We must keep the cost of merging as low as possible if we want to encourage people to collaborate as much as possible. If a merge is awkward, or slow, or results in lots of conflicts, or breaks when people have renamed files and directories, then I’m likely to avoid merging early and merging often. And that just makes it even harder to merge later.

The beauty of distributed version control comes in the form of spontaneous team formation, as people with a common interest in a bug or feature start to work on it, bouncing that work between them by publishing branches and merging from one another. These teams form more easily when the cost of branching and merging is lowered, and taking this to the extreme suggests that it’s very worthwhile investing in the merge experience for developers.

In CVS and SVN, the “time to branch” is low, but merging itself is almost always a painful process. Worse, merging a second time from another branch is WORSE, so the incentives for developers to merge regularly are exactly the wrong way around. For merge to be a smooth experience, the tools need to keep track of what has been merged before, so that you never end up redoing work that you’ve already solved. Bzr and Git both handle this pretty well, remembering which revisions in someone else’s branch you have already integrated into yours, and making sure that you don’t need to bother to do it again.

Once they send patches to you or push their branches, you can do the merge into your git repository and push it to github. Due to the said cron job, the subversion repository (e.g. in Google Code) will get the changes as well. Every now and then, when other contributors commit some changes to the subversion repository, the changes will be also propagated to github. Both parties are happy.