Sync to upstream/release/622 (#1232)

# What's changed?

* Improved the actual message for the type errors for `cannot call
non-function` when attempting to call a union of functions/callable
tables. The error now correctly explains the issue is an inability to
determine the return type of the call in this situation.
* Resolve an issue where tables and metatables were not correctly being
cloned during instantiation (fixes #1176).
* Refactor `luaM_getnextgcopage` to `luaM_getnextpage` (generally
removing `gco` prefix where appropriate).
* Optimize `table.move` between tables for large ranges of elements.
* Reformat a bunch of code automatically using `clang-format`.

### New Type Solver

* Clean up minimally-used or unused constraints in the constraint solver
(`InstantiationConstraint`, `SetOpConstraint`,
`SingletonOrTopTypeConstraint`).
* Add a builtin `singleton` type family to replace
`SingletonOrTopTypeConstraint` when inferring refinements.
* Fixed a crash involving type path reasoning by recording when type
family reduction has taken place in the path.
* Improved constraint ordering by blocking on unreduced types families
that are not yet proven uninhabitable.
* Improved the handling of `SetIndexerConstraints` for both better
inference quality and to resolve crashes.
* Fix a crash when normalizing cyclic unions of intersections.
* Fix a crash when normalizing an intersection with the negation of
`unknown`.
* Fix a number of crashes caused by missing `follow` calls on `TypeId`s.
* Changed type family reduction to correctly use a semantic notion of
uninhabited types, rather than checking for `never` types specifically.
* Refactor the `union` and `intersect` type families to be variadic.

### Native Code Generation

* Improve translation for userdata key get/set and userdata/vector
namecall.
* Provide `[top level]` and `[anonymous]` as function names to
`FunctionStats` as appropriate when no function name is available.
* Disable unwind support on Android platforms since it is unsupported.
*  

---

### 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: Aviral Goel <agoel@roblox.com>
Co-authored-by: Vighnesh Vijay <vvijay@roblox.com>
Co-authored-by: Vyacheslav Egorov <vegorov@roblox.com>

---------

Co-authored-by: Alexander McCord <amccord@roblox.com>
Co-authored-by: Andy Friesen <afriesen@roblox.com>
Co-authored-by: Vighnesh <vvijay@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/Constraint.h

@@ -52,13 +52,6 @@ struct GeneralizationConstraint
     std::vector<TypeId> interiorTypes;
 };
 
-// subType ~ inst superType
-struct InstantiationConstraint
-{
-    TypeId subType;
-    TypeId superType;
-};
-
 // variables ~ iterate iterator
 // Unpack the iterator, figure out what types it iterates over, and bind those types to variables.
 struct IterableConstraint
@@ -229,17 +222,6 @@ struct SetIndexerConstraint
     TypeId propType;
 };
 
-// if negation:
-//   result ~ if isSingleton D then ~D else unknown where D = discriminantType
-// if not negation:
-//   result ~ if isSingleton D then D else unknown where D = discriminantType
-struct SingletonOrTopTypeConstraint
-{
-    TypeId resultType;
-    TypeId discriminantType;
-    bool negated;
-};
-
 // resultType ~ unpack sourceTypePack
 //
 // Similar to PackSubtypeConstraint, but with one important difference: If the
@@ -269,22 +251,6 @@ struct Unpack1Constraint
     bool resultIsLValue = false;
 };
 
-// resultType ~ T0 op T1 op ... op TN
-//
-// op is either union or intersection.  If any of the input types are blocked,
-// this constraint will block unless forced.
-struct SetOpConstraint
-{
-    enum
-    {
-        Intersection,
-        Union
-    } mode;
-
-    TypeId resultType;
-    std::vector<TypeId> types;
-};
-
 // ty ~ reduce ty
 //
 // Try to reduce ty, if it is a TypeFamilyInstanceType. Otherwise, do nothing.
@@ -301,10 +267,9 @@ struct ReducePackConstraint
     TypePackId tp;
 };
 
-using ConstraintV = Variant<SubtypeConstraint, PackSubtypeConstraint, GeneralizationConstraint, InstantiationConstraint, IterableConstraint,
+using ConstraintV = Variant<SubtypeConstraint, PackSubtypeConstraint, GeneralizationConstraint, IterableConstraint, NameConstraint,
-    NameConstraint, TypeAliasExpansionConstraint, FunctionCallConstraint, FunctionCheckConstraint, PrimitiveTypeConstraint, HasPropConstraint,
+    TypeAliasExpansionConstraint, FunctionCallConstraint, FunctionCheckConstraint, PrimitiveTypeConstraint, HasPropConstraint, SetPropConstraint,
-    SetPropConstraint, HasIndexerConstraint, SetIndexerConstraint, SingletonOrTopTypeConstraint, UnpackConstraint, Unpack1Constraint,
+    HasIndexerConstraint, SetIndexerConstraint, UnpackConstraint, Unpack1Constraint, ReduceConstraint, ReducePackConstraint, EqualityConstraint>;
-    SetOpConstraint, ReduceConstraint, ReducePackConstraint, EqualityConstraint>;
 
 struct Constraint
 {

Analysis/include/Luau/ConstraintSolver.h

@@ -91,6 +91,9 @@ struct ConstraintSolver
     // A mapping from free types to the number of unresolved constraints that mention them.
     DenseHashMap<TypeId, size_t> unresolvedConstraints{{}};
 
+    // Irreducible/uninhabited type families or type pack families.
+    DenseHashSet<const void*> uninhabitedTypeFamilies{{}};
+
     // Recorded errors that take place within the solver.
     ErrorVec errors;
 
@@ -124,7 +127,6 @@ struct ConstraintSolver
     bool tryDispatch(const SubtypeConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const PackSubtypeConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const GeneralizationConstraint& c, NotNull<const Constraint> constraint, bool force);
-    bool tryDispatch(const InstantiationConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const IterableConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const NameConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const TypeAliasExpansionConstraint& c, NotNull<const Constraint> constraint);
@@ -134,22 +136,18 @@ struct ConstraintSolver
     bool tryDispatch(const HasPropConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const SetPropConstraint& c, NotNull<const Constraint> constraint);
 
-    bool tryDispatchHasIndexer(int& recursionDepth, NotNull<const Constraint> constraint, TypeId subjectType, TypeId indexType, TypeId resultType, Set<TypeId>& seen);
+    bool tryDispatchHasIndexer(
+        int& recursionDepth, NotNull<const Constraint> constraint, TypeId subjectType, TypeId indexType, TypeId resultType, Set<TypeId>& seen);
     bool tryDispatch(const HasIndexerConstraint& c, NotNull<const Constraint> constraint);
 
-    /// (dispatched, found) where
+    std::pair<bool, std::optional<TypeId>> tryDispatchSetIndexer(
-    /// - dispatched: this constraint can be considered having dispatched.
+        NotNull<const Constraint> constraint, TypeId subjectType, TypeId indexType, TypeId propType, bool expandFreeTypeBounds);
-    /// - found: true if adding an indexer for a particular type was allowed.
-    std::pair<bool, bool> tryDispatchSetIndexer(NotNull<const Constraint> constraint, TypeId subjectType, TypeId indexType, TypeId propType, bool expandFreeTypeBounds);
     bool tryDispatch(const SetIndexerConstraint& c, NotNull<const Constraint> constraint, bool force);
 
-    bool tryDispatch(const SingletonOrTopTypeConstraint& c, NotNull<const Constraint> constraint);
-
     bool tryDispatchUnpack1(NotNull<const Constraint> constraint, TypeId resultType, TypeId sourceType, bool resultIsLValue);
     bool tryDispatch(const UnpackConstraint& c, NotNull<const Constraint> constraint);
     bool tryDispatch(const Unpack1Constraint& c, NotNull<const Constraint> constraint);
 
-    bool tryDispatch(const SetOpConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const ReduceConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const ReducePackConstraint& c, NotNull<const Constraint> constraint, bool force);
     bool tryDispatch(const EqualityConstraint& c, NotNull<const Constraint> constraint, bool force);

Analysis/include/Luau/OverloadResolution.h

@@ -69,7 +69,8 @@ private:
 
 struct SolveResult
 {
-    enum OverloadCallResult {
+    enum OverloadCallResult
+    {
         Ok,
         CodeTooComplex,
         OccursCheckFailed,
@@ -87,16 +88,8 @@ struct SolveResult
 // Helper utility, presently used for binary operator type families.
 //
 // Given a function and a set of arguments, select a suitable overload.
-SolveResult solveFunctionCall(
+SolveResult solveFunctionCall(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, NotNull<Normalizer> normalizer,
-    NotNull<TypeArena> arena,
+    NotNull<InternalErrorReporter> iceReporter, NotNull<TypeCheckLimits> limits, NotNull<Scope> scope, const Location& location, TypeId fn,
-    NotNull<BuiltinTypes> builtinTypes,
+    TypePackId argsPack);
-    NotNull<Normalizer> normalizer,
-    NotNull<InternalErrorReporter> iceReporter,
-    NotNull<TypeCheckLimits> limits,
-    NotNull<Scope> scope,
-    const Location& location,
-    TypeId fn,
-    TypePackId argsPack
-);
 
 } // namespace Luau

Analysis/include/Luau/Subtyping.h

@@ -208,7 +208,8 @@ private:
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const TableIndexer& subIndexer, const TableIndexer& superIndexer);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const Property& subProperty, const Property& superProperty, const std::string& name);
 
-    SubtypingResult isCovariantWith(SubtypingEnvironment& env, const std::shared_ptr<const NormalizedType>& subNorm, const std::shared_ptr<const NormalizedType>& superNorm);
+    SubtypingResult isCovariantWith(
+        SubtypingEnvironment& env, const std::shared_ptr<const NormalizedType>& subNorm, const std::shared_ptr<const NormalizedType>& superNorm);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const NormalizedClassType& subClass, const NormalizedClassType& superClass);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const NormalizedClassType& subClass, const TypeIds& superTables);
     SubtypingResult isCovariantWith(SubtypingEnvironment& env, const NormalizedStringType& subString, const NormalizedStringType& superString);

Analysis/include/Luau/TableLiteralInference.h

@@ -17,4 +17,4 @@ class AstExpr;
 TypeId matchLiteralType(NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes, NotNull<DenseHashMap<const AstExpr*, TypeId>> astExpectedTypes,
     NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, NotNull<Unifier2> unifier, TypeId expectedType, TypeId exprType,
     const AstExpr* expr, std::vector<TypeId>& toBlock);
-}
+} // namespace Luau

Analysis/include/Luau/Type.h

@@ -552,6 +552,27 @@ struct TypeFamilyInstanceType
 
     std::vector<TypeId> typeArguments;
     std::vector<TypePackId> packArguments;
+
+    TypeFamilyInstanceType(NotNull<const TypeFamily> family, std::vector<TypeId> typeArguments, std::vector<TypePackId> packArguments)
+        : family(family)
+        , typeArguments(typeArguments)
+        , packArguments(packArguments)
+    {
+    }
+
+    TypeFamilyInstanceType(const TypeFamily& family, std::vector<TypeId> typeArguments)
+        : family{&family}
+        , typeArguments(typeArguments)
+        , packArguments{}
+    {
+    }
+
+    TypeFamilyInstanceType(const TypeFamily& family, std::vector<TypeId> typeArguments, std::vector<TypePackId> packArguments)
+        : family{&family}
+        , typeArguments(typeArguments)
+        , packArguments(packArguments)
+    {
+    }
 };
 
 /** Represents a pending type alias instantiation.

Analysis/include/Luau/TypeArena.h

@@ -48,6 +48,11 @@ struct TypeArena
     {
         return addTypePack(TypePackVar(std::move(tp)));
     }
+
+    TypeId addTypeFamily(const TypeFamily& family, std::initializer_list<TypeId> types);
+    TypeId addTypeFamily(const TypeFamily& family, std::vector<TypeId> typeArguments, std::vector<TypePackId> packArguments = {});
+    TypePackId addTypePackFamily(const TypePackFamily& family, std::initializer_list<TypeId> types);
+    TypePackId addTypePackFamily(const TypePackFamily& family, std::vector<TypeId> typeArguments, std::vector<TypePackId> packArguments = {});
 };
 
 void freeze(TypeArena& arena);

Analysis/include/Luau/TypeFamily.h

@@ -99,8 +99,8 @@ struct TypeFamilyReductionResult
 };
 
 template<typename T>
-using ReducerFunction =
+using ReducerFunction = std::function<TypeFamilyReductionResult<T>(
-    std::function<TypeFamilyReductionResult<T>(T, NotNull<TypeFamilyQueue>, const std::vector<TypeId>&, const std::vector<TypePackId>&, NotNull<TypeFamilyContext>)>;
+    T, NotNull<TypeFamilyQueue>, const std::vector<TypeId>&, const std::vector<TypePackId>&, NotNull<TypeFamilyContext>)>;
 
 /// Represents a type function that may be applied to map a series of types and
 /// type packs to a single output type.
@@ -189,6 +189,7 @@ struct BuiltinTypeFamilies
     TypeFamily eqFamily;
 
     TypeFamily refineFamily;
+    TypeFamily singletonFamily;
     TypeFamily unionFamily;
     TypeFamily intersectFamily;
 

Analysis/include/Luau/TypePack.h

@@ -92,7 +92,7 @@ struct BlockedTypePack
  */
 struct TypeFamilyInstanceTypePack
 {
-    NotNull<TypePackFamily> family;
+    NotNull<const TypePackFamily> family;
 
     std::vector<TypeId> typeArguments;
     std::vector<TypePackId> packArguments;

Analysis/include/Luau/TypePath.h

@@ -79,9 +79,18 @@ enum class PackField
     Tail,
 };
 
+/// Component that represents the result of a reduction
+/// `resultType` is `never` if the reduction could not proceed
+struct Reduction
+{
+    TypeId resultType;
+
+    bool operator==(const Reduction& other) const;
+};
+
 /// A single component of a path, representing one inner type or type pack to
 /// traverse into.
-using Component = Luau::Variant<Property, Index, TypeField, PackField>;
+using Component = Luau::Variant<Property, Index, TypeField, PackField, Reduction>;
 
 /// A path through a type or type pack accessing a particular type or type pack
 /// contained within.
@@ -156,6 +165,7 @@ struct PathHash
     size_t operator()(const Index& idx) const;
     size_t operator()(const TypeField& field) const;
     size_t operator()(const PackField& field) const;
+    size_t operator()(const Reduction& reduction) const;
     size_t operator()(const Component& component) const;
     size_t operator()(const Path& path) const;
 };

Analysis/include/Luau/Unifier2.h

@@ -48,8 +48,12 @@ struct Unifier2
     int recursionLimit = 0;
 
     std::vector<ConstraintV> incompleteSubtypes;
+    // null if not in a constraint solving context
+    DenseHashSet<const void*>* uninhabitedTypeFamilies;
 
     Unifier2(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, NotNull<Scope> scope, NotNull<InternalErrorReporter> ice);
+    Unifier2(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, NotNull<Scope> scope, NotNull<InternalErrorReporter> ice,
+        DenseHashSet<const void*>* uninhabitedTypeFamilies);
 
     /** Attempt to commit the subtype relation subTy <: superTy to the type
      * graph.

Analysis/src/BuiltinDefinitions.cpp

@@ -24,7 +24,6 @@
  */
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
-LUAU_FASTFLAGVARIABLE(LuauSetMetatableOnUnionsOfTables, false);
 LUAU_FASTFLAGVARIABLE(LuauMakeStringMethodsChecked, false);
 
 namespace Luau
@@ -1067,7 +1066,7 @@ static std::optional<WithPredicate<TypePackId>> magicFunctionSetMetaTable(
     else if (get<AnyType>(target) || get<ErrorType>(target) || isTableIntersection(target))
     {
     }
-    else if (FFlag::LuauSetMetatableOnUnionsOfTables && isTableUnion(target))
+    else if (isTableUnion(target))
     {
         const UnionType* ut = get<UnionType>(target);
         LUAU_ASSERT(ut);

Analysis/src/ConstraintGenerator.cpp

@@ -233,7 +233,8 @@ void ConstraintGenerator::visitModuleRoot(AstStatBlock* block)
     Checkpoint end = checkpoint(this);
 
     TypeId result = arena->addType(BlockedType{});
-    NotNull<Constraint> genConstraint = addConstraint(scope, block->location, GeneralizationConstraint{result, moduleFnTy, std::move(interiorTypes.back())});
+    NotNull<Constraint> genConstraint =
+        addConstraint(scope, block->location, GeneralizationConstraint{result, moduleFnTy, std::move(interiorTypes.back())});
     getMutable<BlockedType>(result)->setOwner(genConstraint);
     forEachConstraint(start, end, this, [genConstraint](const ConstraintPtr& c) {
         genConstraint->dependencies.push_back(NotNull{c.get()});
@@ -407,13 +408,13 @@ void ConstraintGenerator::computeRefinement(const ScopePtr& scope, Location loca
     else if (auto proposition = get<Proposition>(refinement))
     {
         TypeId discriminantTy = proposition->discriminantTy;
-        if (!sense && !eq)
+
-            discriminantTy = arena->addType(NegationType{proposition->discriminantTy});
+        // if we have a negative sense, then we need to negate the discriminant
-        else if (eq)
+        if (!sense)
-        {
+            discriminantTy = arena->addType(NegationType{discriminantTy});
-            discriminantTy = arena->addType(BlockedType{});
+
-            constraints->push_back(SingletonOrTopTypeConstraint{discriminantTy, proposition->discriminantTy, !sense});
+        if (eq)
-        }
+            discriminantTy = arena->addTypeFamily(kBuiltinTypeFamilies.singletonFamily, {discriminantTy});
 
         for (const RefinementKey* key = proposition->key; key; key = key->parent)
         {
@@ -525,11 +526,13 @@ void ConstraintGenerator::applyRefinements(const ScopePtr& scope, Location locat
             {
                 if (mustDeferIntersection(ty) || mustDeferIntersection(dt))
                 {
-                    TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+                    TypeId resultType = createFamilyInstance(
-                        NotNull{&kBuiltinTypeFamilies.refineFamily},
+                        TypeFamilyInstanceType{
-                        {ty, dt},
+                            NotNull{&kBuiltinTypeFamilies.refineFamily},
-                        {},
+                            {ty, dt},
-                    }, scope, location);
+                            {},
+                        },
+                        scope, location);
 
                     ty = resultType;
                 }
@@ -961,7 +964,6 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatFunction* f
     // With or without self
 
     TypeId generalizedType = arena->addType(BlockedType{});
-
     Checkpoint start = checkpoint(this);
     FunctionSignature sig = checkFunctionSignature(scope, function->func, /* expectedType */ std::nullopt, function->name->location);
     bool sigFullyDefined = !hasFreeType(sig.signature);
@@ -1056,7 +1058,16 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatFunction* f
             }
         });
 
-        if (auto blocked = getMutable<BlockedType>(generalizedType))
+
+        // We need to check if the blocked type has no owner here because
+        // if a function is defined twice anywhere in the program like:
+        // `function f() end` and then later like `function f() end`
+        // Then there will be exactly one definition in the scope for it because it's a global
+        // (this is the same as writing f = function() end)
+        // Therefore, when we visit() the multiple different expression of this global variable
+        // They will all be aliased to the same blocked type, which means we can create multiple constraints
+        // for the same blocked type.
+        if (auto blocked = getMutable<BlockedType>(generalizedType); blocked && !blocked->getOwner())
             blocked->setOwner(addConstraint(scope, std::move(c)));
     }
 
@@ -1162,7 +1173,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatCompoundAss
 
     if (typeState)
     {
-        NotNull<Constraint> uc = addConstraint(scope, assign->location, Unpack1Constraint{*typeState, resultTy, /*resultIsLValue=*/ true});
+        NotNull<Constraint> uc = addConstraint(scope, assign->location, Unpack1Constraint{*typeState, resultTy, /*resultIsLValue=*/true});
         if (auto blocked = getMutable<BlockedType>(*typeState); blocked && !blocked->getOwner())
             blocked->setOwner(uc);
 
@@ -1178,7 +1189,7 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatCompoundAss
 
 ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatIf* ifStatement)
 {
-    RefinementId refinement = [&](){
+    RefinementId refinement = [&]() {
         InConditionalContext flipper{&typeContext};
         return check(scope, ifStatement->condition, std::nullopt).refinement;
     }();
@@ -1708,8 +1719,8 @@ InferencePack ConstraintGenerator::checkPack(const ScopePtr& scope, AstExprCall*
          * 4. Solve the call
          */
 
-        NotNull<Constraint> checkConstraint =
+        NotNull<Constraint> checkConstraint = addConstraint(scope, call->func->location,
-            addConstraint(scope, call->func->location, FunctionCheckConstraint{fnType, argPack, call, NotNull{&module->astTypes}, NotNull{&module->astExpectedTypes}});
+            FunctionCheckConstraint{fnType, argPack, call, NotNull{&module->astTypes}, NotNull{&module->astExpectedTypes}});
 
         forEachConstraint(funcBeginCheckpoint, funcEndCheckpoint, this, [checkConstraint](const ConstraintPtr& constraint) {
             checkConstraint->dependencies.emplace_back(constraint.get());
@@ -1901,7 +1912,8 @@ Inference ConstraintGenerator::checkIndexName(const ScopePtr& scope, const Refin
         scope->rvalueRefinements[key->def] = result;
     }
 
-    auto c = addConstraint(scope, indexee->location, HasPropConstraint{result, obj, std::move(index), ValueContext::RValue, inConditional(typeContext)});
+    auto c =
+        addConstraint(scope, indexee->location, HasPropConstraint{result, obj, std::move(index), ValueContext::RValue, inConditional(typeContext)});
     getMutable<BlockedType>(result)->setOwner(c);
 
     if (key)
@@ -1957,7 +1969,8 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprFunction* fun
     Checkpoint endCheckpoint = checkpoint(this);
 
     TypeId generalizedTy = arena->addType(BlockedType{});
-    NotNull<Constraint> gc = addConstraint(sig.signatureScope, func->location, GeneralizationConstraint{generalizedTy, sig.signature, std::move(interiorTypes.back())});
+    NotNull<Constraint> gc =
+        addConstraint(sig.signatureScope, func->location, GeneralizationConstraint{generalizedTy, sig.signature, std::move(interiorTypes.back())});
     getMutable<BlockedType>(generalizedTy)->setOwner(gc);
     interiorTypes.pop_back();
 
@@ -1992,29 +2005,35 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprUnary* unary)
     {
     case AstExprUnary::Op::Not:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.notFamily},
+            TypeFamilyInstanceType{
-            {operandType},
+                NotNull{&kBuiltinTypeFamilies.notFamily},
-            {},
+                {operandType},
-        }, scope, unary->location);
+                {},
+            },
+            scope, unary->location);
         return Inference{resultType, refinementArena.negation(refinement)};
     }
     case AstExprUnary::Op::Len:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.lenFamily},
+            TypeFamilyInstanceType{
-            {operandType},
+                NotNull{&kBuiltinTypeFamilies.lenFamily},
-            {},
+                {operandType},
-        }, scope, unary->location);
+                {},
+            },
+            scope, unary->location);
         return Inference{resultType, refinementArena.negation(refinement)};
     }
     case AstExprUnary::Op::Minus:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.unmFamily},
+            TypeFamilyInstanceType{
-            {operandType},
+                NotNull{&kBuiltinTypeFamilies.unmFamily},
-            {},
+                {operandType},
-        }, scope, unary->location);
+                {},
+            },
+            scope, unary->location);
         return Inference{resultType, refinementArena.negation(refinement)};
     }
     default: // msvc can't prove that this is exhaustive.
@@ -2030,138 +2049,168 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprBinary* binar
     {
     case AstExprBinary::Op::Add:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.addFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.addFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::Sub:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.subFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.subFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::Mul:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.mulFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.mulFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::Div:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.divFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.divFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::FloorDiv:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.idivFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.idivFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::Pow:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.powFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.powFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::Mod:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.modFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.modFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::Concat:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.concatFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.concatFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::And:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.andFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.andFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::Or:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.orFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.orFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::CompareLt:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.ltFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.ltFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::CompareGe:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.ltFamily},
+            TypeFamilyInstanceType{
-            {rightType, leftType}, // lua decided that `__ge(a, b)` is instead just `__lt(b, a)`
+                NotNull{&kBuiltinTypeFamilies.ltFamily},
-            {},
+                {rightType, leftType}, // lua decided that `__ge(a, b)` is instead just `__lt(b, a)`
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::CompareLe:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.leFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.leFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::CompareGt:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.leFamily},
+            TypeFamilyInstanceType{
-            {rightType, leftType}, // lua decided that `__gt(a, b)` is instead just `__le(b, a)`
+                NotNull{&kBuiltinTypeFamilies.leFamily},
-            {},
+                {rightType, leftType}, // lua decided that `__gt(a, b)` is instead just `__le(b, a)`
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::CompareEq:
     case AstExprBinary::Op::CompareNe:
     {
-        TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+        TypeId resultType = createFamilyInstance(
-            NotNull{&kBuiltinTypeFamilies.eqFamily},
+            TypeFamilyInstanceType{
-            {leftType, rightType},
+                NotNull{&kBuiltinTypeFamilies.eqFamily},
-            {},
+                {leftType, rightType},
-        }, scope, binary->location);
+                {},
+            },
+            scope, binary->location);
         return Inference{resultType, std::move(refinement)};
     }
     case AstExprBinary::Op::Op__Count:
@@ -2173,7 +2222,7 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprBinary* binar
 
 Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprIfElse* ifElse, std::optional<TypeId> expectedType)
 {
-    RefinementId refinement = [&](){
+    RefinementId refinement = [&]() {
         InConditionalContext flipper{&typeContext};
         ScopePtr condScope = childScope(ifElse->condition, scope);
         return check(condScope, ifElse->condition).refinement;
@@ -2612,14 +2661,12 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprTable* expr,
         LUAU_ASSERT(!indexValueLowerBound.empty());
 
         TypeId indexKey = indexKeyLowerBound.size() == 1
-            ? *indexKeyLowerBound.begin()
+                              ? *indexKeyLowerBound.begin()
-            : arena->addType(UnionType{std::vector(indexKeyLowerBound.begin(), indexKeyLowerBound.end())})
+                              : arena->addType(UnionType{std::vector(indexKeyLowerBound.begin(), indexKeyLowerBound.end())});
-            ;
 
         TypeId indexValue = indexValueLowerBound.size() == 1
-            ? *indexValueLowerBound.begin()
+                                ? *indexValueLowerBound.begin()
-            : arena->addType(UnionType{std::vector(indexValueLowerBound.begin(), indexValueLowerBound.end())})
+                                : arena->addType(UnionType{std::vector(indexValueLowerBound.begin(), indexValueLowerBound.end())});
-            ;
 
         ttv->indexer = TableIndexer{indexKey, indexValue};
     }
@@ -3236,22 +3283,26 @@ void ConstraintGenerator::reportCodeTooComplex(Location location)
 
 TypeId ConstraintGenerator::makeUnion(const ScopePtr& scope, Location location, TypeId lhs, TypeId rhs)
 {
-    TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+    TypeId resultType = createFamilyInstance(
-        NotNull{&kBuiltinTypeFamilies.unionFamily},
+        TypeFamilyInstanceType{
-        {lhs, rhs},
+            NotNull{&kBuiltinTypeFamilies.unionFamily},
-        {},
+            {lhs, rhs},
-    }, scope, location);
+            {},
+        },
+        scope, location);
 
     return resultType;
 }
 
 TypeId ConstraintGenerator::makeIntersect(const ScopePtr& scope, Location location, TypeId lhs, TypeId rhs)
 {
-    TypeId resultType = createFamilyInstance(TypeFamilyInstanceType{
+    TypeId resultType = createFamilyInstance(
-        NotNull{&kBuiltinTypeFamilies.intersectFamily},
+        TypeFamilyInstanceType{
-        {lhs, rhs},
+            NotNull{&kBuiltinTypeFamilies.intersectFamily},
-        {},
+            {lhs, rhs},
-    }, scope, location);
+            {},
+        },
+        scope, location);
 
     return resultType;
 }
@@ -3329,9 +3380,13 @@ void ConstraintGenerator::fillInInferredBindings(const ScopePtr& globalScope, As
             scope->bindings[symbol] = Binding{tys.front(), location};
         else
         {
-            TypeId ty = arena->addType(BlockedType{});
+            TypeId ty = createFamilyInstance(
-            auto c = addConstraint(globalScope, Location{}, SetOpConstraint{SetOpConstraint::Union, ty, std::move(tys)});
+                TypeFamilyInstanceType{
-            getMutable<BlockedType>(ty)->setOwner(c);
+                    NotNull{&kBuiltinTypeFamilies.unionFamily},
+                    std::move(tys),
+                    {},
+                },
+                globalScope, Location{});
 
             scope->bindings[symbol] = Binding{ty, location};
         }

Analysis/src/ConstraintSolver.cpp

@@ -346,7 +346,8 @@ void ConstraintSolver::run()
 
     if (FFlag::DebugLuauLogSolver)
     {
-        printf("Starting solver for module %s (%s)\n", moduleResolver->getHumanReadableModuleName(currentModuleName).c_str(), currentModuleName.c_str());
+        printf(
+            "Starting solver for module %s (%s)\n", moduleResolver->getHumanReadableModuleName(currentModuleName).c_str(), currentModuleName.c_str());
         dump(this, opts);
         printf("Bindings:\n");
         dumpBindings(rootScope, opts);
@@ -492,8 +493,6 @@ bool ConstraintSolver::tryDispatch(NotNull<const Constraint> constraint, bool fo
         success = tryDispatch(*psc, constraint, force);
     else if (auto gc = get<GeneralizationConstraint>(*constraint))
         success = tryDispatch(*gc, constraint, force);
-    else if (auto ic = get<InstantiationConstraint>(*constraint))
-        success = tryDispatch(*ic, constraint, force);
     else if (auto ic = get<IterableConstraint>(*constraint))
         success = tryDispatch(*ic, constraint, force);
     else if (auto nc = get<NameConstraint>(*constraint))
@@ -514,14 +513,10 @@ bool ConstraintSolver::tryDispatch(NotNull<const Constraint> constraint, bool fo
         success = tryDispatch(*spc, constraint);
     else if (auto spc = get<SetIndexerConstraint>(*constraint))
         success = tryDispatch(*spc, constraint, force);
-    else if (auto sottc = get<SingletonOrTopTypeConstraint>(*constraint))
-        success = tryDispatch(*sottc, constraint);
     else if (auto uc = get<UnpackConstraint>(*constraint))
         success = tryDispatch(*uc, constraint);
     else if (auto uc = get<Unpack1Constraint>(*constraint))
         success = tryDispatch(*uc, constraint);
-    else if (auto soc = get<SetOpConstraint>(*constraint))
-        success = tryDispatch(*soc, constraint, force);
     else if (auto rc = get<ReduceConstraint>(*constraint))
         success = tryDispatch(*rc, constraint, force);
     else if (auto rpc = get<ReducePackConstraint>(*constraint))
@@ -611,40 +606,6 @@ bool ConstraintSolver::tryDispatch(const GeneralizationConstraint& c, NotNull<co
     return true;
 }
 
-bool ConstraintSolver::tryDispatch(const InstantiationConstraint& c, NotNull<const Constraint> constraint, bool force)
-{
-    if (isBlocked(c.superType))
-        return block(c.superType, constraint);
-
-    if (!blockOnPendingTypes(c.superType, constraint))
-        return false;
-
-    // TODO childLimit
-    std::optional<TypeId> instantiated = instantiate(builtinTypes, NotNull{arena}, NotNull{&limits}, constraint->scope, c.superType);
-
-    LUAU_ASSERT(get<BlockedType>(c.subType));
-    LUAU_ASSERT(canMutate(c.subType, constraint));
-
-    if (!instantiated.has_value())
-    {
-        reportError(UnificationTooComplex{}, constraint->location);
-
-        bindBlockedType(c.subType, errorRecoveryType(), c.superType, constraint);
-        unblock(c.subType, constraint->location);
-
-        return true;
-    }
-
-    bindBlockedType(c.subType, *instantiated, c.superType, constraint);
-
-    InstantiationQueuer queuer{constraint->scope, constraint->location, this};
-    queuer.traverse(c.subType);
-
-    unblock(c.subType, constraint->location);
-
-    return true;
-}
-
 bool ConstraintSolver::tryDispatch(const IterableConstraint& c, NotNull<const Constraint> constraint, bool force)
 {
     /*
@@ -936,7 +897,8 @@ bool ConstraintSolver::tryDispatch(const TypeAliasExpansionConstraint& c, NotNul
 
     // Type function application will happily give us the exact same type if
     // there are e.g. generic saturatedTypeArguments that go unused.
-    bool needsClone = follow(tf->type) == target;
+    const TableType* tfTable = getTableType(tf->type);
+    bool needsClone = follow(tf->type) == target || (tfTable != nullptr && tfTable == getTableType(target));
     // Only tables have the properties we're trying to set.
     TableType* ttv = getMutableTableType(target);
 
@@ -1462,7 +1424,8 @@ bool ConstraintSolver::tryDispatch(const SetPropConstraint& c, NotNull<const Con
     return true;
 }
 
-bool ConstraintSolver::tryDispatchHasIndexer(int& recursionDepth, NotNull<const Constraint> constraint, TypeId subjectType, TypeId indexType, TypeId resultType, Set<TypeId>& seen)
+bool ConstraintSolver::tryDispatchHasIndexer(
+    int& recursionDepth, NotNull<const Constraint> constraint, TypeId subjectType, TypeId indexType, TypeId resultType, Set<TypeId>& seen)
 {
     RecursionLimiter _rl{&recursionDepth, FInt::LuauSolverRecursionLimit};
 
@@ -1481,12 +1444,7 @@ bool ConstraintSolver::tryDispatchHasIndexer(int& recursionDepth, NotNull<const
         FreeType freeResult{ft->scope, builtinTypes->neverType, builtinTypes->unknownType};
         asMutable(resultType)->ty.emplace<FreeType>(freeResult);
 
-        TypeId upperBound = arena->addType(TableType{
+        TypeId upperBound = arena->addType(TableType{/* props */ {}, TableIndexer{indexType, resultType}, TypeLevel{}, TableState::Unsealed});
-            /* props */ {},
-            TableIndexer{indexType, resultType},
-            TypeLevel{},
-            TableState::Unsealed
-        });
 
         unify(constraint, subjectType, upperBound);
 
@@ -1538,12 +1496,12 @@ bool ConstraintSolver::tryDispatchHasIndexer(int& recursionDepth, NotNull<const
         // ~(false | nil) <: {[indexType]: resultType}
 
         Set<TypeId> parts{nullptr};
-        for (TypeId part: it)
+        for (TypeId part : it)
             parts.insert(follow(part));
 
         Set<TypeId> results{nullptr};
 
-        for (TypeId part: parts)
+        for (TypeId part : parts)
         {
             TypeId r = arena->addType(BlockedType{});
             getMutable<BlockedType>(r)->setOwner(const_cast<Constraint*>(constraint.get()));
@@ -1570,12 +1528,12 @@ bool ConstraintSolver::tryDispatchHasIndexer(int& recursionDepth, NotNull<const
     else if (auto ut = get<UnionType>(subjectType))
     {
         Set<TypeId> parts{nullptr};
-        for (TypeId part: ut)
+        for (TypeId part : ut)
             parts.insert(follow(part));
 
         Set<TypeId> results{nullptr};
 
-        for (TypeId part: parts)
+        for (TypeId part : parts)
         {
             TypeId r = arena->addType(BlockedType{});
             getMutable<BlockedType>(r)->setOwner(const_cast<Constraint*>(constraint.get()));
@@ -1625,7 +1583,7 @@ struct BlockedTypeFinder : TypeOnceVisitor
     }
 };
 
-}
+} // namespace
 
 bool ConstraintSolver::tryDispatch(const HasIndexerConstraint& c, NotNull<const Constraint> constraint)
 {
@@ -1651,25 +1609,24 @@ bool ConstraintSolver::tryDispatch(const HasIndexerConstraint& c, NotNull<const
     return tryDispatchHasIndexer(recursionDepth, constraint, subjectType, indexType, c.resultType, seen);
 }
 
-std::pair<bool, bool> ConstraintSolver::tryDispatchSetIndexer(NotNull<const Constraint> constraint, TypeId subjectType, TypeId indexType, TypeId propType, bool expandFreeTypeBounds)
+std::pair<bool, std::optional<TypeId>> ConstraintSolver::tryDispatchSetIndexer(
+    NotNull<const Constraint> constraint, TypeId subjectType, TypeId indexType, TypeId propType, bool expandFreeTypeBounds)
 {
     if (isBlocked(subjectType))
-        return {block(subjectType, constraint), false};
+        return {block(subjectType, constraint), std::nullopt};
 
     if (auto tt = getMutable<TableType>(subjectType))
     {
         if (tt->indexer)
         {
             unify(constraint, indexType, tt->indexer->indexType);
-            bindBlockedType(propType, tt->indexer->indexResultType, subjectType, constraint);
+            return {true, tt->indexer->indexResultType};
-
-            return {true, true};
         }
         else if (tt->state == TableState::Free || tt->state == TableState::Unsealed)
         {
-            bindBlockedType(propType, freshType(arena, builtinTypes, constraint->scope.get()), subjectType, constraint);
+            TypeId resultTy = freshType(arena, builtinTypes, constraint->scope.get());
-            tt->indexer = TableIndexer{indexType, propType};
+            tt->indexer = TableIndexer{indexType, resultTy};
-            return {true, true};
+            return {true, resultTy};
         }
     }
     else if (auto ft = getMutable<FreeType>(subjectType); ft && expandFreeTypeBounds)
@@ -1678,41 +1635,51 @@ std::pair<bool, bool> ConstraintSolver::tryDispatchSetIndexer(NotNull<const Cons
         // Therefore, we only care about the upper bound.
         //
         // We'll extend the upper bound if we could dispatch, but could not find a table type to update the indexer.
-        auto [dispatched, found] = tryDispatchSetIndexer(constraint, ft->upperBound, indexType, propType, /*expandFreeTypeBounds=*/ false);
+        auto [dispatched, resultTy] = tryDispatchSetIndexer(constraint, ft->upperBound, indexType, propType, /*expandFreeTypeBounds=*/false);
-        if (dispatched && !found)
+        if (dispatched && !resultTy)
         {
             // Despite that we haven't found a table type, adding a table type causes us to have one that we can /now/ find.
-            found = true;
+            resultTy = freshType(arena, builtinTypes, constraint->scope.get());
-            bindBlockedType(propType, freshType(arena, builtinTypes, constraint->scope.get()), subjectType, constraint);
 
             TypeId tableTy = arena->addType(TableType{TableState::Sealed, TypeLevel{}, constraint->scope.get()});
             TableType* tt2 = getMutable<TableType>(tableTy);
-            tt2->indexer = TableIndexer{indexType, propType};
+            tt2->indexer = TableIndexer{indexType, *resultTy};
 
-            ft->upperBound = simplifyIntersection(builtinTypes, arena, ft->upperBound, tableTy).result; // TODO: intersect type family or a constraint.
+            ft->upperBound =
+                simplifyIntersection(builtinTypes, arena, ft->upperBound, tableTy).result; // TODO: intersect type family or a constraint.
         }
 
-        return {dispatched, found};
+        return {dispatched, resultTy};
     }
     else if (auto it = get<IntersectionType>(subjectType))
     {
-        std::pair<bool, bool> result{true, true};
+        bool dispatched = true;
+        std::vector<TypeId> results;
+
         for (TypeId part : it)
         {
-            auto [dispatched, found] = tryDispatchSetIndexer(constraint, part, indexType, propType, expandFreeTypeBounds);
+            auto [dispatched2, found] = tryDispatchSetIndexer(constraint, part, indexType, propType, expandFreeTypeBounds);
-            result.first &= dispatched;
+            dispatched &= dispatched2;
-            result.second &= found;
+            results.push_back(found.value_or(builtinTypes->errorRecoveryType()));
+
+            if (!dispatched)
+                return {dispatched, std::nullopt};
         }
 
-        return result;
+        TypeId resultTy = arena->addType(TypeFamilyInstanceType{
-    }
+            NotNull{&kBuiltinTypeFamilies.unionFamily},
-    else if (is<AnyType, ErrorType, NeverType>(subjectType) && expandFreeTypeBounds)
+            std::move(results),
-    {
+            {},
-        bindBlockedType(propType, subjectType, subjectType, constraint);
+        });
-        return {true, true};
-    }
 
-    return {true, false};
+        pushConstraint(constraint->scope, constraint->location, ReduceConstraint{resultTy});
+
+        return {dispatched, resultTy};
+    }
+    else if (is<AnyType, ErrorType, NeverType>(subjectType))
+        return {true, subjectType};
+
+    return {true, std::nullopt};
 }
 
 bool ConstraintSolver::tryDispatch(const SetIndexerConstraint& c, NotNull<const Constraint> constraint, bool force)
@@ -1721,54 +1688,38 @@ bool ConstraintSolver::tryDispatch(const SetIndexerConstraint& c, NotNull<const
     if (isBlocked(subjectType))
         return block(subjectType, constraint);
 
-    auto [dispatched, found] = tryDispatchSetIndexer(constraint, subjectType, c.indexType, c.propType, /*expandFreeTypeBounds=*/ true);
+    auto [dispatched, resultTy] = tryDispatchSetIndexer(constraint, subjectType, c.indexType, c.propType, /*expandFreeTypeBounds=*/true);
     if (dispatched)
     {
-        if (!found)
+        bindBlockedType(c.propType, resultTy.value_or(builtinTypes->errorRecoveryType()), subjectType, constraint);
-            bindBlockedType(c.propType, builtinTypes->errorRecoveryType(), subjectType, constraint);
-
         unblock(c.propType, constraint->location);
     }
 
     return dispatched;
 }
 
-bool ConstraintSolver::tryDispatch(const SingletonOrTopTypeConstraint& c, NotNull<const Constraint> constraint)
-{
-    if (isBlocked(c.discriminantType))
-        return false;
-
-    TypeId followed = follow(c.discriminantType);
-
-    // `nil` is a singleton type too! There's only one value of type `nil`.
-    if (c.negated && (get<SingletonType>(followed) || isNil(followed)))
-        *asMutable(c.resultType) = NegationType{c.discriminantType};
-    else if (!c.negated && get<SingletonType>(followed))
-        *asMutable(c.resultType) = BoundType{c.discriminantType};
-    else
-        *asMutable(c.resultType) = BoundType{builtinTypes->anyType};
-
-    unblock(c.resultType, constraint->location);
-
-    return true;
-}
-
 bool ConstraintSolver::tryDispatchUnpack1(NotNull<const Constraint> constraint, TypeId resultTy, TypeId srcTy, bool resultIsLValue)
 {
     resultTy = follow(resultTy);
     LUAU_ASSERT(canMutate(resultTy, constraint));
 
-    if (auto lt = getMutable<LocalType>(resultTy); resultIsLValue && lt)
+    auto tryExpand = [&](TypeId ty) {
-    {
+        LocalType* lt = getMutable<LocalType>(ty);
+        if (!lt || !resultIsLValue)
+            return;
+
         lt->domain = simplifyUnion(builtinTypes, arena, lt->domain, srcTy).result;
         LUAU_ASSERT(lt->blockCount > 0);
         --lt->blockCount;
 
-        LUAU_ASSERT(0 <= lt->blockCount);
-
         if (0 == lt->blockCount)
-            asMutable(resultTy)->ty.emplace<BoundType>(lt->domain);
+            asMutable(ty)->ty.emplace<BoundType>(lt->domain);
-    }
+    };
+
+    if (auto ut = get<UnionType>(resultTy))
+        std::for_each(begin(ut), end(ut), tryExpand);
+    else if (get<LocalType>(resultTy))
+        tryExpand(resultTy);
     else if (get<BlockedType>(resultTy))
     {
         if (follow(srcTy) == resultTy)
@@ -1823,21 +1774,7 @@ bool ConstraintSolver::tryDispatch(const UnpackConstraint& c, NotNull<const Cons
 
         TypeId srcTy = follow(srcPack.head[i]);
         TypeId resultTy = follow(*resultIter);
-
+        tryDispatchUnpack1(constraint, resultTy, srcTy, c.resultIsLValue);
-        if (resultTy)
-        {
-            // when we preserve the error-suppression of types through typestate,
-            // we introduce a union with the error type, so we need to find the local type in those options to update.
-            if (auto ut = getMutable<UnionType>(resultTy))
-            {
-                for (auto opt : ut->options)
-                    tryDispatchUnpack1(constraint, opt, srcTy, c.resultIsLValue);
-            }
-            else
-                tryDispatchUnpack1(constraint, resultTy, srcTy, c.resultIsLValue);
-        }
-        else
-            unify(constraint, srcTy, resultTy);
 
         ++resultIter;
         ++i;
@@ -1877,34 +1814,6 @@ bool ConstraintSolver::tryDispatch(const Unpack1Constraint& c, NotNull<const Con
     return tryDispatchUnpack1(constraint, c.resultType, c.sourceType, c.resultIsLValue);
 }
 
-bool ConstraintSolver::tryDispatch(const SetOpConstraint& c, NotNull<const Constraint> constraint, bool force)
-{
-    bool blocked = false;
-    for (TypeId ty : c.types)
-    {
-        if (isBlocked(ty))
-        {
-            blocked = true;
-            block(ty, constraint);
-        }
-    }
-    if (blocked && !force)
-        return false;
-
-    LUAU_ASSERT(SetOpConstraint::Union == c.mode);
-
-    TypeId res = builtinTypes->neverType;
-
-    for (TypeId ty : c.types)
-        res = simplifyUnion(builtinTypes, arena, res, ty).result;
-
-    bindBlockedType(c.resultType, res, c.resultType, constraint);
-
-    asMutable(c.resultType)->ty.emplace<BoundType>(res);
-
-    return true;
-}
-
 bool ConstraintSolver::tryDispatch(const ReduceConstraint& c, NotNull<const Constraint> constraint, bool force)
 {
     TypeId ty = follow(c.ty);
@@ -1917,6 +1826,20 @@ bool ConstraintSolver::tryDispatch(const ReduceConstraint& c, NotNull<const Cons
     for (TypePackId r : result.reducedPacks)
         unblock(r, constraint->location);
 
+    bool reductionFinished = result.blockedTypes.empty() && result.blockedPacks.empty();
+
+    if (force || reductionFinished)
+    {
+        // if we're completely dispatching this constraint, we want to record any uninhabited type families to unblock.
+        for (auto error : result.errors)
+        {
+            if (auto utf = get<UninhabitedTypeFamily>(error))
+                uninhabitedTypeFamilies.insert(utf->ty);
+            else if (auto utpf = get<UninhabitedTypePackFamily>(error))
+                uninhabitedTypeFamilies.insert(utpf->tp);
+        }
+    }
+
     if (force)
         return true;
 
@@ -1926,7 +1849,7 @@ bool ConstraintSolver::tryDispatch(const ReduceConstraint& c, NotNull<const Cons
     for (TypePackId b : result.blockedPacks)
         block(b, constraint);
 
-    return result.blockedTypes.empty() && result.blockedPacks.empty();
+    return reductionFinished;
 }
 
 bool ConstraintSolver::tryDispatch(const ReducePackConstraint& c, NotNull<const Constraint> constraint, bool force)
@@ -1941,6 +1864,20 @@ bool ConstraintSolver::tryDispatch(const ReducePackConstraint& c, NotNull<const
     for (TypePackId r : result.reducedPacks)
         unblock(r, constraint->location);
 
+    bool reductionFinished = result.blockedTypes.empty() && result.blockedPacks.empty();
+
+    if (force || reductionFinished)
+    {
+        // if we're completely dispatching this constraint, we want to record any uninhabited type families to unblock.
+        for (auto error : result.errors)
+        {
+            if (auto utf = get<UninhabitedTypeFamily>(error))
+                uninhabitedTypeFamilies.insert(utf->ty);
+            else if (auto utpf = get<UninhabitedTypePackFamily>(error))
+                uninhabitedTypeFamilies.insert(utpf->tp);
+        }
+    }
+
     if (force)
         return true;
 
@@ -1950,7 +1887,7 @@ bool ConstraintSolver::tryDispatch(const ReducePackConstraint& c, NotNull<const
     for (TypePackId b : result.blockedPacks)
         block(b, constraint);
 
-    return result.blockedTypes.empty() && result.blockedPacks.empty();
+    return reductionFinished;
 }
 
 bool ConstraintSolver::tryDispatch(const EqualityConstraint& c, NotNull<const Constraint> constraint, bool force)
@@ -2075,7 +2012,7 @@ bool ConstraintSolver::tryDispatchIterableTable(TypeId iteratorTy, const Iterabl
                     LUAU_ASSERT(nextFn);
                     const TypePackId nextRetPack = nextFn->retTypes;
 
-                    pushConstraint(constraint->scope, constraint->location, UnpackConstraint{c.variables, nextRetPack, /* resultIsLValue=*/ true});
+                    pushConstraint(constraint->scope, constraint->location, UnpackConstraint{c.variables, nextRetPack, /* resultIsLValue=*/true});
                     return true;
                 }
                 else
@@ -2405,7 +2342,7 @@ std::pair<std::vector<TypeId>, std::optional<TypeId>> ConstraintSolver::lookupTa
 template<typename TID>
 bool ConstraintSolver::unify(NotNull<const Constraint> constraint, TID subTy, TID superTy)
 {
-    Unifier2 u2{NotNull{arena}, builtinTypes, constraint->scope, NotNull{&iceReporter}};
+    Unifier2 u2{NotNull{arena}, builtinTypes, constraint->scope, NotNull{&iceReporter}, &uninhabitedTypeFamilies};
 
     const bool ok = u2.unify(subTy, superTy);
 
@@ -2672,12 +2609,20 @@ bool ConstraintSolver::isBlocked(TypeId ty)
     if (auto lt = get<LocalType>(ty))
         return lt->blockCount > 0;
 
+    if (auto tfit = get<TypeFamilyInstanceType>(ty))
+        return uninhabitedTypeFamilies.contains(ty) == false;
+
     return nullptr != get<BlockedType>(ty) || nullptr != get<PendingExpansionType>(ty);
 }
 
 bool ConstraintSolver::isBlocked(TypePackId tp)
 {
-    return nullptr != get<BlockedTypePack>(follow(tp));
+    tp = follow(tp);
+
+    if (auto tfitp = get<TypeFamilyInstanceTypePack>(tp))
+        return uninhabitedTypeFamilies.contains(tp) == false;
+
+    return nullptr != get<BlockedTypePack>(tp);
 }
 
 bool ConstraintSolver::isBlocked(NotNull<const Constraint> constraint)

Analysis/src/Error.cpp

@@ -15,6 +15,8 @@
 
 LUAU_FASTINTVARIABLE(LuauIndentTypeMismatchMaxTypeLength, 10)
 
+LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauImproveNonFunctionCallError, false)
+
 static std::string wrongNumberOfArgsString(
     size_t expectedCount, std::optional<size_t> maximumCount, size_t actualCount, const char* argPrefix = nullptr, bool isVariadic = false)
 {
@@ -335,8 +337,65 @@ struct ErrorConverter
         return e.message;
     }
 
+    std::optional<TypeId> findCallMetamethod(TypeId type) const
+    {
+        type = follow(type);
+
+        std::optional<TypeId> metatable;
+        if (const MetatableType* mtType = get<MetatableType>(type))
+            metatable = mtType->metatable;
+        else if (const ClassType* classType = get<ClassType>(type))
+            metatable = classType->metatable;
+
+        if (!metatable)
+            return std::nullopt;
+
+        TypeId unwrapped = follow(*metatable);
+
+        if (get<AnyType>(unwrapped))
+            return unwrapped;
+
+        const TableType* mtt = getTableType(unwrapped);
+        if (!mtt)
+            return std::nullopt;
+
+        auto it = mtt->props.find("__call");
+        if (it != mtt->props.end())
+            return it->second.type();
+        else
+            return std::nullopt;
+    }
+
     std::string operator()(const Luau::CannotCallNonFunction& e) const
     {
+        if (DFFlag::LuauImproveNonFunctionCallError)
+        {
+            if (auto unionTy = get<UnionType>(follow(e.ty)))
+            {
+                std::string err = "Cannot call a value of the union type:";
+
+                for (auto option : unionTy)
+                {
+                    option = follow(option);
+
+                    if (get<FunctionType>(option) || findCallMetamethod(option))
+                    {
+                        err += "\n  | " + toString(option);
+                        continue;
+                    }
+
+                    // early-exit if we find something that isn't callable in the union.
+                    return "Cannot call a value of type " + toString(option) + " in union:\n  " + toString(e.ty);
+                }
+
+                err += "\nWe are unable to determine the appropriate result type for such a call.";
+
+                return err;
+            }
+
+            return "Cannot call a value of type " + toString(e.ty);
+        }
+
         return "Cannot call non-function " + toString(e.ty);
     }
     std::string operator()(const Luau::ExtraInformation& e) const

Analysis/src/Instantiation2.cpp

@@ -31,9 +31,7 @@ TypeId Instantiation2::clean(TypeId ty)
 
     // if we didn't learn anything about the lower bound, we pick the upper bound instead.
     // we default to the lower bound which represents the most specific type for the free type.
-    TypeId res = get<NeverType>(ft->lowerBound)
+    TypeId res = get<NeverType>(ft->lowerBound) ? ft->upperBound : ft->lowerBound;
-        ? ft->upperBound
-        : ft->lowerBound;
 
     // Instantiation should not traverse into the type that we are substituting for.
     dontTraverseInto(res);

Analysis/src/Normalize.cpp

@@ -18,6 +18,8 @@
 LUAU_FASTFLAGVARIABLE(DebugLuauCheckNormalizeInvariant, false)
 LUAU_FASTFLAGVARIABLE(LuauNormalizeAwayUninhabitableTables, false)
 LUAU_FASTFLAGVARIABLE(LuauFixNormalizeCaching, false);
+LUAU_FASTFLAGVARIABLE(LuauNormalizeNotUnknownIntersection, false);
+LUAU_FASTFLAGVARIABLE(LuauFixCyclicUnionsOfIntersections, false);
 
 // This could theoretically be 2000 on amd64, but x86 requires this.
 LUAU_FASTINTVARIABLE(LuauNormalizeIterationLimit, 1200);
@@ -29,6 +31,11 @@ static bool fixNormalizeCaching()
     return FFlag::LuauFixNormalizeCaching || FFlag::DebugLuauDeferredConstraintResolution;
 }
 
+static bool fixCyclicUnionsOfIntersections()
+{
+    return FFlag::LuauFixCyclicUnionsOfIntersections || FFlag::DebugLuauDeferredConstraintResolution;
+}
+
 namespace Luau
 {
 
@@ -910,13 +917,13 @@ static bool isCacheable(TypeId ty, Set<TypeId>& seen)
 
     if (auto tfi = get<TypeFamilyInstanceType>(ty))
     {
-        for (TypeId t: tfi->typeArguments)
+        for (TypeId t : tfi->typeArguments)
         {
             if (!isCacheable(t, seen))
                 return false;
         }
 
-        for (TypePackId tp: tfi->packArguments)
+        for (TypePackId tp : tfi->packArguments)
         {
             if (!isCacheable(tp, seen))
                 return false;
@@ -1768,14 +1775,29 @@ NormalizationResult Normalizer::unionNormalWithTy(NormalizedType& here, TypeId t
     }
     else if (const IntersectionType* itv = get<IntersectionType>(there))
     {
+        if (fixCyclicUnionsOfIntersections())
+        {
+            if (seenSetTypes.count(there))
+                return NormalizationResult::True;
+            seenSetTypes.insert(there);
+        }
+
         NormalizedType norm{builtinTypes};
         norm.tops = builtinTypes->anyType;
         for (IntersectionTypeIterator it = begin(itv); it != end(itv); ++it)
         {
             NormalizationResult res = intersectNormalWithTy(norm, *it, seenSetTypes);
             if (res != NormalizationResult::True)
+            {
+                if (fixCyclicUnionsOfIntersections())
+                    seenSetTypes.erase(there);
                 return res;
+            }
         }
+
+        if (fixCyclicUnionsOfIntersections())
+            seenSetTypes.erase(there);
+
         return unionNormals(here, norm);
     }
     else if (get<UnknownType>(here.tops))
@@ -3194,6 +3216,13 @@ NormalizationResult Normalizer::intersectNormalWithTy(NormalizedType& here, Type
             // this is a noop since an intersection with `unknown` is trivial.
             return NormalizationResult::True;
         }
+        else if ((FFlag::LuauNormalizeNotUnknownIntersection || FFlag::DebugLuauDeferredConstraintResolution) && get<UnknownType>(t))
+        {
+            // if we're intersecting with `~unknown`, this is equivalent to intersecting with `never`
+            // this means we should clear the type entirely.
+            clearNormal(here);
+            return NormalizationResult::True;
+        }
         else if (auto nt = get<NegationType>(t))
             return intersectNormalWithTy(here, nt->ty, seenSetTypes);
         else

Analysis/src/OverloadResolution.cpp

@@ -365,41 +365,25 @@ void OverloadResolver::add(Analysis analysis, TypeId ty, ErrorVec&& errors)
 
 // we wrap calling the overload resolver in a separate function to reduce overall stack pressure in `solveFunctionCall`.
 // this limits the lifetime of `OverloadResolver`, a large type, to only as long as it is actually needed.
-std::optional<TypeId> selectOverload(
+std::optional<TypeId> selectOverload(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, NotNull<Normalizer> normalizer,
-    NotNull<BuiltinTypes> builtinTypes,
+    NotNull<Scope> scope, NotNull<InternalErrorReporter> iceReporter, NotNull<TypeCheckLimits> limits, const Location& location, TypeId fn,
-    NotNull<TypeArena> arena,
+    TypePackId argsPack)
-    NotNull<Normalizer> normalizer,
-    NotNull<Scope> scope,
-    NotNull<InternalErrorReporter> iceReporter,
-    NotNull<TypeCheckLimits> limits,
-    const Location& location,
-    TypeId fn,
-    TypePackId argsPack
-)
 {
-        OverloadResolver resolver{builtinTypes, arena, normalizer, scope, iceReporter, limits, location};
+    OverloadResolver resolver{builtinTypes, arena, normalizer, scope, iceReporter, limits, location};
-        auto [status, overload] = resolver.selectOverload(fn, argsPack);
+    auto [status, overload] = resolver.selectOverload(fn, argsPack);
 
-        if (status == OverloadResolver::Analysis::Ok)
+    if (status == OverloadResolver::Analysis::Ok)
-            return overload;
+        return overload;
 
-        if (get<AnyType>(fn) || get<FreeType>(fn))
+    if (get<AnyType>(fn) || get<FreeType>(fn))
-            return fn;
+        return fn;
 
-        return {};
+    return {};
 }
 
-SolveResult solveFunctionCall(
+SolveResult solveFunctionCall(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, NotNull<Normalizer> normalizer,
-    NotNull<TypeArena> arena,
+    NotNull<InternalErrorReporter> iceReporter, NotNull<TypeCheckLimits> limits, NotNull<Scope> scope, const Location& location, TypeId fn,
-    NotNull<BuiltinTypes> builtinTypes,
+    TypePackId argsPack)
-    NotNull<Normalizer> normalizer,
-    NotNull<InternalErrorReporter> iceReporter,
-    NotNull<TypeCheckLimits> limits,
-    NotNull<Scope> scope,
-    const Location& location,
-    TypeId fn,
-    TypePackId argsPack
-)
 {
     std::optional<TypeId> overloadToUse = selectOverload(builtinTypes, arena, normalizer, scope, iceReporter, limits, location, fn, argsPack);
     if (!overloadToUse)

Analysis/src/Subtyping.cpp

@@ -266,7 +266,8 @@ struct ApplyMappedGenerics : Substitution
     MappedGenericPacks& mappedGenericPacks;
 
 
-    ApplyMappedGenerics(NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, MappedGenerics& mappedGenerics, MappedGenericPacks& mappedGenericPacks)
+    ApplyMappedGenerics(
+        NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena, MappedGenerics& mappedGenerics, MappedGenericPacks& mappedGenericPacks)
         : Substitution(TxnLog::empty(), arena)
         , builtinTypes(builtinTypes)
         , arena(arena)
@@ -1244,18 +1245,18 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Tabl
             {
                 if (superProp.isShared())
                     results.push_back(isInvariantWith(env, subTable->indexer->indexResultType, superProp.type())
-                        .withSubComponent(TypePath::TypeField::IndexResult)
+                                          .withSubComponent(TypePath::TypeField::IndexResult)
-                        .withSuperComponent(TypePath::Property::read(name)));
+                                          .withSuperComponent(TypePath::Property::read(name)));
                 else
                 {
                     if (superProp.readTy)
                         results.push_back(isCovariantWith(env, subTable->indexer->indexResultType, *superProp.readTy)
-                            .withSubComponent(TypePath::TypeField::IndexResult)
+                                              .withSubComponent(TypePath::TypeField::IndexResult)
-                            .withSuperComponent(TypePath::Property::read(name)));
+                                              .withSuperComponent(TypePath::Property::read(name)));
                     if (superProp.writeTy)
                         results.push_back(isContravariantWith(env, subTable->indexer->indexResultType, *superProp.writeTy)
-                            .withSubComponent(TypePath::TypeField::IndexResult)
+                                              .withSubComponent(TypePath::TypeField::IndexResult)
-                            .withSuperComponent(TypePath::Property::write(name)));
+                                              .withSuperComponent(TypePath::Property::write(name)));
                 }
             }
         }
@@ -1310,7 +1311,8 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Clas
     return {isSubclass(subClass, superClass)};
 }
 
-SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, TypeId subTy, const ClassType* subClass, TypeId superTy, const TableType* superTable)
+SubtypingResult Subtyping::isCovariantWith(
+    SubtypingEnvironment& env, TypeId subTy, const ClassType* subClass, TypeId superTy, const TableType* superTable)
 {
     SubtypingResult result{true};
 
@@ -1421,7 +1423,8 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Prop
     return res;
 }
 
-SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const std::shared_ptr<const NormalizedType>& subNorm, const std::shared_ptr<const NormalizedType>& superNorm)
+SubtypingResult Subtyping::isCovariantWith(
+    SubtypingEnvironment& env, const std::shared_ptr<const NormalizedType>& subNorm, const std::shared_ptr<const NormalizedType>& superNorm)
 {
     if (!subNorm || !superNorm)
         return {false, true};
@@ -1584,15 +1587,16 @@ SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const Type
 {
     // Reduce the typefamily instance
     auto [ty, errors] = handleTypeFamilyReductionResult(subFamilyInstance);
+
     // If we return optional, that means the type family was irreducible - we can reduce that to never
-    return isCovariantWith(env, ty, superTy).withErrors(errors);
+    return isCovariantWith(env, ty, superTy).withErrors(errors).withSubComponent(TypePath::Reduction{ty});
 }
 
 SubtypingResult Subtyping::isCovariantWith(SubtypingEnvironment& env, const TypeId subTy, const TypeFamilyInstanceType* superFamilyInstance)
 {
     // Reduce the typefamily instance
     auto [ty, errors] = handleTypeFamilyReductionResult(superFamilyInstance);
-    return isCovariantWith(env, subTy, ty).withErrors(errors);
+    return isCovariantWith(env, subTy, ty).withErrors(errors).withSuperComponent(TypePath::Reduction{ty});
 }
 
 /*

Analysis/src/TableLiteralInference.cpp

@@ -13,14 +13,8 @@ namespace Luau
 
 static bool isLiteral(const AstExpr* expr)
 {
-    return (
+    return (expr->is<AstExprTable>() || expr->is<AstExprFunction>() || expr->is<AstExprConstantNumber>() || expr->is<AstExprConstantString>() ||
-        expr->is<AstExprTable>() ||
+            expr->is<AstExprConstantBool>() || expr->is<AstExprConstantNil>());
-        expr->is<AstExprFunction>() ||
-        expr->is<AstExprConstantNumber>() ||
-        expr->is<AstExprConstantString>() ||
-        expr->is<AstExprConstantBool>() ||
-        expr->is<AstExprConstantNil>()
-    );
 }
 
 // A fast approximation of subTy <: superTy
@@ -52,7 +46,7 @@ static std::optional<TypeId> extractMatchingTableType(std::vector<TypeId>& table
     size_t tableCount = 0;
     std::optional<TypeId> firstTable;
 
-    for (TypeId ty: tables)
+    for (TypeId ty : tables)
     {
         ty = follow(ty);
         if (auto tt = get<TableType>(ty))
@@ -65,7 +59,7 @@ static std::optional<TypeId> extractMatchingTableType(std::vector<TypeId>& table
                 firstTable = ty;
             ++tableCount;
 
-            for (const auto& [name, expectedProp]: tt->props)
+            for (const auto& [name, expectedProp] : tt->props)
             {
                 if (!expectedProp.readTy)
                     continue;
@@ -91,14 +85,12 @@ static std::optional<TypeId> extractMatchingTableType(std::vector<TypeId>& table
 
                 if (ft && get<SingletonType>(ft->lowerBound))
                 {
-                    if (fastIsSubtype(builtinTypes->booleanType, ft->upperBound) &&
+                    if (fastIsSubtype(builtinTypes->booleanType, ft->upperBound) && fastIsSubtype(expectedType, builtinTypes->booleanType))
-                        fastIsSubtype(expectedType, builtinTypes->booleanType))
                     {
                         return ty;
                     }
 
-                    if (fastIsSubtype(builtinTypes->stringType, ft->upperBound) &&
+                    if (fastIsSubtype(builtinTypes->stringType, ft->upperBound) && fastIsSubtype(expectedType, ft->lowerBound))
-                        fastIsSubtype(expectedType, ft->lowerBound))
                     {
                         return ty;
                     }
@@ -149,11 +141,8 @@ TypeId matchLiteralType(NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes,
     if (expr->is<AstExprConstantString>())
     {
         auto ft = get<FreeType>(exprType);
-        if (ft &&
+        if (ft && get<SingletonType>(ft->lowerBound) && fastIsSubtype(builtinTypes->stringType, ft->upperBound) &&
-            get<SingletonType>(ft->lowerBound) &&
+            fastIsSubtype(ft->lowerBound, builtinTypes->stringType))
-            fastIsSubtype(builtinTypes->stringType, ft->upperBound) &&
-            fastIsSubtype(ft->lowerBound, builtinTypes->stringType)
-        )
         {
             // if the upper bound is a subtype of the expected type, we can push the expected type in
             Relation upperBoundRelation = relate(ft->upperBound, expectedType);
@@ -177,11 +166,8 @@ TypeId matchLiteralType(NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes,
     else if (expr->is<AstExprConstantBool>())
     {
         auto ft = get<FreeType>(exprType);
-        if (ft &&
+        if (ft && get<SingletonType>(ft->lowerBound) && fastIsSubtype(builtinTypes->booleanType, ft->upperBound) &&
-            get<SingletonType>(ft->lowerBound) &&
+            fastIsSubtype(ft->lowerBound, builtinTypes->booleanType))
-            fastIsSubtype(builtinTypes->booleanType, ft->upperBound) &&
-            fastIsSubtype(ft->lowerBound, builtinTypes->booleanType)
-        )
         {
             // if the upper bound is a subtype of the expected type, we can push the expected type in
             Relation upperBoundRelation = relate(ft->upperBound, expectedType);
@@ -247,7 +233,7 @@ TypeId matchLiteralType(NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes,
             return exprType;
         }
 
-        for (const AstExprTable::Item& item: exprTable->items)
+        for (const AstExprTable::Item& item : exprTable->items)
         {
             if (isRecord(item))
             {
@@ -391,7 +377,7 @@ TypeId matchLiteralType(NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes,
         for (const auto& [name, _] : expectedTableTy->props)
             missingKeys.insert(name);
 
-        for (const AstExprTable::Item& item: exprTable->items)
+        for (const AstExprTable::Item& item : exprTable->items)
         {
             if (item.key)
             {
@@ -402,7 +388,7 @@ TypeId matchLiteralType(NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes,
             }
         }
 
-        for (const auto& key: missingKeys)
+        for (const auto& key : missingKeys)
         {
             LUAU_ASSERT(key.has_value());
 
@@ -427,4 +413,4 @@ TypeId matchLiteralType(NotNull<DenseHashMap<const AstExpr*, TypeId>> astTypes,
     return exprType;
 }
 
-}
+} // namespace Luau

Analysis/src/ToString.cpp

@@ -1767,12 +1767,6 @@ std::string toString(const Constraint& constraint, ToStringOptions& opts)
             std::string superStr = tos(c.sourceType);
             return subStr + " ~ gen " + superStr;
         }
-        else if constexpr (std::is_same_v<T, InstantiationConstraint>)
-        {
-            std::string subStr = tos(c.subType);
-            std::string superStr = tos(c.superType);
-            return subStr + " ~ inst " + superStr;
-        }
         else if constexpr (std::is_same_v<T, IterableConstraint>)
         {
             std::string iteratorStr = tos(c.iterator);
@@ -1822,37 +1816,10 @@ std::string toString(const Constraint& constraint, ToStringOptions& opts)
         {
             return "setIndexer " + tos(c.subjectType) + " [ " + tos(c.indexType) + " ] " + tos(c.propType);
         }
-        else if constexpr (std::is_same_v<T, SingletonOrTopTypeConstraint>)
-        {
-            std::string result = tos(c.resultType);
-            std::string discriminant = tos(c.discriminantType);
-
-            if (c.negated)
-                return result + " ~ if isSingleton D then ~D else unknown where D = " + discriminant;
-            else
-                return result + " ~ if isSingleton D then D else unknown where D = " + discriminant;
-        }
         else if constexpr (std::is_same_v<T, UnpackConstraint>)
             return tos(c.resultPack) + " ~ ...unpack " + tos(c.sourcePack);
         else if constexpr (std::is_same_v<T, Unpack1Constraint>)
             return tos(c.resultType) + " ~ unpack " + tos(c.sourceType);
-        else if constexpr (std::is_same_v<T, SetOpConstraint>)
-        {
-            const char* op = c.mode == SetOpConstraint::Union ? " | " : " & ";
-            std::string res = tos(c.resultType) + " ~ ";
-            bool first = true;
-            for (TypeId t : c.types)
-            {
-                if (first)
-                    first = false;
-                else
-                    res += op;
-
-                res += tos(t);
-            }
-
-            return res;
-        }
         else if constexpr (std::is_same_v<T, ReduceConstraint>)
             return "reduce " + tos(c.ty);
         else if constexpr (std::is_same_v<T, ReducePackConstraint>)
@@ -1923,7 +1890,7 @@ std::string toString(const Position& position)
 std::string toString(const Location& location, int offset, bool useBegin)
 {
     return "(" + std::to_string(location.begin.line + offset) + ", " + std::to_string(location.begin.column + offset) + ") - (" +
-            std::to_string(location.end.line + offset) + ", " + std::to_string(location.end.column + offset) + ")";
+           std::to_string(location.end.line + offset) + ", " + std::to_string(location.end.column + offset) + ")";
 }
 
 std::string toString(const TypeOrPack& tyOrTp, ToStringOptions& opts)

Analysis/src/Type.cpp

@@ -546,11 +546,13 @@ BlockedType::BlockedType()
 {
 }
 
-Constraint* BlockedType::getOwner() const {
+Constraint* BlockedType::getOwner() const
+{
     return owner;
 }
 
-void BlockedType::setOwner(Constraint* newOwner) {
+void BlockedType::setOwner(Constraint* newOwner)
+{
     LUAU_ASSERT(owner == nullptr);
 
     if (owner != nullptr)

Analysis/src/TypeArena.cpp

@@ -94,6 +94,26 @@ TypePackId TypeArena::addTypePack(TypePackVar tp)
     return allocated;
 }
 
+TypeId TypeArena::addTypeFamily(const TypeFamily& family, std::initializer_list<TypeId> types)
+{
+    return addType(TypeFamilyInstanceType{family, std::move(types)});
+}
+
+TypeId TypeArena::addTypeFamily(const TypeFamily& family, std::vector<TypeId> typeArguments, std::vector<TypePackId> packArguments)
+{
+    return addType(TypeFamilyInstanceType{family, std::move(typeArguments), std::move(packArguments)});
+}
+
+TypePackId TypeArena::addTypePackFamily(const TypePackFamily& family, std::initializer_list<TypeId> types)
+{
+    return addTypePack(TypeFamilyInstanceTypePack{NotNull{&family}, std::move(types)});
+}
+
+TypePackId TypeArena::addTypePackFamily(const TypePackFamily& family, std::vector<TypeId> typeArguments, std::vector<TypePackId> packArguments)
+{
+    return addTypePack(TypeFamilyInstanceTypePack{NotNull{&family}, std::move(typeArguments), std::move(packArguments)});
+}
+
 void freeze(TypeArena& arena)
 {
     if (!FFlag::DebugLuauFreezeArena)

Analysis/src/TypeChecker2.cpp

@@ -441,8 +441,8 @@ struct TypeChecker2
             return instance;
         seenTypeFamilyInstances.insert(instance);
 
-        ErrorVec errors = reduceFamilies(
+        ErrorVec errors = reduceFamilies(instance, location,
-            instance, location, TypeFamilyContext{NotNull{&module->internalTypes}, builtinTypes, stack.back(), NotNull{&normalizer}, ice, limits}, true)
+            TypeFamilyContext{NotNull{&module->internalTypes}, builtinTypes, stack.back(), NotNull{&normalizer}, ice, limits}, true)
                               .errors;
         if (!isErrorSuppressing(location, instance))
             reportErrors(std::move(errors));
@@ -2743,7 +2743,7 @@ struct TypeChecker2
                     fetch(module->internalTypes.addType(IntersectionType{{tyvar, ty}}));
                 }
                 else
-                    fetch(tyvar);
+                    fetch(follow(tyvar));
 
                 if (!normValid)
                     break;
@@ -2871,17 +2871,24 @@ struct TypeChecker2
             for (TypeId part : utv)
             {
                 PropertyType result = hasIndexTypeFromType(part, prop, context, location, seen, astIndexExprType, errors);
+
                 if (result.present != NormalizationResult::True)
                     return {result.present, {}};
                 if (result.result)
                     parts.emplace_back(*result.result);
             }
 
+            if (parts.size() == 0)
+                return {NormalizationResult::False, {}};
+
+            if (parts.size() == 1)
+                return {NormalizationResult::True, {parts[0]}};
+
             TypeId propTy;
             if (context == ValueContext::LValue)
-                module->internalTypes.addType(IntersectionType{parts});
+                propTy = module->internalTypes.addType(IntersectionType{parts});
             else
-                module->internalTypes.addType(UnionType{parts});
+                propTy = module->internalTypes.addType(UnionType{parts});
 
             return {NormalizationResult::True, propTy};
         }

Analysis/src/TypeFamily.cpp

@@ -217,7 +217,8 @@ struct FamilyReducer
             else if (!reduction.uninhabited && !force)
             {
                 if (FFlag::DebugLuauLogSolver)
-                    printf("%s is irreducible; blocked on %zu types, %zu packs\n", toString(subject, {true}).c_str(), reduction.blockedTypes.size(), reduction.blockedPacks.size());
+                    printf("%s is irreducible; blocked on %zu types, %zu packs\n", toString(subject, {true}).c_str(), reduction.blockedTypes.size(),
+                        reduction.blockedPacks.size());
 
                 for (TypeId b : reduction.blockedTypes)
                     result.blockedTypes.insert(b);
@@ -243,7 +244,7 @@ struct FamilyReducer
             if (skip == SkipTestResult::Irreducible)
             {
                 if (FFlag::DebugLuauLogSolver)
-                    printf("%s is irreducible due to a dependency on %s\n" , toString(subject, {true}).c_str(), toString(p, {true}).c_str());
+                    printf("%s is irreducible due to a dependency on %s\n", toString(subject, {true}).c_str(), toString(p, {true}).c_str());
 
                 irreducible.insert(subject);
                 return false;
@@ -251,7 +252,7 @@ struct FamilyReducer
             else if (skip == SkipTestResult::Defer)
             {
                 if (FFlag::DebugLuauLogSolver)
-                    printf("Deferring %s until %s is solved\n" , toString(subject, {true}).c_str(), toString(p, {true}).c_str());
+                    printf("Deferring %s until %s is solved\n", toString(subject, {true}).c_str(), toString(p, {true}).c_str());
 
                 if constexpr (std::is_same_v<T, TypeId>)
                     queuedTys.push_back(subject);
@@ -269,7 +270,7 @@ struct FamilyReducer
             if (skip == SkipTestResult::Irreducible)
             {
                 if (FFlag::DebugLuauLogSolver)
-                    printf("%s is irreducible due to a dependency on %s\n" , toString(subject, {true}).c_str(), toString(p, {true}).c_str());
+                    printf("%s is irreducible due to a dependency on %s\n", toString(subject, {true}).c_str(), toString(p, {true}).c_str());
 
                 irreducible.insert(subject);
                 return false;
@@ -277,7 +278,7 @@ struct FamilyReducer
             else if (skip == SkipTestResult::Defer)
             {
                 if (FFlag::DebugLuauLogSolver)
-                    printf("Deferring %s until %s is solved\n" , toString(subject, {true}).c_str(), toString(p, {true}).c_str());
+                    printf("Deferring %s until %s is solved\n", toString(subject, {true}).c_str(), toString(p, {true}).c_str());
 
                 if constexpr (std::is_same_v<T, TypeId>)
                     queuedTys.push_back(subject);
@@ -346,7 +347,8 @@ struct FamilyReducer
                 return;
 
             TypeFamilyQueue queue{NotNull{&queuedTys}, NotNull{&queuedTps}};
-            TypeFamilyReductionResult<TypeId> result = tfit->family->reducer(subject, NotNull{&queue}, tfit->typeArguments, tfit->packArguments, NotNull{&ctx});
+            TypeFamilyReductionResult<TypeId> result =
+                tfit->family->reducer(subject, NotNull{&queue}, tfit->typeArguments, tfit->packArguments, NotNull{&ctx});
             handleFamilyReduction(subject, result);
         }
     }
@@ -371,7 +373,8 @@ struct FamilyReducer
                 return;
 
             TypeFamilyQueue queue{NotNull{&queuedTys}, NotNull{&queuedTps}};
-            TypeFamilyReductionResult<TypePackId> result = tfit->family->reducer(subject, NotNull{&queue}, tfit->typeArguments, tfit->packArguments, NotNull{&ctx});
+            TypeFamilyReductionResult<TypePackId> result =
+                tfit->family->reducer(subject, NotNull{&queue}, tfit->typeArguments, tfit->packArguments, NotNull{&ctx});
             handleFamilyReduction(subject, result);
         }
     }
@@ -385,8 +388,8 @@ struct FamilyReducer
     }
 };
 
-static FamilyGraphReductionResult reduceFamiliesInternal(
+static FamilyGraphReductionResult reduceFamiliesInternal(VecDeque<TypeId> queuedTys, VecDeque<TypePackId> queuedTps, TypeOrTypePackIdSet shouldGuess,
-    VecDeque<TypeId> queuedTys, VecDeque<TypePackId> queuedTps, TypeOrTypePackIdSet shouldGuess, std::vector<TypeId> cyclics, Location location, TypeFamilyContext ctx, bool force)
+    std::vector<TypeId> cyclics, Location location, TypeFamilyContext ctx, bool force)
 {
     FamilyReducer reducer{std::move(queuedTys), std::move(queuedTps), std::move(shouldGuess), std::move(cyclics), location, ctx, force};
     int iterationCount = 0;
@@ -422,7 +425,8 @@ FamilyGraphReductionResult reduceFamilies(TypeId entrypoint, Location location,
     if (collector.tys.empty() && collector.tps.empty())
         return {};
 
-    return reduceFamiliesInternal(std::move(collector.tys), std::move(collector.tps), std::move(collector.shouldGuess), std::move(collector.cyclicInstance), location, ctx, force);
+    return reduceFamiliesInternal(std::move(collector.tys), std::move(collector.tps), std::move(collector.shouldGuess),
+        std::move(collector.cyclicInstance), location, ctx, force);
 }
 
 FamilyGraphReductionResult reduceFamilies(TypePackId entrypoint, Location location, TypeFamilyContext ctx, bool force)
@@ -441,7 +445,8 @@ FamilyGraphReductionResult reduceFamilies(TypePackId entrypoint, Location locati
     if (collector.tys.empty() && collector.tps.empty())
         return {};
 
-    return reduceFamiliesInternal(std::move(collector.tys), std::move(collector.tps), std::move(collector.shouldGuess), std::move(collector.cyclicInstance), location, ctx, force);
+    return reduceFamiliesInternal(std::move(collector.tys), std::move(collector.tps), std::move(collector.shouldGuess),
+        std::move(collector.cyclicInstance), location, ctx, force);
 }
 
 void TypeFamilyQueue::add(TypeId instanceTy)
@@ -461,8 +466,8 @@ bool isPending(TypeId ty, ConstraintSolver* solver)
     return is<BlockedType, PendingExpansionType, TypeFamilyInstanceType, LocalType>(ty) || (solver && solver->hasUnresolvedConstraints(ty));
 }
 
-TypeFamilyReductionResult<TypeId> notFamilyFn(
+TypeFamilyReductionResult<TypeId> notFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 1 || !packParams.empty())
     {
@@ -479,8 +484,8 @@ TypeFamilyReductionResult<TypeId> notFamilyFn(
     return {ctx->builtins->booleanType, false, {}, {}};
 }
 
-TypeFamilyReductionResult<TypeId> lenFamilyFn(
+TypeFamilyReductionResult<TypeId> lenFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 1 || !packParams.empty())
     {
@@ -496,17 +501,18 @@ TypeFamilyReductionResult<TypeId> lenFamilyFn(
         return {std::nullopt, false, {operandTy}, {}};
 
     std::shared_ptr<const NormalizedType> normTy = ctx->normalizer->normalize(operandTy);
+    NormalizationResult inhabited = ctx->normalizer->isInhabited(normTy.get());
 
     // if the type failed to normalize, we can't reduce, but know nothing about inhabitance.
-    if (!normTy)
+    if (!normTy || inhabited == NormalizationResult::HitLimits)
         return {std::nullopt, false, {}, {}};
 
     // if the operand type is error suppressing, we can immediately reduce to `number`.
     if (normTy->shouldSuppressErrors())
         return {ctx->builtins->numberType, false, {}, {}};
 
-    // if we have a `never`, we can never observe that the operator didn't work.
+    // if we have an uninhabited type (like `never`), we can never observe that the operator didn't work.
-    if (is<NeverType>(operandTy))
+    if (inhabited == NormalizationResult::False)
         return {ctx->builtins->neverType, false, {}, {}};
 
     // if we're checking the length of a string, that works!
@@ -555,8 +561,8 @@ TypeFamilyReductionResult<TypeId> lenFamilyFn(
     return {ctx->builtins->numberType, false, {}, {}};
 }
 
-TypeFamilyReductionResult<TypeId> unmFamilyFn(
+TypeFamilyReductionResult<TypeId> unmFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 1 || !packParams.empty())
     {
@@ -732,25 +738,18 @@ TypeFamilyReductionResult<TypeId> numericBinopFamilyFn(TypeId instance, NotNull<
             // though there exists no arm of the union that is inhabited or have a reduced type.
             ctx->ice->ice("`distributeFamilyApp` failed to add any types to the results vector?");
         }
-        else if (results.size() == 1)
-            return {results[0], false, {}, {}};
-        else if (results.size() == 2)
-        {
-            TypeId resultTy = ctx->arena->addType(TypeFamilyInstanceType{
-                NotNull{&kBuiltinTypeFamilies.unionFamily},
-                std::move(results),
-                {},
-            });
 
-            queue->add(resultTy);
+        if (results.size() == 1)
-            return {resultTy, false, {}, {}};
+            return {results[0], false, {}, {}};
-        }
+
-        else
+        TypeId resultTy = ctx->arena->addType(TypeFamilyInstanceType{
-        {
+            NotNull{&kBuiltinTypeFamilies.unionFamily},
-            // TODO: We need to generalize `union<...>` type family to be variadic.
+            std::move(results),
-            TypeId resultTy = ctx->arena->addType(UnionType{std::move(results)});
+            {},
-            return {resultTy, false, {}, {}};
+        });
-        }
+
+        queue->add(resultTy);
+        return {resultTy, false, {}, {}};
     }
 
     // findMetatableEntry demands the ability to emit errors, so we must give it
@@ -794,8 +793,8 @@ TypeFamilyReductionResult<TypeId> numericBinopFamilyFn(TypeId instance, NotNull<
     return {extracted.head.front(), false, {}, {}};
 }
 
-TypeFamilyReductionResult<TypeId> addFamilyFn(
+TypeFamilyReductionResult<TypeId> addFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -806,8 +805,8 @@ TypeFamilyReductionResult<TypeId> addFamilyFn(
     return numericBinopFamilyFn(instance, queue, typeParams, packParams, ctx, "__add");
 }
 
-TypeFamilyReductionResult<TypeId> subFamilyFn(
+TypeFamilyReductionResult<TypeId> subFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -818,8 +817,8 @@ TypeFamilyReductionResult<TypeId> subFamilyFn(
     return numericBinopFamilyFn(instance, queue, typeParams, packParams, ctx, "__sub");
 }
 
-TypeFamilyReductionResult<TypeId> mulFamilyFn(
+TypeFamilyReductionResult<TypeId> mulFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -830,8 +829,8 @@ TypeFamilyReductionResult<TypeId> mulFamilyFn(
     return numericBinopFamilyFn(instance, queue, typeParams, packParams, ctx, "__mul");
 }
 
-TypeFamilyReductionResult<TypeId> divFamilyFn(
+TypeFamilyReductionResult<TypeId> divFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -842,8 +841,8 @@ TypeFamilyReductionResult<TypeId> divFamilyFn(
     return numericBinopFamilyFn(instance, queue, typeParams, packParams, ctx, "__div");
 }
 
-TypeFamilyReductionResult<TypeId> idivFamilyFn(
+TypeFamilyReductionResult<TypeId> idivFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -854,8 +853,8 @@ TypeFamilyReductionResult<TypeId> idivFamilyFn(
     return numericBinopFamilyFn(instance, queue, typeParams, packParams, ctx, "__idiv");
 }
 
-TypeFamilyReductionResult<TypeId> powFamilyFn(
+TypeFamilyReductionResult<TypeId> powFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -866,8 +865,8 @@ TypeFamilyReductionResult<TypeId> powFamilyFn(
     return numericBinopFamilyFn(instance, queue, typeParams, packParams, ctx, "__pow");
 }
 
-TypeFamilyReductionResult<TypeId> modFamilyFn(
+TypeFamilyReductionResult<TypeId> modFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -878,8 +877,8 @@ TypeFamilyReductionResult<TypeId> modFamilyFn(
     return numericBinopFamilyFn(instance, queue, typeParams, packParams, ctx, "__mod");
 }
 
-TypeFamilyReductionResult<TypeId> concatFamilyFn(
+TypeFamilyReductionResult<TypeId> concatFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -964,8 +963,8 @@ TypeFamilyReductionResult<TypeId> concatFamilyFn(
     return {ctx->builtins->stringType, false, {}, {}};
 }
 
-TypeFamilyReductionResult<TypeId> andFamilyFn(
+TypeFamilyReductionResult<TypeId> andFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -1001,8 +1000,8 @@ TypeFamilyReductionResult<TypeId> andFamilyFn(
     return {overallResult.result, false, std::move(blockedTypes), {}};
 }
 
-TypeFamilyReductionResult<TypeId> orFamilyFn(
+TypeFamilyReductionResult<TypeId> orFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -1093,17 +1092,19 @@ static TypeFamilyReductionResult<TypeId> comparisonFamilyFn(TypeId instance, Not
 
     std::shared_ptr<const NormalizedType> normLhsTy = ctx->normalizer->normalize(lhsTy);
     std::shared_ptr<const NormalizedType> normRhsTy = ctx->normalizer->normalize(rhsTy);
+    NormalizationResult lhsInhabited = ctx->normalizer->isInhabited(normLhsTy.get());
+    NormalizationResult rhsInhabited = ctx->normalizer->isInhabited(normRhsTy.get());
 
     // if either failed to normalize, we can't reduce, but know nothing about inhabitance.
-    if (!normLhsTy || !normRhsTy)
+    if (!normLhsTy || !normRhsTy || lhsInhabited == NormalizationResult::HitLimits || rhsInhabited == NormalizationResult::HitLimits)
         return {std::nullopt, false, {}, {}};
 
     // if one of the types is error suppressing, we can just go ahead and reduce.
     if (normLhsTy->shouldSuppressErrors() || normRhsTy->shouldSuppressErrors())
         return {ctx->builtins->booleanType, false, {}, {}};
 
-    // if we have a `never`, we can never observe that the comparison didn't work.
+    // if we have an uninhabited type (e.g. `never`), we can never observe that the comparison didn't work.
-    if (is<NeverType>(lhsTy) || is<NeverType>(rhsTy))
+    if (lhsInhabited == NormalizationResult::False || rhsInhabited == NormalizationResult::False)
         return {ctx->builtins->booleanType, false, {}, {}};
 
     // If both types are some strict subset of `string`, we can reduce now.
@@ -1153,8 +1154,8 @@ static TypeFamilyReductionResult<TypeId> comparisonFamilyFn(TypeId instance, Not
     return {ctx->builtins->booleanType, false, {}, {}};
 }
 
-TypeFamilyReductionResult<TypeId> ltFamilyFn(
+TypeFamilyReductionResult<TypeId> ltFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -1165,8 +1166,8 @@ TypeFamilyReductionResult<TypeId> ltFamilyFn(
     return comparisonFamilyFn(instance, queue, typeParams, packParams, ctx, "__lt");
 }
 
-TypeFamilyReductionResult<TypeId> leFamilyFn(
+TypeFamilyReductionResult<TypeId> leFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -1177,8 +1178,8 @@ TypeFamilyReductionResult<TypeId> leFamilyFn(
     return comparisonFamilyFn(instance, queue, typeParams, packParams, ctx, "__le");
 }
 
-TypeFamilyReductionResult<TypeId> eqFamilyFn(
+TypeFamilyReductionResult<TypeId> eqFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -1197,9 +1198,11 @@ TypeFamilyReductionResult<TypeId> eqFamilyFn(
 
     std::shared_ptr<const NormalizedType> normLhsTy = ctx->normalizer->normalize(lhsTy);
     std::shared_ptr<const NormalizedType> normRhsTy = ctx->normalizer->normalize(rhsTy);
+    NormalizationResult lhsInhabited = ctx->normalizer->isInhabited(normLhsTy.get());
+    NormalizationResult rhsInhabited = ctx->normalizer->isInhabited(normRhsTy.get());
 
     // if either failed to normalize, we can't reduce, but know nothing about inhabitance.
-    if (!normLhsTy || !normRhsTy)
+    if (!normLhsTy || !normRhsTy || lhsInhabited == NormalizationResult::HitLimits || rhsInhabited == NormalizationResult::HitLimits)
         return {std::nullopt, false, {}, {}};
 
     // if one of the types is error suppressing, we can just go ahead and reduce.
@@ -1207,7 +1210,7 @@ TypeFamilyReductionResult<TypeId> eqFamilyFn(
         return {ctx->builtins->booleanType, false, {}, {}};
 
     // if we have a `never`, we can never observe that the comparison didn't work.
-    if (is<NeverType>(lhsTy) || is<NeverType>(rhsTy))
+    if (lhsInhabited == NormalizationResult::False || rhsInhabited == NormalizationResult::False)
         return {ctx->builtins->booleanType, false, {}, {}};
 
     // findMetatableEntry demands the ability to emit errors, so we must give it
@@ -1282,8 +1285,8 @@ struct FindRefinementBlockers : TypeOnceVisitor
 };
 
 
-TypeFamilyReductionResult<TypeId> refineFamilyFn(
+TypeFamilyReductionResult<TypeId> refineFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 2 || !packParams.empty())
     {
@@ -1340,73 +1343,145 @@ TypeFamilyReductionResult<TypeId> refineFamilyFn(
     return {resultTy, false, {}, {}};
 }
 
-TypeFamilyReductionResult<TypeId> unionFamilyFn(
+TypeFamilyReductionResult<TypeId> singletonFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
-    if (typeParams.size() != 2 || !packParams.empty())
+    if (typeParams.size() != 1 || !packParams.empty())
+    {
+        ctx->ice->ice("singleton type family: encountered a type family instance without the required argument structure");
+        LUAU_ASSERT(false);
+    }
+
+    TypeId type = follow(typeParams.at(0));
+
+    // check to see if both operand types are resolved enough, and wait to reduce if not
+    if (isPending(type, ctx->solver))
+        return {std::nullopt, false, {type}, {}};
+
+    TypeId followed = type;
+    // we want to follow through a negation here as well.
+    if (auto negation = get<NegationType>(followed))
+       followed = follow(negation->ty);
+
+    // if we have a singleton type or `nil`, which is its own singleton type...
+    if (get<SingletonType>(followed) || isNil(followed))
+        return {type, false, {}, {}};
+
+    // otherwise, we'll return the top type, `unknown`.
+    return {ctx->builtins->unknownType, false, {}, {}};
+}
+
+TypeFamilyReductionResult<TypeId> unionFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+{
+    if (!packParams.empty())
     {
         ctx->ice->ice("union type family: encountered a type family instance without the required argument structure");
         LUAU_ASSERT(false);
     }
 
-    TypeId lhsTy = follow(typeParams.at(0));
+    // if we only have one parameter, there's nothing to do.
-    TypeId rhsTy = follow(typeParams.at(1));
+    if (typeParams.size() == 1)
+        return {follow(typeParams[0]), false, {}, {}};
 
-    // check to see if both operand types are resolved enough, and wait to reduce if not
+    // we need to follow all of the type parameters.
-    if (isPending(lhsTy, ctx->solver))
+    std::vector<TypeId> types;
-        return {std::nullopt, false, {lhsTy}, {}};
+    types.reserve(typeParams.size());
-    else if (get<NeverType>(lhsTy)) // if the lhs is never, we don't need this family anymore
+    for (auto ty : typeParams)
-        return {rhsTy, false, {}, {}};
+        types.emplace_back(follow(ty));
-    else if (isPending(rhsTy, ctx->solver))
-        return {std::nullopt, false, {rhsTy}, {}};
-    else if (get<NeverType>(rhsTy)) // if the rhs is never, we don't need this family anymore
-        return {lhsTy, false, {}, {}};
 
+    // unfortunately, we need this short-circuit: if all but one type is `never`, we will return that one type.
+    // this also will early return if _everything_ is `never`, since we already have to check that.
+    std::optional<TypeId> lastType = std::nullopt;
+    for (auto ty : types)
+    {
+        // if we have a previous type and it's not `never` and the current type isn't `never`...
+        if (lastType && !get<NeverType>(lastType) && !get<NeverType>(ty))
+        {
+            // we know we are not taking the short-circuited path.
+            lastType = std::nullopt;
+            break;
+        }
 
-    SimplifyResult result = simplifyUnion(ctx->builtins, ctx->arena, lhsTy, rhsTy);
+        if (get<NeverType>(ty))
-    if (!result.blockedTypes.empty())
+            continue;
-        return {std::nullopt, false, {result.blockedTypes.begin(), result.blockedTypes.end()}, {}};
+        lastType = ty;
+    }
 
-    return {result.result, false, {}, {}};
+    // if we still have a `lastType` at the end, we're taking the short-circuit and reducing early.
+    if (lastType)
+        return {lastType, false, {}, {}};
+
+    // check to see if the operand types are resolved enough, and wait to reduce if not
+    for (auto ty : types)
+        if (isPending(ty, ctx->solver))
+            return {std::nullopt, false, {ty}, {}};
+
+    // fold over the types with `simplifyUnion`
+    TypeId resultTy = ctx->builtins->neverType;
+    for (auto ty : types)
+    {
+        SimplifyResult result = simplifyUnion(ctx->builtins, ctx->arena, resultTy, ty);
+        if (!result.blockedTypes.empty())
+            return {std::nullopt, false, {result.blockedTypes.begin(), result.blockedTypes.end()}, {}};
+
+        resultTy = result.result;
+    }
+
+    return {resultTy, false, {}, {}};
 }
 
 
-TypeFamilyReductionResult<TypeId> intersectFamilyFn(
+TypeFamilyReductionResult<TypeId> intersectFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
-    if (typeParams.size() != 2 || !packParams.empty())
+    if (!packParams.empty())
     {
         ctx->ice->ice("intersect type family: encountered a type family instance without the required argument structure");
         LUAU_ASSERT(false);
     }
 
-    TypeId lhsTy = follow(typeParams.at(0));
+    // if we only have one parameter, there's nothing to do.
-    TypeId rhsTy = follow(typeParams.at(1));
+    if (typeParams.size() == 1)
+        return {follow(typeParams[0]), false, {}, {}};
 
-    // check to see if both operand types are resolved enough, and wait to reduce if not
+    // we need to follow all of the type parameters.
-    if (isPending(lhsTy, ctx->solver))
+    std::vector<TypeId> types;
-        return {std::nullopt, false, {lhsTy}, {}};
+    types.reserve(typeParams.size());
-    else if (get<NeverType>(lhsTy)) // if the lhs is never, we don't need this family anymore
+    for (auto ty : typeParams)
-        return {ctx->builtins->neverType, false, {}, {}};
+        types.emplace_back(follow(ty));
-    else if (isPending(rhsTy, ctx->solver))
-        return {std::nullopt, false, {rhsTy}, {}};
-    else if (get<NeverType>(rhsTy)) // if the rhs is never, we don't need this family anymore
-        return {ctx->builtins->neverType, false, {}, {}};
 
-    SimplifyResult result = simplifyIntersection(ctx->builtins, ctx->arena, lhsTy, rhsTy);
+    // check to see if the operand types are resolved enough, and wait to reduce if not
-    if (!result.blockedTypes.empty())
+    // if any of them are `never`, the intersection will always be `never`, so we can reduce directly.
-        return {std::nullopt, false, {result.blockedTypes.begin(), result.blockedTypes.end()}, {}};
+    for (auto ty : types)
+    {
+        if (isPending(ty, ctx->solver))
+            return {std::nullopt, false, {ty}, {}};
+        else if (get<NeverType>(ty))
+            return {ctx->builtins->neverType, false, {}, {}};
+    }
+
+    // fold over the types with `simplifyIntersection`
+    TypeId resultTy = ctx->builtins->unknownType;
+    for (auto ty : types)
+    {
+        SimplifyResult result = simplifyIntersection(ctx->builtins, ctx->arena, resultTy, ty);
+        if (!result.blockedTypes.empty())
+            return {std::nullopt, false, {result.blockedTypes.begin(), result.blockedTypes.end()}, {}};
+
+        resultTy = result.result;
+    }
 
     // if the intersection simplifies to `never`, this gives us bad autocomplete.
     // we'll just produce the intersection plainly instead, but this might be revisitable
     // if we ever give `never` some kind of "explanation" trail.
-    if (get<NeverType>(result.result))
+    if (get<NeverType>(resultTy))
     {
-        TypeId intersection = ctx->arena->addType(IntersectionType{{lhsTy, rhsTy}});
+        TypeId intersection = ctx->arena->addType(IntersectionType{typeParams});
         return {intersection, false, {}, {}};
     }
 
-    return {result.result, false, {}, {}};
+    return {resultTy, false, {}, {}};
 }
 
 // computes the keys of `ty` into `result`
@@ -1581,8 +1656,8 @@ TypeFamilyReductionResult<TypeId> keyofFamilyImpl(
     return {ctx->arena->addType(UnionType{singletons}), false, {}, {}};
 }
 
-TypeFamilyReductionResult<TypeId> keyofFamilyFn(
+TypeFamilyReductionResult<TypeId> keyofFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 1 || !packParams.empty())
     {
@@ -1593,8 +1668,8 @@ TypeFamilyReductionResult<TypeId> keyofFamilyFn(
     return keyofFamilyImpl(typeParams, packParams, ctx, /* isRaw */ false);
 }
 
-TypeFamilyReductionResult<TypeId> rawkeyofFamilyFn(
+TypeFamilyReductionResult<TypeId> rawkeyofFamilyFn(TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams,
-    TypeId instance, NotNull<TypeFamilyQueue> queue, const std::vector<TypeId>& typeParams, const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
+    const std::vector<TypePackId>& packParams, NotNull<TypeFamilyContext> ctx)
 {
     if (typeParams.size() != 1 || !packParams.empty())
     {
@@ -1623,6 +1698,7 @@ BuiltinTypeFamilies::BuiltinTypeFamilies()
     , leFamily{"le", leFamilyFn}
     , eqFamily{"eq", eqFamilyFn}
     , refineFamily{"refine", refineFamilyFn}
+    , singletonFamily{"singleton", singletonFamilyFn}
     , unionFamily{"union", unionFamilyFn}
     , intersectFamily{"intersect", intersectFamilyFn}
     , keyofFamily{"keyof", keyofFamilyFn}

Analysis/src/TypeInfer.cpp

@@ -33,6 +33,7 @@ LUAU_FASTFLAG(LuauKnowsTheDataModel3)
 LUAU_FASTFLAGVARIABLE(DebugLuauFreezeDuringUnification, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauSharedSelf, false)
 LUAU_FASTFLAG(LuauInstantiateInSubtyping)
+LUAU_FASTFLAGVARIABLE(LuauMetatableInstantiationCloneCheck, false)
 LUAU_FASTFLAGVARIABLE(LuauTinyControlFlowAnalysis, false)
 LUAU_FASTFLAGVARIABLE(LuauAlwaysCommitInferencesOfFunctionCalls, false)
 LUAU_FASTFLAGVARIABLE(LuauRemoveBadRelationalOperatorWarning, false)
@@ -5632,7 +5633,8 @@ TypeId TypeChecker::instantiateTypeFun(const ScopePtr& scope, const TypeFun& tf,
     TypeId instantiated = *maybeInstantiated;
 
     TypeId target = follow(instantiated);
-    bool needsClone = follow(tf.type) == target;
+    const TableType* tfTable = FFlag::LuauMetatableInstantiationCloneCheck ? getTableType(tf.type) : nullptr;
+    bool needsClone = follow(tf.type) == target || (FFlag::LuauMetatableInstantiationCloneCheck && tfTable != nullptr && tfTable == getTableType(target));
     bool shouldMutate = getTableType(tf.type);
     TableType* ttv = getMutableTableType(target);
 

Analysis/src/TypePack.cpp

@@ -6,8 +6,6 @@
 
 #include <stdexcept>
 
-LUAU_FASTFLAGVARIABLE(LuauFollowEmptyTypePacks, false);
-
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 
 namespace Luau
@@ -271,8 +269,7 @@ TypePackId follow(TypePackId tp, const void* context, TypePackId (*mapper)(const
 
         if (const Unifiable::Bound<TypePackId>* btv = get<Unifiable::Bound<TypePackId>>(mapped))
             return btv->boundTo;
-        else if (const TypePack* tp = get<TypePack>(mapped);
+        else if (const TypePack* tp = get<TypePack>(mapped); tp && tp->head.empty())
-                 (FFlag::DebugLuauDeferredConstraintResolution || FFlag::LuauFollowEmptyTypePacks) && tp && tp->head.empty())
             return tp->tail;
         else
             return std::nullopt;

Analysis/src/TypePath.cpp

@@ -52,6 +52,11 @@ bool Index::operator==(const Index& other) const
     return index == other.index;
 }
 
+bool Reduction::operator==(const Reduction& other) const
+{
+    return resultType == other.resultType;
+}
+
 Path Path::append(const Path& suffix) const
 {
     std::vector<Component> joined(components);
@@ -124,6 +129,11 @@ size_t PathHash::operator()(const PackField& field) const
     return static_cast<size_t>(field);
 }
 
+size_t PathHash::operator()(const Reduction& reduction) const
+{
+    return std::hash<TypeId>()(reduction.resultType);
+}
+
 size_t PathHash::operator()(const Component& component) const
 {
     return visit(*this, component);
@@ -472,6 +482,14 @@ struct TraversalState
         return false;
     }
 
+    bool traverse(TypePath::Reduction reduction)
+    {
+        if (checkInvariants())
+            return false;
+        updateCurrent(reduction.resultType);
+        return true;
+    }
+
     bool traverse(TypePath::PackField field)
     {
         if (checkInvariants())
@@ -584,9 +602,14 @@ std::string toString(const TypePath::Path& path, bool prefixDot)
                 result << "tail";
                 break;
             }
-
             result << "()";
         }
+        else if constexpr (std::is_same_v<T, TypePath::Reduction>)
+        {
+            // We need to rework the TypePath system to make subtyping failures easier to understand
+            // https://roblox.atlassian.net/browse/CLI-104422
+            result << "~~>";
+        }
         else
         {
             static_assert(always_false_v<T>, "Unhandled Component variant");

Analysis/src/Unifier.cpp

@@ -1006,7 +1006,8 @@ void Unifier::tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTyp
             if (!subNorm || !superNorm)
                 reportError(location, NormalizationTooComplex{});
             else if ((failedOptionCount == 1 || foundHeuristic) && failedOption)
-                tryUnifyNormalizedTypes(subTy, superTy, *subNorm, *superNorm, "None of the union options are compatible. For example:", *failedOption);
+                tryUnifyNormalizedTypes(
+                    subTy, superTy, *subNorm, *superNorm, "None of the union options are compatible. For example:", *failedOption);
             else
                 tryUnifyNormalizedTypes(subTy, superTy, *subNorm, *superNorm, "none of the union options are compatible");
         }
@@ -1017,7 +1018,8 @@ void Unifier::tryUnifyTypeWithUnion(TypeId subTy, TypeId superTy, const UnionTyp
             if (!subNorm || !superNorm)
                 reportError(location, NormalizationTooComplex{});
             else if ((failedOptionCount == 1 || foundHeuristic) && failedOption)
-                tryUnifyNormalizedTypes(subTy, superTy, *subNorm, *superNorm, "None of the union options are compatible. For example:", *failedOption);
+                tryUnifyNormalizedTypes(
+                    subTy, superTy, *subNorm, *superNorm, "None of the union options are compatible. For example:", *failedOption);
             else
                 tryUnifyNormalizedTypes(subTy, superTy, *subNorm, *superNorm, "none of the union options are compatible");
         }

Analysis/src/Unifier2.cpp

@@ -42,9 +42,7 @@ static bool areCompatible(TypeId left, TypeId right)
 
         LUAU_ASSERT(leftProp.isReadOnly() || leftProp.isShared());
 
-        const TypeId leftType = follow(
+        const TypeId leftType = follow(leftProp.isReadOnly() ? *leftProp.readTy : leftProp.type());
-            leftProp.isReadOnly() ? *leftProp.readTy : leftProp.type()
-        );
 
         if (isOptional(leftType) || get<FreeType>(leftType) || rightTable->state == TableState::Free || rightTable->indexer.has_value())
             return true;
@@ -52,7 +50,7 @@ static bool areCompatible(TypeId left, TypeId right)
         return false;
     };
 
-    for (const auto& [name, leftProp]: leftTable->props)
+    for (const auto& [name, leftProp] : leftTable->props)
     {
         auto it = rightTable->props.find(name);
         if (it == rightTable->props.end())
@@ -62,7 +60,7 @@ static bool areCompatible(TypeId left, TypeId right)
         }
     }
 
-    for (const auto& [name, rightProp]: rightTable->props)
+    for (const auto& [name, rightProp] : rightTable->props)
     {
         auto it = leftTable->props.find(name);
         if (it == leftTable->props.end())
@@ -75,6 +73,18 @@ static bool areCompatible(TypeId left, TypeId right)
     return true;
 }
 
+// returns `true` if `ty` is irressolvable and should be added to `incompleteSubtypes`.
+static bool isIrresolvable(TypeId ty)
+{
+    return get<BlockedType>(ty) || get<TypeFamilyInstanceType>(ty);
+}
+
+// returns `true` if `tp` is irressolvable and should be added to `incompleteSubtypes`.
+static bool isIrresolvable(TypePackId tp)
+{
+    return get<BlockedTypePack>(tp) || get<TypeFamilyInstanceTypePack>(tp);
+}
+
 Unifier2::Unifier2(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, NotNull<Scope> scope, NotNull<InternalErrorReporter> ice)
     : arena(arena)
     , builtinTypes(builtinTypes)
@@ -82,6 +92,19 @@ Unifier2::Unifier2(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes,
     , ice(ice)
     , limits(TypeCheckLimits{}) // TODO: typecheck limits in unifier2
     , recursionLimit(FInt::LuauTypeInferRecursionLimit)
+    , uninhabitedTypeFamilies(nullptr)
+{
+}
+
+Unifier2::Unifier2(NotNull<TypeArena> arena, NotNull<BuiltinTypes> builtinTypes, NotNull<Scope> scope, NotNull<InternalErrorReporter> ice,
+    DenseHashSet<const void*>* uninhabitedTypeFamilies)
+    : arena(arena)
+    , builtinTypes(builtinTypes)
+    , scope(scope)
+    , ice(ice)
+    , limits(TypeCheckLimits{}) // TODO: typecheck limits in unifier2
+    , recursionLimit(FInt::LuauTypeInferRecursionLimit)
+    , uninhabitedTypeFamilies(uninhabitedTypeFamilies)
 {
 }
 
@@ -110,8 +133,11 @@ bool Unifier2::unify(TypeId subTy, TypeId superTy)
     // But we exclude these two subtyping patterns, they are tautological:
     //   - never <: *blocked*
     //   - *blocked* <: unknown
-    if ((get<BlockedType>(subTy) || get<BlockedType>(superTy)) && !get<NeverType>(subTy) && !get<UnknownType>(superTy))
+    if ((isIrresolvable(subTy) || isIrresolvable(superTy)) && !get<NeverType>(subTy) && !get<UnknownType>(superTy))
     {
+        if (uninhabitedTypeFamilies && (uninhabitedTypeFamilies->contains(subTy) || uninhabitedTypeFamilies->contains(superTy)))
+            return true;
+
         incompleteSubtypes.push_back(SubtypeConstraint{subTy, superTy});
         return true;
     }
@@ -473,8 +499,11 @@ bool Unifier2::unify(TypePackId subTp, TypePackId superTp)
     if (subTp == superTp)
         return true;
 
-    if (get<BlockedTypePack>(subTp) || get<BlockedTypePack>(superTp))
+    if (isIrresolvable(subTp) || isIrresolvable(superTp))
     {
+        if (uninhabitedTypeFamilies && (uninhabitedTypeFamilies->contains(subTp) || uninhabitedTypeFamilies->contains(superTp)))
+            return true;
+
         incompleteSubtypes.push_back(PackSubtypeConstraint{subTp, superTp});
         return true;
     }

CodeGen/src/BytecodeAnalysis.cpp

@@ -7,6 +7,8 @@
 
 #include "lobject.h"
 
+LUAU_FASTFLAG(LuauCodegenDirectUserdataFlow)
+
 namespace Luau
 {
 namespace CodeGen
@@ -833,6 +835,27 @@ void analyzeBytecodeTypes(IrFunction& function)
                 bcType.result = regTags[ra];
                 break;
             }
+            case LOP_NAMECALL:
+            {
+                if (FFlag::LuauCodegenDirectUserdataFlow)
+                {
+                    int ra = LUAU_INSN_A(*pc);
+                    int rb = LUAU_INSN_B(*pc);
+                    uint32_t kc = pc[1];
+
+                    bcType.a = regTags[rb];
+                    bcType.b = getBytecodeConstantTag(proto, kc);
+
+                    // While namecall might result in a callable table, we assume the function fast path
+                    regTags[ra] = LBC_TYPE_FUNCTION;
+
+                    // Namecall places source register into target + 1
+                    regTags[ra + 1] = bcType.a;
+
+                    bcType.result = LBC_TYPE_FUNCTION;
+                }
+                break;
+            }
             case LOP_GETGLOBAL:
             case LOP_SETGLOBAL:
             case LOP_CALL:
@@ -866,7 +889,6 @@ void analyzeBytecodeTypes(IrFunction& function)
             case LOP_COVERAGE:
             case LOP_GETIMPORT:
             case LOP_CAPTURE:
-            case LOP_NAMECALL:
             case LOP_PREPVARARGS:
             case LOP_GETVARARGS:
             case LOP_FORGPREP:

CodeGen/src/CodeBlockUnwind.cpp

@@ -163,6 +163,9 @@ bool isUnwindSupported()
 {
 #if defined(_WIN32) && defined(_M_X64)
     return true;
+#elif defined(__ANDROID__)
+    // Current unwind information is not compatible with Android
+    return false;
 #elif defined(__APPLE__) && defined(__aarch64__)
     char ver[256];
     size_t verLength = sizeof(ver);

CodeGen/src/CodeGenAssembly.cpp

@@ -122,7 +122,10 @@ static std::string getAssemblyImpl(AssemblyBuilder& build, const TValue* func, A
         if (stats && (stats->functionStatsFlags & FunctionStats_Enable))
         {
             FunctionStats functionStat;
-            functionStat.name = p->debugname ? getstr(p->debugname) : "";
+
+            // function name is empty for anonymous and pseudo top-level functions
+            // properly name pseudo top-level function because it will be compiled natively if it has loops
+            functionStat.name = p->debugname ? getstr(p->debugname) : p->bytecodeid == root->bytecodeid ? "[top level]" : "[anonymous]";
             functionStat.line = p->linedefined;
             functionStat.bcodeCount = getInstructionCount(p->code, p->sizecode);
             functionStat.irCount = unsigned(ir.function.instructions.size());

CodeGen/src/IrTranslation.cpp

@@ -13,6 +13,7 @@
 #include "ltm.h"
 
 LUAU_FASTFLAGVARIABLE(LuauCodegenLoadTVTag, false)
+LUAU_FASTFLAGVARIABLE(LuauCodegenDirectUserdataFlow, false)
 
 namespace Luau
 {
@@ -1230,6 +1231,14 @@ void translateInstGetTableKS(IrBuilder& build, const Instruction* pc, int pcpos)
         return;
     }
 
+    if (FFlag::LuauCodegenDirectUserdataFlow && bcTypes.a == LBC_TYPE_USERDATA)
+    {
+        build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TUSERDATA), build.vmExit(pcpos));
+
+        build.inst(IrCmd::FALLBACK_GETTABLEKS, build.constUint(pcpos), build.vmReg(ra), build.vmReg(rb), build.vmConst(aux));
+        return;
+    }
+
     IrOp fallback = build.block(IrBlockKind::Fallback);
 
     build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
@@ -1256,10 +1265,20 @@ void translateInstSetTableKS(IrBuilder& build, const Instruction* pc, int pcpos)
     int rb = LUAU_INSN_B(*pc);
     uint32_t aux = pc[1];
 
-    IrOp fallback = build.block(IrBlockKind::Fallback);
     BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
 
     IrOp tb = build.inst(IrCmd::LOAD_TAG, build.vmReg(rb));
+
+    if (FFlag::LuauCodegenDirectUserdataFlow && bcTypes.a == LBC_TYPE_USERDATA)
+    {
+        build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TUSERDATA), build.vmExit(pcpos));
+
+        build.inst(IrCmd::FALLBACK_SETTABLEKS, build.constUint(pcpos), build.vmReg(ra), build.vmReg(rb), build.vmConst(aux));
+        return;
+    }
+
+    IrOp fallback = build.block(IrBlockKind::Fallback);
+
     build.inst(IrCmd::CHECK_TAG, tb, build.constTag(LUA_TTABLE), bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
 
     IrOp vb = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
@@ -1370,12 +1389,31 @@ void translateInstNamecall(IrBuilder& build, const Instruction* pc, int pcpos)
     int rb = LUAU_INSN_B(*pc);
     uint32_t aux = pc[1];
 
+    BytecodeTypes bcTypes = build.function.getBytecodeTypesAt(pcpos);
+
+    if (FFlag::LuauCodegenDirectUserdataFlow && bcTypes.a == LBC_TYPE_VECTOR)
+    {
+        build.loadAndCheckTag(build.vmReg(rb), LUA_TVECTOR, build.vmExit(pcpos));
+
+        build.inst(IrCmd::FALLBACK_NAMECALL, build.constUint(pcpos), build.vmReg(ra), build.vmReg(rb), build.vmConst(aux));
+        return;
+    }
+
+    if (FFlag::LuauCodegenDirectUserdataFlow && bcTypes.a == LBC_TYPE_USERDATA)
+    {
+        build.loadAndCheckTag(build.vmReg(rb), LUA_TUSERDATA, build.vmExit(pcpos));
+
+        build.inst(IrCmd::FALLBACK_NAMECALL, build.constUint(pcpos), build.vmReg(ra), build.vmReg(rb), build.vmConst(aux));
+        return;
+    }
+
     IrOp next = build.blockAtInst(pcpos + getOpLength(LOP_NAMECALL));
     IrOp fallback = build.block(IrBlockKind::Fallback);
     IrOp firstFastPathSuccess = build.block(IrBlockKind::Internal);
     IrOp secondFastPath = build.block(IrBlockKind::Internal);
 
-    build.loadAndCheckTag(build.vmReg(rb), LUA_TTABLE, fallback);
+    build.loadAndCheckTag(
+        build.vmReg(rb), LUA_TTABLE, FFlag::LuauCodegenDirectUserdataFlow && bcTypes.a == LBC_TYPE_TABLE ? build.vmExit(pcpos) : fallback);
     IrOp table = build.inst(IrCmd::LOAD_POINTER, build.vmReg(rb));
 
     CODEGEN_ASSERT(build.function.proto);

Common/include/Luau/ExperimentalFlags.h

@@ -11,9 +11,9 @@ inline bool isFlagExperimental(const char* flag)
     // Flags in this list are disabled by default in various command-line tools. They may have behavior that is not fully final,
     // or critical bugs that are found after the code has been submitted.
     static const char* const kList[] = {
-        "LuauInstantiateInSubtyping",          // requires some fixes to lua-apps code
+        "LuauInstantiateInSubtyping",      // requires some fixes to lua-apps code
-        "LuauTinyControlFlowAnalysis",         // waiting for updates to packages depended by internal builtin plugins
+        "LuauTinyControlFlowAnalysis",     // waiting for updates to packages depended by internal builtin plugins
-        "LuauFixIndexerSubtypingOrdering",     // requires some small fixes to lua-apps code since this fixes a false negative
+        "LuauFixIndexerSubtypingOrdering", // requires some small fixes to lua-apps code since this fixes a false negative
         // makes sure we always have at least one entry
         nullptr,
     };

LICENSE.txt

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2019-2023 Roblox Corporation
+Copyright (c) 2019-2024 Roblox Corporation
 Copyright (c) 1994–2019 Lua.org, PUC-Rio.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of

VM/src/lgc.cpp

@@ -929,7 +929,7 @@ static size_t gcstep(lua_State* L, size_t limit)
     {
         while (g->sweepgcopage && cost < limit)
         {
-            lua_Page* next = luaM_getnextgcopage(g->sweepgcopage); // page sweep might destroy the page
+            lua_Page* next = luaM_getnextpage(g->sweepgcopage); // page sweep might destroy the page
 
             int steps = sweepgcopage(L, g->sweepgcopage);
 

VM/src/lmem.cpp

@@ -196,9 +196,9 @@ struct lua_Page
     lua_Page* prev;
     lua_Page* next;
 
-    // list of all gco pages
+    // list of all pages
-    lua_Page* gcolistprev;
+    lua_Page* listprev;
-    lua_Page* gcolistnext;
+    lua_Page* listnext;
 
     int pageSize;  // page size in bytes, including page header
     int blockSize; // block size in bytes, including block header (for non-GCO)
@@ -220,7 +220,7 @@ l_noret luaM_toobig(lua_State* L)
     luaG_runerror(L, "memory allocation error: block too big");
 }
 
-static lua_Page* newpage(lua_State* L, lua_Page** gcopageset, int pageSize, int blockSize, int blockCount)
+static lua_Page* newpage(lua_State* L, lua_Page** pageset, int pageSize, int blockSize, int blockCount)
 {
     global_State* g = L->global;
 
@@ -236,8 +236,8 @@ static lua_Page* newpage(lua_State* L, lua_Page** gcopageset, int pageSize, int
     page->prev = NULL;
     page->next = NULL;
 
-    page->gcolistprev = NULL;
+    page->listprev = NULL;
-    page->gcolistnext = NULL;
+    page->listnext = NULL;
 
     page->pageSize = pageSize;
     page->blockSize = blockSize;
@@ -249,12 +249,12 @@ static lua_Page* newpage(lua_State* L, lua_Page** gcopageset, int pageSize, int
     page->freeNext = (blockCount - 1) * blockSize;
     page->busyBlocks = 0;
 
-    if (gcopageset)
+    if (pageset)
     {
-        page->gcolistnext = *gcopageset;
+        page->listnext = *pageset;
-        if (page->gcolistnext)
+        if (page->listnext)
-            page->gcolistnext->gcolistprev = page;
+            page->listnext->listprev = page;
-        *gcopageset = page;
+        *pageset = page;
     }
 
     return page;
@@ -263,7 +263,7 @@ static lua_Page* newpage(lua_State* L, lua_Page** gcopageset, int pageSize, int
 // this is part of a cold path in newblock and newgcoblock
 // it is marked as noinline to prevent it from being inlined into those functions
 // if it is inlined, then the compiler may determine those functions are "too big" to be profitably inlined, which results in reduced performance
-LUAU_NOINLINE static lua_Page* newclasspage(lua_State* L, lua_Page** freepageset, lua_Page** gcopageset, uint8_t sizeClass, bool storeMetadata)
+LUAU_NOINLINE static lua_Page* newclasspage(lua_State* L, lua_Page** freepageset, lua_Page** pageset, uint8_t sizeClass, bool storeMetadata)
 {
     if (FFlag::LuauExtendedSizeClasses)
     {
@@ -272,7 +272,7 @@ LUAU_NOINLINE static lua_Page* newclasspage(lua_State* L, lua_Page** freepageset
         int blockSize = sizeOfClass + (storeMetadata ? kBlockHeader : 0);
         int blockCount = (pageSize - offsetof(lua_Page, data)) / blockSize;
 
-        lua_Page* page = newpage(L, gcopageset, pageSize, blockSize, blockCount);
+        lua_Page* page = newpage(L, pageset, pageSize, blockSize, blockCount);
 
         // prepend a page to page freelist (which is empty because we only ever allocate a new page when it is!)
         LUAU_ASSERT(!freepageset[sizeClass]);
@@ -285,7 +285,7 @@ LUAU_NOINLINE static lua_Page* newclasspage(lua_State* L, lua_Page** freepageset
         int blockSize = kSizeClassConfig.sizeOfClass[sizeClass] + (storeMetadata ? kBlockHeader : 0);
         int blockCount = (kSmallPageSize - offsetof(lua_Page, data)) / blockSize;
 
-        lua_Page* page = newpage(L, gcopageset, kSmallPageSize, blockSize, blockCount);
+        lua_Page* page = newpage(L, pageset, kSmallPageSize, blockSize, blockCount);
 
         // prepend a page to page freelist (which is empty because we only ever allocate a new page when it is!)
         LUAU_ASSERT(!freepageset[sizeClass]);
@@ -295,27 +295,27 @@ LUAU_NOINLINE static lua_Page* newclasspage(lua_State* L, lua_Page** freepageset
     }
 }
 
-static void freepage(lua_State* L, lua_Page** gcopageset, lua_Page* page)
+static void freepage(lua_State* L, lua_Page** pageset, lua_Page* page)
 {
     global_State* g = L->global;
 
-    if (gcopageset)
+    if (pageset)
     {
         // remove page from alllist
-        if (page->gcolistnext)
+        if (page->listnext)
-            page->gcolistnext->gcolistprev = page->gcolistprev;
+            page->listnext->listprev = page->listprev;
 
-        if (page->gcolistprev)
+        if (page->listprev)
-            page->gcolistprev->gcolistnext = page->gcolistnext;
+            page->listprev->listnext = page->listnext;
-        else if (*gcopageset == page)
+        else if (*pageset == page)
-            *gcopageset = page->gcolistnext;
+            *pageset = page->listnext;
     }
 
     // so long
     (*g->frealloc)(g->ud, page, page->pageSize, 0);
 }
 
-static void freeclasspage(lua_State* L, lua_Page** freepageset, lua_Page** gcopageset, lua_Page* page, uint8_t sizeClass)
+static void freeclasspage(lua_State* L, lua_Page** freepageset, lua_Page** pageset, lua_Page* page, uint8_t sizeClass)
 {
     // remove page from freelist
     if (page->next)
@@ -326,7 +326,7 @@ static void freeclasspage(lua_State* L, lua_Page** freepageset, lua_Page** gcopa
     else if (freepageset[sizeClass] == page)
         freepageset[sizeClass] = page->next;
 
-    freepage(L, gcopageset, page);
+    freepage(L, pageset, page);
 }
 
 static void* newblock(lua_State* L, int sizeClass)
@@ -645,9 +645,9 @@ void luaM_getpageinfo(lua_Page* page, int* pageBlocks, int* busyBlocks, int* blo
     *pageSize = page->pageSize;
 }
 
-lua_Page* luaM_getnextgcopage(lua_Page* page)
+lua_Page* luaM_getnextpage(lua_Page* page)
 {
-    return page->gcolistnext;
+    return page->listnext;
 }
 
 void luaM_visitpage(lua_Page* page, void* context, bool (*visitor)(void* context, lua_Page* page, GCObject* gco))
@@ -684,7 +684,7 @@ void luaM_visitgco(lua_State* L, void* context, bool (*visitor)(void* context, l
 
     for (lua_Page* curr = g->allgcopages; curr;)
     {
-        lua_Page* next = curr->gcolistnext; // block visit might destroy the page
+        lua_Page* next = curr->listnext; // block visit might destroy the page
 
         luaM_visitpage(curr, context, visitor);
 

VM/src/lmem.h

@@ -27,7 +27,7 @@ LUAI_FUNC l_noret luaM_toobig(lua_State* L);
 
 LUAI_FUNC void luaM_getpagewalkinfo(lua_Page* page, char** start, char** end, int* busyBlocks, int* blockSize);
 LUAI_FUNC void luaM_getpageinfo(lua_Page* page, int* pageBlocks, int* busyBlocks, int* blockSize, int* pageSize);
-LUAI_FUNC lua_Page* luaM_getnextgcopage(lua_Page* page);
+LUAI_FUNC lua_Page* luaM_getnextpage(lua_Page* page);
 
 LUAI_FUNC void luaM_visitpage(lua_Page* page, void* context, bool (*visitor)(void* context, lua_Page* page, GCObject* gco));
 LUAI_FUNC void luaM_visitgco(lua_State* L, void* context, bool (*visitor)(void* context, lua_Page* page, GCObject* gco));

VM/src/ltablib.cpp

@@ -3,6 +3,7 @@
 #include "lualib.h"
 
 #include "lapi.h"
+#include "lnumutils.h"
 #include "lstate.h"
 #include "ltable.h"
 #include "lstring.h"
@@ -10,6 +11,8 @@
 #include "ldebug.h"
 #include "lvm.h"
 
+LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauFastCrossTableMove, false)
+
 static int foreachi(lua_State* L)
 {
     luaL_checktype(L, 1, LUA_TTABLE);
@@ -112,6 +115,68 @@ static void moveelements(lua_State* L, int srct, int dstt, int f, int e, int t)
 
         luaC_barrierfast(L, dst);
     }
+    else if (DFFlag::LuauFastCrossTableMove && dst != src)
+    {
+        // compute the array slice we have to copy over
+        int slicestart = f < 1 ? 0 : (f > src->sizearray ? src->sizearray : f - 1);
+        int sliceend = e < 1 ? 0 : (e > src->sizearray ? src->sizearray : e);
+        LUAU_ASSERT(slicestart <= sliceend);
+
+        int slicecount = sliceend - slicestart;
+
+        if (slicecount > 0)
+        {
+            // array slice starting from INT_MIN is impossible, so we don't have to worry about int overflow
+            int dstslicestart = f < 1 ? -f + 1 : 0;
+
+            // copy over the slice
+            for (int i = 0; i < slicecount; ++i)
+            {
+                lua_rawgeti(L, srct, slicestart + i + 1);
+                lua_rawseti(L, dstt, dstslicestart + t + i);
+            }
+        }
+
+        // copy the remaining elements that could be in the hash part
+        int hashpartsize = sizenode(src);
+
+        // select the strategy with the least amount of steps
+        if (n <= hashpartsize)
+        {
+            for (int i = 0; i < n; ++i)
+            {
+                // skip array slice elements that were already copied over
+                if (cast_to(unsigned int, f + i - 1) < cast_to(unsigned int, src->sizearray))
+                    continue;
+
+                lua_rawgeti(L, srct, f + i);
+                lua_rawseti(L, dstt, t + i);
+            }
+        }
+        else
+        {
+            // source and destination tables are different, so we can iterate over source hash part directly
+            int i = hashpartsize;
+
+            while (i--)
+            {
+                LuaNode* node = gnode(src, i);
+                if (ttisnumber(gkey(node)))
+                {
+                    double n = nvalue(gkey(node));
+
+                    int k;
+                    luai_num2int(k, n);
+
+                    if (luai_numeq(cast_num(k), n) && k >= f && k <= e)
+                    {
+                        lua_rawgeti(L, srct, k);
+                        lua_rawseti(L, dstt, t - f + k);
+                    }
+                }
+            }
+        }
+    }
     else
     {
         if (t > e || t <= f || dst != src)

tests/Autocomplete.test.cpp

@@ -145,36 +145,38 @@ struct ACBuiltinsFixture : ACFixtureImpl<BuiltinsFixture>
 {
 };
 
-#define LUAU_CHECK_HAS_KEY(map, key) do                               \
+#define LUAU_CHECK_HAS_KEY(map, key) \
-    {                                                                 \
+    do \
-        auto&& _m = (map);                                            \
+    { \
-        auto&& _k = (key);                                            \
+        auto&& _m = (map); \
-        const size_t count = _m.count(_k);                            \
+        auto&& _k = (key); \
+        const size_t count = _m.count(_k); \
         CHECK_MESSAGE(count, "Map should have key \"" << _k << "\""); \
-        if (!count)                                                   \
+        if (!count) \
-        {                                                             \
+        { \
-            MESSAGE("Keys: (count " << _m.size() << ")");             \
+            MESSAGE("Keys: (count " << _m.size() << ")"); \
-            for (const auto& [k, v]: _m)                              \
+            for (const auto& [k, v] : _m) \
-            {                                                         \
+            { \
-                MESSAGE("\tkey: " << k);                              \
+                MESSAGE("\tkey: " << k); \
-            }                                                         \
+            } \
-        }                                                             \
+        } \
     } while (false)
 
-#define LUAU_CHECK_HAS_NO_KEY(map, key) do                                 \
+#define LUAU_CHECK_HAS_NO_KEY(map, key) \
-    {                                                                      \
+    do \
-        auto&& _m = (map);                                                 \
+    { \
-        auto&& _k = (key);                                                 \
+        auto&& _m = (map); \
-        const size_t count = _m.count(_k);                                 \
+        auto&& _k = (key); \
+        const size_t count = _m.count(_k); \
         CHECK_MESSAGE(!count, "Map should not have key \"" << _k << "\""); \
-        if (count)                                                         \
+        if (count) \
-        {                                                                  \
+        { \
-            MESSAGE("Keys: (count " << _m.size() << ")");                  \
+            MESSAGE("Keys: (count " << _m.size() << ")"); \
-            for (const auto& [k, v]: _m)                                   \
+            for (const auto& [k, v] : _m) \
-            {                                                              \
+            { \
-                MESSAGE("\tkey: " << k);                                   \
+                MESSAGE("\tkey: " << k); \
-            }                                                              \
+            } \
-        }                                                                  \
+        } \
     } while (false)
 
 TEST_SUITE_BEGIN("AutocompleteTest");

tests/ClassFixture.cpp

@@ -29,8 +29,7 @@ ClassFixture::ClassFixture()
     };
 
     getMutable<ClassType>(connectionType)->props = {
-        {"Connect", {makeFunction(arena, connectionType, {makeFunction(arena, nullopt, {baseClassInstanceType}, {})}, {})}}
+        {"Connect", {makeFunction(arena, connectionType, {makeFunction(arena, nullopt, {baseClassInstanceType}, {})}, {})}}};
-    };
 
     TypeId baseClassType = arena.addType(ClassType{"BaseClass", {}, nullopt, nullopt, {}, {}, "Test"});
     getMutable<ClassType>(baseClassType)->props = {
@@ -103,13 +102,10 @@ ClassFixture::ClassFixture()
     };
     getMutable<TableType>(vector2MetaType)->props = {
         {"__add", {makeFunction(arena, nullopt, {vector2InstanceType, vector2InstanceType}, {vector2InstanceType})}},
-        {"__mul", {
+        {"__mul", {arena.addType(IntersectionType{{
-            arena.addType(IntersectionType{{
+                      makeFunction(arena, vector2InstanceType, {vector2InstanceType}, {vector2InstanceType}),
-                makeFunction(arena, vector2InstanceType, {vector2InstanceType}, {vector2InstanceType}),
+                      makeFunction(arena, vector2InstanceType, {builtinTypes->numberType}, {vector2InstanceType}),
-                makeFunction(arena, vector2InstanceType, {builtinTypes->numberType}, {vector2InstanceType}),
+                  }})}}};
-            }})
-        }}
-    };
     globals.globalScope->exportedTypeBindings["Vector2"] = TypeFun{{}, vector2InstanceType};
     addGlobalBinding(globals, "Vector2", vector2Type, "@test");
 

tests/Conformance.test.cpp

@@ -36,6 +36,7 @@ LUAU_FASTFLAG(LuauCompileRepeatUntilSkippedLocals)
 LUAU_FASTFLAG(LuauCodegenInferNumTag)
 LUAU_FASTFLAG(LuauCodegenDetailedCompilationResult)
 LUAU_FASTFLAG(LuauCodegenCheckTruthyFormB)
+LUAU_DYNAMIC_FASTFLAG(LuauFastCrossTableMove)
 
 static lua_CompileOptions defaultOptions()
 {
@@ -415,6 +416,8 @@ TEST_CASE("Sort")
 
 TEST_CASE("Move")
 {
+    ScopedFastFlag luauFastCrossTableMove{DFFlag::LuauFastCrossTableMove, true};
+
     runConformance("move.lua");
 }
 
@@ -1837,7 +1840,7 @@ TEST_CASE("DebugApi")
     lua_pushnumber(L, 10);
 
     lua_Debug ar;
-    CHECK(lua_getinfo(L, -1, "f", &ar) == 0); // number is not a function
+    CHECK(lua_getinfo(L, -1, "f", &ar) == 0);  // number is not a function
     CHECK(lua_getinfo(L, -10, "f", &ar) == 0); // not on stack
 }
 
@@ -2174,8 +2177,7 @@ TEST_CASE("HugeFunctionLoadFailure")
     static size_t largeAllocationToFail = 0;
     static size_t largeAllocationCount = 0;
 
-    const auto testAllocate = [](void* ud, void* ptr, size_t osize, size_t nsize) -> void*
+    const auto testAllocate = [](void* ud, void* ptr, size_t osize, size_t nsize) -> void* {
-    {
         if (nsize == 0)
         {
             free(ptr);

tests/Instantiation2.test.cpp

@@ -19,12 +19,10 @@ TEST_CASE_FIXTURE(Fixture, "weird_cyclic_instantiation")
 
     TypeId genericT = arena.addType(GenericType{"T"});
 
-    TypeId idTy = arena.addType(FunctionType{
+    TypeId idTy = arena.addType(FunctionType{/* generics */ {genericT},
-        /* generics */ {genericT},
         /* genericPacks */ {},
         /* argTypes */ arena.addTypePack({genericT}),
-        /* retTypes */ arena.addTypePack({genericT})
+        /* retTypes */ arena.addTypePack({genericT})});
-    });
 
     DenseHashMap<TypeId, TypeId> genericSubstitutions{nullptr};
     DenseHashMap<TypePackId, TypePackId> genericPackSubstitutions{nullptr};

tests/IrLowering.test.cpp

@@ -14,6 +14,7 @@
 
 LUAU_FASTFLAG(LuauCodegenRemoveDeadStores5)
 LUAU_FASTFLAG(LuauCodegenLoadTVTag)
+LUAU_FASTFLAG(LuauCodegenDirectUserdataFlow)
 
 static std::string getCodegenAssembly(const char* source)
 {
@@ -402,7 +403,7 @@ local function vecrcp(a: vector)
     return vector(1, 2, 3) + a
 end
 )"),
-R"(
+        R"(
 ; function vecrcp($arg0) line 2
 bb_0:
   CHECK_TAG R0, tvector, exit(entry)
@@ -420,4 +421,128 @@ bb_bytecode_1:
 )");
 }
 
+TEST_CASE("VectorNamecall")
+{
+    ScopedFastFlag luauCodegenDirectUserdataFlow{FFlag::LuauCodegenDirectUserdataFlow, true};
+
+    CHECK_EQ("\n" + getCodegenAssembly(R"(
+local function abs(a: vector)
+    return a:Abs()
+end
+)"),
+        R"(
+; function abs($arg0) line 2
+bb_0:
+  CHECK_TAG R0, tvector, exit(entry)
+  JUMP bb_2
+bb_2:
+  JUMP bb_bytecode_1
+bb_bytecode_1:
+  FALLBACK_NAMECALL 0u, R1, R0, K0
+  INTERRUPT 2u
+  SET_SAVEDPC 3u
+  CALL R1, 1i, -1i
+  INTERRUPT 3u
+  RETURN R1, -1i
+)");
+}
+
+TEST_CASE("UserDataGetIndex")
+{
+    ScopedFastFlag luauCodegenDirectUserdataFlow{FFlag::LuauCodegenDirectUserdataFlow, true};
+
+    CHECK_EQ("\n" + getCodegenAssembly(R"(
+local function getxy(a: Point)
+    return a.x + a.y
+end
+)"),
+        R"(
+; function getxy($arg0) line 2
+bb_0:
+  CHECK_TAG R0, tuserdata, exit(entry)
+  JUMP bb_2
+bb_2:
+  JUMP bb_bytecode_1
+bb_bytecode_1:
+  FALLBACK_GETTABLEKS 0u, R2, R0, K0
+  FALLBACK_GETTABLEKS 2u, R3, R0, K1
+  CHECK_TAG R2, tnumber, bb_fallback_3
+  CHECK_TAG R3, tnumber, bb_fallback_3
+  %14 = LOAD_DOUBLE R2
+  %16 = ADD_NUM %14, R3
+  STORE_DOUBLE R1, %16
+  STORE_TAG R1, tnumber
+  JUMP bb_4
+bb_4:
+  INTERRUPT 5u
+  RETURN R1, 1i
+)");
+}
+
+TEST_CASE("UserDataSetIndex")
+{
+    ScopedFastFlag luauCodegenDirectUserdataFlow{FFlag::LuauCodegenDirectUserdataFlow, true};
+
+    CHECK_EQ("\n" + getCodegenAssembly(R"(
+local function setxy(a: Point)
+    a.x = 3
+    a.y = 4
+end
+)"),
+        R"(
+; function setxy($arg0) line 2
+bb_0:
+  CHECK_TAG R0, tuserdata, exit(entry)
+  JUMP bb_2
+bb_2:
+  JUMP bb_bytecode_1
+bb_bytecode_1:
+  STORE_DOUBLE R1, 3
+  STORE_TAG R1, tnumber
+  FALLBACK_SETTABLEKS 1u, R1, R0, K0
+  STORE_DOUBLE R1, 4
+  FALLBACK_SETTABLEKS 4u, R1, R0, K1
+  INTERRUPT 6u
+  RETURN R0, 0i
+)");
+}
+
+TEST_CASE("UserDataNamecall")
+{
+    ScopedFastFlag luauCodegenDirectUserdataFlow{FFlag::LuauCodegenDirectUserdataFlow, true};
+
+    CHECK_EQ("\n" + getCodegenAssembly(R"(
+local function getxy(a: Point)
+    return a:GetX() + a:GetY()
+end
+)"),
+        R"(
+; function getxy($arg0) line 2
+bb_0:
+  CHECK_TAG R0, tuserdata, exit(entry)
+  JUMP bb_2
+bb_2:
+  JUMP bb_bytecode_1
+bb_bytecode_1:
+  FALLBACK_NAMECALL 0u, R2, R0, K0
+  INTERRUPT 2u
+  SET_SAVEDPC 3u
+  CALL R2, 1i, 1i
+  FALLBACK_NAMECALL 3u, R3, R0, K1
+  INTERRUPT 5u
+  SET_SAVEDPC 6u
+  CALL R3, 1i, 1i
+  CHECK_TAG R2, tnumber, bb_fallback_3
+  CHECK_TAG R3, tnumber, bb_fallback_3
+  %20 = LOAD_DOUBLE R2
+  %22 = ADD_NUM %20, R3
+  STORE_DOUBLE R1, %22
+  STORE_TAG R1, tnumber
+  JUMP bb_4
+bb_4:
+  INTERRUPT 7u
+  RETURN R1, 1i
+)");
+}
+
 TEST_SUITE_END();

tests/Normalize.test.cpp

@@ -11,7 +11,9 @@
 #include "Luau/BuiltinDefinitions.h"
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
-LUAU_FASTFLAG(LuauFixNormalizeCaching);
+LUAU_FASTFLAG(LuauFixNormalizeCaching)
+LUAU_FASTFLAG(LuauNormalizeNotUnknownIntersection)
+LUAU_FASTFLAG(LuauFixCyclicUnionsOfIntersections);
 
 using namespace Luau;
 
@@ -797,6 +799,36 @@ TEST_CASE_FIXTURE(NormalizeFixture, "cyclic_union")
     CHECK("number" == toString(normalizer.typeFromNormal(*nt)));
 }
 
+TEST_CASE_FIXTURE(NormalizeFixture, "cyclic_union_of_intersection")
+{
+    ScopedFastFlag sff{FFlag::LuauFixCyclicUnionsOfIntersections, true};
+
+    // t1 where t1 = (string & t1) | string
+    TypeId boundTy = arena.addType(BlockedType{});
+    TypeId intersectTy = arena.addType(IntersectionType{{builtinTypes->stringType, boundTy}});
+    TypeId unionTy = arena.addType(UnionType{{builtinTypes->stringType, intersectTy}});
+    asMutable(boundTy)->reassign(Type{BoundType{unionTy}});
+
+    std::shared_ptr<const NormalizedType> nt = normalizer.normalize(unionTy);
+
+    CHECK("string" == toString(normalizer.typeFromNormal(*nt)));
+}
+
+TEST_CASE_FIXTURE(NormalizeFixture, "cyclic_intersection_of_unions")
+{
+    ScopedFastFlag sff{FFlag::LuauFixCyclicUnionsOfIntersections, true};
+
+    // t1 where t1 = (string & t1) | string
+    TypeId boundTy = arena.addType(BlockedType{});
+    TypeId unionTy = arena.addType(UnionType{{builtinTypes->stringType, boundTy}});
+    TypeId intersectionTy = arena.addType(IntersectionType{{builtinTypes->stringType, unionTy}});
+    asMutable(boundTy)->reassign(Type{BoundType{intersectionTy}});
+
+    std::shared_ptr<const NormalizedType> nt = normalizer.normalize(intersectionTy);
+
+    CHECK("string" == toString(normalizer.typeFromNormal(*nt)));
+}
+
 TEST_CASE_FIXTURE(NormalizeFixture, "crazy_metatable")
 {
     CHECK("never" == toString(normal("Mt<{}, number> & Mt<{}, string>")));
@@ -919,4 +951,15 @@ TEST_CASE_FIXTURE(NormalizeFixture, "non_final_types_can_be_normalized_but_are_n
     CHECK(na1 != na2);
 }
 
+TEST_CASE_FIXTURE(NormalizeFixture, "intersect_with_not_unknown")
+{
+    ScopedFastFlag sff{FFlag::LuauNormalizeNotUnknownIntersection, true};
+
+    TypeId notUnknown = arena.addType(NegationType{builtinTypes->unknownType});
+    TypeId type = arena.addType(IntersectionType{{builtinTypes->numberType, notUnknown}});
+    std::shared_ptr<const NormalizedType> normalized = normalizer.normalize(type);
+
+    CHECK("never" == toString(normalizer.typeFromNormal(*normalized.get())));
+}
+
 TEST_SUITE_END();

tests/Subtyping.test.cpp

@@ -225,9 +225,9 @@ struct SubtypeFixture : Fixture
                                    });
 
     TypeId readOnlyVec2Class = cls("ReadOnlyVec2", {
-        {"X", Property::readonly(builtinTypes->numberType)},
+                                                       {"X", Property::readonly(builtinTypes->numberType)},
-        {"Y", Property::readonly(builtinTypes->numberType)},
+                                                       {"Y", Property::readonly(builtinTypes->numberType)},
-    });
+                                                   });
 
     // "hello" | "hello"
     TypeId helloOrHelloType = arena.addType(UnionType{{helloType, helloType}});
@@ -1285,6 +1285,30 @@ TEST_CASE_FIXTURE(SubtypeFixture, "<T>({ x: T }) -> T <: ({ method: <T>({ x: T }
     CHECK_IS_SUBTYPE(tableToPropType, otherType);
 }
 
+TEST_CASE_FIXTURE(SubtypeFixture, "subtyping_reasonings_to_follow_a_reduced_type_family_instance")
+{
+    TypeId longTy = arena.addType(UnionType{{builtinTypes->booleanType, builtinTypes->bufferType, builtinTypes->classType, builtinTypes->functionType,
+        builtinTypes->numberType, builtinTypes->stringType, builtinTypes->tableType, builtinTypes->threadType}});
+    TypeId tblTy = tbl({{"depth", builtinTypes->unknownType}});
+    TypeId combined = meet(longTy, tblTy);
+    TypeId subTy = arena.addType(TypeFamilyInstanceType{NotNull{&builtinTypeFamilies.unionFamily}, {combined, builtinTypes->neverType}, {}});
+    TypeId superTy = builtinTypes->neverType;
+    SubtypingResult result = isSubtype(subTy, superTy);
+    CHECK(!result.isSubtype);
+
+    for (const SubtypingReasoning& reasoning : result.reasoning)
+    {
+        if (reasoning.subPath.empty() && reasoning.superPath.empty())
+            continue;
+
+        std::optional<TypeOrPack> optSubLeaf = traverse(subTy, reasoning.subPath, builtinTypes);
+        std::optional<TypeOrPack> optSuperLeaf = traverse(superTy, reasoning.superPath, builtinTypes);
+
+        if (!optSubLeaf || !optSuperLeaf)
+            CHECK(false);
+    }
+}
+
 TEST_SUITE_END();
 
 TEST_SUITE_BEGIN("Subtyping.Subpaths");

tests/ToString.test.cpp

@@ -944,7 +944,8 @@ TEST_CASE_FIXTURE(Fixture, "tostring_error_mismatch")
 
     std::string expected;
     if (FFlag::DebugLuauDeferredConstraintResolution)
-        expected = R"(Type pack '{ a: number, b: string, c: { d: string } }' could not be converted into '{ a: number, b: string, c: { d: number } }'; at [0][read "c"][read "d"], string is not exactly number)";
+        expected =
+            R"(Type pack '{ a: number, b: string, c: { d: string } }' could not be converted into '{ a: number, b: string, c: { d: number } }'; at [0][read "c"][read "d"], string is not exactly number)";
     else
         expected = R"(Type
     '{ a: number, b: string, c: { d: string } }'
@@ -1013,15 +1014,8 @@ TEST_CASE_FIXTURE(Fixture, "cycle_rooted_in_a_pack")
     TypePack* packPtr = getMutable<TypePack>(thePack);
     REQUIRE(packPtr);
 
-    const TableType::Props theProps = {
+    const TableType::Props theProps = {{"BaseField", Property::readonly(builtinTypes->unknownType)},
-        {"BaseField", Property::readonly(builtinTypes->unknownType)},
+        {"BaseMethod", Property::readonly(arena.addType(FunctionType{thePack, arena.addTypePack({})}))}};
-        {"BaseMethod", Property::readonly(arena.addType(
-            FunctionType{
-                thePack,
-                arena.addTypePack({})
-            }
-        ))}
-    };
 
     TypeId theTable = arena.addType(TableType{theProps, {}, TypeLevel{}, TableState::Sealed});
 

tests/TypeInfer.aliases.test.cpp

@@ -221,7 +221,8 @@ TEST_CASE_FIXTURE(Fixture, "dependent_generic_aliases")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    const std::string expected = R"(Type '{ t: { v: string } }' could not be converted into 'U<number>'; at [read "t"][read "v"], string is not exactly number)";
+    const std::string expected =
+        R"(Type '{ t: { v: string } }' could not be converted into 'U<number>'; at [read "t"][read "v"], string is not exactly number)";
 
     CHECK(result.errors[0].location == Location{{4, 31}, {4, 52}});
     CHECK_EQ(expected, toString(result.errors[0]));

tests/TypeInfer.builtins.test.cpp

@@ -10,7 +10,6 @@ using namespace Luau;
 
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 LUAU_FASTFLAG(LuauAlwaysCommitInferencesOfFunctionCalls);
-LUAU_FASTFLAG(LuauSetMetatableOnUnionsOfTables);
 
 TEST_SUITE_BEGIN("BuiltinTests");
 
@@ -371,8 +370,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_unpacks_arg_types_correctly")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "setmetatable_on_union_of_tables")
 {
-    ScopedFastFlag sff{FFlag::LuauSetMetatableOnUnionsOfTables, true};
-
     CheckResult result = check(R"(
         type A = {tag: "A", x: number}
         type B = {tag: "B", y: string}

tests/TypeInfer.classes.test.cpp

@@ -648,32 +648,20 @@ TEST_CASE_FIXTURE(Fixture, "read_write_class_properties")
     unfreeze(arena);
 
     TypeId instanceType = arena.addType(ClassType{"Instance", {}, nullopt, nullopt, {}, {}, "Test"});
-    getMutable<ClassType>(instanceType)->props = {
+    getMutable<ClassType>(instanceType)->props = {{"Parent", Property::rw(instanceType)}};
-        {"Parent", Property::rw(instanceType)}
-    };
 
     //
 
     TypeId workspaceType = arena.addType(ClassType{"Workspace", {}, nullopt, nullopt, {}, {}, "Test"});
 
-    TypeId scriptType = arena.addType(ClassType{
+    TypeId scriptType =
-        "Script", {
+        arena.addType(ClassType{"Script", {{"Parent", Property::rw(workspaceType, instanceType)}}, instanceType, nullopt, {}, {}, "Test"});
-            {"Parent", Property::rw(workspaceType, instanceType)}
-        },
-        instanceType, nullopt, {}, {}, "Test"
-    });
 
-    TypeId partType = arena.addType(ClassType{
+    TypeId partType = arena.addType(
-        "Part", {
+        ClassType{"Part", {{"BrickColor", Property::rw(builtinTypes->stringType)}, {"Parent", Property::rw(workspaceType, instanceType)}},
-            {"BrickColor", Property::rw(builtinTypes->stringType)},
+            instanceType, nullopt, {}, {}, "Test"});
-            {"Parent", Property::rw(workspaceType, instanceType)}
-        },
-        instanceType, nullopt, {}, {}, "Test"});
 
-    getMutable<ClassType>(workspaceType)->props = {
+    getMutable<ClassType>(workspaceType)->props = {{"Script", Property::readonly(scriptType)}, {"Part", Property::readonly(partType)}};
-        {"Script", Property::readonly(scriptType)},
-        {"Part", Property::readonly(partType)}
-    };
 
     frontend.globals.globalScope->bindings[frontend.globals.globalNames.names->getOrAdd("script")] = Binding{scriptType};
 
@@ -703,7 +691,8 @@ TEST_CASE_FIXTURE(ClassFixture, "cannot_index_a_class_with_no_indexer")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    CHECK_MESSAGE(get<DynamicPropertyLookupOnClassesUnsafe>(result.errors[0]), "Expected DynamicPropertyLookupOnClassesUnsafe but got " << result.errors[0]);
+    CHECK_MESSAGE(
+        get<DynamicPropertyLookupOnClassesUnsafe>(result.errors[0]), "Expected DynamicPropertyLookupOnClassesUnsafe but got " << result.errors[0]);
 
     CHECK(builtinTypes->errorType == requireType("c"));
 }

tests/TypeInfer.functions.test.cpp

@@ -20,6 +20,8 @@ LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 LUAU_FASTFLAG(LuauAlwaysCommitInferencesOfFunctionCalls);
 LUAU_FASTINT(LuauTarjanChildLimit);
 
+LUAU_DYNAMIC_FASTFLAG(LuauImproveNonFunctionCallError)
+
 TEST_SUITE_BEGIN("TypeInferFunctions");
 
 TEST_CASE_FIXTURE(Fixture, "general_case_table_literal_blocks")
@@ -2129,10 +2131,20 @@ TEST_CASE_FIXTURE(Fixture, "attempt_to_call_an_intersection_of_tables")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    if (FFlag::DebugLuauDeferredConstraintResolution)
+    if (DFFlag::LuauImproveNonFunctionCallError)
-        CHECK_EQ(toString(result.errors[0]), "Cannot call non-function { x: number } & { y: string }");
+    {
+        if (FFlag::DebugLuauDeferredConstraintResolution)
+            CHECK_EQ(toString(result.errors[0]), "Cannot call a value of type { x: number } & { y: string }");
+        else
+            CHECK_EQ(toString(result.errors[0]), "Cannot call a value of type {| x: number |}");
+    }
     else
-        CHECK_EQ(toString(result.errors[0]), "Cannot call non-function {| x: number |}");
+    {
+        if (FFlag::DebugLuauDeferredConstraintResolution)
+            CHECK_EQ(toString(result.errors[0]), "Cannot call non-function { x: number } & { y: string }");
+        else
+            CHECK_EQ(toString(result.errors[0]), "Cannot call non-function {| x: number |}");
+    }
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "attempt_to_call_an_intersection_of_tables_with_call_metamethod")
@@ -2535,4 +2547,54 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "function_definition_in_a_do_block_with_globa
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "fuzzer_alias_global_function_doesnt_hit_nil_assert")
+{
+    CheckResult result = check(R"(
+function _()
+end
+local function l0()
+    function _()
+    end
+end
+_ = _
+)");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "fuzzer_bug_missing_follow_causes_assertion")
+{
+    CheckResult result = check(R"(
+local _ = ({_=function()
+return _
+end,}),true,_[_()]
+for l0=_[_[_[`{function(l0)
+end}`]]],_[_.n6[_[_.n6]]],_[_[_.n6[_[_.n6]]]] do
+_ += if _ then ""
+end
+return _
+)");
+}
+
+TEST_CASE_FIXTURE(Fixture, "cannot_call_union_of_functions")
+{
+    CheckResult result = check(R"(
+        local f: (() -> ()) | (() -> () -> ()) = nil :: any
+        f()
+    )");
+
+    LUAU_REQUIRE_ERROR_COUNT(1, result);
+
+    if (DFFlag::LuauImproveNonFunctionCallError)
+    {
+        std::string expected = R"(Cannot call a value of the union type:
+  | () -> ()
+  | () -> () -> ()
+We are unable to determine the appropriate result type for such a call.)";
+
+        CHECK(expected == toString(result.errors[0]));
+    }
+    else
+        CHECK("Cannot call non-function (() -> () -> ()) | (() -> ())" == toString(result.errors[0]));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.loops.test.cpp

@@ -17,6 +17,8 @@ using namespace Luau;
 LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution)
 LUAU_FASTFLAG(LuauOkWithIteratingOverTableProperties)
 
+LUAU_DYNAMIC_FASTFLAG(LuauImproveNonFunctionCallError)
+
 TEST_SUITE_BEGIN("TypeInferLoops");
 
 TEST_CASE_FIXTURE(Fixture, "for_loop")
@@ -165,7 +167,11 @@ TEST_CASE_FIXTURE(Fixture, "for_in_loop_should_fail_with_non_function_iterator")
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    CHECK_EQ("Cannot call non-function string", toString(result.errors[0]));
+
+    if (DFFlag::LuauImproveNonFunctionCallError)
+        CHECK_EQ("Cannot call a value of type string", toString(result.errors[0]));
+    else
+        CHECK_EQ("Cannot call non-function string", toString(result.errors[0]));
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "for_in_with_just_one_iterator_is_ok")

tests/TypeInfer.refinements.test.cpp

@@ -338,7 +338,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "refine_unknown_to_table_then_test_a_prop")
     )");
 
     if (FFlag::DebugLuauDeferredConstraintResolution)
-            LUAU_REQUIRE_NO_ERRORS(result);
+        LUAU_REQUIRE_NO_ERRORS(result);
     else
     {
         LUAU_REQUIRE_ERROR_COUNT(2, result);
@@ -592,7 +592,10 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_is_not_nil")
     LUAU_REQUIRE_NO_ERRORS(result);
 
     CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "number | string");    // a ~= nil
-    CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "(number | string)?"); // a == nil
+    if (FFlag::DebugLuauDeferredConstraintResolution)
+        CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "nil"); // a == nil :)
+    else
+        CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "(number | string)?"); // a == nil
 }
 
 TEST_CASE_FIXTURE(Fixture, "free_type_is_equal_to_an_lvalue")

tests/TypeInfer.tables.test.cpp

@@ -22,6 +22,9 @@ LUAU_FASTFLAG(LuauAlwaysCommitInferencesOfFunctionCalls);
 LUAU_FASTFLAG(LuauFixIndexerSubtypingOrdering);
 LUAU_FASTFLAG(DebugLuauSharedSelf);
 LUAU_FASTFLAG(LuauReadWritePropertySyntax);
+LUAU_FASTFLAG(LuauMetatableInstantiationCloneCheck);
+
+LUAU_DYNAMIC_FASTFLAG(LuauImproveNonFunctionCallError)
 
 TEST_SUITE_BEGIN("TableTests");
 
@@ -2383,7 +2386,11 @@ b()
     )");
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
-    CHECK_EQ(toString(result.errors[0]), R"(Cannot call non-function t1 where t1 = { @metatable { __call: t1 }, {  } })");
+
+    if (DFFlag::LuauImproveNonFunctionCallError)
+        CHECK_EQ(toString(result.errors[0]), R"(Cannot call a value of type t1 where t1 = { @metatable { __call: t1 }, {  } })");
+    else
+        CHECK_EQ(toString(result.errors[0]), R"(Cannot call non-function t1 where t1 = { @metatable { __call: t1 }, {  } })");
 }
 
 TEST_CASE_FIXTURE(Fixture, "table_subtyping_shouldn't_add_optional_properties_to_sealed_tables")
@@ -3016,7 +3023,10 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "table_call_metamethod_must_be_callable")
 
     if (FFlag::DebugLuauDeferredConstraintResolution)
     {
-        CHECK("Cannot call non-function { @metatable { __call: number }, {  } }" == toString(result.errors[0]));
+        if (DFFlag::LuauImproveNonFunctionCallError)
+            CHECK("Cannot call a value of type { @metatable { __call: number }, {  } }" == toString(result.errors[0]));
+        else
+            CHECK("Cannot call non-function { @metatable { __call: number }, {  } }" == toString(result.errors[0]));
     }
     else
     {
@@ -3994,9 +4004,10 @@ TEST_CASE_FIXTURE(Fixture, "identify_all_problematic_table_fields")
 
     LUAU_REQUIRE_ERROR_COUNT(1, result);
 
-    std::string expected = "Type '{ a: string, b: boolean, c: number }' could not be converted into 'T'; at [read \"a\"], string is not exactly number"
+    std::string expected =
-                           "\n\tat [read \"b\"], boolean is not exactly string"
+        "Type '{ a: string, b: boolean, c: number }' could not be converted into 'T'; at [read \"a\"], string is not exactly number"
-                           "\n\tat [read \"c\"], number is not exactly boolean";
+        "\n\tat [read \"b\"], boolean is not exactly string"
+        "\n\tat [read \"c\"], number is not exactly boolean";
     CHECK(toString(result.errors[0]) == expected);
 }
 
@@ -4144,10 +4155,7 @@ TEST_CASE_FIXTURE(Fixture, "write_annotations_are_unsupported_even_with_the_new_
 
 TEST_CASE_FIXTURE(Fixture, "read_and_write_only_table_properties_are_unsupported")
 {
-    ScopedFastFlag sff[] = {
+    ScopedFastFlag sff[] = {{FFlag::LuauReadWritePropertySyntax, true}, {FFlag::DebugLuauDeferredConstraintResolution, false}};
-        {FFlag::LuauReadWritePropertySyntax, true},
-        {FFlag::DebugLuauDeferredConstraintResolution, false}
-    };
 
     CheckResult result = check(R"(
         type W = {read x: number}
@@ -4171,10 +4179,7 @@ TEST_CASE_FIXTURE(Fixture, "read_and_write_only_table_properties_are_unsupported
 
 TEST_CASE_FIXTURE(Fixture, "read_ond_write_only_indexers_are_unsupported")
 {
-    ScopedFastFlag sff[] = {
+    ScopedFastFlag sff[] = {{FFlag::LuauReadWritePropertySyntax, true}, {FFlag::DebugLuauDeferredConstraintResolution, false}};
-        {FFlag::LuauReadWritePropertySyntax, true},
-        {FFlag::DebugLuauDeferredConstraintResolution, false}
-    };
 
     CheckResult result = check(R"(
         type T = {read [string]: number}
@@ -4191,10 +4196,7 @@ TEST_CASE_FIXTURE(Fixture, "read_ond_write_only_indexers_are_unsupported")
 
 TEST_CASE_FIXTURE(Fixture, "table_writes_introduce_write_properties")
 {
-    ScopedFastFlag sff[] = {
+    ScopedFastFlag sff[] = {{FFlag::LuauReadWritePropertySyntax, true}, {FFlag::DebugLuauDeferredConstraintResolution, true}};
-        {FFlag::LuauReadWritePropertySyntax, true},
-        {FFlag::DebugLuauDeferredConstraintResolution, true}
-    };
 
     CheckResult result = check(R"(
         function oc(player, speaker)
@@ -4206,8 +4208,8 @@ TEST_CASE_FIXTURE(Fixture, "table_writes_introduce_write_properties")
     LUAU_REQUIRE_NO_ERRORS(result);
 
     CHECK("<a, b...>({{ read Character: t1 }}, { Character: t1 }) -> () "
-        "where "
+          "where "
-        "t1 = { read FindFirstChild: (t1, string) -> (a, b...) }" == toString(requireType("oc")));
+          "t1 = { read FindFirstChild: (t1, string) -> (a, b...) }" == toString(requireType("oc")));
 }
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "tables_can_have_both_metatables_and_indexers")
@@ -4359,4 +4361,47 @@ TEST_CASE_FIXTURE(Fixture, "setindexer_always_transmute")
     CHECK_EQ("(*error-type*) -> ()", toString(requireType("f")));
 }
 
+TEST_CASE_FIXTURE(BuiltinsFixture, "instantiated_metatable_frozen_table_clone_mutation")
+{
+    ScopedFastFlag luauMetatableInstantiationCloneCheck{FFlag::LuauMetatableInstantiationCloneCheck, true};
+
+    fileResolver.source["game/worker"] = R"(
+type WorkerImpl<T..., R...> = {
+    destroy: (self: Worker<T..., R...>) -> boolean,
+}
+
+type WorkerProps = { id: number }
+
+export type Worker<T..., R...> = typeof(setmetatable({} :: WorkerProps, {} :: WorkerImpl<T..., R...>))
+
+return {}
+    )";
+
+    fileResolver.source["game/library"] = R"(
+local Worker = require(game.worker)
+
+export type Worker<T..., R...> = Worker.Worker<T..., R...>
+
+return {}
+    )";
+
+    CheckResult result = frontend.check("game/library");
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "setindexer_multiple_tables_intersection")
+{
+    ScopedFastFlag sff{FFlag::DebugLuauDeferredConstraintResolution, true};
+
+    CheckResult result = check(R"(
+        local function f(t: { [string]: number } & { [thread]: boolean }, x)
+            local k = "a"
+            t[k] = x
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+    CHECK("({ [string]: number } & { [thread]: boolean }, boolean | number) -> ()" == toString(requireType("f")));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.test.cpp

@@ -986,7 +986,7 @@ TEST_CASE_FIXTURE(Fixture, "fuzzer_found_this")
  */
 TEST_CASE_FIXTURE(BuiltinsFixture, "fuzzer_found_this_2")
 {
-    (void) check(R"(
+    (void)check(R"(
         local _
         if _ then
             _ = _
@@ -999,7 +999,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "fuzzer_found_this_2")
 
 TEST_CASE_FIXTURE(Fixture, "indexing_a_cyclic_intersection_does_not_crash")
 {
-    (void) check(R"(
+    (void)check(R"(
         local _
         if _ then
             while nil do

tests/TypeInfer.typestates.test.cpp

@@ -200,7 +200,7 @@ TEST_CASE_FIXTURE(TypeStateFixture, "assignment_swap")
     CHECK("number" == toString(requireType("b")));
 }
 
-TEST_CASE_FIXTURE(TypeStateFixture, "parameter_x_was_constrained_by_two_types")
+TEST_CASE_FIXTURE(TypeStateFixture, "parameter_x_was_constrained_by_two_types_2")
 {
     CheckResult result = check(R"(
         local function f(x): number?

tests/TypeInfer.unionTypes.test.cpp

@@ -12,6 +12,25 @@ LUAU_FASTFLAG(DebugLuauDeferredConstraintResolution);
 
 TEST_SUITE_BEGIN("UnionTypes");
 
+TEST_CASE_FIXTURE(Fixture, "fuzzer_union_with_one_part_assertion")
+{
+    CheckResult result = check(R"(
+local _ = {},nil
+repeat
+
+_,_ = if _.number == "" or _.number or _._ then
+             _
+      elseif _.__index == _._G then
+            tostring
+      elseif _ then
+             _
+      else
+           ``,_._G
+
+until _._
+    )");
+}
+
 TEST_CASE_FIXTURE(Fixture, "return_types_can_be_disjoint")
 {
     CheckResult result = check(R"(
@@ -572,7 +591,8 @@ TEST_CASE_FIXTURE(Fixture, "indexing_into_a_cyclic_union_doesnt_crash")
     UnionType u;
 
     u.options.push_back(badCyclicUnionTy);
-    u.options.push_back(arena.addType(TableType{{}, TableIndexer{builtinTypes->numberType, builtinTypes->numberType}, TypeLevel{}, frontend.globals.globalScope.get(), TableState::Sealed}));
+    u.options.push_back(arena.addType(TableType{
+        {}, TableIndexer{builtinTypes->numberType, builtinTypes->numberType}, TypeLevel{}, frontend.globals.globalScope.get(), TableState::Sealed}));
 
     asMutable(badCyclicUnionTy)->ty.emplace<UnionType>(std::move(u));
 

tests/conformance/move.lua

@@ -64,6 +64,39 @@ do
 
   a = table.move({[minI] = 100}, minI, minI, maxI)
   eqT(a, {[minI] = 100, [maxI] = 100})
+
+  -- moving small amount of elements (array/hash) using a wide range
+  a = {}
+  table.move({1, 2, 3, 4, 5}, -100000000, 100000000, -100000000, a)
+  eqT(a, {1, 2, 3, 4, 5})
+
+  a = {}
+  table.move({1, 2}, -100000000, 100000000, 0, a)
+  eqT(a, {[100000001] = 1, [100000002] = 2})
+
+  -- hash part copy
+  a = {}
+  table.move({[-1000000] = 1, [-100] = 2, [100] = 3, [100000] = 4}, -100000000, 100000000, 0, a)
+  eqT(a, {[99000000] = 1, [99999900] = 2, [100000100] = 3, [100100000] = 4})
+
+  -- precise hash part bounds
+  a = {}
+  table.move({[-100000000 - 1] = -1, [-100000000] = 1, [-100] = 2, [100] = 3, [100000000] = 4, [100000000 + 1] = -1}, -100000000, 100000000, 0, a)
+  eqT(a, {[0] = 1, [99999900] = 2, [100000100] = 3, [200000000] = 4})
+
+  -- no integer undeflow in corner hash part case
+  a = {}
+  table.move({[minI] = 100, [-100] = 2}, minI, minI + 100000000, minI, a)
+  eqT(a, {[minI] = 100})
+
+  -- hash part skips array slice
+  a = {}
+  table.move({[-1] = 1, [0] = 2, [1] = 3, [2] = 4}, -1, 3, 1, a)
+  eqT(a, {[1] = 1, [2] = 2, [3] = 3, [4] = 4})
+
+  a = {}
+  table.move({[-1] = 1, [0] = 2, [1] = 3, [2] = 4, [10] = 5, [100] = 6, [1000] = 7}, -1, 3, 1, a)
+  eqT(a, {[1] = 1, [2] = 2, [3] = 3, [4] = 4})
 end
 
 checkerror("too many", table.move, {}, 0, maxI, 1)

tools/faillist.txt

@@ -49,8 +49,6 @@ GenericsTests.bound_tables_do_not_clone_original_fields
 GenericsTests.correctly_instantiate_polymorphic_member_functions
 GenericsTests.do_not_always_instantiate_generic_intersection_types
 GenericsTests.do_not_infer_generic_functions
-GenericsTests.dont_leak_generic_types
-GenericsTests.dont_leak_inferred_generic_types
 GenericsTests.dont_substitute_bound_types
 GenericsTests.error_detailed_function_mismatch_generic_pack
 GenericsTests.error_detailed_function_mismatch_generic_types
@@ -155,7 +153,6 @@ RefinementTest.x_is_not_instance_or_else_not_part
 TableTests.a_free_shape_can_turn_into_a_scalar_directly
 TableTests.a_free_shape_can_turn_into_a_scalar_if_it_is_compatible
 TableTests.a_free_shape_cannot_turn_into_a_scalar_if_it_is_not_compatible
-TableTests.accidentally_checked_prop_in_opposite_branch
 TableTests.any_when_indexing_into_an_unsealed_table_with_no_indexer_in_nonstrict_mode
 TableTests.array_factory_function
 TableTests.casting_tables_with_props_into_table_with_indexer2
@@ -395,6 +392,8 @@ TypeInferOperators.UnknownGlobalCompoundAssign
 TypeInferPrimitives.CheckMethodsOfNumber
 TypeInferPrimitives.string_index
 TypeInferUnknownNever.assign_to_local_which_is_never
+TypeInferUnknownNever.compare_never
+TypeInferUnknownNever.dont_unify_operands_if_one_of_the_operand_is_never_in_any_ordering_operators
 TypeInferUnknownNever.index_on_union_of_tables_for_properties_that_is_never
 TypeInferUnknownNever.index_on_union_of_tables_for_properties_that_is_sorta_never
 TypeInferUnknownNever.length_of_never
@@ -412,7 +411,6 @@ TypeSingletons.overloaded_function_call_with_singletons_mismatch
 TypeSingletons.return_type_of_f_is_not_widened
 TypeSingletons.table_properties_type_error_escapes
 TypeSingletons.widen_the_supertype_if_it_is_free_and_subtype_has_singleton
-TypeStatesTest.prototyped_recursive_functions_but_has_future_assignments
 TypeStatesTest.typestates_preserve_error_suppression_properties
 UnionTypes.error_detailed_optional
 UnionTypes.error_detailed_union_all