bug#4050: 23.1.50; iswitchb virtual buffers don't play well with symlinks

[Tassilo Horn]

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:

I use iswitchb and the virtual buffer feature
(iswitchb-use-virtual-buffers set to t).  It's a great feature, but it
doesn't play well with symlinks.

I keep all my config files in a git repository.  For example, my
~/.emacs is a symlink to ~/repos/configs/dot-emacs.el.  Now I fire up
iswithb and type ".emacs".  There's no such buffer, so it shows the
virtual buffer ".emacs" and I hit RET.

Now I'm queried:

  Symbolic link to Git-controlled source file; follow link? (y or n) 

That's ok, and I say yes.  The echo area says:

  Followed link to /home/horn/repos/configs/dot-emacs.el

Also, the file is opened, and a buffer dot-emacs.el exists now.  But
then I get another query:

  No buffer matching `.emacs', create one? (y or n) 

When I say yes, an empty .emacs buffer is created.  When I say no, no
new buffer is created, but I stay in the buffer I invoked iswitchb
from.  The dot-emacs.el buffer is open, but not switched to.

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/share/emacs/23.1.50/etc/DEBUG for instructions.


In GNU Emacs 23.1.50.1 (x86_64-pc-linux-gnu, GTK+ Version 2.16.5)
 of 2009-08-02 on localhost
Windowing system distributor `The X.Org Foundation', version 11.0.10603000
configured using `configure  '--prefix=/usr' '--host=x86_64-pc-linux-gnu' 
'--mandir=/usr/share/man' '--infodir=/usr/share/info' '--datadir=/usr/share' 
'--sysconfdir=/etc' '--localstatedir=/var/lib' '--libdir=/usr/lib64' 
'--build=x86_64-pc-linux-gnu' '--program-suffix=-emacs-23-cvs' 
'--infodir=/usr/share/info/emacs-23-cvs' '--with-sound' '--with-x' 
'--with-toolkit-scroll-bars' '--with-gif' '--with-jpeg' '--with-png' 
'--with-rsvg' '--with-tiff' '--with-xpm' '--with-xft' '--with-libotf' 
'--with-m17n-flt' '--with-x-toolkit=gtk' '--without-hesiod' 
'--without-kerberos' '--without-kerberos5' '--with-gpm' '--with-dbus' 
'build_alias=x86_64-pc-linux-gnu' 'host_alias=x86_64-pc-linux-gnu' 
'CFLAGS=-march=core2 -O2 -pipe' 'LDFLAGS=-Wl,-z,now''

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: Group

Minor modes in effect:
  hl-line-mode: t
  gnus-topic-mode: t
  gnus-undo-mode: t
  display-time-mode: t
  yas/global-mode: t
  yas/minor-mode: t
  recentf-mode: t
  iswitchb-mode: t
  window-number-meta-mode: t
  window-number-mode: t
  exec-abbrev-cmd-mode: t
  savehist-mode: t
  show-paren-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
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
n SPC n e w l i n e s SPC i n SPC t h e SPC n a m e 
. SPC SPC M-q <down> <left> <left> <left> <left> <left> 
<left> <left> <left> <left> <left> <left> <left> <left> 
<left> <left> <left> <left> <left> <left> <left> <left> 
<left> <left> <left> <left> <left> <right> <right> 
<right> <right> <right> <right> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> M-q <down> <down> 
<down> <down> <down> <down> C-a C-SPC <down> <down> 
<down> <down> <down> <down> <down> C-c M-m <up> <up> 
<up> <up> <up> <up> <up> <down> <down> <down> <down> 
<down> <down> <down> <down> <down> <down> <down> <down> 
<down> <up> <return> I SPC t h i n k SPC t h a t SPC 
C-h f d i r e <tab> d <tab> - e <tab> <tab> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> m o <tab> v <tab> e n <tab> 
<return> b a s i c a l l y SPC t <M-backspace> <M-backspace> 
` d i r e d - m o r <backspace> v e l <backspace> - 
t o - e n M-/ ' SPC h a s SPC t o SPC b e SPC a d a 
p t e d SPC t o SPC c o n s i d e r SPC t h o s e SPC 
f i l e n a m e s , SPC t o o . M-x t t s s <return> 
C-c C-c c <return> SPC c l s C-x C-b q C-x b . e m 
<return> y n C-x b d o <right> C-s <return> C-x k <return> 
M-x r e b <return>

Recent messages:
(No changes need to be saved)
20090805T210311.609> Saving /home/horn/.newsrc.eld...
Saving file /home/horn/.newsrc.eld...
Wrote /home/horn/.newsrc.eld
20090805T210311.661> Saving /home/horn/.newsrc.eld...done
Symbolic link to Git-controlled source file; follow link? (y or n) 
Followed link to /home/horn/repos/configs/dot-emacs.el
No buffer matching `.emacs', create one? (y or n) 
no buffer matching `.emacs'
call-interactively: End of buffer

Load-path shadows:
/usr/share/emacs/site-lisp/ruby-mode/ruby-mode hides 
/usr/share/emacs/23.1.50/lisp/progmodes/ruby-mode
~/repos/el/org-mode/lisp/org-bbdb hides 
/usr/share/emacs/23.1.50/lisp/org/org-bbdb
~/repos/el/org-mode/lisp/org-colview hides 
/usr/share/emacs/23.1.50/lisp/org/org-colview
~/repos/el/org-mode/lisp/org-footnote hides 
/usr/share/emacs/23.1.50/lisp/org/org-footnote
~/repos/el/org-mode/lisp/org-compat hides 
/usr/share/emacs/23.1.50/lisp/org/org-compat
~/repos/el/org-mode/lisp/org-clock hides 
/usr/share/emacs/23.1.50/lisp/org/org-clock
~/repos/el/org-mode/lisp/org-bibtex hides 
/usr/share/emacs/23.1.50/lisp/org/org-bibtex
~/repos/el/org-mode/lisp/org-faces hides 
/usr/share/emacs/23.1.50/lisp/org/org-faces
~/repos/el/org-mode/lisp/org-timer hides 
/usr/share/emacs/23.1.50/lisp/org/org-timer
~/repos/el/org-mode/lisp/org-vm hides /usr/share/emacs/23.1.50/lisp/org/org-vm
~/repos/el/org-mode/lisp/org-list hides 
/usr/share/emacs/23.1.50/lisp/org/org-list
~/repos/el/org-mode/lisp/org-gnus hides 
/usr/share/emacs/23.1.50/lisp/org/org-gnus
~/repos/el/org-mode/lisp/org-exp hides /usr/share/emacs/23.1.50/lisp/org/org-exp
~/repos/el/org-mode/lisp/org-wl hides /usr/share/emacs/23.1.50/lisp/org/org-wl
~/repos/el/org-mode/lisp/org-plot hides 
/usr/share/emacs/23.1.50/lisp/org/org-plot
~/repos/el/org-mode/lisp/org-w3m hides /usr/share/emacs/23.1.50/lisp/org/org-w3m
~/repos/el/org-mode/lisp/org-agenda hides 
/usr/share/emacs/23.1.50/lisp/org/org-agenda
~/repos/el/org-mode/lisp/org-archive hides 
/usr/share/emacs/23.1.50/lisp/org/org-archive
~/repos/el/org-mode/lisp/org-attach hides 
/usr/share/emacs/23.1.50/lisp/org/org-attach
~/repos/el/org-mode/lisp/org-mhe hides /usr/share/emacs/23.1.50/lisp/org/org-mhe
~/repos/el/org-mode/lisp/org-irc hides /usr/share/emacs/23.1.50/lisp/org/org-irc
~/repos/el/org-mode/lisp/org-table hides 
/usr/share/emacs/23.1.50/lisp/org/org-table
~/repos/el/org-mode/lisp/org-info hides 
/usr/share/emacs/23.1.50/lisp/org/org-info
~/repos/el/org-mode/lisp/org-jsinfo hides 
/usr/share/emacs/23.1.50/lisp/org/org-jsinfo
~/repos/el/org-mode/lisp/org-id hides /usr/share/emacs/23.1.50/lisp/org/org-id
~/repos/el/org-mode/lisp/org-publish hides 
/usr/share/emacs/23.1.50/lisp/org/org-publish
~/repos/el/org-mode/lisp/org-mew hides /usr/share/emacs/23.1.50/lisp/org/org-mew
~/repos/el/org-mode/lisp/org-remember hides 
/usr/share/emacs/23.1.50/lisp/org/org-remember
~/repos/el/org-mode/lisp/org-macs hides 
/usr/share/emacs/23.1.50/lisp/org/org-macs
~/repos/el/org-mode/lisp/org-mouse hides 
/usr/share/emacs/23.1.50/lisp/org/org-mouse
~/repos/el/org-mode/lisp/org-install hides 
/usr/share/emacs/23.1.50/lisp/org/org-install
~/repos/el/org-mode/lisp/org hides /usr/share/emacs/23.1.50/lisp/org/org
~/repos/el/org-mode/lisp/org-rmail hides 
/usr/share/emacs/23.1.50/lisp/org/org-rmail
~/repos/el/org-mode/lisp/org-mac-message hides 
/usr/share/emacs/23.1.50/lisp/org/org-mac-message
~/elisp/elp hides /usr/share/emacs/23.1.50/lisp/emacs-lisp/elp