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

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Date: Mon, 02 Dec 2019 12:06:55 +0100
> 
> 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.
> 
> Git bisect pinpoints the following change:
> 
> aa89c84e00d8dc85100e6fedab7631c415e6364d is the first bad commit
> commit aa89c84e00d8dc85100e6fedab7631c415e6364d
> Author: Juri Linkov <juri@linkov.net>
> Date:   Wed Nov 27 01:43:49 2019 +0200
> 
>     message uses minibuffer-message in the active minibuffer (bug#17272 
> bug#19064)
> 
>     * doc/lispref/display.texi (Displaying Messages): Explain the
>     behavior of using minibuffer-message if the minibuffer is active.
> 
>     * src/editfns.c (Fmessage_in_echo_area): New function with body
>     copied from Fmessage.
>     (Fmessage): Call minibuffer-message in the active minibuffer,
>     otherwise call Fmessage_in_echo_area.
>     (message-in-echo-area): New variable.
> 
>     * lisp/isearch.el (isearch--momentary-message, isearch-message):
>     * lisp/minibuffer.el (minibuffer-message, minibuffer-completion-help):
>     Use 'message-in-echo-area' instead of 'message' where necessary.
> 
>     * lisp/autorevert.el (auto-revert-handler):
>     * lisp/man.el (Man-bgproc-sentinel):
>     * lisp/subr.el (do-after-load-evaluation):
>     Revert recent changes that replaced 'message' with 'minibuffer-message'.
>     This is not needed anymore since 'message' uses 'minibuffer-message'
>     in the active minibuffer.

I guess the new message-in-echo-area confuses dabbrev.el because it
switches buffers, and dabbrev.el has special logic for that, which
triggers the message, and the subsequent wait.