Sync to upstream/release/547 (#690)

- Type aliases can no longer override primitive types; attempts to do
that will result in a type error
- Fix misleading type error messages for mismatches in expression list
length during assignment
- Fix incorrect type name display in certain cases
- setmetatable/getmetatable are now ~2x faster
- tools/perfstat.py can be used to display statistics about profiles
captured via --profile switch

Analysis/include/Luau/BuiltinDefinitions.h

@@ -8,9 +8,11 @@
 namespace Luau
 {
 
-void registerBuiltinTypes(TypeChecker& typeChecker);
 void registerBuiltinTypes(Frontend& frontend);
 
+void registerBuiltinGlobals(TypeChecker& typeChecker);
+void registerBuiltinGlobals(Frontend& frontend);
+
 TypeId makeUnion(TypeArena& arena, std::vector<TypeId>&& types);
 TypeId makeIntersection(TypeArena& arena, std::vector<TypeId>&& types);
 

Analysis/include/Luau/Config.h

@@ -17,12 +17,9 @@ constexpr const char* kConfigName = ".luaurc";
 
 struct Config
 {
-    Config()
+    Config();
-    {
-        enabledLint.setDefaults();
-    }
 
-    Mode mode = Mode::NoCheck;
+    Mode mode;
 
     ParseOptions parseOptions;
 

Analysis/include/Luau/Constraint.h

@@ -94,8 +94,9 @@ struct FunctionCallConstraint
 {
     std::vector<NotNull<const struct Constraint>> innerConstraints;
     TypeId fn;
+    TypePackId argsPack;
     TypePackId result;
-    class AstExprCall* astFragment;
+    class AstExprCall* callSite;
 };
 
 // result ~ prim ExpectedType SomeSingletonType MultitonType

Analysis/include/Luau/ConstraintGraphBuilder.h

@@ -124,6 +124,7 @@ struct ConstraintGraphBuilder
     void visit(const ScopePtr& scope, AstStatDeclareGlobal* declareGlobal);
     void visit(const ScopePtr& scope, AstStatDeclareClass* declareClass);
     void visit(const ScopePtr& scope, AstStatDeclareFunction* declareFunction);
+    void visit(const ScopePtr& scope, AstStatError* error);
 
     TypePackId checkPack(const ScopePtr& scope, AstArray<AstExpr*> exprs, const std::vector<TypeId>& expectedTypes = {});
     TypePackId checkPack(const ScopePtr& scope, AstExpr* expr, const std::vector<TypeId>& expectedTypes = {});

Analysis/include/Luau/ConstraintSolver.h

@@ -104,6 +104,7 @@ struct ConstraintSolver
     bool tryDispatch(const HasPropConstraint& c, NotNull<const Constraint> constraint);
 
     // for a, ... in some_table do
+    // also handles __iter metamethod
     bool tryDispatchIterableTable(TypeId iteratorTy, const IterableConstraint& c, NotNull<const Constraint> constraint, bool force);
 
     // for a, ... in next_function, t, ... do

Analysis/include/Luau/Error.h

@@ -81,7 +81,7 @@ struct OnlyTablesCanHaveMethods
 struct DuplicateTypeDefinition
 {
     Name name;
-    Location previousLocation;
+    std::optional<Location> previousLocation;
 
     bool operator==(const DuplicateTypeDefinition& rhs) const;
 };
@@ -91,7 +91,8 @@ struct CountMismatch
     enum Context
     {
         Arg,
-        Result,
+        FunctionResult,
+        ExprListResult,
         Return,
     };
     size_t expected;

Analysis/include/Luau/Frontend.h

@@ -157,7 +157,8 @@ struct Frontend
     ScopePtr getGlobalScope();
 
 private:
-    ModulePtr check(const SourceModule& sourceModule, Mode mode, const ScopePtr& environmentScope, std::vector<RequireCycle> requireCycles);
+    ModulePtr check(const SourceModule& sourceModule, Mode mode, const ScopePtr& environmentScope, std::vector<RequireCycle> requireCycles,
+        bool forAutocomplete = false);
 
     std::pair<SourceNode*, SourceModule*> getSourceNode(CheckResult& checkResult, const ModuleName& name);
     SourceModule parse(const ModuleName& name, std::string_view src, const ParseOptions& parseOptions);
@@ -171,10 +172,9 @@ private:
     std::unordered_map<std::string, ScopePtr> environments;
     std::unordered_map<std::string, std::function<void(TypeChecker&, ScopePtr)>> builtinDefinitions;
 
-    ScopePtr globalScope;
+    SingletonTypes singletonTypes_;
 
 public:
-    SingletonTypes singletonTypes_;
     const NotNull<SingletonTypes> singletonTypes;
 
     FileResolver* fileResolver;
@@ -186,13 +186,15 @@ public:
     FrontendOptions options;
     InternalErrorReporter iceHandler;
     TypeArena globalTypes;
-    TypeArena arenaForAutocomplete;
 
     std::unordered_map<ModuleName, SourceNode> sourceNodes;
     std::unordered_map<ModuleName, SourceModule> sourceModules;
     std::unordered_map<ModuleName, RequireTraceResult> requireTrace;
 
     Stats stats = {};
+
+private:
+    ScopePtr globalScope;
 };
 
 } // namespace Luau

Analysis/include/Luau/Instantiation.h

@@ -14,16 +14,18 @@ struct TxnLog;
 // A substitution which replaces generic types in a given set by free types.
 struct ReplaceGenerics : Substitution
 {
-    ReplaceGenerics(
+    ReplaceGenerics(const TxnLog* log, TypeArena* arena, TypeLevel level, Scope* scope, const std::vector<TypeId>& generics,
-        const TxnLog* log, TypeArena* arena, TypeLevel level, const std::vector<TypeId>& generics, const std::vector<TypePackId>& genericPacks)
+        const std::vector<TypePackId>& genericPacks)
         : Substitution(log, arena)
         , level(level)
+        , scope(scope)
         , generics(generics)
         , genericPacks(genericPacks)
     {
     }
 
     TypeLevel level;
+    Scope* scope;
     std::vector<TypeId> generics;
     std::vector<TypePackId> genericPacks;
     bool ignoreChildren(TypeId ty) override;
@@ -36,13 +38,15 @@ struct ReplaceGenerics : Substitution
 // A substitution which replaces generic functions by monomorphic functions
 struct Instantiation : Substitution
 {
-    Instantiation(const TxnLog* log, TypeArena* arena, TypeLevel level)
+    Instantiation(const TxnLog* log, TypeArena* arena, TypeLevel level, Scope* scope)
         : Substitution(log, arena)
         , level(level)
+        , scope(scope)
     {
     }
 
     TypeLevel level;
+    Scope* scope;
     bool ignoreChildren(TypeId ty) override;
     bool isDirty(TypeId ty) override;
     bool isDirty(TypePackId tp) override;

Analysis/include/Luau/Scope.h

@@ -49,9 +49,11 @@ struct Scope
     std::unordered_map<Name, TypeFun> exportedTypeBindings;
     std::unordered_map<Name, TypeFun> privateTypeBindings;
     std::unordered_map<Name, Location> typeAliasLocations;
-
     std::unordered_map<Name, std::unordered_map<Name, TypeFun>> importedTypeBindings;
 
+    DenseHashSet<Name> builtinTypeNames{""};
+    void addBuiltinTypeBinding(const Name& name, const TypeFun& tyFun);
+
     std::optional<TypeId> lookup(Symbol sym);
 
     std::optional<TypeFun> lookupType(const Name& name);
@@ -61,7 +63,7 @@ struct Scope
     std::optional<TypePackId> lookupPack(const Name& name);
 
     // WARNING: This function linearly scans for a string key of equal value!  It is thus O(n**2)
-    std::optional<Binding> linearSearchForBinding(const std::string& name, bool traverseScopeChain = true);
+    std::optional<Binding> linearSearchForBinding(const std::string& name, bool traverseScopeChain = true) const;
 
     RefinementMap refinements;
 
@@ -73,4 +75,13 @@ struct Scope
     std::unordered_map<Name, TypePackId> typeAliasTypePackParameters;
 };
 
+// Returns true iff the left scope encloses the right scope.  A Scope* equal to
+// nullptr is considered to be the outermost-possible scope.
+bool subsumesStrict(Scope* left, Scope* right);
+
+// Returns true if the left scope encloses the right scope, or if they are the
+// same scope.  As in subsumesStrict(), nullptr is considered to be the
+// outermost-possible scope.
+bool subsumes(Scope* left, Scope* right);
+
 } // namespace Luau

Analysis/include/Luau/TxnLog.h

@@ -186,6 +186,16 @@ struct TxnLog
     // The pointer returned lives until `commit` or `clear` is called.
     PendingTypePack* changeLevel(TypePackId tp, TypeLevel newLevel);
 
+    // Queues the replacement of a type's scope with the provided scope.
+    //
+    // The pointer returned lives until `commit` or `clear` is called.
+    PendingType* changeScope(TypeId ty, NotNull<Scope> scope);
+
+    // Queues the replacement of a type pack's scope with the provided scope.
+    //
+    // The pointer returned lives until `commit` or `clear` is called.
+    PendingTypePack* changeScope(TypePackId tp, NotNull<Scope> scope);
+
     // Queues a replacement of a table type with another table type with a new
     // indexer.
     //

Analysis/include/Luau/TypeArena.h

@@ -30,6 +30,7 @@ struct TypeArena
 
     TypeId freshType(TypeLevel level);
     TypeId freshType(Scope* scope);
+    TypeId freshType(Scope* scope, TypeLevel level);
 
     TypePackId freshTypePack(Scope* scope);
 

Analysis/include/Luau/TypeInfer.h

@@ -80,10 +80,12 @@ struct TypeChecker
     void check(const ScopePtr& scope, const AstStatForIn& forin);
     void check(const ScopePtr& scope, TypeId ty, const ScopePtr& funScope, const AstStatFunction& function);
     void check(const ScopePtr& scope, TypeId ty, const ScopePtr& funScope, const AstStatLocalFunction& function);
-    void check(const ScopePtr& scope, const AstStatTypeAlias& typealias, int subLevel = 0, bool forwardDeclare = false);
+    void check(const ScopePtr& scope, const AstStatTypeAlias& typealias);
     void check(const ScopePtr& scope, const AstStatDeclareClass& declaredClass);
     void check(const ScopePtr& scope, const AstStatDeclareFunction& declaredFunction);
 
+    void prototype(const ScopePtr& scope, const AstStatTypeAlias& typealias, int subLevel = 0);
+
     void checkBlock(const ScopePtr& scope, const AstStatBlock& statement);
     void checkBlockWithoutRecursionCheck(const ScopePtr& scope, const AstStatBlock& statement);
     void checkBlockTypeAliases(const ScopePtr& scope, std::vector<AstStat*>& sorted);
@@ -392,8 +394,12 @@ private:
     std::vector<std::pair<TypeId, ScopePtr>> deferredQuantification;
 };
 
+using PrintLineProc = void(*)(const std::string&);
+
+extern PrintLineProc luauPrintLine;
+
 // Unit test hook
-void setPrintLine(void (*pl)(const std::string& s));
+void setPrintLine(PrintLineProc pl);
 void resetPrintLine();
 
 } // namespace Luau

Analysis/include/Luau/TypeUtils.h

@@ -25,4 +25,8 @@ std::optional<TypeId> getIndexTypeFromType(const ScopePtr& scope, ErrorVec& erro
 // Returns the minimum and maximum number of types the argument list can accept.
 std::pair<size_t, std::optional<size_t>> getParameterExtents(const TxnLog* log, TypePackId tp, bool includeHiddenVariadics = false);
 
+// "Render" a type pack out to an array of a given length. Expands variadics and
+// various other things to get there.
+std::vector<TypeId> flatten(TypeArena& arena, NotNull<SingletonTypes> singletonTypes, TypePackId pack, size_t length);
+
 } // namespace Luau

Analysis/include/Luau/TypeVar.h

@@ -27,6 +27,7 @@ namespace Luau
 
 struct TypeArena;
 struct Scope;
+using ScopePtr = std::shared_ptr<Scope>;
 
 /**
  * There are three kinds of type variables:
@@ -264,7 +265,15 @@ struct WithPredicate
 using MagicFunction = std::function<std::optional<WithPredicate<TypePackId>>(
     struct TypeChecker&, const std::shared_ptr<struct Scope>&, const class AstExprCall&, WithPredicate<TypePackId>)>;
 
-using DcrMagicFunction = std::function<bool(NotNull<struct ConstraintSolver>, TypePackId, const class AstExprCall*)>;
+struct MagicFunctionCallContext
+{
+    NotNull<struct ConstraintSolver> solver;
+    const class AstExprCall* callSite;
+    TypePackId arguments;
+    TypePackId result;
+};
+
+using DcrMagicFunction = std::function<bool(MagicFunctionCallContext)>;
 
 struct FunctionTypeVar
 {
@@ -277,10 +286,14 @@ struct FunctionTypeVar
 
     // Local monomorphic function
     FunctionTypeVar(TypeLevel level, TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn = {}, bool hasSelf = false);
+    FunctionTypeVar(
+        TypeLevel level, Scope* scope, TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn = {}, bool hasSelf = false);
 
     // Local polymorphic function
     FunctionTypeVar(TypeLevel level, std::vector<TypeId> generics, std::vector<TypePackId> genericPacks, TypePackId argTypes, TypePackId retTypes,
         std::optional<FunctionDefinition> defn = {}, bool hasSelf = false);
+    FunctionTypeVar(TypeLevel level, Scope* scope, std::vector<TypeId> generics, std::vector<TypePackId> genericPacks, TypePackId argTypes,
+        TypePackId retTypes, std::optional<FunctionDefinition> defn = {}, bool hasSelf = false);
 
     TypeLevel level;
     Scope* scope = nullptr;
@@ -345,8 +358,9 @@ struct TableTypeVar
     using Props = std::map<Name, Property>;
 
     TableTypeVar() = default;
-    explicit TableTypeVar(TableState state, TypeLevel level);
+    explicit TableTypeVar(TableState state, TypeLevel level, Scope* scope = nullptr);
     TableTypeVar(const Props& props, const std::optional<TableIndexer>& indexer, TypeLevel level, TableState state);
+    TableTypeVar(const Props& props, const std::optional<TableIndexer>& indexer, TypeLevel level, Scope* scope, TableState state);
 
     Props props;
     std::optional<TableIndexer> indexer;

Analysis/include/Luau/Unifiable.h

@@ -85,6 +85,7 @@ struct Free
 {
     explicit Free(TypeLevel level);
     explicit Free(Scope* scope);
+    explicit Free(Scope* scope, TypeLevel level);
 
     int index;
     TypeLevel level;

Analysis/include/Luau/Unifier.h

@@ -60,6 +60,7 @@ struct Unifier
     Location location;
     Variance variance = Covariant;
     bool anyIsTop = false; // If true, we consider any to be a top type.  If false, it is a familiar but weird mix of top and bottom all at once.
+    bool useScopes = false; // If true, we use the scope hierarchy rather than TypeLevels
     CountMismatch::Context ctx = CountMismatch::Arg;
 
     UnifierSharedState& sharedState;
@@ -140,6 +141,6 @@ private:
     std::optional<int> firstPackErrorPos;
 };
 
-void promoteTypeLevels(TxnLog& log, const TypeArena* arena, TypeLevel minLevel, TypePackId tp);
+void promoteTypeLevels(TxnLog& log, const TypeArena* arena, TypeLevel minLevel, Scope* outerScope, bool useScope, TypePackId tp);
 
 } // namespace Luau

Analysis/src/Autocomplete.cpp

@@ -1208,13 +1208,11 @@ static bool autocompleteIfElseExpression(
     }
 }
 
-static AutocompleteContext autocompleteExpression(const SourceModule& sourceModule, const Module& module, const TypeChecker& typeChecker,
+static AutocompleteContext autocompleteExpression(const SourceModule& sourceModule, const Module& module, NotNull<SingletonTypes> singletonTypes,
     TypeArena* typeArena, const std::vector<AstNode*>& ancestry, Position position, AutocompleteEntryMap& result)
 {
     LUAU_ASSERT(!ancestry.empty());
 
-    NotNull<SingletonTypes> singletonTypes = typeChecker.singletonTypes;
-
     AstNode* node = ancestry.rbegin()[0];
 
     if (node->is<AstExprIndexName>())
@@ -1254,16 +1252,16 @@ static AutocompleteContext autocompleteExpression(const SourceModule& sourceModu
             scope = scope->parent;
         }
 
-        TypeCorrectKind correctForNil = checkTypeCorrectKind(module, typeArena, singletonTypes, node, position, typeChecker.nilType);
+        TypeCorrectKind correctForNil = checkTypeCorrectKind(module, typeArena, singletonTypes, node, position, singletonTypes->nilType);
         TypeCorrectKind correctForTrue = checkTypeCorrectKind(module, typeArena, singletonTypes, node, position, singletonTypes->trueType);
         TypeCorrectKind correctForFalse = checkTypeCorrectKind(module, typeArena, singletonTypes, node, position, singletonTypes->falseType);
         TypeCorrectKind correctForFunction =
             functionIsExpectedAt(module, node, position).value_or(false) ? TypeCorrectKind::Correct : TypeCorrectKind::None;
 
         result["if"] = {AutocompleteEntryKind::Keyword, std::nullopt, false, false};
-        result["true"] = {AutocompleteEntryKind::Keyword, typeChecker.booleanType, false, false, correctForTrue};
+        result["true"] = {AutocompleteEntryKind::Keyword, singletonTypes->booleanType, false, false, correctForTrue};
-        result["false"] = {AutocompleteEntryKind::Keyword, typeChecker.booleanType, false, false, correctForFalse};
+        result["false"] = {AutocompleteEntryKind::Keyword, singletonTypes->booleanType, false, false, correctForFalse};
-        result["nil"] = {AutocompleteEntryKind::Keyword, typeChecker.nilType, false, false, correctForNil};
+        result["nil"] = {AutocompleteEntryKind::Keyword, singletonTypes->nilType, false, false, correctForNil};
         result["not"] = {AutocompleteEntryKind::Keyword};
         result["function"] = {AutocompleteEntryKind::Keyword, std::nullopt, false, false, correctForFunction};
 
@@ -1274,11 +1272,11 @@ static AutocompleteContext autocompleteExpression(const SourceModule& sourceModu
     return AutocompleteContext::Expression;
 }
 
-static AutocompleteResult autocompleteExpression(const SourceModule& sourceModule, const Module& module, const TypeChecker& typeChecker,
+static AutocompleteResult autocompleteExpression(const SourceModule& sourceModule, const Module& module, NotNull<SingletonTypes> singletonTypes,
     TypeArena* typeArena, const std::vector<AstNode*>& ancestry, Position position)
 {
     AutocompleteEntryMap result;
-    AutocompleteContext context = autocompleteExpression(sourceModule, module, typeChecker, typeArena, ancestry, position, result);
+    AutocompleteContext context = autocompleteExpression(sourceModule, module, singletonTypes, typeArena, ancestry, position, result);
     return {result, ancestry, context};
 }
 
@@ -1385,13 +1383,13 @@ static std::optional<AutocompleteEntryMap> autocompleteStringParams(const Source
     return std::nullopt;
 }
 
-static AutocompleteResult autocomplete(const SourceModule& sourceModule, const ModulePtr& module, const TypeChecker& typeChecker,
+static AutocompleteResult autocomplete(const SourceModule& sourceModule, const ModulePtr& module, NotNull<SingletonTypes> singletonTypes,
-    TypeArena* typeArena, Position position, StringCompletionCallback callback)
+    Scope* globalScope, Position position, StringCompletionCallback callback)
 {
     if (isWithinComment(sourceModule, position))
         return {};
 
-    NotNull<SingletonTypes> singletonTypes = typeChecker.singletonTypes;
+    TypeArena typeArena;
 
     std::vector<AstNode*> ancestry = findAncestryAtPositionForAutocomplete(sourceModule, position);
     LUAU_ASSERT(!ancestry.empty());
@@ -1419,11 +1417,10 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
         PropIndexType indexType = indexName->op == ':' ? PropIndexType::Colon : PropIndexType::Point;
 
         if (!FFlag::LuauSelfCallAutocompleteFix3 && isString(ty))
-            return {autocompleteProps(
+            return {autocompleteProps(*module, &typeArena, singletonTypes, globalScope->bindings[AstName{"string"}].typeId, indexType, ancestry),
-                        *module, typeArena, singletonTypes, typeChecker.globalScope->bindings[AstName{"string"}].typeId, indexType, ancestry),
                 ancestry, AutocompleteContext::Property};
         else
-            return {autocompleteProps(*module, typeArena, singletonTypes, ty, indexType, ancestry), ancestry, AutocompleteContext::Property};
+            return {autocompleteProps(*module, &typeArena, singletonTypes, ty, indexType, ancestry), ancestry, AutocompleteContext::Property};
     }
     else if (auto typeReference = node->as<AstTypeReference>())
     {
@@ -1441,7 +1438,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
         if (statLocal->vars.size == 1 && (!statLocal->equalsSignLocation || position < statLocal->equalsSignLocation->begin))
             return {{{"function", AutocompleteEntry{AutocompleteEntryKind::Keyword}}}, ancestry, AutocompleteContext::Unknown};
         else if (statLocal->equalsSignLocation && position >= statLocal->equalsSignLocation->end)
-            return autocompleteExpression(sourceModule, *module, typeChecker, typeArena, ancestry, position);
+            return autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position);
         else
             return {};
     }
@@ -1455,7 +1452,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
 
             if (statFor->from->location.containsClosed(position) || statFor->to->location.containsClosed(position) ||
                 (statFor->step && statFor->step->location.containsClosed(position)))
-                return autocompleteExpression(sourceModule, *module, typeChecker, typeArena, ancestry, position);
+                return autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position);
 
             return {};
         }
@@ -1485,7 +1482,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
             AstExpr* lastExpr = statForIn->values.data[statForIn->values.size - 1];
 
             if (lastExpr->location.containsClosed(position))
-                return autocompleteExpression(sourceModule, *module, typeChecker, typeArena, ancestry, position);
+                return autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position);
 
             if (position > lastExpr->location.end)
                 return {{{"do", AutocompleteEntry{AutocompleteEntryKind::Keyword}}}, ancestry, AutocompleteContext::Keyword};
@@ -1509,7 +1506,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
             return {{{"do", AutocompleteEntry{AutocompleteEntryKind::Keyword}}}, ancestry, AutocompleteContext::Keyword};
 
         if (!statWhile->hasDo || position < statWhile->doLocation.begin)
-            return autocompleteExpression(sourceModule, *module, typeChecker, typeArena, ancestry, position);
+            return autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position);
 
         if (statWhile->hasDo && position > statWhile->doLocation.end)
             return {autocompleteStatement(sourceModule, *module, ancestry, position), ancestry, AutocompleteContext::Statement};
@@ -1526,7 +1523,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
     else if (AstStatIf* statIf = parent->as<AstStatIf>(); statIf && node->is<AstStatBlock>())
     {
         if (statIf->condition->is<AstExprError>())
-            return autocompleteExpression(sourceModule, *module, typeChecker, typeArena, ancestry, position);
+            return autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position);
         else if (!statIf->thenLocation || statIf->thenLocation->containsClosed(position))
             return {{{"then", AutocompleteEntry{AutocompleteEntryKind::Keyword}}}, ancestry, AutocompleteContext::Keyword};
     }
@@ -1534,7 +1531,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
              statIf && (!statIf->thenLocation || statIf->thenLocation->containsClosed(position)))
         return {{{"then", AutocompleteEntry{AutocompleteEntryKind::Keyword}}}, ancestry, AutocompleteContext::Keyword};
     else if (AstStatRepeat* statRepeat = node->as<AstStatRepeat>(); statRepeat && statRepeat->condition->is<AstExprError>())
-        return autocompleteExpression(sourceModule, *module, typeChecker, typeArena, ancestry, position);
+        return autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position);
     else if (AstStatRepeat* statRepeat = extractStat<AstStatRepeat>(ancestry); statRepeat)
         return {autocompleteStatement(sourceModule, *module, ancestry, position), ancestry, AutocompleteContext::Statement};
     else if (AstExprTable* exprTable = parent->as<AstExprTable>(); exprTable && (node->is<AstExprGlobal>() || node->is<AstExprConstantString>()))
@@ -1546,7 +1543,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
             {
                 if (auto it = module->astExpectedTypes.find(exprTable))
                 {
-                    auto result = autocompleteProps(*module, typeArena, singletonTypes, *it, PropIndexType::Key, ancestry);
+                    auto result = autocompleteProps(*module, &typeArena, singletonTypes, *it, PropIndexType::Key, ancestry);
 
                     // Remove keys that are already completed
                     for (const auto& item : exprTable->items)
@@ -1560,7 +1557,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
 
                     // If we know for sure that a key is being written, do not offer general expression suggestions
                     if (!key)
-                        autocompleteExpression(sourceModule, *module, typeChecker, typeArena, ancestry, position, result);
+                        autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position, result);
 
                     return {result, ancestry, AutocompleteContext::Property};
                 }
@@ -1588,7 +1585,7 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
             if (auto idxExpr = ancestry.at(ancestry.size() - 2)->as<AstExprIndexExpr>())
             {
                 if (auto it = module->astTypes.find(idxExpr->expr))
-                    autocompleteProps(*module, typeArena, singletonTypes, follow(*it), PropIndexType::Point, ancestry, result);
+                    autocompleteProps(*module, &typeArena, singletonTypes, follow(*it), PropIndexType::Point, ancestry, result);
             }
             else if (auto binExpr = ancestry.at(ancestry.size() - 2)->as<AstExprBinary>())
             {
@@ -1604,12 +1601,10 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
     }
 
     if (node->is<AstExprConstantNumber>())
-    {
         return {};
-    }
 
     if (node->asExpr())
-        return autocompleteExpression(sourceModule, *module, typeChecker, typeArena, ancestry, position);
+        return autocompleteExpression(sourceModule, *module, singletonTypes, &typeArena, ancestry, position);
     else if (node->asStat())
         return {autocompleteStatement(sourceModule, *module, ancestry, position), ancestry, AutocompleteContext::Statement};
 
@@ -1628,15 +1623,15 @@ AutocompleteResult autocomplete(Frontend& frontend, const ModuleName& moduleName
     if (!sourceModule)
         return {};
 
-    TypeChecker& typeChecker = frontend.typeCheckerForAutocomplete;
     ModulePtr module = frontend.moduleResolverForAutocomplete.getModule(moduleName);
 
     if (!module)
         return {};
 
-    AutocompleteResult autocompleteResult = autocomplete(*sourceModule, module, typeChecker, &frontend.arenaForAutocomplete, position, callback);
+    NotNull<SingletonTypes> singletonTypes = frontend.singletonTypes;
+    Scope* globalScope = frontend.typeCheckerForAutocomplete.globalScope.get();
 
-    frontend.arenaForAutocomplete.clear();
+    AutocompleteResult autocompleteResult = autocomplete(*sourceModule, module, singletonTypes, globalScope, position, callback);
 
     return autocompleteResult;
 }

Analysis/src/BuiltinDefinitions.cpp

@@ -1,18 +1,22 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/BuiltinDefinitions.h"
 
+#include "Luau/Ast.h"
 #include "Luau/Frontend.h"
 #include "Luau/Symbol.h"
 #include "Luau/Common.h"
 #include "Luau/ToString.h"
 #include "Luau/ConstraintSolver.h"
 #include "Luau/TypeInfer.h"
+#include "Luau/TypePack.h"
+#include "Luau/TypeVar.h"
 
 #include <algorithm>
 
 LUAU_FASTFLAGVARIABLE(LuauSetMetaTableArgsCheck, false)
 LUAU_FASTFLAG(LuauUnknownAndNeverType)
 LUAU_FASTFLAGVARIABLE(LuauBuiltInMetatableNoBadSynthetic, false)
+LUAU_FASTFLAG(LuauReportShadowedTypeAlias)
 
 /** FIXME: Many of these type definitions are not quite completely accurate.
  *
@@ -34,7 +38,9 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionPack(
 static std::optional<WithPredicate<TypePackId>> magicFunctionRequire(
     TypeChecker& typechecker, const ScopePtr& scope, const AstExprCall& expr, WithPredicate<TypePackId> withPredicate);
 
-static bool dcrMagicFunctionRequire(NotNull<ConstraintSolver> solver, TypePackId result, const AstExprCall* expr);
+
+static bool dcrMagicFunctionSelect(MagicFunctionCallContext context);
+static bool dcrMagicFunctionRequire(MagicFunctionCallContext context);
 
 TypeId makeUnion(TypeArena& arena, std::vector<TypeId>&& types)
 {
@@ -226,7 +232,22 @@ void assignPropDocumentationSymbols(TableTypeVar::Props& props, const std::strin
     }
 }
 
-void registerBuiltinTypes(TypeChecker& typeChecker)
+void registerBuiltinTypes(Frontend& frontend)
+{
+    frontend.getGlobalScope()->addBuiltinTypeBinding("any", TypeFun{{}, frontend.singletonTypes->anyType});
+    frontend.getGlobalScope()->addBuiltinTypeBinding("nil", TypeFun{{}, frontend.singletonTypes->nilType});
+    frontend.getGlobalScope()->addBuiltinTypeBinding("number", TypeFun{{}, frontend.singletonTypes->numberType});
+    frontend.getGlobalScope()->addBuiltinTypeBinding("string", TypeFun{{}, frontend.singletonTypes->stringType});
+    frontend.getGlobalScope()->addBuiltinTypeBinding("boolean", TypeFun{{}, frontend.singletonTypes->booleanType});
+    frontend.getGlobalScope()->addBuiltinTypeBinding("thread", TypeFun{{}, frontend.singletonTypes->threadType});
+    if (FFlag::LuauUnknownAndNeverType)
+    {
+        frontend.getGlobalScope()->addBuiltinTypeBinding("unknown", TypeFun{{}, frontend.singletonTypes->unknownType});
+        frontend.getGlobalScope()->addBuiltinTypeBinding("never", TypeFun{{}, frontend.singletonTypes->neverType});
+    }
+}
+
+void registerBuiltinGlobals(TypeChecker& typeChecker)
 {
     LUAU_ASSERT(!typeChecker.globalTypes.typeVars.isFrozen());
     LUAU_ASSERT(!typeChecker.globalTypes.typePacks.isFrozen());
@@ -303,6 +324,7 @@ void registerBuiltinTypes(TypeChecker& typeChecker)
     attachMagicFunction(getGlobalBinding(typeChecker, "assert"), magicFunctionAssert);
     attachMagicFunction(getGlobalBinding(typeChecker, "setmetatable"), magicFunctionSetMetaTable);
     attachMagicFunction(getGlobalBinding(typeChecker, "select"), magicFunctionSelect);
+    attachDcrMagicFunction(getGlobalBinding(typeChecker, "select"), dcrMagicFunctionSelect);
 
     if (TableTypeVar* ttv = getMutable<TableTypeVar>(getGlobalBinding(typeChecker, "table")))
     {
@@ -317,12 +339,13 @@ void registerBuiltinTypes(TypeChecker& typeChecker)
     attachDcrMagicFunction(getGlobalBinding(typeChecker, "require"), dcrMagicFunctionRequire);
 }
 
-void registerBuiltinTypes(Frontend& frontend)
+void registerBuiltinGlobals(Frontend& frontend)
 {
     LUAU_ASSERT(!frontend.globalTypes.typeVars.isFrozen());
     LUAU_ASSERT(!frontend.globalTypes.typePacks.isFrozen());
 
-    TypeId nilType = frontend.typeChecker.nilType;
+    if (FFlag::LuauReportShadowedTypeAlias)
+        registerBuiltinTypes(frontend);
 
     TypeArena& arena = frontend.globalTypes;
     NotNull<SingletonTypes> singletonTypes = frontend.singletonTypes;
@@ -352,7 +375,7 @@ void registerBuiltinTypes(Frontend& frontend)
     TypePackId pairsArgsTypePack = arena.addTypePack({mapOfKtoV});
 
     TypeId pairsNext = arena.addType(FunctionTypeVar{nextArgsTypePack, arena.addTypePack(TypePack{{genericK, genericV}})});
-    TypePackId pairsReturnTypePack = arena.addTypePack(TypePack{{pairsNext, mapOfKtoV, nilType}});
+    TypePackId pairsReturnTypePack = arena.addTypePack(TypePack{{pairsNext, mapOfKtoV, frontend.singletonTypes->nilType}});
 
     // pairs<K, V>(t: Table<K, V>) -> ((Table<K, V>, K?) -> (K, V), Table<K, V>, nil)
     addGlobalBinding(frontend, "pairs", arena.addType(FunctionTypeVar{{genericK, genericV}, {}, pairsArgsTypePack, pairsReturnTypePack}), "@luau");
@@ -394,6 +417,7 @@ void registerBuiltinTypes(Frontend& frontend)
     attachMagicFunction(getGlobalBinding(frontend, "assert"), magicFunctionAssert);
     attachMagicFunction(getGlobalBinding(frontend, "setmetatable"), magicFunctionSetMetaTable);
     attachMagicFunction(getGlobalBinding(frontend, "select"), magicFunctionSelect);
+    attachDcrMagicFunction(getGlobalBinding(frontend, "select"), dcrMagicFunctionSelect);
 
     if (TableTypeVar* ttv = getMutable<TableTypeVar>(getGlobalBinding(frontend, "table")))
     {
@@ -408,7 +432,6 @@ void registerBuiltinTypes(Frontend& frontend)
     attachDcrMagicFunction(getGlobalBinding(frontend, "require"), dcrMagicFunctionRequire);
 }
 
-
 static std::optional<WithPredicate<TypePackId>> magicFunctionSelect(
     TypeChecker& typechecker, const ScopePtr& scope, const AstExprCall& expr, WithPredicate<TypePackId> withPredicate)
 {
@@ -450,6 +473,50 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionSelect(
     return std::nullopt;
 }
 
+static bool dcrMagicFunctionSelect(MagicFunctionCallContext context)
+{
+    if (context.callSite->args.size <= 0)
+    {
+        context.solver->reportError(TypeError{context.callSite->location, GenericError{"select should take 1 or more arguments"}});
+        return false;
+    }
+
+    AstExpr* arg1 = context.callSite->args.data[0];
+
+    if (AstExprConstantNumber* num = arg1->as<AstExprConstantNumber>())
+    {
+        const auto& [v, tail] = flatten(context.arguments);
+
+        int offset = int(num->value);
+        if (offset > 0)
+        {
+            if (size_t(offset) < v.size())
+            {
+                std::vector<TypeId> res(v.begin() + offset, v.end());
+                TypePackId resTypePack = context.solver->arena->addTypePack({std::move(res), tail});
+                asMutable(context.result)->ty.emplace<BoundTypePack>(resTypePack);
+            }
+            else if (tail)
+               asMutable(context.result)->ty.emplace<BoundTypePack>(*tail);
+
+            return true;
+        }
+
+        return false;
+    }
+
+    if (AstExprConstantString* str = arg1->as<AstExprConstantString>())
+    {
+        if (str->value.size == 1 && str->value.data[0] == '#') {
+            TypePackId numberTypePack = context.solver->arena->addTypePack({context.solver->singletonTypes->numberType});
+            asMutable(context.result)->ty.emplace<BoundTypePack>(numberTypePack);
+            return true;
+        }
+    }
+
+    return false;
+}
+
 static std::optional<WithPredicate<TypePackId>> magicFunctionSetMetaTable(
     TypeChecker& typechecker, const ScopePtr& scope, const AstExprCall& expr, WithPredicate<TypePackId> withPredicate)
 {
@@ -675,22 +742,22 @@ static bool checkRequirePathDcr(NotNull<ConstraintSolver> solver, AstExpr* expr)
     return good;
 }
 
-static bool dcrMagicFunctionRequire(NotNull<ConstraintSolver> solver, TypePackId result, const AstExprCall* expr)
+static bool dcrMagicFunctionRequire(MagicFunctionCallContext context)
 {
-    if (expr->args.size != 1)
+    if (context.callSite->args.size != 1)
     {
-        solver->reportError(GenericError{"require takes 1 argument"}, expr->location);
+        context.solver->reportError(GenericError{"require takes 1 argument"}, context.callSite->location);
         return false;
     }
 
-    if (!checkRequirePathDcr(solver, expr->args.data[0]))
+    if (!checkRequirePathDcr(context.solver, context.callSite->args.data[0]))
         return false;
 
-    if (auto moduleInfo = solver->moduleResolver->resolveModuleInfo(solver->currentModuleName, *expr))
+    if (auto moduleInfo = context.solver->moduleResolver->resolveModuleInfo(context.solver->currentModuleName, *context.callSite))
     {
-        TypeId moduleType = solver->resolveModule(*moduleInfo, expr->location);
+        TypeId moduleType = context.solver->resolveModule(*moduleInfo, context.callSite->location);
-        TypePackId moduleResult = solver->arena->addTypePack({moduleType});
+        TypePackId moduleResult = context.solver->arena->addTypePack({moduleType});
-        asMutable(result)->ty.emplace<BoundTypePack>(moduleResult);
+        asMutable(context.result)->ty.emplace<BoundTypePack>(moduleResult);
 
         return true;
     }

Analysis/src/Clone.cpp

@@ -220,6 +220,9 @@ void TypeCloner::operator()(const SingletonTypeVar& t)
 
 void TypeCloner::operator()(const FunctionTypeVar& t)
 {
+    // FISHY: We always erase the scope when we clone things.  clone() was
+    // originally written so that we could copy a module's type surface into an
+    // export arena.  This probably dates to that.
     TypeId result = dest.addType(FunctionTypeVar{TypeLevel{0, 0}, {}, {}, nullptr, nullptr, t.definition, t.hasSelf});
     FunctionTypeVar* ftv = getMutable<FunctionTypeVar>(result);
     LUAU_ASSERT(ftv != nullptr);
@@ -436,7 +439,7 @@ TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool alwaysCl
 
     if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(ty))
     {
-        FunctionTypeVar clone = FunctionTypeVar{ftv->level, ftv->argTypes, ftv->retTypes, ftv->definition, ftv->hasSelf};
+        FunctionTypeVar clone = FunctionTypeVar{ftv->level, ftv->scope, ftv->argTypes, ftv->retTypes, ftv->definition, ftv->hasSelf};
         clone.generics = ftv->generics;
         clone.genericPacks = ftv->genericPacks;
         clone.magicFunction = ftv->magicFunction;
@@ -448,7 +451,7 @@ TypeId shallowClone(TypeId ty, TypeArena& dest, const TxnLog* log, bool alwaysCl
     else if (const TableTypeVar* ttv = get<TableTypeVar>(ty))
     {
         LUAU_ASSERT(!ttv->boundTo);
-        TableTypeVar clone = TableTypeVar{ttv->props, ttv->indexer, ttv->level, ttv->state};
+        TableTypeVar clone = TableTypeVar{ttv->props, ttv->indexer, ttv->level, ttv->scope, ttv->state};
         clone.definitionModuleName = ttv->definitionModuleName;
         clone.name = ttv->name;
         clone.syntheticName = ttv->syntheticName;

Analysis/src/Config.cpp

@@ -4,15 +4,18 @@
 #include "Luau/Lexer.h"
 #include "Luau/StringUtils.h"
 
-namespace
+LUAU_FASTFLAGVARIABLE(LuauEnableNonstrictByDefaultForLuauConfig, false)
+
+namespace Luau
 {
 
 using Error = std::optional<std::string>;
 
-}
+Config::Config()
-
+    : mode(FFlag::LuauEnableNonstrictByDefaultForLuauConfig ? Mode::Nonstrict : Mode::NoCheck)
-namespace Luau
 {
+    enabledLint.setDefaults();
+}
 
 static Error parseBoolean(bool& result, const std::string& value)
 {

Analysis/src/ConstraintGraphBuilder.cpp

@@ -11,6 +11,7 @@
 
 LUAU_FASTINT(LuauCheckRecursionLimit);
 LUAU_FASTFLAG(DebugLuauLogSolverToJson);
+LUAU_FASTFLAG(DebugLuauMagicTypes);
 
 #include "Luau/Scope.h"
 
@@ -218,6 +219,8 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStat* stat)
         visit(scope, s);
     else if (auto s = stat->as<AstStatDeclareFunction>())
         visit(scope, s);
+    else if (auto s = stat->as<AstStatError>())
+        visit(scope, s);
     else
         LUAU_ASSERT(0);
 }
@@ -454,8 +457,10 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatFunction* funct
         TypeId containingTableType = check(scope, indexName->expr);
 
         functionType = arena->addType(BlockedTypeVar{});
-        TypeId prospectiveTableType =
+
-            arena->addType(TableTypeVar{}); // TODO look into stack utilization.  This is probably ok because it scales with AST depth.
+        // TODO look into stack utilization.  This is probably ok because it scales with AST depth.
+        TypeId prospectiveTableType = arena->addType(TableTypeVar{TableState::Unsealed, TypeLevel{}, scope.get()});
+
         NotNull<TableTypeVar> prospectiveTable{getMutable<TableTypeVar>(prospectiveTableType)};
 
         Property& prop = prospectiveTable->props[indexName->index.value];
@@ -619,7 +624,7 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatDeclareClass* d
     TypeId classTy = arena->addType(ClassTypeVar(className, {}, superTy, std::nullopt, {}, {}, moduleName));
     ClassTypeVar* ctv = getMutable<ClassTypeVar>(classTy);
 
-    TypeId metaTy = arena->addType(TableTypeVar{TableState::Sealed, scope->level});
+    TypeId metaTy = arena->addType(TableTypeVar{TableState::Sealed, scope->level, scope.get()});
     TableTypeVar* metatable = getMutable<TableTypeVar>(metaTy);
 
     ctv->metatable = metaTy;
@@ -715,7 +720,7 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatDeclareFunction
 
     TypePackId paramPack = resolveTypePack(funScope, global->params);
     TypePackId retPack = resolveTypePack(funScope, global->retTypes);
-    TypeId fnType = arena->addType(FunctionTypeVar{funScope->level, std::move(genericTys), std::move(genericTps), paramPack, retPack});
+    TypeId fnType = arena->addType(FunctionTypeVar{TypeLevel{}, funScope.get(), std::move(genericTys), std::move(genericTps), paramPack, retPack});
     FunctionTypeVar* ftv = getMutable<FunctionTypeVar>(fnType);
 
     ftv->argNames.reserve(global->paramNames.size);
@@ -728,6 +733,14 @@ void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatDeclareFunction
     scope->bindings[global->name] = Binding{fnType, global->location};
 }
 
+void ConstraintGraphBuilder::visit(const ScopePtr& scope, AstStatError* error)
+{
+    for (AstStat* stat : error->statements)
+        visit(scope, stat);
+    for (AstExpr* expr : error->expressions)
+        check(scope, expr);
+}
+
 TypePackId ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstArray<AstExpr*> exprs, const std::vector<TypeId>& expectedTypes)
 {
     std::vector<TypeId> head;
@@ -745,7 +758,9 @@ TypePackId ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstArray<Ast
         }
         else
         {
-            std::vector<TypeId> expectedTailTypes{begin(expectedTypes) + i, end(expectedTypes)};
+            std::vector<TypeId> expectedTailTypes;
+            if (i < expectedTypes.size())
+                expectedTailTypes.assign(begin(expectedTypes) + i, end(expectedTypes));
             tail = checkPack(scope, expr, expectedTailTypes);
         }
     }
@@ -803,7 +818,8 @@ TypePackId ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExpr* exp
             TypeId instantiatedType = arena->addType(BlockedTypeVar{});
             // TODO: How do expectedTypes play into this?  Do they?
             TypePackId rets = arena->addTypePack(BlockedTypePack{});
-            FunctionTypeVar ftv(arena->addTypePack(TypePack{args, {}}), rets);
+            TypePackId argPack = arena->addTypePack(TypePack{args, {}});
+            FunctionTypeVar ftv(TypeLevel{}, scope.get(), argPack, rets);
             TypeId inferredFnType = arena->addType(ftv);
 
             scope->unqueuedConstraints.push_back(
@@ -834,6 +850,7 @@ TypePackId ConstraintGraphBuilder::checkPack(const ScopePtr& scope, AstExpr* exp
                 FunctionCallConstraint{
                     {ic, sc},
                     fnType,
+                    argPack,
                     rets,
                     call,
                 });
@@ -968,6 +985,9 @@ TypeId ConstraintGraphBuilder::check(const ScopePtr& scope, AstExpr* expr, std::
     else if (auto err = expr->as<AstExprError>())
     {
         // Open question: Should we traverse into this?
+        for (AstExpr* subExpr : err->expressions)
+            check(scope, subExpr);
+
         result = singletonTypes->errorRecoveryType();
     }
     else
@@ -988,7 +1008,7 @@ TypeId ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprIndexName* in
 
     TableTypeVar::Props props{{indexName->index.value, Property{result}}};
     const std::optional<TableIndexer> indexer;
-    TableTypeVar ttv{std::move(props), indexer, TypeLevel{}, TableState::Free};
+    TableTypeVar ttv{std::move(props), indexer, TypeLevel{}, scope.get(), TableState::Free};
 
     TypeId expectedTableType = arena->addType(std::move(ttv));
 
@@ -1005,7 +1025,8 @@ TypeId ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprIndexExpr* in
     TypeId result = freshType(scope);
 
     TableIndexer indexer{indexType, result};
-    TypeId tableType = arena->addType(TableTypeVar{TableTypeVar::Props{}, TableIndexer{indexType, result}, TypeLevel{}, TableState::Free});
+    TypeId tableType =
+        arena->addType(TableTypeVar{TableTypeVar::Props{}, TableIndexer{indexType, result}, TypeLevel{}, scope.get(), TableState::Free});
 
     addConstraint(scope, indexExpr->expr->location, SubtypeConstraint{obj, tableType});
 
@@ -1094,6 +1115,9 @@ TypeId ConstraintGraphBuilder::check(const ScopePtr& scope, AstExprTable* expr,
     TableTypeVar* ttv = getMutable<TableTypeVar>(ty);
     LUAU_ASSERT(ttv);
 
+    ttv->state = TableState::Unsealed;
+    ttv->scope = scope.get();
+
     auto createIndexer = [this, scope, ttv](const Location& location, TypeId currentIndexType, TypeId currentResultType) {
         if (!ttv->indexer)
         {
@@ -1195,7 +1219,7 @@ ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionS
     }
     else
     {
-        bodyScope = childScope(fn->body, parent);
+        bodyScope = childScope(fn, parent);
 
         returnType = freshTypePack(bodyScope);
         bodyScope->returnType = returnType;
@@ -1260,7 +1284,7 @@ ConstraintGraphBuilder::FunctionSignature ConstraintGraphBuilder::checkFunctionS
     // TODO: Vararg annotation.
     // TODO: Preserve argument names in the function's type.
 
-    FunctionTypeVar actualFunction{arena->addTypePack(argTypes, varargPack), returnType};
+    FunctionTypeVar actualFunction{TypeLevel{}, parent.get(), arena->addTypePack(argTypes, varargPack), returnType};
     actualFunction.hasNoGenerics = !hasGenerics;
     actualFunction.generics = std::move(genericTypes);
     actualFunction.genericPacks = std::move(genericTypePacks);
@@ -1297,6 +1321,22 @@ TypeId ConstraintGraphBuilder::resolveType(const ScopePtr& scope, AstType* ty, b
 
     if (auto ref = ty->as<AstTypeReference>())
     {
+        if (FFlag::DebugLuauMagicTypes)
+        {
+            if (ref->name == "_luau_ice")
+                ice->ice("_luau_ice encountered", ty->location);
+            else if (ref->name == "_luau_print")
+            {
+                if (ref->parameters.size != 1 || !ref->parameters.data[0].type)
+                {
+                    reportError(ty->location, GenericError{"_luau_print requires one generic parameter"});
+                    return singletonTypes->errorRecoveryType();
+                }
+                else
+                    return resolveType(scope, ref->parameters.data[0].type, topLevel);
+            }
+        }
+
         std::optional<TypeFun> alias = scope->lookupType(ref->name.value);
 
         if (alias.has_value() || ref->prefix.has_value())
@@ -1369,7 +1409,7 @@ TypeId ConstraintGraphBuilder::resolveType(const ScopePtr& scope, AstType* ty, b
             };
         }
 
-        result = arena->addType(TableTypeVar{props, indexer, scope->level, TableState::Sealed});
+        result = arena->addType(TableTypeVar{props, indexer, scope->level, scope.get(), TableState::Sealed});
     }
     else if (auto fn = ty->as<AstTypeFunction>())
     {
@@ -1414,7 +1454,7 @@ TypeId ConstraintGraphBuilder::resolveType(const ScopePtr& scope, AstType* ty, b
 
         // TODO: FunctionTypeVar needs a pointer to the scope so that we know
         // how to quantify/instantiate it.
-        FunctionTypeVar ftv{argTypes, returnTypes};
+        FunctionTypeVar ftv{TypeLevel{}, scope.get(), {}, {}, argTypes, returnTypes};
 
         // This replicates the behavior of the appropriate FunctionTypeVar
         // constructors.

Analysis/src/ConstraintSolver.cpp

@@ -8,9 +8,11 @@
 #include "Luau/ModuleResolver.h"
 #include "Luau/Quantify.h"
 #include "Luau/ToString.h"
+#include "Luau/TypeVar.h"
 #include "Luau/Unifier.h"
 #include "Luau/DcrLogger.h"
 #include "Luau/VisitTypeVar.h"
+#include "Luau/TypeUtils.h"
 
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolver, false);
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJson, false);
@@ -439,6 +441,7 @@ bool ConstraintSolver::tryDispatch(const PackSubtypeConstraint& c, NotNull<const
         return block(c.superPack, constraint);
 
     unify(c.subPack, c.superPack, constraint->scope);
+
     return true;
 }
 
@@ -465,7 +468,7 @@ bool ConstraintSolver::tryDispatch(const InstantiationConstraint& c, NotNull<con
     if (isBlocked(c.superType))
         return block(c.superType, constraint);
 
-    Instantiation inst(TxnLog::empty(), arena, TypeLevel{});
+    Instantiation inst(TxnLog::empty(), arena, TypeLevel{}, constraint->scope);
 
     std::optional<TypeId> instantiated = inst.substitute(c.superType);
     LUAU_ASSERT(instantiated); // TODO FIXME HANDLE THIS
@@ -909,7 +912,7 @@ bool ConstraintSolver::tryDispatch(const FunctionCallConstraint& c, NotNull<cons
 
     if (ftv && ftv->dcrMagicFunction != nullptr)
     {
-        usedMagic = ftv->dcrMagicFunction(NotNull(this), result, c.astFragment);
+        usedMagic = ftv->dcrMagicFunction(MagicFunctionCallContext{NotNull(this), c.callSite, c.argsPack, result});
     }
 
     if (usedMagic)
@@ -1087,6 +1090,63 @@ bool ConstraintSolver::tryDispatchIterableTable(TypeId iteratorTy, const Iterabl
         else
             errorify(c.variables);
     }
+    else if (std::optional<TypeId> iterFn = findMetatableEntry(singletonTypes, errors, iteratorTy, "__iter", Location{}))
+    {
+        if (isBlocked(*iterFn))
+        {
+            return block(*iterFn, constraint);
+        }
+
+        Instantiation instantiation(TxnLog::empty(), arena, TypeLevel{}, constraint->scope);
+
+        if (std::optional<TypeId> instantiatedIterFn = instantiation.substitute(*iterFn))
+        {
+            if (auto iterFtv = get<FunctionTypeVar>(*instantiatedIterFn))
+            {
+                TypePackId expectedIterArgs = arena->addTypePack({iteratorTy});
+                unify(iterFtv->argTypes, expectedIterArgs, constraint->scope);
+
+                std::vector<TypeId> iterRets = flatten(*arena, singletonTypes, iterFtv->retTypes, 2);
+
+                if (iterRets.size() < 1)
+                {
+                    // We've done what we can; this will get reported as an
+                    // error by the type checker.
+                    return true;
+                }
+
+                TypeId nextFn = iterRets[0];
+                TypeId table = iterRets.size() == 2 ? iterRets[1] : arena->freshType(constraint->scope);
+
+                if (std::optional<TypeId> instantiatedNextFn = instantiation.substitute(nextFn))
+                {
+                    const TypeId firstIndex = arena->freshType(constraint->scope);
+
+                    // nextTy : (iteratorTy, indexTy?) -> (indexTy, valueTailTy...)
+                    const TypePackId nextArgPack = arena->addTypePack({table, arena->addType(UnionTypeVar{{firstIndex, singletonTypes->nilType}})});
+                    const TypePackId valueTailTy = arena->addTypePack(FreeTypePack{constraint->scope});
+                    const TypePackId nextRetPack = arena->addTypePack(TypePack{{firstIndex}, valueTailTy});
+
+                    const TypeId expectedNextTy = arena->addType(FunctionTypeVar{nextArgPack, nextRetPack});
+                    unify(*instantiatedNextFn, expectedNextTy, constraint->scope);
+
+                    pushConstraint(constraint->scope, constraint->location, PackSubtypeConstraint{c.variables, nextRetPack});
+                }
+                else
+                {
+                    reportError(UnificationTooComplex{}, constraint->location);
+                }
+            }
+            else
+            {
+                // TODO: Support __call and function overloads (what does an overload even mean for this?)
+            }
+        }
+        else
+        {
+            reportError(UnificationTooComplex{}, constraint->location);
+        }
+    }
     else if (auto iteratorMetatable = get<MetatableTypeVar>(iteratorTy))
     {
         TypeId metaTy = follow(iteratorMetatable->metatable);
@@ -1124,7 +1184,7 @@ bool ConstraintSolver::tryDispatchIterableFunction(
     const TypePackId valueTailTy = arena->addTypePack(FreeTypePack{constraint->scope});
     const TypePackId nextRetPack = arena->addTypePack(TypePack{{firstIndex}, valueTailTy});
 
-    const TypeId expectedNextTy = arena->addType(FunctionTypeVar{nextArgPack, nextRetPack});
+    const TypeId expectedNextTy = arena->addType(FunctionTypeVar{TypeLevel{}, constraint->scope, nextArgPack, nextRetPack});
     unify(nextTy, expectedNextTy, constraint->scope);
 
     pushConstraint(constraint->scope, constraint->location, PackSubtypeConstraint{c.variables, nextRetPack});
@@ -1297,6 +1357,7 @@ void ConstraintSolver::unify(TypeId subType, TypeId superType, NotNull<Scope> sc
 {
     UnifierSharedState sharedState{&iceReporter};
     Unifier u{arena, singletonTypes, Mode::Strict, scope, Location{}, Covariant, sharedState};
+    u.useScopes = true;
 
     u.tryUnify(subType, superType);
 
@@ -1319,6 +1380,7 @@ void ConstraintSolver::unify(TypePackId subPack, TypePackId superPack, NotNull<S
 {
     UnifierSharedState sharedState{&iceReporter};
     Unifier u{arena, singletonTypes, Mode::Strict, scope, Location{}, Covariant, sharedState};
+    u.useScopes = true;
 
     u.tryUnify(subPack, superPack);
 

Analysis/src/Error.cpp

@@ -169,7 +169,10 @@ struct ErrorConverter
 
     std::string operator()(const Luau::DuplicateTypeDefinition& e) const
     {
-        return "Redefinition of type '" + e.name + "', previously defined at line " + std::to_string(e.previousLocation.begin.line + 1);
+        std::string s = "Redefinition of type '" + e.name + "'";
+        if (e.previousLocation)
+            s += ", previously defined at line " + std::to_string(e.previousLocation->begin.line + 1);
+        return s;
     }
 
     std::string operator()(const Luau::CountMismatch& e) const
@@ -183,11 +186,14 @@ struct ErrorConverter
         case CountMismatch::Return:
             return "Expected to return " + std::to_string(e.expected) + " value" + expectedS + ", but " + std::to_string(e.actual) + " " +
                    actualVerb + " returned here";
-        case CountMismatch::Result:
+        case CountMismatch::FunctionResult:
             // It is alright if right hand side produces more values than the
             // left hand side accepts. In this context consider only the opposite case.
-            return "Function only returns " + std::to_string(e.expected) + " value" + expectedS + ". " + std::to_string(e.actual) +
+            return "Function only returns " + std::to_string(e.expected) + " value" + expectedS + ", but " + std::to_string(e.actual) + " " +
-                   " are required here";
+                   actualVerb + " required here";
+        case CountMismatch::ExprListResult:
+            return "Expression list has " + std::to_string(e.expected) + " value" + expectedS + ", but " + std::to_string(e.actual) + " " +
+                   actualVerb + " required here";
         case CountMismatch::Arg:
             if (!e.function.empty())
                 return "Argument count mismatch. Function '" + e.function + "' " +

Analysis/src/Frontend.cpp

@@ -400,6 +400,7 @@ Frontend::Frontend(FileResolver* fileResolver, ConfigResolver* configResolver, c
     , typeCheckerForAutocomplete(&moduleResolverForAutocomplete, singletonTypes, &iceHandler)
     , configResolver(configResolver)
     , options(options)
+    , globalScope(typeChecker.globalScope)
 {
 }
 
@@ -505,7 +506,10 @@ CheckResult Frontend::check(const ModuleName& name, std::optional<FrontendOption
                     typeCheckerForAutocomplete.unifierIterationLimit = std::nullopt;
             }
 
-            ModulePtr moduleForAutocomplete = typeCheckerForAutocomplete.check(sourceModule, Mode::Strict, environmentScope);
+            ModulePtr moduleForAutocomplete = FFlag::DebugLuauDeferredConstraintResolution
+                                                  ? check(sourceModule, mode, environmentScope, requireCycles, /*forAutocomplete*/ true)
+                                                  : typeCheckerForAutocomplete.check(sourceModule, Mode::Strict, environmentScope);
+
             moduleResolverForAutocomplete.modules[moduleName] = moduleForAutocomplete;
 
             double duration = getTimestamp() - timestamp;
@@ -837,7 +841,8 @@ ScopePtr Frontend::getGlobalScope()
     return globalScope;
 }
 
-ModulePtr Frontend::check(const SourceModule& sourceModule, Mode mode, const ScopePtr& environmentScope, std::vector<RequireCycle> requireCycles)
+ModulePtr Frontend::check(
+    const SourceModule& sourceModule, Mode mode, const ScopePtr& environmentScope, std::vector<RequireCycle> requireCycles, bool forAutocomplete)
 {
     ModulePtr result = std::make_shared<Module>();
 
@@ -852,7 +857,11 @@ ModulePtr Frontend::check(const SourceModule& sourceModule, Mode mode, const Sco
         }
     }
 
-    ConstraintGraphBuilder cgb{sourceModule.name, result, &result->internalTypes, NotNull(&moduleResolver), singletonTypes, NotNull(&iceHandler), getGlobalScope(), logger.get()};
+    const NotNull<ModuleResolver> mr{forAutocomplete ? &moduleResolverForAutocomplete : &moduleResolver};
+    const ScopePtr& globalScope{forAutocomplete ? typeCheckerForAutocomplete.globalScope : typeChecker.globalScope};
+
+    ConstraintGraphBuilder cgb{
+        sourceModule.name, result, &result->internalTypes, mr, singletonTypes, NotNull(&iceHandler), globalScope, logger.get()};
     cgb.visit(sourceModule.root);
     result->errors = std::move(cgb.errors);
 

Analysis/src/Instantiation.cpp

@@ -44,7 +44,7 @@ TypeId Instantiation::clean(TypeId ty)
     const FunctionTypeVar* ftv = log->getMutable<FunctionTypeVar>(ty);
     LUAU_ASSERT(ftv);
 
-    FunctionTypeVar clone = FunctionTypeVar{level, ftv->argTypes, ftv->retTypes, ftv->definition, ftv->hasSelf};
+    FunctionTypeVar clone = FunctionTypeVar{level, scope, ftv->argTypes, ftv->retTypes, ftv->definition, ftv->hasSelf};
     clone.magicFunction = ftv->magicFunction;
     clone.dcrMagicFunction = ftv->dcrMagicFunction;
     clone.tags = ftv->tags;
@@ -53,7 +53,7 @@ TypeId Instantiation::clean(TypeId ty)
 
     // Annoyingly, we have to do this even if there are no generics,
     // to replace any generic tables.
-    ReplaceGenerics replaceGenerics{log, arena, level, ftv->generics, ftv->genericPacks};
+    ReplaceGenerics replaceGenerics{log, arena, level, scope, ftv->generics, ftv->genericPacks};
 
     // TODO: What to do if this returns nullopt?
     // We don't have access to the error-reporting machinery
@@ -114,12 +114,12 @@ TypeId ReplaceGenerics::clean(TypeId ty)
     LUAU_ASSERT(isDirty(ty));
     if (const TableTypeVar* ttv = log->getMutable<TableTypeVar>(ty))
     {
-        TableTypeVar clone = TableTypeVar{ttv->props, ttv->indexer, level, TableState::Free};
+        TableTypeVar clone = TableTypeVar{ttv->props, ttv->indexer, level, scope, TableState::Free};
         clone.definitionModuleName = ttv->definitionModuleName;
         return addType(std::move(clone));
     }
     else
-        return addType(FreeTypeVar{level});
+        return addType(FreeTypeVar{scope, level});
 }
 
 TypePackId ReplaceGenerics::clean(TypePackId tp)

Analysis/src/Quantify.cpp

@@ -15,19 +15,6 @@ LUAU_FASTFLAG(LuauClassTypeVarsInSubstitution)
 namespace Luau
 {
 
-/// @return true if outer encloses inner
-static bool subsumes(Scope* outer, Scope* inner)
-{
-    while (inner)
-    {
-        if (inner == outer)
-            return true;
-        inner = inner->parent.get();
-    }
-
-    return false;
-}
-
 struct Quantifier final : TypeVarOnceVisitor
 {
     TypeLevel level;
@@ -43,12 +30,6 @@ struct Quantifier final : TypeVarOnceVisitor
         LUAU_ASSERT(!FFlag::DebugLuauDeferredConstraintResolution);
     }
 
-    explicit Quantifier(Scope* scope)
-        : scope(scope)
-    {
-        LUAU_ASSERT(FFlag::DebugLuauDeferredConstraintResolution);
-    }
-
     /// @return true if outer encloses inner
     bool subsumes(Scope* outer, Scope* inner)
     {
@@ -66,13 +47,10 @@ struct Quantifier final : TypeVarOnceVisitor
     {
         seenMutableType = true;
 
-        if (FFlag::DebugLuauDeferredConstraintResolution ? !subsumes(scope, ftv.scope) : !level.subsumes(ftv.level))
+        if (!level.subsumes(ftv.level))
             return false;
 
-        if (FFlag::DebugLuauDeferredConstraintResolution)
+        *asMutable(ty) = GenericTypeVar{level};
-            *asMutable(ty) = GenericTypeVar{scope};
-        else
-            *asMutable(ty) = GenericTypeVar{level};
 
         generics.push_back(ty);
 
@@ -85,7 +63,7 @@ struct Quantifier final : TypeVarOnceVisitor
 
         seenMutableType = true;
 
-        if (FFlag::DebugLuauDeferredConstraintResolution ? !subsumes(scope, ctv->scope) : !level.subsumes(ctv->level))
+        if (!level.subsumes(ctv->level))
             return false;
 
         std::vector<TypeId> opts = std::move(ctv->parts);
@@ -113,7 +91,7 @@ struct Quantifier final : TypeVarOnceVisitor
         if (ttv.state == TableState::Free)
             seenMutableType = true;
 
-        if (FFlag::DebugLuauDeferredConstraintResolution ? !subsumes(scope, ttv.scope) : !level.subsumes(ttv.level))
+        if (!level.subsumes(ttv.level))
         {
             if (ttv.state == TableState::Unsealed)
                 seenMutableType = true;
@@ -137,7 +115,7 @@ struct Quantifier final : TypeVarOnceVisitor
     {
         seenMutableType = true;
 
-        if (FFlag::DebugLuauDeferredConstraintResolution ? !subsumes(scope, ftp.scope) : !level.subsumes(ftp.level))
+        if (!level.subsumes(ftp.level))
             return false;
 
         *asMutable(tp) = GenericTypePack{level};
@@ -197,20 +175,6 @@ void quantify(TypeId ty, TypeLevel level)
     }
 }
 
-void quantify(TypeId ty, Scope* scope)
-{
-    Quantifier q{scope};
-    q.traverse(ty);
-
-    FunctionTypeVar* ftv = getMutable<FunctionTypeVar>(ty);
-    LUAU_ASSERT(ftv);
-    ftv->generics.insert(ftv->generics.end(), q.generics.begin(), q.generics.end());
-    ftv->genericPacks.insert(ftv->genericPacks.end(), q.genericPacks.begin(), q.genericPacks.end());
-
-    if (ftv->generics.empty() && ftv->genericPacks.empty() && !q.seenMutableType && !q.seenGenericType)
-        ftv->hasNoGenerics = true;
-}
-
 struct PureQuantifier : Substitution
 {
     Scope* scope;
@@ -253,7 +217,7 @@ struct PureQuantifier : Substitution
     {
         if (auto ftv = get<FreeTypeVar>(ty))
         {
-            TypeId result = arena->addType(GenericTypeVar{});
+            TypeId result = arena->addType(GenericTypeVar{scope});
             insertedGenerics.push_back(result);
             return result;
         }
@@ -264,7 +228,8 @@ struct PureQuantifier : Substitution
             LUAU_ASSERT(resultTable);
 
             *resultTable = *ttv;
-            resultTable->scope = nullptr;
+            resultTable->level = TypeLevel{};
+            resultTable->scope = scope;
             resultTable->state = TableState::Generic;
 
             return result;
@@ -306,6 +271,7 @@ TypeId quantify(TypeArena* arena, TypeId ty, Scope* scope)
 
     FunctionTypeVar* ftv = getMutable<FunctionTypeVar>(*result);
     LUAU_ASSERT(ftv);
+    ftv->scope = scope;
     ftv->generics.insert(ftv->generics.end(), quantifier.insertedGenerics.begin(), quantifier.insertedGenerics.end());
     ftv->genericPacks.insert(ftv->genericPacks.end(), quantifier.insertedGenericPacks.begin(), quantifier.insertedGenericPacks.end());
     ftv->hasNoGenerics = ftv->generics.empty() && ftv->genericPacks.empty();

Analysis/src/Scope.cpp

@@ -21,6 +21,12 @@ Scope::Scope(const ScopePtr& parent, int subLevel)
     level.subLevel = subLevel;
 }
 
+void Scope::addBuiltinTypeBinding(const Name& name, const TypeFun& tyFun)
+{
+    exportedTypeBindings[name] = tyFun;
+    builtinTypeNames.insert(name);
+}
+
 std::optional<TypeFun> Scope::lookupType(const Name& name)
 {
     const Scope* scope = this;
@@ -82,9 +88,9 @@ std::optional<TypePackId> Scope::lookupPack(const Name& name)
     }
 }
 
-std::optional<Binding> Scope::linearSearchForBinding(const std::string& name, bool traverseScopeChain)
+std::optional<Binding> Scope::linearSearchForBinding(const std::string& name, bool traverseScopeChain) const
 {
-    Scope* scope = this;
+    const Scope* scope = this;
 
     while (scope)
     {
@@ -122,4 +128,22 @@ std::optional<TypeId> Scope::lookup(Symbol sym)
     }
 }
 
+bool subsumesStrict(Scope* left, Scope* right)
+{
+    while (right)
+    {
+        if (right->parent.get() == left)
+            return true;
+
+        right = right->parent.get();
+    }
+
+    return false;
+}
+
+bool subsumes(Scope* left, Scope* right)
+{
+    return left == right || subsumesStrict(left, right);
+}
+
 } // namespace Luau

Analysis/src/ToString.cpp

@@ -14,6 +14,7 @@ LUAU_FASTFLAG(LuauLowerBoundsCalculation)
 LUAU_FASTFLAG(LuauUnknownAndNeverType)
 LUAU_FASTFLAGVARIABLE(LuauSpecialTypesAsterisked, false)
 LUAU_FASTFLAGVARIABLE(LuauFixNameMaps, false)
+LUAU_FASTFLAGVARIABLE(LuauUnseeArrayTtv, false)
 
 /*
  * Prefix generic typenames with gen-
@@ -632,6 +633,10 @@ struct TypeVarStringifier
             state.emit("{");
             stringify(ttv.indexer->indexResultType);
             state.emit("}");
+
+            if (FFlag::LuauUnseeArrayTtv)
+                state.unsee(&ttv);
+
             return;
         }
 

Analysis/src/TxnLog.cpp

@@ -289,6 +289,45 @@ PendingTypePack* TxnLog::changeLevel(TypePackId tp, TypeLevel newLevel)
     return newTp;
 }
 
+PendingType* TxnLog::changeScope(TypeId ty, NotNull<Scope> newScope)
+{
+    LUAU_ASSERT(get<FreeTypeVar>(ty) || get<TableTypeVar>(ty) || get<FunctionTypeVar>(ty) || get<ConstrainedTypeVar>(ty));
+
+    PendingType* newTy = queue(ty);
+    if (FreeTypeVar* ftv = Luau::getMutable<FreeTypeVar>(newTy))
+    {
+        ftv->scope = newScope;
+    }
+    else if (TableTypeVar* ttv = Luau::getMutable<TableTypeVar>(newTy))
+    {
+        LUAU_ASSERT(ttv->state == TableState::Free || ttv->state == TableState::Generic);
+        ttv->scope = newScope;
+    }
+    else if (FunctionTypeVar* ftv = Luau::getMutable<FunctionTypeVar>(newTy))
+    {
+        ftv->scope = newScope;
+    }
+    else if (ConstrainedTypeVar* ctv = Luau::getMutable<ConstrainedTypeVar>(newTy))
+    {
+        ctv->scope = newScope;
+    }
+
+    return newTy;
+}
+
+PendingTypePack* TxnLog::changeScope(TypePackId tp, NotNull<Scope> newScope)
+{
+    LUAU_ASSERT(get<FreeTypePack>(tp));
+
+    PendingTypePack* newTp = queue(tp);
+    if (FreeTypePack* ftp = Luau::getMutable<FreeTypePack>(newTp))
+    {
+        ftp->scope = newScope;
+    }
+
+    return newTp;
+}
+
 PendingType* TxnLog::changeIndexer(TypeId ty, std::optional<TableIndexer> indexer)
 {
     LUAU_ASSERT(get<TableTypeVar>(ty));

Analysis/src/TypeArena.cpp

@@ -40,6 +40,15 @@ TypeId TypeArena::freshType(Scope* scope)
     return allocated;
 }
 
+TypeId TypeArena::freshType(Scope* scope, TypeLevel level)
+{
+    TypeId allocated = typeVars.allocate(FreeTypeVar{scope, level});
+
+    asMutable(allocated)->owningArena = this;
+
+    return allocated;
+}
+
 TypePackId TypeArena::freshTypePack(Scope* scope)
 {
     TypePackId allocated = typePacks.allocate(FreeTypePack{scope});

Analysis/src/TypeChecker2.cpp

@@ -17,10 +17,16 @@
 #include <algorithm>
 
 LUAU_FASTFLAG(DebugLuauLogSolverToJson);
+LUAU_FASTFLAG(DebugLuauMagicTypes);
 
 namespace Luau
 {
 
+// TypeInfer.h
+// TODO move these
+using PrintLineProc = void(*)(const std::string&);
+extern PrintLineProc luauPrintLine;
+
 /* Push a scope onto the end of a stack for the lifetime of the StackPusher instance.
  * TypeChecker2 uses this to maintain knowledge about which scope encloses every
  * given AstNode.
@@ -114,6 +120,19 @@ struct TypeChecker2
 
     TypeId lookupAnnotation(AstType* annotation)
     {
+        if (FFlag::DebugLuauMagicTypes)
+        {
+            if (auto ref = annotation->as<AstTypeReference>(); ref && ref->name == "_luau_print" && ref->parameters.size > 0)
+            {
+                if (auto ann = ref->parameters.data[0].type)
+                {
+                    TypeId argTy = lookupAnnotation(ref->parameters.data[0].type);
+                    luauPrintLine(format("_luau_print (%d, %d): %s\n", annotation->location.begin.line, annotation->location.begin.column, toString(argTy).c_str()));
+                    return follow(argTy);
+                }
+            }
+        }
+
         TypeId* ty = module->astResolvedTypes.find(annotation);
         LUAU_ASSERT(ty);
         return follow(*ty);
@@ -284,50 +303,49 @@ struct TypeChecker2
 
     void visit(AstStatLocal* local)
     {
-        for (size_t i = 0; i < local->values.size; ++i)
+        size_t count = std::max(local->values.size, local->vars.size);
+        for (size_t i = 0; i < count; ++i)
         {
-            AstExpr* value = local->values.data[i];
+            AstExpr* value = i < local->values.size ? local->values.data[i] : nullptr;
 
-            visit(value);
+            if (value)
+                visit(value);
 
-            if (i == local->values.size - 1)
+            if (i != local->values.size - 1)
             {
-                if (i < local->values.size)
+                AstLocal* var = i < local->vars.size ? local->vars.data[i] : nullptr;
+
+                if (var && var->annotation)
                 {
-                    TypePackId valueTypes = lookupPack(value);
+                    TypeId varType = lookupAnnotation(var->annotation);
-                    auto it = begin(valueTypes);
+                    TypeId valueType = value ? lookupType(value) : nullptr;
-                    for (size_t j = i; j < local->vars.size; ++j)
+                    if (valueType && !isSubtype(varType, valueType, stack.back(), singletonTypes, ice, /* anyIsTop */ false))
-                    {
+                        reportError(TypeMismatch{varType, valueType}, value->location);
-                        if (it == end(valueTypes))
-                        {
-                            break;
-                        }
-
-                        AstLocal* var = local->vars.data[i];
-                        if (var->annotation)
-                        {
-                            TypeId varType = lookupAnnotation(var->annotation);
-                            ErrorVec errors = tryUnify(stack.back(), value->location, *it, varType);
-                            if (!errors.empty())
-                                reportErrors(std::move(errors));
-                        }
-
-                        ++it;
-                    }
                 }
             }
             else
             {
-                TypeId valueType = lookupType(value);
+                LUAU_ASSERT(value);
-                AstLocal* var = local->vars.data[i];
 
-                if (var->annotation)
+                TypePackId valueTypes = lookupPack(value);
+                auto it = begin(valueTypes);
+                for (size_t j = i; j < local->vars.size; ++j)
                 {
-                    TypeId varType = lookupAnnotation(var->annotation);
+                    if (it == end(valueTypes))
-                    if (!isSubtype(varType, valueType, stack.back(), singletonTypes, ice, /* anyIsTop */ false))
                     {
-                        reportError(TypeMismatch{varType, valueType}, value->location);
+                        break;
                     }
+
+                    AstLocal* var = local->vars.data[i];
+                    if (var->annotation)
+                    {
+                        TypeId varType = lookupAnnotation(var->annotation);
+                        ErrorVec errors = tryUnify(stack.back(), value->location, *it, varType);
+                        if (!errors.empty())
+                            reportErrors(std::move(errors));
+                    }
+
+                    ++it;
                 }
             }
         }
@@ -345,50 +363,6 @@ struct TypeChecker2
         visit(forStatement->body);
     }
 
-    // "Render" a type pack out to an array of a given length.  Expands
-    // variadics and various other things to get there.
-    std::vector<TypeId> flatten(TypeArena& arena, TypePackId pack, size_t length)
-    {
-        std::vector<TypeId> result;
-
-        auto it = begin(pack);
-        auto endIt = end(pack);
-
-        while (it != endIt)
-        {
-            result.push_back(*it);
-
-            if (result.size() >= length)
-                return result;
-
-            ++it;
-        }
-
-        if (!it.tail())
-            return result;
-
-        TypePackId tail = *it.tail();
-        if (get<TypePack>(tail))
-            LUAU_ASSERT(0);
-        else if (auto vtp = get<VariadicTypePack>(tail))
-        {
-            while (result.size() < length)
-                result.push_back(vtp->ty);
-        }
-        else if (get<FreeTypePack>(tail) || get<GenericTypePack>(tail))
-        {
-            while (result.size() < length)
-                result.push_back(arena.addType(FreeTypeVar{nullptr}));
-        }
-        else if (auto etp = get<Unifiable::Error>(tail))
-        {
-            while (result.size() < length)
-                result.push_back(singletonTypes->errorRecoveryType());
-        }
-
-        return result;
-    }
-
     void visit(AstStatForIn* forInStatement)
     {
         for (AstLocal* local : forInStatement->vars)
@@ -426,7 +400,7 @@ struct TypeChecker2
         TypePackId iteratorPack = arena.addTypePack(valueTypes, iteratorTail);
 
         // ... and then expand it out to 3 values (if possible)
-        const std::vector<TypeId> iteratorTypes = flatten(arena, iteratorPack, 3);
+        const std::vector<TypeId> iteratorTypes = flatten(arena, singletonTypes, iteratorPack, 3);
         if (iteratorTypes.empty())
         {
             reportError(GenericError{"for..in loops require at least one value to iterate over.  Got zero"}, getLocation(forInStatement->values));
@@ -434,6 +408,72 @@ struct TypeChecker2
         }
         TypeId iteratorTy = follow(iteratorTypes[0]);
 
+        auto checkFunction = [this, &arena, &scope, &forInStatement, &variableTypes](const FunctionTypeVar* iterFtv, std::vector<TypeId> iterTys, bool isMm)
+        {
+            if (iterTys.size() < 1 || iterTys.size() > 3)
+            {
+                if (isMm)
+                    reportError(GenericError{"__iter metamethod must return (next[, table[, state]])"}, getLocation(forInStatement->values));
+                else
+                    reportError(GenericError{"for..in loops must be passed (next[, table[, state]])"}, getLocation(forInStatement->values));
+
+                return;
+            }
+            
+            // It is okay if there aren't enough iterators, but the iteratee must provide enough.
+            std::vector<TypeId> expectedVariableTypes = flatten(arena, singletonTypes, iterFtv->retTypes, variableTypes.size());
+            if (expectedVariableTypes.size() < variableTypes.size())
+            {
+                if (isMm)
+                    reportError(GenericError{"__iter metamethod's next() function does not return enough values"}, getLocation(forInStatement->values));
+                else
+                    reportError(GenericError{"next() does not return enough values"}, forInStatement->values.data[0]->location);
+            }
+
+            for (size_t i = 0; i < std::min(expectedVariableTypes.size(), variableTypes.size()); ++i)
+                reportErrors(tryUnify(scope, forInStatement->vars.data[i]->location, variableTypes[i], expectedVariableTypes[i]));
+            
+            // nextFn is going to be invoked with (arrayTy, startIndexTy)
+
+            // It will be passed two arguments on every iteration save the
+            // first.
+
+            // It may be invoked with 0 or 1 argument on the first iteration.
+            // This depends on the types in iterateePack and therefore
+            // iteratorTypes.
+
+            // If iteratorTypes is too short to be a valid call to nextFn, we have to report a count mismatch error.
+            // If 2 is too short to be a valid call to nextFn, we have to report a count mismatch error.
+            // If 2 is too long to be a valid call to nextFn, we have to report a count mismatch error.
+            auto [minCount, maxCount] = getParameterExtents(TxnLog::empty(), iterFtv->argTypes, /*includeHiddenVariadics*/ true);
+
+            if (minCount > 2)
+                reportError(CountMismatch{2, std::nullopt, minCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
+            if (maxCount && *maxCount < 2)
+                reportError(CountMismatch{2, std::nullopt, *maxCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
+
+            const std::vector<TypeId> flattenedArgTypes = flatten(arena, singletonTypes, iterFtv->argTypes, 2);
+            size_t firstIterationArgCount = iterTys.empty() ? 0 : iterTys.size() - 1;
+            size_t actualArgCount = expectedVariableTypes.size();
+
+            if (firstIterationArgCount < minCount)
+                reportError(CountMismatch{2, std::nullopt, firstIterationArgCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
+            else if (actualArgCount < minCount)
+                reportError(CountMismatch{2, std::nullopt, actualArgCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
+
+            if (iterTys.size() >= 2 && flattenedArgTypes.size() > 0)
+            {
+                size_t valueIndex = forInStatement->values.size > 1 ? 1 : 0;
+                reportErrors(tryUnify(scope, forInStatement->values.data[valueIndex]->location, iterTys[1], flattenedArgTypes[0]));
+            }
+
+            if (iterTys.size() == 3 && flattenedArgTypes.size() > 1)
+            {
+                size_t valueIndex = forInStatement->values.size > 2 ? 2 : 0;
+                reportErrors(tryUnify(scope, forInStatement->values.data[valueIndex]->location, iterTys[2], flattenedArgTypes[1]));
+            }
+        };
+
         /*
          * If the first iterator argument is a function
          *  * There must be 1 to 3 iterator arguments.  Name them (nextTy,
@@ -451,58 +491,7 @@ struct TypeChecker2
          */
         if (const FunctionTypeVar* nextFn = get<FunctionTypeVar>(iteratorTy))
         {
-            if (iteratorTypes.size() < 1 || iteratorTypes.size() > 3)
+            checkFunction(nextFn, iteratorTypes, false);
-                reportError(GenericError{"for..in loops must be passed (next, [table[, state]])"}, getLocation(forInStatement->values));
-
-            // It is okay if there aren't enough iterators, but the iteratee must provide enough.
-            std::vector<TypeId> expectedVariableTypes = flatten(arena, nextFn->retTypes, variableTypes.size());
-            if (expectedVariableTypes.size() < variableTypes.size())
-                reportError(GenericError{"next() does not return enough values"}, forInStatement->vars.data[0]->location);
-
-            for (size_t i = 0; i < std::min(expectedVariableTypes.size(), variableTypes.size()); ++i)
-                reportErrors(tryUnify(scope, forInStatement->vars.data[i]->location, variableTypes[i], expectedVariableTypes[i]));
-
-            // nextFn is going to be invoked with (arrayTy, startIndexTy)
-
-            // It will be passed two arguments on every iteration save the
-            // first.
-
-            // It may be invoked with 0 or 1 argument on the first iteration.
-            // This depends on the types in iterateePack and therefore
-            // iteratorTypes.
-
-            // If iteratorTypes is too short to be a valid call to nextFn, we have to report a count mismatch error.
-            // If 2 is too short to be a valid call to nextFn, we have to report a count mismatch error.
-            // If 2 is too long to be a valid call to nextFn, we have to report a count mismatch error.
-            auto [minCount, maxCount] = getParameterExtents(TxnLog::empty(), nextFn->argTypes, /*includeHiddenVariadics*/ true);
-
-            if (minCount > 2)
-                reportError(CountMismatch{2, std::nullopt, minCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
-            if (maxCount && *maxCount < 2)
-                reportError(CountMismatch{2, std::nullopt, *maxCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
-
-            const std::vector<TypeId> flattenedArgTypes = flatten(arena, nextFn->argTypes, 2);
-            const auto [argTypes, argsTail] = Luau::flatten(nextFn->argTypes);
-
-            size_t firstIterationArgCount = iteratorTypes.empty() ? 0 : iteratorTypes.size() - 1;
-            size_t actualArgCount = expectedVariableTypes.size();
-
-            if (firstIterationArgCount < minCount)
-                reportError(CountMismatch{2, std::nullopt, firstIterationArgCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
-            else if (actualArgCount < minCount)
-                reportError(CountMismatch{2, std::nullopt, actualArgCount, CountMismatch::Arg}, forInStatement->vars.data[0]->location);
-
-            if (iteratorTypes.size() >= 2 && flattenedArgTypes.size() > 0)
-            {
-                size_t valueIndex = forInStatement->values.size > 1 ? 1 : 0;
-                reportErrors(tryUnify(scope, forInStatement->values.data[valueIndex]->location, iteratorTypes[1], flattenedArgTypes[0]));
-            }
-
-            if (iteratorTypes.size() == 3 && flattenedArgTypes.size() > 1)
-            {
-                size_t valueIndex = forInStatement->values.size > 2 ? 2 : 0;
-                reportErrors(tryUnify(scope, forInStatement->values.data[valueIndex]->location, iteratorTypes[2], flattenedArgTypes[1]));
-            }
         }
         else if (const TableTypeVar* ttv = get<TableTypeVar>(iteratorTy))
         {
@@ -519,6 +508,62 @@ struct TypeChecker2
         {
             // nothing
         }
+        else if (std::optional<TypeId> iterMmTy = findMetatableEntry(singletonTypes, module->errors, iteratorTy, "__iter", forInStatement->values.data[0]->location))
+        {
+            Instantiation instantiation{TxnLog::empty(), &arena, TypeLevel{}, scope};
+
+            if (std::optional<TypeId> instantiatedIterMmTy = instantiation.substitute(*iterMmTy))
+            {
+                if (const FunctionTypeVar* iterMmFtv = get<FunctionTypeVar>(*instantiatedIterMmTy))
+                {
+                    TypePackId argPack = arena.addTypePack({iteratorTy});
+                    reportErrors(tryUnify(scope, forInStatement->values.data[0]->location, argPack, iterMmFtv->argTypes));
+
+                    std::vector<TypeId> mmIteratorTypes = flatten(arena, singletonTypes, iterMmFtv->retTypes, 3);
+
+                    if (mmIteratorTypes.size() == 0)
+                    {
+                        reportError(GenericError{"__iter must return at least one value"}, forInStatement->values.data[0]->location);
+                        return;
+                    }
+
+                    TypeId nextFn = follow(mmIteratorTypes[0]);
+
+                    if (std::optional<TypeId> instantiatedNextFn = instantiation.substitute(nextFn))
+                    {
+                        std::vector<TypeId> instantiatedIteratorTypes = mmIteratorTypes;
+                        instantiatedIteratorTypes[0] = *instantiatedNextFn;
+
+                        if (const FunctionTypeVar* nextFtv = get<FunctionTypeVar>(*instantiatedNextFn))
+                        {
+                            checkFunction(nextFtv, instantiatedIteratorTypes, true);
+                        }
+                        else
+                        {
+                            reportError(CannotCallNonFunction{*instantiatedNextFn}, forInStatement->values.data[0]->location);
+                        }
+                    }
+                    else
+                    {
+                        reportError(UnificationTooComplex{}, forInStatement->values.data[0]->location);
+                    }
+                }
+                else
+                {
+                    // TODO: This will not tell the user that this is because the
+                    // metamethod isn't callable. This is not ideal, and we should
+                    // improve this error message.
+                    
+                    // TODO: This will also not handle intersections of functions or
+                    // callable tables (which are supported by the runtime).
+                    reportError(CannotCallNonFunction{*iterMmTy}, forInStatement->values.data[0]->location);
+                }
+            }
+            else
+            {
+                reportError(UnificationTooComplex{}, forInStatement->values.data[0]->location);
+            }
+        }
         else
         {
             reportError(CannotCallNonFunction{iteratorTy}, forInStatement->values.data[0]->location);
@@ -730,7 +775,7 @@ struct TypeChecker2
             visit(arg);
 
         TypeArena arena;
-        Instantiation instantiation{TxnLog::empty(), &arena, TypeLevel{}};
+        Instantiation instantiation{TxnLog::empty(), &arena, TypeLevel{}, stack.back()};
 
         TypePackId expectedRetType = lookupPack(call);
         TypeId functionType = lookupType(call->func);

Analysis/src/TypeInfer.cpp

@@ -47,6 +47,8 @@ LUAU_FASTFLAGVARIABLE(LuauNeverTypesAndOperatorsInference, false)
 LUAU_FASTFLAGVARIABLE(LuauReturnsFromCallsitesAreNotWidened, false)
 LUAU_FASTFLAGVARIABLE(LuauCompleteVisitor, false)
 LUAU_FASTFLAGVARIABLE(LuauUnionOfTypesFollow, false)
+LUAU_FASTFLAGVARIABLE(LuauReportShadowedTypeAlias, false)
+LUAU_FASTFLAGVARIABLE(LuauBetterMessagingOnCountMismatch, false)
 
 namespace Luau
 {
@@ -66,9 +68,7 @@ static void defaultLuauPrintLine(const std::string& s)
     printf("%s\n", s.c_str());
 }
 
-using PrintLineProc = decltype(&defaultLuauPrintLine);
+PrintLineProc luauPrintLine = &defaultLuauPrintLine;
-
-static PrintLineProc luauPrintLine = &defaultLuauPrintLine;
 
 void setPrintLine(PrintLineProc pl)
 {
@@ -270,16 +270,16 @@ TypeChecker::TypeChecker(ModuleResolver* resolver, NotNull<SingletonTypes> singl
 {
     globalScope = std::make_shared<Scope>(globalTypes.addTypePack(TypePackVar{FreeTypePack{TypeLevel{}}}));
 
-    globalScope->exportedTypeBindings["any"] = TypeFun{{}, anyType};
+    globalScope->addBuiltinTypeBinding("any", TypeFun{{}, anyType});
-    globalScope->exportedTypeBindings["nil"] = TypeFun{{}, nilType};
+    globalScope->addBuiltinTypeBinding("nil", TypeFun{{}, nilType});
-    globalScope->exportedTypeBindings["number"] = TypeFun{{}, numberType};
+    globalScope->addBuiltinTypeBinding("number", TypeFun{{}, numberType});
-    globalScope->exportedTypeBindings["string"] = TypeFun{{}, stringType};
+    globalScope->addBuiltinTypeBinding("string", TypeFun{{}, stringType});
-    globalScope->exportedTypeBindings["boolean"] = TypeFun{{}, booleanType};
+    globalScope->addBuiltinTypeBinding("boolean", TypeFun{{}, booleanType});
-    globalScope->exportedTypeBindings["thread"] = TypeFun{{}, threadType};
+    globalScope->addBuiltinTypeBinding("thread", TypeFun{{}, threadType});
     if (FFlag::LuauUnknownAndNeverType)
     {
-        globalScope->exportedTypeBindings["unknown"] = TypeFun{{}, unknownType};
+        globalScope->addBuiltinTypeBinding("unknown", TypeFun{{}, unknownType});
-        globalScope->exportedTypeBindings["never"] = TypeFun{{}, neverType};
+        globalScope->addBuiltinTypeBinding("never", TypeFun{{}, neverType});
     }
 }
 
@@ -534,7 +534,7 @@ void TypeChecker::checkBlockWithoutRecursionCheck(const ScopePtr& scope, const A
     {
         if (const auto& typealias = stat->as<AstStatTypeAlias>())
         {
-            check(scope, *typealias, subLevel, true);
+            prototype(scope, *typealias, subLevel);
             ++subLevel;
         }
     }
@@ -698,6 +698,10 @@ LUAU_NOINLINE void TypeChecker::checkBlockTypeAliases(const ScopePtr& scope, std
             auto& bindings = typealias->exported ? scope->exportedTypeBindings : scope->privateTypeBindings;
 
             Name name = typealias->name.value;
+
+            if (FFlag::LuauReportShadowedTypeAlias && duplicateTypeAliases.contains({typealias->exported, name}))
+                continue;
+
             TypeId type = bindings[name].type;
             if (get<FreeTypeVar>(follow(type)))
             {
@@ -1109,8 +1113,23 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatLocal& local)
         TypePackId valuePack =
             checkExprList(scope, local.location, local.values, /* substituteFreeForNil= */ true, instantiateGenerics, expectedTypes).type;
 
+        // If the expression list only contains one expression and it's a function call or is otherwise within parentheses, use FunctionResult.
+        // Otherwise, we'll want to use ExprListResult to make the error messaging more general.
+        CountMismatch::Context ctx = FFlag::LuauBetterMessagingOnCountMismatch ? CountMismatch::ExprListResult : CountMismatch::FunctionResult;
+        if (FFlag::LuauBetterMessagingOnCountMismatch)
+        {
+            if (local.values.size == 1)
+            {
+                AstExpr* e = local.values.data[0];
+                while (auto group = e->as<AstExprGroup>())
+                    e = group->expr;
+                if (e->is<AstExprCall>())
+                    ctx = CountMismatch::FunctionResult;
+            }
+        }
+
         Unifier state = mkUnifier(scope, local.location);
-        state.ctx = CountMismatch::Result;
+        state.ctx = ctx;
         state.tryUnify(valuePack, variablePack);
         reportErrors(state.errors);
 
@@ -1472,10 +1491,8 @@ void TypeChecker::check(const ScopePtr& scope, TypeId ty, const ScopePtr& funSco
     scope->bindings[function.name] = {quantify(funScope, ty, function.name->location), function.name->location};
 }
 
-void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias, int subLevel, bool forwardDeclare)
+void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias)
 {
-    // This function should be called at most twice for each type alias.
-    // Once with forwardDeclare, and once without.
     Name name = typealias.name.value;
 
     // If the alias is missing a name, we can't do anything with it.  Ignore it.
@@ -1490,14 +1507,134 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias
 
     auto& bindingsMap = typealias.exported ? scope->exportedTypeBindings : scope->privateTypeBindings;
 
-    if (forwardDeclare)
+    // If the first pass failed (this should mean a duplicate definition), the second pass isn't going to be
-    {
+    // interesting.
-        if (binding)
+    if (duplicateTypeAliases.find({typealias.exported, name}))
-        {
+        return;
-            Location location = scope->typeAliasLocations[name];
-            reportError(TypeError{typealias.location, DuplicateTypeDefinition{name, location}});
 
+    // By now this alias must have been `prototype()`d first.
+    if (!binding)
+        ice("Not predeclared");
+
+    ScopePtr aliasScope = childScope(scope, typealias.location);
+    aliasScope->level = scope->level.incr();
+
+    for (auto param : binding->typeParams)
+    {
+        auto generic = get<GenericTypeVar>(param.ty);
+        LUAU_ASSERT(generic);
+        aliasScope->privateTypeBindings[generic->name] = TypeFun{{}, param.ty};
+    }
+
+    for (auto param : binding->typePackParams)
+    {
+        auto generic = get<GenericTypePack>(param.tp);
+        LUAU_ASSERT(generic);
+        aliasScope->privateTypePackBindings[generic->name] = param.tp;
+    }
+
+    TypeId ty = resolveType(aliasScope, *typealias.type);
+    if (auto ttv = getMutable<TableTypeVar>(follow(ty)))
+    {
+        // If the table is already named and we want to rename the type function, we have to bind new alias to a copy
+        // Additionally, we can't modify types that come from other modules
+        if (ttv->name || follow(ty)->owningArena != &currentModule->internalTypes)
+        {
+            bool sameTys = std::equal(ttv->instantiatedTypeParams.begin(), ttv->instantiatedTypeParams.end(), binding->typeParams.begin(),
+                binding->typeParams.end(), [](auto&& itp, auto&& tp) {
+                    return itp == tp.ty;
+                });
+            bool sameTps = std::equal(ttv->instantiatedTypePackParams.begin(), ttv->instantiatedTypePackParams.end(), binding->typePackParams.begin(),
+                binding->typePackParams.end(), [](auto&& itpp, auto&& tpp) {
+                    return itpp == tpp.tp;
+                });
+
+            // Copy can be skipped if this is an identical alias
+            if (!ttv->name || ttv->name != name || !sameTys || !sameTps)
+            {
+                // This is a shallow clone, original recursive links to self are not updated
+                TableTypeVar clone = TableTypeVar{ttv->props, ttv->indexer, ttv->level, ttv->state};
+                clone.definitionModuleName = ttv->definitionModuleName;
+                clone.name = name;
+
+                for (auto param : binding->typeParams)
+                    clone.instantiatedTypeParams.push_back(param.ty);
+
+                for (auto param : binding->typePackParams)
+                    clone.instantiatedTypePackParams.push_back(param.tp);
+
+                bool isNormal = ty->normal;
+                ty = addType(std::move(clone));
+
+                if (FFlag::LuauLowerBoundsCalculation)
+                    asMutable(ty)->normal = isNormal;
+            }
+        }
+        else
+        {
+            ttv->name = name;
+
+            ttv->instantiatedTypeParams.clear();
+            for (auto param : binding->typeParams)
+                ttv->instantiatedTypeParams.push_back(param.ty);
+
+            ttv->instantiatedTypePackParams.clear();
+            for (auto param : binding->typePackParams)
+                ttv->instantiatedTypePackParams.push_back(param.tp);
+        }
+    }
+    else if (auto mtv = getMutable<MetatableTypeVar>(follow(ty)))
+    {
+        // We can't modify types that come from other modules
+        if (follow(ty)->owningArena == &currentModule->internalTypes)
+            mtv->syntheticName = name;
+    }
+
+    TypeId& bindingType = bindingsMap[name].type;
+
+    if (unify(ty, bindingType, aliasScope, typealias.location))
+        bindingType = ty;
+
+    if (FFlag::LuauLowerBoundsCalculation)
+    {
+        auto [t, ok] = normalize(bindingType, currentModule, singletonTypes, *iceHandler);
+        bindingType = t;
+        if (!ok)
+            reportError(typealias.location, NormalizationTooComplex{});
+    }
+}
+
+void TypeChecker::prototype(const ScopePtr& scope, const AstStatTypeAlias& typealias, int subLevel)
+{
+    Name name = typealias.name.value;
+
+    // If the alias is missing a name, we can't do anything with it.  Ignore it.
+    if (name == kParseNameError)
+        return;
+
+    std::optional<TypeFun> binding;
+    if (auto it = scope->exportedTypeBindings.find(name); it != scope->exportedTypeBindings.end())
+        binding = it->second;
+    else if (auto it = scope->privateTypeBindings.find(name); it != scope->privateTypeBindings.end())
+        binding = it->second;
+
+    auto& bindingsMap = typealias.exported ? scope->exportedTypeBindings : scope->privateTypeBindings;
+
+    if (binding)
+    {
+        Location location = scope->typeAliasLocations[name];
+        reportError(TypeError{typealias.location, DuplicateTypeDefinition{name, location}});
+
+        if (!FFlag::LuauReportShadowedTypeAlias)
             bindingsMap[name] = TypeFun{binding->typeParams, binding->typePackParams, errorRecoveryType(anyType)};
+
+        duplicateTypeAliases.insert({typealias.exported, name});
+    }
+    else if (FFlag::LuauReportShadowedTypeAlias)
+    {
+        if (globalScope->builtinTypeNames.contains(name))
+        {
+            reportError(typealias.location, DuplicateTypeDefinition{name});
             duplicateTypeAliases.insert({typealias.exported, name});
         }
         else
@@ -1520,100 +1657,20 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias
     }
     else
     {
-        // If the first pass failed (this should mean a duplicate definition), the second pass isn't going to be
-        // interesting.
-        if (duplicateTypeAliases.find({typealias.exported, name}))
-            return;
-
-        if (!binding)
-            ice("Not predeclared");
-
         ScopePtr aliasScope = childScope(scope, typealias.location);
         aliasScope->level = scope->level.incr();
+        aliasScope->level.subLevel = subLevel;
 
-        for (auto param : binding->typeParams)
+        auto [generics, genericPacks] =
-        {
+            createGenericTypes(aliasScope, scope->level, typealias, typealias.generics, typealias.genericPacks, /* useCache = */ true);
-            auto generic = get<GenericTypeVar>(param.ty);
-            LUAU_ASSERT(generic);
-            aliasScope->privateTypeBindings[generic->name] = TypeFun{{}, param.ty};
-        }
 
-        for (auto param : binding->typePackParams)
+        TypeId ty = freshType(aliasScope);
-        {
+        FreeTypeVar* ftv = getMutable<FreeTypeVar>(ty);
-            auto generic = get<GenericTypePack>(param.tp);
+        LUAU_ASSERT(ftv);
-            LUAU_ASSERT(generic);
+        ftv->forwardedTypeAlias = true;
-            aliasScope->privateTypePackBindings[generic->name] = param.tp;
+        bindingsMap[name] = {std::move(generics), std::move(genericPacks), ty};
-        }
 
-        TypeId ty = resolveType(aliasScope, *typealias.type);
+        scope->typeAliasLocations[name] = typealias.location;
-        if (auto ttv = getMutable<TableTypeVar>(follow(ty)))
-        {
-            // If the table is already named and we want to rename the type function, we have to bind new alias to a copy
-            // Additionally, we can't modify types that come from other modules
-            if (ttv->name || follow(ty)->owningArena != &currentModule->internalTypes)
-            {
-                bool sameTys = std::equal(ttv->instantiatedTypeParams.begin(), ttv->instantiatedTypeParams.end(), binding->typeParams.begin(),
-                    binding->typeParams.end(), [](auto&& itp, auto&& tp) {
-                        return itp == tp.ty;
-                    });
-                bool sameTps = std::equal(ttv->instantiatedTypePackParams.begin(), ttv->instantiatedTypePackParams.end(),
-                    binding->typePackParams.begin(), binding->typePackParams.end(), [](auto&& itpp, auto&& tpp) {
-                        return itpp == tpp.tp;
-                    });
-
-                // Copy can be skipped if this is an identical alias
-                if (!ttv->name || ttv->name != name || !sameTys || !sameTps)
-                {
-                    // This is a shallow clone, original recursive links to self are not updated
-                    TableTypeVar clone = TableTypeVar{ttv->props, ttv->indexer, ttv->level, ttv->state};
-                    clone.definitionModuleName = ttv->definitionModuleName;
-                    clone.name = name;
-
-                    for (auto param : binding->typeParams)
-                        clone.instantiatedTypeParams.push_back(param.ty);
-
-                    for (auto param : binding->typePackParams)
-                        clone.instantiatedTypePackParams.push_back(param.tp);
-
-                    bool isNormal = ty->normal;
-                    ty = addType(std::move(clone));
-
-                    if (FFlag::LuauLowerBoundsCalculation)
-                        asMutable(ty)->normal = isNormal;
-                }
-            }
-            else
-            {
-                ttv->name = name;
-
-                ttv->instantiatedTypeParams.clear();
-                for (auto param : binding->typeParams)
-                    ttv->instantiatedTypeParams.push_back(param.ty);
-
-                ttv->instantiatedTypePackParams.clear();
-                for (auto param : binding->typePackParams)
-                    ttv->instantiatedTypePackParams.push_back(param.tp);
-            }
-        }
-        else if (auto mtv = getMutable<MetatableTypeVar>(follow(ty)))
-        {
-            // We can't modify types that come from other modules
-            if (follow(ty)->owningArena == &currentModule->internalTypes)
-                mtv->syntheticName = name;
-        }
-
-        TypeId& bindingType = bindingsMap[name].type;
-
-        if (unify(ty, bindingType, aliasScope, typealias.location))
-            bindingType = ty;
-
-        if (FFlag::LuauLowerBoundsCalculation)
-        {
-            auto [t, ok] = normalize(bindingType, currentModule, singletonTypes, *iceHandler);
-            bindingType = t;
-            if (!ok)
-                reportError(typealias.location, NormalizationTooComplex{});
-        }
     }
 }
 
@@ -4152,7 +4209,7 @@ std::optional<WithPredicate<TypePackId>> TypeChecker::checkCallOverload(const Sc
             TypePackId adjustedArgPack = addTypePack(TypePack{std::move(adjustedArgTypes), it.tail()});
 
             TxnLog log;
-            promoteTypeLevels(log, &currentModule->internalTypes, level, retPack);
+            promoteTypeLevels(log, &currentModule->internalTypes, level, /*scope*/ nullptr, /*useScope*/ false, retPack);
             log.commit();
 
             *asMutable(fn) = FunctionTypeVar{level, adjustedArgPack, retPack};
@@ -4712,7 +4769,7 @@ TypeId TypeChecker::instantiate(const ScopePtr& scope, TypeId ty, Location locat
     if (ftv && ftv->hasNoGenerics)
         return ty;
 
-    Instantiation instantiation{log, &currentModule->internalTypes, scope->level};
+    Instantiation instantiation{log, &currentModule->internalTypes, scope->level, /*scope*/ nullptr};
 
     if (FFlag::LuauAutocompleteDynamicLimits && instantiationChildLimit)
         instantiation.childLimit = *instantiationChildLimit;

Analysis/src/TypeUtils.cpp

@@ -224,4 +224,46 @@ std::pair<size_t, std::optional<size_t>> getParameterExtents(const TxnLog* log,
         return {minCount, minCount + optionalCount};
 }
 
+std::vector<TypeId> flatten(TypeArena& arena, NotNull<SingletonTypes> singletonTypes, TypePackId pack, size_t length)
+{
+    std::vector<TypeId> result;
+
+    auto it = begin(pack);
+    auto endIt = end(pack);
+
+    while (it != endIt)
+    {
+        result.push_back(*it);
+
+        if (result.size() >= length)
+            return result;
+
+        ++it;
+    }
+
+    if (!it.tail())
+        return result;
+
+    TypePackId tail = *it.tail();
+    if (get<TypePack>(tail))
+        LUAU_ASSERT(0);
+    else if (auto vtp = get<VariadicTypePack>(tail))
+    {
+        while (result.size() < length)
+            result.push_back(vtp->ty);
+    }
+    else if (get<FreeTypePack>(tail) || get<GenericTypePack>(tail))
+    {
+        while (result.size() < length)
+            result.push_back(arena.addType(FreeTypeVar{nullptr}));
+    }
+    else if (auto etp = get<Unifiable::Error>(tail))
+    {
+        while (result.size() < length)
+            result.push_back(singletonTypes->errorRecoveryType());
+    }
+
+    return result;
+}
+
 } // namespace Luau

Analysis/src/TypeVar.cpp

@@ -474,6 +474,17 @@ FunctionTypeVar::FunctionTypeVar(TypeLevel level, TypePackId argTypes, TypePackI
 {
 }
 
+FunctionTypeVar::FunctionTypeVar(
+    TypeLevel level, Scope* scope, TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn, bool hasSelf)
+    : level(level)
+    , scope(scope)
+    , argTypes(argTypes)
+    , retTypes(retTypes)
+    , definition(std::move(defn))
+    , hasSelf(hasSelf)
+{
+}
+
 FunctionTypeVar::FunctionTypeVar(std::vector<TypeId> generics, std::vector<TypePackId> genericPacks, TypePackId argTypes, TypePackId retTypes,
     std::optional<FunctionDefinition> defn, bool hasSelf)
     : generics(generics)
@@ -497,9 +508,23 @@ FunctionTypeVar::FunctionTypeVar(TypeLevel level, std::vector<TypeId> generics,
 {
 }
 
-TableTypeVar::TableTypeVar(TableState state, TypeLevel level)
+FunctionTypeVar::FunctionTypeVar(TypeLevel level, Scope* scope, std::vector<TypeId> generics, std::vector<TypePackId> genericPacks,
+    TypePackId argTypes, TypePackId retTypes, std::optional<FunctionDefinition> defn, bool hasSelf)
+    : level(level)
+    , scope(scope)
+    , generics(generics)
+    , genericPacks(genericPacks)
+    , argTypes(argTypes)
+    , retTypes(retTypes)
+    , definition(std::move(defn))
+    , hasSelf(hasSelf)
+{
+}
+
+TableTypeVar::TableTypeVar(TableState state, TypeLevel level, Scope* scope)
     : state(state)
     , level(level)
+    , scope(scope)
 {
 }
 
@@ -511,6 +536,15 @@ TableTypeVar::TableTypeVar(const Props& props, const std::optional<TableIndexer>
 {
 }
 
+TableTypeVar::TableTypeVar(const Props& props, const std::optional<TableIndexer>& indexer, TypeLevel level, Scope* scope, TableState state)
+    : props(props)
+    , indexer(indexer)
+    , state(state)
+    , level(level)
+    , scope(scope)
+{
+}
+
 // Test TypeVars for equivalence
 // More complex than we'd like because TypeVars can self-reference.
 

Analysis/src/Unifiable.cpp

@@ -18,6 +18,13 @@ Free::Free(Scope* scope)
 {
 }
 
+Free::Free(Scope* scope, TypeLevel level)
+    : index(++nextIndex)
+    , level(level)
+    , scope(scope)
+{
+}
+
 int Free::nextIndex = 0;
 
 Generic::Generic()

Analysis/src/Unifier.cpp

@@ -23,6 +23,7 @@ LUAU_FASTFLAG(LuauUnknownAndNeverType)
 LUAU_FASTFLAGVARIABLE(LuauScalarShapeSubtyping, false)
 LUAU_FASTFLAG(LuauClassTypeVarsInSubstitution)
 LUAU_FASTFLAG(LuauCallUnifyPackTails)
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
 
 namespace Luau
 {
@@ -33,10 +34,15 @@ struct PromoteTypeLevels final : TypeVarOnceVisitor
     const TypeArena* typeArena = nullptr;
     TypeLevel minLevel;
 
-    PromoteTypeLevels(TxnLog& log, const TypeArena* typeArena, TypeLevel minLevel)
+    Scope* outerScope = nullptr;
+    bool useScopes;
+
+    PromoteTypeLevels(TxnLog& log, const TypeArena* typeArena, TypeLevel minLevel, Scope* outerScope, bool useScopes)
         : log(log)
         , typeArena(typeArena)
         , minLevel(minLevel)
+        , outerScope(outerScope)
+        , useScopes(useScopes)
     {
     }
 
@@ -44,9 +50,18 @@ struct PromoteTypeLevels final : TypeVarOnceVisitor
     void promote(TID ty, T* t)
     {
         LUAU_ASSERT(t);
-        if (minLevel.subsumesStrict(t->level))
+
+        if (useScopes)
         {
-            log.changeLevel(ty, minLevel);
+            if (subsumesStrict(outerScope, t->scope))
+                log.changeScope(ty, NotNull{outerScope});
+        }
+        else
+        {
+            if (minLevel.subsumesStrict(t->level))
+            {
+                log.changeLevel(ty, minLevel);
+            }
         }
     }
 
@@ -123,23 +138,23 @@ struct PromoteTypeLevels final : TypeVarOnceVisitor
     }
 };
 
-static void promoteTypeLevels(TxnLog& log, const TypeArena* typeArena, TypeLevel minLevel, TypeId ty)
+static void promoteTypeLevels(TxnLog& log, const TypeArena* typeArena, TypeLevel minLevel, Scope* outerScope, bool useScopes, TypeId ty)
 {
     // Type levels of types from other modules are already global, so we don't need to promote anything inside
     if (ty->owningArena != typeArena)
         return;
 
-    PromoteTypeLevels ptl{log, typeArena, minLevel};
+    PromoteTypeLevels ptl{log, typeArena, minLevel, outerScope, useScopes};
     ptl.traverse(ty);
 }
 
-void promoteTypeLevels(TxnLog& log, const TypeArena* typeArena, TypeLevel minLevel, TypePackId tp)
+void promoteTypeLevels(TxnLog& log, const TypeArena* typeArena, TypeLevel minLevel, Scope* outerScope, bool useScopes, TypePackId tp)
 {
     // Type levels of types from other modules are already global, so we don't need to promote anything inside
     if (tp->owningArena != typeArena)
         return;
 
-    PromoteTypeLevels ptl{log, typeArena, minLevel};
+    PromoteTypeLevels ptl{log, typeArena, minLevel, outerScope, useScopes};
     ptl.traverse(tp);
 }
 
@@ -318,6 +333,16 @@ static std::optional<std::pair<Luau::Name, const SingletonTypeVar*>> getTableMat
     return std::nullopt;
 }
 
+// TODO: Inline and clip with FFlag::DebugLuauDeferredConstraintResolution
+template<typename TY_A, typename TY_B>
+static bool subsumes(bool useScopes, TY_A* left, TY_B* right)
+{
+    if (useScopes)
+        return subsumes(left->scope, right->scope);
+    else
+        return left->level.subsumes(right->level);
+}
+
 Unifier::Unifier(TypeArena* types, NotNull<SingletonTypes> singletonTypes, Mode mode, NotNull<Scope> scope, const Location& location,
     Variance variance, UnifierSharedState& sharedState, TxnLog* parentLog)
     : types(types)
@@ -375,7 +400,7 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
     auto superFree = log.getMutable<FreeTypeVar>(superTy);
     auto subFree = log.getMutable<FreeTypeVar>(subTy);
 
-    if (superFree && subFree && superFree->level.subsumes(subFree->level))
+    if (superFree && subFree && subsumes(useScopes, superFree, subFree))
     {
         if (!occursCheck(subTy, superTy))
             log.replace(subTy, BoundTypeVar(superTy));
@@ -386,7 +411,7 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
     {
         if (!occursCheck(superTy, subTy))
         {
-            if (superFree->level.subsumes(subFree->level))
+            if (subsumes(useScopes, superFree, subFree))
             {
                 log.changeLevel(subTy, superFree->level);
             }
@@ -400,7 +425,7 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
     {
         // Unification can't change the level of a generic.
         auto subGeneric = log.getMutable<GenericTypeVar>(subTy);
-        if (subGeneric && !subGeneric->level.subsumes(superFree->level))
+        if (subGeneric && !subsumes(useScopes, subGeneric, superFree))
         {
             // TODO: a more informative error message? CLI-39912
             reportError(TypeError{location, GenericError{"Generic subtype escaping scope"}});
@@ -409,7 +434,7 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
 
         if (!occursCheck(superTy, subTy))
         {
-            promoteTypeLevels(log, types, superFree->level, subTy);
+            promoteTypeLevels(log, types, superFree->level, superFree->scope, useScopes, subTy);
 
             Widen widen{types, singletonTypes};
             log.replace(superTy, BoundTypeVar(widen(subTy)));
@@ -429,7 +454,7 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
 
         // Unification can't change the level of a generic.
         auto superGeneric = log.getMutable<GenericTypeVar>(superTy);
-        if (superGeneric && !superGeneric->level.subsumes(subFree->level))
+        if (superGeneric && !subsumes(useScopes, superGeneric, subFree))
         {
             // TODO: a more informative error message? CLI-39912
             reportError(TypeError{location, GenericError{"Generic supertype escaping scope"}});
@@ -438,7 +463,7 @@ void Unifier::tryUnify_(TypeId subTy, TypeId superTy, bool isFunctionCall, bool
 
         if (!occursCheck(subTy, superTy))
         {
-            promoteTypeLevels(log, types, subFree->level, superTy);
+            promoteTypeLevels(log, types, subFree->level, subFree->scope, useScopes, superTy);
             log.replace(subTy, BoundTypeVar(superTy));
         }
 
@@ -855,6 +880,7 @@ struct WeirdIter
     size_t index;
     bool growing;
     TypeLevel level;
+    Scope* scope = nullptr;
 
     WeirdIter(TypePackId packId, TxnLog& log)
         : packId(packId)
@@ -915,6 +941,7 @@ struct WeirdIter
         LUAU_ASSERT(log.getMutable<TypePack>(newTail));
 
         level = log.getMutable<Unifiable::Free>(packId)->level;
+        scope = log.getMutable<Unifiable::Free>(packId)->scope;
         log.replace(packId, BoundTypePack(newTail));
         packId = newTail;
         pack = log.getMutable<TypePack>(newTail);
@@ -1055,8 +1082,8 @@ void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCal
         auto superIter = WeirdIter(superTp, log);
         auto subIter = WeirdIter(subTp, log);
 
-        auto mkFreshType = [this](TypeLevel level) {
+        auto mkFreshType = [this](Scope* scope, TypeLevel level) {
-            return types->freshType(level);
+            return types->freshType(scope, level);
         };
 
         const TypePackId emptyTp = types->addTypePack(TypePack{{}, std::nullopt});
@@ -1072,12 +1099,12 @@ void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCal
 
             if (superIter.good() && subIter.growing)
             {
-                subIter.pushType(mkFreshType(subIter.level));
+                subIter.pushType(mkFreshType(subIter.scope, subIter.level));
             }
 
             if (subIter.good() && superIter.growing)
             {
-                superIter.pushType(mkFreshType(superIter.level));
+                superIter.pushType(mkFreshType(superIter.scope, superIter.level));
             }
 
             if (superIter.good() && subIter.good())
@@ -1158,7 +1185,7 @@ void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCal
                 // these to produce the expected error message.
                 size_t expectedSize = size(superTp);
                 size_t actualSize = size(subTp);
-                if (ctx == CountMismatch::Result)
+                if (ctx == CountMismatch::FunctionResult || ctx == CountMismatch::ExprListResult)
                     std::swap(expectedSize, actualSize);
                 reportError(TypeError{location, CountMismatch{expectedSize, std::nullopt, actualSize, ctx}});
 
@@ -1271,7 +1298,7 @@ void Unifier::tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCal
         else if (!innerState.errors.empty())
             reportError(TypeError{location, TypeMismatch{superTy, subTy, "", innerState.errors.front()}});
 
-        innerState.ctx = CountMismatch::Result;
+        innerState.ctx = CountMismatch::FunctionResult;
         innerState.tryUnify_(subFunction->retTypes, superFunction->retTypes);
 
         if (!reported)
@@ -1295,7 +1322,7 @@ void Unifier::tryUnifyFunctions(TypeId subTy, TypeId superTy, bool isFunctionCal
         ctx = CountMismatch::Arg;
         tryUnify_(superFunction->argTypes, subFunction->argTypes, isFunctionCall);
 
-        ctx = CountMismatch::Result;
+        ctx = CountMismatch::FunctionResult;
         tryUnify_(subFunction->retTypes, superFunction->retTypes);
     }
 
@@ -1693,8 +1720,45 @@ void Unifier::tryUnifyWithMetatable(TypeId subTy, TypeId superTy, bool reversed)
         {
         case TableState::Free:
         {
-            tryUnify_(subTy, superMetatable->table);
+            if (FFlag::DebugLuauDeferredConstraintResolution)
-            log.bindTable(subTy, superTy);
+            {
+                Unifier innerState = makeChildUnifier();
+                bool missingProperty = false;
+
+                for (const auto& [propName, prop] : subTable->props)
+                {
+                    if (std::optional<TypeId> mtPropTy = findTablePropertyRespectingMeta(superTy, propName))
+                    {
+                        innerState.tryUnify(prop.type, *mtPropTy);
+                    }
+                    else
+                    {
+                        reportError(mismatchError);
+                        missingProperty = true;
+                        break;
+                    }
+                }
+
+                if (const TableTypeVar* superTable = log.get<TableTypeVar>(log.follow(superMetatable->table)))
+                {
+                    // TODO: Unify indexers.
+                }
+
+                if (auto e = hasUnificationTooComplex(innerState.errors))
+                    reportError(*e);
+                else if (!innerState.errors.empty())
+                    reportError(TypeError{location, TypeMismatch{reversed ? subTy : superTy, reversed ? superTy : subTy, "", innerState.errors.front()}});
+                else if (!missingProperty)
+                {
+                    log.concat(std::move(innerState.log));
+                    log.bindTable(subTy, superTy);
+                }
+            }
+            else
+            {
+                tryUnify_(subTy, superMetatable->table);
+                log.bindTable(subTy, superTy);
+            }
 
             break;
         }

CLI/Analyze.cpp

@@ -270,7 +270,7 @@ int main(int argc, char** argv)
     CliConfigResolver configResolver(mode);
     Luau::Frontend frontend(&fileResolver, &configResolver, frontendOptions);
 
-    Luau::registerBuiltinTypes(frontend.typeChecker);
+    Luau::registerBuiltinGlobals(frontend.typeChecker);
     Luau::freeze(frontend.typeChecker.globalTypes);
 
 #ifdef CALLGRIND

CodeGen/src/Fallbacks.cpp

@@ -720,7 +720,7 @@ const Instruction* execute_LOP_CALL(lua_State* L, const Instruction* pc, Closure
 
         int i;
         for (i = nresults; i != 0 && vali < valend; i--)
-            setobjs2s(L, res++, vali++);
+            setobj2s(L, res++, vali++);
         while (i-- > 0)
             setnilvalue(res++);
 
@@ -756,7 +756,7 @@ const Instruction* execute_LOP_RETURN(lua_State* L, const Instruction* pc, Closu
     // note: in MULTRET context nresults starts as -1 so i != 0 condition never activates intentionally
     int i;
     for (i = nresults; i != 0 && vali < valend; i--)
-        setobjs2s(L, res++, vali++);
+        setobj2s(L, res++, vali++);
     while (i-- > 0)
         setnilvalue(res++);
 
@@ -1667,7 +1667,7 @@ const Instruction* execute_LOP_CONCAT(lua_State* L, const Instruction* pc, Closu
 
     StkId ra = VM_REG(LUAU_INSN_A(insn));
 
-    setobjs2s(L, ra, base + b);
+    setobj2s(L, ra, base + b);
     VM_PROTECT(luaC_checkGC(L));
     return pc;
 }
@@ -2003,9 +2003,9 @@ const Instruction* execute_LOP_FORGLOOP(lua_State* L, const Instruction* pc, Clo
     else
     {
         // note: it's safe to push arguments past top for complicated reasons (see top of the file)
-        setobjs2s(L, ra + 3 + 2, ra + 2);
+        setobj2s(L, ra + 3 + 2, ra + 2);
-        setobjs2s(L, ra + 3 + 1, ra + 1);
+        setobj2s(L, ra + 3 + 1, ra + 1);
-        setobjs2s(L, ra + 3, ra);
+        setobj2s(L, ra + 3, ra);
 
         L->top = ra + 3 + 3; // func + 2 args (state and index)
         LUAU_ASSERT(L->top <= L->stack_last);
@@ -2017,7 +2017,7 @@ const Instruction* execute_LOP_FORGLOOP(lua_State* L, const Instruction* pc, Clo
         ra = VM_REG(LUAU_INSN_A(insn));
 
         // copy first variable back into the iteration index
-        setobjs2s(L, ra + 2, ra + 3);
+        setobj2s(L, ra + 2, ra + 3);
 
         // note that we need to increment pc by 1 to exit the loop since we need to skip over aux
         pc += ttisnil(ra + 3) ? 1 : LUAU_INSN_D(insn);
@@ -2094,7 +2094,7 @@ const Instruction* execute_LOP_GETVARARGS(lua_State* L, const Instruction* pc, C
         StkId ra = VM_REG(LUAU_INSN_A(insn)); // previous call may change the stack
 
         for (int j = 0; j < n; j++)
-            setobjs2s(L, ra + j, base - n + j);
+            setobj2s(L, ra + j, base - n + j);
 
         L->top = ra + n;
         return pc;
@@ -2104,7 +2104,7 @@ const Instruction* execute_LOP_GETVARARGS(lua_State* L, const Instruction* pc, C
         StkId ra = VM_REG(LUAU_INSN_A(insn));
 
         for (int j = 0; j < b && j < n; j++)
-            setobjs2s(L, ra + j, base - n + j);
+            setobj2s(L, ra + j, base - n + j);
         for (int j = n; j < b; j++)
             setnilvalue(ra + j);
         return pc;
@@ -2183,7 +2183,7 @@ const Instruction* execute_LOP_PREPVARARGS(lua_State* L, const Instruction* pc,
 
     for (int i = 0; i < numparams; ++i)
     {
-        setobjs2s(L, base + i, fixed + i);
+        setobj2s(L, base + i, fixed + i);
         setnilvalue(fixed + i);
     }
 

Common/include/Luau/Bytecode.h

@@ -517,6 +517,10 @@ enum LuauBuiltinFunction
 
     // bit32.extract(_, k, k)
     LBF_BIT32_EXTRACTK,
+
+    // get/setmetatable
+    LBF_GETMETATABLE,
+    LBF_SETMETATABLE,
 };
 
 // Capture type, used in LOP_CAPTURE

Compiler/src/Builtins.cpp

@@ -4,6 +4,8 @@
 #include "Luau/Bytecode.h"
 #include "Luau/Compiler.h"
 
+LUAU_FASTFLAGVARIABLE(LuauCompileBuiltinMT, false)
+
 namespace Luau
 {
 namespace Compile
@@ -64,6 +66,14 @@ static int getBuiltinFunctionId(const Builtin& builtin, const CompileOptions& op
     if (builtin.isGlobal("select"))
         return LBF_SELECT_VARARG;
 
+    if (FFlag::LuauCompileBuiltinMT)
+    {
+        if (builtin.isGlobal("getmetatable"))
+            return LBF_GETMETATABLE;
+        if (builtin.isGlobal("setmetatable"))
+            return LBF_SETMETATABLE;
+    }
+
     if (builtin.object == "math")
     {
         if (builtin.method == "abs")

VM/src/lapi.cpp

@@ -235,7 +235,7 @@ void lua_remove(lua_State* L, int idx)
     StkId p = index2addr(L, idx);
     api_checkvalidindex(L, p);
     while (++p < L->top)
-        setobjs2s(L, p - 1, p);
+        setobj2s(L, p - 1, p);
     L->top--;
     return;
 }
@@ -246,8 +246,8 @@ void lua_insert(lua_State* L, int idx)
     StkId p = index2addr(L, idx);
     api_checkvalidindex(L, p);
     for (StkId q = L->top; q > p; q--)
-        setobjs2s(L, q, q - 1);
+        setobj2s(L, q, q - 1);
-    setobjs2s(L, p, L->top);
+    setobj2s(L, p, L->top);
     return;
 }
 
@@ -614,7 +614,7 @@ void lua_pushlstring(lua_State* L, const char* s, size_t len)
 {
     luaC_checkGC(L);
     luaC_threadbarrier(L);
-    setsvalue2s(L, L->top, luaS_newlstr(L, s, len));
+    setsvalue(L, L->top, luaS_newlstr(L, s, len));
     api_incr_top(L);
     return;
 }
@@ -1269,7 +1269,7 @@ void lua_concat(lua_State* L, int n)
     else if (n == 0)
     { // push empty string
         luaC_threadbarrier(L);
-        setsvalue2s(L, L->top, luaS_newlstr(L, "", 0));
+        setsvalue(L, L->top, luaS_newlstr(L, "", 0));
         api_incr_top(L);
     }
     // else n == 1; nothing to do

VM/src/laux.cpp

@@ -400,7 +400,7 @@ char* luaL_extendbuffer(luaL_Buffer* B, size_t additionalsize, int boxloc)
         lua_insert(L, boxloc);
     }
 
-    setsvalue2s(L, L->top + boxloc, newStorage);
+    setsvalue(L, L->top + boxloc, newStorage);
     B->p = newStorage->data + (B->p - base);
     B->end = newStorage->data + nextsize;
     B->storage = newStorage;
@@ -451,11 +451,11 @@ void luaL_pushresult(luaL_Buffer* B)
         // if we finished just at the end of the string buffer, we can convert it to a mutable stirng without a copy
         if (B->p == B->end)
         {
-            setsvalue2s(L, L->top - 1, luaS_buffinish(L, storage));
+            setsvalue(L, L->top - 1, luaS_buffinish(L, storage));
         }
         else
         {
-            setsvalue2s(L, L->top - 1, luaS_newlstr(L, storage->data, B->p - storage->data));
+            setsvalue(L, L->top - 1, luaS_newlstr(L, storage->data, B->p - storage->data));
         }
     }
     else

VM/src/lbuiltins.cpp

@@ -789,7 +789,7 @@ static int luauF_type(lua_State* L, StkId res, TValue* arg0, int nresults, StkId
         int tt = ttype(arg0);
         TString* ttname = L->global->ttname[tt];
 
-        setsvalue2s(L, res, ttname);
+        setsvalue(L, res, ttname);
         return 1;
     }
 
@@ -861,7 +861,7 @@ static int luauF_char(lua_State* L, StkId res, TValue* arg0, int nresults, StkId
 
         buffer[nparams] = 0;
 
-        setsvalue2s(L, res, luaS_newlstr(L, buffer, nparams));
+        setsvalue(L, res, luaS_newlstr(L, buffer, nparams));
         return 1;
     }
 
@@ -887,7 +887,7 @@ static int luauF_typeof(lua_State* L, StkId res, TValue* arg0, int nresults, Stk
     {
         const TString* ttname = luaT_objtypenamestr(L, arg0);
 
-        setsvalue2s(L, res, ttname);
+        setsvalue(L, res, ttname);
         return 1;
     }
 
@@ -904,7 +904,7 @@ static int luauF_sub(lua_State* L, StkId res, TValue* arg0, int nresults, StkId
 
         if (i >= 1 && j >= i && unsigned(j - 1) < unsigned(ts->len))
         {
-            setsvalue2s(L, res, luaS_newlstr(L, getstr(ts) + (i - 1), j - i + 1));
+            setsvalue(L, res, luaS_newlstr(L, getstr(ts) + (i - 1), j - i + 1));
             return 1;
         }
     }
@@ -993,12 +993,13 @@ static int luauF_rawset(lua_State* L, StkId res, TValue* arg0, int nresults, Stk
         else if (ttisvector(key) && luai_vecisnan(vvalue(key)))
             return -1;
 
-        if (hvalue(arg0)->readonly)
+        Table* t = hvalue(arg0);
+        if (t->readonly)
             return -1;
 
         setobj2s(L, res, arg0);
-        setobj2t(L, luaH_set(L, hvalue(arg0), args), args + 1);
+        setobj2t(L, luaH_set(L, t, args), args + 1);
-        luaC_barriert(L, hvalue(arg0), args + 1);
+        luaC_barriert(L, t, args + 1);
         return 1;
     }
 
@@ -1009,12 +1010,13 @@ static int luauF_tinsert(lua_State* L, StkId res, TValue* arg0, int nresults, St
 {
     if (nparams == 2 && nresults <= 0 && ttistable(arg0))
     {
-        if (hvalue(arg0)->readonly)
+        Table* t = hvalue(arg0);
+        if (t->readonly)
             return -1;
 
-        int pos = luaH_getn(hvalue(arg0)) + 1;
+        int pos = luaH_getn(t) + 1;
-        setobj2t(L, luaH_setnum(L, hvalue(arg0), pos), args);
+        setobj2t(L, luaH_setnum(L, t, pos), args);
-        luaC_barriert(L, hvalue(arg0), args);
+        luaC_barriert(L, t, args);
         return 0;
     }
 
@@ -1193,6 +1195,60 @@ static int luauF_extractk(lua_State* L, StkId res, TValue* arg0, int nresults, S
     return -1;
 }
 
+static int luauF_getmetatable(lua_State* L, StkId res, TValue* arg0, int nresults, StkId args, int nparams)
+{
+    if (nparams >= 1 && nresults <= 1)
+    {
+        Table* mt = NULL;
+        if (ttistable(arg0))
+            mt = hvalue(arg0)->metatable;
+        else if (ttisuserdata(arg0))
+            mt = uvalue(arg0)->metatable;
+        else
+            mt = L->global->mt[ttype(arg0)];
+
+        const TValue* mtv = mt ? luaH_getstr(mt, L->global->tmname[TM_METATABLE]) : luaO_nilobject;
+        if (!ttisnil(mtv))
+        {
+            setobj2s(L, res, mtv);
+            return 1;
+        }
+
+        if (mt)
+        {
+            sethvalue(L, res, mt);
+            return 1;
+        }
+        else
+        {
+            setnilvalue(res);
+            return 1;
+        }
+    }
+
+    return -1;
+}
+
+static int luauF_setmetatable(lua_State* L, StkId res, TValue* arg0, int nresults, StkId args, int nparams)
+{
+    // note: setmetatable(_, nil) is rare so we use fallback for it to optimize the fast path
+    if (nparams >= 2 && nresults <= 1 && ttistable(arg0) && ttistable(args))
+    {
+        Table* t = hvalue(arg0);
+        if (t->readonly || t->metatable != NULL)
+            return -1; // note: overwriting non-null metatable is very rare but it requires __metatable check
+
+        Table* mt = hvalue(args);
+        t->metatable = mt;
+        luaC_objbarrier(L, t, mt);
+
+        sethvalue(L, res, t);
+        return 1;
+    }
+
+    return -1;
+}
+
 luau_FastFunction luauF_table[256] = {
     NULL,
     luauF_assert,
@@ -1268,4 +1324,7 @@ luau_FastFunction luauF_table[256] = {
     luauF_rawlen,
 
     luauF_extractk,
+
+    luauF_getmetatable,
+    luauF_setmetatable,
 };

VM/src/ldebug.cpp

@@ -83,7 +83,7 @@ const char* lua_setlocal(lua_State* L, int level, int n)
     Proto* fp = getluaproto(ci);
     const LocVar* var = fp ? luaF_getlocal(fp, n, currentpc(L, ci)) : NULL;
     if (var)
-        setobjs2s(L, ci->base + var->reg, L->top - 1);
+        setobj2s(L, ci->base + var->reg, L->top - 1);
     L->top--; // pop value
     const char* name = var ? getstr(var->varname) : NULL;
     return name;

VM/src/ldo.cpp

@@ -263,18 +263,18 @@ static void seterrorobj(lua_State* L, int errcode, StkId oldtop)
     {
     case LUA_ERRMEM:
     {
-        setsvalue2s(L, oldtop, luaS_newliteral(L, LUA_MEMERRMSG)); // can not fail because string is pinned in luaopen
+        setsvalue(L, oldtop, luaS_newliteral(L, LUA_MEMERRMSG)); // can not fail because string is pinned in luaopen
         break;
     }
     case LUA_ERRERR:
     {
-        setsvalue2s(L, oldtop, luaS_newliteral(L, LUA_ERRERRMSG)); // can not fail because string is pinned in luaopen
+        setsvalue(L, oldtop, luaS_newliteral(L, LUA_ERRERRMSG)); // can not fail because string is pinned in luaopen
         break;
     }
     case LUA_ERRSYNTAX:
     case LUA_ERRRUN:
     {
-        setobjs2s(L, oldtop, L->top - 1); // error message on current top
+        setobj2s(L, oldtop, L->top - 1); // error message on current top
         break;
     }
     }
@@ -419,7 +419,7 @@ static void resume_handle(lua_State* L, void* ud)
 static int resume_error(lua_State* L, const char* msg)
 {
     L->top = L->ci->base;
-    setsvalue2s(L, L->top, luaS_new(L, msg));
+    setsvalue(L, L->top, luaS_new(L, msg));
     incr_top(L);
     return LUA_ERRRUN;
 }
@@ -525,8 +525,8 @@ static void callerrfunc(lua_State* L, void* ud)
 {
     StkId errfunc = cast_to(StkId, ud);
 
-    setobjs2s(L, L->top, L->top - 1);
+    setobj2s(L, L->top, L->top - 1);
-    setobjs2s(L, L->top - 1, errfunc);
+    setobj2s(L, L->top - 1, errfunc);
     incr_top(L);
     luaD_call(L, L->top - 2, 1);
 }

VM/src/lgc.cpp

@@ -118,8 +118,6 @@ LUAU_FASTFLAGVARIABLE(LuauBetterThreadMark, false)
  * slot - upvalues like this are identified since they don't have `markedopen` bit set during thread traversal and closed in `clearupvals`.
  */
 
-LUAU_FASTFLAGVARIABLE(LuauFasterSweep, false)
-
 #define GC_SWEEPPAGESTEPCOST 16
 
 #define GC_INTERRUPT(state) \
@@ -836,28 +834,6 @@ static size_t atomic(lua_State* L)
     return work;
 }
 
-static bool sweepgco(lua_State* L, lua_Page* page, GCObject* gco)
-{
-    LUAU_ASSERT(!FFlag::LuauFasterSweep);
-    global_State* g = L->global;
-
-    int deadmask = otherwhite(g);
-    LUAU_ASSERT(testbit(deadmask, FIXEDBIT)); // make sure we never sweep fixed objects
-
-    int alive = (gco->gch.marked ^ WHITEBITS) & deadmask;
-
-    if (alive)
-    {
-        LUAU_ASSERT(!isdead(g, gco));
-        makewhite(g, gco); // make it white (for next cycle)
-        return false;
-    }
-
-    LUAU_ASSERT(isdead(g, gco));
-    freeobj(L, gco, page);
-    return true;
-}
-
 // a version of generic luaM_visitpage specialized for the main sweep stage
 static int sweepgcopage(lua_State* L, lua_Page* page)
 {
@@ -869,58 +845,36 @@ static int sweepgcopage(lua_State* L, lua_Page* page)
 
     LUAU_ASSERT(busyBlocks > 0);
 
-    if (FFlag::LuauFasterSweep)
+    global_State* g = L->global;
+
+    int deadmask = otherwhite(g);
+    LUAU_ASSERT(testbit(deadmask, FIXEDBIT)); // make sure we never sweep fixed objects
+
+    int newwhite = luaC_white(g);
+
+    for (char* pos = start; pos != end; pos += blockSize)
     {
-        global_State* g = L->global;
+        GCObject* gco = (GCObject*)pos;
 
-        int deadmask = otherwhite(g);
+        // skip memory blocks that are already freed
-        LUAU_ASSERT(testbit(deadmask, FIXEDBIT)); // make sure we never sweep fixed objects
+        if (gco->gch.tt == LUA_TNIL)
+            continue;
 
-        int newwhite = luaC_white(g);
+        // is the object alive?
-
+        if ((gco->gch.marked ^ WHITEBITS) & deadmask)
-        for (char* pos = start; pos != end; pos += blockSize)
         {
-            GCObject* gco = (GCObject*)pos;
+            LUAU_ASSERT(!isdead(g, gco));
-
+            // make it white (for next cycle)
-            // skip memory blocks that are already freed
+            gco->gch.marked = cast_byte((gco->gch.marked & maskmarks) | newwhite);
-            if (gco->gch.tt == LUA_TNIL)
-                continue;
-
-            // is the object alive?
-            if ((gco->gch.marked ^ WHITEBITS) & deadmask)
-            {
-                LUAU_ASSERT(!isdead(g, gco));
-                // make it white (for next cycle)
-                gco->gch.marked = cast_byte((gco->gch.marked & maskmarks) | newwhite);
-            }
-            else
-            {
-                LUAU_ASSERT(isdead(g, gco));
-                freeobj(L, gco, page);
-
-                // if the last block was removed, page would be removed as well
-                if (--busyBlocks == 0)
-                    return int(pos - start) / blockSize + 1;
-            }
         }
-    }
+        else
-    else
-    {
-        for (char* pos = start; pos != end; pos += blockSize)
         {
-            GCObject* gco = (GCObject*)pos;
+            LUAU_ASSERT(isdead(g, gco));
+            freeobj(L, gco, page);
 
-            // skip memory blocks that are already freed
+            // if the last block was removed, page would be removed as well
-            if (gco->gch.tt == LUA_TNIL)
+            if (--busyBlocks == 0)
-                continue;
+                return int(pos - start) / blockSize + 1;
-
-            // when true is returned it means that the element was deleted
-            if (sweepgco(L, page, gco))
-            {
-                // if the last block was removed, page would be removed as well
-                if (--busyBlocks == 0)
-                    return int(pos - start) / blockSize + 1;
-            }
         }
     }
 
@@ -1009,15 +963,8 @@ static size_t gcstep(lua_State* L, size_t limit)
         if (g->sweepgcopage == NULL)
         {
             // don't forget to visit main thread, it's the only object not allocated in GCO pages
-            if (FFlag::LuauFasterSweep)
+            LUAU_ASSERT(!isdead(g, obj2gco(g->mainthread)));
-            {
+            makewhite(g, obj2gco(g->mainthread)); // make it white (for next cycle)
-                LUAU_ASSERT(!isdead(g, obj2gco(g->mainthread)));
-                makewhite(g, obj2gco(g->mainthread)); // make it white (for next cycle)
-            }
-            else
-            {
-                sweepgco(L, NULL, obj2gco(g->mainthread));
-            }
 
             shrinkbuffers(L);
 

VM/src/lobject.cpp

@@ -102,7 +102,7 @@ const char* luaO_pushvfstring(lua_State* L, const char* fmt, va_list argp)
     char result[LUA_BUFFERSIZE];
     vsnprintf(result, sizeof(result), fmt, argp);
 
-    setsvalue2s(L, L->top, luaS_new(L, result));
+    setsvalue(L, L->top, luaS_new(L, result));
     incr_top(L);
     return svalue(L->top - 1);
 }

VM/src/lobject.h

@@ -200,20 +200,14 @@ typedef struct lua_TValue
 ** different types of sets, according to destination
 */
 
-// from stack to (same) stack
+// to stack
-#define setobjs2s setobj
-// to stack (not from same stack)
 #define setobj2s setobj
-#define setsvalue2s setsvalue
+// from table to same table (no barrier)
-#define sethvalue2s sethvalue
-#define setptvalue2s setptvalue
-// from table to same table
 #define setobjt2t setobj
-// to table
+// to table (needs barrier)
 #define setobj2t setobj
-// to new object
+// to new object (no barrier)
 #define setobj2n setobj
-#define setsvalue2n setsvalue
 
 #define setttype(obj, tt) (ttype(obj) = (tt))
 

VM/src/ltm.cpp

@@ -57,6 +57,7 @@ const char* const luaT_eventname[] = {
     "__le",
     "__concat",
     "__type",
+    "__metatable",
 };
 // clang-format on
 

VM/src/ltm.h

@@ -36,6 +36,7 @@ typedef enum
     TM_LE,
     TM_CONCAT,
     TM_TYPE,
+    TM_METATABLE,
 
     TM_N // number of elements in the enum
 } TMS;

VM/src/lvmexecute.cpp

@@ -985,7 +985,7 @@ reentry:
 
                     int i;
                     for (i = nresults; i != 0 && vali < valend; i--)
-                        setobjs2s(L, res++, vali++);
+                        setobj2s(L, res++, vali++);
                     while (i-- > 0)
                         setnilvalue(res++);
 
@@ -1022,7 +1022,7 @@ reentry:
                 // note: in MULTRET context nresults starts as -1 so i != 0 condition never activates intentionally
                 int i;
                 for (i = nresults; i != 0 && vali < valend; i--)
-                    setobjs2s(L, res++, vali++);
+                    setobj2s(L, res++, vali++);
                 while (i-- > 0)
                     setnilvalue(res++);
 
@@ -1945,7 +1945,7 @@ reentry:
 
                 StkId ra = VM_REG(LUAU_INSN_A(insn));
 
-                setobjs2s(L, ra, base + b);
+                setobj2s(L, ra, base + b);
                 VM_PROTECT(luaC_checkGC(L));
                 VM_NEXT();
             }
@@ -2281,9 +2281,9 @@ reentry:
                 else
                 {
                     // note: it's safe to push arguments past top for complicated reasons (see top of the file)
-                    setobjs2s(L, ra + 3 + 2, ra + 2);
+                    setobj2s(L, ra + 3 + 2, ra + 2);
-                    setobjs2s(L, ra + 3 + 1, ra + 1);
+                    setobj2s(L, ra + 3 + 1, ra + 1);
-                    setobjs2s(L, ra + 3, ra);
+                    setobj2s(L, ra + 3, ra);
 
                     L->top = ra + 3 + 3; // func + 2 args (state and index)
                     LUAU_ASSERT(L->top <= L->stack_last);
@@ -2295,7 +2295,7 @@ reentry:
                     ra = VM_REG(LUAU_INSN_A(insn));
 
                     // copy first variable back into the iteration index
-                    setobjs2s(L, ra + 2, ra + 3);
+                    setobj2s(L, ra + 2, ra + 3);
 
                     // note that we need to increment pc by 1 to exit the loop since we need to skip over aux
                     pc += ttisnil(ra + 3) ? 1 : LUAU_INSN_D(insn);
@@ -2372,7 +2372,7 @@ reentry:
                     StkId ra = VM_REG(LUAU_INSN_A(insn)); // previous call may change the stack
 
                     for (int j = 0; j < n; j++)
-                        setobjs2s(L, ra + j, base - n + j);
+                        setobj2s(L, ra + j, base - n + j);
 
                     L->top = ra + n;
                     VM_NEXT();
@@ -2382,7 +2382,7 @@ reentry:
                     StkId ra = VM_REG(LUAU_INSN_A(insn));
 
                     for (int j = 0; j < b && j < n; j++)
-                        setobjs2s(L, ra + j, base - n + j);
+                        setobj2s(L, ra + j, base - n + j);
                     for (int j = n; j < b; j++)
                         setnilvalue(ra + j);
                     VM_NEXT();
@@ -2461,7 +2461,7 @@ reentry:
 
                 for (int i = 0; i < numparams; ++i)
                 {
-                    setobjs2s(L, base + i, fixed + i);
+                    setobj2s(L, base + i, fixed + i);
                     setnilvalue(fixed + i);
                 }
 
@@ -2878,7 +2878,7 @@ int luau_precall(lua_State* L, StkId func, int nresults)
 
         int i;
         for (i = nresults; i != 0 && vali < valend; i--)
-            setobjs2s(L, res++, vali++);
+            setobj2s(L, res++, vali++);
         while (i-- > 0)
             setnilvalue(res++);
 
@@ -2906,7 +2906,7 @@ void luau_poscall(lua_State* L, StkId first)
 
     int i;
     for (i = ci->nresults; i != 0 && vali < valend; i--)
-        setobjs2s(L, res++, vali++);
+        setobj2s(L, res++, vali++);
     while (i-- > 0)
         setnilvalue(res++);
 

VM/src/lvmload.cpp

@@ -240,7 +240,7 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
             case LBC_CONSTANT_STRING:
             {
                 TString* v = readString(strings, data, size, offset);
-                setsvalue2n(L, &p->k[j], v);
+                setsvalue(L, &p->k[j], v);
                 break;
             }
 

VM/src/lvmutils.cpp

@@ -38,7 +38,7 @@ int luaV_tostring(lua_State* L, StkId obj)
         double n = nvalue(obj);
         char* e = luai_num2str(s, n);
         LUAU_ASSERT(e < s + sizeof(s));
-        setsvalue2s(L, obj, luaS_newlstr(L, s, e - s));
+        setsvalue(L, obj, luaS_newlstr(L, s, e - s));
         return 1;
     }
 }
@@ -70,7 +70,7 @@ static StkId callTMres(lua_State* L, StkId res, const TValue* f, const TValue* p
     luaD_call(L, L->top - 3, 1);
     res = restorestack(L, result);
     L->top--;
-    setobjs2s(L, res, L->top);
+    setobj2s(L, res, L->top);
     return res;
 }
 
@@ -350,11 +350,11 @@ void luaV_concat(lua_State* L, int total, int last)
 
             if (tl < LUA_BUFFERSIZE)
             {
-                setsvalue2s(L, top - n, luaS_newlstr(L, buffer, tl));
+                setsvalue(L, top - n, luaS_newlstr(L, buffer, tl));
             }
             else
             {
-                setsvalue2s(L, top - n, luaS_buffinish(L, ts));
+                setsvalue(L, top - n, luaS_buffinish(L, ts));
             }
         }
         total -= n - 1; // got `n' strings to create 1 new
@@ -582,7 +582,7 @@ LUAU_NOINLINE void luaV_tryfuncTM(lua_State* L, StkId func)
     if (!ttisfunction(tm))
         luaG_typeerror(L, func, "call");
     for (StkId p = L->top; p > func; p--) // open space for metamethod
-        setobjs2s(L, p, p - 1);
+        setobj2s(L, p, p - 1);
     L->top++;              // stack space pre-allocated by the caller
     setobj2s(L, func, tm); // tag method is the new function to be called
 }

fuzz/linter.cpp

@@ -21,7 +21,7 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* Data, size_t Size)
     static Luau::NullModuleResolver moduleResolver;
     static Luau::InternalErrorReporter iceHandler;
     static Luau::TypeChecker sharedEnv(&moduleResolver, &iceHandler);
-    static int once = (Luau::registerBuiltinTypes(sharedEnv), 1);
+    static int once = (Luau::registerBuiltinGlobals(sharedEnv), 1);
     (void)once;
     static int once2 = (Luau::freeze(sharedEnv.globalTypes), 1);
     (void)once2;

fuzz/proto.cpp

@@ -96,7 +96,7 @@ int registerTypes(Luau::TypeChecker& env)
     using namespace Luau;
     using std::nullopt;
 
-    Luau::registerBuiltinTypes(env);
+    Luau::registerBuiltinGlobals(env);
 
     TypeArena& arena = env.globalTypes;
 

fuzz/typeck.cpp

@@ -26,7 +26,7 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* Data, size_t Size)
     static Luau::NullModuleResolver moduleResolver;
     static Luau::InternalErrorReporter iceHandler;
     static Luau::TypeChecker sharedEnv(&moduleResolver, &iceHandler);
-    static int once = (Luau::registerBuiltinTypes(sharedEnv), 1);
+    static int once = (Luau::registerBuiltinGlobals(sharedEnv), 1);
     (void)once;
     static int once2 = (Luau::freeze(sharedEnv.globalTypes), 1);
     (void)once2;

tests/Compiler.test.cpp

@@ -798,6 +798,8 @@ RETURN R0 1
 
 TEST_CASE("TableSizePredictionSetMetatable")
 {
+    ScopedFastFlag sff("LuauCompileBuiltinMT", true);
+
     CHECK_EQ("\n" + compileFunction0(R"(
 local t = setmetatable({}, nil)
 t.field1 = 1
@@ -805,14 +807,15 @@ t.field2 = 2
 return t
 )"),
         R"(
-GETIMPORT R0 1
 NEWTABLE R1 2 0
-LOADNIL R2
+FASTCALL2K 61 R1 K0 L0
+LOADK R2 K0
+GETIMPORT R0 2
 CALL R0 2 1
-LOADN R1 1
+L0: LOADN R1 1
-SETTABLEKS R1 R0 K2
-LOADN R1 2
 SETTABLEKS R1 R0 K3
+LOADN R1 2
+SETTABLEKS R1 R0 K4
 RETURN R0 1
 )");
 }

tests/Conformance.test.cpp

@@ -499,7 +499,7 @@ TEST_CASE("Types")
         Luau::SingletonTypes singletonTypes;
         Luau::TypeChecker env(&moduleResolver, Luau::NotNull{&singletonTypes}, &iceHandler);
 
-        Luau::registerBuiltinTypes(env);
+        Luau::registerBuiltinGlobals(env);
         Luau::freeze(env.globalTypes);
 
         lua_newtable(L);

tests/Fixture.cpp

@@ -8,7 +8,6 @@
 #include "Luau/TypeVar.h"
 #include "Luau/TypeAttach.h"
 #include "Luau/Transpiler.h"
-
 #include "Luau/BuiltinDefinitions.h"
 
 #include "doctest.h"
@@ -20,6 +19,8 @@
 static const char* mainModuleName = "MainModule";
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
+LUAU_FASTFLAG(LuauUnknownAndNeverType)
+LUAU_FASTFLAG(LuauReportShadowedTypeAlias)
 
 namespace Luau
 {
@@ -97,6 +98,8 @@ Fixture::Fixture(bool freeze, bool prepareAutocomplete)
     configResolver.defaultConfig.enabledLint.warningMask = ~0ull;
     configResolver.defaultConfig.parseOptions.captureComments = true;
 
+    registerBuiltinTypes(frontend);
+
     Luau::freeze(frontend.typeChecker.globalTypes);
     Luau::freeze(frontend.typeCheckerForAutocomplete.globalTypes);
 
@@ -435,9 +438,9 @@ BuiltinsFixture::BuiltinsFixture(bool freeze, bool prepareAutocomplete)
     Luau::unfreeze(frontend.typeChecker.globalTypes);
     Luau::unfreeze(frontend.typeCheckerForAutocomplete.globalTypes);
 
-    registerBuiltinTypes(frontend);
+    registerBuiltinGlobals(frontend);
     if (prepareAutocomplete)
-        registerBuiltinTypes(frontend.typeCheckerForAutocomplete);
+        registerBuiltinGlobals(frontend.typeCheckerForAutocomplete);
     registerTestTypes();
 
     Luau::freeze(frontend.typeChecker.globalTypes);

tests/Frontend.test.cpp

@@ -1070,12 +1070,12 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "reexport_type_alias")
 
     fileResolver.source["Module/A"] = R"(
         type KeyOfTestEvents = "test-file-start" | "test-file-success" | "test-file-failure" | "test-case-result"
-        type unknown = any
+        type MyAny = any
 
         export type TestFileEvent<T = KeyOfTestEvents> = (
             eventName: T,
             args: any --[[ ROBLOX TODO: Unhandled node for type: TSIndexedAccessType ]] --[[ TestEvents[T] ]]
-        ) -> unknown
+        ) -> MyAny
 
         return {}
     )";

tests/ToString.test.cpp

@@ -790,4 +790,20 @@ TEST_CASE_FIXTURE(Fixture, "toStringNamedFunction_hide_self_param")
     CHECK_EQ("foo:method<a>(arg: string): ()", toStringNamedFunction("foo:method", *ftv, opts));
 }
 
+TEST_CASE_FIXTURE(Fixture, "tostring_unsee_ttv_if_array")
+{
+    ScopedFastFlag sff("LuauUnseeArrayTtv", true);
+
+    CheckResult result = check(R"(
+        local x: {string}
+        -- This code is constructed very specifically to use the same (by pointer
+        -- identity) type in the function twice.
+        local y: (typeof(x), typeof(x)) -> ()
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK(toString(requireType("y")) == "({string}, {string}) -> ()");
+}
+
 TEST_SUITE_END();

tests/TypeInfer.aliases.test.cpp

@@ -443,7 +443,8 @@ TEST_CASE_FIXTURE(Fixture, "reported_location_is_correct_when_type_alias_are_dup
     auto dtd = get<DuplicateTypeDefinition>(result.errors[0]);
     REQUIRE(dtd);
     CHECK_EQ(dtd->name, "B");
-    CHECK_EQ(dtd->previousLocation.begin.line + 1, 3);
+    REQUIRE(dtd->previousLocation);
+    CHECK_EQ(dtd->previousLocation->begin.line + 1, 3);
 }
 
 TEST_CASE_FIXTURE(Fixture, "stringify_optional_parameterized_alias")
@@ -868,4 +869,40 @@ TEST_CASE_FIXTURE(Fixture, "recursive_types_restriction_not_ok")
     LUAU_REQUIRE_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "report_shadowed_aliases")
+{
+    ScopedFastFlag sff{"LuauReportShadowedTypeAlias", true};
+
+    // We allow a previous type alias to depend on a future type alias. That exact feature enables a confusing example, like the following snippet,
+    // which has the type alias FakeString point to the type alias `string` that which points to `number`.
+    CheckResult result = check(R"(
+        type MyString = string
+        type string = number
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK(toString(result.errors[0]) == "Redefinition of type 'string'");
+
+    std::optional<TypeId> t1 = lookupType("MyString");
+    REQUIRE(t1);
+    CHECK(isPrim(*t1, PrimitiveTypeVar::String));
+
+    std::optional<TypeId> t2 = lookupType("string");
+    REQUIRE(t2);
+    CHECK(isPrim(*t2, PrimitiveTypeVar::String));
+}
+
+TEST_CASE_FIXTURE(Fixture, "it_is_ok_to_shadow_user_defined_alias")
+{
+    CheckResult result = check(R"(
+        type T = number
+
+        do
+            type T = string
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.annotations.test.cpp

@@ -745,7 +745,12 @@ TEST_CASE_FIXTURE(Fixture, "luau_ice_is_not_special_without_the_flag")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "luau_print_is_magic_if_the_flag_is_set")
 {
-    // Luau::resetPrintLine();
+    static std::vector<std::string> output;
+    output.clear();
+    Luau::setPrintLine([](const std::string& s) {
+        output.push_back(s);
+    });
+
     ScopedFastFlag sffs{"DebugLuauMagicTypes", true};
 
     CheckResult result = check(R"(
@@ -753,6 +758,8 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "luau_print_is_magic_if_the_flag_is_set")
     )");
 
     LUAU_REQUIRE_NO_ERRORS(result);
+
+    REQUIRE(1 == output.size());
 }
 
 TEST_CASE_FIXTURE(Fixture, "luau_print_is_not_special_without_the_flag")

tests/TypeInfer.builtins.test.cpp

@@ -11,6 +11,7 @@ using namespace Luau;
 LUAU_FASTFLAG(LuauLowerBoundsCalculation);
 LUAU_FASTFLAG(LuauSpecialTypesAsterisked);
 LUAU_FASTFLAG(LuauStringFormatArgumentErrorFix)
+LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
 
 TEST_SUITE_BEGIN("BuiltinTests");
 
@@ -596,6 +597,15 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "xpcall")
     CHECK_EQ("boolean", toString(requireType("c")));
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "trivial_select")
+{
+    CheckResult result = check(R"(
+        local a:number = select(1, 42)
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_CASE_FIXTURE(BuiltinsFixture, "see_thru_select")
 {
     CheckResult result = check(R"(
@@ -679,10 +689,20 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "select_with_variadic_typepack_tail")
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    CHECK_EQ("any", toString(requireType("foo")));
+    if (FFlag::DebugLuauDeferredConstraintResolution && FFlag::LuauSpecialTypesAsterisked)
-    CHECK_EQ("any", toString(requireType("bar")));
+    {
-    CHECK_EQ("any", toString(requireType("baz")));
+        CHECK_EQ("string", toString(requireType("foo")));
-    CHECK_EQ("any", toString(requireType("quux")));
+        CHECK_EQ("*error-type*", toString(requireType("bar")));
+        CHECK_EQ("*error-type*", toString(requireType("baz")));
+        CHECK_EQ("*error-type*", toString(requireType("quux")));
+    }
+    else
+    {
+        CHECK_EQ("any", toString(requireType("foo")));
+        CHECK_EQ("any", toString(requireType("bar")));
+        CHECK_EQ("any", toString(requireType("baz")));
+        CHECK_EQ("any", toString(requireType("quux")));
+    }
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "select_with_variadic_typepack_tail_and_string_head")
@@ -698,10 +718,20 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "select_with_variadic_typepack_tail_and_strin
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    CHECK_EQ("any", toString(requireType("foo")));
+    if (FFlag::DebugLuauDeferredConstraintResolution && FFlag::LuauSpecialTypesAsterisked)
-    CHECK_EQ("any", toString(requireType("bar")));
+    {
-    CHECK_EQ("any", toString(requireType("baz")));
+        CHECK_EQ("string", toString(requireType("foo")));
-    CHECK_EQ("any", toString(requireType("quux")));
+        CHECK_EQ("string", toString(requireType("bar")));
+        CHECK_EQ("*error-type*", toString(requireType("baz")));
+        CHECK_EQ("*error-type*", toString(requireType("quux")));
+    }
+    else
+    {
+        CHECK_EQ("any", toString(requireType("foo")));
+        CHECK_EQ("any", toString(requireType("bar")));
+        CHECK_EQ("any", toString(requireType("baz")));
+        CHECK_EQ("any", toString(requireType("quux")));
+    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "string_format_as_method")
@@ -1099,7 +1129,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "gmatch_capture_types_default_capture")
 
     CountMismatch* acm = get<CountMismatch>(result.errors[0]);
     REQUIRE(acm);
-    CHECK_EQ(acm->context, CountMismatch::Result);
+    CHECK_EQ(acm->context, CountMismatch::FunctionResult);
     CHECK_EQ(acm->expected, 1);
     CHECK_EQ(acm->actual, 4);
 
@@ -1116,7 +1146,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "gmatch_capture_types_balanced_escaped_parens
 
     CountMismatch* acm = get<CountMismatch>(result.errors[0]);
     REQUIRE(acm);
-    CHECK_EQ(acm->context, CountMismatch::Result);
+    CHECK_EQ(acm->context, CountMismatch::FunctionResult);
     CHECK_EQ(acm->expected, 3);
     CHECK_EQ(acm->actual, 4);
 
@@ -1135,7 +1165,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "gmatch_capture_types_parens_in_sets_are_igno
 
     CountMismatch* acm = get<CountMismatch>(result.errors[0]);
     REQUIRE(acm);
-    CHECK_EQ(acm->context, CountMismatch::Result);
+    CHECK_EQ(acm->context, CountMismatch::FunctionResult);
     CHECK_EQ(acm->expected, 2);
     CHECK_EQ(acm->actual, 3);
 
@@ -1288,7 +1318,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "find_capture_types3")
 
     CountMismatch* acm = get<CountMismatch>(result.errors[0]);
     REQUIRE(acm);
-    CHECK_EQ(acm->context, CountMismatch::Result);
+    CHECK_EQ(acm->context, CountMismatch::FunctionResult);
     CHECK_EQ(acm->expected, 2);
     CHECK_EQ(acm->actual, 4);
 

tests/TypeInfer.functions.test.cpp

@@ -837,6 +837,8 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "calling_function_with_anytypepack_doesnt_lea
 
 TEST_CASE_FIXTURE(Fixture, "too_many_return_values")
 {
+    ScopedFastFlag sff{"LuauBetterMessagingOnCountMismatch", true};
+
     CheckResult result = check(R"(
         --!strict
 
@@ -851,7 +853,49 @@ TEST_CASE_FIXTURE(Fixture, "too_many_return_values")
 
     CountMismatch* acm = get<CountMismatch>(result.errors[0]);
     REQUIRE(acm);
-    CHECK_EQ(acm->context, CountMismatch::Result);
+    CHECK_EQ(acm->context, CountMismatch::FunctionResult);
+    CHECK_EQ(acm->expected, 1);
+    CHECK_EQ(acm->actual, 2);
+}
+
+TEST_CASE_FIXTURE(Fixture, "too_many_return_values_in_parentheses")
+{
+    ScopedFastFlag sff{"LuauBetterMessagingOnCountMismatch", true};
+
+    CheckResult result = check(R"(
+        --!strict
+
+        function f()
+            return 55
+        end
+
+        local a, b = (f())
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    CountMismatch* acm = get<CountMismatch>(result.errors[0]);
+    REQUIRE(acm);
+    CHECK_EQ(acm->context, CountMismatch::FunctionResult);
+    CHECK_EQ(acm->expected, 1);
+    CHECK_EQ(acm->actual, 2);
+}
+
+TEST_CASE_FIXTURE(Fixture, "too_many_return_values_no_function")
+{
+    ScopedFastFlag sff{"LuauBetterMessagingOnCountMismatch", true};
+
+    CheckResult result = check(R"(
+        --!strict
+
+        local a, b = 55
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    CountMismatch* acm = get<CountMismatch>(result.errors[0]);
+    REQUIRE(acm);
+    CHECK_EQ(acm->context, CountMismatch::ExprListResult);
     CHECK_EQ(acm->expected, 1);
     CHECK_EQ(acm->actual, 2);
 }
@@ -1271,7 +1315,7 @@ local b: B = a
     LUAU_REQUIRE_ERROR_COUNT(1, result);
     CHECK_EQ(toString(result.errors[0]), R"(Type '(number, number) -> number' could not be converted into '(number, number) -> (number, boolean)'
 caused by:
-  Function only returns 1 value. 2 are required here)");
+  Function only returns 1 value, but 2 are required here)");
 }
 
 TEST_CASE_FIXTURE(Fixture, "error_detailed_function_mismatch_ret")

tests/TypeInfer.loops.test.cpp

@@ -526,6 +526,16 @@ TEST_CASE_FIXTURE(Fixture, "fuzz_fail_missing_instantitation_follow")
     )");
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "for_in_with_generic_next")
+{
+    CheckResult result = check(R"(
+        for k: number, v: number in next, {1, 2, 3} do
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_CASE_FIXTURE(Fixture, "loop_iter_basic")
 {
     CheckResult result = check(R"(
@@ -584,11 +594,48 @@ TEST_CASE_FIXTURE(Fixture, "loop_iter_no_indexer_nonstrict")
     LUAU_REQUIRE_ERROR_COUNT(0, result);
 }
 
-TEST_CASE_FIXTURE(BuiltinsFixture, "loop_iter_iter_metamethod")
+TEST_CASE_FIXTURE(BuiltinsFixture, "loop_iter_metamethod_nil")
 {
+    if (!FFlag::DebugLuauDeferredConstraintResolution)
+        return;
+
     CheckResult result = check(R"(
-        local t = {}
+        local t = setmetatable({}, { __iter = function(o) return next, nil end, })
-        setmetatable(t, { __iter = function(o) return next, o.children end })
+        for k: number, v: string in t do
+        end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK(toString(result.errors[0]) == "Type 'nil' could not be converted into '{- [a]: b -}'");
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "loop_iter_metamethod_not_enough_returns")
+{
+    if (!FFlag::DebugLuauDeferredConstraintResolution)
+        return;
+
+    CheckResult result = check(R"(
+        local t = setmetatable({}, { __iter = function(o) end })
+        for k: number, v: string in t do
+        end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK(result.errors[0] == TypeError{
+        Location{{2, 36}, {2, 37}},
+        GenericError{"__iter must return at least one value"},
+    });
+}
+
+TEST_CASE_FIXTURE(BuiltinsFixture, "loop_iter_metamethod_ok")
+{
+    if (!FFlag::DebugLuauDeferredConstraintResolution)
+        return;
+
+    CheckResult result = check(R"(
+        local t = setmetatable({
+            children = {"foo"}
+        }, { __iter = function(o) return next, o.children end })
         for k: number, v: string in t do
         end
     )");
@@ -596,4 +643,26 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "loop_iter_iter_metamethod")
     LUAU_REQUIRE_ERROR_COUNT(0, result);
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "loop_iter_metamethod_ok_with_inference")
+{
+    if (!FFlag::DebugLuauDeferredConstraintResolution)
+        return;
+
+    CheckResult result = check(R"(
+        local t = setmetatable({
+            children = {"foo"}
+        }, { __iter = function(o) return next, o.children end })
+
+        local a, b
+        for k, v in t do
+            a = k
+            b = v
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+    CHECK(toString(requireType("a")) == "number");
+    CHECK(toString(requireType("b")) == "string");
+}
+
 TEST_SUITE_END();

tests/TypeInfer.provisional.test.cpp

@@ -439,13 +439,15 @@ TEST_CASE_FIXTURE(Fixture, "normalization_fails_on_certain_kinds_of_cyclic_table
 // Belongs in TypeInfer.builtins.test.cpp.
 TEST_CASE_FIXTURE(BuiltinsFixture, "pcall_returns_at_least_two_value_but_function_returns_nothing")
 {
+    ScopedFastFlag sff{"LuauBetterMessagingOnCountMismatch", true};
+
     CheckResult result = check(R"(
         local function f(): () end
         local ok, res = pcall(f)
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    CHECK_EQ("Function only returns 1 value. 2 are required here", toString(result.errors[0]));
+    CHECK_EQ("Function only returns 1 value, but 2 are required here", toString(result.errors[0]));
     // LUAU_REQUIRE_NO_ERRORS(result);
     // CHECK_EQ("boolean", toString(requireType("ok")));
     // CHECK_EQ("any", toString(requireType("res")));

tests/TypeInfer.refinements.test.cpp

@@ -256,28 +256,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "typeguard_in_assert_position")
     REQUIRE_EQ("number", toString(requireType("b")));
 }
 
-TEST_CASE_FIXTURE(Fixture, "typeguard_only_look_up_types_from_global_scope")
-{
-    CheckResult result = check(R"(
-        type ActuallyString = string
-
-        do -- Necessary. Otherwise toposort has ActuallyString come after string type alias.
-            type string = number
-            local foo: string = 1
-
-            if type(foo) == "string" then
-                local bar: ActuallyString = foo
-                local baz: boolean = foo
-            end
-        end
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-
-    CHECK_EQ("never", toString(requireTypeAtPosition({8, 44})));
-    CHECK_EQ("never", toString(requireTypeAtPosition({9, 38})));
-}
-
 TEST_CASE_FIXTURE(Fixture, "call_a_more_specific_function_using_typeguard")
 {
     CheckResult result = check(R"(

tests/TypeInfer.test.cpp

@@ -1159,4 +1159,38 @@ TEST_CASE_FIXTURE(Fixture, "dcr_can_partially_dispatch_a_constraint")
     CHECK("<a>(a, number) -> ()" == toString(requireType("prime_iter")));
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "it_is_ok_to_have_inconsistent_number_of_return_values_in_nonstrict")
+{
+    CheckResult result = check(R"(
+        --!nonstrict
+        function validate(stats, hits, misses)
+            local checked = {}
+
+            for _,l in ipairs(hits) do
+                if not (stats[l] and stats[l] > 0) then
+                    return false, string.format("expected line %d to be hit", l)
+                end
+                checked[l] = true
+            end
+
+            for _,l in ipairs(misses) do
+                if not (stats[l] and stats[l] == 0) then
+                    return false, string.format("expected line %d to be missed", l)
+                end
+                checked[l] = true
+            end
+
+            for k,v in pairs(stats) do
+                if type(k) == "number" and not checked[k] then
+                    return false, string.format("expected line %d to be absent", k)
+                end
+            end
+
+            return true
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.tryUnify.test.cpp

@@ -271,4 +271,40 @@ TEST_CASE_FIXTURE(TryUnifyFixture, "txnlog_preserves_pack_owner")
     CHECK_EQ(a->owningArena, &arena);
 }
 
+TEST_CASE_FIXTURE(TryUnifyFixture, "metatables_unify_against_shape_of_free_table")
+{
+    ScopedFastFlag sff("DebugLuauDeferredConstraintResolution", true);
+
+    TableTypeVar::Props freeProps{
+        {"foo", {typeChecker.numberType}},
+    };
+
+    TypeId free = arena.addType(TableTypeVar{freeProps, std::nullopt, TypeLevel{}, TableState::Free});
+
+    TableTypeVar::Props indexProps{
+        {"foo", {typeChecker.stringType}},
+    };
+
+    TypeId index = arena.addType(TableTypeVar{indexProps, std::nullopt, TypeLevel{}, TableState::Sealed});
+
+    TableTypeVar::Props mtProps{
+        {"__index", {index}},
+    };
+
+    TypeId mt = arena.addType(TableTypeVar{mtProps, std::nullopt, TypeLevel{}, TableState::Sealed});
+
+    TypeId target = arena.addType(TableTypeVar{TableState::Unsealed, TypeLevel{}});
+    TypeId metatable = arena.addType(MetatableTypeVar{target, mt});
+
+    state.tryUnify(metatable, free);
+    state.log.commit();
+
+    REQUIRE_EQ(state.errors.size(), 1);
+
+    std::string expected = "Type '{ @metatable {| __index: {| foo: string |} |}, {  } }' could not be converted into '{- foo: number -}'\n"
+        "caused by:\n"
+        "  Type 'number' could not be converted into 'string'";
+    CHECK_EQ(toString(state.errors[0]), expected);
+}
+
 TEST_SUITE_END();

tests/conformance/events.lua

@@ -24,6 +24,9 @@ assert(getmetatable(nil) == nil)
 a={}; setmetatable(a, {__metatable = "xuxu",
                     __tostring=function(x) return x.name end})
 assert(getmetatable(a) == "xuxu")
+ud=newproxy(true); getmetatable(ud).__metatable = "xuxu"
+assert(getmetatable(ud) == "xuxu")
+
 local res,err = pcall(tostring, a)
 assert(not res and err == "'__tostring' must return a string")
 -- cannot change a protected metatable

tools/faillist.txt

@@ -1,101 +1,47 @@
 AnnotationTests.builtin_types_are_not_exported
+AnnotationTests.corecursive_types_error_on_tight_loop
 AnnotationTests.duplicate_type_param_name
 AnnotationTests.for_loop_counter_annotation_is_checked
 AnnotationTests.generic_aliases_are_cloned_properly
 AnnotationTests.instantiation_clone_has_to_follow
-AnnotationTests.luau_ice_triggers_an_ice
-AnnotationTests.luau_ice_triggers_an_ice_exception_with_flag
-AnnotationTests.luau_ice_triggers_an_ice_exception_with_flag_handler
-AnnotationTests.luau_ice_triggers_an_ice_handler
-AnnotationTests.luau_print_is_magic_if_the_flag_is_set
 AnnotationTests.occurs_check_on_cyclic_intersection_typevar
 AnnotationTests.occurs_check_on_cyclic_union_typevar
+AnnotationTests.too_many_type_params
 AnnotationTests.two_type_params
 AnnotationTests.use_type_required_from_another_file
 AstQuery.last_argument_function_call_type
 AstQuery::getDocumentationSymbolAtPosition.overloaded_fn
-AutocompleteTest.argument_types
-AutocompleteTest.arguments_to_global_lambda
-AutocompleteTest.autocomplete_boolean_singleton
-AutocompleteTest.autocomplete_end_with_fn_exprs
-AutocompleteTest.autocomplete_end_with_lambda
 AutocompleteTest.autocomplete_first_function_arg_expected_type
-AutocompleteTest.autocomplete_for_in_middle_keywords
-AutocompleteTest.autocomplete_for_middle_keywords
-AutocompleteTest.autocomplete_if_middle_keywords
 AutocompleteTest.autocomplete_interpolated_string
-AutocompleteTest.autocomplete_on_string_singletons
 AutocompleteTest.autocomplete_oop_implicit_self
-AutocompleteTest.autocomplete_repeat_middle_keyword
+AutocompleteTest.autocomplete_string_singleton_equality
 AutocompleteTest.autocomplete_string_singleton_escape
 AutocompleteTest.autocomplete_string_singletons
-AutocompleteTest.autocomplete_while_middle_keywords
 AutocompleteTest.autocompleteProp_index_function_metamethod_is_variadic
-AutocompleteTest.bias_toward_inner_scope
 AutocompleteTest.cyclic_table
 AutocompleteTest.do_compatible_self_calls
-AutocompleteTest.do_not_overwrite_context_sensitive_kws
-AutocompleteTest.do_not_suggest_internal_module_type
 AutocompleteTest.do_wrong_compatible_self_calls
-AutocompleteTest.dont_offer_any_suggestions_from_within_a_broken_comment
-AutocompleteTest.dont_offer_any_suggestions_from_within_a_broken_comment_at_the_very_end_of_the_file
-AutocompleteTest.dont_offer_any_suggestions_from_within_a_comment
-AutocompleteTest.dont_suggest_local_before_its_definition
-AutocompleteTest.function_expr_params
-AutocompleteTest.function_in_assignment_has_parentheses
-AutocompleteTest.function_in_assignment_has_parentheses_2
-AutocompleteTest.function_parameters
-AutocompleteTest.function_result_passed_to_function_has_parentheses
-AutocompleteTest.generic_types
-AutocompleteTest.get_suggestions_for_the_very_start_of_the_script
-AutocompleteTest.global_function_params
-AutocompleteTest.global_functions_are_not_scoped_lexically
-AutocompleteTest.globals_are_order_independent
-AutocompleteTest.if_then_else_elseif_completions
 AutocompleteTest.keyword_methods
-AutocompleteTest.library_non_self_calls_are_fine
-AutocompleteTest.library_self_calls_are_invalid
-AutocompleteTest.local_function
-AutocompleteTest.local_function_params
-AutocompleteTest.local_functions_fall_out_of_scope
-AutocompleteTest.method_call_inside_function_body
-AutocompleteTest.nested_member_completions
-AutocompleteTest.nested_recursive_function
-AutocompleteTest.no_function_name_suggestions
 AutocompleteTest.no_incompatible_self_calls
 AutocompleteTest.no_incompatible_self_calls_2
-AutocompleteTest.no_incompatible_self_calls_on_class
 AutocompleteTest.no_wrong_compatible_self_calls_with_generics
-AutocompleteTest.recursive_function
+AutocompleteTest.suggest_table_keys
-AutocompleteTest.recursive_function_global
-AutocompleteTest.recursive_function_local
-AutocompleteTest.return_types
-AutocompleteTest.sometimes_the_metatable_is_an_error
-AutocompleteTest.source_module_preservation_and_invalidation
-AutocompleteTest.statement_between_two_statements
-AutocompleteTest.string_prim_non_self_calls_are_avoided
-AutocompleteTest.string_prim_self_calls_are_fine
-AutocompleteTest.suggest_external_module_type
-AutocompleteTest.table_intersection
-AutocompleteTest.table_union
 AutocompleteTest.type_correct_argument_type_suggestion
 AutocompleteTest.type_correct_expected_argument_type_pack_suggestion
-AutocompleteTest.type_correct_expected_argument_type_suggestion
 AutocompleteTest.type_correct_expected_argument_type_suggestion_optional
 AutocompleteTest.type_correct_expected_argument_type_suggestion_self
+AutocompleteTest.type_correct_expected_return_type_pack_suggestion
 AutocompleteTest.type_correct_expected_return_type_suggestion
 AutocompleteTest.type_correct_full_type_suggestion
 AutocompleteTest.type_correct_function_no_parenthesis
 AutocompleteTest.type_correct_function_return_types
 AutocompleteTest.type_correct_function_type_suggestion
 AutocompleteTest.type_correct_keywords
-AutocompleteTest.type_correct_local_type_suggestion
-AutocompleteTest.type_correct_sealed_table
 AutocompleteTest.type_correct_suggestion_for_overloads
 AutocompleteTest.type_correct_suggestion_in_argument
+AutocompleteTest.type_correct_suggestion_in_table
 AutocompleteTest.unsealed_table
 AutocompleteTest.unsealed_table_2
-AutocompleteTest.user_defined_local_functions_in_own_definition
 BuiltinTests.aliased_string_format
 BuiltinTests.assert_removes_falsy_types
 BuiltinTests.assert_removes_falsy_types2
@@ -149,21 +95,20 @@ BuiltinTests.table_insert_correctly_infers_type_of_array_2_args_overload
 BuiltinTests.table_insert_correctly_infers_type_of_array_3_args_overload
 BuiltinTests.table_pack
 BuiltinTests.table_pack_reduce
+BuiltinTests.table_pack_variadic
 BuiltinTests.tonumber_returns_optional_number_type
 BuiltinTests.tonumber_returns_optional_number_type2
 DefinitionTests.class_definition_overload_metamethods
 DefinitionTests.declaring_generic_functions
 DefinitionTests.definition_file_classes
-FrontendTest.ast_node_at_position
 FrontendTest.automatically_check_dependent_scripts
 FrontendTest.environments
 FrontendTest.imported_table_modification_2
 FrontendTest.it_should_be_safe_to_stringify_errors_when_full_type_graph_is_discarded
 FrontendTest.nocheck_cycle_used_by_checked
-FrontendTest.produce_errors_for_unchanged_file_with_a_syntax_error
 FrontendTest.recheck_if_dependent_script_is_dirty
 FrontendTest.reexport_cyclic_type
-FrontendTest.report_syntax_error_in_required_file
+FrontendTest.reexport_type_alias
 FrontendTest.trace_requires_in_nonstrict_mode
 GenericsTests.apply_type_function_nested_generics1
 GenericsTests.apply_type_function_nested_generics2
@@ -212,13 +157,16 @@ IntersectionTypes.table_intersection_write_sealed_indirect
 IntersectionTypes.table_write_sealed_indirect
 isSubtype.intersection_of_tables
 isSubtype.table_with_table_prop
+ModuleTests.any_persistance_does_not_leak
 ModuleTests.clone_self_property
 ModuleTests.deepClone_cyclic_table
 ModuleTests.do_not_clone_reexports
 NonstrictModeTests.for_in_iterator_variables_are_any
 NonstrictModeTests.function_parameters_are_any
 NonstrictModeTests.inconsistent_module_return_types_are_ok
+NonstrictModeTests.inconsistent_return_types_are_ok
 NonstrictModeTests.infer_nullary_function
+NonstrictModeTests.infer_the_maximum_number_of_values_the_function_could_return
 NonstrictModeTests.inline_table_props_are_also_any
 NonstrictModeTests.local_tables_are_not_any
 NonstrictModeTests.locals_are_any_by_default
@@ -324,7 +272,6 @@ RefinementTest.typeguard_in_if_condition_position
 RefinementTest.typeguard_narrows_for_functions
 RefinementTest.typeguard_narrows_for_table
 RefinementTest.typeguard_not_to_be_string
-RefinementTest.typeguard_only_look_up_types_from_global_scope
 RefinementTest.what_nonsensical_condition
 RefinementTest.x_as_any_if_x_is_instance_elseif_x_is_table
 RefinementTest.x_is_not_instance_or_else_not_part
@@ -349,6 +296,7 @@ TableTests.defining_a_self_method_for_a_builtin_sealed_table_must_fail
 TableTests.defining_a_self_method_for_a_local_sealed_table_must_fail
 TableTests.dont_crash_when_setmetatable_does_not_produce_a_metatabletypevar
 TableTests.dont_hang_when_trying_to_look_up_in_cyclic_metatable_index
+TableTests.dont_invalidate_the_properties_iterator_of_free_table_when_rolled_back
 TableTests.dont_leak_free_table_props
 TableTests.dont_quantify_table_that_belongs_to_outer_scope
 TableTests.dont_suggest_exact_match_keys
@@ -363,13 +311,11 @@ TableTests.found_like_key_in_table_function_call
 TableTests.found_like_key_in_table_property_access
 TableTests.found_multiple_like_keys
 TableTests.function_calls_produces_sealed_table_given_unsealed_table
-TableTests.generalize_table_argument
 TableTests.getmetatable_returns_pointer_to_metatable
 TableTests.give_up_after_one_metatable_index_look_up
 TableTests.hide_table_error_properties
 TableTests.indexer_fn
 TableTests.indexer_on_sealed_table_must_unify_with_free_table
-TableTests.indexer_table
 TableTests.indexing_from_a_table_should_prefer_properties_when_possible
 TableTests.inequality_operators_imply_exactly_matching_types
 TableTests.infer_array_2
@@ -395,11 +341,11 @@ TableTests.open_table_unification_2
 TableTests.pass_a_union_of_tables_to_a_function_that_requires_a_table
 TableTests.pass_a_union_of_tables_to_a_function_that_requires_a_table_2
 TableTests.pass_incompatible_union_to_a_generic_table_without_crashing
-TableTests.passing_compatible_unions_to_a_generic_table_without_crashing
 TableTests.persistent_sealed_table_is_immutable
 TableTests.prop_access_on_key_whose_types_mismatches
 TableTests.property_lookup_through_tabletypevar_metatable
 TableTests.quantify_even_that_table_was_never_exported_at_all
+TableTests.quantify_metatables_of_metatables_of_table
 TableTests.quantifying_a_bound_var_works
 TableTests.reasonable_error_when_adding_a_nonexistent_property_to_an_array_like_table
 TableTests.result_is_always_any_if_lhs_is_any
@@ -435,8 +381,11 @@ ToString.function_type_with_argument_names_generic
 ToString.no_parentheses_around_cyclic_function_type_in_union
 ToString.toStringDetailed2
 ToString.toStringErrorPack
+ToString.toStringNamedFunction_generic_pack
+ToString.toStringNamedFunction_hide_self_param
 ToString.toStringNamedFunction_hide_type_params
 ToString.toStringNamedFunction_id
+ToString.toStringNamedFunction_include_self_param
 ToString.toStringNamedFunction_map
 ToString.toStringNamedFunction_variadics
 TranspilerTests.types_should_not_be_considered_cyclic_if_they_are_not_recursive
@@ -453,6 +402,7 @@ TypeAliases.mutually_recursive_types_restriction_not_ok_1
 TypeAliases.mutually_recursive_types_restriction_not_ok_2
 TypeAliases.mutually_recursive_types_swapsies_not_ok
 TypeAliases.recursive_types_restriction_not_ok
+TypeAliases.report_shadowed_aliases
 TypeAliases.stringify_optional_parameterized_alias
 TypeAliases.stringify_type_alias_of_recursive_template_table_type
 TypeAliases.stringify_type_alias_of_recursive_template_table_type2
@@ -460,11 +410,14 @@ TypeAliases.type_alias_fwd_declaration_is_precise
 TypeAliases.type_alias_local_mutation
 TypeAliases.type_alias_local_rename
 TypeAliases.type_alias_of_an_imported_recursive_generic_type
+TypeAliases.type_alias_of_an_imported_recursive_type
 TypeInfer.checking_should_not_ice
+TypeInfer.dont_report_type_errors_within_an_AstExprError
 TypeInfer.dont_report_type_errors_within_an_AstStatError
 TypeInfer.globals
 TypeInfer.globals2
 TypeInfer.infer_assignment_value_types_mutable_lval
+TypeInfer.it_is_ok_to_have_inconsistent_number_of_return_values_in_nonstrict
 TypeInfer.no_stack_overflow_from_isoptional
 TypeInfer.tc_after_error_recovery_no_replacement_name_in_error
 TypeInfer.tc_if_else_expressions_expected_type_3
@@ -489,6 +442,7 @@ TypeInferClasses.table_class_unification_reports_sane_errors_for_missing_propert
 TypeInferClasses.warn_when_prop_almost_matches
 TypeInferClasses.we_can_report_when_someone_is_trying_to_use_a_table_rather_than_a_class
 TypeInferFunctions.call_o_with_another_argument_after_foo_was_quantified
+TypeInferFunctions.calling_function_with_anytypepack_doesnt_leak_free_types
 TypeInferFunctions.calling_function_with_incorrect_argument_type_yields_errors_spanning_argument
 TypeInferFunctions.dont_give_other_overloads_message_if_only_one_argument_matching_overload_exists
 TypeInferFunctions.dont_infer_parameter_types_for_functions_from_their_call_site
@@ -500,16 +454,20 @@ TypeInferFunctions.function_decl_non_self_sealed_overwrite_2
 TypeInferFunctions.function_decl_non_self_unsealed_overwrite
 TypeInferFunctions.function_does_not_return_enough_values
 TypeInferFunctions.function_statement_sealed_table_assignment_through_indexer
+TypeInferFunctions.ignored_return_values
 TypeInferFunctions.improved_function_arg_mismatch_error_nonstrict
 TypeInferFunctions.improved_function_arg_mismatch_errors
 TypeInferFunctions.inconsistent_higher_order_function
 TypeInferFunctions.inconsistent_return_types
 TypeInferFunctions.infer_anonymous_function_arguments
 TypeInferFunctions.infer_return_type_from_selected_overload
+TypeInferFunctions.infer_return_value_type
 TypeInferFunctions.infer_that_function_does_not_return_a_table
+TypeInferFunctions.it_is_ok_not_to_supply_enough_retvals
 TypeInferFunctions.list_all_overloads_if_no_overload_takes_given_argument_count
 TypeInferFunctions.list_only_alternative_overloads_that_match_argument_count
 TypeInferFunctions.no_lossy_function_type
+TypeInferFunctions.occurs_check_failure_in_function_return_type
 TypeInferFunctions.quantify_constrained_types
 TypeInferFunctions.record_matching_overload
 TypeInferFunctions.report_exiting_without_return_nonstrict
@@ -521,7 +479,13 @@ TypeInferFunctions.too_few_arguments_variadic_generic
 TypeInferFunctions.too_few_arguments_variadic_generic2
 TypeInferFunctions.too_many_arguments
 TypeInferFunctions.too_many_return_values
+TypeInferFunctions.too_many_return_values_in_parentheses
+TypeInferFunctions.too_many_return_values_no_function
 TypeInferFunctions.vararg_function_is_quantified
+TypeInferLoops.for_in_loop_error_on_factory_not_returning_the_right_amount_of_values
+TypeInferLoops.for_in_loop_with_custom_iterator
+TypeInferLoops.for_in_loop_with_next
+TypeInferLoops.for_in_with_generic_next
 TypeInferLoops.for_in_with_just_one_iterator_is_ok
 TypeInferLoops.loop_iter_no_indexer_nonstrict
 TypeInferLoops.loop_iter_trailing_nil
@@ -529,6 +493,9 @@ TypeInferLoops.loop_typecheck_crash_on_empty_optional
 TypeInferLoops.unreachable_code_after_infinite_loop
 TypeInferLoops.varlist_declared_by_for_in_loop_should_be_free
 TypeInferModules.custom_require_global
+TypeInferModules.do_not_modify_imported_types
+TypeInferModules.do_not_modify_imported_types_2
+TypeInferModules.do_not_modify_imported_types_3
 TypeInferModules.general_require_type_mismatch
 TypeInferModules.module_type_conflict
 TypeInferModules.module_type_conflict_instantiated
@@ -539,8 +506,8 @@ TypeInferOOP.CheckMethodsOfSealed
 TypeInferOOP.dont_suggest_using_colon_rather_than_dot_if_another_overload_works
 TypeInferOOP.dont_suggest_using_colon_rather_than_dot_if_it_wont_help_2
 TypeInferOOP.dont_suggest_using_colon_rather_than_dot_if_not_defined_with_colon
-TypeInferOOP.inferred_methods_of_free_tables_have_the_same_level_as_the_enclosing_table
 TypeInferOOP.inferring_hundreds_of_self_calls_should_not_suffocate_memory
+TypeInferOOP.methods_are_topologically_sorted
 TypeInferOperators.and_adds_boolean
 TypeInferOperators.and_adds_boolean_no_superfluous_union
 TypeInferOperators.and_binexps_dont_unify
@@ -564,6 +531,7 @@ TypeInferOperators.expected_types_through_binary_or
 TypeInferOperators.infer_any_in_all_modes_when_lhs_is_unknown
 TypeInferOperators.or_joins_types
 TypeInferOperators.or_joins_types_with_no_extras
+TypeInferOperators.primitive_arith_no_metatable
 TypeInferOperators.primitive_arith_possible_metatable
 TypeInferOperators.produce_the_correct_error_message_when_comparing_a_table_with_a_metatable_with_one_that_does_not
 TypeInferOperators.refine_and_or
@@ -591,6 +559,7 @@ TypeInferUnknownNever.dont_unify_operands_if_one_of_the_operand_is_never_in_any_
 TypeInferUnknownNever.index_on_union_of_tables_for_properties_that_is_never
 TypeInferUnknownNever.index_on_union_of_tables_for_properties_that_is_sorta_never
 TypeInferUnknownNever.math_operators_and_never
+TypeInferUnknownNever.type_packs_containing_never_is_itself_uninhabitable
 TypeInferUnknownNever.type_packs_containing_never_is_itself_uninhabitable2
 TypeInferUnknownNever.unary_minus_of_never
 TypePackTests.higher_order_function

tools/lldb_formatters.lldb

@@ -1,2 +1,7 @@
+type synthetic add -x "^Luau::detail::DenseHashTable<.*>$" -l lldb_formatters.DenseHashTableSyntheticChildrenProvider
+type summary add "Luau::Symbol" -F lldb_formatters.luau_symbol_summary
+
 type synthetic add -x "^Luau::Variant<.+>$" -l lldb_formatters.LuauVariantSyntheticChildrenProvider
-type summary add -x "^Luau::Variant<.+>$" -l lldb_formatters.luau_variant_summary
+type summary add -x "^Luau::Variant<.+>$" -F lldb_formatters.luau_variant_summary
+
+type synthetic add -x "^Luau::AstArray<.+>$" -l lldb_formatters.AstArraySyntheticChildrenProvider

tools/lldb_formatters.py

@@ -4,30 +4,31 @@
 # We're forced to resort to parsing names as strings.
 def templateParams(s):
     depth = 0
-    start = s.find('<') + 1
+    start = s.find("<") + 1
     result = []
     for i, c in enumerate(s[start:], start):
-        if c == '<':
+        if c == "<":
             depth += 1
-        elif c == '>':
+        elif c == ">":
             if depth == 0:
-                result.append(s[start: i].strip())
+                result.append(s[start:i].strip())
                 break
             depth -= 1
-        elif c == ',' and depth == 0:
+        elif c == "," and depth == 0:
-            result.append(s[start: i].strip())
+            result.append(s[start:i].strip())
             start = i + 1
     return result
 
+
 def getType(target, typeName):
     stars = 0
 
     typeName = typeName.strip()
-    while typeName.endswith('*'):
+    while typeName.endswith("*"):
         stars += 1
         typeName = typeName[:-1]
 
-    if typeName.startswith('const '):
+    if typeName.startswith("const "):
         typeName = typeName[6:]
 
     ty = target.FindFirstType(typeName.strip())
@@ -36,13 +37,10 @@ def getType(target, typeName):
 
     return ty
 
+
 def luau_variant_summary(valobj, internal_dict, options):
-    type_id = valobj.GetChildMemberWithName("typeId").GetValueAsUnsigned()
+    return valobj.GetChildMemberWithName("type").GetSummary()[1:-1]
-    storage = valobj.GetChildMemberWithName("storage")
+
-    params = templateParams(valobj.GetType().GetCanonicalType().GetName())
-    stored_type = params[type_id]
-    value = storage.Cast(stored_type.GetPointerType()).Dereference()
-    return stored_type.GetDisplayTypeName() + " [" + value.GetValue() + "]"
 
 class LuauVariantSyntheticChildrenProvider:
     node_names = ["type", "value"]
@@ -74,26 +72,42 @@ class LuauVariantSyntheticChildrenProvider:
 
         if node == "type":
             if self.current_type:
-                return self.valobj.CreateValueFromExpression(node, f"(const char*)\"{self.current_type.GetDisplayTypeName()}\"")
+                return self.valobj.CreateValueFromExpression(
+                    node, f'(const char*)"{self.current_type.GetDisplayTypeName()}"'
+                )
             else:
-                return self.valobj.CreateValueFromExpression(node, "(const char*)\"<unknown type>\"")
+                return self.valobj.CreateValueFromExpression(
+                    node, '(const char*)"<unknown type>"'
+                )
         elif node == "value":
             if self.stored_value is not None:
                 if self.current_type is not None:
-                    return self.valobj.CreateValueFromData(node, self.stored_value.GetData(), self.current_type)
+                    return self.valobj.CreateValueFromData(
+                        node, self.stored_value.GetData(), self.current_type
+                    )
                 else:
-                    return self.valobj.CreateValueExpression(node, "(const char*)\"<unknown type>\"")
+                    return self.valobj.CreateValueExpression(
+                        node, '(const char*)"<unknown type>"'
+                    )
             else:
-                return self.valobj.CreateValueFromExpression(node, "(const char*)\"<no stored value>\"")
+                return self.valobj.CreateValueFromExpression(
+                    node, '(const char*)"<no stored value>"'
+                )
         else:
             return None
 
     def update(self):
-        self.type_index = self.valobj.GetChildMemberWithName("typeId").GetValueAsSigned()
+        self.type_index = self.valobj.GetChildMemberWithName(
-        self.type_params = templateParams(self.valobj.GetType().GetCanonicalType().GetName())
+            "typeId"
+        ).GetValueAsSigned()
+        self.type_params = templateParams(
+            self.valobj.GetType().GetCanonicalType().GetName()
+        )
 
         if len(self.type_params) > self.type_index:
-            self.current_type = getType(self.valobj.GetTarget(), self.type_params[self.type_index])
+            self.current_type = getType(
+                self.valobj.GetTarget(), self.type_params[self.type_index]
+            )
 
             if self.current_type:
                 storage = self.valobj.GetChildMemberWithName("storage")
@@ -105,3 +119,97 @@ class LuauVariantSyntheticChildrenProvider:
             self.stored_value = None
 
         return False
+
+
+class DenseHashTableSyntheticChildrenProvider:
+    def __init__(self, valobj, internal_dict):
+        """this call should initialize the Python object using valobj as the variable to provide synthetic children for"""
+        self.valobj = valobj
+        self.update()
+
+    def num_children(self):
+        """this call should return the number of children that you want your object to have"""
+        return self.capacity
+
+    def get_child_index(self, name):
+        """this call should return the index of the synthetic child whose name is given as argument"""
+        try:
+            if name.startswith("[") and name.endswith("]"):
+                return int(name[1:-1])
+            else:
+                return -1
+        except Exception as e:
+            print("get_child_index exception", e)
+            return -1
+
+    def get_child_at_index(self, index):
+        """this call should return a new LLDB SBValue object representing the child at the index given as argument"""
+        try:
+            dataMember = self.valobj.GetChildMemberWithName("data")
+
+            data = dataMember.GetPointeeData(index)
+
+            return self.valobj.CreateValueFromData(
+                f"[{index}]",
+                data,
+                dataMember.Dereference().GetType(),
+            )
+
+        except Exception as e:
+            print("get_child_at_index error", e)
+
+    def update(self):
+        """this call should be used to update the internal state of this Python object whenever the state of the variables in LLDB changes.[1]
+        Also, this method is invoked before any other method in the interface."""
+        self.capacity = self.valobj.GetChildMemberWithName(
+            "capacity"
+        ).GetValueAsUnsigned()
+
+    def has_children(self):
+        """this call should return True if this object might have children, and False if this object can be guaranteed not to have children.[2]"""
+        return True
+
+
+def luau_symbol_summary(valobj, internal_dict, options):
+    local = valobj.GetChildMemberWithName("local")
+    global_ = valobj.GetChildMemberWithName("global").GetChildMemberWithName("value")
+
+    if local.GetValueAsUnsigned() != 0:
+        return f'local {local.GetChildMemberWithName("name").GetChildMemberWithName("value").GetSummary()}'
+    elif global_.GetValueAsUnsigned() != 0:
+        return f"global {global_.GetSummary()}"
+    else:
+        return "???"
+
+
+class AstArraySyntheticChildrenProvider:
+    def __init__(self, valobj, internal_dict):
+        self.valobj = valobj
+
+    def num_children(self):
+        return self.size
+
+    def get_child_index(self, name):
+        try:
+            if name.startswith("[") and name.endswith("]"):
+                return int(name[1:-1])
+            else:
+                return -1
+        except Exception as e:
+            print("get_child_index error:", e)
+
+    def get_child_at_index(self, index):
+        try:
+            dataMember = self.valobj.GetChildMemberWithName("data")
+            data = dataMember.GetPointeeData(index)
+            return self.valobj.CreateValueFromData(
+                f"[{index}]", data, dataMember.Dereference().GetType()
+            )
+        except Exception as e:
+            print("get_child_index error:", e)
+
+    def update(self):
+        self.size = self.valobj.GetChildMemberWithName("size").GetValueAsUnsigned()
+
+    def has_children(self):
+        return True

tools/perfgraph.py

@@ -4,7 +4,6 @@
 # Given a profile dump, this tool generates a flame graph based on the stacks listed in the profile
 # The result of analysis is a .svg file which can be viewed in a browser
 
-import sys
 import svg
 import argparse
 import json

tools/perfstat.py

@@ -0,0 +1,65 @@
+#!/usr/bin/python
+# This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+# Given a profile dump, this tool displays top functions based on the stacks listed in the profile
+
+import argparse
+
+class Node:
+    def __init__(self):
+        self.function = ""
+        self.source = ""
+        self.line = 0
+        self.hier_ticks = 0
+        self.self_ticks = 0
+
+    def title(self):
+        if self.line > 0:
+            return "{} ({}:{})".format(self.function, self.source, self.line)
+        else:
+            return self.function
+
+argumentParser = argparse.ArgumentParser(description='Display summary statistics from Luau sampling profiler dumps')
+argumentParser.add_argument('source_file', type=open)
+argumentParser.add_argument('--limit', dest='limit', type=int, default=10, help='Display top N functions')
+
+arguments = argumentParser.parse_args()
+
+dump = arguments.source_file.readlines()
+
+stats = {}
+total = 0
+total_gc = 0
+
+for l in dump:
+    ticks, stack = l.strip().split(" ", 1)
+    hier = {}
+
+    for f in reversed(stack.split(";")):
+        source, function, line = f.split(",")
+        node = stats.setdefault(f, Node())
+
+        node.function = function
+        node.source = source
+        node.line = int(line) if len(line) > 0 else 0
+
+        if not node in hier:
+            node.hier_ticks += int(ticks)
+            hier[node] = True
+
+    total += int(ticks)
+    node.self_ticks += int(ticks)
+
+    if node.source == "GC":
+        total_gc += int(ticks)
+
+if total > 0:
+    print(f"Runtime: {total:,} usec ({100.0 * total_gc / total:.2f}% GC)")
+    print()
+    print("Top functions (self time):")
+    for n in sorted(stats.values(), key=lambda node: node.self_ticks, reverse=True)[:arguments.limit]:
+        print(f"{n.self_ticks:12,} usec ({100.0 * n.self_ticks / total:.2f}%): {n.title()}")
+    print()
+    print("Top functions (total time):")
+    for n in sorted(stats.values(), key=lambda node: node.hier_ticks, reverse=True)[:arguments.limit]:
+        print(f"{n.hier_ticks:12,} usec ({100.0 * n.hier_ticks / total:.2f}%): {n.title()}")

tools/test_dcr.py

@@ -39,7 +39,7 @@ class Handler(x.ContentHandler):
 
         elif name == "OverallResultsAsserts":
             if self.currentTest:
-                passed = 0 == safeParseInt(attrs["failures"])
+                passed = attrs["test_case_success"] == "true"
 
                 dottedName = ".".join(self.currentTest)