Re: recenter and visual-line-mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Milan Stanojević <milanst@gmail.com>
> Date: Wed, 8 Apr 2015 15:59:16 -0400
> Cc: help-gnu-emacs@gnu.org
> 
> Here is the elisp code illustrating the issue.

Thanks.

For the future, please try to produce test cases that leave the
offending contents on display, instead of doing everything in a
temporary buffer that is killed when the code completes.  That's
because one cannot debug display problems without having the stuff
displayed.

> This shows that running (recenter 0) at different points of the same
> screen line leads to different behavior and it seems that the
> difference comes from where the point would be without
> visual-line-mode. I think in all cases the point should be at the top
> of the line, but that is not the case for ABCD.

What was missing from your original report was that the first visual
line must be _shorter_ than what the window can display on a single
screen line.  IOW, there should be a whitespace character on which
visual-line-mode can break the line _before_ the last (rightmost)
column in the window.  If that whitespace character is exactly at the
last column, the problem doesn't happen (which is what I tried here,
and thus didn't see the problem).

And yes, it's a (very old) bug.  Shouldn't be hard to fix, I think.

Thanks.