Kotlin - Cannot serialize polymorphic classes. No serializer found

Question

I am trying to serialize polymorphic classes using kotlinx.serialization with kotlin/native. I am using the sample provided in the serialization guide:

val module = SerializersModule {
    polymorphic(Project::class) {
        subclass(OwnedProject::class)
    }
}

val format = Json { serializersModule = module }

@Serializable
abstract class Project {
    abstract val name: String
}
            
@Serializable
@SerialName("owned")
class OwnedProject(override val name: String, val owner: String) : Project()

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

This code works when run with JVM, but when compiled and run with kotlin native for linuxX64 it throws an error:

Uncaught Kotlin exception: kotlinx.serialization.SerializationException: Serializer for class 'Project' is not found. Mark the class as @Serializable or provide the serializer explicitly.
    at kfun:kotlin.Throwable#<init>(kotlin.String?){} (0x294767)
    at kfun:kotlin.Exception#<init>(kotlin.String?){} (0x28ea25)
    at kfun:kotlin.RuntimeException#<init>(kotlin.String?){} (0x28e725)
    at kfun:kotlin.IllegalArgumentException#<init>(kotlin.String?){} (0x28e925)
    at kfun:kotlinx.serialization.SerializationException#<init>(kotlin.String?){} (0x350185)
    at kfun:kotlinx.serialization.internal#[email protected]<*>(){}kotlin.Nothing (0x36fa0d)
    at kfun:kotlinx.serialization#[email protected]<0:0>(){0§<kotlin.Any>}kotlinx.serialization.KSerializer<0:0> (0x3505c8)
    at kfun:kotlinx.serialization.serializer$serializerByKTypeImpl#internal (0x3512d2)
    at kfun:kotlinx.serialization#serializer(kotlin.reflect.KType){}kotlinx.serialization.KSerializer<kotlin.Any?> (0x3503c8)
    ...

Do I understand it incorrectly, that the code should be working on both platforms ? How to make it work on native ?

Paapanen

Answer 1

As i found out from github issues its current limitation.

It is a current limitation that should be properly documented (cc @qwwdfsad ). Please try format.encodeToString(PolymorphicSerializer(Project::class), data). In case of sealed classes, it should work. If it doesnt, simply use format.encodeToString(Project.serializer(), data)

Paapanen

Answer 2

Yes, it's a current limitation, you can check out the Polymorphism documentation here and you can track the issue #1077

Aghast

Answer 3

You missed to declare serializer for the OwnedProject class while define as subclass of SerializersModule.

val module = SerializersModule {
        polymorphic(Project::class) {
            subclass(OwnedProject::class, OwnedProject.serializer()) // add here OwnedProject class serializer
        }
    }

Book