[CS] Don't simplify FunctionResult in simplifyLocator

include/swift/Sema/CSFix.h

@@ -109,12 +109,6 @@ enum class FixKind : uint8_t {
   /// Fix up the generic arguments of two types so they match each other.
   GenericArgumentsMismatch,
 
-  /// Fix up @autoclosure argument to the @autoclosure parameter,
-  /// to for a call to be able to forward it properly, since
-  /// @autoclosure conversions are unsupported starting from
-  /// Swift version 5.
-  AutoClosureForwarding,
-
   /// Remove `!` or `?` because base is not an optional type.
   RemoveUnwrap,
 
@@ -1219,33 +1213,6 @@ class GenericArgumentsMismatch final
   }
 };
 
-/// Detect situations when argument of the @autoclosure parameter is itself
-/// marked as @autoclosure and is not applied. Form a fix which suggests a
-/// proper way to forward such arguments, e.g.:
-///
-/// ```swift
-/// func foo(_ fn: @autoclosure () -> Int) {}
-/// func bar(_ fn: @autoclosure () -> Int) {
-///   foo(fn) // error - fn should be called
-/// }
-/// ```
-class AutoClosureForwarding final : public ConstraintFix {
-  AutoClosureForwarding(ConstraintSystem &cs, ConstraintLocator *locator)
-      : ConstraintFix(cs, FixKind::AutoClosureForwarding, locator) {}
-
-public:
-  std::string getName() const override { return "fix @autoclosure forwarding"; }
-
-  bool diagnose(const Solution &solution, bool asNote = false) const override;
-
-  static AutoClosureForwarding *create(ConstraintSystem &cs,
-                                       ConstraintLocator *locator);
-
-  static bool classof(const ConstraintFix *fix) {
-    return fix->getKind() == FixKind::AutoClosureForwarding;
-  }
-};
-
 class AllowAutoClosurePointerConversion final : public ContextualMismatch {
   AllowAutoClosurePointerConversion(ConstraintSystem &cs, Type pointeeType,
                                     Type pointerType,

lib/Sema/CSDiagnostics.cpp

@@ -3832,14 +3832,6 @@ bool FunctionTypeMismatch::diagnoseAsError() {
   return true;
 }
 
-bool AutoClosureForwardingFailure::diagnoseAsError() {
-  auto argRange = getSourceRange();
-  emitDiagnostic(diag::invalid_autoclosure_forwarding)
-      .highlight(argRange)
-      .fixItInsertAfter(argRange.End, "()");
-  return true;
-}
-
 bool AutoClosurePointerConversionFailure::diagnoseAsError() {
   auto diagnostic = diag::invalid_autoclosure_pointer_conversion;
   emitDiagnostic(diagnostic, getFromType(), getToType())
@@ -3903,18 +3895,11 @@ bool MissingCallFailure::diagnoseAsError() {
       return true;
     }
 
-    case ConstraintLocator::FunctionResult: {
-      path = path.drop_back();
-      if (path.back().getKind() != ConstraintLocator::AutoclosureResult)
-        break;
-
-      LLVM_FALLTHROUGH;
-    }
-
     case ConstraintLocator::AutoclosureResult: {
-      auto loc = getConstraintLocator(getRawAnchor(), path.drop_back());
-      AutoClosureForwardingFailure failure(getSolution(), loc);
-      return failure.diagnoseAsError();
+      emitDiagnostic(diag::invalid_autoclosure_forwarding)
+          .highlight(getSourceRange())
+          .fixItInsertAfter(insertLoc, "()");
+      return true;
     }
     default:
       break;

lib/Sema/CSDiagnostics.h

@@ -1078,17 +1078,6 @@ class FunctionTypeMismatch final : public ContextualFailure {
   bool diagnoseAsError() override;
 };
 
-/// Diagnose situations when @autoclosure argument is passed to @autoclosure
-/// parameter directly without calling it first.
-class AutoClosureForwardingFailure final : public FailureDiagnostic {
-public:
-  AutoClosureForwardingFailure(const Solution &solution,
-                               ConstraintLocator *locator)
-      : FailureDiagnostic(solution, locator) {}
-
-  bool diagnoseAsError() override;
-};
-
 /// Diagnose invalid pointer conversions for an autoclosure result type.
 ///
 /// \code

lib/Sema/CSFix.cpp

@@ -802,17 +802,6 @@ GenericArgumentsMismatch *GenericArgumentsMismatch::create(
       GenericArgumentsMismatch(cs, actual, required, mismatches, locator);
 }
 
-bool AutoClosureForwarding::diagnose(const Solution &solution,
-                                     bool asNote) const {
-  AutoClosureForwardingFailure failure(solution, getLocator());
-  return failure.diagnose(asNote);
-}
-
-AutoClosureForwarding *AutoClosureForwarding::create(ConstraintSystem &cs,
-                                                     ConstraintLocator *locator) {
-  return new (cs.getAllocator()) AutoClosureForwarding(cs, locator);
-}
-
 bool AllowAutoClosurePointerConversion::diagnose(const Solution &solution,
                                                  bool asNote) const {
   AutoClosurePointerConversionFailure failure(solution, getFromType(),

lib/Sema/CSSimplify.cpp

@@ -5186,11 +5186,16 @@ bool ConstraintSystem::repairFailures(
     // side isn't, let's check it would be possible to fix
     // this by forming an explicit call.
     auto convertTo = dstType->lookThroughAllOptionalTypes();
-    // Right-hand side can't be - a function, a type variable or dependent
-    // member, or `Any` (if function conversion to `Any` didn't succeed there
-    // is something else going on e.g. problem with escapiness).
-    if (convertTo->is<FunctionType>() || convertTo->isTypeVariableOrMember() ||
-        convertTo->isAny())
+
+    // If the RHS is a function type, the source must be a function-returning
+    // function.
+    if (convertTo->is<FunctionType>() && !resultType->is<FunctionType>())
+      return false;
+
+    // Right-hand side can't be a type variable or dependent member, or `Any`
+    // (if function conversion to `Any` didn't succeed there is something else
+    // going on e.g. problem with escapiness).
+    if (convertTo->isTypeVariableOrMember() || convertTo->isAny())
       return false;
 
     ConstraintKind matchKind;
@@ -15249,12 +15254,6 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
     return result;
   }
 
-  case FixKind::AutoClosureForwarding: {
-    if (recordFix(fix))
-      return SolutionKind::Error;
-    return matchTypes(type1, type2, matchKind, subflags, locator);
-  }
-
   case FixKind::AllowTupleTypeMismatch: {
     if (fix->getAs<AllowTupleTypeMismatch>()->isElementMismatch()) {
       auto *locator = fix->getLocator();

lib/Sema/ConstraintSystem.cpp

@@ -3389,8 +3389,7 @@ void constraints::simplifyLocator(ASTNode &anchor,
       continue;
     }
 
-    case ConstraintLocator::ApplyFunction:
-    case ConstraintLocator::FunctionResult:
+    case ConstraintLocator::ApplyFunction: {
       // Extract application function.
       if (auto applyExpr = getAsExpr<ApplyExpr>(anchor)) {
         anchor = applyExpr->getFn();
@@ -3412,7 +3411,7 @@ void constraints::simplifyLocator(ASTNode &anchor,
       }
 
       break;
-
+    }
     case ConstraintLocator::AutoclosureResult:
     case ConstraintLocator::LValueConversion:
     case ConstraintLocator::DynamicType:
@@ -3677,6 +3676,7 @@ void constraints::simplifyLocator(ASTNode &anchor,
     case ConstraintLocator::SynthesizedArgument:
       break;
 
+    case ConstraintLocator::FunctionResult:
     case ConstraintLocator::DynamicLookupResult:
     case ConstraintLocator::KeyPathComponentResult:
       break;

test/Constraints/issue-78376.swift

@@ -0,0 +1,15 @@
+// RUN: %target-typecheck-verify-swift %clang-importer-sdk
+
+// REQUIRES: objc_interop
+
+import Foundation
+import CoreGraphics
+
+func foo(_ x: Double) {}
+func bar() -> Double { 0 }
+
+// https://github.com/swiftlang/swift/issues/78376
+let _: (CGFloat) -> Void = foo
+// expected-error@-1 {{cannot convert value of type '(Double) -> ()' to specified type '(CGFloat) -> Void'}}
+let _: () -> CGFloat = bar
+// expected-error@-1 {{cannot convert value of type '() -> Double' to specified type '() -> CGFloat'}}