Django's Git flow

Jun 3, 2020 08:52 · 1079 words · 6 minute read django | git

The web framework for perfectionists with deadlines, and the version control system.

The web framework for perfectionists with deadlines, and the version control system.

Like pretty much every popular open source project nowadays, Django uses Git to manage its code base. It’s hosted on GitHub and you can see how new code gets merged into the repository.

There are plenty of ways to use Git, such as Gitflow or trunk-based development. Well, how does Django use Git?

Before jumping into that, I’d like to talk a bit about how Django manages the work on the code base.

As you can see, there’s no Issues tab on Django’s GitHub repository. Instead of GitHub Issues, Django uses Trac to manage tickets. Most of Django’s workflow is based around the concept of a ticket’s triage stages. The contributing guide has a nice diagram for that:

The triage process.

The triage process. (Django docs)

In short, the stages are:

  • Unreviewed: the ticket hasn’t been reviewed by anyone felt qualified to mark it as a valid issue, a viable feature, or invalid.
  • Accepted: the main stage. The ticket is valid. Some flags may be added to add more information, such as:
    • No flags: no patch has been submitted. Most likely, you can safely start writing the patch for it.
    • Has Patch: a patch has been submitted, waiting for review.
    • Has Patch + Needs …: the ticket and patch have been reviewed, and have been found to need further work. That can either be “Needs tests”, “Needs documentation”, or “Needs improvement”.
  • Ready For Checkin (RFC): the ticket has been reviewed by any member of the community (other than the one who submitted the patch) and found to be ready to be merged. A committer (people with commit access to Django’s main repository) needs to do a final review and merge it if it passes.

There is another stage Someday/Maybe for long term feature requests but it’s uncommon (hence not shown on the diagram). There are also other flags to describe a ticket, such as “Easy pickings”, “Component”, “Version”, etc. but I won’t go into details. You can read more about triaging tickets in Django’s docs.

Security issues aren’t handled on Trac. Instead, they should be reported to security@djangoproject.com.

Now, let’s get back to Git. In Django’s repository, you can see that there are several branches:

  • master: contains the main in-development code. This will be the next packaged release of Django. Most development activity is focused here.
  • stable/A.B.x: branches where release preparation work happens. They’re used for bugfix and security releases as necessary after the initial release of a feature version.

If you’re unfamiliar, Django’s versions are numbered in the form of A.B or A.B.C:

  • A.B is the feature release version number. Each version is mostly backwards-compatible with the previous release otherwise noted in the release notes. New version is released roughly every eight months.
  • C is the patch release version number, incremented for bugfix and security releases.

If you want to submit a patch for the first time, you’ll need to fork Django into your GitHub account and create a new branch. Most of the time, you’re writing a patch for a ticket. It’s common to use ticket_xxxxx as the name of your new branch. You should create the new branch from the branch you’re targeting. So, if you’re fixing a bug that still exists on the master branch, you should create your new branch from there.

Sometimes, you may need to write a patch for a specific (but still supported) feature release of Django. This may happen if the bug no longer exists on the master branch. If that’s the case, you should create your branch from the stable/A.B.x.

From there, you just need to write your patch and create a commit. Then, push the commit to your fork of the repository. After that, create a pull request to the target branch in Django’s main repository.

As with tickets, security patches should be submitted via email, not a Pull Request.

Once your pull request is made, you should update the Trac ticket with a link to the PR and add the appropriate flags (such as “Has patch”). Hopefully, folks from the Django community will review your patch and continue the triage process. You can continue adding commits and pushing them to your fork as needed, and the PR will be updated automatically.

When your pull request is ready to be merged, you would most likely be asked to squash your commits. If you’re unfamiliar with it, the committers would do it for you (very nice of them!).

Finally, a committer would merge your branch into the target branch. This is done with the rebase-and-merge strategy so that it’s merged without a merge commit. If it’s applicable, your commit(s) will be backported into the previous (still supported) feature release branches. If I’m not mistaken, this is done using Git’s cherry-pick feature. You don’t need to do anything for this, that’s the committer’s work. They’ll also reword the commit message with the [A.B.x] prefix to note that it’s a backport.

To illustrate, you can see the following graph of Django’s repository snapshot I took at the time of this writing.

You can see that commits like Fixed typo in docs/ref/templates/language.txt. was first seen on master, then it got backported into stable/3.1.x, stable/3.0.x, and stable/2.2.x. The “same” commit has different hashes on each branch for a number of reasons, including:

  • Each branch has diverged from master, so the parent commit of that typo fix is different.
  • The commit message is different (the backports have the [A.B.x] prefix).
  • The commit timestamp is different (based on the time the committer did cherry-pick).

You can also see that not all patches get backported to other previous releases, such as Fixed #31643 -- Changed virtualenv doc references to Python 3 venv. that didn’t get backported to stable/2.2.x.

If your pull request has been merged, congratulations! Now, you just need to wait until the next release of Django to include your patch.

While it’s often the case, a pull request does not need to be associated with a ticket. If you’re adding small improvements to the docs (fixing typos, etc.), you don’t need to write a ticket. You can also utilize GitHub’s draft PR feature to demonstrate a proof-of-concept and provide a more concrete look of your idea (while also discussing it on Trac and/or the django-developers mailing-list).

Now that you’ve understood how Django’s Git flow works, why not take on the tickets on Trac, and help your web framework grow? Your web framework needs you! ;)