create_mailer_file

# File actionmailer/lib/rails/generators/mailer/mailer_generator.rb, line 12
      def create_mailer_file
        template "mailer.rb", File.join("app/mailers", class_path, "#{file_name}_mailer.rb")

        in_root do
          if behavior == :invoke && !File.exist?(application_mailer_file_name)
            template "application_mailer.rb", application_mailer_file_name
          end
        end
      end