flash loses messages on redirect

The FlashHash discards messages if the hash is ever touched in the action, even if the only operation is to add another message. Consider:

class ThingController < ApplicationController

  def login
    flash[:info] = "Welcome back!"
    # for this example previous_location will be good_times, but it could be any path on the site
    redirect_to current_user.previous_location
  end

  def good_times
    flash[:error] = "Good times are over!"
    redirect_to :action => :homepage
  end

  def homepage
    # XXX: observe the "Welcome back!" message is not present.
    logger.warn flash.inspect #=> {:error=>"Good times are over!"}
  end

end

The expected behavior is that both the info and error messages would be kept until they are displayed. If the error message is removed, the info message makes it all the way to the homepage.

I understand why this is occurring - FlashHash marks all items as "used" any time the "flash" accessor method is used. This however does not correlate to actually displaying the messages, as this example shows. It is possible to hack around this by adding flash.keep to good_times, but if this could be any location on the entire site that means adding flash.keep in front of all redirects. So, correct usage seems difficult.

I can think of two obvious ways to solve this:

• extend redirect_to to always call flash.keep

or:

• fix FlashHash to only mark messages as used on [] access