IntelliJ Platform Plugin SDK Help

Configuring Kotlin Support

This page describes developing plugins using the Kotlin programming language.

Advantages of Developing a Plugin in Kotlin

Using Kotlin to write plugins for the IntelliJ Platform is very similar to writing plugins in Java. Existing Java classes can be converted to their Kotlin equivalents by using the J2K converter (part of Kotlin plugin).

In addition to null safety, type-safe builders, and Kotlin Coroutines, the Kotlin language offers many convenient features for plugin development, which make plugins easier to read and simpler to maintain. Much like Kotlin for Android, the IntelliJ Platform makes extensive use of callbacks, which are straightforward to express as lambdas in Kotlin.

Kotlin classes can be mixed in a project with existing Java code. This might come handy when certain APIs require the use of mentioned Kotlin Coroutines.

Adding Extensions

Likewise, it is possible to customize the behavior of internal classes in the IntelliJ Platform using extensions. For example, it is common practice to guard logging statements to avoid the cost of parameter construction, leading to the following ceremony when using the log:

if (logger.isDebugEnabled()) { logger.debug("..." + expensiveComputation()); }

We can achieve the same result more succinctly in Kotlin, by declaring the following extension method:

inline fun Logger.debug(lazyMessage: () -> String) { if (isDebugEnabled) { debug(lazyMessage()) } }

Now we can directly write:

logger.debug { "..." + expensiveComputation() }

to receive all the benefits of lightweight logging while reducing the code verbosity.

With practice, you will be able to recognize many idioms in the IntelliJ Platform that can be simplified with Kotlin.

UI Forms in Kotlin

The IntelliJ Platform provides a type safe DSL to build UI forms in a declarative way.

Kotlin Coroutines

Kotlin Coroutines are a lightweight and easy to implement alternative to threads with many advantages.

Adding Kotlin Support

IntelliJ IDEA bundles the necessary Kotlin plugin, requiring no further configuration. For detailed instructions, please refer to the Kotlin documentation.

Kotlin Gradle Plugin

Adding Kotlin source files compilation support to the Gradle-based project requires adding and configuring the Kotlin JVM Gradle plugin.

See the build.gradle.kts from kotlin_demo sample plugin:

plugins { id("java") id("org.jetbrains.intellij") version "1.17.4" id("org.jetbrains.kotlin.jvm") version "1.9.24" } group = "org.intellij.sdk" version = "2.0.0" repositories { mavenCentral() } java { sourceCompatibility = JavaVersion.VERSION_17 } // See https://plugins.jetbrains.com/docs/intellij/tools-gradle-intellij-plugin.html intellij { version.set("2023.2.6") } tasks { buildSearchableOptions { enabled = false } patchPluginXml { version.set("${project.version}") sinceBuild.set("232") untilBuild.set("241.*") } compileKotlin { kotlinOptions.jvmTarget = "17" } compileTestKotlin { kotlinOptions.jvmTarget = "17" } }

Kotlin Standard Library (stdlib)

Since Kotlin 1.4, a dependency on the standard library stdlib is added automatically (API Docs). In nearly all cases, it is not necessary to include it in the plugin distribution as the platform already bundles it.

To opt out, add this line in gradle.properties:

kotlin.stdlib.default.dependency = false

The presence of this Gradle property is checked by the Gradle IntelliJ Plugin with the verifyPluginConfiguration task. If the property is not present, a warning will be reported during the plugin configuration verification, as it is a common problem when Kotlin stdlib gets bundled within the plugin archive. To bundle stdlib in the plugin distribution, specify explicitly kotlin.stdlib.default.dependency = true.

If a plugin supports multiple platform versions, it must either target the lowest bundled stdlib version or the specific version must be provided in plugin distribution.

IntelliJ Platform version

Bundled stdlib version

2024.2

1.9.24

2024.1

1.9.22

2023.3

1.9.10

2023.2

1.8.20

2023.1

1.8.0

Earlier Versions

IntelliJ Platform version

Bundled stdlib version

2022.3

1.7.0

2022.2

1.6.21

2022.1

1.6.20

2021.3

1.5.10

2021.2

1.5.10

2021.1

1.4.32

2020.3

1.4.0

2020.2

1.3.70

2020.1

1.3.70

2019.3

1.3.31

2019.2

1.3.3

2019.1

1.3.11

See Dependency on the standard library for more details.

Kotlin Coroutines Libraries (kotlinx.coroutines)

Plugins must always use the bundled library from the target IDE and not bundle their own version. Please make sure it is not added via transitive dependencies either (see View and Debug Dependencies in Gradle user guide).

Since 2024.2, a custom fork with additional patches is bundled.

See Kotlin Coroutines on how to use them in plugins.

IntelliJ Platform version

Bundled kotlinx-coroutines version

2024.2

1.8.0

2024.1

1.7.3

Other Bundled Kotlin Libraries

In general, it is strongly advised to always use the bundled library version.

Please see Third-Party Software and Licenses for an overview of all bundled libraries.

Incremental compilation

The Kotlin Gradle plugin supports incremental compilation, which allows tracking changes in the source files so the compiler handles only updated code.

No action required.

Remove additional kotlin.incremental.useClasspathSnapshot=false property in gradle.properties if present.

Kotlin 1.8.20 has a new incremental compilation approach which is enabled by default. Unfortunately, it is not compatible with the IntelliJ Platform — when reading large JAR files (like app.jar or 3rd-party-rt.jar), leading to an Out of Memory exception:

Execution failed for task ':compileKotlin'. > Failed to transform app.jar to match attributes {artifactType=classpath-entry-snapshot, org.gradle.libraryelements=jar, org.gradle.usage=java-runtime}. > Execution failed for ClasspathEntrySnapshotTransform: .../lib/app.jar. > Java heap space

To avoid this exception, add the following line to gradle.properties:

kotlin.incremental.useClasspathSnapshot=false

Plugin Implementation Notes

Do not use object but class

Plugins may use Kotlin classes (class keyword) to implement declarations in the plugin configuration file. When registering an extension, the platform uses a dependency injection framework to instantiate these classes at runtime. For this reason, plugins must not use Kotlin objects (object keyword) to implement any plugin.xml declarations. Managing the lifecycle of extensions is the platform's responsibility and instantiating these classes as Kotlin singletons may cause issues.

A notable exception is com.intellij.openapi.fileTypes.FileType (com.intellij.fileType extension point), see also the inspection descriptions below.

Problems are highlighted via these inspections (2023.2):

  • Plugin DevKit | Code | Kotlin object registered as extension for Kotlin code

  • Plugin DevKit | Plugin descriptor | Extension class is a Kotlin object for plugin.xml

Do not use companion object in extensions

Kotlin companion object is always created once you try to load its containing class, and extension point implementations are supposed to be cheap to create. To avoid unnecessary classloading (and thus slowdown in IDE startup), companion object in extensions must only contain simple constants or logger. Anything else must be a top-level declaration or stored in an object.

Use inspection Plugin DevKit | Code | Companion object in extensions to highlight such problems (2023.3).

Kotlin Code FAQ

How to shorten references

Example Plugins Implemented in Kotlin

There are many open-source Kotlin plugins built on the IntelliJ Platform. For a readily available source of up-to-date examples of plugins implemented in Kotlin, developers may look to these projects for inspiration:

Last modified: 14 May 2024