Support for deserializing JSON string values as enums in a sealed type hierarchy

[runeflobakk]

I have been playing a bit with the combination of a sealed interface, annotated with @JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION), and some permitted subclasses. I find this feature very nice, with the caveat that the existence of attributes in the JSON must uniquely identify type.

I was wondering if it would make sense to support enums as permitted subtypes of a sealed interface, and using Id.DEDUCTION?

Given e.g. a hierarchy like this:

@JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION)
sealed interface Base {
    record A(String message) implements Base {}
    record B(int code) implements Base {}
    enum Constant implements Base {
        X, Y
    }
}

record MyObject(int id, Base value) {}

I can, as expected, deserialize MyObject and get the Base field mapped as either A or B records automatically. But I think it would be really nice if it was also possible to support JSON string values to be deserialized as a matching enum constant, e.g. to sort of include the standard enum deserializing-support into the support for JsonTypeInfo.Id.DEDUCTION on a sealed interface.

Expressed as a test:

var parsedConstant = JsonMapper.shared().readValue("""
        {
          "id": 42,
          "value": "Y"
        }
        """, MyObject.class);
assertEquals(new MyObject(42, Base.Constant.Y), parsedConstant);

I think the sort of equivalent caveat can apply here as the mentioned "existence of attributes in the JSON must uniquely identify type" for beans/records, i.e. if there are multiple permitted enum subtypes of the sealed interface, as long as the names are unique across all the enums, it is possible to resolve which enum constant to resolve from a JSON string.

I did some tinkering with a custom deserializer, to see if I could inspect JsonParser.hasToken(JsonToken.VALUE_STRING), and in that case delegate to deserializing an enum constant, and otherwise do the regular resolving of the record/bean to deserialize, but this proved to be a too difficult task for me to tap into the existing "plumbing" in Jackson instead of doing my own frail reimplementation of the deserialization facilities already present.

What do you think? :)