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bug#11697: 24.1.50; ERC scroll-to-bottom functionality 'broken' in emacs

From: Deniz Dogan
Subject: bug#11697: 24.1.50; ERC scroll-to-bottom functionality 'broken' in emacs 24.1.x
Date: Thu, 14 Jun 2012 22:51:08 +0200
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120604 Thunderbird/13.0

On 2012-06-14 11:49,, Antoine Levitt wrote:
13/06/12 22:03, Deniz Dogan
On 2012-06-13 18:22,, Brian Fransioli wrote:

After updating to emacs 24.1.x I noticed ERC scroll functionality
changed.  Originally, it would recenter to force the prompt to be near
the bottom of the screen (according to `erc-input-line-position').  Now,
this recentering only happens when I enter text, or perform a mouse
event.  Channel joins/parts and new messages hit the bottom of the
screen, and recentering moves the bottom line to the center of the

The overall effect is input by the user moves the screen to the bottom,
while channel/server inputs bounce around from middle to bottom and back

Looking in erc-goodies.el at `erc-add-scroll-bottom', it's easy to see
the documentation is also out of date.  It states it uses
`window-scroll-functions' but instead adds the hook to

Examining commits, I found the culprit:


view changes via git emacs web:

I see that the changes were reported to fix a bug on tty's, but the
results are severe motion sickness for even moderately chatty channels.

Reproduce by:
(setq erc-input-line-position -2)


Firstly, I agree with you completely that scrolltobottom needs
improvements.  I can't be sure why they changed the behavior, since
the new method is clearly inferior, but I believe it's because
window-scroll-functions is never meant to change "the way the window
is scrolled".


I'm responsible for the mess. Sorry, I don't customize
erc-input-line-position, and it didn't occur to me that it might mess
things up. I tried to think of something better for erc-scrolltobottom,
but I'm not familiar with erc internals and that was the best I could
do. The reason for the change was that as you said,
window-scroll-functions is not intended to be used like that, and it
caused weird bugs.

I've monkey-patched ERC myself to handle the whole thing better.  I've
attached the Lisp.  Just evaluate all the code and you'll be all
set. (I know it's not production-quality code, but it does the job and
relieves you from ever thinking about it again.)

Great! Could you submit a proper patch, so that Someone (tm; there seems
to be a lack of maintainers for ERC) can review it and merge it into
trunk? erc-scrolltobottom has been broken for years, with weird bugs and
excessive CPU consumption, and it's high time it changed.

The excessive CPU consumption comes from the fact that it nowadays uses post-command-hook, which is executed just about all the time. :)

Unfortunately, my patch (ab)uses window-scroll-functions, so it's really no better than the way ERC was before.

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