Currently we expand unmatched fragments by not replacing them at all,
leaving us with `$ident`. This trips up the parser or subsequent macro
calls. Instead it makes more sense to replace these with some reasonable
default depending on the fragment kind which should make more recursive
macro calls work better for completions.
We generally avoid "syntax only" helper wrappers, which don't do much:
they make code easier to write, but harder to read. They also make
investigations harder, as "find_usages" needs to be invoked both for the
wrapped and unwrapped APIs
