cli: optional message for issue comments — heartwood

The From<String> for Message implementation has an interesting interaction between clap and how Message can be used from the command line.

Note that FromStr is not implemented for Message – which usually what is to be expected for use with clap, but in fact, clap also allows From<String>.

This would make Message be a required option when using rad issue comment.

It is not possible to use default_value_t because that required an implementation of Display, which in this case we do not want to implement. Trying to use default_value = "Message::Edit" also would not work – it uses that as the text.

So, the solution is to mark it as optional, and default to Message::Edit when it is not specified.

     /// The body of the comment
     #[arg(long, short)]
     #[arg(value_name = "MESSAGE")]
     message: Message,
     message: Option<Message>,
     /// Optionally, the comment to reply to. If not specified, the comment
     /// will be in reply to the issue itself

             edit,
         }: CommentArgs,
     ) -> Self {
         let message = message.unwrap_or(Message::Edit);
         match (reply_to, edit) {
             (Some(_), Some(_)) => {
                 unreachable!("the argument '--reply-to' cannot be used with '--edit'")