While doing a bit of work on Storm, I decided to try out the loom plugin for Bazaar. The loom plugin is designed to help maintain a stack of changes to a base branch (similar to quilt). Some use cases where this sort of tool are useful include:
- Maintaining a long-running diff to a base branch. Distribution packaging is one such example.
- While developing a new feature, the underlying code may require some refactoring. A loom could be used to keep the refactoring separate from the feature work so that it can be merged ahead of the feature.
- For complex features, code reviewers often prefer to changes to be broken down into a sequence of simpler changes. A loom can help maintain the stack of changes in a coherent fashion.
A loom branch helps to manage these different threads in a coherent manner. Each thread in the loom contains all the changes from the threads below it, so the revision graph ends up looking something like this:
Once the plugin has been installed, a normal branch can be converted to
a loom with the "
bzr loomify" command. The "
command can be used to create a new thread above the current one.
bzr down-thread" and "
bzr up-thread" commands can be used
to switch between threads. When going up a thread, a merge will be
performed if there are new changes from the lower thread. The
bzr show-loom" command shows the current state of the loom, and
which thread is currently selected.
bzr export-loom" command can be used to explode the loom,
creating a standard branch for each thread. The included HOWTO document
gives a more detailed tutorial.
There are a few warts in the UI that I've encountered though:
- The "
bzr combine-thread" command sounds like it should actually merge two threads. Instead it is an advisory command that can be used to remove a thread once its contents have been merged.
- After pulling new changes in from upstream on the bottom thread, it
gets a bit tedious bubbling the changes up with "
bzr up-thread" and "
- As well as committing revisions to individual threads, the
bzr record" command can be used to commit the state of the loom as a whole. I haven't really worked out when I should be using the command.
- No indication is given if there are changes in the loom that
haven't been recorded with "
bzr record". I'd expect some indication from "
bzr status" to this effect.
- When using looms to break a larger feature down into smaller chunks, it'd be nice to have a command that generated a sequence of merge requests that built on top of each other. This would be the form needed to submit them for review on a mailing list.
Despite the quirks in the interface, it does make the relevant work flows easier. It will be interesting to see how the plugin develops.