Re: [2.22.0] difftool no longer passes through to git diff if diff.tool is unset

From: Jeff King <peff@peff.net>
Date: Jun 20, 2019, 05:21 UTC
Message-ID: <20190620052125.GA12434@sigill.intra.peff.net>
In-Reply-To: <20190620024517.GA24321@archbookpro.localdomain>

On Wed, Jun 19, 2019 at 10:45:17PM -0400, Denton Liu wrote:

Show 7 quoted lines

> Using the following command on git.git,
> 
> 	$ HOME=/dev/null ./git --exec-path=. difftool --no-index color.c color.h
> 
> I did a quick bisect on the issue and it seems like the cause of this
> bug is actually 287ab28bfa (diff: reuse diff setup for --no-index case,
> 2019-02-16). I'll do a bit more digging tomorrow.

I don't know much about how git-difftool works, but it looks like it sets GIT_EXTERNAL_DIFF=git-difftool--helper.

Prior to 287ab28bfa, we would not have respected any external diff command when running git-diff. But after it, we do.

In the case that he user has not provided --no-index, then this all works as I guess difftool is meant to: it runs the helper and says "hey, you have not configured this".

It seems like the behavior of the above command prior to 287ab28bfa was not intentional. It would run git-diff, expecting it to trigger the helper, but it never did (and instead just did a normal no-index diff).

So it seems like the new behavior is actually the right thing, as it makes the --no-index case consistent with the regular one? I'm not at all clear why you would run "difftool" here if you it is not configured and you just want the straight diff output.

-Peff