Sync to upstream/release/583 (#974)

* Fixed indexing table intersections using `x["prop"]` syntax:
https://github.com/Roblox/luau/pull/971
* Add console output codepage for Windows:
https://github.com/Roblox/luau/pull/967
* Added `Frontend::parse` for a fast source graph preparation
* luau_load should check GC
* Work toward a type-diff system for nicer error messages

New Solver
* Correctly suppress errors in more cases
* Further improvements to typechecking of function calls and return
statements
* Crash fixes
* Propagate refinements drawn from the condition of a while loop into
the loop body

JIT
* Fix accidental bailout for math.frexp/modf/sign in A64
* Work toward bringing type annotation info in
* Do not propagate Luau IR constants of wrong type into load
instructions
* CHECK_SAFEENV exits to VM on failure
* Implement error handling in A64 reg allocator
* Inline the string.len builtin
* Do not enter native code of a function if arguments don’t match

---------

Co-authored-by: Arseny Kapoulkine <arseny.kapoulkine@gmail.com>
Co-authored-by: Vyacheslav Egorov <vegorov@roblox.com>

Analysis/include/Luau/Constraint.h

@@ -34,6 +34,11 @@ struct PackSubtypeConstraint
 {
     TypePackId subPack;
     TypePackId superPack;
+
+    // HACK!! TODO clip.
+    // We need to know which of `PackSubtypeConstraint` are emitted from `AstStatReturn` vs any others.
+    // Then we force these specific `PackSubtypeConstraint` to only dispatch in the order of the `return`s.
+    bool returns = false;
 };
 
 // generalizedType ~ gen sourceType
@@ -108,13 +113,12 @@ struct FunctionCallConstraint
     TypeId fn;
     TypePackId argsPack;
     TypePackId result;
-    class AstExprCall* callSite;
+    class AstExprCall* callSite = nullptr;
     std::vector<std::optional<TypeId>> discriminantTypes;
 
     // When we dispatch this constraint, we update the key at this map to record
     // the overload that we selected.
-    DenseHashMap<const AstNode*, TypeId>* astOriginalCallTypes;
+    DenseHashMap<const AstNode*, TypeId>* astOverloadResolvedTypes = nullptr;
-    DenseHashMap<const AstNode*, TypeId>* astOverloadResolvedTypes;
 };
 
 // result ~ prim ExpectedType SomeSingletonType MultitonType

Analysis/include/Luau/Differ.h

@@ -0,0 +1,138 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/Type.h"
+#include <optional>
+#include <string>
+
+namespace Luau
+{
+struct DiffPathNode
+{
+    // TODO: consider using Variants to simplify toString implementation
+    enum Kind
+    {
+        TableProperty,
+        FunctionArgument,
+        FunctionReturn,
+        Union,
+        Intersection,
+    };
+    Kind kind;
+    // non-null when TableProperty
+    std::optional<Name> tableProperty;
+    // non-null when FunctionArgument, FunctionReturn, Union, or Intersection (i.e. anonymous fields)
+    std::optional<int> index;
+
+    /**
+     * Do not use for leaf nodes
+     */
+    DiffPathNode(Kind kind)
+        : kind(kind)
+    {
+    }
+
+    DiffPathNode(Kind kind, std::optional<Name> tableProperty, std::optional<int> index)
+        : kind(kind)
+        , tableProperty(tableProperty)
+        , index(index)
+    {
+    }
+
+    std::string toString() const;
+
+    static DiffPathNode constructWithTableProperty(Name tableProperty);
+};
+struct DiffPathNodeLeaf
+{
+    std::optional<TypeId> ty;
+    std::optional<Name> tableProperty;
+    DiffPathNodeLeaf(std::optional<TypeId> ty, std::optional<Name> tableProperty)
+        : ty(ty)
+        , tableProperty(tableProperty)
+    {
+    }
+
+    static DiffPathNodeLeaf nullopts();
+};
+struct DiffPath
+{
+    std::vector<DiffPathNode> path;
+
+    std::string toString(bool prependDot) const;
+};
+struct DiffError
+{
+    enum Kind
+    {
+        Normal,
+        MissingProperty,
+        LengthMismatchInFnArgs,
+        LengthMismatchInFnRets,
+        LengthMismatchInUnion,
+        LengthMismatchInIntersection,
+    };
+    Kind kind;
+
+    DiffPath diffPath;
+    DiffPathNodeLeaf left;
+    DiffPathNodeLeaf right;
+
+    std::string leftRootName;
+    std::string rightRootName;
+
+    DiffError(Kind kind, DiffPathNodeLeaf left, DiffPathNodeLeaf right, std::string leftRootName, std::string rightRootName)
+        : kind(kind)
+        , left(left)
+        , right(right)
+        , leftRootName(leftRootName)
+        , rightRootName(rightRootName)
+    {
+        checkValidInitialization(left, right);
+    }
+    DiffError(Kind kind, DiffPath diffPath, DiffPathNodeLeaf left, DiffPathNodeLeaf right, std::string leftRootName, std::string rightRootName)
+        : kind(kind)
+        , diffPath(diffPath)
+        , left(left)
+        , right(right)
+        , leftRootName(leftRootName)
+        , rightRootName(rightRootName)
+    {
+        checkValidInitialization(left, right);
+    }
+
+    std::string toString() const;
+
+private:
+    std::string toStringALeaf(std::string rootName, const DiffPathNodeLeaf& leaf, const DiffPathNodeLeaf& otherLeaf) const;
+    void checkValidInitialization(const DiffPathNodeLeaf& left, const DiffPathNodeLeaf& right);
+    void checkNonMissingPropertyLeavesHaveNulloptTableProperty() const;
+};
+
+struct DifferResult
+{
+    std::optional<DiffError> diffError;
+
+    DifferResult() {}
+    DifferResult(DiffError diffError)
+        : diffError(diffError)
+    {
+    }
+
+    void wrapDiffPath(DiffPathNode node);
+};
+struct DifferEnvironment
+{
+    TypeId rootLeft;
+    TypeId rootRight;
+};
+DifferResult diff(TypeId ty1, TypeId ty2);
+
+/**
+ * True if ty is a "simple" type, i.e. cannot contain types.
+ * string, number, boolean are simple types.
+ * function and table are not simple types.
+ */
+bool isSimple(TypeId ty);
+
+} // namespace Luau

Analysis/include/Luau/Frontend.h

@@ -144,6 +144,10 @@ struct Frontend
 
     Frontend(FileResolver* fileResolver, ConfigResolver* configResolver, const FrontendOptions& options = {});
 
+    // Parse module graph and prepare SourceNode/SourceModule data, including required dependencies without running typechecking
+    void parse(const ModuleName& name);
+
+    // Parse and typecheck module graph
     CheckResult check(const ModuleName& name, std::optional<FrontendOptions> optionOverride = {}); // new shininess
 
     bool isDirty(const ModuleName& name, bool forAutocomplete = false) const;

Analysis/include/Luau/Normalize.h

@@ -274,6 +274,9 @@ struct NormalizedType
     /// Returns true if the type is a subtype of string(it could be a singleton). Behaves like Type::isString()
     bool isSubtypeOfString() const;
 
+    /// Returns true if this type should result in error suppressing behavior.
+    bool shouldSuppressErrors() const;
+
     // Helpers that improve readability of the above (they just say if the component is present)
     bool hasTops() const;
     bool hasBooleans() const;
@@ -343,7 +346,7 @@ public:
     void unionTablesWithTable(TypeIds& heres, TypeId there);
     void unionTables(TypeIds& heres, const TypeIds& theres);
     bool unionNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
-    bool unionNormalWithTy(NormalizedType& here, TypeId there, int ignoreSmallerTyvars = -1);
+    bool unionNormalWithTy(NormalizedType& here, TypeId there, std::unordered_set<TypeId>& seenSetTypes, int ignoreSmallerTyvars = -1);
 
     // ------- Negations
     std::optional<NormalizedType> negateNormal(const NormalizedType& here);
@@ -365,9 +368,9 @@ public:
     std::optional<TypeId> intersectionOfFunctions(TypeId here, TypeId there);
     void intersectFunctionsWithFunction(NormalizedFunctionType& heress, TypeId there);
     void intersectFunctions(NormalizedFunctionType& heress, const NormalizedFunctionType& theress);
-    bool intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there);
+    bool intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there, std::unordered_set<TypeId>& seenSetTypes);
     bool intersectNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
-    bool intersectNormalWithTy(NormalizedType& here, TypeId there);
+    bool intersectNormalWithTy(NormalizedType& here, TypeId there, std::unordered_set<TypeId>& seenSetTypes);
     bool normalizeIntersections(const std::vector<TypeId>& intersections, NormalizedType& outType);
 
     // Check for inhabitance

Analysis/include/Luau/Type.h

@@ -23,7 +23,6 @@
 
 LUAU_FASTINT(LuauTableTypeMaximumStringifierLength)
 LUAU_FASTINT(LuauTypeMaximumStringifierLength)
-LUAU_FASTFLAG(LuauTypecheckClassTypeIndexers)
 
 namespace Luau
 {
@@ -527,7 +526,6 @@ struct ClassType
         , definitionModuleName(definitionModuleName)
         , indexer(indexer)
     {
-        LUAU_ASSERT(FFlag::LuauTypecheckClassTypeIndexers);
     }
 };
 

Analysis/include/Luau/VisitType.h

@@ -304,13 +304,10 @@ struct GenericTypeVisitor
                 if (ctv->metatable)
                     traverse(*ctv->metatable);
 
-                if (FFlag::LuauTypecheckClassTypeIndexers)
+                if (ctv->indexer)
                 {
-                    if (ctv->indexer)
+                    traverse(ctv->indexer->indexType);
-                    {
+                    traverse(ctv->indexer->indexResultType);
-                        traverse(ctv->indexer->indexType);
-                        traverse(ctv->indexer->indexResultType);
-                    }
                 }
             }
         }

Analysis/src/Clone.cpp

@@ -55,7 +55,6 @@ Property clone(const Property& prop, TypeArena& dest, CloneState& cloneState)
 
 static TableIndexer clone(const TableIndexer& indexer, TypeArena& dest, CloneState& cloneState)
 {
-    LUAU_ASSERT(FFlag::LuauTypecheckClassTypeIndexers);
     return TableIndexer{clone(indexer.indexType, dest, cloneState), clone(indexer.indexResultType, dest, cloneState)};
 }
 
@@ -312,16 +311,8 @@ void TypeCloner::operator()(const TableType& t)
     for (const auto& [name, prop] : t.props)
         ttv->props[name] = clone(prop, dest, cloneState);
 
-    if (FFlag::LuauTypecheckClassTypeIndexers)
+    if (t.indexer)
-    {
+        ttv->indexer = clone(*t.indexer, dest, cloneState);
-        if (t.indexer)
-            ttv->indexer = clone(*t.indexer, dest, cloneState);
-    }
-    else
-    {
-        if (t.indexer)
-            ttv->indexer = TableIndexer{clone(t.indexer->indexType, dest, cloneState), clone(t.indexer->indexResultType, dest, cloneState)};
-    }
 
     for (TypeId& arg : ttv->instantiatedTypeParams)
         arg = clone(arg, dest, cloneState);
@@ -360,11 +351,8 @@ void TypeCloner::operator()(const ClassType& t)
     if (t.metatable)
         ctv->metatable = clone(*t.metatable, dest, cloneState);
 
-    if (FFlag::LuauTypecheckClassTypeIndexers)
+    if (t.indexer)
-    {
+        ctv->indexer = clone(*t.indexer, dest, cloneState);
-        if (t.indexer)
-            ctv->indexer = clone(*t.indexer, dest, cloneState);
-    }
 }
 
 void TypeCloner::operator()(const AnyType& t)

Analysis/src/ConstraintGraphBuilder.cpp

@@ -776,9 +776,10 @@ ControlFlow ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatForIn* f
 
 ControlFlow ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatWhile* while_)
 {
-    check(scope, while_->condition);
+    RefinementId refinement = check(scope, while_->condition).refinement;
 
     ScopePtr whileScope = childScope(while_, scope);
+    applyRefinements(whileScope, while_->condition->location, refinement);
 
     visit(whileScope, while_->body);
 
@@ -825,8 +826,17 @@ ControlFlow ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatLocalFun
     std::unique_ptr<Constraint> c =
         std::make_unique<Constraint>(constraintScope, function->name->location, GeneralizationConstraint{functionType, sig.signature});
 
-    forEachConstraint(start, end, this, [&c](const ConstraintPtr& constraint) {
+    Constraint* previous = nullptr;
+    forEachConstraint(start, end, this, [&c, &previous](const ConstraintPtr& constraint) {
         c->dependencies.push_back(NotNull{constraint.get()});
+
+        if (auto psc = get<PackSubtypeConstraint>(*constraint); psc && psc->returns)
+        {
+            if (previous)
+                constraint->dependencies.push_back(NotNull{previous});
+
+            previous = constraint.get();
+        }
     });
 
     addConstraint(scope, std::move(c));
@@ -915,9 +925,18 @@ ControlFlow ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatFunction
     std::unique_ptr<Constraint> c =
         std::make_unique<Constraint>(constraintScope, function->name->location, GeneralizationConstraint{generalizedType, sig.signature});
 
-    forEachConstraint(start, end, this, [&c, &excludeList](const ConstraintPtr& constraint) {
+    Constraint* previous = nullptr;
+    forEachConstraint(start, end, this, [&c, &excludeList, &previous](const ConstraintPtr& constraint) {
         if (!excludeList.count(constraint.get()))
             c->dependencies.push_back(NotNull{constraint.get()});
+
+        if (auto psc = get<PackSubtypeConstraint>(*constraint); psc && psc->returns)
+        {
+            if (previous)
+                constraint->dependencies.push_back(NotNull{previous});
+
+            previous = constraint.get();
+        }
     });
 
     addConstraint(scope, std::move(c));
@@ -936,7 +955,7 @@ ControlFlow ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatReturn*
         expectedTypes.push_back(ty);
 
     TypePackId exprTypes = checkPack(scope, ret->list, expectedTypes).tp;
-    addConstraint(scope, ret->location, PackSubtypeConstraint{exprTypes, scope->returnType});
+    addConstraint(scope, ret->location, PackSubtypeConstraint{exprTypes, scope->returnType, /*returns*/ true});
 
     return ControlFlow::Returns;
 }
@@ -1408,6 +1427,7 @@ InferencePack ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExprCa
     std::vector<std::optional<TypeId>> expectedTypesForCall = getExpectedCallTypesForFunctionOverloads(fnType);
 
     module->astOriginalCallTypes[call->func] = fnType;
+    module->astOriginalCallTypes[call] = fnType;
 
     TypePackId expectedArgPack = arena->freshTypePack(scope.get());
     TypePackId expectedRetPack = arena->freshTypePack(scope.get());
@@ -1547,7 +1567,6 @@ InferencePack ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExprCa
                 rets,
                 call,
                 std::move(discriminantTypes),
-                &module->astOriginalCallTypes,
                 &module->astOverloadResolvedTypes,
             });
 
@@ -1642,7 +1661,7 @@ Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprConstantSt
     if (expectedType)
     {
         const TypeId expectedTy = follow(*expectedType);
-        if (get<BlockedType>(expectedTy) || get<PendingExpansionType>(expectedTy))
+        if (get<BlockedType>(expectedTy) || get<PendingExpansionType>(expectedTy) || get<FreeType>(expectedTy))
         {
             TypeId ty = arena->addType(BlockedType{});
             TypeId singletonType = arena->addType(SingletonType(StringSingleton{std::string(string->value.data, string->value.size)}));
@@ -1774,8 +1793,17 @@ Inference ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprFunction*
     TypeId generalizedTy = arena->addType(BlockedType{});
     NotNull<Constraint> gc = addConstraint(sig.signatureScope, func->location, GeneralizationConstraint{generalizedTy, sig.signature});
 
-    forEachConstraint(startCheckpoint, endCheckpoint, this, [gc](const ConstraintPtr& constraint) {
+    Constraint* previous = nullptr;
+    forEachConstraint(startCheckpoint, endCheckpoint, this, [gc, &previous](const ConstraintPtr& constraint) {
         gc->dependencies.emplace_back(constraint.get());
+
+        if (auto psc = get<PackSubtypeConstraint>(*constraint); psc && psc->returns)
+        {
+            if (previous)
+                constraint->dependencies.push_back(NotNull{previous});
+
+            previous = constraint.get();
+        }
     });
 
     return Inference{generalizedTy};
@@ -2412,7 +2440,7 @@ void ConstraintGraphBuilder::checkFunctionBody(const ScopePtr& scope, AstExprFun
 
     if (nullptr != getFallthrough(fn->body))
     {
-        TypePackId empty = arena->addTypePack({}); // TODO we could have CSG retain one of these forever
+        TypePackId empty = arena->addTypePack({}); // TODO we could have CGB retain one of these forever
         addConstraint(scope, fn->location, PackSubtypeConstraint{scope->returnType, empty});
     }
 }

Analysis/src/ConstraintSolver.cpp

@@ -1259,18 +1259,13 @@ bool ConstraintSolver::tryDispatch(const FunctionCallConstraint& c, NotNull<cons
     else if (auto it = get<IntersectionType>(fn))
         fn = collapse(it).value_or(fn);
 
-    if (c.callSite)
-        (*c.astOriginalCallTypes)[c.callSite] = fn;
-
     // We don't support magic __call metamethods.
     if (std::optional<TypeId> callMm = findMetatableEntry(builtinTypes, errors, fn, "__call", constraint->location))
     {
-        std::vector<TypeId> args{fn};
+        auto [head, tail] = flatten(c.argsPack);
+        head.insert(head.begin(), fn);
 
-        for (TypeId arg : c.argsPack)
+        argsPack = arena->addTypePack(TypePack{std::move(head), tail});
-            args.push_back(arg);
-
-        argsPack = arena->addTypePack(TypePack{args, {}});
         fn = *callMm;
         asMutable(c.result)->ty.emplace<FreeTypePack>(constraint->scope);
     }
@@ -1890,7 +1885,20 @@ bool ConstraintSolver::tryDispatch(const RefineConstraint& c, NotNull<const Cons
     if (!force && !blockedTypes.empty())
         return block(blockedTypes, constraint);
 
-    asMutable(c.resultType)->ty.emplace<BoundType>(result);
+    const NormalizedType* normType = normalizer->normalize(c.type);
+
+    if (!normType)
+        reportError(NormalizationTooComplex{}, constraint->location);
+
+    if (normType && normType->shouldSuppressErrors())
+    {
+        auto resultOrError = simplifyUnion(builtinTypes, arena, result, builtinTypes->errorType).result;
+        asMutable(c.resultType)->ty.emplace<BoundType>(resultOrError);
+    }
+    else
+    {
+        asMutable(c.resultType)->ty.emplace<BoundType>(result);
+    }
 
     unblock(c.resultType, constraint->location);
 

Analysis/src/Differ.cpp

@@ -0,0 +1,273 @@
+// 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/Error.h"
+#include "Luau/ToString.h"
+#include "Luau/Type.h"
+#include <optional>
+
+namespace Luau
+{
+std::string DiffPathNode::toString() const
+{
+    switch (kind)
+    {
+    case DiffPathNode::Kind::TableProperty:
+    {
+        if (!tableProperty.has_value())
+            throw InternalCompilerError{"DiffPathNode has kind TableProperty but tableProperty is nullopt"};
+        return *tableProperty;
+        break;
+    }
+    default:
+    {
+        throw InternalCompilerError{"DiffPathNode::toString is not exhaustive"};
+    }
+    }
+}
+
+DiffPathNode DiffPathNode::constructWithTableProperty(Name tableProperty)
+{
+    return DiffPathNode{DiffPathNode::Kind::TableProperty, tableProperty, std::nullopt};
+}
+
+DiffPathNodeLeaf DiffPathNodeLeaf::nullopts()
+{
+    return DiffPathNodeLeaf{std::nullopt, std::nullopt};
+}
+
+std::string DiffPath::toString(bool prependDot) const
+{
+    std::string pathStr;
+    bool isFirstInForLoop = !prependDot;
+    for (auto node = path.rbegin(); node != path.rend(); node++)
+    {
+        if (isFirstInForLoop)
+        {
+            isFirstInForLoop = false;
+        }
+        else
+        {
+            pathStr += ".";
+        }
+        pathStr += node->toString();
+    }
+    return pathStr;
+}
+std::string DiffError::toStringALeaf(std::string rootName, const DiffPathNodeLeaf& leaf, const DiffPathNodeLeaf& otherLeaf) const
+{
+    std::string pathStr{rootName + diffPath.toString(true)};
+    switch (kind)
+    {
+    case DiffError::Kind::Normal:
+    {
+        checkNonMissingPropertyLeavesHaveNulloptTableProperty();
+        return pathStr + " has type " + Luau::toString(*leaf.ty);
+    }
+    case DiffError::Kind::MissingProperty:
+    {
+        if (leaf.ty.has_value())
+        {
+            if (!leaf.tableProperty.has_value())
+                throw InternalCompilerError{"leaf.tableProperty is nullopt"};
+            return pathStr + "." + *leaf.tableProperty + " has type " + Luau::toString(*leaf.ty);
+        }
+        else if (otherLeaf.ty.has_value())
+        {
+            if (!otherLeaf.tableProperty.has_value())
+                throw InternalCompilerError{"otherLeaf.tableProperty is nullopt"};
+            return pathStr + " is missing the property " + *otherLeaf.tableProperty;
+        }
+        throw InternalCompilerError{"Both leaf.ty and otherLeaf.ty is nullopt"};
+    }
+    default:
+    {
+        throw InternalCompilerError{"DiffPath::toStringWithLeaf is not exhaustive"};
+    }
+    }
+}
+
+void DiffError::checkNonMissingPropertyLeavesHaveNulloptTableProperty() const
+{
+    if (left.tableProperty.has_value() || right.tableProperty.has_value())
+        throw InternalCompilerError{"Non-MissingProperty DiffError should have nullopt tableProperty in both leaves"};
+}
+
+std::string getDevFixFriendlyName(TypeId ty)
+{
+    if (auto table = get<TableType>(ty))
+    {
+        if (table->name.has_value())
+            return *table->name;
+        else if (table->syntheticName.has_value())
+            return *table->syntheticName;
+    }
+    // else if (auto primitive = get<PrimitiveType>(ty))
+    //{
+    //    return "<unlabeled-symbol>";
+    //}
+    return "<unlabeled-symbol>";
+}
+
+std::string DiffError::toString() const
+{
+    std::string msg = "DiffError: these two types are not equal because the left type at " + toStringALeaf(leftRootName, left, right) +
+                      ", while the right type at " + toStringALeaf(rightRootName, right, left);
+    return msg;
+}
+
+void DiffError::checkValidInitialization(const DiffPathNodeLeaf& left, const DiffPathNodeLeaf& right)
+{
+    if (!left.ty.has_value() || !right.ty.has_value())
+    {
+        // TODO: think about whether this should be always thrown!
+        // For example, Kind::Primitive doesn't make too much sense to have a TypeId
+        // throw InternalCompilerError{"Left and Right fields are leaf nodes and must have a TypeId"};
+    }
+}
+
+void DifferResult::wrapDiffPath(DiffPathNode node)
+{
+    if (!diffError.has_value())
+    {
+        throw InternalCompilerError{"Cannot wrap diffPath because there is no diffError"};
+    }
+
+    diffError->diffPath.path.push_back(node);
+}
+
+static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId right);
+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 diffTable(DifferEnvironment& env, TypeId left, TypeId right)
+{
+    const TableType* leftTable = get<TableType>(left);
+    const TableType* rightTable = get<TableType>(right);
+
+    for (auto const& [field, value] : leftTable->props)
+    {
+        if (rightTable->props.find(field) == rightTable->props.end())
+        {
+            // left has a field the right doesn't
+            return DifferResult{DiffError{
+                DiffError::Kind::MissingProperty,
+                DiffPathNodeLeaf{value.type(), field},
+                DiffPathNodeLeaf::nullopts(),
+                getDevFixFriendlyName(env.rootLeft),
+                getDevFixFriendlyName(env.rootRight),
+            }};
+        }
+    }
+    for (auto const& [field, value] : rightTable->props)
+    {
+        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},
+                getDevFixFriendlyName(env.rootLeft), getDevFixFriendlyName(env.rootRight)}};
+        }
+    }
+    // left and right have the same set of keys
+    for (auto const& [field, leftValue] : leftTable->props)
+    {
+        auto const& rightValue = rightTable->props.at(field);
+        DifferResult differResult = diffUsingEnv(env, leftValue.type(), rightValue.type());
+        if (differResult.diffError.has_value())
+        {
+            differResult.wrapDiffPath(DiffPathNode::constructWithTableProperty(field));
+            return differResult;
+        }
+    }
+    return DifferResult{};
+}
+
+static DifferResult diffPrimitive(DifferEnvironment& env, TypeId left, TypeId right)
+{
+    const PrimitiveType* leftPrimitive = get<PrimitiveType>(left);
+    const PrimitiveType* rightPrimitive = get<PrimitiveType>(right);
+
+    if (leftPrimitive->type != rightPrimitive->type)
+    {
+        return DifferResult{DiffError{
+            DiffError::Kind::Normal,
+            DiffPathNodeLeaf{left, std::nullopt},
+            DiffPathNodeLeaf{right, std::nullopt},
+            getDevFixFriendlyName(env.rootLeft),
+            getDevFixFriendlyName(env.rootRight),
+        }};
+    }
+    return DifferResult{};
+}
+
+static DifferResult diffSingleton(DifferEnvironment& env, TypeId left, TypeId right)
+{
+    const SingletonType* leftSingleton = get<SingletonType>(left);
+    const SingletonType* rightSingleton = get<SingletonType>(right);
+
+    if (*leftSingleton != *rightSingleton)
+    {
+        return DifferResult{DiffError{
+            DiffError::Kind::Normal,
+            DiffPathNodeLeaf{left, std::nullopt},
+            DiffPathNodeLeaf{right, std::nullopt},
+            getDevFixFriendlyName(env.rootLeft),
+            getDevFixFriendlyName(env.rootRight),
+        }};
+    }
+    return DifferResult{};
+}
+
+static DifferResult diffUsingEnv(DifferEnvironment& env, TypeId left, TypeId right)
+{
+    left = follow(left);
+    right = follow(right);
+
+    if (left->ty.index() != right->ty.index())
+    {
+        return DifferResult{DiffError{
+            DiffError::Kind::Normal,
+            DiffPathNodeLeaf{left, std::nullopt},
+            DiffPathNodeLeaf{right, std::nullopt},
+            getDevFixFriendlyName(env.rootLeft),
+            getDevFixFriendlyName(env.rootRight),
+        }};
+    }
+
+    // Both left and right are the same variant
+
+    if (isSimple(left))
+    {
+        if (auto lp = get<PrimitiveType>(left))
+            return diffPrimitive(env, left, right);
+        else if (auto ls = get<SingletonType>(left))
+        {
+            return diffSingleton(env, left, right);
+        }
+
+        throw InternalCompilerError{"Unimplemented Simple TypeId variant for diffing"};
+    }
+
+    // Both left and right are the same non-Simple
+
+    if (auto lt = get<TableType>(left))
+    {
+        return diffTable(env, left, right);
+    }
+    throw InternalCompilerError{"Unimplemented non-simple TypeId variant for diffing"};
+}
+
+DifferResult diff(TypeId ty1, TypeId ty2)
+{
+    DifferEnvironment differEnv{ty1, ty2};
+    return diffUsingEnv(differEnv, ty1, ty2);
+}
+
+bool isSimple(TypeId ty)
+{
+    ty = follow(ty);
+    // TODO: think about GenericType, etc.
+    return get<PrimitiveType>(ty) || get<SingletonType>(ty);
+}
+
+} // namespace Luau

Analysis/src/Frontend.cpp

@@ -415,6 +415,18 @@ Frontend::Frontend(FileResolver* fileResolver, ConfigResolver* configResolver, c
 {
 }
 
+void Frontend::parse(const ModuleName& name)
+{
+    LUAU_TIMETRACE_SCOPE("Frontend::parse", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("name", name.c_str());
+
+    if (getCheckResult(name, false, false))
+        return;
+
+    std::vector<ModuleName> buildQueue;
+    parseGraph(buildQueue, name, false);
+}
+
 CheckResult Frontend::check(const ModuleName& name, std::optional<FrontendOptions> optionOverride)
 {
     LUAU_TIMETRACE_SCOPE("Frontend::check", "Frontend");

Analysis/src/Normalize.cpp

@@ -18,6 +18,7 @@ LUAU_FASTFLAGVARIABLE(DebugLuauCheckNormalizeInvariant, false)
 LUAU_FASTINTVARIABLE(LuauNormalizeIterationLimit, 1200);
 LUAU_FASTINTVARIABLE(LuauNormalizeCacheLimit, 100000);
 LUAU_FASTFLAGVARIABLE(LuauNormalizeBlockedTypes, false);
+LUAU_FASTFLAGVARIABLE(LuauNormalizeCyclicUnions, false);
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
 LUAU_FASTFLAG(LuauTransitiveSubtyping)
 LUAU_FASTFLAG(DebugLuauReadWriteProperties)
@@ -247,6 +248,11 @@ bool NormalizedType::isSubtypeOfString() const
            !hasTables() && !hasFunctions() && !hasTyvars();
 }
 
+bool NormalizedType::shouldSuppressErrors() const
+{
+    return hasErrors() || get<AnyType>(tops);
+}
+
 bool NormalizedType::hasTops() const
 {
     return !get<NeverType>(tops);
@@ -690,7 +696,8 @@ const NormalizedType* Normalizer::normalize(TypeId ty)
         return found->second.get();
 
     NormalizedType norm{builtinTypes};
-    if (!unionNormalWithTy(norm, ty))
+    std::unordered_set<TypeId> seenSetTypes;
+    if (!unionNormalWithTy(norm, ty, seenSetTypes))
         return nullptr;
     std::unique_ptr<NormalizedType> uniq = std::make_unique<NormalizedType>(std::move(norm));
     const NormalizedType* result = uniq.get();
@@ -705,9 +712,12 @@ bool Normalizer::normalizeIntersections(const std::vector<TypeId>& intersections
     NormalizedType norm{builtinTypes};
     norm.tops = builtinTypes->anyType;
     // Now we need to intersect the two types
+    std::unordered_set<TypeId> seenSetTypes;
     for (auto ty : intersections)
-        if (!intersectNormalWithTy(norm, ty))
+    {
+        if (!intersectNormalWithTy(norm, ty, seenSetTypes))
             return false;
+    }
 
     if (!unionNormals(outType, norm))
         return false;
@@ -1438,13 +1448,14 @@ bool Normalizer::withinResourceLimits()
 }
 
 // See above for an explaination of `ignoreSmallerTyvars`.
-bool Normalizer::unionNormalWithTy(NormalizedType& here, TypeId there, int ignoreSmallerTyvars)
+bool Normalizer::unionNormalWithTy(NormalizedType& here, TypeId there, std::unordered_set<TypeId>& seenSetTypes, int ignoreSmallerTyvars)
 {
     RecursionCounter _rc(&sharedState->counters.recursionCount);
     if (!withinResourceLimits())
         return false;
 
     there = follow(there);
+
     if (get<AnyType>(there) || get<UnknownType>(there))
     {
         TypeId tops = unionOfTops(here.tops, there);
@@ -1465,9 +1476,23 @@ bool Normalizer::unionNormalWithTy(NormalizedType& here, TypeId there, int ignor
     }
     else if (const UnionType* utv = get<UnionType>(there))
     {
+        if (FFlag::LuauNormalizeCyclicUnions)
+        {
+            if (seenSetTypes.count(there))
+                return true;
+            seenSetTypes.insert(there);
+        }
+
         for (UnionTypeIterator it = begin(utv); it != end(utv); ++it)
-            if (!unionNormalWithTy(here, *it))
+        {
+            if (!unionNormalWithTy(here, *it, seenSetTypes))
+            {
+                seenSetTypes.erase(there);
                 return false;
+            }
+        }
+
+        seenSetTypes.erase(there);
         return true;
     }
     else if (const IntersectionType* itv = get<IntersectionType>(there))
@@ -1475,8 +1500,10 @@ bool Normalizer::unionNormalWithTy(NormalizedType& here, TypeId there, int ignor
         NormalizedType norm{builtinTypes};
         norm.tops = builtinTypes->anyType;
         for (IntersectionTypeIterator it = begin(itv); it != end(itv); ++it)
-            if (!intersectNormalWithTy(norm, *it))
+        {
+            if (!intersectNormalWithTy(norm, *it, seenSetTypes))
                 return false;
+        }
         return unionNormals(here, norm);
     }
     else if (FFlag::LuauTransitiveSubtyping && get<UnknownType>(here.tops))
@@ -1560,7 +1587,7 @@ bool Normalizer::unionNormalWithTy(NormalizedType& here, TypeId there, int ignor
         LUAU_ASSERT(!"Unreachable");
 
     for (auto& [tyvar, intersect] : here.tyvars)
-        if (!unionNormalWithTy(*intersect, there, tyvarIndex(tyvar)))
+        if (!unionNormalWithTy(*intersect, there, seenSetTypes, tyvarIndex(tyvar)))
             return false;
 
     assertInvariant(here);
@@ -2463,12 +2490,12 @@ void Normalizer::intersectFunctions(NormalizedFunctionType& heres, const Normali
     }
 }
 
-bool Normalizer::intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there)
+bool Normalizer::intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there, std::unordered_set<TypeId>& seenSetTypes)
 {
     for (auto it = here.begin(); it != here.end();)
     {
         NormalizedType& inter = *it->second;
-        if (!intersectNormalWithTy(inter, there))
+        if (!intersectNormalWithTy(inter, there, seenSetTypes))
             return false;
         if (isShallowInhabited(inter))
             ++it;
@@ -2541,13 +2568,14 @@ bool Normalizer::intersectNormals(NormalizedType& here, const NormalizedType& th
     return true;
 }
 
-bool Normalizer::intersectNormalWithTy(NormalizedType& here, TypeId there)
+bool Normalizer::intersectNormalWithTy(NormalizedType& here, TypeId there, std::unordered_set<TypeId>& seenSetTypes)
 {
     RecursionCounter _rc(&sharedState->counters.recursionCount);
     if (!withinResourceLimits())
         return false;
 
     there = follow(there);
+
     if (get<AnyType>(there) || get<UnknownType>(there))
     {
         here.tops = intersectionOfTops(here.tops, there);
@@ -2556,20 +2584,20 @@ bool Normalizer::intersectNormalWithTy(NormalizedType& here, TypeId there)
     else if (!get<NeverType>(here.tops))
     {
         clearNormal(here);
-        return unionNormalWithTy(here, there);
+        return unionNormalWithTy(here, there, seenSetTypes);
     }
     else if (const UnionType* utv = get<UnionType>(there))
     {
         NormalizedType norm{builtinTypes};
         for (UnionTypeIterator it = begin(utv); it != end(utv); ++it)
-            if (!unionNormalWithTy(norm, *it))
+            if (!unionNormalWithTy(norm, *it, seenSetTypes))
                 return false;
         return intersectNormals(here, norm);
     }
     else if (const IntersectionType* itv = get<IntersectionType>(there))
     {
         for (IntersectionTypeIterator it = begin(itv); it != end(itv); ++it)
-            if (!intersectNormalWithTy(here, *it))
+            if (!intersectNormalWithTy(here, *it, seenSetTypes))
                 return false;
         return true;
     }
@@ -2691,7 +2719,7 @@ bool Normalizer::intersectNormalWithTy(NormalizedType& here, TypeId there)
             return true;
         }
         else if (auto nt = get<NegationType>(t))
-            return intersectNormalWithTy(here, nt->ty);
+            return intersectNormalWithTy(here, nt->ty, seenSetTypes);
         else
         {
             // TODO negated unions, intersections, table, and function.
@@ -2706,7 +2734,7 @@ bool Normalizer::intersectNormalWithTy(NormalizedType& here, TypeId there)
     else
         LUAU_ASSERT(!"Unreachable");
 
-    if (!intersectTyvarsWithTy(tyvars, there))
+    if (!intersectTyvarsWithTy(tyvars, there, seenSetTypes))
         return false;
     here.tyvars = std::move(tyvars);
 

Analysis/src/Substitution.cpp

@@ -191,16 +191,8 @@ static TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool a
         {
             if (alwaysClone)
             {
-                if (FFlag::LuauTypecheckClassTypeIndexers)
+                ClassType clone{a.name, a.props, a.parent, a.metatable, a.tags, a.userData, a.definitionModuleName, a.indexer};
-                {
+                return dest.addType(std::move(clone));
-                    ClassType clone{a.name, a.props, a.parent, a.metatable, a.tags, a.userData, a.definitionModuleName, a.indexer};
-                    return dest.addType(std::move(clone));
-                }
-                else
-                {
-                    ClassType clone{a.name, a.props, a.parent, a.metatable, a.tags, a.userData, a.definitionModuleName};
-                    return dest.addType(std::move(clone));
-                }
             }
             else
                 return ty;
@@ -316,13 +308,10 @@ void Tarjan::visitChildren(TypeId ty, int index)
         if (ctv->metatable)
             visitChild(*ctv->metatable);
 
-        if (FFlag::LuauTypecheckClassTypeIndexers)
+        if (ctv->indexer)
         {
-            if (ctv->indexer)
+            visitChild(ctv->indexer->indexType);
-            {
+            visitChild(ctv->indexer->indexResultType);
-                visitChild(ctv->indexer->indexType);
-                visitChild(ctv->indexer->indexResultType);
-            }
         }
     }
     else if (const NegationType* ntv = get<NegationType>(ty))
@@ -1038,13 +1027,10 @@ void Substitution::replaceChildren(TypeId ty)
         if (ctv->metatable)
             ctv->metatable = replace(*ctv->metatable);
 
-        if (FFlag::LuauTypecheckClassTypeIndexers)
+        if (ctv->indexer)
         {
-            if (ctv->indexer)
+            ctv->indexer->indexType = replace(ctv->indexer->indexType);
-            {
+            ctv->indexer->indexResultType = replace(ctv->indexer->indexResultType);
-                ctv->indexer->indexType = replace(ctv->indexer->indexType);
-                ctv->indexer->indexResultType = replace(ctv->indexer->indexResultType);
-            }
         }
     }
     else if (NegationType* ntv = getMutable<NegationType>(ty))

Analysis/src/ToDot.cpp

@@ -258,13 +258,10 @@ void StateDot::visitChildren(TypeId ty, int index)
         if (ctv->metatable)
             visitChild(*ctv->metatable, index, "[metatable]");
 
-        if (FFlag::LuauTypecheckClassTypeIndexers)
+        if (ctv->indexer)
         {
-            if (ctv->indexer)
+            visitChild(ctv->indexer->indexType, index, "[index]");
-            {
+            visitChild(ctv->indexer->indexResultType, index, "[value]");
-                visitChild(ctv->indexer->indexType, index, "[index]");
-                visitChild(ctv->indexer->indexResultType, index, "[value]");
-            }
         }
     }
     else if (const SingletonType* stv = get<SingletonType>(ty))

Analysis/src/TypeChecker2.cpp

@@ -1090,6 +1090,11 @@ struct TypeChecker2
             args.head.push_back(lookupType(indexExpr->expr));
             argLocs.push_back(indexExpr->expr->location);
         }
+        else if (findMetatableEntry(builtinTypes, module->errors, *originalCallTy, "__call", call->func->location))
+        {
+            args.head.insert(args.head.begin(), lookupType(call->func));
+            argLocs.push_back(call->func->location);
+        }
 
         for (size_t i = 0; i < call->args.size; ++i)
         {

Analysis/src/TypeInfer.cpp

@@ -38,7 +38,6 @@ LUAU_FASTFLAGVARIABLE(LuauAllowIndexClassParameters, false)
 LUAU_FASTFLAG(LuauOccursIsntAlwaysFailure)
 LUAU_FASTFLAGVARIABLE(LuauTypecheckTypeguards, false)
 LUAU_FASTFLAGVARIABLE(LuauTinyControlFlowAnalysis, false)
-LUAU_FASTFLAGVARIABLE(LuauTypecheckClassTypeIndexers, false)
 LUAU_FASTFLAGVARIABLE(LuauAlwaysCommitInferencesOfFunctionCalls, false)
 LUAU_FASTFLAG(LuauParseDeclareClassIndexer)
 LUAU_FASTFLAGVARIABLE(LuauIndexTableIntersectionStringExpr, false)
@@ -2108,21 +2107,18 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromTypeImpl(
         if (prop)
             return prop->type();
 
-        if (FFlag::LuauTypecheckClassTypeIndexers)
+        if (auto indexer = cls->indexer)
         {
-            if (auto indexer = cls->indexer)
+            // TODO: Property lookup should work with string singletons or unions thereof as the indexer key type.
-            {
+            ErrorVec errors = tryUnify(stringType, indexer->indexType, scope, location);
-                // TODO: Property lookup should work with string singletons or unions thereof as the indexer key type.
-                ErrorVec errors = tryUnify(stringType, indexer->indexType, scope, location);
 
-                if (errors.empty())
+            if (errors.empty())
-                    return indexer->indexResultType;
+                return indexer->indexResultType;
 
-                if (addErrors)
+            if (addErrors)
-                    reportError(location, UnknownProperty{type, name});
+                reportError(location, UnknownProperty{type, name});
 
-                return std::nullopt;
+            return std::nullopt;
-            }
         }
     }
     else if (const UnionType* utv = get<UnionType>(type))
@@ -3313,38 +3309,24 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
     }
     else if (const ClassType* lhsClass = get<ClassType>(lhs))
     {
-        if (FFlag::LuauTypecheckClassTypeIndexers)
+        if (const Property* prop = lookupClassProp(lhsClass, name))
         {
-            if (const Property* prop = lookupClassProp(lhsClass, name))
-            {
-                return prop->type();
-            }
-
-            if (auto indexer = lhsClass->indexer)
-            {
-                Unifier state = mkUnifier(scope, expr.location);
-                state.tryUnify(stringType, indexer->indexType);
-                if (state.errors.empty())
-                {
-                    state.log.commit();
-                    return indexer->indexResultType;
-                }
-            }
-
-            reportError(TypeError{expr.location, UnknownProperty{lhs, name}});
-            return errorRecoveryType(scope);
-        }
-        else
-        {
-            const Property* prop = lookupClassProp(lhsClass, name);
-            if (!prop)
-            {
-                reportError(TypeError{expr.location, UnknownProperty{lhs, name}});
-                return errorRecoveryType(scope);
-            }
-
             return prop->type();
         }
+
+        if (auto indexer = lhsClass->indexer)
+        {
+            Unifier state = mkUnifier(scope, expr.location);
+            state.tryUnify(stringType, indexer->indexType);
+            if (state.errors.empty())
+            {
+                state.log.commit();
+                return indexer->indexResultType;
+            }
+        }
+
+        reportError(TypeError{expr.location, UnknownProperty{lhs, name}});
+        return errorRecoveryType(scope);
     }
     else if (get<IntersectionType>(lhs))
     {
@@ -3386,32 +3368,19 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
     {
         if (const ClassType* exprClass = get<ClassType>(exprType))
         {
-            if (FFlag::LuauTypecheckClassTypeIndexers)
+            if (const Property* prop = lookupClassProp(exprClass, value->value.data))
             {
-                if (const Property* prop = lookupClassProp(exprClass, value->value.data))
-                {
-                    return prop->type();
-                }
-
-                if (auto indexer = exprClass->indexer)
-                {
-                    unify(stringType, indexer->indexType, scope, expr.index->location);
-                    return indexer->indexResultType;
-                }
-
-                reportError(TypeError{expr.location, UnknownProperty{exprType, value->value.data}});
-                return errorRecoveryType(scope);
-            }
-            else
-            {
-                const Property* prop = lookupClassProp(exprClass, value->value.data);
-                if (!prop)
-                {
-                    reportError(TypeError{expr.location, UnknownProperty{exprType, value->value.data}});
-                    return errorRecoveryType(scope);
-                }
                 return prop->type();
             }
+
+            if (auto indexer = exprClass->indexer)
+            {
+                unify(stringType, indexer->indexType, scope, expr.index->location);
+                return indexer->indexResultType;
+            }
+
+            reportError(TypeError{expr.location, UnknownProperty{exprType, value->value.data}});
+            return errorRecoveryType(scope);
         }
         else if (FFlag::LuauIndexTableIntersectionStringExpr && get<IntersectionType>(exprType))
         {
@@ -3430,15 +3399,12 @@ TypeId TypeChecker::checkLValueBinding(const ScopePtr& scope, const AstExprIndex
     }
     else
     {
-        if (FFlag::LuauTypecheckClassTypeIndexers)
+        if (const ClassType* exprClass = get<ClassType>(exprType))
         {
-            if (const ClassType* exprClass = get<ClassType>(exprType))
+            if (auto indexer = exprClass->indexer)
             {
-                if (auto indexer = exprClass->indexer)
+                unify(indexType, indexer->indexType, scope, expr.index->location);
-                {
+                return indexer->indexResultType;
-                    unify(indexType, indexer->indexType, scope, expr.index->location);
-                    return indexer->indexResultType;
-                }
             }
         }
 

Ast/include/Luau/Location.h

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include <string>
 namespace Luau
 {
 
@@ -38,6 +39,11 @@ 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/include/Luau/TimeTrace.h

@@ -4,6 +4,7 @@
 #include "Luau/Common.h"
 
 #include <vector>
+#include <memory>
 
 #include <stdint.h>
 
@@ -54,7 +55,7 @@ struct Event
 struct GlobalContext;
 struct ThreadContext;
 
-GlobalContext& getGlobalContext();
+std::shared_ptr<GlobalContext> getGlobalContext();
 
 uint16_t createToken(GlobalContext& context, const char* name, const char* category);
 uint32_t createThread(GlobalContext& context, ThreadContext* threadContext);
@@ -66,7 +67,7 @@ struct ThreadContext
     ThreadContext()
         : globalContext(getGlobalContext())
     {
-        threadId = createThread(globalContext, this);
+        threadId = createThread(*globalContext, this);
     }
 
     ~ThreadContext()
@@ -74,16 +75,16 @@ struct ThreadContext
         if (!events.empty())
             flushEvents();
 
-        releaseThread(globalContext, this);
+        releaseThread(*globalContext, this);
     }
 
     void flushEvents()
     {
-        static uint16_t flushToken = createToken(globalContext, "flushEvents", "TimeTrace");
+        static uint16_t flushToken = createToken(*globalContext, "flushEvents", "TimeTrace");
 
         events.push_back({EventType::Enter, flushToken, {getClockMicroseconds()}});
 
-        TimeTrace::flushEvents(globalContext, threadId, events, data);
+        TimeTrace::flushEvents(*globalContext, threadId, events, data);
 
         events.clear();
         data.clear();
@@ -125,7 +126,7 @@ struct ThreadContext
         events.push_back({EventType::ArgValue, 0, {pos}});
     }
 
-    GlobalContext& globalContext;
+    std::shared_ptr<GlobalContext> globalContext;
     uint32_t threadId;
     std::vector<Event> events;
     std::vector<char> data;

Ast/src/Location.cpp

@@ -1,5 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Location.h"
+#include <string>
 
 namespace Luau
 {
@@ -128,4 +129,12 @@ 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

@@ -90,7 +90,6 @@ namespace TimeTrace
 {
 struct GlobalContext
 {
-    GlobalContext() = default;
     ~GlobalContext()
     {
         // Ideally we would want all ThreadContext destructors to run
@@ -110,11 +109,15 @@ struct GlobalContext
     uint32_t nextThreadId = 0;
     std::vector<Token> tokens;
     FILE* traceFile = nullptr;
+    
+private:
+    friend std::shared_ptr<GlobalContext> getGlobalContext();
+    GlobalContext() = default;
 };
 
-GlobalContext& getGlobalContext()
+std::shared_ptr<GlobalContext> getGlobalContext()
 {
-    static GlobalContext context;
+    static std::shared_ptr<GlobalContext> context = std::shared_ptr<GlobalContext>{new GlobalContext};
     return context;
 }
 
@@ -261,7 +264,7 @@ ThreadContext& getThreadContext()
 
 uint16_t createScopeData(const char* name, const char* category)
 {
-    return createToken(Luau::TimeTrace::getGlobalContext(), name, category);
+    return createToken(*Luau::TimeTrace::getGlobalContext(), name, category);
 }
 } // namespace TimeTrace
 } // namespace Luau

CodeGen/include/Luau/IrData.h

@@ -236,6 +236,10 @@ enum class IrCmd : uint8_t
     // A: pointer (Table)
     TABLE_LEN,
 
+    // Get string length
+    // A: pointer (string)
+    STRING_LEN,
+
     // Allocate new table
     // A: int (array element count)
     // B: int (node element count)
@@ -361,8 +365,10 @@ enum class IrCmd : uint8_t
     // Guard against tag mismatch
     // A, B: tag
     // C: block/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
+    // When undef is specified instead of a block, execution is aborted on check failure; if D is true, execution is continued in VM interpreter
+    // instead.
     CHECK_TAG,
 
     // Guard against readonly table
@@ -377,9 +383,9 @@ enum class IrCmd : uint8_t
     // When undef is specified instead of a block, execution is aborted on check failure
     CHECK_NO_METATABLE,
 
-    // Guard against executing in unsafe environment
+    // Guard against executing in unsafe environment, exits to VM on check failure
-    // A: block/undef
+    // A: unsigned int (pcpos)/undef
-    // When undef is specified instead of a block, execution is aborted on check failure
+    // When undef is specified, execution is aborted on check failure
     CHECK_SAFE_ENV,
 
     // Guard against index overflowing the table array size
@@ -610,7 +616,6 @@ struct IrConst
 
     union
     {
-        bool valueBool;
         int valueInt;
         unsigned valueUint;
         double valueDouble;

CodeGen/include/Luau/IrRegAllocX64.h

@@ -39,6 +39,8 @@ struct IrRegAllocX64
     RegisterX64 allocRegOrReuse(SizeX64 size, uint32_t instIdx, std::initializer_list<IrOp> oprefs);
     RegisterX64 takeReg(RegisterX64 reg, uint32_t instIdx);
 
+    bool canTakeReg(RegisterX64 reg) const;
+
     void freeReg(RegisterX64 reg);
     void freeLastUseReg(IrInst& target, uint32_t instIdx);
     void freeLastUseRegs(const IrInst& inst, uint32_t instIdx);

CodeGen/include/Luau/IrUtils.h

@@ -167,6 +167,7 @@ inline bool hasResult(IrCmd cmd)
     case IrCmd::ABS_NUM:
     case IrCmd::NOT_ANY:
     case IrCmd::TABLE_LEN:
+    case IrCmd::STRING_LEN:
     case IrCmd::NEW_TABLE:
     case IrCmd::DUP_TABLE:
     case IrCmd::TRY_NUM_TO_INDEX:
@@ -256,5 +257,8 @@ void foldConstants(IrBuilder& build, IrFunction& function, IrBlock& block, uint3
 
 uint32_t getNativeContextOffset(int bfid);
 
+// Cleans up blocks that were created with no users
+void killUnusedBlocks(IrFunction& function);
+
 } // namespace CodeGen
 } // namespace Luau

CodeGen/src/CodeGenA64.cpp

@@ -24,6 +24,15 @@ struct EntryLocations
     Label epilogueStart;
 };
 
+static void emitClearNativeFlag(AssemblyBuilderA64& build)
+{
+    build.ldr(x0, mem(rState, offsetof(lua_State, ci)));
+    build.ldr(w1, mem(x0, offsetof(CallInfo, flags)));
+    build.mov(w2, ~LUA_CALLINFO_NATIVE);
+    build.and_(w1, w1, w2);
+    build.str(w1, mem(x0, offsetof(CallInfo, flags)));
+}
+
 static void emitExit(AssemblyBuilderA64& build, bool continueInVm)
 {
     build.mov(x0, continueInVm);
@@ -31,6 +40,16 @@ static void emitExit(AssemblyBuilderA64& build, bool continueInVm)
     build.br(x1);
 }
 
+static void emitUpdatePcAndContinueInVm(AssemblyBuilderA64& build)
+{
+    // x0 = pcpos * sizeof(Instruction)
+    build.add(x0, rCode, x0);
+    build.ldr(x1, mem(rState, offsetof(lua_State, ci)));
+    build.str(x0, mem(x1, offsetof(CallInfo, savedpc)));
+
+    emitExit(build, /* continueInVm */ true);
+}
+
 static void emitInterrupt(AssemblyBuilderA64& build)
 {
     // x0 = pc offset
@@ -286,6 +305,11 @@ bool initHeaderFunctions(NativeState& data)
 
 void assembleHelpers(AssemblyBuilderA64& build, ModuleHelpers& helpers)
 {
+    if (build.logText)
+        build.logAppend("; exitContinueVmClearNativeFlag\n");
+    build.setLabel(helpers.exitContinueVmClearNativeFlag);
+    emitClearNativeFlag(build);
+
     if (build.logText)
         build.logAppend("; exitContinueVm\n");
     build.setLabel(helpers.exitContinueVm);
@@ -296,6 +320,11 @@ void assembleHelpers(AssemblyBuilderA64& build, ModuleHelpers& helpers)
     build.setLabel(helpers.exitNoContinueVm);
     emitExit(build, /* continueInVm */ false);
 
+    if (build.logText)
+        build.logAppend("; updatePcAndContinueInVm\n");
+    build.setLabel(helpers.updatePcAndContinueInVm);
+    emitUpdatePcAndContinueInVm(build);
+
     if (build.logText)
         build.logAppend("; reentry\n");
     build.setLabel(helpers.reentry);

CodeGen/src/CodeGenLower.h

@@ -221,6 +221,8 @@ inline bool lowerIr(A64::AssemblyBuilderA64& build, IrBuilder& ir, ModuleHelpers
 template<typename AssemblyBuilder>
 inline bool lowerFunction(IrBuilder& ir, AssemblyBuilder& build, ModuleHelpers& helpers, Proto* proto, AssemblyOptions options)
 {
+    killUnusedBlocks(ir.function);
+
     computeCfgInfo(ir.function);
 
     if (!FFlag::DebugCodegenNoOpt)

CodeGen/src/CodeGenX64.cpp

@@ -180,6 +180,11 @@ bool initHeaderFunctions(NativeState& data)
 
 void assembleHelpers(X64::AssemblyBuilderX64& build, ModuleHelpers& helpers)
 {
+    if (build.logText)
+        build.logAppend("; exitContinueVmClearNativeFlag\n");
+    build.setLabel(helpers.exitContinueVmClearNativeFlag);
+    emitClearNativeFlag(build);
+
     if (build.logText)
         build.logAppend("; exitContinueVm\n");
     build.setLabel(helpers.exitContinueVm);
@@ -190,6 +195,11 @@ void assembleHelpers(X64::AssemblyBuilderX64& build, ModuleHelpers& helpers)
     build.setLabel(helpers.exitNoContinueVm);
     emitExit(build, /* continueInVm */ false);
 
+    if (build.logText)
+        build.logAppend("; updatePcAndContinueInVm\n");
+    build.setLabel(helpers.updatePcAndContinueInVm);
+    emitUpdatePcAndContinueInVm(build);
+
     if (build.logText)
         build.logAppend("; continueCallInVm\n");
     build.setLabel(helpers.continueCallInVm);

CodeGen/src/EmitCommon.h

@@ -24,6 +24,8 @@ struct ModuleHelpers
     // A64/X64
     Label exitContinueVm;
     Label exitNoContinueVm;
+    Label exitContinueVmClearNativeFlag;
+    Label updatePcAndContinueInVm;
     Label return_;
     Label interrupt;
 

CodeGen/src/EmitCommonX64.cpp

@@ -268,6 +268,13 @@ void callStepGc(IrRegAllocX64& regs, AssemblyBuilderX64& build)
     build.setLabel(skip);
 }
 
+
+void emitClearNativeFlag(AssemblyBuilderX64& build)
+{
+    build.mov(rax, qword[rState + offsetof(lua_State, ci)]);
+    build.and_(dword[rax + offsetof(CallInfo, flags)], ~LUA_CALLINFO_NATIVE);
+}
+
 void emitExit(AssemblyBuilderX64& build, bool continueInVm)
 {
     if (continueInVm)
@@ -345,6 +352,16 @@ void emitFallback(IrRegAllocX64& regs, AssemblyBuilderX64& build, int offset, in
     emitUpdateBase(build);
 }
 
+void emitUpdatePcAndContinueInVm(AssemblyBuilderX64& build)
+{
+    // edx = pcpos * sizeof(Instruction)
+    build.add(rdx, sCode);
+    build.mov(rax, qword[rState + offsetof(lua_State, ci)]);
+    build.mov(qword[rax + offsetof(CallInfo, savedpc)], rdx);
+
+    emitExit(build, /* continueInVm */ true);
+}
+
 void emitContinueCallInVm(AssemblyBuilderX64& build)
 {
     RegisterX64 proto = rcx; // Sync with emitInstCall

CodeGen/src/EmitCommonX64.h

@@ -175,11 +175,13 @@ void callBarrierObject(IrRegAllocX64& regs, AssemblyBuilderX64& build, RegisterX
 void callBarrierTableFast(IrRegAllocX64& regs, AssemblyBuilderX64& build, RegisterX64 table, IrOp tableOp);
 void callStepGc(IrRegAllocX64& regs, AssemblyBuilderX64& build);
 
+void emitClearNativeFlag(AssemblyBuilderX64& build);
 void emitExit(AssemblyBuilderX64& build, bool continueInVm);
 void emitUpdateBase(AssemblyBuilderX64& build);
 void emitInterrupt(AssemblyBuilderX64& build);
 void emitFallback(IrRegAllocX64& regs, AssemblyBuilderX64& build, int offset, int pcpos);
 
+void emitUpdatePcAndContinueInVm(AssemblyBuilderX64& build);
 void emitContinueCallInVm(AssemblyBuilderX64& build);
 
 void emitReturn(AssemblyBuilderX64& build, ModuleHelpers& helpers);

CodeGen/src/EmitInstructionX64.cpp

@@ -90,6 +90,11 @@ void emitInstCall(AssemblyBuilderX64& build, ModuleHelpers& helpers, int ra, int
         build.mov(qword[rState + offsetof(lua_State, top)], argi);
         build.setLabel(skipVararg);
 
+        // Keep executing new function
+        // ci->savedpc = p->code;
+        build.mov(rax, qword[proto + offsetof(Proto, code)]);
+        build.mov(qword[ci + offsetof(CallInfo, savedpc)], rax);
+
         // Get native function entry
         build.mov(rax, qword[proto + offsetof(Proto, exectarget)]);
         build.test(rax, rax);

CodeGen/src/IrBuilder.cpp

@@ -22,6 +22,82 @@ IrBuilder::IrBuilder()
 {
 }
 
+static void buildArgumentTypeChecks(IrBuilder& build, Proto* proto)
+{
+    if (!proto->typeinfo || proto->numparams == 0)
+        return;
+
+    for (int i = 0; i < proto->numparams; ++i)
+    {
+        uint8_t et = proto->typeinfo[2 + i];
+
+        uint8_t tag = et & ~LBC_TYPE_OPTIONAL_BIT;
+        uint8_t optional = et & LBC_TYPE_OPTIONAL_BIT;
+
+        if (tag == LBC_TYPE_ANY)
+            continue;
+
+        IrOp load = build.inst(IrCmd::LOAD_TAG, build.vmReg(i));
+
+        IrOp nextCheck;
+        if (optional)
+        {
+            nextCheck = build.block(IrBlockKind::Internal);
+            IrOp fallbackCheck = build.block(IrBlockKind::Internal);
+
+            build.inst(IrCmd::JUMP_EQ_TAG, load, build.constTag(LUA_TNIL), nextCheck, fallbackCheck);
+
+            build.beginBlock(fallbackCheck);
+        }
+
+        switch (tag)
+        {
+        case LBC_TYPE_NIL:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TNIL), build.undef(), build.constInt(1));
+            break;
+        case LBC_TYPE_BOOLEAN:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TBOOLEAN), build.undef(), build.constInt(1));
+            break;
+        case LBC_TYPE_NUMBER:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TNUMBER), build.undef(), build.constInt(1));
+            break;
+        case LBC_TYPE_STRING:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TSTRING), build.undef(), build.constInt(1));
+            break;
+        case LBC_TYPE_TABLE:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TTABLE), build.undef(), build.constInt(1));
+            break;
+        case LBC_TYPE_FUNCTION:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TFUNCTION), build.undef(), build.constInt(1));
+            break;
+        case LBC_TYPE_THREAD:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TTHREAD), build.undef(), build.constInt(1));
+            break;
+        case LBC_TYPE_USERDATA:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TUSERDATA), build.undef(), build.constInt(1));
+            break;
+        case LBC_TYPE_VECTOR:
+            build.inst(IrCmd::CHECK_TAG, load, build.constTag(LUA_TVECTOR), build.undef(), build.constInt(1));
+            break;
+        }
+
+        if (optional)
+        {
+            build.inst(IrCmd::JUMP, nextCheck);
+            build.beginBlock(nextCheck);
+        }
+    }
+
+    // If the last argument is optional, we can skip creating a new internal block since one will already have been created.
+    if (!(proto->typeinfo[2 + proto->numparams - 1] & LBC_TYPE_OPTIONAL_BIT))
+    {
+        IrOp next = build.block(IrBlockKind::Internal);
+        build.inst(IrCmd::JUMP, next);
+
+        build.beginBlock(next);
+    }
+}
+
 void IrBuilder::buildFunctionIr(Proto* proto)
 {
     function.proto = proto;
@@ -47,6 +123,9 @@ void IrBuilder::buildFunctionIr(Proto* proto)
         if (instIndexToBlock[i] != kNoAssociatedBlockIndex)
             beginBlock(blockAtInst(i));
 
+        if (i == 0)
+            buildArgumentTypeChecks(*this, proto);
+
         // We skip dead bytecode instructions when they appear after block was already terminated
         if (!inTerminatedBlock)
             translateInst(op, pc, i);

CodeGen/src/IrCallWrapperX64.cpp

@@ -212,7 +212,13 @@ RegisterX64 IrCallWrapperX64::suggestNextArgumentRegister(SizeX64 size) const
 {
     OperandX64 target = getNextArgumentTarget(size);
 
-    return target.cat == CategoryX64::reg ? regs.takeReg(target.base, kInvalidInstIdx) : regs.allocReg(size, kInvalidInstIdx);
+    if (target.cat != CategoryX64::reg)
+        return regs.allocReg(size, kInvalidInstIdx);
+
+    if (!regs.canTakeReg(target.base))
+        return regs.allocReg(size, kInvalidInstIdx);
+
+    return regs.takeReg(target.base, kInvalidInstIdx);
 }
 
 OperandX64 IrCallWrapperX64::getNextArgumentTarget(SizeX64 size) const

CodeGen/src/IrDump.cpp

@@ -163,6 +163,8 @@ const char* getCmdName(IrCmd cmd)
         return "JUMP_SLOT_MATCH";
     case IrCmd::TABLE_LEN:
         return "TABLE_LEN";
+    case IrCmd::STRING_LEN:
+        return "STRING_LEN";
     case IrCmd::NEW_TABLE:
         return "NEW_TABLE";
     case IrCmd::DUP_TABLE:

CodeGen/src/IrLoweringA64.cpp

@@ -376,8 +376,9 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
             build.add(inst.regA64, regOp(inst.b), uint16_t(intOp(inst.a)));
         else
         {
-            RegisterA64 temp = tempInt(inst.b);
+            RegisterA64 temp1 = tempInt(inst.a);
-            build.add(inst.regA64, regOp(inst.a), temp);
+            RegisterA64 temp2 = tempInt(inst.b);
+            build.add(inst.regA64, temp1, temp2);
         }
         break;
     case IrCmd::SUB_INT:
@@ -386,8 +387,9 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
             build.sub(inst.regA64, regOp(inst.a), uint16_t(intOp(inst.b)));
         else
         {
-            RegisterA64 temp = tempInt(inst.b);
+            RegisterA64 temp1 = tempInt(inst.a);
-            build.sub(inst.regA64, regOp(inst.a), temp);
+            RegisterA64 temp2 = tempInt(inst.b);
+            build.sub(inst.regA64, temp1, temp2);
         }
         break;
     case IrCmd::ADD_NUM:
@@ -689,6 +691,14 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         build.scvtf(inst.regA64, x0);
         break;
     }
+    case IrCmd::STRING_LEN:
+    {
+        RegisterA64 reg = regOp(inst.a);
+        inst.regA64 = regs.allocReg(KindA64::w, index);
+
+        build.ldr(inst.regA64, mem(reg, offsetof(TString, len)));
+        break;
+    }
     case IrCmd::NEW_TABLE:
     {
         regs.spill(build, index);
@@ -816,7 +826,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     }
     case IrCmd::FASTCALL:
         regs.spill(build, index);
-        error |= emitBuiltin(build, function, regs, uintOp(inst.a), vmRegOp(inst.b), vmRegOp(inst.c), inst.d, intOp(inst.e), intOp(inst.f));
+        error |= !emitBuiltin(build, function, regs, uintOp(inst.a), vmRegOp(inst.b), vmRegOp(inst.c), inst.d, intOp(inst.e), intOp(inst.f));
         break;
     case IrCmd::INVOKE_FASTCALL:
     {
@@ -1018,8 +1028,9 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         break;
     case IrCmd::CHECK_TAG:
     {
+        bool continueInVm = (inst.d.kind == IrOpKind::Constant && intOp(inst.d));
         Label abort; // used when guard aborts execution
-        Label& fail = inst.c.kind == IrOpKind::Undef ? abort : labelOp(inst.c);
+        Label& fail = inst.c.kind == IrOpKind::Undef ? (continueInVm ? helpers.exitContinueVmClearNativeFlag : abort) : labelOp(inst.c);
         if (tagOp(inst.b) == 0)
         {
             build.cbnz(regOp(inst.a), fail);
@@ -1029,7 +1040,7 @@ 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)
+        if (abort.id && !continueInVm)
             emitAbort(build, abort);
         break;
     }
@@ -1060,9 +1071,18 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         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, inst.a.kind == IrOpKind::Undef ? abort : labelOp(inst.a));
+
-        if (abort.id)
+        if (inst.a.kind == IrOpKind::Undef)
+        {
+            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:
@@ -1528,7 +1548,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     case IrCmd::BITAND_UINT:
     {
         inst.regA64 = regs.allocReuse(KindA64::w, index, {inst.a, inst.b});
-        if (inst.b.kind == IrOpKind::Constant && AssemblyBuilderA64::isMaskSupported(unsigned(intOp(inst.b))))
+        if (inst.a.kind == IrOpKind::Inst && inst.b.kind == IrOpKind::Constant && AssemblyBuilderA64::isMaskSupported(unsigned(intOp(inst.b))))
             build.and_(inst.regA64, regOp(inst.a), unsigned(intOp(inst.b)));
         else
         {
@@ -1541,7 +1561,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     case IrCmd::BITXOR_UINT:
     {
         inst.regA64 = regs.allocReuse(KindA64::w, index, {inst.a, inst.b});
-        if (inst.b.kind == IrOpKind::Constant && AssemblyBuilderA64::isMaskSupported(unsigned(intOp(inst.b))))
+        if (inst.a.kind == IrOpKind::Inst && inst.b.kind == IrOpKind::Constant && AssemblyBuilderA64::isMaskSupported(unsigned(intOp(inst.b))))
             build.eor(inst.regA64, regOp(inst.a), unsigned(intOp(inst.b)));
         else
         {
@@ -1554,7 +1574,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     case IrCmd::BITOR_UINT:
     {
         inst.regA64 = regs.allocReuse(KindA64::w, index, {inst.a, inst.b});
-        if (inst.b.kind == IrOpKind::Constant && AssemblyBuilderA64::isMaskSupported(unsigned(intOp(inst.b))))
+        if (inst.a.kind == IrOpKind::Inst && inst.b.kind == IrOpKind::Constant && AssemblyBuilderA64::isMaskSupported(unsigned(intOp(inst.b))))
             build.orr(inst.regA64, regOp(inst.a), unsigned(intOp(inst.b)));
         else
         {
@@ -1574,7 +1594,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     case IrCmd::BITLSHIFT_UINT:
     {
         inst.regA64 = regs.allocReuse(KindA64::w, index, {inst.a, inst.b});
-        if (inst.b.kind == IrOpKind::Constant)
+        if (inst.a.kind == IrOpKind::Inst && inst.b.kind == IrOpKind::Constant)
             build.lsl(inst.regA64, regOp(inst.a), uint8_t(unsigned(intOp(inst.b)) & 31));
         else
         {
@@ -1587,7 +1607,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     case IrCmd::BITRSHIFT_UINT:
     {
         inst.regA64 = regs.allocReuse(KindA64::w, index, {inst.a, inst.b});
-        if (inst.b.kind == IrOpKind::Constant)
+        if (inst.a.kind == IrOpKind::Inst && inst.b.kind == IrOpKind::Constant)
             build.lsr(inst.regA64, regOp(inst.a), uint8_t(unsigned(intOp(inst.b)) & 31));
         else
         {
@@ -1600,7 +1620,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     case IrCmd::BITARSHIFT_UINT:
     {
         inst.regA64 = regs.allocReuse(KindA64::w, index, {inst.a, inst.b});
-        if (inst.b.kind == IrOpKind::Constant)
+        if (inst.a.kind == IrOpKind::Inst && inst.b.kind == IrOpKind::Constant)
             build.asr(inst.regA64, regOp(inst.a), uint8_t(unsigned(intOp(inst.b)) & 31));
         else
         {
@@ -1612,7 +1632,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     }
     case IrCmd::BITLROTATE_UINT:
     {
-        if (inst.b.kind == IrOpKind::Constant)
+        if (inst.a.kind == IrOpKind::Inst && inst.b.kind == IrOpKind::Constant)
         {
             inst.regA64 = regs.allocReuse(KindA64::w, index, {inst.a});
             build.ror(inst.regA64, regOp(inst.a), uint8_t((32 - unsigned(intOp(inst.b))) & 31));
@@ -1630,7 +1650,7 @@ void IrLoweringA64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
     case IrCmd::BITRROTATE_UINT:
     {
         inst.regA64 = regs.allocReuse(KindA64::w, index, {inst.a, inst.b});
-        if (inst.b.kind == IrOpKind::Constant)
+        if (inst.a.kind == IrOpKind::Inst && inst.b.kind == IrOpKind::Constant)
             build.ror(inst.regA64, regOp(inst.a), uint8_t(unsigned(intOp(inst.b)) & 31));
         else
         {
@@ -1751,11 +1771,21 @@ void IrLoweringA64::finishFunction()
         build.adr(x1, handler.next);
         build.b(helpers.interrupt);
     }
+
+    if (build.logText)
+        build.logAppend("; exit handlers\n");
+
+    for (ExitHandler& handler : exitHandlers)
+    {
+        build.setLabel(handler.self);
+        build.mov(x0, handler.pcpos * sizeof(Instruction));
+        build.b(helpers.updatePcAndContinueInVm);
+    }
 }
 
 bool IrLoweringA64::hasError() const
 {
-    return error;
+    return error || regs.error;
 }
 
 bool IrLoweringA64::isFallthroughBlock(IrBlock target, IrBlock next)

CodeGen/src/IrLoweringA64.h

@@ -60,6 +60,12 @@ struct IrLoweringA64
         Label next;
     };
 
+    struct ExitHandler
+    {
+        Label self;
+        unsigned int pcpos;
+    };
+
     AssemblyBuilderA64& build;
     ModuleHelpers& helpers;
 
@@ -70,6 +76,7 @@ struct IrLoweringA64
     IrValueLocationTracking valueTracker;
 
     std::vector<InterruptHandler> interruptHandlers;
+    std::vector<ExitHandler> exitHandlers;
 
     bool error = false;
 };

CodeGen/src/IrLoweringX64.cpp

@@ -584,6 +584,13 @@ void IrLoweringX64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         build.vcvtsi2sd(inst.regX64, inst.regX64, eax);
         break;
     }
+    case IrCmd::STRING_LEN:
+    {
+        RegisterX64 ptr = regOp(inst.a);
+        inst.regX64 = regs.allocReg(SizeX64::dword, index);
+        build.mov(inst.regX64, dword[ptr + offsetof(TString, len)]);
+        break;
+    }
     case IrCmd::NEW_TABLE:
     {
         IrCallWrapperX64 callWrap(regs, build, index);
@@ -720,9 +727,6 @@ void IrLoweringX64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         int nparams = intOp(inst.e);
         int nresults = intOp(inst.f);
 
-        ScopedRegX64 func{regs, SizeX64::qword};
-        build.mov(func.reg, qword[rNativeContext + offsetof(NativeContext, luauF_table) + bfid * sizeof(luau_FastFunction)]);
-
         IrCallWrapperX64 callWrap(regs, build, index);
         callWrap.addArgument(SizeX64::qword, rState);
         callWrap.addArgument(SizeX64::qword, luauRegAddress(ra));
@@ -748,6 +752,9 @@ void IrLoweringX64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
             callWrap.addArgument(SizeX64::dword, nparams);
         }
 
+        ScopedRegX64 func{regs, SizeX64::qword};
+        build.mov(func.reg, qword[rNativeContext + offsetof(NativeContext, luauF_table) + bfid * sizeof(luau_FastFunction)]);
+
         callWrap.call(func.release());
         inst.regX64 = regs.takeReg(eax, index); // Result of a builtin call is returned in eax
         break;
@@ -878,9 +885,12 @@ void IrLoweringX64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         callPrepareForN(regs, build, vmRegOp(inst.a), vmRegOp(inst.b), vmRegOp(inst.c));
         break;
     case IrCmd::CHECK_TAG:
+    {
+        bool continueInVm = (inst.d.kind == IrOpKind::Constant && intOp(inst.d));
         build.cmp(memRegTagOp(inst.a), tagOp(inst.b));
-        jumpOrAbortOnUndef(ConditionX64::NotEqual, ConditionX64::Equal, inst.c);
+        jumpOrAbortOnUndef(ConditionX64::NotEqual, ConditionX64::Equal, inst.c, continueInVm);
         break;
+    }
     case IrCmd::CHECK_READONLY:
         build.cmp(byte[regOp(inst.a) + offsetof(Table, readonly)], 0);
         jumpOrAbortOnUndef(ConditionX64::NotEqual, ConditionX64::Equal, inst.b);
@@ -896,7 +906,20 @@ void IrLoweringX64::lowerInst(IrInst& inst, uint32_t index, IrBlock& next)
         build.mov(tmp.reg, sClosure);
         build.mov(tmp.reg, qword[tmp.reg + offsetof(Closure, env)]);
         build.cmp(byte[tmp.reg + offsetof(Table, safeenv)], 0);
-        jumpOrAbortOnUndef(ConditionX64::Equal, ConditionX64::NotEqual, inst.a);
+
+        if (inst.a.kind == IrOpKind::Undef)
+        {
+            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:
@@ -1403,6 +1426,16 @@ void IrLoweringX64::finishFunction()
         build.lea(rbx, handler.next);
         build.jmp(helpers.interrupt);
     }
+
+    if (build.logText)
+        build.logAppend("; exit handlers\n");
+
+    for (ExitHandler& handler : exitHandlers)
+    {
+        build.setLabel(handler.self);
+        build.mov(edx, handler.pcpos * sizeof(Instruction));
+        build.jmp(helpers.updatePcAndContinueInVm);
+    }
 }
 
 bool IrLoweringX64::hasError() const
@@ -1425,10 +1458,16 @@ void IrLoweringX64::jumpOrFallthrough(IrBlock& target, IrBlock& next)
         build.jmp(target.label);
 }
 
-void IrLoweringX64::jumpOrAbortOnUndef(ConditionX64 cond, ConditionX64 condInverse, IrOp targetOrUndef)
+void IrLoweringX64::jumpOrAbortOnUndef(ConditionX64 cond, ConditionX64 condInverse, IrOp targetOrUndef, bool continueInVm)
 {
     if (targetOrUndef.kind == IrOpKind::Undef)
     {
+        if (continueInVm)
+        {
+            build.jcc(cond, helpers.exitContinueVmClearNativeFlag);
+            return;
+        }
+
         Label skip;
         build.jcc(condInverse, skip);
         build.ud2();

CodeGen/src/IrLoweringX64.h

@@ -34,7 +34,7 @@ struct IrLoweringX64
 
     bool isFallthroughBlock(IrBlock target, IrBlock next);
     void jumpOrFallthrough(IrBlock& target, IrBlock& next);
-    void jumpOrAbortOnUndef(ConditionX64 cond, ConditionX64 condInverse, IrOp targetOrUndef);
+    void jumpOrAbortOnUndef(ConditionX64 cond, ConditionX64 condInverse, IrOp targetOrUndef, bool continueInVm = false);
 
     void storeDoubleAsFloat(OperandX64 dst, IrOp src);
 
@@ -60,6 +60,12 @@ struct IrLoweringX64
         Label next;
     };
 
+    struct ExitHandler
+    {
+        Label self;
+        unsigned int pcpos;
+    };
+
     AssemblyBuilderX64& build;
     ModuleHelpers& helpers;
 
@@ -70,6 +76,7 @@ struct IrLoweringX64
     IrValueLocationTracking valueTracker;
 
     std::vector<InterruptHandler> interruptHandlers;
+    std::vector<ExitHandler> exitHandlers;
 };
 
 } // namespace X64

CodeGen/src/IrRegAllocA64.cpp

@@ -18,6 +18,8 @@ namespace CodeGen
 namespace A64
 {
 
+static const int8_t kInvalidSpill = 64;
+
 static int allocSpill(uint32_t& free, KindA64 kind)
 {
     LUAU_ASSERT(kStackSize <= 256); // to support larger stack frames, we need to ensure qN is allocated at 16b boundary to fit in ldr/str encoding
@@ -91,7 +93,8 @@ static void restoreInst(AssemblyBuilderA64& build, uint32_t& freeSpillSlots, IrF
     {
         build.ldr(reg, mem(sp, sSpillArea.data + s.slot * 8));
 
-        freeSpill(freeSpillSlots, reg.kind, s.slot);
+        if (s.slot != kInvalidSpill)
+            freeSpill(freeSpillSlots, reg.kind, s.slot);
     }
     else
     {
@@ -135,9 +138,8 @@ RegisterA64 IrRegAllocA64::allocReg(KindA64 kind, uint32_t index)
 
     if (set.free == 0)
     {
-        // TODO: remember the error and fail lowering
+        error = true;
-        LUAU_ASSERT(!"Out of registers to allocate");
+        return RegisterA64{kind, 0};
-        return noreg;
     }
 
     int reg = 31 - countlz(set.free);
@@ -157,9 +159,8 @@ RegisterA64 IrRegAllocA64::allocTemp(KindA64 kind)
 
     if (set.free == 0)
     {
-        // TODO: remember the error and fail lowering
+        error = true;
-        LUAU_ASSERT(!"Out of registers to allocate");
+        return RegisterA64{kind, 0};
-        return noreg;
     }
 
     int reg = 31 - countlz(set.free);
@@ -332,7 +333,11 @@ size_t IrRegAllocA64::spill(AssemblyBuilderA64& build, uint32_t index, std::init
             else
             {
                 int slot = allocSpill(freeSpillSlots, def.regA64.kind);
-                LUAU_ASSERT(slot >= 0); // TODO: remember the error and fail lowering
+                if (slot < 0)
+                {
+                    slot = kInvalidSpill;
+                    error = true;
+                }
 
                 build.str(def.regA64, mem(sp, sSpillArea.data + slot * 8));
 

CodeGen/src/IrRegAllocA64.h

@@ -77,6 +77,8 @@ struct IrRegAllocA64
 
     // which 8-byte slots are free
     uint32_t freeSpillSlots = 0;
+
+    bool error = false;
 };
 
 } // namespace A64

CodeGen/src/IrRegAllocX64.cpp

@@ -121,6 +121,14 @@ RegisterX64 IrRegAllocX64::takeReg(RegisterX64 reg, uint32_t instIdx)
     return reg;
 }
 
+bool IrRegAllocX64::canTakeReg(RegisterX64 reg) const
+{
+    const std::array<bool, 16>& freeMap = reg.size == SizeX64::xmmword ? freeXmmMap : freeGprMap;
+    const std::array<uint32_t, 16>& instUsers = reg.size == SizeX64::xmmword ? xmmInstUsers : gprInstUsers;
+
+    return freeMap[reg.index] || instUsers[reg.index] != kInvalidInstIdx;
+}
+
 void IrRegAllocX64::freeReg(RegisterX64 reg)
 {
     if (reg.size == SizeX64::xmmword)

CodeGen/src/IrTranslateBuiltins.cpp

@@ -737,6 +737,23 @@ static BuiltinImplResult translateBuiltinVector(IrBuilder& build, int nparams, i
     return {BuiltinImplType::UsesFallback, 1};
 }
 
+static BuiltinImplResult translateBuiltinStringLen(IrBuilder& build, int nparams, int ra, int arg, IrOp args, int nresults, IrOp fallback)
+{
+    if (nparams < 1 || nresults > 1)
+        return {BuiltinImplType::None, -1};
+
+    build.loadAndCheckTag(build.vmReg(arg), LUA_TSTRING, fallback);
+
+    IrOp ts = build.inst(IrCmd::LOAD_POINTER, build.vmReg(arg));
+
+    IrOp len = build.inst(IrCmd::STRING_LEN, ts);
+
+    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};
+}
+
 BuiltinImplResult translateBuiltin(IrBuilder& build, int bfid, int ra, int arg, IrOp args, int nparams, int nresults, IrOp fallback)
 {
     // Builtins are not allowed to handle variadic arguments
@@ -821,6 +838,8 @@ BuiltinImplResult translateBuiltin(IrBuilder& build, int bfid, int ra, int arg,
         return translateBuiltinTypeof(build, nparams, ra, arg, args, nresults, fallback);
     case LBF_VECTOR:
         return translateBuiltinVector(build, nparams, ra, arg, args, nresults, fallback);
+    case LBF_STRING_LEN:
+        return translateBuiltinStringLen(build, nparams, ra, arg, args, nresults, fallback);
     default:
         return {BuiltinImplType::None, -1};
     }

CodeGen/src/IrTranslation.cpp

@@ -516,6 +516,7 @@ void translateInstCloseUpvals(IrBuilder& build, const Instruction* pc)
 
 void translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool customParams, int customParamCount, IrOp customArgs, IrOp next)
 {
+    LuauOpcode opcode = LuauOpcode(LUAU_INSN_OP(*pc));
     int bfid = LUAU_INSN_A(*pc);
     int skip = LUAU_INSN_C(*pc);
 
@@ -540,7 +541,8 @@ void translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool
 
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
-    build.inst(IrCmd::CHECK_SAFE_ENV, 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)));
 
     BuiltinImplResult br = translateBuiltin(build, LuauBuiltinFunction(bfid), ra, arg, builtinArgs, nparams, nresults, fallback);
 
@@ -554,7 +556,7 @@ void translateFastCallN(IrBuilder& build, const Instruction* pc, int pcpos, bool
     else
     {
         // TODO: we can skip saving pc for some well-behaved builtins which we didn't inline
-        build.inst(IrCmd::SET_SAVEDPC, build.constUint(pcpos + 1));
+        build.inst(IrCmd::SET_SAVEDPC, build.constUint(pcpos + getOpLength(opcode)));
 
         IrOp res = build.inst(IrCmd::INVOKE_FASTCALL, build.constUint(bfid), build.vmReg(ra), build.vmReg(arg), args, build.constInt(nparams),
             build.constInt(nresults));
@@ -668,7 +670,7 @@ 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, fallback);
+    build.inst(IrCmd::CHECK_SAFE_ENV, build.constUint(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));
@@ -695,7 +697,7 @@ 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, fallback);
+    build.inst(IrCmd::CHECK_SAFE_ENV, build.constUint(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));
@@ -921,7 +923,7 @@ 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, fallback);
+    build.inst(IrCmd::CHECK_SAFE_ENV, build.constUint(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/IrUtils.cpp

@@ -80,6 +80,8 @@ IrValueKind getCmdValueKind(IrCmd cmd)
         return IrValueKind::None;
     case IrCmd::TABLE_LEN:
         return IrValueKind::Double;
+    case IrCmd::STRING_LEN:
+        return IrValueKind::Int;
     case IrCmd::NEW_TABLE:
     case IrCmd::DUP_TABLE:
         return IrValueKind::Pointer;
@@ -684,8 +686,7 @@ void foldConstants(IrBuilder& build, IrFunction& function, IrBlock& block, uint3
             unsigned op1 = unsigned(function.intOp(inst.a));
             int op2 = function.intOp(inst.b);
 
-            if (unsigned(op2) < 32)
+            substitute(function, inst, build.constInt(op1 << (op2 & 31)));
-                substitute(function, inst, build.constInt(op1 << op2));
         }
         else if (inst.b.kind == IrOpKind::Constant && function.intOp(inst.b) == 0)
         {
@@ -698,8 +699,7 @@ void foldConstants(IrBuilder& build, IrFunction& function, IrBlock& block, uint3
             unsigned op1 = unsigned(function.intOp(inst.a));
             int op2 = function.intOp(inst.b);
 
-            if (unsigned(op2) < 32)
+            substitute(function, inst, build.constInt(op1 >> (op2 & 31)));
-                substitute(function, inst, build.constInt(op1 >> op2));
         }
         else if (inst.b.kind == IrOpKind::Constant && function.intOp(inst.b) == 0)
         {
@@ -712,12 +712,9 @@ void foldConstants(IrBuilder& build, IrFunction& function, IrBlock& block, uint3
             int op1 = function.intOp(inst.a);
             int op2 = function.intOp(inst.b);
 
-            if (unsigned(op2) < 32)
+            // note: technically right shift of negative values is UB, but this behavior is getting defined in C++20 and all compilers do the
-            {
+            // right (shift) thing.
-                // note: technically right shift of negative values is UB, but this behavior is getting defined in C++20 and all compilers do the
+            substitute(function, inst, build.constInt(op1 >> (op2 & 31)));
-                // right (shift) thing.
-                substitute(function, inst, build.constInt(op1 >> op2));
-            }
         }
         else if (inst.b.kind == IrOpKind::Constant && function.intOp(inst.b) == 0)
         {
@@ -794,5 +791,17 @@ uint32_t getNativeContextOffset(int bfid)
     return 0;
 }
 
+void killUnusedBlocks(IrFunction& function)
+{
+    // Start from 1 as the first block is the entry block
+    for (unsigned i = 1; i < function.blocks.size(); i++)
+    {
+        IrBlock& block = function.blocks[i];
+
+        if (block.kind != IrBlockKind::Dead && block.useCount == 0)
+            kill(function, block);
+    }
+}
+
 } // namespace CodeGen
 } // namespace Luau

CodeGen/src/OptimizeConstProp.cpp

@@ -441,17 +441,25 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
             state.substituteOrRecordVmRegLoad(inst);
         break;
     case IrCmd::LOAD_DOUBLE:
-        if (IrOp value = state.tryGetValue(inst.a); value.kind == IrOpKind::Constant)
+    {
+        IrOp value = state.tryGetValue(inst.a);
+
+        if (function.asDoubleOp(value))
             substitute(function, inst, value);
         else if (inst.a.kind == IrOpKind::VmReg)
             state.substituteOrRecordVmRegLoad(inst);
         break;
+    }
     case IrCmd::LOAD_INT:
-        if (IrOp value = state.tryGetValue(inst.a); value.kind == IrOpKind::Constant)
+    {
+        IrOp value = state.tryGetValue(inst.a);
+
+        if (function.asIntOp(value))
             substitute(function, inst, value);
         else if (inst.a.kind == IrOpKind::VmReg)
             state.substituteOrRecordVmRegLoad(inst);
         break;
+    }
     case IrCmd::LOAD_TVALUE:
         if (inst.a.kind == IrOpKind::VmReg)
             state.substituteOrRecordVmRegLoad(inst);
@@ -775,6 +783,7 @@ static void constPropInInst(ConstPropState& state, IrBuilder& build, IrFunction&
     case IrCmd::JUMP_EQ_POINTER:
     case IrCmd::JUMP_SLOT_MATCH:
     case IrCmd::TABLE_LEN:
+    case IrCmd::STRING_LEN:
     case IrCmd::NEW_TABLE:
     case IrCmd::DUP_TABLE:
     case IrCmd::TRY_NUM_TO_INDEX:

Compiler/src/BytecodeBuilder.cpp

@@ -2314,9 +2314,9 @@ static const char* getBaseTypeString(uint8_t type)
     case LBC_TYPE_STRING:
         return "string";
     case LBC_TYPE_TABLE:
-        return "{ }";
+        return "table";
     case LBC_TYPE_FUNCTION:
-        return "function( )";
+        return "function";
     case LBC_TYPE_THREAD:
         return "thread";
     case LBC_TYPE_USERDATA:

Compiler/src/Compiler.cpp

@@ -26,8 +26,7 @@ LUAU_FASTINTVARIABLE(LuauCompileInlineThreshold, 25)
 LUAU_FASTINTVARIABLE(LuauCompileInlineThresholdMaxBoost, 300)
 LUAU_FASTINTVARIABLE(LuauCompileInlineDepth, 5)
 
-LUAU_FASTFLAGVARIABLE(CompileFunctionType, false)
+LUAU_FASTFLAGVARIABLE(LuauCompileFunctionType, false)
-LUAU_FASTFLAG(BytecodeVersion4)
 
 namespace Luau
 {
@@ -103,6 +102,7 @@ struct Compiler
         , locstants(nullptr)
         , tableShapes(nullptr)
         , builtins(nullptr)
+        , typeMap(nullptr)
     {
         // preallocate some buffers that are very likely to grow anyway; this works around std::vector's inefficient growth policy for small arrays
         localStack.reserve(16);
@@ -204,11 +204,11 @@ struct Compiler
 
         setDebugLine(func);
 
-        if (FFlag::BytecodeVersion4 && FFlag::CompileFunctionType)
+        if (FFlag::LuauCompileFunctionType)
         {
-            std::string funcType = getFunctionType(func);
+            // note: we move types out of typeMap which is safe because compileFunction is only called once per function
-            if (!funcType.empty())
+            if (std::string* funcType = typeMap.find(func))
-                bytecode.setFunctionTypeInfo(std::move(funcType));
+                bytecode.setFunctionTypeInfo(std::move(*funcType));
         }
 
         if (func->vararg)
@@ -3807,6 +3807,8 @@ struct Compiler
     DenseHashMap<AstLocal*, Constant> locstants;
     DenseHashMap<AstExprTable*, TableShape> tableShapes;
     DenseHashMap<AstExprCall*, int> builtins;
+    DenseHashMap<AstExprFunction*, std::string> typeMap;
+
     const DenseHashMap<AstExprCall*, int>* builtinsFold = nullptr;
 
     unsigned int regTop = 0;
@@ -3870,6 +3872,11 @@ void compileOrThrow(BytecodeBuilder& bytecode, const ParseResult& parseResult, c
         root->visit(&fenvVisitor);
     }
 
+    if (FFlag::LuauCompileFunctionType)
+    {
+        buildTypeMap(compiler.typeMap, root);
+    }
+
     // gathers all functions with the invariant that all function references are to functions earlier in the list
     // for example, function foo() return function() end end will result in two vector entries, [0] = anonymous and [1] = foo
     std::vector<AstExprFunction*> functions;

Compiler/src/Types.cpp

@@ -6,22 +6,58 @@
 namespace Luau
 {
 
-static LuauBytecodeEncodedType getType(AstType* ty)
+static bool isGeneric(AstName name, const AstArray<AstGenericType>& generics)
+{
+    for (const AstGenericType& gt : generics)
+        if (gt.name == name)
+            return true;
+
+    return false;
+}
+
+static LuauBytecodeEncodedType getPrimitiveType(AstName name)
+{
+    if (name == "nil")
+        return LBC_TYPE_NIL;
+    else if (name == "boolean")
+        return LBC_TYPE_BOOLEAN;
+    else if (name == "number")
+        return LBC_TYPE_NUMBER;
+    else if (name == "string")
+        return LBC_TYPE_STRING;
+    else if (name == "thread")
+        return LBC_TYPE_THREAD;
+    else if (name == "any" || name == "unknown")
+        return LBC_TYPE_ANY;
+    else
+        return LBC_TYPE_INVALID;
+}
+
+static LuauBytecodeEncodedType getType(
+    AstType* ty, const AstArray<AstGenericType>& generics, const DenseHashMap<AstName, AstStatTypeAlias*>& typeAliases, bool resolveAliases)
 {
     if (AstTypeReference* ref = ty->as<AstTypeReference>())
     {
-        if (ref->name == "nil")
+        if (ref->prefix)
-            return LBC_TYPE_NIL;
-        else if (ref->name == "boolean")
-            return LBC_TYPE_BOOLEAN;
-        else if (ref->name == "number")
-            return LBC_TYPE_NUMBER;
-        else if (ref->name == "string")
-            return LBC_TYPE_STRING;
-        else if (ref->name == "thread")
-            return LBC_TYPE_THREAD;
-        else if (ref->name == "any" || ref->name == "unknown")
             return LBC_TYPE_ANY;
+
+        if (AstStatTypeAlias* const* alias = typeAliases.find(ref->name); alias && *alias)
+        {
+            // 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);
+            else
+                return LBC_TYPE_ANY;
+        }
+
+        if (isGeneric(ref->name, generics))
+            return LBC_TYPE_ANY;
+
+        if (LuauBytecodeEncodedType prim = getPrimitiveType(ref->name); prim != LBC_TYPE_INVALID)
+            return prim;
+
+        // not primitive or alias or generic => host-provided, we assume userdata for now
+        return LBC_TYPE_USERDATA;
     }
     else if (AstTypeTable* table = ty->as<AstTypeTable>())
     {
@@ -38,7 +74,7 @@ static LuauBytecodeEncodedType getType(AstType* ty)
 
         for (AstType* ty : un->types)
         {
-            LuauBytecodeEncodedType et = getType(ty);
+            LuauBytecodeEncodedType et = getType(ty, generics, typeAliases, resolveAliases);
 
             if (et == LBC_TYPE_NIL)
             {
@@ -69,11 +105,8 @@ static LuauBytecodeEncodedType getType(AstType* ty)
     return LBC_TYPE_ANY;
 }
 
-std::string getFunctionType(const AstExprFunction* func)
+static std::string getFunctionType(const AstExprFunction* func, const DenseHashMap<AstName, AstStatTypeAlias*>& typeAliases)
 {
-    if (func->vararg || func->generics.size || func->genericPacks.size)
-        return {};
-
     bool self = func->self != 0;
 
     std::string typeInfo;
@@ -88,7 +121,8 @@ std::string getFunctionType(const AstExprFunction* func)
     bool haveNonAnyParam = false;
     for (AstLocal* arg : func->args)
     {
-        LuauBytecodeEncodedType ty = arg->annotation ? getType(arg->annotation) : LBC_TYPE_ANY;
+        LuauBytecodeEncodedType ty =
+            arg->annotation ? getType(arg->annotation, func->generics, typeAliases, /* resolveAliases= */ true) : LBC_TYPE_ANY;
 
         if (ty != LBC_TYPE_ANY)
             haveNonAnyParam = true;
@@ -103,4 +137,88 @@ std::string getFunctionType(const AstExprFunction* func)
     return typeInfo;
 }
 
-} // namespace Luau
+struct TypeMapVisitor : AstVisitor
+{
+    DenseHashMap<AstExprFunction*, std::string>& typeMap;
+
+    DenseHashMap<AstName, AstStatTypeAlias*> typeAliases;
+    std::vector<std::pair<AstName, AstStatTypeAlias*>> typeAliasStack;
+
+    TypeMapVisitor(DenseHashMap<AstExprFunction*, std::string>& typeMap)
+        : typeMap(typeMap)
+        , typeAliases(AstName())
+    {
+    }
+
+    size_t pushTypeAliases(AstStatBlock* block)
+    {
+        size_t aliasStackTop = typeAliasStack.size();
+
+        for (AstStat* stat : block->body)
+            if (AstStatTypeAlias* alias = stat->as<AstStatTypeAlias>())
+            {
+                AstStatTypeAlias*& prevAlias = typeAliases[alias->name];
+
+                typeAliasStack.push_back(std::make_pair(alias->name, prevAlias));
+                prevAlias = alias;
+            }
+
+        return aliasStackTop;
+    }
+
+    void popTypeAliases(size_t aliasStackTop)
+    {
+        while (typeAliasStack.size() > aliasStackTop)
+        {
+            std::pair<AstName, AstStatTypeAlias*>& top = typeAliasStack.back();
+
+            typeAliases[top.first] = top.second;
+            typeAliasStack.pop_back();
+        }
+    }
+
+    bool visit(AstStatBlock* node) override
+    {
+        size_t aliasStackTop = pushTypeAliases(node);
+
+        for (AstStat* stat : node->body)
+            stat->visit(this);
+
+        popTypeAliases(aliasStackTop);
+
+        return false;
+    }
+
+    // repeat..until scoping rules are such that condition (along with any possible functions declared in it) has aliases from repeat body in scope
+    bool visit(AstStatRepeat* node) override
+    {
+        size_t aliasStackTop = pushTypeAliases(node->body);
+
+        for (AstStat* stat : node->body->body)
+            stat->visit(this);
+
+        node->condition->visit(this);
+
+        popTypeAliases(aliasStackTop);
+
+        return false;
+    }
+
+    bool visit(AstExprFunction* node) override
+    {
+        std::string type = getFunctionType(node, typeAliases);
+
+        if (!type.empty())
+            typeMap[node] = std::move(type);
+
+        return true;
+    }
+};
+
+void buildTypeMap(DenseHashMap<AstExprFunction*, std::string>& typeMap, AstNode* root)
+{
+    TypeMapVisitor visitor(typeMap);
+    root->visit(&visitor);
+}
+
+} // namespace Luau

Compiler/src/Types.h

@@ -3,7 +3,11 @@
 
 #include "Luau/Ast.h"
 
+#include <string>
+
 namespace Luau
 {
-std::string getFunctionType(const AstExprFunction* func);
+
+void buildTypeMap(DenseHashMap<AstExprFunction*, std::string>& typeMap, AstNode* root);
+
 } // namespace Luau

Makefile

@@ -176,9 +176,9 @@ coverage: $(TESTS_TARGET) $(COMPILE_CLI_TARGET)
 	mv default.profraw codegen-x64.profraw
 	llvm-profdata merge *.profraw -o default.profdata
 	rm *.profraw
-	llvm-cov show -format=html -show-instantiations=false -show-line-counts=true -show-region-summary=false -ignore-filename-regex=\(tests\|extern\|CLI\)/.* -output-dir=coverage --instr-profile default.profdata build/coverage/luau-tests
+	llvm-cov show -format=html -show-instantiations=false -show-line-counts=true -show-region-summary=false -ignore-filename-regex=\(tests\|extern\|CLI\)/.* -output-dir=coverage --instr-profile default.profdata -object build/coverage/luau-tests -object build/coverage/luau-compile
-	llvm-cov report -ignore-filename-regex=\(tests\|extern\|CLI\)/.* -show-region-summary=false --instr-profile default.profdata build/coverage/luau-tests
+	llvm-cov report -ignore-filename-regex=\(tests\|extern\|CLI\)/.* -show-region-summary=false --instr-profile default.profdata -object build/coverage/luau-tests -object build/coverage/luau-compile
-	llvm-cov export -ignore-filename-regex=\(tests\|extern\|CLI\)/.* -format lcov --instr-profile default.profdata build/coverage/luau-tests >coverage.info
+	llvm-cov export -ignore-filename-regex=\(tests\|extern\|CLI\)/.* -format lcov --instr-profile default.profdata -object build/coverage/luau-tests -object build/coverage/luau-compile >coverage.info
 
 format:
 	git ls-files '*.h' '*.cpp' | xargs clang-format-11 -i

Sources.cmake

@@ -152,6 +152,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/include/Luau/DataFlowGraph.h
     Analysis/include/Luau/DcrLogger.h
     Analysis/include/Luau/Def.h
+    Analysis/include/Luau/Differ.h
     Analysis/include/Luau/Documentation.h
     Analysis/include/Luau/Error.h
     Analysis/include/Luau/FileResolver.h
@@ -209,6 +210,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/src/DataFlowGraph.cpp
     Analysis/src/DcrLogger.cpp
     Analysis/src/Def.cpp
+    Analysis/src/Differ.cpp
     Analysis/src/EmbeddedBuiltinDefinitions.cpp
     Analysis/src/Error.cpp
     Analysis/src/Frontend.cpp
@@ -366,6 +368,7 @@ if(TARGET Luau.UnitTest)
         tests/CostModel.test.cpp
         tests/DataFlowGraph.test.cpp
         tests/DenseHash.test.cpp
+	tests/Differ.test.cpp
         tests/Error.test.cpp
         tests/Frontend.test.cpp
         tests/IrBuilder.test.cpp

VM/src/lfunc.cpp

@@ -34,6 +34,7 @@ Proto* luaF_newproto(lua_State* L)
     f->codeentry = NULL;
     f->execdata = NULL;
     f->exectarget = 0;
+    f->typeinfo = NULL;
 
     return f;
 }
@@ -162,6 +163,9 @@ void luaF_freeproto(lua_State* L, Proto* f, lua_Page* page)
     }
 #endif
 
+    if (f->typeinfo)
+        luaM_freearray(L, f->typeinfo, f->numparams + 2, uint8_t, f->memcat);
+
     luaM_freegco(L, f, sizeof(Proto), f->memcat, page);
 }
 

VM/src/lobject.h

@@ -279,6 +279,8 @@ typedef struct Proto
     void* execdata;
     uintptr_t exectarget;
 
+    uint8_t* typeinfo;
+
     GCObject* gclist;
 
 

VM/src/lvmload.cpp

@@ -13,6 +13,8 @@
 
 #include <string.h>
 
+LUAU_FASTFLAGVARIABLE(LuauLoadCheckGC, false)
+
 // TODO: RAII deallocation doesn't work for longjmp builds if a memory error happens
 template<typename T>
 struct TempBuffer
@@ -178,6 +180,10 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
         return 1;
     }
 
+    // we will allocate a fair amount of memory so check GC before we do
+    if (FFlag::LuauLoadCheckGC)
+        luaC_checkGC(L);
+
     // pause GC for the duration of deserialization - some objects we're creating aren't rooted
     // TODO: if an allocation error happens mid-load, we do not unpause GC!
     size_t GCthreshold = L->global->GCthreshold;
@@ -188,11 +194,11 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
 
     TString* source = luaS_new(L, chunkname);
 
+    uint8_t typesversion = 0;
 
     if (version >= 4)
     {
-        uint8_t typesversion = read<uint8_t>(data, size, offset);
+        typesversion = read<uint8_t>(data, size, offset);
-        LUAU_ASSERT(typesversion == 1);
     }
 
     // string table
@@ -229,7 +235,7 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
 
             uint32_t typesize = readVarInt(data, size, offset);
 
-            if (typesize)
+            if (typesize && typesversion == LBC_TYPE_VERSION)
             {
                 uint8_t* types = (uint8_t*)data + offset;
 
@@ -237,8 +243,11 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
                 LUAU_ASSERT(types[0] == LBC_TYPE_FUNCTION);
                 LUAU_ASSERT(types[1] == p->numparams);
 
-                offset += typesize;
+                p->typeinfo = luaM_newarray(L, typesize, uint8_t, p->memcat);
+                memcpy(p->typeinfo, types, typesize);
             }
+
+            offset += typesize;
         }
 
         p->sizecode = readVarInt(data, size, offset);

fuzz/proto.cpp

@@ -27,12 +27,16 @@ const bool kFuzzTypeck = true;
 const bool kFuzzVM = true;
 const bool kFuzzTranspile = true;
 const bool kFuzzCodegen = true;
+const bool kFuzzCodegenAssembly = true;
 
 // Should we generate type annotations?
 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(!(kFuzzCodegenAssembly && !kFuzzCompiler), "Codegen requires the compiler!");
 
 std::vector<std::string> protoprint(const luau::ModuleSet& stat, bool types);
 
@@ -348,6 +352,23 @@ DEFINE_PROTO_FUZZER(const luau::ModuleSet& message)
         }
     }
 
+    // run codegen on resulting bytecode (in separate state)
+    if (kFuzzCodegenAssembly && bytecode.size())
+    {
+        static lua_State* globalState = luaL_newstate();
+
+        if (luau_load(globalState, "=fuzz", bytecode.data(), bytecode.size(), 0) == 0)
+        {
+            Luau::CodeGen::AssemblyOptions options;
+            options.outputBinary = true;
+            options.target = kFuzzCodegenTarget;
+            Luau::CodeGen::getAssembly(globalState, -1, options);
+        }
+
+        lua_pop(globalState, 1);
+        lua_gc(globalState, LUA_GCCOLLECT, 0);
+    }
+
     // run resulting bytecode (from last successfully compiler module)
     if (kFuzzVM && bytecode.size())
     {

tests/ClassFixture.cpp

@@ -107,7 +107,6 @@ ClassFixture::ClassFixture()
     globals.globalScope->exportedTypeBindings["CallableClass"] = TypeFun{{}, callableClassType};
 
     auto addIndexableClass = [&arena, &globals](const char* className, TypeId keyType, TypeId returnType) {
-        ScopedFastFlag LuauTypecheckClassTypeIndexers("LuauTypecheckClassTypeIndexers", true);
         TypeId indexableClassMetaType = arena.addType(TableType{});
         TypeId indexableClassType =
             arena.addType(ClassType{className, {}, nullopt, indexableClassMetaType, {}, {}, "Test", TableIndexer{keyType, returnType}});

tests/Compiler.test.cpp

@@ -49,7 +49,7 @@ static std::string compileFunction0Coverage(const char* source, int level)
     return bcb.dumpFunction(0);
 }
 
-static std::string compileFunction0TypeTable(const char* source)
+static std::string compileTypeTable(const char* source)
 {
     Luau::BytecodeBuilder bcb;
     bcb.setDumpFlags(Luau::BytecodeBuilder::Dump_Code);
@@ -7080,12 +7080,9 @@ L1: RETURN R3 1
 
 TEST_CASE("EncodedTypeTable")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sff("LuauCompileFunctionType", true);
-        {"BytecodeVersion4", true},
-        {"CompileFunctionType", true},
-    };
 
-    CHECK_EQ("\n" + compileFunction0TypeTable(R"(
+    CHECK_EQ("\n" + compileTypeTable(R"(
 function myfunc(test: string, num: number)
     print(test)
 end
@@ -7104,6 +7101,9 @@ end
 function myfunc5(test: string | number, n: number | boolean)
 end
 
+function myfunc6(test: (number) -> string)
+end
+
 myfunc('test')
 )"),
         R"(
@@ -7111,9 +7111,10 @@ myfunc('test')
 1: function(number?)
 2: function(string, number)
 3: function(any, number)
+5: function(function)
 )");
 
-    CHECK_EQ("\n" + compileFunction0TypeTable(R"(
+    CHECK_EQ("\n" + compileTypeTable(R"(
 local Str = {
     a = 1
 }
@@ -7126,7 +7127,95 @@ end
 Str:test(234)
 )"),
         R"(
-0: function({ }, number)
+0: function(table, number)
+)");
+}
+
+TEST_CASE("HostTypesAreUserdata")
+{
+    ScopedFastFlag sff("LuauCompileFunctionType", true);
+
+    CHECK_EQ("\n" + compileTypeTable(R"(
+function myfunc(test: string, num: number)
+    print(test)
+end
+
+function myfunc2(test: Instance, num: number)
+end
+
+type Foo = string
+
+function myfunc3(test: string, n: Foo)
+end
+
+function myfunc4<Bar>(test: Bar, n: Part)
+end
+)"),
+        R"(
+0: function(string, number)
+1: function(userdata, number)
+2: function(string, string)
+3: function(any, userdata)
+)");
+}
+
+TEST_CASE("TypeAliasScoping")
+{
+    ScopedFastFlag sff("LuauCompileFunctionType", true);
+
+    CHECK_EQ("\n" + compileTypeTable(R"(
+do
+    type Part = number
+end
+
+function myfunc1(test: Part, num: number)
+end
+
+do
+    type Part = number
+
+    function myfunc2(test: Part, num: number)
+    end
+end
+
+repeat
+    type Part = number
+until (function(test: Part, num: number) end)()
+
+function myfunc4(test: Instance, num: number)
+end
+
+type Instance = string
+)"),
+        R"(
+0: function(userdata, number)
+1: function(number, number)
+2: function(number, number)
+3: function(string, number)
+)");
+}
+
+TEST_CASE("TypeAliasResolve")
+{
+    ScopedFastFlag sff("LuauCompileFunctionType", true);
+
+    CHECK_EQ("\n" + compileTypeTable(R"(
+type Foo1 = number
+type Foo2 = { number }
+type Foo3 = Part
+type Foo4 = Foo1 -- we do not resolve aliases within aliases
+type Foo5<X> = X
+
+function myfunc(f1: Foo1, f2: Foo2, f3: Foo3, f4: Foo4, f5: Foo5<number>)
+end
+
+function myfuncerr(f1: Foo1<string>, f2: Foo5)
+end
+
+)"),
+        R"(
+0: function(number, table, userdata, any, any)
+1: function(number, any)
 )");
 }
 

tests/Differ.test.cpp

@@ -0,0 +1,316 @@
+// 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/Error.h"
+#include "Luau/Frontend.h"
+
+#include "Fixture.h"
+
+#include "doctest.h"
+#include <iostream>
+
+using namespace Luau;
+
+TEST_SUITE_BEGIN("Differ");
+
+TEST_CASE_FIXTURE(Fixture, "equal_numbers")
+{
+    CheckResult result = check(R"(
+    local foo = 5
+    local almostFoo = 78
+    almostFoo = foo
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        CHECK(!diffRes.diffError.has_value());
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+}
+
+TEST_CASE_FIXTURE(Fixture, "equal_strings")
+{
+    CheckResult result = check(R"(
+    local foo = "hello"
+    local almostFoo = "world"
+    almostFoo = foo
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        CHECK(!diffRes.diffError.has_value());
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+}
+
+TEST_CASE_FIXTURE(Fixture, "equal_tables")
+{
+    CheckResult result = check(R"(
+    local foo = { x = 1, y = "where" }
+    local almostFoo = { x = 5, y = "when" }
+    almostFoo = foo
+    )");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    TypeId foo = requireType("foo");
+    TypeId almostFoo = requireType("almostFoo");
+    try
+    {
+        DifferResult diffRes = diff(foo, almostFoo);
+        CHECK(!diffRes.diffError.has_value());
+    }
+    catch (const InternalCompilerError& e)
+    {
+        INFO(("InternalCompilerError: " + e.message));
+        CHECK(false);
+    }
+}
+
+TEST_CASE_FIXTURE(Fixture, "a_table_missing_property")
+{
+    CheckResult result = check(R"(
+    local foo = { x = 1, y = 2 }
+    local almostFoo = { x = 1, z = 3 }
+    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("DiffError: these two types are not equal because the left type at foo.y has type number, while the right type at almostFoo is missing "
+             "the property y",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "left_table_missing_property")
+{
+    CheckResult result = check(R"(
+    local foo = { x = 1 }
+    local almostFoo = { x = 1, z = 3 }
+    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("DiffError: these two types are not equal because the left type at foo is missing the property z, while the right type at almostFoo.z "
+             "has type number",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "a_table_wrong_type")
+{
+    CheckResult result = check(R"(
+    local foo = { x = 1, y = 2 }
+    local almostFoo = { x = 1, y = "two" }
+    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("DiffError: these two types are not equal because the left type at foo.y has type number, while the right type at almostFoo.y has type "
+             "string",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "a_table_wrong_type")
+{
+    CheckResult result = check(R"(
+    local foo: string
+    local almostFoo: number
+    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("DiffError: these two types are not equal because the left type at <unlabeled-symbol> has type string, while the right type at "
+             "<unlabeled-symbol> has type number",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "a_nested_table_wrong_type")
+{
+    CheckResult result = check(R"(
+    local foo = { x = 1, inner = { table = { has = { wrong = { value = 5 } } } } }
+    local almostFoo = { x = 1, inner = { table = { has = { wrong = { value = "five" } } } } }
+    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("DiffError: these two types are not equal because the left type at foo.inner.table.has.wrong.value has type number, while the right "
+             "type at almostFoo.inner.table.has.wrong.value has type string",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "a_nested_table_wrong_match")
+{
+    CheckResult result = check(R"(
+    local foo = { x = 1, inner = { table = { has = { wrong = { variant = { because = { it = { goes = { on = "five" } } } } } } } } }
+    local almostFoo = { x = 1, inner = { table = { has = { wrong = { variant = "five" } } } } }
+    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("DiffError: these two types are not equal because the left type at foo.inner.table.has.wrong.variant has type { because: { it: { goes: "
+             "{ on: string } } } }, while the right type at almostFoo.inner.table.has.wrong.variant has type string",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "singleton")
+{
+    CheckResult result = check(R"(
+    local foo: "hello" = "hello"
+    local almostFoo: true = true
+    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> has type "hello", while the right type at <unlabeled-symbol> has type true)",
+        diffMessage);
+}
+
+TEST_CASE_FIXTURE(Fixture, "equal_singleton")
+{
+    CheckResult result = check(R"(
+    local foo: "hello" = "hello"
+    local almostFoo: "hello"
+    almostFoo = foo
+    )");
+    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, "singleton_string")
+{
+    CheckResult result = check(R"(
+    local foo: "hello" = "hello"
+    local almostFoo: "world" = "world"
+    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> has type "hello", while the right type at <unlabeled-symbol> has type "world")",
+        diffMessage);
+}
+
+TEST_SUITE_END();

tests/Frontend.test.cpp

@@ -1146,4 +1146,35 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "module_scope_check")
     CHECK_EQ(toString(ty), "number");
 }
 
+TEST_CASE_FIXTURE(FrontendFixture, "parse_only")
+{
+    fileResolver.source["game/Gui/Modules/A"] = R"(
+        local a: number = 'oh no a type error'
+        return {a=a}
+    )";
+
+    fileResolver.source["game/Gui/Modules/B"] = R"(
+        local Modules = script.Parent
+        local A = require(Modules.A)
+        local b: number = 2
+    )";
+
+    frontend.parse("game/Gui/Modules/B");
+
+    REQUIRE(frontend.sourceNodes.count("game/Gui/Modules/A"));
+    REQUIRE(frontend.sourceNodes.count("game/Gui/Modules/B"));
+
+    auto node = frontend.sourceNodes["game/Gui/Modules/B"];
+    CHECK_EQ(node->requireSet.count("game/Gui/Modules/A"), 1);
+    REQUIRE_EQ(node->requireLocations.size(), 1);
+    CHECK_EQ(node->requireLocations[0].second, Luau::Location(Position(2, 18), Position(2, 36)));
+
+    // Early parse doesn't cause typechecking to be skipped
+    CheckResult result = frontend.check("game/Gui/Modules/B");
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    CHECK_EQ("game/Gui/Modules/A", result.errors[0].moduleName);
+    CHECK_EQ("Type 'string' could not be converted into 'number'", toString(result.errors[0]));
+}
+
 TEST_SUITE_END();

tests/IrBuilder.test.cpp

@@ -526,7 +526,7 @@ bb_0:
 )");
 }
 
-TEST_CASE_FIXTURE(IrBuilderFixture, "Bit32Blocked")
+TEST_CASE_FIXTURE(IrBuilderFixture, "Bit32RangeReduction")
 {
     IrOp block = build.block(IrBlockKind::Internal);
 
@@ -534,10 +534,10 @@ TEST_CASE_FIXTURE(IrBuilderFixture, "Bit32Blocked")
 
     build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITLSHIFT_UINT, build.constInt(0xf), build.constInt(-10)));
     build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITLSHIFT_UINT, build.constInt(0xf), build.constInt(140)));
-    build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITRSHIFT_UINT, build.constInt(0xf), build.constInt(-10)));
+    build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITRSHIFT_UINT, build.constInt(0xffffff), build.constInt(-10)));
-    build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITRSHIFT_UINT, build.constInt(0xf), build.constInt(140)));
+    build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITRSHIFT_UINT, build.constInt(0xffffff), build.constInt(140)));
-    build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITARSHIFT_UINT, build.constInt(0xf), build.constInt(-10)));
+    build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITARSHIFT_UINT, build.constInt(0xffffff), build.constInt(-10)));
-    build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITARSHIFT_UINT, build.constInt(0xf), build.constInt(140)));
+    build.inst(IrCmd::STORE_INT, build.vmReg(10), build.inst(IrCmd::BITARSHIFT_UINT, build.constInt(0xffffff), build.constInt(140)));
 
     build.inst(IrCmd::RETURN, build.constUint(0));
 
@@ -546,18 +546,12 @@ TEST_CASE_FIXTURE(IrBuilderFixture, "Bit32Blocked")
 
     CHECK("\n" + toString(build.function, /* includeUseInfo */ false) == R"(
 bb_0:
-   %0 = BITLSHIFT_UINT 15i, -10i
+   STORE_INT R10, 62914560i
-   STORE_INT R10, %0
+   STORE_INT R10, 61440i
-   %2 = BITLSHIFT_UINT 15i, 140i
+   STORE_INT R10, 3i
-   STORE_INT R10, %2
+   STORE_INT R10, 4095i
-   %4 = BITRSHIFT_UINT 15i, -10i
+   STORE_INT R10, 3i
-   STORE_INT R10, %4
+   STORE_INT R10, 4095i
-   %6 = BITRSHIFT_UINT 15i, 140i
-   STORE_INT R10, %6
-   %8 = BITARSHIFT_UINT 15i, -10i
-   STORE_INT R10, %8
-   %10 = BITARSHIFT_UINT 15i, 140i
-   STORE_INT R10, %10
    RETURN 0u
 
 )");
@@ -1864,6 +1858,34 @@ bb_0:
 )");
 }
 
+TEST_CASE_FIXTURE(IrBuilderFixture, "LoadPropagatesOnlyRightType")
+{
+    IrOp block = build.block(IrBlockKind::Internal);
+
+    build.beginBlock(block);
+
+    build.inst(IrCmd::STORE_INT, build.vmReg(0), build.constInt(2));
+    IrOp value1 = build.inst(IrCmd::LOAD_DOUBLE, build.vmReg(0));
+    build.inst(IrCmd::STORE_DOUBLE, build.vmReg(1), value1);
+    IrOp value2 = build.inst(IrCmd::LOAD_INT, build.vmReg(1));
+    build.inst(IrCmd::STORE_INT, build.vmReg(2), value2);
+    build.inst(IrCmd::RETURN, build.constUint(0));
+
+    updateUseCounts(build.function);
+    constPropInBlockChains(build, true);
+
+    CHECK("\n" + toString(build.function, /* includeUseInfo */ false) == R"(
+bb_0:
+   STORE_INT R0, 2i
+   %1 = LOAD_DOUBLE R0
+   STORE_DOUBLE R1, %1
+   %3 = LOAD_INT R1
+   STORE_INT R2, %3
+   RETURN 0u
+
+)");
+}
+
 TEST_SUITE_END();
 
 TEST_SUITE_BEGIN("Analysis");

tests/IrCallWrapperX64.test.cpp

@@ -10,8 +10,8 @@ using namespace Luau::CodeGen::X64;
 class IrCallWrapperX64Fixture
 {
 public:
-    IrCallWrapperX64Fixture()
+    IrCallWrapperX64Fixture(ABIX64 abi = ABIX64::Windows)
-        : build(/* logText */ true, ABIX64::Windows)
+        : build(/* logText */ true, abi)
         , regs(build, function)
         , callWrap(regs, build, ~0u)
     {
@@ -42,6 +42,15 @@ public:
     static constexpr RegisterX64 rArg4d = r9d;
 };
 
+class IrCallWrapperX64FixtureSystemV : public IrCallWrapperX64Fixture
+{
+public:
+    IrCallWrapperX64FixtureSystemV()
+        : IrCallWrapperX64Fixture(ABIX64::SystemV)
+    {
+    }
+};
+
 TEST_SUITE_BEGIN("IrCallWrapperX64");
 
 TEST_CASE_FIXTURE(IrCallWrapperX64Fixture, "SimpleRegs")
@@ -519,4 +528,35 @@ TEST_CASE_FIXTURE(IrCallWrapperX64Fixture, "ImmediateConflictWithFunction")
 )");
 }
 
+TEST_CASE_FIXTURE(IrCallWrapperX64FixtureSystemV, "SuggestedConflictWithReserved")
+{
+    ScopedRegX64 tmp{regs, regs.takeReg(r9, kInvalidInstIdx)};
+
+    IrCallWrapperX64 callWrap(regs, build);
+    callWrap.addArgument(SizeX64::qword, r12);
+    callWrap.addArgument(SizeX64::qword, r13);
+    callWrap.addArgument(SizeX64::qword, r14);
+    callWrap.addArgument(SizeX64::dword, 2);
+    callWrap.addArgument(SizeX64::qword, 1);
+
+    RegisterX64 reg = callWrap.suggestNextArgumentRegister(SizeX64::dword);
+    build.mov(reg, 10);
+    callWrap.addArgument(SizeX64::dword, reg);
+
+    callWrap.call(tmp.release());
+
+    checkMatch(R"(
+ mov         eax,Ah
+ mov         rdi,r12
+ mov         rsi,r13
+ mov         rdx,r14
+ mov         rcx,r9
+ mov         r9d,eax
+ mov         rax,rcx
+ mov         ecx,2
+ mov         r8,1
+ call        rax
+)");
+}
+
 TEST_SUITE_END();

tests/Normalize.test.cpp

@@ -735,6 +735,37 @@ TEST_CASE_FIXTURE(NormalizeFixture, "intersection_of_metatables_where_the_metata
     CHECK("{ @metatable *error-type*, {|  |} }" == toString(normal("Mt<{}, any> & Mt<{}, err>")));
 }
 
+TEST_CASE_FIXTURE(NormalizeFixture, "recurring_intersection")
+{
+    CheckResult result = check(R"(
+        type A = any?
+        type B = A & A
+    )");
+
+    std::optional<TypeId> t = lookupType("B");
+    REQUIRE(t);
+
+    const NormalizedType* nt = normalizer.normalize(*t);
+    REQUIRE(nt);
+
+    CHECK("any" == toString(normalizer.typeFromNormal(*nt)));
+}
+
+TEST_CASE_FIXTURE(NormalizeFixture, "cyclic_union")
+{
+    ScopedFastFlag sff{"LuauNormalizeCyclicUnions", true};
+
+    // T where T = any & (number | T)
+    TypeId t = arena.addType(BlockedType{});
+    TypeId u = arena.addType(UnionType{{builtinTypes->numberType, t}});
+    asMutable(t)->ty.emplace<IntersectionType>(IntersectionType{{builtinTypes->anyType, u}});
+
+    const NormalizedType* nt = normalizer.normalize(t);
+    REQUIRE(nt);
+
+    CHECK("number" == toString(normalizer.typeFromNormal(*nt)));
+}
+
 TEST_CASE_FIXTURE(NormalizeFixture, "crazy_metatable")
 {
     CHECK("never" == toString(normal("Mt<{}, number> & Mt<{}, string>")));

tests/TypeInfer.classes.test.cpp

@@ -479,7 +479,6 @@ TEST_CASE_FIXTURE(ClassFixture, "callable_classes")
 TEST_CASE_FIXTURE(ClassFixture, "indexable_classes")
 {
     // Test reading from an index
-    ScopedFastFlag LuauTypecheckClassTypeIndexers("LuauTypecheckClassTypeIndexers", true);
     {
         CheckResult result = check(R"(
             local x : IndexableClass

tests/TypeInfer.definitions.test.cpp

@@ -398,7 +398,6 @@ TEST_CASE_FIXTURE(Fixture, "class_definition_string_props")
 TEST_CASE_FIXTURE(Fixture, "class_definition_indexer")
 {
     ScopedFastFlag LuauParseDeclareClassIndexer("LuauParseDeclareClassIndexer", true);
-    ScopedFastFlag LuauTypecheckClassTypeIndexers("LuauTypecheckClassTypeIndexers", true);
 
     loadDefinition(R"(
         declare class Foo

tests/TypeInfer.functions.test.cpp

@@ -2096,4 +2096,46 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "attempt_to_call_an_intersection_of_tables_wi
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "num_is_solved_before_num_or_str")
+{
+    CheckResult result = check(R"(
+        function num()
+            return 5
+        end
+
+        local function num_or_str()
+            if math.random() > 0.5 then
+                return num()
+            else
+                return "some string"
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ("Type 'string' could not be converted into 'number'", toString(result.errors[0]));
+    CHECK_EQ("() -> number", toString(requireType("num_or_str")));
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "num_is_solved_after_num_or_str")
+{
+    CheckResult result = check(R"(
+        local function num_or_str()
+            if math.random() > 0.5 then
+                return num()
+            else
+                return "some string"
+            end
+        end
+
+        function num()
+            return 5
+        end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ("Type 'string' could not be converted into 'number'", toString(result.errors[0]));
+    CHECK_EQ("() -> number", toString(requireType("num_or_str")));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.refinements.test.cpp

@@ -917,6 +917,52 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "type_comparison_ifelse_expression")
         CHECK_EQ("any", toString(requireTypeAtPosition({6, 66})));
 }
 
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "is_truthy_constraint_while_expression")
+{
+    CheckResult result = check(R"(
+        function f(v:string?)
+            while v do
+                local foo = v
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("string", toString(requireTypeAtPosition({3, 28})));
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "invert_is_truthy_constraint_while_expression")
+{
+    CheckResult result = check(R"(
+        function f(v:string?)
+            while not v do
+                local foo = v
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("nil", toString(requireTypeAtPosition({3, 28})));
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "refine_the_correct_types_opposite_of_while_a_is_not_number_or_string")
+{
+    CheckResult result = check(R"(
+        local function f(a: string | number | boolean)
+            while type(a) ~= "number" and type(a) ~= "string" do
+                local foo = a
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("boolean", toString(requireTypeAtPosition({3, 28})));
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "correctly_lookup_a_shadowed_local_that_which_was_previously_refined")
 {
     CheckResult result = check(R"(
@@ -1580,8 +1626,6 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "refine_a_param_that_got_resolved_duri
 
 TEST_CASE_FIXTURE(Fixture, "refine_a_property_of_some_global")
 {
-    ScopedFastFlag sff{"DebugLuauDeferredConstraintResolution", true};
-
     CheckResult result = check(R"(
         foo = { bar = 5 :: number? }
 
@@ -1590,9 +1634,12 @@ TEST_CASE_FIXTURE(Fixture, "refine_a_property_of_some_global")
         end
     )");
 
-    LUAU_REQUIRE_ERROR_COUNT(3, result);
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+    {
+        LUAU_REQUIRE_ERROR_COUNT(3, result);
 
-    CHECK_EQ("~(false?)", toString(requireTypeAtPosition({4, 30})));
+        CHECK_EQ("~(false?)", toString(requireTypeAtPosition({4, 30})));
+    }
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "dataflow_analysis_can_tell_refinements_when_its_appropriate_to_refine_into_nil_or_never")
@@ -1757,4 +1804,20 @@ TEST_CASE_FIXTURE(Fixture, "refinements_should_not_affect_assignment")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "refinements_should_preserve_error_suppression")
+{
+    CheckResult result = check(R"(
+        local a: any = {}
+        local b
+        if typeof(a) == "table" then
+           b = a.field
+        end
+    )");
+
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+        LUAU_REQUIRE_NO_ERRORS(result);
+    else
+        LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.singletons.test.cpp

@@ -9,6 +9,20 @@ using namespace Luau;
 
 TEST_SUITE_BEGIN("TypeSingletons");
 
+TEST_CASE_FIXTURE(Fixture, "function_args_infer_singletons")
+{
+    CheckResult result = check(R"(
+--!strict
+type Phase = "A" | "B" | "C"
+local function f(e : Phase) : number
+    return 0
+end
+local e = f("B")
+)");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_CASE_FIXTURE(Fixture, "bool_singletons")
 {
     CheckResult result = check(R"(

tests/conformance/native.lua

@@ -61,4 +61,35 @@ end
 
 assert(pcall(fuzzfail5) == false)
 
+local function fuzzfail6(_)
+  return bit32.extract(_,671088640,_)
+end
+
+assert(pcall(fuzzfail6, 1) == false)
+
+local function fuzzfail7(_)
+  return bit32.extract(_,_,671088640)
+end
+
+assert(pcall(fuzzfail7, 1) == false)
+
+local function fuzzfail8(...)
+  local _ = _,_
+  _.n0,_,_,_,_,_,_,_,_._,_,_,_[...],_,_,_ = nil
+  _,n0,_,_,_,_,_,_,_,_,l0,_,_,_,_ = nil
+  function _()
+  end
+  _._,_,_,_,_,_,_,_,_,_,_[...],_,n0[l0],_ = nil
+  _[...],_,_,_,_,_,_,_,_()[_],_,_,_,_,_ = _(),...
+end
+
+assert(pcall(fuzzfail8) == false)
+
+local function fuzzfail9()
+  local _ = bit32.bor
+  local x = _(_(_,_),_(_,_),_(-16834560,_),_(_(- _,-2130706432)),- _),_(_(_,_),_(-16834560,-2130706432))
+end
+
+assert(pcall(fuzzfail9) == false)
+
 return('OK')

tools/faillist.txt

@@ -54,6 +54,8 @@ ProvisionalTests.table_insert_with_a_singleton_argument
 ProvisionalTests.typeguard_inference_incomplete
 RefinementTest.discriminate_from_truthiness_of_x
 RefinementTest.not_t_or_some_prop_of_t
+RefinementTest.refine_a_property_of_some_global
+RefinementTest.refinements_should_preserve_error_suppression
 RefinementTest.truthy_constraint_on_properties
 RefinementTest.type_narrow_to_vector
 RefinementTest.typeguard_cast_free_table_to_vector
@@ -96,7 +98,6 @@ TableTests.shared_selfs
 TableTests.shared_selfs_from_free_param
 TableTests.shared_selfs_through_metatables
 TableTests.table_call_metamethod_basic
-TableTests.table_call_metamethod_generic
 TableTests.table_simple_call
 TableTests.table_subtyping_with_missing_props_dont_report_multiple_errors
 TableTests.used_colon_instead_of_dot
@@ -131,7 +132,6 @@ TypeInfer.tc_after_error_recovery_no_replacement_name_in_error
 TypeInfer.type_infer_recursion_limit_no_ice
 TypeInfer.type_infer_recursion_limit_normalizer
 TypeInferAnyError.for_in_loop_iterator_is_any2
-TypeInferClasses.callable_classes
 TypeInferClasses.class_type_mismatch_with_name_conflict
 TypeInferClasses.index_instance_property
 TypeInferFunctions.cannot_hoist_interior_defns_into_signature