module ActiveSupport::DescendantsTracker

def clear(classes) # :nodoc:
  raise "DescendantsTracker.clear was disabled because config.cache_classes = true" if @clear_disabled
  classes.each do |klass|
    @@excluded_descendants[klass] = true
    klass.descendants.each do |descendant|
      @@excluded_descendants[descendant] = true
    end
  end
end