kotlin  1.3.30
About: Kotlin is a Java like statically typed programming language for the JVM, Android and the browser. Source code.
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kotlin Documentation

official project TeamCity (simple build status) Maven Central GitHub license

Kotlin Programming Language

Welcome to Kotlin! Some handy links:

Editing Kotlin

Build environment requirements

In order to build Kotlin distribution you need to have:

  • JDK 1.6, 1.7, 1.8 and 9
  • Setup environment variables as following:
      JAVA_HOME="path to JDK 1.8"
      JDK_16="path to JDK 1.6"
      JDK_17="path to JDK 1.7"
      JDK_18="path to JDK 1.8"
      JDK_9="path to JDK 9"

For local development, if you're not working on bytecode generation or the standard library, it's OK to have only JDK 1.8 and JDK 9 installed, and to point JDK_16 and JDK_17 environment variables to your JDK 1.8 installation.

You also can use Gradle properties to setup JDK_* variables.

Note: The JDK 6 for MacOS is not available on Oracle's site. You can download it here.


The project is built with Gradle. Run Gradle to build the project and to run the tests using the following command on Unix/macOS:

./gradlew <tasks-and-options>

or the following command on Windows:

gradlew <tasks-and-options>

On the first project configuration gradle will download and 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 the plugin module.

These dependencies are quite large, so depending on the quality of your internet connection you might face timeouts getting them. In this case you can increase timeout by specifying the following command line parameters on the first run:

./gradlew -Dhttp.socketTimeout=60000 -Dhttp.connectionTimeout=60000

Important gradle tasks

  • clean - clean build results
  • dist - assembles the compiler distribution into dist/kotlinc/ folder
  • ideaPlugin - assembles the Kotlin IDEA plugin distribution into dist/artifacts/Kotlin folder
  • install - build and install all public artifacts into local maven repository
  • runIde - build IDEA plugin and run IDEA with it
  • coreLibsTest - build and run stdlib, reflect and kotlin-test tests
  • gradlePluginTest - build and run gradle plugin tests
  • compilerTest - build and run all compiler tests
  • ideaPluginTest - build and run all IDEA plugin tests

OPTIONAL: Some artifacts, mainly Maven plugin ones, are built separately with Maven. Refer to libraries/ReadMe.md for details.

Building for different versions of IntelliJ IDEA and Android Studio

Kotlin plugin is intended to work with several recent versions of IntelliJ IDEA and Android Studio. Each platform is allowed to have a different set of features and might provide a slightly different API. Instead of using several parallel Git branches, project stores everything in a single branch, but files may have counterparts with version extensions (*.as32, *.172, *.181). The primary file is expected to be replaced with its counterpart when targeting non-default platform.

More detailed description of this scheme can be found at https://github.com/JetBrains/bunches/blob/master/ReadMe.md.

Usually, there's no need to care about multiple platforms as all features are enabled everywhere by default. Additional counterparts should be created if there's an expected difference in behavior or an incompatible API usage is required and there's no reasonable workaround to save source compatibility. Kotlin plugin contains a pre-commit check that shows a warning if a file has been updated without its counterparts.

Development for some particular platform is possible after 'switching' that can be done with Bunch Tool from the command line.

cd kotlin-project-dir
# switching to IntelliJ Idea 2018.2
bunch switch . 182

<a name="working-in-idea"></a> Working with the project in IntelliJ IDEA

Working with the Kotlin project requires at least IntelliJ IDEA 2017.3. You can download IntelliJ IDEA 2017.3 here.

After cloning the project, to import the project in Intellij choose the project directory in the Open project dialog. Then, after project opened, Select File -> New... -> Module from Existing Sources in the menu, and select build.gradle.kts file in the project's root folder.

In the import dialog, select use default gradle wrapper.

To be able to run tests from IntelliJ easily, check Delegate IDE build/run actions to Gradle and choose Gradle Test Runner in the Gradle runner settings after importing the project.

At this time, you can use the latest released 1.2.x version of the Kotlin plugin for working with the code. To make sure you have the latest version installed, use Tools | Kotlin | Configure Kotlin Plugin Updates and press "Check for updates now".

Compiling and running

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 the "IDEA" run configuration in the project
  • a child IntelliJ IDEA with the Kotlin plugin will then startup

Including into composite build

To include kotlin compiler into composite build you need to define dependencySubstitution for kotlin-compiler module in settings.gradle

includeBuild('/path/to/kotlin') {
dependencySubstitution {
substitute module('org.jetbrains.kotlin:kotlin-compiler') with project(':include:kotlin-compiler')


Please be sure to review Kotlin's contributing guidelines to learn how to help the project.