[java] add highlighting when package is present in unnamed class

GitOrigin-RevId: 64e5c38ba1c56741857d2f3331562bbe7f2f65cb

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

@@ -1176,6 +1176,12 @@ public class HighlightVisitorImpl extends JavaElementVisitor implements Highligh
     if (myLanguageLevel.isAtLeast(LanguageLevel.JDK_1_9)) {
       if (!myHolder.hasErrorResults()) add(ModuleHighlightUtil.checkPackageStatement(statement, myFile, myJavaModule));
     }
+    if (!myHolder.hasErrorResults()) {
+      if (HighlightingFeature.UNNAMED_CLASSES.isAvailable(myFile) && JavaUnnamedClassUtil.isFileWithUnnamedClass(myFile)) {
+        add(HighlightInfo.newHighlightInfo(HighlightInfoType.ERROR).range(statement).descriptionAndTooltip(
+          JavaErrorBundle.message("text.package.statement.not.allowed.for.unnamed.class")));
+      }
+    }
   }
 
   @Override

java/java-psi-impl/src/com/intellij/psi/util/JavaUnnamedClassUtil.java

@@ -0,0 +1,21 @@
+// Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.intellij.psi.util;
+
+import com.intellij.psi.PsiClass;
+import com.intellij.psi.PsiFile;
+import com.intellij.psi.PsiJavaFile;
+import com.intellij.psi.PsiUnnamedClass;
+import org.jetbrains.annotations.NotNull;
+
+public final class JavaUnnamedClassUtil {
+  public static boolean isFileWithUnnamedClass(@NotNull PsiFile file) {
+    if (file instanceof PsiJavaFile) {
+      PsiJavaFile javaFile = (PsiJavaFile)file;
+      PsiClass[] classes = javaFile.getClasses();
+      if (classes.length == 1 && classes[0] instanceof PsiUnnamedClass) {
+        return true;
+      }
+    }
+    return false;
+  }
+}

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

@@ -575,4 +575,5 @@ too.many.array.dimensions=Too many array dimensions
 error.cannot.infer.pattern.type=Cannot infer pattern type: {0}
 error.extra.semicolons.between.import.statements.not.allowed=Extra semicolons between import statements are not allowed
 error.guard.allowed.after.patterns.only=Guard is allowed after patterns only
-error.unnamed.class.contains.no.main.method=Unnamed class contains no 'main' method
+error.unnamed.class.contains.no.main.method=Unnamed class contains no 'main' method
+text.package.statement.not.allowed.for.unnamed.class=Package statement is not allowed for unnamed class

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/unnamedClass/WithPackageStatement.java

@@ -0,0 +1,5 @@
+<error descr="Unnamed class contains no 'main' method"><error descr="Package statement is not allowed for unnamed class">package pack.bar;</error>
+
+void foo() {
+
+}</error>

java/java-tests/testSrc/com/intellij/java/codeInsight/daemon/UnnamedClassHighlightingTest.kt

@@ -16,7 +16,7 @@ class UnnamedClassHighlightingTest : LightJavaCodeInsightFixtureTestCase() {
     })
   }
 
-  fun testNoMainMethod() {
+  fun testWithPackageStatement() {
     doTest()
   }