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Contributing to

Thanks for taking the time to contribute to!

Contributing is not limited to writing code and submitting a PR. Feel free to submit an issue or comment on an existing one to report a bug, provide feedback, or suggest a new feature. You can also join us on GitHub Discussions.

Of course, contributing code is more than welcome! If you're planning to submit a PR to implement a new feature or fix a bug, please open an issue that explains the change and the motivation for it.

If you are interested in contributing documentation, please note the following:

  • Doc issues are labeled with the doc label.
  • The docs content is in the docs/src/ directory.

How to build from source.

Pull request and git commit guidance

To assure a consistent level of quality and appearance, the project has some rules for contributors to follow.

Opening PRs and organizing commits

PRs should generally address only 1 issue at a time. If you need to fix two bugs, open two separate PRs. This will keep the scope of your pull requests smaller and allow them to be reviewed and merged more quickly.

When possible, fill out as much detail in the pull request template as is reasonable. Most important is to reference the GitHub issue that you are addressing with the PR.

NOTE: GitHub has a feature that will automatically close issues referenced with a keyword (such as "Fixes") by a PR or commit once the PR/commit is merged. Don't use these keywords. We don't want issues to be automatically closed. We want our testers to independently verify and close them.

Writing good commit messages

Having clear, concise and well-written commit messages for all changes is not only an indicator for the seriousness of the project, but also a way to ensure sustainable development via replicability of the sources of the project.

Because of this, we try to ensure the highest possible quality for each individual commit message.

Because such a thing cannot necessarily or in full be enforced via tooling, it remains mainly the obligation of a reviewer of a change-set to ensure

  • Atomicity of the individual commits
  • that one commit is one atomic change, and not an accumulation of several individual and separate changes
  • that the commit message of the change expresses why the change was made

Every reviewer of a pull request is asked to review not only the changes, but also the commit messages. Reviewers are explicitly empowered and actually encouraged to block pull requests that contain commit messages that do not meet a certain standard even and especially also if the proposed changes are acknowledged.

The contributor should document why they implemented a change. A good rule of thumb is that if a change is larger than 60 lines, a commit message without a body won't suffice anymore. The more lines are touched by an individual commit, the more lines should be used to explain the change.

Also, some hard criteria are checked via github action lints:

  • The Signed-off-by trailer lint must be present in all commits (also see section "Ensuring the Signed-off-by-trailer")
  • The commit body must meet the default formatting of a commit message, that is
    • Subject line not longer than 50 characters
    • Subject capitalized
    • No period at the end of the subject
    • Imperative mood in the subject
    • Second line empty
    • Body lines not longer than 72 characters

You can also read about commit messages in this excellent guide.

Commits using the --fixup or --squash feature of git-commit are allowed, but will have to be squashed by the pull request author before being merged.

Ensuring the Signed-off-by-trailer

Contributors need to sign the "Contributor License Agreement". They do so by signing off each individual commit with a so-called "Signed-off-by Trailer". Git offers the --signoff/-s flags when using git-commit to commit changes.

To ensure that all commits have the trailer present in the commit message, a CI lint is installed in the github actions workflows of the project. This lint blocks pull requests from being merged if one or more of the commits of the pull request misses the Signed-off-by trailer.

As a result, it is not possible to merge pull requests that miss the trailer.

Coding style, Documentation, Testing

Coding style is enforced via rustfmt in its default configuration. Compliance with the coding style is enforced via CI.

Source code documentation as well as other documentation is tested via github actions workflows as well, to ensure that a developer is able to build all relevant documentation on their local machine.

Testing is done via workflows in github actions using cargo test --all-features for all crates. The main objective with this is that a developer should be able to simply run cargo test on their local machine to be able to see whether CI would succeed for changes they submit in a pull request. Thus, all CI tests (unit tests, but also integration tests) are implemented in Rust and do not rely on external services. End-to-end system tests - that depend on external services - are run outside the CI pipeline, to avoid inconsistent test outcomes because of external issues.

Reviewing, addressing feedback

Generally, pull requests need at least an approval from one maintainer to be merged.

When addressing review feedback, it is helpful to the reviewer if additional changes are made in new commits. This allows the reviewer to easily see the delta between what they previously reviewed and the changes you added to address their feedback. If applicable, the git commit --fixup=<sha> feature should be used. These fixup commits should then be squashed (usually git rebase -i --autosquash main) by the author of the PR after it passed review and before it is merged.

Pull request merging and evergreen-master

The project pursues the "evergreen master" strategy. That means that at every point in time, the commit that master/main points to must successfully build and pass all tests.

Because of that, merging is implemented in a certain way that forbids several bad practices which could lead to a breaking build on the master/main branch, and a special workflow is implemented to ensure not only the "evergreen master" but also to streamline the workflow for integrating pull requests.

The following actions are not allowed:

  • Committing to master/main directly. The GitHub repository is configured to block pushing to master/main.
  • Squash-Merging of pull requests (which is equivalent to committing to master/main directly). The github repository is configured to not allow squash merges.
  • Merging of "fixup!" or "squash!" commits. A github actions job is employed to block pull requests from being merged if such commits are in the branch of the pull request. Rebase should be used to clean those up.

It is explicitly not forbidden to have merge-commits in a pull request. Long-running pull requests that contain a large number of changes and are developed over a long period might contain merges. They might even merge master/main to get up-to-date with the latest developments. Though it is not encouraged to have such long-running pull requests and discouraged to merge master/main into a PR branch, the project acknowledges that sometimes it is not avoidable.

To summarize, the following requirements have to be met before a pull request can be merged:

  • Reviews of the relevant people (ensured via github setting)
  • Status checks (CI, lints, etc) (ensured via github setting)
    • builds, tests, lints are green (ensured via github action)
    • Commit linting (ensured via github action)
    • No missing Signed-off-by lines (ensured via github action)
    • No "fixup!"/"squash!" commits in the pull request (ensured via github action)

Merging itself is implemented via a "merge bot": bors-ng. bors-ng is used to prevent "merge skew" or "semantic merge conflicts" (read more here).

Dependency updates

Dependencies should be kept in sync over all crates in the project. That means that different crates of the project should try to use dependencies in the same versions, but also that dependencies should be harmonized in a way that a specific problem should not be solved with more than one external library at a time. Updates of dependencies is automated via a github bot (dependabot). To ensure harmonization of dependencies, a dedicated team (see "Team Structure") is responsible for keeping an eye on the list of dependencies.

License linting

License linting describes the act of checking the licenses of dependencies and whether they meet a certain criteria. For example, it is not feasible to import an external library that is licensed as GPL-3.0 in an Apache-2.0 licensed codebase. Because of this, a github action is installed to lint the licenses of dependencies. This action runs as a normal lint (see "evergreen master") and blocks pull requests if dependencies get imported that do not meet a set of rules agreed upon by the project maintainers.

Contributor License Agreement

We do not want to bother you with too much legalese, but there are two pages you have to read carefully, this page and the CONTRIBUTOR LICENSE AGREEMENT.


Each Contribution to Software AG's Open Source Projects must be accompanied by a sign-off indicating acceptance of current version of the CONTRIBUTOR LICENSE AGREEMENT, which is derived from the Apache Foundation's Individual Contributor License Agreement, sign-off time stamp relates to corresponding version of the CONTRIBUTOR LICENSE AGREEMENT maintained here on GitHub as well. Sign-Off and acceptance of the CONTRIBUTOR LICENSE AGREEMENT is declared by using the option "-s" in

git commit -s

which will automatically generate a sign-off statement in the form:

Signed-off-by: Max Mustermann <>

By adding this sign-off statement, you are certifying:

By signing-off on this Submission, I agree to be bound by the terms of the then current CONTRIBUTOR LICENSE AGREEMENT located at, which I have read and understood and I agree that this Submission constitutes a "Contribution" under this Agreement.

Note on Privacy

Please note that this project and any contributions to it are public and that a record of all contributions (including any personal information submitted with it, including a sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved.

In addition to GitHub's privacy statement extracting personal data from these projects for any other use than maintaining the projects and communication related to it is prohibited, explicitly prohibited is extracting email addresses for unsolicited bulk mails.

If you'd like to keep your personal email address private, you can use a GitHub-provided no-reply email address as your commit email address. You can choose which verified email address to author changes with when you edit, delete, or create files or merge a pull request on GitHub. If you enabled email address privacy, then the commit author email address cannot be changed and is <username> by default.

See setting your commit email address on GitHub.

In the upper-right corner of any page, click your profile photo, then click Settings.

  1. In the left sidebar, click Emails.
  2. In "Add email address", type your email address and click Add.
  3. Verify your email address.
  4. In the "Primary email address" list, select the email address you'd like to associate with your web-based Git operations.
  5. To keep your email address private when performing web-based Git operations, click Keep my email address private.
  6. You can use the git config command to change the email address you associate with your Git commits.

See setting your commit email address in Git.

  1. Open Git Bash.
  2. Set an email address in Git. You can use your GitHub-provided no-reply email addressor any email address. >$ git config --global ""
  3. Confirm that you have set the email address correctly in Git:

$ git config --global

  1. Add the email address to your account on GitHub, so that your commits are attributed to you and appear in your contributions graph.