anchor.diff:    }
   
     void _addContextFile(String path) {
  -    if (!_contextPathList.contains(path)) {
  -      _contextPathList.add(path);
  -    }
  +    _contextPathSet.add(path);
     }
   
     /// Add known libraries, other then in the context itself, or the SDK.
     void _addKnownLibraries(List<Library> libraries) {
  -    var contextPathSet = _contextPathList.toSet();
       var sdkPathSet = _sdkLibraryPathList.toSet();
   
       for (var path in _knownPathList) {
  -      if (contextPathSet.contains(path) || sdkPathSet.contains(path)) {
  +      if (_contextPathSet.contains(path) || sdkPathSet.contains(path)) {
           continue;
         }
   
  
positive.code:       }
  
        if (package != null) {
          var containingFolder = package.folderInRootContaining(path);
          if (containingFolder != null) {
            for (var contextPath in _contextPathList) {
              // `lib/` can see only libraries in `lib/`.
              // `test/` can see libraries in `lib/` and in `test/`.
              if (package.containsInLib(contextPath) ||
  
negative.code:     }
    }
  
    void _addLibrariesWithPaths(List<Library> libraries, Iterable<String> paths,
        {String? excludingLibraryOfPath}) {
      var excludedFile = _tracker._pathToFile[excludingLibraryOfPath];
      var excludedLibraryPath = (excludedFile?.library ?? excludedFile)?.path;
  
      for (var path in paths) {
        if (path == excludedLibraryPath) continue;
  
        var file = _tracker._pathToFile[path];
  