code: func PrintFs(fs afero.Fs, path string, w io.Writer) {
  	if fs == nil {
  		return
  	}
  	afero.Walk(fs, path, func(path string, info os.FileInfo, err error) error {
  		if info != nil && !info.IsDir() {
  			s := path
  			if lang, ok := info.(hugofs.LanguageAnnouncer); ok {
  				s = s + "\tLANG: " + lang.Lang()
  			}
  			if fp, ok := info.(hugofs.FilePather); ok {
  				s = s + "\tRF: " + fp.Filename() + "\tBP: " + fp.BaseDir()
  			}
  			fmt.Fprintln(w, "    ", s)
  		}
  		return nil
  	})
  }
docs: // PrintFs prints the given filesystem to the given writer starting from the given path.
  // This is useful for debugging.