Empty `type Query {\n}` in the sdl response

I encountered this issue when Apollo-Gateway has trouble recognizing sdl from a graphql service served from federation-jvm. The schema is copied from Apollo-Gateway sample for the inventory service, with a little modification by removing the extend keyword in the front and adding @extends directive:

  type Product @key(fields: "upc") @extends {
    upc: String! @external
    weight: Int @external
    price: Int @external
    shippingEstimate: Int @requires(fields: "price weight")
  }

This schema works well in the NodeJs version of graphql federation. However, with the same schema copied to the side of federation-jvm, Apollo-Gateway stopped to recognize the schema. The following message showed in the Apollo-Gateway log:

Encountered error when loading productsExt at http://localhost:9000/graphql: Syntax Error: Expected Name, found }

Looking at the response body of sdl query from federation-jvm, the @extends was pulled in front of @keyword and there is an empty type Query {\n}.

{
  "data": {
    "_service": {
      "sdl": "type Product @extends @key(fields : \"upc\") {\n  price: Int @external\n  shippingEstimate: Int @requires(fields : \"price weight\")\n  upc: String! @external\n  weight: Int @external\n}\n\ntype Query {\n}\n"
    }
  }
}

The order of the @extends directive seemed to have no negative effect, as verified in by switching the order of @extends and @keyword in the NodeJS graphql federation. The empty type Query {} is probably the cause.

[yuhanz]

To work around this issue, you can include the trivial type Query in your schema so that it is not empty, for example:

type Product @key(fields: "upc") @extends {
    upc: String! @external
    inStock: Boolean
    quantity: Int
}

type Query @extends {
    trivial: Product
}

[sachindshinde]

@yuhanz In the meanwhile, we’ve copied their printer and patched it, so if you use federation-jvm v0.3.4 or later you shouldn’t have any issues (note that using v0.3.4 requires upgrading to graphql-java v13).

I’ll close out this issue, but let me know if you still experience similar issues and I can reopen.