bug#9246: Scrolling bug with word-wrap in emacs -nw

[Eli Zaretskii <eliz@gnu.org>]

> From: Antoine Levitt <antoine.levitt@gmail.com>
> Cc: riccardi.thomas@gmail.com,  9246@debbugs.gnu.org
> Date: Sat, 24 Dec 2011 16:29:56 +0100
> 
> > Can you copy-paste the exact text you type into the ERC window to
> > reproduce this bug, starting with the connection, and everything you
> > do afterwards?
> 
> Alright. So emacs -Q -nw (the -nw is important). M-x erc RET RET RET
> RET, connect to freenode, you get to the server window. Type
> 
> /join #somethingtest RET, you get to the channel window.
> 
> M-: (setq word-wrap t) RET
> M-x erc-scrolltobottom-enable RET
> 
> http://wowthisislongveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylong.com RET
> a RET
> a RET
> ... etc until end of buffer. Then point goes to top, and the scrolling
> doesn't work anymore.
> 
> I verified with latest trunk, I still see this.

Yes, I see it as well, but it's a bug in erc.  "(elisp)Window Hooks"
says:

 -- Variable: window-scroll-functions
     [...]
     *Warning:* don't use this feature to alter the way the window is
     scrolled.  It's not designed for that, and such use probably won't
     work.

But erc does precisely that which the manual says not to do.  It
shouldn't.

Incidentally, all this trickery is no longer needed with Emacs 24:
just setting scroll-conservatively to a value larger than 100 will do
the job nicely and without any problems.