Re: Regarding "git log" on "git series" metadata

From: Jeff King <peff@peff.net>
Date: Nov 5, 2016, 04:44 UTC
Message-ID: <20161105044440.u5imqcrsmpdbtonp@sigill.intra.peff.net>
In-Reply-To: <xmqq60o2edy5.fsf@gitster.mtv.corp.google.com>

On Fri, Nov 04, 2016 at 09:41:06PM -0700, Junio C Hamano wrote:

Show 16 quoted lines

> > I think the main complication is that the reachability rules are used
> > during object transfer. So you'd probably want to introduce some
> > protocol extension to say "I understand gitrefs", so that when one side
> > says "I have sha1 X and its reachable objects", we know whether they are
> > including gitrefs there. And likewise receivers with
> > transfer.fsckObjects may complain about the new gitref tree mode
> > (fortunately a new object type shouldn't be needed).
> 
> Quite honestly I do not think backward compatibility here matters.
> When gitlinks were introduced, a repository that was created with
> gitlink capable version of Git would have failed "git fsck" that is
> not gitlink aware, and I think this new "link with reachability" is
> the same deal.  No existing implemention understands a tree entry
> whose mode bits are 140000 or whatever new bit pattern we would
> assign to this thing.  You have to wait until both ends understand
> the new thing, and that is perfectly OK.

I'm OK with saying "if you use the gitref feature, you cannot push or pull those objects with remotes that do not understand it". But unlike gitlink, if we fail to notice the situation, we run into a case where we might silently lose objects, which is bad. So I think we need to be a bit more careful.

I don't think the problems are insurmountable. I just think that's where the real complexity is, not in the changes to teach a single git about gitrefs.

I'm happy to stand back and let you or Josh figure out all the corner cases. :)

-Peff