Suggestion: flags share aliases

[InCogNiTo124]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Clap Version

3.2.17

Describe your use case

My use case is reproducing something along of this feature:

• -H
  • Same as ‘--header-in --header-out’. A short option indicating the input file has a header line, and the output should contain a header line as well.

So basically, an boolean flag which enables two other flags. Currently, clap does not permit this:

'short option names must be unique, but '-H' is in use by both 'headers-in' and 'headers-out''

Describe the solution you'd like

Ideally, the code should be allowed to look like this:

Command::new()
.arg(
    Arg::new("headers-in")
        .long("headers-in")
        .short_visible_alias('H')
        .action(ArgAction::SetTrue))
.arg(
    Arg::new("headers-out")
        .long("headers-out")
        .short_visible_alias('H')
        .action(ArgAction::SetTrue))

and the invocation would then look something like:

$ my_program -H x.txt
Headers in detected!
Headers out detected!

Alternatives, if applicable

Right now, the alternative is to have a complicated condition in if:

Code right now:

if *matches.get_one::<bool>("headers-in").unwrap_or(&false) || *matches.get_one::<bool>("headers").unwrap_or(&false) {
.... something ...
}

Ideally, this should look like

if *matches.get_one::<bool>("headers-in").unwrap_or(&false) {
.... something ...
}

Additional Context

I'm struggling with the source code a bit, however I imagine a hashmap of aliases to an iterable of args. The value of the alias would be the value which is given to the original arguments.

[epage]

We have the unstable feature Command::replace that is meant to help with cases like this. The tracking issue is #2836. No one has stepped up to see it completed though.

Another option is to use default_value_if. It would look something like

Command::new()
.arg(
    Arg::new("all-headers")
        .short('H')
        .action(ArgAction::SetTrue))
.arg(
    Arg::new("headers-in")
        .long("headers-in")
        .default_value_if("all-headers", Some("true"), Some("true"))
        .action(ArgAction::SetTrue))
.arg(
    Arg::new("headers-out")
        .long("headers-out")
        .short_visible_alias('H')
        .default_value_if("all-headers", Some("true"), Some("true"))
        .action(ArgAction::SetTrue))

[InCogNiTo124]

The second suggestion seems better than what I've come up with so I'll use this from now on