Avoid duplicated selectors when Kotlin class inherits from muliple ba… (#4145)

Issue: RuntimeAssert in AddMethods (ObjCInterop.mm) when kotlin class overrides the same
selector from multiple bases, e.g. from the base objc class and a protocol(s).

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/InteropLowering.kt

@@ -864,12 +864,14 @@ private class InteropTransformer(val context: Context, override val irFile: IrFi
     override fun visitClass(declaration: IrClass): IrStatement {
         super.visitClass(declaration)
         if (declaration.isKotlinObjCClass()) {
+            val uniq = mutableSetOf<String>()  // remove duplicates [KT-38234]
             val imps = declaration.simpleFunctions().filter { it.isReal }.flatMap { function ->
                 function.overriddenSymbols.mapNotNull {
-                    val info = it.owner.getExternalObjCMethodInfo()
-                    if (info == null) {
+                    val selector = it.owner.getExternalObjCMethodInfo()?.selector
+                    if (selector == null || selector in uniq) {
                         null
                     } else {
+                        uniq += selector
                         generateWithStubs(it.owner) {
                             generateCFunctionAndFakeKotlinExternalFunction(
                                     function,

backend.native/tests/interop/objc/tests/KT38234_override.h

@@ -0,0 +1,9 @@
+#import <Foundation/NSObject.h>
+
+@protocol KT38234_P1
+-(int)foo;
+@end;
+
+@interface KT38234_Base : NSObject <KT38234_P1>
+-(int)callFoo;
+@end;

backend.native/tests/interop/objc/tests/KT38234_override.kt

@@ -0,0 +1,10 @@
+import kotlin.test.*
+import objcTests.*
+
+class KT38234_Impl : KT38234_P1Protocol, KT38234_Base() {
+    override fun foo(): Int = 566
+}
+
+@Test fun testKT38234() {
+    assertEquals(566, KT38234_Impl().callFoo())
+}

backend.native/tests/interop/objc/tests/KT38234_override.m

@@ -0,0 +1,10 @@
+#include "KT38234_override.h"
+
+@implementation KT38234_Base
+-(int)foo {
+    return 1;
+}
+-(int)callFoo {
+    return [self foo];
+}
+@end;