Re: Google Summer of Code 2009: GIT

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 12, 2009, 20:18 UTC
Message-ID: <7vmybqjxzy.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <alpine.DEB.1.10.0903121214390.16753@asgard.lang.hm>

david@lang.hm writes:

Show 12 quoted lines

> defining terminology that was mentioned before
>
> merge drivers are run by git to do the merges and create the conflict
> markers. git already has a 'plug-in architecture' for these drivers
> (you can define file types and tell git to use a particular merge
> driver for this file type)
>
> merge helpers are run by the users if there is a conflict and make use
> of the markers. depending on what you end up using for conflict
> markers, you may not need to write a merge helper (for OO, if your
> conflict markers are good enough you can use OO to resolve conflicts
> easily, no need for a new tool)

Not really. A merge helper can look at the stages in the index to get the (original, ours, theirs) tuple and start to work from there (and doing a helper as a backend of mergetool will be one way to make it easier), and for such helper the driver does not have to do anything.

> with this terminology, you can't do merge helpers without doing the
> merge drivers first (what does the helper look for as an indicator of
> a conflict?)

The answer to that question is "the index", and your "you can't" is too strong.

I agree with you that the original "editor" for the specific type of document (e.g. OOo, inkskape, ...) can be used to fix things up if a driver can leave conflict markers in such a way that the helper does not have to do three-file merge, and that would be a nice thing to have. But for a helper that can do a real three-file merge (and in this thread I think somebody said OOo can do that), then it is Ok for a driver to punt.

But even then, *if* there is a driver *and* it can do trivial merges cleanly and safely, it would be a huge productivity win, as you do not have to run a helper every time you see two branching touching the same document even they did so to edit totally unrelated parts of it.