Running generator on swapi, getting compiler error

[bvankuik]

I ran the generator on the swapi, as follows:

$ swift-graphql -o Generated.swift https://swapi-graphql.netlify.app/.netlify/functions/index

I started a new project, and included the above generated file, and typed the following code:

struct MyStarship {
    var name: String
}

And:

let url = URL(string: "https://swapi-graphql.netlify.app/.netlify/functions/index")!
let client = SwiftGraphQLClient.Client(request: URLRequest(url: url))
let starshipSelection = Selection.Starship {
    MyStarship(name: try $0.name())
}
let query = Objects.Root.starship(selection: starshipSelection))
client.query(query)

I'm getting the following compiler error:

Cannot convert value of type 'Selection<MyService.MyStarship?, Objects.Starship>'
to expected argument type 'Selection<MyService.MyStarship?, Objects.Starship?>'

Looking at the generated code, it states the following extension:

extension Selection where T == Never, TypeLock == Never {
    public typealias Starship<T> = Selection<T, Objects.Starship>
}

However, it also states:

extension Fields where TypeLock == Objects.Root {
    public func starship<T>(
    id: OptionalArgument<String> = .init(), starshipId: OptionalArgument<String> = .init(),
    selection: Selection<T, Objects.Starship?>
  ) throws -> T {
      // ...
}

So I wrote out all lines with explicit types, to make sure I understood the error:

    let decoder: (Fields<Objects.Starship>) throws -> MyStarship = {
        MyStarship(name: try $0.name() ?? "")
    }
    let starshipSelection = Selection<MyStarship, Objects.Starship?>(decoder: decoder)
    let query = Objects.Root.starship(selection: starshipSelection))
    client.query(query)

The compiler complains at the let starshipSelection, saying:

Cannot convert value of type '(Fields<Objects.Starship>) throws -> MyService.MyStarship'
to expected argument type '(Fields<Objects.Starship?>) throws -> MyService.MyStarship'

I don't really understand what's going on here. Why must the Objects.Root.starship(selection:) parameter be of type Selection<MyStarship, Objects.Starship?> ? That'd basically mean that the Fields object is typed to an optional Objects.Starship but such an object doesn't make sense, IMHO.

I have the feeling that I'm overlooking something. What's going on?

[maticzav]

From the top of my head, I think you need to make your query nullable.

let query = Objects.Root.starship(selection: starshipSelection.nullable)
client.query(query)

If you check the error you are getting

Cannot convert value of type 'Selection<MyService.MyStarship?, Objects.Starship>' to expected argument type 'Selection<MyService.MyStarship?, Objects.Starship?>'

It's saying that the TypeLock should be nullable but yours is not (the Objects.Starship vs Objects.Starship?).