vc-git-previous-revision and cmd.exe

vc-git-previous-revision and cmd.exe

[Eli Zaretskii]

vc-git-previous-revision appends "^" to a revision to get the previous
one.  But "^" is a special character for the Windows cmd.exe shell, so
'D' in the *vc-change-log* buffer doesn't work if the 'git' command is
actually a batch file that invokes the real Git executable, in which
case we call cmd.exe to run the batch file, and cmd.exe removes the ^
(because it's the escape character).

Can we use "~1" instead?  If that's bad for Unix, we can do that only
on Windows.

Comments?

Re: vc-git-previous-revision and cmd.exe

[Andreas Schwab]

Eli Zaretskii <eliz@gnu.org> writes:

> vc-git-previous-revision appends "^" to a revision to get the previous
> one.  But "^" is a special character for the Windows cmd.exe shell, so
> 'D' in the *vc-change-log* buffer doesn't work if the 'git' command is
> actually a batch file that invokes the real Git executable, in which
> case we call cmd.exe to run the batch file, and cmd.exe removes the ^
> (because it's the escape character).

Why is that a problem?  process-file should properly quote the arguments
when it needs to go through a shell.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: vc-git-previous-revision and cmd.exe

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: emacs-devel@gnu.org
> Date: Mon, 17 Nov 2014 18:55:10 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > vc-git-previous-revision appends "^" to a revision to get the previous
> > one.  But "^" is a special character for the Windows cmd.exe shell, so
> > 'D' in the *vc-change-log* buffer doesn't work if the 'git' command is
> > actually a batch file that invokes the real Git executable, in which
> > case we call cmd.exe to run the batch file, and cmd.exe removes the ^
> > (because it's the escape character).
> 
> Why is that a problem?  process-file should properly quote the arguments
> when it needs to go through a shell.

It's a Windows-specific conundrum: '^' is only special to cmd.exe, not
to argv[] processing of any other .exe program.  On top of that, the
only way to escape '^' is to double it.  But if we always double it,
then passing it to anything except cmd.exe will result in 2 ^^ in the
program's argv[].  And since most of the programs we invoke are not
cmd.exe or batch files, we don't quote '^' in shell-quote-argument.

On top of that, I don't think process-file knows it will go through a
shell in this case, since git.cmd it finds is just an executable file
for it.

(I bumped into this because 'D' in the *vc-change-log* buffer claimed
there were "no differences between 1234567 and 123456789...abc",
because cmd.exe removed the ^ part.)

Re: vc-git-previous-revision and cmd.exe

[Eli Zaretskii]

> Date: Mon, 17 Nov 2014 18:51:40 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> 
> vc-git-previous-revision appends "^" to a revision to get the previous
> one.  But "^" is a special character for the Windows cmd.exe shell, so
> 'D' in the *vc-change-log* buffer doesn't work if the 'git' command is
> actually a batch file that invokes the real Git executable, in which
> case we call cmd.exe to run the batch file, and cmd.exe removes the ^
> (because it's the escape character).
> 
> Can we use "~1" instead?  If that's bad for Unix, we can do that only
> on Windows.

Pushed a change to that effect to emacs-24.