required_if support for arg_enum!

[wcampbell0x2a]

It would be interesting to have required_if to work with the generated enum from arg_enum! instead of just allowing string input

[CreepySkeleton]

Mind give us an example of what it should look like so we can have an idea of what you mean?

[wcampbell0x2a]

Here would be an example:

use clap::{arg_enum, value_t, App, Arg};

arg_enum! {
    #[derive(Debug)]
    enum Foo {
        Bar,
        Baz,
        Qux
    }
}

fn main() {
    // Create the application like normal
    let enum_vals = ["fast", "slow"];
    let m = App::new("myapp")
        // Use a single positional argument that is required
        .arg(Arg::from_usage("<foo> 'The Foo to use'").possible_values(&Foo::variants()))
        // This would be my additional syntax
        .arg(Arg::with_name("nice").required_if("foo", Foo::Bar))
        .get_matches();

    let t = value_t!(m.value_of("foo"), Foo).unwrap();

    // Now we can use our enum like normal.
    match t {
        Foo::Bar => println!("Found a Bar"),
        Foo::Baz => println!("Found a Baz"),
        Foo::Qux => println!("Found a Qux"),
    }
}

[CreepySkeleton]

First of all, the old arg_enum macro is removed from clap 3.0 as it's being superseded with #[derive(ArgEnum)].

If we talk about the new derive, it's already supported via

use clap::{App, Arg, ArgEnum};

#[derive(Debug, ArgEnum)]
enum Foo {
        Bar,
        Baz,
        Qux
}

fn main() {
    let m = App::new("myapp")
        .arg(Arg::from"<foo> 'The Foo to use'").possible_values(&Foo::VARIANTS()))
        // You still have to use a string here, not a variant
        .arg(Arg::new("nice").required_if("foo", "bar"))
        .get_matches();
    // value_t! is removed in favor of value_of_t
    // which benefits from type inference
    let t = m.value_of_t("foo").unwrap();

    // Now we can use our enum like normal.
    match t {
        Foo::Bar => println!("Found a Bar"),
        Foo::Baz => println!("Found a Baz"),
        Foo::Qux => println!("Found a Qux"),
    }
}

[pksunkara]

But I think he was asking for something like required_if("foo", Foo::Bar) which will be covered by #1694. We have already done some base work in the code with ids and keys.

[wcampbell0x2a]

sweet