serializer

abstract class Foo<Self : Foo<Self>> {
    abstract val serializer: KSerializer<Self>

    @ExperimentalSerializationApi
    @InternalSerializationApi
    object Serializer : SerializationStrategy<Foo<*>> {
        override val descriptor: SerialDescriptor =
            buildSerialDescriptor(Foo::class.qualifiedName!!, PolymorphicKind.OPEN)

        @Suppress("UNCHECKED_CAST")
        override fun serialize(encoder: Encoder, value: Foo<*>) {
            encoder.encodeSerializableValue(value.serializer as SerializationStrategy<Foo<*>>, value)
        }
    }
}

@Serializable
class FooImpl : Foo<FooImpl>() {
    override val serializer: KSerializer<FooImpl>
        get() = serializer()
}

@OptIn(ExperimentalSerializationApi::class, InternalSerializationApi::class)
fun main() {
    println(Json.encodeToString(Foo.Serializer, FooImpl()))
}