Re: git-core: conflictstyle=diff3 doesn't actually use diff3 compatible format

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Mar 8, 2010, 04:54 UTC
Message-ID: <20100308045454.GA22672@progeny.tock>
In-Reply-To: <7vpr3itn89.fsf@alter.siamese.dyndns.org>

Junio C Hamano wrote:

> Jonathan Nieder <jrnieder@gmail.com> writes:

Show 9 quoted lines

>> I’d be interested to hear from xdiff people
>> whether it should be easy to add the ancestor name to the output.
>
> I don't think there was any xdiff people involved in this area.
> 
> I suspect that our tools actually rely on the common ancestor markers not
> having any extra cruft after them, so it would be introducing a bug if you
> change this output without changing the places that read them (I know
> about "rerere", but there may be others).

I guess the relevant xdiff person was you. ;-)

Thank you for the quick response. On the xdiff level, it looks like all that is needed is to pass the ancestor label as a member of struct s_xmparam, and then fill_conflict_hunk() could respect that. Not complicated at all.

For merge_trees() users, the ancestor label could be passed with branch1 and branch2 in struct merge_options.

That leaves the question of merge_recursive(). With merge_recursive(), there is more than one ancestor, so it is not completely clear what the diff3 merge should do. Currently it writes something like this:

 <<<<<<< HEAD
 Conflict resolution is hard;
 let's go shopping.
 |||||||
 <<<<<<< Temporary merge branch 1
 Who knows whose this is?
 |||||||
 Ancient history.
 =======
 Another intermediate result.
 >>>>>>> Temporary merge branch 2
 =======
 Git makes conflict resolution easy.
 >>>>>>> topic

which is hard to read [1]. Probably it would be better to use a consolidated common ancestor, by cocatenating the internal common ancestors; in this simple case, that would look like this:

 <<<<<<< HEAD
 Conflict resolution is hard;
 let's go shopping.
 ||||||||
 Ancient history.
 ========
 Git makes conflict resolution easy.
 >>>>>>>> topic

What should be the label of this possibly fictional merge base?

Jonathan

[1] For people and for rerere.  See http://bugs.debian.org/569645