Re: [PATCH 2/2] difftool: add a feature flag for the builtin vs scripted version

Johannes Schindelin [off-list ref] writes:

The downside is that we actually *do* go through Perl to do that. Only to
go back to a builtin. Which is exactly the thing I intended to avoid.

If we do not go through Perl, we have to set up the git directory and
parse the config in git.c *just* to figure out whether we want to
magically forward difftool to builtin-difftool. That is not only ugly, but
has potential side effects I was not willing to risk.

I won't accept the latter anyway, so do not worry ;-)

In any case, this feature flag will be there only for one or two Git for
Windows releases, to give early adopters a chance to send me bug reports
about any regressions.

I think that is sensible.  I suspect that for early detection of
breakages, you do not need to invent and force people to use a
completely new "mechanism" to switch between two implementations.

Can't you route the control upon seeing "git difftool" to your
experimental "C" difftool and check the configuration there?  Then
you can decide to run_command() a non-builtin one depending what the
configuration says---that way, you would incur cost of spawning Perl
only when you need it, no?