Welcome to the Mojo community! 🔥 We’re very excited that you’re interested in contributing to the project. To help you get started and ensure a smooth process, we’ve put together this contributor guide.
There are many ways to contribute to the project, from joining the Discord community, to filing bugs, to contributing documentation, examples, or code.
To ensure a streamlined process, contributors are encouraged to focus on enhancements, bug fixes, and optimizations aligned with the library's overarching goals. These guidelines aim to facilitate a collaborative environment where contributors and the standard library team can work together effectively toward the continued improvement of Mojo.
For more information on our priorities, see the following documents:
- Our Vision document describes the guiding principles behind our development efforts.
- Our Roadmap identifies concrete development goals as we work towards an even more robust and feature-rich standard library.
For technical details on developing for the standard library, see the following documents:
- Developing the standard library covers building, testing, and other information you’ll need to work in the standard library.
- Coding Standards and Style Guide provides guidelines for writing code for the standard library.
These changes are uncontroversial, easier to review, and more likely to be accepted:
- Well-documented bug fixes submitted with code reproducing the issue in a test or benchmark.
- Performance improvements that don’t sacrifice code readability or maintainability and are accompanied by benchmarks.
- Improvements to stdlib documentation or that expand on it.
- Improvements to the test coverage.
- Porting of tests from
FileCheckto usingassert_*functions from thetestingmodule. - Changes that address security vulnerabilities.
If you’re interested in making a more significant change, we ask that you first go through our proposal process.
Changes that don’t align with our vision and roadmap are unlikely to be accepted. For example:
- Changes that do not align with the published roadmap or the core principles of the standard library.
- Changes to the math module until more thorough performance benchmarking is available.
- Code without tests—especially for core primitives.
- Changes that break existing API or implicit behavior semantics.
- Changes where the contributors’ favorite feature or system isn’t being used and they submit a change unilaterally switching the project to use it. For example, the contributor doesn’t like CMake as a build system and submits a PR changing the repository to use their favorite build system.
- Adding support for esoteric platforms.
- Adding dependencies to the code base.
- Broad formatting or refactoring changes.
- Changes that need broad community consensus.
- Changes if contributors are not responsive.
- Adding an entire new module without going through the RFC/proposal process.
We ask that contributors make pull requests as small as possible. When you are opening a pull request, check the number of lines modified in GitHub. The smaller the better (but don't exclude the tests or docstrings). If your pull request is over 100 lines, please try to split it into multiple pull requests. If you make them independent, it's even better as no synchronization will be needed for the merge.
This guideline is here for the following reasons:
- Higher quality reviews: It is much easier to spot a bug in a few lines than in 1000 lines.
- Faster overall review: Reviewers, to approve a pull request, need to understand every line and understand how it fits into your overall change. They also need to go back and forth between files and functions to understand the flow of the code. This is exponentially hard as there are more lines in the code.
- Avoiding blocking changes that are valid: In a huge pull request, it's likely that some changes are valid and some need to be reworked/discussed. If all the changes are in the same pull request, then the valid changes will be blocked until all discussions have been resolved.
- Reducing the number of git conflicts: Bigger pull request means slower reviews, thus means that the pull request will be open longer and will have more git conflicts to be resolved before being merged.
- Parallel processing: All programmers like to parallelize. Well, reviewers also like to parallelize code reviews to merge your code faster. If you open two pull requests that are independent, then two reviewers will be able to work on your code.
- Finding the time for a code review: Doing a code review often requires that the code is reviewed in one go, as it's hard to remember functions and code logic from one review session to another. Thus a big pull request will require the reviewer to allocate a big chunk of time to do the code review, which is not always possible and might delay the review and merge of your pull request for multiple days.
Smaller pull requests means less work for the maintainers and faster reviews and merges for the contributors. It's a win-win!
If you’re interested in making a significant change—one that doesn’t fall into the list of “Changes we accept,” your first step is a written proposal. The proposals process ensures feedback from the widest possible set of community members and serves as an audit log of past proposal changes with most importantly the rationale behind it.
Proposals consist of a GitHub Pull Request that adds a
document to the proposals/ directory. Contributors are
encouraged to react with a thumbs-up to proposal PRs if they are generally
interested and supportive of the high-level direction. These are assigned to
Mojo standard library leads to decide. The proposal PR can be merged once the
assigned lead approves, all blocking issues have been decided, and any related
decisions are incorporated. If the leads choose to defer or reject the proposal,
the reviewing lead should explain why and close the PR.
This process is heavily inspired by the process used by several other open-source projects. We’ll add more documentation in the future as we gain experience with the process.
For details about how to submit a pull request, see the repo's primary contributing guide.
Thank you for your contributions! ❤️