Using enum argument without implementing FromStr

[kirillbobyrev]

Hi! I'm building a CLI app using clap-rs and I'd like to have an enum argument for it but this requires implementing FromStr trait. The code I have right now is this:

use clap::Clap;

use std::io::Error;
use std::io::ErrorKind;
use std::str::FromStr;

#[derive(Clap, Debug)]
enum LogLevel {
    Error,
    Info,
    Verbose,
}

impl FromStr for LogLevel {
    type Err = Error;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "error" => Ok(LogLevel::Error),
            "info" => Ok(LogLevel::Info),
            "verbose" => Ok(LogLevel::Verbose),
            _ => Err(Error::new(
                ErrorKind::InvalidInput,
                "Invalid LogLevel string, options are 'error', 'info', 'verbose'",
            )),
        }
    }
}

#[derive(Clap)]
#[clap(
    version = "0.0.1",
    author = "Kirill Bobyrev <[email protected]>"
)]
struct Opts {
    /// Logging level.
    #[clap(long, possible_values(&["error", "info", "verbose"]))]
    log: LogLevel,
}

Is there any way to avoid implementing FromStr for LogLevel? Ideally, I'd be also happy if I didn't have to provide possible_values to the argument in Opts if I had a way to specify all possible string values beforehand. The general problem I'm solving is not having a string field in struct Opts as it doesn't look very nice.

[CreepySkeleton]

This is implemented in master. Not sure if we released it though. Probably not. You can use the git dependency, I guess.

[kirillbobyrev]

I see, thanks! Yeah, sorry, I should have mentioned that I'm using clap = "3.0.0-beta.1".

Besides, I figured that log::Level already implements FromStr, so this works:

#[derive(Clap)]
#[clap(
    version = "0.0.1",
    author = "Kirill Bobyrev <[email protected]>"
)]
struct Opts {
    /// Logging level.
    #[clap(long, possible_values(&["error", "info", "verbose"]), default_value("error"))]
    log: log::Level,
}

Hence, my problem is solved but I'm really curious about how to do this in general: is there any code I could look at to see how this would work in master when it is released?

[CreepySkeleton]

clap/clap_derive/tests/arg_enum.rs

Lines 14 to 24 in a4bc1f2

	#[derive(Clap, PartialEq, Debug)]
	enum ArgChoice {
	Foo,
	Bar,
	}
	#[derive(Clap, PartialEq, Debug)]
	struct Opt {
	#[clap(arg_enum)]
	arg: ArgChoice,
	};

[kirillbobyrev]

Ah, I see, nice, thank you very much!