private function findSourceFilesFromList(array $filenames): void
  {
    foreach ($filenames as $filename)
    {
      if (!file_exists($filename))
      {
        $this->io->error(sprintf("File not exists: '%s'", $filename));
        $this->errorFilenames[] = $filename;
      }
      else
      {
        $routineName     = pathinfo($filename, PATHINFO_FILENAME);
        $this->sources[] = ['path_name'    => $filename,
                            'routine_name' => $routineName,
                            'method_name'  => $this->methodName($routineName)];
      }
    }
  }