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# Kotlin Programming Language

Welcome to [Kotlin](https://kotlinlang.org/)!   
It is an open-source, statically typed programming language supported and developed by [JetBrains](https://www.jetbrains.com/) and open-source contributors.

Some handy links:

 * [Kotlin Site](https://kotlinlang.org/)
 * [Getting Started Guide](https://kotlinlang.org/docs/tutorials/getting-started.html)
 * [Try Kotlin](https://play.kotlinlang.org/)
 * [Kotlin Standard Library](https://kotlinlang.org/api/latest/jvm/stdlib/index.html)
 * [Issue Tracker](https://youtrack.jetbrains.com/issues/KT)
 * [Kotlin YouTube Channel](https://www.youtube.com/channel/UCP7uiEZIqci43m22KDl0sNw)
 * [Forum](https://discuss.kotlinlang.org/)
 * [Kotlin Blog](https://blog.jetbrains.com/kotlin/)
 * [Subscribe to Kotlin YouTube channel](https://www.youtube.com/channel/UCP7uiEZIqci43m22KDl0sNw)
 * [Follow Kotlin on Twitter](https://twitter.com/kotlin)
 * [Public Slack channel](https://slack.kotlinlang.org/)
 * [TeamCity CI build](https://teamcity.jetbrains.com/project.html?tab=projectOverview&projectId=Kotlin)

## 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](https://kotlinlang.org/docs/reference/mpp-supported-platforms.html) while retaining the flexibility and benefits of native programming.

 * [Kotlin Multiplatform Mobile](https://kotlinlang.org/lp/mobile/) for sharing code between Android and iOS
 * [Getting Started with Kotlin Multiplatform Mobile Guide](https://kotlinlang.org/docs/mobile/create-first-app.html)
 * [Kotlin Multiplatform Benefits](https://kotlinlang.org/docs/reference/multiplatform.html)
 * [Share code on all platforms](https://kotlinlang.org/docs/reference/mpp-share-on-platforms.html#share-code-on-all-platforms)
 * [Share code on similar platforms](https://kotlinlang.org/docs/reference/mpp-share-on-platforms.html#share-code-on-similar-platforms)

## Editing Kotlin

 * [Kotlin IntelliJ IDEA Plugin](https://kotlinlang.org/docs/tutorials/getting-started.html) ([source code](https://github.com/JetBrains/intellij-community/tree/master/plugins/kotlin))
 * [Kotlin Eclipse Plugin](https://kotlinlang.org/docs/tutorials/getting-started-eclipse.html)
 * [Kotlin Sublime Text Package](https://github.com/vkostyukov/kotlin-sublime-package)

## Build environment requirements

This repository is using [Gradle toolchains](https://docs.gradle.org/current/userguide/toolchains.html) feature
to select and auto-provision required JDKs from [AdoptOpenJdk](https://adoptopenjdk.net) project. 

Unfortunately [AdoptOpenJdk](https://adoptopenjdk.net) 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:
- [Asdf-vm](https://asdf-vm.com/)
- [Jabba](https://github.com/shyiko/jabba)
- [SDKMAN!](https://sdkman.io/)

Alternatively, it is still possible to only provide required JDKs via environment variables 
(see [gradle.properties](./gradle.properties#L5) 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

```bash
$ 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 

## Building

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](libraries/ReadMe.md) for details.

To build Kotlin/Native, see
[kotlin-native/README.md](kotlin-native/README.md#building-from-source).

## <a name="working-in-idea"></a> 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](https://www.jetbrains.com/idea/download).

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](https://github.com/demiurg906/test-data-helper-plugin)

### Dependency verification

We have a [dependencies verification](https://docs.gradle.org/current/userguide/dependency_verification.html) 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](https://github.com/JetBrains/kotlin/blob/master/gradle/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:

- Delete `components` section of `verification-metadata.xml` to avoid stockpiling of old unused dependencies. You may use the following command:
```bash
#macOS
sed -i '' -e '/<components>/,/<\/components>/d' gradle/verification-metadata.xml
#Linux & Git for Windows
sed -i -e '/<components>/,/<\/components>/d' gradle/verification-metadata.xml
```
- Re-generate dependencies with Gradle's `--write-verification-metadata` command (verify update relates to your changes)

```bash
./gradlew -i --write-verification-metadata sha256,md5 -Pkotlin.native.enabled=true resolveDependencies
```

*`resolveDependencies` task resolves dependencies for all platforms including dependencies downloaded by plugins.*

Keep in mind:

- If you’re adding a dependency with OS mentioned in an artifact name (`darwin`, `mac`, `osx`, `linux`, `windows`), remember to add them to 
  `implicitDependencies` configuration or update `resolveDependencies` task if needed. `resolveDependencies` should resolve all dependencies
  including dependencies for different platforms.
- If you have a `local.properties` file in your Kotlin project folder, make sure that it doesn't contain `kotlin.native.enabled=false`.
  Otherwise, native-only dependencies may not be added to the verification metadata. This is because `local.properties` has higher 
  precedence than the `-Pkotlin.native.enabled=true` specified in the Gradle command.

## Using -dev and -SNAPSHOT versions

We publish `-dev` and `-SNAPSHOT` versions frequently.

For `-dev` versions you can use the [list of available versions](https://maven.pkg.jetbrains.space/kotlin/p/kotlin/bootstrap/org/jetbrains/kotlin/kotlin-compiler/maven-metadata.xml) and include this maven repository:

```kotlin
maven("https://maven.pkg.jetbrains.space/kotlin/p/kotlin/bootstrap")
```

For `-SNAPSHOT` versions that are updated daily, you can use the [list of available versions](https://oss.sonatype.org/content/repositories/snapshots/org/jetbrains/kotlin/kotlin-compiler/maven-metadata.xml) and include this maven repository:

```kotlin
maven("https://oss.sonatype.org/content/repositories/snapshots/")
```

# License
Kotlin is distributed under the terms of the Apache License (Version 2.0). See [license folder](license/README.md) for details.

# Contributing

Please be sure to review Kotlin's [contributing guidelines](docs/contributing.md) to learn how to help the project.