anchor.diff:  
     /// The class member names defined by the file.
     Set<String> get definedClassMemberNames {
  -    return _definedClassMemberNames ??=
  -        _driverUnlinkedUnit!.definedClassMemberNames.toSet();
  +    return _driverUnlinkedUnit!.definedClassMemberNames;
     }
   
     /// The top-level names defined by the file.
     Set<String> get definedTopLevelNames {
  -    return _definedTopLevelNames ??=
  -        _driverUnlinkedUnit!.definedTopLevelNames.toSet();
  +    return _driverUnlinkedUnit!.definedTopLevelNames;
     }
   
     /// Return the set of all directly referenced files - imported, exported or
  
positive.code: 
    /// The external names referenced by the file.
    Set<String> get referencedNames {
      return _referencedNames ??= _driverUnlinkedUnit!.referencedNames.toSet();
    }
  
    @visibleForTesting
  
negative.code:   String? _content;
    String? _contentHash;
    LineInfo? _lineInfo;
    Uint8List? _unlinkedSignature;
    String? _unlinkedKey;
    String? _informativeKey;
  