JS: fix copying fun with default args from interface to abstract class

See KT-20451

compiler/testData/codegen/box/defaultArguments/inheritedFromInterfaceViaAbstractSuperclass.kt

@@ -0,0 +1,17 @@
+interface I {
+    fun foo(x: Int = 23): String
+}
+
+abstract class Base : I
+
+class C : Base(), I {
+    override fun foo(x: Int) = "C:$x"
+}
+
+fun box(): String {
+    val x: I = C()
+    val r = x.foo() + ";" + x.foo(42)
+    if (r != "C:23;C:42") return "fail: $r"
+
+    return "OK"
+}

compiler/tests-ir-jvm/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -6479,6 +6479,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             throw new AssertionError("Looks like this test can be unmuted. Remove IGNORE_BACKEND directive for that.");
         }
 
+        @TestMetadata("inheritedFromInterfaceViaAbstractSuperclass.kt")
+        public void testInheritedFromInterfaceViaAbstractSuperclass() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/defaultArguments/inheritedFromInterfaceViaAbstractSuperclass.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("kt6382.kt")
         public void testKt6382() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/defaultArguments/kt6382.kt");

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -6479,6 +6479,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             throw new AssertionError("Looks like this test can be unmuted. Remove IGNORE_BACKEND directive for that.");
         }
 
+        @TestMetadata("inheritedFromInterfaceViaAbstractSuperclass.kt")
+        public void testInheritedFromInterfaceViaAbstractSuperclass() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/defaultArguments/inheritedFromInterfaceViaAbstractSuperclass.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("kt6382.kt")
         public void testKt6382() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/defaultArguments/kt6382.kt");

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -6479,6 +6479,12 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/defaultArguments"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
         }
 
+        @TestMetadata("inheritedFromInterfaceViaAbstractSuperclass.kt")
+        public void testInheritedFromInterfaceViaAbstractSuperclass() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/defaultArguments/inheritedFromInterfaceViaAbstractSuperclass.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("kt6382.kt")
         public void testKt6382() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/defaultArguments/kt6382.kt");

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

@@ -7151,6 +7151,12 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
             doTest(fileName);
         }
 
+        @TestMetadata("inheritedFromInterfaceViaAbstractSuperclass.kt")
+        public void testInheritedFromInterfaceViaAbstractSuperclass() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/defaultArguments/inheritedFromInterfaceViaAbstractSuperclass.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("kt6382.kt")
         public void testKt6382() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/box/defaultArguments/kt6382.kt");

js/js.translator/src/org/jetbrains/kotlin/js/translate/declaration/ClassModelGenerator.kt

@@ -54,7 +54,7 @@ class ClassModelGenerator(val context: TranslationContext) {
 
         // Traverse fake non-abstract member. Current class does not provide their implementation,
         // it can be inherited from interface.
-        for (member in members.filter { !it.kind.isReal && it.modality != Modality.ABSTRACT }) {
+        for (member in members.filter { !it.kind.isReal }) {
             if (member is FunctionDescriptor) {
                 tryCopyWhenImplementingInterfaceWithDefaultArgs(member, model)
             }
@@ -63,7 +63,7 @@ class ClassModelGenerator(val context: TranslationContext) {
 
             // Copy *implementation* functions (i.e. those ones which end with `$default` suffix)
             // of Kotlin functions with optional parameters.
-            if (member is FunctionDescriptor && !hasImplementationInPrototype(member)) {
+            if (member is FunctionDescriptor && !hasImplementationInPrototype(member) && member.modality != Modality.ABSTRACT) {
                 copyMemberWithOptionalArgs(descriptor, member, model, Namer.DEFAULT_PARAMETER_IMPLEMENTOR_SUFFIX)
             }
         }
@@ -155,7 +155,10 @@ class ClassModelGenerator(val context: TranslationContext) {
         // When none found, we have nothing to copy, ignore.
         // When multiple found, our current class should provide implementation, ignore.
         val memberToCopy = member.findNonRepeatingOverriddenDescriptors({ overriddenDescriptors }, { original })
-                                   .singleOrNull { it.modality != Modality.ABSTRACT } ?: return null
+                                   .singleOrNull {
+                                       it.modality != Modality.ABSTRACT ||
+                                       (it is FunctionDescriptor && it.hasOwnParametersWithDefaultValue())
+                                   } ?: return null
 
         // If found member is not from interface, we don't need to copy it, it's already in prototype
         if ((memberToCopy.containingDeclaration as ClassDescriptor).kind != ClassKind.INTERFACE) return null