bug#64351: probabe bug associated with “completion-regexp-list”

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: one.last.kiss@outlook.com,  64351@debbugs.gnu.org
> Date: Sat, 01 Jul 2023 10:19:50 -0400
> 
> > Would you mind telling more about valid uses of this?
> > I'd like to improve the documentation.
> 
> Here's what I know: `completion-regexp-list` used to be virtually unused
> in Emacs's code base, so I don't know what was its intended use.
> 
> But when completion UIs started to offer other styles than just
> prefix-based completion, they also started to use
> `try/all/test-completion` more "internally" (i.e. for intermediate
> computations rather than to compute the final list of completions
> displayed to the user) and they did it without paying attention to
> `completion-regexp-list`, i.e. in ways which tended to just misbehave
> when `completion-regexp-list` wasn't nil.
> 
> So, in practice nowadays, the only reliable way to use
> `completion-regexp-list` is to think of it as an optional argument to
> `try/all/test-completion`, but one that has to be provided via a nearby
> let-binding rather than by listing it explicitly at the call site.

Thanks, I added something along these lines to the documentation.

> > You are saying that you don't like my proposed patch for the emacs-29
> > branch, and would even prefer to leave it unfixed?
> 
> Your patch is harmless, IMO, so it's OK to install it.

Installed on the emacs-29 branch, and closing the bug.