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Drupal example source code file (module.inc)

This example Drupal source code file (module.inc) is included in the DevDaily.com "Drupal Source Code Warehouse" project. The intent of this project is to help you "Learn Drupal by Example".

PHP - Drupal tags/keywords

array, as, foreach, function, hook, if, implementations, isset, module, module_list, php, return, type, variable

The module.inc Drupal example source code

<?php
// $Id: module.inc,v 1.209 2010/11/27 20:41:38 dries Exp $

/**
 * @file
 * API for loading and interacting with Drupal modules.
 */

/**
 * Load all the modules that have been enabled in the system table.
 *
 * @param $bootstrap
 *   Whether to load only the reduced set of modules loaded in "bootstrap mode"
 *   for cached pages. See bootstrap.inc.
 *
 * @return
 *   If $bootstrap is NULL, return a boolean indicating whether all modules
 *   have been loaded.
 */
function module_load_all($bootstrap = FALSE) {
  static $has_run = FALSE;

  if (isset($bootstrap)) {
    foreach (module_list(TRUE, $bootstrap) as $module) {
      drupal_load('module', $module);
    }
    // $has_run will be TRUE if $bootstrap is FALSE.
    $has_run = !$bootstrap;
  }
  return $has_run;
}


/**
 * Returns a list of currently active modules.
 *
 * Usually, this returns a list of all enabled modules. When called early on in
 * the bootstrap, it will return a list of vital modules only (those needed to
 * generate cached pages).
 *
 * All parameters to this function are optional and should generally not be
 * changed from their defaults.
 *
 * @param $refresh
 *   (optional) Whether to force the module list to be regenerated (such as
 *   after the administrator has changed the system settings). Defaults to
 *   FALSE.
 * @param $bootstrap_refresh
 *   (optional) When $refresh is TRUE, setting $bootstrap_refresh to TRUE forces
 *   the module list to be regenerated using the reduced set of modules loaded
 *   in "bootstrap mode" for cached pages. Otherwise, setting $refresh to TRUE
 *   generates the complete list of enabled modules.
 * @param $sort
 *   (optional) By default, modules are ordered by weight and module name. Set
 *   this option to TRUE to return a module list ordered only by module name.
 * @param $fixed_list
 *   (optional) If an array of module names is provided, this will override the
 *   module list with the given set of modules. This will persist until the next
 *   call with $refresh set to TRUE or with a new $fixed_list passed in. This
 *   parameter is primarily intended for internal use (e.g., in install.php and
 *   update.php).
 *
 * @return
 *   An associative array whose keys and values are the names of the modules in
 *   the list.
 */
function module_list($refresh = FALSE, $bootstrap_refresh = FALSE, $sort = FALSE, $fixed_list = NULL) {
  static $list = array(), $sorted_list;

  if (empty($list) || $refresh || $fixed_list) {
    $list = array();
    $sorted_list = NULL;
    if ($fixed_list) {
      foreach ($fixed_list as $name => $module) {
        drupal_get_filename('module', $name, $module['filename']);
        $list[$name] = $name;
      }
    }
    else {
      if ($refresh) {
        // For the $refresh case, make sure that system_list() returns fresh
        // data.
        drupal_static_reset('system_list');
      }
      if ($bootstrap_refresh) {
        $list = system_list('bootstrap');
      }
      else {
        // Not using drupal_map_assoc() here as that requires common.inc.
        $list = array_keys(system_list('module_enabled'));
        $list = (!empty($list) ? array_combine($list, $list) : array());
      }
    }
  }
  if ($sort) {
    if (!isset($sorted_list)) {
      $sorted_list = $list;
      ksort($sorted_list);
    }
    return $sorted_list;
  }
  return $list;
}

/**
 * Build a list of bootstrap modules and enabled modules and themes.
 *
 * @param $type
 *   The type of list to return:
 *   - module_enabled: All enabled modules.
 *   - bootstrap: All enabled modules required for bootstrap.
 *   - theme: All themes.
 *
 * @return
 *   An associative array of modules or themes, keyed by name. For $type
 *   'bootstrap', the array values equal the keys. For $type 'module_enabled'
 *   or 'theme', the array values are objects representing the respective
 *   database row, with the 'info' property already unserialized.
 *
 * @see module_list()
 * @see list_themes()
 */
function system_list($type) {
  $lists = &drupal_static(__FUNCTION__);

  // For bootstrap modules, attempt to fetch the list from cache if possible.
  // if not fetch only the required information to fire bootstrap hooks
  // in case we are going to serve the page from cache.
  if ($type == 'bootstrap') {
    if ($cached = cache_get('bootstrap_modules', 'cache_bootstrap')) {
      $bootstrap_list = $cached->data;
    }
    else {
      $bootstrap_list = db_query("SELECT name, filename FROM {system} WHERE status = 1 AND bootstrap = 1 AND type = 'module' ORDER BY weight ASC, name ASC")->fetchAllAssoc('name');
      cache_set('bootstrap_modules', $bootstrap_list, 'cache_bootstrap');
    }
    // To avoid a separate database lookup for the filepath, prime the
    // drupal_get_filename() static cache for bootstrap modules only.
    // The rest is stored separately to keep the bootstrap module cache small.
    foreach ($bootstrap_list as $module) {
      drupal_get_filename('module', $module->name, $module->filename);
    }
    // We only return the module names here since module_list() doesn't need
    // the filename itself.
    $lists['bootstrap'] = array_keys($bootstrap_list);
  }
  // Otherwise build the list for enabled modules and themes.
  elseif (!isset($lists['module_enabled'])) {
    if ($cached = cache_get('system_list', 'cache_bootstrap')) {
      $lists = $cached->data;
    }
    else {
      $lists = array(
        'module_enabled' => array(),
        'theme' => array(),
        'filepaths' => array(),
      );
      // The module name (rather than the filename) is used as the fallback
      // weighting in order to guarantee consistent behavior across different
      // Drupal installations, which might have modules installed in different
      // locations in the file system. The ordering here must also be
      // consistent with the one used in module_implements().
      $result = db_query("SELECT * FROM {system} WHERE type = 'theme' OR (type = 'module' AND status = 1) ORDER BY weight ASC, name ASC");
      foreach ($result as $record) {
        $record->info = unserialize($record->info);
        // Build a list of all enabled modules.
        if ($record->type == 'module') {
          $lists['module_enabled'][$record->name] = $record;
        }
        // Build a list of themes.
        if ($record->type == 'theme') {
          $lists['theme'][$record->name] = $record;
        }
        // Build a list of filenames so drupal_get_filename can use it.
        if ($record->status) {
          $lists['filepaths'][] = array('type' => $record->type, 'name' => $record->name, 'filepath' => $record->filename);
        }
      }
      cache_set('system_list', $lists, 'cache_bootstrap');
    }
    // To avoid a separate database lookup for the filepath, prime the
    // drupal_get_filename() static cache with all enabled modules and themes.
    foreach ($lists['filepaths'] as $item) {
      drupal_get_filename($item['type'], $item['name'], $item['filepath']);
    }
  }

  return $lists[$type];
}

/**
 * Reset all system_list() caches.
 */
function system_list_reset() {
  drupal_static_reset('system_list');
  drupal_static_reset('system_rebuild_module_data');
  drupal_static_reset('list_themes');
  cache_clear_all('bootstrap_modules', 'cache_bootstrap');
  cache_clear_all('system_list', 'cache_bootstrap');
}

/**
 * Find dependencies any level deep and fill in required by information too.
 *
 * @param $files
 *   The array of filesystem objects used to rebuild the cache.
 *
 * @return
 *   The same array with the new keys for each module:
 *   - requires: An array with the keys being the modules that this module
 *     requires.
 *   - required_by: An array with the keys being the modules that will not work
 *     without this module.
 */
function _module_build_dependencies($files) {
  require_once DRUPAL_ROOT . '/includes/graph.inc';
  foreach ($files as $filename => $file) {
    $graph[$file->name]['edges'] = array();
    if (isset($file->info['dependencies']) && is_array($file->info['dependencies'])) {
      foreach ($file->info['dependencies'] as $dependency) {
        $dependency_data = drupal_parse_dependency($dependency);
        $graph[$file->name]['edges'][$dependency_data['name']] = $dependency_data;
      }
    }
  }
  drupal_depth_first_search($graph);
  foreach ($graph as $module => $data) {
    $files[$module]->required_by = isset($data['reverse_paths']) ? $data['reverse_paths'] : array();
    $files[$module]->requires = isset($data['paths']) ? $data['paths'] : array();
    $files[$module]->sort = $data['weight'];
  }
  return $files;
}

/**
 * Determine whether a given module exists.
 *
 * @param $module
 *   The name of the module (without the .module extension).
 *
 * @return
 *   TRUE if the module is both installed and enabled.
 */
function module_exists($module) {
  $list = module_list();
  return isset($list[$module]);
}

/**
 * Load a module's installation hooks.
 *
 * @param $module
 *   The name of the module (without the .module extension).
 *
 * @return
 *   The name of the module's install file, if successful; FALSE otherwise.
 */
function module_load_install($module) {
  // Make sure the installation API is available
  include_once DRUPAL_ROOT . '/includes/install.inc';

  return module_load_include('install', $module);
}

/**
 * Load a module include file.
 *
 * Examples:
 * @code
 *   // Load node.admin.inc from the node module.
 *   module_load_include('inc', 'node', 'node.admin');
 *   // Load content_types.inc from the node module.
 *   module_load_include('inc', 'node', 'content_types');
 * @endcode
 *
 * Do not use this function to load an install file, use module_load_install()
 * instead. Do not use this function in a global context since it requires
 * Drupal to be fully bootstrapped, use require_once DRUPAL_ROOT . '/path/file'
 * instead.
 *
 * @param $type
 *   The include file's type (file extension).
 * @param $module
 *   The module to which the include file belongs.
 * @param $name
 *   (optional) The base file name (without the $type extension). If omitted,
 *   $module is used; i.e., resulting in "$module.$type" by default.
 *
 * @return
 *   The name of the included file, if successful; FALSE otherwise.
 */
function module_load_include($type, $module, $name = NULL) {
  if (!isset($name)) {
    $name = $module;
  }

  if (function_exists('drupal_get_path')) {
    $file = DRUPAL_ROOT . '/' . drupal_get_path('module', $module) . "/$name.$type";
    if (is_file($file)) {
      require_once $file;
      return $file;
    }
  }
  return FALSE;
}

/**
 * Load an include file for each of the modules that have been enabled in
 * the system table.
 */
function module_load_all_includes($type, $name = NULL) {
  $modules = module_list();
  foreach ($modules as $module) {
    module_load_include($type, $module, $name);
  }
}

/**
 * Enables or installs a given list of modules.
 *
 * Definitions:
 * - "Enabling" is the process of activating a module for use by Drupal.
 * - "Disabling" is the process of deactivating a module.
 * - "Installing" is the process of enabling it for the first time or after it
 *   has been uninstalled.
 * - "Uninstalling" is the process of removing all traces of a module.
 *
 * Order of events:
 * - Gather and add module dependencies to $module_list (if applicable).
 * - For each module that is being enabled:
 *   - Install module schema and update system registries and caches.
 *   - If the module is being enabled for the first time or had been
 *     uninstalled, invoke hook_install() and add it to the list of installed
 *     modules.
 *   - Invoke hook_enable().
 * - Invoke hook_modules_installed().
 * - Invoke hook_modules_enabled().
 *
 * @param $module_list
 *   An array of module names.
 * @param $enable_dependencies
 *   If TRUE, dependencies will automatically be added and enabled in the
 *   correct order. This incurs a significant performance cost, so use FALSE
 *   if you know $module_list is already complete and in the correct order.
 *
 * @return
 *   FALSE if one or more dependencies are missing, TRUE otherwise.
 *
 * @see hook_install()
 * @see hook_enable()
 * @see hook_modules_installed()
 * @see hook_modules_enabled()
 */
function module_enable($module_list, $enable_dependencies = TRUE) {
  if ($enable_dependencies) {
    // Get all module data so we can find dependencies and sort.
    $module_data = system_rebuild_module_data();
    // Create an associative array with weights as values.
    $module_list = array_flip(array_values($module_list));

    while (list($module) = each($module_list)) {
      if (!isset($module_data[$module])) {
        // This module is not found in the filesystem, abort.
        return FALSE;
      }
      if ($module_data[$module]->status) {
        // Skip already enabled modules.
        unset($module_list[$module]);
        continue;
      }
      $module_list[$module] = $module_data[$module]->sort;

      // Add dependencies to the list, with a placeholder weight.
      // The new modules will be processed as the while loop continues.
      foreach ($module_data[$module]->info['dependencies'] as $dependency) {
        if (!isset($module_list[$dependency])) {
          $module_list[$dependency] = 0;
        }
      }
    }

    if (!$module_list) {
      // Nothing to do. All modules already enabled.
      return TRUE;
    }

    // Sort the module list by pre-calculated weights.
    arsort($module_list);
    $module_list = array_keys($module_list);
  }

  // Required for module installation checks.
  include_once DRUPAL_ROOT . '/includes/install.inc';

  $modules_installed = array();
  $modules_enabled = array();
  foreach ($module_list as $module) {
    // Only process modules that are not already enabled.
    $existing = db_query("SELECT status FROM {system} WHERE type = :type AND name = :name", array(
      ':type' => 'module',
      ':name' => $module))
      ->fetchObject();
    if ($existing->status == 0) {
      // Load the module's code.
      drupal_load('module', $module);
      module_load_install($module);

      // Update the database and module list to reflect the new module. This
      // needs to be done first so that the module's hook implementations,
      // hook_schema() in particular, can be called while it is being
      // installed.
      db_update('system')
        ->fields(array('status' => 1))
        ->condition('type', 'module')
        ->condition('name', $module)
        ->execute();
      // Refresh the module list to include it.
      system_list_reset();
      module_list(TRUE);
      module_implements('', FALSE, TRUE);
      _system_update_bootstrap_status();
      // Update the registry to include it.
      registry_update();
      // Refresh the schema to include it.
      drupal_get_schema(NULL, TRUE);
      // Clear entity cache.
      entity_info_cache_clear();

      // Now install the module if necessary.
      if (drupal_get_installed_schema_version($module, TRUE) == SCHEMA_UNINSTALLED) {
        drupal_install_schema($module);

        // Set the schema version to the number of the last update provided
        // by the module.
        $versions = drupal_get_schema_versions($module);
        $version = $versions ? max($versions) : SCHEMA_INSTALLED;

        // If the module has no current updates, but has some that were
        // previously removed, set the version to the value of
        // hook_update_last_removed().
        if ($last_removed = module_invoke($module, 'update_last_removed')) {
          $version = max($version, $last_removed);
        }
        drupal_set_installed_schema_version($module, $version);
        // Allow the module to perform install tasks.
        module_invoke($module, 'install');
        // Record the fact that it was installed.
        $modules_installed[] = $module;
        watchdog('system', '%module module installed.', array('%module' => $module), WATCHDOG_INFO);
      }

      // Enable the module.
      module_invoke($module, 'enable');

      // Record the fact that it was enabled.
      $modules_enabled[] = $module;
      watchdog('system', '%module module enabled.', array('%module' => $module), WATCHDOG_INFO);
    }
  }

  // If any modules were newly installed, invoke hook_modules_installed().
  if (!empty($modules_installed)) {
    module_invoke_all('modules_installed', $modules_installed);
  }

  // If any modules were newly enabled, invoke hook_modules_enabled().
  if (!empty($modules_enabled)) {
    module_invoke_all('modules_enabled', $modules_enabled);
  }

  return TRUE;
}

/**
 * Disable a given set of modules.
 *
 * @param $module_list
 *   An array of module names.
 * @param $disable_dependents
 *   If TRUE, dependent modules will automatically be added and disabled in the
 *   correct order. This incurs a significant performance cost, so use FALSE
 *   if you know $module_list is already complete and in the correct order.
 */
function module_disable($module_list, $disable_dependents = TRUE) {
  if ($disable_dependents) {
    // Get all module data so we can find dependents and sort.
    $module_data = system_rebuild_module_data();
    // Create an associative array with weights as values.
    $module_list = array_flip(array_values($module_list));

    $profile = drupal_get_profile();
    while (list($module) = each($module_list)) {
      if (!isset($module_data[$module]) || !$module_data[$module]->status) {
        // This module doesn't exist or is already disabled, skip it.
        unset($module_list[$module]);
        continue;
      }
      $module_list[$module] = $module_data[$module]->sort;

      // Add dependent modules to the list, with a placeholder weight.
      // The new modules will be processed as the while loop continues.
      foreach ($module_data[$module]->required_by as $dependent => $dependent_data) {
        if (!isset($module_list[$dependent]) && $dependent != $profile) {
          $module_list[$dependent] = 0;
        }
      }
    }

    // Sort the module list by pre-calculated weights.
    asort($module_list);
    $module_list = array_keys($module_list);
  }

  $invoke_modules = array();

  foreach ($module_list as $module) {
    if (module_exists($module)) {
      // Check if node_access table needs rebuilding.
      if (!node_access_needs_rebuild() && module_hook($module, 'node_grants')) {
        node_access_needs_rebuild(TRUE);
      }

      module_load_install($module);
      module_invoke($module, 'disable');
      db_update('system')
        ->fields(array('status' => 0))
        ->condition('type', 'module')
        ->condition('name', $module)
        ->execute();
      $invoke_modules[] = $module;
      watchdog('system', '%module module disabled.', array('%module' => $module), WATCHDOG_INFO);
    }
  }

  if (!empty($invoke_modules)) {
    // Refresh the module list to exclude the disabled modules.
    system_list_reset();
    module_list(TRUE);
    module_implements('', FALSE, TRUE);
    // Invoke hook_modules_disabled before disabling modules,
    // so we can still call module hooks to get information.
    module_invoke_all('modules_disabled', $invoke_modules);
    // Update the registry to remove the newly-disabled module.
    registry_update();
    _system_update_bootstrap_status();
  }

  // If there remains no more node_access module, rebuilding will be
  // straightforward, we can do it right now.
  if (node_access_needs_rebuild() && count(module_implements('node_grants')) == 0) {
    node_access_rebuild();
  }
}

/**
 * @defgroup hooks Hooks
 * @{
 * Allow modules to interact with the Drupal core.
 *
 * Drupal's module system is based on the concept of "hooks". A hook is a PHP
 * function that is named foo_bar(), where "foo" is the name of the module
 * (whose filename is thus foo.module) and "bar" is the name of the hook. Each
 * hook has a defined set of parameters and a specified result type.
 *
 * To extend Drupal, a module need simply implement a hook. When Drupal wishes
 * to allow intervention from modules, it determines which modules implement a
 * hook and calls that hook in all enabled modules that implement it.
 *
 * The available hooks to implement are explained here in the Hooks section of
 * the developer documentation. The string "hook" is used as a placeholder for
 * the module name in the hook definitions. For example, if the module file is
 * called example.module, then hook_help() as implemented by that module would
 * be defined as example_help().
 *
 * The example functions included are not part of the Drupal core, they are
 * just models that you can modify. Only the hooks implemented within modules
 * are executed when running Drupal.
 *
 * See also @link themeable the themeable group page. @endlink
 */

/**
 * Determine whether a module implements a hook.
 *
 * @param $module
 *   The name of the module (without the .module extension).
 * @param $hook
 *   The name of the hook (e.g. "help" or "menu").
 *
 * @return
 *   TRUE if the module is both installed and enabled, and the hook is
 *   implemented in that module.
 */
function module_hook($module, $hook) {
  $function = $module . '_' . $hook;
  if (function_exists($function)) {
    return TRUE;
  }
  // If the hook implementation does not exist, check whether it may live in an
  // optional include file registered via hook_hook_info().
  $hook_info = module_hook_info();
  if (isset($hook_info[$hook]['group'])) {
    module_load_include('inc', $module, $module . '.' . $hook_info[$hook]['group']);
    if (function_exists($function)) {
      return TRUE;
    }
  }
  return FALSE;
}

/**
 * Determine which modules are implementing a hook.
 *
 * @param $hook
 *   The name of the hook (e.g. "help" or "menu").
 * @param $sort
 *   By default, modules are ordered by weight and filename, settings this option
 *   to TRUE, module list will be ordered by module name.
 * @param $reset
 *   For internal use only: Whether to force the stored list of hook
 *   implementations to be regenerated (such as after enabling a new module,
 *   before processing hook_enable).
 *
 * @return
 *   An array with the names of the modules which are implementing this hook.
 *
 * @see module_implements_write_cache()
 */
function module_implements($hook, $sort = FALSE, $reset = FALSE) {
  // Use the advanced drupal_static() pattern, since this is called very often.
  static $drupal_static_fast;
  if (!isset($drupal_static_fast)) {
    $drupal_static_fast['implementations'] = &drupal_static(__FUNCTION__);
  }
  $implementations = &$drupal_static_fast['implementations'];

  // We maintain a persistent cache of hook implementations in addition to the
  // static cache to avoid looping through every module and every hook on each
  // request. Benchmarks show that the benefit of this caching outweighs the
  // additional database hit even when using the default database caching
  // backend and only a small number of modules are enabled. The cost of the
  // cache_get() is more or less constant and reduced further when non-database
  // caching backends are used, so there will be more significant gains when a
  // large number of modules are installed or hooks invoked, since this can
  // quickly lead to module_hook() being called several thousand times
  // per request.
  if ($reset) {
    $implementations = array();
    cache_set('module_implements', array(), 'cache_bootstrap');
    drupal_static_reset('module_hook_info');
    drupal_static_reset('drupal_alter');
    cache_clear_all('hook_info', 'cache_bootstrap');
    return;
  }

  // Fetch implementations from cache.
  if (empty($implementations)) {
    $implementations = cache_get('module_implements', 'cache_bootstrap');
    if ($implementations === FALSE) {
      $implementations = array();
    }
    else {
      $implementations = $implementations->data;
    }
  }

  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;
    $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') {
      drupal_alter('module_implements', $implementations[$hook], $hook);
    }
  }
  else {
    foreach ($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;
      }
    }
  }

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

/**
 * Retrieve a list of what hooks are explicitly declared.
 */
function module_hook_info() {
  // This function is indirectly invoked from bootstrap_invoke_all(), in which
  // case common.inc, subsystems, and modules are not loaded yet, so it does not
  // make sense to support hook groups resp. lazy-loaded include files prior to
  // full bootstrap.
  if (drupal_bootstrap(NULL, FALSE) != DRUPAL_BOOTSTRAP_FULL) {
    return array();
  }
  $hook_info = &drupal_static(__FUNCTION__);

  if (!isset($hook_info)) {
    $hook_info = array();
    $cache = cache_get('hook_info', 'cache_bootstrap');
    if ($cache === FALSE) {
      // Rebuild the cache and save it.
      // We can't use module_invoke_all() here or it would cause an infinite
      // loop.
      foreach (module_list() as $module) {
        $function = $module . '_hook_info';
        if (function_exists($function)) {
          $result = $function();
          if (isset($result) && is_array($result)) {
            $hook_info = array_merge_recursive($hook_info, $result);
          }
        }
      }
      // We can't use drupal_alter() for the same reason as above.
      foreach (module_list() as $module) {
        $function = $module . '_hook_info_alter';
        if (function_exists($function)) {
          $function($hook_info);
        }
      }
      cache_set('hook_info', $hook_info, 'cache_bootstrap');
    }
    else {
      $hook_info = $cache->data;
    }
  }

  return $hook_info;
}

/**
 * Writes the hook implementation cache.
 *
 * @see module_implements()
 */
function module_implements_write_cache() {
  $implementations = &drupal_static('module_implements');
  // Check whether we need to write the cache. We do not want to cache hooks
  // which are only invoked on HTTP POST requests since these do not need to be
  // optimized as tightly, and not doing so keeps the cache entry smaller.
  if (isset($implementations['#write_cache']) && ($_SERVER['REQUEST_METHOD'] == 'GET' || $_SERVER['REQUEST_METHOD'] == 'HEAD')) {
    unset($implementations['#write_cache']);
    cache_set('module_implements', $implementations, 'cache_bootstrap');
  }
}

/**
 * Invoke a hook in a particular module.
 *
 * @param $module
 *   The name of the module (without the .module extension).
 * @param $hook
 *   The name of the hook to invoke.
 * @param ...
 *   Arguments to pass to the hook implementation.
 *
 * @return
 *   The return value of the hook implementation.
 */
function module_invoke() {
  $args = func_get_args();
  $module = $args[0];
  $hook = $args[1];
  unset($args[0], $args[1]);
  if (module_hook($module, $hook)) {
    return call_user_func_array($module . '_' . $hook, $args);
  }
}

/**
 * Invoke a hook in all enabled modules that implement it.
 *
 * @param $hook
 *   The name of the hook to invoke.
 * @param ...
 *   Arguments to pass to the hook.
 *
 * @return
 *   An array of return values of the hook implementations. If modules return
 *   arrays from their implementations, those are merged into one array.
 */
function module_invoke_all() {
  $args = func_get_args();
  $hook = $args[0];
  unset($args[0]);
  $return = array();
  foreach (module_implements($hook) as $module) {
    $function = $module . '_' . $hook;
    if (function_exists($function)) {
      $result = call_user_func_array($function, $args);
      if (isset($result) && is_array($result)) {
        $return = array_merge_recursive($return, $result);
      }
      elseif (isset($result)) {
        $return[] = $result;
      }
    }
  }

  return $return;
}

/**
 * @} End of "defgroup hooks".
 */

/**
 * Array of modules required by core.
 */
function drupal_required_modules() {
  $files = drupal_system_listing('/^' . DRUPAL_PHP_FUNCTION_PATTERN . '\.info$/', 'modules', 'name', 0);
  $required = array();

  // An install profile is required and one must always be loaded.
  $required[] = drupal_get_profile();

  foreach ($files as $name => $file) {
    $info = drupal_parse_info_file($file->uri);
    if (!empty($info) && !empty($info['required']) && $info['required']) {
      $required[] = $name;
    }
  }

  return $required;
}

/**
 * Hands off alterable variables to type-specific *_alter implementations.
 *
 * This dispatch function hands off the passed in variables to type-specific
 * hook_TYPE_alter() implementations in modules. It ensures a consistent
 * interface for all altering operations.
 *
 * A maximum of 2 alterable arguments is supported. In case more arguments need
 * to be passed and alterable, modules provide additional variables assigned by
 * reference in the last $context argument:
 * @code
 *   $context = array(
 *     'alterable' => &$alterable,
 *     'unalterable' => $unalterable,
 *     'foo' => 'bar',
 *   );
 *   drupal_alter('mymodule_data', $alterable1, $alterable2, $context);
 * @endcode
 *
 * Note that objects are always passed by reference in PHP5. If it is absolutely
 * required that no implementation alters a passed object in $context, then an
 * object needs to be cloned:
 * @code
 *   $context = array(
 *     'unalterable_object' => clone $object,
 *   );
 *   drupal_alter('mymodule_data', $data, $context);
 * @endcode
 *
 * @param $type
 *   A string describing the type of the alterable $data. 'form', 'links',
 *   'node_content', and so on are several examples. Alternatively can be an
 *   array, in which case hook_TYPE_alter() is invoked for each value in the
 *   array, ordered first by module, and then for each module, in the order of
 *   values in $type. For example, when Form API is using drupal_alter() to
 *   execute both hook_form_alter() and hook_form_FORM_ID_alter()
 *   implementations, it passes array('form', 'form_' . $form_id) for $type.
 * @param &$data
 *   The variable that will be passed to hook_TYPE_alter() implementations to be
 *   altered. The type of this variable depends on the value of the $type
 *   argument. For example, when altering a 'form', $data will be a structured
 *   array. When altering a 'profile', $data will be an object.
 * @param &$context1
 *   (optional) An additional variable that is passed by reference.
 * @param &$context2
 *   (optional) An additional variable that is passed by reference. If more
 *   context needs to be provided to implementations, then this should be an
 *   associative array as described above.
 */
function drupal_alter($type, &$data, &$context1 = NULL, &$context2 = NULL) {
  // Use the advanced drupal_static() pattern, since this is called very often.
  static $drupal_static_fast;
  if (!isset($drupal_static_fast)) {
    $drupal_static_fast['functions'] = &drupal_static(__FUNCTION__);
  }
  $functions = &$drupal_static_fast['functions'];

  // Most of the time, $type is passed as a string, so for performance,
  // normalize it to that. When passed as an array, usually the first item in
  // the array is a generic type, and additional items in the array are more
  // specific variants of it, as in the case of array('form', 'form_FORM_ID').
  if (is_array($type)) {
    $cid = implode(',', $type);
    $extra_types = $type;
    $type = array_shift($extra_types);
    // Allow if statements in this function to use the faster isset() rather
    // than !empty() both when $type is passed as a string, or as an array with
    // one item.
    if (empty($extra_types)) {
      unset($extra_types);
    }
  }
  else {
    $cid = $type;
  }

  // Some alter hooks are invoked many times per page request, so statically
  // cache the list of functions to call, and on subsequent calls, iterate
  // through them quickly.
  if (!isset($functions[$cid])) {
    $functions[$cid] = array();
    $hook = $type . '_alter';
    $modules = module_implements($hook);
    if (!isset($extra_types)) {
      // For the more common case of a single hook, we do not need to call
      // function_exists(), since module_implements() returns only modules with
      // implementations.
      foreach ($modules as $module) {
        $functions[$cid][] = $module . '_' . $hook;
      }
    }
    else {
      // For multiple hooks, we need $modules to contain every module that
      // implements at least one of them.
      $extra_modules = array();
      foreach ($extra_types as $extra_type) {
        $extra_modules = array_merge($extra_modules, module_implements($extra_type . '_alter'));
      }
      // If any modules implement one of the extra hooks that do not implement
      // the primary hook, we need to add them to the $modules array in their
      // appropriate order.
      if (array_diff($extra_modules, $modules)) {
        // Order the modules by the order returned by module_list().
        $modules = array_intersect(module_list(), array_merge($modules, $extra_modules));
      }
      foreach ($modules as $module) {
        // Since $modules is a merged array, for any given module, we do not
        // know whether it has any particular implementation, so we need a
        // function_exists().
        $function = $module . '_' . $hook;
        if (function_exists($function)) {
          $functions[$cid][] = $function;
        }
        foreach ($extra_types as $extra_type) {
          $function = $module . '_' . $extra_type . '_alter';
          if (function_exists($function)) {
            $functions[$cid][] = $function;
          }
        }
      }
    }
    // Allow the theme to alter variables after the theme system has been
    // initialized.
    global $theme, $base_theme_info;
    if (isset($theme)) {
      $theme_keys = array();
      foreach ($base_theme_info as $base) {
        $theme_keys[] = $base->name;
      }
      $theme_keys[] = $theme;
      foreach ($theme_keys as $theme_key) {
        $function = $theme_key . '_' . $hook;
        if (function_exists($function)) {
          $functions[$cid][] = $function;
        }
        if (isset($extra_types)) {
          foreach ($extra_types as $extra_type) {
            $function = $theme_key . '_' . $extra_type . '_alter';
            if (function_exists($function)) {
              $functions[$cid][] = $function;
            }
          }
        }
      }
    }
  }

  foreach ($functions[$cid] as $function) {
    $function($data, $context1, $context2);
  }
}

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