merge completion suggestions based upon relevance

pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library services.completion.dart.manager;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
@@ skipping 29 matching lines @@
 
     DartCompletionRequestImpl dartRequest =
         await DartCompletionRequestImpl.from(request);
 
     // Don't suggest in comments.
     if (dartRequest.target.isCommentText) {
       return EMPTY_LIST;
     }
 
     // Request Dart specific completions from each contributor
-    List<CompletionSuggestion> suggestions = <CompletionSuggestion>[];
-    for (DartCompletionContributor c in dartCompletionPlugin.contributors) {
-      suggestions.addAll(await c.computeSuggestions(dartRequest));
+    Map<String, CompletionSuggestion> suggestionMap =
+        <String, CompletionSuggestion>{};
+    for (DartCompletionContributor contributor
+        in dartCompletionPlugin.contributors) {
+      for (CompletionSuggestion newSuggestion
+          in await contributor.computeSuggestions(dartRequest)) {
+        var oldSuggestion = suggestionMap.putIfAbsent(
+            newSuggestion.completion, () => newSuggestion);
+        if (newSuggestion != oldSuggestion &&
+            newSuggestion.relevance > oldSuggestion.relevance) {
+          suggestionMap[newSuggestion.completion] = newSuggestion;
+        }
+      }
     }
-    return suggestions;
+    return suggestionMap.values.toList();
   }
 }
 
 /**
  * The information about a requested list of completions within a Dart file.
  */
 class DartCompletionRequestImpl extends CompletionRequestImpl
     implements DartCompletionRequest {
   /**
    * The [LibraryElement] representing dart:core
@@ skipping 196 matching lines @@
     if (dartRequest.target.maybeFunctionalArgument()) {
       AstNode node = dartRequest.target.containingNode.parent;
       if (node is Expression) {
         await dartRequest.resolveExpression(node);
       }
     }
 
     return dartRequest;
   }
 }