Function check_aliases 

fn check_aliases(
    choices: &[String],
    aliases: &[(LitStr, usize, bool)],
) -> Result<()>

Refuse the aliases #[match_arg(alias = "...")] can’t have, all at once (one error per bad alias, spanned on its literal): an alias that is empty (pmatch() matches "" to nothing, while the R check’s match() would map it), "NA" (it would read as a missing value), a choice, given twice (on any variant), or a prefix of another variant’s choice, since the alias would change what typing it selects. A prefix of its own choice only is harmless. The wrappers writer applies the same rules to a hand-written MatchArg::ALIASES (miniextendr_api::registry::match_arg_aliases_arg).