Bug: ruler-mode breaks scroll-conservatively (HEAD)

[Karl Chen <quarl@hkn.eecs.berkeley.edu>]

This bug exists in Emacs HEAD 2002-12-14. Emacs 21.2 with ruler-mode.el from
HEAD has a similar problem.

Synopsis:

     emacs-21-3.50 -q    # in X (the bug doesn't occur with -nw)

     C-x C-f file_with_more_lines_than_window_height.txt

     M-x set-variable scroll-conservatively 99999

     ;; Scrolling occurs one line at a time when the cursor moves past the
     ;; first or last lines in the window (expected/desired behavior)

     M-x ruler-mode

     ;; Moving point past to/past the last line of the window recenters it
     ;; rather than scrolling by one line (bug).

Actually if you try to even move to the last displayable line in the window
(e.g. <down>, clicking on the last line, resizing the window smaller), it
recenters. So actually, ruler-mode breaks being able to have point on the last
line of the window.  Moving point upward isn't affected. Setting scroll-step
to 1 has the same problem.

In Emacs 21.2 with ruler-mode.el from HEAD, the problem exists slightly
differently. Point can exist on the first and last lines in the window, but
scrolling behaves non-conservatively when you move past the top/bottom.

This may ahve to do with the fact that with ruler-mode on, the last line of
text has one or two pixels less than without it.

--
Karl Chen / quarl@quarl.org



In GNU Emacs 21.3.50.8 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-12-14 on quack.quarl.org
configured using `configure '--prefix=/usr/local/stow/emacs' 'CC=distcc''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: C
  locale-coding-system: nil
  default-enable-multibyte-characters: t