function module_implements

Determines which modules are implementing a hook.

Lazy-loaded include files specified with "group" via hook_hook_info() or hook_module_implements_alter() will be automatically included as part of module_implements(*, *, FALSE).

Parameters

string $hook: The name of the hook (e.g. "help" or "menu").

bool $sort: By default, modules are ordered by weight and filename, settings this option to TRUE, module list will be ordered by module name.

Return value

string[]|null: An array with the names of the modules which are implementing this hook.

See also

module_implements_write_cache()

Related topics

File

core/includes/module.inc, line 736

API for loading and interacting with Backdrop modules.

Code

function module_implements($hook, $sort = FALSE) {
  // Use the advanced backdrop_static() pattern, since this is called very often.
  static $backdrop_static_fast;
  if (!isset($backdrop_static_fast)) {
    $backdrop_static_fast['implementations'] = &backdrop_static(__FUNCTION__, array());
    $backdrop_static_fast['verified'] = &backdrop_static(__FUNCTION__ . ':verified');
  }
  $implementations = &$backdrop_static_fast['implementations'];
  $verified = &$backdrop_static_fast['verified'];

  // Fetch implementations from cache.
  // This happens on the first call to module_implements(*, *, FALSE) during a
  // request, but also when $implementations have been reset, e.g. after
  // module_enable().
  if (empty($implementations) && function_exists('cache')) {
    if ($implementation_cache = cache('bootstrap')->get('module_implements')) {
      $implementations = $implementation_cache->data;
    }
    // Forget all previously "verified" hooks, in case that $implementations
    // were cleared via backdrop_static_reset('module_implements') instead of
    // module_implements(*, *, TRUE).
    $verified = array();
  }

  if (!isset($implementations[$hook])) {
    // The hook is not cached, so ensure that whether or not it has
    // implementations, that the cache is updated at the end of the request.
    $implementations['#write_cache'] = TRUE;
    // Discover implementations for this hook.
    $hook_info = module_hook_info();
    $implementations[$hook] = array();
    $list = module_list(FALSE, FALSE, $sort);
    foreach ($list as $module) {
      $include_file = isset($hook_info[$hook]['group']) && module_load_include('inc', $module, $module . '.' . $hook_info[$hook]['group']);
      // Since module_hook() may needlessly try to load the include file again,
      // function_exists() is used directly here.
      if (function_exists($module . '_' . $hook)) {
        $implementations[$hook][$module] = $include_file ? $hook_info[$hook]['group'] : FALSE;
      }
    }
    // Allow modules to change the weight of specific implementations, but avoid
    // an infinite loop.
    if ($hook != 'module_implements_alter') {
      // Remember the implementations before hook_module_implements_alter().
      $implementations_before = $implementations[$hook];
      backdrop_alter('module_implements', $implementations[$hook], $hook);

      // Verify implementations that were added or modified.
      foreach (array_diff_assoc($implementations[$hook], $implementations_before) as $module => $group) {
        // If backdrop_alter('module_implements') changed or added a $group, the
        // respective file needs to be included.
        if ($group) {
          module_load_include('inc', $module, "$module.$group");
        }
        // If a new implementation was added, verify that the function exists.
        if (!function_exists($module . '_' . $hook)) {
          unset($implementations[$hook][$module]);
        }
      }
    }
    // Implementations for this hook are now "verified"
    $verified[$hook] = TRUE;
  }
  elseif (!isset($verified[$hook])) {
    // Implementations for this hook were in the cache, but they are not
    // "verified" yet.
    foreach ($implementations[$hook] as $module => $group) {
      // If this hook implementation is stored in a lazy-loaded file, so include
      // that file first.
      if ($group) {
        module_load_include('inc', $module, "$module.$group");
      }
      // It is possible that a module removed a hook implementation without the
      // implementations cache being rebuilt yet, so we check whether the
      // function exists on each request to avoid undefined function errors.
      // Since module_hook() may needlessly try to load the include file again,
      // function_exists() is used directly here.
      if (!function_exists($module . '_' . $hook)) {
        // Clear out the stale implementation from the cache and force a cache
        // refresh to forget about no longer existing hook implementations.
        unset($implementations[$hook][$module]);
        $implementations['#write_cache'] = TRUE;
      }
    }
    $verified[$hook] = TRUE;
  }

  return array_keys($implementations[$hook]);
}