Merge branch 'upstream' into merge

Analysis/include/Luau/BuiltinDefinitions.h

@@ -1,7 +1,8 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
-#include "TypeInfer.h"
+#include "Luau/Scope.h"
+#include "Luau/TypeInfer.h"
 
 namespace Luau
 {

Analysis/include/Luau/Error.h

@@ -120,6 +120,7 @@ struct IncorrectGenericParameterCount
     Name name;
     TypeFun typeFun;
     size_t actualParameters;
+    size_t actualPackParameters;
 
     bool operator==(const IncorrectGenericParameterCount& rhs) const;
 };

Analysis/include/Luau/FileResolver.h

@@ -25,51 +25,39 @@ struct SourceCode
     Type type;
 };
 
+struct ModuleInfo
+{
+    ModuleName name;
+    bool optional = false;
+};
+
 struct FileResolver
 {
     virtual ~FileResolver() {}
 
-    /** Fetch the source code associated with the provided ModuleName.
-     *
-     * FIXME: This requires a string copy!
-     *
-     * @returns The actual Lua code on success.
-     * @returns std::nullopt if no such file exists.  When this occurs, type inference will report an UnknownRequire error.
-     */
     virtual std::optional<SourceCode> readSource(const ModuleName& name) = 0;
 
-    /** Does the module exist?
+    virtual std::optional<ModuleInfo> resolveModule(const ModuleInfo* context, AstExpr* expr)
-     *
+    {
-     * Saves a string copy over reading the source and throwing it away.
+        return std::nullopt;
-     */
+    }
-    virtual bool moduleExists(const ModuleName& name) const = 0;
 
-    virtual std::optional<ModuleName> fromAstFragment(AstExpr* expr) const = 0;
+    virtual std::string getHumanReadableModuleName(const ModuleName& name) const
-
-    /** Given a valid module name and a string of arbitrary data, figure out the concatenation.
-     */
-    virtual ModuleName concat(const ModuleName& lhs, std::string_view rhs) const = 0;
-
-    /** Goes "up" a level in the hierarchy that the ModuleName represents.
-     *
-     * For instances, this is analogous to someInstance.Parent; for paths, this is equivalent to removing the last
-     * element of the path. Other ModuleName representations may have other ways of doing this.
-     *
-     * @returns The parent ModuleName, if one exists.
-     * @returns std::nullopt if there is no parent for this module name.
-     */
-    virtual std::optional<ModuleName> getParentModuleName(const ModuleName& name) const = 0;
-
-    virtual std::optional<std::string> getHumanReadableModuleName_(const ModuleName& name) const
     {
         return name;
     }
 
-    virtual std::optional<std::string> getEnvironmentForModule(const ModuleName& name) const = 0;
+    virtual std::optional<std::string> getEnvironmentForModule(const ModuleName& name) const
+    {
+        return std::nullopt;
+    }
 
-    /** LanguageService only:
+    // DEPRECATED APIS
-     * std::optional<ModuleName> fromInstance(Instance* inst)
+    // These are going to be removed with LuauNewRequireTracer
-     */
+    virtual bool moduleExists(const ModuleName& name) const = 0;
+    virtual std::optional<ModuleName> fromAstFragment(AstExpr* expr) const = 0;
+    virtual ModuleName concat(const ModuleName& lhs, std::string_view rhs) const = 0;
+    virtual std::optional<ModuleName> getParentModuleName(const ModuleName& name) const = 0;
 };
 
 struct NullFileResolver : FileResolver
@@ -94,10 +82,6 @@ struct NullFileResolver : FileResolver
     {
         return std::nullopt;
     }
-    std::optional<std::string> getEnvironmentForModule(const ModuleName& name) const override
-    {
-        return std::nullopt;
-    }
 };
 
 } // namespace Luau

Analysis/include/Luau/Module.h

@@ -90,10 +90,12 @@ struct Module
     TypeArena internalTypes;
 
     std::vector<std::pair<Location, ScopePtr>> scopes; // never empty
-    std::unordered_map<const AstExpr*, TypeId> astTypes;
+
-    std::unordered_map<const AstExpr*, TypeId> astExpectedTypes;
+    DenseHashMap<const AstExpr*, TypeId> astTypes{nullptr};
-    std::unordered_map<const AstExpr*, TypeId> astOriginalCallTypes;
+    DenseHashMap<const AstExpr*, TypeId> astExpectedTypes{nullptr};
-    std::unordered_map<const AstExpr*, TypeId> astOverloadResolvedTypes;
+    DenseHashMap<const AstExpr*, TypeId> astOriginalCallTypes{nullptr};
+    DenseHashMap<const AstExpr*, TypeId> astOverloadResolvedTypes{nullptr};
+
     std::unordered_map<Name, TypeId> declaredGlobals;
     ErrorVec errors;
     Mode mode;

Analysis/include/Luau/ModuleResolver.h

@@ -15,12 +15,6 @@ struct Module;
 
 using ModulePtr = std::shared_ptr<Module>;
 
-struct ModuleInfo
-{
-    ModuleName name;
-    bool optional = false;
-};
-
 struct ModuleResolver
 {
     virtual ~ModuleResolver() {}

Analysis/include/Luau/RequireTracer.h

@@ -17,12 +17,11 @@ struct AstLocal;
 
 struct RequireTraceResult
 {
-    DenseHashMap<const AstExpr*, ModuleName> exprs{0};
+    DenseHashMap<const AstExpr*, ModuleInfo> exprs{nullptr};
-    DenseHashMap<const AstExpr*, bool> optional{0};
 
     std::vector<std::pair<ModuleName, Location>> requires;
 };
 
-RequireTraceResult traceRequires(FileResolver* fileResolver, AstStatBlock* root, ModuleName currentModuleName);
+RequireTraceResult traceRequires(FileResolver* fileResolver, AstStatBlock* root, const ModuleName& currentModuleName);
 
 } // namespace Luau

Analysis/include/Luau/Scope.h

@@ -0,0 +1,67 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/Location.h"
+#include "Luau/TypeVar.h"
+
+#include <unordered_map>
+#include <optional>
+#include <memory>
+
+namespace Luau
+{
+
+struct Scope;
+
+using ScopePtr = std::shared_ptr<Scope>;
+
+struct Binding
+{
+    TypeId typeId;
+    Location location;
+    bool deprecated = false;
+    std::string deprecatedSuggestion;
+    std::optional<std::string> documentationSymbol;
+};
+
+struct Scope
+{
+    explicit Scope(TypePackId returnType);                    // root scope
+    explicit Scope(const ScopePtr& parent, int subLevel = 0); // child scope.  Parent must not be nullptr.
+
+    const ScopePtr parent; // null for the root
+    std::unordered_map<Symbol, Binding> bindings;
+    TypePackId returnType;
+    bool breakOk = false;
+    std::optional<TypePackId> varargPack;
+
+    TypeLevel level;
+
+    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;
+
+    std::optional<TypeId> lookup(const Symbol& name);
+
+    std::optional<TypeFun> lookupType(const Name& name);
+    std::optional<TypeFun> lookupImportedType(const Name& moduleAlias, const Name& name);
+
+    std::unordered_map<Name, TypePackId> privateTypePackBindings;
+    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);
+
+    RefinementMap refinements;
+
+    // For mutually recursive type aliases, it's important that
+    // they use the same types for the same names.
+    // For instance, in `type Tree<T> { data: T, children: Forest<T> } type Forest<T> = {Tree<T>}`
+    // we need that the generic type `T` in both cases is the same, so we use a cache.
+    std::unordered_map<Name, TypeId> typeAliasTypeParameters;
+    std::unordered_map<Name, TypePackId> typeAliasTypePackParameters;
+};
+
+} // namespace Luau

Analysis/include/Luau/Substitution.h

@@ -52,8 +52,6 @@
 // `T`, and the type of `f` are in the same SCC, which is why `f` gets
 // replaced.
 
-LUAU_FASTFLAG(DebugLuauTrackOwningArena)
-
 namespace Luau
 {
 
@@ -188,20 +186,12 @@ struct Substitution : FindDirty
     template<typename T>
     TypeId addType(const T& tv)
     {
-        TypeId allocated = currentModule->internalTypes.typeVars.allocate(tv);
+        return currentModule->internalTypes.addType(tv);
-        if (FFlag::DebugLuauTrackOwningArena)
-            asMutable(allocated)->owningArena = &currentModule->internalTypes;
-
-        return allocated;
     }
     template<typename T>
     TypePackId addTypePack(const T& tp)
     {
-        TypePackId allocated = currentModule->internalTypes.typePacks.allocate(tp);
+        return currentModule->internalTypes.addTypePack(TypePackVar{tp});
-        if (FFlag::DebugLuauTrackOwningArena)
-            asMutable(allocated)->owningArena = &currentModule->internalTypes;
-
-        return allocated;
     }
 };
 

Analysis/include/Luau/TypeInfer.h

@@ -86,7 +86,10 @@ struct ApplyTypeFunction : Substitution
 {
     TypeLevel level;
     bool encounteredForwardedType;
-    std::unordered_map<TypeId, TypeId> arguments;
+    std::unordered_map<TypeId, TypeId> typeArguments;
+    std::unordered_map<TypePackId, TypePackId> typePackArguments;
+    bool ignoreChildren(TypeId ty) override;
+    bool ignoreChildren(TypePackId tp) override;
     bool isDirty(TypeId ty) override;
     bool isDirty(TypePackId tp) override;
     TypeId clean(TypeId ty) override;
@@ -328,7 +331,8 @@ private:
     TypeId resolveType(const ScopePtr& scope, const AstType& annotation, bool canBeGeneric = false);
     TypePackId resolveTypePack(const ScopePtr& scope, const AstTypeList& types);
     TypePackId resolveTypePack(const ScopePtr& scope, const AstTypePack& annotation);
-    TypeId instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf, const std::vector<TypeId>& typeParams, const Location& location);
+    TypeId instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf, const std::vector<TypeId>& typeParams,
+        const std::vector<TypePackId>& typePackParams, const Location& location);
 
     // Note: `scope` must be a fresh scope.
     std::pair<std::vector<TypeId>, std::vector<TypePackId>> createGenericTypes(
@@ -398,54 +402,6 @@ private:
     int recursionCount = 0;
 };
 
-struct Binding
-{
-    TypeId typeId;
-    Location location;
-    bool deprecated = false;
-    std::string deprecatedSuggestion;
-    std::optional<std::string> documentationSymbol;
-};
-
-struct Scope
-{
-    explicit Scope(TypePackId returnType);                    // root scope
-    explicit Scope(const ScopePtr& parent, int subLevel = 0); // child scope.  Parent must not be nullptr.
-
-    const ScopePtr parent; // null for the root
-    std::unordered_map<Symbol, Binding> bindings;
-    TypePackId returnType;
-    bool breakOk = false;
-    std::optional<TypePackId> varargPack;
-
-    TypeLevel level;
-
-    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;
-
-    std::optional<TypeId> lookup(const Symbol& name);
-
-    std::optional<TypeFun> lookupType(const Name& name);
-    std::optional<TypeFun> lookupImportedType(const Name& moduleAlias, const Name& name);
-
-    std::unordered_map<Name, TypePackId> privateTypePackBindings;
-    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);
-
-    RefinementMap refinements;
-
-    // For mutually recursive type aliases, it's important that
-    // they use the same types for the same names.
-    // For instance, in `type Tree<T> { data: T, children: Forest<T> } type Forest<T> = {Tree<T>}`
-    // we need that the generic type `T` in both cases is the same, so we use a cache.
-    std::unordered_map<Name, TypeId> typeAliasParameters;
-};
-
 // Unit test hook
 void setPrintLine(void (*pl)(const std::string& s));
 void resetPrintLine();

Analysis/include/Luau/TypePack.h

@@ -117,7 +117,8 @@ bool areEqual(SeenSet& seen, const TypePackVar& lhs, const TypePackVar& rhs);
 
 TypePackId follow(TypePackId tp);
 
-size_t size(const TypePackId tp);
+size_t size(TypePackId tp);
+bool finite(TypePackId tp);
 size_t size(const TypePack& tp);
 std::optional<TypeId> first(TypePackId tp);
 

Analysis/include/Luau/TypeVar.h

@@ -228,6 +228,7 @@ struct TableTypeVar
 
     std::map<Name, Location> methodDefinitionLocations;
     std::vector<TypeId> instantiatedTypeParams;
+    std::vector<TypePackId> instantiatedTypePackParams;
     ModuleName definitionModuleName;
 
     std::optional<TypeId> boundTo;
@@ -284,8 +285,9 @@ struct ClassTypeVar
 
 struct TypeFun
 {
-    /// These should all be generic
+    // These should all be generic
     std::vector<TypeId> typeParams;
+    std::vector<TypePackId> typePackParams;
 
     /** The underlying type.
      *
@@ -293,6 +295,20 @@ struct TypeFun
      * You must first use TypeChecker::instantiateTypeFun to turn it into a real type.
      */
     TypeId type;
+
+    TypeFun() = default;
+    TypeFun(std::vector<TypeId> typeParams, TypeId type)
+        : typeParams(std::move(typeParams))
+        , type(type)
+    {
+    }
+
+    TypeFun(std::vector<TypeId> typeParams, std::vector<TypePackId> typePackParams, TypeId type)
+        : typeParams(std::move(typeParams))
+        , typePackParams(std::move(typePackParams))
+        , type(type)
+    {
+    }
 };
 
 // Anything!  All static checking is off.
@@ -524,8 +540,4 @@ UnionTypeVarIterator end(const UnionTypeVar* utv);
 using TypeIdPredicate = std::function<std::optional<TypeId>(TypeId)>;
 std::vector<TypeId> filterMap(TypeId type, TypeIdPredicate predicate);
 
-// TEMP: Clip this prototype with FFlag::LuauStringMetatable
-std::optional<ExprResult<TypePackId>> magicFunctionFormat(
-    struct TypeChecker& typechecker, const std::shared_ptr<struct Scope>& scope, const AstExprCall& expr, ExprResult<TypePackId> exprResult);
-
 } // namespace Luau

Analysis/include/Luau/Unifier.h

@@ -36,12 +36,17 @@ struct Unifier
     Variance variance = Covariant;
     CountMismatch::Context ctx = CountMismatch::Arg;
 
-    std::shared_ptr<UnifierCounters> counters;
+    UnifierCounters* counters;
+    UnifierCounters countersData;
+
+    std::shared_ptr<UnifierCounters> counters_DEPRECATED;
+
     InternalErrorReporter* iceHandler;
 
     Unifier(TypeArena* types, Mode mode, ScopePtr globalScope, const Location& location, Variance variance, InternalErrorReporter* iceHandler);
     Unifier(TypeArena* types, Mode mode, ScopePtr globalScope, const std::vector<std::pair<TypeId, TypeId>>& seen, const Location& location,
-        Variance variance, InternalErrorReporter* iceHandler, const std::shared_ptr<UnifierCounters>& counters = nullptr);
+        Variance variance, InternalErrorReporter* iceHandler, const std::shared_ptr<UnifierCounters>& counters_DEPRECATED = nullptr,
+        UnifierCounters* counters = nullptr);
 
     // Test whether the two type vars unify.  Never commits the result.
     ErrorVec canUnify(TypeId superTy, TypeId subTy);
@@ -58,11 +63,13 @@ private:
     void tryUnifyPrimitives(TypeId superTy, TypeId subTy);
     void tryUnifyFunctions(TypeId superTy, TypeId subTy, bool isFunctionCall = false);
     void tryUnifyTables(TypeId left, TypeId right, bool isIntersection = false);
+    void DEPRECATED_tryUnifyTables(TypeId left, TypeId right, bool isIntersection = false);
     void tryUnifyFreeTable(TypeId free, TypeId other);
     void tryUnifySealedTables(TypeId left, TypeId right, bool isIntersection);
     void tryUnifyWithMetatable(TypeId metatable, TypeId other, bool reversed);
     void tryUnifyWithClass(TypeId superTy, TypeId subTy, bool reversed);
     void tryUnify(const TableIndexer& superIndexer, const TableIndexer& subIndexer);
+    TypeId deeplyOptional(TypeId ty, std::unordered_map<TypeId,TypeId> seen = {});
 
 public:
     void tryUnify(TypePackId superTy, TypePackId subTy, bool isFunctionCall = false);
@@ -80,9 +87,9 @@ private:
 public:
     // Report an "infinite type error" if the type "needle" already occurs within "haystack"
     void occursCheck(TypeId needle, TypeId haystack);
-    void occursCheck(std::unordered_set<TypeId>& seen, TypeId needle, TypeId haystack);
+    void occursCheck(std::unordered_set<TypeId>& seen_DEPRECATED, DenseHashSet<TypeId>& seen, TypeId needle, TypeId haystack);
     void occursCheck(TypePackId needle, TypePackId haystack);
-    void occursCheck(std::unordered_set<TypePackId>& seen, TypePackId needle, TypePackId haystack);
+    void occursCheck(std::unordered_set<TypePackId>& seen_DEPRECATED, DenseHashSet<TypePackId>& seen, TypePackId needle, TypePackId haystack);
 
     Unifier makeChildUnifier();
 
@@ -93,6 +100,9 @@ private:
 
     [[noreturn]] void ice(const std::string& message, const Location& location);
     [[noreturn]] void ice(const std::string& message);
+
+    DenseHashSet<TypeId> tempSeenTy{nullptr};
+    DenseHashSet<TypePackId> tempSeenTp{nullptr};
 };
 
 } // namespace Luau

Analysis/src/AstQuery.cpp

@@ -2,6 +2,7 @@
 #include "Luau/AstQuery.h"
 
 #include "Luau/Module.h"
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypeVar.h"
 #include "Luau/ToString.h"
@@ -143,8 +144,8 @@ std::optional<TypeId> findTypeAtPosition(const Module& module, const SourceModul
 {
     if (auto expr = findExprAtPosition(sourceModule, pos))
     {
-        if (auto it = module.astTypes.find(expr); it != module.astTypes.end())
+        if (auto it = module.astTypes.find(expr))
-            return it->second;
+            return *it;
     }
 
     return std::nullopt;
@@ -154,8 +155,8 @@ std::optional<TypeId> findExpectedTypeAtPosition(const Module& module, const Sou
 {
     if (auto expr = findExprAtPosition(sourceModule, pos))
     {
-        if (auto it = module.astExpectedTypes.find(expr); it != module.astExpectedTypes.end())
+        if (auto it = module.astExpectedTypes.find(expr))
-            return it->second;
+            return *it;
     }
 
     return std::nullopt;
@@ -322,9 +323,9 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
                 TypeId matchingOverload = nullptr;
                 if (parentExpr && parentExpr->is<AstExprCall>())
                 {
-                    if (auto it = module.astOverloadResolvedTypes.find(parentExpr); it != module.astOverloadResolvedTypes.end())
+                    if (auto it = module.astOverloadResolvedTypes.find(parentExpr))
                     {
-                        matchingOverload = it->second;
+                        matchingOverload = *it;
                     }
                 }
 
@@ -345,9 +346,9 @@ std::optional<DocumentationSymbol> getDocumentationSymbolAtPosition(const Source
     {
         if (AstExprIndexName* indexName = targetExpr->as<AstExprIndexName>())
         {
-            if (auto it = module.astTypes.find(indexName->expr); it != module.astTypes.end())
+            if (auto it = module.astTypes.find(indexName->expr))
             {
-                TypeId parentTy = follow(it->second);
+                TypeId parentTy = follow(*it);
                 if (const TableTypeVar* ttv = get<TableTypeVar>(parentTy))
                 {
                     if (auto propIt = ttv->props.find(indexName->index.value); propIt != ttv->props.end())

Analysis/src/Autocomplete.cpp

@@ -210,10 +210,10 @@ static TypeCorrectKind checkTypeCorrectKind(const Module& module, TypeArena* typ
         return TypeCorrectKind::None;
 
     auto it = module.astExpectedTypes.find(expr);
-    if (it == module.astExpectedTypes.end())
+    if (!it)
         return TypeCorrectKind::None;
 
-    TypeId expectedType = follow(it->second);
+    TypeId expectedType = follow(*it);
 
     if (canUnify(expectedType, ty))
         return TypeCorrectKind::Correct;
@@ -682,10 +682,10 @@ static std::optional<bool> functionIsExpectedAt(const Module& module, AstNode* n
         return std::nullopt;
 
     auto it = module.astExpectedTypes.find(expr);
-    if (it == module.astExpectedTypes.end())
+    if (!it)
         return std::nullopt;
 
-    TypeId expectedType = follow(it->second);
+    TypeId expectedType = follow(*it);
 
     if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(expectedType))
         return true;
@@ -784,9 +784,9 @@ AutocompleteEntryMap autocompleteTypeNames(const Module& module, Position positi
 
                 if (AstExprCall* exprCall = expr->as<AstExprCall>())
                 {
-                    if (auto it = module.astTypes.find(exprCall->func); it != module.astTypes.end())
+                    if (auto it = module.astTypes.find(exprCall->func))
                     {
-                        if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(follow(it->second)))
+                        if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(follow(*it)))
                         {
                             if (auto ty = tryGetTypePackTypeAt(ftv->retType, tailPos))
                                 inferredType = *ty;
@@ -798,8 +798,8 @@ AutocompleteEntryMap autocompleteTypeNames(const Module& module, Position positi
                     if (tailPos != 0)
                         break;
 
-                    if (auto it = module.astTypes.find(expr); it != module.astTypes.end())
+                    if (auto it = module.astTypes.find(expr))
-                        inferredType = it->second;
+                        inferredType = *it;
                 }
 
                 if (inferredType)
@@ -815,10 +815,10 @@ AutocompleteEntryMap autocompleteTypeNames(const Module& module, Position positi
         auto tryGetExpectedFunctionType = [](const Module& module, AstExpr* expr) -> const FunctionTypeVar* {
             auto it = module.astExpectedTypes.find(expr);
 
-            if (it == module.astExpectedTypes.end())
+            if (!it)
                 return nullptr;
 
-            TypeId ty = follow(it->second);
+            TypeId ty = follow(*it);
 
             if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(ty))
                 return ftv;
@@ -1129,9 +1129,8 @@ static void autocompleteExpression(const SourceModule& sourceModule, const Modul
 
     if (node->is<AstExprIndexName>())
     {
-        auto it = module.astTypes.find(node->asExpr());
+        if (auto it = module.astTypes.find(node->asExpr()))
-        if (it != module.astTypes.end())
+            autocompleteProps(module, typeArena, *it, PropIndexType::Point, ancestry, result);
-            autocompleteProps(module, typeArena, it->second, PropIndexType::Point, ancestry, result);
     }
     else if (FFlag::LuauIfElseExpressionAnalysisSupport && autocompleteIfElseExpression(node, ancestry, position, result))
         return;
@@ -1203,13 +1202,13 @@ static std::optional<const ClassTypeVar*> getMethodContainingClass(const ModuleP
         return std::nullopt;
     }
 
-    auto parentIter = module->astTypes.find(parentExpr);
+    auto parentIt = module->astTypes.find(parentExpr);
-    if (parentIter == module->astTypes.end())
+    if (!parentIt)
     {
         return std::nullopt;
     }
 
-    Luau::TypeId parentType = Luau::follow(parentIter->second);
+    Luau::TypeId parentType = Luau::follow(*parentIt);
 
     if (auto parentClass = Luau::get<ClassTypeVar>(parentType))
     {
@@ -1250,8 +1249,8 @@ static std::optional<AutocompleteEntryMap> autocompleteStringParams(const Source
         return std::nullopt;
     }
 
-    auto iter = module->astTypes.find(candidate->func);
+    auto it = module->astTypes.find(candidate->func);
-    if (iter == module->astTypes.end())
+    if (!it)
     {
         return std::nullopt;
     }
@@ -1267,7 +1266,7 @@ static std::optional<AutocompleteEntryMap> autocompleteStringParams(const Source
         return std::nullopt;
     };
 
-    auto followedId = Luau::follow(iter->second);
+    auto followedId = Luau::follow(*it);
     if (auto functionType = Luau::get<FunctionTypeVar>(followedId))
     {
         return performCallback(functionType);
@@ -1316,10 +1315,10 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
     if (auto indexName = node->as<AstExprIndexName>())
     {
         auto it = module->astTypes.find(indexName->expr);
-        if (it == module->astTypes.end())
+        if (!it)
             return {};
 
-        TypeId ty = follow(it->second);
+        TypeId ty = follow(*it);
         PropIndexType indexType = indexName->op == ':' ? PropIndexType::Colon : PropIndexType::Point;
 
         if (isString(ty))
@@ -1447,9 +1446,9 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
             // If item doesn't have a key, maybe the value is actually the key
             if (key ? key == node : node->is<AstExprGlobal>() && value == node)
             {
-                if (auto it = module->astExpectedTypes.find(exprTable); it != module->astExpectedTypes.end())
+                if (auto it = module->astExpectedTypes.find(exprTable))
                 {
-                    auto result = autocompleteProps(*module, typeArena, it->second, PropIndexType::Key, finder.ancestry);
+                    auto result = autocompleteProps(*module, typeArena, *it, PropIndexType::Key, finder.ancestry);
 
                     // Remove keys that are already completed
                     for (const auto& item : exprTable->items)
@@ -1485,9 +1484,9 @@ static AutocompleteResult autocomplete(const SourceModule& sourceModule, const M
         {
             if (auto idxExpr = finder.ancestry.at(finder.ancestry.size() - 2)->as<AstExprIndexExpr>())
             {
-                if (auto it = module->astTypes.find(idxExpr->expr); it != module->astTypes.end())
+                if (auto it = module->astTypes.find(idxExpr->expr))
                 {
-                    return {autocompleteProps(*module, typeArena, follow(it->second), PropIndexType::Point, finder.ancestry), finder.ancestry};
+                    return {autocompleteProps(*module, typeArena, follow(*it), PropIndexType::Point, finder.ancestry), finder.ancestry};
                 }
             }
         }

Analysis/src/BuiltinDefinitions.cpp

@@ -11,7 +11,7 @@
 LUAU_FASTFLAG(LuauParseGenericFunctions)
 LUAU_FASTFLAG(LuauGenericFunctions)
 LUAU_FASTFLAG(LuauRankNTypes)
-LUAU_FASTFLAG(LuauStringMetatable)
+LUAU_FASTFLAG(LuauNewRequireTrace)
 
 /** FIXME: Many of these type definitions are not quite completely accurate.
  *
@@ -218,7 +218,6 @@ void registerBuiltinTypes(TypeChecker& typeChecker)
     TypePackId anyTypePack = typeChecker.anyTypePack;
 
     TypePackId numberVariadicList = arena.addTypePack(TypePackVar{VariadicTypePack{numberType}});
-    TypePackId stringVariadicList = arena.addTypePack(TypePackVar{VariadicTypePack{stringType}});
     TypePackId listOfAtLeastOneNumber = arena.addTypePack(TypePack{{numberType}, numberVariadicList});
 
     TypeId listOfAtLeastOneNumberToNumberType = arena.addType(FunctionTypeVar{
@@ -255,85 +254,18 @@ void registerBuiltinTypes(TypeChecker& typeChecker)
     TypeId genericV = arena.addType(GenericTypeVar{"V"});
     TypeId mapOfKtoV = arena.addType(TableTypeVar{{}, TableIndexer(genericK, genericV), typeChecker.globalScope->level});
 
-    if (FFlag::LuauStringMetatable)
+    std::optional<TypeId> stringMetatableTy = getMetatable(singletonTypes.stringType);
+    LUAU_ASSERT(stringMetatableTy);
+    const TableTypeVar* stringMetatableTable = get<TableTypeVar>(follow(*stringMetatableTy));
+    LUAU_ASSERT(stringMetatableTable);
+
+    auto it = stringMetatableTable->props.find("__index");
+    LUAU_ASSERT(it != stringMetatableTable->props.end());
+
+    addGlobalBinding(typeChecker, "string", it->second.type, "@luau");
+
+    if (!FFlag::LuauParseGenericFunctions || !FFlag::LuauGenericFunctions)
     {
-        std::optional<TypeId> stringMetatableTy = getMetatable(singletonTypes.stringType);
-        LUAU_ASSERT(stringMetatableTy);
-        const TableTypeVar* stringMetatableTable = get<TableTypeVar>(follow(*stringMetatableTy));
-        LUAU_ASSERT(stringMetatableTable);
-
-        auto it = stringMetatableTable->props.find("__index");
-        LUAU_ASSERT(it != stringMetatableTable->props.end());
-
-        TypeId stringLib = it->second.type;
-        addGlobalBinding(typeChecker, "string", stringLib, "@luau");
-    }
-
-    if (FFlag::LuauParseGenericFunctions && FFlag::LuauGenericFunctions)
-    {
-        if (!FFlag::LuauStringMetatable)
-        {
-            TypeId stringLibTy = getGlobalBinding(typeChecker, "string");
-            TableTypeVar* stringLib = getMutable<TableTypeVar>(stringLibTy);
-            TypeId replArgType = makeUnion(
-                arena, {stringType,
-                           arena.addType(TableTypeVar({}, TableIndexer(stringType, stringType), typeChecker.globalScope->level, TableState::Generic)),
-                           makeFunction(arena, std::nullopt, {stringType}, {stringType})});
-            TypeId gsubFunc = makeFunction(arena, stringType, {stringType, replArgType, optionalNumber}, {stringType, numberType});
-
-            stringLib->props["gsub"] = makeProperty(gsubFunc, "@luau/global/string.gsub");
-        }
-    }
-    else
-    {
-        if (!FFlag::LuauStringMetatable)
-        {
-            TypeId stringToStringType = makeFunction(arena, std::nullopt, {stringType}, {stringType});
-
-            TypeId gmatchFunc = makeFunction(arena, stringType, {stringType}, {arena.addType(FunctionTypeVar{emptyPack, stringVariadicList})});
-
-            TypeId replArgType = makeUnion(
-                arena, {stringType,
-                           arena.addType(TableTypeVar({}, TableIndexer(stringType, stringType), typeChecker.globalScope->level, TableState::Generic)),
-                           makeFunction(arena, std::nullopt, {stringType}, {stringType})});
-            TypeId gsubFunc = makeFunction(arena, stringType, {stringType, replArgType, optionalNumber}, {stringType, numberType});
-
-            TypeId formatFn = arena.addType(FunctionTypeVar{arena.addTypePack(TypePack{{stringType}, anyTypePack}), oneStringPack});
-
-            TableTypeVar::Props stringLib = {
-                // FIXME string.byte "can" return a pack of numbers, but only if 2nd or 3rd arguments were supplied
-                {"byte", {makeFunction(arena, stringType, {optionalNumber, optionalNumber}, {optionalNumber})}},
-                // FIXME char takes a variadic pack of numbers
-                {"char", {makeFunction(arena, std::nullopt, {numberType, optionalNumber, optionalNumber, optionalNumber}, {stringType})}},
-                {"find", {makeFunction(arena, stringType, {stringType, optionalNumber, optionalBoolean}, {optionalNumber, optionalNumber})}},
-                {"format", {formatFn}}, // FIXME
-                {"gmatch", {gmatchFunc}},
-                {"gsub", {gsubFunc}},
-                {"len", {makeFunction(arena, stringType, {}, {numberType})}},
-                {"lower", {stringToStringType}},
-                {"match", {makeFunction(arena, stringType, {stringType, optionalNumber}, {optionalString})}},
-                {"rep", {makeFunction(arena, stringType, {numberType}, {stringType})}},
-                {"reverse", {stringToStringType}},
-                {"sub", {makeFunction(arena, stringType, {numberType, optionalNumber}, {stringType})}},
-                {"upper", {stringToStringType}},
-                {"split", {makeFunction(arena, stringType, {stringType, optionalString},
-                              {arena.addType(TableTypeVar{{}, TableIndexer{numberType, stringType}, typeChecker.globalScope->level})})}},
-                {"pack", {arena.addType(FunctionTypeVar{
-                             arena.addTypePack(TypePack{{stringType}, anyTypePack}),
-                             oneStringPack,
-                         })}},
-                {"packsize", {makeFunction(arena, stringType, {}, {numberType})}},
-                {"unpack", {arena.addType(FunctionTypeVar{
-                               arena.addTypePack(TypePack{{stringType, stringType, optionalNumber}}),
-                               anyTypePack,
-                           })}},
-            };
-
-            assignPropDocumentationSymbols(stringLib, "@luau/global/string");
-            addGlobalBinding(typeChecker, "string",
-                arena.addType(TableTypeVar{stringLib, std::nullopt, typeChecker.globalScope->level, TableState::Sealed}), "@luau");
-        }
-
         TableTypeVar::Props debugLib{
             {"info", {makeIntersection(arena,
                          {
@@ -601,9 +533,6 @@ void registerBuiltinTypes(TypeChecker& typeChecker)
     auto tableLib = getMutable<TableTypeVar>(getGlobalBinding(typeChecker, "table"));
     attachMagicFunction(tableLib->props["pack"].type, magicFunctionPack);
 
-    auto stringLib = getMutable<TableTypeVar>(getGlobalBinding(typeChecker, "string"));
-    attachMagicFunction(stringLib->props["format"].type, magicFunctionFormat);
-
     attachMagicFunction(getGlobalBinding(typeChecker, "require"), magicFunctionRequire);
 }
 
@@ -791,11 +720,11 @@ static std::optional<ExprResult<TypePackId>> magicFunctionRequire(
         return std::nullopt;
     }
 
-    AstExpr* require = expr.args.data[0];
+    if (!checkRequirePath(typechecker, expr.args.data[0]))
-
-    if (!checkRequirePath(typechecker, require))
         return std::nullopt;
 
+    const AstExpr* require = FFlag::LuauNewRequireTrace ? &expr : expr.args.data[0];
+
     if (auto moduleInfo = typechecker.resolver->resolveModuleInfo(typechecker.currentModuleName, *require))
         return ExprResult<TypePackId>{arena.addTypePack({typechecker.checkRequire(scope, *moduleInfo, expr.location)})};
 

Analysis/src/EmbeddedBuiltinDefinitions.cpp

@@ -206,27 +206,6 @@ std::string getBuiltinDefinitionSource()
                 graphemes: (string, number?, number?) -> (() -> (number, number)),
             }
 
-            declare string: {
-                byte: (string, number?, number?) -> ...number,
-                char: (number, ...number) -> string,
-                find: (string, string, number?, boolean?) -> (number?, number?),
-                -- `string.format` has a magic function attached that will provide more type information for literal format strings.
-                format: <A...>(string, A...) -> string,
-                gmatch: (string, string) -> () -> (...string),
-                -- gsub is defined in C++ because we don't have syntax for describing a generic table.
-                len: (string) -> number,
-                lower: (string) -> string,
-                match: (string, string, number?) -> string?,
-                rep: (string, number) -> string,
-                reverse: (string) -> string,
-                sub: (string, number, number?) -> string,
-                upper: (string) -> string,
-                split: (string, string, string?) -> {string},
-                pack: <A...>(string, A...) -> string,
-                packsize: (string) -> number,
-                unpack: <R...>(string, string, number?) -> R...,
-            }
-
             -- Cannot use `typeof` here because it will produce a polytype when we expect a monotype.
             declare function unpack<V>(tab: {V}, i: number?, j: number?): ...V
         )";

Analysis/src/Error.cpp

@@ -7,9 +7,9 @@
 
 #include <stdexcept>
 
-LUAU_FASTFLAG(LuauFasterStringifier)
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
-static std::string wrongNumberOfArgsString(size_t expectedCount, size_t actualCount, bool isTypeArgs = false)
+static std::string wrongNumberOfArgsString_DEPRECATED(size_t expectedCount, size_t actualCount, bool isTypeArgs = false)
 {
     std::string s = "expects " + std::to_string(expectedCount) + " ";
 
@@ -41,6 +41,52 @@ static std::string wrongNumberOfArgsString(size_t expectedCount, size_t actualCo
     return s;
 }
 
+static std::string wrongNumberOfArgsString(size_t expectedCount, size_t actualCount, const char* argPrefix = nullptr, bool isVariadic = false)
+{
+    std::string s;
+
+    if (FFlag::LuauTypeAliasPacks)
+    {
+        s = "expects ";
+
+        if (isVariadic)
+            s += "at least ";
+
+        s += std::to_string(expectedCount) + " ";
+    }
+    else
+    {
+        s = "expects " + std::to_string(expectedCount) + " ";
+    }
+
+    if (argPrefix)
+        s += std::string(argPrefix) + " ";
+
+    s += "argument";
+    if (expectedCount != 1)
+        s += "s";
+
+    s += ", but ";
+
+    if (actualCount == 0)
+    {
+        s += "none";
+    }
+    else
+    {
+        if (actualCount < expectedCount)
+            s += "only ";
+
+        s += std::to_string(actualCount);
+    }
+
+    s += (actualCount == 1) ? " is" : " are";
+
+    s += " specified";
+
+    return s;
+}
+
 namespace Luau
 {
 
@@ -127,7 +173,10 @@ struct ErrorConverter
             return "Function only returns " + std::to_string(e.expected) + " value" + expectedS + ". " +
                    std::to_string(e.actual) + " are required here";
         case CountMismatch::Arg:
-            return "Argument count mismatch. Function " + wrongNumberOfArgsString(e.expected, e.actual);
+            if (FFlag::LuauTypeAliasPacks)
+                return "Argument count mismatch. Function " + wrongNumberOfArgsString(e.expected, e.actual);
+            else
+                return "Argument count mismatch. Function " + wrongNumberOfArgsString_DEPRECATED(e.expected, e.actual);
         }
 
         LUAU_ASSERT(!"Unknown context");
@@ -159,13 +208,16 @@ struct ErrorConverter
 
     std::string operator()(const Luau::UnknownRequire& e) const
     {
-        return "Unknown require: " + e.modulePath;
+        if (e.modulePath.empty())
+            return "Unknown require: unsupported path";
+        else
+            return "Unknown require: " + e.modulePath;
     }
 
     std::string operator()(const Luau::IncorrectGenericParameterCount& e) const
     {
         std::string name = e.name;
-        if (!e.typeFun.typeParams.empty())
+        if (!e.typeFun.typeParams.empty() || (FFlag::LuauTypeAliasPacks && !e.typeFun.typePackParams.empty()))
         {
             name += "<";
             bool first = true;
@@ -178,10 +230,37 @@ struct ErrorConverter
 
                 name += toString(t);
             }
+
+            if (FFlag::LuauTypeAliasPacks)
+            {
+                for (TypePackId t : e.typeFun.typePackParams)
+                {
+                    if (first)
+                        first = false;
+                    else
+                        name += ", ";
+
+                    name += toString(t);
+                }
+            }
+
             name += ">";
         }
 
-        return "Generic type '" + name + "' " + wrongNumberOfArgsString(e.typeFun.typeParams.size(), e.actualParameters, /*isTypeArgs*/ true);
+        if (FFlag::LuauTypeAliasPacks)
+        {
+            if (e.typeFun.typeParams.size() != e.actualParameters)
+                return "Generic type '" + name + "' " +
+                       wrongNumberOfArgsString(e.typeFun.typeParams.size(), e.actualParameters, "type", !e.typeFun.typePackParams.empty());
+
+            return "Generic type '" + name + "' " +
+                   wrongNumberOfArgsString(e.typeFun.typePackParams.size(), e.actualPackParameters, "type pack", /*isVariadic*/ false);
+        }
+        else
+        {
+            return "Generic type '" + name + "' " +
+                   wrongNumberOfArgsString_DEPRECATED(e.typeFun.typeParams.size(), e.actualParameters, /*isTypeArgs*/ true);
+        }
     }
 
     std::string operator()(const Luau::SyntaxError& e) const
@@ -470,9 +549,26 @@ bool IncorrectGenericParameterCount::operator==(const IncorrectGenericParameterC
     if (typeFun.typeParams.size() != rhs.typeFun.typeParams.size())
         return false;
 
+    if (FFlag::LuauTypeAliasPacks)
+    {
+        if (typeFun.typePackParams.size() != rhs.typeFun.typePackParams.size())
+            return false;
+    }
+
     for (size_t i = 0; i < typeFun.typeParams.size(); ++i)
+    {
         if (typeFun.typeParams[i] != rhs.typeFun.typeParams[i])
             return false;
+    }
+
+    if (FFlag::LuauTypeAliasPacks)
+    {
+        for (size_t i = 0; i < typeFun.typePackParams.size(); ++i)
+        {
+            if (typeFun.typePackParams[i] != rhs.typeFun.typePackParams[i])
+                return false;
+        }
+    }
 
     return true;
 }

Analysis/src/Frontend.cpp

@@ -1,9 +1,12 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Frontend.h"
 
+#include "Luau/Common.h"
 #include "Luau/Config.h"
 #include "Luau/FileResolver.h"
+#include "Luau/Scope.h"
 #include "Luau/StringUtils.h"
+#include "Luau/TimeTrace.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/Variant.h"
 #include "Luau/Common.h"
@@ -19,6 +22,7 @@ LUAU_FASTFLAGVARIABLE(LuauSecondTypecheckKnowsTheDataModel, false)
 LUAU_FASTFLAGVARIABLE(LuauResolveModuleNameWithoutACurrentModule, false)
 LUAU_FASTFLAG(LuauTraceRequireLookupChild)
 LUAU_FASTFLAGVARIABLE(LuauPersistDefinitionFileTypes, false)
+LUAU_FASTFLAG(LuauNewRequireTrace)
 
 namespace Luau
 {
@@ -69,6 +73,8 @@ static void generateDocumentationSymbols(TypeId ty, const std::string& rootName)
 
 LoadDefinitionFileResult loadDefinitionFile(TypeChecker& typeChecker, ScopePtr targetScope, std::string_view source, const std::string& packageName)
 {
+    LUAU_TIMETRACE_SCOPE("loadDefinitionFile", "Frontend");
+
     Luau::Allocator allocator;
     Luau::AstNameTable names(allocator);
 
@@ -350,6 +356,9 @@ FrontendModuleResolver::FrontendModuleResolver(Frontend* frontend)
 
 CheckResult Frontend::check(const ModuleName& name)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::check", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("name", name.c_str());
+
     CheckResult checkResult;
 
     auto it = sourceNodes.find(name);
@@ -479,6 +488,9 @@ CheckResult Frontend::check(const ModuleName& name)
 
 bool Frontend::parseGraph(std::vector<ModuleName>& buildQueue, CheckResult& checkResult, const ModuleName& root)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::parseGraph", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("root", root.c_str());
+
     // https://en.wikipedia.org/wiki/Topological_sorting#Depth-first_search
     enum Mark
     {
@@ -597,6 +609,9 @@ ScopePtr Frontend::getModuleEnvironment(const SourceModule& module, const Config
 
 LintResult Frontend::lint(const ModuleName& name, std::optional<Luau::LintOptions> enabledLintWarnings)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::lint", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("name", name.c_str());
+
     CheckResult checkResult;
     auto [_sourceNode, sourceModule] = getSourceNode(checkResult, name);
 
@@ -608,6 +623,8 @@ LintResult Frontend::lint(const ModuleName& name, std::optional<Luau::LintOption
 
 std::pair<SourceModule, LintResult> Frontend::lintFragment(std::string_view source, std::optional<Luau::LintOptions> enabledLintWarnings)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::lintFragment", "Frontend");
+
     const Config& config = configResolver->getConfig("");
 
     SourceModule sourceModule = parse(ModuleName{}, source, config.parseOptions);
@@ -627,6 +644,9 @@ std::pair<SourceModule, LintResult> Frontend::lintFragment(std::string_view sour
 
 CheckResult Frontend::check(const SourceModule& module)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::check", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("module", module.name.c_str());
+
     const Config& config = configResolver->getConfig(module.name);
 
     Mode mode = module.mode.value_or(config.mode);
@@ -648,6 +668,9 @@ CheckResult Frontend::check(const SourceModule& module)
 
 LintResult Frontend::lint(const SourceModule& module, std::optional<Luau::LintOptions> enabledLintWarnings)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::lint", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("module", module.name.c_str());
+
     const Config& config = configResolver->getConfig(module.name);
 
     LintOptions options = enabledLintWarnings.value_or(config.enabledLint);
@@ -746,6 +769,9 @@ const SourceModule* Frontend::getSourceModule(const ModuleName& moduleName) cons
 // Read AST into sourceModules if necessary.  Trace require()s.  Report parse errors.
 std::pair<SourceNode*, SourceModule*> Frontend::getSourceNode(CheckResult& checkResult, const ModuleName& name)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::getSourceNode", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("name", name.c_str());
+
     auto it = sourceNodes.find(name);
     if (it != sourceNodes.end() && !it->second.dirty)
     {
@@ -815,6 +841,9 @@ std::pair<SourceNode*, SourceModule*> Frontend::getSourceNode(CheckResult& check
  */
 SourceModule Frontend::parse(const ModuleName& name, std::string_view src, const ParseOptions& parseOptions)
 {
+    LUAU_TIMETRACE_SCOPE("Frontend::parse", "Frontend");
+    LUAU_TIMETRACE_ARGUMENT("name", name.c_str());
+
     SourceModule sourceModule;
 
     double timestamp = getTimestamp();
@@ -864,20 +893,11 @@ std::optional<ModuleInfo> FrontendModuleResolver::resolveModuleInfo(const Module
 
     const auto& exprs = it->second.exprs;
 
-    const ModuleName* relativeName = exprs.find(&pathExpr);
+    const ModuleInfo* info = exprs.find(&pathExpr);
-    if (!relativeName || relativeName->empty())
+    if (!info || (!FFlag::LuauNewRequireTrace && info->name.empty()))
         return std::nullopt;
 
-    if (FFlag::LuauTraceRequireLookupChild)
+    return *info;
-    {
-        const bool* optional = it->second.optional.find(&pathExpr);
-
-        return {{*relativeName, optional ? *optional : false}};
-    }
-    else
-    {
-        return {{*relativeName, false}};
-    }
 }
 
 const ModulePtr FrontendModuleResolver::getModule(const ModuleName& moduleName) const
@@ -891,12 +911,15 @@ const ModulePtr FrontendModuleResolver::getModule(const ModuleName& moduleName)
 
 bool FrontendModuleResolver::moduleExists(const ModuleName& moduleName) const
 {
-    return frontend->fileResolver->moduleExists(moduleName);
+    if (FFlag::LuauNewRequireTrace)
+        return frontend->sourceNodes.count(moduleName) != 0;
+    else
+        return frontend->fileResolver->moduleExists(moduleName);
 }
 
 std::string FrontendModuleResolver::getHumanReadableModuleName(const ModuleName& moduleName) const
 {
-    return frontend->fileResolver->getHumanReadableModuleName_(moduleName).value_or(moduleName);
+    return frontend->fileResolver->getHumanReadableModuleName(moduleName);
 }
 
 ScopePtr Frontend::addEnvironment(const std::string& environmentName)

Analysis/src/IostreamHelpers.cpp

@@ -2,6 +2,8 @@
 #include "Luau/IostreamHelpers.h"
 #include "Luau/ToString.h"
 
+LUAU_FASTFLAG(LuauTypeAliasPacks)
+
 namespace Luau
 {
 
@@ -92,7 +94,7 @@ std::ostream& operator<<(std::ostream& stream, const IncorrectGenericParameterCo
 {
     stream << "IncorrectGenericParameterCount { name = " << error.name;
 
-    if (!error.typeFun.typeParams.empty())
+    if (!error.typeFun.typeParams.empty() || (FFlag::LuauTypeAliasPacks && !error.typeFun.typePackParams.empty()))
     {
         stream << "<";
         bool first = true;
@@ -105,6 +107,20 @@ std::ostream& operator<<(std::ostream& stream, const IncorrectGenericParameterCo
 
             stream << toString(t);
         }
+
+        if (FFlag::LuauTypeAliasPacks)
+        {
+            for (TypePackId t : error.typeFun.typePackParams)
+            {
+                if (first)
+                    first = false;
+                else
+                    stream << ", ";
+
+                stream << toString(t);
+            }
+        }
+
         stream << ">";
     }
 

Analysis/src/JsonEncoder.cpp

@@ -3,6 +3,9 @@
 
 #include "Luau/Ast.h"
 #include "Luau/StringUtils.h"
+#include "Luau/Common.h"
+
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
 namespace Luau
 {
@@ -612,6 +615,12 @@ struct AstJsonEncoder : public AstVisitor
         writeNode(node, "AstStatTypeAlias", [&]() {
             PROP(name);
             PROP(generics);
+
+            if (FFlag::LuauTypeAliasPacks)
+            {
+                PROP(genericPacks);
+            }
+
             PROP(type);
             PROP(exported);
         });
@@ -664,13 +673,21 @@ struct AstJsonEncoder : public AstVisitor
         });
     }
 
+    void write(struct AstTypeOrPack node)
+    {
+        if (node.type)
+            write(node.type);
+        else
+            write(node.typePack);
+    }
+
     void write(class AstTypeReference* node)
     {
         writeNode(node, "AstTypeReference", [&]() {
             if (node->hasPrefix)
                 PROP(prefix);
             PROP(name);
-            PROP(generics);
+            PROP(parameters);
         });
     }
 
@@ -734,6 +751,13 @@ struct AstJsonEncoder : public AstVisitor
         });
     }
 
+    void write(class AstTypePackExplicit* node)
+    {
+        writeNode(node, "AstTypePackExplicit", [&]() {
+            PROP(typeList);
+        });
+    }
+
     void write(class AstTypePackVariadic* node)
     {
         writeNode(node, "AstTypePackVariadic", [&]() {
@@ -1018,6 +1042,12 @@ struct AstJsonEncoder : public AstVisitor
         return false;
     }
 
+    bool visit(class AstTypePackExplicit* node) override
+    {
+        write(node);
+        return false;
+    }
+
     bool visit(class AstTypePackVariadic* node) override
     {
         write(node);

Analysis/src/Linter.cpp

@@ -3,6 +3,7 @@
 
 #include "Luau/AstQuery.h"
 #include "Luau/Module.h"
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/StringUtils.h"
 #include "Luau/Common.h"
@@ -12,6 +13,7 @@
 #include <limits.h>
 
 LUAU_FASTFLAGVARIABLE(LuauLinterUnknownTypeVectorAware, false)
+LUAU_FASTFLAGVARIABLE(LuauLinterTableMoveZero, false)
 
 namespace Luau
 {
@@ -85,10 +87,10 @@ struct LintContext
             return std::nullopt;
 
         auto it = module->astTypes.find(expr);
-        if (it == module->astTypes.end())
+        if (!it)
             return std::nullopt;
 
-        return it->second;
+        return *it;
     }
 };
 
@@ -2144,6 +2146,19 @@ private:
                     "wrap it in parentheses to silence");
         }
 
+        if (FFlag::LuauLinterTableMoveZero && func->index == "move" && node->args.size >= 4)
+        {
+            // table.move(t, 0, _, _)
+            if (isConstant(args[1], 0.0))
+                emitWarning(*context, LintWarning::Code_TableOperations, args[1]->location,
+                    "table.move uses index 0 but arrays are 1-based; did you mean 1 instead?");
+
+            // table.move(t, _, _, 0)
+            else if (isConstant(args[3], 0.0))
+                emitWarning(*context, LintWarning::Code_TableOperations, args[3]->location,
+                    "table.move uses index 0 but arrays are 1-based; did you mean 1 instead?");
+        }
+
         return true;
     }
 

Analysis/src/Module.cpp

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Module.h"
 
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypePack.h"
 #include "Luau/TypeVar.h"
@@ -13,6 +14,7 @@ LUAU_FASTFLAGVARIABLE(DebugLuauFreezeArena, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauTrackOwningArena, false)
 LUAU_FASTFLAG(LuauSecondTypecheckKnowsTheDataModel)
 LUAU_FASTFLAG(LuauCaptureBrokenCommentSpans)
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
 namespace Luau
 {
@@ -188,7 +190,7 @@ struct TypePackCloner
     template<typename T>
     void defaultClone(const T& t)
     {
-        TypePackId cloned = dest.typePacks.allocate(t);
+        TypePackId cloned = dest.addTypePack(TypePackVar{t});
         seenTypePacks[typePackId] = cloned;
     }
 
@@ -197,7 +199,7 @@ struct TypePackCloner
         if (encounteredFreeType)
             *encounteredFreeType = true;
 
-        seenTypePacks[typePackId] = dest.typePacks.allocate(TypePackVar{Unifiable::Error{}});
+        seenTypePacks[typePackId] = dest.addTypePack(TypePackVar{Unifiable::Error{}});
     }
 
     void operator()(const Unifiable::Generic& t)
@@ -219,13 +221,13 @@ struct TypePackCloner
 
     void operator()(const VariadicTypePack& t)
     {
-        TypePackId cloned = dest.typePacks.allocate(VariadicTypePack{clone(t.ty, dest, seenTypes, seenTypePacks, encounteredFreeType)});
+        TypePackId cloned = dest.addTypePack(TypePackVar{VariadicTypePack{clone(t.ty, dest, seenTypes, seenTypePacks, encounteredFreeType)}});
         seenTypePacks[typePackId] = cloned;
     }
 
     void operator()(const TypePack& t)
     {
-        TypePackId cloned = dest.typePacks.allocate(TypePack{});
+        TypePackId cloned = dest.addTypePack(TypePack{});
         TypePack* destTp = getMutable<TypePack>(cloned);
         LUAU_ASSERT(destTp != nullptr);
         seenTypePacks[typePackId] = cloned;
@@ -241,7 +243,7 @@ struct TypePackCloner
 template<typename T>
 void TypeCloner::defaultClone(const T& t)
 {
-    TypeId cloned = dest.typeVars.allocate(t);
+    TypeId cloned = dest.addType(t);
     seenTypes[typeId] = cloned;
 }
 
@@ -250,7 +252,7 @@ void TypeCloner::operator()(const Unifiable::Free& t)
     if (encounteredFreeType)
         *encounteredFreeType = true;
 
-    seenTypes[typeId] = dest.typeVars.allocate(ErrorTypeVar{});
+    seenTypes[typeId] = dest.addType(ErrorTypeVar{});
 }
 
 void TypeCloner::operator()(const Unifiable::Generic& t)
@@ -275,7 +277,7 @@ void TypeCloner::operator()(const PrimitiveTypeVar& t)
 
 void TypeCloner::operator()(const FunctionTypeVar& t)
 {
-    TypeId result = dest.typeVars.allocate(FunctionTypeVar{TypeLevel{0, 0}, {}, {}, nullptr, nullptr, t.definition, t.hasSelf});
+    TypeId result = dest.addType(FunctionTypeVar{TypeLevel{0, 0}, {}, {}, nullptr, nullptr, t.definition, t.hasSelf});
     FunctionTypeVar* ftv = getMutable<FunctionTypeVar>(result);
     LUAU_ASSERT(ftv != nullptr);
 
@@ -297,7 +299,7 @@ void TypeCloner::operator()(const FunctionTypeVar& t)
 
 void TypeCloner::operator()(const TableTypeVar& t)
 {
-    TypeId result = dest.typeVars.allocate(TableTypeVar{});
+    TypeId result = dest.addType(TableTypeVar{});
     TableTypeVar* ttv = getMutable<TableTypeVar>(result);
     LUAU_ASSERT(ttv != nullptr);
 
@@ -323,7 +325,13 @@ void TypeCloner::operator()(const TableTypeVar& t)
         ttv->boundTo = clone(*t.boundTo, dest, seenTypes, seenTypePacks, encounteredFreeType);
 
     for (TypeId& arg : ttv->instantiatedTypeParams)
-        arg = (clone(arg, dest, seenTypes, seenTypePacks, encounteredFreeType));
+        arg = clone(arg, dest, seenTypes, seenTypePacks, encounteredFreeType);
+
+    if (FFlag::LuauTypeAliasPacks)
+    {
+        for (TypePackId& arg : ttv->instantiatedTypePackParams)
+            arg = clone(arg, dest, seenTypes, seenTypePacks, encounteredFreeType);
+    }
 
     if (ttv->state == TableState::Free)
     {
@@ -343,7 +351,7 @@ void TypeCloner::operator()(const TableTypeVar& t)
 
 void TypeCloner::operator()(const MetatableTypeVar& t)
 {
-    TypeId result = dest.typeVars.allocate(MetatableTypeVar{});
+    TypeId result = dest.addType(MetatableTypeVar{});
     MetatableTypeVar* mtv = getMutable<MetatableTypeVar>(result);
     seenTypes[typeId] = result;
 
@@ -353,7 +361,7 @@ void TypeCloner::operator()(const MetatableTypeVar& t)
 
 void TypeCloner::operator()(const ClassTypeVar& t)
 {
-    TypeId result = dest.typeVars.allocate(ClassTypeVar{t.name, {}, std::nullopt, std::nullopt, t.tags, t.userData});
+    TypeId result = dest.addType(ClassTypeVar{t.name, {}, std::nullopt, std::nullopt, t.tags, t.userData});
     ClassTypeVar* ctv = getMutable<ClassTypeVar>(result);
 
     seenTypes[typeId] = result;
@@ -378,7 +386,7 @@ void TypeCloner::operator()(const AnyTypeVar& t)
 
 void TypeCloner::operator()(const UnionTypeVar& t)
 {
-    TypeId result = dest.typeVars.allocate(UnionTypeVar{});
+    TypeId result = dest.addType(UnionTypeVar{});
     seenTypes[typeId] = result;
 
     UnionTypeVar* option = getMutable<UnionTypeVar>(result);
@@ -390,7 +398,7 @@ void TypeCloner::operator()(const UnionTypeVar& t)
 
 void TypeCloner::operator()(const IntersectionTypeVar& t)
 {
-    TypeId result = dest.typeVars.allocate(IntersectionTypeVar{});
+    TypeId result = dest.addType(IntersectionTypeVar{});
     seenTypes[typeId] = result;
 
     IntersectionTypeVar* option = getMutable<IntersectionTypeVar>(result);
@@ -451,8 +459,14 @@ TypeId clone(TypeId typeId, TypeArena& dest, SeenTypes& seenTypes, SeenTypePacks
 TypeFun clone(const TypeFun& typeFun, TypeArena& dest, SeenTypes& seenTypes, SeenTypePacks& seenTypePacks, bool* encounteredFreeType)
 {
     TypeFun result;
-    for (TypeId param : typeFun.typeParams)
+    for (TypeId ty : typeFun.typeParams)
-        result.typeParams.push_back(clone(param, dest, seenTypes, seenTypePacks, encounteredFreeType));
+        result.typeParams.push_back(clone(ty, dest, seenTypes, seenTypePacks, encounteredFreeType));
+
+    if (FFlag::LuauTypeAliasPacks)
+    {
+        for (TypePackId tp : typeFun.typePackParams)
+            result.typePackParams.push_back(clone(tp, dest, seenTypes, seenTypePacks, encounteredFreeType));
+    }
 
     result.type = clone(typeFun.type, dest, seenTypes, seenTypePacks, encounteredFreeType);
 

Analysis/src/RequireTracer.cpp

@@ -5,6 +5,7 @@
 #include "Luau/Module.h"
 
 LUAU_FASTFLAGVARIABLE(LuauTraceRequireLookupChild, false)
+LUAU_FASTFLAGVARIABLE(LuauNewRequireTrace, false)
 
 namespace Luau
 {
@@ -12,17 +13,18 @@ namespace Luau
 namespace
 {
 
-struct RequireTracer : AstVisitor
+struct RequireTracerOld : AstVisitor
 {
-    explicit RequireTracer(FileResolver* fileResolver, ModuleName currentModuleName)
+    explicit RequireTracerOld(FileResolver* fileResolver, const ModuleName& currentModuleName)
         : fileResolver(fileResolver)
-        , currentModuleName(std::move(currentModuleName))
+        , currentModuleName(currentModuleName)
     {
+        LUAU_ASSERT(!FFlag::LuauNewRequireTrace);
     }
 
     FileResolver* const fileResolver;
     ModuleName currentModuleName;
-    DenseHashMap<AstLocal*, ModuleName> locals{0};
+    DenseHashMap<AstLocal*, ModuleName> locals{nullptr};
     RequireTraceResult result;
 
     std::optional<ModuleName> fromAstFragment(AstExpr* expr)
@@ -50,9 +52,9 @@ struct RequireTracer : AstVisitor
                 AstExpr* expr = stat->values.data[i];
                 expr->visit(this);
 
-                const ModuleName* name = result.exprs.find(expr);
+                const ModuleInfo* info = result.exprs.find(expr);
-                if (name)
+                if (info)
-                    locals[local] = *name;
+                    locals[local] = info->name;
             }
         }
 
@@ -63,7 +65,7 @@ struct RequireTracer : AstVisitor
     {
         std::optional<ModuleName> name = fromAstFragment(global);
         if (name)
-            result.exprs[global] = *name;
+            result.exprs[global] = {*name};
 
         return false;
     }
@@ -72,7 +74,7 @@ struct RequireTracer : AstVisitor
     {
         const ModuleName* name = locals.find(local->local);
         if (name)
-            result.exprs[local] = *name;
+            result.exprs[local] = {*name};
 
         return false;
     }
@@ -81,16 +83,16 @@ struct RequireTracer : AstVisitor
     {
         indexName->expr->visit(this);
 
-        const ModuleName* name = result.exprs.find(indexName->expr);
+        const ModuleInfo* info = result.exprs.find(indexName->expr);
-        if (name)
+        if (info)
         {
             if (indexName->index == "parent" || indexName->index == "Parent")
             {
-                if (auto parent = fileResolver->getParentModuleName(*name))
+                if (auto parent = fileResolver->getParentModuleName(info->name))
-                    result.exprs[indexName] = *parent;
+                    result.exprs[indexName] = {*parent};
             }
             else
-                result.exprs[indexName] = fileResolver->concat(*name, indexName->index.value);
+                result.exprs[indexName] = {fileResolver->concat(info->name, indexName->index.value)};
         }
 
         return false;
@@ -100,11 +102,11 @@ struct RequireTracer : AstVisitor
     {
         indexExpr->expr->visit(this);
 
-        const ModuleName* name = result.exprs.find(indexExpr->expr);
+        const ModuleInfo* info = result.exprs.find(indexExpr->expr);
         const AstExprConstantString* str = indexExpr->index->as<AstExprConstantString>();
-        if (name && str)
+        if (info && str)
         {
-            result.exprs[indexExpr] = fileResolver->concat(*name, std::string_view(str->value.data, str->value.size));
+            result.exprs[indexExpr] = {fileResolver->concat(info->name, std::string_view(str->value.data, str->value.size))};
         }
 
         indexExpr->index->visit(this);
@@ -129,8 +131,8 @@ struct RequireTracer : AstVisitor
         AstExprGlobal* globalName = call->func->as<AstExprGlobal>();
         if (globalName && globalName->name == "require" && call->args.size >= 1)
         {
-            if (const ModuleName* moduleName = result.exprs.find(call->args.data[0]))
+            if (const ModuleInfo* moduleInfo = result.exprs.find(call->args.data[0]))
-                result.requires.push_back({*moduleName, call->location});
+                result.requires.push_back({moduleInfo->name, call->location});
 
             return false;
         }
@@ -143,8 +145,8 @@ struct RequireTracer : AstVisitor
 
         if (FFlag::LuauTraceRequireLookupChild && !rootName)
         {
-            if (const ModuleName* moduleName = result.exprs.find(indexName->expr))
+            if (const ModuleInfo* moduleInfo = result.exprs.find(indexName->expr))
-                rootName = *moduleName;
+                rootName = moduleInfo->name;
         }
 
         if (!rootName)
@@ -167,24 +169,183 @@ struct RequireTracer : AstVisitor
         if (v.end() != std::find(v.begin(), v.end(), '/'))
             return false;
 
-        result.exprs[call] = fileResolver->concat(*rootName, v);
+        result.exprs[call] = {fileResolver->concat(*rootName, v)};
 
         // 'WaitForChild' can be used on modules that are not available at the typecheck time, but will be available at runtime
         // If we fail to find such module, we will not report an UnknownRequire error
         if (FFlag::LuauTraceRequireLookupChild && indexName->index == "WaitForChild")
-            result.optional[call] = true;
+            result.exprs[call].optional = true;
 
         return false;
     }
 };
 
+struct RequireTracer : AstVisitor
+{
+    RequireTracer(RequireTraceResult& result, FileResolver * fileResolver, const ModuleName& currentModuleName)
+        : result(result)
+        , fileResolver(fileResolver)
+        , currentModuleName(currentModuleName)
+        , locals(nullptr)
+    {
+        LUAU_ASSERT(FFlag::LuauNewRequireTrace);
+    }
+
+    bool visit(AstExprTypeAssertion* expr) override
+    {
+        // suppress `require() :: any`
+        return false;
+    }
+
+    bool visit(AstExprCall* expr) override
+    {
+        AstExprGlobal* global = expr->func->as<AstExprGlobal>();
+
+        if (global && global->name == "require" && expr->args.size >= 1)
+            requires.push_back(expr);
+
+        return true;
+    }
+
+    bool visit(AstStatLocal* stat) override
+    {
+        for (size_t i = 0; i < stat->vars.size && i < stat->values.size; ++i)
+        {
+            AstLocal* local = stat->vars.data[i];
+            AstExpr* expr = stat->values.data[i];
+
+            // track initializing expression to be able to trace modules through locals
+            locals[local] = expr;
+        }
+
+        return true;
+    }
+
+    bool visit(AstStatAssign* stat) override
+    {
+        for (size_t i = 0; i < stat->vars.size; ++i)
+        {
+            // locals that are assigned don't have a known expression
+            if (AstExprLocal* expr = stat->vars.data[i]->as<AstExprLocal>())
+                locals[expr->local] = nullptr;
+        }
+
+        return true;
+    }
+
+    bool visit(AstType* node) override
+    {
+        // allow resolving require inside `typeof` annotations
+        return true;
+    }
+
+    AstExpr* getDependent(AstExpr* node)
+    {
+        if (AstExprLocal* expr = node->as<AstExprLocal>())
+            return locals[expr->local];
+        else if (AstExprIndexName* expr = node->as<AstExprIndexName>())
+            return expr->expr;
+        else if (AstExprIndexExpr* expr = node->as<AstExprIndexExpr>())
+            return expr->expr;
+        else if (AstExprCall* expr = node->as<AstExprCall>(); expr && expr->self)
+            return expr->func->as<AstExprIndexName>()->expr;
+        else
+            return nullptr;
+    }
+
+    void process()
+    {
+        ModuleInfo moduleContext{currentModuleName};
+
+        // seed worklist with require arguments
+        work.reserve(requires.size());
+
+        for (AstExprCall* require: requires)
+            work.push_back(require->args.data[0]);
+
+        // push all dependent expressions to the work stack; note that the vector is modified during traversal
+        for (size_t i = 0; i < work.size(); ++i)
+            if (AstExpr* dep = getDependent(work[i]))
+                work.push_back(dep);
+
+        // resolve all expressions to a module info
+        for (size_t i = work.size(); i > 0; --i)
+        {
+            AstExpr* expr = work[i - 1];
+
+            // when multiple expressions depend on the same one we push it to work queue multiple times
+            if (result.exprs.contains(expr))
+                continue;
+
+            std::optional<ModuleInfo> info;
+
+            if (AstExpr* dep = getDependent(expr))
+            {
+                const ModuleInfo* context = result.exprs.find(dep);
+
+                // locals just inherit their dependent context, no resolution required
+                if (expr->is<AstExprLocal>())
+                    info = context ? std::optional<ModuleInfo>(*context) : std::nullopt;
+                else
+                    info = fileResolver->resolveModule(context, expr);
+            }
+            else
+            {
+                info = fileResolver->resolveModule(&moduleContext, expr);
+            }
+
+            if (info)
+                result.exprs[expr] = std::move(*info);
+        }
+
+        // resolve all requires according to their argument
+        result.requires.reserve(requires.size());
+
+        for (AstExprCall* require : requires)
+        {
+            AstExpr* arg = require->args.data[0];
+
+            if (const ModuleInfo* info = result.exprs.find(arg))
+            {
+                result.requires.push_back({info->name, require->location});
+
+                ModuleInfo infoCopy = *info; // copy *info out since next line invalidates info!
+                result.exprs[require] = std::move(infoCopy);
+            }
+            else
+            {
+                result.exprs[require] = {}; // mark require as unresolved
+            }
+        }
+    }
+
+    RequireTraceResult& result;
+    FileResolver* fileResolver;
+    ModuleName currentModuleName;
+
+    DenseHashMap<AstLocal*, AstExpr*> locals;
+    std::vector<AstExpr*> work;
+    std::vector<AstExprCall*> requires;
+};
+
 } // anonymous namespace
 
-RequireTraceResult traceRequires(FileResolver* fileResolver, AstStatBlock* root, ModuleName currentModuleName)
+RequireTraceResult traceRequires(FileResolver* fileResolver, AstStatBlock* root, const ModuleName& currentModuleName)
 {
-    RequireTracer tracer{fileResolver, std::move(currentModuleName)};
+    if (FFlag::LuauNewRequireTrace)
-    root->visit(&tracer);
+    {
-    return tracer.result;
+        RequireTraceResult result;
+        RequireTracer tracer{result, fileResolver, currentModuleName};
+        root->visit(&tracer);
+        tracer.process();
+        return result;
+    }
+    else
+    {
+        RequireTracerOld tracer{fileResolver, currentModuleName};
+        root->visit(&tracer);
+        return tracer.result;
+    }
 }
 
 } // namespace Luau

Analysis/src/Scope.cpp

@@ -0,0 +1,123 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#include "Luau/Scope.h"
+
+namespace Luau
+{
+
+Scope::Scope(TypePackId returnType)
+    : parent(nullptr)
+    , returnType(returnType)
+    , level(TypeLevel())
+{
+}
+
+Scope::Scope(const ScopePtr& parent, int subLevel)
+    : parent(parent)
+    , returnType(parent->returnType)
+    , level(parent->level.incr())
+{
+    level.subLevel = subLevel;
+}
+
+std::optional<TypeId> Scope::lookup(const Symbol& name)
+{
+    Scope* scope = this;
+
+    while (scope)
+    {
+        auto it = scope->bindings.find(name);
+        if (it != scope->bindings.end())
+            return it->second.typeId;
+
+        scope = scope->parent.get();
+    }
+
+    return std::nullopt;
+}
+
+std::optional<TypeFun> Scope::lookupType(const Name& name)
+{
+    const Scope* scope = this;
+    while (true)
+    {
+        auto it = scope->exportedTypeBindings.find(name);
+        if (it != scope->exportedTypeBindings.end())
+            return it->second;
+
+        it = scope->privateTypeBindings.find(name);
+        if (it != scope->privateTypeBindings.end())
+            return it->second;
+
+        if (scope->parent)
+            scope = scope->parent.get();
+        else
+            return std::nullopt;
+    }
+}
+
+std::optional<TypeFun> Scope::lookupImportedType(const Name& moduleAlias, const Name& name)
+{
+    const Scope* scope = this;
+    while (scope)
+    {
+        auto it = scope->importedTypeBindings.find(moduleAlias);
+        if (it == scope->importedTypeBindings.end())
+        {
+            scope = scope->parent.get();
+            continue;
+        }
+
+        auto it2 = it->second.find(name);
+        if (it2 == it->second.end())
+        {
+            scope = scope->parent.get();
+            continue;
+        }
+
+        return it2->second;
+    }
+
+    return std::nullopt;
+}
+
+std::optional<TypePackId> Scope::lookupPack(const Name& name)
+{
+    const Scope* scope = this;
+    while (true)
+    {
+        auto it = scope->privateTypePackBindings.find(name);
+        if (it != scope->privateTypePackBindings.end())
+            return it->second;
+
+        if (scope->parent)
+            scope = scope->parent.get();
+        else
+            return std::nullopt;
+    }
+}
+
+std::optional<Binding> Scope::linearSearchForBinding(const std::string& name, bool traverseScopeChain)
+{
+    Scope* scope = this;
+
+    while (scope)
+    {
+        for (const auto& [n, binding] : scope->bindings)
+        {
+            if (n.local && n.local->name == name.c_str())
+                return binding;
+            else if (n.global.value && n.global == name.c_str())
+                return binding;
+        }
+
+        scope = scope->parent.get();
+
+        if (!traverseScopeChain)
+            break;
+    }
+
+    return std::nullopt;
+}
+
+} // namespace Luau

Analysis/src/Substitution.cpp

@@ -6,9 +6,11 @@
 #include <algorithm>
 #include <stdexcept>
 
-LUAU_FASTINTVARIABLE(LuauTarjanChildLimit, 0)
+LUAU_FASTINTVARIABLE(LuauTarjanChildLimit, 1000)
+LUAU_FASTFLAGVARIABLE(LuauSubstitutionDontReplaceIgnoredTypes, false)
 LUAU_FASTFLAG(LuauSecondTypecheckKnowsTheDataModel)
 LUAU_FASTFLAG(LuauRankNTypes)
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
 namespace Luau
 {
@@ -35,8 +37,15 @@ void Tarjan::visitChildren(TypeId ty, int index)
             visitChild(ttv->indexer->indexType);
             visitChild(ttv->indexer->indexResultType);
         }
+
         for (TypeId itp : ttv->instantiatedTypeParams)
             visitChild(itp);
+
+        if (FFlag::LuauTypeAliasPacks)
+        {
+            for (TypePackId itp : ttv->instantiatedTypePackParams)
+                visitChild(itp);
+        }
     }
     else if (const MetatableTypeVar* mtv = get<MetatableTypeVar>(ty))
     {
@@ -332,9 +341,11 @@ std::optional<TypeId> Substitution::substitute(TypeId ty)
         return std::nullopt;
 
     for (auto [oldTy, newTy] : newTypes)
-        replaceChildren(newTy);
+        if (!FFlag::LuauSubstitutionDontReplaceIgnoredTypes || !ignoreChildren(oldTy))
+            replaceChildren(newTy);
     for (auto [oldTp, newTp] : newPacks)
-        replaceChildren(newTp);
+        if (!FFlag::LuauSubstitutionDontReplaceIgnoredTypes || !ignoreChildren(oldTp))
+            replaceChildren(newTp);
     TypeId newTy = replace(ty);
     return newTy;
 }
@@ -350,9 +361,11 @@ std::optional<TypePackId> Substitution::substitute(TypePackId tp)
         return std::nullopt;
 
     for (auto [oldTy, newTy] : newTypes)
-        replaceChildren(newTy);
+        if (!FFlag::LuauSubstitutionDontReplaceIgnoredTypes || !ignoreChildren(oldTy))
+            replaceChildren(newTy);
     for (auto [oldTp, newTp] : newPacks)
-        replaceChildren(newTp);
+        if (!FFlag::LuauSubstitutionDontReplaceIgnoredTypes || !ignoreChildren(oldTp))
+            replaceChildren(newTp);
     TypePackId newTp = replace(tp);
     return newTp;
 }
@@ -382,6 +395,10 @@ TypeId Substitution::clone(TypeId ty)
         clone.name = ttv->name;
         clone.syntheticName = ttv->syntheticName;
         clone.instantiatedTypeParams = ttv->instantiatedTypeParams;
+
+        if (FFlag::LuauTypeAliasPacks)
+            clone.instantiatedTypePackParams = ttv->instantiatedTypePackParams;
+
         if (FFlag::LuauSecondTypecheckKnowsTheDataModel)
             clone.tags = ttv->tags;
         result = addType(std::move(clone));
@@ -487,8 +504,15 @@ void Substitution::replaceChildren(TypeId ty)
             ttv->indexer->indexType = replace(ttv->indexer->indexType);
             ttv->indexer->indexResultType = replace(ttv->indexer->indexResultType);
         }
+
         for (TypeId& itp : ttv->instantiatedTypeParams)
             itp = replace(itp);
+
+        if (FFlag::LuauTypeAliasPacks)
+        {
+            for (TypePackId& itp : ttv->instantiatedTypePackParams)
+                itp = replace(itp);
+        }
     }
     else if (MetatableTypeVar* mtv = getMutable<MetatableTypeVar>(ty))
     {

Analysis/src/ToString.cpp

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/ToString.h"
 
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypePack.h"
 #include "Luau/TypeVar.h"
@@ -9,10 +10,10 @@
 #include <algorithm>
 #include <stdexcept>
 
-LUAU_FASTFLAG(LuauToStringFollowsBoundTo)
 LUAU_FASTFLAG(LuauExtraNilRecovery)
 LUAU_FASTFLAG(LuauOccursCheckOkWithRecursiveFunctions)
 LUAU_FASTFLAGVARIABLE(LuauInstantiatedTypeParamRecursion, false)
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
 namespace Luau
 {
@@ -59,6 +60,13 @@ struct FindCyclicTypes
         {
             for (TypeId itp : ttv.instantiatedTypeParams)
                 visitTypeVar(itp, *this, seen);
+
+            if (FFlag::LuauTypeAliasPacks)
+            {
+                for (TypePackId itp : ttv.instantiatedTypePackParams)
+                    visitTypeVar(itp, *this, seen);
+            }
+
             return exhaustive;
         }
 
@@ -258,23 +266,60 @@ struct TypeVarStringifier
     void stringify(TypePackId tp);
     void stringify(TypePackId tpid, const std::vector<std::optional<FunctionArgument>>& names);
 
-    void stringify(const std::vector<TypeId>& types)
+    void stringify(const std::vector<TypeId>& types, const std::vector<TypePackId>& typePacks)
     {
-        if (types.size() == 0)
+        if (types.size() == 0 && (!FFlag::LuauTypeAliasPacks || typePacks.size() == 0))
             return;
 
-        if (types.size())
+        if (types.size() || (FFlag::LuauTypeAliasPacks && typePacks.size()))
             state.emit("<");
 
-        for (size_t i = 0; i < types.size(); ++i)
+        if (FFlag::LuauTypeAliasPacks)
         {
-            if (i > 0)
+            bool first = true;
-                state.emit(", ");
 
-            stringify(types[i]);
+            for (TypeId ty : types)
+            {
+                if (!first)
+                    state.emit(", ");
+                first = false;
+
+                stringify(ty);
+            }
+
+            bool singleTp = typePacks.size() == 1;
+
+            for (TypePackId tp : typePacks)
+            {
+                if (isEmpty(tp) && singleTp)
+                    continue;
+
+                if (!first)
+                    state.emit(", ");
+                else
+                    first = false;
+
+                if (!singleTp)
+                    state.emit("(");
+
+                stringify(tp);
+
+                if (!singleTp)
+                    state.emit(")");
+            }
+        }
+        else
+        {
+            for (size_t i = 0; i < types.size(); ++i)
+            {
+                if (i > 0)
+                    state.emit(", ");
+
+                stringify(types[i]);
+            }
         }
 
-        if (types.size())
+        if (types.size() || (FFlag::LuauTypeAliasPacks && typePacks.size()))
             state.emit(">");
     }
 
@@ -388,7 +433,7 @@ struct TypeVarStringifier
 
     void operator()(TypeId, const TableTypeVar& ttv)
     {
-        if (FFlag::LuauToStringFollowsBoundTo && ttv.boundTo)
+        if (ttv.boundTo)
             return stringify(*ttv.boundTo);
 
         if (!state.exhaustive)
@@ -411,14 +456,14 @@ struct TypeVarStringifier
                 }
 
                 state.emit(*ttv.name);
-                stringify(ttv.instantiatedTypeParams);
+                stringify(ttv.instantiatedTypeParams, ttv.instantiatedTypePackParams);
                 return;
             }
             if (ttv.syntheticName)
             {
                 state.result.invalid = true;
                 state.emit(*ttv.syntheticName);
-                stringify(ttv.instantiatedTypeParams);
+                stringify(ttv.instantiatedTypeParams, ttv.instantiatedTypePackParams);
                 return;
             }
         }
@@ -900,13 +945,26 @@ ToStringResult toStringDetailed(TypeId ty, const ToStringOptions& opts)
 
             result.name += ttv->name ? *ttv->name : *ttv->syntheticName;
 
-            if (ttv->instantiatedTypeParams.empty())
+            if (ttv->instantiatedTypeParams.empty() && (!FFlag::LuauTypeAliasPacks || ttv->instantiatedTypePackParams.empty()))
                 return result;
 
             std::vector<std::string> params;
             for (TypeId tp : ttv->instantiatedTypeParams)
                 params.push_back(toString(tp));
 
+            if (FFlag::LuauTypeAliasPacks)
+            {
+                // Doesn't preserve grouping of multiple type packs
+                // But this is under a parent block of code that is being removed later
+                for (TypePackId tp : ttv->instantiatedTypePackParams)
+                {
+                    std::string content = toString(tp);
+
+                    if (!content.empty())
+                        params.push_back(std::move(content));
+                }
+            }
+
             result.name += "<" + join(params, ", ") + ">";
             return result;
         }
@@ -950,30 +1008,37 @@ ToStringResult toStringDetailed(TypeId ty, const ToStringOptions& opts)
 
             result.name += ttv->name ? *ttv->name : *ttv->syntheticName;
 
-            if (ttv->instantiatedTypeParams.empty())
+            if (FFlag::LuauTypeAliasPacks)
-                return result;
-
-            result.name += "<";
-
-            bool first = true;
-            for (TypeId ty : ttv->instantiatedTypeParams)
             {
-                if (!first)
+                tvs.stringify(ttv->instantiatedTypeParams, ttv->instantiatedTypePackParams);
-                    result.name += ", ";
-                else
-                    first = false;
-
-                tvs.stringify(ty);
-            }
-
-            if (opts.maxTypeLength > 0 && result.name.length() > opts.maxTypeLength)
-            {
-                result.truncated = true;
-                result.name += "... <TRUNCATED>";
             }
             else
             {
-                result.name += ">";
+                if (ttv->instantiatedTypeParams.empty() && (!FFlag::LuauTypeAliasPacks || ttv->instantiatedTypePackParams.empty()))
+                    return result;
+
+                result.name += "<";
+
+                bool first = true;
+                for (TypeId ty : ttv->instantiatedTypeParams)
+                {
+                    if (!first)
+                        result.name += ", ";
+                    else
+                        first = false;
+
+                    tvs.stringify(ty);
+                }
+
+                if (opts.maxTypeLength > 0 && result.name.length() > opts.maxTypeLength)
+                {
+                    result.truncated = true;
+                    result.name += "... <TRUNCATED>";
+                }
+                else
+                {
+                    result.name += ">";
+                }
             }
 
             return result;

Analysis/src/Transpiler.cpp

@@ -11,6 +11,7 @@
 #include <math.h>
 
 LUAU_FASTFLAG(LuauGenericFunctions)
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
 namespace
 {
@@ -280,10 +281,19 @@ struct Printer
 
     void visualizeTypePackAnnotation(const AstTypePack& annotation)
     {
-        if (const AstTypePackVariadic* variadic = annotation.as<AstTypePackVariadic>())
+        if (const AstTypePackVariadic* variadicTp = annotation.as<AstTypePackVariadic>())
         {
             writer.symbol("...");
-            visualizeTypeAnnotation(*variadic->variadicType);
+            visualizeTypeAnnotation(*variadicTp->variadicType);
+        }
+        else if (const AstTypePackGeneric* genericTp = annotation.as<AstTypePackGeneric>())
+        {
+            writer.symbol(genericTp->genericName.value);
+            writer.symbol("...");
+        }
+        else if (const AstTypePackExplicit* explicitTp = annotation.as<AstTypePackExplicit>())
+        {
+            visualizeTypeList(explicitTp->typeList, true);
         }
         else
         {
@@ -807,7 +817,7 @@ struct Printer
 
                 writer.keyword("type");
                 writer.identifier(a->name.value);
-                if (a->generics.size > 0)
+                if (a->generics.size > 0 || (FFlag::LuauTypeAliasPacks && a->genericPacks.size > 0))
                 {
                     writer.symbol("<");
                     CommaSeparatorInserter comma(writer);
@@ -817,6 +827,17 @@ struct Printer
                         comma();
                         writer.identifier(o.value);
                     }
+
+                    if (FFlag::LuauTypeAliasPacks)
+                    {
+                        for (auto o : a->genericPacks)
+                        {
+                            comma();
+                            writer.identifier(o.value);
+                            writer.symbol("...");
+                        }
+                    }
+
                     writer.symbol(">");
                 }
                 writer.maybeSpace(a->type->location.begin, 2);
@@ -960,15 +981,20 @@ struct Printer
         if (const auto& a = typeAnnotation.as<AstTypeReference>())
         {
             writer.write(a->name.value);
-            if (a->generics.size > 0)
+            if (a->parameters.size > 0)
             {
                 CommaSeparatorInserter comma(writer);
                 writer.symbol("<");
-                for (auto o : a->generics)
+                for (auto o : a->parameters)
                 {
                     comma();
-                    visualizeTypeAnnotation(*o);
+
+                    if (o.type)
+                        visualizeTypeAnnotation(*o.type);
+                    else
+                        visualizeTypePackAnnotation(*o.typePack);
                 }
+
                 writer.symbol(">");
             }
         }

Analysis/src/TypeAttach.cpp

@@ -5,6 +5,7 @@
 #include "Luau/Module.h"
 #include "Luau/Parser.h"
 #include "Luau/RecursionCounter.h"
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypePack.h"
 #include "Luau/TypeVar.h"
@@ -12,6 +13,7 @@
 #include <string>
 
 LUAU_FASTFLAG(LuauGenericFunctions)
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
 static char* allocateString(Luau::Allocator& allocator, std::string_view contents)
 {
@@ -33,7 +35,6 @@ static char* allocateString(Luau::Allocator& allocator, const char* format, Data
 
 namespace Luau
 {
-
 class TypeRehydrationVisitor
 {
     mutable std::map<void*, int> seen;
@@ -57,6 +58,8 @@ public:
     {
     }
 
+    AstTypePack* rehydrate(TypePackId tp) const;
+
     AstType* operator()(const PrimitiveTypeVar& ptv) const
     {
         switch (ptv.type)
@@ -85,16 +88,24 @@ public:
 
         if (ttv.name && options.bannedNames.find(*ttv.name) == options.bannedNames.end())
         {
-            AstArray<AstType*> generics;
+            AstArray<AstTypeOrPack> parameters;
-            generics.size = ttv.instantiatedTypeParams.size();
+            parameters.size = ttv.instantiatedTypeParams.size();
-            generics.data = static_cast<AstType**>(allocator->allocate(sizeof(AstType*) * generics.size));
+            parameters.data = static_cast<AstTypeOrPack*>(allocator->allocate(sizeof(AstTypeOrPack) * parameters.size));
 
             for (size_t i = 0; i < ttv.instantiatedTypeParams.size(); ++i)
             {
-                generics.data[i] = Luau::visit(*this, ttv.instantiatedTypeParams[i]->ty);
+                parameters.data[i] = {Luau::visit(*this, ttv.instantiatedTypeParams[i]->ty), {}};
             }
 
-            return allocator->alloc<AstTypeReference>(Location(), std::nullopt, AstName(ttv.name->c_str()), generics);
+            if (FFlag::LuauTypeAliasPacks)
+            {
+                for (size_t i = 0; i < ttv.instantiatedTypePackParams.size(); ++i)
+                {
+                    parameters.data[i] = {{}, rehydrate(ttv.instantiatedTypePackParams[i])};
+                }
+            }
+
+            return allocator->alloc<AstTypeReference>(Location(), std::nullopt, AstName(ttv.name->c_str()), parameters.size != 0, parameters);
         }
 
         if (hasSeen(&ttv))
@@ -222,10 +233,17 @@ public:
         AstTypePack* argTailAnnotation = nullptr;
         if (argTail)
         {
-            TypePackId tail = *argTail;
+            if (FFlag::LuauTypeAliasPacks)
-            if (const VariadicTypePack* vtp = get<VariadicTypePack>(tail))
             {
-                argTailAnnotation = allocator->alloc<AstTypePackVariadic>(Location(), Luau::visit(*this, vtp->ty->ty));
+                argTailAnnotation = rehydrate(*argTail);
+            }
+            else
+            {
+                TypePackId tail = *argTail;
+                if (const VariadicTypePack* vtp = get<VariadicTypePack>(tail))
+                {
+                    argTailAnnotation = allocator->alloc<AstTypePackVariadic>(Location(), Luau::visit(*this, vtp->ty->ty));
+                }
             }
         }
 
@@ -255,10 +273,17 @@ public:
         AstTypePack* retTailAnnotation = nullptr;
         if (retTail)
         {
-            TypePackId tail = *retTail;
+            if (FFlag::LuauTypeAliasPacks)
-            if (const VariadicTypePack* vtp = get<VariadicTypePack>(tail))
             {
-                retTailAnnotation = allocator->alloc<AstTypePackVariadic>(Location(), Luau::visit(*this, vtp->ty->ty));
+                retTailAnnotation = rehydrate(*retTail);
+            }
+            else
+            {
+                TypePackId tail = *retTail;
+                if (const VariadicTypePack* vtp = get<VariadicTypePack>(tail))
+                {
+                    retTailAnnotation = allocator->alloc<AstTypePackVariadic>(Location(), Luau::visit(*this, vtp->ty->ty));
+                }
             }
         }
 
@@ -313,6 +338,68 @@ private:
     const TypeRehydrationOptions& options;
 };
 
+class TypePackRehydrationVisitor
+{
+public:
+    TypePackRehydrationVisitor(Allocator* allocator, const TypeRehydrationVisitor& typeVisitor)
+        : allocator(allocator)
+        , typeVisitor(typeVisitor)
+    {
+    }
+
+    AstTypePack* operator()(const BoundTypePack& btp) const
+    {
+        return Luau::visit(*this, btp.boundTo->ty);
+    }
+
+    AstTypePack* operator()(const TypePack& tp) const
+    {
+        AstArray<AstType*> head;
+        head.size = tp.head.size();
+        head.data = static_cast<AstType**>(allocator->allocate(sizeof(AstType*) * tp.head.size()));
+
+        for (size_t i = 0; i < tp.head.size(); i++)
+            head.data[i] = Luau::visit(typeVisitor, tp.head[i]->ty);
+
+        AstTypePack* tail = nullptr;
+
+        if (tp.tail)
+            tail = Luau::visit(*this, (*tp.tail)->ty);
+
+        return allocator->alloc<AstTypePackExplicit>(Location(), AstTypeList{head, tail});
+    }
+
+    AstTypePack* operator()(const VariadicTypePack& vtp) const
+    {
+        return allocator->alloc<AstTypePackVariadic>(Location(), Luau::visit(typeVisitor, vtp.ty->ty));
+    }
+
+    AstTypePack* operator()(const GenericTypePack& gtp) const
+    {
+        return allocator->alloc<AstTypePackGeneric>(Location(), AstName(gtp.name.c_str()));
+    }
+
+    AstTypePack* operator()(const FreeTypePack& gtp) const
+    {
+        return allocator->alloc<AstTypePackGeneric>(Location(), AstName("free"));
+    }
+
+    AstTypePack* operator()(const Unifiable::Error&) const
+    {
+        return allocator->alloc<AstTypePackGeneric>(Location(), AstName("Unifiable<Error>"));
+    }
+
+private:
+    Allocator* allocator;
+    const TypeRehydrationVisitor& typeVisitor;
+};
+
+AstTypePack* TypeRehydrationVisitor::rehydrate(TypePackId tp) const
+{
+    TypePackRehydrationVisitor tprv(allocator, *this);
+    return Luau::visit(tprv, tp->ty);
+}
+
 class TypeAttacher : public AstVisitor
 {
 public:
@@ -406,9 +493,16 @@ public:
 
                 if (tail)
                 {
-                    TypePackId tailPack = *tail;
+                    if (FFlag::LuauTypeAliasPacks)
-                    if (const VariadicTypePack* vtp = get<VariadicTypePack>(tailPack))
+                    {
-                        variadicAnnotation = allocator->alloc<AstTypePackVariadic>(Location(), typeAst(vtp->ty));
+                        variadicAnnotation = TypeRehydrationVisitor(allocator).rehydrate(*tail);
+                    }
+                    else
+                    {
+                        TypePackId tailPack = *tail;
+                        if (const VariadicTypePack* vtp = get<VariadicTypePack>(tailPack))
+                            variadicAnnotation = allocator->alloc<AstTypePackVariadic>(Location(), typeAst(vtp->ty));
+                    }
                 }
 
                 fn->returnAnnotation = AstTypeList{typeAstPack(ret), variadicAnnotation};

Analysis/src/TypeInfer.cpp

@@ -5,21 +5,22 @@
 #include "Luau/ModuleResolver.h"
 #include "Luau/Parser.h"
 #include "Luau/RecursionCounter.h"
+#include "Luau/Scope.h"
 #include "Luau/Substitution.h"
 #include "Luau/TopoSortStatements.h"
 #include "Luau/ToString.h"
 #include "Luau/TypePack.h"
 #include "Luau/TypeUtils.h"
 #include "Luau/TypeVar.h"
+#include "Luau/TimeTrace.h"
 
 #include <deque>
 #include <algorithm>
 
 LUAU_FASTFLAGVARIABLE(DebugLuauMagicTypes, false)
-LUAU_FASTINTVARIABLE(LuauTypeInferRecursionLimit, 0)
+LUAU_FASTINTVARIABLE(LuauTypeInferRecursionLimit, 500)
-LUAU_FASTINTVARIABLE(LuauTypeInferTypePackLoopLimit, 0)
+LUAU_FASTINTVARIABLE(LuauTypeInferTypePackLoopLimit, 5000)
 LUAU_FASTINTVARIABLE(LuauCheckRecursionLimit, 500)
-LUAU_FASTFLAGVARIABLE(LuauIndexTablesWithIndexers, false)
 LUAU_FASTFLAGVARIABLE(LuauGenericFunctions, false)
 LUAU_FASTFLAGVARIABLE(LuauGenericVariadicsUnification, false)
 LUAU_FASTFLAG(LuauKnowsTheDataModel3)
@@ -27,14 +28,11 @@ LUAU_FASTFLAG(LuauSecondTypecheckKnowsTheDataModel)
 LUAU_FASTFLAGVARIABLE(LuauClassPropertyAccessAsString, false)
 LUAU_FASTFLAGVARIABLE(LuauEqConstraint, false)
 LUAU_FASTFLAGVARIABLE(LuauWeakEqConstraint, false) // Eventually removed as false.
-LUAU_FASTFLAGVARIABLE(LuauImprovedTypeGuardPredicate2, false)
 LUAU_FASTFLAG(LuauTraceRequireLookupChild)
-LUAU_FASTFLAG(DebugLuauTrackOwningArena)
 LUAU_FASTFLAGVARIABLE(LuauCloneCorrectlyBeforeMutatingTableType, false)
 LUAU_FASTFLAGVARIABLE(LuauStoreMatchingOverloadFnType, false)
 LUAU_FASTFLAGVARIABLE(LuauRankNTypes, false)
 LUAU_FASTFLAGVARIABLE(LuauOrPredicate, false)
-LUAU_FASTFLAGVARIABLE(LuauFixTableTypeAliasClone, false)
 LUAU_FASTFLAGVARIABLE(LuauExtraNilRecovery, false)
 LUAU_FASTFLAGVARIABLE(LuauMissingUnionPropertyError, false)
 LUAU_FASTFLAGVARIABLE(LuauInferReturnAssertAssign, false)
@@ -45,6 +43,10 @@ LUAU_FASTFLAGVARIABLE(LuauSlightlyMoreFlexibleBinaryPredicates, false)
 LUAU_FASTFLAGVARIABLE(LuauInferFunctionArgsFix, false)
 LUAU_FASTFLAGVARIABLE(LuauFollowInTypeFunApply, false)
 LUAU_FASTFLAGVARIABLE(LuauIfElseExpressionAnalysisSupport, false)
+LUAU_FASTFLAGVARIABLE(LuauStrictRequire, false)
+LUAU_FASTFLAG(LuauSubstitutionDontReplaceIgnoredTypes)
+LUAU_FASTFLAG(LuauNewRequireTrace)
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
 namespace Luau
 {
@@ -216,9 +218,8 @@ TypeChecker::TypeChecker(ModuleResolver* resolver, InternalErrorReporter* iceHan
     , nilType(singletonTypes.nilType)
     , numberType(singletonTypes.numberType)
     , stringType(singletonTypes.stringType)
-    , booleanType(
+    , booleanType(singletonTypes.booleanType)
-          FFlag::LuauImprovedTypeGuardPredicate2 ? singletonTypes.booleanType : globalTypes.addType(PrimitiveTypeVar(PrimitiveTypeVar::Boolean)))
+    , threadType(singletonTypes.threadType)
-    , threadType(FFlag::LuauImprovedTypeGuardPredicate2 ? singletonTypes.threadType : globalTypes.addType(PrimitiveTypeVar(PrimitiveTypeVar::Thread)))
     , anyType(singletonTypes.anyType)
     , errorType(singletonTypes.errorType)
     , optionalNumberType(globalTypes.addType(UnionTypeVar{{numberType, nilType}}))
@@ -237,6 +238,9 @@ TypeChecker::TypeChecker(ModuleResolver* resolver, InternalErrorReporter* iceHan
 
 ModulePtr TypeChecker::check(const SourceModule& module, Mode mode, std::optional<ScopePtr> environmentScope)
 {
+    LUAU_TIMETRACE_SCOPE("TypeChecker::check", "TypeChecker");
+    LUAU_TIMETRACE_ARGUMENT("module", module.name.c_str());
+
     currentModule.reset(new Module());
     currentModule->type = module.type;
 
@@ -1177,44 +1181,61 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias
         {
             Location location = scope->typeAliasLocations[name];
             reportError(TypeError{typealias.location, DuplicateTypeDefinition{name, location}});
-            bindingsMap[name] = TypeFun{binding->typeParams, errorType};
+
+            if (FFlag::LuauTypeAliasPacks)
+                bindingsMap[name] = TypeFun{binding->typeParams, binding->typePackParams, errorType};
+            else
+                bindingsMap[name] = TypeFun{binding->typeParams, errorType};
         }
         else
         {
             ScopePtr aliasScope = childScope(scope, typealias.location);
 
-            std::vector<TypeId> generics;
+            if (FFlag::LuauTypeAliasPacks)
-            for (AstName generic : typealias.generics)
             {
-                Name n = generic.value;
+                auto [generics, genericPacks] = createGenericTypes(aliasScope, typealias, typealias.generics, typealias.genericPacks);
 
-                // These generics are the only thing that will ever be added to aliasScope, so we can be certain that
+                TypeId ty = (FFlag::LuauRankNTypes ? freshType(aliasScope) : DEPRECATED_freshType(scope, true));
-                // a collision can only occur when two generic typevars have the same name.
+                FreeTypeVar* ftv = getMutable<FreeTypeVar>(ty);
-                if (aliasScope->privateTypeBindings.end() != aliasScope->privateTypeBindings.find(n))
+                LUAU_ASSERT(ftv);
-                {
+                ftv->forwardedTypeAlias = true;
-                    // TODO(jhuelsman): report the exact span of the generic type parameter whose name is a duplicate.
+                bindingsMap[name] = {std::move(generics), std::move(genericPacks), ty};
-                    reportError(TypeError{typealias.location, DuplicateGenericParameter{n}});
-                }
-
-                TypeId g;
-                if (FFlag::LuauRecursiveTypeParameterRestriction)
-                {
-                    TypeId& cached = scope->typeAliasParameters[n];
-                    if (!cached)
-                        cached = addType(GenericTypeVar{aliasScope->level, n});
-                    g = cached;
-                }
-                else
-                    g = addType(GenericTypeVar{aliasScope->level, n});
-                generics.push_back(g);
-                aliasScope->privateTypeBindings[n] = TypeFun{{}, g};
             }
+            else
+            {
+                std::vector<TypeId> generics;
+                for (AstName generic : typealias.generics)
+                {
+                    Name n = generic.value;
 
-            TypeId ty = (FFlag::LuauRankNTypes ? freshType(aliasScope) : DEPRECATED_freshType(scope, true));
+                    // These generics are the only thing that will ever be added to aliasScope, so we can be certain that
-            FreeTypeVar* ftv = getMutable<FreeTypeVar>(ty);
+                    // a collision can only occur when two generic typevars have the same name.
-            LUAU_ASSERT(ftv);
+                    if (aliasScope->privateTypeBindings.end() != aliasScope->privateTypeBindings.find(n))
-            ftv->forwardedTypeAlias = true;
+                    {
-            bindingsMap[name] = {std::move(generics), ty};
+                        // TODO(jhuelsman): report the exact span of the generic type parameter whose name is a duplicate.
+                        reportError(TypeError{typealias.location, DuplicateGenericParameter{n}});
+                    }
+
+                    TypeId g;
+                    if (FFlag::LuauRecursiveTypeParameterRestriction)
+                    {
+                        TypeId& cached = scope->typeAliasTypeParameters[n];
+                        if (!cached)
+                            cached = addType(GenericTypeVar{aliasScope->level, n});
+                        g = cached;
+                    }
+                    else
+                        g = addType(GenericTypeVar{aliasScope->level, n});
+                    generics.push_back(g);
+                    aliasScope->privateTypeBindings[n] = TypeFun{{}, g};
+                }
+
+                TypeId ty = (FFlag::LuauRankNTypes ? freshType(aliasScope) : DEPRECATED_freshType(scope, true));
+                FreeTypeVar* ftv = getMutable<FreeTypeVar>(ty);
+                LUAU_ASSERT(ftv);
+                ftv->forwardedTypeAlias = true;
+                bindingsMap[name] = {std::move(generics), ty};
+            }
         }
     }
     else
@@ -1231,6 +1252,16 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias
             aliasScope->privateTypeBindings[generic->name] = TypeFun{{}, ty};
         }
 
+        if (FFlag::LuauTypeAliasPacks)
+        {
+            for (TypePackId tp : binding->typePackParams)
+            {
+                auto generic = get<GenericTypePack>(tp);
+                LUAU_ASSERT(generic);
+                aliasScope->privateTypePackBindings[generic->name] = tp;
+            }
+        }
+
         TypeId ty = (FFlag::LuauRankNTypes ? resolveType(aliasScope, *typealias.type) : resolveType(aliasScope, *typealias.type, true));
         if (auto ttv = getMutable<TableTypeVar>(follow(ty)))
         {
@@ -1238,7 +1269,8 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias
             if (ttv->name)
             {
                 // Copy can be skipped if this is an identical alias
-                if (!FFlag::LuauFixTableTypeAliasClone || ttv->name != name || ttv->instantiatedTypeParams != binding->typeParams)
+                if (ttv->name != name || ttv->instantiatedTypeParams != binding->typeParams ||
+                    (FFlag::LuauTypeAliasPacks && ttv->instantiatedTypePackParams != binding->typePackParams))
                 {
                     // This is a shallow clone, original recursive links to self are not updated
                     TableTypeVar clone = TableTypeVar{ttv->props, ttv->indexer, ttv->level, ttv->state};
@@ -1249,6 +1281,9 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias
                     clone.name = name;
                     clone.instantiatedTypeParams = binding->typeParams;
 
+                    if (FFlag::LuauTypeAliasPacks)
+                        clone.instantiatedTypePackParams = binding->typePackParams;
+
                     ty = addType(std::move(clone));
                 }
             }
@@ -1256,6 +1291,9 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatTypeAlias& typealias
             {
                 ttv->name = name;
                 ttv->instantiatedTypeParams = binding->typeParams;
+
+                if (FFlag::LuauTypeAliasPacks)
+                    ttv->instantiatedTypePackParams = binding->typePackParams;
             }
         }
         else if (auto mtv = getMutable<MetatableTypeVar>(follow(ty)))
@@ -1280,7 +1318,7 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatDeclareClass& declar
         }
 
         // We don't have generic classes, so this assertion _should_ never be hit.
-        LUAU_ASSERT(lookupType->typeParams.size() == 0);
+        LUAU_ASSERT(lookupType->typeParams.size() == 0 && (!FFlag::LuauTypeAliasPacks || lookupType->typePackParams.size() == 0));
         superTy = lookupType->type;
 
         if (FFlag::LuauAddMissingFollow)
@@ -1465,7 +1503,8 @@ ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExpr&
 
     if (FFlag::LuauStoreMatchingOverloadFnType)
     {
-        currentModule->astTypes.try_emplace(&expr, result.type);
+        if (!currentModule->astTypes.find(&expr))
+            currentModule->astTypes[&expr] = result.type;
     }
     else
     {
@@ -2193,7 +2232,7 @@ TypeId TypeChecker::checkRelationalOperation(
          * have a better, more descriptive error teed up.
          */
         Unifier state = mkUnifier(expr.location);
-        if (!FFlag::LuauEqConstraint || !isEquality)
+        if (!isEquality)
             state.tryUnify(lhsType, rhsType);
 
         bool needsMetamethod = !isEquality;
@@ -2262,7 +2301,7 @@ TypeId TypeChecker::checkRelationalOperation(
             }
         }
 
-        if (get<FreeTypeVar>(FFlag::LuauAddMissingFollow ? follow(lhsType) : lhsType) && (!FFlag::LuauEqConstraint || !isEquality))
+        if (get<FreeTypeVar>(FFlag::LuauAddMissingFollow ? follow(lhsType) : lhsType) && !isEquality)
         {
             auto name = getIdentifierOfBaseVar(expr.left);
             reportError(expr.location, CannotInferBinaryOperation{expr.op, name, CannotInferBinaryOperation::Comparison});
@@ -2276,18 +2315,6 @@ TypeId TypeChecker::checkRelationalOperation(
             return errorType;
         }
 
-        if (!FFlag::LuauEqConstraint)
-        {
-            if (isEquality)
-            {
-                ErrorVec errVec = tryUnify(rhsType, lhsType, expr.location);
-                if (!state.errors.empty() && !errVec.empty())
-                    reportError(expr.location, TypeMismatch{lhsType, rhsType});
-            }
-            else
-                reportErrors(state.errors);
-        }
-
         return booleanType;
     }
 
@@ -2443,7 +2470,7 @@ ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExprBi
         TypeId result = checkBinaryOperation(innerScope, expr, lhs.type, rhs.type, lhs.predicates);
         return {result, {OrPredicate{std::move(lhs.predicates), std::move(rhs.predicates)}}};
     }
-    else if (FFlag::LuauEqConstraint && (expr.op == AstExprBinary::CompareEq || expr.op == AstExprBinary::CompareNe))
+    else if (expr.op == AstExprBinary::CompareEq || expr.op == AstExprBinary::CompareNe)
     {
         if (auto predicate = tryGetTypeGuardPredicate(expr))
             return {booleanType, {std::move(*predicate)}};
@@ -2466,14 +2493,6 @@ ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExprBi
     }
     else
     {
-        // Once we have EqPredicate, we should break this else branch into its' own branch.
-        // For now, fall through is intentional.
-        if (expr.op == AstExprBinary::CompareEq || expr.op == AstExprBinary::CompareNe)
-        {
-            if (auto predicate = tryGetTypeGuardPredicate(expr))
-                return {booleanType, {std::move(*predicate)}};
-        }
-
         ExprResult<TypeId> lhs = checkExpr(scope, *expr.left);
         ExprResult<TypeId> rhs = checkExpr(scope, *expr.right);
 
@@ -2755,12 +2774,6 @@ std::pair<TypeId, TypeId*> TypeChecker::checkLValueBinding(const ScopePtr& scope
         exprTable->indexer = TableIndexer{anyIfNonstrict(indexType), anyIfNonstrict(resultType)};
         return std::pair(resultType, nullptr);
     }
-    else if (FFlag::LuauIndexTablesWithIndexers)
-    {
-        // We allow t[x] where x:string for tables without an indexer
-        unify(indexType, stringType, expr.location);
-        return std::pair(anyType, nullptr);
-    }
     else
     {
         TypeId resultType = freshType(scope);
@@ -3076,6 +3089,13 @@ static Location getEndLocation(const AstExprFunction& function)
 
 void TypeChecker::checkFunctionBody(const ScopePtr& scope, TypeId ty, const AstExprFunction& function)
 {
+    LUAU_TIMETRACE_SCOPE("TypeChecker::checkFunctionBody", "TypeChecker");
+
+    if (function.debugname.value)
+        LUAU_TIMETRACE_ARGUMENT("name", function.debugname.value);
+    else
+        LUAU_TIMETRACE_ARGUMENT("line", std::to_string(function.location.begin.line).c_str());
+
     if (FunctionTypeVar* funTy = getMutable<FunctionTypeVar>(ty))
     {
         check(scope, *function.body);
@@ -3885,6 +3905,20 @@ std::optional<AstExpr*> TypeChecker::matchRequire(const AstExprCall& call)
 
 TypeId TypeChecker::checkRequire(const ScopePtr& scope, const ModuleInfo& moduleInfo, const Location& location)
 {
+    LUAU_TIMETRACE_SCOPE("TypeChecker::checkRequire", "TypeChecker");
+    LUAU_TIMETRACE_ARGUMENT("moduleInfo", moduleInfo.name.c_str());
+
+    if (FFlag::LuauNewRequireTrace && moduleInfo.name.empty())
+    {
+        if (FFlag::LuauStrictRequire && currentModule->mode == Mode::Strict)
+        {
+            reportError(TypeError{location, UnknownRequire{}});
+            return errorType;
+        }
+
+        return anyType;
+    }
+
     ModulePtr module = resolver->getModule(moduleInfo.name);
     if (!module)
     {
@@ -4472,7 +4506,7 @@ TypeId TypeChecker::freshType(const ScopePtr& scope)
 
 TypeId TypeChecker::freshType(TypeLevel level)
 {
-    return currentModule->internalTypes.typeVars.allocate(TypeVar(FreeTypeVar(level)));
+    return currentModule->internalTypes.addType(TypeVar(FreeTypeVar(level)));
 }
 
 TypeId TypeChecker::DEPRECATED_freshType(const ScopePtr& scope, bool canBeGeneric)
@@ -4482,11 +4516,7 @@ TypeId TypeChecker::DEPRECATED_freshType(const ScopePtr& scope, bool canBeGeneri
 
 TypeId TypeChecker::DEPRECATED_freshType(TypeLevel level, bool canBeGeneric)
 {
-    TypeId allocated = currentModule->internalTypes.typeVars.allocate(TypeVar(FreeTypeVar(level, canBeGeneric)));
+    return currentModule->internalTypes.addType(TypeVar(FreeTypeVar(level, canBeGeneric)));
-    if (FFlag::DebugLuauTrackOwningArena)
-        asMutable(allocated)->owningArena = &currentModule->internalTypes;
-
-    return allocated;
 }
 
 std::optional<TypeId> TypeChecker::filterMap(TypeId type, TypeIdPredicate predicate)
@@ -4506,20 +4536,12 @@ TypeId TypeChecker::addType(const UnionTypeVar& utv)
 
 TypeId TypeChecker::addTV(TypeVar&& tv)
 {
-    TypeId allocated = currentModule->internalTypes.typeVars.allocate(std::move(tv));
+    return currentModule->internalTypes.addType(std::move(tv));
-    if (FFlag::DebugLuauTrackOwningArena)
-        asMutable(allocated)->owningArena = &currentModule->internalTypes;
-
-    return allocated;
 }
 
 TypePackId TypeChecker::addTypePack(TypePackVar&& tv)
 {
-    TypePackId allocated = currentModule->internalTypes.typePacks.allocate(std::move(tv));
+    return currentModule->internalTypes.addTypePack(std::move(tv));
-    if (FFlag::DebugLuauTrackOwningArena)
-        asMutable(allocated)->owningArena = &currentModule->internalTypes;
-
-    return allocated;
 }
 
 TypePackId TypeChecker::addTypePack(TypePack&& tp)
@@ -4578,7 +4600,7 @@ TypeId TypeChecker::resolveType(const ScopePtr& scope, const AstType& annotation
 
         else if (FFlag::DebugLuauMagicTypes && lit->name == "_luau_print")
         {
-            if (lit->generics.size != 1)
+            if (lit->parameters.size != 1 || !lit->parameters.data[0].type)
             {
                 reportError(TypeError{annotation.location, GenericError{"_luau_print requires one generic parameter"}});
                 return addType(ErrorTypeVar{});
@@ -4588,7 +4610,7 @@ TypeId TypeChecker::resolveType(const ScopePtr& scope, const AstType& annotation
             opts.exhaustive = true;
             opts.maxTableLength = 0;
 
-            TypeId param = resolveType(scope, *lit->generics.data[0]);
+            TypeId param = resolveType(scope, *lit->parameters.data[0].type);
             luauPrintLine(format("_luau_print\t%s\t|\t%s", toString(param, opts).c_str(), toString(lit->location).c_str()));
             return param;
         }
@@ -4614,18 +4636,86 @@ TypeId TypeChecker::resolveType(const ScopePtr& scope, const AstType& annotation
             return addType(ErrorTypeVar{});
         }
 
-        if (lit->generics.size == 0 && tf->typeParams.empty())
+        if (lit->parameters.size == 0 && tf->typeParams.empty() && (!FFlag::LuauTypeAliasPacks || tf->typePackParams.empty()))
-            return tf->type;
-        else if (lit->generics.size != tf->typeParams.size())
         {
-            reportError(TypeError{annotation.location, IncorrectGenericParameterCount{lit->name.value, *tf, lit->generics.size}});
+            return tf->type;
+        }
+        else if (!FFlag::LuauTypeAliasPacks && lit->parameters.size != tf->typeParams.size())
+        {
+            reportError(TypeError{annotation.location, IncorrectGenericParameterCount{lit->name.value, *tf, lit->parameters.size, 0}});
             return addType(ErrorTypeVar{});
         }
+        else if (FFlag::LuauTypeAliasPacks)
+        {
+            if (!lit->hasParameterList && !tf->typePackParams.empty())
+            {
+                reportError(TypeError{annotation.location, GenericError{"Type parameter list is required"}});
+                return addType(ErrorTypeVar{});
+            }
+
+            std::vector<TypeId> typeParams;
+            std::vector<TypeId> extraTypes;
+            std::vector<TypePackId> typePackParams;
+
+            for (size_t i = 0; i < lit->parameters.size; ++i)
+            {
+                if (AstType* type = lit->parameters.data[i].type)
+                {
+                    TypeId ty = resolveType(scope, *type);
+
+                    if (typeParams.size() < tf->typeParams.size() || tf->typePackParams.empty())
+                        typeParams.push_back(ty);
+                    else if (typePackParams.empty())
+                        extraTypes.push_back(ty);
+                    else
+                        reportError(TypeError{annotation.location, GenericError{"Type parameters must come before type pack parameters"}});
+                }
+                else if (AstTypePack* typePack = lit->parameters.data[i].typePack)
+                {
+                    TypePackId tp = resolveTypePack(scope, *typePack);
+
+                    // If we have collected an implicit type pack, materialize it
+                    if (typePackParams.empty() && !extraTypes.empty())
+                        typePackParams.push_back(addTypePack(extraTypes));
+
+                    // If we need more regular types, we can use single element type packs to fill those in
+                    if (typeParams.size() < tf->typeParams.size() && size(tp) == 1 && finite(tp) && first(tp))
+                        typeParams.push_back(*first(tp));
+                    else
+                        typePackParams.push_back(tp);
+                }
+            }
+
+            // If we still haven't meterialized an implicit type pack, do it now
+            if (typePackParams.empty() && !extraTypes.empty())
+                typePackParams.push_back(addTypePack(extraTypes));
+
+            // If we didn't combine regular types into a type pack and we're still one type pack short, provide an empty type pack
+            if (extraTypes.empty() && typePackParams.size() + 1 == tf->typePackParams.size())
+                typePackParams.push_back(addTypePack({}));
+
+            if (typeParams.size() != tf->typeParams.size() || typePackParams.size() != tf->typePackParams.size())
+            {
+                reportError(
+                    TypeError{annotation.location, IncorrectGenericParameterCount{lit->name.value, *tf, typeParams.size(), typePackParams.size()}});
+                return addType(ErrorTypeVar{});
+            }
+
+            if (FFlag::LuauRecursiveTypeParameterRestriction && typeParams == tf->typeParams && typePackParams == tf->typePackParams)
+            {
+                // If the generic parameters and the type arguments are the same, we are about to
+                // perform an identity substitution, which we can just short-circuit.
+                return tf->type;
+            }
+
+            return instantiateTypeFun(scope, *tf, typeParams, typePackParams, annotation.location);
+        }
         else
         {
             std::vector<TypeId> typeParams;
-            for (AstType* paramAnnot : lit->generics)
+
-                typeParams.push_back(resolveType(scope, *paramAnnot));
+            for (const auto& param : lit->parameters)
+                typeParams.push_back(resolveType(scope, *param.type));
 
             if (FFlag::LuauRecursiveTypeParameterRestriction && typeParams == tf->typeParams)
             {
@@ -4634,7 +4724,7 @@ TypeId TypeChecker::resolveType(const ScopePtr& scope, const AstType& annotation
                 return tf->type;
             }
 
-            return instantiateTypeFun(scope, *tf, typeParams, annotation.location);
+            return instantiateTypeFun(scope, *tf, typeParams, {}, annotation.location);
         }
     }
     else if (const auto& table = annotation.as<AstTypeTable>())
@@ -4765,6 +4855,18 @@ TypePackId TypeChecker::resolveTypePack(const ScopePtr& scope, const AstTypePack
 
         return *genericTy;
     }
+    else if (const AstTypePackExplicit* explicitTp = annotation.as<AstTypePackExplicit>())
+    {
+        std::vector<TypeId> types;
+
+        for (auto type : explicitTp->typeList.types)
+            types.push_back(resolveType(scope, *type));
+
+        if (auto tailType = explicitTp->typeList.tailType)
+            return addTypePack(types, resolveTypePack(scope, *tailType));
+
+        return addTypePack(types);
+    }
     else
     {
         ice("Unknown AstTypePack kind");
@@ -4799,12 +4901,28 @@ bool ApplyTypeFunction::isDirty(TypePackId tp)
         return false;
 }
 
+bool ApplyTypeFunction::ignoreChildren(TypeId ty)
+{
+    if (FFlag::LuauSubstitutionDontReplaceIgnoredTypes && get<GenericTypeVar>(ty))
+        return true;
+    else
+        return false;
+}
+
+bool ApplyTypeFunction::ignoreChildren(TypePackId tp)
+{
+    if (FFlag::LuauSubstitutionDontReplaceIgnoredTypes && get<GenericTypePack>(tp))
+        return true;
+    else
+        return false;
+}
+
 TypeId ApplyTypeFunction::clean(TypeId ty)
 {
     // Really this should just replace the arguments,
     // but for bug-compatibility with existing code, we replace
     // all generics by free type variables.
-    TypeId& arg = arguments[ty];
+    TypeId& arg = typeArguments[ty];
     if (arg)
         return arg;
     else
@@ -4816,17 +4934,37 @@ TypePackId ApplyTypeFunction::clean(TypePackId tp)
     // Really this should just replace the arguments,
     // but for bug-compatibility with existing code, we replace
     // all generics by free type variables.
-    return addTypePack(FreeTypePack{level});
+    if (FFlag::LuauTypeAliasPacks)
+    {
+        TypePackId& arg = typePackArguments[tp];
+        if (arg)
+            return arg;
+        else
+            return addTypePack(FreeTypePack{level});
+    }
+    else
+    {
+        return addTypePack(FreeTypePack{level});
+    }
 }
 
-TypeId TypeChecker::instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf, const std::vector<TypeId>& typeParams, const Location& location)
+TypeId TypeChecker::instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf, const std::vector<TypeId>& typeParams,
+    const std::vector<TypePackId>& typePackParams, const Location& location)
 {
-    if (tf.typeParams.empty())
+    if (tf.typeParams.empty() && (!FFlag::LuauTypeAliasPacks || tf.typePackParams.empty()))
         return tf.type;
 
-    applyTypeFunction.arguments.clear();
+    applyTypeFunction.typeArguments.clear();
     for (size_t i = 0; i < tf.typeParams.size(); ++i)
-        applyTypeFunction.arguments[tf.typeParams[i]] = typeParams[i];
+        applyTypeFunction.typeArguments[tf.typeParams[i]] = typeParams[i];
+
+    if (FFlag::LuauTypeAliasPacks)
+    {
+        applyTypeFunction.typePackArguments.clear();
+        for (size_t i = 0; i < tf.typePackParams.size(); ++i)
+            applyTypeFunction.typePackArguments[tf.typePackParams[i]] = typePackParams[i];
+    }
+
     applyTypeFunction.currentModule = currentModule;
     applyTypeFunction.level = scope->level;
     applyTypeFunction.encounteredForwardedType = false;
@@ -4875,6 +5013,9 @@ TypeId TypeChecker::instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf,
         if (ttv)
         {
             ttv->instantiatedTypeParams = typeParams;
+
+            if (FFlag::LuauTypeAliasPacks)
+                ttv->instantiatedTypePackParams = typePackParams;
         }
     }
     else
@@ -4890,6 +5031,9 @@ TypeId TypeChecker::instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf,
             }
 
             ttv->instantiatedTypeParams = typeParams;
+
+            if (FFlag::LuauTypeAliasPacks)
+                ttv->instantiatedTypePackParams = typePackParams;
         }
     }
 
@@ -4899,6 +5043,8 @@ TypeId TypeChecker::instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf,
 std::pair<std::vector<TypeId>, std::vector<TypePackId>> TypeChecker::createGenericTypes(
     const ScopePtr& scope, const AstNode& node, const AstArray<AstName>& genericNames, const AstArray<AstName>& genericPackNames)
 {
+    LUAU_ASSERT(scope->parent);
+
     std::vector<TypeId> generics;
     for (const AstName& generic : genericNames)
     {
@@ -4912,7 +5058,19 @@ std::pair<std::vector<TypeId>, std::vector<TypePackId>> TypeChecker::createGener
             reportError(TypeError{node.location, DuplicateGenericParameter{n}});
         }
 
-        TypeId g = addType(Unifiable::Generic{scope->level, n});
+        TypeId g;
+        if (FFlag::LuauRecursiveTypeParameterRestriction && FFlag::LuauTypeAliasPacks)
+        {
+            TypeId& cached = scope->parent->typeAliasTypeParameters[n];
+            if (!cached)
+                cached = addType(GenericTypeVar{scope->level, n});
+            g = cached;
+        }
+        else
+        {
+            g = addType(Unifiable::Generic{scope->level, n});
+        }
+
         generics.push_back(g);
         scope->privateTypeBindings[n] = TypeFun{{}, g};
     }
@@ -4930,7 +5088,19 @@ std::pair<std::vector<TypeId>, std::vector<TypePackId>> TypeChecker::createGener
             reportError(TypeError{node.location, DuplicateGenericParameter{n}});
         }
 
-        TypePackId g = addTypePack(TypePackVar{Unifiable::Generic{scope->level, n}});
+        TypePackId g;
+        if (FFlag::LuauRecursiveTypeParameterRestriction && FFlag::LuauTypeAliasPacks)
+        {
+            TypePackId& cached = scope->parent->typeAliasTypePackParameters[n];
+            if (!cached)
+                cached = addTypePack(TypePackVar{Unifiable::Generic{scope->level, n}});
+            g = cached;
+        }
+        else
+        {
+            g = addTypePack(TypePackVar{Unifiable::Generic{scope->level, n}});
+        }
+
         genericPacks.push_back(g);
         scope->privateTypePackBindings[n] = g;
     }
@@ -5013,13 +5183,8 @@ void TypeChecker::resolve(const Predicate& predicate, ErrorVec& errVec, Refineme
     else if (auto isaP = get<IsAPredicate>(predicate))
         resolve(*isaP, errVec, refis, scope, sense);
     else if (auto typeguardP = get<TypeGuardPredicate>(predicate))
-    {
+        resolve(*typeguardP, errVec, refis, scope, sense);
-        if (FFlag::LuauImprovedTypeGuardPredicate2)
+    else if (auto eqP = get<EqPredicate>(predicate))
-            resolve(*typeguardP, errVec, refis, scope, sense);
-        else
-            DEPRECATED_resolve(*typeguardP, errVec, refis, scope, sense);
-    }
-    else if (auto eqP = get<EqPredicate>(predicate); eqP && FFlag::LuauEqConstraint)
         resolve(*eqP, errVec, refis, scope, sense);
     else
         ice("Unhandled predicate kind");
@@ -5145,7 +5310,7 @@ void TypeChecker::resolve(const IsAPredicate& isaP, ErrorVec& errVec, Refinement
                     return isaP.ty;
             }
         }
-        else if (FFlag::LuauImprovedTypeGuardPredicate2)
+        else
         {
             auto lctv = get<ClassTypeVar>(option);
             auto rctv = get<ClassTypeVar>(isaP.ty);
@@ -5159,19 +5324,6 @@ void TypeChecker::resolve(const IsAPredicate& isaP, ErrorVec& errVec, Refinement
             if (canUnify(option, isaP.ty, isaP.location).empty() == sense)
                 return isaP.ty;
         }
-        else
-        {
-            auto lctv = get<ClassTypeVar>(option);
-            auto rctv = get<ClassTypeVar>(isaP.ty);
-
-            if (lctv && rctv)
-            {
-                if (isSubclass(lctv, rctv) == sense)
-                    return option;
-                else if (isSubclass(rctv, lctv) == sense)
-                    return isaP.ty;
-            }
-        }
 
         return std::nullopt;
     };
@@ -5266,7 +5418,7 @@ void TypeChecker::resolve(const TypeGuardPredicate& typeguardP, ErrorVec& errVec
         return fail(UnknownSymbol{typeguardP.kind, UnknownSymbol::Type});
 
     auto typeFun = globalScope->lookupType(typeguardP.kind);
-    if (!typeFun || !typeFun->typeParams.empty())
+    if (!typeFun || !typeFun->typeParams.empty() || (FFlag::LuauTypeAliasPacks && !typeFun->typePackParams.empty()))
         return fail(UnknownSymbol{typeguardP.kind, UnknownSymbol::Type});
 
     TypeId type = follow(typeFun->type);
@@ -5292,7 +5444,8 @@ void TypeChecker::DEPRECATED_resolve(const TypeGuardPredicate& typeguardP, Error
         "userdata", // no op. Requires special handling.
     };
 
-    if (auto typeFun = globalScope->lookupType(typeguardP.kind); typeFun && typeFun->typeParams.empty())
+    if (auto typeFun = globalScope->lookupType(typeguardP.kind);
+        typeFun && typeFun->typeParams.empty() && (!FFlag::LuauTypeAliasPacks || typeFun->typePackParams.empty()))
     {
         if (auto it = std::find(primitives.begin(), primitives.end(), typeguardP.kind); it != primitives.end())
             addRefinement(refis, typeguardP.lvalue, typeFun->type);
@@ -5319,38 +5472,41 @@ void TypeChecker::resolve(const EqPredicate& eqP, ErrorVec& errVec, RefinementMa
         return;
     }
 
-    std::optional<TypeId> ty = resolveLValue(refis, scope, eqP.lvalue);
+    if (FFlag::LuauEqConstraint)
-    if (!ty)
-        return;
-
-    std::vector<TypeId> lhs = options(*ty);
-    std::vector<TypeId> rhs = options(eqP.type);
-
-    if (sense && std::any_of(lhs.begin(), lhs.end(), isUndecidable))
     {
-        addRefinement(refis, eqP.lvalue, eqP.type);
+        std::optional<TypeId> ty = resolveLValue(refis, scope, eqP.lvalue);
-        return;
+        if (!ty)
-    }
+            return;
-    else if (sense && std::any_of(rhs.begin(), rhs.end(), isUndecidable))
-        return; // Optimization: the other side has unknown types, so there's probably an overlap. Refining is no-op here.
 
-    std::unordered_set<TypeId> set;
+        std::vector<TypeId> lhs = options(*ty);
-    for (TypeId left : lhs)
+        std::vector<TypeId> rhs = options(eqP.type);
-    {
+
-        for (TypeId right : rhs)
+        if (sense && std::any_of(lhs.begin(), lhs.end(), isUndecidable))
         {
-            // When singleton types arrive, `isNil` here probably should be replaced with `isLiteral`.
+            addRefinement(refis, eqP.lvalue, eqP.type);
-            if (canUnify(left, right, eqP.location).empty() == sense || (!sense && !isNil(left)))
+            return;
-                set.insert(left);
         }
+        else if (sense && std::any_of(rhs.begin(), rhs.end(), isUndecidable))
+            return; // Optimization: the other side has unknown types, so there's probably an overlap. Refining is no-op here.
+
+        std::unordered_set<TypeId> set;
+        for (TypeId left : lhs)
+        {
+            for (TypeId right : rhs)
+            {
+                // When singleton types arrive, `isNil` here probably should be replaced with `isLiteral`.
+                if (canUnify(left, right, eqP.location).empty() == sense || (!sense && !isNil(left)))
+                    set.insert(left);
+            }
+        }
+
+        if (set.empty())
+            return;
+
+        std::vector<TypeId> viable(set.begin(), set.end());
+        TypeId result = viable.size() == 1 ? viable[0] : addType(UnionTypeVar{std::move(viable)});
+        addRefinement(refis, eqP.lvalue, result);
     }
-
-    if (set.empty())
-        return;
-
-    std::vector<TypeId> viable(set.begin(), set.end());
-    TypeId result = viable.size() == 1 ? viable[0] : addType(UnionTypeVar{std::move(viable)});
-    addRefinement(refis, eqP.lvalue, result);
 }
 
 bool TypeChecker::isNonstrictMode() const
@@ -5379,119 +5535,4 @@ std::vector<std::pair<Location, ScopePtr>> TypeChecker::getScopes() const
     return currentModule->scopes;
 }
 
-Scope::Scope(TypePackId returnType)
-    : parent(nullptr)
-    , returnType(returnType)
-    , level(TypeLevel())
-{
-}
-
-Scope::Scope(const ScopePtr& parent, int subLevel)
-    : parent(parent)
-    , returnType(parent->returnType)
-    , level(parent->level.incr())
-{
-    level.subLevel = subLevel;
-}
-
-std::optional<TypeId> Scope::lookup(const Symbol& name)
-{
-    Scope* scope = this;
-
-    while (scope)
-    {
-        auto it = scope->bindings.find(name);
-        if (it != scope->bindings.end())
-            return it->second.typeId;
-
-        scope = scope->parent.get();
-    }
-
-    return std::nullopt;
-}
-
-std::optional<TypeFun> Scope::lookupType(const Name& name)
-{
-    const Scope* scope = this;
-    while (true)
-    {
-        auto it = scope->exportedTypeBindings.find(name);
-        if (it != scope->exportedTypeBindings.end())
-            return it->second;
-
-        it = scope->privateTypeBindings.find(name);
-        if (it != scope->privateTypeBindings.end())
-            return it->second;
-
-        if (scope->parent)
-            scope = scope->parent.get();
-        else
-            return std::nullopt;
-    }
-}
-
-std::optional<TypeFun> Scope::lookupImportedType(const Name& moduleAlias, const Name& name)
-{
-    const Scope* scope = this;
-    while (scope)
-    {
-        auto it = scope->importedTypeBindings.find(moduleAlias);
-        if (it == scope->importedTypeBindings.end())
-        {
-            scope = scope->parent.get();
-            continue;
-        }
-
-        auto it2 = it->second.find(name);
-        if (it2 == it->second.end())
-        {
-            scope = scope->parent.get();
-            continue;
-        }
-
-        return it2->second;
-    }
-
-    return std::nullopt;
-}
-
-std::optional<TypePackId> Scope::lookupPack(const Name& name)
-{
-    const Scope* scope = this;
-    while (true)
-    {
-        auto it = scope->privateTypePackBindings.find(name);
-        if (it != scope->privateTypePackBindings.end())
-            return it->second;
-
-        if (scope->parent)
-            scope = scope->parent.get();
-        else
-            return std::nullopt;
-    }
-}
-
-std::optional<Binding> Scope::linearSearchForBinding(const std::string& name, bool traverseScopeChain)
-{
-    Scope* scope = this;
-
-    while (scope)
-    {
-        for (const auto& [n, binding] : scope->bindings)
-        {
-            if (n.local && n.local->name == name.c_str())
-                return binding;
-            else if (n.global.value && n.global == name.c_str())
-                return binding;
-        }
-
-        scope = scope->parent.get();
-
-        if (!traverseScopeChain)
-            break;
-    }
-
-    return std::nullopt;
-}
-
 } // namespace Luau

Analysis/src/TypePack.cpp

@@ -209,6 +209,19 @@ size_t size(TypePackId tp)
         return 0;
 }
 
+bool finite(TypePackId tp)
+{
+    tp = follow(tp);
+
+    if (auto pack = get<TypePack>(tp))
+        return pack->tail ? finite(*pack->tail) : true;
+
+    if (auto pack = get<VariadicTypePack>(tp))
+        return false;
+
+    return true;
+}
+
 size_t size(const TypePack& tp)
 {
     size_t result = tp.head.size();

Analysis/src/TypeUtils.cpp

@@ -1,11 +1,10 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/TypeUtils.h"
 
+#include "Luau/Scope.h"
 #include "Luau/ToString.h"
 #include "Luau/TypeInfer.h"
 
-LUAU_FASTFLAG(LuauStringMetatable)
-
 namespace Luau
 {
 
@@ -13,21 +12,6 @@ std::optional<TypeId> findMetatableEntry(ErrorVec& errors, const ScopePtr& globa
 {
     type = follow(type);
 
-    if (!FFlag::LuauStringMetatable)
-    {
-        if (const PrimitiveTypeVar* primType = get<PrimitiveTypeVar>(type))
-        {
-            if (primType->type != PrimitiveTypeVar::String || "__index" != entry)
-                return std::nullopt;
-
-            auto it = globalScope->bindings.find(AstName{"string"});
-            if (it != globalScope->bindings.end())
-                return it->second.typeId;
-            else
-                return std::nullopt;
-        }
-    }
-
     std::optional<TypeId> metatable = getMetatable(type);
     if (!metatable)
         return std::nullopt;

Analysis/src/TypeVar.cpp

@@ -19,11 +19,9 @@
 
 LUAU_FASTINTVARIABLE(LuauTypeMaximumStringifierLength, 500)
 LUAU_FASTINTVARIABLE(LuauTableTypeMaximumStringifierLength, 0)
-LUAU_FASTFLAG(LuauImprovedTypeGuardPredicate2)
-LUAU_FASTFLAGVARIABLE(LuauToStringFollowsBoundTo, false)
 LUAU_FASTFLAG(LuauRankNTypes)
-LUAU_FASTFLAGVARIABLE(LuauStringMetatable, false)
 LUAU_FASTFLAG(LuauTypeGuardPeelsAwaySubclasses)
+LUAU_FASTFLAG(LuauTypeAliasPacks)
 
 namespace Luau
 {
@@ -193,27 +191,11 @@ bool isOptional(TypeId ty)
 
 bool isTableIntersection(TypeId ty)
 {
-    if (FFlag::LuauImprovedTypeGuardPredicate2)
+    if (!get<IntersectionTypeVar>(follow(ty)))
-    {
-        if (!get<IntersectionTypeVar>(follow(ty)))
-            return false;
-
-        std::vector<TypeId> parts = flattenIntersection(ty);
-        return std::all_of(parts.begin(), parts.end(), getTableType);
-    }
-    else
-    {
-        if (const IntersectionTypeVar* itv = get<IntersectionTypeVar>(ty))
-        {
-            for (TypeId part : itv->parts)
-            {
-                if (getTableType(follow(part)))
-                    return true;
-            }
-        }
-
         return false;
-    }
+
+    std::vector<TypeId> parts = flattenIntersection(ty);
+    return std::all_of(parts.begin(), parts.end(), getTableType);
 }
 
 bool isOverloadedFunction(TypeId ty)
@@ -236,7 +218,7 @@ std::optional<TypeId> getMetatable(TypeId type)
     else if (const ClassTypeVar* classType = get<ClassTypeVar>(type))
         return classType->metatable;
     else if (const PrimitiveTypeVar* primitiveType = get<PrimitiveTypeVar>(type);
-             FFlag::LuauStringMetatable && primitiveType && primitiveType->metatable)
+             primitiveType && primitiveType->metatable)
     {
         LUAU_ASSERT(primitiveType->type == PrimitiveTypeVar::String);
         return primitiveType->metatable;
@@ -871,6 +853,12 @@ void StateDot::visitChildren(TypeId ty, int index)
         }
         for (TypeId itp : ttv->instantiatedTypeParams)
             visitChild(itp, index, "typeParam");
+
+        if (FFlag::LuauTypeAliasPacks)
+        {
+            for (TypePackId itp : ttv->instantiatedTypePackParams)
+                visitChild(itp, index, "typePackParam");
+        }
     }
     else if (const MetatableTypeVar* mtv = get<MetatableTypeVar>(ty))
     {

Analysis/src/Unifier.cpp

@@ -3,23 +3,25 @@
 
 #include "Luau/Common.h"
 #include "Luau/RecursionCounter.h"
+#include "Luau/Scope.h"
 #include "Luau/TypePack.h"
 #include "Luau/TypeUtils.h"
+#include "Luau/TimeTrace.h"
 
 #include <algorithm>
 
 LUAU_FASTINT(LuauTypeInferRecursionLimit);
 LUAU_FASTINT(LuauTypeInferTypePackLoopLimit);
-LUAU_FASTINTVARIABLE(LuauTypeInferIterationLimit, 0);
+LUAU_FASTINTVARIABLE(LuauTypeInferIterationLimit, 2000);
-LUAU_FASTFLAGVARIABLE(LuauLogTableTypeVarBoundTo, false)
 LUAU_FASTFLAG(LuauGenericFunctions)
+LUAU_FASTFLAGVARIABLE(LuauTableSubtypingVariance, false);
 LUAU_FASTFLAGVARIABLE(LuauDontMutatePersistentFunctions, false)
 LUAU_FASTFLAG(LuauRankNTypes)
-LUAU_FASTFLAG(LuauStringMetatable)
 LUAU_FASTFLAGVARIABLE(LuauUnionHeuristic, false)
 LUAU_FASTFLAGVARIABLE(LuauTableUnificationEarlyTest, false)
 LUAU_FASTFLAGVARIABLE(LuauSealedTableUnifyOptionalFix, false)
 LUAU_FASTFLAGVARIABLE(LuauOccursCheckOkWithRecursiveFunctions, false)
+LUAU_FASTFLAGVARIABLE(LuauTypecheckOpts, false)
 
 namespace Luau
 {
@@ -43,21 +45,23 @@ Unifier::Unifier(TypeArena* types, Mode mode, ScopePtr globalScope, const Locati
     , globalScope(std::move(globalScope))
     , location(location)
     , variance(variance)
-    , counters(std::make_shared<UnifierCounters>())
+    , counters(&countersData)
+    , counters_DEPRECATED(std::make_shared<UnifierCounters>())
     , iceHandler(iceHandler)
 {
     LUAU_ASSERT(iceHandler);
 }
 
 Unifier::Unifier(TypeArena* types, Mode mode, ScopePtr globalScope, const std::vector<std::pair<TypeId, TypeId>>& seen, const Location& location,
-    Variance variance, InternalErrorReporter* iceHandler, const std::shared_ptr<UnifierCounters>& counters)
+    Variance variance, InternalErrorReporter* iceHandler, const std::shared_ptr<UnifierCounters>& counters_DEPRECATED, UnifierCounters* counters)
     : types(types)
     , mode(mode)
     , globalScope(std::move(globalScope))
     , log(seen)
     , location(location)
     , variance(variance)
-    , counters(counters ? counters : std::make_shared<UnifierCounters>())
+    , counters(counters ? counters : &countersData)
+    , counters_DEPRECATED(counters_DEPRECATED ? counters_DEPRECATED : std::make_shared<UnifierCounters>())
     , iceHandler(iceHandler)
 {
     LUAU_ASSERT(iceHandler);
@@ -65,16 +69,26 @@ Unifier::Unifier(TypeArena* types, Mode mode, ScopePtr globalScope, const std::v
 
 void Unifier::tryUnify(TypeId superTy, TypeId subTy, bool isFunctionCall, bool isIntersection)
 {
-    counters->iterationCount = 0;
+    if (FFlag::LuauTypecheckOpts)
+        counters->iterationCount = 0;
+    else
+        counters_DEPRECATED->iterationCount = 0;
+
     return tryUnify_(superTy, subTy, isFunctionCall, isIntersection);
 }
 
 void Unifier::tryUnify_(TypeId superTy, TypeId subTy, bool isFunctionCall, bool isIntersection)
 {
-    RecursionLimiter _ra(&counters->recursionCount, FInt::LuauTypeInferRecursionLimit);
+    RecursionLimiter _ra(
+        FFlag::LuauTypecheckOpts ? &counters->recursionCount : &counters_DEPRECATED->recursionCount, FInt::LuauTypeInferRecursionLimit);
 
-    ++counters->iterationCount;
+    if (FFlag::LuauTypecheckOpts)
-    if (FInt::LuauTypeInferIterationLimit > 0 && FInt::LuauTypeInferIterationLimit < counters->iterationCount)
+        ++counters->iterationCount;
+    else
+        ++counters_DEPRECATED->iterationCount;
+
+    if (FInt::LuauTypeInferIterationLimit > 0 &&
+        FInt::LuauTypeInferIterationLimit < (FFlag::LuauTypecheckOpts ? counters->iterationCount : counters_DEPRECATED->iterationCount))
     {
         errors.push_back(TypeError{location, UnificationTooComplex{}});
         return;
@@ -440,7 +454,11 @@ ErrorVec Unifier::canUnify(TypePackId superTy, TypePackId subTy, bool isFunction
 
 void Unifier::tryUnify(TypePackId superTp, TypePackId subTp, bool isFunctionCall)
 {
-    counters->iterationCount = 0;
+    if (FFlag::LuauTypecheckOpts)
+        counters->iterationCount = 0;
+    else
+        counters_DEPRECATED->iterationCount = 0;
+
     return tryUnify_(superTp, subTp, isFunctionCall);
 }
 
@@ -450,10 +468,16 @@ void Unifier::tryUnify(TypePackId superTp, TypePackId subTp, bool isFunctionCall
  */
 void Unifier::tryUnify_(TypePackId superTp, TypePackId subTp, bool isFunctionCall)
 {
-    RecursionLimiter _ra(&counters->recursionCount, FInt::LuauTypeInferRecursionLimit);
+    RecursionLimiter _ra(
+        FFlag::LuauTypecheckOpts ? &counters->recursionCount : &counters_DEPRECATED->recursionCount, FInt::LuauTypeInferRecursionLimit);
 
-    ++counters->iterationCount;
+    if (FFlag::LuauTypecheckOpts)
-    if (FInt::LuauTypeInferIterationLimit > 0 && FInt::LuauTypeInferIterationLimit < counters->iterationCount)
+        ++counters->iterationCount;
+    else
+        ++counters_DEPRECATED->iterationCount;
+
+    if (FInt::LuauTypeInferIterationLimit > 0 &&
+        FInt::LuauTypeInferIterationLimit < (FFlag::LuauTypecheckOpts ? counters->iterationCount : counters_DEPRECATED->iterationCount))
     {
         errors.push_back(TypeError{location, UnificationTooComplex{}});
         return;
@@ -762,9 +786,210 @@ struct Resetter
 
 void Unifier::tryUnifyTables(TypeId left, TypeId right, bool isIntersection)
 {
-    std::unique_ptr<Resetter> resetter;
+    if (!FFlag::LuauTableSubtypingVariance)
+        return DEPRECATED_tryUnifyTables(left, right, isIntersection);
 
-    resetter.reset(new Resetter{&variance});
+    TableTypeVar* lt = getMutable<TableTypeVar>(left);
+    TableTypeVar* rt = getMutable<TableTypeVar>(right);
+    if (!lt || !rt)
+        ice("passed non-table types to unifyTables");
+
+    std::vector<std::string> missingProperties;
+    std::vector<std::string> extraProperties;
+
+    // Reminder: left is the supertype, right is the subtype.
+    // Width subtyping: any property in the supertype must be in the subtype,
+    // and the types must agree.
+    for (const auto& [name, prop] : lt->props)
+    {
+        const auto& r = rt->props.find(name);
+        if (r != rt->props.end())
+        {
+            // TODO: read-only properties don't need invariance
+            Resetter resetter{&variance};
+            variance = Invariant;
+
+            Unifier innerState = makeChildUnifier();
+            innerState.tryUnify_(prop.type, r->second.type);
+            checkChildUnifierTypeMismatch(innerState.errors, left, right);
+            if (innerState.errors.empty())
+                log.concat(std::move(innerState.log));
+            else
+                innerState.log.rollback();
+        }
+        else if (rt->indexer && isString(rt->indexer->indexType))
+        {
+            // TODO: read-only indexers don't need invariance
+            // TODO: really we should only allow this if prop.type is optional.
+            Resetter resetter{&variance};
+            variance = Invariant;
+
+            Unifier innerState = makeChildUnifier();
+            innerState.tryUnify_(prop.type, rt->indexer->indexResultType);
+            checkChildUnifierTypeMismatch(innerState.errors, left, right);
+            if (innerState.errors.empty())
+                log.concat(std::move(innerState.log));
+            else
+                innerState.log.rollback();
+        }
+        else if (isOptional(prop.type) || get<AnyTypeVar>(follow(prop.type)))
+            // TODO: this case is unsound, but without it our test suite fails. CLI-46031
+            // TODO: should isOptional(anyType) be true?
+            {}
+        else if (rt->state == TableState::Free)
+        {
+            log(rt);
+            rt->props[name] = prop;
+        }
+        else
+            missingProperties.push_back(name);
+    }
+
+    for (const auto& [name, prop] : rt->props)
+    {
+        if (lt->props.count(name))
+        {
+            // If both lt and rt contain the property, then
+            // we're done since we already unified them above
+        }
+        else if (lt->indexer && isString(lt->indexer->indexType))
+        {
+            // TODO: read-only indexers don't need invariance
+            // TODO: really we should only allow this if prop.type is optional.
+            Resetter resetter{&variance};
+            variance = Invariant;
+
+            Unifier innerState = makeChildUnifier();
+            innerState.tryUnify_(prop.type, lt->indexer->indexResultType);
+            checkChildUnifierTypeMismatch(innerState.errors, left, right);
+            if (innerState.errors.empty())
+                log.concat(std::move(innerState.log));
+            else
+                innerState.log.rollback();
+        }
+        else if (lt->state == TableState::Unsealed)
+        {
+            // TODO: this case is unsound when variance is Invariant, but without it lua-apps fails to typecheck.
+            // TODO: file a JIRA
+            // TODO: hopefully readonly/writeonly properties will fix this.
+            Property clone = prop;
+            clone.type = deeplyOptional(clone.type);
+            log(lt);
+            lt->props[name] = clone;
+        }
+        else if (variance == Covariant)
+            {}
+        else if (isOptional(prop.type) || get<AnyTypeVar>(follow(prop.type)))
+            // TODO: this case is unsound, but without it our test suite fails. CLI-46031
+            // TODO: should isOptional(anyType) be true?
+            {}
+        else if (lt->state == TableState::Free)
+        {
+            log(lt);
+            lt->props[name] = prop;
+        }
+        else
+            extraProperties.push_back(name);
+    }
+
+    // Unify indexers
+    if (lt->indexer && rt->indexer)
+    {
+        // TODO: read-only indexers don't need invariance
+        Resetter resetter{&variance};
+        variance = Invariant;
+
+        Unifier innerState = makeChildUnifier();
+        innerState.tryUnify(*lt->indexer, *rt->indexer);
+        checkChildUnifierTypeMismatch(innerState.errors, left, right);
+        if (innerState.errors.empty())
+            log.concat(std::move(innerState.log));
+        else
+            innerState.log.rollback();
+    }
+    else if (lt->indexer)
+    {
+        if (rt->state == TableState::Unsealed || rt->state == TableState::Free)
+        {
+            // passing/assigning a table without an indexer to something that has one
+            // e.g. table.insert(t, 1) where t is a non-sealed table and doesn't have an indexer.
+            // TODO: we only need to do this if the supertype's indexer is read/write
+            // since that can add indexed elements.
+            log(rt);
+            rt->indexer = lt->indexer;
+        }
+    }
+    else if (rt->indexer && variance == Invariant)
+    {
+        // Symmetric if we are invariant
+        if (lt->state == TableState::Unsealed || lt->state == TableState::Free)
+        {
+            log(lt);
+            lt->indexer = rt->indexer;
+        }
+    }
+
+    if (!missingProperties.empty())
+    {
+        errors.push_back(TypeError{location, MissingProperties{left, right, std::move(missingProperties)}});
+        return;
+    }
+
+    if (!extraProperties.empty())
+    {
+        errors.push_back(TypeError{location, MissingProperties{left, right, std::move(extraProperties), MissingProperties::Extra}});
+        return;
+    }
+
+    /*
+     * TypeVars are commonly cyclic, so it is entirely possible
+     * for unifying a property of a table to change the table itself!
+     * We need to check for this and start over if we notice this occurring.
+     *
+     * I believe this is guaranteed to terminate eventually because this will
+     * only happen when a free table is bound to another table.
+     */
+    if (lt->boundTo || rt->boundTo)
+        return tryUnify_(left, right);
+
+    if (lt->state == TableState::Free)
+    {
+        log(lt);
+        lt->boundTo = right;
+    }
+    else if (rt->state == TableState::Free)
+    {
+        log(rt);
+        rt->boundTo = left;
+    }
+}
+
+TypeId Unifier::deeplyOptional(TypeId ty, std::unordered_map<TypeId, TypeId> seen)
+{
+    ty = follow(ty);
+    if (get<AnyTypeVar>(ty))
+        return ty;
+    else if (isOptional(ty))
+        return ty;
+    else if (const TableTypeVar* ttv = get<TableTypeVar>(ty))
+    {
+        TypeId& result = seen[ty];
+        if (result)
+            return result;
+        result = types->addType(*ttv);
+        TableTypeVar* resultTtv = getMutable<TableTypeVar>(result);
+        for (auto& [name, prop] : resultTtv->props)
+            prop.type = deeplyOptional(prop.type, seen);
+        return types->addType(UnionTypeVar{{ singletonTypes.nilType, result }});;
+    }
+    else
+        return types->addType(UnionTypeVar{{ singletonTypes.nilType, ty }});
+}
+
+void Unifier::DEPRECATED_tryUnifyTables(TypeId left, TypeId right, bool isIntersection)
+{
+    LUAU_ASSERT(!FFlag::LuauTableSubtypingVariance);
+    Resetter resetter{&variance};
     variance = Invariant;
 
     TableTypeVar* lt = getMutable<TableTypeVar>(left);
@@ -894,10 +1119,7 @@ void Unifier::tryUnifyFreeTable(TypeId freeTypeId, TypeId otherTypeId)
 
     if (!freeTable->boundTo && otherTable->state != TableState::Free)
     {
-        if (FFlag::LuauLogTableTypeVarBoundTo)
+        log(freeTable);
-            log(freeTable);
-        else
-            log(freeTypeId);
         freeTable->boundTo = otherTypeId;
     }
 }
@@ -1196,9 +1418,11 @@ void Unifier::tryUnify(const TableIndexer& superIndexer, const TableIndexer& sub
     tryUnify_(superIndexer.indexResultType, subIndexer.indexResultType);
 }
 
-static void queueTypePack(
+static void queueTypePack_DEPRECATED(
     std::vector<TypeId>& queue, std::unordered_set<TypePackId>& seenTypePacks, Unifier& state, TypePackId a, TypePackId anyTypePack)
 {
+    LUAU_ASSERT(!FFlag::LuauTypecheckOpts);
+
     while (true)
     {
         if (FFlag::LuauAddMissingFollow)
@@ -1244,6 +1468,55 @@ static void queueTypePack(
     }
 }
 
+static void queueTypePack(std::vector<TypeId>& queue, DenseHashSet<TypePackId>& seenTypePacks, Unifier& state, TypePackId a, TypePackId anyTypePack)
+{
+    LUAU_ASSERT(FFlag::LuauTypecheckOpts);
+
+    while (true)
+    {
+        if (FFlag::LuauAddMissingFollow)
+            a = follow(a);
+
+        if (seenTypePacks.find(a))
+            break;
+        seenTypePacks.insert(a);
+
+        if (FFlag::LuauAddMissingFollow)
+        {
+            if (get<Unifiable::Free>(a))
+            {
+                state.log(a);
+                *asMutable(a) = Unifiable::Bound{anyTypePack};
+            }
+            else if (auto tp = get<TypePack>(a))
+            {
+                queue.insert(queue.end(), tp->head.begin(), tp->head.end());
+                if (tp->tail)
+                    a = *tp->tail;
+                else
+                    break;
+            }
+        }
+        else
+        {
+            if (get<Unifiable::Free>(a))
+            {
+                state.log(a);
+                *asMutable(a) = Unifiable::Bound{anyTypePack};
+            }
+
+            if (auto tp = get<TypePack>(a))
+            {
+                queue.insert(queue.end(), tp->head.begin(), tp->head.end());
+                if (tp->tail)
+                    a = *tp->tail;
+                else
+                    break;
+            }
+        }
+    }
+}
+
 void Unifier::tryUnifyVariadics(TypePackId superTp, TypePackId subTp, bool reversed, int subOffset)
 {
     const VariadicTypePack* lv = get<VariadicTypePack>(superTp);
@@ -1297,9 +1570,11 @@ void Unifier::tryUnifyVariadics(TypePackId superTp, TypePackId subTp, bool rever
     }
 }
 
-static void tryUnifyWithAny(
+static void tryUnifyWithAny_DEPRECATED(
     std::vector<TypeId>& queue, Unifier& state, std::unordered_set<TypePackId>& seenTypePacks, TypeId anyType, TypePackId anyTypePack)
 {
+    LUAU_ASSERT(!FFlag::LuauTypecheckOpts);
+
     std::unordered_set<TypeId> seen;
 
     while (!queue.empty())
@@ -1310,6 +1585,59 @@ static void tryUnifyWithAny(
             continue;
         seen.insert(ty);
 
+        if (get<FreeTypeVar>(ty))
+        {
+            state.log(ty);
+            *asMutable(ty) = BoundTypeVar{anyType};
+        }
+        else if (auto fun = get<FunctionTypeVar>(ty))
+        {
+            queueTypePack_DEPRECATED(queue, seenTypePacks, state, fun->argTypes, anyTypePack);
+            queueTypePack_DEPRECATED(queue, seenTypePacks, state, fun->retType, anyTypePack);
+        }
+        else if (auto table = get<TableTypeVar>(ty))
+        {
+            for (const auto& [_name, prop] : table->props)
+                queue.push_back(prop.type);
+
+            if (table->indexer)
+            {
+                queue.push_back(table->indexer->indexType);
+                queue.push_back(table->indexer->indexResultType);
+            }
+        }
+        else if (auto mt = get<MetatableTypeVar>(ty))
+        {
+            queue.push_back(mt->table);
+            queue.push_back(mt->metatable);
+        }
+        else if (get<ClassTypeVar>(ty))
+        {
+            // ClassTypeVars never contain free typevars.
+        }
+        else if (auto union_ = get<UnionTypeVar>(ty))
+            queue.insert(queue.end(), union_->options.begin(), union_->options.end());
+        else if (auto intersection = get<IntersectionTypeVar>(ty))
+            queue.insert(queue.end(), intersection->parts.begin(), intersection->parts.end());
+        else
+        {
+        } // Primitives, any, errors, and generics are left untouched.
+    }
+}
+
+static void tryUnifyWithAny(std::vector<TypeId>& queue, Unifier& state, DenseHashSet<TypeId>& seen, DenseHashSet<TypePackId>& seenTypePacks,
+    TypeId anyType, TypePackId anyTypePack)
+{
+    LUAU_ASSERT(FFlag::LuauTypecheckOpts);
+
+    while (!queue.empty())
+    {
+        TypeId ty = follow(queue.back());
+        queue.pop_back();
+        if (seen.find(ty))
+            continue;
+        seen.insert(ty);
+
         if (get<FreeTypeVar>(ty))
         {
             state.log(ty);
@@ -1354,14 +1682,33 @@ void Unifier::tryUnifyWithAny(TypeId any, TypeId ty)
 {
     LUAU_ASSERT(get<AnyTypeVar>(any) || get<ErrorTypeVar>(any));
 
+    if (FFlag::LuauTypecheckOpts)
+    {
+        // These types are not visited in general loop below
+        if (get<PrimitiveTypeVar>(ty) || get<AnyTypeVar>(ty) || get<ClassTypeVar>(ty))
+            return;
+    }
+
     const TypePackId anyTypePack = types->addTypePack(TypePackVar{VariadicTypePack{singletonTypes.anyType}});
 
     const TypePackId anyTP = get<AnyTypeVar>(any) ? anyTypePack : types->addTypePack(TypePackVar{Unifiable::Error{}});
 
-    std::unordered_set<TypePackId> seenTypePacks;
+    if (FFlag::LuauTypecheckOpts)
-    std::vector<TypeId> queue = {ty};
+    {
+        std::vector<TypeId> queue = {ty};
 
-    Luau::tryUnifyWithAny(queue, *this, seenTypePacks, singletonTypes.anyType, anyTP);
+        tempSeenTy.clear();
+        tempSeenTp.clear();
+
+        Luau::tryUnifyWithAny(queue, *this, tempSeenTy, tempSeenTp, singletonTypes.anyType, anyTP);
+    }
+    else
+    {
+        std::unordered_set<TypePackId> seenTypePacks;
+        std::vector<TypeId> queue = {ty};
+
+        Luau::tryUnifyWithAny_DEPRECATED(queue, *this, seenTypePacks, singletonTypes.anyType, anyTP);
+    }
 }
 
 void Unifier::tryUnifyWithAny(TypePackId any, TypePackId ty)
@@ -1370,12 +1717,26 @@ void Unifier::tryUnifyWithAny(TypePackId any, TypePackId ty)
 
     const TypeId anyTy = singletonTypes.errorType;
 
-    std::unordered_set<TypePackId> seenTypePacks;
+    if (FFlag::LuauTypecheckOpts)
-    std::vector<TypeId> queue;
+    {
+        std::vector<TypeId> queue;
 
-    queueTypePack(queue, seenTypePacks, *this, ty, any);
+        tempSeenTy.clear();
+        tempSeenTp.clear();
 
-    Luau::tryUnifyWithAny(queue, *this, seenTypePacks, anyTy, any);
+        queueTypePack(queue, tempSeenTp, *this, ty, any);
+
+        Luau::tryUnifyWithAny(queue, *this, tempSeenTy, tempSeenTp, anyTy, any);
+    }
+    else
+    {
+        std::unordered_set<TypePackId> seenTypePacks;
+        std::vector<TypeId> queue;
+
+        queueTypePack_DEPRECATED(queue, seenTypePacks, *this, ty, any);
+
+        Luau::tryUnifyWithAny_DEPRECATED(queue, *this, seenTypePacks, anyTy, any);
+    }
 }
 
 std::optional<TypeId> Unifier::findTablePropertyRespectingMeta(TypeId lhsType, Name name)
@@ -1387,21 +1748,6 @@ std::optional<TypeId> Unifier::findMetatableEntry(TypeId type, std::string entry
 {
     type = follow(type);
 
-    if (!FFlag::LuauStringMetatable)
-    {
-        if (const PrimitiveTypeVar* primType = get<PrimitiveTypeVar>(type))
-        {
-            if (primType->type != PrimitiveTypeVar::String || "__index" != entry)
-                return std::nullopt;
-
-            auto found = globalScope->bindings.find(AstName{"string"});
-            if (found == globalScope->bindings.end())
-                return std::nullopt;
-            else
-                return found->second.typeId;
-        }
-    }
-
     std::optional<TypeId> metatable = getMetatable(type);
     if (!metatable)
         return std::nullopt;
@@ -1427,21 +1773,36 @@ std::optional<TypeId> Unifier::findMetatableEntry(TypeId type, std::string entry
 
 void Unifier::occursCheck(TypeId needle, TypeId haystack)
 {
-    std::unordered_set<TypeId> seen;
+    std::unordered_set<TypeId> seen_DEPRECATED;
-    return occursCheck(seen, needle, haystack);
+
+    if (FFlag::LuauTypecheckOpts)
+        tempSeenTy.clear();
+
+    return occursCheck(seen_DEPRECATED, tempSeenTy, needle, haystack);
 }
 
-void Unifier::occursCheck(std::unordered_set<TypeId>& seen, TypeId needle, TypeId haystack)
+void Unifier::occursCheck(std::unordered_set<TypeId>& seen_DEPRECATED, DenseHashSet<TypeId>& seen, TypeId needle, TypeId haystack)
 {
-    RecursionLimiter _ra(&counters->recursionCount, FInt::LuauTypeInferRecursionLimit);
+    RecursionLimiter _ra(
+        FFlag::LuauTypecheckOpts ? &counters->recursionCount : &counters_DEPRECATED->recursionCount, FInt::LuauTypeInferRecursionLimit);
 
     needle = follow(needle);
     haystack = follow(haystack);
 
-    if (seen.end() != seen.find(haystack))
+    if (FFlag::LuauTypecheckOpts)
-        return;
+    {
+        if (seen.find(haystack))
+            return;
 
-    seen.insert(haystack);
+        seen.insert(haystack);
+    }
+    else
+    {
+        if (seen_DEPRECATED.end() != seen_DEPRECATED.find(haystack))
+            return;
+
+        seen_DEPRECATED.insert(haystack);
+    }
 
     if (get<Unifiable::Error>(needle))
         return;
@@ -1458,7 +1819,7 @@ void Unifier::occursCheck(std::unordered_set<TypeId>& seen, TypeId needle, TypeI
     }
 
     auto check = [&](TypeId tv) {
-        occursCheck(seen, needle, tv);
+        occursCheck(seen_DEPRECATED, seen, needle, tv);
     };
 
     if (get<FreeTypeVar>(haystack))
@@ -1488,19 +1849,33 @@ void Unifier::occursCheck(std::unordered_set<TypeId>& seen, TypeId needle, TypeI
 
 void Unifier::occursCheck(TypePackId needle, TypePackId haystack)
 {
-    std::unordered_set<TypePackId> seen;
+    std::unordered_set<TypePackId> seen_DEPRECATED;
-    return occursCheck(seen, needle, haystack);
+
+    if (FFlag::LuauTypecheckOpts)
+        tempSeenTp.clear();
+
+    return occursCheck(seen_DEPRECATED, tempSeenTp, needle, haystack);
 }
 
-void Unifier::occursCheck(std::unordered_set<TypePackId>& seen, TypePackId needle, TypePackId haystack)
+void Unifier::occursCheck(std::unordered_set<TypePackId>& seen_DEPRECATED, DenseHashSet<TypePackId>& seen, TypePackId needle, TypePackId haystack)
 {
     needle = follow(needle);
     haystack = follow(haystack);
 
-    if (seen.find(haystack) != seen.end())
+    if (FFlag::LuauTypecheckOpts)
-        return;
+    {
+        if (seen.find(haystack))
+            return;
 
-    seen.insert(haystack);
+        seen.insert(haystack);
+    }
+    else
+    {
+        if (seen_DEPRECATED.end() != seen_DEPRECATED.find(haystack))
+            return;
+
+        seen_DEPRECATED.insert(haystack);
+    }
 
     if (get<Unifiable::Error>(needle))
         return;
@@ -1508,7 +1883,8 @@ void Unifier::occursCheck(std::unordered_set<TypePackId>& seen, TypePackId needl
     if (!get<Unifiable::Free>(needle))
         ice("Expected needle pack to be free");
 
-    RecursionLimiter _ra(&counters->recursionCount, FInt::LuauTypeInferRecursionLimit);
+    RecursionLimiter _ra(
+        FFlag::LuauTypecheckOpts ? &counters->recursionCount : &counters_DEPRECATED->recursionCount, FInt::LuauTypeInferRecursionLimit);
 
     while (!get<ErrorTypeVar>(haystack))
     {
@@ -1528,8 +1904,8 @@ void Unifier::occursCheck(std::unordered_set<TypePackId>& seen, TypePackId needl
                 {
                     if (auto f = get<FunctionTypeVar>(FFlag::LuauAddMissingFollow ? follow(ty) : ty))
                     {
-                        occursCheck(seen, needle, f->argTypes);
+                        occursCheck(seen_DEPRECATED, seen, needle, f->argTypes);
-                        occursCheck(seen, needle, f->retType);
+                        occursCheck(seen_DEPRECATED, seen, needle, f->retType);
                     }
                 }
             }
@@ -1546,7 +1922,7 @@ void Unifier::occursCheck(std::unordered_set<TypePackId>& seen, TypePackId needl
 
 Unifier Unifier::makeChildUnifier()
 {
-    return Unifier{types, mode, globalScope, log.seen, location, variance, iceHandler, counters};
+    return Unifier{types, mode, globalScope, log.seen, location, variance, iceHandler, counters_DEPRECATED, counters};
 }
 
 bool Unifier::isNonstrictMode() const

Ast/include/Luau/Ast.h

@@ -264,6 +264,10 @@ public:
     {
         return false;
     }
+    virtual bool visit(class AstTypePackExplicit* node)
+    {
+        return visit((class AstTypePack*)node);
+    }
     virtual bool visit(class AstTypePackVariadic* node)
     {
         return visit((class AstTypePack*)node);
@@ -930,12 +934,14 @@ class AstStatTypeAlias : public AstStat
 public:
     LUAU_RTTI(AstStatTypeAlias)
 
-    AstStatTypeAlias(const Location& location, const AstName& name, const AstArray<AstName>& generics, AstType* type, bool exported);
+    AstStatTypeAlias(const Location& location, const AstName& name, const AstArray<AstName>& generics, const AstArray<AstName>& genericPacks,
+        AstType* type, bool exported);
 
     void visit(AstVisitor* visitor) override;
 
     AstName name;
     AstArray<AstName> generics;
+    AstArray<AstName> genericPacks;
     AstType* type;
     bool exported;
 };
@@ -1007,19 +1013,28 @@ public:
     }
 };
 
+// Don't have Luau::Variant available, it's a bit of an overhead, but a plain struct is nice to use
+struct AstTypeOrPack
+{
+    AstType* type = nullptr;
+    AstTypePack* typePack = nullptr;
+};
+
 class AstTypeReference : public AstType
 {
 public:
     LUAU_RTTI(AstTypeReference)
 
-    AstTypeReference(const Location& location, std::optional<AstName> prefix, AstName name, const AstArray<AstType*>& generics = {});
+    AstTypeReference(const Location& location, std::optional<AstName> prefix, AstName name, bool hasParameterList = false,
+        const AstArray<AstTypeOrPack>& parameters = {});
 
     void visit(AstVisitor* visitor) override;
 
     bool hasPrefix;
+    bool hasParameterList;
     AstName prefix;
     AstName name;
-    AstArray<AstType*> generics;
+    AstArray<AstTypeOrPack> parameters;
 };
 
 struct AstTableProp
@@ -1152,6 +1167,18 @@ public:
     }
 };
 
+class AstTypePackExplicit : public AstTypePack
+{
+public:
+    LUAU_RTTI(AstTypePackExplicit)
+
+    AstTypePackExplicit(const Location& location, AstTypeList typeList);
+
+    void visit(AstVisitor* visitor) override;
+
+    AstTypeList typeList;
+};
+
 class AstTypePackVariadic : public AstTypePack
 {
 public:

Ast/include/Luau/DenseHash.h

@@ -136,7 +136,10 @@ public:
             const Key& key = ItemInterface::getKey(data[i]);
 
             if (!eq(key, empty_key))
-                *newtable.insert_unsafe(key) = data[i];
+            {
+                Item* item = newtable.insert_unsafe(key);
+                *item = std::move(data[i]);
+            }
         }
 
         LUAU_ASSERT(count == newtable.count);

Ast/include/Luau/Parser.h

@@ -218,13 +218,14 @@ private:
 
     AstTableIndexer* parseTableIndexerAnnotation();
 
-    AstType* parseFunctionTypeAnnotation();
+    AstTypeOrPack parseFunctionTypeAnnotation(bool allowPack);
     AstType* parseFunctionTypeAnnotationTail(const Lexeme& begin, AstArray<AstName> generics, AstArray<AstName> genericPacks,
         AstArray<AstType*>& params, AstArray<std::optional<AstArgumentName>>& paramNames, AstTypePack* varargAnnotation);
 
     AstType* parseTableTypeAnnotation();
-    AstType* parseSimpleTypeAnnotation();
+    AstTypeOrPack parseSimpleTypeAnnotation(bool allowPack);
 
+    AstTypeOrPack parseTypeOrPackAnnotation();
     AstType* parseTypeAnnotation(TempVector<AstType*>& parts, const Location& begin);
     AstType* parseTypeAnnotation();
 
@@ -284,7 +285,7 @@ private:
     std::pair<AstArray<AstName>, AstArray<AstName>> parseGenericTypeListIfFFlagParseGenericFunctions();
 
     // `<' typeAnnotation[, ...] `>'
-    AstArray<AstType*> parseTypeParams();
+    AstArray<AstTypeOrPack> parseTypeParams();
 
     AstExpr* parseString();
 
@@ -413,6 +414,7 @@ private:
     std::vector<AstLocal*> scratchLocal;
     std::vector<AstTableProp> scratchTableTypeProps;
     std::vector<AstType*> scratchAnnotation;
+    std::vector<AstTypeOrPack> scratchTypeOrPackAnnotation;
     std::vector<AstDeclaredClassProp> scratchDeclaredClassProps;
     std::vector<AstExprTable::Item> scratchItem;
     std::vector<AstArgumentName> scratchArgName;

Ast/include/Luau/TimeTrace.h

@@ -0,0 +1,223 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Common.h"
+
+#include <vector>
+
+#include <stdint.h>
+
+LUAU_FASTFLAG(DebugLuauTimeTracing)
+
+#if defined(LUAU_ENABLE_TIME_TRACE)
+
+namespace Luau
+{
+namespace TimeTrace
+{
+uint32_t getClockMicroseconds();
+
+struct Token
+{
+    const char* name;
+    const char* category;
+};
+
+enum class EventType : uint8_t
+{
+    Enter,
+    Leave,
+
+    ArgName,
+    ArgValue,
+};
+
+struct Event
+{
+    EventType type;
+    uint16_t token;
+
+    union
+    {
+        uint32_t microsec; // 1 hour trace limit
+        uint32_t dataPos;
+    } data;
+};
+
+struct GlobalContext;
+struct ThreadContext;
+
+GlobalContext& getGlobalContext();
+
+uint16_t createToken(GlobalContext& context, const char* name, const char* category);
+uint32_t createThread(GlobalContext& context, ThreadContext* threadContext);
+void releaseThread(GlobalContext& context, ThreadContext* threadContext);
+void flushEvents(GlobalContext& context, uint32_t threadId, const std::vector<Event>& events, const std::vector<char>& data);
+
+struct ThreadContext
+{
+    ThreadContext()
+        : globalContext(getGlobalContext())
+    {
+        threadId = createThread(globalContext, this);
+    }
+
+    ~ThreadContext()
+    {
+        if (!events.empty())
+            flushEvents();
+
+        releaseThread(globalContext, this);
+    }
+
+    void flushEvents()
+    {
+        static uint16_t flushToken = createToken(globalContext, "flushEvents", "TimeTrace");
+
+        events.push_back({EventType::Enter, flushToken, {getClockMicroseconds()}});
+
+        TimeTrace::flushEvents(globalContext, threadId, events, data);
+
+        events.clear();
+        data.clear();
+
+        events.push_back({EventType::Leave, 0, {getClockMicroseconds()}});
+    }
+
+    void eventEnter(uint16_t token)
+    {
+        eventEnter(token, getClockMicroseconds());
+    }
+
+    void eventEnter(uint16_t token, uint32_t microsec)
+    {
+        events.push_back({EventType::Enter, token, {microsec}});
+    }
+
+    void eventLeave()
+    {
+        eventLeave(getClockMicroseconds());
+    }
+
+    void eventLeave(uint32_t microsec)
+    {
+        events.push_back({EventType::Leave, 0, {microsec}});
+
+        if (events.size() > kEventFlushLimit)
+            flushEvents();
+    }
+
+    void eventArgument(const char* name, const char* value)
+    {
+        uint32_t pos = uint32_t(data.size());
+        data.insert(data.end(), name, name + strlen(name) + 1);
+        events.push_back({EventType::ArgName, 0, {pos}});
+
+        pos = uint32_t(data.size());
+        data.insert(data.end(), value, value + strlen(value) + 1);
+        events.push_back({EventType::ArgValue, 0, {pos}});
+    }
+
+    GlobalContext& globalContext;
+    uint32_t threadId;
+    std::vector<Event> events;
+    std::vector<char> data;
+
+    static constexpr size_t kEventFlushLimit = 8192;
+};
+
+ThreadContext& getThreadContext();
+
+struct Scope
+{
+    explicit Scope(ThreadContext& context, uint16_t token)
+        : context(context)
+    {
+        if (!FFlag::DebugLuauTimeTracing)
+            return;
+
+        context.eventEnter(token);
+    }
+
+    ~Scope()
+    {
+        if (!FFlag::DebugLuauTimeTracing)
+            return;
+
+        context.eventLeave();
+    }
+
+    ThreadContext& context;
+};
+
+struct OptionalTailScope
+{
+    explicit OptionalTailScope(ThreadContext& context, uint16_t token, uint32_t threshold)
+        : context(context)
+        , token(token)
+        , threshold(threshold)
+    {
+        if (!FFlag::DebugLuauTimeTracing)
+            return;
+
+        pos = uint32_t(context.events.size());
+        microsec = getClockMicroseconds();
+    }
+
+    ~OptionalTailScope()
+    {
+        if (!FFlag::DebugLuauTimeTracing)
+            return;
+
+        if (pos == context.events.size())
+        {
+            uint32_t curr = getClockMicroseconds();
+
+            if (curr - microsec > threshold)
+            {
+                context.eventEnter(token, microsec);
+                context.eventLeave(curr);
+            }
+        }
+    }
+
+    ThreadContext& context;
+    uint16_t token;
+    uint32_t threshold;
+    uint32_t microsec;
+    uint32_t pos;
+};
+
+LUAU_NOINLINE std::pair<uint16_t, Luau::TimeTrace::ThreadContext&> createScopeData(const char* name, const char* category);
+
+} // namespace TimeTrace
+} // namespace Luau
+
+// Regular scope
+#define LUAU_TIMETRACE_SCOPE(name, category)                                       \
+    static auto lttScopeStatic = Luau::TimeTrace::createScopeData(name, category); \
+    Luau::TimeTrace::Scope lttScope(lttScopeStatic.second, lttScopeStatic.first)
+
+// A scope without nested scopes that may be skipped if the time it took is less than the threshold
+#define LUAU_TIMETRACE_OPTIONAL_TAIL_SCOPE(name, category, microsec)                      \
+    static auto lttScopeStaticOptTail = Luau::TimeTrace::createScopeData(name, category); \
+    Luau::TimeTrace::OptionalTailScope lttScope(lttScopeStaticOptTail.second, lttScopeStaticOptTail.first, microsec)
+
+// Extra key/value data can be added to regular scopes
+#define LUAU_TIMETRACE_ARGUMENT(name, value)                  \
+    do                                                        \
+    {                                                         \
+        if (FFlag::DebugLuauTimeTracing)                      \
+            lttScopeStatic.second.eventArgument(name, value); \
+    } while (false)
+
+#else
+
+#define LUAU_TIMETRACE_SCOPE(name, category)
+#define LUAU_TIMETRACE_OPTIONAL_TAIL_SCOPE(name, category, microsec)
+#define LUAU_TIMETRACE_ARGUMENT(name, value) \
+    do                                       \
+    {                                        \
+    } while (false)
+
+#endif

Ast/src/Ast.cpp

@@ -641,10 +641,12 @@ void AstStatLocalFunction::visit(AstVisitor* visitor)
         func->visit(visitor);
 }
 
-AstStatTypeAlias::AstStatTypeAlias(const Location& location, const AstName& name, const AstArray<AstName>& generics, AstType* type, bool exported)
+AstStatTypeAlias::AstStatTypeAlias(const Location& location, const AstName& name, const AstArray<AstName>& generics,
+    const AstArray<AstName>& genericPacks, AstType* type, bool exported)
     : AstStat(ClassIndex(), location)
     , name(name)
     , generics(generics)
+    , genericPacks(genericPacks)
     , type(type)
     , exported(exported)
 {
@@ -729,12 +731,14 @@ void AstStatError::visit(AstVisitor* visitor)
     }
 }
 
-AstTypeReference::AstTypeReference(const Location& location, std::optional<AstName> prefix, AstName name, const AstArray<AstType*>& generics)
+AstTypeReference::AstTypeReference(
+    const Location& location, std::optional<AstName> prefix, AstName name, bool hasParameterList, const AstArray<AstTypeOrPack>& parameters)
     : AstType(ClassIndex(), location)
     , hasPrefix(bool(prefix))
+    , hasParameterList(hasParameterList)
     , prefix(prefix ? *prefix : AstName())
     , name(name)
-    , generics(generics)
+    , parameters(parameters)
 {
 }
 
@@ -742,8 +746,13 @@ void AstTypeReference::visit(AstVisitor* visitor)
 {
     if (visitor->visit(this))
     {
-        for (AstType* generic : generics)
+        for (const AstTypeOrPack& param : parameters)
-            generic->visit(visitor);
+        {
+            if (param.type)
+                param.type->visit(visitor);
+            else
+                param.typePack->visit(visitor);
+        }
     }
 }
 
@@ -849,6 +858,24 @@ void AstTypeError::visit(AstVisitor* visitor)
     }
 }
 
+AstTypePackExplicit::AstTypePackExplicit(const Location& location, AstTypeList typeList)
+    : AstTypePack(ClassIndex(), location)
+    , typeList(typeList)
+{
+}
+
+void AstTypePackExplicit::visit(AstVisitor* visitor)
+{
+    if (visitor->visit(this))
+    {
+        for (AstType* type : typeList.types)
+            type->visit(visitor);
+
+        if (typeList.tailType)
+            typeList.tailType->visit(visitor);
+    }
+}
+
 AstTypePackVariadic::AstTypePackVariadic(const Location& location, AstType* variadicType)
     : AstTypePack(ClassIndex(), location)
     , variadicType(variadicType)

Ast/src/Parser.cpp

@@ -1,6 +1,8 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Parser.h"
 
+#include "Luau/TimeTrace.h"
+
 #include <algorithm>
 
 // Warning: If you are introducing new syntax, ensure that it is behind a separate
@@ -13,6 +15,8 @@ LUAU_FASTFLAGVARIABLE(LuauParseGenericFunctions, false)
 LUAU_FASTFLAGVARIABLE(LuauCaptureBrokenCommentSpans, false)
 LUAU_FASTFLAGVARIABLE(LuauIfElseExpressionBaseSupport, false)
 LUAU_FASTFLAGVARIABLE(LuauIfStatementRecursionGuard, false)
+LUAU_FASTFLAGVARIABLE(LuauTypeAliasPacks, false)
+LUAU_FASTFLAGVARIABLE(LuauParseTypePackTypeParameters, false)
 
 namespace Luau
 {
@@ -148,6 +152,8 @@ static bool shouldParseTypePackAnnotation(Lexer& lexer)
 
 ParseResult Parser::parse(const char* buffer, size_t bufferSize, AstNameTable& names, Allocator& allocator, ParseOptions options)
 {
+    LUAU_TIMETRACE_SCOPE("Parser::parse", "Parser");
+
     Parser p(buffer, bufferSize, names, allocator);
 
     try
@@ -769,14 +775,14 @@ AstStat* Parser::parseTypeAlias(const Location& start, bool exported)
     if (!name)
         name = Name(nameError, lexer.current().location);
 
-    // TODO: support generic type pack parameters in type aliases CLI-39907
     auto [generics, genericPacks] = parseGenericTypeList();
 
     expectAndConsume('=', "type alias");
 
     AstType* type = parseTypeAnnotation();
 
-    return allocator.alloc<AstStatTypeAlias>(Location(start, type->location), name->name, generics, type, exported);
+    return allocator.alloc<AstStatTypeAlias>(
+        Location(start, type->location), name->name, generics, FFlag::LuauTypeAliasPacks ? genericPacks : AstArray<AstName>{}, type, exported);
 }
 
 AstDeclaredClassProp Parser::parseDeclaredClassMethod()
@@ -1333,7 +1339,7 @@ AstType* Parser::parseTableTypeAnnotation()
 
 // ReturnType ::= TypeAnnotation | `(' TypeList `)'
 // FunctionTypeAnnotation ::= [`<' varlist `>'] `(' [TypeList] `)' `->` ReturnType
-AstType* Parser::parseFunctionTypeAnnotation()
+AstTypeOrPack Parser::parseFunctionTypeAnnotation(bool allowPack)
 {
     incrementRecursionCounter("type annotation");
 
@@ -1364,14 +1370,23 @@ AstType* Parser::parseFunctionTypeAnnotation()
 
     matchRecoveryStopOnToken[Lexeme::SkinnyArrow]--;
 
-    // Not a function at all.  Just a parenthesized type.
-    if (params.size() == 1 && !varargAnnotation && monomorphic && lexer.current().type != Lexeme::SkinnyArrow)
-        return params[0];
-
     AstArray<AstType*> paramTypes = copy(params);
+
+    // Not a function at all. Just a parenthesized type. Or maybe a type pack with a single element
+    if (params.size() == 1 && !varargAnnotation && monomorphic && lexer.current().type != Lexeme::SkinnyArrow)
+    {
+        if (allowPack)
+            return {{}, allocator.alloc<AstTypePackExplicit>(begin.location, AstTypeList{paramTypes, nullptr})};
+        else
+            return {params[0], {}};
+    }
+
+    if (lexer.current().type != Lexeme::SkinnyArrow && monomorphic && allowPack)
+        return {{}, allocator.alloc<AstTypePackExplicit>(begin.location, AstTypeList{paramTypes, varargAnnotation})};
+
     AstArray<std::optional<AstArgumentName>> paramNames = copy(names);
 
-    return parseFunctionTypeAnnotationTail(begin, generics, genericPacks, paramTypes, paramNames, varargAnnotation);
+    return {parseFunctionTypeAnnotationTail(begin, generics, genericPacks, paramTypes, paramNames, varargAnnotation), {}};
 }
 
 AstType* Parser::parseFunctionTypeAnnotationTail(const Lexeme& begin, AstArray<AstName> generics, AstArray<AstName> genericPacks,
@@ -1421,7 +1436,7 @@ AstType* Parser::parseTypeAnnotation(TempVector<AstType*>& parts, const Location
         if (c == '|')
         {
             nextLexeme();
-            parts.push_back(parseSimpleTypeAnnotation());
+            parts.push_back(parseSimpleTypeAnnotation(false).type);
             isUnion = true;
         }
         else if (c == '?')
@@ -1434,7 +1449,7 @@ AstType* Parser::parseTypeAnnotation(TempVector<AstType*>& parts, const Location
         else if (c == '&')
         {
             nextLexeme();
-            parts.push_back(parseSimpleTypeAnnotation());
+            parts.push_back(parseSimpleTypeAnnotation(false).type);
             isIntersection = true;
         }
         else
@@ -1462,6 +1477,30 @@ AstType* Parser::parseTypeAnnotation(TempVector<AstType*>& parts, const Location
     ParseError::raise(begin, "Composite type was not an intersection or union.");
 }
 
+AstTypeOrPack Parser::parseTypeOrPackAnnotation()
+{
+    unsigned int oldRecursionCount = recursionCounter;
+    incrementRecursionCounter("type annotation");
+
+    Location begin = lexer.current().location;
+
+    TempVector<AstType*> parts(scratchAnnotation);
+
+    auto [type, typePack] = parseSimpleTypeAnnotation(true);
+
+    if (typePack)
+    {
+        LUAU_ASSERT(!type);
+        return {{}, typePack};
+    }
+
+    parts.push_back(type);
+
+    recursionCounter = oldRecursionCount;
+
+    return {parseTypeAnnotation(parts, begin), {}};
+}
+
 AstType* Parser::parseTypeAnnotation()
 {
     unsigned int oldRecursionCount = recursionCounter;
@@ -1470,7 +1509,7 @@ AstType* Parser::parseTypeAnnotation()
     Location begin = lexer.current().location;
 
     TempVector<AstType*> parts(scratchAnnotation);
-    parts.push_back(parseSimpleTypeAnnotation());
+    parts.push_back(parseSimpleTypeAnnotation(false).type);
 
     recursionCounter = oldRecursionCount;
 
@@ -1479,7 +1518,7 @@ AstType* Parser::parseTypeAnnotation()
 
 // typeannotation ::= nil | Name[`.' Name] [ `<' typeannotation [`,' ...] `>' ] | `typeof' `(' expr `)' | `{' [PropList] `}'
 //   | [`<' varlist `>'] `(' [TypeList] `)' `->` ReturnType
-AstType* Parser::parseSimpleTypeAnnotation()
+AstTypeOrPack Parser::parseSimpleTypeAnnotation(bool allowPack)
 {
     incrementRecursionCounter("type annotation");
 
@@ -1488,7 +1527,7 @@ AstType* Parser::parseSimpleTypeAnnotation()
     if (lexer.current().type == Lexeme::ReservedNil)
     {
         nextLexeme();
-        return allocator.alloc<AstTypeReference>(begin, std::nullopt, nameNil);
+        return {allocator.alloc<AstTypeReference>(begin, std::nullopt, nameNil), {}};
     }
     else if (lexer.current().type == Lexeme::Name)
     {
@@ -1514,22 +1553,41 @@ AstType* Parser::parseSimpleTypeAnnotation()
 
             expectMatchAndConsume(')', typeofBegin);
 
-            return allocator.alloc<AstTypeTypeof>(Location(begin, end), expr);
+            return {allocator.alloc<AstTypeTypeof>(Location(begin, end), expr), {}};
         }
 
-        AstArray<AstType*> generics = parseTypeParams();
+        if (FFlag::LuauParseTypePackTypeParameters)
+        {
+            bool hasParameters = false;
+            AstArray<AstTypeOrPack> parameters{};
 
-        Location end = lexer.previousLocation();
+            if (lexer.current().type == '<')
+            {
+                hasParameters = true;
+                parameters = parseTypeParams();
+            }
 
-        return allocator.alloc<AstTypeReference>(Location(begin, end), prefix, name.name, generics);
+            Location end = lexer.previousLocation();
+
+            return {allocator.alloc<AstTypeReference>(Location(begin, end), prefix, name.name, hasParameters, parameters), {}};
+        }
+        else
+        {
+            AstArray<AstTypeOrPack> generics = parseTypeParams();
+
+            Location end = lexer.previousLocation();
+
+            // false in 'hasParameterList' as it is not used without FFlagLuauTypeAliasPacks
+            return {allocator.alloc<AstTypeReference>(Location(begin, end), prefix, name.name, false, generics), {}};
+        }
     }
     else if (lexer.current().type == '{')
     {
-        return parseTableTypeAnnotation();
+        return {parseTableTypeAnnotation(), {}};
     }
     else if (lexer.current().type == '(' || (FFlag::LuauParseGenericFunctions && lexer.current().type == '<'))
     {
-        return parseFunctionTypeAnnotation();
+        return parseFunctionTypeAnnotation(allowPack);
     }
     else
     {
@@ -1538,7 +1596,7 @@ AstType* Parser::parseSimpleTypeAnnotation()
         // For a missing type annotation, capture 'space' between last token and the next one
         location = Location(lexer.previousLocation().end, lexer.current().location.begin);
 
-        return reportTypeAnnotationError(location, {}, /*isMissing*/ true, "Expected type, got %s", lexer.current().toString().c_str());
+        return {reportTypeAnnotationError(location, {}, /*isMissing*/ true, "Expected type, got %s", lexer.current().toString().c_str()), {}};
     }
 }
 
@@ -2312,18 +2370,59 @@ std::pair<AstArray<AstName>, AstArray<AstName>> Parser::parseGenericTypeList()
     return {generics, genericPacks};
 }
 
-AstArray<AstType*> Parser::parseTypeParams()
+AstArray<AstTypeOrPack> Parser::parseTypeParams()
 {
-    TempVector<AstType*> result{scratchAnnotation};
+    TempVector<AstTypeOrPack> parameters{scratchTypeOrPackAnnotation};
 
     if (lexer.current().type == '<')
     {
         Lexeme begin = lexer.current();
         nextLexeme();
 
+        bool seenPack = false;
         while (true)
         {
-            result.push_back(parseTypeAnnotation());
+            if (FFlag::LuauParseTypePackTypeParameters)
+            {
+                if (shouldParseTypePackAnnotation(lexer))
+                {
+                    seenPack = true;
+
+                    auto typePack = parseTypePackAnnotation();
+
+                    if (FFlag::LuauTypeAliasPacks) // Type packs are recorded only is we can handle them
+                        parameters.push_back({{}, typePack});
+                }
+                else if (lexer.current().type == '(')
+                {
+                    auto [type, typePack] = parseTypeOrPackAnnotation();
+
+                    if (typePack)
+                    {
+                        seenPack = true;
+
+                        if (FFlag::LuauTypeAliasPacks) // Type packs are recorded only is we can handle them
+                            parameters.push_back({{}, typePack});
+                    }
+                    else
+                    {
+                        parameters.push_back({type, {}});
+                    }
+                }
+                else if (lexer.current().type == '>' && parameters.empty())
+                {
+                    break;
+                }
+                else
+                {
+                    parameters.push_back({parseTypeAnnotation(), {}});
+                }
+            }
+            else
+            {
+                parameters.push_back({parseTypeAnnotation(), {}});
+            }
+
             if (lexer.current().type == ',')
                 nextLexeme();
             else
@@ -2333,7 +2432,7 @@ AstArray<AstType*> Parser::parseTypeParams()
         expectMatchAndConsume('>', begin);
     }
 
-    return copy(result);
+    return copy(parameters);
 }
 
 AstExpr* Parser::parseString()

Ast/src/TimeTrace.cpp

@@ -0,0 +1,248 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#include "Luau/TimeTrace.h"
+
+#include "Luau/StringUtils.h"
+
+#include <mutex>
+#include <string>
+
+#include <stdlib.h>
+
+#ifdef _WIN32
+#include <Windows.h>
+#endif
+
+#ifdef __APPLE__
+#include <mach/mach.h>
+#include <mach/mach_time.h>
+#endif
+
+#include <time.h>
+
+LUAU_FASTFLAGVARIABLE(DebugLuauTimeTracing, false)
+
+#if defined(LUAU_ENABLE_TIME_TRACE)
+
+namespace Luau
+{
+namespace TimeTrace
+{
+static double getClockPeriod()
+{
+#if defined(_WIN32)
+    LARGE_INTEGER result = {};
+    QueryPerformanceFrequency(&result);
+    return 1.0 / double(result.QuadPart);
+#elif defined(__APPLE__)
+    mach_timebase_info_data_t result = {};
+    mach_timebase_info(&result);
+    return double(result.numer) / double(result.denom) * 1e-9;
+#elif defined(__linux__)
+    return 1e-9;
+#else
+    return 1.0 / double(CLOCKS_PER_SEC);
+#endif
+}
+
+static double getClockTimestamp()
+{
+#if defined(_WIN32)
+    LARGE_INTEGER result = {};
+    QueryPerformanceCounter(&result);
+    return double(result.QuadPart);
+#elif defined(__APPLE__)
+    return double(mach_absolute_time());
+#elif defined(__linux__)
+    timespec now;
+    clock_gettime(CLOCK_MONOTONIC, &now);
+    return now.tv_sec * 1e9 + now.tv_nsec;
+#else
+    return double(clock());
+#endif
+}
+
+uint32_t getClockMicroseconds()
+{
+    static double period = getClockPeriod() * 1e6;
+    static double start = getClockTimestamp();
+
+    return uint32_t((getClockTimestamp() - start) * period);
+}
+
+struct GlobalContext
+{
+    GlobalContext() = default;
+    ~GlobalContext()
+    {
+        // Ideally we would want all ThreadContext destructors to run
+        // But in VS, not all thread_local object instances are destroyed
+        for (ThreadContext* context : threads)
+            context->flushEvents();
+
+        if (traceFile)
+            fclose(traceFile);
+    }
+
+    std::mutex mutex;
+    std::vector<ThreadContext*> threads;
+    uint32_t nextThreadId = 0;
+    std::vector<Token> tokens;
+    FILE* traceFile = nullptr;
+};
+
+GlobalContext& getGlobalContext()
+{
+    static GlobalContext context;
+    return context;
+}
+
+uint16_t createToken(GlobalContext& context, const char* name, const char* category)
+{
+    std::scoped_lock lock(context.mutex);
+
+    LUAU_ASSERT(context.tokens.size() < 64 * 1024);
+
+    context.tokens.push_back({name, category});
+    return uint16_t(context.tokens.size() - 1);
+}
+
+uint32_t createThread(GlobalContext& context, ThreadContext* threadContext)
+{
+    std::scoped_lock lock(context.mutex);
+
+    context.threads.push_back(threadContext);
+
+    return ++context.nextThreadId;
+}
+
+void releaseThread(GlobalContext& context, ThreadContext* threadContext)
+{
+    std::scoped_lock lock(context.mutex);
+
+    if (auto it = std::find(context.threads.begin(), context.threads.end(), threadContext); it != context.threads.end())
+        context.threads.erase(it);
+}
+
+void flushEvents(GlobalContext& context, uint32_t threadId, const std::vector<Event>& events, const std::vector<char>& data)
+{
+    std::scoped_lock lock(context.mutex);
+
+    if (!context.traceFile)
+    {
+        context.traceFile = fopen("trace.json", "w");
+
+        if (!context.traceFile)
+            return;
+
+        fprintf(context.traceFile, "[\n");
+    }
+
+    std::string temp;
+    const unsigned tempReserve = 64 * 1024;
+    temp.reserve(tempReserve);
+
+    const char* rawData = data.data();
+
+    // Formatting state
+    bool unfinishedEnter = false;
+    bool unfinishedArgs = false;
+
+    for (const Event& ev : events)
+    {
+        switch (ev.type)
+        {
+        case EventType::Enter:
+        {
+            if (unfinishedArgs)
+            {
+                formatAppend(temp, "}");
+                unfinishedArgs = false;
+            }
+
+            if (unfinishedEnter)
+            {
+                formatAppend(temp, "},\n");
+                unfinishedEnter = false;
+            }
+
+            Token& token = context.tokens[ev.token];
+
+            formatAppend(temp, R"({"name": "%s", "cat": "%s", "ph": "B", "ts": %u, "pid": 0, "tid": %u)", token.name, token.category,
+                ev.data.microsec, threadId);
+            unfinishedEnter = true;
+        }
+        break;
+        case EventType::Leave:
+            if (unfinishedArgs)
+            {
+                formatAppend(temp, "}");
+                unfinishedArgs = false;
+            }
+            if (unfinishedEnter)
+            {
+                formatAppend(temp, "},\n");
+                unfinishedEnter = false;
+            }
+
+            formatAppend(temp,
+                R"({"ph": "E", "ts": %u, "pid": 0, "tid": %u},)"
+                "\n",
+                ev.data.microsec, threadId);
+            break;
+        case EventType::ArgName:
+            LUAU_ASSERT(unfinishedEnter);
+
+            if (!unfinishedArgs)
+            {
+                formatAppend(temp, R"(, "args": { "%s": )", rawData + ev.data.dataPos);
+                unfinishedArgs = true;
+            }
+            else
+            {
+                formatAppend(temp, R"(, "%s": )", rawData + ev.data.dataPos);
+            }
+            break;
+        case EventType::ArgValue:
+            LUAU_ASSERT(unfinishedArgs);
+            formatAppend(temp, R"("%s")", rawData + ev.data.dataPos);
+            break;
+        }
+
+        // Don't want to hit the string capacity and reallocate
+        if (temp.size() > tempReserve - 1024)
+        {
+            fwrite(temp.data(), 1, temp.size(), context.traceFile);
+            temp.clear();
+        }
+    }
+
+    if (unfinishedArgs)
+    {
+        formatAppend(temp, "}");
+        unfinishedArgs = false;
+    }
+    if (unfinishedEnter)
+    {
+        formatAppend(temp, "},\n");
+        unfinishedEnter = false;
+    }
+
+    fwrite(temp.data(), 1, temp.size(), context.traceFile);
+    fflush(context.traceFile);
+}
+
+ThreadContext& getThreadContext()
+{
+    thread_local ThreadContext context;
+    return context;
+}
+
+std::pair<uint16_t, Luau::TimeTrace::ThreadContext&> createScopeData(const char* name, const char* category)
+{
+    uint16_t token = createToken(Luau::TimeTrace::getGlobalContext(), name, category);
+    return {token, Luau::TimeTrace::getThreadContext()};
+}
+} // namespace TimeTrace
+} // namespace Luau
+
+#endif

CLI/Analyze.cpp

@@ -111,11 +111,24 @@ struct CliFileResolver : Luau::FileResolver
         return Luau::SourceCode{*source, Luau::SourceCode::Module};
     }
 
+    std::optional<Luau::ModuleInfo> resolveModule(const Luau::ModuleInfo* context, Luau::AstExpr* node) override
+    {
+        if (Luau::AstExprConstantString* expr = node->as<Luau::AstExprConstantString>())
+        {
+            Luau::ModuleName name = std::string(expr->value.data, expr->value.size) + ".lua";
+
+            return {{name}};
+        }
+
+        return std::nullopt;
+    }
+
     bool moduleExists(const Luau::ModuleName& name) const override
     {
         return !!readFile(name);
     }
 
+
     std::optional<Luau::ModuleName> fromAstFragment(Luau::AstExpr* expr) const override
     {
         return std::nullopt;
@@ -130,11 +143,6 @@ struct CliFileResolver : Luau::FileResolver
     {
         return std::nullopt;
     }
-
-    std::optional<std::string> getEnvironmentForModule(const Luau::ModuleName& name) const override
-    {
-        return std::nullopt;
-    }
 };
 
 struct CliConfigResolver : Luau::ConfigResolver

Compiler/src/Compiler.cpp

@@ -4,6 +4,7 @@
 #include "Luau/Parser.h"
 #include "Luau/BytecodeBuilder.h"
 #include "Luau/Common.h"
+#include "Luau/TimeTrace.h"
 
 #include <algorithm>
 #include <bitset>
@@ -137,6 +138,11 @@ struct Compiler
 
     uint32_t compileFunction(AstExprFunction* func)
     {
+        LUAU_TIMETRACE_SCOPE("Compiler::compileFunction", "Compiler");
+
+        if (func->debugname.value)
+            LUAU_TIMETRACE_ARGUMENT("name", func->debugname.value);
+
         LUAU_ASSERT(!functions.contains(func));
         LUAU_ASSERT(regTop == 0 && stackSize == 0 && localStack.empty() && upvals.empty());
 
@@ -3686,6 +3692,8 @@ struct Compiler
 
 void compileOrThrow(BytecodeBuilder& bytecode, AstStatBlock* root, const AstNameTable& names, const CompileOptions& options)
 {
+    LUAU_TIMETRACE_SCOPE("compileOrThrow", "Compiler");
+
     Compiler compiler(bytecode, options);
 
     // since access to some global objects may result in values that change over time, we block table imports
@@ -3748,6 +3756,8 @@ void compileOrThrow(BytecodeBuilder& bytecode, const std::string& source, const
 
 std::string compile(const std::string& source, const CompileOptions& options, const ParseOptions& parseOptions, BytecodeEncoder* encoder)
 {
+    LUAU_TIMETRACE_SCOPE("compile", "Compiler");
+
     Allocator allocator;
     AstNameTable names(allocator);
     ParseResult result = Parser::parse(source.c_str(), source.size(), names, allocator, parseOptions);

Sources.cmake

@@ -9,6 +9,7 @@ target_sources(Luau.Ast PRIVATE
     Ast/include/Luau/ParseOptions.h
     Ast/include/Luau/Parser.h
     Ast/include/Luau/StringUtils.h
+    Ast/include/Luau/TimeTrace.h
 
     Ast/src/Ast.cpp
     Ast/src/Confusables.cpp
@@ -16,6 +17,7 @@ target_sources(Luau.Ast PRIVATE
     Ast/src/Location.cpp
     Ast/src/Parser.cpp
     Ast/src/StringUtils.cpp
+    Ast/src/TimeTrace.cpp
 )
 
 # Luau.Compiler Sources
@@ -46,6 +48,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/include/Luau/Predicate.h
     Analysis/include/Luau/RecursionCounter.h
     Analysis/include/Luau/RequireTracer.h
+    Analysis/include/Luau/Scope.h
     Analysis/include/Luau/Substitution.h
     Analysis/include/Luau/Symbol.h
     Analysis/include/Luau/TopoSortStatements.h
@@ -75,6 +78,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/src/Module.cpp
     Analysis/src/Predicate.cpp
     Analysis/src/RequireTracer.cpp
+    Analysis/src/Scope.cpp
     Analysis/src/Substitution.cpp
     Analysis/src/Symbol.cpp
     Analysis/src/TopoSortStatements.cpp
@@ -188,6 +192,7 @@ if(TARGET Luau.UnitTest)
         tests/TopoSort.test.cpp
         tests/ToString.test.cpp
         tests/Transpiler.test.cpp
+        tests/TypeInfer.aliases.test.cpp
         tests/TypeInfer.annotations.test.cpp
         tests/TypeInfer.builtins.test.cpp
         tests/TypeInfer.classes.test.cpp

VM/src/ldo.cpp

@@ -8,9 +8,13 @@
 #include "lmem.h"
 #include "lvm.h"
 
-#include <stdexcept>
+#if LUA_USE_LONGJMP
-
 #include <setjmp.h>
+#include <stdlib.h>
+#else
+#include <stdexcept>
+#endif
+
 #include <string.h>
 
 LUAU_FASTFLAGVARIABLE(LuauExceptionMessageFix, false)
@@ -51,8 +55,8 @@ l_noret luaD_throw(lua_State* L, int errcode)
         longjmp(jb->buf, 1);
     }
 
-    if (L->global->panic)
+    if (L->global->cb.panic)
-        L->global->panic(L, errcode);
+        L->global->cb.panic(L, errcode);
 
     abort();
 }

VM/src/lgc.cpp

@@ -16,6 +16,8 @@ LUAU_FASTFLAGVARIABLE(LuauRescanGrayAgain, false)
 LUAU_FASTFLAGVARIABLE(LuauRescanGrayAgainForwardBarrier, false)
 LUAU_FASTFLAGVARIABLE(LuauGcFullSkipInactiveThreads, false)
 LUAU_FASTFLAGVARIABLE(LuauShrinkWeakTables, false)
+LUAU_FASTFLAGVARIABLE(LuauConsolidatedStep, false)
+
 LUAU_FASTFLAG(LuauArrayBoundary)
 
 #define GC_SWEEPMAX 40
@@ -810,6 +812,133 @@ static size_t singlestep(lua_State* L)
     return cost;
 }
 
+static size_t gcstep(lua_State* L, size_t limit)
+{
+    size_t cost = 0;
+    global_State* g = L->global;
+    switch (g->gcstate)
+    {
+    case GCSpause:
+    {
+        markroot(L); /* start a new collection */
+        break;
+    }
+    case GCSpropagate:
+    {
+        if (FFlag::LuauRescanGrayAgain)
+        {
+            while (g->gray && cost < limit)
+            {
+                g->gcstats.currcycle.markitems++;
+
+                cost += propagatemark(g);
+            }
+
+            if (!g->gray)
+            {
+                // perform one iteration over 'gray again' list
+                g->gray = g->grayagain;
+                g->grayagain = NULL;
+
+                g->gcstate = GCSpropagateagain;
+            }
+        }
+        else
+        {
+            while (g->gray && cost < limit)
+            {
+                g->gcstats.currcycle.markitems++;
+
+                cost += propagatemark(g);
+            }
+
+            if (!g->gray) /* no more `gray' objects */
+            {
+                double starttimestamp = lua_clock();
+
+                g->gcstats.currcycle.atomicstarttimestamp = starttimestamp;
+                g->gcstats.currcycle.atomicstarttotalsizebytes = g->totalbytes;
+
+                atomic(L); /* finish mark phase */
+
+                g->gcstats.currcycle.atomictime += lua_clock() - starttimestamp;
+            }
+        }
+        break;
+    }
+    case GCSpropagateagain:
+    {
+        while (g->gray && cost < limit)
+        {
+            g->gcstats.currcycle.markitems++;
+
+            cost += propagatemark(g);
+        }
+
+        if (!g->gray) /* no more `gray' objects */
+        {
+            double starttimestamp = lua_clock();
+
+            g->gcstats.currcycle.atomicstarttimestamp = starttimestamp;
+            g->gcstats.currcycle.atomicstarttotalsizebytes = g->totalbytes;
+
+            atomic(L); /* finish mark phase */
+
+            g->gcstats.currcycle.atomictime += lua_clock() - starttimestamp;
+        }
+        break;
+    }
+    case GCSsweepstring:
+    {
+        while (g->sweepstrgc < g->strt.size && cost < limit)
+        {
+            size_t traversedcount = 0;
+            sweepwholelist(L, &g->strt.hash[g->sweepstrgc++], &traversedcount);
+
+            g->gcstats.currcycle.sweepitems += traversedcount;
+            cost += GC_SWEEPCOST;
+        }
+
+        // nothing more to sweep?
+        if (g->sweepstrgc >= g->strt.size)
+        {
+            // sweep string buffer list and preserve used string count
+            uint32_t nuse = L->global->strt.nuse;
+
+            size_t traversedcount = 0;
+            sweepwholelist(L, &g->strbufgc, &traversedcount);
+
+            L->global->strt.nuse = nuse;
+
+            g->gcstats.currcycle.sweepitems += traversedcount;
+            g->gcstate = GCSsweep; // end sweep-string phase
+        }
+        break;
+    }
+    case GCSsweep:
+    {
+        while (*g->sweepgc && cost < limit)
+        {
+            size_t traversedcount = 0;
+            g->sweepgc = sweeplist(L, g->sweepgc, GC_SWEEPMAX, &traversedcount);
+
+            g->gcstats.currcycle.sweepitems += traversedcount;
+            cost += GC_SWEEPMAX * GC_SWEEPCOST;
+        }
+
+        if (*g->sweepgc == NULL)
+        { /* nothing more to sweep? */
+            shrinkbuffers(L);
+            g->gcstate = GCSpause; /* end collection */
+        }
+        break;
+    }
+    default:
+        LUAU_ASSERT(0);
+    }
+    return cost;
+}
+
 static int64_t getheaptriggererroroffset(GCHeapTriggerStats* triggerstats, GCCycleStats* cyclestats)
 {
     // adjust for error using Proportional-Integral controller
@@ -878,33 +1007,40 @@ void luaC_step(lua_State* L, bool assist)
     if (g->gcstate == GCSpause)
         startGcCycleStats(g);
 
-    if (assist)
-        g->gcstats.currcycle.assistwork += lim;
-    else
-        g->gcstats.currcycle.explicitwork += lim;
-
     int lastgcstate = g->gcstate;
     double lasttimestamp = lua_clock();
 
-    // always perform at least one single step
+    if (FFlag::LuauConsolidatedStep)
-    do
     {
-        lim -= singlestep(L);
+        size_t work = gcstep(L, lim);
 
-        // if we have switched to a different state, capture the duration of last stage
+        if (assist)
-        // this way we reduce the number of timer calls we make
+            g->gcstats.currcycle.assistwork += work;
-        if (lastgcstate != g->gcstate)
+        else
+            g->gcstats.currcycle.explicitwork += work;
+    }
+    else
+    {
+        // always perform at least one single step
+        do
         {
-            GC_INTERRUPT(lastgcstate);
+            lim -= singlestep(L);
 
-            double now = lua_clock();
+            // if we have switched to a different state, capture the duration of last stage
+            // this way we reduce the number of timer calls we make
+            if (lastgcstate != g->gcstate)
+            {
+                GC_INTERRUPT(lastgcstate);
 
-            recordGcStateTime(g, lastgcstate, now - lasttimestamp, assist);
+                double now = lua_clock();
 
-            lasttimestamp = now;
+                recordGcStateTime(g, lastgcstate, now - lasttimestamp, assist);
-            lastgcstate = g->gcstate;
+
-        }
+                lasttimestamp = now;
-    } while (lim > 0 && g->gcstate != GCSpause);
+                lastgcstate = g->gcstate;
+            }
+        } while (lim > 0 && g->gcstate != GCSpause);
+    }
 
     recordGcStateTime(g, lastgcstate, lua_clock() - lasttimestamp, assist);
 
@@ -931,7 +1067,14 @@ void luaC_step(lua_State* L, bool assist)
             g->GCthreshold -= debt;
     }
 
-    GC_INTERRUPT(g->gcstate);
+    if (FFlag::LuauConsolidatedStep)
+    {
+        GC_INTERRUPT(lastgcstate);
+    }
+    else
+    {
+        GC_INTERRUPT(g->gcstate);
+    }
 }
 
 void luaC_fullgc(lua_State* L)
@@ -957,7 +1100,10 @@ void luaC_fullgc(lua_State* L)
     while (g->gcstate != GCSpause)
     {
         LUAU_ASSERT(g->gcstate == GCSsweepstring || g->gcstate == GCSsweep);
-        singlestep(L);
+        if (FFlag::LuauConsolidatedStep)
+            gcstep(L, SIZE_MAX);
+        else
+            singlestep(L);
     }
 
     finishGcCycleStats(g);
@@ -968,7 +1114,10 @@ void luaC_fullgc(lua_State* L)
     markroot(L);
     while (g->gcstate != GCSpause)
     {
-        singlestep(L);
+        if (FFlag::LuauConsolidatedStep)
+            gcstep(L, SIZE_MAX);
+        else
+            singlestep(L);
     }
     /* reclaim as much buffer memory as possible (shrinkbuffers() called during sweep is incremental) */
     shrinkbuffersfull(L);

VM/src/ltablib.cpp

@@ -9,14 +9,8 @@
 #include "ldebug.h"
 #include "lvm.h"
 
-LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauTableMoveTelemetry, false)
-
 LUAU_FASTFLAGVARIABLE(LuauTableFreeze, false)
 
-bool lua_telemetry_table_move_oob_src_from = false;
-bool lua_telemetry_table_move_oob_src_to = false;
-bool lua_telemetry_table_move_oob_dst = false;
-
 static int foreachi(lua_State* L)
 {
     luaL_checktype(L, 1, LUA_TTABLE);
@@ -202,22 +196,6 @@ static int tmove(lua_State* L)
     int tt = !lua_isnoneornil(L, 5) ? 5 : 1; /* destination table */
     luaL_checktype(L, tt, LUA_TTABLE);
 
-    if (DFFlag::LuauTableMoveTelemetry)
-    {
-        int nf = lua_objlen(L, 1);
-        int nt = lua_objlen(L, tt);
-
-        // source index range must be in bounds in source table unless the table is empty (permits 1..#t moves)
-        if (!(f == 1 || (f >= 1 && f <= nf)))
-            lua_telemetry_table_move_oob_src_from = true;
-        if (!(e == nf || (e >= 1 && e <= nf)))
-            lua_telemetry_table_move_oob_src_to = true;
-
-        // destination index must be in bounds in dest table or be exactly at the first empty element (permits concats)
-        if (!(t == nt + 1 || (t >= 1 && t <= nt + 1)))
-            lua_telemetry_table_move_oob_dst = true;
-    }
-
     if (e >= f)
     { /* otherwise, nothing to move */
         luaL_argcheck(L, f > 0 || e < INT_MAX + f, 3, "too many elements to move");

VM/src/lvmexecute.cpp

@@ -16,8 +16,6 @@
 
 #include <string.h>
 
-LUAU_FASTFLAGVARIABLE(LuauLoopUseSafeenv, false)
-
 // Disable c99-designator to avoid the warning in CGOTO dispatch table
 #ifdef __clang__
 #if __has_warning("-Wc99-designator")
@@ -292,10 +290,6 @@ inline bool luau_skipstep(uint8_t op)
     return op == LOP_PREPVARARGS || op == LOP_BREAK;
 }
 
-// declared in lbaselib.cpp, needed to support cases when pairs/ipairs have been replaced via setfenv
-LUAI_FUNC int luaB_inext(lua_State* L);
-LUAI_FUNC int luaB_next(lua_State* L);
-
 template<bool SingleStep>
 static void luau_execute(lua_State* L)
 {
@@ -2223,8 +2217,7 @@ static void luau_execute(lua_State* L)
                 StkId ra = VM_REG(LUAU_INSN_A(insn));
 
                 // fast-path: ipairs/inext
-                bool safeenv = FFlag::LuauLoopUseSafeenv ? cl->env->safeenv : ttisfunction(ra) && clvalue(ra)->isC && clvalue(ra)->c.f == luaB_inext;
+                if (cl->env->safeenv && ttistable(ra + 1) && ttisnumber(ra + 2) && nvalue(ra + 2) == 0.0)
-                if (safeenv && ttistable(ra + 1) && ttisnumber(ra + 2) && nvalue(ra + 2) == 0.0)
                 {
                     setpvalue(ra + 2, reinterpret_cast<void*>(uintptr_t(0)));
                 }
@@ -2304,8 +2297,7 @@ static void luau_execute(lua_State* L)
                 StkId ra = VM_REG(LUAU_INSN_A(insn));
 
                 // fast-path: pairs/next
-                bool safeenv = FFlag::LuauLoopUseSafeenv ? cl->env->safeenv : ttisfunction(ra) && clvalue(ra)->isC && clvalue(ra)->c.f == luaB_next;
+                if (cl->env->safeenv && ttistable(ra + 1) && ttisnil(ra + 2))
-                if (safeenv && ttistable(ra + 1) && ttisnil(ra + 2))
                 {
                     setpvalue(ra + 2, reinterpret_cast<void*>(uintptr_t(0)));
                 }

VM/src/lvmload.cpp

@@ -12,7 +12,32 @@
 
 #include <string.h>
 
-#include <vector>
+// TODO: RAII deallocation doesn't work for longjmp builds if a memory error happens
+template <typename T>
+struct TempBuffer
+{
+    lua_State* L;
+    T* data;
+    size_t count;
+
+    TempBuffer(lua_State* L, size_t count)
+        : L(L)
+        , data(luaM_newarray(L, count, T, 0))
+        , count(count)
+    {
+    }
+
+    ~TempBuffer()
+    {
+        luaM_freearray(L, data, count, T, 0);
+    }
+
+    T& operator[](size_t index)
+    {
+        LUAU_ASSERT(index < count);
+        return data[index];
+    }
+};
 
 void luaV_getimport(lua_State* L, Table* env, TValue* k, uint32_t id, bool propagatenil)
 {
@@ -67,7 +92,7 @@ static unsigned int readVarInt(const char* data, size_t size, size_t& offset)
     return result;
 }
 
-static TString* readString(std::vector<TString*>& strings, const char* data, size_t size, size_t& offset)
+static TString* readString(TempBuffer<TString*>& strings, const char* data, size_t size, size_t& offset)
 {
     unsigned int id = readVarInt(data, size, offset);
 
@@ -133,6 +158,7 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
     }
 
     // pause GC for the duration of deserialization - some objects we're creating aren't rooted
+    // TODO: if an allocation error happens mid-load, we do not unpause GC!
     size_t GCthreshold = L->global->GCthreshold;
     L->global->GCthreshold = SIZE_MAX;
 
@@ -144,7 +170,7 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
 
     // string table
     unsigned int stringCount = readVarInt(data, size, offset);
-    std::vector<TString*> strings(stringCount);
+    TempBuffer<TString*> strings(L, stringCount);
 
     for (unsigned int i = 0; i < stringCount; ++i)
     {
@@ -156,7 +182,7 @@ int luau_load(lua_State* L, const char* chunkname, const char* data, size_t size
 
     // proto table
     unsigned int protoCount = readVarInt(data, size, offset);
-    std::vector<Proto*> protos(protoCount);
+    TempBuffer<Proto*> protos(L, protoCount);
 
     for (unsigned int i = 0; i < protoCount; ++i)
     {

bench/tests/deltablue.lua

@@ -1,934 +0,0 @@
-local bench = script and require(script.Parent.bench_support) or require("bench_support")
-
--- Copyright 2008 the V8 project authors. All rights reserved.
--- Copyright 1996 John Maloney and Mario Wolczko.
-
--- This program is free software; you can redistribute it and/or modify
--- it under the terms of the GNU General Public License as published by
--- the Free Software Foundation; either version 2 of the License, or
--- (at your option) any later version.
---
--- This program is distributed in the hope that it will be useful,
--- but WITHOUT ANY WARRANTY; without even the implied warranty of
--- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
--- GNU General Public License for more details.
---
--- You should have received a copy of the GNU General Public License
--- along with this program; if not, write to the Free Software
--- Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-
-
--- This implementation of the DeltaBlue benchmark is derived
--- from the Smalltalk implementation by John Maloney and Mario
--- Wolczko. Some parts have been translated directly, whereas
--- others have been modified more aggressively to make it feel
--- more like a JavaScript program.
-
-
---
--- A JavaScript implementation of the DeltaBlue constraint-solving
--- algorithm, as described in:
---
--- "The DeltaBlue Algorithm: An Incremental Constraint Hierarchy Solver"
---   Bjorn N. Freeman-Benson and John Maloney
---   January 1990 Communications of the ACM,
---   also available as University of Washington TR 89-08-06.
---
--- Beware: this benchmark is written in a grotesque style where
--- the constraint model is built by side-effects from constructors.
--- I've kept it this way to avoid deviating too much from the original
--- implementation.
---
-
-function class(base)
-	local T = {}
-	T.__index = T
-
-	if base then
-		T.super = base
-		setmetatable(T, base)
-	end
-
-	function T.new(...)
-		local O = {}
-		setmetatable(O, T)
-		O:constructor(...)
-		return O
-	end
-
-	return T
-end
-
-local planner
-
---- O b j e c t   M o d e l ---
-
-local function alert (...) print(...) end
-
-local OrderedCollection = class()
-
-function OrderedCollection:constructor()
-	 self.elms = {}
-end
-
-function OrderedCollection:add(elm)
-	 self.elms[#self.elms + 1] = elm
-end
-
-function OrderedCollection:at (index)
-	 return self.elms[index]
-end
-
-function OrderedCollection:size ()
-	 return #self.elms
-end
-
-function OrderedCollection:removeFirst ()
-	 local e = self.elms[#self.elms]
-	 self.elms[#self.elms] = nil
-	 return e
-end
-
-function OrderedCollection:remove (elm)
-	 local index = 0
-	 local skipped = 0
-
-	 for i = 1, #self.elms do
-			local value = self.elms[i]
-			if value ~= elm then
-				 self.elms[index] = value
-				 index = index + 1
-			else
-				 skipped = skipped + 1
-			end
-	 end
-
-	 local l = #self.elms
-	 for i = 1, skipped do self.elms[l - i + 1] = nil end
-end
-
---
--- S t r e n g t h
---
-
---
--- Strengths are used to measure the relative importance of constraints.
--- New strengths may be inserted in the strength hierarchy without
--- disrupting current constraints.  Strengths cannot be created outside
--- this class, so pointer comparison can be used for value comparison.
---
-
-local Strength = class()
-
-function Strength:constructor(strengthValue, name)
-	 self.strengthValue = strengthValue
-	 self.name = name
-end
-
-function Strength.stronger (s1, s2)
-	 return s1.strengthValue < s2.strengthValue
-end
-
-function Strength.weaker (s1, s2)
-	 return s1.strengthValue > s2.strengthValue
-end
-
-function Strength.weakestOf (s1, s2)
-	 return Strength.weaker(s1, s2) and s1 or s2
-end
-
-function Strength.strongest (s1, s2)
-	 return Strength.stronger(s1, s2) and s1 or s2
-end
-
-function Strength:nextWeaker ()
-	 local v = self.strengthValue
-	 if v == 0 then return Strength.WEAKEST
-	 elseif v == 1 then return Strength.WEAK_DEFAULT
-	 elseif v == 2 then return Strength.NORMAL
-	 elseif v == 3 then return Strength.STRONG_DEFAULT
-	 elseif v == 4 then return Strength.PREFERRED
-	 elseif v == 5 then return Strength.REQUIRED
-	 end
-end
-
--- Strength constants.
-Strength.REQUIRED        = Strength.new(0, "required");
-Strength.STONG_PREFERRED = Strength.new(1, "strongPreferred");
-Strength.PREFERRED       = Strength.new(2, "preferred");
-Strength.STRONG_DEFAULT  = Strength.new(3, "strongDefault");
-Strength.NORMAL          = Strength.new(4, "normal");
-Strength.WEAK_DEFAULT    = Strength.new(5, "weakDefault");
-Strength.WEAKEST         = Strength.new(6, "weakest");
-
---
--- C o n s t r a i n t
---
-
---
--- An abstract class representing a system-maintainable relationship
--- (or "constraint") between a set of variables. A constraint supplies
--- a strength instance variable; concrete subclasses provide a means
--- of storing the constrained variables and other information required
--- to represent a constraint.
---
-
-local Constraint = class ()
-
-function Constraint:constructor(strength)
-	 self.strength = strength
-end
-
---
--- Activate this constraint and attempt to satisfy it.
---
-function Constraint:addConstraint ()
-	 self:addToGraph()
-	 planner:incrementalAdd(self)
-end
-
---
--- Attempt to find a way to enforce this constraint. If successful,
--- record the solution, perhaps modifying the current dataflow
--- graph. Answer the constraint that this constraint overrides, if
--- there is one, or nil, if there isn't.
--- Assume: I am not already satisfied.
---
-function Constraint:satisfy (mark)
-	 self:chooseMethod(mark)
-	 if not self:isSatisfied() then
-			if self.strength == Strength.REQUIRED then
-				 alert("Could not satisfy a required constraint!")
-			end
-			return nil
-	 end
-	 self:markInputs(mark)
-	 local out = self:output()
-	 local overridden = out.determinedBy
-	 if overridden ~= nil then overridden:markUnsatisfied() end
-	 out.determinedBy = self
-	 if not planner:addPropagate(self, mark) then alert("Cycle encountered") end
-	 out.mark = mark
-	 return overridden
-end
-
-function Constraint:destroyConstraint ()
-	 if self:isSatisfied()
-	 then planner:incrementalRemove(self)
-	 else self:removeFromGraph()
-	 end
-end
-
---
--- Normal constraints are not input constraints.  An input constraint
--- is one that depends on external state, such as the mouse, the
--- keyboard, a clock, or some arbitrary piece of imperative code.
---
-function Constraint:isInput ()
-	 return false
-end
-
-
---
--- U n a r y   C o n s t r a i n t
---
-
---
--- Abstract superclass for constraints having a single possible output
--- variable.
---
-
-local UnaryConstraint = class(Constraint)
-
-function UnaryConstraint:constructor (v, strength)
-	 UnaryConstraint.super.constructor(self, strength)
-	 self.myOutput = v
-	 self.satisfied = false
-	 self:addConstraint()
-end
-
---
--- Adds this constraint to the constraint graph
---
-function UnaryConstraint:addToGraph ()
-	 self.myOutput:addConstraint(self)
-	 self.satisfied = false
-end
-
---
--- Decides if this constraint can be satisfied and records that
--- decision.
---
-function UnaryConstraint:chooseMethod (mark)
-	 self.satisfied = (self.myOutput.mark ~= mark)
-	 and Strength.stronger(self.strength, self.myOutput.walkStrength);
-end
-
---
--- Returns true if this constraint is satisfied in the current solution.
---
-function UnaryConstraint:isSatisfied ()
-	 return self.satisfied;
-end
-
-function UnaryConstraint:markInputs (mark)
-	 -- has no inputs
-end
-
---
--- Returns the current output variable.
---
-function UnaryConstraint:output ()
-	 return self.myOutput
-end
-
---
--- Calculate the walkabout strength, the stay flag, and, if it is
--- 'stay', the value for the current output of this constraint. Assume
--- this constraint is satisfied.
---
-function UnaryConstraint:recalculate ()
-	 self.myOutput.walkStrength = self.strength
-	 self.myOutput.stay = not self:isInput()
-	 if self.myOutput.stay then
-			self:execute() -- Stay optimization
-	 end
-end
-
---
--- Records that this constraint is unsatisfied
---
-function UnaryConstraint:markUnsatisfied ()
-	 self.satisfied = false
-end
-
-function UnaryConstraint:inputsKnown ()
-	 return true
-end
-
-function UnaryConstraint:removeFromGraph ()
-	 if self.myOutput ~= nil then
-			self.myOutput:removeConstraint(self)
-	 end
-	 self.satisfied = false
-end
-
---
--- S t a y   C o n s t r a i n t
---
-
---
--- Variables that should, with some level of preference, stay the same.
--- Planners may exploit the fact that instances, if satisfied, will not
--- change their output during plan execution.  This is called "stay
--- optimization".
---
-
-local StayConstraint = class(UnaryConstraint)
-
-function StayConstraint:constructor(v, str)
-	 StayConstraint.super.constructor(self, v, str) 
-end
-
-function StayConstraint:execute ()
-	 -- Stay constraints do nothing
-end
-
---
--- E d i t   C o n s t r a i n t
---
-
---
--- A unary input constraint used to mark a variable that the client
--- wishes to change.
---
-
-local EditConstraint = class (UnaryConstraint)
-
-function EditConstraint:constructor(v, str)
-	 EditConstraint.super.constructor(self, v, str)
-end
-
---
--- Edits indicate that a variable is to be changed by imperative code.
---
-function EditConstraint:isInput ()
-	 return true
-end
-
-function EditConstraint:execute ()
-	 -- Edit constraints do nothing
-end
-
---
--- B i n a r y   C o n s t r a i n t
---
-
-local Direction = {}
-Direction.NONE     = 0
-Direction.FORWARD  = 1
-Direction.BACKWARD = -1
-
---
--- Abstract superclass for constraints having two possible output
--- variables.
---
-
-local BinaryConstraint = class(Constraint)
-
-function BinaryConstraint:constructor(var1, var2, strength)
-	 BinaryConstraint.super.constructor(self, strength);
-	 self.v1 = var1
-	 self.v2 = var2
-	 self.direction = Direction.NONE
-	 self:addConstraint()
-end
-
-
---
--- Decides if this constraint can be satisfied and which way it
--- should flow based on the relative strength of the variables related,
--- and record that decision.
---
-function BinaryConstraint:chooseMethod (mark)
-	 if self.v1.mark == mark then
-			self.direction = (self.v2.mark ~= mark and Strength.stronger(self.strength, self.v2.walkStrength)) and Direction.FORWARD or Direction.NONE
-	 end
-	 if self.v2.mark == mark then
-			self.direction = (self.v1.mark ~= mark and Strength.stronger(self.strength, self.v1.walkStrength)) and Direction.BACKWARD or Direction.NONE
-	 end
-	 if Strength.weaker(self.v1.walkStrength, self.v2.walkStrength) then
-			self.direction = Strength.stronger(self.strength, self.v1.walkStrength) and Direction.BACKWARD or Direction.NONE
-	 else
-			self.direction = Strength.stronger(self.strength, self.v2.walkStrength) and Direction.FORWARD or Direction.BACKWARD
-	 end
-end
-
---
--- Add this constraint to the constraint graph
---
-function BinaryConstraint:addToGraph ()
-	 self.v1:addConstraint(self)
-	 self.v2:addConstraint(self)
-	 self.direction = Direction.NONE
-end
-
---
--- Answer true if this constraint is satisfied in the current solution.
---
-function BinaryConstraint:isSatisfied ()
-	 return self.direction ~= Direction.NONE
-end
-
---
--- Mark the input variable with the given mark.
---
-function BinaryConstraint:markInputs (mark)
-	 self:input().mark = mark
-end
-
---
--- Returns the current input variable
---
-function BinaryConstraint:input ()
-	 return (self.direction == Direction.FORWARD) and self.v1 or self.v2
-end
-
---
--- Returns the current output variable
---
-function BinaryConstraint:output ()
-	 return (self.direction == Direction.FORWARD) and self.v2 or self.v1
-end
-
---
--- Calculate the walkabout strength, the stay flag, and, if it is
--- 'stay', the value for the current output of this
--- constraint. Assume this constraint is satisfied.
---
-function BinaryConstraint:recalculate ()
-	 local ihn = self:input()
-	 local out = self:output()
-	 out.walkStrength = Strength.weakestOf(self.strength, ihn.walkStrength);
-	 out.stay = ihn.stay
-	 if out.stay then self:execute() end
-end
-
---
--- Record the fact that self constraint is unsatisfied.
---
-function BinaryConstraint:markUnsatisfied ()
-	 self.direction = Direction.NONE
-end
-
-function BinaryConstraint:inputsKnown (mark)
-	 local i = self:input()
-	 return i.mark == mark or i.stay or i.determinedBy == nil
-end
-
-function BinaryConstraint:removeFromGraph ()
-	 if (self.v1 ~= nil) then self.v1:removeConstraint(self) end
-	 if (self.v2 ~= nil) then self.v2:removeConstraint(self) end
-	 self.direction = Direction.NONE
-end
-
---
--- S c a l e   C o n s t r a i n t
--- 
-
---
--- Relates two variables by the linear scaling relationship: "v2 =
--- (v1 * scale) + offset". Either v1 or v2 may be changed to maintain
--- this relationship but the scale factor and offset are considered
--- read-only.
---
-
-local ScaleConstraint = class (BinaryConstraint)
-
-function ScaleConstraint:constructor(src, scale, offset, dest, strength)
-	 self.direction = Direction.NONE
-	 self.scale = scale
-	 self.offset = offset
-	 ScaleConstraint.super.constructor(self, src, dest, strength)
-end
-
-
---
--- Adds this constraint to the constraint graph.
---
-function ScaleConstraint:addToGraph ()
-	 ScaleConstraint.super.addToGraph(self)
-	 self.scale:addConstraint(self)
-	 self.offset:addConstraint(self)
-end
-
-function ScaleConstraint:removeFromGraph ()
-	 ScaleConstraint.super.removeFromGraph(self)
-	 if (self.scale ~= nil) then self.scale:removeConstraint(self) end
-	 if (self.offset ~= nil) then self.offset:removeConstraint(self) end
-end
-
-function ScaleConstraint:markInputs (mark)
-	 ScaleConstraint.super.markInputs(self, mark);
-	 self.offset.mark = mark
-	 self.scale.mark = mark
-end
-
---
--- Enforce this constraint. Assume that it is satisfied.
---
-function ScaleConstraint:execute ()
-	 if self.direction == Direction.FORWARD then
-			self.v2.value = self.v1.value * self.scale.value + self.offset.value
-	 else
-			self.v1.value = (self.v2.value - self.offset.value) / self.scale.value
-	 end
-end
-
---
--- Calculate the walkabout strength, the stay flag, and, if it is
--- 'stay', the value for the current output of this constraint. Assume
--- this constraint is satisfied.
---
-function ScaleConstraint:recalculate ()
-	 local ihn = self:input()
-	 local out = self:output()
-	 out.walkStrength = Strength.weakestOf(self.strength, ihn.walkStrength)
-	 out.stay = ihn.stay and self.scale.stay and self.offset.stay
-	 if out.stay then self:execute() end
-end
-
---
--- E q u a l i t  y   C o n s t r a i n t
---
-
---
--- Constrains two variables to have the same value.
---
-
-local EqualityConstraint = class (BinaryConstraint)
-
-function EqualityConstraint:constructor(var1, var2, strength)
-	 EqualityConstraint.super.constructor(self, var1, var2, strength)
-end
-
-
---
--- Enforce this constraint. Assume that it is satisfied.
---
-function EqualityConstraint:execute ()
-	 self:output().value = self:input().value
-end
-
---
--- V a r i a b l e
---
-
---
--- A constrained variable. In addition to its value, it maintain the
--- structure of the constraint graph, the current dataflow graph, and
--- various parameters of interest to the DeltaBlue incremental
--- constraint solver.
---
-local Variable = class ()
-
-function Variable:constructor(name, initialValue)
-	 self.value = initialValue or 0
-	 self.constraints = OrderedCollection.new()
-	 self.determinedBy = nil
-	 self.mark = 0
-	 self.walkStrength = Strength.WEAKEST
-	 self.stay = true
-	 self.name = name
-end
-
---
--- Add the given constraint to the set of all constraints that refer
--- this variable.
---
-function Variable:addConstraint (c)
-	 self.constraints:add(c)
-end
-
---
--- Removes all traces of c from this variable.
---
-function Variable:removeConstraint (c)
-	 self.constraints:remove(c)
-	 if self.determinedBy == c then
-			self.determinedBy = nil
-	 end
-end
-
---
--- P l a n n e r
---
-
---
--- The DeltaBlue planner
---
-local Planner = class()
-function Planner:constructor()
-	 self.currentMark = 0
-end
-
---
--- Attempt to satisfy the given constraint and, if successful,
--- incrementally update the dataflow graph.  Details: If satisfying
--- the constraint is successful, it may override a weaker constraint
--- on its output. The algorithm attempts to resatisfy that
--- constraint using some other method. This process is repeated
--- until either a) it reaches a variable that was not previously
--- determined by any constraint or b) it reaches a constraint that
--- is too weak to be satisfied using any of its methods. The
--- variables of constraints that have been processed are marked with
--- a unique mark value so that we know where we've been. This allows
--- the algorithm to avoid getting into an infinite loop even if the
--- constraint graph has an inadvertent cycle.
---
-function Planner:incrementalAdd (c)
-	 local mark = self:newMark()
-	 local overridden = c:satisfy(mark)
-	 while overridden ~= nil do
-			overridden = overridden:satisfy(mark)
-	 end
-end
-
---
--- Entry point for retracting a constraint. Remove the given
--- constraint and incrementally update the dataflow graph.
--- Details: Retracting the given constraint may allow some currently
--- unsatisfiable downstream constraint to be satisfied. We therefore collect
--- a list of unsatisfied downstream constraints and attempt to
--- satisfy each one in turn. This list is traversed by constraint
--- strength, strongest first, as a heuristic for avoiding
--- unnecessarily adding and then overriding weak constraints.
--- Assume: c is satisfied.
---
-function Planner:incrementalRemove (c)
-	 local out = c:output()
-	 c:markUnsatisfied()
-	 c:removeFromGraph()
-	 local unsatisfied = self:removePropagateFrom(out)
-	 local strength = Strength.REQUIRED
-	 repeat
-			for i = 1, unsatisfied:size() do
-				 local u = unsatisfied:at(i)
-				 if u.strength == strength then
-						self:incrementalAdd(u)
-				 end
-			end
-			strength = strength:nextWeaker()
-	 until strength == Strength.WEAKEST
-end
-
---
--- Select a previously unused mark value.
---
-function Planner:newMark ()
-	 self.currentMark = self.currentMark + 1
-	 return self.currentMark
-end
-
---
--- Extract a plan for resatisfaction starting from the given source
--- constraints, usually a set of input constraints. This method
--- assumes that stay optimization is desired; the plan will contain
--- only constraints whose output variables are not stay. Constraints
--- that do no computation, such as stay and edit constraints, are
--- not included in the plan.
--- Details: The outputs of a constraint are marked when it is added
--- to the plan under construction. A constraint may be appended to
--- the plan when all its input variables are known. A variable is
--- known if either a) the variable is marked (indicating that has
--- been computed by a constraint appearing earlier in the plan), b)
--- the variable is 'stay' (i.e. it is a constant at plan execution
--- time), or c) the variable is not determined by any
--- constraint. The last provision is for past states of history
--- variables, which are not stay but which are also not computed by
--- any constraint.
--- Assume: sources are all satisfied.
---
-local Plan -- FORWARD DECLARATION
-function Planner:makePlan (sources)
-	 local mark = self:newMark()
-	 local plan = Plan.new()
-	 local todo = sources
-	 while todo:size() > 0 do
-			local c = todo:removeFirst()
-			if c:output().mark ~= mark and c:inputsKnown(mark) then
-				 plan:addConstraint(c)
-				 c:output().mark = mark
-				 self:addConstraintsConsumingTo(c:output(), todo)
-			end
-	 end
-	 return plan
-end
-
---
--- Extract a plan for resatisfying starting from the output of the
--- given constraints, usually a set of input constraints.
---
-function Planner:extractPlanFromConstraints (constraints)
-	 local sources = OrderedCollection.new()
-	 for i = 1, constraints:size() do
-			local c = constraints:at(i)
-			if c:isInput() and c:isSatisfied() then
-				 -- not in plan already and eligible for inclusion
-				 sources:add(c)
-			end
-	 end
-	 return self:makePlan(sources)
-end
-
---
--- Recompute the walkabout strengths and stay flags of all variables
--- downstream of the given constraint and recompute the actual
--- values of all variables whose stay flag is true. If a cycle is
--- detected, remove the given constraint and answer
--- false. Otherwise, answer true.
--- Details: Cycles are detected when a marked variable is
--- encountered downstream of the given constraint. The sender is
--- assumed to have marked the inputs of the given constraint with
--- the given mark. Thus, encountering a marked node downstream of
--- the output constraint means that there is a path from the
--- constraint's output to one of its inputs.
---
-function Planner:addPropagate (c, mark)
-	 local todo = OrderedCollection.new()
-	 todo:add(c)
-	 while todo:size() > 0 do
-			local d = todo:removeFirst()
-			if d:output().mark == mark then
-				 self:incrementalRemove(c)
-				 return false
-			end
-			d:recalculate()
-			self:addConstraintsConsumingTo(d:output(), todo)
-	 end
-	 return true
-end
-
-
---
--- Update the walkabout strengths and stay flags of all variables
--- downstream of the given constraint. Answer a collection of
--- unsatisfied constraints sorted in order of decreasing strength.
---
-function Planner:removePropagateFrom (out)
-	 out.determinedBy = nil
-	 out.walkStrength = Strength.WEAKEST
-	 out.stay = true
-	 local unsatisfied = OrderedCollection.new()
-	 local todo = OrderedCollection.new()
-	 todo:add(out)
-	 while todo:size() > 0 do
-			local v = todo:removeFirst()
-			for i = 1, v.constraints:size() do
-				 local c = v.constraints:at(i)
-				 if not c:isSatisfied() then unsatisfied:add(c) end
-			end
-			local determining = v.determinedBy
-			for i = 1, v.constraints:size() do
-				 local next = v.constraints:at(i);
-				 if next ~= determining and next:isSatisfied() then
-						next:recalculate()
-						todo:add(next:output())
-				 end
-			end
-	 end
-	 return unsatisfied
-end
-
-function Planner:addConstraintsConsumingTo (v, coll)
-	 local determining = v.determinedBy
-	 local cc = v.constraints
-	 for i = 1, cc:size() do
-			local c = cc:at(i)
-			if c ~= determining and c:isSatisfied() then
-				 coll:add(c)
-			end
-	 end
-end
-
---
--- P l a n
---
-
---
--- A Plan is an ordered list of constraints to be executed in sequence
--- to resatisfy all currently satisfiable constraints in the face of
--- one or more changing inputs.
---
-Plan = class()
-function Plan:constructor()
-	 self.v = OrderedCollection.new()
-end
-
-function Plan:addConstraint (c)
-	 self.v:add(c)
-end
-
-function Plan:size ()
-	 return self.v:size()
-end
-
-function Plan:constraintAt (index)
-	 return self.v:at(index)
-end
-
-function Plan:execute ()
-	 for i = 1, self:size() do
-			local c = self:constraintAt(i)
-			c:execute()
-	 end
-end
-
---
--- M a i n
---
-
---
--- This is the standard DeltaBlue benchmark. A long chain of equality
--- constraints is constructed with a stay constraint on one end. An
--- edit constraint is then added to the opposite end and the time is
--- measured for adding and removing this constraint, and extracting
--- and executing a constraint satisfaction plan. There are two cases.
--- In case 1, the added constraint is stronger than the stay
--- constraint and values must propagate down the entire length of the
--- chain. In case 2, the added constraint is weaker than the stay
--- constraint so it cannot be accommodated. The cost in this case is,
--- of course, very low. Typical situations lie somewhere between these
--- two extremes.
---
-local function chainTest(n)
-	 planner = Planner.new()
-	 local prev = nil
-	 local first = nil
-	 local last = nil
-
-	 -- Build chain of n equality constraints
-	 for i = 0, n do
-			local name = "v" .. i;
-			local v = Variable.new(name)
-			if prev ~= nil then EqualityConstraint.new(prev, v, Strength.REQUIRED) end
-			if i == 0 then first = v end
-			if i == n then last = v end
-			prev = v
-	 end
-
-	 StayConstraint.new(last, Strength.STRONG_DEFAULT)
-	 local edit = EditConstraint.new(first, Strength.PREFERRED)
-	 local edits = OrderedCollection.new()
-	 edits:add(edit)
-	 local plan = planner:extractPlanFromConstraints(edits)
-	 for i = 0, 99 do
-			first.value = i
-			plan:execute()
-			if last.value ~= i then
-				 alert("Chain test failed.")
-			end
-	 end
-end
-
-local function change(v, newValue)
-	 local edit = EditConstraint.new(v, Strength.PREFERRED)
-	 local edits = OrderedCollection.new()
-	 edits:add(edit)
-	 local plan = planner:extractPlanFromConstraints(edits)
-	 for i = 1, 10 do
-			v.value = newValue
-			plan:execute()
-	 end
-	 edit:destroyConstraint()
-end
-
---
--- This test constructs a two sets of variables related to each
--- other by a simple linear transformation (scale and offset). The
--- time is measured to change a variable on either side of the
--- mapping and to change the scale and offset factors.
---
-local function projectionTest(n)
-	 planner = Planner.new();
-	 local scale = Variable.new("scale", 10);
-	 local offset = Variable.new("offset", 1000);
-	 local src = nil
-	 local dst = nil;
-
-	 local dests = OrderedCollection.new();
-	 for i = 0, n - 1 do
-			src = Variable.new("src" .. i, i);
-			dst = Variable.new("dst" .. i, i);
-			dests:add(dst);
-			StayConstraint.new(src, Strength.NORMAL);
-			ScaleConstraint.new(src, scale, offset, dst, Strength.REQUIRED);
-	 end
-
-	 change(src, 17)
-	 if dst.value ~= 1170 then alert("Projection 1 failed") end
-	 change(dst, 1050)
-	 if src.value ~= 5 then alert("Projection 2 failed") end
-	 change(scale, 5)
-	 for i = 0, n - 2 do
-			if dests:at(i + 1).value ~= i * 5 + 1000 then
-				 alert("Projection 3 failed")
-			end
-	 end
-	 change(offset, 2000)
-	 for i = 0, n - 2 do
-			if dests:at(i + 1).value ~= i * 5 + 2000 then
-				 alert("Projection 4 failed")
-			end
-	 end
-end
-
-function test()
-	local t0 = os.clock()
-	chainTest(1000);
-	projectionTest(1000);
-	local t1 = os.clock()
-	return t1-t0
-end	
-
-bench.runCode(test, "deltablue")

tests/Fixture.cpp

@@ -32,6 +32,55 @@ std::optional<ModuleName> TestFileResolver::fromAstFragment(AstExpr* expr) const
     return std::nullopt;
 }
 
+std::optional<ModuleInfo> TestFileResolver::resolveModule(const ModuleInfo* context, AstExpr* expr)
+{
+    if (AstExprGlobal* g = expr->as<AstExprGlobal>())
+    {
+        if (g->name == "game")
+            return ModuleInfo{"game"};
+        if (g->name == "workspace")
+            return ModuleInfo{"workspace"};
+        if (g->name == "script")
+            return context ? std::optional<ModuleInfo>(*context) : std::nullopt;
+    }
+    else if (AstExprIndexName* i = expr->as<AstExprIndexName>(); i && context)
+    {
+        if (i->index == "Parent")
+        {
+            std::string_view view = context->name;
+            size_t lastSeparatorIndex = view.find_last_of('/');
+
+            if (lastSeparatorIndex == std::string_view::npos)
+                return std::nullopt;
+
+            return ModuleInfo{ModuleName(view.substr(0, lastSeparatorIndex)), context->optional};
+        }
+        else
+        {
+            return ModuleInfo{context->name + '/' + i->index.value, context->optional};
+        }
+    }
+    else if (AstExprIndexExpr* i = expr->as<AstExprIndexExpr>(); i && context)
+    {
+        if (AstExprConstantString* index = i->index->as<AstExprConstantString>())
+        {
+            return ModuleInfo{context->name + '/' + std::string(index->value.data, index->value.size), context->optional};
+        }
+    }
+    else if (AstExprCall* call = expr->as<AstExprCall>(); call && call->self && call->args.size >= 1 && context)
+    {
+        if (AstExprConstantString* index = call->args.data[0]->as<AstExprConstantString>())
+        {
+            AstName func = call->func->as<AstExprIndexName>()->index;
+
+            if (func == "GetService" && context->name == "game")
+                return ModuleInfo{"game/" + std::string(index->value.data, index->value.size)};
+        }
+    }
+
+    return std::nullopt;
+}
+
 ModuleName TestFileResolver::concat(const ModuleName& lhs, std::string_view rhs) const
 {
     return lhs + "/" + ModuleName(rhs);

tests/Fixture.h

@@ -65,6 +65,8 @@ struct TestFileResolver
     }
 
     std::optional<ModuleName> fromAstFragment(AstExpr* expr) const override;
+    std::optional<ModuleInfo> resolveModule(const ModuleInfo* context, AstExpr* expr) override;
+
     ModuleName concat(const ModuleName& lhs, std::string_view rhs) const override;
     std::optional<ModuleName> getParentModuleName(const ModuleName& name) const override;
 

tests/Frontend.test.cpp

@@ -58,6 +58,35 @@ struct NaiveFileResolver : NullFileResolver
         return std::nullopt;
     }
 
+    std::optional<ModuleInfo> resolveModule(const ModuleInfo* context, AstExpr* expr) override
+    {
+        if (AstExprGlobal* g = expr->as<AstExprGlobal>())
+        {
+            if (g->name == "Modules")
+                return ModuleInfo{"Modules"};
+
+            if (g->name == "game")
+                return ModuleInfo{"game"};
+        }
+        else if (AstExprIndexName* i = expr->as<AstExprIndexName>())
+        {
+            if (context)
+                return ModuleInfo{context->name + '/' + i->index.value, context->optional};
+        }
+        else if (AstExprCall* call = expr->as<AstExprCall>(); call && call->self && call->args.size >= 1 && context)
+        {
+            if (AstExprConstantString* index = call->args.data[0]->as<AstExprConstantString>())
+            {
+                AstName func = call->func->as<AstExprIndexName>()->index;
+
+                if (func == "GetService" && context->name == "game")
+                    return ModuleInfo{"game/" + std::string(index->value.data, index->value.size)};
+            }
+        }
+
+        return std::nullopt;
+    }
+
     ModuleName concat(const ModuleName& lhs, std::string_view rhs) const override
     {
         return lhs + "/" + ModuleName(rhs);
@@ -528,7 +557,7 @@ TEST_CASE_FIXTURE(FrontendFixture, "ignore_require_to_nonexistent_file")
 {
     fileResolver.source["Modules/A"] = R"(
         local Modules = script
-        local B = require(Modules.B :: any)
+        local B = require(Modules.B) :: any
     )";
 
     CheckResult result = frontend.check("Modules/A");

tests/Linter.test.cpp

@@ -1400,6 +1400,8 @@ end
 
 TEST_CASE_FIXTURE(Fixture, "TableOperations")
 {
+    ScopedFastFlag sff("LuauLinterTableMoveZero", true);
+
     LintResult result = lintTyped(R"(
 local t = {}
 local tt = {}
@@ -1417,9 +1419,12 @@ table.remove(t, 0)
 table.remove(t, #t-1)
 
 table.insert(t, string.find("hello", "h"))
+
+table.move(t, 0, #t, 1, tt)
+table.move(t, 1, #t, 0, tt)
 )");
 
-    REQUIRE_EQ(result.warnings.size(), 6);
+    REQUIRE_EQ(result.warnings.size(), 8);
     CHECK_EQ(result.warnings[0].text, "table.insert will insert the value before the last element, which is likely a bug; consider removing the "
                                       "second argument or wrap it in parentheses to silence");
     CHECK_EQ(result.warnings[1].text, "table.insert will append the value to the table; consider removing the second argument for efficiency");
@@ -1429,6 +1434,8 @@ table.insert(t, string.find("hello", "h"))
                                       "second argument or wrap it in parentheses to silence");
     CHECK_EQ(result.warnings[5].text,
         "table.insert may change behavior if the call returns more than one result; consider adding parentheses around second argument");
+    CHECK_EQ(result.warnings[6].text, "table.move uses index 0 but arrays are 1-based; did you mean 1 instead?");
+    CHECK_EQ(result.warnings[7].text, "table.move uses index 0 but arrays are 1-based; did you mean 1 instead?");
 }
 
 TEST_CASE_FIXTURE(Fixture, "DuplicateConditions")

tests/Module.test.cpp

@@ -1,5 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Module.h"
+#include "Luau/Scope.h"
 
 #include "Fixture.h"
 

tests/NonstrictMode.test.cpp

@@ -1,5 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Parser.h"
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypeVar.h"
 

tests/Parser.test.cpp

@@ -2519,4 +2519,19 @@ TEST_CASE_FIXTURE(Fixture, "parse_if_else_expression")
     }
 }
 
+TEST_CASE_FIXTURE(Fixture, "parse_type_pack_type_parameters")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    AstStat* stat = parse(R"(
+type Packed<T...> = () -> T...
+
+type A<X...> = Packed<X...>
+type B<X...> = Packed<...number>
+type C<X...> = Packed<(number, X...)>
+    )");
+    REQUIRE(stat != nullptr);
+}
+
 TEST_SUITE_END();

tests/RequireTracer.test.cpp

@@ -57,6 +57,7 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "trace_local")
 {
     AstStatBlock* block = parse(R"(
         local m = workspace.Foo.Bar.Baz
+        require(m)
     )");
 
     RequireTraceResult result = traceRequires(&fileResolver, block, "ModuleName");
@@ -70,22 +71,22 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "trace_local")
     AstExprIndexName* value = loc->values.data[0]->as<AstExprIndexName>();
     REQUIRE(value);
     REQUIRE(result.exprs.contains(value));
-    CHECK_EQ("workspace/Foo/Bar/Baz", result.exprs[value]);
+    CHECK_EQ("workspace/Foo/Bar/Baz", result.exprs[value].name);
 
     value = value->expr->as<AstExprIndexName>();
     REQUIRE(value);
     REQUIRE(result.exprs.contains(value));
-    CHECK_EQ("workspace/Foo/Bar", result.exprs[value]);
+    CHECK_EQ("workspace/Foo/Bar", result.exprs[value].name);
 
     value = value->expr->as<AstExprIndexName>();
     REQUIRE(value);
     REQUIRE(result.exprs.contains(value));
-    CHECK_EQ("workspace/Foo", result.exprs[value]);
+    CHECK_EQ("workspace/Foo", result.exprs[value].name);
 
     AstExprGlobal* workspace = value->expr->as<AstExprGlobal>();
     REQUIRE(workspace);
     REQUIRE(result.exprs.contains(workspace));
-    CHECK_EQ("workspace", result.exprs[workspace]);
+    CHECK_EQ("workspace", result.exprs[workspace].name);
 }
 
 TEST_CASE_FIXTURE(RequireTracerFixture, "trace_transitive_local")
@@ -93,9 +94,10 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "trace_transitive_local")
     AstStatBlock* block = parse(R"(
         local m = workspace.Foo.Bar.Baz
         local n = m.Quux
+        require(n)
     )");
 
-    REQUIRE_EQ(2, block->body.size);
+    REQUIRE_EQ(3, block->body.size);
 
     RequireTraceResult result = traceRequires(&fileResolver, block, "ModuleName");
 
@@ -104,13 +106,13 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "trace_transitive_local")
     REQUIRE_EQ(1, local->vars.size);
 
     REQUIRE(result.exprs.contains(local->values.data[0]));
-    CHECK_EQ("workspace/Foo/Bar/Baz/Quux", result.exprs[local->values.data[0]]);
+    CHECK_EQ("workspace/Foo/Bar/Baz/Quux", result.exprs[local->values.data[0]].name);
 }
 
 TEST_CASE_FIXTURE(RequireTracerFixture, "trace_function_arguments")
 {
     AstStatBlock* block = parse(R"(
-        local M = require(workspace.Game.Thing, workspace.Something.Else)
+        local M = require(workspace.Game.Thing)
     )");
     REQUIRE_EQ(1, block->body.size);
 
@@ -124,52 +126,9 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "trace_function_arguments")
     AstExprCall* call = local->values.data[0]->as<AstExprCall>();
     REQUIRE(call != nullptr);
 
-    REQUIRE_EQ(2, call->args.size);
-
-    CHECK_EQ("workspace/Game/Thing", result.exprs[call->args.data[0]]);
-    CHECK_EQ("workspace/Something/Else", result.exprs[call->args.data[1]]);
-}
-
-TEST_CASE_FIXTURE(RequireTracerFixture, "follow_GetService_calls")
-{
-    AstStatBlock* block = parse(R"(
-        local R = game:GetService('ReplicatedStorage').Roact
-        local Roact = require(R)
-    )");
-    REQUIRE_EQ(2, block->body.size);
-
-    RequireTraceResult result = traceRequires(&fileResolver, block, "ModuleName");
-
-    AstStatLocal* local = block->body.data[0]->as<AstStatLocal>();
-    REQUIRE(local != nullptr);
-
-    CHECK_EQ("game/ReplicatedStorage/Roact", result.exprs[local->values.data[0]]);
-
-    AstStatLocal* local2 = block->body.data[1]->as<AstStatLocal>();
-    REQUIRE(local2 != nullptr);
-    REQUIRE_EQ(1, local2->values.size);
-
-    AstExprCall* call = local2->values.data[0]->as<AstExprCall>();
-    REQUIRE(call != nullptr);
     REQUIRE_EQ(1, call->args.size);
 
-    CHECK_EQ("game/ReplicatedStorage/Roact", result.exprs[call->args.data[0]]);
+    CHECK_EQ("workspace/Game/Thing", result.exprs[call->args.data[0]].name);
-}
-
-TEST_CASE_FIXTURE(RequireTracerFixture, "follow_WaitForChild_calls")
-{
-    ScopedFastFlag luauTraceRequireLookupChild("LuauTraceRequireLookupChild", true);
-
-    AstStatBlock* block = parse(R"(
-local A = require(workspace:WaitForChild('ReplicatedStorage').Content)
-local B = require(workspace:FindFirstChild('ReplicatedFirst').Data)
-    )");
-
-    RequireTraceResult result = traceRequires(&fileResolver, block, "ModuleName");
-
-    REQUIRE_EQ(2, result.requires.size());
-    CHECK_EQ("workspace/ReplicatedStorage/Content", result.requires[0].first);
-    CHECK_EQ("workspace/ReplicatedFirst/Data", result.requires[1].first);
 }
 
 TEST_CASE_FIXTURE(RequireTracerFixture, "follow_typeof")
@@ -200,22 +159,23 @@ TEST_CASE_FIXTURE(RequireTracerFixture, "follow_typeof")
     REQUIRE(call != nullptr);
     REQUIRE_EQ(1, call->args.size);
 
-    CHECK_EQ("workspace/CoolThing", result.exprs[call->args.data[0]]);
+    CHECK_EQ("workspace/CoolThing", result.exprs[call->args.data[0]].name);
 }
 
 TEST_CASE_FIXTURE(RequireTracerFixture, "follow_string_indexexpr")
 {
     AstStatBlock* block = parse(R"(
         local R = game["Test"]
+        require(R)
     )");
-    REQUIRE_EQ(1, block->body.size);
+    REQUIRE_EQ(2, block->body.size);
 
     RequireTraceResult result = traceRequires(&fileResolver, block, "ModuleName");
 
     AstStatLocal* local = block->body.data[0]->as<AstStatLocal>();
     REQUIRE(local != nullptr);
 
-    CHECK_EQ("game/Test", result.exprs[local->values.data[0]]);
+    CHECK_EQ("game/Test", result.exprs[local->values.data[0]].name);
 }
 
 TEST_SUITE_END();

tests/ToString.test.cpp

@@ -1,5 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 
+#include "Luau/Scope.h"
 #include "Luau/ToString.h"
 
 #include "Fixture.h"
@@ -416,8 +417,6 @@ function foo(a, b) return a(b) end
 
 TEST_CASE_FIXTURE(Fixture, "toString_the_boundTo_table_type_contained_within_a_TypePack")
 {
-    ScopedFastFlag sff{"LuauToStringFollowsBoundTo", true};
-
     TypeVar tv1{TableTypeVar{}};
     TableTypeVar* ttv = getMutable<TableTypeVar>(&tv1);
     ttv->state = TableState::Sealed;

tests/TypeInfer.aliases.test.cpp

@@ -0,0 +1,557 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#include "Fixture.h"
+
+#include "doctest.h"
+#include "Luau/BuiltinDefinitions.h"
+
+using namespace Luau;
+
+TEST_SUITE_BEGIN("TypeAliases");
+
+TEST_CASE_FIXTURE(Fixture, "cyclic_function_type_in_type_alias")
+{
+    ScopedFastFlag sff{"LuauOccursCheckOkWithRecursiveFunctions", true};
+
+    CheckResult result = check(R"(
+        type F = () -> F?
+        local function f()
+            return f
+        end
+
+        local g: F = f
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+    CHECK_EQ("t1 where t1 = () -> t1?", toString(requireType("g")));
+}
+
+TEST_CASE_FIXTURE(Fixture, "cyclic_types_of_named_table_fields_do_not_expand_when_stringified")
+{
+    CheckResult result = check(R"(
+        --!strict
+        type Node = { Parent: Node?; }
+        local node: Node;
+        node.Parent = 1
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
+    REQUIRE(tm);
+    CHECK_EQ("Node?", toString(tm->wantedType));
+    CHECK_EQ(typeChecker.numberType, tm->givenType);
+}
+
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types")
+{
+    CheckResult result = check(R"(
+        --!strict
+        type T<a> = { f: a, g: U<a> }
+        type U<a> = { h: a, i: T<a>? }
+        local x: T<number> = { f = 37, g = { h = 5, i = nil } }
+        x.g.i = x
+        local y: T<string> = { f = "hi", g = { h = "lo", i = nil } }
+        y.g.i = y
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_errors")
+{
+    CheckResult result = check(R"(
+        --!strict
+        type T<a> = { f: a, g: U<a> }
+        type U<b> = { h: b, i: T<b>? }
+        local x: T<number> = { f = 37, g = { h = 5, i = nil } }
+        x.g.i = x
+        local y: T<string> = { f = "hi", g = { h = 5, i = nil } }
+        y.g.i = y
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+
+    // We had a UAF in this example caused by not cloning type function arguments
+    ModulePtr module = frontend.moduleResolver.getModule("MainModule");
+    unfreeze(module->interfaceTypes);
+    copyErrors(module->errors, module->interfaceTypes);
+    freeze(module->interfaceTypes);
+    module->internalTypes.clear();
+    module->astTypes.clear();
+
+    // Make sure the error strings don't include "VALUELESS"
+    for (auto error : module->errors)
+        CHECK_MESSAGE(toString(error).find("VALUELESS") == std::string::npos, toString(error));
+}
+
+TEST_CASE_FIXTURE(Fixture, "use_table_name_and_generic_params_in_errors")
+{
+    CheckResult result = check(R"(
+        type Pair<T, U> = {first: T, second: U}
+        local a: Pair<string, number>
+        local b: Pair<string, string>
+
+        a = b
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
+    REQUIRE(tm);
+
+    CHECK_EQ("Pair<string, number>", toString(tm->wantedType));
+    CHECK_EQ("Pair<string, string>", toString(tm->givenType));
+}
+
+TEST_CASE_FIXTURE(Fixture, "dont_stop_typechecking_after_reporting_duplicate_type_definition")
+{
+    CheckResult result = check(R"(
+        type A = number
+        type A = string -- Redefinition of type 'A', previously defined at line 1
+        local foo: string = 1 -- No "Type 'number' could not be converted into 'string'"
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(2, result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "stringify_type_alias_of_recursive_template_table_type")
+{
+    CheckResult result = check(R"(
+        type Table<T> = { a: T }
+        type Wrapped = Table<Wrapped>
+        local l: Wrapped = 2
+        )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
+    REQUIRE(tm);
+    CHECK_EQ("Wrapped", toString(tm->wantedType));
+    CHECK_EQ(typeChecker.numberType, tm->givenType);
+}
+
+TEST_CASE_FIXTURE(Fixture, "stringify_type_alias_of_recursive_template_table_type2")
+{
+    CheckResult result = check(R"(
+        type Table<T> = { a: T }
+        type Wrapped = (Table<Wrapped>) -> string
+        local l: Wrapped = 2
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
+    REQUIRE(tm);
+    CHECK_EQ("t1 where t1 = ({| a: t1 |}) -> string", toString(tm->wantedType));
+    CHECK_EQ(typeChecker.numberType, tm->givenType);
+}
+
+// Check that recursive intersection type doesn't generate an OOM
+TEST_CASE_FIXTURE(Fixture, "cli_38393_recursive_intersection_oom")
+{
+    CheckResult result = check(R"(
+        function _(l0:(t0)&((t0)&(((t0)&((t0)->()))->(typeof(_),typeof(# _)))),l39,...):any
+        end
+        type t0<t0> = ((typeof(_))&((t0)&(((typeof(_))&(t0))->typeof(_))),{n163:any,})->(any,typeof(_))
+        _(_)
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_fwd_declaration_is_precise")
+{
+    CheckResult result = check(R"(
+        local foo: Id<number> = 1
+        type Id<T> = T
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "corecursive_types_generic")
+{
+    const std::string code = R"(
+        type A<T> = {v:T, b:B<T>}
+        type B<T> = {v:T, a:A<T>}
+        local aa:A<number>
+        local bb = aa
+    )";
+
+    const std::string expected = R"(
+        type A<T> = {v:T, b:B<T>}
+        type B<T> = {v:T, a:A<T>}
+        local aa:A<number>
+        local bb:A<number>=aa
+    )";
+
+    CHECK_EQ(expected, decorateWithTypes(code));
+    CheckResult result = check(code);
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "corecursive_function_types")
+{
+    ScopedFastFlag sff{"LuauOccursCheckOkWithRecursiveFunctions", true};
+
+    CheckResult result = check(R"(
+        type A = () -> (number, B)
+        type B = () -> (string, A)
+        local a: A
+        local b: B
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("t1 where t1 = () -> (number, () -> (string, t1))", toString(requireType("a")));
+    CHECK_EQ("t1 where t1 = () -> (string, () -> (number, t1))", toString(requireType("b")));
+}
+
+TEST_CASE_FIXTURE(Fixture, "generic_param_remap")
+{
+    const std::string code = R"(
+        -- An example of a forwarded use of a type that has different type arguments than parameters
+        type A<T,U> = {t:T, u:U, next:A<U,T>?}
+        local aa:A<number,string> = { t = 5, u = 'hi', next = { t = 'lo', u = 8 } }
+        local bb = aa
+    )";
+
+    const std::string expected = R"(
+
+        type A<T,U> = {t:T, u:U, next:A<U,T>?}
+        local aa:A<number,string> = { t = 5, u = 'hi', next = { t = 'lo', u = 8 } }
+        local bb:A<number,string>=aa
+    )";
+
+    CHECK_EQ(expected, decorateWithTypes(code));
+    CheckResult result = check(code);
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "export_type_and_type_alias_are_duplicates")
+{
+    CheckResult result = check(R"(
+        export type Foo = number
+        type Foo = number
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    auto dtd = get<DuplicateTypeDefinition>(result.errors[0]);
+    REQUIRE(dtd);
+    CHECK_EQ(dtd->name, "Foo");
+}
+
+TEST_CASE_FIXTURE(Fixture, "stringify_optional_parameterized_alias")
+{
+    ScopedFastFlag sffs3{"LuauGenericFunctions", true};
+    ScopedFastFlag sffs4{"LuauParseGenericFunctions", true};
+
+    CheckResult result = check(R"(
+        type Node<T> = { value: T, child: Node<T>? }
+
+        local function visitor<T>(node: Node<T>?)
+            local a: Node<T>
+
+            if node then
+                a = node.child -- Observe the output of the error message.
+            end
+        end
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    auto e = get<TypeMismatch>(result.errors[0]);
+    CHECK_EQ("Node<T>?", toString(e->givenType));
+    CHECK_EQ("Node<T>", toString(e->wantedType));
+}
+
+TEST_CASE_FIXTURE(Fixture, "general_require_multi_assign")
+{
+    fileResolver.source["workspace/A"] = R"(
+        export type myvec2 = {x: number, y: number}
+        return {}
+    )";
+
+    fileResolver.source["workspace/B"] = R"(
+        export type myvec3 = {x: number, y: number, z: number}
+        return {}
+    )";
+
+    fileResolver.source["workspace/C"] = R"(
+        local Foo, Bar = require(workspace.A), require(workspace.B)
+
+        local a: Foo.myvec2
+        local b: Bar.myvec3
+    )";
+
+    CheckResult result = frontend.check("workspace/C");
+    LUAU_REQUIRE_NO_ERRORS(result);
+    ModulePtr m = frontend.moduleResolver.modules["workspace/C"];
+
+    REQUIRE(m != nullptr);
+
+    std::optional<TypeId> aTypeId = lookupName(m->getModuleScope(), "a");
+    REQUIRE(aTypeId);
+    const Luau::TableTypeVar* aType = get<TableTypeVar>(follow(*aTypeId));
+    REQUIRE(aType);
+    REQUIRE(aType->props.size() == 2);
+
+    std::optional<TypeId> bTypeId = lookupName(m->getModuleScope(), "b");
+    REQUIRE(bTypeId);
+    const Luau::TableTypeVar* bType = get<TableTypeVar>(follow(*bTypeId));
+    REQUIRE(bType);
+    REQUIRE(bType->props.size() == 3);
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_import_mutation")
+{
+    CheckResult result = check("type t10<x> = typeof(table)");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    TypeId ty = getGlobalBinding(frontend.typeChecker, "table");
+    CHECK_EQ(toString(ty), "table");
+
+    const TableTypeVar* ttv = get<TableTypeVar>(ty);
+    REQUIRE(ttv);
+
+    CHECK(ttv->instantiatedTypeParams.empty());
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_local_mutation")
+{
+    CheckResult result = check(R"(
+type Cool = { a: number, b: string }
+local c: Cool = { a = 1, b = "s" }
+type NotCool<x> = Cool
+)");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    std::optional<TypeId> ty = requireType("c");
+    REQUIRE(ty);
+    CHECK_EQ(toString(*ty), "Cool");
+
+    const TableTypeVar* ttv = get<TableTypeVar>(*ty);
+    REQUIRE(ttv);
+
+    CHECK(ttv->instantiatedTypeParams.empty());
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_local_rename")
+{
+    CheckResult result = check(R"(
+type Cool = { a: number, b: string }
+type NotCool = Cool
+local c: Cool = { a = 1, b = "s" }
+local d: NotCool = { a = 1, b = "s" }
+)");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    std::optional<TypeId> ty = requireType("c");
+    REQUIRE(ty);
+    CHECK_EQ(toString(*ty), "Cool");
+
+    ty = requireType("d");
+    REQUIRE(ty);
+    CHECK_EQ(toString(*ty), "NotCool");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_local_synthetic_mutation")
+{
+    CheckResult result = check(R"(
+local c = { a = 1, b = "s" }
+type Cool = typeof(c)
+)");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    std::optional<TypeId> ty = requireType("c");
+    REQUIRE(ty);
+
+    const TableTypeVar* ttv = get<TableTypeVar>(*ty);
+    REQUIRE(ttv);
+    CHECK_EQ(ttv->name, "Cool");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_of_an_imported_recursive_type")
+{
+    fileResolver.source["game/A"] = R"(
+export type X = { a: number, b: X? }
+return {}
+    )";
+
+    CheckResult aResult = frontend.check("game/A");
+    LUAU_REQUIRE_NO_ERRORS(aResult);
+
+    CheckResult bResult = check(R"(
+local Import = require(game.A)
+type X = Import.X
+    )");
+    LUAU_REQUIRE_NO_ERRORS(bResult);
+
+    std::optional<TypeId> ty1 = lookupImportedType("Import", "X");
+    REQUIRE(ty1);
+
+    std::optional<TypeId> ty2 = lookupType("X");
+    REQUIRE(ty2);
+
+    CHECK_EQ(follow(*ty1), follow(*ty2));
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_of_an_imported_recursive_generic_type")
+{
+    fileResolver.source["game/A"] = R"(
+export type X<T, U> = { a: T, b: U, C: X<T, U>? }
+return {}
+    )";
+
+    CheckResult aResult = frontend.check("game/A");
+    LUAU_REQUIRE_NO_ERRORS(aResult);
+
+    CheckResult bResult = check(R"(
+local Import = require(game.A)
+type X<T, U> = Import.X<T, U>
+    )");
+    LUAU_REQUIRE_NO_ERRORS(bResult);
+
+    std::optional<TypeId> ty1 = lookupImportedType("Import", "X");
+    REQUIRE(ty1);
+
+    std::optional<TypeId> ty2 = lookupType("X");
+    REQUIRE(ty2);
+
+    CHECK_EQ(toString(*ty1, {true}), toString(*ty2, {true}));
+
+    bResult = check(R"(
+local Import = require(game.A)
+type X<T, U> = Import.X<U, T>
+    )");
+    LUAU_REQUIRE_NO_ERRORS(bResult);
+
+    ty1 = lookupImportedType("Import", "X");
+    REQUIRE(ty1);
+
+    ty2 = lookupType("X");
+    REQUIRE(ty2);
+
+    CHECK_EQ(toString(*ty1, {true}), "t1 where t1 = {| C: t1?, a: T, b: U |}");
+    CHECK_EQ(toString(*ty2, {true}), "{| C: t1, a: U, b: T |} where t1 = {| C: t1, a: U, b: T |}?");
+}
+
+TEST_CASE_FIXTURE(Fixture, "module_export_free_type_leak")
+{
+    CheckResult result = check(R"(
+function get()
+    return function(obj) return true end
+end
+
+export type f = typeof(get())
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "module_export_wrapped_free_type_leak")
+{
+    CheckResult result = check(R"(
+function get()
+    return {a = 1, b = function(obj) return true end}
+end
+
+export type f = typeof(get())
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_restriction_ok")
+{
+    CheckResult result = check(R"(
+        type Tree<T> = { data: T, children: Forest<T> }
+        type Forest<T> = {Tree<T>}
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_restriction_not_ok_1")
+{
+    ScopedFastFlag sff{"LuauRecursiveTypeParameterRestriction", true};
+
+    CheckResult result = check(R"(
+        -- OK because forwarded types are used with their parameters.
+        type Tree<T> = { data: T, children: Forest<T> }
+        type Forest<T> = {Tree<{T}>}
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_restriction_not_ok_2")
+{
+    ScopedFastFlag sff{"LuauRecursiveTypeParameterRestriction", true};
+
+    CheckResult result = check(R"(
+        -- Not OK because forwarded types are used with different types than their parameters.
+        type Forest<T> = {Tree<{T}>}
+        type Tree<T> = { data: T, children: Forest<T> }
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_swapsies_ok")
+{
+    CheckResult result = check(R"(
+        type Tree1<T,U> = { data: T, children: {Tree2<U,T>} }
+        type Tree2<U,T> = { data: U, children: {Tree1<T,U>} }
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_swapsies_not_ok")
+{
+    ScopedFastFlag sff{"LuauRecursiveTypeParameterRestriction", true};
+
+    CheckResult result = check(R"(
+        type Tree1<T,U> = { data: T, children: {Tree2<U,T>} }
+        type Tree2<T,U> = { data: U, children: {Tree1<T,U>} }
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "free_variables_from_typeof_in_aliases")
+{
+    CheckResult result = check(R"(
+        function f(x) return x[1] end
+        -- x has type X? for a free type variable X
+        local x = f ({})
+        type ContainsFree<a> = { this: a, that: typeof(x) }
+        type ContainsContainsFree = { that: ContainsFree<number> }
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "non_recursive_aliases_that_reuse_a_generic_name")
+{
+    ScopedFastFlag sff1{"LuauSubstitutionDontReplaceIgnoredTypes", true};
+
+    CheckResult result = check(R"(
+        type Array<T> = { [number]: T }
+        type Tuple<T, V> = Array<T | V>
+
+        local p: Tuple<number, string>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ("{number | string}", toString(requireType("p"), {true}));
+}
+
+TEST_SUITE_END();

tests/TypeInfer.provisional.test.cpp

@@ -30,6 +30,8 @@ TEST_SUITE_BEGIN("ProvisionalTests");
  */
 TEST_CASE_FIXTURE(Fixture, "typeguard_inference_incomplete")
 {
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+
     const std::string code = R"(
         function f(a)
             if type(a) == "boolean" then
@@ -41,11 +43,11 @@ TEST_CASE_FIXTURE(Fixture, "typeguard_inference_incomplete")
     )";
 
     const std::string expected = R"(
-        function f(a:{fn:()->(free)}): ()
+        function f(a:{fn:()->(free,free...)}): ()
             if type(a) == 'boolean'then
                 local a1:boolean=a
             elseif a.fn()then
-                local a2:{fn:()->(free)}=a
+                local a2:{fn:()->(free,free...)}=a
             end
         end
     )";
@@ -231,16 +233,7 @@ TEST_CASE_FIXTURE(Fixture, "operator_eq_completely_incompatible")
         local r2 = b == a
     )");
 
-    if (FFlag::LuauEqConstraint)
+    LUAU_REQUIRE_NO_ERRORS(result);
-    {
-        LUAU_REQUIRE_NO_ERRORS(result);
-    }
-    else
-    {
-        LUAU_REQUIRE_ERROR_COUNT(2, result);
-        CHECK_EQ(toString(result.errors[0]), "Type '{| x: string |}?' could not be converted into 'number | string'");
-        CHECK_EQ(toString(result.errors[1]), "Type 'number | string' could not be converted into '{| x: string |}?'");
-    }
 }
 
 // Belongs in TypeInfer.refinements.test.cpp.
@@ -542,6 +535,25 @@ TEST_CASE_FIXTURE(Fixture, "bail_early_on_typescript_port_of_Result_type" * doct
     }
 }
 
+TEST_CASE_FIXTURE(Fixture, "table_subtyping_shouldn't_add_optional_properties_to_sealed_tables")
+{
+    CheckResult result = check(R"(
+        --!strict
+        local function setNumber(t: { p: number? }, x:number) t.p = x end
+        local function getString(t: { p: string? }):string return t.p or "" end
+        -- This shouldn't type-check!
+        local function oh(x:number): string
+          local t: {} = {}
+          setNumber(t, x)
+          return getString(t)
+        end
+        local s: string = oh(37)
+    )");
+
+    // Really this should return an error, but it doesn't
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 // Should be in TypeInfer.tables.test.cpp
 // It's unsound to instantiate tables containing generic methods,
 // since mutating properties means table properties should be invariant.

tests/TypeInfer.refinements.test.cpp

@@ -1,4 +1,5 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 
 #include "Fixture.h"
@@ -6,7 +7,6 @@
 #include "doctest.h"
 
 LUAU_FASTFLAG(LuauWeakEqConstraint)
-LUAU_FASTFLAG(LuauImprovedTypeGuardPredicate2)
 LUAU_FASTFLAG(LuauOrPredicate)
 
 using namespace Luau;
@@ -199,16 +199,8 @@ TEST_CASE_FIXTURE(Fixture, "typeguard_only_look_up_types_from_global_scope")
         end
     )");
 
-    if (FFlag::LuauImprovedTypeGuardPredicate2)
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
-    {
+    CHECK_EQ("Type 'number' has no overlap with 'string'", toString(result.errors[0]));
-        LUAU_REQUIRE_ERROR_COUNT(1, result);
-        CHECK_EQ("Type 'number' has no overlap with 'string'", toString(result.errors[0]));
-    }
-    else
-    {
-        LUAU_REQUIRE_ERROR_COUNT(1, result);
-        CHECK_EQ("Type 'string' could not be converted into 'boolean'", toString(result.errors[0]));
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "call_a_more_specific_function_using_typeguard")
@@ -526,8 +518,6 @@ TEST_CASE_FIXTURE(Fixture, "narrow_property_of_a_bounded_variable")
 
 TEST_CASE_FIXTURE(Fixture, "type_narrow_to_vector")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local function f(x)
             if type(x) == "vector" then
@@ -544,8 +534,6 @@ TEST_CASE_FIXTURE(Fixture, "type_narrow_to_vector")
 
 TEST_CASE_FIXTURE(Fixture, "nonoptional_type_can_narrow_to_nil_if_sense_is_true")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local t = {"hello"}
         local v = t[2]
@@ -573,8 +561,6 @@ TEST_CASE_FIXTURE(Fixture, "nonoptional_type_can_narrow_to_nil_if_sense_is_true"
 
 TEST_CASE_FIXTURE(Fixture, "typeguard_not_to_be_string")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local function f(x: string | number | boolean)
             if type(x) ~= "string" then
@@ -593,8 +579,6 @@ TEST_CASE_FIXTURE(Fixture, "typeguard_not_to_be_string")
 
 TEST_CASE_FIXTURE(Fixture, "typeguard_narrows_for_table")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local function f(x: string | {x: number} | {y: boolean})
             if type(x) == "table" then
@@ -613,8 +597,6 @@ TEST_CASE_FIXTURE(Fixture, "typeguard_narrows_for_table")
 
 TEST_CASE_FIXTURE(Fixture, "typeguard_narrows_for_functions")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local function weird(x: string | ((number) -> string))
             if type(x) == "function" then
@@ -698,8 +680,6 @@ struct RefinementClassFixture : Fixture
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "typeguard_cast_free_table_to_vector")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local function f(vec)
             local X, Y, Z = vec.X, vec.Y, vec.Z
@@ -726,8 +706,6 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "typeguard_cast_free_table_to_vector")
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "typeguard_cast_instance_or_vector3_to_vector")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local function f(x: Instance | Vector3)
             if typeof(x) == "Vector3" then
@@ -746,8 +724,6 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "typeguard_cast_instance_or_vector3_to
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "type_narrow_for_all_the_userdata")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local function f(x: string | number | Instance | Vector3)
             if type(x) == "userdata" then
@@ -766,10 +742,7 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "type_narrow_for_all_the_userdata")
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "eliminate_subclasses_of_instance")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sff{"LuauTypeGuardPeelsAwaySubclasses", true};
-        {"LuauImprovedTypeGuardPredicate2", true},
-        {"LuauTypeGuardPeelsAwaySubclasses", true},
-    };
 
     CheckResult result = check(R"(
         local function f(x: Part | Folder | string)
@@ -789,10 +762,7 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "eliminate_subclasses_of_instance")
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "narrow_this_large_union")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sff{"LuauTypeGuardPeelsAwaySubclasses", true};
-        {"LuauImprovedTypeGuardPredicate2", true},
-        {"LuauTypeGuardPeelsAwaySubclasses", true},
-    };
 
     CheckResult result = check(R"(
         local function f(x: Part | Folder | Instance | string | Vector3 | any)
@@ -812,10 +782,7 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "narrow_this_large_union")
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "x_as_any_if_x_is_instance_elseif_x_is_table")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sff{"LuauOrPredicate", true};
-        {"LuauOrPredicate", true},
-        {"LuauImprovedTypeGuardPredicate2", true},
-    };
 
     CheckResult result = check(R"(
         --!nonstrict
@@ -839,7 +806,6 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "x_is_not_instance_or_else_not_part")
 {
     ScopedFastFlag sffs[] = {
         {"LuauOrPredicate", true},
-        {"LuauImprovedTypeGuardPredicate2", true},
         {"LuauTypeGuardPeelsAwaySubclasses", true},
     };
 
@@ -861,8 +827,6 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "x_is_not_instance_or_else_not_part")
 
 TEST_CASE_FIXTURE(Fixture, "type_guard_can_filter_for_intersection_of_tables")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         type XYCoord = {x: number} & {y: number}
         local function f(t: XYCoord?)
@@ -882,8 +846,6 @@ TEST_CASE_FIXTURE(Fixture, "type_guard_can_filter_for_intersection_of_tables")
 
 TEST_CASE_FIXTURE(Fixture, "type_guard_can_filter_for_overloaded_function")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         type SomeOverloadedFunction = ((number) -> string) & ((string) -> number)
         local function f(g: SomeOverloadedFunction?)
@@ -903,8 +865,6 @@ TEST_CASE_FIXTURE(Fixture, "type_guard_can_filter_for_overloaded_function")
 
 TEST_CASE_FIXTURE(Fixture, "type_guard_warns_on_no_overlapping_types_only_when_sense_is_true")
 {
-    ScopedFastFlag sff2{"LuauImprovedTypeGuardPredicate2", true};
-
     CheckResult result = check(R"(
         local function f(t: {x: number})
             if type(t) ~= "table" then
@@ -999,10 +959,7 @@ TEST_CASE_FIXTURE(Fixture, "not_a_and_not_b2")
 
 TEST_CASE_FIXTURE(Fixture, "either_number_or_string")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sff{"LuauOrPredicate", true};
-        {"LuauOrPredicate", true},
-        {"LuauImprovedTypeGuardPredicate2", true},
-    };
 
     CheckResult result = check(R"(
         local function f(x: any)
@@ -1036,10 +993,7 @@ TEST_CASE_FIXTURE(Fixture, "not_t_or_some_prop_of_t")
 
 TEST_CASE_FIXTURE(Fixture, "assert_a_to_be_truthy_then_assert_a_to_be_number")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sff{"LuauOrPredicate", true};
-        {"LuauOrPredicate", true},
-        {"LuauImprovedTypeGuardPredicate2", true},
-    };
 
     CheckResult result = check(R"(
         local a: (number | string)?
@@ -1057,10 +1011,7 @@ TEST_CASE_FIXTURE(Fixture, "assert_a_to_be_truthy_then_assert_a_to_be_number")
 
 TEST_CASE_FIXTURE(Fixture, "merge_should_be_fully_agnostic_of_hashmap_ordering")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sff{"LuauOrPredicate", true};
-        {"LuauOrPredicate", true},
-        {"LuauImprovedTypeGuardPredicate2", true},
-    };
 
     // This bug came up because there was a mistake in Luau::merge where zipping on two maps would produce the wrong merged result.
     CheckResult result = check(R"(
@@ -1081,10 +1032,7 @@ TEST_CASE_FIXTURE(Fixture, "merge_should_be_fully_agnostic_of_hashmap_ordering")
 
 TEST_CASE_FIXTURE(Fixture, "refine_the_correct_types_opposite_of_when_a_is_not_number_or_string")
 {
-    ScopedFastFlag sffs[] = {
+    ScopedFastFlag sff{"LuauOrPredicate", true};
-        {"LuauOrPredicate", true},
-        {"LuauImprovedTypeGuardPredicate2", true},
-    };
 
     CheckResult result = check(R"(
         local function f(a: string | number | boolean)

tests/TypeInfer.tables.test.cpp

@@ -46,6 +46,21 @@ TEST_CASE_FIXTURE(Fixture, "augment_table")
     CHECK(tType->props.find("foo") != tType->props.end());
 }
 
+TEST_CASE_FIXTURE(Fixture, "augment_nested_table")
+{
+    CheckResult result = check("local t = { p = {} }  t.p.foo = 'bar'");
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    TableTypeVar* tType = getMutable<TableTypeVar>(requireType("t"));
+    REQUIRE(tType != nullptr);
+
+    REQUIRE(tType->props.find("p") != tType->props.end());
+    const TableTypeVar* pType = get<TableTypeVar>(tType->props["p"].type);
+    REQUIRE(pType != nullptr);
+
+    CHECK(pType->props.find("foo") != pType->props.end());
+}
+
 TEST_CASE_FIXTURE(Fixture, "cannot_augment_sealed_table")
 {
     CheckResult result = check("local t = {prop=999}    t.foo = 'bar'");
@@ -260,6 +275,8 @@ TEST_CASE_FIXTURE(Fixture, "open_table_unification")
 
 TEST_CASE_FIXTURE(Fixture, "open_table_unification_2")
 {
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
     CheckResult result = check(R"(
         local a = {}
         a.x = 99
@@ -272,10 +289,11 @@ TEST_CASE_FIXTURE(Fixture, "open_table_unification_2")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
     TypeError& err = result.errors[0];
-    UnknownProperty* error = get<UnknownProperty>(err);
+    MissingProperties* error = get<MissingProperties>(err);
     REQUIRE(error != nullptr);
+    REQUIRE(error->properties.size() == 1);
 
-    CHECK_EQ(error->key, "y");
+    CHECK_EQ("y", error->properties[0]);
     // TODO(rblanckaert): Revist when we can bind self at function creation time
     // CHECK_EQ(err.location, Location(Position{5, 19}, Position{5, 25}));
 
@@ -328,6 +346,8 @@ TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_1")
 
 TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_2")
 {
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
     CheckResult result = check(R"(
         --!strict
         function foo(o)
@@ -340,14 +360,17 @@ TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_2")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    UnknownProperty* error = get<UnknownProperty>(result.errors[0]);
+    MissingProperties* error = get<MissingProperties>(result.errors[0]);
     REQUIRE(error != nullptr);
+    REQUIRE(error->properties.size() == 1);
 
-    CHECK_EQ("baz", error->key);
+    CHECK_EQ("baz", error->properties[0]);
 }
 
 TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_3")
 {
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
     CheckResult result = check(R"(
         local T = {}
         T.bar = 'hello'
@@ -359,8 +382,11 @@ TEST_CASE_FIXTURE(Fixture, "table_param_row_polymorphism_3")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
     TypeError& err = result.errors[0];
-    UnknownProperty* error = get<UnknownProperty>(err);
+    MissingProperties* error = get<MissingProperties>(err);
     REQUIRE(error != nullptr);
+    REQUIRE(error->properties.size() == 1);
+
+    CHECK_EQ("baz", error->properties[0]);
 
     // TODO(rblanckaert): Revist when we can bind self at function creation time
     /*
@@ -448,6 +474,73 @@ TEST_CASE_FIXTURE(Fixture, "ok_to_add_property_to_free_table")
     dumpErrors(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "okay_to_add_property_to_unsealed_tables_by_assignment")
+{
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
+    CheckResult result = check(R"(
+        --!strict
+        local t = { u = {} }
+        t = { u = { p = 37 } }
+        t = { u = { q = "hi" } }
+        local x = t.u.p
+        local y = t.u.q
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+    CHECK_EQ("number?", toString(requireType("x")));
+    CHECK_EQ("string?", toString(requireType("y")));
+}
+
+TEST_CASE_FIXTURE(Fixture, "okay_to_add_property_to_unsealed_tables_by_function_call")
+{
+    CheckResult result = check(R"(
+        --!strict
+        function get(x) return x.opts["MYOPT"] end
+        function set(x,y) x.opts["MYOPT"] = y end
+        local t = { opts = {} }
+        set(t,37)
+        local x = get(t)
+    )");
+
+    // Currently this errors but it shouldn't, since set only needs write access
+    // TODO: file a JIRA for this
+    LUAU_REQUIRE_ERRORS(result);
+    // CHECK_EQ("number?", toString(requireType("x")));
+}
+
+TEST_CASE_FIXTURE(Fixture, "width_subtyping")
+{
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
+    CheckResult result = check(R"(
+        --!strict
+        function f(x : { q : number })
+           x.q = 8
+        end
+        local t : { q : number, r : string } = { q = 8, r = "hi" }
+        f(t)
+        local x : string = t.r
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "width_subtyping_needs_covariance")
+{
+    CheckResult result = check(R"(
+        --!strict
+        function f(x : { p : { q : number }})
+           x.p = { q = 8, r = 5 }
+        end
+        local t : { p : { q : number, r : string } } = { p = { q = 8, r = "hi" } }
+        f(t) -- Shouldn't typecheck
+        local x : string = t.p.r -- x is 5
+    )");
+
+    LUAU_REQUIRE_ERRORS(result);
+}
+
 TEST_CASE_FIXTURE(Fixture, "infer_array")
 {
     CheckResult result = check(R"(
@@ -676,16 +769,27 @@ TEST_CASE_FIXTURE(Fixture, "infer_indexer_for_left_unsealed_table_from_right_han
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
-TEST_CASE_FIXTURE(Fixture, "sealed_table_value_must_not_infer_an_indexer")
+TEST_CASE_FIXTURE(Fixture, "sealed_table_value_can_infer_an_indexer")
 {
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
     CheckResult result = check(R"(
         local t: { a: string, [number]: string } = { a = "foo" }
     )");
 
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
 
-    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
+TEST_CASE_FIXTURE(Fixture, "array_factory_function")
-    REQUIRE(tm != nullptr);
+{
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
+    CheckResult result = check(R"(
+        function empty() return {} end
+        local array: {string} = empty()
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
 }
 
 TEST_CASE_FIXTURE(Fixture, "sealed_table_indexers_must_unify")
@@ -756,37 +860,6 @@ TEST_CASE_FIXTURE(Fixture, "indexing_from_a_table_should_prefer_properties_when_
     CHECK_MESSAGE(nullptr != get<TypeMismatch>(result.errors[0]), "Expected a TypeMismatch but got " << result.errors[0]);
 }
 
-TEST_CASE_FIXTURE(Fixture, "indexing_from_a_table_with_a_string")
-{
-    ScopedFastFlag fflag("LuauIndexTablesWithIndexers", true);
-
-    CheckResult result = check(R"(
-        local t: { a: string }
-        function f(x: string) return t[x] end
-        local a = f("a")
-        local b = f("b")
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-
-    CHECK_EQ(*typeChecker.anyType, *requireType("a"));
-    CHECK_EQ(*typeChecker.anyType, *requireType("b"));
-}
-
-TEST_CASE_FIXTURE(Fixture, "indexing_from_a_table_with_a_number")
-{
-    ScopedFastFlag fflag("LuauIndexTablesWithIndexers", true);
-
-    CheckResult result = check(R"(
-        local t = { a = true }
-        function f(x: number) return t[x] end
-    )");
-
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-    CHECK_MESSAGE(nullptr != get<TypeMismatch>(result.errors[0]), "Expected a TypeMismatch but got " << result.errors[0]);
-}
-
 TEST_CASE_FIXTURE(Fixture, "assigning_to_an_unsealed_table_with_string_literal_should_infer_new_properties_over_indexer")
 {
     CheckResult result = check(R"(
@@ -1392,6 +1465,8 @@ TEST_CASE_FIXTURE(Fixture, "casting_tables_with_props_into_table_with_indexer2")
 
 TEST_CASE_FIXTURE(Fixture, "casting_tables_with_props_into_table_with_indexer3")
 {
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
     CheckResult result = check(R"(
         local function foo(a: {[string]: number, a: string}) end
         foo({ a = 1 })
@@ -1402,8 +1477,21 @@ TEST_CASE_FIXTURE(Fixture, "casting_tables_with_props_into_table_with_indexer3")
     ToStringOptions o{/* exhaustive= */ true};
     TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
     REQUIRE(tm);
-    CHECK_EQ("string", toString(tm->wantedType, o));
+    CHECK_EQ("{| [string]: number, a: string |}", toString(tm->wantedType, o));
-    CHECK_EQ("number", toString(tm->givenType, o));
+    CHECK_EQ("{| a: number |}", toString(tm->givenType, o));
+}
+
+TEST_CASE_FIXTURE(Fixture, "casting_tables_with_props_into_table_with_indexer4")
+{
+    CheckResult result = check(R"(
+        local function foo(a: {[string]: number, a: string}, i: string)
+            return a[i]
+        end
+        local hi: number = foo({ a = "hi" }, "a") -- shouldn't typecheck since at runtime hi is "hi"
+    )");
+
+    // This typechecks but shouldn't
+    LUAU_REQUIRE_NO_ERRORS(result);
 }
 
 TEST_CASE_FIXTURE(Fixture, "table_subtyping_with_missing_props_dont_report_multiple_errors")
@@ -1446,22 +1534,32 @@ TEST_CASE_FIXTURE(Fixture, "table_subtyping_with_missing_props_dont_report_multi
 TEST_CASE_FIXTURE(Fixture, "table_subtyping_with_extra_props_dont_report_multiple_errors")
 {
     CheckResult result = check(R"(
-        local vec3 = {x = 1, y = 2, z = 3}
+        local vec3 = {{x = 1, y = 2, z = 3}}
-        local vec1 = {x = 1}
+        local vec1 = {{x = 1}}
 
         vec1 = vec3
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    MissingProperties* mp = get<MissingProperties>(result.errors[0]);
+    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
-    REQUIRE(mp);
+    REQUIRE(tm);
-    CHECK_EQ(mp->context, MissingProperties::Extra);
+    CHECK_EQ("vec1", toString(tm->wantedType));
-    REQUIRE_EQ(2, mp->properties.size());
+    CHECK_EQ("vec3", toString(tm->givenType));
-    CHECK_EQ(mp->properties[0], "y");
+}
-    CHECK_EQ(mp->properties[1], "z");
+
-    CHECK_EQ("vec1", toString(mp->superType));
+TEST_CASE_FIXTURE(Fixture, "table_subtyping_with_extra_props_is_ok")
-    CHECK_EQ("vec3", toString(mp->subType));
+{
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
+    CheckResult result = check(R"(
+        local vec3 = {x = 1, y = 2, z = 3}
+        local vec1 = {x = 1}
+
+        vec1 = vec3
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
 }
 
 TEST_CASE_FIXTURE(Fixture, "type_mismatch_on_massive_table_is_cut_short")
@@ -1824,4 +1922,32 @@ TEST_CASE_FIXTURE(Fixture, "invariant_table_properties_means_instantiating_table
     LUAU_REQUIRE_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "table_insert_should_cope_with_optional_properties_in_nonstrict")
+{
+    CheckResult result = check(R"(
+        --!nonstrict
+        local buttons = {}
+        table.insert(buttons, { a = 1 })
+        table.insert(buttons, { a = 2, b = true })
+        table.insert(buttons, { a = 3 })
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "table_insert_should_cope_with_optional_properties_in_strict")
+{
+    ScopedFastFlag sff{"LuauTableSubtypingVariance", true};
+
+    CheckResult result = check(R"(
+        --!strict
+        local buttons = {}
+        table.insert(buttons, { a = 1 })
+        table.insert(buttons, { a = 2, b = true })
+        table.insert(buttons, { a = 3 })
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.test.cpp

@@ -3,6 +3,7 @@
 #include "Luau/AstQuery.h"
 #include "Luau/BuiltinDefinitions.h"
 #include "Luau/Parser.h"
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypeVar.h"
 #include "Luau/VisitTypeVar.h"
@@ -978,23 +979,6 @@ TEST_CASE_FIXTURE(Fixture, "cyclic_function_type_in_args")
     CHECK_EQ("t1 where t1 = (t1) -> ()", toString(requireType("f")));
 }
 
-TEST_CASE_FIXTURE(Fixture, "cyclic_function_type_in_type_alias")
-{
-    ScopedFastFlag sff{"LuauOccursCheckOkWithRecursiveFunctions", true};
-
-    CheckResult result = check(R"(
-        type F = () -> F?
-        local function f()
-            return f
-        end
-
-        local g: F = f
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-    CHECK_EQ("t1 where t1 = () -> t1?", toString(requireType("g")));
-}
-
 // TODO: File a Jira about this
 /*
 TEST_CASE_FIXTURE(Fixture, "unifying_vararg_pack_with_fixed_length_pack_produces_fixed_length_pack")
@@ -1257,23 +1241,6 @@ TEST_CASE_FIXTURE(Fixture, "instantiate_cyclic_generic_function")
     REQUIRE_EQ(follow(*methodArg), follow(arg));
 }
 
-TEST_CASE_FIXTURE(Fixture, "cyclic_types_of_named_table_fields_do_not_expand_when_stringified")
-{
-    CheckResult result = check(R"(
-        --!strict
-        type Node = { Parent: Node?; }
-        local node: Node;
-        node.Parent = 1
-    )");
-
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
-    REQUIRE(tm);
-    CHECK_EQ("Node?", toString(tm->wantedType));
-    CHECK_EQ(typeChecker.numberType, tm->givenType);
-}
-
 TEST_CASE_FIXTURE(Fixture, "varlist_declared_by_for_in_loop_should_be_free")
 {
     CheckResult result = check(R"(
@@ -2591,48 +2558,6 @@ TEST_CASE_FIXTURE(Fixture, "toposort_doesnt_break_mutual_recursion")
     dumpErrors(result);
 }
 
-TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types")
-{
-    CheckResult result = check(R"(
-        --!strict
-        type T<a> = { f: a, g: U<a> }
-        type U<a> = { h: a, i: T<a>? }
-        local x: T<number> = { f = 37, g = { h = 5, i = nil } }
-        x.g.i = x
-        local y: T<string> = { f = "hi", g = { h = "lo", i = nil } }
-        y.g.i = y
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_errors")
-{
-    CheckResult result = check(R"(
-        --!strict
-        type T<a> = { f: a, g: U<a> }
-        type U<b> = { h: b, i: T<b>? }
-        local x: T<number> = { f = 37, g = { h = 5, i = nil } }
-        x.g.i = x
-        local y: T<string> = { f = "hi", g = { h = 5, i = nil } }
-        y.g.i = y
-    )");
-
-    LUAU_REQUIRE_ERRORS(result);
-
-    // We had a UAF in this example caused by not cloning type function arguments
-    ModulePtr module = frontend.moduleResolver.getModule("MainModule");
-    unfreeze(module->interfaceTypes);
-    copyErrors(module->errors, module->interfaceTypes);
-    freeze(module->interfaceTypes);
-    module->internalTypes.clear();
-    module->astTypes.clear();
-
-    // Make sure the error strings don't include "VALUELESS"
-    for (auto error : module->errors)
-        CHECK_MESSAGE(toString(error).find("VALUELESS") == std::string::npos, toString(error));
-}
-
 TEST_CASE_FIXTURE(Fixture, "object_constructor_can_refer_to_method_of_self")
 {
     // CLI-30902
@@ -3388,16 +3313,7 @@ TEST_CASE_FIXTURE(Fixture, "unknown_type_in_comparison")
         end
     )");
 
-    if (FFlag::LuauEqConstraint)
+    LUAU_REQUIRE_NO_ERRORS(result);
-    {
-        LUAU_REQUIRE_NO_ERRORS(result);
-    }
-    else
-    {
-        LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-        REQUIRE(get<CannotInferBinaryOperation>(result.errors[0]));
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "relation_op_on_any_lhs_where_rhs_maybe_has_metatable")
@@ -3407,18 +3323,8 @@ TEST_CASE_FIXTURE(Fixture, "relation_op_on_any_lhs_where_rhs_maybe_has_metatable
         print((x == true and (x .. "y")) .. 1) 
     )");
 
-    if (FFlag::LuauEqConstraint)
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
-    {
+    REQUIRE(get<CannotInferBinaryOperation>(result.errors[0]));
-        LUAU_REQUIRE_ERROR_COUNT(1, result);
-        REQUIRE(get<CannotInferBinaryOperation>(result.errors[0]));
-    }
-    else
-    {
-        LUAU_REQUIRE_ERROR_COUNT(2, result);
-
-        CHECK_EQ("Type 'boolean' could not be converted into 'number | string'", toString(result.errors[0]));
-        CHECK_EQ("Type 'boolean | string' could not be converted into 'number | string'", toString(result.errors[1]));
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "concat_op_on_string_lhs_and_free_rhs")
@@ -3530,25 +3436,6 @@ _(...)(...,setfenv,_):_G()
 )");
 }
 
-TEST_CASE_FIXTURE(Fixture, "use_table_name_and_generic_params_in_errors")
-{
-    CheckResult result = check(R"(
-        type Pair<T, U> = {first: T, second: U}
-        local a: Pair<string, number>
-        local b: Pair<string, string>
-
-        a = b
-    )");
-
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
-    REQUIRE(tm);
-
-    CHECK_EQ("Pair<string, number>", toString(tm->wantedType));
-    CHECK_EQ("Pair<string, string>", toString(tm->givenType));
-}
-
 TEST_CASE_FIXTURE(Fixture, "cyclic_type_packs")
 {
     // this has a risk of creating cyclic type packs, causing infinite loops / OOMs
@@ -3658,17 +3545,6 @@ TEST_CASE_FIXTURE(Fixture, "for_in_loop_where_iteratee_is_free")
     )");
 }
 
-TEST_CASE_FIXTURE(Fixture, "dont_stop_typechecking_after_reporting_duplicate_type_definition")
-{
-    CheckResult result = check(R"(
-        type A = number
-        type A = string -- Redefinition of type 'A', previously defined at line 1
-        local foo: string = 1 -- No "Type 'number' could not be converted into 'string'"
-    )");
-
-    LUAU_REQUIRE_ERROR_COUNT(2, result);
-}
-
 TEST_CASE_FIXTURE(Fixture, "tc_after_error_recovery")
 {
     CheckResult result = check(R"(
@@ -3771,38 +3647,6 @@ TEST_CASE_FIXTURE(Fixture, "error_on_invalid_operand_types_to_relational_operato
     CHECK_EQ("Type 'number | string' cannot be compared with relational operator <", ge->message);
 }
 
-TEST_CASE_FIXTURE(Fixture, "stringify_type_alias_of_recursive_template_table_type")
-{
-    CheckResult result = check(R"(
-        type Table<T> = { a: T }
-        type Wrapped = Table<Wrapped>
-        local l: Wrapped = 2
-        )");
-
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
-    REQUIRE(tm);
-    CHECK_EQ("Wrapped", toString(tm->wantedType));
-    CHECK_EQ(typeChecker.numberType, tm->givenType);
-}
-
-TEST_CASE_FIXTURE(Fixture, "stringify_type_alias_of_recursive_template_table_type2")
-{
-    CheckResult result = check(R"(
-        type Table<T> = { a: T }
-        type Wrapped = (Table<Wrapped>) -> string
-        local l: Wrapped = 2
-    )");
-
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-    TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
-    REQUIRE(tm);
-    CHECK_EQ("t1 where t1 = ({| a: t1 |}) -> string", toString(tm->wantedType));
-    CHECK_EQ(typeChecker.numberType, tm->givenType);
-}
-
 TEST_CASE_FIXTURE(Fixture, "index_expr_should_be_checked")
 {
     CheckResult result = check(R"(
@@ -3928,19 +3772,6 @@ TEST_CASE_FIXTURE(Fixture, "stringify_nested_unions_with_optionals")
     CHECK_EQ("(boolean | number | string)?", toString(tm->givenType));
 }
 
-// Check that recursive intersection type doesn't generate an OOM
-TEST_CASE_FIXTURE(Fixture, "cli_38393_recursive_intersection_oom")
-{
-    CheckResult result = check(R"(
-        function _(l0:(t0)&((t0)&(((t0)&((t0)->()))->(typeof(_),typeof(# _)))),l39,...):any
-        end
-        type t0<t0> = ((typeof(_))&((t0)&(((typeof(_))&(t0))->typeof(_))),{n163:any,})->(any,typeof(_))
-        _(_)
-    )");
-
-    LUAU_REQUIRE_ERRORS(result);
-}
-
 TEST_CASE_FIXTURE(Fixture, "UnknownGlobalCompoundAssign")
 {
     // In non-strict mode, global definition is still allowed
@@ -3993,16 +3824,6 @@ TEST_CASE_FIXTURE(Fixture, "loop_typecheck_crash_on_empty_optional")
     LUAU_REQUIRE_ERROR_COUNT(2, result);
 }
 
-TEST_CASE_FIXTURE(Fixture, "type_alias_fwd_declaration_is_precise")
-{
-    CheckResult result = check(R"(
-        local foo: Id<number> = 1
-        type Id<T> = T
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
 TEST_CASE_FIXTURE(Fixture, "cli_39932_use_unifier_in_ensure_methods")
 {
     CheckResult result = check(R"(
@@ -4033,81 +3854,6 @@ end
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
-TEST_CASE_FIXTURE(Fixture, "corecursive_types_generic")
-{
-    const std::string code = R"(
-        type A<T> = {v:T, b:B<T>}
-        type B<T> = {v:T, a:A<T>}
-        local aa:A<number>
-        local bb = aa
-    )";
-
-    const std::string expected = R"(
-        type A<T> = {v:T, b:B<T>}
-        type B<T> = {v:T, a:A<T>}
-        local aa:A<number>
-        local bb:A<number>=aa
-    )";
-
-    CHECK_EQ(expected, decorateWithTypes(code));
-    CheckResult result = check(code);
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "corecursive_function_types")
-{
-    ScopedFastFlag sff{"LuauOccursCheckOkWithRecursiveFunctions", true};
-
-    CheckResult result = check(R"(
-        type A = () -> (number, B)
-        type B = () -> (string, A)
-        local a: A
-        local b: B
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-
-    CHECK_EQ("t1 where t1 = () -> (number, () -> (string, t1))", toString(requireType("a")));
-    CHECK_EQ("t1 where t1 = () -> (string, () -> (number, t1))", toString(requireType("b")));
-}
-
-TEST_CASE_FIXTURE(Fixture, "generic_param_remap")
-{
-    const std::string code = R"(
-        -- An example of a forwarded use of a type that has different type arguments than parameters
-        type A<T,U> = {t:T, u:U, next:A<U,T>?}
-        local aa:A<number,string> = { t = 5, u = 'hi', next = { t = 'lo', u = 8 } }
-        local bb = aa
-    )";
-
-    const std::string expected = R"(
-
-        type A<T,U> = {t:T, u:U, next:A<U,T>?}
-        local aa:A<number,string> = { t = 5, u = 'hi', next = { t = 'lo', u = 8 } }
-        local bb:A<number,string>=aa
-    )";
-
-    CHECK_EQ(expected, decorateWithTypes(code));
-    CheckResult result = check(code);
-
-    LUAU_REQUIRE_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "export_type_and_type_alias_are_duplicates")
-{
-    CheckResult result = check(R"(
-        export type Foo = number
-        type Foo = number
-    )");
-
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-    auto dtd = get<DuplicateTypeDefinition>(result.errors[0]);
-    REQUIRE(dtd);
-    CHECK_EQ(dtd->name, "Foo");
-}
-
 TEST_CASE_FIXTURE(Fixture, "dont_report_type_errors_within_an_AstStatError")
 {
     CheckResult result = check(R"(
@@ -4212,30 +3958,6 @@ TEST_CASE_FIXTURE(Fixture, "luau_resolves_symbols_the_same_way_lua_does")
     REQUIRE_MESSAGE(get<UnknownSymbol>(e) != nullptr, "Expected UnknownSymbol, but got " << e);
 }
 
-TEST_CASE_FIXTURE(Fixture, "stringify_optional_parameterized_alias")
-{
-    ScopedFastFlag sffs3{"LuauGenericFunctions", true};
-    ScopedFastFlag sffs4{"LuauParseGenericFunctions", true};
-
-    CheckResult result = check(R"(
-        type Node<T> = { value: T, child: Node<T>? }
-
-        local function visitor<T>(node: Node<T>?)
-            local a: Node<T>
-
-            if node then
-                a = node.child -- Observe the output of the error message.
-            end
-        end
-    )");
-
-    LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-    auto e = get<TypeMismatch>(result.errors[0]);
-    CHECK_EQ("Node<T>?", toString(e->givenType));
-    CHECK_EQ("Node<T>", toString(e->wantedType));
-}
-
 TEST_CASE_FIXTURE(Fixture, "operator_eq_verifies_types_do_intersect")
 {
     CheckResult result = check(R"(
@@ -4291,181 +4013,6 @@ local tbl: string = require(game.A)
     CHECK_EQ("Type '{| def: number |}' could not be converted into 'string'", toString(result.errors[0]));
 }
 
-TEST_CASE_FIXTURE(Fixture, "general_require_multi_assign")
-{
-    fileResolver.source["workspace/A"] = R"(
-        export type myvec2 = {x: number, y: number}
-        return {}
-    )";
-
-    fileResolver.source["workspace/B"] = R"(
-        export type myvec3 = {x: number, y: number, z: number}
-        return {}
-    )";
-
-    fileResolver.source["workspace/C"] = R"(
-        local Foo, Bar = require(workspace.A), require(workspace.B)
-
-        local a: Foo.myvec2
-        local b: Bar.myvec3
-    )";
-
-    CheckResult result = frontend.check("workspace/C");
-    LUAU_REQUIRE_NO_ERRORS(result);
-    ModulePtr m = frontend.moduleResolver.modules["workspace/C"];
-
-    REQUIRE(m != nullptr);
-
-    std::optional<TypeId> aTypeId = lookupName(m->getModuleScope(), "a");
-    REQUIRE(aTypeId);
-    const Luau::TableTypeVar* aType = get<TableTypeVar>(follow(*aTypeId));
-    REQUIRE(aType);
-    REQUIRE(aType->props.size() == 2);
-
-    std::optional<TypeId> bTypeId = lookupName(m->getModuleScope(), "b");
-    REQUIRE(bTypeId);
-    const Luau::TableTypeVar* bType = get<TableTypeVar>(follow(*bTypeId));
-    REQUIRE(bType);
-    REQUIRE(bType->props.size() == 3);
-}
-
-TEST_CASE_FIXTURE(Fixture, "type_alias_import_mutation")
-{
-    CheckResult result = check("type t10<x> = typeof(table)");
-    LUAU_REQUIRE_NO_ERRORS(result);
-
-    TypeId ty = getGlobalBinding(frontend.typeChecker, "table");
-    CHECK_EQ(toString(ty), "table");
-
-    const TableTypeVar* ttv = get<TableTypeVar>(ty);
-    REQUIRE(ttv);
-
-    CHECK(ttv->instantiatedTypeParams.empty());
-}
-
-TEST_CASE_FIXTURE(Fixture, "type_alias_local_mutation")
-{
-    CheckResult result = check(R"(
-type Cool = { a: number, b: string }
-local c: Cool = { a = 1, b = "s" }
-type NotCool<x> = Cool
-)");
-    LUAU_REQUIRE_NO_ERRORS(result);
-
-    std::optional<TypeId> ty = requireType("c");
-    REQUIRE(ty);
-    CHECK_EQ(toString(*ty), "Cool");
-
-    const TableTypeVar* ttv = get<TableTypeVar>(*ty);
-    REQUIRE(ttv);
-
-    CHECK(ttv->instantiatedTypeParams.empty());
-}
-
-TEST_CASE_FIXTURE(Fixture, "type_alias_local_rename")
-{
-    CheckResult result = check(R"(
-type Cool = { a: number, b: string }
-type NotCool = Cool
-local c: Cool = { a = 1, b = "s" }
-local d: NotCool = { a = 1, b = "s" }
-)");
-    LUAU_REQUIRE_NO_ERRORS(result);
-
-    std::optional<TypeId> ty = requireType("c");
-    REQUIRE(ty);
-    CHECK_EQ(toString(*ty), "Cool");
-
-    ty = requireType("d");
-    REQUIRE(ty);
-    CHECK_EQ(toString(*ty), "NotCool");
-}
-
-TEST_CASE_FIXTURE(Fixture, "type_alias_local_synthetic_mutation")
-{
-    CheckResult result = check(R"(
-local c = { a = 1, b = "s" }
-type Cool = typeof(c)
-)");
-    LUAU_REQUIRE_NO_ERRORS(result);
-
-    std::optional<TypeId> ty = requireType("c");
-    REQUIRE(ty);
-
-    const TableTypeVar* ttv = get<TableTypeVar>(*ty);
-    REQUIRE(ttv);
-    CHECK_EQ(ttv->name, "Cool");
-}
-
-TEST_CASE_FIXTURE(Fixture, "type_alias_of_an_imported_recursive_type")
-{
-    ScopedFastFlag luauFixTableTypeAliasClone{"LuauFixTableTypeAliasClone", true};
-
-    fileResolver.source["game/A"] = R"(
-export type X = { a: number, b: X? }
-return {}
-    )";
-
-    CheckResult aResult = frontend.check("game/A");
-    LUAU_REQUIRE_NO_ERRORS(aResult);
-
-    CheckResult bResult = check(R"(
-local Import = require(game.A)
-type X = Import.X
-    )");
-    LUAU_REQUIRE_NO_ERRORS(bResult);
-
-    std::optional<TypeId> ty1 = lookupImportedType("Import", "X");
-    REQUIRE(ty1);
-
-    std::optional<TypeId> ty2 = lookupType("X");
-    REQUIRE(ty2);
-
-    CHECK_EQ(follow(*ty1), follow(*ty2));
-}
-
-TEST_CASE_FIXTURE(Fixture, "type_alias_of_an_imported_recursive_generic_type")
-{
-    ScopedFastFlag luauFixTableTypeAliasClone{"LuauFixTableTypeAliasClone", true};
-
-    fileResolver.source["game/A"] = R"(
-export type X<T, U> = { a: T, b: U, C: X<T, U>? }
-return {}
-    )";
-
-    CheckResult aResult = frontend.check("game/A");
-    LUAU_REQUIRE_NO_ERRORS(aResult);
-
-    CheckResult bResult = check(R"(
-local Import = require(game.A)
-type X<T, U> = Import.X<T, U>
-    )");
-    LUAU_REQUIRE_NO_ERRORS(bResult);
-
-    std::optional<TypeId> ty1 = lookupImportedType("Import", "X");
-    REQUIRE(ty1);
-
-    std::optional<TypeId> ty2 = lookupType("X");
-    REQUIRE(ty2);
-
-    CHECK_EQ(toString(*ty1, {true}), toString(*ty2, {true}));
-
-    bResult = check(R"(
-local Import = require(game.A)
-type X<T, U> = Import.X<U, T>
-    )");
-    LUAU_REQUIRE_NO_ERRORS(bResult);
-
-    ty1 = lookupImportedType("Import", "X");
-    REQUIRE(ty1);
-
-    ty2 = lookupType("X");
-    REQUIRE(ty2);
-
-    CHECK_EQ(toString(*ty1, {true}), "t1 where t1 = {| C: t1?, a: T, b: U |}");
-    CHECK_EQ(toString(*ty2, {true}), "{| C: t1, a: U, b: T |} where t1 = {| C: t1, a: U, b: T |}?");
-}
-
 TEST_CASE_FIXTURE(Fixture, "nonstrict_self_mismatch_tail")
 {
     CheckResult result = check(R"(
@@ -4579,32 +4126,6 @@ local c = a(2) -- too many arguments
     CHECK_EQ("Argument count mismatch. Function expects 1 argument, but 2 are specified", toString(result.errors[0]));
 }
 
-TEST_CASE_FIXTURE(Fixture, "module_export_free_type_leak")
-{
-    CheckResult result = check(R"(
-function get()
-    return function(obj) return true end
-end
-
-export type f = typeof(get())
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "module_export_wrapped_free_type_leak")
-{
-    CheckResult result = check(R"(
-function get()
-    return {a = 1, b = function(obj) return true end}
-end
-
-export type f = typeof(get())
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
 TEST_CASE_FIXTURE(Fixture, "custom_require_global")
 {
     CheckResult result = check(R"(
@@ -4787,8 +4308,6 @@ TEST_CASE_FIXTURE(Fixture, "no_heap_use_after_free_error")
 
 TEST_CASE_FIXTURE(Fixture, "dont_invalidate_the_properties_iterator_of_free_table_when_rolled_back")
 {
-    ScopedFastFlag sff{"LuauLogTableTypeVarBoundTo", true};
-
     fileResolver.source["Module/Backend/Types"] = R"(
         export type Fiber = {
             return_: Fiber?
@@ -4868,8 +4387,8 @@ TEST_CASE_FIXTURE(Fixture, "record_matching_overload")
 
     ModulePtr module = getMainModule();
     auto it = module->astOverloadResolvedTypes.find(parentExpr);
-    REQUIRE(it != module->astOverloadResolvedTypes.end());
+    REQUIRE(it);
-    CHECK_EQ(toString(it->second), "(number) -> number");
+    CHECK_EQ(toString(*it), "(number) -> number");
 }
 
 TEST_CASE_FIXTURE(Fixture, "infer_anonymous_function_arguments")
@@ -5032,76 +4551,6 @@ g12({x=1}, {x=2}, function(x, y) return {x=x.x + y.x} end)
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
-TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_restriction_ok")
-{
-    CheckResult result = check(R"(
-        type Tree<T> = { data: T, children: Forest<T> }
-        type Forest<T> = {Tree<T>}
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_restriction_not_ok_1")
-{
-    ScopedFastFlag sff{"LuauRecursiveTypeParameterRestriction", true};
-
-    CheckResult result = check(R"(
-        -- OK because forwarded types are used with their parameters.
-        type Tree<T> = { data: T, children: Forest<T> }
-        type Forest<T> = {Tree<{T}>}
-    )");
-
-    LUAU_REQUIRE_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_restriction_not_ok_2")
-{
-    ScopedFastFlag sff{"LuauRecursiveTypeParameterRestriction", true};
-
-    CheckResult result = check(R"(
-        -- Not OK because forwarded types are used with different types than their parameters.
-        type Forest<T> = {Tree<{T}>}
-        type Tree<T> = { data: T, children: Forest<T> }
-    )");
-
-    LUAU_REQUIRE_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_swapsies_ok")
-{
-    CheckResult result = check(R"(
-        type Tree1<T,U> = { data: T, children: {Tree2<U,T>} }
-        type Tree2<U,T> = { data: U, children: {Tree1<T,U>} }
-
-    LUAU_REQUIRE_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "mutually_recursive_types_swapsies_not_ok")
-{
-    ScopedFastFlag sff{"LuauRecursiveTypeParameterRestriction", true};
-
-    CheckResult result = check(R"(
-        type Tree1<T,U> = { data: T, children: {Tree2<U,T>} }
-        type Tree2<T,U> = { data: U, children: {Tree1<T,U>} }
-    )");
-
-    LUAU_REQUIRE_ERRORS(result);
-}
-
-TEST_CASE_FIXTURE(Fixture, "free_variables_from_typeof_in_aliases")
-{
-    CheckResult result = check(R"(
-        function f(x) return x[1] end
-        -- x has type X? for a free type variable X
-        local x = f ({})
-        type ContainsFree<a> = { this: a, that: typeof(x) }
-        type ContainsContainsFree = { that: ContainsFree<number> }
-    )");
-
-    LUAU_REQUIRE_NO_ERRORS(result);
-}
-
 TEST_CASE_FIXTURE(Fixture, "infer_generic_lib_function_function_argument")
 {
     CheckResult result = check(R"(

tests/TypeInfer.tryUnify.test.cpp

@@ -1,5 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Parser.h"
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypeVar.h"
 

tests/TypeInfer.typePacks.cpp

@@ -294,4 +294,370 @@ end
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_packs")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    CheckResult result = check(R"(
+type Packed<T...> = (T...) -> T...
+local a: Packed<>
+local b: Packed<number>
+local c: Packed<string, number>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    auto tf = lookupType("Packed");
+    REQUIRE(tf);
+    CHECK_EQ(toString(*tf), "(T...) -> (T...)");
+    CHECK_EQ(toString(requireType("a")), "() -> ()");
+    CHECK_EQ(toString(requireType("b")), "(number) -> number");
+    CHECK_EQ(toString(requireType("c")), "(string, number) -> (string, number)");
+
+    result = check(R"(
+-- (U..., T) cannot be parsed right now
+type Packed<T, U...> = { f: (a: T, U...) -> (T, U...) }
+local a: Packed<number>
+local b: Packed<string, number>
+local c: Packed<string, number, boolean>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    tf = lookupType("Packed");
+    REQUIRE(tf);
+    CHECK_EQ(toString(*tf), "Packed<T, U...>");
+    CHECK_EQ(toString(*tf, {true}), "{| f: (T, U...) -> (T, U...) |}");
+
+    auto ttvA = get<TableTypeVar>(requireType("a"));
+    REQUIRE(ttvA);
+    CHECK_EQ(toString(requireType("a")), "Packed<number>");
+    CHECK_EQ(toString(requireType("a"), {true}), "{| f: (number) -> (number) |}");
+    REQUIRE(ttvA->instantiatedTypeParams.size() == 1);
+    REQUIRE(ttvA->instantiatedTypePackParams.size() == 1);
+    CHECK_EQ(toString(ttvA->instantiatedTypeParams[0], {true}), "number");
+    CHECK_EQ(toString(ttvA->instantiatedTypePackParams[0], {true}), "");
+
+    auto ttvB = get<TableTypeVar>(requireType("b"));
+    REQUIRE(ttvB);
+    CHECK_EQ(toString(requireType("b")), "Packed<string, number>");
+    CHECK_EQ(toString(requireType("b"), {true}), "{| f: (string, number) -> (string, number) |}");
+    REQUIRE(ttvB->instantiatedTypeParams.size() == 1);
+    REQUIRE(ttvB->instantiatedTypePackParams.size() == 1);
+    CHECK_EQ(toString(ttvB->instantiatedTypeParams[0], {true}), "string");
+    CHECK_EQ(toString(ttvB->instantiatedTypePackParams[0], {true}), "number");
+
+    auto ttvC = get<TableTypeVar>(requireType("c"));
+    REQUIRE(ttvC);
+    CHECK_EQ(toString(requireType("c")), "Packed<string, number, boolean>");
+    CHECK_EQ(toString(requireType("c"), {true}), "{| f: (string, number, boolean) -> (string, number, boolean) |}");
+    REQUIRE(ttvC->instantiatedTypeParams.size() == 1);
+    REQUIRE(ttvC->instantiatedTypePackParams.size() == 1);
+    CHECK_EQ(toString(ttvC->instantiatedTypeParams[0], {true}), "string");
+    CHECK_EQ(toString(ttvC->instantiatedTypePackParams[0], {true}), "number, boolean");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_packs_import")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    fileResolver.source["game/A"] = R"(
+export type Packed<T, U...> = { a: T, b: (U...) -> () }
+return {}
+    )";
+
+    CheckResult aResult = frontend.check("game/A");
+    LUAU_REQUIRE_NO_ERRORS(aResult);
+
+    CheckResult bResult = check(R"(
+local Import = require(game.A)
+local a: Import.Packed<number>
+local b: Import.Packed<string, number>
+local c: Import.Packed<string, number, boolean>
+local d: { a: typeof(c) }
+    )");
+    LUAU_REQUIRE_NO_ERRORS(bResult);
+
+    auto tf = lookupImportedType("Import", "Packed");
+    REQUIRE(tf);
+    CHECK_EQ(toString(*tf), "Packed<T, U...>");
+    CHECK_EQ(toString(*tf, {true}), "{| a: T, b: (U...) -> () |}");
+
+    CHECK_EQ(toString(requireType("a"), {true}), "{| a: number, b: () -> () |}");
+    CHECK_EQ(toString(requireType("b"), {true}), "{| a: string, b: (number) -> () |}");
+    CHECK_EQ(toString(requireType("c"), {true}), "{| a: string, b: (number, boolean) -> () |}");
+    CHECK_EQ(toString(requireType("d")), "{| a: Packed<string, number, boolean> |}");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_pack_type_parameters")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    fileResolver.source["game/A"] = R"(
+export type Packed<T, U...> = { a: T, b: (U...) -> () }
+return {}
+    )";
+
+    CheckResult cResult = check(R"(
+local Import = require(game.A)
+type Alias<S, T, R...> = Import.Packed<S, (T, R...)>
+local a: Alias<string, number, boolean>
+
+type B<X...> = Import.Packed<string, X...>
+type C<X...> = Import.Packed<string, (number, X...)>
+    )");
+    LUAU_REQUIRE_NO_ERRORS(cResult);
+
+    auto tf = lookupType("Alias");
+    REQUIRE(tf);
+    CHECK_EQ(toString(*tf), "Alias<S, T, R...>");
+    CHECK_EQ(toString(*tf, {true}), "{| a: S, b: (T, R...) -> () |}");
+
+    CHECK_EQ(toString(requireType("a"), {true}), "{| a: string, b: (number, boolean) -> () |}");
+
+    tf = lookupType("B");
+    REQUIRE(tf);
+    CHECK_EQ(toString(*tf), "B<X...>");
+    CHECK_EQ(toString(*tf, {true}), "{| a: string, b: (X...) -> () |}");
+
+    tf = lookupType("C");
+    REQUIRE(tf);
+    CHECK_EQ(toString(*tf), "C<X...>");
+    CHECK_EQ(toString(*tf, {true}), "{| a: string, b: (number, X...) -> () |}");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_packs_nested")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    CheckResult result = check(R"(
+type Packed1<T...> = (T...) -> (T...)
+type Packed2<T...> = (Packed1<T...>, T...) -> (Packed1<T...>, T...)
+type Packed3<T...> = (Packed2<T...>, T...) -> (Packed2<T...>, T...)
+type Packed4<T...> = (Packed3<T...>, T...) -> (Packed3<T...>, T...)
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    auto tf = lookupType("Packed4");
+    REQUIRE(tf);
+    CHECK_EQ(toString(*tf),
+        "((((T...) -> (T...), T...) -> ((T...) -> (T...), T...), T...) -> (((T...) -> (T...), T...) -> ((T...) -> (T...), T...), T...), T...) -> "
+        "((((T...) -> (T...), T...) -> ((T...) -> (T...), T...), T...) -> (((T...) -> (T...), T...) -> ((T...) -> (T...), T...), T...), T...)");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_variadic")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    CheckResult result = check(R"(
+type X<T...> = (T...) -> (string, T...)
+
+type D = X<...number>
+type E = X<(number, ...string)>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ(toString(*lookupType("D")), "(...number) -> (string, ...number)");
+    CHECK_EQ(toString(*lookupType("E")), "(number, ...string) -> (string, number, ...string)");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_multi")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    CheckResult result = check(R"(
+type Y<T..., U...> = (T...) -> (U...)
+type A<S...> = Y<S..., S...>
+type B<S...> = Y<(number, ...string), S...>
+
+type Z<T, U...> = (T) -> (U...)
+type E<S...> = Z<number, S...>
+type F<S...> = Z<number, (string, S...)>
+
+type W<T, U..., V...> = (T, U...) -> (T, V...)
+type H<S..., R...> = W<number, S..., R...>
+type I<S..., R...> = W<number, (string, S...), R...>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ(toString(*lookupType("A")), "(S...) -> (S...)");
+    CHECK_EQ(toString(*lookupType("B")), "(number, ...string) -> (S...)");
+
+    CHECK_EQ(toString(*lookupType("E")), "(number) -> (S...)");
+    CHECK_EQ(toString(*lookupType("F")), "(number) -> (string, S...)");
+
+    CHECK_EQ(toString(*lookupType("H")), "(number, S...) -> (number, R...)");
+    CHECK_EQ(toString(*lookupType("I")), "(number, string, S...) -> (number, R...)");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_explicit")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    CheckResult result = check(R"(
+type X<T...> = (T...) -> (T...)
+
+type A<S...> = X<(S...)>
+type B = X<()>
+type C = X<(number)>
+type D = X<(number, string)>
+type E = X<(...number)>
+type F = X<(string, ...number)>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ(toString(*lookupType("A")), "(S...) -> (S...)");
+    CHECK_EQ(toString(*lookupType("B")), "() -> ()");
+    CHECK_EQ(toString(*lookupType("C")), "(number) -> number");
+    CHECK_EQ(toString(*lookupType("D")), "(number, string) -> (number, string)");
+    CHECK_EQ(toString(*lookupType("E")), "(...number) -> (...number)");
+    CHECK_EQ(toString(*lookupType("F")), "(string, ...number) -> (string, ...number)");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_explicit_multi")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    CheckResult result = check(R"(
+type Y<T..., U...> = (T...) -> (U...)
+
+type A = Y<(number, string), (boolean)>
+type B = Y<(), ()>
+type C<S...> = Y<...string, (number, S...)>
+type D<X...> = Y<X..., (number, string, X...)>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ(toString(*lookupType("A")), "(number, string) -> boolean");
+    CHECK_EQ(toString(*lookupType("B")), "() -> ()");
+    CHECK_EQ(toString(*lookupType("C")), "(...string) -> (number, S...)");
+    CHECK_EQ(toString(*lookupType("D")), "(X...) -> (number, string, X...)");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_pack_explicit_multi_tostring")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+    ScopedFastFlag luauInstantiatedTypeParamRecursion("LuauInstantiatedTypeParamRecursion", true); // For correct toString block
+
+    CheckResult result = check(R"(
+type Y<T..., U...> = { f: (T...) -> (U...) }
+
+local a: Y<(number, string), (boolean)>
+local b: Y<(), ()>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ(toString(requireType("a")), "Y<(number, string), (boolean)>");
+    CHECK_EQ(toString(requireType("b")), "Y<(), ()>");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_backwards_compatible")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    CheckResult result = check(R"(
+type X<T> = () -> T
+type Y<T, U> = (T) -> U
+
+type A = X<(number)>
+type B = Y<(number), (boolean)>
+type C = Y<(number), boolean>
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+
+    CHECK_EQ(toString(*lookupType("A")), "() -> number");
+    CHECK_EQ(toString(*lookupType("B")), "(number) -> boolean");
+    CHECK_EQ(toString(*lookupType("C")), "(number) -> boolean");
+}
+
+TEST_CASE_FIXTURE(Fixture, "type_alias_type_packs_errors")
+{
+    ScopedFastFlag luauParseGenericFunctions("LuauParseGenericFunctions", true);
+    ScopedFastFlag luauTypeAliasPacks("LuauTypeAliasPacks", true);
+    ScopedFastFlag luauParseTypePackTypeParameters("LuauParseTypePackTypeParameters", true);
+
+    CheckResult result = check(R"(
+type Packed<T, U, V...> = (T, U) -> (V...)
+local b: Packed<number>
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T, U, V...>' expects at least 2 type arguments, but only 1 is specified");
+
+    result = check(R"(
+type Packed<T, U> = (T, U) -> ()
+type B<X...> = Packed<number, string, X...>
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T, U>' expects 0 type pack arguments, but 1 is specified");
+
+    result = check(R"(
+type Packed<T..., U...> = (T...) -> (U...)
+type Other<S...> = Packed<S..., string>
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type parameters must come before type pack parameters");
+
+    result = check(R"(
+type Packed<T, U> = (T) -> U
+type Other<S...> = Packed<number, S...>
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T, U>' expects 2 type arguments, but only 1 is specified");
+
+    result = check(R"(
+type Packed<T...> = (T...) -> T...
+local a: Packed
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Type parameter list is required");
+
+    result = check(R"(
+type Packed<T..., U...> = (T...) -> (U...)
+type Other = Packed<>
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T..., U...>' expects 2 type pack arguments, but none are specified");
+
+    result = check(R"(
+type Packed<T..., U...> = (T...) -> (U...)
+type Other = Packed<number, string>
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+    CHECK_EQ(toString(result.errors[0]), "Generic type 'Packed<T..., U...>' expects 2 type pack arguments, but only 1 is specified");
+}
+
 TEST_SUITE_END();

tests/TypeInfer.unionTypes.test.cpp

@@ -237,21 +237,7 @@ TEST_CASE_FIXTURE(Fixture, "union_equality_comparisons")
         local z = a == c
     )");
 
-    if (FFlag::LuauEqConstraint)
+    LUAU_REQUIRE_NO_ERRORS(result);
-    {
-        LUAU_REQUIRE_NO_ERRORS(result);
-    }
-    else
-    {
-        LUAU_REQUIRE_ERROR_COUNT(1, result);
-        CHECK_EQ(*typeChecker.booleanType, *requireType("x"));
-        CHECK_EQ(*typeChecker.booleanType, *requireType("y"));
-
-        TypeMismatch* tm = get<TypeMismatch>(result.errors[0]);
-        REQUIRE(tm);
-        CHECK_EQ("(number | string)?", toString(*tm->wantedType));
-        CHECK_EQ("boolean | number", toString(*tm->givenType));
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "optional_union_members")

tests/TypeVar.test.cpp

@@ -1,5 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #include "Luau/Parser.h"
+#include "Luau/Scope.h"
 #include "Luau/TypeInfer.h"
 #include "Luau/TypeVar.h"
 

tools/tracegraph.py

@@ -0,0 +1,95 @@
+#!/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 trace event file, this tool generates a flame graph based on the event scopes present in the file
+# The result of analysis is a .svg file which can be viewed in a browser
+
+import sys
+import svg
+import json
+
+class Node(svg.Node):
+    def __init__(self):
+        svg.Node.__init__(self)
+        self.caption = ""
+        self.description = ""
+        self.ticks = 0
+
+    def text(self):
+        return self.caption
+
+    def title(self):
+        return self.caption
+
+    def details(self, root):
+        return "{} ({:,} usec, {:.1%}); self: {:,} usec".format(self.description, self.width, self.width / root.width, self.ticks)
+
+with open(sys.argv[1]) as f:
+    dump = f.read()
+
+root = Node()
+
+# Finish the file
+if not dump.endswith("]"):
+    dump += "{}]"
+
+data = json.loads(dump)
+
+stacks = {}
+
+for l in data:
+    if len(l) == 0:
+        continue
+
+    # Track stack of each thread, but aggregate values together
+    tid = l["tid"]
+
+    if not tid in stacks:
+        stacks[tid] = []
+    stack = stacks[tid]
+
+    if l["ph"] == 'B':
+        stack.append(l)
+    elif l["ph"] == 'E':
+        node = root
+
+        for e in stack:
+            caption = e["name"]
+            description = ''
+
+            if "args" in e:
+                for arg in e["args"]:
+                    if len(description) != 0:
+                        description += ", "
+
+                    description += "{}: {}".format(arg, e["args"][arg])
+
+            child = node.child(caption + description)
+            child.caption = caption
+            child.description = description
+
+            node = child
+
+        begin = stack[-1]
+
+        ticks = l["ts"] - begin["ts"]
+        rawticks = ticks
+
+        # Flame graph requires ticks without children duration
+        if "childts" in begin:
+            ticks -= begin["childts"]
+
+        node.ticks += int(ticks)
+
+        stack.pop()
+
+        if len(stack):
+            parent = stack[-1]
+
+            if "childts" in parent:
+                parent["childts"] += rawticks
+            else:
+                parent["childts"] = rawticks
+
+svg.layout(root, lambda n: n.ticks)
+svg.display(root, "Flame Graph", "hot", flip = True)