Re: Re: native-git-svn: A Summer of Code 2010 proposal

From: Dave Olszewski <cxreg@pobox.com>
Date: Mar 21, 2010, 23:51 UTC
Message-ID: <alpine.DEB.2.00.1003211643470.21433@narbuckle.genericorp.net>
In-Reply-To: <32541b131003191430ld0eaa9cw1d2aac08cff15682@mail.gmail.com>

On Fri, 19 Mar 2010, Avery Pennarun wrote:

Show 15 quoted lines

> For example, I'd be very happy to learn that your new design would
> allow two people to independently pull from svn://, do work in their
> respective copies of the git repositories, branch and merge all day
> long, pull from each other, and then push back to svn without a)
> making a mess of the svn repo and causing zillions of conflicts, or b)
> linearizing history and losing git's complex DAG.
>
> In the current version of git-svn this is very hard. 'git svn dcommit'
> generates entirely new git commit objects corresponding to the ones
> that were created in svn... but which nevertheless have your merge
> history included, which is awesome.  But if a new person clones the
> svn repo from scratch, he will end up with git commits corresponding
> to those same ones from svn, but *without* the merge history, and
> therefore with different commit ids, and which therefore prevent
> push/pulling between other people who have cloned the repo.

I've been working on a script that does 2-way integration with an upstream CVS repo, using git-cvsimport and git-cvsexportcommit to do the difficult parts.

I solved this problem you mention by rebasing in both directions onto detached HEADs and exporting the result, meaning that the history is permanently diverged from a DAG standpoint. Of course, over time, the rebase would become increasingly messy and horrible, so I created a couple of placeholder refs which are updated after the import/export is finished. These mark the last time it was done, and allow you only to attempt to apply the commits which are new on each side.

It's still very green and I've already worked though a number of pretty hairy problems, so I'm not going to say it's a bulletproof solution. But it does work.

     Dave