serializer<KType>() throws SerializationException when used with sealed class on JS

[rnett]

I have a sealed class Trait in common code:

@Serializable
sealed class Trait() {
    abstract val name: String
    ...
}

I want to get it's serializer via serializer<Trait>(). On JVM this works fine and I get a SealedClassSerializer. On JS (IR) I get:

"SerializationException: Serializer for class 'Trait' is not found.
Mark the class as @Serializable or provide the serializer explicitly.
On Kotlin/JS explicitly declared serializer should be used for interfaces and enums without @Serializable annotation
    at platformSpecificSerializerNotRegistered (http://localhost:8080/static/spellbook.js:159984:11)
    at serializer (http://localhost:8080/static/spellbook.js:155641:7)
    at main (http://localhost:8080/static/spellbook.js:188469:25)
    at Object.<anonymous> (http://localhost:8080/static/spellbook.js:195282:3)
    at http://localhost:8080/static/spellbook.js:136257:37
    at Object.<anonymous> (http://localhost:8080/static/spellbook.js:136260:2)
    at Object.H:\Google Drive\My Stuff\spellbook\build\js\packages\spellbook\kotlin\spellbook.js (http://localhost:8080/static/spellbook.js:195286:30)
    at __webpack_require__ (http://localhost:8080/static/spellbook.js:30:30)
    at Object.0 (http://localhost:8080/static/spellbook.js:106:18)
    at __webpack_require__ (http://localhost:8080/static/spellbook.js:30:30)
    at http://localhost:8080/static/spellbook.js:94:18
    at http://localhost:8080/static/spellbook.js:97:10
    at webpackUniversalModuleDefinition (http://localhost:8080/static/spellbook.js:9:23)
    at http://localhost:8080/static/spellbook.js:10:3"

This is with 1.0.0-RC2.

[rnett]

More info: it is definitely related to resolving the serializer. Using Trait.serializer() directly works just fine, it is only when I try to get it via serializer<Trait>() or use it in another serializable class I get this error. Even adding it to the serialization module explicitly using something like:

SerializersModule {
    polymorphic(Trait::class, Trait.serializer())
}

doesn't help, it causes Serializer for Trait can't be registered as a subclass for polymorphic serialization because its kind SEALED is not concrete. To work with multiple hierarchies, register it as a base class. even though I am passing it as the base class serializer.

Full stack trace:

"IllegalArgumentException: Serializer for Trait can't be registered as a subclass for polymorphic serialization because its kind SEALED is not concrete. To work with multiple hierarchies, register it as a base class.
    at checkKind_0 (http://localhost:8080/static/spellbook.js:147781:13)
    at PolymorphismValidator.polymorphic_1 (http://localhost:8080/static/spellbook.js:147759:5)
    at SerialModuleImpl.dumpTo_0 (http://localhost:8080/static/spellbook.js:145927:19)
    at validateConfiguration (http://localhost:8080/static/spellbook.js:146289:40)
    at new JsonImpl (http://localhost:8080/static/spellbook.js:146263:5)
    at Json_1 (http://localhost:8080/static/spellbook.js:146195:12)
    at Json$default (http://localhost:8080/static/spellbook.js:146199:12)
    at main (http://localhost:8080/static/spellbook.js:174473:18)
    at Object.<anonymous> (http://localhost:8080/static/spellbook.js:181357:3)
    at http://localhost:8080/static/spellbook.js:122208:37
    at Object.<anonymous> (http://localhost:8080/static/spellbook.js:122211:2)
    at Object.H:\Google Drive\My Stuff\spellbook\build\js\packages\spellbook\kotlin\spellbook.js (http://localhost:8080/static/spellbook.js:181361:30)
    at __webpack_require__ (http://localhost:8080/static/spellbook.js:30:30)
    at Object.0 (http://localhost:8080/static/spellbook.js:106:18)
    at __webpack_require__ (http://localhost:8080/static/spellbook.js:30:30)
    at http://localhost:8080/static/spellbook.js:94:18
    at http://localhost:8080/static/spellbook.js:97:10
    at webpackUniversalModuleDefinition (http://localhost:8080/static/spellbook.js:9:23)
    at http://localhost:8080/static/spellbook.js:10:3"

Specifying the subclasses explicitly without a base serializer does work. E.g.:

polymorphic(Trait::class){
    subclass(Trait.Attack::class, Trait.Attack.serializer())
    subclass(Trait.Other::class, Trait.Other.serializer())
}

Although note that this only fixes serialization/deserialization of the class, serializer<KType>() still won't work.

[sandwwraith]

Yes, that's unfortunately a current limitation on Kotlin/JS and Kotlin/Native — serializer<T>() does not work with sealed/abstract classes

[rnett]

Is this something that's planned to be fixed by 1.0 or soonish, or is it a longer term issue?

[sandwwraith]

It is likely won't be fixed in 1.0 but we have it on our radar for future releases

[theromis]

@sandwwraith my kotlin/js serializer just hangs:

@Serializable(with = LonjeDateSerializer::class)
actual class LonjeDate {
    actual val format: String
        get() {
            return "format"
        }
}

@Serializer(LonjeDate::class)
actual object LonjeDateSerializer : KSerializer<LonjeDate> {
    override val descriptor: SerialDescriptor =
        PrimitiveSerialDescriptor("kotlinx.serialization.LonjeDateSerializer", PrimitiveKind.STRING)

    override fun serialize(encoder: Encoder, value: LonjeDate) {
    }

    override fun deserialize(decoder: Decoder): LonjeDate {
        return LonjeDate()
    }
}

is it known issue?
Asked question here #1086

[rnett]

As a workaround, it seems to work as long as the sealed class has type parameters.

[rjaros]

Is this issue fixed in 1.2.0?

[sandwwraith]

Nope, it will likely be fixed in Kotlin 1.5.20

[nschulzke]

What version will this be fixed in for Kotlin/JS? I'm seeing it right now in Kotlin 1.5.21 and Kotlinx.Serialization 1.2.1.

[sandwwraith]

@nschulzke Do you use JS IR?

[nschulzke]

Yes, I'm using IR.

[sandwwraith]

Can you post your reproducer, please?

[nschulzke]

Ah, wait, I thought this issue would resolve the error "Serializer for ___ can't be registered as a subclass for polymorphic serialization because its kind SEALED is not concrete." It looks like that error was related, but not changed here.

I'll ask a question on the Kotlin Slack and maybe file a different issue.

Sorry for the confusion!

[bcwhite-code]

I'm encountering the same issue with the IR compiler. If I switch to LEGACY, it works fine. Doing the test via JVM is also fine.

build.gradle.kts:

plugins {
    kotlin("multiplatform") version "1.7.+"
    kotlin("plugin.serialization") version "1.7.+"
    application
}

AccessibleRegionsRequest.kt:

import kotlinx.serialization.Serializable
@Serializable
data class AccessibleRegionsRequest(
    val worldId: String,
)

AccessibleRegionsTest.kt:

class AccessibleRegionsTest {
    @Test
    fun testFakeCall() {
        val req = AccessibleRegionsRequest(
            worldId = "foo-bar",
        )
        val reqs = Json.encodeToString(req)
        assertEquals("""{"worldId":"foo-bar"}""", reqs)
        val req2 = Json.decodeFromString<AccessibleRegionsRequest>(reqs)
        assertEquals(req, req2)
    }
}

Test Output:

SerializationException: Serializer for class 'AccessibleRegionsRequest' is not found.
Please ensure that class is marked as '@Serializable' and that the serialization compiler plugin is applied.
On Kotlin/JS explicitly declared serializer should be used for interfaces and enums without @Serializable annotation
SerializationException: Serializer for class 'AccessibleRegionsRequest' is not found.
Please ensure that class is marked as '@Serializable' and that the serialization compiler plugin is applied.
On Kotlin/JS explicitly declared serializer should be used for interfaces and enums without @Serializable annotation
	at <global>.platformSpecificSerializerNotRegistered(C:/Users/bcwhite/AppData/Local/Temp/_karma_webpack_539458/commons.js:40973)
	at <global>.serializer(C:/Users/bcwhite/AppData/Local/Temp/_karma_webpack_539458/commons.js:35040)
	at com.riverworth.deity.common.api.AccessibleRegionsTest.testFakeCall_flu7nw(C:/Users/bcwhite/AppData/Local/Temp/_karma_webpack_539458/commons.js:5455)
	at <global>.test_fun$AccessibleRegionsTest_test_fun$testFakeCall_test_fun_9hdub3(C:/Users/bcwhite/AppData/Local/Temp/_karma_webpack_539458/commons.js:5486)
	at Context.<anonymous>(C:/Users/bcwhite/AppData/Local/Temp/_karma_webpack_539458/commons.js:47604)

[Coneys]

Any update about this? I have the same issue with IR backend, on Legacy it works fine

[bcwhite-code]

I think it'll need to be re-opened as a new issue.