anchor.diff:  
     Future<int> run({
       @required SnapshotType snapshotType,
  -    @required String packagesPath,
       IOSArch iosArch,
       Iterable<String> additionalArgs = const <String>[],
     }) {
       final List<String> args = <String>[
         '--causal_async_stacks',
  -      '--packages=$packagesPath',
       ]..addAll(additionalArgs);
   
       final String snapshotterPath = getSnapshotterPath(snapshotType);
  
positive.code:     final SnapshotType snapshotType = SnapshotType(platform, buildMode);
      final int genSnapshotExitCode = await genSnapshot.run(
        snapshotType: snapshotType,
        packagesPath: packageMap.packagesPath,
        additionalArgs: genSnapshotArgs,
        iosArch: iosArch,
      );
  
negative.code:     final SnapshotType snapshotType = SnapshotType(platform, buildMode);
      final int genSnapshotExitCode = await genSnapshot.run(
        snapshotType: snapshotType,
        additionalArgs: genSnapshotArgs,
      );
      if (genSnapshotExitCode != 0) {
  