Different help text for bool and Option<bool>

[andioz]

Hello everybody! I'm starting to learn using the clap crate, which is awesome! It has a lot of functionality, which is not easy to grasp when starting using it. But since CLI argument handling is often required, I want to figure out how to implement different requirements the right way, and how to work around some possible obstacles.

I started with some simple arguments, and for some (unknown?) reason I used Option<T> for every value. This worked fine. Then I tried to change it to use the types directly, in combination with default values. It works so far, but I see some unexpected behavior in help text, especially for bool fields. Here is a simple example:

#[cfg(test)]
mod tests {
    use clap::builder::Styles;
    use clap::Parser;

    #[derive(Parser, Debug)]
    #[command(styles = Styles::plain())]
    struct Args {
        #[arg(long, value_name = "BOOL", help = "First option")]
        first: Option<bool>,
        #[arg(
            long,
            value_name = "BOOL",
            default_value_t = true,
            help = "Second option"
        )]
        second: bool,
    }

    #[test]
    fn test_help_text() {
        let error = Args::try_parse_from(["app", "--help"]).err().unwrap();
        let help_text = [
            "Usage: app [OPTIONS]",
            "",
            "Options:",
            "      --first <BOOL>  First option [possible values: true, false]",
            "      --second        Second option",
            "  -h, --help          Print help",
            "",
        ]
        .join("\n");
        assert_eq!(format!("{error}"), help_text);
    }
}

When using Option<bool> I get "possible values" in the help text, which looks nice. Switching to bool with default value, I would have expected to get the same plus a "[default value: true]" info. But this is not the case. And the "value_name" is not shown too.

I wonder, is this the expected output? Do I have a chance to tweak it? Using the hide_xyz(false) functions doesn't seem to work.

Many thanks in advance,
BR Andi

---

rustc version 1.80.1
clap version 4.5.16
Ubuntu Mate 22.04

[andioz]

Stupid me, I completely missed the fact that bool is treated as flag by default. Using action = ArgAction::Set seems to work as expected.