What this repository is

This repository contains sources of:

Kotlin compiler: frontend and jvm, js, wasm and native backends.
Plugins extending compiler functionality.
Kotlin standard library and others including
- kotlin-test
- kotlinx-metadata
- kotlin-reflect
Build systems support: Gradle (incl. Dukat), Maven, JPS and Ant.
Kotlin scripting support.

What this repository is not

There are other activities around the language residing in different repositories.

Kotlin language support in IntelliJ Kotlin plugin comprising the compiler and IDE specifics (code highlighting, intentions, inspections, refactorings, etc.).
Starting from IntelliJ version 2021.2 its code is a part of JetBrains/intellij repository.
Platforms 2021.1 and earlier get plugin built from JetBrains/intellij-kotlin.

Contributing

We love contributions! There is a lot to do on Kotlin and on the standard library so why not chat with us about what you're interested in doing? Please join the #kontributors channel in our Slack chat and let us know about your plans.

If you want to find some issues to start off with, try this query which should find all open Kotlin issues that are marked as "up-for-grabs".

Currently only committers can assign issues to themselves so just add a comment if you're starting work on it.

A nice gentle way to contribute would be to review the standard library docs and find classes or functions which are not documented very well and submit a patch.

In particular, it'd be great if all functions included a nice example of how to use it such as for the hashMapOf() function. This is implemented using the @sample macro to include code from a test function. The benefits of this approach are twofold; First, the API's documentation is improved via beneficial examples that help new users and second, the code coverage is increased.

Some of the code in the standard library is created by generating code from templates. See the README in the stdlib section for how to run the code generator. The existing templates can be used as examples for creating new ones.

Also the JavaScript back-end could really use your help. See the JavaScript contribution section for more details.

You can also contribute to Kotlin/Native.

If you want to contribute a new language feature, it is important to discuss it through a KEEP first and get an approval from the language designers. This way you'll make sure your work will be in line with the overall language evolution plan and no other design decisions or considerations will block its acceptance.

Submitting patches

The best way to submit a patch is to fork the project on GitHub and then send us a pull request to the master branch via GitHub.

If you create your own fork, it might help to enable rebase by default when you pull by executing

git config --global pull.rebase true

This will avoid your local repo having too many merge commits which will help keep your pull request simple and easy to apply.

Rules for commit messages

Most of these rules are originated from the How to Write a Git Commit Message article, and it's highly recommended to read it.

Rules on commit messages' content

Use the body to explain what and why vs. how
- Please make an extra effort to explain why changes are needed for every non-trivial modification.
Significant commits must mention relevant YouTrack issues in their messages
Commit changes together with the corresponding tests, unless the resulting commit becomes too unwieldy to grasp
Try to avoid commits like "Fixes after review" whenever it's possible and squash them with meaningful ones instead
Keep the subject (first line of the commit message) clean and readable. All additional information and directives for external tools should be moved to the message body.
If you mention “^KTIJ-235 Fixed” in the message body - then the VCS integration will add Fix in Builds field to the issue in the YouTrack and automatically mark issue as fixed. For details see YouTrack Integrations and Apply Commands in VCS Commits.

Rules on commit messages' style/formatting

Separate subject from body with a blank line
Capitalize the subject line
Do not end the subject line with a period
Use the imperative mood in the subject line
Limit the commit messages lines to 72 characters
- Use “Commit Message Inspections” in IntelliJ IDE Settings -> Version Control -> Commit
- vim: autocmd FileType gitcommit setlocal textwidth=72

Checklist

Before submitting the pull request, make sure that you can say "YES" to each point in this short checklist:

You provided the link to the related issue(s) from YouTrack
You made a reasonable amount of changes related only to the provided issues
You can explain changes made in the pull request
You ran the build locally and verified new functionality
You ran related tests locally and they passed
You do not have merge commits in the pull request