From: Jeff King <peff@peff.net>
Date: Thu, 03 Jan 2013 08:37:12 GMT
Subject: Re: [BUG] two-way read-tree can write null sha1s into index
Message-ID: <20130103083712.GC32377@sigill.intra.peff.net>
In-Reply-To: <7vvcbg7d8x.fsf@alter.siamese.dyndns.org>

On Tue, Jan 01, 2013 at 02:24:46PM -0800, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> > So I think we need to update twoway_merge to recognize unmerged entries,
> > which gives us two options:
> >
> >   1. Reject the merge.
> >
> >   2. Throw away the current unmerged entry in favor of the "new" entry
> >      (when old and new are the same, of course; otherwise we would
> >      reject).
> >
> > I think (2) is the right thing.
> 
> As "--reset" in "read-tree --reset -u A B" is a way to say "we know
> we are based on A and we want to go to B no matter what", I agree we
> should not reject the merge.
> 
> With -m instead of --reset, I am not sure what the right semantics
> should be, though.

Good point; I was just thinking about the --reset case.

With "-m", though, we could in theory carry over the unmerged entries
(again, assuming that "old" and "new" are the same; otherwise it is an
obvious reject). But those entries would be confused with any new
unmerged entries we create. It seems we already protect against this,
though: "read-tree -m" will not run at all if you have unmerged entries.

Likewise, "checkout" seems to have similar protections.

So I think it may be a non-issue.

-Peff