bug#1135: 23.0.60; (expand-file-name ".." "/") produces surprising results

[Daniel Pittman]

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 some code that uses (setq dir (expand-file-name ".." dir)) to walk
up a directory tree to the root.  This works fine on the local disk, but
has some surprising results -- infinite loop -- on Tramp files.

I debugged this down to the unexpected (to me) behaviour of

    (expand-file-name ".." "/")
    => "/.."

    (expand-file-name ".." "/..")
    => "/"

This was causing the code, which checked if the current and previous
result of (expand-file-name ".." dir) were the same, to go into an
infinite loop cycling between those two values...


I would have expected that the result was:

    (expand-file-name ".." "/")
    => "/"

Regards,
        Daniel


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/23.0.60/etc/DEBUG for instructions.


In GNU Emacs 23.0.60.1 (x86_64-pc-linux-gnu, GTK+ Version 2.12.9)
 of 2008-03-20 on yellow, modified by Debian
 (emacs-snapshot package, version 1:20080228-1ubuntu1)
Windowing system distributor `The X.Org Foundation', version 11.0.10400090
configured using `configure  '--build' 'x86_64-linux-gnu' '--host' 
'x86_64-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' 
'--libexecdir=/usr/lib' '--localstatedir=/var' '--infodir=/usr/share/info' 
'--mandir=/usr/share/man' '--with-pop=yes' 
'--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/23.0.60/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.0.60/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.0.60/leim'
 '--with-x=yes' '--with-x-toolkit=gtk' '--enable-font-backend' 
'build_alias=x86_64-linux-gnu' 'host_alias=x86_64-linux-gnu' 'CFLAGS=-DDEBIAN 
-DSITELOAD_PURESIZE_EXTRA=5000 -g -O2' 'LDFLAGS=-g -Wl,--as-needed' 'CPPFLAGS=''

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

Major mode: Emacs-Lisp

Minor modes in effect:
  eldoc-mode: t
  highlight-parentheses-mode: t
  flyspell-mode: t
  shell-dirtrack-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
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
c c c c c d d d d d d d d d c c c c c c c c c c c c 
c c C-x k <return> C-x C-f <up> <return> c c c c c 
c c c c c c c c c c c c c c c c c c c c c c c c c c 
c c c c c c c c c c c c c c c c c c c c c c c c c c 
c c c c c c c c c c c c c c c c c c c c c c c c c c 
c c c c c c c c c c c c c c d d d d d d d d d d d c 
c c c q C-/ C-/ C-M-x C-x k <return> M-: ( e x p a 
n d - f i l e - n a m e SPC " . . " S-SPC " / " ) <return> 
M-: <up> C-e <left> <left> <left> <left> <right> <right> 
. p . <backspace> <backspace> . <return> <tab> C-h 
f e x p a n d - f i l / <tab> <backspace> <tab> <return> 
<switch-frame> SPC n q C-s g n u <down> <down> <down> 
<down> <return> SPC C-k C-k C-k C-k q p p g n SPC SPC 
n n n <switch-frame> <switch-frame> <switch-frame> 
<switch-frame> <switch-frame> <switch-frame> <C-tab> 
C-p C-p C-p C-f C-f C-f C-f C-f C-f C-f C-f C-f C-SPC 
M-f M-f M-f <C-insert> <switch-frame> <switch-frame> 
<switch-frame> <switch-frame> <switch-frame> M-x r 
e p o r t <tab> C-g <switch-frame> M-x C-g M-x r e 
p o r t - e m <tab> b <tab> <return>

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