bug#2893: 23.0.91; vc-diff on git-controlled file fails

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 [email protected] mailing list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

I did `M-x v =' and got this:

Debugger entered--Lisp error: (wrong-type-argument stringp ("/Users/dave/src/elisp.repo/elisp/custom.el"))
  expand-file-name(("/Users/dave/src/elisp.repo/elisp/custom.el"))
  file-relative-name(("/Users/dave/src/elisp.repo/elisp/custom.el"))
  vc-git-diff(("/Users/dave/src/elisp.repo/elisp/custom.el") nil nil "*vc-diff*")
  apply(vc-git-diff (("/Users/dave/src/elisp.repo/elisp/custom.el") nil nil "*vc-diff*"))
  vc-call-backend(Git diff ("/Users/dave/src/elisp.repo/elisp/custom.el") nil nil "*vc-diff*")
  vc-diff-internal(t (Git ("/Users/dave/src/elisp.repo/elisp/custom.el")) nil nil t)
  vc-diff(nil t)
  call-interactively(vc-diff nil nil)


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
/Applications/Emacs.app/Contents/Resources/etc/DEBUG for instructions.


In GNU Emacs 23.0.91.1 (i386-apple-darwin9.6.0, NS apple-appkit-949.43)
 of 2009-03-05 on black.local
Windowing system distributor `Apple', version 10.3.949
configured using `configure  '--with-ns''

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: nil
  value of $XMODIFIERS: nil
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Major mode: Emacs-Lisp

Minor modes in effect:
  diff-auto-refine-mode: t
  shell-dirtrack-mode: t
  show-paren-mode: t
  server-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-x C-n M-< C-s C-x C-p G C-n C-n C-n C-n C-n C-n C-n 
C-p <tab> <tab> 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 s p p s s s s C-s g n u 
s C-a C-p s M-> C-p C-p <tab> 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 M-> C-SPC M-< M-w C-p C-n C-n 
C-n C-p C-p C-s a n d b a <backspace> 5 <backspace> 
4 a c k C-n C-n C-n M-x m a g i <tab> <tab> b u g <tab> 
<backspace> <backspace> <backspace> <backspace> r e 
<backspace> <backspace> - r e p <tab> C-g C-g C-x C-n 
C-x C-p C-x b * G r <tab> C-g 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 1 2 3 4 3 2 1 2 3 4 C-x C-n C-s u n s t 
a g e C-a C-p C-p C-p C-p C-x C-p U 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 
p n p n p n <return> C-x C-b C-p C-p C-p C-p C-p C-p 
C-x C-b C-x v = <wheel-up> <double-wheel-up> <wheel-down> 
<double-wheel-down> <triple-wheel-up> <down-mouse-1> 
<mouse-1> C-a <menu-bar> <options> <debug-on-error> 
<down-mouse-1> <mouse-1> C-x v = C-x C-n C-x C-n C-p 
C-SPC C-n C-n C-n C-n C-n C-n C-n C-n C-n M-w C-x C-p 
M-x r e p o r t - e m a <tab> <return>

Recent messages:
Quit [3 times]
Mark saved where search started
`working-revision' not found: using the old `workfile-version' instead
Mark set
Finding changes in /Users/dave/src/elisp.repo/elisp/custom.el...
file-relative-name: Wrong type argument: stringp, ("/Users/dave/src/elisp.repo/elisp/custom.el")
Debug on Error enabled globally
Finding changes in /Users/dave/src/elisp.repo/elisp/custom.el...
Entering debugger...
Mark set

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