How do I create short option -1?

[vi]

It says error: invalid flags syntax, long option is required for '-' if I try to do

   let flags = xflags::parse_or_exit! {
        /// Serve only one upload
        optional -1,--once
    };

[matklad]

I am inclined to explicitly not support this:

• this complicates macro parsing, as 1 is not an ident
• fuchsia guidelines, which we mostly follow, explictly tells

Do not create numeric options, such as -1 or -2. E.g. rather than having -1 mean to do something once, add a --once option. If a numeric value is needed, make a keyed option, like --repeat .

We should provide a nicer error message here though!