Merge pull request swiftlang#84501 from slavapestov/fix-rdar160389221

Sema: Workaround for broken existential opening behavior

Author: slavapestov

lib/Sema/CSSimplify.cpp

@@ -13394,8 +13394,12 @@ bool ConstraintSystem::simplifyAppliedOverloadsImpl(
  choiceType = objectType;
  }
 
+ // FIXME: The !getSelfProtocolDecl() check is load-bearing, because
+ // this optimization interacts poorly with existential opening
+ // somehow. It should all be removed.
  if (auto *choiceFnType = choiceType->getAs<FunctionType>()) {
- if (isa<ConstructorDecl>(choice.getDecl())) {
+ if (isa<ConstructorDecl>(choice.getDecl()) &&
+ !choice.getDecl()->getDeclContext()->getSelfProtocolDecl()) {
  auto choiceResultType = choice.getBaseType()
  ->getRValueType()
  ->getMetatypeInstanceType();

test/Constraints/opened_existentials_overload.swift

@@ -0,0 +1,30 @@
+// RUN: %target-typecheck-verify-swift
+
+protocol P {}
+
+func g(_: some P) {}
+// expected-note@-1 {{required by global function 'g' where 'some P' = 'any P'}}
+
+// rdar://problem/160389221
+func good(_ x: Array<any P>) {
+ Array(x).forEach { y in g(y) }
+}
+
+extension Array {
+ var ffirst: Element? { fatalError() }
+ func ffirst(wwhere: (Element) -> Bool) -> Element { fatalError() }
+}
+
+func bad(_ x: Array<any P>) {
+ let y = x.ffirst!
+ g(y) // ok
+
+ let yy = x.ffirst
+ g(yy!) // ok
+
+ // FIXME: This is broken
+
+ g(x.ffirst!)
+ // expected-error@-1 {{type 'any P' cannot conform to 'P'}}
+ // expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
+}