Merge pull request rmosolgo#978 from rmosolgo/fix-dynamic-field-traversal

fix(Traversal) don't apply instrumentation to Query.__type

Author: Robert Mosolgo

lib/graphql/schema/traversal.rb

@@ -104,10 +104,13 @@ def visit_fields(type_defn)
       end
 
       def visit_field_on_type(type_defn, field_defn, dynamic_field: false)
-        instrumented_field_defn = @field_instrumenters.reduce(field_defn) do |defn, inst|
-          inst.instrument(type_defn, defn)
-        end
-        if !dynamic_field
+        if dynamic_field
+          # Don't apply instrumentation to dynamic fields since they're shared constants
+          instrumented_field_defn = field_defn
+        else
+          instrumented_field_defn = @field_instrumenters.reduce(field_defn) do |defn, inst|
+            inst.instrument(type_defn, defn)
+          end
           @instrumented_field_map[type_defn.name][instrumented_field_defn.name] = instrumented_field_defn
         end
         @type_reference_map[instrumented_field_defn.type.unwrap.name] << instrumented_field_defn

spec/graphql/introspection/type_by_name_field_spec.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+require "spec_helper"
+
+describe GraphQL::Introspection::TypeByNameField do
+  describe "after instrumentation" do
+    # Just make sure it returns a new object, not the original field
+    class DupInstrumenter
+      def self.instrument(t, f)
+        f.redefine {
+          resolve ->(o, a, c) { :no_op }
+        }
+      end
+    end
+
+    class ArgAnalyzer
+      def call(_, _, node)
+        if node.ast_node.is_a?(GraphQL::Language::Nodes::Field)
+          node.arguments
+        end
+      end
+    end
+
+    let(:instrumented_schema) {
+      # This was probably assigned earlier in the test suite, but to simulate an application, clear it.
+      GraphQL::Introspection::TypeByNameField.arguments_class = nil
+
+      Dummy::Schema.redefine {
+        instrument(:field, DupInstrumenter)
+        query_analyzer(ArgAnalyzer.new)
+      }
+    }
+
+    it "still works with __type" do
+      res = instrumented_schema.execute("{ __type(name: \"X\") { name } }")
+      assert_equal({"data"=>{"__type"=>nil}}, res)
+    end
+  end
+end