abstract overrides abstract: ignore if also overrides default and resolves ambiguity (IDEA-140376)

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/inheritance/AbstractMethodOverridesAbstractMethodInspection.java

@@ -115,22 +115,28 @@ public class AbstractMethodOverridesAbstractMethodInspection extends BaseInspect
       if (!method.hasModifierProperty(PsiModifier.ABSTRACT) && !containingClass.isInterface()) {
         return;
       }
+      boolean overrideDefault = false;
+      boolean accept = false;
       final PsiMethod[] superMethods = method.findSuperMethods();
       for (final PsiMethod superMethod : superMethods) {
+        overrideDefault |= superMethod.hasModifierProperty(PsiModifier.DEFAULT);
         if (!isAbstract(superMethod)) {
           continue;
         }
-        if (!methodsHaveSameReturnTypes(method, superMethod) || !haveSameExceptionSignatures(method, superMethod)) {
-          continue;
+        if (overrideDefault) {
+          return;
         }
+        accept |= methodsHaveSameReturnTypes(method, superMethod) && haveSameExceptionSignatures(method, superMethod);
+
         if (ignoreJavaDoc && !haveSameJavaDoc(method, superMethod)) {
           return;
         }
         if (ignoreAnnotations && !methodsHaveSameAnnotations(method, superMethod)) {
           return;
         }
+      }
+      if (accept && !overrideDefault) {
         registerMethodError(method);
-        return;
       }
     }
 

plugins/InspectionGadgets/test/com/siyeh/igtest/inheritance/abstract_method_overrides_abstract_method/AbstractMethodOverridesAbstractMethod.java

@@ -62,6 +62,23 @@ class SuperclassSubst {
 }
 
 class Java8DefaultMethods {
+
+  interface A {
+    String method();
+  }
+
+  interface B {
+    default String method() {
+      return null;
+    }
+  }
+
+  //without override would inherit abstract & default - red code
+  interface C extends A, B {
+    @Override
+    String method();
+  }
+
   interface Super
   {
       default void method()

plugins/InspectionGadgets/testsrc/com/siyeh/ig/inheritance/AbstractMethodOverridesAbstractMethodInspectionTest.java

@@ -1,5 +1,9 @@
 package com.siyeh.ig.inheritance;
 
+import com.intellij.openapi.projectRoots.Sdk;
+import com.intellij.openapi.roots.LanguageLevelProjectExtension;
+import com.intellij.pom.java.LanguageLevel;
+import com.intellij.testFramework.IdeaTestUtil;
 import com.siyeh.ig.IGInspectionTestCase;
 
 public class AbstractMethodOverridesAbstractMethodInspectionTest extends IGInspectionTestCase {
@@ -10,4 +14,11 @@ public class AbstractMethodOverridesAbstractMethodInspectionTest extends IGInspe
     tool.ignoreJavaDoc = true;
     doTest("com/siyeh/igtest/inheritance/abstract_method_overrides_abstract_method", tool);
   }
+
+  @Override
+  protected Sdk getTestProjectSdk() {
+    Sdk sdk = IdeaTestUtil.getMockJdk17();
+    LanguageLevelProjectExtension.getInstance(getProject()).setLanguageLevel(LanguageLevel.HIGHEST);
+    return sdk;
+  }
 }