A require* method that expressing and(&&) condition when requesting an argument

[zzz845zz]

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• Searched the closed issues

Describe your use case

I think the function that requires some arguments only if multiple conditions are satisfied is helpful.

The example of required_ifs below is similar to or(||) expression, not and(&&) (from here).

• In this example, cfg is required when --extra=val or --option=spec
• I want a way to require cfg when --extra=val and --option=spec

let res = App::new("prog")
    .arg(Arg::with_name("cfg")
        .required_ifs(&[
            ("extra", "val"),
            ("option", "spec")
        ])
        .takes_value(true)
        .long("config"))
    .arg(Arg::with_name("extra")
        .takes_value(true)
        .long("extra"))
    .arg(Arg::with_name("option")
        .takes_value(true)
        .long("option"))
    .get_matches_from_safe(vec![
        "prog", "--option", "other"
    ]);

assert!(res.is_ok()); // We didn't use --option=spec, or --extra=val so "cfg" isn't required

For more simply, the case above likes

if (extra=="val" || option=="spec") {
    // use cfg!!
}

But what i want is the example below

if (extra=="val" && option=="spec") {
    // use cfg!!
} 

Additional context

Related to #2323

[pksunkara]

The name should be require_if_eq_all