Add proper support for custom JSON object / list scalar types

[sav007]

Add support for encoding / decoding custom GraphQL scalar type value represented by JSON object into Map.
Add support for encoding / decoding custom GraphQL scalar type value represented by JSON list into List.

[martinbonnin]

Just curious: are JSON objects/lists scalar types actually part of the spec or just some handy extensions that we allow ?

[sav007]

@martinbonnin Well I didn't find in spec that custom scalar type should be strictly a string, and looking into the introspection query response, this is how scalar type is defined:

{
          "kind": "SCALAR",
          "name": "Date",
          "description": "The `Date` scalar type represents date format.",
          "fields": null,
          "inputFields": null,
          "interfaces": null,
          "enumValues": null,
          "possibleTypes": null
        }

At the same time custom scalar type probably should be true scalar. But in the past I remember that it was a feature request to add support to map custom scalar type into Map, like for instance to be able to map geo coordinates {"longitude": ..., "latitude": } into Map.

So yes it's probably smth we offer as convenience.

[martinbonnin]

👍 I guess users can still override the default behaviour if they're not happy with it, right ? So the default new adapters will be handy for 99% of users. Those who have specific use cases can still override them ?

[sav007]

For sure, we just provide a default adapter for list and map.

[taion]

They are explicitly allowed by the spec, which is why GraphQLJSON works. Just somewhat underdocumented.