A query analyzer for debugging the broadcastability of GraphQL-Ruby subscriptions

broadcast_debug.rb

require "bundler/inline"

gemfile do
  gem "graphql", path: "./" # "2.3.0"
end

class MySchema < GraphQL::Schema
  class SubThing < GraphQL::Schema::Object
    field :name, String, broadcastable: true
    field :viewer_can_edit, Boolean # not broadcastable
  end

  class Thing < GraphQL::Schema::Object
    field :name, String, broadcastable: true
    field :sub_thing, SubThing, broadcastable: true
  end

  class Subscription < GraphQL::Schema::Object
    field :thing_updated, Thing, broadcastable: true
  end
  subscription(Subscription)
  use GraphQL::Subscriptions, broadcast: true, default_broadcastable: false

  class BroadcastDebugAnalyzer < GraphQL::Analysis::AST::Analyzer
    def on_enter_field(node, parent, visitor)
      if visitor.skipping?
        return
      end
      current_field = visitor.field_definition
      check_broadcastable(current_field)

      current_type = visitor.parent_type_definition
      if current_type.kind.interface?
        pt = @query.possible_types(current_type)
        pt.each do |object_type|
          ot_field = @query.get_field(object_type, current_field.graphql_name)
          # Inherited fields would be exactly the same object;
          # only check fields that are overrides of the inherited one
          if ot_field && ot_field != current_field
            check_broadcastable(ot_field)
          end
        end
      end
    end

    def check_broadcastable(field_defn)
      field_broadcastable = field_defn.introspection? || field_defn.broadcastable?
      if !field_broadcastable
        puts "Not broadcastable: #{field_defn.path}"
      end
    end

    def result
      nil
    end
  end

  query_analyzer(MySchema::BroadcastDebugAnalyzer)
end

puts MySchema.subscriptions.broadcastable?("subscription { thingUpdated { name subThing { name } } }").inspect
# => true
#
puts MySchema.subscriptions.broadcastable?("subscription { thingUpdated { name subThing { name viewerCanEdit } } }").inspect
# Not broadcastable: SubThing.viewerCanEdit
# => false