jsonb field with "path" arg applied can lead to json decode error

[john-kelly]

first off, incredible work!

relevant data to reproduce error

this example comes from the https://pokeapi.co/ graphql api

query:

query AllPokemonWithSprites {
  pokemon_v2_pokemonsprites {
    sprites(path: "front_default")
    pokemon_v2_pokemon {
      name
      id
    }
  }
}

elm-gql / elm-prefab config:

  "graphql": {
    "schema": "https://beta.pokeapi.co/graphql/v1beta",
    "header": []
  }

generated elm decoder:

decoder_ : Int -> Json.Decode.Decoder Response
decoder_ version_ =
    Json.Decode.succeed Response
        |> GraphQL.Decode.versionedField
            version_
            "pokemon_v2_pokemonsprites"
            (Json.Decode.list
                (Json.Decode.succeed Pokemon_v2_pokemonsprites
                    |> GraphQL.Decode.field "sprites" Api.jsonb.decoder
                    |> GraphQL.Decode.field
                        "pokemon_v2_pokemon"
                        (Json.Decode.nullable
                            (Json.Decode.succeed Pokemon_v2_pokemon
                                |> GraphQL.Decode.field
                                    "name"
                                    Json.Decode.string
                                |> GraphQL.Decode.field "id" Json.Decode.int
                            )
                        )
                )
            )

relevant sprites field part of the schema (in case you didnt want to ping schema endpoint):

{
    "name": "sprites",
    "description": null,
    "args": [
        {
            "name": "path",
            "description": "JSON select path",
            "type": {
                "kind": "SCALAR",
                "name": "String",
                "ofType": null
            },
            "defaultValue": null
        }
    ],
    "type": {
        "kind": "NON_NULL",
        "name": null,
        "ofType": {
            "kind": "SCALAR",
            "name": "jsonb",
            "ofType": null
        }
    },
    "isDeprecated": false,
    "deprecationReason": null
}

i found some docs on this kind "json select path" arg in the hasura docs. i'm not sure if this feature is a typical graphql pattern! so apologies if the above link is unnecessary

experimentation

from my testing, it seems that this particular field can be null when you search for a path that isn't found!
i changed the generated code to just be a "nullable string" for this field and everything worked. seems the jsonb decoder is just a Json.Decode.string. not sure the right API change in this case but thought this info could be useful!

i imagine this could be an error with the graphql server/schema itself rather than the elm-gql library? i'm not familiar enough with graphql client vs server to make that claim. i was under the impression that the schema was always correct, but i'm not sure!