bug#64735: 29.0.92; find invocations are ~15x slower because of ignores

[Eli Zaretskii]

> Date: Sun, 23 Jul 2023 13:46:30 +0300
> Cc: luangruo@yahoo.com, sbaugh@janestreet.com, yantar92@posteo.net,
>  64735@debbugs.gnu.org
> From: Dmitry Gutov <dmitry@gutov.dev>
> 
> On 23/07/2023 08:11, Eli Zaretskii wrote:
> > Even better: compute completion-regexp-list so that IGNOREs are
> > filtered by file-name-all-completions in the first place.
> 
> We don't have lookahead in Emacs regexps, so I'm not sure it's possible 
> to construct regexp that says "don't match entries A, B and C".

Well, maybe just having a way of telling file-name-all-completions to
negate the sense of completion-regexp-list would be enough to make
that happen?