PERF: Add endpoint to check if a group can be mentioned by user.

app/controllers/groups_controller.rb

@@ -1,6 +1,6 @@
 class GroupsController < ApplicationController
 
-  before_filter :ensure_logged_in, only: [:set_notifications]
+  before_filter :ensure_logged_in, only: [:set_notifications, :mentionable]
   skip_before_filter :preload_json, :check_xhr, only: [:posts_feed, :mentions_feed]
 
   def show
@@ -120,6 +120,16 @@ class GroupsController < ApplicationController
     end
   end
 
+  def mentionable
+    group = find_group(:name)
+
+    if group
+      render json: { mentionable: Group.mentionable(current_user).where(id: group.id).present? }
+    else
+      raise Discourse::InvalidAccess.new
+    end
+  end
+
   def remove_member
     group = Group.find(params[:id])
     guardian.ensure_can_edit!(group)