code: func (e *Env) completionFlagTimestamp() (time.Time, error) {
  	// Read the complete flag file's timestamp.
  	switch st, err := os.Stat(e.completeFlagPath); {
  	case err == nil:
  		return st.ModTime(), nil
  
  	case os.IsNotExist(err):
  		return time.Time{}, nil
  
  	default:
  		return time.Time{}, errors.Annotate(err, "failed to stat completion flag: %s",
  			e.completeFlagPath).Err()
  	}
  }
docs: // completionFlagTimestamp returns the timestamp on the environment's completion
  // flag.
  //
  // If the completion flag does not exist (incomplete environment), a zero time
  // will be returned with no error.
  //
  // If an error is encountered while checking for the timestamp, it will be
  // returned.