using friendly format for claps help message

[junapur]

use clap::{Parser};
use jiff::{Span, ToSpan};

#[derive(Parser)]
#[command(version, about)]
struct Args {
    #[arg(short, long, default_value_t = 5.minutes())]
    time: Span,
}

when running this with --help, it will show this:

Options:
 -t, --time <TIME> [default: PT5m]

how can i have it show the friendly format, like [default: 5m] instead?

[BurntSushi]

You probably need a wrapper type here. Clap is probably just using the standard Display impl for Span, which will emit the ISO 8601 format for interoperability reasons. You can do {span:#} to get the "alternate" impl, and that will emit the friendly format.

Example:

use clap::Parser;
use jiff::{Span, ToSpan};

#[derive(Parser)]
#[command(version, about)]
struct Args {
    #[arg(short, long, default_value_t = FriendlySpan(5.minutes()))]
    time: FriendlySpan,
}

fn main() {
    let args = Args::parse();
    println!("{}", args.time.0);
}

#[derive(Clone, Copy, Debug)]
struct FriendlySpan(Span);

impl std::fmt::Display for FriendlySpan {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{:#}", self.0)
    }
}

impl std::str::FromStr for FriendlySpan {
    type Err = jiff::Error;
    fn from_str(s: &str) -> Result<FriendlySpan, jiff::Error> {
        Ok(FriendlySpan(s.parse()?))
    }
}

Kinda annoying, but I don't see a simpler way. Caveat emptor is that I'm not an expert in Clap's derive API. If it had a way to override how the default is displayed, then that would probably make this much easier.