Merge pull request #8140 from TheOtherDave/SR-4232

A clarification of an error message

include/swift/AST/DiagnosticsSema.def

@@ -2952,7 +2952,7 @@ ERROR(invalid_nonobjc_decl,none,
 ERROR(objc_in_extension_context,none,
       "members of constrained extensions cannot be declared @objc", ())
 ERROR(objc_in_generic_extension,none,
-      "@objc is not supported within extensions of generic classes", ())
+      "@objc is not supported within extensions of generic classes or classes that inherit from generic classes", ())
 ERROR(objc_operator, none,
       "operator methods cannot be declared @objc", ())
 ERROR(objc_operator_proto, none,

test/decl/ext/extension-generic-objc.swift

@@ -0,0 +1,49 @@
+// RUN: %target-swift-frontend -typecheck -verify %s
+
+// REQUIRES: objc_interop
+
+import Foundation
+
+// Tests for correct detection of the "objc_in_generic_extension" error,
+// declared in {Swift Source}/include/swift/AST/DiagnosticsSema.def
+
+// Test "0 levels" deep
+class A<T> : NSObject {
+    init(a: ()) {
+        super.init()
+    }
+}
+extension A {
+    // This should throw an error
+    @objc func a1() {} // expected-error{{@objc is not supported within extensions of generic classes or classes that inherit from generic classes}}
+    // This should *not* throw an error
+    func a2() {}
+}
+
+// Test "1 level" deep
+class B : A<Int> {
+    init(b: ()) {
+        super.init(a: ())
+    }
+}
+extension B {
+    // This should throw an error
+    @objc func b1() {} // expected-error{{@objc is not supported within extensions of generic classes or classes that inherit from generic classes}}
+    // This should *not* throw an error
+    func b2() {}
+}
+
+// Test "many levels" deep
+class C : B {}
+class D : C {
+    init(d: ()) {
+        super.init(b: ())
+    }
+}
+extension D {
+    // This should throw an error
+    @objc func d1() {} // expected-error{{@objc is not supported within extensions of generic classes or classes that inherit from generic classes}}
+    // This should *not* throw an error
+    func d2() {}
+}
+