support @FunctionalInterface

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

@@ -406,6 +406,14 @@ public class AnnotationsHighlightUtil {
     return null;
   }
 
+  public static HighlightInfo checkFunctionalInterface(PsiAnnotation annotation) {
+    final String errorMessage = LambdaUtil.checkFunctionalInterface(annotation);
+    if (errorMessage != null) {
+      return HighlightInfo.createHighlightInfo(HighlightInfoType.ERROR, annotation, errorMessage);
+    }
+    return null;
+  }
+
   public static class AnnotationReturnTypeVisitor extends PsiTypeVisitor<Boolean> {
     public static final AnnotationReturnTypeVisitor INSTANCE = new AnnotationReturnTypeVisitor();
     @Override

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

@@ -182,6 +182,7 @@ public class HighlightVisitorImpl extends JavaElementVisitor implements Highligh
     if (!myHolder.hasErrorResults()) myHolder.add(AnnotationsHighlightUtil.checkTargetAnnotationDuplicates(annotation));
     if (!myHolder.hasErrorResults()) myHolder.add(AnnotationsHighlightUtil.checkDuplicateAnnotations(annotation));
     if (!myHolder.hasErrorResults()) myHolder.add(AnnotationsHighlightUtil.checkForeignInnerClassesUsed(annotation));
+    if (!myHolder.hasErrorResults()) myHolder.add(AnnotationsHighlightUtil.checkFunctionalInterface(annotation));
   }
 
   @Override

java/java-psi-api/src/com/intellij/psi/LambdaUtil.java

@@ -25,6 +25,7 @@ import com.intellij.psi.codeStyle.JavaCodeStyleManager;
 import com.intellij.psi.infos.CandidateInfo;
 import com.intellij.psi.infos.MethodCandidateInfo;
 import com.intellij.psi.util.*;
+import org.jetbrains.annotations.NonNls;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -37,6 +38,7 @@ import java.util.*;
 public class LambdaUtil {
   private static final Logger LOG = Logger.getInstance("#" + LambdaUtil.class.getName());
   public static ThreadLocal<Set<PsiParameterList>> ourParams = new ThreadLocal<Set<PsiParameterList>>();
+  @NonNls public static final String JAVA_LANG_FUNCTIONAL_INTERFACE = "java.lang.FunctionalInterface";
 
   @Nullable
   public static PsiType getFunctionalInterfaceReturnType(PsiLambdaExpression expr) {
@@ -659,6 +661,20 @@ public class LambdaUtil {
     return getFunctionalInterfaceReturnType(functionalInterfaceType);
   }
 
+  @Nullable
+  public static String checkFunctionalInterface(PsiAnnotation annotation) {
+    if (PsiUtil.isLanguageLevel8OrHigher(annotation) && Comparing.strEqual(annotation.getQualifiedName(), JAVA_LANG_FUNCTIONAL_INTERFACE)) {
+      final PsiAnnotationOwner owner = annotation.getOwner();
+      if (owner instanceof PsiModifierList) {
+        final PsiElement parent = ((PsiModifierList)owner).getParent();
+        if (parent instanceof PsiClass) {
+          return LambdaHighlightingUtil.checkInterfaceFunctional((PsiClass)parent);
+        }
+      }
+    }
+    return null;
+  }
+
   static class TypeParamsChecker extends PsiTypeVisitor<Boolean> {
     private PsiMethod myMethod;
     private final PsiClass myClass;

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/highlighting/FunctionalInterfaceAnnotation.java

@@ -0,0 +1,5 @@
+<error descr="Multiple non-overriding abstract methods found">@FunctionalInterface</error>
+interface Test {
+  void foo();
+  void bar();
+}

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

@@ -200,6 +200,10 @@ public class LambdaHighlightingTest extends LightDaemonAnalyzerTestCase {
     doTest(true);
   }
 
+  public void testFunctionalInterfaceAnnotation() throws Exception {
+    doTest();
+  }
+
   private void doTest() throws Exception {
     doTest(false);
   }