The array returned by the completion function follows a special
convention. If the first element is set, it is used as the
completion. Otherwise, the remaining entries are the possible
completions.
_meta_abstract_complete() just returned an array of matching words and
so the first element was always used as completion. Instead, we must
use rl_completion_matches() to generate the array passing a generator
function.
https://bugzilla.redhat.com/show_bug.cgi?id=1588952
1669377110