Kotlin Toolchain 0.12: Multiplatform Library Publishing, Wasm Apps, and More

Kotlin Toolchain 0.12.0 expands multiplatform library publishing beyond JVM targets to include Android, iOS, and Wasm. The configuration mirrors existing JVM publishing, requiring only a `platforms` list and `publishing.enabled: true`. This unifies the workflow for distributing libraries across all supported targets, eliminating the need for platform-specific adjustments. However, Compose Multiplatform resources are not yet included in publications, which may limit adoption for UI-heavy libraries until the feature matures.

The preview of Wasm application support introduces a new `wasm-js/app` module type that compiles to a deployable web application. Developers can customize `index.html` and other resources, while transitive npm dependencies from Kotlin Multiplatform libraries are automatically resolved. This simplifies Wasm adoption but remains in preview, meaning production use may require workarounds for unsupported edge cases. The integration with the `kotlin run` command suggests a focus on developer experience, though long-term stability will depend on community feedback.

To comply with Maven Central’s upcoming quotas, the toolchain now publishes only `.md5` and `.sha1` checksums by default, omitting `.sha256` and `.sha512` unless explicitly configured. This change reduces the number of published files but may break workflows relying on stronger checksums. Teams will need to audit their publishing pipelines to ensure compatibility. The removal of `.asc.sha1` checksums for signature files is a minor but welcome reduction in redundancy.

IDE and tooling improvements in this release target productivity gaps for Android, iOS, and Compose developers. Compose preview support now extends to Android and KMP modules, while iOS run configurations gain device selection and Xcode option customization. These changes address long-standing friction points but require IntelliJ IDEA 2026.2.1 or newer, which may delay adoption for teams on older IDE versions. The focus on stability in Kotlin/Swift interoperability suggests ongoing investment in iOS tooling.

The release also includes smaller but impactful quality-of-life updates, such as inlay hints for catalog dependencies and better test diagnostics in the status widget. These changes reflect a broader effort to reduce verbosity in the `kotlin` command output. While not groundbreaking, they demonstrate a commitment to incremental tooling refinement. Engineers should expect further polish in future releases, particularly around Compose Hot Reload and Wasm support.