Mirror branches

A primary difference when using distributed workflows to develop is that your main local branch is not the place to make changes. Instead, it is kept as a pristine copy of the central branch, i.e. it’s a mirror branch.

To create a mirror branch, set-up a shared repository (if you haven’t already) and then use the branch (or checkout) command to create the mirror. For example:

bzr init-repo PROJECT
cd PROJECT
bzr branch sftp://centralhost/srv/bzr/PROJECT/trunk

Task branches

Each new feature or fix is developed in its own branch. These branches are referred to as feature branches or task branches - the terms are used interchangeably.

To create a task branch, use the branch command against your mirror branch. For example:

bzr branch trunk fix-123
cd fix-123
(hack, hack, hack)

There are numerous advantages to this approach:

1. You can work on multiple changes in parallel
2. There is reduced coupling between changes
3. Multiple people can work in a peer-to-peer mode on a branch until it is ready to go.

In particular, some changes take longer to cook than others so you can ask for reviews, apply feedback, ask for another review, etc. By completing work to sufficient quality in separate branches before merging into a central branch, the quality and stability of the central branch are maintained at higher level than they otherwise would be.

Refreshing a mirror branch

Use the pull command to do this:

cd trunk
bzr pull

Merging the latest trunk into a feature branch

Use the merge command to do this:

cd fix-123
bzr merge
(resolve any conflicts)
bzr commit -m "merged trunk"

Merging a feature into the trunk

The policies for different distributed workflows vary here. The simple case where all developers have commit rights to the main trunk are shown below.

If your mirror is a checkout:

cd trunk
bzr update
bzr merge ../fix-123
(resolve any conflicts)
bzr commit -m "Fixed bug #123"

If your mirror is a branch:

cd trunk
bzr pull
bzr merge ../fix-123
(resolve any conflicts)
bzr commit -m "Fixed bug #123"
bzr push

Backing up task branches

One of the side effects of centralized workflows is that changes get frequently committed to a central location which is backed up as part of normal IT operations. When developing on task branches, it is a good idea to publish your work to a central location (but not necessarily a shared location) that will be backed up. You may even wish to bind local task branches to remote ones established on a backup server just for this purpose.