bug#7033: 23.2; M-n in diff mode causes unwanted face changes

[Martin Jambor <mjambor@suse.cz>]

When I open almost any patch in the diff mode and press M-n to get to
the next hunk, random portions of the text (just parts of a line) change
their face from diff-added or diff-removed to diff-refine change.  This
causes the text to be displayed in a wrong background, causing it to be
rather difficult to read (and is always unpleasant).  I have not
observed any pattern as to what text is changed but it is always exactly
the same text in the given file.

This does not happen with emacs 22, only with 23, I have observeed it on
Suse and Debian linux distributions.  I can reproduce the bug when I run
emacs with the -Q switch like e.g.

emacs -Q patch.diff

Where patch.diff is downloaded from
http://gcc.gnu.org/cgi-bin/get-raw-msg?listname=gcc-patches&date=2010-09&msgid=20100914130012.GB27066%40virgil.arch.suse.de
(but it happens regularly with almost any patch) and then press M-n once.

BTW, pressing M-p to get to the previous hunk has the same effect.

Thanks for looking into this,

Martin



In GNU Emacs 23.2.1 (i486-pc-linux-gnu, GTK+ Version 2.20.0)
 of 2010-08-14 on raven, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
configured using `configure  '--build' 'i486-linux-gnu' '--build' 'i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var/lib' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.2/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.2/leim' '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 'build_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: en_US.UTF-8
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: en_US.UTF-8
  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: Diff

Minor modes in effect:
  diff-auto-refine-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
M-n M-n <down> <down> <down> <down> <right> <right> 
<right> <right> <right> <right> <right> <right> <right> 
<right> <right> <right> <right> <right> <right> <right> 
<right> <right> <right> <right> <right> <right> <right> 
<right> <right> <right> <right> <right> <right> <right> 
<right> <down> <down> M-x e m a <tab> r e p o <tab> 
r <backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> r e p o r t SPC e m a <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Loading vc-git...done

Load-path shadows:
/usr/share/emacs/23.2/site-lisp/debian-startup hides /usr/share/emacs/site-lisp/debian-startup
/usr/share/emacs/23.2/site-lisp/crypt++ hides /usr/share/emacs/site-lisp/crypt++
/usr/share/emacs/23.2/site-lisp/dictionaries-common/flyspell hides /usr/share/emacs/23.2/lisp/textmodes/flyspell
/usr/share/emacs/23.2/site-lisp/dictionaries-common/ispell hides /usr/share/emacs/23.2/lisp/textmodes/ispell
/usr/share/emacs/23.2/site-lisp/latex-cjk-thai/thai-word hides /usr/share/emacs/23.2/lisp/language/thai-word

Features:
(shadow sort mail-extr message sendmail regexp-opt ecomplete rfc822 mml
mml-sec password-cache mm-decode mm-bodies mm-encode mailcap mail-parse
rfc2231 rfc2047 rfc2045 qp ietf-drums mailabbrev nnheader gnus-util
netrc time-date mm-util mail-prsvr gmm-utils wid-edit mailheader canlock
sha1 hex-util hashcash mail-utils emacsbug smerge-mode vc-git diff-mode
easymenu easy-mmode tooltip ediff-hook vc-hooks lisp-float-type mwheel
x-win x-dnd font-setting tool-bar dnd fontset image fringe lisp-mode
register page menu-bar rfn-eshadow timer select scroll-bar mldrag mouse
jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
loaddefs button minibuffer faces cus-face files text-properties overlay
md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process dbusbind
system-font-setting font-render-setting gtk x-toolkit x multi-tty emacs)