[cxx-interop] Wrap methods that take Obj-C params in #if defined(__OBJC__)

When generating a C++ header for a Swift module, we wrap declarations that require Objective-C++ in `#if defined(__OBJC__)` blocks, to make the headers usable with Obj-C interop disabled. This logic wasn't being applied to Swift methods and initializers that take an Objective-C class.

rdar://164465358
(cherry picked from commit 50035f4)

Author: egorzhdan

lib/AST/SwiftNameTranslation.cpp

@@ -266,6 +266,10 @@ bool swift::cxx_translation::isObjCxxOnly(const ValueDecl *VD) {
 
 bool swift::cxx_translation::isObjCxxOnly(const clang::Decl *D,
                                           const ASTContext &ctx) {
+  // Check if this is decl can only be referred to from Objective-C.
+  if (isa<clang::ObjCInterfaceDecl>(D))
+    return true;
+
   // By default, we import all modules in Obj-C++ mode, so there is no robust
   // way to tell if something is coming from an Obj-C module. Use the
   // requirements and the language options to check if we should actually

test/Interop/ObjCToSwiftToObjCxx/Inputs/module.modulemap

@@ -0,0 +1,4 @@
+module ObjCTypes {
+  header "objc-types.h"
+  export *
+}

test/Interop/ObjCToSwiftToObjCxx/Inputs/objc-types.h

@@ -0,0 +1,3 @@
+@interface ObjCKlass
+-(ObjCKlass * _Nonnull) init;
+@end

test/Interop/ObjCToSwiftToObjCxx/bridge-objc-types-back-to-objcxx.swift

@@ -105,10 +105,19 @@ public class KVOCookieMonster {
 // CHECK-NEXT: SWIFT_EXTERN id <ObjCProtocol> _Nullable $s9UseObjCTy03retB17CProtocolNullableSo0bE0_pSgyF(void) SWIFT_NOEXCEPT SWIFT_CALL; // retObjCProtocolNullable()
 // CHECK-NEXT: #endif
 // CHECK: ObjCKlass *_Nonnull $s9UseObjCTy03retB5ClassSo0B6CKlassCyF(void) SWIFT_NOEXCEPT SWIFT_CALL;
+// CHECK-NEXT: #endif // defined(__OBJC__)
+// CHECK-NEXT: #if defined(__OBJC__)
 // CHECK-NEXT: ObjCKlass *_Nullable $s9UseObjCTy03retB13ClassNullableSo0B6CKlassCSgyF(void) SWIFT_NOEXCEPT SWIFT_CALL;
+// CHECK-NEXT: #endif // defined(__OBJC__)
+// CHECK-NEXT: #if defined(__OBJC__)
 // CHECK-NEXT: void $s9UseObjCTy04takeB6CClassyySo0B6CKlassCF(ObjCKlass *_Nonnull x) SWIFT_NOEXCEPT SWIFT_CALL;
+// CHECK-NEXT: #endif // defined(__OBJC__)
+// CHECK-NEXT: #if defined(__OBJC__)
 // CHECK-NEXT: void $s9UseObjCTy04takeB11CClassInoutyySo0B6CKlassCzF(ObjCKlass *_Nonnull __strong * _Nonnull x) SWIFT_NOEXCEPT SWIFT_CALL;
+// CHECK-NEXT: #endif // defined(__OBJC__)
+// CHECK-NEXT: #if defined(__OBJC__)
 // CHECK-NEXT: void $s9UseObjCTy04takeB14CClassNullableyySo0B6CKlassCSgF(ObjCKlass *_Nullable x) SWIFT_NOEXCEPT SWIFT_CALL;
+// CHECK-NEXT: #endif // defined(__OBJC__)
 // CHECK-NEXT: #if defined(__OBJC__)
 // CHECK-NEXT: SWIFT_EXTERN void $s9UseObjCTy04takeB9CProtocolyySo0bE0_pF(id <ObjCProtocol> _Nonnull x) SWIFT_NOEXCEPT SWIFT_CALL; // takeObjCProtocol(_:)
 // CHECK-NEXT: #endif
@@ -124,17 +133,16 @@ public class KVOCookieMonster {
 // CHECK-NEXT:   }
 // CHECK-NEXT: };
 
-// CHECK: #if defined(__OBJC__)
-// CHECK-NEXT: SWIFT_INLINE_THUNK id <ObjCProtocol> _Nonnull retObjCProtocol() noexcept SWIFT_SYMBOL("s:9UseObjCTy03retB9CProtocolSo0bE0_pyF") SWIFT_WARN_UNUSED_RESULT {
+// CHECK: SWIFT_INLINE_THUNK id <ObjCProtocol> _Nonnull retObjCProtocol() noexcept SWIFT_SYMBOL("s:9UseObjCTy03retB9CProtocolSo0bE0_pyF") SWIFT_WARN_UNUSED_RESULT {
 // CHECK-NEXT:  return (__bridge_transfer id <ObjCProtocol>)(__bridge void *)UseObjCTy::_impl::$s9UseObjCTy03retB9CProtocolSo0bE0_pyF();
 // CHECK-NEXT: }
-// CHECK-NEXT: #endif
+// CHECK-NEXT: #endif // defined(__OBJC__)
 
 // CHECK: #if defined(__OBJC__)
 // CHECK-NEXT: SWIFT_INLINE_THUNK id <ObjCProtocol> _Nullable retObjCProtocolNullable() noexcept SWIFT_SYMBOL("s:9UseObjCTy03retB17CProtocolNullableSo0bE0_pSgyF") SWIFT_WARN_UNUSED_RESULT {
 // CHECK-NEXT: return (__bridge_transfer id <ObjCProtocol>)(__bridge void *)UseObjCTy::_impl::$s9UseObjCTy03retB17CProtocolNullableSo0bE0_pSgyF();
 // CHECK-NEXT: }
-// CHECK-NEXT: #endif
+// CHECK-NEXT: #endif // defined(__OBJC__)
 
 // CHECK: SWIFT_INLINE_THUNK ObjCKlass *_Nonnull retObjClass() noexcept SWIFT_SYMBOL({{.*}}) SWIFT_WARN_UNUSED_RESULT {
 // CHECK-NEXT: return (__bridge_transfer ObjCKlass *)(__bridge void *)UseObjCTy::_impl::$s9UseObjCTy03retB5ClassSo0B6CKlassCyF();

test/Interop/ObjCToSwiftToObjCxx/objc-types-in-cxx-mode.swift

@@ -0,0 +1,32 @@
+// RUN: %target-swift-frontend %s -module-name ObjCInCXX -typecheck -verify -I %S/Inputs -emit-clang-header-path %t/ObjCInCXX.h -I %t -cxx-interoperability-mode=default
+// RUN: %FileCheck %s < %t/ObjCInCXX.h
+
+// Make sure the header is valid when parsed in C++ language mode, without Obj-C.
+// RUN: %target-interop-build-clang -fobjc-arc -c -x c++-header %t/ObjCInCXX.h -o %t/o.o
+
+// REQUIRES: objc_interop
+
+import ObjCTypes
+
+public struct HasObjCInit {
+  private let privateField: Int = 0
+
+  public init(_ o: ObjCKlass) {}
+}
+
+public struct HasObjCMethod {
+  private let privateField: Int = 0
+
+  public func takesObjCKlass(_ o: ObjCKlass) {}
+}
+
+// CHECK:      SWIFT_INLINE_THUNK HasObjCInit HasObjCInit::init(ObjCKlass *_Nonnull o) {
+// CHECK:        return {{.*}} {
+// CHECK:        }
+// CHECK-NEXT: }
+// CHECK-NEXT: #endif // defined(__OBJC__)
+
+// CHECK:      SWIFT_INLINE_THUNK void HasObjCMethod::takesObjCKlass(ObjCKlass *_Nonnull o) const {
+// CHECK-NEXT:   ObjCInCXX::{{.*}}
+// CHECK-NEXT: }
+// CHECK-NEXT: #endif // defined(__OBJC__)