ViaKotlinPlus

ViaKotlinPlus is a Kotlin rewrite of ViaFabricPlus 5.1.4. Every source file under src/ and viafabricplus-api/src/ is Kotlin; no .java sources remain.

The mod keeps ViaFabricPlus' purpose: a Fabric client mod that lets a modern Minecraft client join servers running older Minecraft versions through ViaVersion, ViaBackwards, ViaLegacy and ViaAprilFools.

Requirements

• Java 25
• A Minecraft 26.3 Fabric development environment (the Gradle wrapper and Loom handle this)

Build

./gradlew build

The built mod is in build/libs/.

Run

./gradlew runClient

Verified

The rewrite was built and launched against a locally running offline Spigot 1.8.8 server. A client joined the server, received the world and stayed in game.

For repeatable testing, the JVM property viakotlinplus.test.targetVersion forces the target protocol version before connecting:

JAVA_TOOL_OPTIONS="-Dviakotlinplus.test.targetVersion=1.8" \
  ./gradlew runClient --args="--quickPlayMultiplayer 127.0.0.1:25565"

Notes on the Mixin port

SpongePowered Mixin requires injector methods to live on the mixin class itself and, for static targets, to be static. Kotlin can only express static members through a companion object, and Mixin rejects the Companion field. The build therefore post-processes the compiled mixin classes: companion bodies are moved onto the mixin class, and a private static bridge with the original signature and Mixin annotations forwards into the body. Static fields are made private, shadow field initialisers are removed, and Kotlin's constructor NOPs are stripped, all of which Mixin requires.

The transformation lives in build.gradle.kts and runs after compileKotlin. All mixins are enabled in viafabricplus.mixins.json.

License

GPL-3.0, inherited from ViaFabricPlus. See LICENSE.