Sync to upstream/release/620 (#1223)

# What's Changed

## New Type Solver
- Many more fixes to crashes, assertions, and hangs
- Annotated locals now countermand the inferred types of locals, meaning
that for a type `type MyType = number | string`, `local foo : MyType =
5` behaves the same as `local foo = 5 :: MyType`, where before, foo
would be assigned the type of the value on the rhs.
- Type Normalization now respects resource limits.
- Subtyping between classes and cyclic tables now supported

## Native Code Generation
- Work on the Native Code Generation(NCG) allocator continues

---

# Internal Contributors

Co-authored-by: Aaron Weiss <aaronweiss@roblox.com>
Co-authored-by: Alexander McCord <amccord@roblox.com>
Co-authored-by: Andy Friesen <afriesen@roblox.com>
Co-authored-by: James McNellis <jmcnellis@roblox.com>
Co-authored-by: Vighnesh Vijay <vvijay@roblox.com>
Co-authored-by: Vyacheslav Egorov <vegorov@roblox.com>

---------

Co-authored-by: Aaron Weiss <aaronweiss@roblox.com>
Co-authored-by: Alexander McCord <amccord@roblox.com>
Co-authored-by: Andy Friesen <afriesen@roblox.com>
Co-authored-by: Aviral Goel <agoel@roblox.com>
Co-authored-by: David Cope <dcope@roblox.com>
Co-authored-by: Lily Brown <lbrown@roblox.com>
Co-authored-by: Vyacheslav Egorov <vegorov@roblox.com>

Analysis/include/Luau/Normalize.h

@@ -216,6 +216,20 @@ struct NormalizedFunctionType
 struct NormalizedType;
 using NormalizedTyvars = std::unordered_map<TypeId, std::unique_ptr<NormalizedType>>;
 
+// Operations provided by `Normalizer` can have ternary results:
+//   1. The operation returned true.
+//   2. The operation returned false.
+//   3. They can hit resource limitations, which invalidates _all normalized types_.
+enum class NormalizationResult
+{
+    // The operation returned true or succeeded.
+    True,
+    // The operation returned false or failed.
+    False,
+    // Resource limits were hit, invalidating all normalized types.
+    HitLimits,
+};
+
 // A normalized type is either any, unknown, or one of the form P | T | F | G where
 // * P is a union of primitive types (including singletons, classes and the error type)
 // * T is a union of table types
@@ -366,8 +380,8 @@ class Normalizer
     void unionFunctions(NormalizedFunctionType& heress, const NormalizedFunctionType& theress);
     void unionTablesWithTable(TypeIds& heres, TypeId there);
     void unionTables(TypeIds& heres, const TypeIds& theres);
-    bool unionNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
-    bool unionNormalWithTy(NormalizedType& here, TypeId there, Set<TypeId>& seenSetTypes, int ignoreSmallerTyvars = -1);
+    NormalizationResult unionNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
+    NormalizationResult unionNormalWithTy(NormalizedType& here, TypeId there, Set<TypeId>& seenSetTypes, int ignoreSmallerTyvars = -1);
 
     // ------- Negations
     std::optional<NormalizedType> negateNormal(const NormalizedType& here);
@@ -389,19 +403,19 @@ class Normalizer
     std::optional<TypeId> intersectionOfFunctions(TypeId here, TypeId there);
     void intersectFunctionsWithFunction(NormalizedFunctionType& heress, TypeId there);
     void intersectFunctions(NormalizedFunctionType& heress, const NormalizedFunctionType& theress);
-    bool intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there, Set<TypeId>& seenSetTypes);
-    bool intersectNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
-    bool intersectNormalWithTy(NormalizedType& here, TypeId there, Set<TypeId>& seenSetTypes);
-    bool normalizeIntersections(const std::vector<TypeId>& intersections, NormalizedType& outType);
+    NormalizationResult intersectTyvarsWithTy(NormalizedTyvars& here, TypeId there, Set<TypeId>& seenSetTypes);
+    NormalizationResult intersectNormals(NormalizedType& here, const NormalizedType& there, int ignoreSmallerTyvars = -1);
+    NormalizationResult intersectNormalWithTy(NormalizedType& here, TypeId there, Set<TypeId>& seenSetTypes);
+    NormalizationResult normalizeIntersections(const std::vector<TypeId>& intersections, NormalizedType& outType);
 
     // Check for inhabitance
-    bool isInhabited(TypeId ty);
-    bool isInhabited(TypeId ty, Set<TypeId>& seen);
-    bool isInhabited(const NormalizedType* norm);
-    bool isInhabited(const NormalizedType* norm, Set<TypeId>& seen);
+    NormalizationResult isInhabited(TypeId ty);
+    NormalizationResult isInhabited(TypeId ty, Set<TypeId>& seen);
+    NormalizationResult isInhabited(const NormalizedType* norm);
+    NormalizationResult isInhabited(const NormalizedType* norm, Set<TypeId>& seen);
 
     // Check for intersections being inhabited
-    bool isIntersectionInhabited(TypeId left, TypeId right);
+    NormalizationResult isIntersectionInhabited(TypeId left, TypeId right);
 
     // -------- Convert back from a normalized type to a type
     TypeId typeFromNormal(const NormalizedType& norm);

Analysis/include/Luau/Subtyping.h

@@ -103,6 +103,14 @@ struct SubtypingEnvironment
     DenseHashMap<TypeId, GenericBounds> mappedGenerics{nullptr};
     DenseHashMap<TypePackId, TypePackId> mappedGenericPacks{nullptr};
 
+    /*
+     * See the test cyclic_tables_are_assumed_to_be_compatible_with_classes for
+     * details.
+     *
+     * An empty value is equivalent to a nonexistent key.
+     */
+    DenseHashMap<TypeId, TypeId> substitutions{nullptr};
+
     DenseHashMap<std::pair<TypeId, TypeId>, SubtypingResult, TypePairHash> ephemeralCache{{}};
 
     /// Applies `mappedGenerics` to the given type.
@@ -192,7 +200,7 @@ struct Subtyping
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const MetatableType* subMt, const MetatableType* superMt);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const MetatableType* subMt, const TableType* superTable);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const ClassType* subClass, const ClassType* superClass);
-    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const ClassType* subClass, const TableType* superTable);
+    SubtypingResult isCovariantWith(SubtypingEnvironment& env, TypeId subTy, const ClassType* subClass, TypeId superTy, const TableType* superTable);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const FunctionType* subFunction, const FunctionType* superFunction);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const PrimitiveType* subPrim, const TableType* superTable);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const SingletonType* subSingleton, const TableType* superTable);

Analysis/src/Autocomplete.cpp

@@ -14,7 +14,6 @@
 #include <utility>
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
-LUAU_FASTFLAGVARIABLE(LuauAutocompleteStringLiteralBounds, false);
 
 static const std::unordered_set<std::string> kStatementStartingKeywords = {
     "while", "if", "local", "repeat", "function", "do", "for", "return", "break", "continue", "type", "export"};
@@ -465,15 +464,12 @@ AutocompleteEntryMap autocompleteModuleTypes(const Module& module, Position posi
 
 static void autocompleteStringSingleton(TypeId ty, bool addQuotes, AstNode* node, Position position, AutocompleteEntryMap& result)
 {
-    if (FFlag::LuauAutocompleteStringLiteralBounds)
+    if (position == node->location.begin || position == node->location.end)
     {
-        if (position == node->location.begin || position == node->location.end)
-        {
-            if (auto str = node->as<AstExprConstantString>(); str && str->quoteStyle == AstExprConstantString::Quoted)
-                return;
-            else if (node->is<AstExprInterpString>())
-                return;
-        }
+        if (auto str = node->as<AstExprConstantString>(); str && str->quoteStyle == AstExprConstantString::Quoted)
+            return;
+        else if (node->is<AstExprInterpString>())
+            return;
     }
 
     auto formatKey = [addQuotes](const std::string& key) {

Analysis/src/ConstraintGenerator.cpp

@@ -738,14 +738,18 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatLocal* stat
         scope->lvalueTypes[def] = assignee;
     }
 
-    TypePackId resultPack = checkPack(scope, statLocal->values, expectedTypes).tp;
-    addConstraint(scope, statLocal->location, UnpackConstraint{arena->addTypePack(std::move(assignees)), resultPack, /*resultIsLValue*/ true});
+    TypePackId rvaluePack = checkPack(scope, statLocal->values, expectedTypes).tp;
 
-    // Types must flow between whatever annotations were provided and the rhs expression.
     if (hasAnnotation)
-        addConstraint(scope, statLocal->location, PackSubtypeConstraint{resultPack, arena->addTypePack(std::move(annotatedTypes))});
+    {
+        TypePackId annotatedPack = arena->addTypePack(std::move(annotatedTypes));
+        addConstraint(scope, statLocal->location, UnpackConstraint{arena->addTypePack(std::move(assignees)), annotatedPack, /*resultIsLValue*/ true});
+        addConstraint(scope, statLocal->location, PackSubtypeConstraint{rvaluePack, annotatedPack});
+    }
+    else
+        addConstraint(scope, statLocal->location, UnpackConstraint{arena->addTypePack(std::move(assignees)), rvaluePack, /*resultIsLValue*/ true});
 
-    if (statLocal->vars.size == 1 && statLocal->values.size == 1 && firstValueType && scope.get() == rootScope)
+    if (statLocal->vars.size == 1 && statLocal->values.size == 1 && firstValueType && scope.get() == rootScope && !hasAnnotation)
     {
         AstLocal* var = statLocal->vars.data[0];
         AstExpr* value = statLocal->values.data[0];

Analysis/src/ConstraintSolver.cpp

@@ -27,7 +27,7 @@
 #include <utility>
 
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolver, false);
-
+LUAU_FASTFLAGVARIABLE(DebugLuauLogBindings, false);
 LUAU_FASTINTVARIABLE(LuauSolverRecursionLimit, 500);
 
 namespace Luau
@@ -465,10 +465,8 @@ void ConstraintSolver::run()
             reduceFamilies(instance, Location{}, TypeFamilyContext{arena, builtinTypes, rootScope, normalizer, NotNull{&iceReporter}, NotNull{&limits}}, false);
     }
 
-    if (FFlag::DebugLuauLogSolver)
-    {
+    if (FFlag::DebugLuauLogSolver || FFlag::DebugLuauLogBindings)
         dumpBindings(rootScope, opts);
-    }
 
     if (logger)
     {
@@ -1761,7 +1759,7 @@ bool ConstraintSolver::tryDispatchUnpack1(NotNull<const Constraint> constraint,
     else
     {
         LUAU_ASSERT(resultIsLValue);
-        unify(constraint, resultTy, srcTy);
+        unify(constraint, srcTy, resultTy);
     }
 
     unblock(resultTy, constraint->location);
@@ -1812,7 +1810,7 @@ bool ConstraintSolver::tryDispatch(const UnpackConstraint& c, NotNull<const Cons
                 tryDispatchUnpack1(constraint, resultTy, srcTy, c.resultIsLValue);
         }
         else
-            unify(constraint, resultTy, srcTy);
+            unify(constraint, srcTy, resultTy);
 
         ++resultIter;
         ++i;

Analysis/src/EmbeddedBuiltinDefinitions.cpp

@@ -314,9 +314,9 @@ type DateTypeResult = {
 }
 
 declare os: {
-    time: @checked (time: DateTypeArg?) -> number,
+    time: (time: DateTypeArg?) -> number,
     date: ((formatString: "*t" | "!*t", time: number?) -> DateTypeResult) & ((formatString: string?, time: number?) -> string),
-    difftime: @checked (t2: DateTypeResult | number, t1: DateTypeResult | number) -> number,
+    difftime: (t2: DateTypeResult | number, t1: DateTypeResult | number) -> number,
     clock: () -> number,
 }
 

Analysis/src/Frontend.cpp

@@ -38,6 +38,8 @@ LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJson, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauLogSolverToJsonFile, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauForbidInternalTypes, false)
+LUAU_FASTFLAGVARIABLE(DebugLuauForceStrictMode, false)
+LUAU_FASTFLAGVARIABLE(DebugLuauForceNonStrictMode, false)
 
 namespace Luau
 {
@@ -891,7 +893,13 @@ void Frontend::checkBuildQueueItem(BuildQueueItem& item)
     SourceNode& sourceNode = *item.sourceNode;
     const SourceModule& sourceModule = *item.sourceModule;
     const Config& config = item.config;
-    Mode mode = sourceModule.mode.value_or(config.mode);
+    Mode mode;
+    if (FFlag::DebugLuauForceStrictMode)
+        mode = Mode::Strict;
+    else if (FFlag::DebugLuauForceNonStrictMode)
+        mode = Mode::Nonstrict;
+    else
+        mode = sourceModule.mode.value_or(config.mode);
     ScopePtr environmentScope = item.environmentScope;
     double timestamp = getTimestamp();
     const std::vector<RequireCycle>& requireCycles = item.requireCycles;