caches_page :if not executing (but caches_action :if) does

Hi folks -

Seeing a weird problem and would love some help. It's documented in
http://pastie.org/278310 to be more readable.

In short, I have a

caches_page "action", :if => {stuff}

but the :if is never being called - the action is just caching every
time. (If I put a debugger call in the :if block, it never stops.)

If I replace caches_page with caches_action, the if evaluates
correctly.

There are before_filters in the controller, but they do not apply to
this action. (There's one in the supercontroller but it seems
similarly irrelevant - just trims www. from URLs.)

What am I missing? Did I uncover an :if bug (which I doubt) or am I
misunderstanding?

Full example (also in pastie):

#In this case, the :if is ignored, and all pages cache

class PagesController < ApplicationController
  caches_page :show, :if => Proc.new {|c| ["home", "something-
else"].index(c.request.path_parameters["id"])}

  before_filter :admin_required, :only =>
[ :index, :new, :create, :delete, :edit, :update ]
  before_filter :IP_restricted, :only =>
[ :index, :new, :create, :delete, :edit, :update ]

#In this case, the :if executes correctly

class PagesController < ApplicationController
# just changing caches_page to caches_action works
  caches_action :show, :if => Proc.new {|c| ["home", "something-
else"].index(c.request.path_parameters["id"])}

  before_filter :admin_required, :only =>
[ :index, :new, :create, :delete, :edit, :update ]
  before_filter :IP_restricted, :only =>
[ :index, :new, :create, :delete, :edit, :update ]

Page caching (after the first access to a page) will write out a
straight HTML file in /public/model/action.html to be found on any
subsequent requests to that URL.

Subsequent requests to that URL will hit the cached page only, without
ever invoking Rails. The notion of caches_page 'action', :if =>{stuff}
is a non-starter.

caches_action always invokes Rails and runs your filters et al, hence
the working :if => {stuff}

Check out http://www.railsenvy.com/2007/2/28/rails-caching-tutorial for
an excellent tutorial on caching.

I'm confused by this. I get why once the page is cached that Rails
won't execute again, but before the first cache attempt when Rails
does run, the :if should fail.

There's documentation on caches_page 'action', :if => {}, so I know
I'm not making up that format. So I'm still confused.

Well... the caches_page in my action_controller/caching/pages.rb uses an
after_filter

def caches_page(*actions)
  return unless perform_caching
  options = actions.extract_options!
  after_filter({:only => actions}.merge(options)) { |c| c.cache_page }
end

whereas the caches_action in my action_controller/caching/actions.rb
uses an around_filter

def caches_action(*actions)
  return unless cache_configured?
  options = actions.extract_options!
  around_filter(ActionCacheFilter.new(:cache_path =>
options.delete(:cache_path)), {:only => actions}.merge(options))
end

Perhaps the caches_page should be an around_filter as well??? (This is
an absolute shot-in-the-dark on my part)