prefer extensions methods als interface (IDEA-96719)

java/java-psi-impl/src/com/intellij/psi/impl/PsiSuperMethodImplUtil.java

@@ -271,7 +271,9 @@ public class PsiSuperMethodImplUtil {
             if (superClass != null) {
               if (superClass.isInterface() ||
                   CommonClassNames.JAVA_LANG_OBJECT.equals(superClass.getQualifiedName())) {
-                return true;
+                if (!superMethod.hasModifierProperty(PsiModifier.DEFAULT) || !InheritanceUtil.isInheritorOrSelf(superClass, containingClass, true)) {
+                  return true;
+                }
               }
 
               if (containingClass != null) {

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advHighlighting7/DefaultMethodVisibility.java

@@ -0,0 +1,14 @@
+interface OfInt extends Sink<Integer> {
+  default void accept(Integer i) {}
+}
+interface Sink<T> extends Block<T> {
+}
+
+interface Block<T> {
+  public void accept(T t);
+}
+
+
+class Hello1 implements Sink<Integer>, OfInt {}
+class Hello2 implements OfInt, Sink<Integer>{}
+

java/java-tests/testSrc/com/intellij/codeInsight/daemon/LightAdvHighlightingJdk7Test.java

@@ -158,4 +158,5 @@ public class LightAdvHighlightingJdk7Test extends LightDaemonAnalyzerTestCase {
   public void testUncheckedWarningIDEA60166() throws Exception { doTest(true, false); }
   public void testUncheckedWarningIDEA21432() throws Exception { doTest(true, false); }
   public void testUncheckedWarningIDEA26738() throws Exception { doTest(true, false); }
+  public void testDefaultMethodVisibility() throws Exception { doTest(true, false); }
 }