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The Kotlin Programming Language
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.idea JPS Build: add type-system to kotlin-reflect.jar Apr 19, 2019
android-studio Prepare building plugins modules against 1.8 JDK Apr 4, 2016
annotations Remove KotlinSignature annotations from project code Oct 13, 2015
build-common Rename SourceFileToPathConverter->FileToPathConverter Apr 22, 2019
buildSrc Switch default for parallel execution Apr 18, 2019
compiler Rename SourceFileToPathConverter->FileToPathConverter Apr 22, 2019
docs Add a point about invalidated state between inspection checks and qui… Apr 2, 2019
generators Disable scripting plugin in JPS tests Apr 22, 2019
idea-runner Build: exclude annotations.jar from Intellij Feb 27, 2019
idea Include FIR modules into compiler #KT-30243 Fixed Apr 22, 2019
include JPS Build: exclude :core:builtins, use prebuilt bootstrap version Mar 28, 2019
j2k Fix "Should be replaced with Kotlin function" warnings Apr 18, 2019
jps-plugin Rename SourceFileToPathConverter->FileToPathConverter Apr 22, 2019
js Parallelize compiler tests Apr 18, 2019
libraries [JS IR BE] Workaround for println Apr 22, 2019
license Add the whole content of the Apache 2.0 license to the Kotlin repo Mar 20, 2019
nj2k Fix "Should be replaced with Kotlin function" warnings Apr 18, 2019
plugins Parallelize compiler tests Apr 18, 2019
prepare Include FIR modules into compiler #KT-30243 Fixed Apr 22, 2019
resources Inline some properties from that were used … May 5, 2017
third-party KT-29586: Add android.annotation annotations Jan 31, 2019
ultimate Move scripting support classes to the scripting compiler impl module Apr 17, 2019
.gitattributes Exclude generated test classes from language statistics Jan 3, 2018
.gitignore Build: embed jps artifact kotlin-plugin.jar into ideaPlugin Apr 10, 2019 Code of Conduct for Kotlin project Feb 19, 2019
build.gradle.kts Include FIR modules into compiler #KT-30243 Fixed Apr 22, 2019 CIDR: New way of building CLion and AppCode plugins Feb 14, 2019 Build: Remove intellijEnforceCommunitySdk flag, use `currentIde` instead Mar 20, 2019 Build: Remove intellijEnforceCommunitySdk flag, use `currentIde` instead Mar 20, 2019 as35: Upgrade to AS 3.5 C10 Apr 9, 2019
gradlew Use Gradle 4.3 Nov 1, 2017
gradlew.bat add Gradle wrapper to project Nov 15, 2016
settings.gradle Drop refactored-out frontend.script module Apr 17, 2019
upload_plugins.gradle Build: Fix upload_plugins.gradle broken after migration to gradle 5.0 Apr 2, 2019

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.

On Windows you might need to add long paths setting to the repo:

git config core.longpaths true 


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/ 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

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

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.

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