module.inc

<?php


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

/**
 * Loads 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;
}

/**
 * Builds 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 (isset($lists['bootstrap'])) {
            return $lists['bootstrap'];
        }
        if ($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);
        }
        // Only return module names here since module_list() doesn't need the
        // filename itself. Don't use drupal_map_assoc() as that requires common.inc.
        $list = array_keys($bootstrap_list);
        $lists['bootstrap'] = !empty($list) ? array_combine($list, $list) : array();
    }
    elseif (!isset($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' => $record->filename,
                    );
                }
            }
            foreach ($lists['theme'] as $key => $theme) {
                if (!empty($theme->info['base theme'])) {
                    // Make a list of the theme's base themes.
                    require_once DRUPAL_ROOT . '/includes/theme.inc';
                    $lists['theme'][$key]->base_themes = drupal_find_base_themes($lists['theme'], $key);
                    // Don't proceed if there was a problem with the root base theme.
                    if (!current($lists['theme'][$key]->base_themes)) {
                        continue;
                    }
                    // Determine the root base theme.
                    $base_key = key($lists['theme'][$key]->base_themes);
                    // Add to the list of sub-themes for each of the theme's base themes.
                    foreach (array_keys($lists['theme'][$key]->base_themes) as $base_theme) {
                        $lists['theme'][$base_theme]->sub_themes[$key] = $lists['theme'][$key]->info['name'];
                    }
                    // Add the base theme's theme engine info.
                    $lists['theme'][$key]->info['engine'] = isset($lists['theme'][$base_key]->info['engine']) ? $lists['theme'][$base_key]->info['engine'] : 'theme';
                }
                else {
                    // A plain theme is its own engine.
                    $base_key = $key;
                    if (!isset($lists['theme'][$key]->info['engine'])) {
                        $lists['theme'][$key]->info['engine'] = 'theme';
                    }
                }
                // Set the theme engine prefix.
                $lists['theme'][$key]->prefix = $lists['theme'][$key]->info['engine'] == 'theme' ? $base_key : $lists['theme'][$key]->info['engine'];
            }
            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];
}

/**
 * Resets 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');
    // Clean up the bootstrap file scan cache.
    drupal_static_reset('_drupal_file_scan_cache');
    cache_clear_all('_drupal_file_scan_cache', 'cache_bootstrap');
}

/**
 * Determines which modules require and are required by each module.
 *
 * @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;
}

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

/**
 * Loads 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);
}

/**
 * Loads 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) {
    static $files = array();
    if (!isset($name)) {
        $name = $module;
    }
    $key = $type . ':' . $module . ':' . $name;
    if (isset($files[$key])) {
        return $files[$key];
    }
    if (function_exists('drupal_get_path')) {
        $file = DRUPAL_ROOT . '/' . drupal_get_path('module', $module) . "/{$name}.{$type}";
        if (is_file($file)) {
            require_once $file;
            $files[$key] = $file;
            return $file;
        }
        else {
            $files[$key] = FALSE;
        }
    }
    return FALSE;
}

/**
 * Loads an include file for each module 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 string[] $module_list
 *   An array of module names.
 * @param bool $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 $module_list is already complete and in the correct order.
 *
 * @return bool
 *   FALSE if one or more dependencies are missing, TRUE otherwise.
 *
 * @see hook_install()
 * @see hook_enable()
 * @see hook_modules_installed()
 * @see hook_modules_enabled()
 * @see module_disable()
 * @see drupal_uninstall_modules()
 */
function module_enable($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));
        // The array is iterated over manually (instead of using a foreach) because
        // modules may be added to the list within the loop and we need to process
        // them.
        while ($module = key($module_list)) {
            next($module_list);
            if (!isset($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 (array_keys($module_data[$module]->requires) 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', $module)
                ->execute();
            // Refresh the module list to include it.
            system_list_reset();
            module_list(TRUE);
            module_implements('', FALSE, TRUE);
            _system_update_bootstrap_status();
            // Update the registry to include it.
            registry_update();
            // Refresh the schema to include it.
            drupal_get_schema(NULL, TRUE);
            // Update the theme registry to include it.
            drupal_theme_rebuild();
            // Clear entity cache.
            entity_info_cache_clear();
            // Now install the module if necessary.
            if (drupal_get_installed_schema_version($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;
}

/**
 * Disables a given set of modules.
 *
 * @param string[] $module_list
 *   An array of module names.
 * @param bool $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 $module_list is already complete and in the correct order.
 *
 * @see drupal_uninstall_modules()
 * @see module_enable()
 */
function module_disable($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));
        $profile = drupal_get_profile();
        // The array is iterated over manually (instead of using a foreach) because
        // modules may be added to the list within the loop and we need to process
        // them.
        while ($module = key($module_list)) {
            next($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);
        entity_info_cache_clear();
        // 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();
        // Update the theme registry to remove the newly-disabled module.
        drupal_theme_rebuild();
    }
    // 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 themeable
 * @see callbacks
 */

/**
 * @defgroup callbacks Callbacks
 * @{
 * Callback function signatures.
 *
 * Drupal's API sometimes uses callback functions to allow you to define how
 * some type of processing happens. A callback is a function with a defined
 * signature, which you define in a module. Then you pass the function name as
 * a parameter to a Drupal API function or return it as part of a hook
 * implementation return value, and your function is called at an appropriate
 * time. For instance, when setting up batch processing you might need to
 * provide a callback function for each processing step and/or a callback for
 * when processing is finished; you would do that by defining these functions
 * and passing their names into the batch setup function.
 *
 * Callback function signatures, like hook definitions, are described by
 * creating and documenting dummy functions in a *.api.php file; normally, the
 * dummy callback function's name should start with "callback_", and you should
 * document the parameters and return value and provide a sample function body.
 * Then your API documentation can refer to this callback function in its
 * documentation. A user of your API can usually name their callback function
 * anything they want, although a standard name would be to replace "callback_"
 * with the module name.
 *
 * @see hooks
 * @see themeable
 *
 * @}
 */

/**
 * Determines 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;
}

/**
 * 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 by this
 * function when necessary.
 *
 * @param string $hook
 *   The name of the hook (e.g. "help" or "menu").
 * @param bool $sort
 *   By default, modules are ordered by weight and filename, settings this option
 *   to TRUE, module list will be ordered by module name.
 * @param bool $reset
 *   For internal use only: Whether to force the stored list of hook
 *   implementations to be regenerated (such as after enabling a new module,
 *   before processing hook_enable).
 *
 * @return
 *   An array with the names of the modules which are implementing this hook.
 *
 * @see module_implements_write_cache()
 */
function module_implements($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__);
        $drupal_static_fast['verified'] =& drupal_static(__FUNCTION__ . ':verified');
    }
    $implementations =& $drupal_static_fast['implementations'];
    $verified =& $drupal_static_fast['verified'];
    // We maintain a persistent cache of hook implementations in addition to the
    // static cache to avoid looping through every module and every hook on each
    // request. Benchmarks show that the benefit of this caching outweighs the
    // additional database hit even when using the default database caching
    // backend and only a small number of modules are enabled. The cost of the
    // cache_get() is more or less constant and reduced further when non-database
    // caching backends are used, so there will be more significant gains when a
    // large number of modules are installed or hooks invoked, since this can
    // quickly lead to module_hook() being called several thousand times
    // per request.
    if ($reset) {
        $implementations = array();
        $verified = 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');
        cache_clear_all('system_cache_tables', 'cache');
        return;
    }
    // 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)) {
        $implementations = cache_get('module_implements', 'cache_bootstrap');
        if ($implementations === FALSE) {
            $implementations = array();
        }
        else {
            $implementations = $implementations->data;
        }
        // Forget all previously "verified" hooks, in case that $implementations
        // were cleared via drupal_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];
            drupal_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 drupal_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]);
}

/**
 * Retrieves a list of hooks that are declared through hook_hook_info().
 *
 * @return
 *   An associative array whose keys are hook names and whose values are an
 *   associative array containing a group name. The structure of the array
 *   is the same as the return value of hook_hook_info().
 *
 * @see hook_hook_info()
 */
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() {
    // The list of implementations includes vital modules only before full
    // bootstrap, so do not write cache if we are not fully bootstrapped yet.
    if (drupal_get_bootstrap_phase() != DRUPAL_BOOTSTRAP_FULL) {
        return;
    }
    $implementations =& drupal_static('module_implements');
    if (isset($implementations['#write_cache'])) {
        unset($implementations['#write_cache']);
        cache_set('module_implements', $implementations, 'cache_bootstrap');
    }
}

/**
 * Invokes a hook in a particular module.
 *
 * All arguments are passed by value. Use drupal_alter() if you need to pass
 * arguments by reference.
 *
 * @param $module
 *   The name of the module (without the .module extension).
 * @param $hook
 *   The name of the hook to invoke.
 * @param ...
 *   Arguments to pass to the hook implementation.
 *
 * @return
 *   The return value of the hook implementation.
 *
 * @see drupal_alter()
 */
function module_invoke($module, $hook) {
    $args = func_get_args();
    // Remove $module and $hook from the arguments.
    unset($args[0], $args[1]);
    if (module_hook($module, $hook)) {
        return call_user_func_array($module . '_' . $hook, $args);
    }
}

/**
 * Invokes a hook in all enabled modules that implement it.
 *
 * All arguments are passed by value. Use drupal_alter() if you need to pass
 * arguments by reference.
 *
 * @param $hook
 *   The name of the hook to invoke.
 * @param ...
 *   Arguments to pass to the hook.
 *
 * @return
 *   An array of return values of the hook implementations. If modules return
 *   arrays from their implementations, those are merged into one array
 *   recursively. Note: integer keys in arrays will be lost, as the merge is
 *   done using array_merge_recursive().
 *
 * @see drupal_alter()
 */
function module_invoke_all($hook) {
    $args = func_get_args();
    // Remove $hook from the arguments.
    unset($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".
 */

/**
 * Returns an 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 installation 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;
}

/**
 * Passes alterable variables to specific hook_TYPE_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 (a third is supported for
 * legacy reasons, but should not be used in new code). 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.
 * @param $context3
 *   (optional) An additional variable that is passed by reference. This
 *   parameter is deprecated and will not exist in Drupal 8; consequently, it
 *   should not be used for new Drupal 7 code either. It is here only for
 *   backwards compatibility with older code that passed additional arguments
 *   to drupal_alter().
 */
function drupal_alter($type, &$data, &$context1 = NULL, &$context2 = NULL, &$context3 = 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 $modules array in their
            // appropriate order. module_implements() can only return ordered
            // implementations of a single hook. To get the ordered implementations
            // of multiple hooks, we mimic the module_implements() logic of first
            // ordering by module_list(), and then calling
            // drupal_alter('module_implements').
            if (array_diff($extra_modules, $modules)) {
                // Merge the arrays and order by module_list().
                $modules = array_intersect(module_list(), array_merge($modules, $extra_modules));
                // Since module_implements() already took care of loading the necessary
                // include files, we can safely pass FALSE for the array values.
                $implementations = array_fill_keys($modules, FALSE);
                // Let modules adjust the order solely based on the primary hook. This
                // ensures the same module order regardless of whether this if block
                // runs. Calling drupal_alter() recursively in this way does not result
                // in an infinite loop, because this call is for a single $type, so we
                // won't end up in this code block again.
                drupal_alter('module_implements', $implementations, $hook);
                $modules = array_keys($implementations);
            }
            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, $context3);
    }
}