anchor.diff:  /// `.packages` file present.
   ///
   /// A [reader] and [writer] may also be supplied, which can read/write assets
  -/// to arbitrary locations or file systems. By default they will write to the
  -/// current directory, and will use the `packageGraph` to know where to read
  -/// files from.
  +/// to arbitrary locations or file systems. By default they will write directly
  +/// to the root package directory, and will use the [packageGraph] to know where
  +/// to read files from.
   Future<BuildResult> build(List<List<Phase>> phaseGroups,
       {PackageGraph packageGraph, AssetReader reader, AssetWriter writer}) async {
     packageGraph ??= new PackageGraph.forThisPackage();
  
positive.code: import 'dart:io';
  
  import 'package:path/path.dart' as path;
  import 'package:yaml/yaml.dart';
  
  import '../asset/asset.dart';
  import '../asset/file_based.dart';
  
negative.code: AssetReader get _reader => Zone.current[_assetReaderKey];
  AssetWriter get _writer => Zone.current[_assetWriterKey];
  PackageGraph get _packageGraph => Zone.current[_packageGraphKey];
  
  /// Validates the phases.
  void _validatePhases(List<List<Phase>> phaseGroups) {
  