code: func TempDir(dir, prefix string) (string, error) {
  	tempDir, err := ioutil.TempDir(dir, prefix)
  	if err != nil {
  		return "", err
  	}
  	return longpath.AddPrefix(tempDir), nil
  }
docs: // TempDir is the equivalent of ioutil.TempDir, except that the result is in Windows longpath format.