Support inheritance from java 8 interfaces

#KT-5969 In Progress

compiler/backend/src/org/jetbrains/jet/codegen/ImplementationBodyCodegen.java

@@ -49,6 +49,7 @@ import org.jetbrains.jet.lang.resolve.calls.model.VarargValueArgument;
 import org.jetbrains.jet.lang.resolve.java.AsmTypeConstants;
 import org.jetbrains.jet.lang.resolve.java.JvmAbi;
 import org.jetbrains.jet.lang.resolve.java.JvmAnnotationNames;
+import org.jetbrains.jet.lang.resolve.java.descriptor.JavaCallableMemberDescriptor;
 import org.jetbrains.jet.lang.resolve.java.diagnostics.JvmDeclarationOrigin;
 import org.jetbrains.jet.lang.resolve.java.jvmSignature.JvmClassSignature;
 import org.jetbrains.jet.lang.resolve.java.jvmSignature.JvmMethodParameterKind;
@@ -1412,8 +1413,12 @@ public class ImplementationBodyCodegen extends ClassBodyCodegen {
     private void generateTraitMethods() {
         if (JetPsiUtil.isTrait(myClass)) return;
 
-        for(Map.Entry<FunctionDescriptor, FunctionDescriptor> entry : CodegenUtil.getTraitMethods(descriptor).entrySet()) {
-            generateDelegationToTraitImpl(entry.getKey(), entry.getValue());
+        for (Map.Entry<FunctionDescriptor, FunctionDescriptor> entry : CodegenUtil.getTraitMethods(descriptor).entrySet()) {
+            FunctionDescriptor traitFun = entry.getKey();
+            //skip java 8 default methods
+            if (!(traitFun instanceof JavaCallableMemberDescriptor)) {
+                generateDelegationToTraitImpl(traitFun, entry.getValue());
+            }
         }
     }
 

compiler/testData/codegen/boxWithJava/trait/MyInt.java

@@ -0,0 +1,4 @@
+public interface MyInt {
+
+    String test();
+}

compiler/testData/codegen/boxWithJava/trait/interfaceInheritance.kt

@@ -0,0 +1,11 @@
+trait A : MyInt {
+    override public fun test(): String? {
+        return "OK"
+    }
+}
+
+class B: A
+
+fun box() : String {
+    return B().test()!!
+}

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxWithJavaCodegenTestGenerated.java

@@ -45,6 +45,12 @@ public class BlackBoxWithJavaCodegenTestGenerated extends AbstractBlackBoxCodege
         doTestWithJava(fileName);
     }
     
+    @TestMetadata("trait")
+    public void testTrait() throws Exception {
+        String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/boxWithJava/trait/");
+        doTestWithJava(fileName);
+    }
+    
     @TestMetadata("compiler/testData/codegen/boxWithJava/platformStatic")
     @TestDataPath("$PROJECT_ROOT")
     @InnerTestClasses({})