Key selects a field on a value type

[tinnou]

I'm trying to understand why @key fieldSet can not reference a field on a value type? In other words, why is below not allowed?

          extend type Car @key(fields: "model { name kit { upc } }") {
              model: Model! @external
          }
          type Model {
              name: String!
              kit: Kit
          }
          type Kit {
              upc: String!
          }

I added a test that fails validation to reproduce.

[apollo-cla]

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