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Kotlin Multiplatform Gradle DSL Reference

Multiplatform projects are an experimental feature in Kotlin 1.2 and 1.3. All of the language and tooling features described in this document are subject to change in future Kotlin versions.

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. For the concepts of Kotlin multiplatform projects and instructions on writing build scripts with the plugin, see Building Multiplatform Projects with Gradle.

Table of Contents

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 1.3.72.

plugins {
    id 'org.jetbrains.kotlin.multiplatform' version '1.3.72'
}
plugins {
    kotlin("multiplatform") version "1.3.72"
}

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.

Targets

Target is a part of the build responsible for compiling, testing, and packaging a piece of software aimed for one of the supported platforms. 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:

Name Description
jvm Java Virtual Machine
js JavaScript
android Android (APK)
androidNativeArm32 Android NDK on ARM (ARM32) platforms
androidNativeArm64 Android NDK on ARM64 platforms
androidNativeX86 Android NDK on x86 platforms
androidNativeX64 Android NDK on x86_64 platforms
iosArm32 Apple iOS on ARM (ARM32) platforms (Apple iPhone 5 and earlier)
iosArm64 Apple iOS on ARM64 platforms (Apple iPhone 5s and newer)
iosX64 Apple iOS 64-bit simulator
watchosArm32 Apple watchOS on ARM (ARM32) platforms (Apple Watch Series 3 and earlier)
watchosArm64 Apple watchOS on ARM64_32 platforms (Apple Watch Series 4 and newer)
watchosX86 Apple watchOS simulator
tvosArm64 Apple tvOS on ARM64 platforms (Apple TV 4th generation and newer)
tvosX64 Apple tvOS simulator
linuxArm64 Linux on ARM64 platforms, for example, Raspberry Pi
linuxArm32Hfp Linux on hard-float ARM (ARM32) platforms
linuxMips32 Linux on MIPS platforms
linuxMipsel32 Linux on little-endian MIPS (mipsel) platforms
linuxX64 Linux on x86_64 platforms
macosX64 Apple macOS
mingwX64 64-bit Microsoft Windows
mingwX86 32-bit Microsoft Windows
wasm32 WebAssembly
kotlin {
    jvm()
    iosX64()
    macosX64()
    js().browser()
}

Configuration of a target can include two parts:

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. Avaiable values: jvm, androidJvm, js, native, common.
artifactsTaskName The name of the task that builds the resulting artifacts of this target.
components The components used to setup Gradle publications.

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. For more information, see Java support in JVM targets.

kotlin {
    jvm {
        withJava()
    } 
}

JavaScript targets

The js block describes the configuration of JavaScript targets. It 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.

For details about configuring Kotlin/JS projects, see Setting up a Kotlin/JS project.

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.
dceTask Configuration of Dead Code Elimination.
distribution Path to output files.
kotlin {
    js().browser {
        webpackTask { /* ... */ }
        testRuns { /* ... */ }
        dceTask {
            keep("myKotlinJsApplication.org.example.keepFromDce")
        }
        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 binaries 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', [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
    }
}
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
    }
}

For more information on configuring binaries, see Building final 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
defFile 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.

For more information on Kotlin interop with C libraries, see CInterop support.

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
                    defFile 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")
                }

                anotherInterop { /* ... */ }
            }
        }
    }
}
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
                defFile(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")
            }

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

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. For usage instructions, see Publishing Android libraries.
publishAllLibraryVariants() Publishes all build variants.
kotlin {
    android {
        publishLibraryVariants("release", "debug")
    }
}

For more details about configuring Android targets of multiplatform projects, see Android Support.

Note that the android configuration inside kotlin doesn’t replace the build configuration of any Android project. For information on writing build scripts for Android projects, see the Android developer documentation.

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. For instructions on creating and configuring source sets, see Configuring source sets.

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

For more information about the predefined source sets, see Default Project Layout.

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 { 
        myMain { /* ... */ } // create or configure a source set by the name 'myMain' 
    }
}
kotlin { 
    sourceSets { 
        val myMain by creating { /* ... */ } // create a new 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 as described in Connecting 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. The instructions on connecting source sets are provided in Connecting source sets.
dependencies Dependencies of the source set.
languageSettings Language settings applied to the source set.
kotlin { 
    sourceSets { 
        commonMain {
            kotlin.srcDir('src')
            resources.srcDir('res')
            
            dependencies {
                /* ... */
            }           
        } 
    }
}
kotlin { 
    sourceSets { 
        val commonMain by getting {
            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. Developers 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.

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 {
        compilations.main.output // get the main compilation output
        compilations.test.runtimeDependencyFiles // get the test runtime classpath
    }
}
kotlin {
    jvm {
        val main by compilations.getting {
            output // get the main compilation output
        }
        
        compilations["test"].runtimeDependencyFiles // get the test runtime classpath
    }
}

Custom compilations

In addition to predefined compilations, developers can create their 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.

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

            // Create a test task to run the tests produced by this compilation:
            tasks.create('jvmIntegrationTest', Test) {
                /* ... */
            }
        }
    }
}
kotlin {
    jvm() {
        compilations {
            val integrationTest by compilations.creating {
                defaultSourceSet {
                    dependencies {
                        /* ... */
                    }
                }

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

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().
kotlinOptions 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.
runtimeDependencyFiles Runtime dependency files (classpath) of the compilation.
kotlin {
    jvm {
        compilations.main.kotlinOptions { 
            // Setup the Kotlin compiler options for the 'main' compilation:
            jvmTarget = "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 {
            kotlinOptions {
                allWarningsAsErrors = true
            }
        }
    }
}
kotlin {
    jvm {
        val main by compilations.getting {
            kotlinOptions { 
                // Setup the Kotlin compiler options for the 'main' compilation:
                jvmTarget = "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 {
            kotlinOptions {
                allWarningsAsErrors = true
            }
        }
    }
}

Dependencies

The dependencies block of the source set declaration contains the dependencies of this source set. There are four kinds 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 {
        commonMain {
            dependencies {
                api 'com.example:foo-metadata:1.0'
            }
        }
        jvm6Main {
            dependencies {
                implementation 'com.example:foo-jvm6:1.0'
            }
        }
    }
}
kotlin {
    sourceSets {
        val commonMain by getting {
            dependencies {
                api("com.example:foo-metadata:1.0")
            }
        }
        val jvm6Main by getting {
            dependencies {
                implementation("com.example:foo-jvm6:1.0")
            }
        }
    }
}

Additionally, source sets can depend on each other. In this case, the dependsOn() function 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.
useExperimentalAnnotation Allows using the specified opt-in annotation.
progressiveMode Enables the progressive mode.
kotlin {
    sourceSets {
        commonMain {
            languageSettings {
                languageVersion = '1.3' // possible values: '1.0', '1.1', '1.2', '1.3'
                apiVersion = '1.3' // possible values: '1.0', '1.1', '1.2', '1.3'
                enableLanguageFeature('InlineClasses') // language feature name
                useExperimentalAnnotation('kotlin.ExperimentalUnsignedTypes') // annotation FQ-name
                progressiveMode = true // false by default
            }
        }
    }
}
kotlin {
    sourceSets {
        val commonMain by getting {
            languageSettings.apply {
                languageVersion = "1.3" // possible values: '1.0', '1.1', '1.2', '1.3'
                apiVersion = "1.3" // possible values: '1.0', '1.1', '1.2', '1.3'
                enableLanguageFeature("InlineClasses") // language feature name
                useExperimentalAnnotation("kotlin.ExperimentalUnsignedTypes") // annotation FQ-name
                progressiveMode = true // false by default
            }
        }
    }
}