anchor.diff:  
   import 'dart:async';
   
  -import 'package:async/async.dart';
   import 'package:build/build.dart';
   import 'package:pub_semver/pub_semver.dart';
   import 'package:pubspec_parse/pubspec_parse.dart';
  
positive.code:   return null;
  }
  
  class _OncePerBuild<S, T> {
    final S state;
    final FutureOr<T> Function(S, BuildStep) _callback;
    AsyncMemoizer<T>? _memo;
  
    static Resource<_OncePerBuild<State, T>> resource<State, T>(
      State state,
      FutureOr<T> Function(State, BuildStep) callback,
    ) =>
        Resource<_OncePerBuild<State, T>>(
          () => _OncePerBuild._(state, callback),
          dispose: (c) => c._dispose(),
        );
  
    _OncePerBuild._(this.state, this._callback);
  
    Future<T> run(BuildStep buildStep) =>
        (_memo ??= AsyncMemoizer()).runOnce(() => _callback(state, buildStep));
  
    void _dispose() {
      _memo = null;
    }
  }
  
  
negative.code:       'Could not read the "pubspec.yaml` file associated with this package. '
        'Usage of package:$_annotationPkgName could not be verified.',
      );
      return;
    }
  
    Future<Pubspec> readPubspec(AssetId asset) async {
  