Example usage of arg_enum in Clap 3.0.0-beta.2

Cargo.toml

[package]
name = "clap-argenum-for-ed"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
clap = "= 3.0.0-beta.2"
clap_derive = " = 3.0.0-beta.2"
thiserror = "1.0.30"

main.rs

use std::str::FromStr;

use clap::Clap;

#[derive(Debug, thiserror::Error)]
pub enum MyError {
    #[error("Error parsing enum: `{0}`")]
    EnumParseError(String),
}

/// Specifies which region should be captured.
#[derive(Debug, Clone, Clap)]
pub enum CaptureRegion {
    /// The entire history.
    ///
    /// This will end up sending `-S - -E -` to `tmux capture-pane`.
    EntireHistory,
    /// The visible area.
    VisibleArea,
}

impl FromStr for CaptureRegion {
    type Err = MyError;

    fn from_str(s: &str) -> Result<Self, MyError> {
        match s {
            "entire-history" => Ok(CaptureRegion::EntireHistory),
            "visible-area" => Ok(CaptureRegion::VisibleArea),
            _ => Err(MyError::EnumParseError(format!(
                "entire-history or visible-area, got {}",
                s
            ))),
        }
    }
}

/// Main configuration, parsed from command line.
#[derive(Clap, Debug)]
#[clap(author, about, version)]
pub struct Config {
    /// Specifies which region of the terminal buffer to capture.
    #[clap(arg_enum, default_value = "visible-area")]
    pub capture_region: CaptureRegion,
}

fn main() {
    let _ = Config::parse();
}

A few notes:

• use of arg_enum without directly using clap::ArgEnum
• this compiles and runs in beta.2
• on lines 15-16 above, the long_about is accepted but will be refused in beta.5.

I much prefer beta.5 way of doing things.

use of arg_enum without directly using clap::ArgEnum

derive(Clap) is what allowed this. This predecessor to Parser was a magic "derive any clap related trait possible", including ArgEnum but we moved away from that in the later betas.

on lines 15-16 above, the long_about is accepted but will be refused in beta.5.

Mind creating an Issue for this?

but the provided from_str conflicts with my existing FromStr impl

I upgraded the code to beta5 and did not see any conflicts.

Thanks Ed for the explanation! It confirms my previous vague understanding of it.

I'll now open an issue for long_about.

I upgraded the code to beta5 and did not see any conflicts.

Sounds surprising to me, as I spent some time adapting to beta.5, but granted I'm not very experienced with Rust. Nevermind.

Best