Emacs 24.3 previous-line on empty line moves pointer up two lines

[imfranklin]

With version 1.84 in Emacs 24.3 on Mac OS X 10.8.3 previous-line (via or C-p) on an empty line moves the pointer up twice (to the previous, previous line).

[alpaker]

Thanks for the report. This is a known issue, caused by a bug that was introduced into Emacs's redisplay engine shortly before the release of 24.3. The bug has been fixed in Emacs trunk, so fci-mode will work correctly with head-of-line Emacs, as well as with 24.2 and earlier versions; it's only the current release that's affected. Unfortunately, since the bug is in C code, not Lisp, it isn't possible to monkey patch it: a fix requires that you rebuild Emacs itself.

I'll update the package header with a mention of this issue. But the only fix I can offer is to upgrade to Emacs rev. 112274 or later or to apply the below patch to 24.3 and rebuild. Sorry.

=== modified file 'src/indent.c'
--- src/indent.c    2013-04-02 01:54:56 +0000
+++ src/indent.c    2013-04-13 08:54:02 +0000
@@ -2006,11 +2006,15 @@
      const char *s = SSDATA (it.string);
      const char *e = s + SBYTES (it.string);

+     disp_string_at_start_p =
      /* If it.area is anything but TEXT_AREA, we need not bother
         about the display string, as it doesn't affect cursor
         positioning.  */
-     disp_string_at_start_p =
-       it.string_from_display_prop_p && it.area == TEXT_AREA;
+       it.area == TEXT_AREA
+       && it.string_from_display_prop_p
+       /* A display string on anything but buffer text (e.g., on
+          an overlay string) doesn't affect cursor positioning.  */
+       && (it.sp > 0 && it.stack[it.sp - 1].method == GET_FROM_BUFFER);
      while (s < e)
        {
          if (*s++ == '\n')

[remvee]

Here's a workaround:

(defadvice previous-line (around avoid-jumpy-fci activate)
  (if (symbol-value 'fci-mode)
      (prog (fci-mode -1) ad-do-it (fci-mode 1))
    ad-do-it))

[joncol]

Good stuff remvee. Only complaint is that your fix caused some problems when standing on line 1. Small modification:

(make-variable-buffer-local 'line-move-visual)
(defadvice previous-line (around avoid-jumpy-fci activate)
  (if (and (symbol-value 'fci-mode) (> (count-lines 1 (point)) 0))
      (progn (fci-mode -1) ad-do-it (fci-mode 1))
    ad-do-it))

[djs52]

For anyone who needs this fix still (e.g., if you are on Ubuntu 14.04), "prog" should be "progn", so:

(make-variable-buffer-local 'line-move-visual)
(defadvice previous-line (around avoid-jumpy-fci activate)
  (if (and (symbol-value 'fci-mode) (> (count-lines 1 (point)) 0))
      (progn (fci-mode -1) ad-do-it (fci-mode 1))
    ad-do-it))

[qrilka]

Shouldn't this issue be removed from the README?