Kotlin Multiplatform Gradle DSL Reference

Multiplatform projects are in Alpha. Language features and tooling may 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. Learn the concepts of Kotlin multiplatform projects, how to create and configure them.

Table of Contents

• Id and version
• Top-level blocks
• Targets
  • Common target configuration
  • JVM targets
  • JavaScript targets
  • Native targets
  • Android targets
• Source sets
  • Predefined source sets
  • Custom source sets
  • Source set parameters
• Compilations
  • Predefine compilations
  • Custom compilations
  • Compilation parameters
• Dependencies
• Language settings

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 1.4.21.

plugins {
    id 'org.jetbrains.kotlin.multiplatform' version '1.4.21'
}

plugins {
    kotlin("multiplatform") version "1.4.21"
}

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:

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.

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:

kotlin {
    jvm()
    iosX64()
    macosX64()
    js().browser()
}

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:

JVM targets

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

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 how to include Java sources in JVM compilations.

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:

Learn more about configuring Kotlin/JS projects.

Browser

browser can contain the following configuration blocks:

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:

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

Native targets

For native targets, the following specific blocks are available:

Binaries

There are the following kinds of binaries:

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

For binaries configuration, the following parameters are available:

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
    }
}

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:

Learn more how to configure interop with native languages.

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:

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

Learn more about compilation for Android.

The android configuration inside kotlin doesn’t replace the build configuration of any Android project. Learn more about writing build scripts for Android projects in 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.

Predefined source sets

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

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

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

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

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 { 
        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.

Source set parameters

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

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. 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:

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

Compilation parameters

A compilation has the following parameters:

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.

Learn more about configuring dependencies.

There are four types of dependencies:

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 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:

kotlin {
    sourceSets.all {
        languageSettings {
            languageVersion = '1.4' // possible values: '1.0', '1.1', '1.2', '1.3', '1.4'
            apiVersion = '1.4' // possible values: '1.0', '1.1', '1.2', '1.3', '1.4'
            enableLanguageFeature('InlineClasses') // language feature name
            useExperimentalAnnotation('kotlin.ExperimentalUnsignedTypes') // annotation FQ-name
            progressiveMode = true // false by default
        }
    }
}

kotlin {
    sourceSets.all {
        languageSettings.apply {
            languageVersion = "1.4" // possible values: "1.0", "1.1", "1.2", "1.3", "1.4"
            apiVersion = "1.4" // possible values: "1.0", "1.1", "1.2", "1.3", "1.4"
            enableLanguageFeature("InlineClasses") // language feature name
            useExperimentalAnnotation("kotlin.ExperimentalUnsignedTypes") // annotation FQ-name
            progressiveMode = true // false by default
        }
    }
}