bug#11348: 24.0.95; TAB-completion in shell-command produces d:\/foo on MS-Windows

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: 11348@debbugs.gnu.org
> Date: Sat, 05 May 2012 00:20:17 -0400
> 
> >> This said, based on your description, the problem may simply come from
> >> shell.el's setting of pcomplete-arg-quote-list which tells pcomplete
> >> that \ is an escape char.
> >> I.e. does the patch below fix the problem?
> > No, I still get "d:\/gnu/".
> 
> I installed the patch below, which seems to fix this specific problem
> (according to my testing under Wine ;-)

I'm not sure why it worked for you, because it still doesn't for me.
Are you applying the changes to the emacs-24 branch?  Because that's
what I do, this bug being against Emacs 24.0.96 and a regression from
Emacs 23.4.

According to my debugging inside shell-parse-pcomplete-arguments, what
happens there is that this fragment

          (while (looking-at
                  (eval-when-compile
                    (concat
                     "\\(?:[^\s\t\n\\\"']+"
                     "\\|'\\([^']*\\)'?"
                     "\\|\"\\(\\(?:[^\"\\]\\|\\\\.\\)*\\)\"?"
                     "\\|\\\\\\(\\(?:.\\|\n\\)?\\)\\)")))

decides that \g is an escape sequence.  (Btw, what's the purpose of
using eval-when-compile here?)  Therefore, the value of args at the
end of the loop is

   ("nu" "g" "d:")

After this line:

          (push (mapconcat #'identity (nreverse arg) "") args)))

it becomes

   ("d:" "g" "nu")

and the result of the function is therefore

   (("cd" "d:gnu") 16 19)

By contrast, if I type "M-! cd d:/gnu TAB", the results are,
correspondingly,

   ("d:/gnu")

and

   (("cd" "d:/gnu") 16 19)

IOW, the problem is that shell-parse-pcomplete-arguments removes the
backslash in "d:\gnu", because the last alternative in the above
regexp treats backslashes as escape characters, which on MS-DOS and
MS-Windows is true (for shell commands) only when the backslash
precedes a quote character (").

Thanks.