Undeclared variable in fragment not used by operation

[xiongtx]

When multiple queries are declared in a query document but the chosen operation doesn't reference a schema that requires a variable, there is a parse error.

Given the following schema, which we'll call schema:

{:objects
 {:Business {:fields {:name {:type String}
                      :owners {:type (list :Owner)}}}
  :Owner {:fields {:name {:type String}
                   :owned_businesses {:type (list :Business)
                                      :args {:location {:type String}}
                                      :resolve :placeholder}}}}

 :queries
 {:owners {:type (list :Owner)
           :resolve :placeholder}
  :businesses {:type (list :Business)
               :args {:location {:type String}}
               :resolve :placeholder}}}

And query document, which we'll call query-doc:

query BusinessesQuery($location: String) {
 businesses(location: $location) {
  owners {
   ...OwnerFields
  }
 }
}

fragment OwnerFields on Owner {
 name
 owned_businesses(location: $location)
}

query OwnerNamesQuery {
 owners {
  name
 }
}

This parses fine:

(require '[com.walmartlabs.lacinia.parser :as lacinia-parser])

(lacinia-parser/parse-query schema query-doc "BusinessesQuery")

But this throws an exception:

(lacinia-parser/parse-query schema query-doc "OwnerNamesQuery")

Argument references undeclared variable `location'.
   {:locations [{:line 10, :column 2}],
    :field :Owner/owned_businesses,
    :argument :Owner/owned_businesses.location,
    :unknown-variable :location,
    :declared-variables ()}

The problem appears to be that fragments are included without considering whether the chosen operation makes use of them.

[hlship]

I'm noodling on a way to do the checks for this that aren't too expensive in terms of navigating around the selection set. I'd probably want to catch recursive fragments at the same time.

[hlship]

This looks like a bug, but I'm struggling to figure out a way to properly recognize defined-by-not-referenced fragments, as well as exclude fragments such as in this case. I probably need to look into spec to see what is required w.r.t validation of fragments in cases such as this.