Archive for November, 2011

Jonathan Riddell

What I did on my Rotation

Canonical has a company scheme where after working there for a few years you can rotate to work at another part of the company for 6 months. Having worked on the desktop team for over five years I decided to do a rotation to Bazaar. My hopes for this were to build up my own programming skills by learning more Python and by experiencing different programming practices from the ones I’m used to in KDE.

I started off with some fixes to the developer documentation. This got me used to the process that you can not commit directly to bzr’s trunk, instead all committers are required to make merge proposals on Launchpad, have those approved by a fellow developer, then send it to a programme called Patch Queue Manager which will integrate the patch and run the test suite to check everything still works.

Next I started fixing a few easy command line UI bugs, improving error messages or stopping exception output and so forth. This got me into the world of writing test cases. Everything in bzr needs a test case, merge proposals will not be accepted without them. Like much of bzr I find that the test cases lack API documentation and comments but it turns out they are easy enough to read and similarly easy to write. There are both internal test cases, which run a small part of the code within bzr, and blackbox test cases which run a bzr command.

Bazaar is the version control system used by top open source project hosting site Launchpad so I was surprised to come across a bug which prevented bzr from talking to Launchpad properly on errors. “This is really important to fix. We need error reporting.” said Jonathan Lange over 2 years before. Pleasingly I could fix it, very satisfying. I had to learn about the hooks mechanism in bzr which shows up some of the downside of Python, you have to guess the arguments to send the hook. But who needs API documentation when you can just read the code? 🙂

Bazaar’s main GUI is qbzr (which provides GUIs for individual commands) and Bazaar Explorer (which provides a complete GUI). I worked with Martin (gz) to make these two talk to the normal Ubuntu crash system, Apport, rather than showing a nasty crash backtrace to the user.

Then I noticed that Bazaar Explorer has a lot of “Refresh” toolbar buttons about the place, any time you make a change to the file you have to click one before the UI will update. Not very user friendly. So I added file watchers about the place to make it magically update. Nifty, except that after release it turns out this breaks horribly when doing some commands outside of Bazaar Explorer, oops. Quick fix and message to packagers, hang head in shame.

The first large feature I worked on was GPG signing of commits. The documentation for Bazaar promised that this was implemented and all you need do was set the various options in the config file. Alas it lied. I fixed up the documentation and started looking into the GPG python bindings, which turn out to be completely undocumented on the Python side and surprisingly badly documented on the C side. Security critical code which is badly documented seems scary to me, mistakes could easily be made which go unnoticed until it appears on full-disclosure. But I manage to implement signing and adding a GUI to Bazaar Explorer being cautious as I go.

Bazaar has a scheme called patch pilot where we review patches submitted by the community and help them on their way to being integrated. I started out with this by following John Meinel who can write code faster than I can write English prose. We made small changes to some patches and integrated them, we gave feedback to newer patches that needed some work and we chased up contributors who had not responded. The barrier to entry in Bazaar is pleasingly small, if you don’t have the skills to write a perfect patch it’s encouraged to say so and someone else will finish it off.

Why, I wondered, is bzr (the command line UI to Bazaar) not translated? There were parts of gettext scattered around the code, and some code to extract strings but it didn’t get used. Turns out this code was a half completed feature that had never been taken to completion. I finished off translations by adding gettext()s throughout the code, ensuring tests still pass, fix the installation of .mos and enable the generation of .pot. This missed the 2.4 release so I’m still waiting to see how it works for 2.5, I suspect some strings will be missing context needed to do a good translation and of course the occasionally technical output of bzr might need some thought on how to translate but it should make bzr easier to use for non-English speakers.

Ubuntu Distributed Development is the project to put all of Ubuntu’s packages and history into Bazaar branches and change our packages processes to use Bazaar. This makes a lot of sense, the Ubuntu archive is already a primitive revision control system (you upload for each new version, often its useful to look at older versions). This project has been a long time coming and is one of the original reasons why Canonical started Bazaar back in the day. It suffers from a number of problems, notably the failure of quite a lot of packages to import into Bazaar including currently the whole of KDE due to a patch into openSUSE’s bz2 package. Also the quilt patch system we use tends to clash with being held within a revision control system so you end up with diffs of diffs. I tend to think that would have been an easier win to import only the debian/ packaging into Bazaar branches.

I tidied up the new Ubuntu Packaging Guide which is a guide to packaging with UDD branches (named in the hope that UDD will soon become the definitive way to do packaging). I also added a new command bzr get-orig-source to make it easier to do packaging in the current directory rather than a separate directory as used by bzr builddeb. I also added a hook to set the bzr changelog from the debian/changelog entry which is the current behaviour with debcommit. I got mixed feedback on this so I added a config option to disable it too. I also tidied up some of the bzr-builddeb code by removing weird terms like “larstiq” and removing acronyms by default.

My Python programming has improved a lot and I’m a convert to the cause of unit tests. Python is a fun and productive language but the lack of culture for documenting APIs is disappointing and being dynamic it’s that much easier to make mistakes without realising it. My productivity is nothing like as high as others on the Bazaar team but it seems I’m better at improving (graphical and command) user interfaces than my colleagues who can memorise internal data structures trivially. My six months is now up, I’ve enjoyed them and now I’m looking forward to getting back into Kubuntu and KDE.