Merge pull request #78872 from tshortli/unavailable-witness-in-extens…

…ion-diag-regression-test

Tests: Test conformance checker with witnesses in unavailable extensions

test/decl/protocol/req/unavailable.swift

@@ -26,7 +26,7 @@ class Bar : NonObjCProto { // expected-error {{type 'Bar' does not conform to pr
 
 // Complain about unavailable witnesses (error in Swift 4, warning in Swift 3)
 protocol P {
-  func foo(bar: Foo) // expected-note 2 {{requirement 'foo(bar:)' declared here}}
+  func foo(bar: Foo) // expected-note 3 {{requirement 'foo(bar:)' declared here}}
 }
 
 struct ConformsToP : P { // expected-error{{type 'ConformsToP' does not conform to protocol 'P'}}
@@ -64,6 +64,14 @@ extension ConformsToP5: P {
   func foo(bar: Foo) { }
 }
 
+struct ConformsToP6: P {} // expected-error{{type 'ConformsToP6' does not conform to protocol 'P'}}
+// expected-error@-1 {{unavailable instance method 'foo(bar:)' was used to satisfy a requirement of protocol 'P'}}
+
+@available(*, unavailable)
+extension ConformsToP6 {
+  func foo(bar: Foo) { } // expected-note {{'foo(bar:)' declared here}}
+}
+
 @available(*, unavailable)
 enum UnavailableEnum {
   struct ConformsToP6: P {