Subject: bug#78737: sit-for behavior changes when byte-compiled

From: Pip Cet <[email-masked]>
Date: Tue, 10 Jun 2025 09:13:03 +0000

"Daniel Colascione" <[email-masked]> writes:

> Consider (while-no-input (sit-for 100)).
>
> Run it and press any key, say, f to terminate the wait. You'll see "f"
> inserted wherever point was.
>
> Now eval-defun on sit-for from subr.el and try (while-no-input (sit-for
> 100)) again. The "f" disappears.
>
> Why? Because Fread_event returns with Vquit_flag set; the byte-compiled
> sit-for is able to push the event onto Vunread_command_events before
> Lisp does something quit-able, but the interpreted sit-for doesn't get
> so far and loses Fread_event's return value.
>
> Fread_event should probably look for Vquit_flag and !Vinhibit_quit and
> in this case stick the event on Vunread_command_events itself and
> return nil.

Until we fix sit-for by adding a mechanism to peek at rather than read
and dequeue input events, would it be sufficient just to bind
inhibit-quit while reading and unreading the event?  It appears to work,
at least.

Pip