feat: add YamlContentPolymorphicSerializer, similar to JsonContentPolymorphicSerializer

[Jojo4GH]

• Implemented YamlContentPolymorphicSerializer in the same manner as JsonContentPolymorphicSerializer
• Implemented tests for YamlContentPolymorphicSerializer
• Depends on:
  • fix: Decoder does not represent the current node correctly #617
  • Prepare fix for contextual deserialization of polymorphic scalars #618

Example usage:

@Serializable(with = AnimalSerializer::class)
sealed interface Animal {
    @Serializable data class Cat(val isPurring: Boolean)
    @Serializable data class Dog(val isBarking: Boolean)
}

object AnimalSerializer : YamlContentPolymorphicSerializer<Animal>(Animal::class) {
    override fun selectDeserializer(node: YamlNode): DeserializationStrategy<Animal> = when {
        node.yamlMap.getKey("isPurring") != null -> Animal.Cat.serializer()
        node.yamlMap.getKey("isBarking") != null -> Animal.Dog.serializer()
        else -> error("Unknown animal")
    }
}

[Jojo4GH]

Optional improvement: Make the YamlNode API a bit more consumer friendly (especially for getting keys in YamlMap)

If this should be implemented in this PR, then I can do it

[charleskorn]

• Fixed bug with YamlInput::node
• Fixed bug with sealed polymorphism for scalars represented as inline value classes

Could you please elaborate on these? Perhaps they could be separate PRs to help keep this one smaller and easier to review.

Optional improvement: Make the YamlNode API a bit more consumer friendly (especially for getting keys in YamlMap)

If this should be implemented in this PR, then I can do it

Sounds like something for a separate PR.

[Jojo4GH]

Fixed bug with YamlInput::node

Previously the node property on the decoders was not traversed in deep YAML trees (e.g. with YamlMapLikeInputBase and YamlListInput). This behaviour is different from the JSON serialization library and makes it impossible to implement a content based polymorphic KSerializer in a meaningful way without knowing of the whole YAML tree. See also the DecodingFromYamlNodeSerializer in YamlReadingTest.kt for an affected case

Fixed bug with sealed polymorphism for scalars represented as inline value classes

Previously it was not possible to implement a content based polymorphic serializer in the case that one of the types involved is a scalar. Different from the JSON serialization library it was therefore impossible to implement something like:

myCats:
  myFirstCat: "Bella"
  mySecondCat:
    name: "Daisy"
    age: 2

typealias MyCats = Map<String, CatDetails>

@Serializable(with = MyContentBasedSerializer::class)
sealed interface CatDetails {

    @Serializable
    value class InlineName(val name: String) : CatDetails

    @Serializable
    data class More(
        val name: String,
        val age: String?
    ) : CatDetails
}

object MyContentBasedSerializer : YamlContentPolymorphicSerializer<CatDetails>(CatDetails::class) {
    override fun selectDeserializer(node: YamlNode) = when (node) {
        is YamlScalar -> CatDetails.InlineName.serializer()
        is YamlMap -> CatDetails.More.serializer()
        else -> error("Unsupported node type ${node::class.simpleName}")
    }
}

Optional improvement: [...]

Will do it sometime later in a separate PR.

[charleskorn]

Could you please split the two bug fixes out as their own separate PR? This is quite a big PR and so breaking it down into smaller pieces will make it easier for me to review.

[Jojo4GH]

Could you please split the two bug fixes out as their own separate PR? This is quite a big PR and so breaking it down into smaller pieces will make it easier for me to review.

This PR now depends on:

• fix: Decoder does not represent the current node correctly #617
• Prepare fix for contextual deserialization of polymorphic scalars #618

[Jojo4GH]

Could you please split the two bug fixes out as their own separate PR? This is quite a big PR and so breaking it down into smaller pieces will make it easier for me to review.

This PR now depends on:

• fix: Decoder does not represent the current node correctly #617
• Prepare fix for contextual deserialization of polymorphic scalars #618

The necessary PRs are now merged so I merged main for easier review @charleskorn

[charleskorn]

Rather than checking the name like this, what if we introduced an annotation that is added to the SerialDescriptor created by YamlContentPolymorphicSerializer, then checked for its presence here?

[Jojo4GH]

The annotation is implemented as internal for now. Or should it be public?