Serializable(with = PolymorphicSerializer::class) is not recognized at the top level

[elizarov]

Consider this code:

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

import kotlinx.serialization.modules.*

val module = SerializersModule {
    polymorphic(Repository::class) {
        subclass(OwnedRepository::class)
    }
}

val format = Json { serializersModule = module }

@Serializable(with = PolymorphicSerializer::class)
interface Repository {
    val name: String
}

@Serializable
@SerialName("owned")
class OwnedRepository(override val name: String, val owner: String) : Repository

fun main() {
    val data: Repository = OwnedRepository("kotlinx.coroutines", "kotlin")
    println(format.encodeToString(data))
}    

Here an interface is annotated with @Serializable(with = PolymorphicSerializer::class) and then the variable data of type Repository is serialized with format.encodeToString(data) function. It fails to retrieve the serializer from this annotation:

Exception in thread "main" kotlinx.serialization.SerializationException: Serializer for class 'Repository' is not found. Mark the class as @Serializable or provide the serializer explicitly.

Expected: It should work just as it works when Repository is used as a property in another serializable class.