===============
Committing code
===============

This section is addressed to the mergers and to anyone interested in knowing
how code gets committed into Django. The :ref:`committing-guidelines` apply
to all contributors, with or without commit rights.

If you're a community member who wants to contribute code to Django, look at
:doc:`/internals/contributing/writing-code/working-with-git` instead.

.. _handling-pull-requests:

Handling pull requests
======================

Since Django is hosted on GitHub, patches are provided in the form of pull
requests.

When committing a pull request, make sure each individual commit matches the
commit guidelines described below. Contributors are expected to provide the
best pull requests possible. In practice mergers - who will likely be more
familiar with the commit guidelines - may decide to bring a commit up to
standard themselves.

You may want to have Jenkins or GitHub actions test the pull request with one
of the pull request builders that doesn't run automatically, such as Oracle or
Selenium. See the `CI wiki page`_ for instructions.

.. _CI wiki page: https://code.djangoproject.com/wiki/CI

If you find yourself checking out pull requests locally more often, this git
alias will be helpful:

.. code-block:: ini

    [alias]
        pr = !sh -c \"git fetch upstream pull/${1}/head:pr/${1} && git checkout pr/${1}\"

Add it to your ``~/.gitconfig``, and set ``upstream`` to be ``django/django``.
Then you can run ``git pr ####`` to checkout the corresponding pull request.

At this point, you can work on the code. Use ``git rebase -i`` and ``git
commit --amend`` to make sure the commits have the expected level of quality.
Once you're ready:

.. console::

    $ # Pull in the latest changes from main.
    $ git checkout main
    $ git pull upstream main
    $ # Rebase the pull request on main.
    $ git checkout pr/####
    $ git rebase main
    $ git checkout main
    $ # Merge the work as "fast-forward" to main to avoid a merge commit.
    $ # (in practice, you can omit "--ff-only" since you just rebased)
    $ git merge --ff-only pr/XXXX
    $ # If you're not sure if you did things correctly, check that only the
    $ # changes you expect will be pushed to upstream.
    $ git push --dry-run upstream main
    $ # Push!
    $ git push upstream main
    $ # Delete the pull request branch.
    $ git branch -d pr/xxxx

Force push to the branch after rebasing on main but before merging and pushing
to upstream. This allows the commit hashes on main and the branch to match
which automatically closes the pull request.

If a pull request doesn't need to be merged as multiple commits, you can use
GitHub's "Squash and merge" button on the website. Edit the commit message as
needed to conform to :ref:`the guidelines <committing-guidelines>` and remove
the pull request number that's automatically appended to the message's first
line.

When rewriting the commit history of a pull request, the goal is to make
Django's commit history as usable as possible:

* If a patch contains back-and-forth commits, then rewrite those into one.
  For example, if a commit adds some code and a second commit fixes stylistic
  issues introduced in the first commit, those commits should be squashed
  before merging.

* Separate changes to different commits by logical grouping: if you do a
  stylistic cleanup at the same time as you do other changes to a file,
  separating the changes into two different commits will make reviewing
  history easier.

* Beware of merges of upstream branches in the pull requests.

* Tests should pass and docs should build after each commit. Neither the
  tests nor the docs should emit warnings.

* Trivial and small patches usually are best done in one commit. Medium to
  large work may be split into multiple commits if it makes sense.

Practicality beats purity, so it is up to each merger to decide how much
history mangling to do for a pull request. The main points are engaging the
community, getting work done, and having a usable commit history.

.. _committing-guidelines:

Committing guidelines
=====================

These guidelines apply to all commits to Django's Git repository, whether
submitted by a contributor via a pull request or landed directly by a merger:

* Never change the published history of ``django/django`` branches by force
  pushing. If you absolutely must (for security reasons for example), first
  discuss the situation with the team.

* For any medium-to-big changes, where "medium-to-big" is according to
  your judgment, please bring things up on the `Django Forum`_ before making
  the change.

  If you bring something up and nobody responds, please don't take that
  to mean your idea is great and should be implemented immediately because
  nobody contested it. Everyone doesn't always have a lot of time to read
  discussions immediately, so you may have to wait a couple of days before
  getting a response.

* Write detailed commit messages in the past tense, not present tense, and
  end the subject line with a period.

  * Correct: "Fixed Unicode bug in RSS API."
  * Incorrect: "Fixes Unicode bug in RSS API." (present tense)
  * Incorrect: "Fixing Unicode bug in RSS API." ("-ing" form)
  * Incorrect: "Fixed Unicode bug in RSS API" (missing trailing period)

  The commit message should be in lines of 72 chars maximum. There should be
  a subject line, separated by a blank line and then paragraphs of 72 char
  lines. The limits are soft. For the subject line, shorter is better.

  In the body of the commit message more detail is better than less, and should
  explain *why* the change was made, not *what* was changed or *how*. The code
  itself shows what changed; the commit message should provide the context and
  reasoning that the code cannot.

  Credit the contributors in the commit message: "Thanks A for the report and B
  for review." Use git's `Co-Authored-By`_ as appropriate, including anyone
  whose earlier work the change builds on.

  For example:

  .. code-block:: none

      Fixed #18307 -- Added git workflow guidelines.

      Refactored the Django's documentation to remove mentions of SVN
      specific tasks. Added guidelines of how to use Git, GitHub, and
      how to use pull request together with Trac instead.

      Thanks to Full Name for the report, and to Reviewer for reviews.

  .. _Co-Authored-By: https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors

* Limit commits to the most granular change that makes sense. This means,
  use frequent small commits rather than infrequent large commits. For
  example, if implementing feature X requires a small change to library Y,
  first commit the change to library Y, then commit feature X in a separate
  commit. This goes a *long way* in helping everyone follow your changes.

* Separate bug fixes from feature changes. Bugfixes may need to be
  :ref:`backported <backports>`.

* If your commit closes a ticket in the Django `ticket tracker`_, begin
  your commit message with the text "Fixed #xxxxx", where "xxxxx" is the
  number of the ticket your commit fixes. Example: "Fixed #123 -- Added
  whizbang feature.". We've rigged Trac so that any commit message in that
  format will automatically close the referenced ticket and post a comment
  to it with the full commit message.

  For the curious, we're using a `Trac plugin`_ for this.

.. note::

    Note that the Trac integration doesn't know anything about pull requests.
    So if you try to close a pull request with the phrase "closes #400" in your
    commit message, GitHub will close the pull request, but the Trac plugin
    will not close the same numbered ticket in Trac.

.. _Trac plugin: https://github.com/trac-hacks/trac-github

* If your commit references a ticket in the Django `ticket tracker`_ but
  does *not* close the ticket, include the phrase "Refs #xxxxx", where "xxxxx"
  is the number of the ticket your commit references. This will automatically
  post a comment to the appropriate ticket.

.. _backports:

Backports
=========

Bug fix backports to stable branches are done exclusively by mergers, following
the :ref:`supported-versions-policy`. A backport consists of cherry-picking a
commit from ``main`` onto the target ``stable/A.B.x`` branch.

A backport commit must include two things beyond the original commit message:

* A prefix ``[A.B.x]`` on the subject line, where ``A.B.x`` is the name of the
  ``stable/A.B.x`` branch being targeted.

* A suffix ``Backport of <sha> from main.`` line in the commit body, pointing
  to the original commit hash.

For example:

.. code-block:: none

    [1.3.x] Fixed #17028 -- Changed diveintopython.org -> diveintopython.net.

    Backport of 80c0cbf1c97047daed2c5b41b296bbc56fe1d7e3 from main.

If the backport also fixes a regression, add a line identifying the commit that
introduced it:

.. code-block:: none

    Regression in 6ecccad711b52f9273b1acb07a57d3f806e93928.

There are three ways to do a backport, depending on your workflow:

**Option 1: fully manual**

Cherry-pick the commit onto the stable branch, then amend the commit message to
add the required prefix and backport note:

.. code-block:: shell

    git cherry-pick <sha>
    git commit --amend

If the cherry-pick produces conflicts, resolve them, stage the changes, then
run ``git cherry-pick --continue`` before amending. This option requires no
setup but relies entirely on remembering to format the message correctly.

**Option 2: using the helper script in the repo**

The ``scripts/backport.sh`` Bash script automates the cherry-pick and rewrites
the commit message with the correct prefix and backport note. Run it from the
target stable branch:

.. code-block:: shell

    bash scripts/backport.sh <sha>

This is straightforward for clean cherry-picks, but if conflicts are produced,
you will need to resolve them manually and add the prefix and backport note to
the commit message yourself.

**Option 3: using the** ``prepare-commit-msg`` **git hook**

The ``scripts/prepare_commit_msg.py`` Python script can be installed as a
``prepare-commit-msg`` git hook. It automatically adds the ``[A.B.x]`` prefix
to the subject line, appends ``Backport of <sha> from main.`` to the commit
body, and ensures the subject line ends with a period, even when the
cherry-pick produces conflicts. To install it, create an executable file
``.git/hooks/prepare-commit-msg`` containing:

.. code-block:: sh

    #!/bin/sh
    exec python scripts/prepare_commit_msg.py "$@"

Once installed, a plain ``git cherry-pick <sha>`` on a stable branch is
sufficient; the hook handles the message formatting in all cases.

Reverting commits
=================

Nobody's perfect; mistakes will be committed.

But try very hard to ensure that mistakes don't happen. Just because we have a
reversion policy doesn't relax your responsibility to aim for the highest
quality possible. Really: double-check your work, or have it checked by
another merger **before** you commit it in the first place!

When a mistaken commit is discovered, please follow these guidelines:

* If possible, have the original author revert their own commit.

* Don't revert another author's changes without permission from the
  original author.

* Use git revert -- this will make a reverse commit, but the original
  commit will still be part of the commit history.

* If the original author can't be reached (within a reasonable amount
  of time -- a day or so) and the problem is severe -- crashing bug,
  major test failures, etc. -- then ask for objections on the `Django Forum`_
  then revert if there are none.

* If the problem is small (a feature commit after feature freeze,
  say), wait it out.

* If there's a disagreement between the merger and the reverter-to-be then try
  to work it out on the `Django Forum`_ . If an agreement can't be reached then
  it should be put to a vote.

* If the commit introduced a confirmed, disclosed security
  vulnerability then the commit may be reverted immediately without
  permission from anyone.

* The release branch maintainer may back out commits to the release
  branch without permission if the commit breaks the release branch.

* If you mistakenly push a topic branch to ``django/django``, delete it.
  For instance, if you did: ``git push upstream feature_antigravity``,
  do a reverse push: ``git push upstream :feature_antigravity``.

.. _ticket tracker: https://code.djangoproject.com/
.. _Django Forum: https://forum.djangoproject.com/
