Proposal: Allow to create an argument that are required only for certain patterns.

[puripuri2100]

I propose to add a function fn required_paterns(self, patterns: &[&'a str]) -> Self.

This function imposes looser constraints than the required function.

test code:

let app = App::new("prog")
    .arg(Arg::with_name("cfg")
        .takes_value(true)
        .required_paterns(&["foo", "bar"])
        .long("cfg"))
    .arg(Arg::with_name("foo")
        .takes_value(true)
        .long("foo"))
    .arg(Arg::with_name("bar")
        .long("bar"))
    .arg(Arg::with_name("baz")
        .long("baz"));

assert!(app.get_matches_from_safe(vec!["prog", "--foo", "foo", "--cfg", "cfg"]).is_ok());
assert!(app.get_matches_from_safe(vec!["prog", "--foo", "foo", "--bar", "--cfg", "cfg"]).is_ok());
assert!(app.get_matches_from_safe(vec!["prog", "--foo", "foo"]).is_err());
assert!(app.get_matches_from_safe(vec!["prog", "--bar"]).is_err());
assert!(app.get_matches_from_safe(vec!["prog", "--baz"]).is_ok());
assert!(app.get_matches_from_safe(vec!["prog", "--baz", "--cfg", "cfg"]).is_ok());

I plan the following uses:

• By default, I want to execute based on the value.
• But, no value is needed when the --list flag is specified.

let app = App::new("prog")
    .arg(Arg::with_name("cfg")
        .takes_value(true)
        .required_paterns(&["key"]))
    .arg(Arg::with_name("key")
       .takes_value(true)
        .long("key"))
    .arg(Arg::with_name("list")
        .long("list"));

$ prog cfg
$ prog --key value cfg
$
$ prog --list

[pksunkara]

I still have no idea what exactly you are asking for.

[pksunkara]

@puripuri2100 Can you please elaborate?

[puripuri2100]

I want to create an argument that becomes an "essential argument" only when a pre-specified argument is given.

[ldm0]

Please check this: https://docs.rs/clap/3.0.0-beta.2/clap/struct.Arg.html#method.requires_if
and this: https://docs.rs/clap/3.0.0-beta.2/clap/struct.Arg.html#method.required_unless_present

[puripuri2100]

thanks!