bug#32874: Unwanted scrolling in edebug `f' command when follow-mode is active

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 29 Sep 2018 15:37:29 +0000
> Cc: 32874@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> > That's not true: pre-redisplay-function is called _before_ the display
> > engine determines what window(s) might need to be redrawn.
> 
> Thanks!  I'll have a look at pre-redisplay-function, and see if I can do
> anything with it.

I'd actually urge you to have a good look at window-scroll-functions
as well.  (Follow mode already uses it, but I think it could use it
for quite a lot more.)  This hook is called when Emacs concludes that
a window may need to be scrolled to bring point into view.  This is
exactly where Follow mode wants to be able to affect the decision of
the display engine, right?  I think by making a few simple
changes/extensions where this hook is called, we could make the work
of Follow mode quite a lot easier, by letting it rely on the display
engine instead of trying to maneuver the display engine to do what it
wants.