anchor.diff:  
     LibraryCycle? get internal_libraryCycle => _libraryCycle;
   
  -  /// Return `true` if the file is a stub created for a library in the provided
  -  /// external summary store.
  -  bool get isExternalLibrary {
  -    return _fsState.externalSummaries != null &&
  -        _fsState.externalSummaries!.hasLinkedLibrary(uriStr);
  -  }
  -
     /// Return `true` if the file does not have a `library` directive, and has a
     /// `part of` directive, so is probably a part.
     bool get isPart {
  -    if (_fsState.externalSummaries != null &&
  -        _fsState.externalSummaries!.hasUnlinkedUnit(uriStr)) {
  -      return _fsState.externalSummaries!.isPartUnit(uriStr);
  -    }
       return !_unlinked2!.hasLibraryDirective && _unlinked2!.hasPartOfDirective;
     }
   
  
positive.code: class ExternalLibrary {
    final Uri uri;
  
    ExternalLibrary(this.uri);
  }
  
  /// [FileContentOverlay] is used to temporary override content of files.
  
negative.code:   Either2<FileState?, ExternalLibrary> getFileForUri(Uri uri) {
      // If the external store has this URI, create a stub file for it.
      // We are given all required unlinked and linked summaries for it.
      final externalSummaries = this.externalSummaries;
      if (externalSummaries != null) {
        String uriStr = uri.toString();
        if (externalSummaries.hasLinkedLibrary(uriStr)) {
          return Either2.t2(ExternalLibrary._(uri));
        }
      }
  
  