code: func NewFileQuery(s string) (*FileQuery, error) {
  	s = strings.TrimSpace(s)
  	if s == "" {
  		return nil, fmt.Errorf("file: invalid format: %q", s)
  	}
  
  	return &FileQuery{
  		stopCh: make(chan struct{}, 1),
  		path:   s,
  	}, nil
  }
docs: // NewFileQuery creates a file dependency from the given path.