bug#17453: Isearch doesn't work properly with Follow Mode.

[Eli Zaretskii]

PLEASE let's keep emacs-devel out of this??

> Date: Tue, 3 Nov 2015 12:31:16 +0000
> From: Alan Mackenzie <acm@muc.de>
> Cc: 17453@debbugs.gnu.org, Artur Malabarba <bruce.connor.am@gmail.com>,
>       emacs-devel <emacs-devel@gnu.org>
> 
> This is complicated.  Ideally, the Follow Mode windows should be
> synchronised in FM's post-command-hook, not isearch's.  It is not
> isearch's job to realign windows.  follow-post-command-hook both realigns
> windows and choses an appropriate window to put point in.  We should let
> it.

Once again, if some code in Isearch calls the same function that is
used in follow-post-command-hook, the above is not an issue.
Moreover, saving some calls to the hook will make Emacs more
responsive.  (Right now, using Follow mode is a pain due to the hook:
even a simple C-f is annoyingly slow.)

> What I'm proposing is to schedule the timer always, and do the checks
> (for whether we need to start a new lazy highlight loop) in the function
> that the timer triggers.  The advantage is that when the timer triggers,
> redisplay will already have taken place[*]

I don't think you can count on that: if there's a ripe timer, it will
be processed before redisplay.  I think.