bug#74437: 30.0.92; completion-preview-idle-delay is delayed by flyspell

[Eli Zaretskii <eliz@gnu.org>]

> Cc: mail@alternateved.com
> Date: Tue, 19 Nov 2024 17:13:16 +0100
> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> The root cause is a peculiarity of flyspell-mode: it calls sit-for and
> blocks Emacs for 3 whole seconds (by default, see flyspell-delay) after
> certain commands, including after (org-)self-insert-command.  This also
> blocks the idle timer that Completion Preview mode uses, unfortunately.
> 
> A quick search shows that this behavior of flyspell affects other
> features as well.  For example, IIUC, auto completion in Corfu switched
> to using run-at-time instead of run-with-idle-timer due to this issue.
> 
> I think flyspell should be modified to use a timer instead of sit-for,
> so as to avoid blocking idle timers.  I can come up with such a patch,
> but it's not quite trivial, so I wonder what others think about this
> issue and how it should be addressed.

This is likely to cause differences in behavior that some users will
be unhappy about (how do you support delaying only after some
commands? and how do you interact with async subprocess from an idle
timer?).  So if you want to install such a patch, it must be an opt-in
feature, so we could let users try it for some time before we decide
whether to retire the old behavior based on sit-for.

> As a stopgap, you can try setting flyspell-delay to 0.

That will make flyspell-mode get in the way of fast typing, AFAIU, but
maybe the OP doesn't care about that.