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

[Eli Zaretskii]

> Date: Sun, 23 Jul 2023 20:46:19 +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 14:18, Eli Zaretskii wrote:
> >> 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?
> 
> Some way to do that is certainly possible (e.g. a new option and 
> corresponding code, maybe; maybe not), it's just that the person 
> implementing it should consider the performance of the resulting solution.

I agree.  However, if we are going to implement filtering of file
names, I don't think it matters where in the pipeline to perform the
filtering.  The advantage of using completion-regexp-list is that the
matching is done in C, so is probably at least a tad faster.

> And, ideally, do all the relevant benchmarking when proposing the change.

Of course.  Although the benchmarks until now already show quite a
variability.