args_from_usage() has issues with non-ASCII identifiers

[tormol]

Non-ASCII help on its own is OK:
clap::App::new("").args_from_usage("<h> 'with ŭnicode'"); works

If the last character is non-ascii there are slice errors:
clap::App::new("").args_from_usage("<hæ> 'comment doesn't matter'");

If both name and help has non-ascii the program hangs:
clap::App::new("").args_from_usage("<øh> 'with ŭnicode'");

If only the name is non-ascii the argument is not detected:
clap::App::new("").args_from_usage("<øh> 'ASCII or empty'").get_matches().value_of("øh").unwrap()

The first three act the same with options, but this is different:
clap::App::new("").args_from_usage("--øh 'ASCII'").get_matches(); gives this error:

error: Found argument '--øh' which wasn't expected, or isn't valid in this context
    Did you mean --ø?

USAGE:
    clapbug --ø <ASCII'>

For more information try --help

Arg::with_name() has none of these issues.

[kbknapp]

Originally the from_usage parser was designed around ASCII only support (where as full Arg methods support any valid UTF-8). I agree this is something I need to add, and a feature I'd like to have. I'll add it to the issue tracker, but there a few other things I need to implement before this.

Thanks for taking the time to request and file this! 👍

[tormol]

This is a niche issue, and easy to work around.
Asserting that the identifiers are ascii to fail in a consistent way should be enough.

[nabijaczleweli]

Why'd you ever fail when it can actually work though?

[tormol]

If it was difficult to make it work. I did it anyway.