Using JSON.stringify on object without serializer

Using kotlin plugin 1.3.10 in Android Studio, when I try to stringify a simple class' object to JSON, it wont compile:

This declaration is experimental and its usage must be marked with '@kotlinx.serialization.ImplicitReflectionSerializer' or '@UseExperimental(kotlinx.serialization.ImplicitReflectionSerializer::class)'

@Serializable data class Data(val a: Int, val b: Int)
val data = Data(1, 2)
val x = JSON.stringify(data)

However, giving a serialiser works:

val x = JSON.stringify(Data.serializer(), data)

I can't see anybody else having this problem, any idea what the problem is? I've set up using serialisation in gradle.build.

I import with:

import kotlinx.serialization.*
import kotlinx.serialization.json.JSON

The overload of StringFormat.stringify which doesn't take in a serializer (SerializationStrategy) is still experimental. If you view its definition (e.g. ctrl+click on it in the IDE) you'll see it looks as follows:

@ImplicitReflectionSerializer
inline fun <reified T : Any> StringFormat.stringify(obj: T): String = stringify(context.getOrDefault(T::class), obj)

Where that ImplicitReflectionSerializer annotation is itself declared in that same file (SerialImplicits.kt):

@Experimental
annotation class ImplicitReflectionSerializer

So because it's still experimental, you need to do exactly as the warning says, i.e. tell the compiler to allow the use of experimental features, by adding an annotation such as @UseExperimental... where you're using it.

Note that the quick example shown on the kotlinx.serialization GitHub repo's main readme shows that you need to pass in a serializer when calling stringify.