anchor.diff:  
     factory PubspecPlatform.fromJson(String value) {
       switch (value) {
  -      case 'flutter':
  +      case PlatformFlags.flutter:
           return flutter;
  -      case 'undefined':
  +      case PlatformFlags.undefined:
           return undefined;
         default:
           throw new ArgumentError.value(value, 'value', 'Not a supported value.');
  
positive.code: }
  
  abstract class PlatformFlags {
    /// Denotes a package that references Flutter in `pubspec.yaml`.
    static const String flutter = 'flutter';
  
    /// Denotes a library that depends on a native extensions via `dart-ext:`
    static const String dartExtension = 'dart-ext';
  }
  
  @JsonSerializable()
  
negative.code: class PubspecPlatform {
    final String description;
  
    static const PubspecPlatform flutter =
        const PubspecPlatform._(PlatformFlags.flutter);
  
    static const PubspecPlatform undefined =
        const PubspecPlatform._(PlatformFlags.undefined);
  
    bool get isFlutter => description == flutter.description;
  
  