[java] ambiguous module refs highlighting (IDEA-164553)

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

@@ -413,13 +413,20 @@ public class ModuleHighlightUtil {
   }
 
   private static HighlightInfo moduleResolveError(PsiJavaModuleReferenceElement refElement, PsiPolyVariantReference ref) {
-    boolean missing = ref.multiResolve(true).length == 0;
-    String message = JavaErrorMessages.message(missing ? "module.not.found" : "module.not.on.path", refElement.getReferenceText());
-    HighlightInfo info = HighlightInfo.newHighlightInfo(HighlightInfoType.WRONG_REF).range(refElement).description(message).create();
-    if (!missing) {
+    if (ref.multiResolve(true).length == 0) {
+      String message = JavaErrorMessages.message("module.not.found", refElement.getReferenceText());
+      return HighlightInfo.newHighlightInfo(HighlightInfoType.WRONG_REF).range(refElement).description(message).create();
+    }
+    else if (ref.multiResolve(false).length > 1) {
+      String message = JavaErrorMessages.message("module.ambiguous", refElement.getReferenceText());
+      return HighlightInfo.newHighlightInfo(HighlightInfoType.WARNING).range(refElement).description(message).create();
+    }
+    else {
+      String message = JavaErrorMessages.message("module.not.on.path", refElement.getReferenceText());
+      HighlightInfo info = HighlightInfo.newHighlightInfo(HighlightInfoType.WRONG_REF).range(refElement).description(message).create();
       factory().registerOrderEntryFixes(new QuickFixActionRegistrarImpl(info), ref);
+      return info;
     }
-    return info;
   }
 
   private static QuickFixFactory factory() {

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

@@ -400,6 +400,7 @@ module.duplicate.provides=Duplicate provides: {0}
 module.file.wrong.location=Module declaration should be located in a module's source root
 module.open.duplicate.text=Go to duplicate
 module.not.found=Module not found: {0}
+module.ambiguous=Ambiguous module reference: {0}
 module.not.on.path=Module is not in dependencies: {0}
 module.cyclic.dependence=Cyclic dependence: {0}
 package.not.found=Package not found: {0}

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

@@ -72,6 +72,7 @@ class ModuleHighlightingTest : LightJava9ModulesCodeInsightFixtureTestCase() {
           requires <error descr="Cyclic dependence: M1">M1</error>;
           requires <error descr="Cyclic dependence: M1, M2">M2</error>;
           requires <error descr="Module is not in dependencies: M3">M3</error>;
+          requires <warning descr="Ambiguous module reference: lib.auto">lib.auto</warning>;
         }""".trimIndent())
   }