Add CSV download for User

app/controllers/admin/users_controller.rb

@@ -5,6 +5,10 @@ class Admin::UsersController < Admin::BaseController
     @users = params[:show_deleted] ? User.deleted : User.undeleted
     @users = @users.includes(:mail_delivery_status)
 
+    if request.format.csv?
+      send_data UsersCsv.new(@users).to_csv, filename: 'users.csv', type: 'text/csv'
+    end
+
     # if somebody uses the search field:
     @users = @users.natural_search(params[:user_name]) unless params[:user_name].blank?
 

app/views/admin/users/index.html.haml

@@ -2,6 +2,9 @@
 
 - content_for :actionbar do
   = link_to t('.new_user'), new_admin_user_path, class: 'btn btn-primary'
+  = link_to url_for(search: params[:q], format: :csv), class: 'btn' do
+    = glyph :download
+    CSV
 
 - content_for :sidebar do
   %p= t('.first_paragraph', url: link_to(t('.new_users'), new_admin_user_path)).html_safe