From: Michal Sojka <sojkam1@fel.cvut.cz>
Date: Sun, 14 Mar 2010 19:24:24 GMT
Subject: Re: [PATCH] Bug: failed octopus merge does not create MERGE_HEAD
Message-ID: <87r5nmzoyf.fsf@steelpick.localdomain>
In-Reply-To: <7vr5no7xlo.fsf@alter.siamese.dyndns.org>

On Sat, 13 Mar 2010, Junio C Hamano wrote:
> Hmm.
> 
> When it detects conflicts, and refuses to make a merge, the octopus
> backend says "should not be doing an octopus".  As far as I can tell,
> MERGE_HEAD is useful only when resolving conflicts, and the octopus

There is also another use - see below.

> strongly discourages recording anything but the simplest conflict-free
> merges.

How can I know in advance that the merge will be conflict free? I have a
script which merges a bunch of (simple) topic branches which usually
merge without conflict, but from time to time some branch evolves and
conflicts.

> That makes me think that not writing the file out would be the more
> correct thing to do.

> 
> One possibility I can think of is that we try to prevent user mistakes by
> checking the existence of MERGE_HEAD (i.e. "can't do this, you are still
> during a merge"), and not writing MERGE_HEAD in this case, but still
> potentially leaving the index unmerged, may allow some operations that we
> should prevent from being invoked to proceed.  Is that the issue you are
> trying to address?  Or is there something else?  Why do you want to have
> MERGE_HEAD?

I'm using zsh and vcs_info which shows me git repo status in my prompt
(see e.g. http://www.jukie.net/~bart/blog/pimping-out-zsh-prompt).
vcs_info tests for existence of MERGE_HEAD to signalize that you are in
the middle of merge. If MERGE_HEAD is not created I do not see a big red
waning in my prompt and I expect the merge to be successful.

In my experiments I found that octopus creates MERGE_HEAD in several
situations but not in the one when a branch modifies the file and
another deletes it. Therefore I think it is a bug.

-Michal