bug#22338: 25.0.50; deactivate-mark regression

[Eli Zaretskii <eliz@gnu.org>]

> From: Leo Liu <sdl.web@gmail.com>
> Date: Sat, 09 Jan 2016 23:39:37 +0800
> 
> 1. Emacs -q
> 2. Open a file and mark an active region
> 3. (revert-buffer nil t t)
> 
> The mark is still active after the buffer revert. This isn't the case
> for emacs 24.5.

When I try this with different files and different changes actually
made to the file behind Emacs's back, I see the region deactivate
every time I revert and the file on disk was really changed.  Maybe it
doesn't always deactivate the region, but it certainly doesn't always
keep it active, except when the file on disk didn't change at all.

Do you really see the region remain active every revert, no matter
what the changes to the file on disk?  Can you show a detailed recipe
for that?

Anyway, since the documentation never says what will happen with the
region, I tend to consider this behavior unspecified: why should Lisp
programs expect anything specific to happen to the region during a
revert?

> The trouble is if the file has changed on disk (e.g. by another process
> such as vim), the mark is still active after the revert.

Why is that trouble?

Thanks.