bug#11697: 24.1.50; ERC scroll-to-bottom functionality 'broken' in emacs 24.1.x

[Antoine Levitt]

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
>> buffer.
>>
>> 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
>> again.
>>
>> 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 the documentation is also out of date.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
>> `post-command-hook'.
>>
>> Examining commits, I found the culprit:
>>
>> commit:
>> a1d63e03c3eda51dcec158d6027adf9dbdcfd8dd
>>
>> view changes via git emacs web:
>> http://git.savannah.gnu.org/cgit/emacs.git/commit/lisp/erc/erc-goodies.el?id=a1d63e03c3eda51dcec158d6027adf9dbdcfd8dd
>>
>>
>> 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:
>> (erc-scrolltobottom-mode)
>> (setq erc-input-line-position -2)
>>
>> Regards,
>> Brian
>>
>
> 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".

Hi,

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.