vc arch modeline issue

[Raphaël Berbain]

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

I am using Emacs' multi-tty branch (updated yesterday - full version:
address@hidden/emacs--multi-tty--0--patch-277), but I don't
think the problem is related to this particular version.  I am CC'ing
Stefan Monnier since he is the author of vc-arch.el and I think he is
the person to contact for anything VC-related, as well as Károly
Lörentey (sorry if I mispelled your name) as he is the multi-tty
person.  I am also not sure where the emacs-pretest-bug address goes,
so I'd like to ensure this report reaches the right people.  Please CC
me any further developments.

Now, the actual report:

Emacs errors out when trying to open some arch-controlled files (but
not all).  To reproduce:

$ tla register-archive http://mirrors.sourcecontrol.net/address@hidden
$ tla get address@hidden/monkeyplexer--0.8 monkeyplexer
$ emacs -q --no-site-file --eval '(setq debug-on-error t)' 
monkeyplexer/monkeyplexer

produces the following backtrace:

,----
| Debugger entered--Lisp error: (wrong-type-argument stringp nil)
|   string-match("\\`.*--\\(.*--.*\\)--\\(v?\\).*-\\([0-9]+\\)\\'" nil)
|   vc-arch-mode-line-string("/home/rgb/sandbox/monkeyplexer/src/monkeyplexer")
|   apply(vc-arch-mode-line-string 
"/home/rgb/sandbox/monkeyplexer/src/monkeyplexer")
|   vc-call-backend(Arch mode-line-string 
"/home/rgb/sandbox/monkeyplexer/src/monkeyplexer")
|   vc-mode-line("/home/rgb/sandbox/monkeyplexer/src/monkeyplexer")
|   vc-find-file-hook()
|   run-hooks(find-file-hook)
|   after-find-file(nil t)
|   find-file-noselect-1(#<buffer monkeyplexer> 
"~/sandbox/monkeyplexer/src/monkeyplexer" nil nil 
"~/sandbox/monkeyplexer/src/monkeyplexer" (528683 774))
|   find-file-noselect("/home/rgb/sandbox/monkeyplexer/src/monkeyplexer" nil 
nil nil)
|   find-file("/home/rgb/sandbox/monkeyplexer/src/monkeyplexer")
|   command-line-1(("--eval" "(setq debug-on-error t)" 
"sandbox/monkeyplexer/src/monkeyplexer"))
|   command-line()
|   normal-top-level()
`----

In GNU Emacs 21.3.50.1 (i686-pc-linux-gnu, X toolkit, multi-tty)
 of 2004-12-28 on nol
configured using `configure '--prefix=/opt/emacs' '--with-xpm' '--with-jpeg' 
'--with-tiff' '--with-gif' '--with-png' '--with-x' '--with-x-toolkit=lucid' 
'--without-toolkit-scro\
ll-bars''

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
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  menu-bar-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  line-number-mode: t

Recent input:
ESC x r e p o r t - e m a c s - b u g RET

Recent messages:
(emacs -q --no-site-file)
For information about the GNU Project and its goals, type C-h C-p.
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