Json decoding using non JsonOutput

For now, it is impossible to decode JsonElement from decoder inside of serializer if that decoder was not created by Json. Example:

object : KSerializer<Any> {
    override val descriptor = StringDescriptor.withName("Example")

    override fun deserialize(decoder: Decoder) {
        val json = JsonElementSerializer.deserialize(decoder)
    }

    override serialize(encoder: Encoder, obj: Any) {
        TODO()
    }
}

Object will throw exception in deserialize method each time when this serializer will not be used with Json formatter.

Is it possible to solve this problem?

[qwwdfsad]

Closing as won’t fix

[qwwdfsad]

Yes, and values of these objects can still be either primitives or nested objects. I’ve already described it above (https://github.com/Kotlin/kotlinx.serialization/issues/615#issuecomment-564563279) why it is impossible to do with non json-specific decoder and why it works for json-specific ones.

It is not the matter of “we don’t want to allow to deserialize JsonElement with a non-JsonInput decoder”, it is just impossible for an arbitrary JsonElement.

Non-polymorphic serialization of JsonElement with a custom decoder is, though, possible, but then it will be impossible to deserialize it back. But such serialization doesn’t follow the principle of least surprise and, thus, is inappropriate.

Polymorphic serialization is possible (and enables deserialization by an arbitrary decoder), but produces a really weird format that definitely is not an expected JSON and also doesn’t follow PoLA. Moreover, if an unprepared user will just wrap a JsonInput into any kind of delegation, his JSON, from a pretty {"key": "value", "key2", null} representation will become ["kotlinx.serialization.json.JsonObject", {"key": ["kotlinx.serialization.json.JsonPrimitive", "value"], "key2": ["kotlinx.serialization.json.JsonNull", "Unit"]}]. Also a no-go