// MarkFlagFilename adds the BashCompFilenameExt annotation to the named flag in the flag set, if it exists.
// Generated bash autocompletion will select filenames for the flag, limiting to named extensions if provided.
func MarkFlagFilename(flags *pflag.FlagSet, name string, extensions ...string) error {
	return flags.SetAnnotation(name, BashCompFilenameExt, extensions)
}
// MarkFlagRequired adds the BashCompOneRequiredFlag annotation to the named flag in the flag set, if it exists.
func MarkFlagRequired(flags *pflag.FlagSet, name string) error {
	return flags.SetAnnotation(name, BashCompOneRequiredFlag, []string{"true"})
}