How to have an multi-valued option with auto generated help?

[VorpalBlade]

I want something like this in the help message:

my-command [-t] <other args and stuff here>

...
    -t, --template STYLE    Style of template (a (default), b or c)
...

Where I have the following code:

enum Style {
    A,
    B,
    C,
}

impl FromStr for Style {
    // ...
}

#[derive(Debug, Clone, Bpaf)]
#[bpaf(options, version)]
struct Args {
    // ...
    /// Style of template
    #[bpaf(short, long, fallback(Style::A))]
    template: Style,
    // ...
}

This clearly doesn't work as is, (the Bpaf macro cannot inspect Style for what styles are supported), I couldn't get any version of this working. I tried adding the Bpaf macro to Style as well and using bpaf(external), but that resulted in [-a | -b | -c] which is different from what I want (i.e. I tried https://docs.rs/bpaf/0.7.10/bpaf/params/index.html#required-flag and various variations of that).

I would also like support for completion for this Style enum. Again a custom one could be coded by hand.

Thus my question is: Is there an elegant/automatic way of doing it that I'm missing? Or should I do the complicated hand written one (where I have to keep multiple different lists of things in sync)? And should I file a feature request?

[pacak]

It should be possible to implement as combinatoric function similar to here.

You define a parser for template field something like this:

fn template() -> impl Parser<Style> {
    let help_msg = format!("....."); // <- you can use `strum` to get exact names and put it in the help message in a way you like

    // again, with help of strum you can get a list of values and decide if it maches
    fn complete_fn(input: &String) -> Vec<...> {}

    // name
    short('t').long("template")
        .help(help_msg) // help mesage generated by strum
        .argument::<String>("ARG")  // consume it as string because completion will need a string to work with
        .complete(complete_fn) // try to complete with help of strum
        .parse(|x| x.parse()) // use `FromStr` to parse it to `Style`
}

Then use it in your parser via external.

I can try to make a working example if it's still unclear.

[pacak]

Do you have above code somewhere in a branch so I can experiment with it?

[VorpalBlade]

Do you have above code somewhere in a branch so I can experiment with it?

Yes, the v2 branch of https://github.com/VorpalBlade/chezmoi_modify_manager/tree/v2 has this. (Not all features do anything yet, as it is a work in progress)

[pacak]

Okay, thanks for the example. This was a bug in my code, I'm fixing it in #201

If your app is not yet ready to be released to users - you can try running of master branch and somewhere next week I'll try to publish either 0.7.11 with this bug fixed or 0.8 with a bit more changes. If it's urgent - I'll make 0.7.11 with just this bugfix backported.

Also if you are doing something interesting with bpaf like what you are doing in chezmoi and something is not quite working - don't hesitate to make a ticket. While I'm using bpaf completions myself on a daily basis - I'm not covering all the combinations. Here the problem was caused by fallback function not propagating collected values.

[VorpalBlade]

If your app is not yet ready to be released to users - you can try running of master branch and somewhere next week I'll try to publish either 0.7.11 with this bug fixed or 0.8 with a bit more changes. If it's urgent - I'll make 0.7.11 with just this bugfix backported.

Not urgent for me, I expect it to be a week or two before the v2 branch is ready anyways. Don't worry.

Also if you are doing something interesting with bpaf like what you are doing in chezmoi and something is not quite working - don't hesitate to make a ticket.

So people doing boring stuff shouldn't file tickets? ;-)

Seriously though, thanks for taking the time to look into this!

[pacak]

I expect it to be a week or two before the v2 branch is ready anyways.

Okay, I should be done by then.

So people doing boring stuff shouldn't file tickets? ;-)

Well, I would help either way but I'm assuming boring stuff to be mostly working as expected so just poking for a bit more in boring cases would yield the answer faster.

[pacak]

Took a bit longer but changes to generate better help are in master branch, will release soon-ish after going over documentation.