hook_menu_alter() is not working

Question

I have implemented hook_menu_alter() in a module I have created. I have printed something inside that function call but nothing shows up, though the function hook_init() is executed from the same module. The output of hook_init() shows up in the page, but not from the hook_menu_alter() even after clearing the cache.

Does anybody have any idea regarding this issue?

function mymodule_init(){
print "here";
}

function mymodule_menu_alter(&$items) {
print "I am here";
return $items;
}

Answer 1

hook_menu() and hook_menu_alter() are not always invoked; they are invoked only when Drupal rebuilds the menus, such as when a module is enabled, disabled, installed, or uninstalled, or when the Drupal cache is cleared.

Anatomy of hook_menu reports the following sentence:

hook_menu() is called rarely, such as when modules are enabled. If you edit a module’s hook_menu(), you must visit admin/build/modules for the changes to take effect.

The function that invokes the implementations of hook_menu() and hook_menu_alter() is menu_router_build(), which contains the following code (in Drupal 7).

$callbacks = array();
foreach (module_implements('menu') as $module) {
  $router_items = call_user_func($module . '_menu');
  if (isset($router_items) && is_array($router_items)) {
    foreach (array_keys($router_items) as $path) {
      $router_items[$path]['module'] = $module;
    }
    $callbacks = array_merge($callbacks, $router_items);
  }
}
drupal_alter('menu', $callbacks);
list($menu, $masks) = _menu_router_build($callbacks);
_menu_router_cache($menu);

return array($menu, $masks);

The function is called by menu_rebuild(), which is then called by:

• drupal_flush_all_caches()
• menu_enable(), the implementation of hook_enable()
• menu_uninstall(), the implementation of hook_uninstall()
• 12 other functions, and 1 method

drupal_flush_all_caches() is invoked by system_modules_submit(), which is the submission handler for the module page where modules are enabled, and disabled; every time a module is enable, or disabled, the menu is rebuilt, and both the menu hooks are invoked.

Answer 2

In short: It does.

A print will most like not be visible, because of the timing of the function call. If you use drupal_set_message, you should see a message displayed.

The reason is that the menu is rebuilt as part of the action on the form submit which happens before the page is actually rendered. drupal_set_message is instead stored in the users session, so it will persist a page refresh, much like error messages on form validation.

Also hook_menu_alter should not return anything, instead you change the referenced variable. This is how all drupal's *_alter hooks work.

Answer 3

in *_alter hooks the argument is passed by reference (in this case $items), so rather than returning anything just print directly from the alter function.

echo"<pre>";
print_r($items);

and clear cache.

You will able to see the whole array.