I believe I'm running into an issue where I can't have fields on implementers of interfaces, have fields with different implementations that also implement a common interface.

For example, I'm trying to create a schema like this:

schema @link(
  url: "https://specs.apollo.dev/federation/v2.7",
  import: ["@key", "@interfaceObject", "@shareable", "@inaccessible"]
) {
  query: RootQueryType
}

type RootQueryType {
  events: [Event]
}

interface Event {
  id: ID!
  Team: Team
}

type SportsballEvent implements Event {
  id: ID!

  ballColor: String
  Team: SportsballTeam
}

type BasketWeavingEvent implements Event {
  id: ID!

  basketType: String
  Team: BasketWeavingTeam
}


interface Team {
  id: ID!
}

type SportsballTeam implements Team {
  id: ID!
  sportsballPlayers: [String!]!
}

type BasketWeavingTeam implements Team {
  id: ID!
  basketWeavingPlayers: [String!]!
}

Notably SportsballEvent.Team and BasketWeavingEvent.Team are different types (SportsballTeam and BasketWeavingTeam respectively) yet implement the common interface defined on the parent of SportsballEvent and BasketWeavingEvent - Team. However, the check for subtypes found here:

Expected Behavior

I should be able to create a schema like this

Actual Behavior

Error: Field "SportsballEvent.Team" is not sub-type of "Event.Team"

Other

It looks like that is_subtype is stripping out null and list types around a type and comparing they are the same. I may be unclear on what subtype means here, but It seems to basically just be checking type equality (maybe stripping out nills but not checking "inheritance"?

I can potentially look into fixing this. However, I'm just wanted to check if i'm on the correct track here. I suppose it might be tricky since you are only getting the TypeRefs at this point and don't know what types have been registered or their interface/implementer relationship.