anchor.diff:          "Libraries changed: ${delta.newProgram.libraries.length}");
       print("Change '${changeSet.name}' - "
           "Incremental compilation took: ${iterTimer.elapsedMilliseconds}ms");
  +    if (delta.newProgram.libraries.length < 1) {
  +      throw "No libraries were changed";
  +    }
     }
   
     dir.deleteSync(recursive: true);
  
positive.code:   String toString() => 'ChangeSet($name, $edits)';
  }
  
  _resolveOverlayUri(String uriString) =>
      Uri.base.resolve(uriString).replace(scheme: 'org-dartlang-overlay');
  
  ArgParser argParser = new ArgParser()
    ..addOption('target',
  
negative.code:   final String replacement;
  
    Edit(String uriString, this.original, this.replacement)
        : uri = _resolveOverlayUri(uriString);
  
    String toString() => 'Edit($uri, "$original" -> "$replacement")';
  }
  