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

From: Tomasz Hołubowicz <[email-masked]>
Date: Tue, 19 Nov 2024 17:56:46 +0100

Hello,

On Tue, Nov 19 2024, Eshel Yaron wrote:

> Side note: it is better to use (completion-preview-active-mode -1)
> instead of (completion-preview-hide) to dismiss the preview, since
> disabling the minor mode performs additional cleanup.  Perhaps I should
> mention that in the documentation somewhere... :)
>
Thank you for that tip!

> Thank you for this report.  I can reproduce the extended delay here.
> (In the future, please provide a minimal recipe to reproduce the issue
> starting from emacs -Q, if possible.)

Apologies for a bit noisy report, I wrote it in a bit of a rush.

If anyone would like to reproduce this issue, I believe below recipe
should be helpful:

(require 'flyspell)
(add-hook 'org-mode-hook #'flyspell-mode)

(require 'completion-preview)
(setopt completion-preview-idle-delay 0.2)
(push 'org-self-insert-command completion-preview-commands)

(global-completion-preview-mode 1)

After that open an Org file and try to trigger completion-preview by
writing a part of a word. Completion results most likely depend on the
contents of file pointed by ispell-alternate-dictionary value. If that
file is empty there might be no completions available.

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

Thank you for help and explanation. I will try flyspell-delay 0 for a
time (or stick with completion-preview-mode only for prog-mode buffers
at it seems more appropriate).

Kind wishes,
Tomasz Hołubowicz