code: func (o RevListOrder) Flag() (string, bool) {
  	switch o {
  	case DefaultRevListOrder:
  		return "", false
  	case DateRevListOrder:
  		return "--date-order", true
  	case AuthorDateRevListOrder:
  		return "--author-date-order", true
  	case TopoRevListOrder:
  		return "--topo-order", true
  	default:
  		panic(fmt.Sprintf("git/rev_list_scanner: unknown RevListOrder %d", o))
  	}
  }
docs: // Flag returns the command-line flag to be passed to git-rev-list(1) in order
  // to order the output according to the given RevListOrder. It returns both the
  // flag ("--date-order", "--topo-order", etc) and a bool, whether or not to
  // append the flag (for instance, DefaultRevListOrder requires no flag).
  //
  // Given a type other than those defined above, Flag() will panic().