bug#8155: 23.2; erratic cursor movement with visual-line-mode and wrap-prefix property

[Nicolas Goaziou]

This bug report will be sent to the Free Software Foundation,
not to your local site managers!
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 bug-gnu-emacs@gnu.org mailing list,
and to the gnu.emacs.bug news group.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug.  If you can, give
a recipe starting from `emacs -Q':

>From `emacs -Q', C-x b whatever to open a new buffer. Then M-x
visual-line-mode. Now fill a bit more than a screenfull of text without
inserting a newline. Eventually use (put-text-property 1 (point-max)
'wrap-prefix "   ").

Now, going from (point-min), use C-n to move down. Near the end of that
huge paragraph, C-n will not keep a constant column. In the same area,
C-e and C-a will change line. C-p will go through the same path as C-n,
thus not keeping the first column as well.

Under certain conditions that I have yet to find (but related to that
property and visual-line-mode), `next-line', when reaching the last line
of the window, will put point back in the middle of the screen while
keeping the same buffer portion visible (so it's a loopback, as the next
part of the buffer is never shown). When it happens, the cursor is stuck
forever in that loop if the user keep moving with `next-line'. This
doesn't happen with C-p, and C-v can get out of the loop.

In GNU Emacs 23.2.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.20.0)
 of 2010-05-08 on pidsley.hoetzel.info
Windowing system distributor `The X.Org Foundation', version 11.0.10904000
configured using `configure  '--prefix=/usr' '--sysconfdir=/etc' 
'--libexecdir=/usr/lib' '--localstatedir=/var' '--mandir=/usr/share/man' 
'--without-sound' '-with-x-toolkit=gtk' 'CFLAGS=-march=x86-64 -mtune=generic 
-O2 -pipe -fno-optimize-sibling-calls' 'LDFLAGS=-Wl,--hash-style=gnu 
-Wl,--as-needed''

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: fr_FR.utf8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Fundamental

Minor modes in effect:
  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
  blink-cursor-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  visual-line-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-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-n C-n C-n C-n C-n C-n C-n C-n 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 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 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-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-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 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 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 
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-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-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 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 
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 M-t <f1> f C-g <f1> c C-n <f1> c C-n 
M-t M-x r e p o r t - e m <tab> <return>

Recent messages:
Visual-Line mode enabled
Mark set [6 times]
Scanning for dabbrevs...100%
dabbrev-expand: No dynamic expansion for `put-text-pro' found
Scanning for dabbrevs...100%
dabbrev-expand: No dynamic expansion for `put-text-proper' found
call-interactively: End of buffer
nil
Quit
C-n runs the command next-line
C-n runs the command next-line

Load-path shadows:
None found.

Features:
(shadow sort mail-extr message sendmail regexp-opt ecomplete rfc822 mml
easymenu 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 help-fns
dabbrev 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)

-- 
Nicolas Goaziou