PR workflow

Making a pull request

If you want to contribute code that implements a solution or feature, the workflow is as follows:

  1. Fork the Arbor repository.

  2. Create a branch off of master and implement your feature.

  3. Make a pull request (PR) and refer to the issue(s) that the PR addresses. Some tips on how to write a good PR description:

    • You can use labels to categorize your PR. For very large PRs, it is likely the reviewer will have many questions and comments. It can be helpful to reach out on our Slack, Discussions or by email beforehand if you’ve big things planned for Arbor!

    • Commit logical units with clear commit messages.

    • Add a change summary to the PR message. If you remembered to commit logical units, this could simply be a bulleted list of all commit messages in the PR. If during the review process you make changes to the features in the PR, keep the PR description updated.

    • Use text like fixes #123 in the description to refer to an issue.

  4. We will accept contributions licensed with the same BSD 3-Clause “New” or “Revised” License, as the Arbor project. If this is a problem for you, please contact us at

  5. A PR on Github is automatically built and tested by GitHub Actions CI pipelines. You can run these tests yourself by building them first (make tests) and then running them (./bin/*unit*).

    • If you make changes effecting simulations on GPUs, you can post a reply to your PR with bors try, which will run the test-suite with GPU and MPI enabled on Piz Daint.

  6. A member of the Arbor development team will review your contribution. If they approve, your PR will be merged! Normally this should happen within a few days.

Refer to the Github documentation for more explanation of the Git workflow described above.

Reviewing a PR

Each pull request is reviewed according to these guidelines:

  • At least one core Arbor team member needs to mark your PR with a positive review.

  • GitHub Actions CI must produce a favourable result on your PR.

  • An Arbor team member will (squash) merge the PR with the PR change summary as commit message.

  • Consider using Gitpod to review larger PRs, see under checks on the Github PR page.

Merging a PR

  • Use PR comment as commit message and verify it covers the changes in the PR.

  • ONLY squash-and-merge (Github should not allow anything else anymore).

  • The creator of a pull request should not review or merge their own pull request.

  • A reviewer can merge if their own review is favourable and other criteria are met.

  • A reviewer can poke another Arbor core team member to do the merge.