How to enforce some custom logic after an object of a certain type is resolved?

[WingT]

What happened?

I tried to add a directive on an SomeType, which implements SomeInterface, the generated directive code behaves like this:

1. If a resolver returns []*SomeType, the directive also receives a []*SomeType variable as argument

func (ec *executionContext) _Query_todos(ctx context.Context, field graphql.CollectedField) (ret graphql.Marshaler) {
	//...
	resTmp, err := ec.ResolverMiddleware(ctx, func(rctx context.Context) (interface{}, error) {
		directive0 := func(rctx context.Context) (interface{}, error) {
			ctx = rctx // use context from middleware stack in children
			return ec.resolvers.Query().Todos(rctx)
		}
		directive1 := func(ctx context.Context) (interface{}, error) {
                         // ...
                         //  directive0 will return a slice of Todo, we cannot modify child context of each element
			return ec.directives.Scope(ctx, nil, directive0, scope)
		}
// ...
	})
// ...
	res := resTmp.([]*model.Todo)
	fc.Result = res
	return ec.marshalNTodo2ᚕᚖgqlgenᚑtodosᚋgraphᚋmodelᚐTodoᚄ(ctx, field.Selections, res)
}

3. If a resolver's signature returns SomeInterface, and it returns SomeType , the directive is not called

func (ec *executionContext) _Query_node(ctx context.Context, field graphql.CollectedField) (ret graphql.Marshaler) {
	// ...
	resTmp, err := ec.ResolverMiddleware(ctx, func(rctx context.Context) (interface{}, error) {
		ctx = rctx // use context from middleware stack in children
		return ec.resolvers.Query().Node(rctx, fc.Args["id"].(string))
        // directive "scope" on "Todo" is not called at all
	})
	// ...
	res := resTmp.(model.Node)
	fc.Result = res
	return ec.marshalONode2gqlgenᚑtodosᚋgraphᚋmodelᚐNode(ctx, field.Selections, res)
}

What did you expect?

The generated directive will be called if the concrete type of resolver result is SomeType, with exactly one element

Minimal graphql.schema and models to reproduce

# GraphQL schema example
#
# https://gqlgen.com/getting-started/

directive @scope(scope: String) on OBJECT | FIELD_DEFINITION

interface Node {
  id: ID!
}

type Todo implements Node @scope(scope: "todo:read") {
  id: ID!
  text: String!
  done: Boolean!
  user: User!
  secret: String @scope(scope: "todo.secret:read")
}

type User implements Node {
  id: ID! @scope(scope: "user:read")
  name: String! @scope(scope: "user:read")
}

type Query {
  todos: [Todo!]!
  todo(
    id: ID!
  ): Todo
  node(
    id: ID!
  ): Node
  nodes(ids: [ID!]!): [Node]!
}

input NewTodo {
  text: String!
  userId: String!
}

type Mutation {
  createTodo(input: NewTodo!): Todo!
}

versions

• go run github.com/99designs/gqlgen version: v0.17.49
• go version: go version go1.23.1 darwin/arm64