All AJAX Behaviors Broken for Forms in .inc files

Oh I meant to mention comment forms. Comment forms do not need changing because comment_form is already in comment.module, so it works because it's always loaded.

Drupal 6 manages this because fields can only be assigned to nodes. For example poll module just straight-up cheats and includes this file when doing AJAX requests:

/**
 * Menu callback for AHAH additions.
 */
function poll_choice_js() {
  include_once 'modules/node/node.pages.inc';

But in D7, field can be attached to just about anything (such as terms, nodes, comments), not to mention my "managed_file" widget would pretty much add an AJAX behavior to any form, the list of includes that could potentially include AJAX behaviors is overwhelming and nearly impossible to compensate for. Especially if we start using the generic AJAX handler (ajax_form_callback), then just "cheating" and including the file isn't possible at all unless that callback knows which file needs to be included, which is what this patch does.

Hey sun, that's actually what I tried first, but the problem is the second time the form is rebuilt, it's being rebuild at "system/ajax" instead of the original menu path, so menu_get_item() works the first time but the second time (say you click "Add another item" twice), then you get "system/ajax" instead of "node/add/story".

I wasn't using $form_state['storage'] in my implementation though, since even touching that completely changes the way the form is built, something I'd rather not get in to.

I did some more thinking about why this is necessary in D7 but not D6, it mostly has to do with our changes to how AJAX forms are handled. In D6 we'd attempt to load the cached form, modify the cached copy, then save it back. This had the inherent problem that it was really fricking hard to accurately modify just a part of the form (say when you need to add another complete CCK field, it's a lot of processing). So in D7 with the new approach, we rebuild the entire form during the AJAX request, then pull out the changed part. This essentially makes it so that AJAX and non-AJAX forms behave identically, since the same thing would happen if JavaScript was disabled (the entire form is rebuilt).

A lot of people figured out this problem during the D6 release cycle and started doing the same thing that we're now doing in D7. katbailey and dmitri even wrote up this nice handbook page on it: http://drupal.org/node/331941. I agree that this is the best approach, even though it's not what we used in several other places (such as CCK's "Add another item" is actually *not* dependent on this in D6). However this entire approach is dependent the form function actually being available.