Send notification email when all discussions are resolved

app/mailers/emails/merge_requests.rb

@@ -42,6 +42,13 @@ module Emails
       mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id))
     end
 
+    def resolved_all_discussions_email(recipient_id, merge_request_id, resolved_by_user_id)
+      setup_merge_request_mail(merge_request_id, recipient_id)
+
+      @resolved_by = User.find(resolved_by_user_id)
+      mail_answer_thread(@merge_request, merge_request_thread_options(resolved_by_user_id, recipient_id))
+    end
+
     private
 
     def setup_merge_request_mail(merge_request_id, recipient_id)

app/services/merge_requests/all_discussions_resolved_service.rb

@@ -4,6 +4,7 @@ module MergeRequests
       return unless merge_request.discussions_resolved?
 
       SystemNoteService.resolve_all_discussions(merge_request, project, current_user)
+      notification_service.resolve_all_discussions(merge_request, current_user)
     end
   end
 end

app/services/notification_service.rb

@@ -120,6 +120,14 @@ class NotificationService
     )
   end
 
+  def resolve_all_discussions(merge_request, current_user)
+    recipients = build_recipients(merge_request, merge_request.target_project, current_user, action: "resolve_all_discussions")
+
+    recipients.each do |recipient|
+      mailer.resolved_all_discussions_email(recipient.id, merge_request.id, current_user.id).deliver_later
+    end
+  end
+
   # Notify new user with email after creation
   def new_user(user, token = nil)
     # Don't email omniauth created users

app/views/notify/resolved_all_discussions_email.html.haml

+%p
+  All discussions on Merge Request #{@merge_request.to_reference} were resolved by #{@resolved_by.name}

app/views/notify/resolved_all_discussions_email.text.erb

+All discussions on Merge Request <%= @merge_request.to_reference %> were resolved by <%= @resolved_by.name %>
+
+<%= url_for(namespace_project_merge_request_url(@merge_request.target_project.namespace, @merge_request.target_project, @merge_request)) %>