types nested under interface always marked as optional

[mattkrick]

OK bear with me on this one: All Animals make noise. A Dog is an Animal. A Bark is the kind of Noise a Dog makes.

IDL:

interface Animal {
  id: ID
  noise: Noise!
}
interface Noise {
  name: String!
}
type Dog implements Animal {
  id: ID
  noise: Bark!
}
type Bark implements Noise {
  name: String!
}

fragment:

animal {
  ... on Dog {
    noise {
    ... on Bark {
        name
      }
    }
  }
}

artifact:

readonly animal: ({
  readonly noise?: {
    readonly name: string;
  };
})

I believe it's a bug that noise is marked as optional here. Noise is guaranteed for all Animals, and therefore all Dogs (graphql forces all sub-type to be sub-classed & to have matching nullability).

This seems very close to #64, but it's a little nuanced since it only crops up when 2 interfaces are used.
Reproduction branch is here: https://github.com/mattkrick/relay-compiler-language-typescript/tree/double-int-null/example

[kastermester]

This is because you don't request noise on something of type Animal but only on a Dog. If you remove the ... on Dog part this should work as intended.

animal {
  noise {
  ... on Bark {
      name
    }
  }
}

[mattkrick]

you're exactly right! i was thinking that as long as every non-abstract type of animal was accounted for & requested noise that it would be guaranteed, which still holds true! But I guess that tightly couples the nullability to the resolveType of animal, which would put it in the same annoying boat as enums that aren't future proof.