anchor.diff:    void changeFile(String path) {
       // TODO(scheglov) Don't clear, schedule API signature validation.
       _fileContentHashMap.clear();
  +    _linkedHashMap.clear();
       _filesToAnalyze.add(path);
       _filesToAnalyze.addAll(_explicitFiles);
       // TODO(scheglov) name?!
  
positive.code:   /**
     * The current file state.
     *
     * It maps file paths to MD5 hash of the file content.
     */
    final _fileContentHashMap = <String, String>{};
  
    /**
     * TODO(scheglov) document and improve
  
negative.code:   bool get isReady => linked != null;
  
    String get linkedHash {
      _linkedHash ??= driver._linkedHashMap.putIfAbsent(uri, () {
        computeTransitiveDependencies();
  
        // Add all unlinked API signatures.
        List<String> signatures = <String>[];
  