bug#38457: 27.0.50; dabbrev-expand regression due to message change

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Date: Tue, 03 Dec 2019 01:00:40 +0200
> Cc: 38457@debbugs.gnu.org
> 
> > 0. emacs -Q
> > 1. M-! te M-/
> >
> > => It takes about 4 seconds on my machine for the expansion "text" to
> > appear, during which the minibuffer displays "[Scanning for
> > dabbrevs...100%]" and then "[Scanning for dabbrevs...done]".  On builds
> > without this regression, the expansion is virtually instantaneous and no
> > message is seen in the minibuffer.
> 
> This is because of the current limitation of minibuffer-message.
> It uses sit-for to wait for 2 seconds per every message.
> This should be fixed by using the timer, so there will be no delays
> anymore:

Please don't make this change, or any other changes in this stuff that
significantly modify the internals of these basic APIs.  I'm that
close to ask to revert the entire message-in-echo-area change, because
it's already too invasive and runs a high risk of disrupting too many
commands.  We don't want the pretest of Emacs 27.1 to last forever for
these reasons.

So please try to find a simpler fix for this problem, one that doesn't
involve a timer.  If it isn't possible, let's indeed consider removing
the message-in-echo-area changes for now.

Sorry for that, but we should keep in mind that Emacs 27.1 pretest is
coming soon, and any deep changes in low-level infrastructure used all
over the place should wait for the next release.

Thanks.