gitlabhq/app/observers/user_observer.rb

class UserObserver < BaseObserver
  def after_create(user)
    log_info("User \"#{user.name}\" (#{user.email}) was created")

    notification.new_user(user)
  end

  def after_destroy user
    log_info("User \"#{user.name}\" (#{user.email})  was removed")
  end

  def after_save user
    if user.username_changed?
      if user.namespace
        user.namespace.update_attributes(path: user.username)
      else
        user.create_namespace!(path: user.username, name: user.username)
      end
    end
  end
end