Re: Weird revision walk behaviour

From: Jeff King <peff@peff.net>
Date: May 23, 2018, 17:32 UTC
Message-ID: <20180523173246.GA10299@sigill.intra.peff.net>
In-Reply-To: <CAM0VKjkr71qLfksxZy59o4DYCM-x=podsCf6Qv+PzZuSe1gXZw@mail.gmail.com>

On Wed, May 23, 2018 at 07:10:58PM +0200, SZEDER Gábor wrote:

Show 10 quoted lines

>   $ git log --oneline master..ba95710a3b -- ci/
>   ea44c0a594 Merge branch 'bw/protocol-v2' into jt/partial-clone-proto-v2
> 
> But as far as I can tell, there are no changes in the 'ci/' directory
> on any of the merge's parents:
> 
>   $ git log --oneline master..ea44c0a594^1 -- ci/
>   # Nothing.
>   $ git log --oneline master..ea44c0a594^2 -- ci/
>   # Nothing!

Hmm. That commit does touch "ci/" with respect to one of its parents. It should get simplified away because it completely matches the other parent, so it does sound like a bug.

Show 5 quoted lines

> This is not specific to the 'ci/' directory, it seems that any
> untouched directory does the trick:
> 
>   $ git log --oneline master..ea44c0a594 -- contrib/coccinelle/ t/lib-httpd/
>   ea44c0a594 Merge branch 'bw/protocol-v2' into jt/partial-clone-proto-v2

Both of those directories also differ between one parent. If you try it with "contrib/remote-helpers", which does not, then the commit does not appear.

So it does seem like a bug where we should be simplifying away the merge but are not (or I'm missing the corner case, too ;) ).

> I get the same behavior with Git built from current master and from
> past releases as well (tried it as far back as v2.0.0).

I keep some older builds around, and it does not reproduce with v1.6.6.3 (that's my usual goto for "old"). Bisecting turns up d0af663e42 (revision.c: Make --full-history consider more merges, 2013-05-16). It looks like an unintended change (the commit message claims that the non-full-history case shouldn't be affected).

-Peff