Properly parse fields named on and directive

Author: rmosolgo

lib/graphql/language/parser.rb

@@ -566,6 +566,12 @@ def parse_name
         when :NULL
           advance_token
           "null"
+        when :ON
+          advance_token
+          "on"
+        when :DIRECTIVE
+          advance_token
+          "directive"
         else
           expect_token(:NAME)
         end

spec/graphql/language/parser_spec.rb

@@ -28,6 +28,10 @@
     assert GraphQL.parse("{ field(null: false) ... null } fragment null on Query { null }")
   end
 
+  it "allows fields and arguments named on and directive" do
+    assert GraphQL.parse("{ on(on: false) directive(directive: false)}")
+  end
+
   it "raises an error when unicode is used as names" do
     err = assert_raises(GraphQL::ParseError) {
       GraphQL.parse('query 😘 { a b }')