23.0.50; (pos-visible-in-window-p) returns error with 'before-string overlay

23.0.50; (pos-visible-in-window-p) returns error with 'before-string overlay

[Yoshiaki Kasahara]

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the emacs-pretest-bug@gnu.org mailing list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

When there is an overlay with 'before-string property at the beginning
of a line in a buffer, the point in the buffer is on the overlay, and
both the overlay and the point are placed at the bottom of the window,
(pos-visible-in-window-p) returns 'Args out of range: 0'.

To reproduce, insert some blank lines to *scratch* buffer, and eval
the following:

(overlay-put (make-overlay (point-max) (point-max)) 'before-string "[before-string]")

Then place the overlay and the point at the bottom of the window like
this, and eval (pos-visible-in-window-p):

--------------

[before-string]<- point is here
-EEJ:**--....  <- modeline
Eval: (pos-visible-in-window-p)
--------------

Currently I'm using emacs before-merge-unicode-to-trunk.  I reproduced
the same symptom in CVS HEAD (23.0.60) of today.  It doesn't happen in
emacs-21.3 (it returns t).

In some cases the emacs process starts to consume 100% CPU and doesn't
respond to keyboard-quit after the error.  I have to kill the process.
But I cannot reliably reproduce the lock-up.  Nexttime I'll try to
attach GDB to get a backtrace.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
If you would like to further debug the crash, please read the file
/usr/local/share/emacs/23.0.50/etc/DEBUG for instructions.


In GNU Emacs 23.0.50.2 (x86_64-unknown-freebsd7.0, X toolkit, Xaw3d scroll bars)
 of 2008-03-04 on elvenbow.cc.kyushu-u.ac.jp
configured using `configure  '--with-x-toolkit=lucid' '--without-xim' '--without-gtk''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: ja_JP.eucJP
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: C
  value of $LANG: ja_JP.eucJP
  locale-coding-system: japanese-iso-8bit
  default-enable-multibyte-characters: t

Major mode: Apropos

Minor modes in effect:
  show-paren-mode: t
  iswitchb-mode: t
  icomplete-mode: t
  display-time-mode: t
  shell-dirtrack-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t