Version Control Workflow

Havoc: we are looking at ways to better integrate version control in Launchpad. There are many areas that could benefit from better use of version control, but I'll focus on bug tracking since you mentioned it.

Take the attachment handling in Bugzilla, for instance. In non-ancient versions, you can attach statuses to attachments such as "obsolete" (which has some special handling in the UI — striking out obsolete attachments and making it easy to mark attachments as obsolete when uploading a new attachment). This makes it easy to track and manage a sequence of patches as a fix for a bug is developed (bug 118372 is a metacity bug with such a chain of patches).

If you look at this from a version control perspective, this sequence of patches forms a branch off the mainline of the software, where each newly attached patch is a new revision. The main differences being:

  • No explicit indication of what the patch was made against (code base or revision), or what options were used to create the patch.
  • No linkage between successive patches (can be a bit confusing if multiple patch series are attached to the same bug report).

So why not just use real version control to manage patches in the bug tracker? The big reason for projects using CVS or Subversion is that only authenticated users can create branches in the repository, and you don't want to require contributors to ask permission before submitting fixes.

So this is an area where a distributed version control system can help: anyone can make a branch, so potential contributors don't need permission to begin working on a bug. This also has the benefit that the contributors get access to the same tools as the developers (which is also helpful if they ever become a regular developer).

Now if you combine this with history sensitive merging and tell the bug tracker what the mainline branches of the products are, you can do some useful things:

  • Try and merge the changes from the bug fix branch onto the mainline, and see if it merges cleanly. This can tell a developer at a glance whether the patch has bitrotted. This could also be used to produce an up to date diff to the mainline, which can aid review of the changes.
  • Check if the bug fix branch has been merged into the mainline. No need for developers to manually flag the attachment as such.

We discussed some of these features in the context of Launchpad at the recent Brazil meeting.