Deserialization failure for polymorphic (or sealed) classes

[zigzago]

with this bson:

{"_id":ObjectId(5d17ab793b4083d41f829821),"___type": "int-value", "value": 1}

and this class:

@Serializable
sealed class Value

@Serializable
@SerialName("int-value")
data class IntValue(val value: Int) : Value()

there is a failure during deserialization. This is because PolymorphismDecoder should use decodeSequentially at false and its decodeElementIndex should be updated to not infer that the discriminator property is always first.

I'm going to propose on a fix ;)