Correct way to use hook_menu_alter

Question

What is the correct way of using hook_menu_later.

I did this in my module to redirect (see also redirect in hook_init makes body text disappear):

function MYMODULE_menu_alter(&$items) {
  $items['node/%node']['page callback'] = 'citykidz_node_page_view';
}

function MYMODULE_node_page_view($node) {
  if ($node->type == 'event') {
    if ($items = field_get_items('node', $node, 'field_event_date')) {
      $date = date_create($items[0]['value']);
      drupal_goto('news/events/day/' . date_format($date, 'Y-m-d'));
    }
  }
  else {
    return node_page_view($node);
  }
}

And this got me wondering: what if other modules are also overriding hook_menu_alter and setting their own page callbacks on 'node/%node'? Or even on access or whatever. This is the standard Drupal way of doing things, but surely it will lead to problems (that can be hard to detect). I see there is a module Chain Menu Access API that addresses this. Has anyone had success using this module? And has this issue been addressed in Drupal 8?

Answer 1

If two modules are altering the same menu item / form / page etc, last one will "win".

If you need some control over this, and are expecting collisions, you need to implement hook_module_implements_alter:

This hook is invoked during module_implements(). A module may implement this hook in order to reorder the implementing modules, which are otherwise ordered by the module's system weight.

Do your best to have your hook fire last, and if menu item you are altering does not look like the one you are expecting (it was altered already), write a warning message to watchdog.