Multiplatform Gradle DSL reference

The Kotlin Multiplatform Gradle plugin is a tool for creating Kotlin Multiplatform projects. Here we provide a reference of its contents; use it as a reminder when writing Gradle build scripts for Kotlin Multiplatform projects. Learn the concepts of Kotlin Multiplatform projects, how to create and configure them.

Id and version

The fully qualified name of the Kotlin Multiplatform Gradle plugin is org.jetbrains.kotlin.multiplatform. If you use the Kotlin Gradle DSL, you can apply the plugin with kotlin("multiplatform"). The plugin versions match the Kotlin release versions. The most recent version is 2.0.21.

plugins {
    kotlin("multiplatform") version "2.0.21"
}

plugins {
    id 'org.jetbrains.kotlin.multiplatform' version '2.0.21'
}

Top-level blocks

kotlin {} is the top-level block for multiplatform project configuration in the Gradle build script. Inside kotlin {}, you can write the following blocks:

Block	Description
<targetName>	Declares a particular target of a project. The names of available targets are listed in the Targets section.
`targets`	All targets of the project.
`presets`	All predefined targets. Use this for configuring multiple predefined targets at once.
`sourceSets`	Configures predefined and declares custom source sets of the project.
`compilerOptions`	Extension-level common compiler options that are used as defaults for all targets and shared source sets. To use it, add the following opt-in: `@OptIn(ExperimentalKotlinGradlePluginApi::class)`

Targets

Target is a part of the build responsible for compiling, testing, and packaging a piece of software aimed at one of the supported platforms. Kotlin provides target presets for each platform. See how to use a target preset.

Each target can have one or more compilations. In addition to default compilations for test and production purposes, you can create custom compilations.

The targets of a multiplatform project are described in the corresponding blocks inside kotlin {}, for example, jvm, android, iosArm64. The complete list of available targets is the following:

Target platform	Target preset	Comments
Kotlin/JVM	`jvm`
Kotlin/Wasm	`wasmJs`	Use it if you plan to run your projects in the JavaScript runtime.
Kotlin/Wasm	`wasmWasi`	Use it if you need support for the WASI system interface.
Kotlin/JS	`js`	Select the execution environment: `browser {}` for applications running in the browser. `nodejs {}` for applications running on Node.js. Learn more in Setting up a Kotlin/JS project.
Kotlin/Native		Learn about currently supported targets for the macOS, Linux, and Windows hosts in Kotlin/Native target support.
Android applications and libraries	`android`	Manually apply an Android Gradle plugin: `com.android.application` or `com.android.library`. You can only create one Android target per Gradle subproject.

kotlin {
    jvm()
    iosArm64()
    macosX64()
    js().browser()
}

The configuration of a target can include two parts:

Common configuration available for all targets.
Target-specific configuration.

Each target can have one or more compilations.

Common target configuration

In any target block, you can use the following declarations:

Name	Description
`attributes`	Attributes used for disambiguating targets for a single platform.
`preset`	The preset that the target has been created from, if any.
`platformType`	Designates the Kotlin platform of this target. Available values: `jvm`, `androidJvm`, `js`, `wasm`, `native`, `common`.
`artifactsTaskName`	The name of the task that builds the resulting artifacts of this target.
`components`	The components used to setup Gradle publications.
`compilerOptions`	The compiler options used for the target. This declaration overrides any `compilerOptions {}` configured at top level. To use it, add the following opt-in: `@OptIn(ExperimentalKotlinGradlePluginApi::class)`

JVM targets

In addition to common target configuration, jvm targets have a specific function:

Name	Description
`withJava()`	Includes Java sources into the JVM target's compilations.

Use this function for projects that contain both Java and Kotlin source files. Note that the default source directories for Java sources don't follow the Java plugin's defaults. Instead, they are derived from the Kotlin source sets. For example, if the JVM target has the default name jvm, the paths are src/jvmMain/java (for production Java sources) and src/jvmTest/java for test Java sources. Learn more about Java sources in JVM compilations.

kotlin {
    jvm {
        withJava()
    } 
}

Web targets

The js {} block describes the configuration of Kotlin/JS targets, and the wasmJs {} block describes the configuration of Kotlin/Wasm targets interoperable with JavaScript. They can contain one of two blocks depending on the target execution environment:

Name	Description
`browser`	Configuration of the browser target.
`nodejs`	Configuration of the Node.js target.

Learn more about configuring Kotlin/JS projects.

A separate wasmWasi {} block describes the configuration of Kotlin/Wasm targets that support the WASI system interface. Here, only the nodejs execution environment is available:

kotlin {
    wasmWasi {
        nodejs()
        binaries.executable()
    }
}

All the web targets, js, wasmJs, and wasmWasi, also support the binaries.executable() call. It explicitly instructs the Kotlin compiler to emit executable files. For more information, see Execution environments in the Kotlin/JS documentation.

Browser

browser {} can contain the following configuration blocks:

Name	Description
`testRuns`	Configuration of test execution.
`runTask`	Configuration of project running.
`webpackTask`	Configuration of project bundling with Webpack.
`distribution`	Path to output files.

kotlin {
    js().browser {
        webpackTask { /* ... */ }
        testRuns { /* ... */ }
        distribution {
            directory = File("$projectDir/customdir/")
        }
    }
}

Node.js

nodejs {} can contain configurations of test and run tasks:

Name	Description
`testRuns`	Configuration of test execution.
`runTask`	Configuration of project running.

kotlin {
    js().nodejs {
        runTask { /* ... */ }
        testRuns { /* ... */ }
    }
}

Native targets

For native targets, the following specific blocks are available:

Name	Description
`binaries`	Configuration of binaries to produce.
`cinterops`	Configuration of interop with C libraries.

Binaries

There are the following kinds of binaries:

Name	Description
`executable`	Product executable.
`test`	Test executable.
`sharedLib`	Shared library.
`staticLib`	Static library.
`framework`	Objective-C framework.

kotlin {
    linuxX64 { // Use your target instead.
        binaries {
            executable {
                // Binary configuration.
            }
        }
    }
}

For binary configuration, the following parameters are available:

Name	Description
`compilation`	The compilation from which the binary is built. By default, `test` binaries are based on the `test` compilation while other binaries - on the `main` compilation.
`linkerOpts`	Options passed to a system linker during binary building.
`baseName`	Custom base name for the output file. The final file name will be formed by adding system-dependent prefix and postfix to this base name.
`entryPoint`	The entry point function for executable binaries. By default, it's `main()` in the root package.
`outputFile`	Access to the output file.
`linkTask`	Access to the link task.
`runTask`	Access to the run task for executable binaries. For targets other than `linuxX64`, `macosX64`, or `mingwX64` the value is `null`.
`isStatic`	For Objective-C frameworks. Includes a static library instead of a dynamic one.

binaries {
    executable("my_executable", listOf(RELEASE)) {
        // Build a binary on the basis of the test compilation.
        compilation = compilations["test"]

        // Custom command line options for the linker.
        linkerOpts = mutableListOf("-L/lib/search/path", "-L/another/search/path", "-lmylib")

        // Base name for the output file.
        baseName = "foo"

        // Custom entry point function.
        entryPoint = "org.example.main"

        // Accessing the output file.
        println("Executable path: ${outputFile.absolutePath}")

        // Accessing the link task.
        linkTask.dependsOn(additionalPreprocessingTask)

        // Accessing the run task.
        // Note that the runTask is null for non-host platforms.
        runTask?.dependsOn(prepareForRun)
    }

    framework("my_framework" listOf(RELEASE)) {
        // Include a static library instead of a dynamic one into the framework.
        isStatic = true
    }
}

binaries {
    executable('my_executable', [RELEASE]) {
        // Build a binary on the basis of the test compilation.
        compilation = compilations.test

        // Custom command line options for the linker.
        linkerOpts = ['-L/lib/search/path', '-L/another/search/path', '-lmylib']

        // Base name for the output file.
        baseName = 'foo'

        // Custom entry point function.
        entryPoint = 'org.example.main'

        // Accessing the output file.
        println("Executable path: ${outputFile.absolutePath}")

        // Accessing the link task.
        linkTask.dependsOn(additionalPreprocessingTask)

        // Accessing the run task.
        // Note that the runTask is null for non-host platforms.
        runTask?.dependsOn(prepareForRun)
    }

    framework('my_framework' [RELEASE]) {
        // Include a static library instead of a dynamic one into the framework.
        isStatic = true
    }
}

Learn more about building native binaries.

CInterops

cinterops is a collection of descriptions for interop with native libraries. To provide an interop with a library, add an entry to cinterops and define its parameters:

Name	Description
`definitionFile`	The `.def` file describing the native API.
`packageName`	Package prefix for the generated Kotlin API.
`compilerOpts`	Options to pass to the compiler by the cinterop tool.
`includeDirs`	Directories to look for headers.
`header`	Header to be included in the bindings.
`headers`	The list of headers to be included in the bindings.

kotlin {
    linuxX64 { // Replace with a target you need.
        compilations.getByName("main") {
            val myInterop by cinterops.creating {
                // Def-file describing the native API.
                // The default path is src/nativeInterop/cinterop/<interop-name>.def
                definitionFile.set(project.file("def-file.def"))

                // Package to place the Kotlin API generated.
                packageName("org.sample")

                // Options to be passed to compiler by cinterop tool.
                compilerOpts("-Ipath/to/headers")

                // Directories for header search (an analogue of the -I<path> compiler option).
                includeDirs.allHeaders("path1", "path2")

                // A shortcut for includeDirs.allHeaders.
                includeDirs("include/directory", "another/directory")

                // Header files to be included in the bindings.
                header("path/to/header.h")
                headers("path/to/header1.h", "path/to/header2.h")
            }

            val anotherInterop by cinterops.creating { /* ... */ }
        }
    }
}

kotlin {
    linuxX64 { // Replace with a target you need.
        compilations.main {
            cinterops {
                myInterop {
                    // Def-file describing the native API.
                    // The default path is src/nativeInterop/cinterop/<interop-name>.def
                    definitionFile = project.file("def-file.def")

                    // Package to place the Kotlin API generated.
                    packageName 'org.sample'

                    // Options to be passed to compiler by cinterop tool.
                    compilerOpts '-Ipath/to/headers'

                    // Directories for header search (an analogue of the -I<path> compiler option).
                    includeDirs.allHeaders("path1", "path2")

                    // A shortcut for includeDirs.allHeaders.
                    includeDirs("include/directory", "another/directory")

                    // Header files to be included in the bindings.
                    header("path/to/header.h")
                    headers("path/to/header1.h", "path/to/header2.h")
                }

                anotherInterop { /* ... */ }
            }
        }
    }
}

For more cinterop properties, see Definition file.

Android targets

The Kotlin Multiplatform plugin contains two specific functions for android targets. Two functions help you configure build variants:

Name	Description
`publishLibraryVariants()`	Specifies build variants to publish. Learn more about publishing Android libraries.
`publishAllLibraryVariants()`	Publishes all build variants.

kotlin {
    android {
        publishLibraryVariants("release", "debug")
    }
}

Learn more about compilation for Android.

Source sets

The sourceSets {} block describes source sets of the project. A source set contains Kotlin source files that participate in compilations together, along with their resources, dependencies, and language settings.

A multiplatform project contains predefined source sets for its targets; developers can also create custom source sets for their needs.

Predefined source sets

Predefined source sets are set up automatically upon creation of a multiplatform project. Available predefined source sets are the following:

Name	Description
`commonMain`	Code and resources shared between all platforms. Available in all multiplatform projects. Used in all main compilations of a project.
`commonTest`	Test code and resources shared between all platforms. Available in all multiplatform projects. Used in all test compilations of a project.
<targetName><compilationName>	Target-specific sources for a compilation. <targetName> is the name of a predefined target and <compilationName> is the name of a compilation for this target. Examples: `jsTest`, `jvmMain`.

With Kotlin Gradle DSL, the sections of predefined source sets should be marked by getting.

kotlin {
    sourceSets {
        val commonMain by getting { /* ... */ }
    }
}

kotlin { 
    sourceSets { 
        commonMain { /* ... */ } 
    }
}

Learn more about source sets.

Custom source sets

Custom source sets are created by the project developers manually. To create a custom source set, add a section with its name inside the sourceSets section. If using Kotlin Gradle DSL, mark custom source sets by creating.

kotlin { 
    sourceSets { 
        val myMain by creating { /* ... */ } // create a new source set by the name 'MyMain'
    }
}

kotlin { 
    sourceSets { 
        myMain { /* ... */ } // create or configure a source set by the name 'myMain' 
    }
}

Note that a newly created source set isn't connected to other ones. To use it in the project's compilations, connect it with other source sets.

Source set parameters

Configurations of source sets are stored inside the corresponding blocks of sourceSets {}. A source set has the following parameters:

Name	Description
`kotlin.srcDir`	Location of Kotlin source files inside the source set directory.
`resources.srcDir`	Location of resources inside the source set directory.
`dependsOn`	Connection with another source set.
`dependencies`	Dependencies of the source set.
`languageSettings`	Language settings applied to the source set.

kotlin { 
    sourceSets { 
        val commonMain by getting {
            kotlin.srcDir("src")
            resources.srcDir("res")

            dependencies {
                /* ... */
            }
        }
    }
}

kotlin { 
    sourceSets { 
        commonMain {
            kotlin.srcDir('src')
            resources.srcDir('res')

            dependencies {
                /* ... */
            }
        }
    }
}

Compilations

A target can have one or more compilations, for example, for production or testing. There are predefined compilations that are added automatically upon target creation. You can additionally create custom compilations.

To refer to all or some particular compilations of a target, use the compilations object collection. From compilations, you can refer to a compilation by its name.

Learn more about configuring compilations.

Predefined compilations

Predefined compilations are created automatically for each target of a project except for Android targets. Available predefined compilations are the following:

Name	Description
`main`	Compilation for production sources.
`test`	Compilation for tests.

kotlin {
    jvm {
        val main by compilations.getting {
            output // get the main compilation output
        }

        compilations["test"].runtimeDependencyFiles // get the test runtime classpath
    }
}

kotlin {
    jvm {
        compilations.main.output // get the main compilation output
        compilations.test.runtimeDependencyFiles // get the test runtime classpath
    }
}

Custom compilations

In addition to predefined compilations, you can create your own custom compilations. To create a custom compilation, add a new item into the compilations collection. If using Kotlin Gradle DSL, mark custom compilations by creating.

Learn more about creating a custom compilation.

kotlin {
    jvm() {
        compilations {
            val integrationTest by compilations.creating {
                defaultSourceSet {
                    dependencies {
                        /* ... */
                    }
                }

                // Create a test task to run the tests produced by this compilation:
                tasks.register<Test>("integrationTest") {
                    /* ... */
                }
            }
        }
    }
}

kotlin {
    jvm() {
        compilations.create('integrationTest') {
            defaultSourceSet {
                dependencies {
                    /* ... */
                }
            }

            // Create a test task to run the tests produced by this compilation:
            tasks.register('jvmIntegrationTest', Test) {
                /* ... */
            }
        }
    }
}

Compilation parameters

A compilation has the following parameters:

Name	Description
`defaultSourceSet`	The compilation's default source set.
`kotlinSourceSets`	Source sets participating in the compilation.
`allKotlinSourceSets`	Source sets participating in the compilation and their connections via `dependsOn()`.
`compilerOptions`	Compiler options applied to the compilation. For the list of available options, see Compiler options.
`compileKotlinTask`	Gradle task for compiling Kotlin sources.
`compileKotlinTaskName`	Name of `compileKotlinTask`.
`compileAllTaskName`	Name of the Gradle task for compiling all sources of a compilation.
`output`	The compilation output.
`compileDependencyFiles`	Compile-time dependency files (classpath) of the compilation. For all Kotlin/Native compilations, this automatically includes standard library and platform dependencies.
`runtimeDependencyFiles`	Runtime dependency files (classpath) of the compilation.

kotlin {
    jvm {
        val main by compilations.getting {
            compilerOptions.configure { 
                // Set up the Kotlin compiler options for the 'main' compilation:
                jvmTarget.set(JvmTarget.JVM_1_8)
            }
        
            compileKotlinTask // get the Kotlin task 'compileKotlinJvm' 
            output // get the main compilation output
        }
        
        compilations["test"].runtimeDependencyFiles // get the test runtime classpath
    }

    // Configure all compilations of all targets:
    targets.all {
        compilations.all {
            compilerOptions.configure {
                allWarningsAsErrors.set(true)
            }
        }
    }
}

kotlin {
    jvm {
        compilations.main.compilerOptions.configure { 
            // Setup the Kotlin compiler options for the 'main' compilation:
            jvmTarget = JvmTarget.JVM_1_8
        }

        compilations.main.compileKotlinTask // get the Kotlin task 'compileKotlinJvm' 
        compilations.main.output // get the main compilation output
        compilations.test.runtimeDependencyFiles // get the test runtime classpath
    }

    // Configure all compilations of all targets:
    targets.all {
        compilations.all {
            compilerOptions.configure {
                allWarningsAsErrors = true
            }
        }
    }
}

Alternatively, to configure compiler options that are common for all targets, you can use the compilerOptions {} top-level block:

kotlin {
    
    // Configure all compilations of all targets:
    @OptIn(ExperimentalKotlinGradlePluginApi::class)
    compilerOptions {
        allWarningsAsErrors.set(true)
    }
}

kotlin {
    
    // Configure all compilations of all targets:
    compilerOptions {
        allWarningsAsErrors = true
    }
}

Dependencies

The dependencies {} block of the source set declaration contains the dependencies of this source set.

Learn more about configuring dependencies.

There are four types of dependencies:

Name	Description
`api`	Dependencies used in the API of the current module.
`implementation`	Dependencies used in the module but not exposed outside it.
`compileOnly`	Dependencies used only for compilation of the current module.
`runtimeOnly`	Dependencies available at runtime but not visible during compilation of any module.

kotlin {
    sourceSets {
        val commonMain by getting {
            dependencies {
                api("com.example:foo-metadata:1.0")
            }
        }
        val jvmMain by getting {
            dependencies {
                implementation("com.example:foo-jvm:1.0")
            }
        }
    }
}

kotlin {
    sourceSets {
        commonMain {
            dependencies {
                api 'com.example:foo-metadata:1.0'
            }
        }
        jvmMain {
            dependencies {
                implementation 'com.example:foo-jvm:1.0'
            }
        }
    }
}

Additionally, source sets can depend on each other and form a hierarchy. In this case, the dependsOn() relation is used.

Source set dependencies can also be declared in the top-level dependencies {} block of the build script. In this case, their declarations follow the pattern <sourceSetName><DependencyKind>, for example, commonMainApi.

dependencies {
    "commonMainApi"("com.example:foo-common:1.0")
    "jvm6MainApi"("com.example:foo-jvm6:1.0")
}

dependencies {
    commonMainApi 'com.example:foo-common:1.0'
    jvm6MainApi 'com.example:foo-jvm6:1.0'
}

Language settings

The languageSettings {} block of a source set defines certain aspects of project analysis and build. The following language settings are available:

Name	Description
`languageVersion`	Provides source compatibility with the specified version of Kotlin.
`apiVersion`	Allows using declarations only from the specified version of Kotlin bundled libraries.
`enableLanguageFeature`	Enables the specified language feature. The available values correspond to the language features that are currently experimental or have been introduced as such at some point.
`optIn`	Allows using the specified opt-in annotation.
`progressiveMode`	Enables the progressive mode.

kotlin {
    sourceSets.all {
        languageSettings.apply {
            languageVersion = "2.0" // possible values: '1.6', '1.7', '1.8', '1.9', `2.0`
            apiVersion = "2.0" // possible values: '1.6', '1.7', '1.8', '1.9', `2.0`
            enableLanguageFeature("InlineClasses") // language feature name
            optIn("kotlin.ExperimentalUnsignedTypes") // annotation FQ-name
            progressiveMode = true // false by default
        }
    }
}

kotlin {
    sourceSets.all {
        languageSettings {
            languageVersion = '2.0' // possible values: '1.6', '1.7', '1.8', '1.9', `2.0`
            apiVersion = '2.0' // possible values: '1.6', '1.7', '1.8', '1.9', `2.0`
            enableLanguageFeature('InlineClasses') // language feature name
            optIn('kotlin.ExperimentalUnsignedTypes') // annotation FQ-name
            progressiveMode = true // false by default
        }
    }
}

Last modified: 14 October 2024