bug#29664: 26.0.90; Auto Hscroll Mode + Visual Line Mode + Truncate don't work well together

[Eli Zaretskii]

> Date: Fri, 03 Sep 2021 10:23:40 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 29664@debbugs.gnu.org, kaushal.modi@gmail.com
> 
> > From: Lars Ingebrigtsen <larsi@gnus.org>
> > Cc: kaushal.modi@gmail.com,  29664@debbugs.gnu.org
> > Date: Fri, 03 Sep 2021 09:12:59 +0200
> > 
> > Eli Zaretskii <eliz@gnu.org> writes:
> > 
> > > But if the user turns on truncate-lines by changing the variable
> > > manually, visual-line-mode will still stay turned on, right?  Isn't
> > > that a problem?
> > >
> > > Also, what about truncate-partial-width-windows?
> > 
> > It is a problem, but I don't know what to do about that except saying
> > "don't do that".
> 
> So maybe some change in the docs is in order?

Alternatively, we could use add-variable-watcher to disable
visual-line-mode when one of these variables is set, similarly with
what we do to force redisplay of a buffer when some variables are
modified (see the end of frame.el).