[java] highlights package statements in module files

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

@@ -983,6 +983,9 @@ public class HighlightVisitorImpl extends JavaElementVisitor implements Highligh
   public void visitPackageStatement(PsiPackageStatement statement) {
     super.visitPackageStatement(statement);
     myHolder.add(AnnotationsHighlightUtil.checkPackageAnnotationContainingFile(statement, myFile));
+    if (myLanguageLevel.isAtLeast(LanguageLevel.JDK_1_9)) {
+      if (!myHolder.hasErrorResults()) myHolder.add(ModuleHighlightUtil.checkPackageStatement(statement, myFile));
+    }
   }
 
   @Override

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

@@ -92,6 +92,17 @@ public class ModuleHighlightUtil {
       .orElse(null);
   }
 
+  static HighlightInfo checkPackageStatement(@NotNull PsiPackageStatement statement, @NotNull PsiFile file) {
+    if (PsiUtil.isModuleFile(file)) {
+      String message = JavaErrorMessages.message("module.no.package");
+      HighlightInfo info = HighlightInfo.newHighlightInfo(HighlightInfoType.ERROR).range(statement).description(message).create();
+      QuickFixAction.registerQuickFixAction(info, new DeleteElementFix(statement));
+      return info;
+    }
+
+    return null;
+  }
+
   @Nullable
   static HighlightInfo checkFileName(@NotNull PsiJavaModule element, @NotNull PsiFile file) {
     if (!MODULE_INFO_FILE.equals(file.getName())) {

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

@@ -391,6 +391,7 @@ underscore.identifier.warn=Use of '_' as an identifier might not be supported in
 underscore.identifier.error=As of Java 9, '_' is a keyword, and may not be used as an identifier
 underscore.lambda.identifier=Use of '_' as a lambda parameter name is not allowed
 
+module.no.package=A module file should not have 'package' statement
 module.file.wrong.name=Module declaration should be in a file named 'module-info.java'
 module.file.duplicate='module-info.java' already exists in the module
 module.duplicate.requires=Duplicate requires: {0}

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

@@ -28,6 +28,14 @@ class ModuleHighlightingTest : LightJava9ModulesCodeInsightFixtureTestCase() {
     addFile("module-info.java", "module M3 { }", M3)
   }
 
+  fun testPackageStatement() {
+    highlight("package pkg;")
+    highlight("""
+        <error descr="A module file should not have 'package' statement">package pkg;</error>
+        module M { }""".trimIndent())
+    fixes("<caret>package pkg;\nmodule M { }", "DeleteElementFix")
+  }
+
   fun testSoftKeywords() {
     addFile("pkg/module/C.java", "package pkg.module;\npublic class C { }")
     myFixture.configureByText("module-info.java", "module M { exports pkg.module; }")