bug#1742: 23.0.60; ediff-skip-merge-regions-that-differ-from-default breaks simple ediffs

[David Abrahams]

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:

0. Extract the enclosed files to /tmp

1. Evaluate:

  (custom-set-variables
   '(ediff-skip-merge-regions-that-differ-from-default t)
  )
  (ediff "/tmp/x" "/tmp/y")
  
2. Hit the spacebar

Result: "You have killed a vital Ediff buffer---you must leave Ediff
now!"

This happens even with "emacs -q"

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/23.0.60/etc/DEBUG for instructions.


In GNU Emacs 23.0.60.1 (i686-pc-linux-gnu, GTK+ Version 2.14.4)
 of 2008-12-12 on mcbain
Windowing system distributor `The X.Org Foundation', version 11.0.10502000
configured using `configure  '--with-x-toolkit=gtk' '--prefix=/usr/local''

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: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Custom

Minor modes in effect:
  diff-auto-refine-mode: t
  show-paren-mode: t
  global-auto-revert-mode: t
  delete-selection-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n 
C-n C-n C-n C-n C-n C-n C-p R x <return> C-p C-p C-p 
C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p C-p 
C-p C-p R y <return> M-x e d i f f <return> x <return> 
y <return> SPC q y y y M-x e d i f f - b u f <tab> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <tab> u <tab> C-g C-g C-x b e d i <tab> 
<return> M-< C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n 
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-x 
C-f e d <tab> i <tab> . <tab> <return> C-s b u f <backspace> 
g C-s C-s C-p C-p C-p C-p C-n C-n C-n C-n C-n C-p C-p 
C-p C-p C-. C-. C-. C-. C-. C-. C-. C-n C-n C-n C-n 
C-n C-n C-n C-n C-x C-k C-x C-k <help-echo> <down-mouse-1> 
<mouse-1> C-x C-p <return> M-> M-< C-x C-k <down-mouse-1> 
<mouse-1> M-x c u s t o m <tab> - a p <tab> <return> 
e d i f f <return> C-n C-n C-n C-n C-n C-n C-n C-n 
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-s m e r g e SPC 
p r e M-< C-s p r e f i x C-n C-p C-n C-a C-. C-b C-s 
s k i p C-e C-, C-, C-, C-, <return> C-n C-, C-, C-a 
C-, C-a C-n C-f C-f C-f C-f C-f C-f C-f <return> 0 
M-x M-p M-p <return> x <return> y <return> SPC SPC 
SPC p p p q y y y C-p C-e C-, C-, C-, M-x r e p o r 
t - e m a <tab> b u <tab> <return>

Recent messages:
Computing differences between x and y ...
Buffer A: Processing difference region 0 of 2
Buffer B: Processing difference region 0 of 2
Processing difference regions ... done
Region 1 in buffer A is empty [2 times]
Region 2 in buffer A is empty [4 times]
Region 1 in buffer A is empty [2 times]
Quit this Ediff session? (y or n) 
Kill buffer A [x]? (y or n) 
Kill buffer B [y]? (y or n)

x
Description: Text document

y
Description: Text document

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com