What is a user category exactly? - drupal

Question

I wanted to add a tab to the user edit page ie user/%/edit/foo, and was using the twitter module as a model. After much spelunking and stepping through with a debugger, I realised that I needed to add a hook_user function in my module so that the %user_category part of the menu router path would work.
It's now functioning as expected, but I don't really have a solid idea of what I just did, and haven't found a good explanation anywhere.
Can anyone explain to me what it's about?

Answer 1

user_category_loads fails if given a category that does not exist, which happens at user/uid/edit/not_a_category, and it passes that category for access checks to user/uid/edit/is_a_category and thus access to those is set to false, so bam, wonky menu :'(.

Answer 2

When you use %user_category it means that user_category_load function is called with that argument (the uid).
The function is defined in the user module. These functions serve as a validation, if False it return FALSE, it will result in a 404, but if it return something else, like a user object, that will be passed to whatever callback function / form is run for that url.
In your case, you could probably have used %user instead which would have called user_load which is more simple, and you wouldn't have needed to do all the extra stuff to make user_category_load pass.
Summary
So user_category_load does two things.
Check that the category exist so you just can't do user/%/edit/foo.
Caches the user object.

Answer 3

After much trial and error, I was able to get a page working as a child of the user/%/edit path using code like this:
<?php
/**
* Implementation of hook_menu().
*/
function noc_profile_privacy_menu() {
return array(
'user/%user_category/edit/privacy' => array(
'title' => 'Portfolio privacy',
'page callback' => 'drupal_get_form',
'page arguments' => array('noc_profile_privacy_form', 1),
'access callback' => 'content_profile_page_access',
'access arguments' => array('profile', 1),
'type' => MENU_LOCAL_TASK,
'load arguments' => array('%map', '%index'),
),
);
}
/**
* Implementation of hook_user().
*/
function noc_profile_privacy_user($op, &$edit, &$account, $category = NULL) {
if ($op === 'categories') {
return array(array(
'name' => 'privacy',
'title' => t('Profile privacy'),
'weight' => 0,
));
}
}
Note that the 'name' key of what I'm returning in hook_user() is the same as what comes after user/%user/category/edit in my hook_menu() definition. I believe that is key. You will also get an error if you omit the 'load arguments' item, with exactly that value.
So I believe what the user category is is the 'privacy' in my case - the bit after edit in the path of the menu item definition.
Is this an unnecessary complication? Yes, so it seems.
Edit: I see my co-worker hefox beat me to replying to this question. I wouldn't have been able to figure all of this out without Fox's help, so mad props to the Fox.