IDEA-91785 (sometimes extension method is abstract)

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

@@ -235,6 +235,12 @@ public class HighlightUtil {
       if (modifierList.hasModifierProperty(incompatible)) {
         return incompatible;
       }
+      else if (PsiModifier.ABSTRACT.equals(incompatible)) {
+        final PsiElement owner = modifierList.getParent();
+        if (owner instanceof PsiMethod && PsiUtil.isExtensionMethod((PsiMethod)owner)) {
+          return incompatible;
+        }
+      }
     }
     return null;
   }

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

@@ -47,4 +47,9 @@ class C {
 
 class D {
   <error descr="Extension methods can only be used within an interface">void m()</error> default { }
+}
+
+interface IllegalMods {
+  <error descr="Illegal combination of modifiers: 'static' and 'abstract'">static</error> void sm1();
+  <error descr="Illegal combination of modifiers: 'static' and 'abstract'">static</error> void sm2() default { }
 }