Sync to upstream/release/695 (#2043)

Hey there friends, apologies for the late release this week! Most of the
changes amount to essentially spring (really, autumn) cleaning as we
prepare for the next stage of release for the New Type Solver! We've
cleaned up lots of flags, enabled regression tests that had been
disabled because the New Type Solver did not support them, done some
refactoring and otherwise cleaned up bits of code. None of these are
really worth capturing beyond the high-level of saying we cleaned things
up, but there's also a few small runtime fixes that we'll describe
below.

### Runtime

- Fix a bug with the argument ordering for the `vblendvps` and
`vblendvpd` instructions in our Native Code Generation IR that led to
`vector.lerp` having the wrong argument order in some situations when
using NCG. `vector.lerp` should now behave correctly under NCG.
- Remove an incorrect debug assertion in Native Code Generation's
register allocation implementation for A64 assembly (i.e. for ARM's
64-bit architecture).

--- 

Co-authored-by: Andy Friesen <[email protected]>
Co-authored-by: Annie Tang <[email protected]>
Co-authored-by: Ariel Weiss <[email protected]>
Co-authored-by: Hunter Goldstein <[email protected]>
Co-authored-by: Ilya Rezvov <[email protected]>
Co-authored-by: Sora Kanosue <[email protected]>
Co-authored-by: Vyacheslav Egorov <[email protected]>

---------

Co-authored-by: Hunter Goldstein <[email protected]>
Co-authored-by: Varun Saini <[email protected]>
Co-authored-by: Alexander Youngblood <[email protected]>
Co-authored-by: Menarul Alam <[email protected]>
Co-authored-by: Aviral Goel <[email protected]>
Co-authored-by: Vighnesh <[email protected]>
Co-authored-by: Vyacheslav Egorov <[email protected]>
Co-authored-by: Andy Friesen <[email protected]>

Author: 9 people

Analysis/include/Luau/Subtyping.h

@@ -178,8 +178,9 @@ struct SubtypingEnvironment
     GenericBounds& getMappedTypeBounds(TypeId ty, NotNull<InternalErrorReporter> iceReporter);
     // TODO: Clip with LuauSubtypingGenericsDoesntUseVariance
     GenericBounds_DEPRECATED& getMappedTypeBounds_DEPRECATED(TypeId ty);
-    // TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance
+    // TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance2
     TypePackId* getMappedPackBounds_DEPRECATED(TypePackId tp);
+    MappedGenericEnvironment::LookupResult lookupGenericPack(TypePackId tp) const;
 
     /*
      * When we encounter a generic over the course of a subtyping test, we need
@@ -192,7 +193,7 @@ struct SubtypingEnvironment
     DenseHashMap<TypeId, GenericBounds_DEPRECATED> mappedGenerics_DEPRECATED{nullptr};
 
     MappedGenericEnvironment mappedGenericPacks;
-    // TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance
+    // TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance2
     DenseHashMap<TypePackId, TypePackId> mappedGenericPacks_DEPRECATED{nullptr};
 
     /*
@@ -452,8 +453,19 @@ struct Subtyping
         NotNull<Scope> scope
     );
 
+    // Markers to help overload selection.
+    struct Anything{};
+    struct Nothing{};
+
+    SubtypingResult isTailCovariantWithTail(SubtypingEnvironment& env, NotNull<Scope> scope, TypePackId subTp, const VariadicTypePack* sub, TypePackId superTp, const VariadicTypePack* super);
+    SubtypingResult isTailCovariantWithTail(SubtypingEnvironment& env, NotNull<Scope> scope, TypePackId subTp, const GenericTypePack* sub, TypePackId superTp, const GenericTypePack* super);
+    SubtypingResult isTailCovariantWithTail(SubtypingEnvironment& env, NotNull<Scope> scope, TypePackId subTp, const VariadicTypePack* sub, TypePackId superTp, const GenericTypePack* super);
+    SubtypingResult isTailCovariantWithTail(SubtypingEnvironment& env, NotNull<Scope> scope, TypePackId subTp, const GenericTypePack* sub, TypePackId superTp, const VariadicTypePack* super);
+    SubtypingResult isTailCovariantWithTail(SubtypingEnvironment& env, NotNull<Scope> scope, TypePackId subTp, const GenericTypePack* sub, Nothing);
+    SubtypingResult isTailCovariantWithTail(SubtypingEnvironment& env, NotNull<Scope> scope, Nothing, TypePackId superTp, const GenericTypePack* super);
+
     bool bindGeneric(SubtypingEnvironment& env, TypeId subTp, TypeId superTp);
-    // Clip with LuauSubtypingGenericPacksDoesntUseVariance
+    // Clip with LuauSubtypingGenericPacksDoesntUseVariance2
     bool bindGeneric_DEPRECATED(SubtypingEnvironment& env, TypePackId subTp, TypePackId superTp) const;
 
     template<typename T, typename Container>

Analysis/include/Luau/TypePack.h

@@ -231,7 +231,7 @@ bool isEmpty(TypePackId tp);
 /// Flattens out a type pack.  Also returns a valid TypePackId tail if the type pack's full size is not known
 std::pair<std::vector<TypeId>, std::optional<TypePackId>> flatten(TypePackId tp);
 std::pair<std::vector<TypeId>, std::optional<TypePackId>> flatten(TypePackId tp, const TxnLog& log);
-// TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance
+// TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance2
 std::pair<std::vector<TypeId>, std::optional<TypePackId>> flatten_DEPRECATED(
     TypePackId tp,
     const DenseHashMap<TypePackId, TypePackId>& mappedGenericPacks

Analysis/include/Luau/TypePath.h

@@ -243,13 +243,13 @@ std::string toStringHuman(const TypePath::Path& path);
 
 // To keep my head straight when clipping:
 // LuauReturnMappedGenericPacksFromSubtyping3 expects mappedGenericPacks AND arena
-// LuauSubtypingGenericPacksDoesntUseVariance expects just arena. this is the final state
+// LuauSubtypingGenericPacksDoesntUseVariance2 expects just arena. this is the final state
 
 // TODO: clip below two along with `LuauReturnMappedGenericPacksFromSubtyping3`
 std::optional<TypeOrPack> traverse_DEPRECATED(TypeId root, const Path& path, NotNull<BuiltinTypes> builtinTypes);
 std::optional<TypeOrPack> traverse_DEPRECATED(TypePackId root, const Path& path, NotNull<BuiltinTypes> builtinTypes);
 std::optional<TypeOrPack> traverse(TypePackId root, const Path& path, NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena);
-// TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance
+// TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance2
 std::optional<TypeOrPack> traverse_DEPRECATED(
     TypePackId root,
     const Path& path,
@@ -258,7 +258,7 @@ std::optional<TypeOrPack> traverse_DEPRECATED(
     NotNull<TypeArena> arena
 );
 std::optional<TypeOrPack> traverse(TypeId root, const Path& path, NotNull<BuiltinTypes> builtinTypes, NotNull<TypeArena> arena);
-// TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance
+// TODO: Clip with LuauSubtypingGenericPacksDoesntUseVariance2
 std::optional<TypeOrPack> traverse_DEPRECATED(
     TypeId root,
     const Path& path,

Analysis/src/Autocomplete.cpp

@@ -10,7 +10,6 @@
 #include "AutocompleteCore.h"
 
 LUAU_FASTFLAG(LuauSolverV2)
-LUAU_FASTFLAG(LuauSuggestHotComments)
 
 namespace Luau
 {
@@ -41,33 +40,17 @@ AutocompleteResult autocomplete(Frontend& frontend, const ModuleName& moduleName
         globalScope = frontend.globalsForAutocomplete.globalScope.get();
 
     TypeArena typeArena;
-    if (FFlag::LuauSuggestHotComments)
-    {
-        bool isInHotComment = isWithinHotComment(*sourceModule, position);
-        if (isWithinComment(*sourceModule, position) && !isInHotComment)
-            return {};
-
-        std::vector<AstNode*> ancestry = findAncestryAtPositionForAutocomplete(*sourceModule, position);
-        LUAU_ASSERT(!ancestry.empty());
-        ScopePtr startScope = findScopeAtPosition(*module, position);
-
-        return autocomplete_(
-            module, builtinTypes, &typeArena, ancestry, globalScope, startScope, position, frontend.fileResolver, std::move(callback), isInHotComment
-        );
-    }
-    else
-    {
-        if (isWithinComment(*sourceModule, position))
-            return {};
+    bool isInHotComment = isWithinHotComment(*sourceModule, position);
+    if (isWithinComment(*sourceModule, position) && !isInHotComment)
+        return {};
 
-        std::vector<AstNode*> ancestry = findAncestryAtPositionForAutocomplete(*sourceModule, position);
-        LUAU_ASSERT(!ancestry.empty());
-        ScopePtr startScope = findScopeAtPosition(*module, position);
+    std::vector<AstNode*> ancestry = findAncestryAtPositionForAutocomplete(*sourceModule, position);
+    LUAU_ASSERT(!ancestry.empty());
+    ScopePtr startScope = findScopeAtPosition(*module, position);
 
-        return autocomplete_(
-            module, builtinTypes, &typeArena, ancestry, globalScope, startScope, position, frontend.fileResolver, std::move(callback)
-        );
-    }
+    return autocomplete_(
+        module, builtinTypes, &typeArena, ancestry, globalScope, startScope, position, frontend.fileResolver, std::move(callback), isInHotComment
+    );
 }
 
 } // namespace Luau

Analysis/src/AutocompleteCore.cpp

@@ -27,7 +27,6 @@ LUAU_FASTFLAG(LuauSolverV2)
 LUAU_FASTINT(LuauTypeInferIterationLimit)
 LUAU_FASTINT(LuauTypeInferRecursionLimit)
 LUAU_FASTFLAGVARIABLE(DebugLuauMagicVariableNames)
-LUAU_FASTFLAGVARIABLE(LuauSuggestHotComments)
 LUAU_FASTFLAG(LuauAutocompleteAttributes)
 
 static constexpr std::array<std::string_view, 12> kStatementStartingKeywords =
@@ -1824,16 +1823,13 @@ AutocompleteResult autocomplete_(
 {
     LUAU_TIMETRACE_SCOPE("Luau::autocomplete_", "AutocompleteCore");
 
-    if (FFlag::LuauSuggestHotComments)
+    if (isInHotComment)
     {
-        if (isInHotComment)
-        {
-            AutocompleteEntryMap result;
+        AutocompleteEntryMap result;
 
-            for (const std::string_view hc : kHotComments)
-                result.emplace(hc, AutocompleteEntry{AutocompleteEntryKind::HotComment});
-            return {std::move(result), ancestry, AutocompleteContext::HotComment};
-        }
+        for (const std::string_view hc : kHotComments)
+            result.emplace(hc, AutocompleteEntry{AutocompleteEntryKind::HotComment});
+        return {std::move(result), ancestry, AutocompleteContext::HotComment};
     }
 
     AstNode* node = ancestry.back();

Analysis/src/BuiltinTypeFunctions.cpp

@@ -20,7 +20,6 @@
 LUAU_FASTFLAG(DebugLuauEqSatSimplification)
 LUAU_DYNAMIC_FASTINT(LuauTypeFamilyApplicationCartesianProductLimit)
 LUAU_DYNAMIC_FASTINTVARIABLE(LuauStepRefineRecursionLimit, 64)
-LUAU_FASTFLAGVARIABLE(LuauRefineOccursCheckDirectRecursion)
 LUAU_FASTFLAG(LuauReduceSetTypeStackPressure)
 
 LUAU_FASTFLAGVARIABLE(LuauRefineNoRefineAlways)
@@ -1184,7 +1183,7 @@ struct RefineTypeScrubber : public Substitution
                     return true;
             }
         }
-        return FFlag::LuauRefineOccursCheckDirectRecursion ? ty == needle : false;
+        return ty == needle;
     }
 
     bool ignoreChildren(TypeId ty) override
@@ -1226,7 +1225,7 @@ struct RefineTypeScrubber : public Substitution
             else
                 return ctx->arena->addType(IntersectionType{newParts.take()});
         }
-        else if (FFlag::LuauRefineOccursCheckDirectRecursion && ty == needle)
+        else if (ty == needle)
             return ctx->builtins->unknownType;
         else
             return ty;

Analysis/src/ConstraintGenerator.cpp

@@ -37,10 +37,7 @@ LUAU_DYNAMIC_FASTINTVARIABLE(LuauConstraintGeneratorRecursionLimit, 300)
 LUAU_FASTINT(LuauCheckRecursionLimit)
 LUAU_FASTFLAG(DebugLuauLogSolverToJson)
 LUAU_FASTFLAG(DebugLuauMagicTypes)
-LUAU_FASTFLAGVARIABLE(LuauEnableWriteOnlyProperties)
 LUAU_FASTINTVARIABLE(LuauPrimitiveInferenceInTableLimit, 500)
-LUAU_FASTFLAGVARIABLE(LuauInferActualIfElseExprType2)
-LUAU_FASTFLAG(LuauLimitDynamicConstraintSolving3)
 LUAU_FASTFLAG(LuauEmplaceNotPushBack)
 LUAU_FASTFLAG(LuauReduceSetTypeStackPressure)
 LUAU_FASTFLAG(LuauParametrizedAttributeSyntax)
@@ -2080,13 +2077,10 @@ ControlFlow ConstraintGenerator::visit(const ScopePtr& scope, AstStatDeclareExte
                 }
             );
 
-            if (FFlag::LuauLimitDynamicConstraintSolving3)
-            {
-                // If we don't emplace an error type here, then later we'll be
-                // exposing a blocked type in this file's type interface. This
-                // is _normally_ harmless.
-                emplaceType<BoundType>(asMutable(bindingIt->second.type), builtinTypes->errorType);
-            }
+            // If we don't emplace an error type here, then later we'll be
+            // exposing a blocked type in this file's type interface. This
+            // is _normally_ harmless.
+            emplaceType<BoundType>(asMutable(bindingIt->second.type), builtinTypes->errorType);
 
             return ControlFlow::None;
         }
@@ -3333,10 +3327,7 @@ Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprIfElse* ifEls
     applyRefinements(elseScope, ifElse->falseExpr->location, refinementArena.negation(refinement));
     TypeId elseType = check(elseScope, ifElse->falseExpr, expectedType).ty;
 
-    if (FFlag::LuauInferActualIfElseExprType2)
-        return Inference{makeUnion(scope, ifElse->location, thenType, elseType)};
-    else
-        return Inference{expectedType ? *expectedType : makeUnion(scope, ifElse->location, thenType, elseType)};
+    return Inference{makeUnion(scope, ifElse->location, thenType, elseType)};
 }
 
 Inference ConstraintGenerator::check(const ScopePtr& scope, AstExprTypeAssertion* typeAssert)
@@ -3987,7 +3978,7 @@ TypeId ConstraintGenerator::resolveReferenceType(
             else
                 return resolveType_(scope, ref->parameters.data[0].type, inTypeArguments);
         }
-        else if (FFlag::LuauLimitDynamicConstraintSolving3 && ref->name == "_luau_blocked_type")
+        else if (ref->name == "_luau_blocked_type")
         {
             return arena->addType(BlockedType{});
         }

Analysis/src/ConstraintSolver.cpp

@@ -14,6 +14,7 @@
 #include "Luau/ModuleResolver.h"
 #include "Luau/OverloadResolution.h"
 #include "Luau/RecursionCounter.h"
+#include "Luau/ScopedSeenSet.h"
 #include "Luau/Simplify.h"
 #include "Luau/TableLiteralInference.h"
 #include "Luau/TimeTrace.h"
@@ -40,8 +41,6 @@ LUAU_FASTFLAGVARIABLE(DebugLuauEqSatSimplification)
 LUAU_FASTFLAG(LuauTrackUniqueness)
 LUAU_FASTFLAG(LuauLimitUnification)
 LUAU_FASTFLAGVARIABLE(LuauCollapseShouldNotCrash)
-LUAU_FASTFLAGVARIABLE(LuauContainsAnyGenericFollowBeforeChecking)
-LUAU_FASTFLAGVARIABLE(LuauLimitDynamicConstraintSolving3)
 LUAU_FASTFLAGVARIABLE(LuauDontDynamicallyCreateRedundantSubtypeConstraints)
 LUAU_FASTFLAGVARIABLE(LuauExtendSealedTableUpperBounds)
 LUAU_FASTFLAG(LuauReduceSetTypeStackPressure)
@@ -57,28 +56,6 @@ LUAU_FASTFLAGVARIABLE(LuauAvoidOverloadSelectionForFunctionType)
 namespace Luau
 {
 
-struct SeenScope
-{
-    Set<TypeId>& seen;
-    TypeId ty;
-
-    SeenScope(Set<TypeId>& seen, TypeId ty)
-        : seen(seen)
-        , ty(ty)
-    {
-        seen.insert(ty);
-    }
-
-    ~SeenScope()
-    {
-        seen.erase(ty);
-    }
-
-    // Delete copy constructor and copy assignment operator to prevent copying
-    SeenScope(const SeenScope&) = delete;
-    SeenScope& operator=(const SeenScope&) = delete;
-};
-
 bool SubtypeConstraintRecord::operator==(const SubtypeConstraintRecord& other) const
 {
     return (subTy == other.subTy) && (superTy == other.superTy) && (variance == other.variance);
@@ -530,7 +507,7 @@ void ConstraintSolver::run()
 
             // If we were _given_ a limit, and the current limit has hit zero, ]
             // then early exit from constraint solving.
-            if (FFlag::LuauLimitDynamicConstraintSolving3 && FInt::LuauSolverConstraintLimit > 0 && solverConstraintLimit == 0)
+            if (FInt::LuauSolverConstraintLimit > 0 && solverConstraintLimit == 0)
                 break;
 
             std::string saveMe = FFlag::DebugLuauLogSolver ? toString(*c, opts) : std::string{};
@@ -2756,10 +2733,7 @@ struct ContainsAnyGeneric final : public TypeOnceVisitor
 
     bool visit(TypePackId ty) override
     {
-        if (FFlag::LuauContainsAnyGenericFollowBeforeChecking)
-            found = found || is<GenericTypePack>(follow(ty));
-        else
-            found = found || is<GenericTypePack>(ty);
+        found = found || is<GenericTypePack>(follow(ty));
         return !found;
     }
 
@@ -3103,7 +3077,8 @@ TablePropLookupResult ConstraintSolver::lookupTableProp(
     if (seen.contains(subjectType))
         return {};
 
-    std::optional<SeenScope> ss;
+    std::optional<ScopedSeenSet<Set<TypeId>, TypeId>> ss; // This won't be needed once LuauScopedSeenSetInLookupTableProp is clipped.
+
     if (FFlag::LuauScopedSeenSetInLookupTableProp)
         ss.emplace(seen, subjectType);
     else
@@ -3673,15 +3648,12 @@ NotNull<Constraint> ConstraintSolver::pushConstraint(NotNull<Scope> scope, const
     solverConstraints.push_back(std::move(c));
     unsolvedConstraints.emplace_back(borrow);
 
-    if (FFlag::LuauLimitDynamicConstraintSolving3)
+    if (solverConstraintLimit > 0)
     {
-        if (solverConstraintLimit > 0)
-        {
-            --solverConstraintLimit;
+        --solverConstraintLimit;
 
-            if (solverConstraintLimit == 0)
-                reportError(CodeTooComplex{}, location);
-        }
+        if (solverConstraintLimit == 0)
+            reportError(CodeTooComplex{}, location);
     }
 
     return borrow;