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The Kotlin Programming Language.

Project README

official project TeamCity (simple build status) Maven Central GitHub license Revved up by Gradle Enterprise

Kotlin Programming Language

Welcome to Kotlin!
It is an open-source, statically typed programming language supported and developed by JetBrains and open-source contributors.

Some handy links:

Kotlin Multiplatform capabilities

Support for multiplatform programming is one of Kotlin’s key benefits. It reduces time spent writing and maintaining the same code for different platforms while retaining the flexibility and benefits of native programming.

Editing Kotlin

Build environment requirements

This repository is using Gradle toolchains feature to select and auto-provision required JDKs from AdoptOpenJdk project.

Unfortunately AdoptOpenJdk project does not provide required JDK 1.6 and 1.7 images, so you could either download them manually and provide path to installation via JDK_1_6 and JDK_1_7 environment variables or use following SDK managers:

Alternatively, it is still possible to only provide required JDKs via environment variables (see gradle.properties for supported variable names). To ensure Gradle uses only JDKs from environmental variables - disable Gradle toolchain auto-detection by passing -Porg.gradle.java.installations.auto-detect=false option (or put it into $GRADLE_USER_HOME/gradle.properties).

For local development, if you're not working on the standard library, it's OK to avoid installing JDK 1.6 and JDK 1.7. Add kotlin.build.isObsoleteJdkOverrideEnabled=true to the local.properties file, so build will only use JDK 1.8+. Note, that in this case, build will have Gradle remote build cache misses for some tasks.

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

$ brew tap homebrew/cask-versions
$ brew install --cask java6

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
  • install - build and install all public artifacts into local maven repository
  • coreLibsTest - build and run stdlib, reflect and kotlin-test tests
  • gradlePluginTest - build and run gradle plugin tests
  • compilerTest - build and run all compiler tests

To reproduce TeamCity build use -Pteamcity=true flag. Local builds don't run proguard and have jar compression disabled by default.

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

To build Kotlin/Native, see kotlin-native/README.md.

Working with the project in IntelliJ IDEA

It is recommended to use the latest released version of Intellij IDEA (Community or Ultimate Edition). You can download IntelliJ IDEA here.

After cloning the project, import the project in IntelliJ by choosing the project directory in the Open project dialog.

For handy work with compiler tests it's recommended to use Kotlin Compiler Test Helper

Dependency verification

We have a dependencies verification feature enabled in the repository for all Gradle builds. Gradle will check hashes (md5 and sha256) of used dependencies and will fail builds with Dependency verification failed errors when local artifacts are absent or have different hashes listed in the verification-metadata.xml file.

It's expected that verification-metadata.xml should only be updated with the commits that modify the build. There are some tips how to perform such updates:

  • Use auto-generation for getting an initial list of new hashes (verify updates relate to you changes).
./gradlew -i --write-verification-metadata sha256,md5 -Pkotlin.native.enabled=true help

(any other task may be used instead of help)

  • Consider removing old versions from the file if you are updating dependencies.
  • Leave meaningful origin attribute (instead of Generated by Gradle) if you did some manual verification of the artifact.
  • Always do manual verification if several hashes are needed, and a new also-trust tag has to be added.
  • If you’re adding a dependency with OS mentioning in an artifact name (darwin, mac, osx, linux, windows), remember to add counterparts for other platforms.

Using -dev and -SNAPSHOT versions

We publish -dev and -SNAPSHOT versions frequently.

For -dev versions you can use the list of available versions and include this maven repository:


For -SNAPSHOT versions that are updated daily, you can use the list of available versions and include this maven repository:



Kotlin is distributed under the terms of the Apache License (Version 2.0). See license folder for details.


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

Open Source Agenda is not affiliated with "Kotlin" Project. README Source: JetBrains/kotlin
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