Pull request guidelines

Pull requests (PRs) are the mechanism for contributing to Matplotlibs code and documentation.

Summary for PR authors

Note

  • We value contributions from people with all levels of experience. In particular if this is your first PR not everything has to be perfect. We'll guide you through the PR process.

  • Nevertheless, try to follow the guidelines below as well as you can to help make the PR process quick and smooth.

  • Be patient with reviewers. We try our best to respond quickly, but we have limited bandwidth. If there is no feedback within a couple of days, please ping us by posting a comment to your PR.

When making a PR, pay attention to:

  • Target the main branch.

  • Adhere to the Coding guidelines.

  • Update the documentation if necessary.

  • Aim at making the PR as "ready-to-go" as you can. This helps to speed up the review process.

  • It is ok to open incomplete or work-in-progress PRs if you need help or feedback from the developers. You may mark these as draft pull requests on GitHub.

  • When updating your PR, instead of adding new commits to fix something, please consider amending your initial commit(s) to keep the history clean. You can achieve this using

    git commit --amend --no-edit
    git push [your-remote-repo] [your-branch] --force-with-lease
    

See also Contributing for how to make a PR.

Summary for PR reviewers

Note

  • If you have commit rights, then you are trusted to use them. Please help review and merge PRs!

  • Be patient and kind with contributors.

Content topics:

  • Is the feature / bugfix reasonable?

  • Does the PR conform with the Coding guidelines?

  • Is the documentation (docstrings, examples, what's new, API changes) updated?

Organizational topics:

Detailed guidelines

Documentation

  • Every new feature should be documented. If it's a new module, don't forget to add a new rst file to the API docs.

  • Each high-level plotting function should have a small example in the Examples section of the docstring. This should be as simple as possible to demonstrate the method. More complex examples should go into a dedicated example file in the examples directory, which will be rendered to the examples gallery in the documentation.

  • Build the docs and make sure all formatting warnings are addressed.

  • See Writing documentation for our documentation style guide.

  • If your change is a major new feature, add an entry to doc/users/whats_new.rst.

  • If you change the API in a backward-incompatible way, please document it by adding a file in the relevant subdirectory of doc/api/next_api_changes/, probably in the behavior/ subdirectory.

Labels

  • If you have the rights to set labels, tag the PR with descriptive labels. See the list of labels.

Milestones

  • Set the milestone according to these rules:

    • New features and API changes are milestoned for the next minor release v3.X.0.

    • Bugfixes and docstring changes are milestoned for the next patch release v3.X.Y

    • Documentation changes (all .rst files and examples) are milestoned v3.X-doc

    If multiple rules apply, choose the first matching from the above list.

    Setting a milestone does not imply or guarantee that a PR will be merged for that release, but if it were to be merged what release it would be in.

    All of these PRs should target the main branch. The milestone tag triggers an automatic backport for milestones which have a corresponding branch.

Merging

  • Documentation and examples may be merged by the first reviewer. Use the threshold "is this better than it was?" as the review criteria.

  • For code changes (anything in src or lib) at least two core developers (those with commit rights) should review all pull requests. If you are the first to review a PR and approve of the changes use the GitHub 'approve review' tool to mark it as such. If you are a subsequent reviewer please approve the review and if you think no more review is needed, merge the PR.

    Ensure that all API changes are documented in a file in one of the subdirectories of doc/api/next_api_changes, and significant new features have an entry in doc/user/whats_new.

    • If a PR already has a positive review, a core developer (e.g. the first reviewer, but not necessarily) may champion that PR for merging. In order to do so, they should ping all core devs both on GitHub and on the dev mailing list, and label the PR with the "Merge with single review?" label. Other core devs can then either review the PR and merge or reject it, or simply request that it gets a second review before being merged. If no one asks for such a second review within a week, the PR can then be merged on the basis of that single review.

      A core dev should only champion one PR at a time and we should try to keep the flow of championed PRs reasonable.

  • Do not self merge, except for 'small' patches to un-break the CI or when another reviewer explicitly allows it (ex, "Approve modulo CI passing, may self merge when green").

Automated tests

Whenever a pull request is created or updated, various automated test tools will run on all supported platforms and versions of Python.

  • Make sure the Linting, GitHub Actions, AppVeyor, CircleCI, and Azure pipelines are passing before merging (All checks are listed at the bottom of the GitHub page of your pull request). Here are some tips for finding the cause of the test failure:

    • If Linting fails, you have a code style issue, which will be listed as annotations on the pull request's diff.

    • If a GitHub Actions or AppVeyor run fails, search the log for FAILURES. The subsequent section will contain information on the failed tests.

    • If CircleCI fails, likely you have some reStructuredText style issue in the docs. Search the CircleCI log for WARNING.

    • If Azure pipelines fail with an image comparison error, you can find the images as artifacts of the Azure job:

      • Click Details on the check on the GitHub PR page.

      • Click View more details on Azure Pipelines to go to Azure.

      • On the overview page artifacts are listed in the section Related.

  • Codecov and LGTM are currently for information only. Their failure is not necessarily a blocker.

  • tox is not used in the automated testing. It is supported for testing locally.

  • If you know your changes do not need to be tested (this is very rare!), all CIs can be skipped for a given commit by including [ci skip] or [skip ci] in the commit message. If you know only a subset of CIs need to be run (e.g., if you are changing some block of plain reStructuredText and want only CircleCI to run to render the result), individual CIs can be skipped on individual commits as well by using the following substrings in commit messages:

    • GitHub Actions: [skip actions]

    • AppVeyor: [skip appveyor] (must be in the first line of the commit)

    • Azure Pipelines: [skip azp]

    • CircleCI: [skip circle]

Number of commits and squashing

  • Squashing is case-by-case. The balance is between burden on the contributor, keeping a relatively clean history, and keeping a history usable for bisecting. The only time we are really strict about it is to eliminate binary files (ex multiple test image re-generations) and to remove upstream merges.

  • Do not let perfect be the enemy of the good, particularly for documentation or example PRs. If you find yourself making many small suggestions, either open a PR against the original branch, push changes to the contributor branch, or merge the PR and then open a new PR against upstream.

  • If you push to a contributor branch leave a comment explaining what you did, ex "I took the liberty of pushing a small clean-up PR to your branch, thanks for your work.". If you are going to make substantial changes to the code or intent of the PR please check with the contributor first.

Branches and backports

Current branches

The current active branches are

main

The current development version. Future minor releases (v3.N.0) will be branched from this. Supports Python 3.7+.

v3.N.x

Maintenance branch for Matplotlib 3.N. Future patch releases will be branched from this. Supports Python 3.6+.

v3.N.M-doc

Documentation for the current release. On a patch release, this will be replaced by a properly named branch for the new release.

Branch selection for pull requests

Generally, all pull requests should target the main branch.

Other branches are fed through automatic or manual. Directly targeting other branches is only rarely necessary for special maintenance work.

Backport strategy

We will always backport to the patch release branch (v3.N.x):

  • critical bug fixes (segfault, failure to import, things that the user can not work around)

  • fixes for regressions against the last two releases.

Everything else (regressions against older releases, bugs/api inconsistencies the user can work around in their code) are on a case-by-case basis, should be low-risk, and need someone to advocate for and shepherd through the backport.

The only changes to be backported to the documentation branch (v3.N.M-doc) are changes to doc, examples, or tutorials. Any changes to lib or src including docstring-only changes should not be backported to this branch.

Automated backports

We use meeseeksdev bot to automatically backport merges to the correct maintenance branch base on the milestone. To work properly the milestone must be set before merging. If you have commit rights, the bot can also be manually triggered after a merge by leaving a message @meeseeksdev backport to BRANCH on the PR. If there are conflicts meeseekdevs will inform you that the backport needs to be done manually.

The target branch is configured by putting on-merge: backport to TARGETBRANCH in the milestone description on it's own line.

If the bot is not working as expected, please report issues to Meeseeksdev.

Manual backports

When doing backports please copy the form used by meeseekdev, Backport PR #XXXX: TITLE OF PR. If you need to manually resolve conflicts make note of them and how you resolved them in the commit message.

We do a backport from main to v2.2.x assuming:

  • matplotlib is a read-only remote branch of the matplotlib/matplotlib repo

The TARGET_SHA is the hash of the merge commit you would like to backport. This can be read off of the GitHub PR page (in the UI with the merge notification) or through the git CLI tools.

Assuming that you already have a local branch v2.2.x (if not, then git checkout -b v2.2.x), and that your remote pointing to https://github.com/matplotlib/matplotlib is called upstream:

git fetch upstream
git checkout v2.2.x  # or include -b if you don't already have this.
git reset --hard upstream/v2.2.x
git cherry-pick -m 1 TARGET_SHA
# resolve conflicts and commit if required

Files with conflicts can be listed by git status, and will have to be fixed by hand (search on >>>>>). Once the conflict is resolved, you will have to re-add the file(s) to the branch and then continue the cherry pick:

git add lib/matplotlib/conflicted_file.py
git add lib/matplotlib/conflicted_file2.py
git cherry-pick --continue

Use your discretion to push directly to upstream or to open a PR; be sure to push or PR against the v2.2.x upstream branch, not main!