bug#15712: 24.3; Point forgets what column it was in when vertical movement causes horizontal scroll

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 25 Oct 2013 16:42:03 +1000
> From: Adam Nielsen <a.nielsen@shikadi.net>
> 
> Say you have a number of long lines, which are truncated because they
> are wider than Emacs can display.  There are blank lines in between
> them.  Like this: (the "..." should be expanded until the line is wider
> than the Emacs window)
> 
> long 1 longlonglong...2
> long 1 longlonglong...2
> 
> long 1 longlonglong...2
> long 1 longlonglong...2
> 
> If you place the point on the "1" and move down one line, the point will
> move to the "1" on the line below (i.e. it stays on the same column.)
> Moving down another line (to the blank line) the point changes column,
> but moving down a third time the point returns to the original column
> and is again on the "1".  This is normal and correct.
> 
> However if this process is repeated on the "2" instead, when the point
> is moved to the blank line Emacs will scroll horizontally to ensure the
> point remains visible.  This scrolling however, causes the point to
> forget what column it was on, so when moving down below the blank line,
> it does not return to the "2" and instead moves to the "l", as if the
> point had been commanded to return to the first column.
> 
> I believe this is a bug because the behaviour is not consistent, and
> changes depending on the width of the Emacs window - it only affects
> lines too long to display.

Fixed in trunk revision 114799.

Thanks.