Typescript generation does not accurately reflect interface types

[mgagliardo91]

Intended outcome:
With interface types, the codegen fails to produce the expected hierarchy of types.

For example:

GraphQL Schema

interface Auto {
  wheelCount: Int
}

type Car implements Auto {
  wheelCount: Int
  name?: String!
}

type Truck implements Auto {
  wheelCount: Int
  bedSize: Int!
}

Queries

// Top-level query
query GetAutos {
  autos {
    wheelCount
  }
}

// Specific query
query GetCars {
  autos {
    wheelCount
    ... on Car {
      name
    }
  }
}

Generated Code

interface GetAutos_autos {
  __typename: "Car" || "Truck"
  wheelCount: number;
}

interface GetCars_autos_Car {
  __typename: "Car"
  wheelCount: number;
  name: string;
}

interface GetCars_autos_Truck {
  __typename: "Truck"
  wheelCount: number;
  bedSize: number;
}

In the generated code above, I would have expected some interface <> extends <> structure so that we could pass a parent type around in our codebase.

interface Auto {
  __typename: "Car" || "Truck"
  wheelCount: number;
}

interface Car extends Auto {
  __typename: "Car"
  wheelCount: number;
  name: string;
}

interface Truck extends Auto {
  __typename: "Truck"
  wheelCount: number;
  bedSize: number;
}

Actual outcome:

There is no hierarchy and therefore I have to use fixed (non-dynamic) types in order for typescript to compile.

How to reproduce the issue:

See above example.

Versions

[HosseinAgha]

@JakeDawkins When you have an interface in the schema with no Object implementing it, This gets into a major error. Codegen generates wrong field types with empty values. I think it is because it cannot detect the __typename for the interface type.

[KennyHammerlund]

Kind of a feature request, I didn't want to open a new one as I think it relates to this issue : It would also be nice if this would only generate the car type on autos instead of the union of car | truck as nothing from this query would be anything but a car

query GetCars {
  autos {
    ... on Car {
      wheelCount   <- moved inside interface
      name
    }
  }
}