Polymorphic deserialization with kotlinx.serialization in Kotlin/Native - json

Question

I want to decode a json string containing a list of objects in a polymorphic class structure using kotlinx.serialization in a Kotlin Multiplatform project, but it works only on JVM, not on Native. Here is a minimum reproducible example:
#Serializable
abstract class Project {
abstract val name: String
}
#Serializable
#SerialName("BasicProject")
data class BasicProject(override val name: String): Project()
#Serializable
#SerialName("OwnedProject")
data class OwnedProject(override val name: String, val owner: String) : Project()
fun main() {
val data = Json.decodeFromString<List<Project>>("""
[
{"type":"BasicProject","name":"example"},
{"type":"OwnedProject","name":"kotlinx.serialization","owner":"kotlin"}
]
"""))
}
This works on JVM but throws the following exception on Native:
kotlinx.serialization.SerializationException: Serializer for class ‘Project’ is not found.
Mark the class as #Serializable or provide the serializer explicitly.
On Kotlin/Native explicitly declared serializer should be used for interfaces and enums without #Serializable annotation.message
This problem has been discussed before in the context of encoding and some workarounds have been suggested, e.g. here, but my problem is decoding. Is there a workaround, or do I simply have to implement my own json parser?

Answer 1

You need to explicitly pass respectful serializer and serializersModule:
object ListOfProjectSerializer : KSerializer<List<Project>> by ListSerializer(Project.serializer())
val module = SerializersModule {
polymorphic(Project::class) {
subclass(BasicProject::class)
subclass(OwnedProject::class)
}
}
fun main() {
val data = Json { serializersModule = module }.decodeFromString(
ListOfProjectSerializer,
"""
[
{"type":"BasicProject","name":"example"},
{"type":"OwnedProject","name":"kotlinx.serialization","owner":"kotlin"}
]
"""
)
}