Re: [PATCH] combine-diff: handle --find-object in multitree code path

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 30, 2020, 22:07 UTC
Message-ID: <xmqqmu16gbqk.fsf@gitster.c.googlers.com>
In-Reply-To: <20200930115240.GA1899467@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

Show 13 quoted lines

>  2. It doesn't catch all cases where a particular path is interesting.
>     Consider a merge with parent blobs X and Y for a particular path,
>     and end result Z. That should be interesting according to "-c",
>     because the result doesn't match either parent. And it should be
>     interesting even with "--find-object=X", because "X" went away in
>     the merge.
>
>     But because we perform each pairwise diff independently, this
>     confuses the intersection code. The change from X to Z is still
>     interesting according to --find-object. But in the other parent we
>     went from Y to Z, so the diff appears empty! That causes the
>     intersection code to think that parent didn't change the path, and
>     thus it's not interesting for "-c".

Hmmmm....

> +test_expect_success 'do not detect merge that does not touch blob' '
> +	git checkout -B merge interesting &&
> +	git merge -m "untouched blob" base &&
> +	git diff-tree --format=%s --find-object=$blob -c --name-status HEAD >actual &&

You learn new things every day ;-)

I've always thought that for --find-object to do a good job, you'd need "--full-history" and perhaps "-m". Especially, I didn't expect "-c" or "--cc" to make a difference.