code: func rollbackFiles(files map[string]string, originalErr error) error {
  	errs := []error{originalErr}
  	for from, to := range files {
  		if err := os.Rename(from, to); err != nil {
  			errs = append(errs, err)
  		}
  	}
  	return errors.Errorf("couldn't move these files: %v. Got errors: %v", files, errorsutil.NewAggregate(errs))
  }
docs: // rollbackFiles moves the files back to the original directory.