code: func (err GenerationError) CodeWithLineNumbers() string {
  	var buf bytes.Buffer
  	scanner := bufio.NewScanner(bytes.NewReader(err.Code))
  	var i int
  	for scanner.Scan() {
  		i++
  		fmt.Fprintf(&buf, "%d: %s\n", i, scanner.Text())
  	}
  	return buf.String()
  }
docs: // CodeWithLineNumbers returns all the code including line numbers