anchor.diff:    void _destroyAnalysisContexts() {
       var collection = _collection;
       if (collection != null) {
  +      for (final subscription in watcherSubscriptions) {
  +        subscription.cancel();
  +      }
         for (var analysisContext in collection.contexts) {
           _destroyAnalysisContext(analysisContext);
         }
  
positive.code:   void _destroyAnalysisContext(DriverBasedAnalysisContext context) {
      context.driver.dispose();
      var rootFolder = context.contextRoot.root;
      changeSubscriptions.remove(rootFolder)?.cancel();
      var watched = bazelWatchedPathsPerFolder.remove(rootFolder);
      if (watched != null) {
        for (var path in watched.paths) {
  
negative.code:   final Map<Folder, AnalysisDriver> driverMap =
        HashMap<Folder, AnalysisDriver>();
  
    /// Subscriptions to watch included resources for changes.
    final List<StreamSubscription<WatchEvent>> watcherSubscriptions = [];
  
    /// For each folder, stores the subscription to the Bazel workspace so that we
    /// can establish watches for the generated files.
  