GNU bug report logs - #18545
24.4.50: Bug - forward-line inside with-selected-window

Previous Next

Full log

View this message in rfc822 format

From: Eli Zaretskii <eliz <at> gnu.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: lompik <at> voila.fr, 18545 <at> debbugs.gnu.org
Subject: bug#18545: 24.4.50: Bug - forward-line inside with-selected-window
Date: Fri, 26 Sep 2014 18:20:48 +0300

> From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> Cc: lompik <at> voila.fr,  18545 <at> debbugs.gnu.org
> Date: Fri, 26 Sep 2014 10:13:45 -0400
> 
> >> Why does
> >> (with-selected-window (get-buffer-window "*Completions*")
> >> (recenter 5))
> >> require an explicit call to wset_redisplay from recenter, whereas
> >> (with-selected-window (get-buffer-window "*Completions*")
> >> (forward-line 1))
> >> doesn't need an explicit call to wset_redisplay (or bset_redisplay) from
> >> forward-line?
> > I think that's because forward-line moves point, while recenter
> > doesn't.
> 
> But I don't see why moving point would help: calling wset_redisplay
> should only change the fact that this window is considered for
> redisplay

There are redisplay optimizations that don't depend on whether we
consider a window for redisplay; see around line 13700 in xdisp.c from
emacs-24.  You will see a little ways below that place that we test
point against its recorded value in w->last_point, for example.

> so if it's needed for the recenter case, that means that
> without it, the window would not be considered at all

'with-selected-window makes' the offending window selected, and the
selected window is always considered for redisplay, right?

> which in turn should imply that in the forward-line case we wouldn't
> notice that point has changed, unless set_point_both ends up calling
> bset_redisplay somehow (but I fail to see how).

If you really want me to come up with a detailed explanation of why
the forward-line case doesn't need wset_redisplay, I can do that, but
it will require some digging.

My fixes where based on turning on trace-redisplay and observing
thereafter that, in the forward-line case the offending window was
shown in the trace, but always with an indication that the forced
window-start was OK, whereas in the recenter case the offending window
was not shown at all in the trace.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.