Stop requiring to inherit NSObject when passing Swift object to Kotlin

OBJC_INTEROP.md

@@ -239,9 +239,6 @@ val nsNumber = 42 as NSNumber
 
 Kotlin classes and interfaces can be subclassed by Swift/Objective-C classes
 and protocols.
-Currently a class that adopts the Kotlin protocol should inherit `NSObject`
-(either directly or indirectly). Note that all Kotlin classes do inherit `NSObject`,
-so a Swift/Objective-C subclass of Kotlin class can adopt the Kotlin protocol.
 
 ### Subclassing Swift/Objective-C classes and protocols from Kotlin
 

backend.native/tests/framework/values/values.kt

@@ -145,6 +145,8 @@ interface I {
     fun iFun(): String = "I::iFun"
 }
 
+fun I.iFunExt() = iFun()
+
 private interface PI {
     fun piFun(): Any
     fun iFun(): String = "PI::iFun"
@@ -261,4 +263,6 @@ class Bridge : BridgeBase() {
     override fun foo2() = throw MyException()
     override fun foo3() = throw MyException()
     override fun foo4() = throw MyException()
-}
+}
+
+fun Any.same() = this

backend.native/tests/framework/values/values.swift

@@ -470,6 +470,26 @@ func testShared() throws {
     try assertNotFrozen(FinalClassExtOpen())
 }
 
+class PureSwiftClass {
+}
+
+struct PureSwiftStruct {
+    var x: Int
+}
+class PureSwiftKotlinInterfaceImpl : I {
+    func iFun() -> String {
+        return "pure"
+    }
+}
+
+func testPureSwiftClasses() throws {
+    let pureSwiftClass = PureSwiftClass()
+    try assertTrue(ValuesKt.same(pureSwiftClass) as? AnyObject === pureSwiftClass)
+
+    try assertEquals(actual: 123, expected: (ValuesKt.same(PureSwiftStruct(x: 123)) as? PureSwiftStruct)?.x)
+    try assertEquals(actual: "pure", expected: ValuesKt.iFunExt(PureSwiftKotlinInterfaceImpl()))
+}
+
 // -------- Execution of the test --------
 
 class ValuesTests : TestProvider {
@@ -505,6 +525,7 @@ class ValuesTests : TestProvider {
             TestCase(name: "TestCompanionObj", method: withAutorelease(testCompanionObj)),
             TestCase(name: "TestInlineClasses", method: withAutorelease(testInlineClasses)),
             TestCase(name: "TestShared", method: withAutorelease(testShared)),
+            TestCase(name: "TestPureSwiftClasses", method: withAutorelease(testPureSwiftClasses)),
         ]
     }
 }

runtime/src/main/cpp/ObjCExport.mm

@@ -135,6 +135,8 @@ static inline id AtomicSetAssociatedObject(ObjHeader* obj, id associatedObject)
 @interface KotlinBase : NSObject <ConvertibleToKotlin, NSCopying>
 @end;
 
+static void initializeObjCExport();
+
 @implementation KotlinBase {
   KRefSharedHolder refHolder;
 }
@@ -144,6 +146,9 @@ static inline id AtomicSetAssociatedObject(ObjHeader* obj, id associatedObject)
 }
 
 +(void)initialize {
+  if (self == [KotlinBase class]) {
+    initializeObjCExport();
+  }
   initializeClass(self);
 }
 
@@ -376,16 +381,22 @@ static ALWAYS_INLINE OBJ_GETTER(convertUnmappedObjCObject, id obj) {
 static OBJ_GETTER(blockToKotlinImp, id self, SEL cmd);
 static OBJ_GETTER(boxedBooleanToKotlinImp, NSNumber* self, SEL cmd);
 
+static OBJ_GETTER(SwiftObject_toKotlinImp, id self, SEL cmd);
+static void SwiftObject_releaseAsAssociatedObjectImp(id self, SEL cmd);
+
 static void checkLoadedOnce();
 
 static void initializeObjCExport() {
-  checkLoadedOnce();
-
   SEL toKotlinSelector = @selector(toKotlin:);
   Method toKotlinMethod = class_getClassMethod([NSObject class], toKotlinSelector);
   RuntimeAssert(toKotlinMethod != nullptr, "");
   const char* toKotlinTypeEncoding = method_getTypeEncoding(toKotlinMethod);
 
+  SEL releaseAsAssociatedObjectSelector = @selector(releaseAsAssociatedObject);
+  Method releaseAsAssociatedObjectMethod = class_getClassMethod([NSObject class], releaseAsAssociatedObjectSelector);
+  RuntimeAssert(releaseAsAssociatedObjectMethod != nullptr, "");
+  const char* releaseAsAssociatedObjectTypeEncoding = method_getTypeEncoding(releaseAsAssociatedObjectMethod);
+
   Class nsBlockClass = objc_getClass("NSBlock");
   RuntimeAssert(nsBlockClass != nullptr, "NSBlock class not found");
 
@@ -399,6 +410,20 @@ static void initializeObjCExport() {
 
   added = class_addMethod(booleanClass, toKotlinSelector, (IMP)boxedBooleanToKotlinImp, toKotlinTypeEncoding);
   RuntimeAssert(added, "Unable to add 'toKotlin:' method to __NSCFBoolean class");
+
+  for (const char* swiftRootClassName : { "SwiftObject", "_TtCs12_SwiftObject" }) {
+    Class swiftRootClass = objc_getClass(swiftRootClassName);
+    if (swiftRootClass != nullptr) {
+      added = class_addMethod(swiftRootClass, toKotlinSelector, (IMP)SwiftObject_toKotlinImp, toKotlinTypeEncoding);
+      RuntimeAssert(added, "Unable to add 'toKotlin:' method to SwiftObject class");
+
+      added = class_addMethod(
+        swiftRootClass, releaseAsAssociatedObjectSelector,
+        (IMP)SwiftObject_releaseAsAssociatedObjectImp, releaseAsAssociatedObjectTypeEncoding
+      );
+      RuntimeAssert(added, "Unable to add 'releaseAsAssociatedObject' method to SwiftObject class");
+    }
+  }
 }
 
 @interface NSObject (NSObjectToKotlin) <ConvertibleToKotlin>
@@ -416,11 +441,19 @@ static void initializeObjCExport() {
 +(void)load {
   static dispatch_once_t onceToken = 0;
   dispatch_once(&onceToken, ^{
-    initializeObjCExport();
+    checkLoadedOnce();
   });
 }
 @end;
 
+static OBJ_GETTER(SwiftObject_toKotlinImp, id self, SEL cmd) {
+  RETURN_RESULT_OF(convertUnmappedObjCObject, self);
+}
+
+static void SwiftObject_releaseAsAssociatedObjectImp(id self, SEL cmd) {
+  objc_release(self);
+}
+
 @interface NSString (NSStringToKotlin) <ConvertibleToKotlin>
 @end;