Add section on keeping CI green (#1215)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Co-authored-by: Ezio Melotti <ezio.melotti@gmail.com>

getting-started/git-boot-camp.rst

@@ -476,9 +476,11 @@ You can read more about what to look for before accepting a change
 :ref:`here <committing>`.
 
 All pull requests have required checks that need to pass before a change
-can be merged. At any point, a core developer can schedule an automatic merge
-of the change by
-clicking the gray ``Enable auto-merge (squash)`` button. You will find
+can be merged. See :ref:`"Keeping CI green" <keeping-ci-green>` for some
+simple things you can do to help the checks turn green.
+
+At any point, a core developer can schedule an automatic merge of the change
+by clicking the gray ``Enable auto-merge (squash)`` button. You will find
 it at the bottom of the pull request page. The auto-merge will only
 happen if all the required checks pass, but the PR does not need to have been
 approved for a successful auto-merge to take place.

getting-started/pull-request-lifecycle.rst

@@ -41,8 +41,8 @@ Here is a quick overview of how you can contribute to CPython:
 
 #. `Create Pull Request`_ on GitHub to merge a branch from your fork
 
-#. Make sure the continuous integration checks on your Pull Request
-   are green (i.e. successful)
+#. Make sure the :ref:`continuous integration checks on your Pull Request
+   are green <keeping-ci-green>` (i.e. successful)
 
 #. Review and address `comments on your Pull Request`_
 
@@ -472,7 +472,7 @@ code and leave comments in the pull request or issue tracker.
    'merge-ready', you should always make sure the entire test suite passes.
 
 Leaving a pull request review on GitHub
-=======================================
+---------------------------------------
 
 When you review a pull request, you should provide additional details and context
 of your review process.
@@ -487,14 +487,55 @@ Instead of simply "approving" the pull request, leave comments.  For example:
 #. Comment on what is "good" about the pull request, not just the "bad". Doing
    so will make it easier for the PR author to find the good in your comments.
 
+#. Look at any failures in CI on the current PR. See :ref:`"Keeping CI green"
+   <keeping-ci-green>` below for simple things you can do to help move the PR forward.
+
 Dismissing review from another core developer
-=============================================
+---------------------------------------------
 
 A core developer can dismiss another core developer's review if they confirmed
 that the requested changes have been made.  When a core developer has assigned
 the PR to themselves, then it is a sign that they are actively looking after
 the PR, and their review should not be dismissed.
 
+.. _keeping-ci-green:
+
+Keeping continuous integration green
+====================================
+
+Our change management workflows generally won't allow merging PRs with
+failures. Therefore, if you see a CI failure on a PR, have a look
+what it is about.
+
+Usually the failure will be directly related to the changes in the current
+PR. If you happen to have any insight into the failure, let the author know
+in a review comment. CI runs sometimes generate thousands of lines of output.
+Even something as simple as finding the traceback and putting it in the
+comment will be helpful to the PR author.
+
+If the failure doesn't look related to the change you're looking at, check
+if it's not present on the `Release Status`_ Buildbot dashboard as well.
+If so, that means the failure was introduced in a prior change. Using Buildbot's
+UI you can find which PR introduced the issue and comment that it
+affects other PRs.
+
+If you still don't see where the failure originates from, check for
+a "This branch is out-of-date with the base branch" sign next to the
+list of executed checks. Clicking "Update branch" next to this message
+will merge in the latest changes from the base branch into the PR.
+
+If this still doesn't help with the failure on the PR, you can try
+to re-run that particular failed check. Go to the red GitHub Action job,
+click on the "Re-run jobs" button on the top right, and select
+"Re-run failed jobs". The button will only be present when all other jobs
+finished running.
+
+Re-running failed jobs shouldn't be your first instinct but it is occasionally
+helpful because distributed systems can have intermittent failures, and
+some of our unit tests are sensitive to overloaded virtual machines.
+If you identify such flaky behavior, look for an issue in the `issue tracker`_
+that describes this particular flakiness. Create a new issue if you can't
+find one.
 
 Committing/rejecting
 ====================
@@ -522,3 +563,4 @@ accepts your pull request.
 
 .. _issue tracker: https://github.com/python/cpython/issues
 .. _Core Development Discourse category: https://discuss.python.org/c/core-dev/23
+.. _Release Status: https://buildbot.python.org/all/#/release_status

triage/triaging.rst

@@ -94,6 +94,7 @@ you can help by making sure the pull request:
 * includes a :ref:`NEWS entry <news-entry>` (if needed)
 * includes the author in ``Misc/ACKS``, either already or the patch adds them
 * doesn't have conflicts with the ``main`` branch
+* :ref:`doesn't have failing CI checks <keeping-ci-green>`
 
 Doing all of this allows core developers and :ref:`triagers <triage-team>`
 to more quickly look for subtle issues that only people with extensive