class GraphQL::StaticValidation::SubscriptionRootExists

def validate(context)
  return if context.warden.root_type_for_operation("subscription")
  visitor = context.visitor
  visitor[GraphQL::Language::Nodes::OperationDefinition].enter << ->(ast_node, prev_ast_node) {
    if ast_node.operation_type == 'subscription'
      context.errors << message('Schema is not configured for subscriptions', ast_node, context: context)
      return GraphQL::Language::Visitor::SKIP
    end
  }
end