unrelated defaults: check if current class contains explicit method (IDEA-164732)

java/java-analysis-impl/src/com/intellij/codeInsight/daemon/impl/analysis/GenericsHighlightUtil.java

@@ -458,6 +458,7 @@ public class GenericsHighlightUtil {
 
       if (!hasConcrete && defaults != null) {
         final PsiMethod defaultMethod = defaults.get(0);
+        if (MethodSignatureUtil.findMethodBySuperMethod(aClass, defaultMethod, false) != null) continue;
         final PsiClass defaultMethodContainingClass = defaultMethod.getContainingClass();
         if (defaultMethodContainingClass == null) continue;
         final PsiMethod unrelatedMethod = abstracts != null ? abstracts.get(0) : defaults.get(1);

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/interfaceMethods/UnrelatedDefaultsWhenOverridingIsPresentExplicitly.java

@@ -0,0 +1,27 @@
+interface A<E> {
+  void foo(E item);
+}
+
+interface B1<E> extends A<E> {
+  @Override
+  default void foo(E item) {}
+}
+
+interface B2<E> extends A<E> {
+  @Override
+  default void foo(E item) {}
+}
+
+interface C1<E> extends B1<E> {}
+
+interface C2<E> extends B2<E> {}
+
+interface Bottom1<E> extends C2<E>, C1<E> {
+  @Override
+  default void foo(E item) {}
+}
+interface Bottom2<E> extends C2<E>, C1<E> {
+  @Override
+  void foo(E item);
+}
+interface <error descr="Bottom3 inherits unrelated defaults for foo(E) from types B2 and B1">Bottom3</error><E> extends C2<E>, C1<E> {}

java/java-tests/testSrc/com/intellij/codeInsight/daemon/lambda/Interface8MethodsHighlightingTest.java

@@ -71,6 +71,10 @@ public class Interface8MethodsHighlightingTest extends LightCodeInsightFixtureTe
     doTest(false, false);
   }
 
+  public void testUnrelatedDefaultsWhenOverridingIsPresentExplicitly() throws Exception {
+    doTest(false, false);
+  }
+
   public void testStaticMethodAccessibleBothThroughStaticImportAndInheritance() throws Exception {
     myFixture.addClass("package p; public interface Foo {" +
                        "    static void foo() {}" +