Always produce nullable type for result out parameter in Obj-C header

Otherwise it would be unusable when passing reference to local variable
from Swift as it would require a non-null initializer then.

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/objcexport/ObjCExportHeaderGenerator.kt

@@ -639,8 +639,14 @@ internal class ObjCExportTranslatorImpl(
                     MethodBridgeValueParameter.ErrorOutParameter ->
                         ObjCPointerType(ObjCNullableReferenceType(ObjCClassType("NSError")), nullable = true)
 
-                    is MethodBridgeValueParameter.KotlinResultOutParameter ->
+                    is MethodBridgeValueParameter.KotlinResultOutParameter -> {
-                        ObjCPointerType(mapType(method.returnType!!, bridge.bridge, objCExportScope), nullable = true)
+                        val resultType = mapType(method.returnType!!, bridge.bridge, objCExportScope)
+                        // Note: non-nullable reference or pointer type is unusable here
+                        // when passing reference to local variable from Swift because it
+                        // would require a non-null initializer then.
+                        val pointeeType = resultType.makeNullableIfReferenceOrPointer()
+                        ObjCPointerType(pointeeType, nullable = true)
+                    }
                 }
 
                 parameters += ObjCParameter(uniqueName, p, type)
@@ -981,7 +987,6 @@ abstract class ObjCExportHeaderGenerator internal constructor(
         listOf(
                 "-Wunknown-warning-option",
                 "-Wnullability",
-                "-Wnullability-completeness",
                 "-Wswift-name-attribute"
         ).forEach {
             add("#pragma clang diagnostic ignored \"$it\"")

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/objcexport/objcTypes.kt

@@ -130,3 +130,11 @@ internal enum class ObjCValueType(val encoding: String) {
     DOUBLE("d"),
     POINTER("^v")
 }
+
+internal fun ObjCType.makeNullableIfReferenceOrPointer(): ObjCType = when (this) {
+    is ObjCPointerType -> ObjCPointerType(this.pointee, nullable = true)
+
+    is ObjCNonNullReferenceType -> ObjCNullableReferenceType(this)
+
+    is ObjCNullableReferenceType, is ObjCRawType, is ObjCPrimitiveType, ObjCVoidType -> this
+}

backend.native/tests/framework/values/expectedLazy.h

@@ -297,7 +297,7 @@ __attribute__((swift_name("Bridge")))
 - (ValuesKotlinNothing * _Nullable)foo1AndReturnError:(NSError * _Nullable * _Nullable)error __attribute__((swift_name("foo1()")));
 - (BOOL)foo2AndReturnResult:(int32_t * _Nullable)result error:(NSError * _Nullable * _Nullable)error __attribute__((swift_name("foo2(result:)")));
 - (BOOL)foo3AndReturnError:(NSError * _Nullable * _Nullable)error __attribute__((swift_name("foo3()")));
-- (BOOL)foo4AndReturnResult:(ValuesKotlinNothing ** _Nullable)result error:(NSError * _Nullable * _Nullable)error __attribute__((swift_name("foo4(result:)")));
+- (BOOL)foo4AndReturnResult:(ValuesKotlinNothing * _Nullable * _Nullable)result error:(NSError * _Nullable * _Nullable)error __attribute__((swift_name("foo4(result:)")));
 @end;
 
 __attribute__((objc_subclassing_restricted))