bug#63253: 29.0.90; with-delayed-message fails in combination with inhibit-message

[Eli Zaretskii]

> Cc: 63253@debbugs.gnu.org
> Date: Mon, 08 May 2023 09:54:35 -0400
> From:  Stefan Monnier via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> > There seems to exist an interaction issue of `with-delayed-message' with
> > `inhibit-message'.
> 
> Very much so, indeed.  The issue is fundamentally linked to
> `set-message-function`:
> 
> `with-delayed-message` calls `message3` (via
> `with_delayed_message_display`) from an "atimer", i.e. a thing that can
> be run from `process_pending_signals`, `unblock_input`, `maybe_quit`, ...
> 
> AFAIK these are places where it's safe to run some C code, but not
> places where it's safe to run arbitrary ELisp code.
> 
> So `set-message-function` is "dangerous" because it runs ELisp code from
> `message3` => `message3_nolog` => `set_message`.

So I guess we need to have run_timers bind some variable, and then in
set_message, if that variable is non-nil, we should avoid calling
functions from set-message-function?