Short flag with optional value but no space?

[brian-pane]

Is there a clean way to implement this argument pattern?

-x[ARG]

I.e., the -x short flag takes zero or one arguments, with no equals, and (this is the part that's eluded me so far) no space allowed before the argument. Thus

-xFOO

is the -x flag with an argument value of FOO, whereas

-x FOO

is the -x flag with no argument, followed by a positional parameter with value FOO.

(The use case is: building a drop-in replacement for an existing program that uses this very specific argument pattern.)

I can almost do this with

Arg::new("x")
    .short('x')
    .num_args(0..=1)
    .require_equals(false)
    .value_parser(clap::value_parser!(String))

but that doesn't properly parse the -x FOO case.

[epage]

That is not currently support. There is some discussion for this at #3030 but it has been a while since I caught up on it.