SerializationException: Class 'ArrayList' is not registered for polymorphic serialization in the scope of 'Any'.

Describe the bug

Following code work on serialization pre-release artifact org.jetbrains.kotlinx:kotlinx-serialization-runtime. When using same code with 1.0.0-RC2 or later with artifact org.jetbrains.kotlinx:kotlinx-serialization-json

I get runtime exception

SerializationException: Class 'ArrayList' is not registered for polymorphic serialization in the scope of 'Any'.

I’ve tried to pull out the essential parts from a larger project.

#1252 may be related. I’m not sure if this is a duplicate of different use case, or a separate issue.

To Reproduce

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


interface RpcSerializer<ReqT, ResT> {

    fun serializeRequest(rpcRequest: RpcRequest): ReqT
    fun serializeResponse(rpcResponse: RpcResponse): ResT

    fun deserializeRequest(request: ReqT): RpcRequest
    fun deserializeResponse(response: ResT): RpcResponse

}

class JsonRpcSerializer(serializerModule: SerializersModule) : RpcSerializer<String, String> {

    private val serializer = Json {
        useArrayPolymorphism = true
        encodeDefaults = true
        serializersModule = serializerModule
    }

    override fun serializeRequest(rpcRequest: RpcRequest): String {
        return serializer.encodeToString(rpcRequest)
    }

    override fun serializeResponse(rpcResponse: RpcResponse): String {
        return serializer.encodeToString(rpcResponse)
    }

    override fun deserializeRequest(request: String): RpcRequest {
        return serializer.decodeFromString(request)
    }

    override fun deserializeResponse(response: String): RpcResponse {
        return serializer.decodeFromString(response)
    }

}

class RpcSerializerImpl constructor(

    private val actualSerializer: RpcSerializer<String, String> = JsonRpcSerializer(
        module
    )
) : RpcSerializer<String, String> {

    override fun serializeRequest(rpcRequest: RpcRequest) = actualSerializer.serializeRequest(rpcRequest)
    override fun serializeResponse(rpcResponse: RpcResponse) = actualSerializer.serializeResponse(rpcResponse)
    override fun deserializeRequest(request: String) = actualSerializer.deserializeRequest(request)
    override fun deserializeResponse(response: String) = actualSerializer.deserializeResponse(response)
}

@Serializable
data class Identifier(val name: String, val description: String)

@Serializable
data class Point(val x: Double, val y: Double, val id: Identifier)

@Serializable
data class RpcIdentifier(
    val serviceName: String,
    val name: String,
    val parameters: List<String>,
    val returnType: String
)

@Serializable
data class RpcRequest(
    val id: Long,
    val functionSignature: RpcIdentifier,
    val arguments: List<RpcData>
)


@Serializable
class RpcSynchronousResponse(
    override val id: Long,
    @Polymorphic
    val data: RpcData
): RpcResponse() {
    override fun toString(): String {
        return "RpcSynchronousResponse[$id]($data)"
    }
}


val module = SerializersModule {
    polymorphic(Any::class) {
        subclass(RpcSynchronousResponse::class)
        subclass(RpcData::class)
        subclass(Point::class)

    }
    polymorphic(RpcData::class) {
        subclass(RpcData::class)
    }

    polymorphic(RpcResponse::class) {
        subclass(RpcSynchronousResponse::class)
    }
}

val format = Json { serializersModule = module }

@Serializable
data class RpcData(
    @Polymorphic
    val value: Any?
)


@Serializable
abstract class RpcResponse {
    abstract val id: Long
}

@Serializable
class RpcExceptionResponse(
    override val id: Long,
    val exception: String
): RpcResponse() {
    override fun toString(): String {
        return "RpcExceptionResponse[$id]($exception)"
    }
}



fun main() {

    val serializer = RpcSerializerImpl()

    val point1 = Point(1.0,1.0,Identifier("one","111"))
    val point2 = Point(2.0,-1.0,Identifier("two","222"))
    val data = RpcData(listOf(point1,point2))

    val responseToSerialize = RpcSynchronousResponse(42L, data)
    println("responseToSerialize: $responseToSerialize")

    val jsonString = serializer.serializeResponse(responseToSerialize)
    println("jsonString $jsonString")

    val backAgain = serializer.deserializeResponse(jsonString)
    println("backAgain: $backAgain")
}

Expected behavior

Same result as when using pre-release org.jetbrains.kotlinx:kotlinx-serialization-runtime version 1.0-M1-1.4.0-rc, printout as follows:

responseToSerialize: RpcSynchronousResponse[42](RpcData(value=[Point(x=1.0, y=1.0, id=Identifier(name=one, description=111)), Point(x=2.0, y=-1.0, id=Identifier(name=two, description=222))])) jsonString [“RpcSynchronousResponse”,{“id”:42,“data”:[“RpcData”,{“value”:[“kotlin.collections.ArrayList”,[[“Point”,{“x”:1.0,“y”:1.0,“id”:{“name”:“one”,“description”:“111”}}],[“Point”,{“x”:2.0,“y”:-1.0,“id”:{“name”:“two”,“description”:“222”}}]]]}]}] backAgain: RpcSynchronousResponse[42](RpcData(value=[Point(x=1.0, y=1.0, id=Identifier(name=one, description=111)), Point(x=2.0, y=-1.0, id=Identifier(name=two, description=222))]))

Environment

• Kotlin version: 1.4.30
• Library version: 1.1.0-RC
• Kotlin platforms: JVM,
• Gradle version: 6.6.1
• IDE version (if bug is related to the IDE) [e.g. IntellijIDEA 2020.3.2
• Other relevant context [e.g. OS version, JRE version, … ] Java 1.8

[GeorgePap-719]

@jannehof this worked for me by adding a simple cast fun. My code: subClass(ArrayList::class, ListSerializer(PolymorphicSerializer(Any::class)).cast()) the extension fun: @Suppress("UNCHECKED_CAST", "NOTHING_TO_INLINE") private inline fun <T> KSerializer<List<Any>>.cast(): KSerializer<T> { return this as KSerializer<T> }

My use case: I needed to serializer a list which was either a string or a customDto. If u you need any more info for my code let me know. @sandwwraith i think it’s ok to close this issue as your example works.

[GeorgePap-719]

Im guessing you are using this factory fun:

public fun <T> listOf(element: T): List<T> = java.util.Collections.singletonList(element)

Try to use this fun from stdlib which is not returning singletonList :

public fun <T> listOf(vararg elements: T): List<T> = if (elements.size > 0) elements.asList() else emptyList()