Thursday, May 15, 2008

This Week in Bazaar

This is the second in a mostly-every-week series of posts about whats been happening in the development world of the Bazaar distributed version control system. The series is co-authored by John Arbash Meinel, one of the primary developers on Bazaar, and Elliot Murphy, Launchpad developer and compulsive conflict avoider.


One of the nice things about Bazaar is the API, which enables new features to be added with plugins. Once a feature is polished and proves widely useful, it can move from a plugin into core bazaar. Most of the plugins are hosted/mirrored on Launchpad, and are a simple "bzr branch lp:bzr-plugin ~/.bazaar/plugins/plugin" away. For the rest, they are indexed at Here's a quick summary of some of the plugins we are using on our laptops right now:

bookmarks: This allows me to store an alias for a branch location, so it is easier to branch/push to a common location. So I can type 'bzr get bm:work/foo' instead of 'bzr get bzr+ssh://'

bzrtools: a collection of commands which provide extended functionality. Such as 'bzr cdiff' to display colored diffs and 'bzr shelve' to temporarily revert sections of changes.

difftools and extmerge: These plugins let me view differences in meld or kdiff3 (or anything that you want to configure, really), and do merges via meld.

email: Keep people informed of what you are working on by sending an email after every commit.

fastimport: This plugin allows me to import code from my friends mercurial repository and push it to launchpad.

git: this gives me read access to a local git repository

gtk: This is the Bazaar Gtk GUI, which has some nice tools like visualize and gcommit.

htmllog: Useful for generating html formatted logs for publishing on the web.

loom: Allows me to manage several "layers" of development in a single branch, and colloborate on those layers with other people.

notification: Gives a GUI popup when a pull or push completes

pqm: This formats a merge request to PQM. PQM then takes my branch, merges to main, runs tests, and commits the merge if all was well. This ensures that we always have passing tests in the main tree!

push_and_update: This updates the working tree when I push my branch to a remote server. Very useful for doing website updates.

removable: I try to keep all branches very small for easier review, so I have a lot of branches at one time. This tells me which branches have already been merged to the main tree (and thus can be removed). It can also let me know why something is not ready to be removed.

stats: Provides 'bzr stats' which gives a simple view of how many people have committed to your project and how many commits each has done.

update_mirrors: 'bzr update-mirrors' recursively scans for Bazaar branches and updates them to their latest upstream.

vimdiff: Adds the commands 'bzr vimdiff' and 'bzr gvimdiff'. Which opens vim in side-by-side mode, showing you your changes.

qbzr: Another great GUI for bzr, this one is written using Qt.

1.5rc1, 1.5 this Friday

Continuing our pattern of having time-based releases, bzr 1.5rc1 was released last Friday, and 1.5 final should be released tomorrow. Ever wonder how we churn out releases so regularly? The biggest factor enabling us to make consistent releases is our use of a Patch Queue Manager. It ensures that all of our 11,724 unit tests pass before allowing any merge into mainline. Even when lots of changes are landing, the trunk can be considered release quality. Most of the developers use the tip of mainline for their day-to-day work, which means that any changes get immediate use, rather than waiting for a release candidate.

By releasing every month, we have reduced the tendency to rush patches, trying to sneak them in before the next release. We know that there will be another release just around the corner, so we can land complex patches right after a release. For each release cycle, we have 3 weeks of "open" development, where any approved (peer reviewed) patch can be merged. Then we have a feature freeze week, where only bug fixes are supposed to be merged. At the end of the freeze week, we release RC1 and reopen mainline for development. If no regressions are found in RC1, it is tagged as final and released after one week.

The bzr-1.5 release is mostly focused on fixing small ui bugs, a couple of performance improvements, and some documentation updates.

(edit: 2008-05-16, the merged plugin changed and is now called bzr-removable)


Anonymous said...

I can't seem to find the "merged" plugin -- any pointers?

jam said...
This comment has been removed by the author.
jam said...

It seems that the "merged" plugin itself is called "bzr-removable" from

You'll have to look more closely, as it seems it doesn't follow the standard plugin layout. So you actually have to have it checked out elsewhere, and then create a symlink in ~/.bazaar/plugins/merged => ~/removable/merged

I don't know why, you'll have to ask ~jml on Launchpad.

(I had a typo, and it seems you can't edit comments, only delete them and resubmit.)