5.4.1.4 - Fragments must be used

[jlouis]

The system must reject the following query, which has a fragment which is never used in the system.

fragment nameFragment on Dog { # unused
  name
}

{
  dog {
    name
  }
}

[jlouis]

To solve this, we can use #107. We can simply compute this by folding over mutations/queries and tracking the fragments they refer to. Once this is known, we can build the transitive closure of fragments the fragments refer to. Finally, every fragment not in this set is unused.