Using index_of()/indices_of() with optional arguments that take optional values

[epage]

Issue by cptpcrd
Saturday Mar 20, 2021 at 17:21 GMT
Originally opened as clap-rs/clap#2419

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Please complete the following tasks

• I have searched the discussions
• I have searched the existing issues

Describe your use case

I have multiple optional arguments with optional values. If several of them were specified without passing a value, I want to determine the indices of the arguments so I can find out which one was specified first. However, it seems that this is one of the few cases where Arg::index_of()/Arg::indices_of() doesn't work.

A simple example can be found below.

Describe the solution you'd like

Ideally, Arg::index_of() would work for arguments with optional values.

Alternatives, if applicable

Perhaps a new method, say Args::index_of_opt() (which would return the index of the flag like -a or --all`, instead of the value) could be added?

Additional Context

I'm using structopt, but I've translated this to clap code.

Example with clap 2.33:

fn main() {
    use clap::{Arg, App};
    
    let app = App::new("Basic Test")
        .arg(Arg::with_name("abc")
            .short("a")
            .long("abc")
            .takes_value(true)
            .multiple(false)
            .min_values(0)
            .max_values(1));

    // I can get the index in all of these cases (because clap returns the index of the value)

    let matches = app.clone().get_matches_from(&["", "-a1"]);
    println!("{:?}", matches.index_of("abc"));

    let matches = app.clone().get_matches_from(&["", "--abc=1"]);
    println!("{:?}", matches.index_of("abc"));

    let matches = app.clone().get_matches_from(&["", "-a", "1"]);
    println!("{:?}", matches.index_of("abc"));

    let matches = app.clone().get_matches_from(&["", "--abc", "1"]);
    println!("{:?}", matches.index_of("abc"));

    // But I can't get the index in these cases (which is when I really need it!)

    let matches = app.clone().get_matches_from(&["", "-a"]);
    println!("{:?}", matches.index_of("abc"));

    let matches = app.clone().get_matches_from(&["", "--abc"]);
    println!("{:?}", matches.index_of("abc"));
}

This produces the following output:

Some(2)
Some(2)
Some(2)
Some(2)
None
None

Updated for clap 3 (produces the same output as the above version when run against the latest master):

fn main() {
    use clap::{Arg, App};
    
    let app = App::new("Basic Test")
        .arg(Arg::new("abc")
            .short('a')
            .long("abc")
            .takes_value(true)
            .multiple(false)
            .min_values(0)
            .max_values(1));

    // I can get the index in all of these cases (because clap returns the index of the value)

    let matches = app.clone().get_matches_from(&["", "-a1"]);
    println!("{:?}", matches.index_of("abc"));

    let matches = app.clone().get_matches_from(&["", "--abc=1"]);
    println!("{:?}", matches.index_of("abc"));

    let matches = app.clone().get_matches_from(&["", "-a", "1"]);
    println!("{:?}", matches.index_of("abc"));

    let matches = app.clone().get_matches_from(&["", "--abc", "1"]);
    println!("{:?}", matches.index_of("abc"));

    // But I can't get the index in these cases (which is when I really need it!)

    let matches = app.clone().get_matches_from(&["", "-a"]);
    println!("{:?}", matches.index_of("abc"));

    let matches = app.clone().get_matches_from(&["", "--abc"]);
    println!("{:?}", matches.index_of("abc"));
}