Using Bazaar to hack on Twisted

At PyCon, I helped several Twisted developers to use Bazaar to work on Twisted, even though the repository is still SVN. Here's how to do it.

First, install bzr and the bzr-svn plugin. I strongly recommend using the latest release of bzr-svn, 0.4.9, as Jelmer is fixing bugs and improving the speed at an impressive rate. 0.4.9 is in Ubuntu Hardy.

Then make a shared repository for your Twisted branches:

bzr init-repo --rich-root-pack Twisted

(Forgetting --rich-root-pack is a common gotcha: the default repository format in bzr 1.3 doesn't have a feature bzr-svn needs.)

Then checkout the SVN trunk into the repository. You could do this direct from SVN, but it's much faster to use an already converted copy:

cd Twisted
bzr checkout http://www.twistedmatrix.com/users/spiv/bzr/twisted/trunk/
cd trunk
bzr switch svn://svn.twistedmatrix.com/svn/Twisted/trunk

To work on a branch already in SVN, you can just checkout or branch (depending on which workflow you prefer) it directly into your local repository. Checkouts will be more familiar to SVN users than independent branches, but if you want to make commits you'll need write access to Twisted's SVN repository.

cd ..
bzr checkout svn://svn.twistedmatrix.com/svn/Twisted/branches/feature-branch-1
cd feature-branch-1
hack hack hack...
bzr commit

(Don't worry too much about branches vs. checkouts. You can always use bzr reconfigure to change a checkout into a branch and vice versa if you change your mind later.)

To make a new branch in the SVN repository it's best to just use svn cp as before, then make a checkout/branch of that with bzr. (See bug 203368)

svn cp svn://svn.twistedmatrix.com/svn/Twisted/trunk svn://svn.twistedmatrix.com/svn/Twisted/branches/new-branch
bzr checkout svn://svn.twistedmatrix.com/svn/Twisted/branches/new-branch

If you can't commit to Twisted SVN you can still use bzr. Just make independent branches rather than checkouts. To share your branches with other people you can simply bzr push them to anywhere you like, including Launchpad.

And that's really it. Everything else is just regular bzr, including the excellent merging and offline commits.

For example, here's how you'd merge a branch to trunk and commit it:

bzr checkout svn+ssh://svn.twistedmatrix.com/svn/Twisted/trunk
cd trunk
bzr merge ../my-branch   # or you could use an SVN url!
bzr commit