Kotlin SDK

Kotlin uses the same runtime, agent, annotations, and registry binding as the Java SDK — read that page for interception, RegistryBinding, control annotations, and troubleshooting. What differs is the compile-time half: Kotlin code is processed by a KSP plugin, io.varianz.sdk.kotlin, not the Java annotation processor.

Setup

plugins {
    id("com.google.devtools.ksp") version "2.1.10-1.0.29" // must come before the Varianz plugin
    id("io.varianz.sdk.kotlin")
}

dependencies {
    ksp("com.github.javaparser:javaparser-core:3.27.0")   // the plugin does not add this
}

configure<io.varianz.gradle.kotlin.VarianzKotlinExtension> {
    sdkVersion.set("0.2.1")
}

Four things trip up first-time setup:

The plugin id is io.varianz.sdk.kotlin, not io.varianz.sdk.
Apply KSP first — the plugin throws unless com.google.devtools.ksp precedes it in the plugins {} block.
Add JavaParser to ksp yourself — without it the processor dies with NoClassDefFoundError: com/github/javaparser/ast/Node.
Configure via the typed extension (configure<VarianzKotlinExtension>) — the generated varianz {} accessor isn’t available when the plugin is applied dynamically.

The pluginManagement repository setup is the same as Java’s.

Defining VPoints

import io.varianz.annotations.vpoint.VPoint

class PricingService {
    @VPoint(name = "pricing/calculate")
    fun calculatePrice(amount: Double, discount: Double): Double =
        amount * (1 - discount)
}

Annotation attributes require named arguments: @VPoint(name = "…"), never positional.
Data-class fields map naturally: val becomes read-only in the schema, var read-write. Names convert to snake_case for CEL.

Not supported in `@VPoint` signatures

Two Kotlin features are rejected at compile time with clear errors:

@JvmInline value class parameters or returns
suspend fun — wrap the suspending call in a plain function and instrument that

Runtime and deployment

Everything on the Java page applies: the varianz-agent must be attached (automatic for Gradle test/run, explicit for production launchers), RegistryBinding.init(...) + <Class>VPoints.bind(instance) at startup, and --enable-native-access=io.varianz.native_loader on Java 22+. For session propagation with coroutines, carry the session in a context the caller thread can read — with OpenTelemetry, opentelemetry-extension-kotlin’s asContextElement() keeps Baggage flowing across suspensions. See Propagate sessions.

Testing

Kotlin tests use the JUnit 5 extension (see Testing → JUnit); a Kotest extension (io.varianz:varianz-kotest) provides the same session lifecycle for Kotest specs:

class PricingTests : FunSpec({
    val varianz = VarianzExtension()
    extension(varianz)

    test("stage overrides price") {
        val session = varianz.session()
        session.insert(cel("pricing/calculate", """Quote { price: 999.0, currency: "USD" }"""))
        // ...
    }
})

Getting started

Core concepts

Guides

SDK reference

Testing

Reference

Setup

Defining VPoints

Not supported in `@VPoint` signatures

Runtime and deployment

Testing

​Setup

​Defining VPoints

​Not supported in @VPoint signatures

​Runtime and deployment

​Testing

Setup

Defining VPoints

Not supported in `@VPoint` signatures

Runtime and deployment

Testing