IDEA-121952 (Java 1.8: "Interface may be annotated with @FunctionalInterface" inspection reports already annotated interfaces)

plugins/InspectionGadgets/InspectionGadgetsAnalysis/src/com/siyeh/ig/classlayout/InterfaceMayBeAnnotatedFunctionalInspection.java

@@ -15,6 +15,7 @@
  */
 package com.siyeh.ig.classlayout;
 
+import com.intellij.codeInsight.AnnotationUtil;
 import com.intellij.codeInsight.intention.AddAnnotationPsiFix;
 import com.intellij.psi.LambdaHighlightingUtil;
 import com.intellij.psi.LambdaUtil;
@@ -71,7 +72,7 @@ public class InterfaceMayBeAnnotatedFunctionalInspection extends BaseInspection
         return;
       }
       super.visitClass(aClass);
-      if (!aClass.isInterface()) {
+      if (!aClass.isInterface() || AnnotationUtil.isAnnotated(aClass, "java.lang.FunctionalInterface", false)) {
         return;
       }
       if (LambdaHighlightingUtil.checkInterfaceFunctional(aClass) != null) {

plugins/InspectionGadgets/testsrc/com/siyeh/ig/classlayout/InterfaceMayBeAnnotatedFunctionalInspectionTest.java

@@ -44,6 +44,12 @@ public class InterfaceMayBeAnnotatedFunctionalInspectionTest extends LightInspec
            "}");
   }
 
+  public void testAlreadyAnnotated() {
+    doTest("@FunctionalInterface interface Asd {" +
+           "    boolean doSmth();" +
+           "}");
+  }
+
   public void testAnnotationType() {
     doTest("@interface A {}");
   }