class Rails::Generators::MailerGenerator

def application_mailer_file_name
  @_application_mailer_file_name ||= if mountable_engine?
    "app/mailers/#{namespaced_path}/application_mailer.rb"
  else
    "app/mailers/application_mailer.rb"
  end
end

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

def file_name # :doc:
  @_file_name ||= super.sub(/_mailer\z/i, "")
end