Kotlin Programming Language
Welcome to Kotlin! Some handy links:
- Kotlin Site
- Getting Started Guide
- Try Kotlin
- Kotlin Standard Library
- Issue Tracker
- Kotlin Blog
- Follow Kotlin on Twitter
- Public Slack channel
- TeamCity CI build
Build environment requirements
In order to build Kotlin distribution you need to have:
Apache Ant 1.9.4 and higher
JDK 1.6, 1.7 and 1.8
Setup environment variables as following:
JAVA_HOME="path to JDK 1.6" JDK_16="path to JDK 1.6" JDK_17="path to JDK 1.7" JDK_18="path to JDK 1.8"
To build this project, first time you try to build you need to run this:
ant -f update_dependencies.xml
which will setup the dependencies on
- intellij-core: is a part of command line compiler and contains only necessary APIs.
- idea-full: is a full blown IntelliJ IDEA Community Edition to be used in former plugin module.
Then, you need to run
ant -f build.xml
which will build the binaries of the compiler and put them into the 'dist' directory. You may need to increase the heap size for Ant using ANT_OPTS.
OPTIONAL: Maven distribution is built separately, run
from 'libraries' directory after building the compiler. Refer to libraries/ReadMe.md for details.
Working with the project in IntelliJ IDEA
The root kotlin project already has an IntelliJ IDEA project, you can just open it in IntelliJ IDEA.
You may need to set the Project SDK (File -> Project Structure -> Project).
You may also need to add
tools.jar to your SDK: File -> Project Structure -> SDKs -> -> Classpath,
then choose the
tools.jar in the JDK's
If you are not dealing with Android, you may need to disable the Android Plugin in order to compile the project.
Since Kotlin project contains code written in Kotlin itself, you will also need a Kotlin plugin to build the project in IntelliJ IDEA. To keep the plugin version in sync with the rest of the team and our Continuous Integration server you should install the according to the instructions below.
If you want to have an IntelliJ IDEA installation without the Kotlin plugin which is separate to your default IntelliJ IDEA installation which has the Kotlin plugin see this document which describes how to have multiple IntelliJ IDEA installations using different configurations and plugin directories.
From this root project there are Run/Debug Configurations for running IDEA or the Compiler Tests for example; so if you want to try out the latest and greatest IDEA plugin
- VCS -> Git -> Pull
- Run IntelliJ IDEA
- a child IntelliJ IDEA with the Kotlin plugin will then startup
- you can now open the kotlin libraries project to then work with the various kotlin libraries etc.
There are several options for getting Kotlin plugin. A stable version can be obtained as any other plugin for IntelliJ IDEA:
Preferences -> Plugins -> Install JetBrains plugin... -> Search with "Kotlin" string
The most recent version of the plugin can be downloaded from the IDEA Plugin and Tests CI build. When downloading is finished you can install it with "Install plugin from disk...":
Preferences -> Plugins -> Install plugin from disk...
You can now open any Kotlin based projects.
Note for contributors: If you are planning to contribute to Kotlin project you probably want to have locally the same version of plugin that build server is using for building. As this version is constantly moving, the best way to always be updated is to let IntelliJ IDEA notify you when it is time to renew your plugin.
Preferences -> Plugins -> Browse Repositories -> Manage Repositories...
and add the following URL to your repositories:
Then update the list of plugins in "Browse Repositories", you'll see two versions of Kotlin there, install the one with the higher version number.
We love contributions! There's lots 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 Kotlin issues that 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
This is implemented using the
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.
If you want to work on the compiler
The Kotlin compiler is written in Java and Kotlin (we gradually migrate more and more of it to pure Kotlin). So the easiest way to work on the compiler or IntelliJ IDEA plugin is
- download a clean IDEA 15 EAP build
- install the Kotlin plugin
- open the root kotlin project in IDEA (opening the kotlin directory)
You can now run the various Run/Debug Configurations such as
- All Compiler Tests
- All IDEA Plugin Tests
If you want to work on the Kotlin libraries
Then build via
cd libraries mvn install
Some of the code in the standard library is created by generating code from templates. See the README in the stdlib section for how run the code generator. The existing templates can be used as examples for creating new ones.
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.
If you include in your comment this text (where KT-1234 is the Issue ID in the Issue Tracker, the issue will get automatically marked as fixed.