bug#40774: Error messages shouldn't be hidden when the user is idle

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: larsi@gnus.org,  40774@debbugs.gnu.org,  ndame@protonmail.com
> Date: Sun, 12 Dec 2021 21:19:41 +0200
> 
> >> +** The return value of 'clear-message-function' is not ignored anymore.
> >> +If the function returns t, then the message is not cleared,
> >> +with the assumption that the function cleared it itself.
> >
> > I could perhaps agree to this if the special new behavior was the
> > result of a very special return value, and only that value.  Having
> > the new behavior kick in for t is out of the question for the release
> > branch, as it is highly likely to trip unsuspecting Lisp programs.
> 
> What a special value would you prefer?  Maybe, a symbol 'no'?

More like 'no-clear or even 'dont-clear-message, I think.

> > Btw, what does the change of the order between the call of
> > clear-message-function and setting echo_area_buffer[0] to nil mean,
> > compatibility-wise? won't it also produce different results, even if
> > the return value is nil?
> 
> When the return value is nil, it will still clear the echo area.

That wasn't what I asked.  I asked whether the change in the order
could matter.  Specifically, we now set echo_area_buffer[0] to nil
after we run clear-message-function, not before.  Can that affect
some customization of clear-message-function?

> > More generally, I fear that we are trying very hard to tweak a
> > particular infrastructure for a job for which it was hardly meant.
> 
> This is the most simple and thus reliable solution.
> 
> > IOW, shouldn't we provide some completely different optional feature
> > for this use case?  Like a special buffer that pops up or a special
> > frame?  Echo-area is not suited for showing large chunks of text, and
> > my gut feeling is that we will bump into problems on this path.  E.g.,
> > what happens when there are enough accumulated messages that they can
> > no longer be shown with the maximum allowed height of the mini-window?
> 
> This is exactly what functions bound to clear-message-function intended to do.

??? This function is about _clearing_ the echo-area, whereas I was
talking about the _display_ in the echo-area.  I'm saying that I'm not
sure echo-area display is suited for the jobs that this bug wants it
to do.  As an example, I asked what would happen when the echo-area
can no longer be resized to accommodate all the messages that were not
cleared.