bug#22338: 25.0.50; deactivate-mark regression

[Eli Zaretskii <eliz@gnu.org>]

> From: Leo Liu <sdl.web@gmail.com>
> Date: Thu, 18 Feb 2016 18:14:42 +0800
> 
> On 2016-02-16 15:27 +0800, Leo Liu wrote:
> > The bug is still there however I can only reproduce this with a local
> > setup involving Erlang + wrangler + emacs (24.5, 25.0.91).
> 
> I have found a recipe to partially reproduce the bug.
> 
> 1. start emacs -Q
> 2. define a command
> 
>    (defun test ()
>      (interactive)
>      (shell-command (format "echo 'test' >> %s" buffer-file-name))
>      (revert-buffer nil t t))
> 
> 3. Open a file, mark an active region and M-x test
> 
> You should observe the mark stay active. The active region goes off
> after 2 seconds. In emacs 24.5 the mark will go off immediately. With my
> local setup the active region stays on. Thus I am calling this recipe
> ``partial''.
> 
> I wonder if it helps understand the issue.

Not really.  In "emacs -Q", the region is deactivated by the command
loop, when it notices that the variable deactivate-mark is non-nil.
It is non-nil because the buffer was modified.  So this sounds like
Emacs working as designed to me.  In Emacs 24.5, the region is
deactivated by the same code for the same reason.  I don't know why in
24.5 this happens immediately, whereas in 25.0 it takes an extra
second (my guess is this is related to redisplay, and perhaps also to
the changed implementation of displaying the region).