Proper concrete implementation filtering in java 8 interface case

compiler/backend-common/src/org/jetbrains/kotlin/backend/common/bridges/bridges.kt

@@ -23,6 +23,12 @@ interface FunctionHandle {
     val isDeclaration: Boolean
     val isAbstract: Boolean
 
+    /** On finding concrete super declaration we should distinguish non-abstract java8/js default methods from
+    * class ones (see [findConcreteSuperDeclaration] method in bridges.kt).
+    * Note that interface methods with body compiled to jvm 8 target are assumed to be non-abstract in bridges method calculation
+    * (more details in [DescriptorBasedFunctionHandle.isBodyOwner] comment).*/
+    val isInterfaceDeclaration: Boolean
+
     fun getOverridden(): Iterable<FunctionHandle>
 }
 
@@ -108,7 +114,7 @@ fun <Function : FunctionHandle> findConcreteSuperDeclaration(function: Function)
     }
     result.removeAll(toRemove)
 
-    val concreteRelevantDeclarations = result.filter { !it.isAbstract }
+    val concreteRelevantDeclarations = result.filter { !it.isAbstract && !it.isInterfaceDeclaration }
     if (concreteRelevantDeclarations.size != 1) {
         error("Concrete fake override $function should have exactly one concrete super-declaration: $concreteRelevantDeclarations")
     }

compiler/backend-common/src/org/jetbrains/kotlin/backend/common/bridges/impl.kt

@@ -72,6 +72,9 @@ class DescriptorBasedFunctionHandle(
             descriptor.modality == Modality.ABSTRACT ||
             isBodyOwner(descriptor.containingDeclaration)
 
+    override val isInterfaceDeclaration: Boolean
+        get() = DescriptorUtils.isInterface(descriptor.containingDeclaration)
+
     override fun getOverridden() = overridden
 
     override fun hashCode(): Int {