-        return translateBuiltinMathUnary(build, IrCmd::SQRT_NUM, nparams, ra, arg, nresults, fallback);
+        return translateBuiltinMathUnary(build, IrCmd::SQRT_NUM, nparams, ra, arg, nresults, pcpos);
     case LBF_MATH_ABS:
-        return translateBuiltinMathUnary(build, IrCmd::ABS_NUM, nparams, ra, arg, nresults, fallback);
+        return translateBuiltinMathUnary(build, IrCmd::ABS_NUM, nparams, ra, arg, nresults, pcpos);
     case LBF_MATH_ROUND:
-        return translateBuiltinMathUnary(build, IrCmd::ROUND_NUM, nparams, ra, arg, nresults, fallback);
+        return translateBuiltinMathUnary(build, IrCmd::ROUND_NUM, nparams, ra, arg, nresults, pcpos);
     case LBF_MATH_EXP:
     case LBF_MATH_ASIN:
     case LBF_MATH_SIN:
@@ -797,49 +797,49 @@ BuiltinImplResult translateBuiltin(IrBuilder& build, int bfid, int ra, int arg,
     case LBF_MATH_TAN:
     case LBF_MATH_TANH:
     case LBF_MATH_LOG10:
-        return translateBuiltinNumberToNumberLibm(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinNumberToNumberLibm(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_SIGN:
-        return translateBuiltinNumberToNumber(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinNumberToNumber(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_POW:
     case LBF_MATH_FMOD:
     case LBF_MATH_ATAN2:
-        return translateBuiltin2NumberToNumberLibm(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltin2NumberToNumberLibm(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_LDEXP:
-        return translateBuiltinMathLdexp(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinMathLdexp(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_MATH_FREXP:
     case LBF_MATH_MODF:
-        return translateBuiltinNumberTo2Number(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinNumberTo2Number(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_BIT32_BAND:
     case LBF_BIT32_BOR:
     case LBF_BIT32_BXOR:
     case LBF_BIT32_BTEST:
-        return translateBuiltinBit32BinaryOp(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinBit32BinaryOp(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_BIT32_BNOT:
-        return translateBuiltinBit32Bnot(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinBit32Bnot(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_BIT32_LSHIFT:
     case LBF_BIT32_RSHIFT:
     case LBF_BIT32_ARSHIFT:
-        return translateBuiltinBit32Shift(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinBit32Shift(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback, pcpos);
     case LBF_BIT32_LROTATE:
     case LBF_BIT32_RROTATE:
-        return translateBuiltinBit32Rotate(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinBit32Rotate(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_BIT32_EXTRACT:
-        return translateBuiltinBit32Extract(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinBit32Extract(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback, pcpos);
     case LBF_BIT32_EXTRACTK:
-        return translateBuiltinBit32ExtractK(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinBit32ExtractK(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_BIT32_COUNTLZ:
     case LBF_BIT32_COUNTRZ:
-        return translateBuiltinBit32Countz(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinBit32Countz(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, pcpos);
     case LBF_BIT32_REPLACE:
-        return translateBuiltinBit32Replace(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinBit32Replace(build, LuauBuiltinFunction(bfid), nparams, ra, arg, args, nresults, fallback, pcpos);
     case LBF_TYPE:
-        return translateBuiltinType(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinType(build, nparams, ra, arg, args, nresults);
     case LBF_TYPEOF:
-        return translateBuiltinTypeof(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinTypeof(build, nparams, ra, arg, args, nresults);
     case LBF_VECTOR:
-        return translateBuiltinVector(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinVector(build, nparams, ra, arg, args, nresults, pcpos);
     case LBF_STRING_LEN:
-        return translateBuiltinStringLen(build, nparams, ra, arg, args, nresults, fallback);
+        return translateBuiltinStringLen(build, nparams, ra, arg, args, nresults, pcpos);
     default:
         return {BuiltinImplType::None, -1};
     }

CodeGen/src/IrTranslateBuiltins.h

@@ -13,6 +13,7 @@ enum class BuiltinImplType
 {
     None,
     UsesFallback, // Uses fallback for unsupported cases
+    Full,         // Is either implemented in full, or exits to VM
 };
 
 struct BuiltinImplResult
@@ -21,7 +22,7 @@ struct BuiltinImplResult
     int actualResultCount;
 };
 
-BuiltinImplResult translateBuiltin(IrBuilder& build, int bfid, int ra, int arg, IrOp args, int nparams, int nresults, IrOp fallback);
+BuiltinImplResult translateBuiltin(IrBuilder& build, int bfid, int ra, int arg, IrOp args, int nparams, int nresults, IrOp fallback, int pcpos);
 
 } // namespace CodeGen
 } // namespace Luau

CodeGen/src/IrTranslation.cpp

@@ -514,7 +514,7 @@ void translateInstCloseUpvals(IrBuilder& build, const Instruction* pc)
     build.inst(IrCmd::CLOSE_UPVALS, build.vmReg(ra));
 }
 
-void translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool customParams, int customParamCount, IrOp customArgs, IrOp next)
+IrOp translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool customParams, int customParamCount, IrOp customArgs)
 {
     LuauOpcode opcode = LuauOpcode(LUAU_INSN_OP(*pc));
     int bfid = LUAU_INSN_A(*pc);
@@ -542,16 +542,25 @@ void translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
     // In unsafe environment, instead of retrying fastcall at 'pcpos' we side-exit directly to fallback sequence
-    build.inst(IrCmd::CHECK_SAFE_ENV, build.constUint(pcpos + getOpLength(opcode)));
+    build.inst(IrCmd::CHECK_SAFE_ENV, build.vmExit(pcpos + getOpLength(opcode)));
 
-    BuiltinImplResult br = translateBuiltin(build, LuauBuiltinFunction(bfid), ra, arg, builtinArgs, nparams, nresults, fallback);
+    BuiltinImplResult br =
+        translateBuiltin(build, LuauBuiltinFunction(bfid), ra, arg, builtinArgs, nparams, nresults, fallback, pcpos + getOpLength(opcode));
 
-    if (br.type == BuiltinImplType::UsesFallback)
+    if (br.type != BuiltinImplType::None)
     {
         LUAU_ASSERT(nparams != LUA_MULTRET && "builtins are not allowed to handle variadic arguments");
 
         if (nresults == LUA_MULTRET)
             build.inst(IrCmd::ADJUST_STACK_TO_REG, build.vmReg(ra), build.constInt(br.actualResultCount));
+
+        if (br.type != BuiltinImplType::UsesFallback)
+        {
+            // We ended up not using the fallback block, kill it
+            build.function.blockOp(fallback).kind = IrBlockKind::Dead;
+
+            return build.undef();
+        }
     }
     else
     {
@@ -568,10 +577,7 @@ void translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool
             build.inst(IrCmd::ADJUST_STACK_TO_TOP);
     }
 
-    build.inst(IrCmd::JUMP, next);
+    return fallback;
-
-    // this will be filled with IR corresponding to instructions after FASTCALL until skip+1
-    build.beginBlock(fallback);
 }
 
 void translateInstForNPrep(IrBuilder& build, const Instruction* pc, int pcpos)
@@ -670,7 +676,7 @@ void translateInstForGPrepNext(IrBuilder& build, const Instruction* pc, int pcpo
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
     // fast-path: pairs/next
-    build.inst(IrCmd::CHECK_SAFE_ENV, build.constUint(pcpos));
+    build.inst(IrCmd::CHECK_SAFE_ENV, build.vmExit(pcpos));
     IrOp tagB = build.inst(IrCmd::LOAD_TAG, build.vmReg(ra + 1));
     build.inst(IrCmd::CHECK_TAG, tagB, build.constTag(LUA_TTABLE), fallback);
     IrOp tagC = build.inst(IrCmd::LOAD_TAG, build.vmReg(ra + 2));
@@ -697,7 +703,7 @@ void translateInstForGPrepInext(IrBuilder& build, const Instruction* pc, int pcp
     IrOp finish = build.block(IrBlockKind::Internal);
 
     // fast-path: ipairs/inext
-    build.inst(IrCmd::CHECK_SAFE_ENV, build.constUint(pcpos));
+    build.inst(IrCmd::CHECK_SAFE_ENV, build.vmExit(pcpos));
     IrOp tagB = build.inst(IrCmd::LOAD_TAG, build.vmReg(ra + 1));
     build.inst(IrCmd::CHECK_TAG, tagB, build.constTag(LUA_TTABLE), fallback);
     IrOp tagC = build.inst(IrCmd::LOAD_TAG, build.vmReg(ra + 2));
@@ -923,7 +929,7 @@ void translateInstGetImport(IrBuilder& build, const Instruction* pc, int pcpos)
     IrOp fastPath = build.block(IrBlockKind::Internal);
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
-    build.inst(IrCmd::CHECK_SAFE_ENV, build.constUint(pcpos));
+    build.inst(IrCmd::CHECK_SAFE_ENV, build.vmExit(pcpos));
 
     // note: if import failed, k[] is nil; we could check this during codegen, but we instead use runtime fallback
     // this allows us to handle ahead-of-time codegen smoothly when an import fails to resolve at runtime

CodeGen/src/IrTranslation.h

@@ -45,7 +45,7 @@ void translateInstDupTable(IrBuilder& build, const Instruction* pc, int pcpos);
 void translateInstGetUpval(IrBuilder& build, const Instruction* pc, int pcpos);
 void translateInstSetUpval(IrBuilder& build, const Instruction* pc, int pcpos);
 void translateInstCloseUpvals(IrBuilder& build, const Instruction* pc);
-void translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool customParams, int customParamCount, IrOp customArgs, IrOp next);
+IrOp translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool customParams, int customParamCount, IrOp customArgs);
 void translateInstForNPrep(IrBuilder& build, const Instruction* pc, int pcpos);
 void translateInstForNLoop(IrBuilder& build, const Instruction* pc, int pcpos);
 void translateInstForGPrepNext(IrBuilder& build, const Instruction* pc, int pcpos);

CodeGen/src/OptimizeConstProp.cpp

@@ -977,7 +977,7 @@ static void constPropInBlockChain(IrBuilder& build, std::vector<uint8_t>& visite
 
         // Unconditional jump into a block with a single user (current block) allows us to continue optimization
         // with the information we have gathered so far (unless we have already visited that block earlier)
-        if (termInst.cmd == IrCmd::JUMP)
+        if (termInst.cmd == IrCmd::JUMP && termInst.a.kind != IrOpKind::VmExit)
         {
             IrBlock& target = function.blockOp(termInst.a);
             uint32_t targetIdx = function.getBlockIndex(target);
@@ -1011,7 +1011,7 @@ static std::vector<uint32_t> collectDirectBlockJumpPath(IrFunction& function, st
         IrBlock* nextBlock = nullptr;
 
         // A chain is made from internal blocks that were not a part of bytecode CFG
-        if (termInst.cmd == IrCmd::JUMP)
+        if (termInst.cmd == IrCmd::JUMP && termInst.a.kind != IrOpKind::VmExit)
         {
             IrBlock& target = function.blockOp(termInst.a);
             uint32_t targetIdx = function.getBlockIndex(target);
@@ -1052,6 +1052,10 @@ static void tryCreateLinearBlock(IrBuilder& build, std::vector<uint8_t>& visited
     if (termInst.cmd != IrCmd::JUMP)
         return;
 
+    // And it can't be jump to a VM exit
+    if (termInst.a.kind == IrOpKind::VmExit)
+        return;
+
     // And it has to jump to a block with more than one user
     // If there's only one use, it should already be optimized by constPropInBlockChain
     if (function.blockOp(termInst.a).useCount == 1)
@@ -1084,7 +1088,8 @@ static void tryCreateLinearBlock(IrBuilder& build, std::vector<uint8_t>& visited
 
     build.beginBlock(newBlock);
 
-    // By default, blocks are ordered according to start instruction; we alter sort order to make sure linearized block is placed right after the starting block
+    // By default, blocks are ordered according to start instruction; we alter sort order to make sure linearized block is placed right after the
+    // starting block
     function.blocks[newBlock.index].sortkey = startingInsn + 1;
 
     replace(function, termInst.a, newBlock);

Common/include/Luau/Bytecode.h

@@ -428,7 +428,7 @@ enum LuauBytecodeTag
 };
 
 // Type table tags
-enum LuauBytecodeEncodedType
+enum LuauBytecodeType
 {
     LBC_TYPE_NIL = 0,
     LBC_TYPE_BOOLEAN,

Compiler/include/Luau/BytecodeBuilder.h

@@ -47,7 +47,7 @@ public:
     BytecodeBuilder(BytecodeEncoder* encoder = 0);
 
     uint32_t beginFunction(uint8_t numparams, bool isvararg = false);
-    void endFunction(uint8_t maxstacksize, uint8_t numupvalues);
+    void endFunction(uint8_t maxstacksize, uint8_t numupvalues, uint8_t flags = 0);
 
     void setMainFunction(uint32_t fid);
 
@@ -274,7 +274,7 @@ private:
     void dumpConstant(std::string& result, int k) const;
     void dumpInstruction(const uint32_t* opcode, std::string& output, int targetLabel) const;
 
-    void writeFunction(std::string& ss, uint32_t id) const;
+    void writeFunction(std::string& ss, uint32_t id, uint8_t flags) const;
     void writeLineInfo(std::string& ss) const;
     void writeStringTable(std::string& ss) const;
 

Compiler/include/Luau/Compiler.h

@@ -35,6 +35,9 @@ struct CompileOptions
     const char* vectorLib = nullptr;
     const char* vectorCtor = nullptr;
 
+    // vector type name for type tables; disabled by default
+    const char* vectorType = nullptr;
+
     // null-terminated array of globals that are mutable; disables the import optimization for fields accessed through these
     const char** mutableGlobals = nullptr;
 };

Compiler/include/luacode.h

@@ -31,6 +31,9 @@ struct lua_CompileOptions
     const char* vectorLib;
     const char* vectorCtor;
 
+    // vector type name for type tables; disabled by default
+    const char* vectorType;
+
     // null-terminated array of globals that are mutable; disables the import optimization for fields accessed through these
     const char** mutableGlobals;
 };

Compiler/src/BytecodeBuilder.cpp

@@ -249,7 +249,7 @@ uint32_t BytecodeBuilder::beginFunction(uint8_t numparams, bool isvararg)
     return id;
 }
 
-void BytecodeBuilder::endFunction(uint8_t maxstacksize, uint8_t numupvalues)
+void BytecodeBuilder::endFunction(uint8_t maxstacksize, uint8_t numupvalues, uint8_t flags)
 {
     LUAU_ASSERT(currentFunction != ~0u);
 
@@ -265,7 +265,7 @@ void BytecodeBuilder::endFunction(uint8_t maxstacksize, uint8_t numupvalues)
     // very approximate: 4 bytes per instruction for code, 1 byte for debug line, and 1-2 bytes for aux data like constants plus overhead
     func.data.reserve(32 + insns.size() * 7);
 
-    writeFunction(func.data, currentFunction);
+    writeFunction(func.data, currentFunction, flags);
 
     currentFunction = ~0u;
 
@@ -631,7 +631,7 @@ void BytecodeBuilder::finalize()
     writeVarInt(bytecode, mainFunction);
 }
 
-void BytecodeBuilder::writeFunction(std::string& ss, uint32_t id) const
+void BytecodeBuilder::writeFunction(std::string& ss, uint32_t id, uint8_t flags) const
 {
     LUAU_ASSERT(id < functions.size());
     const Function& func = functions[id];
@@ -644,7 +644,7 @@ void BytecodeBuilder::writeFunction(std::string& ss, uint32_t id) const
 
     if (FFlag::BytecodeVersion4)
     {
-        writeByte(ss, 0); // Reserved for cgflags
+        writeByte(ss, flags);
 
         writeVarInt(ss, uint32_t(func.typeinfo.size()));
         ss.append(func.typeinfo);
@@ -1213,10 +1213,15 @@ void BytecodeBuilder::validateInstructions() const
             break;
 
         case LOP_GETIMPORT:
+        {
             VREG(LUAU_INSN_A(insn));
             VCONST(LUAU_INSN_D(insn), Import);
-            // TODO: check insn[i + 1] for conformance with 10-bit import encoding
+            uint32_t id = insns[i + 1];
-            break;
+            LUAU_ASSERT((id >> 30) != 0); // import chain with length 1-3
+            for (unsigned int j = 0; j < (id >> 30); ++j)
+                VCONST((id >> (20 - 10 * j)) & 1023, String);
+        }
+        break;
 
         case LOP_GETTABLE:
         case LOP_SETTABLE:

Compiler/src/Compiler.cpp

@@ -3874,7 +3874,7 @@ void compileOrThrow(BytecodeBuilder& bytecode, const ParseResult& parseResult, c
 
     if (FFlag::LuauCompileFunctionType)
     {
-        buildTypeMap(compiler.typeMap, root);
+        buildTypeMap(compiler.typeMap, root, options.vectorType);
     }
 
     // gathers all functions with the invariant that all function references are to functions earlier in the list

Compiler/src/Types.cpp

@@ -15,7 +15,7 @@ static bool isGeneric(AstName name, const AstArray<AstGenericType>& generics)
     return false;
 }
 
-static LuauBytecodeEncodedType getPrimitiveType(AstName name)
+static LuauBytecodeType getPrimitiveType(AstName name)
 {
     if (name == "nil")
         return LBC_TYPE_NIL;
@@ -33,8 +33,8 @@ static LuauBytecodeEncodedType getPrimitiveType(AstName name)
         return LBC_TYPE_INVALID;
 }
 
-static LuauBytecodeEncodedType getType(
+static LuauBytecodeType getType(AstType* ty, const AstArray<AstGenericType>& generics, const DenseHashMap<AstName, AstStatTypeAlias*>& typeAliases,
-    AstType* ty, const AstArray<AstGenericType>& generics, const DenseHashMap<AstName, AstStatTypeAlias*>& typeAliases, bool resolveAliases)
+    bool resolveAliases, const char* vectorType)
 {
     if (AstTypeReference* ref = ty->as<AstTypeReference>())
     {
@@ -45,7 +45,7 @@ static LuauBytecodeEncodedType getType(
         {
             // note: we only resolve aliases to the depth of 1 to avoid dealing with recursive aliases
             if (resolveAliases)
-                return getType((*alias)->type, (*alias)->generics, typeAliases, /* resolveAliases= */ false);
+                return getType((*alias)->type, (*alias)->generics, typeAliases, /* resolveAliases= */ false, vectorType);
             else
                 return LBC_TYPE_ANY;
         }
@@ -53,7 +53,10 @@ static LuauBytecodeEncodedType getType(
         if (isGeneric(ref->name, generics))
             return LBC_TYPE_ANY;
 
-        if (LuauBytecodeEncodedType prim = getPrimitiveType(ref->name); prim != LBC_TYPE_INVALID)
+        if (vectorType && ref->name == vectorType)
+            return LBC_TYPE_VECTOR;
+
+        if (LuauBytecodeType prim = getPrimitiveType(ref->name); prim != LBC_TYPE_INVALID)
             return prim;
 
         // not primitive or alias or generic => host-provided, we assume userdata for now
@@ -70,11 +73,11 @@ static LuauBytecodeEncodedType getType(
     else if (AstTypeUnion* un = ty->as<AstTypeUnion>())
     {
         bool optional = false;
-        LuauBytecodeEncodedType type = LBC_TYPE_INVALID;
+        LuauBytecodeType type = LBC_TYPE_INVALID;
 
         for (AstType* ty : un->types)
         {
-            LuauBytecodeEncodedType et = getType(ty, generics, typeAliases, resolveAliases);
+            LuauBytecodeType et = getType(ty, generics, typeAliases, resolveAliases, vectorType);
 
             if (et == LBC_TYPE_NIL)
             {
@@ -95,7 +98,7 @@ static LuauBytecodeEncodedType getType(
         if (type == LBC_TYPE_INVALID)
             return LBC_TYPE_ANY;
 
-        return LuauBytecodeEncodedType(type | (optional && (type != LBC_TYPE_ANY) ? LBC_TYPE_OPTIONAL_BIT : 0));
+        return LuauBytecodeType(type | (optional && (type != LBC_TYPE_ANY) ? LBC_TYPE_OPTIONAL_BIT : 0));
     }
     else if (AstTypeIntersection* inter = ty->as<AstTypeIntersection>())
     {
@@ -105,7 +108,7 @@ static LuauBytecodeEncodedType getType(
     return LBC_TYPE_ANY;
 }
 
-static std::string getFunctionType(const AstExprFunction* func, const DenseHashMap<AstName, AstStatTypeAlias*>& typeAliases)
+static std::string getFunctionType(const AstExprFunction* func, const DenseHashMap<AstName, AstStatTypeAlias*>& typeAliases, const char* vectorType)
 {
     bool self = func->self != 0;
 
@@ -121,8 +124,8 @@ static std::string getFunctionType(const AstExprFunction* func, const DenseHashM
     bool haveNonAnyParam = false;
     for (AstLocal* arg : func->args)
     {
-        LuauBytecodeEncodedType ty =
+        LuauBytecodeType ty =
-            arg->annotation ? getType(arg->annotation, func->generics, typeAliases, /* resolveAliases= */ true) : LBC_TYPE_ANY;
+            arg->annotation ? getType(arg->annotation, func->generics, typeAliases, /* resolveAliases= */ true, vectorType) : LBC_TYPE_ANY;
 
         if (ty != LBC_TYPE_ANY)
             haveNonAnyParam = true;
@@ -140,12 +143,14 @@ static std::string getFunctionType(const AstExprFunction* func, const DenseHashM
 struct TypeMapVisitor : AstVisitor
 {
     DenseHashMap<AstExprFunction*, std::string>& typeMap;
+    const char* vectorType;
 
     DenseHashMap<AstName, AstStatTypeAlias*> typeAliases;
     std::vector<std::pair<AstName, AstStatTypeAlias*>> typeAliasStack;
 
-    TypeMapVisitor(DenseHashMap<AstExprFunction*, std::string>& typeMap)
+    TypeMapVisitor(DenseHashMap<AstExprFunction*, std::string>& typeMap, const char* vectorType)
         : typeMap(typeMap)
+        , vectorType(vectorType)
         , typeAliases(AstName())
     {
     }
@@ -206,7 +211,7 @@ struct TypeMapVisitor : AstVisitor
 
     bool visit(AstExprFunction* node) override
     {
-        std::string type = getFunctionType(node, typeAliases);
+        std::string type = getFunctionType(node, typeAliases, vectorType);
 
         if (!type.empty())
             typeMap[node] = std::move(type);
@@ -215,9 +220,9 @@ struct TypeMapVisitor : AstVisitor
     }
 };
 
-void buildTypeMap(DenseHashMap<AstExprFunction*, std::string>& typeMap, AstNode* root)
+void buildTypeMap(DenseHashMap<AstExprFunction*, std::string>& typeMap, AstNode* root, const char* vectorType)
 {
-    TypeMapVisitor visitor(typeMap);
+    TypeMapVisitor visitor(typeMap, vectorType);
     root->visit(&visitor);
 }
 

Compiler/src/Types.h

@@ -8,6 +8,6 @@
 namespace Luau
 {
 
-void buildTypeMap(DenseHashMap<AstExprFunction*, std::string>& typeMap, AstNode* root);
+void buildTypeMap(DenseHashMap<AstExprFunction*, std::string>& typeMap, AstNode* root, const char* vectorType);
 
 } // namespace Luau

Sources.cmake

@@ -143,6 +143,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/include/Luau/Autocomplete.h
     Analysis/include/Luau/Breadcrumb.h
     Analysis/include/Luau/BuiltinDefinitions.h
+    Analysis/include/Luau/Cancellation.h
     Analysis/include/Luau/Clone.h
     Analysis/include/Luau/Config.h
     Analysis/include/Luau/Constraint.h

VM/src/ldebug.cpp

@@ -35,6 +35,10 @@ int lua_getargument(lua_State* L, int level, int n)
         return 0;
 
     CallInfo* ci = L->ci - level;
+    // changing tables in native functions externally may invalidate safety contracts wrt table state (metatable/size/readonly)
+    if (ci->flags & LUA_CALLINFO_NATIVE)
+        return 0;
+
     Proto* fp = getluaproto(ci);
     int res = 0;
 
@@ -60,9 +64,13 @@ int lua_getargument(lua_State* L, int level, int n)
 const char* lua_getlocal(lua_State* L, int level, int n)
 {
     if (unsigned(level) >= unsigned(L->ci - L->base_ci))
-        return 0;
+        return NULL;
 
     CallInfo* ci = L->ci - level;
+    // changing tables in native functions externally may invalidate safety contracts wrt table state (metatable/size/readonly)
+    if (ci->flags & LUA_CALLINFO_NATIVE)
+        return NULL;
+
     Proto* fp = getluaproto(ci);
     const LocVar* var = fp ? luaF_getlocal(fp, n, currentpc(L, ci)) : NULL;
     if (var)
@@ -77,9 +85,13 @@ const char* lua_getlocal(lua_State* L, int level, int n)
 const char* lua_setlocal(lua_State* L, int level, int n)
 {
     if (unsigned(level) >= unsigned(L->ci - L->base_ci))
-        return 0;
+        return NULL;
 
     CallInfo* ci = L->ci - level;
+    // changing registers in native functions externally may invalidate safety contracts wrt register type tags
+    if (ci->flags & LUA_CALLINFO_NATIVE)
+        return NULL;
+
     Proto* fp = getluaproto(ci);
     const LocVar* var = fp ? luaF_getlocal(fp, n, currentpc(L, ci)) : NULL;
     if (var)
@@ -321,7 +333,8 @@ void luaG_pusherror(lua_State* L, const char* error)
 
 void luaG_breakpoint(lua_State* L, Proto* p, int line, bool enable)
 {
-    if (p->lineinfo)
+    // since native code doesn't support breakpoints, we would need to update all call frames with LUAU_CALLINFO_NATIVE that refer to p
+    if (p->lineinfo && !p->execdata)
     {
         for (int i = 0; i < p->sizecode; ++i)
         {
@@ -347,11 +360,6 @@ void luaG_breakpoint(lua_State* L, Proto* p, int line, bool enable)
             p->code[i] |= op;
             LUAU_ASSERT(LUAU_INSN_OP(p->code[i]) == op);
 
-#if LUA_CUSTOM_EXECUTION
-            if (L->global->ecb.setbreakpoint)
-                L->global->ecb.setbreakpoint(L, p, i);
-#endif
-
             // note: this is important!
             // we only patch the *first* instruction in each proto that's attributed to a given line
             // this can be changed, but if requires making patching a bit more nuanced so that we don't patch AUX words
@@ -410,11 +418,11 @@ static int getmaxline(Proto* p)
     return result;
 }
 
-// Find the line number with instructions. If the provided line doesn't have any instruction, it should return the next line number with
+// Find the line number with instructions. If the provided line doesn't have any instruction, it should return the next valid line number.
-// instructions.
 static int getnextline(Proto* p, int line)
 {
     int closest = -1;
+
     if (p->lineinfo)
     {
         for (int i = 0; i < p->sizecode; ++i)
@@ -435,7 +443,6 @@ static int getnextline(Proto* p, int line)
 
     for (int i = 0; i < p->sizep; ++i)
     {
-        // Find the closest line number to the intended one.
         int candidate = getnextline(p->p[i], line);
 
         if (candidate == line)
@@ -454,14 +461,12 @@ int lua_breakpoint(lua_State* L, int funcindex, int line, int enabled)
     api_check(L, ttisfunction(func) && !clvalue(func)->isC);
 
     Proto* p = clvalue(func)->l.p;
-    // Find line number to add the breakpoint to.
+
+    // set the breakpoint to the next closest line with valid instructions
     int target = getnextline(p, line);
 
     if (target != -1)
-    {
-        // Add breakpoint on the exact line
         luaG_breakpoint(L, p, target, bool(enabled));
-    }
 
     return target;
 }

VM/src/lfunc.cpp

@@ -22,6 +22,7 @@ Proto* luaF_newproto(lua_State* L)
     f->numparams = 0;
     f->is_vararg = 0;
     f->maxstacksize = 0;
+    f->flags = 0;
     f->sizelineinfo = 0;
     f->linegaplog2 = 0;
     f->lineinfo = NULL;
@@ -155,13 +156,8 @@ void luaF_freeproto(lua_State* L, Proto* f, lua_Page* page)
     if (f->debuginsn)
         luaM_freearray(L, f->debuginsn, f->sizecode, uint8_t, f->memcat);
 
-#if LUA_CUSTOM_EXECUTION
     if (f->execdata)
-    {
-        LUAU_ASSERT(L->global->ecb.destroy);
         L->global->ecb.destroy(L, f);
-    }
-#endif
 
     if (f->typeinfo)
         luaM_freearray(L, f->typeinfo, f->numparams + 2, uint8_t, f->memcat);

VM/src/lgc.h

@@ -134,5 +134,7 @@ LUAI_FUNC void luaC_barriertable(lua_State* L, Table* t, GCObject* v);
 LUAI_FUNC void luaC_barrierback(lua_State* L, GCObject* o, GCObject** gclist);
 LUAI_FUNC void luaC_validate(lua_State* L);
 LUAI_FUNC void luaC_dump(lua_State* L, void* file, const char* (*categoryName)(lua_State* L, uint8_t memcat));
+LUAI_FUNC void luaC_enumheap(lua_State* L, void* context, void (*node)(void* context, void* ptr, uint8_t tt, uint8_t memcat, const char* name),
+    void (*edge)(void* context, void* from, void* to, const char* name));
 LUAI_FUNC int64_t luaC_allocationrate(lua_State* L);
 LUAI_FUNC const char* luaC_statename(int state);

VM/src/lgcdebug.cpp

@@ -602,3 +602,229 @@ void luaC_dump(lua_State* L, void* file, const char* (*categoryName)(lua_State*
     fprintf(f, "}\n");
     fprintf(f, "}}\n");
 }
+
+struct EnumContext
+{
+    lua_State* L;
+    void* context;
+    void (*node)(void* context, void* ptr, uint8_t tt, uint8_t memcat, const char* name);
+    void (*edge)(void* context, void* from, void* to, const char* name);
+};
+
+static void* enumtopointer(GCObject* gco)
+{
+    // To match lua_topointer, userdata pointer is represented as a pointer to internal data
+    return gco->gch.tt == LUA_TUSERDATA ? (void*)gco2u(gco)->data : (void*)gco;
+}
+
+static void enumnode(EnumContext* ctx, GCObject* gco, const char* objname)
+{
+    ctx->node(ctx->context, enumtopointer(gco), gco->gch.tt, gco->gch.memcat, objname);
+}
+
+static void enumedge(EnumContext* ctx, GCObject* from, GCObject* to, const char* edgename)
+{
+    ctx->edge(ctx->context, enumtopointer(from), enumtopointer(to), edgename);
+}
+
+static void enumedges(EnumContext* ctx, GCObject* from, TValue* data, size_t size, const char* edgename)
+{
+    for (size_t i = 0; i < size; ++i)
+    {
+        if (iscollectable(&data[i]))
+            enumedge(ctx, from, gcvalue(&data[i]), edgename);
+    }
+}
+
+static void enumstring(EnumContext* ctx, TString* ts)
+{
+    enumnode(ctx, obj2gco(ts), NULL);
+}
+
+static void enumtable(EnumContext* ctx, Table* h)
+{
+    // Provide a name for a special registry table
+    enumnode(ctx, obj2gco(h), h == hvalue(registry(ctx->L)) ? "registry" : NULL);
+
+    if (h->node != &luaH_dummynode)
+    {
+        for (int i = 0; i < sizenode(h); ++i)
+        {
+            const LuaNode& n = h->node[i];
+
+            if (!ttisnil(&n.val) && (iscollectable(&n.key) || iscollectable(&n.val)))
+            {
+                if (iscollectable(&n.key))
+                    enumedge(ctx, obj2gco(h), gcvalue(&n.key), "[key]");
+
+                if (iscollectable(&n.val))
+                {
+                    if (ttisstring(&n.key))
+                    {
+                        enumedge(ctx, obj2gco(h), gcvalue(&n.val), svalue(&n.key));
+                    }
+                    else if (ttisnumber(&n.key))
+                    {
+                        char buf[32];
+                        snprintf(buf, sizeof(buf), "%.14g", nvalue(&n.key));
+                        enumedge(ctx, obj2gco(h), gcvalue(&n.val), buf);
+                    }
+                    else
+                    {
+                        enumedge(ctx, obj2gco(h), gcvalue(&n.val), NULL);
+                    }
+                }
+            }
+        }
+    }
+
+    if (h->sizearray)
+        enumedges(ctx, obj2gco(h), h->array, h->sizearray, "array");
+
+    if (h->metatable)
+        enumedge(ctx, obj2gco(h), obj2gco(h->metatable), "metatable");
+}
+
+static void enumclosure(EnumContext* ctx, Closure* cl)
+{
+    if (cl->isC)
+    {
+        enumnode(ctx, obj2gco(cl), cl->c.debugname);
+    }
+    else
+    {
+        Proto* p = cl->l.p;
+
+        char buf[LUA_IDSIZE];
+
+        if (p->source)
+            snprintf(buf, sizeof(buf), "%s:%d %s", p->debugname ? getstr(p->debugname) : "", p->linedefined, getstr(p->source));
+        else
+            snprintf(buf, sizeof(buf), "%s:%d", p->debugname ? getstr(p->debugname) : "", p->linedefined);
+
+        enumnode(ctx, obj2gco(cl), buf);
+    }
+
+    enumedge(ctx, obj2gco(cl), obj2gco(cl->env), "env");
+
+    if (cl->isC)
+    {
+        if (cl->nupvalues)
+            enumedges(ctx, obj2gco(cl), cl->c.upvals, cl->nupvalues, "upvalue");
+    }
+    else
+    {
+        enumedge(ctx, obj2gco(cl), obj2gco(cl->l.p), "proto");
+
+        if (cl->nupvalues)
+            enumedges(ctx, obj2gco(cl), cl->l.uprefs, cl->nupvalues, "upvalue");
+    }
+}
+
+static void enumudata(EnumContext* ctx, Udata* u)
+{
+    enumnode(ctx, obj2gco(u), NULL);
+
+    if (u->metatable)
+        enumedge(ctx, obj2gco(u), obj2gco(u->metatable), "metatable");
+}
+
+static void enumthread(EnumContext* ctx, lua_State* th)
+{
+    Closure* tcl = NULL;
+    for (CallInfo* ci = th->base_ci; ci <= th->ci; ++ci)
+    {
+        if (ttisfunction(ci->func))
+        {
+            tcl = clvalue(ci->func);
+            break;
+        }
+    }
+
+    if (tcl && !tcl->isC && tcl->l.p->source)
+    {
+        Proto* p = tcl->l.p;
+
+        enumnode(ctx, obj2gco(th), getstr(p->source));
+    }
+    else
+    {
+        enumnode(ctx, obj2gco(th), NULL);
+    }
+
+    enumedge(ctx, obj2gco(th), obj2gco(th->gt), "globals");
+
+    if (th->top > th->stack)
+        enumedges(ctx, obj2gco(th), th->stack, th->top - th->stack, "stack");
+}
+
+static void enumproto(EnumContext* ctx, Proto* p)
+{
+    enumnode(ctx, obj2gco(p), p->source ? getstr(p->source) : NULL);
+
+    if (p->sizek)
+        enumedges(ctx, obj2gco(p), p->k, p->sizek, "constants");
+
+    for (int i = 0; i < p->sizep; ++i)
+        enumedge(ctx, obj2gco(p), obj2gco(p->p[i]), "protos");
+}
+
+static void enumupval(EnumContext* ctx, UpVal* uv)
+{
+    enumnode(ctx, obj2gco(uv), NULL);
+
+    if (iscollectable(uv->v))
+        enumedge(ctx, obj2gco(uv), gcvalue(uv->v), "value");
+}
+
+static void enumobj(EnumContext* ctx, GCObject* o)
+{
+    switch (o->gch.tt)
+    {
+    case LUA_TSTRING:
+        return enumstring(ctx, gco2ts(o));
+
+    case LUA_TTABLE:
+        return enumtable(ctx, gco2h(o));
+
+    case LUA_TFUNCTION:
+        return enumclosure(ctx, gco2cl(o));
+
+    case LUA_TUSERDATA:
+        return enumudata(ctx, gco2u(o));
+
+    case LUA_TTHREAD:
+        return enumthread(ctx, gco2th(o));
+
+    case LUA_TPROTO:
+        return enumproto(ctx, gco2p(o));
+
+    case LUA_TUPVAL:
+        return enumupval(ctx, gco2uv(o));
+
+    default:
+        LUAU_ASSERT(!"Unknown object tag");
+    }
+}
+
+static bool enumgco(void* context, lua_Page* page, GCObject* gco)
+{
+    enumobj((EnumContext*)context, gco);
+    return false;
+}
+
+void luaC_enumheap(lua_State* L, void* context, void (*node)(void* context, void* ptr, uint8_t tt, uint8_t memcat, const char* name),
+    void (*edge)(void* context, void* from, void* to, const char* name))
+{
+    global_State* g = L->global;
+
+    EnumContext ctx;
+    ctx.L = L;
+    ctx.context = context;
+    ctx.node = node;
+    ctx.edge = edge;
+
+    enumgco(&ctx, NULL, obj2gco(g->mainthread));
+
+    luaM_visitgco(L, &ctx, enumgco);
+}

VM/src/lobject.h

@@ -263,9 +263,22 @@ typedef struct Proto
     CommonHeader;
 
 
+    uint8_t nups; // number of upvalues
+    uint8_t numparams;
+    uint8_t is_vararg;
+    uint8_t maxstacksize;
+    uint8_t flags;
+
+
     TValue* k;              // constants used by the function
     Instruction* code;      // function bytecode
     struct Proto** p;       // functions defined inside the function
+    const Instruction* codeentry;
+
+    void* execdata;
+    uintptr_t exectarget;
+
+
     uint8_t* lineinfo;      // for each instruction, line number as a delta from baseline
     int* abslineinfo;       // baseline line info, one entry for each 1<<linegaplog2 instructions; allocated after lineinfo
     struct LocVar* locvars; // information about local variables
@@ -275,10 +288,6 @@ typedef struct Proto
     TString* debugname;
     uint8_t* debuginsn; // a copy of code[] array with just opcodes
 
-    const Instruction* codeentry;
-    void* execdata;
-    uintptr_t exectarget;
-
     uint8_t* typeinfo;
 
     GCObject* gclist;
@@ -293,12 +302,6 @@ typedef struct Proto
     int linegaplog2;
     int linedefined;
     int bytecodeid;
-
-
-    uint8_t nups; // number of upvalues
-    uint8_t numparams;
-    uint8_t is_vararg;
-    uint8_t maxstacksize;
 } Proto;
 // clang-format on
 

VM/src/lstate.cpp

@@ -101,10 +101,8 @@ static void close_state(lua_State* L)
     for (int i = 1; i < LUA_MEMORY_CATEGORIES; i++)
         LUAU_ASSERT(g->memcatbytes[i] == 0);
 
-#if LUA_CUSTOM_EXECUTION
     if (L->global->ecb.close)
         L->global->ecb.close(L);
-#endif
 
     (*g->frealloc)(g->ud, L, sizeof(LG), 0);
 }

VM/src/lstate.h

@@ -154,7 +154,6 @@ struct lua_ExecutionCallbacks
     void (*close)(lua_State* L);                 // called when global VM state is closed
     void (*destroy)(lua_State* L, Proto* proto); // called when function is destroyed
     int (*enter)(lua_State* L, Proto* proto);    // called when function is about to start/resume (when execdata is present), return 0 to exit VM
-    void (*setbreakpoint)(lua_State* L, Proto* proto, int line); // called when a breakpoint is set in a function
 };
 
 /*

VM/src/lvmload.cpp

@@ -230,8 +230,7 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
 
         if (version >= 4)
         {
-            uint8_t cgflags = read<uint8_t>(data, size, offset);
+            p->flags = read<uint8_t>(data, size, offset);
-            LUAU_ASSERT(cgflags == 0);
 
             uint32_t typesize = readVarInt(data, size, offset);
 

fuzz/proto.cpp

@@ -26,7 +26,7 @@ const bool kFuzzLinter = true;
 const bool kFuzzTypeck = true;
 const bool kFuzzVM = true;
 const bool kFuzzTranspile = true;
-const bool kFuzzCodegen = true;
+const bool kFuzzCodegenVM = true;
 const bool kFuzzCodegenAssembly = true;
 
 // Should we generate type annotations?
@@ -35,7 +35,7 @@ const bool kFuzzTypes = true;
 const Luau::CodeGen::AssemblyOptions::Target kFuzzCodegenTarget = Luau::CodeGen::AssemblyOptions::A64;
 
 static_assert(!(kFuzzVM && !kFuzzCompiler), "VM requires the compiler!");
-static_assert(!(kFuzzCodegen && !kFuzzVM), "Codegen requires the VM!");
+static_assert(!(kFuzzCodegenVM && !kFuzzCompiler), "Codegen requires the compiler!");
 static_assert(!(kFuzzCodegenAssembly && !kFuzzCompiler), "Codegen requires the compiler!");
 
 std::vector<std::string> protoprint(const luau::ModuleSet& stat, bool types);
@@ -47,6 +47,7 @@ LUAU_FASTINT(LuauTableTypeMaximumStringifierLength)
 LUAU_FASTINT(LuauTypeInferIterationLimit)
 LUAU_FASTINT(LuauTarjanChildLimit)
 LUAU_FASTFLAG(DebugLuauFreezeArena)
+LUAU_FASTFLAG(DebugLuauAbortingChecks)
 
 std::chrono::milliseconds kInterruptTimeout(10);
 std::chrono::time_point<std::chrono::system_clock> interruptDeadline;
@@ -90,7 +91,7 @@ lua_State* createGlobalState()
 {
     lua_State* L = lua_newstate(allocate, NULL);
 
-    if (kFuzzCodegen && Luau::CodeGen::isSupported())
+    if (kFuzzCodegenVM && Luau::CodeGen::isSupported())
         Luau::CodeGen::create(L);
 
     lua_callbacks(L)->interrupt = interrupt;
@@ -228,6 +229,7 @@ DEFINE_PROTO_FUZZER(const luau::ModuleSet& message)
             flag->value = true;
 
     FFlag::DebugLuauFreezeArena.value = true;
+    FFlag::DebugLuauAbortingChecks.value = true;
 
     std::vector<std::string> sources = protoprint(message, kFuzzTypes);
 
@@ -370,7 +372,7 @@ DEFINE_PROTO_FUZZER(const luau::ModuleSet& message)
     }
 
     // run resulting bytecode (from last successfully compiler module)
-    if (kFuzzVM && bytecode.size())
+    if ((kFuzzVM || kFuzzCodegenVM) && bytecode.size())
     {
         static lua_State* globalState = createGlobalState();
 
@@ -395,9 +397,10 @@ DEFINE_PROTO_FUZZER(const luau::ModuleSet& message)
             LUAU_ASSERT(heapSize < 256 * 1024);
         };
 
-        runCode(bytecode, false);
+        if (kFuzzVM)
+            runCode(bytecode, false);
 
-        if (kFuzzCodegen && Luau::CodeGen::isSupported())
+        if (kFuzzCodegenVM && Luau::CodeGen::isSupported())
             runCode(bytecode, true);
     }
 }

tests/Compiler.test.cpp

@@ -53,7 +53,10 @@ static std::string compileTypeTable(const char* source)
 {
     Luau::BytecodeBuilder bcb;
     bcb.setDumpFlags(Luau::BytecodeBuilder::Dump_Code);
-    Luau::compileOrThrow(bcb, source);
+
+    Luau::CompileOptions opts;
+    opts.vectorType = "Vector3";
+    Luau::compileOrThrow(bcb, source, opts);
 
     return bcb.dumpTypeInfo();
 }
@@ -7159,6 +7162,31 @@ end
 )");
 }
 
+TEST_CASE("HostTypesVector")
+{
+    ScopedFastFlag sff("LuauCompileFunctionType", true);
+
+    CHECK_EQ("\n" + compileTypeTable(R"(
+function myfunc(test: Instance, pos: Vector3)
+end
+
+function myfunc2<Vector3>(test: Instance, pos: Vector3)
+end
+
+do
+    type Vector3 = number
+
+    function myfunc3(test: Instance, pos: Vector3)
+    end
+end
+)"),
+        R"(
+0: function(userdata, vector)
+1: function(userdata, any)
+2: function(userdata, number)
+)");
+}
+
 TEST_CASE("TypeAliasScoping")
 {
     ScopedFastFlag sff("LuauCompileFunctionType", true);

tests/Conformance.test.cpp

@@ -5,6 +5,7 @@
 #include "luacodegen.h"
 
 #include "Luau/BuiltinDefinitions.h"
+#include "Luau/DenseHash.h"
 #include "Luau/ModuleResolver.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/StringUtils.h"
@@ -15,6 +16,7 @@
 #include "ScopedFlags.h"
 
 #include <fstream>
+#include <string>
 #include <vector>
 #include <math.h>
 
@@ -1244,6 +1246,8 @@ TEST_CASE("GCDump")
 {
     // internal function, declared in lgc.h - not exposed via lua.h
     extern void luaC_dump(lua_State * L, void* file, const char* (*categoryName)(lua_State * L, uint8_t memcat));
+    extern void luaC_enumheap(lua_State * L, void* context, void (*node)(void* context, void* ptr, uint8_t tt, uint8_t memcat, const char* name),
+        void (*edge)(void* context, void* from, void* to, const char* name));
 
     StateRef globalState(luaL_newstate(), lua_close);
     lua_State* L = globalState.get();
@@ -1287,6 +1291,40 @@ TEST_CASE("GCDump")
     luaC_dump(L, f, nullptr);
 
     fclose(f);
+
+    struct Node
+    {
+        void* ptr;
+        uint8_t tag;
+        uint8_t memcat;
+        std::string name;
+    };
+
+    struct EnumContext
+    {
+        EnumContext()
+            : nodes{nullptr}
+            , edges{nullptr}
+        {
+        }
+
+        Luau::DenseHashMap<void*, Node> nodes;
+        Luau::DenseHashMap<void*, void*> edges;
+    } ctx;
+
+    luaC_enumheap(
+        L, &ctx,
+        [](void* ctx, void* gco, uint8_t tt, uint8_t memcat, const char* name) {
+            EnumContext& context = *(EnumContext*)ctx;
+            context.nodes[gco] = {gco, tt, memcat, name ? name : ""};
+        },
+        [](void* ctx, void* s, void* t, const char*) {
+            EnumContext& context = *(EnumContext*)ctx;
+            context.edges[s] = t;
+        });
+
+    CHECK(!ctx.nodes.empty());
+    CHECK(!ctx.edges.empty());
 }
 
 TEST_CASE("Interrupt")

tests/Differ.test.cpp

@@ -1,15 +1,20 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Differ.h"
+#include "Luau/Common.h"
 #include "Luau/Error.h"
 #include "Luau/Frontend.h"
 
 #include "Fixture.h"
 
+#include "Luau/Symbol.h"
+#include "ScopedFlags.h"
 #include "doctest.h"
 #include <iostream>
 
 using namespace Luau;
 
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
+
 TEST_SUITE_BEGIN("Differ");
 
 TEST_CASE_FIXTURE(Fixture, "equal_numbers")
@@ -313,4 +318,685 @@ TEST_CASE_FIXTURE(Fixture, "singleton_string")
         diffMessage);
 }
 
+TEST_CASE_FIXTURE(Fixture, "equal_function")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number)
+        return x
+    end
+    function almostFoo(y: number)
+        return y + 10
+    end
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        INFO(diffRes.diffError->toString());
+        CHECK(!diffRes.diffError.has_value());
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+}
+
+TEST_CASE_FIXTURE(Fixture, "equal_function_inferred_ret_length")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function bar(x: number, y: string)
+        return x, y
+    end
+    function almostBar(a: number, b: string)
+        return a, b
+    end
+    function foo(x: number, y: string, z: boolean)
+        return z, bar(x, y)
+    end
+    function almostFoo(a: number, b: string, c: boolean)
+        return c, almostBar(a, b)
+    end
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        INFO(diffRes.diffError->toString());
+        CHECK(!diffRes.diffError.has_value());
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+}
+
+TEST_CASE_FIXTURE(Fixture, "equal_function_inferred_ret_length_2")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function bar(x: number, y: string)
+        return x, y
+    end
+    function foo(x: number, y: string, z: boolean)
+        return bar(x, y), z
+    end
+    function almostFoo(a: number, b: string, c: boolean)
+        return a, c
+    end
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        INFO(diffRes.diffError->toString());
+        CHECK(!diffRes.diffError.has_value());
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_arg_normal")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: number, z: number)
+        return x * y * z
+    end
+    function almostFoo(a: number, b: number, msg: string)
+        return a
+    almostFoo = foo
+    )");
+    LUAU_REQUIRE_ERRORS(result);
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        diffMessage = diff(foo, almostFoo).diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol>.Arg[3] has type number, while the right type at <unlabeled-symbol>.Arg[3] has type string)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_arg_normal_2")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: number, z: string)
+        return x * y
+    end
+    function almostFoo(a: number, y: string, msg: string)
+        return a
+    almostFoo = foo
+    )");
+    LUAU_REQUIRE_ERRORS(result);
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        diffMessage = diff(foo, almostFoo).diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol>.Arg[2] has type number, while the right type at <unlabeled-symbol>.Arg[2] has type string)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_ret_normal")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: number, z: string)
+        return x
+    end
+    function almostFoo(a: number, b: number, msg: string)
+        return msg
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol>.Ret[1] has type number, while the right type at <unlabeled-symbol>.Ret[1] has type string)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_arg_length")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: number)
+        return x
+    end
+    function almostFoo(x: number, y: number, c: number)
+        return x
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> takes 2 or more arguments, while the right type at <unlabeled-symbol> takes 3 or more arguments)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_arg_length_2")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: string, z: number)
+        return z
+    end
+    function almostFoo(x: number, y: string)
+        return x
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> takes 3 or more arguments, while the right type at <unlabeled-symbol> takes 2 or more arguments)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_arg_length_none")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo()
+        return 5
+    end
+    function almostFoo(x: number, y: string)
+        return x
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> takes 0 or more arguments, while the right type at <unlabeled-symbol> takes 2 or more arguments)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_arg_length_none_2")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number)
+        return x
+    end
+    function almostFoo()
+        return 5
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> takes 1 or more arguments, while the right type at <unlabeled-symbol> takes 0 or more arguments)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_ret_length")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: number)
+        return x
+    end
+    function almostFoo(x: number, y: number)
+        return x, y
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> returns 1 values, while the right type at <unlabeled-symbol> returns 2 values)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_ret_length_2")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: string, z: number)
+        return y, x, z
+    end
+    function almostFoo(x: number, y: string, z: number)
+        return y, x
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> returns 3 values, while the right type at <unlabeled-symbol> returns 2 values)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_ret_length_none")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: string)
+        return
+    end
+    function almostFoo(x: number, y: string)
+        return x
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> returns 0 values, while the right type at <unlabeled-symbol> returns 1 values)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_ret_length_none_2")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo()
+        return 5
+    end
+    function almostFoo()
+        return
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> returns 1 values, while the right type at <unlabeled-symbol> returns 0 values)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_variadic_arg_normal")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: string, ...: number)
+        return x, y
+    end
+    function almostFoo(a: number, b: string, ...: string)
+        return a, b
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol>.Arg[Variadic] has type number, while the right type at <unlabeled-symbol>.Arg[Variadic] has type string)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_variadic_arg_missing")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: string, ...: number)
+        return x, y
+    end
+    function almostFoo(a: number, b: string)
+        return a, b
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol>.Arg[Variadic] has type number, while the right type at <unlabeled-symbol>.Arg[Variadic] has type any)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_variadic_arg_missing_2")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    function foo(x: number, y: string)
+        return x, y
+    end
+    function almostFoo(a: number, b: string, ...: string)
+        return a, b
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol>.Arg[Variadic] has type any, while the right type at <unlabeled-symbol>.Arg[Variadic] has type string)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_variadic_oversaturation")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    -- allowed to be oversaturated
+    function foo(x: number, y: string)
+        return x, y
+    end
+    -- must not be oversaturated
+    local almostFoo: (number, string) -> (number, string) = foo
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> takes 2 or more arguments, while the right type at <unlabeled-symbol> takes 2 arguments)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "function_variadic_oversaturation_2")
+{
+    // Old solver does not correctly infer function typepacks
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    CheckResult result = check(R"(
+    -- must not be oversaturated
+    local foo: (number, string) -> (number, string)
+    -- allowed to be oversaturated
+    function almostFoo(x: number, y: string)
+        return x, y
+    end
+    )");
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    std::string diffMessage;
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        if (!diffRes.diffError.has_value())
+        {
+            INFO("Differ did not report type error, even though types are unequal");
+            CHECK(false);
+        }
+        diffMessage = diffRes.diffError->toString();
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+    CHECK_EQ(
+        R"(DiffError: these two types are not equal because the left type at <unlabeled-symbol> takes 2 arguments, while the right type at <unlabeled-symbol> takes 2 or more arguments)",
+        diffMessage);
+}
+
 TEST_SUITE_END();

tests/Module.test.cpp

@@ -407,19 +407,15 @@ type B = A
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "do_not_clone_reexports")
 {
-    ScopedFastFlag flags[] = {
-        {"LuauClonePublicInterfaceLess2", true},
-    };
-
     fileResolver.source["Module/A"] = R"(
-export type A = {p : number}
+        export type A = {p : number}
-return {}
+        return {}
     )";
 
     fileResolver.source["Module/B"] = R"(
-local a = require(script.Parent.A)
+        local a = require(script.Parent.A)
-export type B = {q : a.A}
+        export type B = {q : a.A}
-return {}
+        return {}
     )";
 
     CheckResult result = frontend.check("Module/B");
@@ -442,19 +438,15 @@ return {}
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "do_not_clone_types_of_reexported_values")
 {
-    ScopedFastFlag flags[] = {
-        {"LuauClonePublicInterfaceLess2", true},
-    };
-
     fileResolver.source["Module/A"] = R"(
-local exports = {a={p=5}}
+        local exports = {a={p=5}}
-return exports
+        return exports
     )";
 
     fileResolver.source["Module/B"] = R"(
-local a = require(script.Parent.A)
+        local a = require(script.Parent.A)
-local exports = {b=a.a}
+        local exports = {b=a.a}
-return exports
+        return exports
     )";
 
     CheckResult result = frontend.check("Module/B");

tests/Parser.test.cpp

@@ -54,8 +54,7 @@ TEST_SUITE_BEGIN("AllocatorTests");
 TEST_CASE("allocator_can_be_moved")
 {
     Counter* c = nullptr;
-    auto inner = [&]()
+    auto inner = [&]() {
-    {
         Luau::Allocator allocator;
         c = allocator.alloc<Counter>();
         Luau::Allocator moved{std::move(allocator)};
@@ -922,8 +921,7 @@ TEST_CASE_FIXTURE(Fixture, "parse_interpolated_string_double_brace_mid")
 
 TEST_CASE_FIXTURE(Fixture, "parse_interpolated_string_without_end_brace")
 {
-    auto columnOfEndBraceError = [this](const char* code)
+    auto columnOfEndBraceError = [this](const char* code) {
-    {
         try
         {
             parse(code);
@@ -2387,8 +2385,7 @@ public:
 
 TEST_CASE_FIXTURE(Fixture, "recovery_of_parenthesized_expressions")
 {
-    auto checkAstEquivalence = [this](const char* codeWithErrors, const char* code)
+    auto checkAstEquivalence = [this](const char* codeWithErrors, const char* code) {
-    {
         try
         {
             parse(codeWithErrors);
@@ -2408,8 +2405,7 @@ TEST_CASE_FIXTURE(Fixture, "recovery_of_parenthesized_expressions")
         CHECK_EQ(counterWithErrors.count, counter.count);
     };
 
-    auto checkRecovery = [this, checkAstEquivalence](const char* codeWithErrors, const char* code, unsigned expectedErrorCount)
+    auto checkRecovery = [this, checkAstEquivalence](const char* codeWithErrors, const char* code, unsigned expectedErrorCount) {
-    {
         try
         {
             parse(codeWithErrors);

tests/TypeFamily.test.cpp

@@ -225,7 +225,8 @@ TEST_CASE_FIXTURE(Fixture, "internal_families_raise_errors")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    CHECK(toString(result.errors[0]) == "Type family instance Add<a, b> depends on generic function parameters but does not appear in the function signature; this construct cannot be type-checked at this time");
+    CHECK(toString(result.errors[0]) == "Type family instance Add<a, b> depends on generic function parameters but does not appear in the function "
+                                        "signature; this construct cannot be type-checked at this time");
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "type_families_inhabited_with_normalization")

tests/TypeInfer.functions.test.cpp

@@ -1913,8 +1913,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "dont_assert_when_the_tarjan_limit_is_exceede
     ScopedFastInt sfi{"LuauTarjanChildLimit", 2};
     ScopedFastFlag sff[] = {
         {"DebugLuauDeferredConstraintResolution", true},
-        {"LuauClonePublicInterfaceLess2", true},
-        {"LuauCloneSkipNonInternalVisit", true},
     };
 
     CheckResult result = check(R"(

tests/TypeInfer.operators.test.cpp

@@ -670,7 +670,9 @@ TEST_CASE_FIXTURE(Fixture, "strict_binary_op_where_lhs_unknown")
     if (FFlag::DebugLuauDeferredConstraintResolution)
     {
         LUAU_REQUIRE_ERROR_COUNT(ops.size(), result);
-        CHECK_EQ("Type family instance Add<a, b> depends on generic function parameters but does not appear in the function signature; this construct cannot be type-checked at this time", toString(result.errors[0]));
+        CHECK_EQ("Type family instance Add<a, b> depends on generic function parameters but does not appear in the function signature; this "
+                 "construct cannot be type-checked at this time",
+            toString(result.errors[0]));
         CHECK_EQ("Unknown type used in - operation; consider adding a type annotation to 'a'", toString(result.errors[1]));
     }
     else

tests/TypeInfer.unionTypes.test.cpp

@@ -789,4 +789,19 @@ TEST_CASE_FIXTURE(Fixture, "lookup_prop_of_intersection_containing_unions")
     CHECK("variables" == unknownProp->key);
 }
 
+TEST_CASE_FIXTURE(Fixture, "suppress_errors_for_prop_lookup_of_a_union_that_includes_error")
+{
+    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
+
+    registerHiddenTypes(&frontend);
+
+    CheckResult result = check(R"(
+        local a : err | Not<nil>
+
+        local b = a.foo
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/conformance/native.lua

@@ -92,4 +92,13 @@ end
 
 assert(pcall(fuzzfail9) == false)
 
+local function fuzzfail10()
+  local _
+  _ = false,if _ then _ else _
+  _ = not _
+  l0,_[l0] = not _
+end
+
+assert(pcall(fuzzfail10) == false)
+
 return('OK')