Re: [PATCH v5] gitk: Use git-difftool for external diffs when git >= 1.7.0

[Paul Mackerras <paulus@samba.org>]

On Thu, Apr 08, 2010 at 02:08:10AM -0700, David Aguilar wrote:

> git-difftool is used instead of the built-in external diff
> code when git is >= 1.7.0.  git-difftool's '--extcmd=frotz'
> feature was first introduced in 1.7.0 and is the mechanism
> through which we launch the configured difftool.
> 
> A benefit of this change is that gitk's external diff feature
> no longer needs write-access to the current directory.

I applied this one, and in testing it I noticed that if the git
difftool invocation fails, for example because the user doesn't have
meld installed, there is no notification via the GUI.  Instead an
error message is printed to stderr.  We need to do something more like
what we do in the old-git case -- use open rather than exec -- and pop
up an error dialog with error_popup on error so that the user knows
what the problem is.

Another minor problem is that the file names that meld (or other diff
tool) displays are less informative now.  For example I see
"KyaZ5d_gitk : 8iucke_gitk" as the tab label in meld instead of the
"[87d24ec87abc...e236e0833ff] gitk" label that we got before, which
was a little more informative, though the e236e0833ff is the end of
the second SHA1 rather than the beginning.

So I backed it out.  The error handling needs to be fixed using
something like what delete_at_eof does (except that obviously we don't
have any files to delete).

Paul.