Hcon: error while trying to decode MAP + sealed class

[SchweinchenFuntik]

additions to #1046

package khocon

import com.typesafe.config.ConfigFactory
import kotlinx.serialization.ExperimentalSerializationApi
import kotlinx.serialization.Serializable
import kotlinx.serialization.hocon.Hocon
import kotlinx.serialization.hocon.decodeFromConfig

@Serializable
sealed class Node

@Serializable
data class Root(val name: String): Node()

@Serializable
data class Simple(val a: String)


private val configSimpleClass = """
    key1 {
       a = "simple"
    }
    
    key2 {
       a = "simple"
    }
    """

private val configSealedClass = """
    key1 {
       type = "khocon.Root"
       name = "seale"
    }
    
    key2 {
       type = "khocon.Root"
       name = "sealed"
    }
    """

private val configSealedClassSimple = """
    {
   type = "khocon.Root"
   name = "sealed"
   }
    """

@OptIn(ExperimentalSerializationApi::class)
fun main() {
    val simpleClassConfig = ConfigFactory.parseString(configSimpleClass)
    val sealedClassConfigSimple = ConfigFactory.parseString(configSealedClassSimple)
    val sealedClassConfig = ConfigFactory.parseString(configSealedClass)
    val hocon = Hocon {
      // useArrayPolymorphism = true // error val sealedSimple = hocon.decodeFromConfig<Node>(sealedClassConfigSimple)
    }
    val simple = hocon.decodeFromConfig<Map<String, Simple>>(simpleClassConfig) // Work
    println(simple)
    val sealedSimple = hocon.decodeFromConfig<Node>(sealedClassConfigSimple)
    println(sealedSimple)
    val sealed = hocon.decodeFromConfig<Map<String, Node>>(sealedClassConfig)
    println(sealed)
}

output

Exception in thread "main" java.lang.ClassCastException: class com.typesafe.config.impl.SimpleConfigObject cannot be cast to class com.typesafe.config.ConfigList (com.typesafe.config.impl.SimpleConfigObject and com.typesafe.config.ConfigList are in unnamed module of loader 'app')
	at kotlinx.serialization.hocon.Hocon$MapConfigReader.beginStructure(Hocon.kt:200)
	at kotlinx.serialization.internal.AbstractPolymorphicSerializer.deserialize(AbstractPolymorphicSerializer.kt:130)
	at kotlinx.serialization.encoding.Decoder$DefaultImpls.decodeSerializableValue(Decoding.kt:260)
	at kotlinx.serialization.internal.TaggedDecoder.decodeSerializableValue(Tagged.kt:177)
	at kotlinx.serialization.internal.TaggedDecoder.decodeSerializableValue(Tagged.kt:206)
	at kotlinx.serialization.internal.TaggedDecoder$decodeSerializableElement$1.invoke(Tagged.kt:279)
	at kotlinx.serialization.internal.TaggedDecoder.tagBlock(Tagged.kt:296)
	at kotlinx.serialization.internal.TaggedDecoder.decodeSerializableElement(Tagged.kt:279)
	at kotlinx.serialization.encoding.CompositeDecoder$DefaultImpls.decodeSerializableElement$default(Decoding.kt:535)
	at kotlinx.serialization.internal.MapLikeSerializer.readElement(CollectionSerializers.kt:111)
	at kotlinx.serialization.internal.MapLikeSerializer.readElement(CollectionSerializers.kt:84)
	at kotlinx.serialization.internal.AbstractCollectionSerializer.readElement$default(CollectionSerializers.kt:51)
	at kotlinx.serialization.internal.AbstractCollectionSerializer.merge(CollectionSerializers.kt:36)
	at kotlinx.serialization.internal.AbstractCollectionSerializer.deserialize(CollectionSerializers.kt:43)
	at kotlinx.serialization.hocon.Hocon$ConfigReader.decodeSerializableValue(Hocon.kt:126)
	at kotlinx.serialization.hocon.Hocon.decodeFromConfig(Hocon.kt:36)
	at khocon.MainKt.main(main.kt:69)
	at khocon.MainKt.main(main.kt)

Process finished with exit code 1

output: useArrayPolymorphism = true

{key2=Simple(a=simple), key1=Simple(a=simple)}
Exception in thread "main" java.util.NoSuchElementException: List is empty.
	at kotlin.collections.CollectionsKt___CollectionsKt.last(_Collections.kt:416)
	at kotlinx.serialization.internal.TaggedDecoder.getCurrentTag(Tagged.kt:306)
	at kotlinx.serialization.hocon.Hocon$ConfigReader.beginStructure(Hocon.kt:154)
	at kotlinx.serialization.internal.AbstractPolymorphicSerializer.deserialize(AbstractPolymorphicSerializer.kt:130)
	at kotlinx.serialization.hocon.Hocon$ConfigReader.decodeSerializableValue(Hocon.kt:126)
	at kotlinx.serialization.hocon.Hocon.decodeFromConfig(Hocon.kt:36)
	at khocon.MainKt.main(main.kt:66)
	at khocon.MainKt.main(main.kt)

Environment

• Kotlin version: 1.5.10
• kotlinx-serialization-hocon: 1.2.1
• Kotlin platforms: JVM
• Gradle version: 6.8.1
• IDE version IntellijIDEA 2021.1,

[sandwwraith]

Seems like that polymorphism is not implemented in HOCON correctly

[LichtHund]

Any updates on this?

[martypitt]

I just hit a variation of this issue, which is that a List<T> (where T is a sealed class) doesn't deserialize correctly.

Usng the OP's strutruces:

@Serializable
sealed class Node

@Serializable
data class Root(val name: String): Node()

@Serializable
data class Simple(val a: String)

data class Wrapper(nodes: List<Node>)

val wrapper = Wrapper( ... )
val hocon = Hocon.encodeToConfig(wrapper)
val deserialized = Hocon.decodeFromConfig<Wrapper>(hocon)

Results in this exception:

java.lang.ClassCastException: class com.typesafe.config.impl.SimpleConfigObject cannot be cast to class com.typesafe.config.ConfigList (com.typesafe.config.impl.SimpleConfigObject and com.typesafe.config.ConfigList are in unnamed module of loader 'app')

	at kotlinx.serialization.hocon.Hocon$ListConfigReader.beginStructure(Hocon.kt:219)
	at kotlinx.serialization.internal.AbstractPolymorphicSerializer.deserialize(AbstractPolymorphicSerializer.kt:121)
	at kotlinx.serialization.encoding.Decoder$DefaultImpls.decodeSerializableValue(Decoding.kt:257)
	...

Tested using kotlinx-serialization-hocon-1.5.1.jar

[H4kt]

+1
Was trying to decode a List of sealed interface and got the same exception.
Had to fall back to YAML because of this.
Any chance of this being fixed?

@sandwwraith

[LichtHund]

I have updated my PR with a fix for this. Ended up forgetting it was still marked as draft.