Gracefully degrade if no source for completion

pkg/analysis_server/lib/src/domain_completion.dart

 // Copyright (c) 2014, 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 domain.completion;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
@@ skipping 159 matching lines @@
   Response processRequest(Request request, [CompletionManager manager]) {
     performance = new CompletionPerformance();
     // extract params
     CompletionGetSuggestionsParams params =
         new CompletionGetSuggestionsParams.fromRequest(request);
     // schedule completion analysis
     String completionId = (_nextCompletionId++).toString();
     ContextSourcePair contextSource = server.getContextSourcePair(params.file);
     AnalysisContext context = contextSource.context;
     Source source = contextSource.source;
+    if (!context.exists(source)) {

[scheglov, 2015/03/30 21:10:48]

Actually it is not guaranteed that AnalysisContext is not null.
It might be if the file is not a part of any context.

[danrubel, 2015/03/30 21:40:48]

Good catch. Fixed.

+      return new Response.unknownSource(request);
+    }
     recordRequest(performance, context, source, params.offset);
     if (manager == null) {
       manager = completionManagerFor(context, source);
     }
     CompletionRequest completionRequest =
         new CompletionRequest(params.offset, performance);
     int notificationCount = 0;
     manager.results(completionRequest).listen((CompletionResult result) {
       ++notificationCount;
       performance.logElapseTime("notification $notificationCount send", () {
@@ skipping 77 matching lines @@
     if (_sourcesChangedSubscription != null) {
       _sourcesChangedSubscription.cancel();
       _sourcesChangedSubscription = null;
     }
     if (_manager != null) {
       _manager.dispose();
       _manager = null;
     }
   }
 }