Make sure to allow '@objc' on enum elements

Previously they were ignored by the checking of '@objc', but in the
refactoring to a request the attribute started getting marked as
invalid without a diagnostic.

rdar://problem/43401047
(cherry picked from commit a394205)

Author: jrose-apple

lib/Sema/TypeCheckDeclObjC.cpp

@@ -49,6 +49,7 @@ bool swift::shouldDiagnoseObjCReason(ObjCReason reason, ASTContext &ctx) {
 
   case ObjCReason::MemberOfObjCSubclass:
   case ObjCReason::MemberOfObjCMembersClass:
+  case ObjCReason::ElementOfObjCEnum:
   case ObjCReason::Accessor:
     return false;
   }
@@ -73,6 +74,7 @@ unsigned swift::getObjCDiagnosticAttrKind(ObjCReason reason) {
 
   case ObjCReason::MemberOfObjCSubclass:
   case ObjCReason::MemberOfObjCMembersClass:
+  case ObjCReason::ElementOfObjCEnum:
   case ObjCReason::Accessor:
     llvm_unreachable("should not diagnose this @objc reason");
   }
@@ -1272,6 +1274,14 @@ bool IsObjCRequest::evaluate(Evaluator &evaluator, ValueDecl *VD) const {
     // as an arithmetic type in C.
     if (isEnumObjC(enumDecl))
       isObjC = ObjCReason(ObjCReason::ExplicitlyObjC);
+  } else if (auto enumElement = dyn_cast<EnumElementDecl>(VD)) {
+    // Enum elements can be @objc so long as the containing enum is @objc.
+    if (enumElement->getParentEnum()->isObjC()) {
+      if (enumElement->getAttrs().hasAttribute<ObjCAttr>())
+        isObjC = ObjCReason::ExplicitlyObjC;
+      else
+        isObjC = ObjCReason::ElementOfObjCEnum;
+    }
   } else if (auto proto = dyn_cast<ProtocolDecl>(VD)) {
     if (proto->getAttrs().hasAttribute<ObjCAttr>()) {
       isObjC = ObjCReason(ObjCReason::ExplicitlyObjC);
@@ -1520,7 +1530,7 @@ void markAsObjC(ValueDecl *D, ObjCReason reason,
     ctx.getLazyResolver()->resolveDeclSignature(D);
   }
 
-  if (!isa<AccessorDecl>(D)) {
+  if (!isa<TypeDecl>(D) && !isa<AccessorDecl>(D) && !isa<EnumElementDecl>(D)) {
     useObjectiveCBridgeableConformances(D->getInnermostDeclContext(),
                                         D->getInterfaceType());
   }

lib/Sema/TypeCheckObjC.h

@@ -65,10 +65,15 @@ class ObjCReason {
     ExplicitlyGKInspectable,
     /// Is it a member of an @objc extension of a class.
     MemberOfObjCExtension,
+
+    // These kinds do not appear in diagnostics.
+
     /// Is it a member of an @objcMembers class.
     MemberOfObjCMembersClass,
     /// A member of an Objective-C-defined class or subclass.
     MemberOfObjCSubclass,
+    /// Is a member of an @objc enum.
+    ElementOfObjCEnum,
     /// An accessor to a property.
     Accessor,
   };

test/PrintAsObjC/enums.swift

@@ -1,11 +1,18 @@
 // RUN: %empty-directory(%t)
+
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-source-import -emit-module -emit-module-doc -o %t %s -import-objc-header %S/Inputs/enums.h -disable-objc-attr-requires-foundation-module
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -parse-as-library %t/enums.swiftmodule -typecheck -emit-objc-header-path %t/enums.h -import-objc-header %S/Inputs/enums.h -disable-objc-attr-requires-foundation-module
 // RUN: %FileCheck %s < %t/enums.h
 // RUN: %FileCheck -check-prefix=NEGATIVE %s < %t/enums.h
 // RUN: %check-in-clang %t/enums.h
 // RUN: %check-in-clang -fno-modules -Qunused-arguments %t/enums.h -include ctypes.h -include CoreFoundation.h
 
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -enable-source-import -emit-module -o /dev/null -emit-module-doc-path /dev/null -module-name enums %s -emit-objc-header-path %t/enums.WMO.h -import-objc-header %S/Inputs/enums.h -disable-objc-attr-requires-foundation-module
+// RUN: %FileCheck %s < %t/enums.WMO.h
+// RUN: %FileCheck -check-prefix=NEGATIVE %s < %t/enums.WMO.h
+// RUN: %check-in-clang %t/enums.WMO.h
+// RUN: %check-in-clang -fno-modules -Qunused-arguments %t/enums.WMO.h -include ctypes.h -include CoreFoundation.h
+
 // REQUIRES: objc_interop
 
 import Foundation

test/attr/attr_nonobjc.swift

@@ -111,3 +111,7 @@ protocol SR4226_Protocol : class {}
 extension SR4226_Protocol {
   @nonobjc func function() {} // expected-error {{only class members and extensions of classes can be declared @nonobjc}}
 }
+
+@objc enum SomeEnum: Int {
+  @nonobjc case what // expected-error {{'@nonobjc' attribute cannot be applied to this declaration}}
+}