Allowing argument -x, -x123, but not '-x 123'

[GunterSchmidt]

I am trying to set up a very odd parsing requirement (mimic GNU diffutils, so no workaround):

Requirement:
-x: defaults to 5
-x123: value 123
-x 123: default to 5 (must not use argument after -x, which is required for something else)
-x=123: either 123 or error, I do not care

    let m = Command::new("prog")
        .arg(
            Arg::new("my_x")
                .short('x')
                .num_args(0..=1)
                // .require_equals(true)
                .default_missing_value("5")
                .action(ArgAction::Set),
        )
        .arg(Arg::new("my_texts").action(ArgAction::Append))
        // These two lines must have identical outcome
        // .get_matches_from(vec!["prog", "-x5", "some_text", "some_more_text"]);
        .get_matches_from(vec!["prog", "-x", "some_text", "some_more_text"]);

I seem to be in a catch 22 here:

• if I set .require_equals(true)
  I can do '-x', but not '-x5'.

• if I set .require_equals(false)
  I can do '-x5', but not '-x', as it will use the next argument as value.

Is there any way to configure my requirement?

[epage]

The author also opened #6312 which was closed in favor of #3030.