[CS] Restore a type variable for compatibility with rdar://85263844

include/swift/AST/DiagnosticsSema.def

@@ -1191,6 +1191,10 @@ WARNING(coercion_may_fail_warning,none,
         "coercion from %0 to %1 may fail; use 'as?' or 'as!' instead",
         (Type, Type))
 
+WARNING(tuple_label_mismatch_warning,none,
+        "tuple conversion from %0 to %1 mismatches labels",
+        (Type, Type))
+
 ERROR(missing_explicit_conversion,none,
       "%0 is not implicitly convertible to %1; "
       "did you mean to use 'as' to explicitly convert?", (Type, Type))

include/swift/Sema/CSFix.h

@@ -376,6 +376,9 @@ enum class FixKind : uint8_t {
   /// Ignore a type mismatch between deduced element type and externally
   /// imposed one.
   IgnoreCollectionElementContextualMismatch,
+
+  /// Produce a warning for a tuple label mismatch.
+  AllowTupleLabelMismatch,
 };
 
 class ConstraintFix {
@@ -2798,6 +2801,27 @@ class AllowInvalidStaticMemberRefOnProtocolMetatype final
   }
 };
 
+/// Emit a warning for mismatched tuple labels.
+class AllowTupleLabelMismatch final : public ContextualMismatch {
+  AllowTupleLabelMismatch(ConstraintSystem &cs, Type fromType, Type toType,
+                          ConstraintLocator *locator)
+      : ContextualMismatch(cs, FixKind::AllowTupleLabelMismatch, fromType,
+                           toType, locator, /*warning*/ true) {}
+
+public:
+  std::string getName() const override { return "allow tuple label mismatch"; }
+
+  bool diagnose(const Solution &solution, bool asNote = false) const override;
+
+  static AllowTupleLabelMismatch *create(ConstraintSystem &cs, Type fromType,
+                                         Type toType,
+                                         ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::AllowTupleLabelMismatch;
+  }
+};
+
 class AllowNonOptionalWeak final : public ConstraintFix {
   AllowNonOptionalWeak(ConstraintSystem &cs, ConstraintLocator *locator)
       : ConstraintFix(cs, FixKind::AllowNonOptionalWeak, locator) {}

include/swift/Sema/Constraint.h

@@ -213,6 +213,12 @@ enum class ConstraintKind : char {
   /// one type - type variable representing type of a node, other side is
   /// the AST node to infer the type for.
   ClosureBodyElement,
+  /// Do not add new uses of this, it only exists to retain compatibility for
+  /// rdar://85263844.
+  ///
+  /// Binds the RHS type to a tuple of the params of a function typed LHS. Note
+  /// this discards function parameter flags.
+  BindTupleOfFunctionParams
 };
 
 /// Classification of the different kinds of constraints.
@@ -685,6 +691,7 @@ class Constraint final : public llvm::ilist_node<Constraint>,
     case ConstraintKind::KeyPath:
     case ConstraintKind::KeyPathApplication:
     case ConstraintKind::Defaultable:
+    case ConstraintKind::BindTupleOfFunctionParams:
       return ConstraintClassification::TypeProperty;
 
     case ConstraintKind::Disjunction:

include/swift/Sema/ConstraintSystem.h

@@ -4748,6 +4748,12 @@ class ConstraintSystem {
                                          TypeMatchOptions flags,
                                          ConstraintLocatorBuilder locator);
 
+  /// Attempt to simplify a BindTupleOfFunctionParams constraint.
+  SolutionKind
+  simplifyBindTupleOfFunctionParamsConstraint(Type first, Type second,
+                                              TypeMatchOptions flags,
+                                              ConstraintLocatorBuilder locator);
+
   /// Attempt to simplify the ApplicableFunction constraint.
   SolutionKind simplifyApplicableFnConstraint(
       Type type1, Type type2,

lib/Sema/CSBindings.cpp

@@ -1378,6 +1378,7 @@ void PotentialBindings::infer(Constraint *constraint) {
   case ConstraintKind::KeyPath:
   case ConstraintKind::ClosureBodyElement:
   case ConstraintKind::Conjunction:
+  case ConstraintKind::BindTupleOfFunctionParams:
     // Constraints from which we can't do anything.
     break;
 

lib/Sema/CSDiagnostics.cpp

@@ -7867,6 +7867,12 @@ bool InvalidWeakAttributeUse::diagnoseAsError() {
   return true;
 }
 
+bool TupleLabelMismatchWarning::diagnoseAsError() {
+  emitDiagnostic(diag::tuple_label_mismatch_warning, getFromType(), getToType())
+      .highlight(getSourceRange());
+  return true;
+}
+
 bool SwiftToCPointerConversionInInvalidContext::diagnoseAsError() {
   auto argInfo = getFunctionArgApplyInfo(getLocator());
   if (!argInfo)

lib/Sema/CSDiagnostics.h

@@ -2620,6 +2620,16 @@ class InvalidWeakAttributeUse final : public FailureDiagnostic {
   bool diagnoseAsError() override;
 };
 
+/// Emit a warning for mismatched tuple labels.
+class TupleLabelMismatchWarning final : public ContextualFailure {
+public:
+  TupleLabelMismatchWarning(const Solution &solution, Type fromType,
+                            Type toType, ConstraintLocator *locator)
+      : ContextualFailure(solution, fromType, toType, locator) {}
+
+  bool diagnoseAsError() override;
+};
+
 /// Diagnose situations where Swift -> C pointer implicit conversion
 /// is attempted on a Swift function instead of one imported from C header.
 ///

lib/Sema/CSFix.cpp

@@ -2024,6 +2024,20 @@ AllowNonOptionalWeak *AllowNonOptionalWeak::create(ConstraintSystem &cs,
   return new (cs.getAllocator()) AllowNonOptionalWeak(cs, locator);
 }
 
+AllowTupleLabelMismatch *
+AllowTupleLabelMismatch::create(ConstraintSystem &cs, Type fromType,
+                                Type toType, ConstraintLocator *locator) {
+  return new (cs.getAllocator())
+      AllowTupleLabelMismatch(cs, fromType, toType, locator);
+}
+
+bool AllowTupleLabelMismatch::diagnose(const Solution &solution,
+                                       bool asNote) const {
+  TupleLabelMismatchWarning warning(solution, getFromType(), getToType(),
+                                    getLocator());
+  return warning.diagnose(asNote);
+}
+
 bool AllowSwiftToCPointerConversion::diagnose(const Solution &solution,
                                               bool asNote) const {
   SwiftToCPointerConversionInInvalidContext failure(solution, getLocator());

lib/Sema/CSGen.cpp

@@ -1525,6 +1525,19 @@ namespace {
         auto methodTy =
             CS.createTypeVariable(memberTypeLoc, TVO_CanBindToNoEscape);
 
+        // HACK: Bind the function's parameter list as a tuple to a type
+        // variable. This only exists to preserve compatibility with
+        // rdar://85263844, as it can affect the prioritization of bindings,
+        // which can affect behavior for tuple matching as tuple subtyping is
+        // currently a *weaker* constraint than tuple conversion.
+        if (!CS.getASTContext().isSwiftVersionAtLeast(6)) {
+          auto paramTypeVar = CS.createTypeVariable(
+              CS.getConstraintLocator(expr, ConstraintLocator::ApplyArgument),
+              TVO_CanBindToLValue | TVO_CanBindToInOut | TVO_CanBindToNoEscape);
+          CS.addConstraint(ConstraintKind::BindTupleOfFunctionParams, methodTy,
+                           paramTypeVar, CS.getConstraintLocator(expr));
+        }
+
         CS.addValueMemberConstraint(
             baseTy, expr->getName(), methodTy, CurDC,
             expr->getFunctionRefKind(),

lib/Sema/CSSimplify.cpp

@@ -1620,6 +1620,7 @@ ConstraintSystem::matchTupleTypes(TupleType *tuple1, TupleType *tuple2,
       }
     }
 
+    auto hasLabelMismatch = false;
     for (unsigned i = 0, n = tuple1->getNumElements(); i != n; ++i) {
       const auto &elt1 = tuple1->getElement(i);
       const auto &elt2 = tuple2->getElement(i);
@@ -1641,6 +1642,11 @@ ConstraintSystem::matchTupleTypes(TupleType *tuple1, TupleType *tuple2,
           // used at some other position.
           if (elt2.hasName() && tuple1->getNamedElementId(elt2.getName()) != -1)
             return getTypeMatchFailure(locator);
+
+          // If both elements have names and they mismatch, make a note of it
+          // so we can emit a warning.
+          if (elt1.hasName() && elt2.hasName())
+            hasLabelMismatch = true;
         }
       }
 
@@ -1656,6 +1662,13 @@ ConstraintSystem::matchTupleTypes(TupleType *tuple1, TupleType *tuple2,
         return result;
     }
 
+    if (hasLabelMismatch) {
+      // If we had a label mismatch, emit a warning. This is something we
+      // shouldn't permit, as it's more permissive than what a conversion would
+      // allow. Ideally we'd turn this into an error in Swift 6 mode.
+      recordFix(AllowTupleLabelMismatch::create(
+          *this, tuple1, tuple2, getConstraintLocator(locator)));
+    }
     return getTypeMatchSuccess();
   }
 
@@ -1700,6 +1713,7 @@ ConstraintSystem::matchTupleTypes(TupleType *tuple1, TupleType *tuple2,
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::ClosureBodyElement:
+  case ConstraintKind::BindTupleOfFunctionParams:
     llvm_unreachable("Not a conversion");
   }
 
@@ -1839,6 +1853,7 @@ static bool matchFunctionRepresentations(FunctionType::ExtInfo einfo1,
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::ClosureBodyElement:
+  case ConstraintKind::BindTupleOfFunctionParams:
     return true;
   }
 
@@ -2250,6 +2265,7 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::ClosureBodyElement:
+  case ConstraintKind::BindTupleOfFunctionParams:
     llvm_unreachable("Not a relational constraint");
   }
 
@@ -5337,6 +5353,7 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
     case ConstraintKind::UnresolvedMemberChainBase:
     case ConstraintKind::PropertyWrapper:
     case ConstraintKind::ClosureBodyElement:
+    case ConstraintKind::BindTupleOfFunctionParams:
       llvm_unreachable("Not a relational constraint");
     }
   }
@@ -6308,6 +6325,19 @@ ConstraintSystem::simplifyConstructionConstraint(
                              fnLocator, 
                              ConstraintLocator::ConstructorMember));
 
+  // HACK: Bind the function's parameter list as a tuple to a type variable.
+  // This only exists to preserve compatibility with rdar://85263844, as it can
+  // affect the prioritization of bindings, which can affect behavior for tuple
+  // matching as tuple subtyping is currently a *weaker* constraint than tuple
+  // conversion.
+  if (!getASTContext().isSwiftVersionAtLeast(6)) {
+    auto paramTypeVar = createTypeVariable(
+        getConstraintLocator(locator, ConstraintLocator::ApplyArgument),
+        TVO_CanBindToLValue | TVO_CanBindToInOut | TVO_CanBindToNoEscape);
+    addConstraint(ConstraintKind::BindTupleOfFunctionParams, memberType,
+                  paramTypeVar, locator);
+  }
+
   addConstraint(ConstraintKind::ApplicableFunction, fnType, memberType,
                 fnLocator);
 
@@ -7131,6 +7161,59 @@ ConstraintSystem::simplifyOptionalObjectConstraint(
   return SolutionKind::Solved;
 }
 
+ConstraintSystem::SolutionKind
+ConstraintSystem::simplifyBindTupleOfFunctionParamsConstraint(
+    Type first, Type second, TypeMatchOptions flags,
+    ConstraintLocatorBuilder locator) {
+  auto simplified = simplifyType(first);
+  auto simplifiedCopy = simplified;
+
+  unsigned unwrapCount = 0;
+  if (shouldAttemptFixes()) {
+    while (auto objectTy = simplified->getOptionalObjectType()) {
+      simplified = objectTy;
+
+      // Track how many times we do this so that we can record a fix for each.
+      ++unwrapCount;
+    }
+
+    if (simplified->isPlaceholder()) {
+      if (auto *typeVar = second->getAs<TypeVariableType>())
+        recordPotentialHole(typeVar);
+      return SolutionKind::Solved;
+    }
+  }
+
+  if (simplified->isTypeVariableOrMember()) {
+    if (!flags.contains(TMF_GenerateConstraints))
+      return SolutionKind::Unsolved;
+
+    addUnsolvedConstraint(
+        Constraint::create(*this, ConstraintKind::BindTupleOfFunctionParams,
+                           simplified, second, getConstraintLocator(locator)));
+    return SolutionKind::Solved;
+  }
+
+  auto *funcTy = simplified->getAs<FunctionType>();
+  if (!funcTy)
+    return SolutionKind::Error;
+
+  auto tupleTy =
+      AnyFunctionType::composeTuple(getASTContext(), funcTy->getParams(),
+                                    /*wantParamFlags*/ false);
+
+  addConstraint(ConstraintKind::Bind, tupleTy, second,
+                locator.withPathElement(ConstraintLocator::FunctionArgument));
+
+  if (unwrapCount > 0) {
+    auto *fix = ForceOptional::create(*this, simplifiedCopy, second,
+                                      getConstraintLocator(locator));
+    if (recordFix(fix, /*impact=*/unwrapCount))
+      return SolutionKind::Error;
+  }
+  return SolutionKind::Solved;
+}
+
 static bool isForKeyPathSubscript(ConstraintSystem &cs,
                                   ConstraintLocator *locator) {
   if (!locator || !locator->getAnchor())
@@ -11961,6 +12044,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::DropThrowsAttribute:
   case FixKind::DropAsyncAttribute:
   case FixKind::AllowSwiftToCPointerConversion:
+  case FixKind::AllowTupleLabelMismatch:
     llvm_unreachable("handled elsewhere");
   }
 
@@ -12046,6 +12130,10 @@ ConstraintSystem::addConstraintImpl(ConstraintKind kind, Type first,
     return simplifyUnresolvedMemberChainBaseConstraint(first, second, subflags,
                                                        locator);
 
+  case ConstraintKind::BindTupleOfFunctionParams:
+    return simplifyBindTupleOfFunctionParamsConstraint(first, second, subflags,
+                                                       locator);
+
   case ConstraintKind::ValueMember:
   case ConstraintKind::UnresolvedValueMember:
   case ConstraintKind::ValueWitness:
@@ -12588,6 +12676,11 @@ ConstraintSystem::simplifyConstraint(const Constraint &constraint) {
     return simplifyClosureBodyElementConstraint(
         constraint.getClosureElement(), constraint.getElementContext(),
         /*flags=*/None, constraint.getLocator());
+
+  case ConstraintKind::BindTupleOfFunctionParams:
+    return simplifyBindTupleOfFunctionParamsConstraint(
+        constraint.getFirstType(), constraint.getSecondType(), /*flags*/ None,
+        constraint.getLocator());
   }
 
   llvm_unreachable("Unhandled ConstraintKind in switch.");

lib/Sema/Constraint.cpp

@@ -77,6 +77,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second,
   case ConstraintKind::OneWayBindParam:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
+  case ConstraintKind::BindTupleOfFunctionParams:
     assert(!First.isNull());
     assert(!Second.isNull());
     break;
@@ -161,6 +162,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second, Type Third,
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
   case ConstraintKind::ClosureBodyElement:
+  case ConstraintKind::BindTupleOfFunctionParams:
     llvm_unreachable("Wrong constructor");
 
   case ConstraintKind::KeyPath:
@@ -303,6 +305,7 @@ Constraint *Constraint::clone(ConstraintSystem &cs) const {
   case ConstraintKind::DefaultClosureType:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
+  case ConstraintKind::BindTupleOfFunctionParams:
     return create(cs, getKind(), getFirstType(), getSecondType(), getLocator());
 
   case ConstraintKind::ApplicableFunction:
@@ -503,6 +506,10 @@ void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm) const {
     Out << " can default to ";
     break;
 
+  case ConstraintKind::BindTupleOfFunctionParams:
+    Out << " bind tuple of function params to ";
+    break;
+
   case ConstraintKind::Disjunction:
     llvm_unreachable("disjunction handled above");
   case ConstraintKind::Conjunction:
@@ -663,6 +670,7 @@ gatherReferencedTypeVars(Constraint *constraint,
   case ConstraintKind::DefaultClosureType:
   case ConstraintKind::UnresolvedMemberChainBase:
   case ConstraintKind::PropertyWrapper:
+  case ConstraintKind::BindTupleOfFunctionParams:
     constraint->getFirstType()->getTypeVariables(typeVars);
     constraint->getSecondType()->getTypeVariables(typeVars);
     break;