java sealed types: functional interface can't be sealed (IDEA-243536)

GitOrigin-RevId: 7660808963e79d51b8d1507927d1095d119bcdb5

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

@@ -565,10 +565,18 @@ public class AnnotationsHighlightUtil {
       if (owner instanceof PsiModifierList) {
         final PsiElement parent = ((PsiModifierList)owner).getParent();
         if (parent instanceof PsiClass) {
-          final String errorMessage = LambdaHighlightingUtil.checkInterfaceFunctional((PsiClass)parent, ((PsiClass)parent).getName() + " is not a functional interface");
+          final String errorMessage = LambdaHighlightingUtil.checkInterfaceFunctional((PsiClass)parent, JavaErrorBundle.message("not.a.functional.interface", ((PsiClass)parent).getName()));
           if (errorMessage != null) {
             return HighlightInfo.newHighlightInfo(HighlightInfoType.ERROR).range(annotation).descriptionAndTooltip(errorMessage).create();
           }
+          
+          if (HighlightingFeature.SEALED_CLASSES.isSufficient(languageLevel) && 
+              ((PsiClass)parent).hasModifierProperty(PsiModifier.SEALED)) {
+            return HighlightInfo.newHighlightInfo(HighlightInfoType.ERROR)
+              .range(annotation)
+              .descriptionAndTooltip(JavaErrorBundle.message("functional.interface.must.not.be.sealed.error.description", PsiModifier.SEALED))
+              .create();
+          }
         }
       }
     }

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

@@ -24,6 +24,7 @@ import com.intellij.psi.util.MethodSignature;
 import com.intellij.psi.util.PsiTypesUtil;
 import com.intellij.psi.util.PsiUtil;
 import com.intellij.psi.util.TypeConversionUtil;
+import org.jetbrains.annotations.Nls;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.HashSet;
@@ -37,7 +38,7 @@ public class LambdaHighlightingUtil {
     return checkInterfaceFunctional(psiClass, JavaErrorBundle.message("target.type.of.a.lambda.conversion.must.be.an.interface"));
   }
 
-  static String checkInterfaceFunctional(@NotNull PsiClass psiClass, @NotNull String interfaceNonFunctionalMessage) {
+  static String checkInterfaceFunctional(@NotNull PsiClass psiClass, @NotNull @Nls String interfaceNonFunctionalMessage) {
     if (psiClass instanceof PsiTypeParameter) return null; //should be logged as cyclic inference
     final List<HierarchicalMethodSignature> signatures = LambdaUtil.findFunctionCandidates(psiClass);
     if (signatures == null) return interfaceNonFunctionalMessage;

java/java-psi-impl/src/messages/JavaErrorBundle.properties

@@ -464,3 +464,4 @@ class.cannot.be.inherited.with.different.arguments={0} cannot be inherited with
 bad.type.in.switch.expression=Bad type in switch expression: {0} cannot be converted to {1}
 switch.expression.cannot.be.void=Target type for switch expression cannot be void
 annotation.on.static.member.qualifying.type.family.name=Move type annotation
+functional.interface.must.not.be.sealed.error.description=Functional interface can''t be declared as ''{0}''

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advHighlightingSealedTypes/SealedFunctionalInterface.java

@@ -0,0 +1,4 @@
+<error descr="Functional interface can't be declared as 'sealed'">@FunctionalInterface</error>
+sealed interface I {
+  void m();
+}

java/java-tests/testSrc/com/intellij/java/codeInsight/daemon/LightSealedTypesHighlightingTest.java

@@ -18,9 +18,8 @@ public class LightSealedTypesHighlightingTest extends LightJavaCodeInsightFixtur
     return JAVA_15;
   }
 
-  public void testSealedTypesBasics() {
-    doTest();
-  }
+  public void testSealedTypesBasics() { doTest(); }
+  public void testSealedFunctionalInterface() { doTest(); }
   
   private void doTest() {
     myFixture.configureByFile(getTestName(false) + ".java");