Reviewing proposed changes to Bazaar

All non-trivial code changes coming in to Bazaar are reviewed by someone else.

Anyone is welcome to review any patch. You don’t need to have a full understanding of the codebase to find problems in the code, the documentation, or the concept of the patch.

Normally changes by core contributors are reviewed by one other core developer, and changes from other people are reviewed by two core developers. Use intelligent discretion about whether if the patch is trivial.

No one likes their merge requests sitting in a queue going nowhere: this is pure waste. We prioritize reviewing existing proposals. Canonical dedicates some staff time to providing prompt helpful reviews. (See <http://wiki.bazaar.canonical.com/PatchPilot/>.)

From late 2009 on, we do all our code reviews through Launchpad’s merge proposal interface.

Reviewing proposed changes

There are three main requirements for code to get in:

  • Doesn’t reduce test coverage: if it adds new methods or commands, there should be tests for them. There is a good test framework and plenty of examples to crib from, but if you are having trouble working out how to test something feel free to post a draft patch and ask for help.
  • Doesn’t reduce design clarity, such as by entangling objects we’re trying to separate. This is mostly something the more experienced reviewers need to help check.
  • Improves bugs, features, speed, or code simplicity.

Code that goes in should not degrade any of these aspects. Patches are welcome that only cleanup the code without changing the external behaviour. The core developers take care to keep the code quality high and understandable while recognising that perfect is sometimes the enemy of good.

It is easy for reviews to make people notice other things which should be fixed but those things should not hold up the original fix being accepted. New things can easily be recorded in the bug tracker instead.

It’s normally much easier to review several smaller patches than one large one. You might want to use bzr-loom to maintain threads of related work, or submit a preparatory patch that will make your “real” change easier.

Checklist for reviewers

  • Do you understand what the code’s doing and why?
  • Will it perform reasonably for large inputs, both in memory size and run time? Are there some scenarios where performance should be measured?
  • Is it tested, and are the tests at the right level? Are there both blackbox (command-line level) and API-oriented tests?
  • If this change will be visible to end users or API users, is it appropriately documented in NEWS?
  • Does it meet the coding standards below?
  • If it changes the user-visible behaviour, does it update the help strings and user documentation?
  • If it adds a new major concept or standard practice, does it update the developer documentation?
  • (your ideas here...)

Reviews on Launchpad

Anyone can propose or comment on a merge proposal just by creating a Launchpad account.

From <https://code.launchpad.net/bzr/+activereviews> you can see all currently active reviews, and choose one to comment on. This page also shows proposals that are now approved and should be merged by someone with PQM access.

<https://help.launchpad.net/Code/Review> explains the various merge proposal states. Note that we don’t use state Approved until the patch is completely ready to merge.

Landing approved changes

Once a merge proposal is approved and finished, it’s sent to PQM (the patch queue manager) which will automatically test and integrate it. The recommended way to start this off is by running the feed-pqm script from <https://launchpad.net/hydrazine/>.

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