completion: show a "no suggestions" hint in dumb mode

platform/lang-impl/src/com/intellij/codeInsight/completion/CompletionProgressIndicator.java

@@ -17,6 +17,7 @@ import com.intellij.diagnostic.PerformanceWatcher;
 import com.intellij.featureStatistics.FeatureUsageTracker;
 import com.intellij.injected.editor.DocumentWindow;
 import com.intellij.injected.editor.EditorWindow;
+import com.intellij.lang.LangBundle;
 import com.intellij.openapi.Disposable;
 import com.intellij.openapi.actionSystem.IdeActions;
 import com.intellij.openapi.application.ApplicationManager;
@@ -743,29 +744,25 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
 
     LOG.assertTrue(!isAutopopupCompletion());
 
-    if (!myHandler.invokedExplicitly) {
-      CompletionServiceImpl.setCompletionPhase(CompletionPhase.NoCompletion);
-      return;
-    }
-
     CompletionParameters parameters = getParameters();
-    if (parameters != null && runContributorsOnEmptyLookup(awaitSecondInvocation, parameters)) {
-      return;
+    if (myHandler.invokedExplicitly && parameters != null) {
+      LightweightHint hint = showErrorHint(getProject(), getEditor(), getNoSuggestionsMessage(parameters));
+      if (awaitSecondInvocation) {
+        CompletionServiceImpl.setCompletionPhase(new CompletionPhase.NoSuggestionsHint(hint, this));
+        return;
+      }
     }
     CompletionServiceImpl.setCompletionPhase(CompletionPhase.NoCompletion);
   }
 
-  private boolean runContributorsOnEmptyLookup(boolean awaitSecondInvocation, CompletionParameters parameters) {
-    for (CompletionContributor contributor : CompletionContributor.forParameters(parameters)) {
-      final String text = contributor.handleEmptyLookup(parameters, getEditor());
-      if (StringUtil.isNotEmpty(text)) {
-        LightweightHint hint = showErrorHint(getProject(), getEditor(), text);
-        CompletionServiceImpl.setCompletionPhase(
-          awaitSecondInvocation ? new CompletionPhase.NoSuggestionsHint(hint, this) : CompletionPhase.NoCompletion);
-        return true;
-      }
-    }
-    return false;
+  private String getNoSuggestionsMessage(CompletionParameters parameters) {
+    String text = CompletionContributor.forParameters(parameters)
+                                       .stream()
+                                       .map(c -> c.handleEmptyLookup(parameters, getEditor()))
+                                       .filter(StringUtil::isNotEmpty)
+                                       .findFirst()
+                                       .orElse(LangBundle.message("completion.no.suggestions"));
+    return DumbService.isDumb(getProject()) ? text + "; results might be incomplete while indexing is in progress" : text;
   }
 
   private static LightweightHint showErrorHint(Project project, Editor editor, String text) {

platform/lang-impl/src/com/intellij/codeInsight/completion/DefaultCompletionContributor.java

@@ -21,7 +21,6 @@ import com.intellij.codeInsight.lookup.LookupElement;
 import com.intellij.codeInsight.lookup.impl.LookupImpl;
 import com.intellij.lang.LangBundle;
 import com.intellij.openapi.actionSystem.IdeActions;
-import com.intellij.openapi.editor.Editor;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.util.text.StringUtil;
 import org.jetbrains.annotations.NotNull;
@@ -62,11 +61,6 @@ public class DefaultCompletionContributor extends CompletionContributor {
     }
   }
 
-  @Override
-  public String handleEmptyLookup(@NotNull final CompletionParameters parameters, final Editor editor) {
-    return LangBundle.message("completion.no.suggestions");
-  }
-
   @Override
   public AutoCompletionDecision handleAutoCompletionPossibility(@NotNull AutoCompletionContext context) {
     final LookupElement[] items = context.getItems();