JS: allow to inherit external classes with overloaded functions in case we don't override them (see KT-13910).

compiler/testData/diagnostics/testsWithJsStdLib/name/overrideOverloadedNativeFunction.kt

@@ -0,0 +1,9 @@
+external open class A {
+    open fun f(x: Int): Unit
+
+    <!JS_NAME_CLASH!>open fun f(x: String): Unit<!>
+}
+
+class InheritClass : A() {
+    <!JS_NAME_CLASH!>override fun f(x: Int): Unit<!> { }
+}

compiler/testData/diagnostics/testsWithJsStdLib/name/overrideOverloadedNativeFunction.txt

@@ -0,0 +1,19 @@
+package
+
+public external open class A {
+    public constructor A()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open fun f(/*0*/ x: kotlin.Int): kotlin.Unit
+    public open fun f(/*0*/ x: kotlin.String): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class InheritClass : A {
+    public constructor InheritClass()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ fun f(/*0*/ x: kotlin.Int): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun f(/*0*/ x: kotlin.String): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithJsStdLibGenerated.java

@@ -476,6 +476,12 @@ public class DiagnosticsTestWithJsStdLibGenerated extends AbstractDiagnosticsTes
             doTest(fileName);
         }
 
+        @TestMetadata("overrideOverloadedNativeFunction.kt")
+        public void testOverrideOverloadedNativeFunction() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithJsStdLib/name/overrideOverloadedNativeFunction.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("packageAndMethod.kt")
         public void testPackageAndMethod() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithJsStdLib/name/packageAndMethod.kt");

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsNameClashChecker.kt

@@ -73,8 +73,8 @@ class JsNameClashChecker : SimpleDeclarationChecker {
                 val overrideFqn = nameSuggestion.suggest(override)!!
                 val scope = getScope(overrideFqn.scope)
                 val name = overrideFqn.names.last()
-                val existing = scope[name]
-                if (existing != null && existing != overrideFqn.descriptor) {
+                val existing = scope[name] as? CallableMemberDescriptor
+                if (existing != null && existing != overrideFqn.descriptor && !isFakeOverridingNative(existing)) {
                     diagnosticHolder.report(ErrorsJs.JS_FAKE_NAME_CLASH.on(declaration, name, override, existing))
                     break
                 }
@@ -89,6 +89,11 @@ class JsNameClashChecker : SimpleDeclarationChecker {
         }
     }
 
+    private fun isFakeOverridingNative(descriptor: CallableMemberDescriptor): Boolean {
+        return descriptor.kind == CallableMemberDescriptor.Kind.FAKE_OVERRIDE &&
+               descriptor.overriddenDescriptors.all { !presentsInGeneratedCode(it) }
+    }
+
     private fun getScope(descriptor: DeclarationDescriptor) = scopes.getOrPut(descriptor) {
         val scope = mutableMapOf<String, DeclarationDescriptor>()
         when (descriptor) {

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/BoxJsTestGenerated.java

@@ -5681,6 +5681,12 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
             doTest(fileName);
         }
 
+        @TestMetadata("overrideNativeOverloadedFunction.kt")
+        public void testOverrideNativeOverloadedFunction() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/native/overrideNativeOverloadedFunction.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("passExtLambdaFromNative.kt")
         public void testPassExtLambdaFromNative() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("js/js.translator/testData/box/native/passExtLambdaFromNative.kt");

js/js.translator/testData/box/native/overrideNativeOverloadedFunction.js

@@ -0,0 +1,5 @@
+function A() {
+}
+A.prototype.f = function(x) {
+    return typeof x;
+};

js/js.translator/testData/box/native/overrideNativeOverloadedFunction.kt

@@ -0,0 +1,36 @@
+external open class A {
+    open fun f(x: Int) = "number"
+
+    open fun f(x: String) = "string"
+}
+
+class B : A() {
+    fun g(x: Int) = "[${f(x)}]"
+
+    fun g(x: String) = "[${f(x)}]"
+}
+
+interface I {
+    fun f(x: Int): String
+}
+
+class C : A(), I
+
+external interface J {
+    fun f(x: Int): String
+}
+
+class D : A(), J
+
+fun box(): String {
+    var result = B().g(23) + B().g("foo")
+    if (result != "[number][string]") return "fail1: $result"
+
+    result = C().f(42)
+    if (result != "number") return "fail2: $result"
+
+    result = D().f("bar")
+    if (result != "string") return "fail3: $result"
+
+    return "OK"
+}