FieldResult<TResult> fails field resolver

[DovydasNavickas]

Product

Hot Chocolate

Version

14.0.0-rc.3.4

Link to minimal reproduction

https://github.com/MartynasZilinskas/hotchocolate-fieldresult-bug-repro/tree/main

Steps to reproduce

1. Run the repro project
2. Run query successfully, because createdBy resolver doesn't use FieldResult<TResult> and returns TResult directly:

   query {
   book {
   id
   title
   createdBy {
     id
     name
   }
   }
   }

3. Run failing query, because modifiedBy resolver returns FieldResult<TResult>:

   query {
   book {
   id
   title
   createdBy {
     id
     name
   }
   modifiedBy {
     id
     name
   }
   }
   }

What is expected?

I expect FieldResult<TResult> to successfully return both in the root field resolver and in a non-root field resolver.

What is actually happening?

Query:

query {
  book {
    id
    title
    createdBy {
      id
      name
    }
    modifiedBy {
      id
      name
    }
  }
}

Response:

{
  "errors": [
    {
      "message": "Cannot return null for non-nullable field.",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "book"
      ],
      "extensions": {
        "code": "HC0018"
      }
    },
    {
      "message": "Cannot return null for non-nullable field.",
      "locations": [
        {
          "line": 9,
          "column": 5
        }
      ],
      "path": [
        "book",
        "modifiedBy"
      ],
      "extensions": {
        "code": "HC0018"
      }
    },
    {
      "message": "The resolver parent type of field `Author.id` is `HotChocolate.FieldResult`1[Graphql.ApiService.Contracts.Author]` but the resolver requested the type `Graphql.ApiService.Contracts.Author`. The resolver was unable to cast the parent type to the requested type.",
      "path": [
        "book",
        "modifiedBy",
        "id"
      ],
      "extensions": {
        "fieldCoordinate": "Author.id",
        "code": "HC0053"
      }
    }
  ],
  "data": null
}

Relevant log output

No additional logs are output with default settings, only the failing response output.

Additional context

No response

[DovydasNavickas]

As discussed with @michaelstaib in Slack, there were 2 problems:

1. Missing .AddQueryConventions() while configuring the GraphQL server.
2. Missing [Error<ModifiedByUserNotFoundError>] attribute on the resolver returning FieldResult<TResult>

Commit fixing both is here.

The only difference is the resulting query is now a union: And need to be queried as such:

query {
  book {
    id
    title
    createdBy {
      id
      name
    }
    modifiedBy {
      ... on Author { # <----------- query on successful result
        id
        name
      }
      ...on ModifiedByUserNotFoundError { # <----------- query on specific error
        message
      }
      ...on Error { # <----------- query on any error
        message
      }
    }
  }
}

We also agreed that the error should be a schema error and not the one returned right now.