code: func IDsFromStat(rootPath, file string, r *UidRange) (Resolver, error) {
  	if strings.HasPrefix(file, "/") {
  		return idsFromStat{filepath.Join(rootPath, file), r}, nil
  	}
  
  	return nil, fmt.Errorf("invalid filename %q", file)
  }
docs: // IDsFromStat returns a new UID/GID resolver deriving the UID/GID from file attributes
  // and unshifts the UID/GID if the given range is not nil.
  // If the given id does not start with a slash "/" an error is returned.