Sync to upstream/release/527 (#491)

Analysis/include/Luau/Clone.h

@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include "Luau/TypeArena.h"
 #include "Luau/TypeVar.h"
 
 #include <unordered_map>
@@ -18,7 +19,6 @@ struct CloneState
     SeenTypePacks seenTypePacks;
 
     int recursionCount = 0;
-    bool encounteredFreeType = false; // TODO: Remove with LuauLosslessClone.
 };
 
 TypePackId clone(TypePackId tp, TypeArena& dest, CloneState& cloneState);

Analysis/include/Luau/Error.h

@@ -5,6 +5,7 @@
 #include "Luau/Location.h"
 #include "Luau/TypeVar.h"
 #include "Luau/Variant.h"
+#include "Luau/TypeArena.h"
 
 namespace Luau
 {
@@ -108,9 +109,6 @@ struct FunctionDoesNotTakeSelf
 
 struct FunctionRequiresSelf
 {
-    // TODO: Delete with LuauAnyInIsOptionalIsOptional
-    int requiredExtraNils = 0;
-
     bool operator==(const FunctionRequiresSelf& rhs) const;
 };
 

Analysis/include/Luau/LValue.h

@@ -34,10 +34,6 @@ const LValue* baseof(const LValue& lvalue);
 
 std::optional<LValue> tryGetLValue(const class AstExpr& expr);
 
-// Utility function: breaks down an LValue to get at the Symbol, and reverses the vector of keys.
-// TODO: remove with FFlagLuauTypecheckOptPass
-std::pair<Symbol, std::vector<std::string>> getFullName(const LValue& lvalue);
-
 // Utility function: breaks down an LValue to get at the Symbol
 Symbol getBaseSymbol(const LValue& lvalue);
 

Analysis/include/Luau/Module.h

@@ -2,11 +2,10 @@
 #pragma once
 
 #include "Luau/FileResolver.h"
-#include "Luau/TypePack.h"
-#include "Luau/TypedAllocator.h"
 #include "Luau/ParseOptions.h"
 #include "Luau/Error.h"
 #include "Luau/ParseResult.h"
+#include "Luau/TypeArena.h"
 
 #include <memory>
 #include <vector>
@@ -54,35 +53,6 @@ struct RequireCycle
     std::vector<ModuleName> path; // one of the paths for a require() to go all the way back to the originating module
 };
 
-struct TypeArena
-{
-    TypedAllocator<TypeVar> typeVars;
-    TypedAllocator<TypePackVar> typePacks;
-
-    void clear();
-
-    template<typename T>
-    TypeId addType(T tv)
-    {
-        if constexpr (std::is_same_v<T, UnionTypeVar>)
-            LUAU_ASSERT(tv.options.size() >= 2);
-
-        return addTV(TypeVar(std::move(tv)));
-    }
-
-    TypeId addTV(TypeVar&& tv);
-
-    TypeId freshType(TypeLevel level);
-
-    TypePackId addTypePack(std::initializer_list<TypeId> types);
-    TypePackId addTypePack(std::vector<TypeId> types);
-    TypePackId addTypePack(TypePack pack);
-    TypePackId addTypePack(TypePackVar pack);
-};
-
-void freeze(TypeArena& arena);
-void unfreeze(TypeArena& arena);
-
 struct Module
 {
     ~Module();
@@ -111,9 +81,7 @@ struct Module
 
     // Once a module has been typechecked, we clone its public interface into a separate arena.
     // This helps us to force TypeVar ownership into a DAG rather than a DCG.
-    // Returns true if there were any free types encountered in the public interface. This
+    void clonePublicInterface(InternalErrorReporter& ice);
-    // indicates a bug in the type checker that we want to surface.
-    bool clonePublicInterface(InternalErrorReporter& ice);
 };
 
 } // namespace Luau

Analysis/include/Luau/Substitution.h

@@ -1,8 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
-#include "Luau/Module.h"
+#include "Luau/TypeArena.h"
-#include "Luau/ModuleResolver.h"
 #include "Luau/TypePack.h"
 #include "Luau/TypeVar.h"
 #include "Luau/DenseHash.h"

Analysis/include/Luau/TxnLog.h

@@ -7,8 +7,6 @@
 #include "Luau/TypeVar.h"
 #include "Luau/TypePack.h"
 
-LUAU_FASTFLAG(LuauTypecheckOptPass)
-
 namespace Luau
 {
 
@@ -93,15 +91,6 @@ struct TxnLog
     {
     }
 
-    TxnLog(TxnLog* parent, std::vector<std::pair<TypeOrPackId, TypeOrPackId>>* sharedSeen)
-        : typeVarChanges(nullptr)
-        , typePackChanges(nullptr)
-        , parent(parent)
-        , sharedSeen(sharedSeen)
-    {
-        LUAU_ASSERT(!FFlag::LuauTypecheckOptPass);
-    }
-
     TxnLog(const TxnLog&) = delete;
     TxnLog& operator=(const TxnLog&) = delete;
 

Analysis/include/Luau/TypeArena.h

@@ -0,0 +1,42 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+#pragma once
+
+#include "Luau/TypedAllocator.h"
+#include "Luau/TypeVar.h"
+#include "Luau/TypePack.h"
+
+#include <vector>
+
+namespace Luau
+{
+
+struct TypeArena
+{
+    TypedAllocator<TypeVar> typeVars;
+    TypedAllocator<TypePackVar> typePacks;
+
+    void clear();
+
+    template<typename T>
+    TypeId addType(T tv)
+    {
+        if constexpr (std::is_same_v<T, UnionTypeVar>)
+            LUAU_ASSERT(tv.options.size() >= 2);
+
+        return addTV(TypeVar(std::move(tv)));
+    }
+
+    TypeId addTV(TypeVar&& tv);
+
+    TypeId freshType(TypeLevel level);
+
+    TypePackId addTypePack(std::initializer_list<TypeId> types);
+    TypePackId addTypePack(std::vector<TypeId> types);
+    TypePackId addTypePack(TypePack pack);
+    TypePackId addTypePack(TypePackVar pack);
+};
+
+void freeze(TypeArena& arena);
+void unfreeze(TypeArena& arena);
+
+}

Analysis/include/Luau/TypeInfer.h

@@ -187,7 +187,6 @@ struct TypeChecker
     ExprResult<TypeId> checkExpr(const ScopePtr& scope, const AstExprIndexExpr& expr);
     ExprResult<TypeId> checkExpr(const ScopePtr& scope, const AstExprFunction& expr, std::optional<TypeId> expectedType = std::nullopt);
     ExprResult<TypeId> checkExpr(const ScopePtr& scope, const AstExprTable& expr, std::optional<TypeId> expectedType = std::nullopt);
-    ExprResult<TypeId> checkExpr_(const ScopePtr& scope, const AstExprTable& expr, std::optional<TypeId> expectedType = std::nullopt);
     ExprResult<TypeId> checkExpr(const ScopePtr& scope, const AstExprUnary& expr);
     TypeId checkRelationalOperation(
         const ScopePtr& scope, const AstExprBinary& expr, TypeId lhsType, TypeId rhsType, const PredicateVec& predicates = {});
@@ -395,7 +394,7 @@ private:
         const AstArray<AstGenericType>& genericNames, const AstArray<AstGenericTypePack>& genericPackNames, bool useCache = false);
 
 public:
-    ErrorVec resolve(const PredicateVec& predicates, const ScopePtr& scope, bool sense);
+    void resolve(const PredicateVec& predicates, const ScopePtr& scope, bool sense);
 
 private:
     void refineLValue(const LValue& lvalue, RefinementMap& refis, const ScopePtr& scope, TypeIdPredicate predicate);
@@ -403,14 +402,14 @@ private:
     std::optional<TypeId> resolveLValue(const ScopePtr& scope, const LValue& lvalue);
     std::optional<TypeId> resolveLValue(const RefinementMap& refis, const ScopePtr& scope, const LValue& lvalue);
 
-    void resolve(const PredicateVec& predicates, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr = false);
+    void resolve(const PredicateVec& predicates, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr = false);
-    void resolve(const Predicate& predicate, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr);
+    void resolve(const Predicate& predicate, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr);
-    void resolve(const TruthyPredicate& truthyP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr);
+    void resolve(const TruthyPredicate& truthyP, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr);
-    void resolve(const AndPredicate& andP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
+    void resolve(const AndPredicate& andP, RefinementMap& refis, const ScopePtr& scope, bool sense);
-    void resolve(const OrPredicate& orP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
+    void resolve(const OrPredicate& orP, RefinementMap& refis, const ScopePtr& scope, bool sense);
-    void resolve(const IsAPredicate& isaP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
+    void resolve(const IsAPredicate& isaP, RefinementMap& refis, const ScopePtr& scope, bool sense);
-    void resolve(const TypeGuardPredicate& typeguardP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
+    void resolve(const TypeGuardPredicate& typeguardP, RefinementMap& refis, const ScopePtr& scope, bool sense);
-    void resolve(const EqPredicate& eqP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense);
+    void resolve(const EqPredicate& eqP, RefinementMap& refis, const ScopePtr& scope, bool sense);
 
     bool isNonstrictMode() const;
     bool useConstrainedIntersections() const;

Analysis/include/Luau/Unifier.h

@@ -5,7 +5,7 @@
 #include "Luau/Location.h"
 #include "Luau/TxnLog.h"
 #include "Luau/TypeInfer.h"
-#include "Luau/Module.h" // FIXME: For TypeArena.  It merits breaking out into its own header.
+#include "Luau/TypeArena.h"
 #include "Luau/UnifierSharedState.h"
 
 #include <unordered_set>
@@ -55,8 +55,6 @@ struct Unifier
     UnifierSharedState& sharedState;
 
     Unifier(TypeArena* types, Mode mode, const Location& location, Variance variance, UnifierSharedState& sharedState, TxnLog* parentLog = nullptr);
-    Unifier(TypeArena* types, Mode mode, std::vector<std::pair<TypeOrPackId, TypeOrPackId>>* sharedSeen, const Location& location, Variance variance,
-        UnifierSharedState& sharedState, TxnLog* parentLog = nullptr);
 
     // Test whether the two type vars unify.  Never commits the result.
     ErrorVec canUnify(TypeId subTy, TypeId superTy);

Analysis/include/Luau/VisitTypeVar.h

@@ -10,6 +10,7 @@
 
 LUAU_FASTFLAG(LuauUseVisitRecursionLimit)
 LUAU_FASTINT(LuauVisitRecursionLimit)
+LUAU_FASTFLAG(LuauNormalizeFlagIsConservative)
 
 namespace Luau
 {
@@ -471,18 +472,21 @@ struct GenericTypeVarVisitor
 
         else if (auto pack = get<TypePack>(tp))
         {
-            visit(tp, *pack);
+            bool res = visit(tp, *pack);
+            if (!FFlag::LuauNormalizeFlagIsConservative || res)
+            {
+                for (TypeId ty : pack->head)
+                    traverse(ty);
 
-            for (TypeId ty : pack->head)
+                if (pack->tail)
-                traverse(ty);
+                    traverse(*pack->tail);
-
+            }
-            if (pack->tail)
-                traverse(*pack->tail);
         }
         else if (auto pack = get<VariadicTypePack>(tp))
         {
-            visit(tp, *pack);
+            bool res = visit(tp, *pack);
-            traverse(pack->ty);
+            if (!FFlag::LuauNormalizeFlagIsConservative || res)
+                traverse(pack->ty);
         }
         else
             LUAU_ASSERT(!"GenericTypeVarVisitor::traverse(TypePackId) is not exhaustive!");

Analysis/src/BuiltinDefinitions.cpp

@@ -8,7 +8,6 @@
 
 #include <algorithm>
 
-LUAU_FASTFLAG(LuauAssertStripsFalsyTypes)
 LUAU_FASTFLAGVARIABLE(LuauSetMetaTableArgsCheck, false)
 
 /** FIXME: Many of these type definitions are not quite completely accurate.
@@ -408,41 +407,29 @@ static std::optional<ExprResult<TypePackId>> magicFunctionAssert(
 {
     auto [paramPack, predicates] = exprResult;
 
-    if (FFlag::LuauAssertStripsFalsyTypes)
+    TypeArena& arena = typechecker.currentModule->internalTypes;
+
+    auto [head, tail] = flatten(paramPack);
+    if (head.empty() && tail)
     {
-        TypeArena& arena = typechecker.currentModule->internalTypes;
+        std::optional<TypeId> fst = first(*tail);
-
+        if (!fst)
-        auto [head, tail] = flatten(paramPack);
-        if (head.empty() && tail)
-        {
-            std::optional<TypeId> fst = first(*tail);
-            if (!fst)
-                return ExprResult<TypePackId>{paramPack};
-            head.push_back(*fst);
-        }
-
-        typechecker.reportErrors(typechecker.resolve(predicates, scope, true));
-
-        if (head.size() > 0)
-        {
-            std::optional<TypeId> newhead = typechecker.pickTypesFromSense(head[0], true);
-            if (!newhead)
-                head = {typechecker.nilType};
-            else
-                head[0] = *newhead;
-        }
-
-        return ExprResult<TypePackId>{arena.addTypePack(TypePack{std::move(head), tail})};
-    }
-    else
-    {
-        if (expr.args.size < 1)
             return ExprResult<TypePackId>{paramPack};
-
+        head.push_back(*fst);
-        typechecker.reportErrors(typechecker.resolve(predicates, scope, true));
-
-        return ExprResult<TypePackId>{paramPack};
     }
+
+    typechecker.resolve(predicates, scope, true);
+
+    if (head.size() > 0)
+    {
+        std::optional<TypeId> newhead = typechecker.pickTypesFromSense(head[0], true);
+        if (!newhead)
+            head = {typechecker.nilType};
+        else
+            head[0] = *newhead;
+    }
+
+    return ExprResult<TypePackId>{arena.addTypePack(TypePack{std::move(head), tail})};
 }
 
 static std::optional<ExprResult<TypePackId>> magicFunctionPack(

Analysis/src/Clone.cpp

@@ -1,7 +1,6 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 
 #include "Luau/Clone.h"
-#include "Luau/Module.h"
 #include "Luau/RecursionCounter.h"
 #include "Luau/TypePack.h"
 #include "Luau/Unifiable.h"
@@ -9,8 +8,6 @@
 LUAU_FASTFLAG(DebugLuauCopyBeforeNormalizing)
 
 LUAU_FASTINTVARIABLE(LuauTypeCloneRecursionLimit, 300)
-LUAU_FASTFLAG(LuauTypecheckOptPass)
-LUAU_FASTFLAGVARIABLE(LuauLosslessClone, false)
 LUAU_FASTFLAG(LuauNoMethodLocations)
 
 namespace Luau
@@ -89,20 +86,8 @@ struct TypePackCloner
 
     void operator()(const Unifiable::Free& t)
     {
-        if (FFlag::LuauLosslessClone)
+        defaultClone(t);
-        {
-            defaultClone(t);
-        }
-        else
-        {
-            cloneState.encounteredFreeType = true;
-
-            TypePackId err = getSingletonTypes().errorRecoveryTypePack(getSingletonTypes().anyTypePack);
-            TypePackId cloned = dest.addTypePack(*err);
-            seenTypePacks[typePackId] = cloned;
-        }
     }
-
     void operator()(const Unifiable::Generic& t)
     {
         defaultClone(t);
@@ -152,18 +137,7 @@ void TypeCloner::defaultClone(const T& t)
 
 void TypeCloner::operator()(const Unifiable::Free& t)
 {
-    if (FFlag::LuauLosslessClone)
+    defaultClone(t);
-    {
-        defaultClone(t);
-    }
-    else
-    {
-        cloneState.encounteredFreeType = true;
-
-        TypeId err = getSingletonTypes().errorRecoveryType(getSingletonTypes().anyType);
-        TypeId cloned = dest.addType(*err);
-        seenTypes[typeId] = cloned;
-    }
 }
 
 void TypeCloner::operator()(const Unifiable::Generic& t)
@@ -191,9 +165,6 @@ void TypeCloner::operator()(const PrimitiveTypeVar& t)
 
 void TypeCloner::operator()(const ConstrainedTypeVar& t)
 {
-    if (!FFlag::LuauLosslessClone)
-        cloneState.encounteredFreeType = true;
-
     TypeId res = dest.addType(ConstrainedTypeVar{t.level});
     ConstrainedTypeVar* ctv = getMutable<ConstrainedTypeVar>(res);
     LUAU_ASSERT(ctv);
@@ -230,9 +201,7 @@ void TypeCloner::operator()(const FunctionTypeVar& t)
     ftv->argTypes = clone(t.argTypes, dest, cloneState);
     ftv->argNames = t.argNames;
     ftv->retType = clone(t.retType, dest, cloneState);
-
+    ftv->hasNoGenerics = t.hasNoGenerics;
-    if (FFlag::LuauTypecheckOptPass)
-        ftv->hasNoGenerics = t.hasNoGenerics;
 }
 
 void TypeCloner::operator()(const TableTypeVar& t)
@@ -270,13 +239,6 @@ void TypeCloner::operator()(const TableTypeVar& t)
     for (TypePackId& arg : ttv->instantiatedTypePackParams)
         arg = clone(arg, dest, cloneState);
 
-    if (!FFlag::LuauLosslessClone && ttv->state == TableState::Free)
-    {
-        cloneState.encounteredFreeType = true;
-
-        ttv->state = TableState::Sealed;
-    }
-
     ttv->definitionModuleName = t.definitionModuleName;
     if (!FFlag::LuauNoMethodLocations)
         ttv->methodDefinitionLocations = t.methodDefinitionLocations;

Analysis/src/Error.cpp

@@ -2,7 +2,6 @@
 #include "Luau/Error.h"
 
 #include "Luau/Clone.h"
-#include "Luau/Module.h"
 #include "Luau/StringUtils.h"
 #include "Luau/ToString.h"
 
@@ -178,15 +177,7 @@ struct ErrorConverter
 
     std::string operator()(const Luau::FunctionRequiresSelf& e) const
     {
-        if (e.requiredExtraNils)
+        return "This function must be called with self. Did you mean to use a colon instead of a dot?";
-        {
-            const char* plural = e.requiredExtraNils == 1 ? "" : "s";
-            return format("This function was declared to accept self, but you did not pass enough arguments. Use a colon instead of a dot or "
-                          "pass %i extra nil%s to suppress this warning",
-                e.requiredExtraNils, plural);
-        }
-        else
-            return "This function must be called with self. Did you mean to use a colon instead of a dot?";
     }
 
     std::string operator()(const Luau::OccursCheckFailed&) const
@@ -539,7 +530,7 @@ bool FunctionDoesNotTakeSelf::operator==(const FunctionDoesNotTakeSelf&) const
 
 bool FunctionRequiresSelf::operator==(const FunctionRequiresSelf& e) const
 {
-    return requiredExtraNils == e.requiredExtraNils;
+    return true;
 }
 
 bool OccursCheckFailed::operator==(const OccursCheckFailed&) const

Analysis/src/IostreamHelpers.cpp

@@ -48,7 +48,7 @@ static void errorToString(std::ostream& stream, const T& err)
     else if constexpr (std::is_same_v<T, FunctionDoesNotTakeSelf>)
         stream << "FunctionDoesNotTakeSelf { }";
     else if constexpr (std::is_same_v<T, FunctionRequiresSelf>)
-        stream << "FunctionRequiresSelf { extraNils " << err.requiredExtraNils << " }";
+        stream << "FunctionRequiresSelf { }";
     else if constexpr (std::is_same_v<T, OccursCheckFailed>)
         stream << "OccursCheckFailed { }";
     else if constexpr (std::is_same_v<T, UnknownRequire>)

Analysis/src/LValue.cpp

@@ -5,8 +5,6 @@
 
 #include <vector>
 
-LUAU_FASTFLAG(LuauTypecheckOptPass)
-
 namespace Luau
 {
 
@@ -79,27 +77,8 @@ std::optional<LValue> tryGetLValue(const AstExpr& node)
     return std::nullopt;
 }
 
-std::pair<Symbol, std::vector<std::string>> getFullName(const LValue& lvalue)
-{
-    LUAU_ASSERT(!FFlag::LuauTypecheckOptPass);
-
-    const LValue* current = &lvalue;
-    std::vector<std::string> keys;
-    while (auto field = get<Field>(*current))
-    {
-        keys.push_back(field->key);
-        current = baseof(*current);
-    }
-
-    const Symbol* symbol = get<Symbol>(*current);
-    LUAU_ASSERT(symbol);
-    return {*symbol, std::vector<std::string>(keys.rbegin(), keys.rend())};
-}
-
 Symbol getBaseSymbol(const LValue& lvalue)
 {
-    LUAU_ASSERT(FFlag::LuauTypecheckOptPass);
-
     const LValue* current = &lvalue;
     while (auto field = get<Field>(*current))
         current = baseof(*current);

Analysis/src/Module.cpp

@@ -13,9 +13,8 @@
 
 #include <algorithm>
 
-LUAU_FASTFLAGVARIABLE(DebugLuauFreezeArena, false)
+LUAU_FASTFLAG(LuauLowerBoundsCalculation);
-LUAU_FASTFLAG(LuauLowerBoundsCalculation)
+LUAU_FASTFLAG(LuauNormalizeFlagIsConservative);
-LUAU_FASTFLAG(LuauLosslessClone)
 
 namespace Luau
 {
@@ -55,89 +54,25 @@ bool isWithinComment(const SourceModule& sourceModule, Position pos)
     return contains(pos, *iter);
 }
 
-void TypeArena::clear()
+struct ForceNormal : TypeVarOnceVisitor
 {
-    typeVars.clear();
+    bool visit(TypeId ty) override
-    typePacks.clear();
+    {
-}
+        asMutable(ty)->normal = true;
+        return true;
+    }
 
-TypeId TypeArena::addTV(TypeVar&& tv)
+    bool visit(TypeId ty, const FreeTypeVar& ftv) override
-{
+    {
-    TypeId allocated = typeVars.allocate(std::move(tv));
+        visit(ty);
+        return true;
+    }
 
-    asMutable(allocated)->owningArena = this;
+    bool visit(TypePackId tp, const FreeTypePack& ftp) override
-
+    {
-    return allocated;
+        return true;
-}
+    }
-
+};
-TypeId TypeArena::freshType(TypeLevel level)
-{
-    TypeId allocated = typeVars.allocate(FreeTypeVar{level});
-
-    asMutable(allocated)->owningArena = this;
-
-    return allocated;
-}
-
-TypePackId TypeArena::addTypePack(std::initializer_list<TypeId> types)
-{
-    TypePackId allocated = typePacks.allocate(TypePack{std::move(types)});
-
-    asMutable(allocated)->owningArena = this;
-
-    return allocated;
-}
-
-TypePackId TypeArena::addTypePack(std::vector<TypeId> types)
-{
-    TypePackId allocated = typePacks.allocate(TypePack{std::move(types)});
-
-    asMutable(allocated)->owningArena = this;
-
-    return allocated;
-}
-
-TypePackId TypeArena::addTypePack(TypePack tp)
-{
-    TypePackId allocated = typePacks.allocate(std::move(tp));
-
-    asMutable(allocated)->owningArena = this;
-
-    return allocated;
-}
-
-TypePackId TypeArena::addTypePack(TypePackVar tp)
-{
-    TypePackId allocated = typePacks.allocate(std::move(tp));
-
-    asMutable(allocated)->owningArena = this;
-
-    return allocated;
-}
-
-ScopePtr Module::getModuleScope() const
-{
-    LUAU_ASSERT(!scopes.empty());
-    return scopes.front().second;
-}
-
-void freeze(TypeArena& arena)
-{
-    if (!FFlag::DebugLuauFreezeArena)
-        return;
-
-    arena.typeVars.freeze();
-    arena.typePacks.freeze();
-}
-
-void unfreeze(TypeArena& arena)
-{
-    if (!FFlag::DebugLuauFreezeArena)
-        return;
-
-    arena.typeVars.unfreeze();
-    arena.typePacks.unfreeze();
-}
 
 Module::~Module()
 {
@@ -145,7 +80,7 @@ Module::~Module()
     unfreeze(internalTypes);
 }
 
-bool Module::clonePublicInterface(InternalErrorReporter& ice)
+void Module::clonePublicInterface(InternalErrorReporter& ice)
 {
     LUAU_ASSERT(interfaceTypes.typeVars.empty());
     LUAU_ASSERT(interfaceTypes.typePacks.empty());
@@ -165,11 +100,22 @@ bool Module::clonePublicInterface(InternalErrorReporter& ice)
             normalize(*moduleScope->varargPack, interfaceTypes, ice);
     }
 
+    ForceNormal forceNormal;
+
     for (auto& [name, tf] : moduleScope->exportedTypeBindings)
     {
         tf = clone(tf, interfaceTypes, cloneState);
         if (FFlag::LuauLowerBoundsCalculation)
+        {
             normalize(tf.type, interfaceTypes, ice);
+
+            if (FFlag::LuauNormalizeFlagIsConservative)
+            {
+                // We're about to freeze the memory.  We know that the flag is conservative by design.  Cyclic tables
+                // won't be marked normal.  If the types aren't normal by now, they never will be.
+                forceNormal.traverse(tf.type);
+            }
+        }
     }
 
     for (TypeId ty : moduleScope->returnType)
@@ -191,11 +137,12 @@ bool Module::clonePublicInterface(InternalErrorReporter& ice)
 
     freeze(internalTypes);
     freeze(interfaceTypes);
+}
 
-    if (FFlag::LuauLosslessClone)
+ScopePtr Module::getModuleScope() const
-        return false; // TODO: make function return void.
+{
-    else
+    LUAU_ASSERT(!scopes.empty());
-        return cloneState.encounteredFreeType;
+    return scopes.front().second;
 }
 
 } // namespace Luau

Analysis/src/Normalize.cpp

@@ -14,6 +14,7 @@ LUAU_FASTFLAGVARIABLE(DebugLuauCopyBeforeNormalizing, false)
 // This could theoretically be 2000 on amd64, but x86 requires this.
 LUAU_FASTINTVARIABLE(LuauNormalizeIterationLimit, 1200);
 LUAU_FASTFLAGVARIABLE(LuauNormalizeCombineTableFix, false);
+LUAU_FASTFLAGVARIABLE(LuauNormalizeFlagIsConservative, false);
 
 namespace Luau
 {
@@ -260,8 +261,13 @@ static bool areNormal_(const T& t, const std::unordered_set<void*>& seen, Intern
         if (count >= FInt::LuauNormalizeIterationLimit)
             ice.ice("Luau::areNormal hit iteration limit");
 
-        // The follow is here because a bound type may not be normal, but the bound type is normal.
+        if (FFlag::LuauNormalizeFlagIsConservative)
-        return ty->normal || follow(ty)->normal || seen.find(asMutable(ty)) != seen.end();
+            return ty->normal;
+        else
+        {
+            // The follow is here because a bound type may not be normal, but the bound type is normal.
+            return ty->normal || follow(ty)->normal || seen.find(asMutable(ty)) != seen.end();
+        }
     };
 
     return std::all_of(begin(t), end(t), isNormal);
@@ -1003,8 +1009,15 @@ std::pair<TypeId, bool> normalize(TypeId ty, TypeArena& arena, InternalErrorRepo
         (void)clone(ty, arena, state);
 
     Normalize n{arena, ice};
-    std::unordered_set<void*> seen;
+    if (FFlag::LuauNormalizeFlagIsConservative)
-    DEPRECATED_visitTypeVar(ty, n, seen);
+    {
+        DEPRECATED_visitTypeVar(ty, n);
+    }
+    else
+    {
+        std::unordered_set<void*> seen;
+        DEPRECATED_visitTypeVar(ty, n, seen);
+    }
 
     return {ty, !n.limitExceeded};
 }
@@ -1028,8 +1041,15 @@ std::pair<TypePackId, bool> normalize(TypePackId tp, TypeArena& arena, InternalE
         (void)clone(tp, arena, state);
 
     Normalize n{arena, ice};
-    std::unordered_set<void*> seen;
+    if (FFlag::LuauNormalizeFlagIsConservative)
-    DEPRECATED_visitTypeVar(tp, n, seen);
+    {
+        DEPRECATED_visitTypeVar(tp, n);
+    }
+    else
+    {
+        std::unordered_set<void*> seen;
+        DEPRECATED_visitTypeVar(tp, n, seen);
+    }
 
     return {tp, !n.limitExceeded};
 }

Analysis/src/Quantify.cpp

@@ -4,7 +4,7 @@
 
 #include "Luau/VisitTypeVar.h"
 
-LUAU_FASTFLAG(LuauTypecheckOptPass)
+LUAU_FASTFLAG(LuauAlwaysQuantify)
 
 namespace Luau
 {
@@ -59,8 +59,7 @@ struct Quantifier final : TypeVarOnceVisitor
 
     bool visit(TypeId ty, const FreeTypeVar& ftv) override
     {
-        if (FFlag::LuauTypecheckOptPass)
+        seenMutableType = true;
-            seenMutableType = true;
 
         if (!level.subsumes(ftv.level))
             return false;
@@ -76,20 +75,17 @@ struct Quantifier final : TypeVarOnceVisitor
         LUAU_ASSERT(getMutable<TableTypeVar>(ty));
         TableTypeVar& ttv = *getMutable<TableTypeVar>(ty);
 
-        if (FFlag::LuauTypecheckOptPass)
+        if (ttv.state == TableState::Generic)
-        {
+            seenGenericType = true;
-            if (ttv.state == TableState::Generic)
-                seenGenericType = true;
 
-            if (ttv.state == TableState::Free)
+        if (ttv.state == TableState::Free)
-                seenMutableType = true;
+            seenMutableType = true;
-        }
 
         if (ttv.state == TableState::Sealed || ttv.state == TableState::Generic)
             return false;
         if (!level.subsumes(ttv.level))
         {
-            if (FFlag::LuauTypecheckOptPass && ttv.state == TableState::Unsealed)
+            if (ttv.state == TableState::Unsealed)
                 seenMutableType = true;
             return false;
         }
@@ -97,9 +93,7 @@ struct Quantifier final : TypeVarOnceVisitor
         if (ttv.state == TableState::Free)
         {
             ttv.state = TableState::Generic;
-
+            seenGenericType = true;
-            if (FFlag::LuauTypecheckOptPass)
-                seenGenericType = true;
         }
         else if (ttv.state == TableState::Unsealed)
             ttv.state = TableState::Sealed;
@@ -111,8 +105,7 @@ struct Quantifier final : TypeVarOnceVisitor
 
     bool visit(TypePackId tp, const FreeTypePack& ftp) override
     {
-        if (FFlag::LuauTypecheckOptPass)
+        seenMutableType = true;
-            seenMutableType = true;
 
         if (!level.subsumes(ftp.level))
             return false;
@@ -131,10 +124,18 @@ void quantify(TypeId ty, TypeLevel level)
 
     FunctionTypeVar* ftv = getMutable<FunctionTypeVar>(ty);
     LUAU_ASSERT(ftv);
-    ftv->generics = q.generics;
+    if (FFlag::LuauAlwaysQuantify)
-    ftv->genericPacks = q.genericPacks;
+    {
+        ftv->generics.insert(ftv->generics.end(), q.generics.begin(), q.generics.end());
+        ftv->genericPacks.insert(ftv->genericPacks.end(), q.genericPacks.begin(), q.genericPacks.end());
+    }
+    else
+    {
+        ftv->generics = q.generics;
+        ftv->genericPacks = q.genericPacks;
+    }
 
-    if (FFlag::LuauTypecheckOptPass && ftv->generics.empty() && ftv->genericPacks.empty() && !q.seenMutableType && !q.seenGenericType)
+    if (ftv->generics.empty() && ftv->genericPacks.empty() && !q.seenMutableType && !q.seenGenericType)
         ftv->hasNoGenerics = true;
 }
 

Analysis/src/Substitution.cpp

@@ -9,9 +9,6 @@
 
 LUAU_FASTFLAG(LuauLowerBoundsCalculation)
 LUAU_FASTINTVARIABLE(LuauTarjanChildLimit, 10000)
-LUAU_FASTFLAG(LuauTypecheckOptPass)
-LUAU_FASTFLAGVARIABLE(LuauSubstituteFollowNewTypes, false)
-LUAU_FASTFLAGVARIABLE(LuauSubstituteFollowPossibleMutations, false)
 LUAU_FASTFLAG(LuauNoMethodLocations)
 
 namespace Luau
@@ -19,26 +16,20 @@ namespace Luau
 
 void Tarjan::visitChildren(TypeId ty, int index)
 {
-    if (FFlag::LuauTypecheckOptPass)
+    LUAU_ASSERT(ty == log->follow(ty));
-        LUAU_ASSERT(ty == log->follow(ty));
-    else
-        ty = log->follow(ty);
 
     if (ignoreChildren(ty))
         return;
 
-    if (FFlag::LuauTypecheckOptPass)
+    if (auto pty = log->pending(ty))
-    {
+        ty = &pty->pending;
-        if (auto pty = log->pending(ty))
-            ty = &pty->pending;
-    }
 
-    if (const FunctionTypeVar* ftv = FFlag::LuauTypecheckOptPass ? get<FunctionTypeVar>(ty) : log->getMutable<FunctionTypeVar>(ty))
+    if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(ty))
     {
         visitChild(ftv->argTypes);
         visitChild(ftv->retType);
     }
-    else if (const TableTypeVar* ttv = FFlag::LuauTypecheckOptPass ? get<TableTypeVar>(ty) : log->getMutable<TableTypeVar>(ty))
+    else if (const TableTypeVar* ttv = get<TableTypeVar>(ty))
     {
         LUAU_ASSERT(!ttv->boundTo);
         for (const auto& [name, prop] : ttv->props)
@@ -55,17 +46,17 @@ void Tarjan::visitChildren(TypeId ty, int index)
         for (TypePackId itp : ttv->instantiatedTypePackParams)
             visitChild(itp);
     }
-    else if (const MetatableTypeVar* mtv = FFlag::LuauTypecheckOptPass ? get<MetatableTypeVar>(ty) : log->getMutable<MetatableTypeVar>(ty))
+    else if (const MetatableTypeVar* mtv = get<MetatableTypeVar>(ty))
     {
         visitChild(mtv->table);
         visitChild(mtv->metatable);
     }
-    else if (const UnionTypeVar* utv = FFlag::LuauTypecheckOptPass ? get<UnionTypeVar>(ty) : log->getMutable<UnionTypeVar>(ty))
+    else if (const UnionTypeVar* utv = get<UnionTypeVar>(ty))
     {
         for (TypeId opt : utv->options)
             visitChild(opt);
     }
-    else if (const IntersectionTypeVar* itv = FFlag::LuauTypecheckOptPass ? get<IntersectionTypeVar>(ty) : log->getMutable<IntersectionTypeVar>(ty))
+    else if (const IntersectionTypeVar* itv = get<IntersectionTypeVar>(ty))
     {
         for (TypeId part : itv->parts)
             visitChild(part);
@@ -79,28 +70,22 @@ void Tarjan::visitChildren(TypeId ty, int index)
 
 void Tarjan::visitChildren(TypePackId tp, int index)
 {
-    if (FFlag::LuauTypecheckOptPass)
+    LUAU_ASSERT(tp == log->follow(tp));
-        LUAU_ASSERT(tp == log->follow(tp));
-    else
-        tp = log->follow(tp);
 
     if (ignoreChildren(tp))
         return;
 
-    if (FFlag::LuauTypecheckOptPass)
+    if (auto ptp = log->pending(tp))
-    {
+        tp = &ptp->pending;
-        if (auto ptp = log->pending(tp))
-            tp = &ptp->pending;
-    }
 
-    if (const TypePack* tpp = FFlag::LuauTypecheckOptPass ? get<TypePack>(tp) : log->getMutable<TypePack>(tp))
+    if (const TypePack* tpp = get<TypePack>(tp))
     {
         for (TypeId tv : tpp->head)
             visitChild(tv);
         if (tpp->tail)
             visitChild(*tpp->tail);
     }
-    else if (const VariadicTypePack* vtp = FFlag::LuauTypecheckOptPass ? get<VariadicTypePack>(tp) : log->getMutable<VariadicTypePack>(tp))
+    else if (const VariadicTypePack* vtp = get<VariadicTypePack>(tp))
     {
         visitChild(vtp->ty);
     }
@@ -108,10 +93,7 @@ void Tarjan::visitChildren(TypePackId tp, int index)
 
 std::pair<int, bool> Tarjan::indexify(TypeId ty)
 {
-    if (FFlag::LuauTypecheckOptPass && !FFlag::LuauSubstituteFollowPossibleMutations)
+    ty = log->follow(ty);
-        LUAU_ASSERT(ty == log->follow(ty));
-    else
-        ty = log->follow(ty);
 
     bool fresh = !typeToIndex.contains(ty);
     int& index = typeToIndex[ty];
@@ -129,10 +111,7 @@ std::pair<int, bool> Tarjan::indexify(TypeId ty)
 
 std::pair<int, bool> Tarjan::indexify(TypePackId tp)
 {
-    if (FFlag::LuauTypecheckOptPass && !FFlag::LuauSubstituteFollowPossibleMutations)
+    tp = log->follow(tp);
-        LUAU_ASSERT(tp == log->follow(tp));
-    else
-        tp = log->follow(tp);
 
     bool fresh = !packToIndex.contains(tp);
     int& index = packToIndex[tp];
@@ -150,8 +129,7 @@ std::pair<int, bool> Tarjan::indexify(TypePackId tp)
 
 void Tarjan::visitChild(TypeId ty)
 {
-    if (!FFlag::LuauSubstituteFollowPossibleMutations)
+    ty = log->follow(ty);
-        ty = log->follow(ty);
 
     edgesTy.push_back(ty);
     edgesTp.push_back(nullptr);
@@ -159,8 +137,7 @@ void Tarjan::visitChild(TypeId ty)
 
 void Tarjan::visitChild(TypePackId tp)
 {
-    if (!FFlag::LuauSubstituteFollowPossibleMutations)
+    tp = log->follow(tp);
-        tp = log->follow(tp);
 
     edgesTy.push_back(nullptr);
     edgesTp.push_back(tp);
@@ -389,13 +366,10 @@ TypeId Substitution::clone(TypeId ty)
 
     TypeId result = ty;
 
-    if (FFlag::LuauTypecheckOptPass)
+    if (auto pty = log->pending(ty))
-    {
+        ty = &pty->pending;
-        if (auto pty = log->pending(ty))
-            ty = &pty->pending;
-    }
 
-    if (const FunctionTypeVar* ftv = FFlag::LuauTypecheckOptPass ? get<FunctionTypeVar>(ty) : log->getMutable<FunctionTypeVar>(ty))
+    if (const FunctionTypeVar* ftv = get<FunctionTypeVar>(ty))
     {
         FunctionTypeVar clone = FunctionTypeVar{ftv->level, ftv->argTypes, ftv->retType, ftv->definition, ftv->hasSelf};
         clone.generics = ftv->generics;
@@ -405,7 +379,7 @@ TypeId Substitution::clone(TypeId ty)
         clone.argNames = ftv->argNames;
         result = addType(std::move(clone));
     }
-    else if (const TableTypeVar* ttv = FFlag::LuauTypecheckOptPass ? get<TableTypeVar>(ty) : log->getMutable<TableTypeVar>(ty))
+    else if (const TableTypeVar* ttv = get<TableTypeVar>(ty))
     {
         LUAU_ASSERT(!ttv->boundTo);
         TableTypeVar clone = TableTypeVar{ttv->props, ttv->indexer, ttv->level, ttv->state};
@@ -419,19 +393,19 @@ TypeId Substitution::clone(TypeId ty)
         clone.tags = ttv->tags;
         result = addType(std::move(clone));
     }
-    else if (const MetatableTypeVar* mtv = FFlag::LuauTypecheckOptPass ? get<MetatableTypeVar>(ty) : log->getMutable<MetatableTypeVar>(ty))
+    else if (const MetatableTypeVar* mtv = get<MetatableTypeVar>(ty))
     {
         MetatableTypeVar clone = MetatableTypeVar{mtv->table, mtv->metatable};
         clone.syntheticName = mtv->syntheticName;
         result = addType(std::move(clone));
     }
-    else if (const UnionTypeVar* utv = FFlag::LuauTypecheckOptPass ? get<UnionTypeVar>(ty) : log->getMutable<UnionTypeVar>(ty))
+    else if (const UnionTypeVar* utv = get<UnionTypeVar>(ty))
     {
         UnionTypeVar clone;
         clone.options = utv->options;
         result = addType(std::move(clone));
     }
-    else if (const IntersectionTypeVar* itv = FFlag::LuauTypecheckOptPass ? get<IntersectionTypeVar>(ty) : log->getMutable<IntersectionTypeVar>(ty))
+    else if (const IntersectionTypeVar* itv = get<IntersectionTypeVar>(ty))
     {
         IntersectionTypeVar clone;
         clone.parts = itv->parts;
@@ -451,20 +425,17 @@ TypePackId Substitution::clone(TypePackId tp)
 {
     tp = log->follow(tp);
 
-    if (FFlag::LuauTypecheckOptPass)
+    if (auto ptp = log->pending(tp))
-    {
+        tp = &ptp->pending;
-        if (auto ptp = log->pending(tp))
-            tp = &ptp->pending;
-    }
 
-    if (const TypePack* tpp = FFlag::LuauTypecheckOptPass ? get<TypePack>(tp) : log->getMutable<TypePack>(tp))
+    if (const TypePack* tpp = get<TypePack>(tp))
     {
         TypePack clone;
         clone.head = tpp->head;
         clone.tail = tpp->tail;
         return addTypePack(std::move(clone));
     }
-    else if (const VariadicTypePack* vtp = FFlag::LuauTypecheckOptPass ? get<VariadicTypePack>(tp) : log->getMutable<VariadicTypePack>(tp))
+    else if (const VariadicTypePack* vtp = get<VariadicTypePack>(tp))
     {
         VariadicTypePack clone;
         clone.ty = vtp->ty;
@@ -476,28 +447,22 @@ TypePackId Substitution::clone(TypePackId tp)
 
 void Substitution::foundDirty(TypeId ty)
 {
-    if (FFlag::LuauTypecheckOptPass && !FFlag::LuauSubstituteFollowPossibleMutations)
+    ty = log->follow(ty);
-        LUAU_ASSERT(ty == log->follow(ty));
-    else
-        ty = log->follow(ty);
 
     if (isDirty(ty))
-        newTypes[ty] = FFlag::LuauSubstituteFollowNewTypes ? follow(clean(ty)) : clean(ty);
+        newTypes[ty] = follow(clean(ty));
     else
-        newTypes[ty] = FFlag::LuauSubstituteFollowNewTypes ? follow(clone(ty)) : clone(ty);
+        newTypes[ty] = follow(clone(ty));
 }
 
 void Substitution::foundDirty(TypePackId tp)
 {
-    if (FFlag::LuauTypecheckOptPass && !FFlag::LuauSubstituteFollowPossibleMutations)
+    tp = log->follow(tp);
-        LUAU_ASSERT(tp == log->follow(tp));
-    else
-        tp = log->follow(tp);
 
     if (isDirty(tp))
-        newPacks[tp] = FFlag::LuauSubstituteFollowNewTypes ? follow(clean(tp)) : clean(tp);
+        newPacks[tp] = follow(clean(tp));
     else
-        newPacks[tp] = FFlag::LuauSubstituteFollowNewTypes ? follow(clone(tp)) : clone(tp);
+        newPacks[tp] = follow(clone(tp));
 }
 
 TypeId Substitution::replace(TypeId ty)
@@ -525,10 +490,7 @@ void Substitution::replaceChildren(TypeId ty)
     if (BoundTypeVar* btv = log->getMutable<BoundTypeVar>(ty); FFlag::LuauLowerBoundsCalculation && btv)
         btv->boundTo = replace(btv->boundTo);
 
-    if (FFlag::LuauTypecheckOptPass)
+    LUAU_ASSERT(ty == log->follow(ty));
-        LUAU_ASSERT(ty == log->follow(ty));
-    else
-        ty = log->follow(ty);
 
     if (ignoreChildren(ty))
         return;
@@ -579,10 +541,7 @@ void Substitution::replaceChildren(TypeId ty)
 
 void Substitution::replaceChildren(TypePackId tp)
 {
-    if (FFlag::LuauTypecheckOptPass)
+    LUAU_ASSERT(tp == log->follow(tp));
-        LUAU_ASSERT(tp == log->follow(tp));
-    else
-        tp = log->follow(tp);
 
     if (ignoreChildren(tp))
         return;

Analysis/src/ToString.cpp

@@ -219,6 +219,8 @@ struct StringifierState
         return generateName(s);
     }
 
+    int previousNameIndex = 0;
+
     std::string getName(TypePackId ty)
     {
         const size_t s = result.nameMap.typePacks.size();
@@ -228,9 +230,10 @@ struct StringifierState
 
         for (int count = 0; count < 256; ++count)
         {
-            std::string candidate = generateName(usedNames.size() + count);
+            std::string candidate = generateName(previousNameIndex + count);
             if (!usedNames.count(candidate))
             {
+                previousNameIndex += count;
                 usedNames.insert(candidate);
                 n = candidate;
                 return candidate;
@@ -399,6 +402,7 @@ struct TypeVarStringifier
     {
         if (gtv.explicitName)
         {
+            state.usedNames.insert(gtv.name);
             state.result.nameMap.typeVars[ty] = gtv.name;
             state.emit(gtv.name);
         }
@@ -943,6 +947,7 @@ struct TypePackStringifier
             state.emit("gen-");
         if (pack.explicitName)
         {
+            state.usedNames.insert(pack.name);
             state.result.nameMap.typePacks[tp] = pack.name;
             state.emit(pack.name);
         }

Analysis/src/TxnLog.cpp

@@ -7,8 +7,6 @@
 #include <algorithm>
 #include <stdexcept>
 
-LUAU_FASTFLAGVARIABLE(LuauJustOneCallFrameForHaveSeen, false)
-
 namespace Luau
 {
 
@@ -150,37 +148,13 @@ void TxnLog::popSeen(TypePackId lhs, TypePackId rhs)
 
 bool TxnLog::haveSeen(TypeOrPackId lhs, TypeOrPackId rhs) const
 {
-    if (FFlag::LuauJustOneCallFrameForHaveSeen && !FFlag::LuauTypecheckOptPass)
+    const std::pair<TypeOrPackId, TypeOrPackId> sortedPair = (lhs > rhs) ? std::make_pair(lhs, rhs) : std::make_pair(rhs, lhs);
+    if (sharedSeen->end() != std::find(sharedSeen->begin(), sharedSeen->end(), sortedPair))
     {
-        // This function will technically work if `this` is nullptr, but this
+        return true;
-        // indicates a bug, so we explicitly assert.
-        LUAU_ASSERT(static_cast<const void*>(this) != nullptr);
-
-        const std::pair<TypeOrPackId, TypeOrPackId> sortedPair = (lhs > rhs) ? std::make_pair(lhs, rhs) : std::make_pair(rhs, lhs);
-
-        for (const TxnLog* current = this; current; current = current->parent)
-        {
-            if (current->sharedSeen->end() != std::find(current->sharedSeen->begin(), current->sharedSeen->end(), sortedPair))
-                return true;
-        }
-
-        return false;
     }
-    else
-    {
-        const std::pair<TypeOrPackId, TypeOrPackId> sortedPair = (lhs > rhs) ? std::make_pair(lhs, rhs) : std::make_pair(rhs, lhs);
-        if (sharedSeen->end() != std::find(sharedSeen->begin(), sharedSeen->end(), sortedPair))
-        {
-            return true;
-        }
 
-        if (!FFlag::LuauTypecheckOptPass && parent)
+    return false;
-        {
-            return parent->haveSeen(lhs, rhs);
-        }
-
-        return false;
-    }
 }
 
 void TxnLog::pushSeen(TypeOrPackId lhs, TypeOrPackId rhs)

Analysis/src/TypeArena.cpp

@@ -0,0 +1,88 @@
+// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
+
+#include "Luau/TypeArena.h"
+
+LUAU_FASTFLAGVARIABLE(DebugLuauFreezeArena, false);
+
+namespace Luau
+{
+
+void TypeArena::clear()
+{
+    typeVars.clear();
+    typePacks.clear();
+}
+
+TypeId TypeArena::addTV(TypeVar&& tv)
+{
+    TypeId allocated = typeVars.allocate(std::move(tv));
+
+    asMutable(allocated)->owningArena = this;
+
+    return allocated;
+}
+
+TypeId TypeArena::freshType(TypeLevel level)
+{
+    TypeId allocated = typeVars.allocate(FreeTypeVar{level});
+
+    asMutable(allocated)->owningArena = this;
+
+    return allocated;
+}
+
+TypePackId TypeArena::addTypePack(std::initializer_list<TypeId> types)
+{
+    TypePackId allocated = typePacks.allocate(TypePack{std::move(types)});
+
+    asMutable(allocated)->owningArena = this;
+
+    return allocated;
+}
+
+TypePackId TypeArena::addTypePack(std::vector<TypeId> types)
+{
+    TypePackId allocated = typePacks.allocate(TypePack{std::move(types)});
+
+    asMutable(allocated)->owningArena = this;
+
+    return allocated;
+}
+
+TypePackId TypeArena::addTypePack(TypePack tp)
+{
+    TypePackId allocated = typePacks.allocate(std::move(tp));
+
+    asMutable(allocated)->owningArena = this;
+
+    return allocated;
+}
+
+TypePackId TypeArena::addTypePack(TypePackVar tp)
+{
+    TypePackId allocated = typePacks.allocate(std::move(tp));
+
+    asMutable(allocated)->owningArena = this;
+
+    return allocated;
+}
+
+void freeze(TypeArena& arena)
+{
+    if (!FFlag::DebugLuauFreezeArena)
+        return;
+
+    arena.typeVars.freeze();
+    arena.typePacks.freeze();
+}
+
+void unfreeze(TypeArena& arena)
+{
+    if (!FFlag::DebugLuauFreezeArena)
+        return;
+
+    arena.typeVars.unfreeze();
+    arena.typePacks.unfreeze();
+}
+
+}

Analysis/src/TypeInfer.cpp

@@ -32,32 +32,25 @@ LUAU_FASTFLAG(LuauKnowsTheDataModel3)
 LUAU_FASTFLAG(LuauSeparateTypechecks)
 LUAU_FASTFLAG(LuauAutocompleteDynamicLimits)
 LUAU_FASTFLAGVARIABLE(LuauDoNotRelyOnNextBinding, false)
-LUAU_FASTFLAGVARIABLE(LuauEqConstraint, false)
+LUAU_FASTFLAGVARIABLE(LuauExpectedPropTypeFromIndexer, false)
 LUAU_FASTFLAGVARIABLE(LuauWeakEqConstraint, false) // Eventually removed as false.
 LUAU_FASTFLAGVARIABLE(LuauLowerBoundsCalculation, false)
 LUAU_FASTFLAGVARIABLE(DebugLuauFreezeDuringUnification, false)
-LUAU_FASTFLAGVARIABLE(LuauInstantiateFollows, false)
 LUAU_FASTFLAGVARIABLE(LuauSelfCallAutocompleteFix, false)
-LUAU_FASTFLAGVARIABLE(LuauDiscriminableUnions2, false)
 LUAU_FASTFLAGVARIABLE(LuauReduceUnionRecursion, false)
 LUAU_FASTFLAGVARIABLE(LuauOnlyMutateInstantiatedTables, false)
-LUAU_FASTFLAGVARIABLE(LuauTypecheckOptPass, false)
 LUAU_FASTFLAGVARIABLE(LuauUnsealedTableLiteral, false)
 LUAU_FASTFLAGVARIABLE(LuauTwoPassAliasDefinitionFix, false)
-LUAU_FASTFLAGVARIABLE(LuauAssertStripsFalsyTypes, false)
 LUAU_FASTFLAGVARIABLE(LuauReturnAnyInsteadOfICE, false) // Eventually removed as false.
+LUAU_FASTFLAG(LuauNormalizeFlagIsConservative)
 LUAU_FASTFLAG(LuauWidenIfSupertypeIsFree2)
-LUAU_FASTFLAGVARIABLE(LuauDoNotTryToReduce, false)
-LUAU_FASTFLAGVARIABLE(LuauDoNotAccidentallyDependOnPointerOrdering, false)
-LUAU_FASTFLAGVARIABLE(LuauCheckImplicitNumbericKeys, false)
-LUAU_FASTFLAG(LuauAnyInIsOptionalIsOptional)
-LUAU_FASTFLAGVARIABLE(LuauTableUseCounterInstead, false)
 LUAU_FASTFLAGVARIABLE(LuauReturnTypeInferenceInNonstrict, false)
 LUAU_FASTFLAGVARIABLE(LuauRecursionLimitException, false);
-LUAU_FASTFLAG(LuauLosslessClone)
+LUAU_FASTFLAGVARIABLE(LuauApplyTypeFunctionFix, false);
 LUAU_FASTFLAGVARIABLE(LuauTypecheckIter, false);
 LUAU_FASTFLAGVARIABLE(LuauSuccessTypingForEqualityOperations, false)
 LUAU_FASTFLAGVARIABLE(LuauNoMethodLocations, false);
+LUAU_FASTFLAGVARIABLE(LuauAlwaysQuantify, false);
 
 namespace Luau
 {
@@ -371,12 +364,7 @@ ModulePtr TypeChecker::checkWithoutRecursionCheck(const SourceModule& module, Mo
 
     prepareErrorsForDisplay(currentModule->errors);
 
-    bool encounteredFreeType = currentModule->clonePublicInterface(*iceHandler);
+    currentModule->clonePublicInterface(*iceHandler);
-    if (!FFlag::LuauLosslessClone && encounteredFreeType)
-    {
-        reportError(TypeError{module.root->location,
-            GenericError{"Free types leaked into this module's public interface. This is an internal Luau error; please report it."}});
-    }
 
     // Clear unifier cache since it's keyed off internal types that get deallocated
     // This avoids fake cross-module cache hits and keeps cache size at bay when typechecking large module graphs.
@@ -701,7 +689,7 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatIf& statement)
     ExprResult<TypeId> result = checkExpr(scope, *statement.condition);
 
     ScopePtr ifScope = childScope(scope, statement.thenbody->location);
-    reportErrors(resolve(result.predicates, ifScope, true));
+    resolve(result.predicates, ifScope, true);
     check(ifScope, *statement.thenbody);
 
     if (statement.elsebody)
@@ -734,7 +722,7 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatWhile& statement)
     ExprResult<TypeId> result = checkExpr(scope, *statement.condition);
 
     ScopePtr whileScope = childScope(scope, statement.body->location);
-    reportErrors(resolve(result.predicates, whileScope, true));
+    resolve(result.predicates, whileScope, true);
     check(whileScope, *statement.body);
 }
 
@@ -1154,10 +1142,7 @@ void TypeChecker::check(const ScopePtr& scope, const AstStatForIn& forin)
     }
     else
     {
-        if (FFlag::LuauInstantiateFollows)
+        iterTy = instantiate(scope, checkExpr(scope, *firstValue).type, firstValue->location);
-            iterTy = instantiate(scope, checkExpr(scope, *firstValue).type, firstValue->location);
-        else
-            iterTy = follow(instantiate(scope, checkExpr(scope, *firstValue).type, firstValue->location));
     }
 
     if (FFlag::LuauTypecheckIter)
@@ -1849,23 +1834,11 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromType(
 
     tablify(type);
 
-    if (FFlag::LuauDiscriminableUnions2)
+    if (isString(type))
     {
-        if (isString(type))
+        std::optional<TypeId> mtIndex = findMetatableEntry(stringType, "__index", location);
-        {
+        LUAU_ASSERT(mtIndex);
-            std::optional<TypeId> mtIndex = findMetatableEntry(stringType, "__index", location);
+        type = *mtIndex;
-            LUAU_ASSERT(mtIndex);
-            type = *mtIndex;
-        }
-    }
-    else
-    {
-        const PrimitiveTypeVar* primitiveType = get<PrimitiveTypeVar>(type);
-        if (primitiveType && primitiveType->type == PrimitiveTypeVar::String)
-        {
-            if (std::optional<TypeId> mtIndex = findMetatableEntry(type, "__index", location))
-                type = *mtIndex;
-        }
     }
 
     if (TableTypeVar* tableType = getMutableTableType(type))
@@ -1966,23 +1939,10 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromType(
             return std::nullopt;
         }
 
-        if (FFlag::LuauDoNotTryToReduce)
+        if (parts.size() == 1)
-        {
+            return parts[0];
-            if (parts.size() == 1)
-                return parts[0];
 
-            return addType(IntersectionTypeVar{std::move(parts)}); // Not at all correct.
+        return addType(IntersectionTypeVar{std::move(parts)}); // Not at all correct.
-        }
-        else
-        {
-            // TODO(amccord): Write some logic to correctly handle intersections. CLI-34659
-            std::vector<TypeId> result = reduceUnion(parts);
-
-            if (result.size() == 1)
-                return result[0];
-
-            return addType(IntersectionTypeVar{result});
-        }
     }
 
     if (addErrors)
@@ -1993,103 +1953,55 @@ std::optional<TypeId> TypeChecker::getIndexTypeFromType(
 
 std::vector<TypeId> TypeChecker::reduceUnion(const std::vector<TypeId>& types)
 {
-    if (FFlag::LuauDoNotAccidentallyDependOnPointerOrdering)
+    std::vector<TypeId> result;
+    for (TypeId t : types)
     {
-        std::vector<TypeId> result;
+        t = follow(t);
-        for (TypeId t : types)
+        if (get<ErrorTypeVar>(t) || get<AnyTypeVar>(t))
+            return {t};
+
+        if (const UnionTypeVar* utv = get<UnionTypeVar>(t))
         {
-            t = follow(t);
+            if (FFlag::LuauReduceUnionRecursion)
-            if (get<ErrorTypeVar>(t) || get<AnyTypeVar>(t))
-                return {t};
-
-            if (const UnionTypeVar* utv = get<UnionTypeVar>(t))
             {
-                if (FFlag::LuauReduceUnionRecursion)
+                for (TypeId ty : utv)
                 {
-                    for (TypeId ty : utv)
+                    if (FFlag::LuauNormalizeFlagIsConservative)
-                    {
-                        if (get<ErrorTypeVar>(ty) || get<AnyTypeVar>(ty))
-                            return {ty};
-
-                        if (result.end() == std::find(result.begin(), result.end(), ty))
-                            result.push_back(ty);
-                    }
-                }
-                else
-                {
-                    std::vector<TypeId> r = reduceUnion(utv->options);
-                    for (TypeId ty : r)
-                    {
                         ty = follow(ty);
-                        if (get<ErrorTypeVar>(ty) || get<AnyTypeVar>(ty))
+                    if (get<ErrorTypeVar>(ty) || get<AnyTypeVar>(ty))
-                            return {ty};
+                        return {ty};
 
-                        if (std::find(result.begin(), result.end(), ty) == result.end())
+                    if (result.end() == std::find(result.begin(), result.end(), ty))
-                            result.push_back(ty);
+                        result.push_back(ty);
-                    }
                 }
             }
-            else if (std::find(result.begin(), result.end(), t) == result.end())
+            else
-                result.push_back(t);
-        }
-
-        return result;
-    }
-    else
-    {
-        std::set<TypeId> s;
-
-        for (TypeId t : types)
-        {
-            if (const UnionTypeVar* utv = get<UnionTypeVar>(follow(t)))
             {
                 std::vector<TypeId> r = reduceUnion(utv->options);
                 for (TypeId ty : r)
-                    s.insert(ty);
+                {
+                    ty = follow(ty);
+                    if (get<ErrorTypeVar>(ty) || get<AnyTypeVar>(ty))
+                        return {ty};
+
+                    if (std::find(result.begin(), result.end(), ty) == result.end())
+                        result.push_back(ty);
+                }
             }
-            else
-                s.insert(t);
         }
-
+        else if (std::find(result.begin(), result.end(), t) == result.end())
-        // If any of them are ErrorTypeVars/AnyTypeVars, decay into them.
+            result.push_back(t);
-        for (TypeId t : s)
-        {
-            t = follow(t);
-            if (get<ErrorTypeVar>(t) || get<AnyTypeVar>(t))
-                return {t};
-        }
-
-        std::vector<TypeId> r(s.begin(), s.end());
-        std::sort(r.begin(), r.end());
-        return r;
     }
+
+    return result;
 }
 
 std::optional<TypeId> TypeChecker::tryStripUnionFromNil(TypeId ty)
 {
     if (const UnionTypeVar* utv = get<UnionTypeVar>(ty))
     {
-        if (FFlag::LuauAnyInIsOptionalIsOptional)
+        if (!std::any_of(begin(utv), end(utv), isNil))
-        {
+            return ty;
-            if (!std::any_of(begin(utv), end(utv), isNil))
-                return ty;
-        }
-        else
-        {
-            bool hasNil = false;
-
-            for (TypeId option : utv)
-            {
-                if (isNil(option))
-                {
-                    hasNil = true;
-                    break;
-                }
-            }
-
-            if (!hasNil)
-                return ty;
-        }
 
         std::vector<TypeId> result;
 
@@ -2110,32 +2022,18 @@ std::optional<TypeId> TypeChecker::tryStripUnionFromNil(TypeId ty)
 
 TypeId TypeChecker::stripFromNilAndReport(TypeId ty, const Location& location)
 {
-    if (FFlag::LuauAnyInIsOptionalIsOptional)
+    ty = follow(ty);
+
+    if (auto utv = get<UnionTypeVar>(ty))
     {
-        ty = follow(ty);
+        if (!std::any_of(begin(utv), end(utv), isNil))
-
+            return ty;
-        if (auto utv = get<UnionTypeVar>(ty))
-        {
-            if (!std::any_of(begin(utv), end(utv), isNil))
-                return ty;
-        }
-
-        if (std::optional<TypeId> strippedUnion = tryStripUnionFromNil(ty))
-        {
-            reportError(location, OptionalValueAccess{ty});
-            return follow(*strippedUnion);
-        }
     }
-    else
+
+    if (std::optional<TypeId> strippedUnion = tryStripUnionFromNil(ty))
     {
-        if (isOptional(ty))
+        reportError(location, OptionalValueAccess{ty});
-        {
+        return follow(*strippedUnion);
-            if (std::optional<TypeId> strippedUnion = tryStripUnionFromNil(follow(ty)))
-            {
-                reportError(location, OptionalValueAccess{ty});
-                return follow(*strippedUnion);
-            }
-        }
     }
 
     return ty;
@@ -2194,8 +2092,7 @@ TypeId TypeChecker::checkExprTable(
 
             if (indexer)
             {
-                if (FFlag::LuauCheckImplicitNumbericKeys)
+                unify(numberType, indexer->indexType, value->location);
-                    unify(numberType, indexer->indexType, value->location);
                 unify(valueType, indexer->indexResultType, value->location);
             }
             else
@@ -2219,7 +2116,8 @@ TypeId TypeChecker::checkExprTable(
                         if (errors.empty())
                             exprType = expectedProp.type;
                     }
-                    else if (expectedTable->indexer && isString(expectedTable->indexer->indexType))
+                    else if (expectedTable->indexer && (FFlag::LuauExpectedPropTypeFromIndexer ? maybeString(expectedTable->indexer->indexType)
+                                                                                               : isString(expectedTable->indexer->indexType)))
                     {
                         ErrorVec errors = tryUnify(exprType, expectedTable->indexer->indexResultType, k->location);
                         if (errors.empty())
@@ -2259,26 +2157,13 @@ TypeId TypeChecker::checkExprTable(
 
 ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExprTable& expr, std::optional<TypeId> expectedType)
 {
-    if (FFlag::LuauTableUseCounterInstead)
+    RecursionCounter _rc(&checkRecursionCount);
+    if (FInt::LuauCheckRecursionLimit > 0 && checkRecursionCount >= FInt::LuauCheckRecursionLimit)
     {
-        RecursionCounter _rc(&checkRecursionCount);
+        reportErrorCodeTooComplex(expr.location);
-        if (FInt::LuauCheckRecursionLimit > 0 && checkRecursionCount >= FInt::LuauCheckRecursionLimit)
+        return {errorRecoveryType(scope)};
-        {
-            reportErrorCodeTooComplex(expr.location);
-            return {errorRecoveryType(scope)};
-        }
-
-        return checkExpr_(scope, expr, expectedType);
     }
-    else
-    {
-        RecursionLimiter _rl(&recursionCount, FInt::LuauTypeInferRecursionLimit, "checkExpr for tables");
-        return checkExpr_(scope, expr, expectedType);
-    }
-}
 
-ExprResult<TypeId> TypeChecker::checkExpr_(const ScopePtr& scope, const AstExprTable& expr, std::optional<TypeId> expectedType)
-{
     std::vector<std::pair<TypeId, TypeId>> fieldTypes(expr.items.size);
 
     const TableTypeVar* expectedTable = nullptr;
@@ -2324,6 +2209,8 @@ ExprResult<TypeId> TypeChecker::checkExpr_(const ScopePtr& scope, const AstExprT
                 {
                     if (auto prop = expectedTable->props.find(key->value.data); prop != expectedTable->props.end())
                         expectedResultType = prop->second.type;
+                    else if (FFlag::LuauExpectedPropTypeFromIndexer && expectedIndexType && maybeString(*expectedIndexType))
+                        expectedResultType = expectedIndexResultType;
                 }
                 else if (expectedUnion)
                 {
@@ -2529,7 +2416,7 @@ TypeId TypeChecker::checkRelationalOperation(
         if (expr.op == AstExprBinary::Or && subexp->op == AstExprBinary::And)
         {
             ScopePtr subScope = childScope(scope, subexp->location);
-            reportErrors(resolve(predicates, subScope, true));
+            resolve(predicates, subScope, true);
             return unionOfTypes(rhsType, stripNil(checkExpr(subScope, *subexp->right).type, true), expr.location);
         }
     }
@@ -2851,8 +2738,7 @@ ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExprBi
 
         auto [rhsTy, rhsPredicates] = checkExpr(innerScope, *expr.right);
 
-        return {checkBinaryOperation(FFlag::LuauDiscriminableUnions2 ? scope : innerScope, expr, lhsTy, rhsTy),
+        return {checkBinaryOperation(scope, expr, lhsTy, rhsTy), {AndPredicate{std::move(lhsPredicates), std::move(rhsPredicates)}}};
-            {AndPredicate{std::move(lhsPredicates), std::move(rhsPredicates)}}};
     }
     else if (expr.op == AstExprBinary::Or)
     {
@@ -2864,7 +2750,7 @@ ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExprBi
         auto [rhsTy, rhsPredicates] = checkExpr(innerScope, *expr.right);
 
         // Because of C++, I'm not sure if lhsPredicates was not moved out by the time we call checkBinaryOperation.
-        TypeId result = checkBinaryOperation(FFlag::LuauDiscriminableUnions2 ? scope : innerScope, expr, lhsTy, rhsTy, lhsPredicates);
+        TypeId result = checkBinaryOperation(scope, expr, lhsTy, rhsTy, lhsPredicates);
         return {result, {OrPredicate{std::move(lhsPredicates), std::move(rhsPredicates)}}};
     }
     else if (expr.op == AstExprBinary::CompareEq || expr.op == AstExprBinary::CompareNe)
@@ -2872,8 +2758,8 @@ ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExprBi
         if (auto predicate = tryGetTypeGuardPredicate(expr))
             return {booleanType, {std::move(*predicate)}};
 
-        ExprResult<TypeId> lhs = checkExpr(scope, *expr.left, std::nullopt, /*forceSingleton=*/FFlag::LuauDiscriminableUnions2);
+        ExprResult<TypeId> lhs = checkExpr(scope, *expr.left, std::nullopt, /*forceSingleton=*/true);
-        ExprResult<TypeId> rhs = checkExpr(scope, *expr.right, std::nullopt, /*forceSingleton=*/FFlag::LuauDiscriminableUnions2);
+        ExprResult<TypeId> rhs = checkExpr(scope, *expr.right, std::nullopt, /*forceSingleton=*/true);
 
         PredicateVec predicates;
 
@@ -2931,12 +2817,12 @@ ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExprEr
 ExprResult<TypeId> TypeChecker::checkExpr(const ScopePtr& scope, const AstExprIfElse& expr, std::optional<TypeId> expectedType)
 {
     ExprResult<TypeId> result = checkExpr(scope, *expr.condition);
+
     ScopePtr trueScope = childScope(scope, expr.trueExpr->location);
-    reportErrors(resolve(result.predicates, trueScope, true));
+    resolve(result.predicates, trueScope, true);
     ExprResult<TypeId> trueType = checkExpr(trueScope, *expr.trueExpr, expectedType);
 
     ScopePtr falseScope = childScope(scope, expr.falseExpr->location);
-    // Don't report errors for this scope to avoid potentially duplicating errors reported for the first scope.
     resolve(result.predicates, falseScope, false);
     ExprResult<TypeId> falseType = checkExpr(falseScope, *expr.falseExpr, expectedType);
 
@@ -3668,9 +3554,6 @@ void TypeChecker::checkArgumentList(
                 else if (state.log.getMutable<ErrorTypeVar>(t))
                 {
                 } // ok
-                else if (!FFlag::LuauAnyInIsOptionalIsOptional && isNonstrictMode() && state.log.get<AnyTypeVar>(t))
-                {
-                } // ok
                 else
                 {
                     size_t minParams = getMinParameterCount(&state.log, paramPack);
@@ -3823,9 +3706,6 @@ ExprResult<TypePackId> TypeChecker::checkExprPack(const ScopePtr& scope, const A
         actualFunctionType = instantiate(scope, functionType, expr.func->location);
     }
 
-    if (!FFlag::LuauInstantiateFollows)
-        actualFunctionType = follow(actualFunctionType);
-
     TypePackId retPack;
     if (FFlag::LuauLowerBoundsCalculation || !FFlag::LuauWidenIfSupertypeIsFree2)
     {
@@ -4096,32 +3976,6 @@ std::optional<ExprResult<TypePackId>> TypeChecker::checkCallOverload(const Scope
     {
         state.log.commit();
 
-        if (!FFlag::LuauAnyInIsOptionalIsOptional && isNonstrictMode() && !expr.self && expr.func->is<AstExprIndexName>() && ftv->hasSelf)
-        {
-            // If we are running in nonstrict mode, passing fewer arguments than the function is declared to take AND
-            // the function is declared with colon notation AND we use dot notation, warn.
-            auto [providedArgs, providedTail] = flatten(argPack);
-
-            // If we have a variadic tail, we can't say how many arguments were actually provided
-            if (!providedTail)
-            {
-                std::vector<TypeId> actualArgs = flatten(ftv->argTypes).first;
-
-                size_t providedCount = providedArgs.size();
-                size_t requiredCount = actualArgs.size();
-
-                // Ignore optional arguments
-                while (providedCount < requiredCount && requiredCount != 0 && isOptional(actualArgs[requiredCount - 1]))
-                    requiredCount--;
-
-                if (providedCount < requiredCount)
-                {
-                    int requiredExtraNils = int(requiredCount - providedCount);
-                    reportError(TypeError{expr.func->location, FunctionRequiresSelf{requiredExtraNils}});
-                }
-            }
-        }
-
         currentModule->astOverloadResolvedTypes[&expr] = fn;
 
         // We select this overload
@@ -4525,7 +4379,7 @@ bool Instantiation::isDirty(TypeId ty)
 {
     if (const FunctionTypeVar* ftv = log->getMutable<FunctionTypeVar>(ty))
     {
-        if (FFlag::LuauTypecheckOptPass && ftv->hasNoGenerics)
+        if (ftv->hasNoGenerics)
             return false;
 
         return true;
@@ -4582,7 +4436,7 @@ bool ReplaceGenerics::ignoreChildren(TypeId ty)
 {
     if (const FunctionTypeVar* ftv = log->getMutable<FunctionTypeVar>(ty))
     {
-        if (FFlag::LuauTypecheckOptPass && ftv->hasNoGenerics)
+        if (ftv->hasNoGenerics)
             return true;
 
         // We aren't recursing in the case of a generic function which
@@ -4701,8 +4555,17 @@ TypeId TypeChecker::quantify(const ScopePtr& scope, TypeId ty, Location location
     ty = follow(ty);
 
     const FunctionTypeVar* ftv = get<FunctionTypeVar>(ty);
-    if (ftv && ftv->generics.empty() && ftv->genericPacks.empty())
+
-        Luau::quantify(ty, scope->level);
+    if (FFlag::LuauAlwaysQuantify)
+    {
+        if (ftv)
+            Luau::quantify(ty, scope->level);
+    }
+    else
+    {
+        if (ftv && ftv->generics.empty() && ftv->genericPacks.empty())
+            Luau::quantify(ty, scope->level);
+    }
 
     if (FFlag::LuauLowerBoundsCalculation && ftv)
     {
@@ -4717,15 +4580,11 @@ TypeId TypeChecker::quantify(const ScopePtr& scope, TypeId ty, Location location
 
 TypeId TypeChecker::instantiate(const ScopePtr& scope, TypeId ty, Location location, const TxnLog* log)
 {
-    if (FFlag::LuauInstantiateFollows)
+    ty = follow(ty);
-        ty = follow(ty);
 
-    if (FFlag::LuauTypecheckOptPass)
+    const FunctionTypeVar* ftv = get<FunctionTypeVar>(ty);
-    {
+    if (ftv && ftv->hasNoGenerics)
-        const FunctionTypeVar* ftv = get<FunctionTypeVar>(FFlag::LuauInstantiateFollows ? ty : follow(ty));
+        return ty;
-        if (ftv && ftv->hasNoGenerics)
-            return ty;
-    }
 
     Instantiation instantiation{log, &currentModule->internalTypes, scope->level};
 
@@ -5392,10 +5251,9 @@ TypePackId TypeChecker::resolveTypePack(const ScopePtr& scope, const AstTypePack
 
 bool ApplyTypeFunction::isDirty(TypeId ty)
 {
-    // Really this should just replace the arguments,
+    if (FFlag::LuauApplyTypeFunctionFix && typeArguments.count(ty))
-    // but for bug-compatibility with existing code, we replace
+        return true;
-    // all generics.
+    else if (!FFlag::LuauApplyTypeFunctionFix && get<GenericTypeVar>(ty))
-    if (get<GenericTypeVar>(ty))
         return true;
     else if (const FreeTypeVar* ftv = get<FreeTypeVar>(ty))
     {
@@ -5409,10 +5267,9 @@ bool ApplyTypeFunction::isDirty(TypeId ty)
 
 bool ApplyTypeFunction::isDirty(TypePackId tp)
 {
-    // Really this should just replace the arguments,
+    if (FFlag::LuauApplyTypeFunctionFix && typePackArguments.count(tp))
-    // but for bug-compatibility with existing code, we replace
+        return true;
-    // all generics.
+    else if (!FFlag::LuauApplyTypeFunctionFix && get<GenericTypePack>(tp))
-    if (get<GenericTypePack>(tp))
         return true;
     else
         return false;
@@ -5436,11 +5293,13 @@ bool ApplyTypeFunction::ignoreChildren(TypePackId tp)
 
 TypeId ApplyTypeFunction::clean(TypeId ty)
 {
-    // Really this should just replace the arguments,
-    // but for bug-compatibility with existing code, we replace
-    // all generics by free type variables.
     TypeId& arg = typeArguments[ty];
-    if (arg)
+    if (FFlag::LuauApplyTypeFunctionFix)
+    { 
+        LUAU_ASSERT(arg);
+        return arg;
+    }
+    else if (arg)
         return arg;
     else
         return addType(FreeTypeVar{level});
@@ -5448,11 +5307,13 @@ TypeId ApplyTypeFunction::clean(TypeId ty)
 
 TypePackId ApplyTypeFunction::clean(TypePackId tp)
 {
-    // Really this should just replace the arguments,
-    // but for bug-compatibility with existing code, we replace
-    // all generics by free type variables.
     TypePackId& arg = typePackArguments[tp];
-    if (arg)
+    if (FFlag::LuauApplyTypeFunctionFix)
+    { 
+        LUAU_ASSERT(arg);
+        return arg;
+    }
+    else if (arg)
         return arg;
     else
         return addTypePack(FreeTypePack{level});
@@ -5596,8 +5457,6 @@ GenericTypeDefinitions TypeChecker::createGenericTypes(const ScopePtr& scope, st
 
 void TypeChecker::refineLValue(const LValue& lvalue, RefinementMap& refis, const ScopePtr& scope, TypeIdPredicate predicate)
 {
-    LUAU_ASSERT(FFlag::LuauDiscriminableUnions2 || FFlag::LuauAssertStripsFalsyTypes);
-
     const LValue* target = &lvalue;
     std::optional<LValue> key; // If set, we know we took the base of the lvalue path and should be walking down each option of the base's type.
 
@@ -5683,66 +5542,6 @@ std::optional<TypeId> TypeChecker::resolveLValue(const ScopePtr& scope, const LV
     //  We need to search in the provided Scope. Find t.x.y first.
     //  We fail to find t.x.y. Try t.x. We found it. Now we must return the type of the property y from the mapped-to type of t.x.
     //  If we completely fail to find the Symbol t but the Scope has that entry, then we should walk that all the way through and terminate.
-    if (!FFlag::LuauTypecheckOptPass)
-    {
-        const auto& [symbol, keys] = getFullName(lvalue);
-
-        ScopePtr currentScope = scope;
-        while (currentScope)
-        {
-            std::optional<TypeId> found;
-
-            std::vector<LValue> childKeys;
-            const LValue* currentLValue = &lvalue;
-            while (currentLValue)
-            {
-                if (auto it = currentScope->refinements.find(*currentLValue); it != currentScope->refinements.end())
-                {
-                    found = it->second;
-                    break;
-                }
-
-                childKeys.push_back(*currentLValue);
-                currentLValue = baseof(*currentLValue);
-            }
-
-            if (!found)
-            {
-                // Should not be using scope->lookup. This is already recursive.
-                if (auto it = currentScope->bindings.find(symbol); it != currentScope->bindings.end())
-                    found = it->second.typeId;
-                else
-                {
-                    // Nothing exists in this Scope. Just skip and try the parent one.
-                    currentScope = currentScope->parent;
-                    continue;
-                }
-            }
-
-            for (auto it = childKeys.rbegin(); it != childKeys.rend(); ++it)
-            {
-                const LValue& key = *it;
-
-                // Symbol can happen. Skip.
-                if (get<Symbol>(key))
-                    continue;
-                else if (auto field = get<Field>(key))
-                {
-                    found = getIndexTypeFromType(scope, *found, field->key, Location(), false);
-                    if (!found)
-                        return std::nullopt; // Turns out this type doesn't have the property at all. We're done.
-                }
-                else
-                    LUAU_ASSERT(!"New LValue alternative not handled here.");
-            }
-
-            return found;
-        }
-
-        // No entry for it at all. Can happen when LValue root is a global.
-        return std::nullopt;
-    }
-
     const Symbol symbol = getBaseSymbol(lvalue);
 
     ScopePtr currentScope = scope;
@@ -5820,85 +5619,47 @@ static bool isUndecidable(TypeId ty)
     return get<AnyTypeVar>(ty) || get<ErrorTypeVar>(ty) || get<FreeTypeVar>(ty);
 }
 
-ErrorVec TypeChecker::resolve(const PredicateVec& predicates, const ScopePtr& scope, bool sense)
+void TypeChecker::resolve(const PredicateVec& predicates, const ScopePtr& scope, bool sense)
 {
-    ErrorVec errVec;
+    resolve(predicates, scope->refinements, scope, sense);
-    resolve(predicates, errVec, scope->refinements, scope, sense);
-    return errVec;
 }
 
-void TypeChecker::resolve(const PredicateVec& predicates, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr)
+void TypeChecker::resolve(const PredicateVec& predicates, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr)
 {
     for (const Predicate& c : predicates)
-        resolve(c, errVec, refis, scope, sense, fromOr);
+        resolve(c, refis, scope, sense, fromOr);
 }
 
-void TypeChecker::resolve(const Predicate& predicate, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr)
+void TypeChecker::resolve(const Predicate& predicate, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr)
 {
     if (auto truthyP = get<TruthyPredicate>(predicate))
-        resolve(*truthyP, errVec, refis, scope, sense, fromOr);
+        resolve(*truthyP, refis, scope, sense, fromOr);
     else if (auto andP = get<AndPredicate>(predicate))
-        resolve(*andP, errVec, refis, scope, sense);
+        resolve(*andP, refis, scope, sense);
     else if (auto orP = get<OrPredicate>(predicate))
-        resolve(*orP, errVec, refis, scope, sense);
+        resolve(*orP, refis, scope, sense);
     else if (auto notP = get<NotPredicate>(predicate))
-        resolve(notP->predicates, errVec, refis, scope, !sense, fromOr);
+        resolve(notP->predicates, refis, scope, !sense, fromOr);
     else if (auto isaP = get<IsAPredicate>(predicate))
-        resolve(*isaP, errVec, refis, scope, sense);
+        resolve(*isaP, refis, scope, sense);
     else if (auto typeguardP = get<TypeGuardPredicate>(predicate))
-        resolve(*typeguardP, errVec, refis, scope, sense);
+        resolve(*typeguardP, refis, scope, sense);
     else if (auto eqP = get<EqPredicate>(predicate))
-        resolve(*eqP, errVec, refis, scope, sense);
+        resolve(*eqP, refis, scope, sense);
     else
         ice("Unhandled predicate kind");
 }
 
-void TypeChecker::resolve(const TruthyPredicate& truthyP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr)
+void TypeChecker::resolve(const TruthyPredicate& truthyP, RefinementMap& refis, const ScopePtr& scope, bool sense, bool fromOr)
 {
-    if (FFlag::LuauAssertStripsFalsyTypes)
+    std::optional<TypeId> ty = resolveLValue(refis, scope, truthyP.lvalue);
-    {
+    if (ty && fromOr)
-        std::optional<TypeId> ty = resolveLValue(refis, scope, truthyP.lvalue);
+        return addRefinement(refis, truthyP.lvalue, *ty);
-        if (ty && fromOr)
-            return addRefinement(refis, truthyP.lvalue, *ty);
 
-        refineLValue(truthyP.lvalue, refis, scope, mkTruthyPredicate(sense));
+    refineLValue(truthyP.lvalue, refis, scope, mkTruthyPredicate(sense));
-    }
-    else
-    {
-        auto predicate = [sense](TypeId option) -> std::optional<TypeId> {
-            if (isUndecidable(option) || isBoolean(option) || isNil(option) != sense)
-                return option;
-
-            return std::nullopt;
-        };
-
-        if (FFlag::LuauDiscriminableUnions2)
-        {
-            std::optional<TypeId> ty = resolveLValue(refis, scope, truthyP.lvalue);
-            if (ty && fromOr)
-                return addRefinement(refis, truthyP.lvalue, *ty);
-
-            refineLValue(truthyP.lvalue, refis, scope, predicate);
-        }
-        else
-        {
-            std::optional<TypeId> ty = resolveLValue(refis, scope, truthyP.lvalue);
-            if (!ty)
-                return;
-
-            // This is a hack. :(
-            // Without this, the expression 'a or b' might refine 'b' to be falsy.
-            // I'm not yet sure how else to get this to do the right thing without this hack, so we'll do this for now in the meantime.
-            if (fromOr)
-                return addRefinement(refis, truthyP.lvalue, *ty);
-
-            if (std::optional<TypeId> result = filterMap(*ty, predicate))
-                addRefinement(refis, truthyP.lvalue, *result);
-        }
-    }
 }
 
-void TypeChecker::resolve(const AndPredicate& andP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense)
+void TypeChecker::resolve(const AndPredicate& andP, RefinementMap& refis, const ScopePtr& scope, bool sense)
 {
     if (!sense)
     {
@@ -5907,14 +5668,14 @@ void TypeChecker::resolve(const AndPredicate& andP, ErrorVec& errVec, Refinement
             {NotPredicate{std::move(andP.rhs)}},
         };
 
-        return resolve(orP, errVec, refis, scope, !sense);
+        return resolve(orP, refis, scope, !sense);
     }
 
-    resolve(andP.lhs, errVec, refis, scope, sense);
+    resolve(andP.lhs, refis, scope, sense);
-    resolve(andP.rhs, errVec, refis, scope, sense);
+    resolve(andP.rhs, refis, scope, sense);
 }
 
-void TypeChecker::resolve(const OrPredicate& orP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense)
+void TypeChecker::resolve(const OrPredicate& orP, RefinementMap& refis, const ScopePtr& scope, bool sense)
 {
     if (!sense)
     {
@@ -5923,28 +5684,24 @@ void TypeChecker::resolve(const OrPredicate& orP, ErrorVec& errVec, RefinementMa
             {NotPredicate{std::move(orP.rhs)}},
         };
 
-        return resolve(andP, errVec, refis, scope, !sense);
+        return resolve(andP, refis, scope, !sense);
     }
 
-    ErrorVec discarded;
-
     RefinementMap leftRefis;
-    resolve(orP.lhs, errVec, leftRefis, scope, sense);
+    resolve(orP.lhs, leftRefis, scope, sense);
 
     RefinementMap rightRefis;
-    resolve(orP.lhs, discarded, rightRefis, scope, !sense);
+    resolve(orP.lhs, rightRefis, scope, !sense);
-    resolve(orP.rhs, errVec, rightRefis, scope, sense, true); // :(
+    resolve(orP.rhs, rightRefis, scope, sense, true); // :(
 
     merge(refis, leftRefis);
     merge(refis, rightRefis);
 }
 
-void TypeChecker::resolve(const IsAPredicate& isaP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense)
+void TypeChecker::resolve(const IsAPredicate& isaP, RefinementMap& refis, const ScopePtr& scope, bool sense)
 {
     auto predicate = [&](TypeId option) -> std::optional<TypeId> {
         // This by itself is not truly enough to determine that A is stronger than B or vice versa.
-        // The best unambiguous way about this would be to have a function that returns the relationship ordering of a pair.
-        // i.e. TypeRelationship relationshipOf(TypeId superTy, TypeId subTy)
         bool optionIsSubtype = canUnify(option, isaP.ty, isaP.location).empty();
         bool targetIsSubtype = canUnify(isaP.ty, option, isaP.location).empty();
 
@@ -5985,32 +5742,15 @@ void TypeChecker::resolve(const IsAPredicate& isaP, ErrorVec& errVec, Refinement
         return res;
     };
 
-    if (FFlag::LuauDiscriminableUnions2)
+    refineLValue(isaP.lvalue, refis, scope, predicate);
-    {
-        refineLValue(isaP.lvalue, refis, scope, predicate);
-    }
-    else
-    {
-        std::optional<TypeId> ty = resolveLValue(refis, scope, isaP.lvalue);
-        if (!ty)
-            return;
-
-        if (std::optional<TypeId> result = filterMap(*ty, predicate))
-            addRefinement(refis, isaP.lvalue, *result);
-        else
-        {
-            addRefinement(refis, isaP.lvalue, errorRecoveryType(scope));
-            errVec.push_back(TypeError{isaP.location, TypeMismatch{isaP.ty, *ty}});
-        }
-    }
 }
 
-void TypeChecker::resolve(const TypeGuardPredicate& typeguardP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense)
+void TypeChecker::resolve(const TypeGuardPredicate& typeguardP, RefinementMap& refis, const ScopePtr& scope, bool sense)
 {
     // Rewrite the predicate 'type(foo) == "vector"' to be 'typeof(foo) == "Vector3"'. They're exactly identical.
     // This allows us to avoid writing in edge cases.
     if (!typeguardP.isTypeof && typeguardP.kind == "vector")
-        return resolve(TypeGuardPredicate{std::move(typeguardP.lvalue), typeguardP.location, "Vector3", true}, errVec, refis, scope, sense);
+        return resolve(TypeGuardPredicate{std::move(typeguardP.lvalue), typeguardP.location, "Vector3", true}, refis, scope, sense);
 
     std::optional<TypeId> ty = resolveLValue(refis, scope, typeguardP.lvalue);
     if (!ty)
@@ -6060,52 +5800,29 @@ void TypeChecker::resolve(const TypeGuardPredicate& typeguardP, ErrorVec& errVec
 
     if (auto it = primitives.find(typeguardP.kind); it != primitives.end())
     {
-        if (FFlag::LuauDiscriminableUnions2)
+        refineLValue(typeguardP.lvalue, refis, scope, it->second(sense));
-        {
+        return;
-            refineLValue(typeguardP.lvalue, refis, scope, it->second(sense));
-            return;
-        }
-        else
-        {
-            if (std::optional<TypeId> result = filterMap(*ty, it->second(sense)))
-                addRefinement(refis, typeguardP.lvalue, *result);
-            else
-            {
-                addRefinement(refis, typeguardP.lvalue, errorRecoveryType(scope));
-                if (sense)
-                    errVec.push_back(
-                        TypeError{typeguardP.location, GenericError{"Type '" + toString(*ty) + "' has no overlap with '" + typeguardP.kind + "'"}});
-            }
-
-            return;
-        }
     }
 
-    auto fail = [&](const TypeErrorData& err) {
-        if (!FFlag::LuauDiscriminableUnions2)
-            errVec.push_back(TypeError{typeguardP.location, err});
-        addRefinement(refis, typeguardP.lvalue, errorRecoveryType(scope));
-    };
-
     if (!typeguardP.isTypeof)
-        return fail(UnknownSymbol{typeguardP.kind, UnknownSymbol::Type});
+        return addRefinement(refis, typeguardP.lvalue, errorRecoveryType(scope));
 
     auto typeFun = globalScope->lookupType(typeguardP.kind);
     if (!typeFun || !typeFun->typeParams.empty() || !typeFun->typePackParams.empty())
-        return fail(UnknownSymbol{typeguardP.kind, UnknownSymbol::Type});
+        return addRefinement(refis, typeguardP.lvalue, errorRecoveryType(scope));
 
     TypeId type = follow(typeFun->type);
 
     // We're only interested in the root class of any classes.
     if (auto ctv = get<ClassTypeVar>(type); !ctv || ctv->parent)
-        return fail(UnknownSymbol{typeguardP.kind, UnknownSymbol::Type});
+        return addRefinement(refis, typeguardP.lvalue, errorRecoveryType(scope));
 
     // This probably hints at breaking out type filtering functions from the predicate solver so that typeof is not tightly coupled with IsA.
     // Until then, we rewrite this to be the same as using IsA.
-    return resolve(IsAPredicate{std::move(typeguardP.lvalue), typeguardP.location, type}, errVec, refis, scope, sense);
+    return resolve(IsAPredicate{std::move(typeguardP.lvalue), typeguardP.location, type}, refis, scope, sense);
 }
 
-void TypeChecker::resolve(const EqPredicate& eqP, ErrorVec& errVec, RefinementMap& refis, const ScopePtr& scope, bool sense)
+void TypeChecker::resolve(const EqPredicate& eqP, RefinementMap& refis, const ScopePtr& scope, bool sense)
 {
     // This refinement will require success typing to do everything correctly. For now, we can get most of the way there.
     auto options = [](TypeId ty) -> std::vector<TypeId> {
@@ -6114,82 +5831,33 @@ void TypeChecker::resolve(const EqPredicate& eqP, ErrorVec& errVec, RefinementMa
         return {ty};
     };
 
-    if (FFlag::LuauDiscriminableUnions2)
+    std::vector<TypeId> rhs = options(eqP.type);
-    {
-        std::vector<TypeId> rhs = options(eqP.type);
 
-        if (sense && std::any_of(rhs.begin(), rhs.end(), isUndecidable))
+    if (sense && std::any_of(rhs.begin(), rhs.end(), isUndecidable))
-            return; // Optimization: the other side has unknown types, so there's probably an overlap. Refining is no-op here.
+        return; // Optimization: the other side has unknown types, so there's probably an overlap. Refining is no-op here.
 
-        auto predicate = [&](TypeId option) -> std::optional<TypeId> {
+    auto predicate = [&](TypeId option) -> std::optional<TypeId> {
-            if (sense && isUndecidable(option))
+        if (sense && isUndecidable(option))
-                return FFlag::LuauWeakEqConstraint ? option : eqP.type;
+            return FFlag::LuauWeakEqConstraint ? option : eqP.type;
 
-            if (!sense && isNil(eqP.type))
+        if (!sense && isNil(eqP.type))
-                return (isUndecidable(option) || !isNil(option)) ? std::optional<TypeId>(option) : std::nullopt;
+            return (isUndecidable(option) || !isNil(option)) ? std::optional<TypeId>(option) : std::nullopt;
 
-            if (maybeSingleton(eqP.type))
+        if (maybeSingleton(eqP.type))
-            {
-                // Normally we'd write option <: eqP.type, but singletons are always the subtype, so we flip this.
-                if (!sense || canUnify(eqP.type, option, eqP.location).empty())
-                    return sense ? eqP.type : option;
-
-                // local variable works around an odd gcc 9.3 warning: <anonymous> may be used uninitialized
-                std::optional<TypeId> res = std::nullopt;
-                return res;
-            }
-
-            return option;
-        };
-
-        refineLValue(eqP.lvalue, refis, scope, predicate);
-    }
-    else
-    {
-        if (FFlag::LuauWeakEqConstraint)
         {
-            if (!sense && isNil(eqP.type))
+            // Normally we'd write option <: eqP.type, but singletons are always the subtype, so we flip this.
-                resolve(TruthyPredicate{std::move(eqP.lvalue), eqP.location}, errVec, refis, scope, true, /* fromOr= */ false);
+            if (!sense || canUnify(eqP.type, option, eqP.location).empty())
+                return sense ? eqP.type : option;
 
-            return;
+            // local variable works around an odd gcc 9.3 warning: <anonymous> may be used uninitialized
+            std::optional<TypeId> res = std::nullopt;
+            return res;
         }
 
-        if (FFlag::LuauEqConstraint)
+        return option;
-        {
+    };
-            std::optional<TypeId> ty = resolveLValue(refis, scope, eqP.lvalue);
-            if (!ty)
-                return;
 
-            std::vector<TypeId> lhs = options(*ty);
+    refineLValue(eqP.lvalue, refis, scope, predicate);
-            std::vector<TypeId> rhs = options(eqP.type);
-
-            if (sense && std::any_of(lhs.begin(), lhs.end(), isUndecidable))
-            {
-                addRefinement(refis, eqP.lvalue, eqP.type);
-                return;
-            }
-            else if (sense && std::any_of(rhs.begin(), rhs.end(), isUndecidable))
-                return; // Optimization: the other side has unknown types, so there's probably an overlap. Refining is no-op here.
-
-            std::unordered_set<TypeId> set;
-            for (TypeId left : lhs)
-            {
-                for (TypeId right : rhs)
-                {
-                    // When singleton types arrive, `isNil` here probably should be replaced with `isLiteral`.
-                    if (canUnify(right, left, eqP.location).empty() == sense || (!sense && !isNil(left)))
-                        set.insert(left);
-                }
-            }
-
-            if (set.empty())
-                return;
-
-            std::vector<TypeId> viable(set.begin(), set.end());
-            TypeId result = viable.size() == 1 ? viable[0] : addType(UnionTypeVar{std::move(viable)});
-            addRefinement(refis, eqP.lvalue, result);
-        }
-    }
 }
 
 bool TypeChecker::isNonstrictMode() const

Analysis/src/TypeUtils.cpp

@@ -5,8 +5,6 @@
 #include "Luau/ToString.h"
 #include "Luau/TypeInfer.h"
 
-LUAU_FASTFLAGVARIABLE(LuauTerminateCyclicMetatableIndexLookup, false)
-
 namespace Luau
 {
 
@@ -55,13 +53,10 @@ std::optional<TypeId> findTablePropertyRespectingMeta(ErrorVec& errors, TypeId t
     {
         TypeId index = follow(*mtIndex);
 
-        if (FFlag::LuauTerminateCyclicMetatableIndexLookup)
+        if (count >= 100)
-        {
+            return std::nullopt;
-            if (count >= 100)
-                return std::nullopt;
 
-            ++count;
+        ++count;
-        }
 
         if (const auto& itt = getTableType(index))
         {

Analysis/src/TypeVar.cpp

@@ -24,8 +24,6 @@ LUAU_FASTINTVARIABLE(LuauTypeMaximumStringifierLength, 500)
 LUAU_FASTINTVARIABLE(LuauTableTypeMaximumStringifierLength, 0)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
 LUAU_FASTFLAG(LuauSubtypingAddOptPropsToUnsealedTables)
-LUAU_FASTFLAG(LuauDiscriminableUnions2)
-LUAU_FASTFLAGVARIABLE(LuauAnyInIsOptionalIsOptional, false)
 LUAU_FASTFLAGVARIABLE(LuauClassDefinitionModuleInError, false)
 
 namespace Luau
@@ -204,14 +202,14 @@ bool isOptional(TypeId ty)
 
     ty = follow(ty);
 
-    if (FFlag::LuauAnyInIsOptionalIsOptional && get<AnyTypeVar>(ty))
+    if (get<AnyTypeVar>(ty))
         return true;
 
     auto utv = get<UnionTypeVar>(ty);
     if (!utv)
         return false;
 
-    return std::any_of(begin(utv), end(utv), FFlag::LuauAnyInIsOptionalIsOptional ? isOptional : isNil);
+    return std::any_of(begin(utv), end(utv), isOptional);
 }
 
 bool isTableIntersection(TypeId ty)
@@ -378,8 +376,7 @@ bool hasLength(TypeId ty, DenseHashSet<TypeId>& seen, int* recursionCount)
     if (seen.contains(ty))
         return true;
 
-    bool isStr = FFlag::LuauDiscriminableUnions2 ? isString(ty) : isPrim(ty, PrimitiveTypeVar::String);
+    if (isString(ty) || get<AnyTypeVar>(ty) || get<TableTypeVar>(ty) || get<MetatableTypeVar>(ty))
-    if (isStr || get<AnyTypeVar>(ty) || get<TableTypeVar>(ty) || get<MetatableTypeVar>(ty))
         return true;
 
     if (auto uty = get<UnionTypeVar>(ty))

Analysis/src/Unifier.cpp

@@ -24,8 +24,6 @@ LUAU_FASTFLAGVARIABLE(LuauSubtypingAddOptPropsToUnsealedTables, false)
 LUAU_FASTFLAGVARIABLE(LuauWidenIfSupertypeIsFree2, false)
 LUAU_FASTFLAGVARIABLE(LuauDifferentOrderOfUnificationDoesntMatter2, false)
 LUAU_FASTFLAGVARIABLE(LuauTxnLogRefreshFunctionPointers, false)
-LUAU_FASTFLAG(LuauAnyInIsOptionalIsOptional)
-LUAU_FASTFLAG(LuauTypecheckOptPass)
 
 namespace Luau
 {
@@ -382,19 +380,6 @@ Unifier::Unifier(TypeArena* types, Mode mode, const Location& location, Variance
     LUAU_ASSERT(sharedState.iceHandler);
 }
 
-Unifier::Unifier(TypeArena* types, Mode mode, std::vector<std::pair<TypeOrPackId, TypeOrPackId>>* sharedSeen, const Location& location,
-    Variance variance, UnifierSharedState& sharedState, TxnLog* parentLog)
-    : types(types)
-    , mode(mode)
-    , log(parentLog, sharedSeen)
-    , location(location)
-    , variance(variance)
-    , sharedState(sharedState)
-{
-    LUAU_ASSERT(!FFlag::LuauTypecheckOptPass);
-    LUAU_ASSERT(sharedState.iceHandler);
-}
-
 void Unifier::tryUnify(TypeId subTy, TypeId superTy, bool isFunctionCall, bool isIntersection)
 {
     sharedState.counters.iterationCount = 0;
@@ -1219,14 +1204,6 @@ void Unifier::tryUnify_(TypePackId subTp, TypePackId superTp, bool isFunctionCal
                     continue;
                 }
 
-                // In nonstrict mode, any also marks an optional argument.
-                else if (!FFlag::LuauAnyInIsOptionalIsOptional && superIter.good() && isNonstrictMode() &&
-                         log.getMutable<AnyTypeVar>(log.follow(*superIter)))
-                {
-                    superIter.advance();
-                    continue;
-                }
-
                 if (log.getMutable<VariadicTypePack>(superIter.packId))
                 {
                     tryUnifyVariadics(subIter.packId, superIter.packId, false, int(subIter.index));
@@ -1454,21 +1431,9 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
         {
             auto subIter = subTable->props.find(propName);
 
-            if (FFlag::LuauAnyInIsOptionalIsOptional)
+            if (subIter == subTable->props.end() && (!FFlag::LuauSubtypingAddOptPropsToUnsealedTables || subTable->state == TableState::Unsealed) &&
-            {
+                !isOptional(superProp.type))
-                if (subIter == subTable->props.end() &&
+                missingProperties.push_back(propName);
-                    (!FFlag::LuauSubtypingAddOptPropsToUnsealedTables || subTable->state == TableState::Unsealed) && !isOptional(superProp.type))
-                    missingProperties.push_back(propName);
-            }
-            else
-            {
-                bool isAny = log.getMutable<AnyTypeVar>(log.follow(superProp.type));
-
-                if (subIter == subTable->props.end() &&
-                    (!FFlag::LuauSubtypingAddOptPropsToUnsealedTables || subTable->state == TableState::Unsealed) && !isOptional(superProp.type) &&
-                    !isAny)
-                    missingProperties.push_back(propName);
-            }
         }
 
         if (!missingProperties.empty())
@@ -1485,18 +1450,8 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
         {
             auto superIter = superTable->props.find(propName);
 
-            if (FFlag::LuauAnyInIsOptionalIsOptional)
+            if (superIter == superTable->props.end() && (FFlag::LuauSubtypingAddOptPropsToUnsealedTables || !isOptional(subProp.type)))
-            {
+                extraProperties.push_back(propName);
-                if (superIter == superTable->props.end() && (FFlag::LuauSubtypingAddOptPropsToUnsealedTables || !isOptional(subProp.type)))
-                    extraProperties.push_back(propName);
-            }
-            else
-            {
-                bool isAny = log.is<AnyTypeVar>(log.follow(subProp.type));
-                if (superIter == superTable->props.end() &&
-                    (FFlag::LuauSubtypingAddOptPropsToUnsealedTables || (!isOptional(subProp.type) && !isAny)))
-                    extraProperties.push_back(propName);
-            }
         }
 
         if (!extraProperties.empty())
@@ -1540,21 +1495,12 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
             if (innerState.errors.empty())
                 log.concat(std::move(innerState.log));
         }
-        else if (FFlag::LuauAnyInIsOptionalIsOptional &&
+        else if ((!FFlag::LuauSubtypingAddOptPropsToUnsealedTables || subTable->state == TableState::Unsealed) && isOptional(prop.type))
-                 (!FFlag::LuauSubtypingAddOptPropsToUnsealedTables || subTable->state == TableState::Unsealed) && isOptional(prop.type))
         // This is sound because unsealed table types are precise, so `{ p : T } <: { p : T, q : U? }`
         // since if `t : { p : T }` then we are guaranteed that `t.q` is `nil`.
         // TODO: if the supertype is written to, the subtype may no longer be precise (alias analysis?)
         {
         }
-        else if ((!FFlag::LuauSubtypingAddOptPropsToUnsealedTables || subTable->state == TableState::Unsealed) &&
-                 (isOptional(prop.type) || get<AnyTypeVar>(follow(prop.type))))
-        // This is sound because unsealed table types are precise, so `{ p : T } <: { p : T, q : U? }`
-        // since if `t : { p : T }` then we are guaranteed that `t.q` is `nil`.
-        // TODO: should isOptional(anyType) be true?
-        // TODO: if the supertype is written to, the subtype may no longer be precise (alias analysis?)
-        {
-        }
         else if (subTable->state == TableState::Free)
         {
             PendingType* pendingSub = log.queue(subTy);
@@ -1618,10 +1564,7 @@ void Unifier::tryUnifyTables(TypeId subTy, TypeId superTy, bool isIntersection)
         else if (variance == Covariant)
         {
         }
-        else if (FFlag::LuauAnyInIsOptionalIsOptional && !FFlag::LuauSubtypingAddOptPropsToUnsealedTables && isOptional(prop.type))
+        else if (!FFlag::LuauSubtypingAddOptPropsToUnsealedTables && isOptional(prop.type))
-        {
-        }
-        else if (!FFlag::LuauSubtypingAddOptPropsToUnsealedTables && (isOptional(prop.type) || get<AnyTypeVar>(follow(prop.type))))
         {
         }
         else if (superTable->state == TableState::Free)
@@ -1753,9 +1696,7 @@ TypePackId Unifier::widen(TypePackId tp)
 TypeId Unifier::deeplyOptional(TypeId ty, std::unordered_map<TypeId, TypeId> seen)
 {
     ty = follow(ty);
-    if (!FFlag::LuauAnyInIsOptionalIsOptional && get<AnyTypeVar>(ty))
+    if (isOptional(ty))
-        return ty;
-    else if (isOptional(ty))
         return ty;
     else if (const TableTypeVar* ttv = get<TableTypeVar>(ty))
     {
@@ -2666,14 +2607,7 @@ void Unifier::occursCheck(DenseHashSet<TypePackId>& seen, TypePackId needle, Typ
 
 Unifier Unifier::makeChildUnifier()
 {
-    if (FFlag::LuauTypecheckOptPass)
+    Unifier u = Unifier{types, mode, location, variance, sharedState, &log};
-    {
-        Unifier u = Unifier{types, mode, location, variance, sharedState, &log};
-        u.anyIsTop = anyIsTop;
-        return u;
-    }
-
-    Unifier u = Unifier{types, mode, log.sharedSeen, location, variance, sharedState, &log};
     u.anyIsTop = anyIsTop;
     return u;
 }

Compiler/include/Luau/BytecodeBuilder.h

@@ -224,6 +224,7 @@ private:
 
     DenseHashMap<ConstantKey, int32_t, ConstantKeyHash> constantMap;
     DenseHashMap<TableShape, int32_t, TableShapeHash> tableShapeMap;
+    DenseHashMap<uint32_t, int16_t> protoMap;
 
     int debugLine = 0;
 

Compiler/src/BytecodeBuilder.cpp

@@ -6,6 +6,8 @@
 #include <algorithm>
 #include <string.h>
 
+LUAU_FASTFLAG(LuauCompileNestedClosureO2)
+
 namespace Luau
 {
 
@@ -181,6 +183,7 @@ size_t BytecodeBuilder::TableShapeHash::operator()(const TableShape& v) const
 BytecodeBuilder::BytecodeBuilder(BytecodeEncoder* encoder)
     : constantMap({Constant::Type_Nil, ~0ull})
     , tableShapeMap(TableShape())
+    , protoMap(~0u)
     , stringTable({nullptr, 0})
     , encoder(encoder)
 {
@@ -250,6 +253,7 @@ void BytecodeBuilder::endFunction(uint8_t maxstacksize, uint8_t numupvalues)
 
     constantMap.clear();
     tableShapeMap.clear();
+    protoMap.clear();
 
     debugRemarks.clear();
     debugRemarkBuffer.clear();
@@ -372,11 +376,17 @@ int32_t BytecodeBuilder::addConstantClosure(uint32_t fid)
 
 int16_t BytecodeBuilder::addChildFunction(uint32_t fid)
 {
+    if (FFlag::LuauCompileNestedClosureO2)
+        if (int16_t* cache = protoMap.find(fid))
+            return *cache;
+
     uint32_t id = uint32_t(protos.size());
 
     if (id >= kMaxClosureCount)
         return -1;
 
+    if (FFlag::LuauCompileNestedClosureO2)
+        protoMap[fid] = int16_t(id);
     protos.push_back(fid);
 
     return int16_t(id);

Compiler/src/Compiler.cpp

@@ -17,8 +17,6 @@
 #include <math.h>
 #include <limits.h>
 
-LUAU_FASTFLAGVARIABLE(LuauCompileSupportInlining, false)
-
 LUAU_FASTFLAGVARIABLE(LuauCompileIter, false)
 LUAU_FASTFLAGVARIABLE(LuauCompileIterNoReserve, false)
 LUAU_FASTFLAGVARIABLE(LuauCompileIterNoPairs, false)
@@ -30,6 +28,8 @@ LUAU_FASTINTVARIABLE(LuauCompileInlineThreshold, 25)
 LUAU_FASTINTVARIABLE(LuauCompileInlineThresholdMaxBoost, 300)
 LUAU_FASTINTVARIABLE(LuauCompileInlineDepth, 5)
 
+LUAU_FASTFLAGVARIABLE(LuauCompileNestedClosureO2, false)
+
 namespace Luau
 {
 
@@ -100,13 +100,11 @@ struct Compiler
         upvals.reserve(16);
     }
 
-    uint8_t getLocal(AstLocal* local)
+    int getLocalReg(AstLocal* local)
     {
         Local* l = locals.find(local);
-        LUAU_ASSERT(l);
-        LUAU_ASSERT(l->allocated);
 
-        return l->reg;
+        return l && l->allocated ? l->reg : -1;
     }
 
     uint8_t getUpval(AstLocal* local)
@@ -159,17 +157,19 @@ struct Compiler
 
     AstExprFunction* getFunctionExpr(AstExpr* node)
     {
-        if (AstExprLocal* le = node->as<AstExprLocal>())
+        if (AstExprLocal* expr = node->as<AstExprLocal>())
         {
-            Variable* lv = variables.find(le->local);
+            Variable* lv = variables.find(expr->local);
 
             if (!lv || lv->written || !lv->init)
                 return nullptr;
 
             return getFunctionExpr(lv->init);
         }
-        else if (AstExprGroup* ge = node->as<AstExprGroup>())
+        else if (AstExprGroup* expr = node->as<AstExprGroup>())
-            return getFunctionExpr(ge->expr);
+            return getFunctionExpr(expr->expr);
+        else if (AstExprTypeAssertion* expr = node->as<AstExprTypeAssertion>())
+            return getFunctionExpr(expr->expr);
         else
             return node->as<AstExprFunction>();
     }
@@ -180,13 +180,13 @@ struct Compiler
         {
             bool result = true;
 
-            bool visit(AstExpr* node) override
+            bool visit(AstExprFunction* node) override
             {
-                // nested functions may capture function arguments, and our upval handling doesn't handle elided variables (constant)
+                if (!FFlag::LuauCompileNestedClosureO2)
-                // TODO: we could remove this case if we changed function compilation to create temporary locals for constant upvalues
+                    result = false;
-                // TODO: additionally we would need to change upvalue handling in compileExprFunction to handle upvalue->local migration
+
-                result = result && !node->is<AstExprFunction>();
+                // short-circuit to avoid analyzing nested closure bodies
-                return result;
+                return false;
             }
 
             bool visit(AstStat* node) override
@@ -275,8 +275,7 @@ struct Compiler
         f.upvals = upvals;
 
         // record information for inlining
-        if (FFlag::LuauCompileSupportInlining && options.optimizationLevel >= 2 && !func->vararg && canInlineFunctionBody(func->body) &&
+        if (options.optimizationLevel >= 2 && !func->vararg && canInlineFunctionBody(func->body) && !getfenvUsed && !setfenvUsed)
-            !getfenvUsed && !setfenvUsed)
         {
             f.canInline = true;
             f.stackSize = stackSize;
@@ -346,8 +345,8 @@ struct Compiler
 
         uint8_t argreg;
 
-        if (isExprLocalReg(arg))
+        if (int reg = getExprLocalReg(arg); reg >= 0)
-            argreg = getLocal(arg->as<AstExprLocal>()->local);
+            argreg = uint8_t(reg);
         else
         {
             argreg = uint8_t(regs + 1);
@@ -403,8 +402,8 @@ struct Compiler
                 }
             }
 
-            if (isExprLocalReg(expr->args.data[i]))
+            if (int reg = getExprLocalReg(expr->args.data[i]); reg >= 0)
-                args[i] = getLocal(expr->args.data[i]->as<AstExprLocal>()->local);
+                args[i] = uint8_t(reg);
             else
             {
                 args[i] = uint8_t(regs + 1 + i);
@@ -489,19 +488,18 @@ struct Compiler
             return false;
         }
 
-        // TODO: we can compile functions with mismatching arity at call site but it's more annoying
+        // compute constant bitvector for all arguments to feed the cost model
-        if (func->args.size != expr->args.size)
-        {
-            bytecode.addDebugRemark("inlining failed: argument count mismatch (expected %d, got %d)", int(func->args.size), int(expr->args.size));
-            return false;
-        }
-
-        // we use a dynamic cost threshold that's based on the fixed limit boosted by the cost advantage we gain due to inlining
         bool varc[8] = {};
-        for (size_t i = 0; i < expr->args.size && i < 8; ++i)
+        for (size_t i = 0; i < func->args.size && i < expr->args.size && i < 8; ++i)
             varc[i] = isConstant(expr->args.data[i]);
 
-        int inlinedCost = computeCost(fi->costModel, varc, std::min(int(expr->args.size), 8));
+        // if the last argument only returns a single value, all following arguments are nil
+        if (expr->args.size != 0 && !(expr->args.data[expr->args.size - 1]->is<AstExprCall>() || expr->args.data[expr->args.size - 1]->is<AstExprVarargs>()))
+            for (size_t i = expr->args.size; i < func->args.size && i < 8; ++i)
+                varc[i] = true;
+
+        // we use a dynamic cost threshold that's based on the fixed limit boosted by the cost advantage we gain due to inlining
+        int inlinedCost = computeCost(fi->costModel, varc, std::min(int(func->args.size), 8));
         int baselineCost = computeCost(fi->costModel, nullptr, 0) + 3;
         int inlineProfit = (inlinedCost == 0) ? thresholdMaxBoost : std::min(thresholdMaxBoost, 100 * baselineCost / inlinedCost);
 
@@ -533,15 +531,44 @@ struct Compiler
         for (size_t i = 0; i < func->args.size; ++i)
         {
             AstLocal* var = func->args.data[i];
-            AstExpr* arg = expr->args.data[i];
+            AstExpr* arg = i < expr->args.size ? expr->args.data[i] : nullptr;
 
-            if (Variable* vv = variables.find(var); vv && vv->written)
+            if (i + 1 == expr->args.size && func->args.size > expr->args.size && (arg->is<AstExprCall>() || arg->is<AstExprVarargs>()))
+            {
+                // if the last argument can return multiple values, we need to compute all of them into the remaining arguments
+                unsigned int tail = unsigned(func->args.size - expr->args.size) + 1;
+                uint8_t reg = allocReg(arg, tail);
+
+                if (AstExprCall* expr = arg->as<AstExprCall>())
+                    compileExprCall(expr, reg, tail, /* targetTop= */ true);
+                else if (AstExprVarargs* expr = arg->as<AstExprVarargs>())
+                    compileExprVarargs(expr, reg, tail);
+                else
+                    LUAU_ASSERT(!"Unexpected expression type");
+
+                for (size_t j = i; j < func->args.size; ++j)
+                    pushLocal(func->args.data[j], uint8_t(reg + (j - i)));
+
+                // all remaining function arguments have been allocated and assigned to
+                break;
+            }
+            else if (Variable* vv = variables.find(var); vv && vv->written)
             {
                 // if the argument is mutated, we need to allocate a fresh register even if it's a constant
                 uint8_t reg = allocReg(arg, 1);
-                compileExprTemp(arg, reg);
+
+                if (arg)
+                    compileExprTemp(arg, reg);
+                else
+                    bytecode.emitABC(LOP_LOADNIL, reg, 0, 0);
+
                 pushLocal(var, reg);
             }
+            else if (arg == nullptr)
+            {
+                // since the argument is not mutated, we can simply fold the value into the expressions that need it
+                locstants[var] = {Constant::Type_Nil};
+            }
             else if (const Constant* cv = constants.find(arg); cv && cv->type != Constant::Type_Unknown)
             {
                 // since the argument is not mutated, we can simply fold the value into the expressions that need it
@@ -553,20 +580,26 @@ struct Compiler
                 Variable* lv = le ? variables.find(le->local) : nullptr;
 
                 // if the argument is a local that isn't mutated, we will simply reuse the existing register
-                if (isExprLocalReg(arg) && (!lv || !lv->written))
+                if (int reg = le ? getExprLocalReg(le) : -1; reg >= 0 && (!lv || !lv->written))
                 {
-                    uint8_t reg = getLocal(le->local);
+                    pushLocal(var, uint8_t(reg));
-                    pushLocal(var, reg);
                 }
                 else
                 {
-                    uint8_t reg = allocReg(arg, 1);
+                    uint8_t temp = allocReg(arg, 1);
-                    compileExprTemp(arg, reg);
+                    compileExprTemp(arg, temp);
-                    pushLocal(var, reg);
+                    pushLocal(var, temp);
                 }
             }
         }
 
+        // evaluate extra expressions for side effects
+        for (size_t i = func->args.size; i < expr->args.size; ++i)
+        {
+            RegScope rsi(this);
+            compileExprAuto(expr->args.data[i], rsi);
+        }
+
         // fold constant values updated above into expressions in the function body
         foldConstants(constants, variables, locstants, func->body);
 
@@ -627,12 +660,15 @@ struct Compiler
                     FInt::LuauCompileInlineThresholdMaxBoost, FInt::LuauCompileInlineDepth))
                 return;
 
-            if (fi && !fi->canInline)
+            // add a debug remark for cases when we didn't even call tryCompileInlinedCall
+            if (func && !(fi && fi->canInline))
             {
                 if (func->vararg)
                     bytecode.addDebugRemark("inlining failed: function is variadic");
-                else
+                else if (fi)
                     bytecode.addDebugRemark("inlining failed: complex constructs in function body");
+                else
+                    bytecode.addDebugRemark("inlining failed: can't inline recursive calls");
             }
         }
 
@@ -677,9 +713,9 @@ struct Compiler
             LUAU_ASSERT(fi);
 
             // Optimization: use local register directly in NAMECALL if possible
-            if (isExprLocalReg(fi->expr))
+            if (int reg = getExprLocalReg(fi->expr); reg >= 0)
             {
-                selfreg = getLocal(fi->expr->as<AstExprLocal>()->local);
+                selfreg = uint8_t(reg);
             }
             else
             {
@@ -785,6 +821,8 @@ struct Compiler
 
     void compileExprFunction(AstExprFunction* expr, uint8_t target)
     {
+        RegScope rs(this);
+
         const Function* f = functions.find(expr);
         LUAU_ASSERT(f);
 
@@ -795,6 +833,67 @@ struct Compiler
         if (pid < 0)
             CompileError::raise(expr->location, "Exceeded closure limit; simplify the code to compile");
 
+        if (FFlag::LuauCompileNestedClosureO2)
+        {
+            captures.clear();
+            captures.reserve(f->upvals.size());
+
+            for (AstLocal* uv : f->upvals)
+            {
+                LUAU_ASSERT(uv->functionDepth < expr->functionDepth);
+
+                if (int reg = getLocalReg(uv); reg >= 0)
+                {
+                    // note: we can't check if uv is an upvalue in the current frame because inlining can migrate from upvalues to locals
+                    Variable* ul = variables.find(uv);
+                    bool immutable = !ul || !ul->written;
+
+                    captures.push_back({immutable ? LCT_VAL : LCT_REF, uint8_t(reg)});
+                }
+                else if (const Constant* uc = locstants.find(uv); uc && uc->type != Constant::Type_Unknown)
+                {
+                    // inlining can result in an upvalue capture of a constant, in which case we can't capture without a temporary register
+                    uint8_t reg = allocReg(expr, 1);
+                    compileExprConstant(expr, uc, reg);
+
+                    captures.push_back({LCT_VAL, reg});
+                }
+                else
+                {
+                    LUAU_ASSERT(uv->functionDepth < expr->functionDepth - 1);
+
+                    // get upvalue from parent frame
+                    // note: this will add uv to the current upvalue list if necessary
+                    uint8_t uid = getUpval(uv);
+
+                    captures.push_back({LCT_UPVAL, uid});
+                }
+            }
+
+            // Optimization: when closure has no upvalues, or upvalues are safe to share, instead of allocating it every time we can share closure
+            // objects (this breaks assumptions about function identity which can lead to setfenv not working as expected, so we disable this when it
+            // is used)
+            int16_t shared = -1;
+
+            if (options.optimizationLevel >= 1 && shouldShareClosure(expr) && !setfenvUsed)
+            {
+                int32_t cid = bytecode.addConstantClosure(f->id);
+
+                if (cid >= 0 && cid < 32768)
+                    shared = int16_t(cid);
+            }
+
+            if (shared >= 0)
+                bytecode.emitAD(LOP_DUPCLOSURE, target, shared);
+            else
+                bytecode.emitAD(LOP_NEWCLOSURE, target, pid);
+
+            for (const Capture& c : captures)
+                bytecode.emitABC(LOP_CAPTURE, uint8_t(c.type), c.data, 0);
+
+            return;
+        }
+
         bool shared = false;
 
         // Optimization: when closure has no upvalues, or upvalues are safe to share, instead of allocating it every time we can share closure
@@ -824,9 +923,10 @@ struct Compiler
             if (uv->functionDepth == expr->functionDepth - 1)
             {
                 // get local variable
-                uint8_t reg = getLocal(uv);
+                int reg = getLocalReg(uv);
+                LUAU_ASSERT(reg >= 0);
 
-                bytecode.emitABC(LOP_CAPTURE, uint8_t(immutable ? LCT_VAL : LCT_REF), reg, 0);
+                bytecode.emitABC(LOP_CAPTURE, uint8_t(immutable ? LCT_VAL : LCT_REF), uint8_t(reg), 0);
             }
             else
             {
@@ -1213,10 +1313,10 @@ struct Compiler
         if (!isConditionFast(expr->left))
         {
             // Optimization: when right hand side is a local variable, we can use AND/OR
-            if (isExprLocalReg(expr->right))
+            if (int reg = getExprLocalReg(expr->right); reg >= 0)
             {
                 uint8_t lr = compileExprAuto(expr->left, rs);
-                uint8_t rr = getLocal(expr->right->as<AstExprLocal>()->local);
+                uint8_t rr = uint8_t(reg);
 
                 bytecode.emitABC(and_ ? LOP_AND : LOP_OR, target, lr, rr);
                 return;
@@ -1803,19 +1903,18 @@ struct Compiler
         }
         else if (AstExprLocal* expr = node->as<AstExprLocal>())
         {
-            if (FFlag::LuauCompileSupportInlining ? !isExprLocalReg(expr) : expr->upvalue)
+            // note: this can't check expr->upvalue because upvalues may be upgraded to locals during inlining
+            if (int reg = getExprLocalReg(expr); reg >= 0)
+            {
+                bytecode.emitABC(LOP_MOVE, target, uint8_t(reg), 0);
+            }
+            else
             {
                 LUAU_ASSERT(expr->upvalue);
                 uint8_t uid = getUpval(expr->local);
 
                 bytecode.emitABC(LOP_GETUPVAL, target, uid, 0);
             }
-            else
-            {
-                uint8_t reg = getLocal(expr->local);
-
-                bytecode.emitABC(LOP_MOVE, target, reg, 0);
-            }
         }
         else if (AstExprGlobal* expr = node->as<AstExprGlobal>())
         {
@@ -1879,8 +1978,8 @@ struct Compiler
     uint8_t compileExprAuto(AstExpr* node, RegScope&)
     {
         // Optimization: directly return locals instead of copying them to a temporary
-        if (isExprLocalReg(node))
+        if (int reg = getExprLocalReg(node); reg >= 0)
-            return getLocal(node->as<AstExprLocal>()->local);
+            return uint8_t(reg);
 
         // note: the register is owned by the parent scope
         uint8_t reg = allocReg(node, 1);
@@ -1910,7 +2009,7 @@ struct Compiler
             for (size_t i = 0; i < targetCount; ++i)
                 compileExprTemp(list.data[i], uint8_t(target + i));
 
-            // compute expressions with values that go nowhere; this is required to run side-effecting code if any
+            // evaluate extra expressions for side effects
             for (size_t i = targetCount; i < list.size; ++i)
             {
                 RegScope rsi(this);
@@ -2008,20 +2107,21 @@ struct Compiler
 
         if (AstExprLocal* expr = node->as<AstExprLocal>())
         {
-            if (FFlag::LuauCompileSupportInlining ? !isExprLocalReg(expr) : expr->upvalue)
+            // note: this can't check expr->upvalue because upvalues may be upgraded to locals during inlining
+            if (int reg = getExprLocalReg(expr); reg >= 0)
             {
-                LUAU_ASSERT(expr->upvalue);
+                LValue result = {LValue::Kind_Local};
-
+                result.reg = uint8_t(reg);
-                LValue result = {LValue::Kind_Upvalue};
-                result.upval = getUpval(expr->local);
                 result.location = node->location;
 
                 return result;
             }
             else
             {
-                LValue result = {LValue::Kind_Local};
+                LUAU_ASSERT(expr->upvalue);
-                result.reg = getLocal(expr->local);
+
+                LValue result = {LValue::Kind_Upvalue};
+                result.upval = getUpval(expr->local);
                 result.location = node->location;
 
                 return result;
@@ -2115,15 +2215,21 @@ struct Compiler
         compileLValueUse(lv, source, /* set= */ true);
     }
 
-    bool isExprLocalReg(AstExpr* expr)
+    int getExprLocalReg(AstExpr* node)
     {
-        AstExprLocal* le = expr->as<AstExprLocal>();
+        if (AstExprLocal* expr = node->as<AstExprLocal>())
-        if (!le || (!FFlag::LuauCompileSupportInlining && le->upvalue))
+        {
-            return false;
+            // note: this can't check expr->upvalue because upvalues may be upgraded to locals during inlining
+            Local* l = locals.find(expr->local);
 
-        Local* l = locals.find(le->local);
+            return l && l->allocated ? l->reg : -1;
-
+        }
-        return l && l->allocated;
+        else if (AstExprGroup* expr = node->as<AstExprGroup>())
+            return getExprLocalReg(expr->expr);
+        else if (AstExprTypeAssertion* expr = node->as<AstExprTypeAssertion>())
+            return getExprLocalReg(expr->expr);
+        else
+            return -1;
     }
 
     bool isStatBreak(AstStat* node)
@@ -2352,20 +2458,17 @@ struct Compiler
 
         // Optimization: return locals directly instead of copying them into a temporary
         // this is very important for a single return value and occasionally effective for multiple values
-        if (stat->list.size > 0 && isExprLocalReg(stat->list.data[0]))
+        if (int reg = stat->list.size > 0 ? getExprLocalReg(stat->list.data[0]) : -1; reg >= 0)
         {
-            temp = getLocal(stat->list.data[0]->as<AstExprLocal>()->local);
+            temp = uint8_t(reg);
             consecutive = true;
 
             for (size_t i = 1; i < stat->list.size; ++i)
-            {
+                if (getExprLocalReg(stat->list.data[i]) != int(temp + i))
-                AstExpr* v = stat->list.data[i];
-                if (!isExprLocalReg(v) || getLocal(v->as<AstExprLocal>()->local) != temp + i)
                 {
                     consecutive = false;
                     break;
                 }
-            }
         }
 
         if (!consecutive && stat->list.size > 0)
@@ -2438,12 +2541,13 @@ struct Compiler
         {
             bool result = true;
 
-            bool visit(AstExpr* node) override
+            bool visit(AstExprFunction* node) override
             {
-                // functions may capture loop variable, and our upval handling doesn't handle elided variables (constant)
+                if (!FFlag::LuauCompileNestedClosureO2)
-                // TODO: we could remove this case if we changed function compilation to create temporary locals for constant upvalues
+                    result = false;
-                result = result && !node->is<AstExprFunction>();
+
-                return result;
+                // short-circuit to avoid analyzing nested closure bodies
+                return false;
             }
 
             bool visit(AstStat* node) override
@@ -2874,12 +2978,9 @@ struct Compiler
     void compileStatFunction(AstStatFunction* stat)
     {
         // Optimization: compile value expresion directly into target local register
-        if (isExprLocalReg(stat->name))
+        if (int reg = getExprLocalReg(stat->name); reg >= 0)
         {
-            AstExprLocal* le = stat->name->as<AstExprLocal>();
+            compileExpr(stat->func, uint8_t(reg));
-            LUAU_ASSERT(le);
-
-            compileExpr(stat->func, getLocal(le->local));
             return;
         }
 
@@ -3399,6 +3500,12 @@ struct Compiler
         std::vector<size_t> returnJumps;
     };
 
+    struct Capture
+    {
+        LuauCaptureType type;
+        uint8_t data;
+    };
+
     BytecodeBuilder& bytecode;
 
     CompileOptions options;
@@ -3422,6 +3529,7 @@ struct Compiler
     std::vector<LoopJump> loopJumps;
     std::vector<Loop> loops;
     std::vector<InlineFrame> inlineFrames;
+    std::vector<Capture> captures;
 };
 
 void compileOrThrow(BytecodeBuilder& bytecode, AstStatBlock* root, const AstNameTable& names, const CompileOptions& options)
@@ -3465,6 +3573,9 @@ void compileOrThrow(BytecodeBuilder& bytecode, AstStatBlock* root, const AstName
         /* self= */ nullptr, AstArray<AstLocal*>(), /* vararg= */ Luau::Location(), root, /* functionDepth= */ 0, /* debugname= */ AstName());
     uint32_t mainid = compiler.compileFunction(&main);
 
+    const Compiler::Function* mainf = compiler.functions.find(&main);
+    LUAU_ASSERT(mainf && mainf->upvals.empty());
+
     bytecode.setMainFunction(mainid);
     bytecode.finalize();
 }

Compiler/src/ConstantFolding.cpp

@@ -3,8 +3,6 @@
 
 #include <math.h>
 
-LUAU_FASTFLAG(LuauCompileSupportInlining)
-
 namespace Luau
 {
 namespace Compile
@@ -330,7 +328,7 @@ struct ConstantVisitor : AstVisitor
     {
         if (value.type != Constant::Type_Unknown)
             map[key] = value;
-        else if (!FFlag::LuauCompileSupportInlining || wasEmpty)
+        else if (wasEmpty)
             ;
         else if (Constant* old = map.find(key))
             old->type = Constant::Type_Unknown;

Sources.cmake

@@ -73,6 +73,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/include/Luau/ToString.h
     Analysis/include/Luau/Transpiler.h
     Analysis/include/Luau/TxnLog.h
+    Analysis/include/Luau/TypeArena.h
     Analysis/include/Luau/TypeAttach.h
     Analysis/include/Luau/TypedAllocator.h
     Analysis/include/Luau/TypeInfer.h
@@ -108,6 +109,7 @@ target_sources(Luau.Analysis PRIVATE
     Analysis/src/ToString.cpp
     Analysis/src/Transpiler.cpp
     Analysis/src/TxnLog.cpp
+    Analysis/src/TypeArena.cpp
     Analysis/src/TypeAttach.cpp
     Analysis/src/TypedAllocator.cpp
     Analysis/src/TypeInfer.cpp

VM/src/ltablib.cpp

@@ -10,10 +10,6 @@
 #include "ldebug.h"
 #include "lvm.h"
 
-LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauTableMoveTelemetry2, false)
-
-void (*lua_table_move_telemetry)(lua_State* L, int f, int e, int t, int nf, int nt);
-
 static int foreachi(lua_State* L)
 {
     luaL_checktype(L, 1, LUA_TTABLE);
@@ -199,29 +195,6 @@ static int tmove(lua_State* L)
     int tt = !lua_isnoneornil(L, 5) ? 5 : 1; /* destination table */
     luaL_checktype(L, tt, LUA_TTABLE);
 
-    void (*telemetrycb)(lua_State * L, int f, int e, int t, int nf, int nt) = lua_table_move_telemetry;
-
-    if (DFFlag::LuauTableMoveTelemetry2 && telemetrycb && e >= f)
-    {
-        int nf = lua_objlen(L, 1);
-        int nt = lua_objlen(L, tt);
-
-        bool report = false;
-
-        // source index range must be in bounds in source table unless the table is empty (permits 1..#t moves)
-        if (!(f == 1 || (f >= 1 && f <= nf)))
-            report = true;
-        if (!(e == nf || (e >= 1 && e <= nf)))
-            report = true;
-
-        // destination index must be in bounds in dest table or be exactly at the first empty element (permits concats)
-        if (!(t == nt + 1 || (t >= 1 && t <= nt)))
-            report = true;
-
-        if (report)
-            telemetrycb(L, f, e, t, nf, nt);
-    }
-
     if (e >= f)
     { /* otherwise, nothing to move */
         luaL_argcheck(L, f > 0 || e < INT_MAX + f, 3, "too many elements to move");

VM/src/lvmexecute.cpp

@@ -17,9 +17,6 @@
 #include <string.h>
 
 LUAU_FASTFLAGVARIABLE(LuauIter, false)
-LUAU_DYNAMIC_FASTFLAGVARIABLE(LuauIterCallTelemetry, false)
-
-void (*lua_iter_call_telemetry)(lua_State* L);
 
 // Disable c99-designator to avoid the warning in CGOTO dispatch table
 #ifdef __clang__
@@ -157,17 +154,6 @@ LUAU_NOINLINE static bool luau_loopFORG(lua_State* L, int a, int c)
     StkId ra = &L->base[a];
     LUAU_ASSERT(ra + 3 <= L->top);
 
-    if (DFFlag::LuauIterCallTelemetry)
-    {
-        /* TODO: we might be able to stop supporting this depending on whether it's used in practice */
-        void (*telemetrycb)(lua_State* L) = lua_iter_call_telemetry;
-
-        if (telemetrycb && ttistable(ra) && fasttm(L, hvalue(ra)->metatable, TM_CALL))
-            telemetrycb(L);
-        if (telemetrycb && ttisuserdata(ra) && fasttm(L, uvalue(ra)->metatable, TM_CALL))
-            telemetrycb(L);
-    }
-
     setobjs2s(L, ra + 3 + 2, ra + 2);
     setobjs2s(L, ra + 3 + 1, ra + 1);
     setobjs2s(L, ra + 3, ra);

tests/Autocomplete.test.cpp

@@ -2772,6 +2772,8 @@ TEST_CASE_FIXTURE(ACBuiltinsFixture, "autocomplete_on_string_singletons")
 
 TEST_CASE_FIXTURE(ACFixture, "autocomplete_string_singletons")
 {
+    ScopedFastFlag sff{"LuauTwoPassAliasDefinitionFix", true};
+
     check(R"(
         type tag = "cat" | "dog"
         local function f(a: tag) end
@@ -2844,6 +2846,8 @@ f(@1)
 
 TEST_CASE_FIXTURE(ACFixture, "autocomplete_string_singleton_escape")
 {
+        ScopedFastFlag sff{"LuauTwoPassAliasDefinitionFix", true};
+
     check(R"(
         type tag = "strange\t\"cat\"" | 'nice\t"dog"'
         local function f(x: tag) end

tests/Compiler.test.cpp

@@ -4269,22 +4269,26 @@ FORNLOOP R3 -6
 FORNLOOP R0 -11
 RETURN R0 0
 )");
+}
 
-    // can't unroll loops if the body has functions that refer to loop variables
+TEST_CASE("LoopUnrollNestedClosure")
+{
+    ScopedFastFlag sff("LuauCompileNestedClosureO2", true);
+
+    // if the body has functions that refer to loop variables, we unroll the loop and use MOVE+CAPTURE for upvalues
     CHECK_EQ("\n" + compileFunction(R"(
-for i=1,1 do
+for i=1,2 do
     local x = function() return i end
 end
 )",
                         1, 2),
         R"(
-LOADN R2 1
-LOADN R0 1
 LOADN R1 1
-FORNPREP R0 +3
+NEWCLOSURE R0 P0
-NEWCLOSURE R3 P0
+CAPTURE VAL R1
-CAPTURE VAL R2
+LOADN R1 2
-FORNLOOP R0 -3
+NEWCLOSURE R0 P0
+CAPTURE VAL R1
 RETURN R0 0
 )");
 }
@@ -4469,8 +4473,6 @@ RETURN R0 0
 
 TEST_CASE("InlineBasic")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // inline function that returns a constant
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo()
@@ -4550,10 +4552,72 @@ RETURN R1 1
 )");
 }
 
+TEST_CASE("InlineBasicProhibited")
+{
+    ScopedFastFlag sff("LuauCompileNestedClosureO2", true);
+
+    // we can't inline variadic functions
+    CHECK_EQ("\n" + compileFunction(R"(
+local function foo(...)
+    return 42
+end
+
+local x = foo()
+return x
+)",
+                        1, 2),
+        R"(
+DUPCLOSURE R0 K0
+MOVE R1 R0
+CALL R1 0 1
+RETURN R1 1
+)");
+
+    // we also can't inline functions that have internal loops
+    CHECK_EQ("\n" + compileFunction(R"(
+local function foo()
+    for i=1,4 do end
+end
+
+local x = foo()
+return x
+)",
+                        1, 2),
+        R"(
+DUPCLOSURE R0 K0
+MOVE R1 R0
+CALL R1 0 1
+RETURN R1 1
+)");
+}
+
+TEST_CASE("InlineNestedClosures")
+{
+    ScopedFastFlag sff("LuauCompileNestedClosureO2", true);
+
+    // we can inline functions that contain/return functions
+    CHECK_EQ("\n" + compileFunction(R"(
+local function foo(x)
+    return function(y) return x + y end
+end
+
+local x = foo(1)(2)
+return x
+)",
+                        2, 2),
+        R"(
+DUPCLOSURE R0 K0
+LOADN R2 1
+NEWCLOSURE R1 P1
+CAPTURE VAL R2
+LOADN R2 2
+CALL R1 1 1
+RETURN R1 1
+)");
+}
+
 TEST_CASE("InlineMutate")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // if the argument is mutated, it gets a register even if the value is constant
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a)
@@ -4636,8 +4700,6 @@ RETURN R1 1
 
 TEST_CASE("InlineUpval")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // if the argument is an upvalue, we naturally need to copy it to a local
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a)
@@ -4705,8 +4767,6 @@ RETURN R1 1
 
 TEST_CASE("InlineFallthrough")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // if the function doesn't return, we still fill the results with nil
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo()
@@ -4759,8 +4819,6 @@ RETURN R1 -1
 
 TEST_CASE("InlineCapture")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // can't inline function with nested functions that capture locals because they might be constants
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a)
@@ -4782,12 +4840,9 @@ RETURN R2 -1
 
 TEST_CASE("InlineArgMismatch")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // when inlining a function, we must respect all the usual rules
 
     // caller might not have enough arguments
-    // TODO: we don't inline this atm
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a)
     return a
@@ -4799,13 +4854,11 @@ return x
                         1, 2),
         R"(
 DUPCLOSURE R0 K0
-MOVE R1 R0
+LOADNIL R1
-CALL R1 0 1
 RETURN R1 1
 )");
 
     // caller might be using multret for arguments
-    // TODO: we don't inline this atm
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a, b)
     return a + b
@@ -4817,17 +4870,32 @@ return x
                         1, 2),
         R"(
 DUPCLOSURE R0 K0
-MOVE R1 R0
 LOADK R3 K1
 FASTCALL1 20 R3 +2
 GETIMPORT R2 4
-CALL R2 1 -1
+CALL R2 1 2
-CALL R1 -1 1
+ADD R1 R2 R3
+RETURN R1 1
+)");
+
+    // caller might be using varargs for arguments
+    CHECK_EQ("\n" + compileFunction(R"(
+local function foo(a, b)
+    return a + b
+end
+
+local x = foo(...)
+return x
+)",
+                        1, 2),
+        R"(
+DUPCLOSURE R0 K0
+GETVARARGS R2 2
+ADD R1 R2 R3
 RETURN R1 1
 )");
 
     // caller might have too many arguments, but we still need to compute them for side effects
-    // TODO: we don't inline this atm
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a)
     return a
@@ -4839,19 +4907,34 @@ return x
                         1, 2),
         R"(
 DUPCLOSURE R0 K0
-MOVE R1 R0
+GETIMPORT R2 2
+CALL R2 0 1
+LOADN R1 42
+RETURN R1 1
+)");
+
+    // caller might not have enough arguments, and the arg might be mutated so it needs a register
+    CHECK_EQ("\n" + compileFunction(R"(
+local function foo(a)
+    a = 42
+    return a
+end
+
+local x = foo()
+return x
+)",
+                        1, 2),
+        R"(
+DUPCLOSURE R0 K0
+LOADNIL R2
 LOADN R2 42
-GETIMPORT R3 2
+MOVE R1 R2
-CALL R3 0 -1
-CALL R1 -1 1
 RETURN R1 1
 )");
 }
 
 TEST_CASE("InlineMultiple")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // we call this with a different set of variable/constant args
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a, b)
@@ -4880,8 +4963,6 @@ RETURN R3 4
 
 TEST_CASE("InlineChain")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // inline a chain of functions
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a, b)
@@ -4912,8 +4993,6 @@ RETURN R3 1
 
 TEST_CASE("InlineThresholds")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     ScopedFastInt sfis[] = {
         {"LuauCompileInlineThreshold", 25},
         {"LuauCompileInlineThresholdMaxBoost", 300},
@@ -4988,8 +5067,6 @@ RETURN R3 1
 
 TEST_CASE("InlineIIFE")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // IIFE with arguments
     CHECK_EQ("\n" + compileFunction(R"(
 function choose(a, b, c)
@@ -5025,8 +5102,6 @@ RETURN R3 1
 
 TEST_CASE("InlineRecurseArguments")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     // we can't inline a function if it's used to compute its own arguments
     CHECK_EQ("\n" + compileFunction(R"(
 local function foo(a, b)
@@ -5036,22 +5111,20 @@ foo(foo(foo,foo(foo,foo))[foo])
                         1, 2),
         R"(
 DUPCLOSURE R0 K0
-MOVE R1 R0
+MOVE R2 R0
+MOVE R3 R0
 MOVE R4 R0
 MOVE R5 R0
 MOVE R6 R0
-CALL R4 2 1
+CALL R4 2 -1
-LOADNIL R3
+CALL R2 -1 1
-GETTABLE R2 R3 R0
+GETTABLE R1 R2 R0
-CALL R1 1 0
 RETURN R0 0
 )");
 }
 
 TEST_CASE("InlineFastCallK")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     CHECK_EQ("\n" + compileFunction(R"(
 local function set(l0)
     rawset({}, l0)
@@ -5080,8 +5153,6 @@ RETURN R0 0
 
 TEST_CASE("InlineExprIndexK")
 {
-    ScopedFastFlag sff("LuauCompileSupportInlining", true);
-
     CHECK_EQ("\n" + compileFunction(R"(
 local _ = function(l0)
 local _ = nil
@@ -5141,6 +5212,58 @@ RETURN R0 0
 )");
 }
 
+TEST_CASE("InlineHiddenMutation")
+{
+    // when the argument is assigned inside the function, we can't reuse the local
+    CHECK_EQ("\n" + compileFunction(R"(
+local function foo(a)
+    a = 42
+    return a
+end
+
+local x = ...
+local y = foo(x :: number)
+return y
+)",
+                        1, 2),
+        R"(
+DUPCLOSURE R0 K0
+GETVARARGS R1 1
+MOVE R3 R1
+LOADN R3 42
+MOVE R2 R3
+RETURN R2 1
+)");
+
+    // and neither can we do that when it's assigned outside the function
+    CHECK_EQ("\n" + compileFunction(R"(
+local function foo(a)
+    mutator()
+    return a
+end
+
+local x = ...
+mutator = function() x = 42 end
+
+local y = foo(x :: number)
+return y
+)",
+                        2, 2),
+        R"(
+DUPCLOSURE R0 K0
+GETVARARGS R1 1
+NEWCLOSURE R2 P1
+CAPTURE REF R1
+SETGLOBAL R2 K1
+MOVE R3 R1
+GETGLOBAL R4 K1
+CALL R4 0 0
+MOVE R2 R3
+CLOSEUPVALS R1
+RETURN R2 1
+)");
+}
+
 TEST_CASE("ReturnConsecutive")
 {
     // we can return a single local directly
@@ -5193,6 +5316,16 @@ return
 )"),
         R"(
 RETURN R0 0
+)");
+
+    // this optimization also works in presence of group / type casts
+    CHECK_EQ("\n" + compileFunction0(R"(
+local x, y = ...
+return (x), y :: number
+)"),
+        R"(
+GETVARARGS R0 2
+RETURN R0 2
 )");
 }
 

tests/Module.test.cpp

@@ -198,10 +198,6 @@ TEST_CASE_FIXTURE(Fixture, "clone_class")
 
 TEST_CASE_FIXTURE(Fixture, "clone_free_types")
 {
-    ScopedFastFlag sff[]{
-        {"LuauLosslessClone", true},
-    };
-
     TypeVar freeTy(FreeTypeVar{TypeLevel{}});
     TypePackVar freeTp(FreeTypePack{TypeLevel{}});
 
@@ -218,8 +214,6 @@ TEST_CASE_FIXTURE(Fixture, "clone_free_types")
 
 TEST_CASE_FIXTURE(Fixture, "clone_free_tables")
 {
-    ScopedFastFlag sff{"LuauLosslessClone", true};
-
     TypeVar tableTy{TableTypeVar{}};
     TableTypeVar* ttv = getMutable<TableTypeVar>(&tableTy);
     ttv->state = TableState::Free;
@@ -252,8 +246,6 @@ TEST_CASE_FIXTURE(Fixture, "clone_constrained_intersection")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "clone_self_property")
 {
-    ScopedFastFlag sff{"LuauAnyInIsOptionalIsOptional", true};
-
     fileResolver.source["Module/A"] = R"(
         --!nonstrict
         local a = {}

tests/NonstrictMode.test.cpp

@@ -150,8 +150,6 @@ TEST_CASE_FIXTURE(Fixture, "parameters_having_type_any_are_optional")
 
 TEST_CASE_FIXTURE(Fixture, "local_tables_are_not_any")
 {
-    ScopedFastFlag sff{"LuauAnyInIsOptionalIsOptional", true};
-
     CheckResult result = check(R"(
         --!nonstrict
         local T = {}
@@ -169,8 +167,6 @@ TEST_CASE_FIXTURE(Fixture, "local_tables_are_not_any")
 
 TEST_CASE_FIXTURE(Fixture, "offer_a_hint_if_you_use_a_dot_instead_of_a_colon")
 {
-    ScopedFastFlag sff{"LuauAnyInIsOptionalIsOptional", true};
-
     CheckResult result = check(R"(
         --!nonstrict
         local T = {}

tests/Normalize.test.cpp

@@ -683,6 +683,7 @@ TEST_CASE_FIXTURE(Fixture, "cyclic_table_is_marked_normal")
 {
     ScopedFastFlag flags[] = {
         {"LuauLowerBoundsCalculation", true},
+        {"LuauNormalizeFlagIsConservative", false}
     };
 
     check(R"(
@@ -697,6 +698,26 @@ TEST_CASE_FIXTURE(Fixture, "cyclic_table_is_marked_normal")
     CHECK(t->normal);
 }
 
+// Unfortunately, getting this right in the general case is difficult.
+TEST_CASE_FIXTURE(Fixture, "cyclic_table_is_not_marked_normal")
+{
+    ScopedFastFlag flags[] = {
+        {"LuauLowerBoundsCalculation", true},
+        {"LuauNormalizeFlagIsConservative", true}
+    };
+
+    check(R"(
+        type Fiber = {
+            return_: Fiber?
+        }
+
+        local f: Fiber
+    )");
+
+    TypeId t = requireType("f");
+    CHECK(!t->normal);
+}
+
 TEST_CASE_FIXTURE(Fixture, "variadic_tail_is_marked_normal")
 {
     ScopedFastFlag flags[] = {
@@ -997,4 +1018,28 @@ TEST_CASE_FIXTURE(Fixture, "fuzz_failure_bound_type_is_normal_but_not_its_bounde
     LUAU_REQUIRE_ERRORS(result);
 }
 
+// We had an issue where a normal BoundTypeVar might point at a non-normal BoundTypeVar if it in turn pointed to a
+// normal TypeVar because we were calling follow() in an improper place.
+TEST_CASE_FIXTURE(Fixture, "bound_typevars_should_only_be_marked_normal_if_their_pointee_is_normal")
+{
+    ScopedFastFlag sff[]{
+        {"LuauLowerBoundsCalculation", true},
+        {"LuauNormalizeFlagIsConservative", true},
+    };
+
+    CheckResult result = check(R"(
+        local T = {}
+
+        function T:M()
+            local function f(a)
+                print(self.prop)
+                self:g(a)
+                self.prop = a
+            end
+        end
+
+        return T
+    )");
+}
+
 TEST_SUITE_END();

tests/RuntimeLimits.test.cpp

@@ -22,8 +22,6 @@ struct LimitFixture : BuiltinsFixture
 #if defined(_NOOPT) || defined(_DEBUG)
     ScopedFastInt LuauTypeInferRecursionLimit{"LuauTypeInferRecursionLimit", 100};
 #endif
-
-    ScopedFastFlag LuauJustOneCallFrameForHaveSeen{"LuauJustOneCallFrameForHaveSeen", true};
 };
 
 template <typename T>

tests/ToString.test.cpp

@@ -650,6 +650,19 @@ TEST_CASE_FIXTURE(Fixture, "toStringNamedFunction_overrides_param_names")
     CHECK_EQ("test<a>(first: a, second: string, ...: number): a", toStringNamedFunction("test", *ftv, opts));
 }
 
+TEST_CASE_FIXTURE(Fixture, "pick_distinct_names_for_mixed_explicit_and_implicit_generics")
+{
+    ScopedFastFlag sff[] = {
+        {"LuauAlwaysQuantify", true},
+    };
+
+    CheckResult result = check(R"(
+        function foo<a>(x: a, y) end
+    )");
+
+    CHECK("<a, b>(a, b) -> ()" == toString(requireType("foo")));
+}
+
 TEST_CASE_FIXTURE(Fixture, "toStringNamedFunction_include_self_param")
 {
     ScopedFastFlag flag{"LuauDocFuncParameters", true};
@@ -685,5 +698,4 @@ TEST_CASE_FIXTURE(Fixture, "toStringNamedFunction_hide_self_param")
     CHECK_EQ("foo:method<a>(arg: string): ()", toStringNamedFunction("foo:method", *ftv, opts));
 }
 
-
 TEST_SUITE_END();

tests/TypeInfer.builtins.test.cpp

@@ -878,8 +878,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "dont_add_definitions_to_persistent_types")
 TEST_CASE_FIXTURE(BuiltinsFixture, "assert_removes_falsy_types")
 {
     ScopedFastFlag sff[]{
-        {"LuauAssertStripsFalsyTypes", true},
-        {"LuauDiscriminableUnions2", true},
         {"LuauWidenIfSupertypeIsFree2", true},
     };
 
@@ -899,8 +897,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "assert_removes_falsy_types")
 TEST_CASE_FIXTURE(BuiltinsFixture, "assert_removes_falsy_types2")
 {
     ScopedFastFlag sff[]{
-        {"LuauAssertStripsFalsyTypes", true},
-        {"LuauDiscriminableUnions2", true},
         {"LuauWidenIfSupertypeIsFree2", true},
     };
 
@@ -916,11 +912,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "assert_removes_falsy_types2")
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "assert_removes_falsy_types_even_from_type_pack_tail_but_only_for_the_first_type")
 {
-    ScopedFastFlag sff[]{
-        {"LuauAssertStripsFalsyTypes", true},
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         local function f(...: number?)
             return assert(...)
@@ -933,11 +924,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "assert_removes_falsy_types_even_from_type_pa
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "assert_returns_false_and_string_iff_it_knows_the_first_argument_cannot_be_truthy")
 {
-    ScopedFastFlag sff[]{
-        {"LuauAssertStripsFalsyTypes", true},
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         local function f(x: nil)
             return assert(x, "hmm")

tests/TypeInfer.functions.test.cpp

@@ -1496,8 +1496,6 @@ caused by:
 
 TEST_CASE_FIXTURE(Fixture, "strict_mode_ok_with_missing_arguments")
 {
-    ScopedFastFlag sff{"LuauAnyInIsOptionalIsOptional", true};
-
     CheckResult result = check(R"(
         local function f(x: any) end
         f()

tests/TypeInfer.generics.test.cpp

@@ -1121,4 +1121,78 @@ TEST_CASE_FIXTURE(Fixture, "substitution_with_bound_table")
     LUAU_REQUIRE_NO_ERRORS(result);
 }
 
+TEST_CASE_FIXTURE(Fixture, "apply_type_function_nested_generics1")
+{
+    ScopedFastFlag sff{"LuauApplyTypeFunctionFix", true};
+
+    // https://github.com/Roblox/luau/issues/484
+    CheckResult result = check(R"(
+--!strict
+type MyObject = {
+	getReturnValue: <V>(cb: () -> V) -> V
+}
+local object: MyObject = {
+	getReturnValue = function<U>(cb: () -> U): U
+		return cb()
+	end,
+}
+
+type ComplexObject<T> = {
+	id: T,
+	nested: MyObject
+}
+
+local complex: ComplexObject<string> = {
+	id = "Foo",
+	nested = object,
+}
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "apply_type_function_nested_generics2")
+{
+    ScopedFastFlag sff{"LuauApplyTypeFunctionFix", true};
+
+    // https://github.com/Roblox/luau/issues/484
+    CheckResult result = check(R"(
+--!strict
+type MyObject = {
+	getReturnValue: <V>(cb: () -> V) -> V
+}
+type ComplexObject<T> = {
+	id: T,
+	nested: MyObject
+}
+
+local complex2: ComplexObject<string> = nil
+
+local x = complex2.nested.getReturnValue(function(): string
+	return ""
+end)
+
+local y = complex2.nested.getReturnValue(function()
+	return 3
+end)
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "quantify_functions_even_if_they_have_an_explicit_generic")
+{
+    ScopedFastFlag sff[] = {
+        {"LuauAlwaysQuantify", true},
+    };
+
+    CheckResult result = check(R"(
+        function foo<X>(f, x: X)
+            return f(x)
+        end
+    )");
+
+    CHECK("<X, a...>((X) -> (a...), X) -> (a...)" == toString(requireType("foo")));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.intersectionTypes.test.cpp

@@ -177,8 +177,6 @@ TEST_CASE_FIXTURE(Fixture, "index_on_an_intersection_type_with_property_guarante
 
 TEST_CASE_FIXTURE(Fixture, "index_on_an_intersection_type_works_at_arbitrary_depth")
 {
-    ScopedFastFlag sff{"LuauDoNotTryToReduce", true};
-
     CheckResult result = check(R"(
         type A = {x: {y: {z: {thing: string}}}}
         type B = {x: {y: {z: {thing: string}}}}

tests/TypeInfer.loops.test.cpp

@@ -475,8 +475,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "loop_typecheck_crash_on_empty_optional")
 
 TEST_CASE_FIXTURE(Fixture, "fuzz_fail_missing_instantitation_follow")
 {
-    ScopedFastFlag luauInstantiateFollows{"LuauInstantiateFollows", true};
-
     // Just check that this doesn't assert
     check(R"(
         --!nonstrict

tests/TypeInfer.operators.test.cpp

@@ -728,8 +728,6 @@ TEST_CASE_FIXTURE(Fixture, "operator_eq_verifies_types_do_intersect")
 
 TEST_CASE_FIXTURE(Fixture, "operator_eq_operands_are_not_subtypes_of_each_other_but_has_overlap")
 {
-    ScopedFastFlag sff1{"LuauEqConstraint", true};
-
     CheckResult result = check(R"(
         local function f(a: string | number, b: boolean | number)
             return a == b

tests/TypeInfer.provisional.test.cpp

@@ -7,7 +7,6 @@
 
 #include <algorithm>
 
-LUAU_FASTFLAG(LuauEqConstraint)
 LUAU_FASTFLAG(LuauLowerBoundsCalculation)
 
 using namespace Luau;
@@ -183,8 +182,6 @@ TEST_CASE_FIXTURE(Fixture, "operator_eq_completely_incompatible")
 // We'll need to not only report an error on `a == b`, but also to refine both operands as `never` in the `==` branch.
 TEST_CASE_FIXTURE(Fixture, "lvalue_equals_another_lvalue_with_no_overlap")
 {
-    ScopedFastFlag sff1{"LuauEqConstraint", true};
-
     CheckResult result = check(R"(
         local function f(a: string, b: boolean?)
             if a == b then
@@ -208,8 +205,6 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_equals_another_lvalue_with_no_overlap")
 // Just needs to fully support equality refinement. Which is annoying without type states.
 TEST_CASE_FIXTURE(Fixture, "discriminate_from_x_not_equal_to_nil")
 {
-    ScopedFastFlag sff{"LuauDiscriminableUnions2", true};
-
     CheckResult result = check(R"(
         type T = {x: string, y: number} | {x: nil, y: nil}
 
@@ -471,4 +466,35 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "function_returns_many_things_but_first_of_it
     CHECK_EQ("boolean", toString(requireType("b")));
 }
 
+TEST_CASE_FIXTURE(Fixture, "constrained_is_level_dependent")
+{
+    ScopedFastFlag sff[]{
+        {"LuauLowerBoundsCalculation", true},
+        {"LuauNormalizeFlagIsConservative", true},
+    };
+
+    CheckResult result = check(R"(
+        local function f(o)
+            local t = {}
+            t[o] = true
+
+            local function foo(o)
+                o:m1()
+                t[o] = nil
+            end
+
+            local function bar(o)
+                o:m2()
+                t[o] = true
+            end
+
+            return t
+        end
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+    // TODO: We're missing generics a... and b...
+    CHECK_EQ("(t1) -> {| [t1]: boolean |} where t1 = t2 ; t2 = {+ m1: (t1) -> (a...), m2: (t2) -> (b...) +}", toString(requireType("f")));
+}
+
 TEST_SUITE_END();

tests/TypeInfer.refinements.test.cpp

@@ -7,7 +7,6 @@
 
 #include "doctest.h"
 
-LUAU_FASTFLAG(LuauDiscriminableUnions2)
 LUAU_FASTFLAG(LuauWeakEqConstraint)
 LUAU_FASTFLAG(LuauLowerBoundsCalculation)
 
@@ -268,18 +267,10 @@ TEST_CASE_FIXTURE(Fixture, "typeguard_only_look_up_types_from_global_scope")
         end
     )");
 
-    if (FFlag::LuauDiscriminableUnions2)
+    LUAU_REQUIRE_NO_ERRORS(result);
-    {
-        LUAU_REQUIRE_NO_ERRORS(result);
 
-        CHECK_EQ("*unknown*", toString(requireTypeAtPosition({8, 44})));
+    CHECK_EQ("*unknown*", toString(requireTypeAtPosition({8, 44})));
-        CHECK_EQ("*unknown*", toString(requireTypeAtPosition({9, 38})));
+    CHECK_EQ("*unknown*", toString(requireTypeAtPosition({9, 38})));
-    }
-    else
-    {
-        LUAU_REQUIRE_ERROR_COUNT(1, result);
-        CHECK_EQ("Type 'number' has no overlap with 'string'", toString(result.errors[0]));
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "call_a_more_specific_function_using_typeguard")
@@ -378,8 +369,6 @@ caused by:
 
 TEST_CASE_FIXTURE(Fixture, "lvalue_is_equal_to_another_lvalue")
 {
-    ScopedFastFlag sff1{"LuauEqConstraint", true};
-
     CheckResult result = check(R"(
         local function f(a: (string | number)?, b: boolean?)
             if a == b then
@@ -392,28 +381,15 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_is_equal_to_another_lvalue")
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    if (FFlag::LuauWeakEqConstraint)
+    CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "(number | string)?"); // a == b
-    {
+    CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "boolean?");           // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "(number | string)?"); // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "boolean?");           // a == b
 
-        CHECK_EQ(toString(requireTypeAtPosition({5, 33})), "(number | string)?"); // a ~= b
+    CHECK_EQ(toString(requireTypeAtPosition({5, 33})), "(number | string)?"); // a ~= b
-        CHECK_EQ(toString(requireTypeAtPosition({5, 36})), "boolean?");           // a ~= b
+    CHECK_EQ(toString(requireTypeAtPosition({5, 36})), "boolean?");           // a ~= b
-    }
-    else
-    {
-        CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "nil"); // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "nil"); // a == b
-
-        CHECK_EQ(toString(requireTypeAtPosition({5, 33})), "(number | string)?"); // a ~= b
-        CHECK_EQ(toString(requireTypeAtPosition({5, 36})), "boolean?");           // a ~= b
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "lvalue_is_equal_to_a_term")
 {
-    ScopedFastFlag sff1{"LuauEqConstraint", true};
-
     CheckResult result = check(R"(
         local function f(a: (string | number)?)
             if a == 1 then
@@ -426,24 +402,12 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_is_equal_to_a_term")
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    if (FFlag::LuauWeakEqConstraint)
+    CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "(number | string)?"); // a == 1
-    {
+    CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "(number | string)?"); // a ~= 1
-        CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "(number | string)?"); // a == 1
-        CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "(number | string)?"); // a ~= 1
-    }
-    else
-    {
-        CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "number");             // a == 1
-        CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "(number | string)?"); // a ~= 1
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "term_is_equal_to_an_lvalue")
 {
-    ScopedFastFlag sff[] = {
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         local function f(a: (string | number)?)
             if "hello" == a then
@@ -462,8 +426,6 @@ TEST_CASE_FIXTURE(Fixture, "term_is_equal_to_an_lvalue")
 
 TEST_CASE_FIXTURE(Fixture, "lvalue_is_not_nil")
 {
-    ScopedFastFlag sff1{"LuauEqConstraint", true};
-
     CheckResult result = check(R"(
         local function f(a: (string | number)?)
             if a ~= nil then
@@ -476,21 +438,12 @@ TEST_CASE_FIXTURE(Fixture, "lvalue_is_not_nil")
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    if (FFlag::LuauWeakEqConstraint)
+    CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "number | string");    // a ~= nil
-    {
+    CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "(number | string)?"); // a == nil
-        CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "number | string");    // a ~= nil
-        CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "(number | string)?"); // a == nil
-    }
-    else
-    {
-        CHECK_EQ(toString(requireTypeAtPosition({3, 28})), "number | string"); // a ~= nil
-        CHECK_EQ(toString(requireTypeAtPosition({5, 28})), "nil");             // a == nil
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "free_type_is_equal_to_an_lvalue")
 {
-    ScopedFastFlag sff{"LuauDiscriminableUnions2", true};
     ScopedFastFlag sff2{"LuauWeakEqConstraint", true};
 
     CheckResult result = check(R"(
@@ -509,8 +462,6 @@ TEST_CASE_FIXTURE(Fixture, "free_type_is_equal_to_an_lvalue")
 
 TEST_CASE_FIXTURE(Fixture, "unknown_lvalue_is_not_synonymous_with_other_on_not_equal")
 {
-    ScopedFastFlag sff1{"LuauEqConstraint", true};
-
     CheckResult result = check(R"(
         local function f(a: any, b: {x: number}?)
             if a ~= b then
@@ -521,22 +472,12 @@ TEST_CASE_FIXTURE(Fixture, "unknown_lvalue_is_not_synonymous_with_other_on_not_e
 
     LUAU_REQUIRE_NO_ERRORS(result);
 
-    if (FFlag::LuauWeakEqConstraint)
+    CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "any");              // a ~= b
-    {
+    CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "{| x: number |}?"); // a ~= b
-        CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "any");              // a ~= b
-        CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "{| x: number |}?"); // a ~= b
-    }
-    else
-    {
-        CHECK_EQ(toString(requireTypeAtPosition({3, 33})), "any");             // a ~= b
-        CHECK_EQ(toString(requireTypeAtPosition({3, 36})), "{| x: number |}"); // a ~= b
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "string_not_equal_to_string_or_nil")
 {
-    ScopedFastFlag sff1{"LuauEqConstraint", true};
-
     CheckResult result = check(R"(
         local t: {string} = {"hello"}
 
@@ -554,18 +495,8 @@ TEST_CASE_FIXTURE(Fixture, "string_not_equal_to_string_or_nil")
     CHECK_EQ(toString(requireTypeAtPosition({6, 29})), "string");  // a ~= b
     CHECK_EQ(toString(requireTypeAtPosition({6, 32})), "string?"); // a ~= b
 
-    if (FFlag::LuauWeakEqConstraint)
+    CHECK_EQ(toString(requireTypeAtPosition({8, 29})), "string");  // a == b
-    {
+    CHECK_EQ(toString(requireTypeAtPosition({8, 32})), "string?"); // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({8, 29})), "string");  // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({8, 32})), "string?"); // a == b
-    }
-    else
-    {
-        // This is technically not wrong, but it's also wrong at the same time.
-        // The refinement code is none the wiser about the fact we pulled a string out of an array, so it has no choice but to narrow as just string.
-        CHECK_EQ(toString(requireTypeAtPosition({8, 29})), "string"); // a == b
-        CHECK_EQ(toString(requireTypeAtPosition({8, 32})), "string"); // a == b
-    }
 }
 
 TEST_CASE_FIXTURE(Fixture, "narrow_property_of_a_bounded_variable")
@@ -594,16 +525,7 @@ TEST_CASE_FIXTURE(Fixture, "type_narrow_to_vector")
         end
     )");
 
-    if (FFlag::LuauDiscriminableUnions2)
+    LUAU_REQUIRE_NO_ERRORS(result);
-    {
-        LUAU_REQUIRE_NO_ERRORS(result);
-    }
-    else
-    {
-        // This is kinda weird to see, but this actually only happens in Luau without Roblox type bindings because we don't have a Vector3 type.
-        LUAU_REQUIRE_ERROR_COUNT(1, result);
-        CHECK_EQ("Unknown type 'Vector3'", toString(result.errors[0]));
-    }
 
     CHECK_EQ("*unknown*", toString(requireTypeAtPosition({3, 28})));
 }
@@ -1009,10 +931,6 @@ TEST_CASE_FIXTURE(Fixture, "apply_refinements_on_astexprindexexpr_whose_subscrip
 
 TEST_CASE_FIXTURE(Fixture, "discriminate_from_truthiness_of_x")
 {
-    ScopedFastFlag sff[] = {
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         type T = {tag: "missing", x: nil} | {tag: "exists", x: string}
 
@@ -1033,10 +951,6 @@ TEST_CASE_FIXTURE(Fixture, "discriminate_from_truthiness_of_x")
 
 TEST_CASE_FIXTURE(Fixture, "discriminate_tag")
 {
-    ScopedFastFlag sff[] = {
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         type Cat = {tag: "Cat", name: string, catfood: string}
         type Dog = {tag: "Dog", name: string, dogfood: string}
@@ -1070,11 +984,6 @@ TEST_CASE_FIXTURE(Fixture, "and_or_peephole_refinement")
 
 TEST_CASE_FIXTURE(Fixture, "narrow_boolean_to_true_or_false")
 {
-    ScopedFastFlag sff[]{
-        {"LuauDiscriminableUnions2", true},
-        {"LuauAssertStripsFalsyTypes", true},
-    };
-
     CheckResult result = check(R"(
         local function is_true(b: true) end
         local function is_false(b: false) end
@@ -1093,11 +1002,6 @@ TEST_CASE_FIXTURE(Fixture, "narrow_boolean_to_true_or_false")
 
 TEST_CASE_FIXTURE(Fixture, "discriminate_on_properties_of_disjoint_tables_where_that_property_is_true_or_false")
 {
-    ScopedFastFlag sff[]{
-        {"LuauDiscriminableUnions2", true},
-        {"LuauAssertStripsFalsyTypes", true},
-    };
-
     CheckResult result = check(R"(
         type Ok<T> = { ok: true, value: T }
         type Err<E> = { ok: false, error: E }
@@ -1117,8 +1021,6 @@ TEST_CASE_FIXTURE(Fixture, "discriminate_on_properties_of_disjoint_tables_where_
 
 TEST_CASE_FIXTURE(Fixture, "refine_a_property_not_to_be_nil_through_an_intersection_table")
 {
-    ScopedFastFlag sff{"LuauDoNotTryToReduce", true};
-
     CheckResult result = check(R"(
         type T = {} & {f: ((string) -> string)?}
         local function f(t: T, x)
@@ -1133,10 +1035,6 @@ TEST_CASE_FIXTURE(Fixture, "refine_a_property_not_to_be_nil_through_an_intersect
 
 TEST_CASE_FIXTURE(RefinementClassFixture, "discriminate_from_isa_of_x")
 {
-    ScopedFastFlag sff[] = {
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         type T = {tag: "Part", x: Part} | {tag: "Folder", x: Folder}
 
@@ -1171,14 +1069,7 @@ TEST_CASE_FIXTURE(RefinementClassFixture, "typeguard_cast_free_table_to_vector")
         end
     )");
 
-    if (FFlag::LuauDiscriminableUnions2)
+    LUAU_REQUIRE_NO_ERRORS(result);
-        LUAU_REQUIRE_NO_ERRORS(result);
-    else
-    {
-        LUAU_REQUIRE_ERROR_COUNT(1, result);
-
-        CHECK_EQ("Type '{+ X: a, Y: b, Z: c +}' could not be converted into 'Instance'", toString(result.errors[0]));
-    }
 
     CHECK_EQ("Vector3", toString(requireTypeAtPosition({5, 28}))); // type(vec) == "vector"
 

tests/TypeInfer.singletons.test.cpp

@@ -139,6 +139,8 @@ TEST_CASE_FIXTURE(Fixture, "enums_using_singletons")
 
 TEST_CASE_FIXTURE(Fixture, "enums_using_singletons_mismatch")
 {
+    ScopedFastFlag sff{"LuauTwoPassAliasDefinitionFix", true};
+
     CheckResult result = check(R"(
         type MyEnum = "foo" | "bar" | "baz"
         local a : MyEnum = "bang"
@@ -325,8 +327,6 @@ local a: Animal = if true then { tag = 'cat', catfood = 'something' } else { tag
 TEST_CASE_FIXTURE(Fixture, "widen_the_supertype_if_it_is_free_and_subtype_has_singleton")
 {
     ScopedFastFlag sff[]{
-        {"LuauEqConstraint", true},
-        {"LuauDiscriminableUnions2", true},
         {"LuauWidenIfSupertypeIsFree2", true},
         {"LuauWeakEqConstraint", false},
     };
@@ -350,11 +350,8 @@ TEST_CASE_FIXTURE(Fixture, "widen_the_supertype_if_it_is_free_and_subtype_has_si
 TEST_CASE_FIXTURE(Fixture, "return_type_of_f_is_not_widened")
 {
     ScopedFastFlag sff[]{
-        {"LuauDiscriminableUnions2", true},
-        {"LuauEqConstraint", true},
         {"LuauWidenIfSupertypeIsFree2", true},
         {"LuauWeakEqConstraint", false},
-        {"LuauDoNotAccidentallyDependOnPointerOrdering", true},
     };
 
     CheckResult result = check(R"(
@@ -390,7 +387,6 @@ TEST_CASE_FIXTURE(Fixture, "widening_happens_almost_everywhere")
 TEST_CASE_FIXTURE(Fixture, "widening_happens_almost_everywhere_except_for_tables")
 {
     ScopedFastFlag sff[]{
-        {"LuauDiscriminableUnions2", true},
         {"LuauWidenIfSupertypeIsFree2", true},
     };
 
@@ -419,6 +415,7 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "table_insert_with_a_singleton_argument")
 {
     ScopedFastFlag sff[]{
         {"LuauWidenIfSupertypeIsFree2", true},
+        {"LuauWeakEqConstraint", true},
     };
 
     CheckResult result = check(R"(
@@ -456,10 +453,6 @@ TEST_CASE_FIXTURE(Fixture, "functions_are_not_to_be_widened")
 
 TEST_CASE_FIXTURE(Fixture, "indexing_on_string_singletons")
 {
-    ScopedFastFlag sff[]{
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         local a: string = "hi"
         if a == "hi" then
@@ -474,10 +467,6 @@ TEST_CASE_FIXTURE(Fixture, "indexing_on_string_singletons")
 
 TEST_CASE_FIXTURE(Fixture, "indexing_on_union_of_string_singletons")
 {
-    ScopedFastFlag sff[]{
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         local a: string = "hi"
         if a == "hi" or a == "bye" then
@@ -492,10 +481,6 @@ TEST_CASE_FIXTURE(Fixture, "indexing_on_union_of_string_singletons")
 
 TEST_CASE_FIXTURE(Fixture, "taking_the_length_of_string_singleton")
 {
-    ScopedFastFlag sff[]{
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         local a: string = "hi"
         if a == "hi" then
@@ -510,10 +495,6 @@ TEST_CASE_FIXTURE(Fixture, "taking_the_length_of_string_singleton")
 
 TEST_CASE_FIXTURE(Fixture, "taking_the_length_of_union_of_string_singleton")
 {
-    ScopedFastFlag sff[]{
-        {"LuauDiscriminableUnions2", true},
-    };
-
     CheckResult result = check(R"(
         local a: string = "hi"
         if a == "hi" or a == "bye" then

tests/TypeInfer.tables.test.cpp

@@ -2279,8 +2279,6 @@ local y = #x
 
 TEST_CASE_FIXTURE(BuiltinsFixture, "dont_hang_when_trying_to_look_up_in_cyclic_metatable_index")
 {
-    ScopedFastFlag sff{"LuauTerminateCyclicMetatableIndexLookup", true};
-
     // t :: t1 where t1 = {metatable {__index: t1, __tostring: (t1) -> string}}
     CheckResult result = check(R"(
         local mt = {}
@@ -2313,8 +2311,6 @@ TEST_CASE_FIXTURE(BuiltinsFixture, "give_up_after_one_metatable_index_look_up")
 
 TEST_CASE_FIXTURE(Fixture, "confusing_indexing")
 {
-    ScopedFastFlag sff{"LuauDoNotTryToReduce", true};
-
     CheckResult result = check(R"(
         type T = {} & {p: number | string}
         local function f(t: T)
@@ -2971,8 +2967,6 @@ TEST_CASE_FIXTURE(Fixture, "inferred_return_type_of_free_table")
 
 TEST_CASE_FIXTURE(Fixture, "mixed_tables_with_implicit_numbered_keys")
 {
-    ScopedFastFlag sff{"LuauCheckImplicitNumbericKeys", true};
-
     CheckResult result = check(R"(
         local t: { [string]: number } = { 5, 6, 7 }
     )");
@@ -2984,4 +2978,32 @@ TEST_CASE_FIXTURE(Fixture, "mixed_tables_with_implicit_numbered_keys")
     CHECK_EQ("Type 'number' could not be converted into 'string'", toString(result.errors[2]));
 }
 
+TEST_CASE_FIXTURE(Fixture, "expected_indexer_value_type_extra")
+{
+    ScopedFastFlag luauExpectedPropTypeFromIndexer{"LuauExpectedPropTypeFromIndexer", true};
+    ScopedFastFlag luauSubtypingAddOptPropsToUnsealedTables{"LuauSubtypingAddOptPropsToUnsealedTables", true};
+
+    CheckResult result = check(R"(
+        type X = { { x: boolean?, y: boolean? } }
+
+        local l1: {[string]: X} = { key = { { x = true }, { y = true } } }
+        local l2: {[any]: X} = { key = { { x = true }, { y = true } } }
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
+TEST_CASE_FIXTURE(Fixture, "expected_indexer_value_type_extra_2")
+{
+    ScopedFastFlag luauExpectedPropTypeFromIndexer{"LuauExpectedPropTypeFromIndexer", true};
+
+    CheckResult result = check(R"(
+        type X = {[any]: string | boolean}
+
+        local x: X = { key = "str" }
+    )");
+
+    LUAU_REQUIRE_NO_ERRORS(result);
+}
+
 TEST_SUITE_END();

tests/TypeInfer.test.cpp

@@ -15,7 +15,6 @@
 
 LUAU_FASTFLAG(LuauLowerBoundsCalculation)
 LUAU_FASTFLAG(LuauFixLocationSpanTableIndexExpr)
-LUAU_FASTFLAG(LuauEqConstraint)
 
 using namespace Luau;
 
@@ -308,7 +307,6 @@ TEST_CASE_FIXTURE(Fixture, "check_type_infer_recursion_count")
     int limit = 600;
 #endif
 
-    ScopedFastFlag sff{"LuauTableUseCounterInstead", true};
     ScopedFastInt sfi{"LuauCheckRecursionLimit", limit};
 
     CheckResult result = check("function f() return " + rep("{a=", limit) + "'a'" + rep("}", limit) + " end");
@@ -1011,8 +1009,6 @@ TEST_CASE_FIXTURE(Fixture, "type_infer_recursion_limit_no_ice")
 
 TEST_CASE_FIXTURE(Fixture, "follow_on_new_types_in_substitution")
 {
-    ScopedFastFlag substituteFollowNewTypes{"LuauSubstituteFollowNewTypes", true};
-
     CheckResult result = check(R"(
         local obj = {}
 

tests/TypeInfer.unionTypes.test.cpp

@@ -7,7 +7,6 @@
 #include "doctest.h"
 
 LUAU_FASTFLAG(LuauLowerBoundsCalculation)
-LUAU_FASTFLAG(LuauEqConstraint)
 
 using namespace Luau;