Unable to add an interface extending an entity interface without breaking dependent subgraphs

[bluepichu]

Issue Description

Consider these subgraphs:

Products

Reviews

extend schema @link( url: "https://specs.apollo.dev/federation/v2.3" import: ["@key", "@interfaceObject"] ) type Query { products: [Product] } interface Product @key(fields: "id") { id: String! name: String } interface PhysicalProduct implements Product @key(fields: "id") { id: String! name: String weight: Int } type Book implements PhysicalProduct & Product @key(fields: "id") { id: String! name: String weight: Int } type Pen implements PhysicalProduct & Product @key(fields: "id") { id: String! name: String weight: Int } type Movie implements Product @key(fields: "id") { id: String! name: String }

extend schema @link( url: "https://specs.apollo.dev/federation/v2.3" import: ["@key", "@interfaceObject"] ) type Query { reviews: [Review] } type Review { id: String! content: String } type Product @key(fields: "id") @interfaceObject { id: String! reviews: [Review] }

I would expect this to compose ok, because the gateway should understand that all PhysicalProduct objects are also Product objects, so resolving reviews on them should be possible via the reviews subgraph. However, attempting to compose the above results in an error:

Interface field "Product.reviews" is declared in  but type "PhysicalProduct", which implements "Product" only in subgraph "products" does not have field "reviews".

This can be worked around by instead declaring the following in the reviews subgraph:

type Product @key(fields: "id") @interfaceObject {
  id: String!
  reviews: [Review] @shareable
}

type PhysicalProduct @key(fields: "id") @interfaceObject {
  id: String!
  reviews: [Review] @shareable
}

But this solution is pretty undesirable, since it means that we can't actually separate concerns between the two subgraphs (as the reviews subgraph needs to be aware of all interfaces extending Product in the products subgraph instead of just the Product interface).

Link to Reproduction

https://codesandbox.io/p/devbox/stoic-jennings-dmtcpt?workspaceId=f349a0f5-d280-4992-b1d5-8f95a3bc8dda