deprecated_false_terminator.rb

      def deprecated_false_terminator # :nodoc:
        Proc.new do |target, result_lambda|
          terminate = true
          catch(:abort) do
            result = result_lambda.call if result_lambda.is_a?(Proc)
            if Callbacks.halt_and_display_warning_on_return_false && result == false
              display_deprecation_warning_for_false_terminator
            else
              terminate = false
            end
          end
          terminate
        end
      end

Originally from https://github.com/rails/rails/blob/c4d3e202e10ae627b3b9c34498afb45450652421/activesupport/lib/active_support/callbacks.rb#L766-L779