Migrating multiplatform projects to Kotlin 1.4.0
Kotlin 1.4.0 comes with lots of features and improvements in the tooling for multiplatform programming. Some of them just work out of the box on existing projects, and some require additional configuration steps. This guide will help you migrate your multiplatform projects to 1.4.0 or higher and get the benefits of all its new features.
For multiplatform project authors
Starting with 1.4.0, Kotlin multiplatform projects require Gradle 6.0 or later. Make sure that your projects use the proper version of Gradle and upgrade it if needed. See the Gradle documentation for non-Kotlin-specific migration instructions.
Simplify your build configuration
Gradle module metadata provides rich publishing and dependency resolution features that are used in Kotlin Multiplatform Projects. In Gradle 6.0 and above, module metadata is used in dependency resolution and included in publications by default. Thus, once you update to such a version, you can remove
enableFeaturePreview("GRADLE_METADATA") from the project’s
If you use libraries published with metadata, you only have to specify dependencies on them only once in the shared source set, as opposed to specifying dependencies on different variants of the same library in the shared and platform-specific source sets prior to 1.4.0.
Starting from 1.4.0, you also no longer need to declare a dependency on
stdlib in each source set manually – it will now be added by default. The version of the automatically added standard library will be the same as the version of the Kotlin Gradle plugin, since they have the same versioning.
With these features, you can make your Gradle build file much more concise and easy to read:
Don’t use kotlinx library artifact names with suffixes
-native, as they are no longer supported. Instead, use the library root artifact name, which in the example above is
Try the hierarchical project structure
With the new hierarchical project structure support, you can share code among several targets in a multiplatform project. You can use platform-dependent libraries, such as
posix in source sets shared among several native targets. This can help you share more native code without being limited by platform-specific dependencies.
By enabling the hierarchical structure along with its ability to use platform-dependent libraries in shared source sets, you can eliminate the need to use certain workarounds to get IDE support for sharing source sets among several native targets, for example
Instead of doing this, you can create a hierarchical structure with target shortcuts available for typical multi-target scenarios, or you can manually declare and connect the source sets. For example, you can create two iOS targets and a shared source set with the
To enable the hierarchical project structure along with the use of platform-dependent libraries in shared source sets, just add the following to your
In future versions, the hierarchical project structure will become default for Kotlin multiplatform project, so we strongly encourage you to start using it now.
For library authors
Migrate from Gradle Bintray plugin to Maven Publish plugin
If you're using
gradle-bintray-plugin for library publication, migrate your projects to
maven-publish plugin instead. See how we've done this for
kotlinx.serialization. Learn more about publishing multiplatform libraries.
If for some reason you need to publish to Bintray and use the Gradle Bintray plugin, remember that this plugin doesn’t support publishing Gradle module metadata. Use this workaround to fix this.
Follow the default libraries’ layout
The layout of kotlinx libraries has changed and now corresponds to the default layout, which we recommend using: The root or umbrella library module now has a name without a suffix (for example,
kotlinx-coroutines-core instead of
kotlinx-coroutines-core-native). Publishing libraries with maven-publish Gradle plugin follows this layout by default. Learn more about publishing multiplatform libraries.
Migrate to the hierarchical project structure
A hierarchical project structure allows reusing code in similar targets, as well as publishing and consuming libraries with granular APIs targeting similar platforms. We recommend that you switch to the hierarchical project structure in your libraries when migrating to Kotlin 1.4.0 or higher:
By default, libraries published with the hierarchical project structure are compatible only with projects that have hierarchical project structure. To enable compatibility with non-hierarchical projects, add the following to the
gradle.propertiesfile in your library project:kotlin.mpp.enableCompatibilityMetadataVariant=true
Libraries published without the hierarchical project structure can’t be used in a shared native source set. For example, users with
ios()shortcuts in their
build.gradle.(kts)files won’t be able to use your library in their iOS-shared code.
The compatibility between multiplatform projects and libraries is as follows:
Library with hierarchical project structure
Project with hierarchical project structure
Need to enable with
Library can’t be used in a shared native source set
In future versions, the hierarchical project structure with the usage of platform-dependent libraries in shared source sets will be the default in multiplatform projects. So the sooner you support it, the sooner users will be able to migrate. We’ll also be very grateful if you report any bugs you find to our issue tracker.
To enable hierarchical project structure support, add the following to your
For build authors
Check task names
The introduction of the hierarchical project structure in multiplatform projects resulted in a couple of changes to the names of some Gradle tasks:
metadataJartask has been renamed to
There are new
compile<SourceSet>KotlinMetadatatasks for all published intermediate source sets.
These changes are relevant only for projects with the hierarchical project structure.
For using the Kotlin/JS target
Changes related to npm dependency management
When declaring dependencies on npm packages, you are now required to explicitly specify a version or version range based on npm’s semver syntax. Specifying multiple version ranges is also supported.
While we don’t recommend it, you can use a wildcard
* in place of a version number if you do not want to specify a version or version range explicitly.
Changes related to the Kotlin/JS IR compiler
Kotlin 1.4.0 introduces the Alpha IR compiler for Kotlin/JS. Learn more about the Kotlin/JS IR compiler’s backend and how to configure it.
To choose between the different Kotlin/JS compiler options, set the key
kotlin.js.compiler in your
both. Alternatively, pass
BOTH to the
js function in your
Changes in both mode
both as the compiler option (so that it will compile with both the legacy and the IR backend) means that some Gradle tasks are renamed to explicitly mark them as only affecting the legacy compilation.
compileKotlinJs is renamed to
compileTestKotlinJs is renamed to
Explicitly toggling the creation of executable files
When using the IR compiler, the
binaries.executable() instruction must be present in the
js target configuration block of your
build.gradle(.kts). If this option is omitted, only Kotlin-internal library files are generated. These files can be used from other projects, but not run on their own.
For backwards compatibility, when using the legacy compiler for Kotlin/JS, including or omitting
binaries.executable() will have no effect – executable files will be generated in either case. To make the legacy backend stop producing executable files without the presence of
binaries.executable() (for example, to improve build times where runnable artifacts aren't required), set
kotlin.js.generate.executable.default=false in your
Changes related to Dukat
The Dukat integration for Gradle has received minor naming and functionality changes with Kotlin 1.4.0.
kotlin.js.experimental.generateKotlinExternalsflag has been renamed to
kotlin.js.generate.externals. It controls the default behavior of Dukat for all specified npm dependencies.
npmdependency function now takes a third parameter after the package name and version:
generateExternals. This allows you to individually control whether Dukat should generate declarations for a specific dependency, and it overrides the
Learn how to manually trigger the generation of Kotlin externals.
Using artifacts built with Kotlin 1.4.x in a Kotlin 1.3.x project
The choice between the
LEGACY compilers was not yet available in Kotlin 1.3.xx. Because of this, you may encounter a Gradle error
Cannot choose between the following variants... if one of your dependencies (or any transitive dependency) was built using Kotlin 1.4+ but your project uses Kotlin 1.3.xx. A workaround is provided here.