Handle a failure in "pub list-package-dirs".

pkg/analysis_server/lib/src/context_directory_manager.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 context.directory.manager;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/package_map_provider.dart';
@@ skipping 100 matching lines @@
    * Create a new context associated with the given folder.
    */
   void _createContext(Folder folder) {
     _ContextDirectoryInfo info = new _ContextDirectoryInfo();
     _currentDirectoryInfo[folder] = info;
     info.changeSubscription = folder.changes.listen((WatchEvent event) {
       _handleWatchEvent(folder, info, event);
     });
     File pubspecFile = folder.getChild(PUBSPEC_NAME);
     PackageMapInfo packageMapInfo = packageMapProvider.computePackageMap(folder);
-    // TODO(paulberry): handle null return from computePackageMap.
     info.packageMapDependencies = packageMapInfo.dependencies;
     // TODO(paulberry): if any of the dependencies is outside of [folder],
     // we'll need to watch their parent folders as well.
     addContext(folder, packageMapInfo.packageMap);
     ChangeSet changeSet = new ChangeSet();
     _addSourceFiles(changeSet, folder, info);
     applyChangesToContext(folder, changeSet);
   }
 
   /**
@@ skipping 46 matching lines @@
         }
         break;
     }
 
     if (info.packageMapDependencies.contains(event.path)) {
       // TODO(paulberry): when computePackageMap is changed into an
       // asynchronous API call, we'll want to suspend analysis for this context
       // while we're rerunning "pub list", since any analysis we complete while
       // "pub list" is in progress is just going to get thrown away anyhow.
       PackageMapInfo packageMapInfo = packageMapProvider.computePackageMap(folder);
-      // TODO(paulberry): handle null return from computePackageMap.
       info.packageMapDependencies = packageMapInfo.dependencies;
       updateContextPackageMap(folder, packageMapInfo.packageMap);
     }
   }
 
   /**
    * Determine if the path from [folder] to [path] contains a 'packages'
    * directory.
    */
   bool _isInPackagesDir(String path, Folder folder) {
@@ skipping 51 matching lines @@
    * Remove the context associated with the given [folder].
    */
   void removeContext(Folder folder);
 
   /**
    * Called when the package map for a context has changed.
    */
   void updateContextPackageMap(Folder contextFolder,
                                Map<String, List<Folder>> packageMap);
 }