code: func (s DiffIndexStatus) Format(state fmt.State, c rune) {
  	switch c {
  	case 'd', 's', 'v':
  		if state.Flag('+') {
  			state.Write([]byte(s.String()))
  		} else {
  			state.Write([]byte{byte(rune(s))})
  		}
  	default:
  		panic(fmt.Sprintf("cannot format %v for DiffIndexStatus", c))
  	}
  }
docs: // Format implements fmt.Formatter. If printed as "%+d", "%+s", or "%+v", the
  // status will be written out as an English word: i.e., "addition", "copy",
  // "deletion", etc.
  //
  // If the '+' flag is not given, the shorthand will be used instead: 'A', 'C',
  // and 'D', respectively.
  //
  // If any other format verb is given, this function will panic().