Merge pull request #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}}
+}