Show the type of arguments in help message?

[tigerros]

Let's say you have this:

#[derive(Parser, Debug)]
#[command(author, version, about, long_about = None)]
pub struct MyParser {
    #[arg(long)]
    pub foo: u32,
}

Running --help will show this message:

Options:
      --foo <FOO>
  -h, --help       Print help
  -V, --version    Print version

Is it possible to also show the type? For example:

--foo <FOO> (unsigned 32 bit integer)

u32 would be nice, but it's not standard.

[epage]

There is an argument parser for another language that does this; I wish I could remember which.

If we did this, it could work to fill in similar to [possible values: foo, bar] in style.

However, I'm concerned about

• Clutter in the help output
• Not being in the user's terms (while most CLI users are programmers, not all are), even if its "unsigned 32 bit integer".

However, the value_name fills a similar role and I think it'd be a worthwhile to look into leveraging that. long and id are more akin to a field name while value_name is more akin to the type (in flags, positionals are weird in that they need to convey both). Framing this way, makes me feel like we could have a type associated term as the value name.

I had considered such a thing in #2683 but held off in #3732.

Going to convert this into an issue for further exploration.

[tigerros]

Ok, so not implemented right now. I do hope this becomes a feature though!