system.api.php

<?php

/**
 * @file
 * Hooks provided by Drupal core and the System module.
 */

use Drupal\Component\Utility\String;
use Drupal\Core\Utility\UpdateException;

/**
 * @addtogroup hooks
 * @{
 */

/**
 * Defines one or more hooks that are exposed by a module.
 *
 * Normally hooks do not need to be explicitly defined. However, by declaring a
 * hook explicitly, a module may define a "group" for it. Modules that implement
 * a hook may then place their implementation in either $module.module or in
 * $module.$group.inc. If the hook is located in $module.$group.inc, then that
 * file will be automatically loaded when needed.
 * In general, hooks that are rarely invoked and/or are very large should be
 * placed in a separate include file, while hooks that are very short or very
 * frequently called should be left in the main module file so that they are
 * always available.
 *
 * @return
 *   An associative array whose keys are hook names and whose values are an
 *   associative array containing:
 *   - group: A string defining the group to which the hook belongs. The module
 *     system will determine whether a file with the name $module.$group.inc
 *     exists, and automatically load it when required.
 *
 * See system_hook_info() for all hook groups defined by Drupal core.
 *
 * @see hook_hook_info_alter().
 */
function hook_hook_info() {
  $hooks['token_info'] = array(
    'group' => 'tokens',
  );
  $hooks['tokens'] = array(
    'group' => 'tokens',
  );
  return $hooks;
}

/**
 * Perform periodic actions.
 *
 * Modules that require some commands to be executed periodically can
 * implement hook_cron(). The engine will then call the hook whenever a cron
 * run happens, as defined by the administrator. Typical tasks managed by
 * hook_cron() are database maintenance, backups, recalculation of settings
 * or parameters, automated mailing, and retrieving remote data.
 *
 * Short-running or non-resource-intensive tasks can be executed directly in
 * the hook_cron() implementation.
 *
 * Long-running tasks and tasks that could time out, such as retrieving remote
 * data, sending email, and intensive file tasks, should use the queue API
 * instead of executing the tasks directly. To do this, first define one or
 * more queues via hook_queue_info(). Then, add items that need to be
 * processed to the defined queues.
 */
function hook_cron() {
  // Short-running operation example, not using a queue:
  // Delete all expired records since the last cron run.
  $expires = \Drupal::state()->get('mymodule.cron_last_run', REQUEST_TIME);
  db_delete('mymodule_table')
    ->condition('expires', $expires, '>=')
    ->execute();
  \Drupal::state()->set('mymodule.cron_last_run', REQUEST_TIME);

  // Long-running operation example, leveraging a queue:
  // Fetch feeds from other sites.
  $result = db_query('SELECT * FROM {aggregator_feed} WHERE checked + refresh < :time AND refresh <> :never', array(
    ':time' => REQUEST_TIME,
    ':never' => AGGREGATOR_CLEAR_NEVER,
  ));
  $queue = \Drupal::queue('aggregator_feeds');
  foreach ($result as $feed) {
    $queue->createItem($feed);
  }
}

/**
 * Alter available data types for typed data wrappers.
 *
 * @param array $data_types
 *   An array of data type information.
 *
 * @see hook_data_type_info()
 */
function hook_data_type_info_alter(&$data_types) {
  $data_types['email']['class'] = '\Drupal\mymodule\Type\Email';
}

/**
 * Declare queues holding items that need to be run periodically.
 *
 * While there can be only one hook_cron() process running at the same time,
 * there can be any number of processes defined here running. Because of
 * this, long running tasks are much better suited for this API. Items queued
 * in hook_cron() might be processed in the same cron run if there are not many
 * items in the queue, otherwise it might take several requests, which can be
 * run in parallel.
 *
 * You can create queues, add items to them, claim them, etc without declaring
 * the queue in this hook if you want, however, you need to take care of
 * processing the items in the queue in that case.
 *
 * @return
 *   An associative array where the key is the queue name and the value is
 *   again an associative array. Possible keys are:
 *   - 'worker callback': A PHP callable to call that is an implementation of
 *     callback_queue_worker().
 *   - 'cron': (optional) An associative array containing the optional key:
 *     - 'time': (optional) How much time Drupal cron should spend on calling
 *       this worker in seconds. Defaults to 15.
 *     If the cron key is not defined, the queue will not be processed by cron,
 *     and must be processed by other means.
 *
 * @see hook_cron()
 * @see hook_queue_info_alter()
 */
function hook_queue_info() {
  $queues['aggregator_feeds'] = array(
    'title' => t('Aggregator refresh'),
    'worker callback' => array('Drupal\my_module\MyClass', 'aggregatorRefresh'),
    // Only needed if this queue should be processed by cron.
    'cron' => array(
      'time' => 60,
    ),
  );
  return $queues;
}

/**
 * Alter cron queue information before cron runs.
 *
 * Called by \Drupal\Core\Cron to allow modules to alter cron queue settings
 * before any jobs are processesed.
 *
 * @param array $queues
 *   An array of cron queue information.
 *
 * @see hook_queue_info()
 * @see \Drupal\Core\Cron
 */
function hook_queue_info_alter(&$queues) {
  // This site has many feeds so let's spend 90 seconds on each cron run
  // updating feeds instead of the default 60.
  $queues['aggregator_feeds']['cron']['time'] = 90;
}

/**
 * Work on a single queue item.
 *
 * Callback for hook_queue_info().
 *
 * @param $queue_item_data
 *   The data that was passed to \Drupal\Core\Queue\QueueInterface::createItem()
 *   when the item was queued.
 *
 * @throws \Exception
 *   The worker callback may throw an exception to indicate there was a problem.
 *   The cron process will log the exception, and leave the item in the queue to
 *   be processed again later.
 * @throws \Drupal\Core\Queue\SuspendQueueException
 *   More specifically, a SuspendQueueException should be thrown when the
 *   callback is aware that the problem will affect all subsequent workers of
 *   its queue. For example, a callback that makes HTTP requests may find that
 *   the remote server is not responding. The cron process will behave as with a
 *   normal Exception, and in addition will not attempt to process further items
 *   from the current item's queue during the current cron run.
 *
 * @see \Drupal\Core\Cron::run()
 */
function callback_queue_worker($queue_item_data) {
  $node = node_load($queue_item_data);
  $node->title = 'Updated title';
  $node->save();
}

/**
 * Allows modules to declare their own Form API element types and specify their
 * default values.
 *
 * This hook allows modules to declare their own form element types and to
 * specify their default values. The values returned by this hook will be
 * merged with the elements returned by form constructor implementations and so
 * can return defaults for any Form APIs keys in addition to those explicitly
 * documented by \Drupal\Core\Render\ElementInfoManagerInterface::getInfo().
 *
 * @return array
 *   An associative array with structure identical to that of the return value
 *   of \Drupal\Core\Render\ElementInfoManagerInterface::getInfo().
 *
 * @deprecated Use an annotated class instead, see
 *   \Drupal\Core\Render\Element\ElementInterface.
 *
 * @see hook_element_info_alter()
 */
function hook_element_info() {
  $types['filter_format'] = array(
    '#input' => TRUE,
  );
  return $types;
}

/**
 * Alter the element type information returned from modules.
 *
 * A module may implement this hook in order to alter the element type defaults
 * defined by a module.
 *
 * @param array $types
 *   An associative array with structure identical to that of the return value
 *   of \Drupal\Core\Render\ElementInfoManagerInterface::getInfo().
 *
 * @see hook_element_info()
 */
function hook_element_info_alter(array &$types) {
  // Decrease the default size of textfields.
  if (isset($types['textfield']['#size'])) {
    $types['textfield']['#size'] = 40;
  }
}

/**
 * Perform necessary alterations to the JavaScript before it is presented on
 * the page.
 *
 * @param $javascript
 *   An array of all JavaScript being presented on the page.
 *
 * @see _drupal_add_js()
 * @see drupal_get_js()
 * @see drupal_js_defaults()
 */
function hook_js_alter(&$javascript) {
  // Swap out jQuery to use an updated version of the library.
  $javascript['core/assets/vendor/jquery/jquery.js']['data'] = drupal_get_path('module', 'jquery_update') . '/jquery.js';
}

/**
 * Alters the JavaScript/CSS library registry.
 *
 * Allows certain, contributed modules to update libraries to newer versions
 * while ensuring backwards compatibility. In general, such manipulations should
 * only be done by designated modules, since most modules that integrate with a
 * certain library also depend on the API of a certain library version.
 *
 * @param $libraries
 *   The JavaScript/CSS libraries provided by $module. Keyed by internal library
 *   name and passed by reference.
 * @param $module
 *   The name of the module that registered the libraries.
 */
function hook_library_info_alter(&$libraries, $module) {
  // Update Farbtastic to version 2.0.
  if ($module == 'core' && isset($libraries['jquery.farbtastic'])) {
    // Verify existing version is older than the one we are updating to.
    if (version_compare($libraries['jquery.farbtastic']['version'], '2.0', '<')) {
      // Update the existing Farbtastic to version 2.0.
      $libraries['jquery.farbtastic']['version'] = '2.0';
      // To accurately replace library files, the order of files and the options
      // of each file have to be retained; e.g., like this:
      $old_path = 'assets/vendor/farbtastic';
      // Since the replaced library files are no longer located in a directory
      // relative to the original extension, specify an absolute path (relative
      // to DRUPAL_ROOT / base_path()) to the new location.
      $new_path = '/' . drupal_get_path('module', 'farbtastic_update') . '/js';
      $new_js = array();
      $replacements = array(
        $old_path . '/farbtastic.js' => $new_path . '/farbtastic-2.0.js',
      );
      foreach ($libraries['jquery.farbtastic']['js'] as $source => $options) {
        if (isset($replacements[$source])) {
          $new_js[$replacements[$source]] = $options;
        }
        else {
          $new_js[$source] = $options;
        }
      }
      $libraries['jquery.farbtastic']['js'] = $new_js;
    }
  }
}

/**
 * Alters a JavaScript/CSS library before it is attached.
 *
 * Allows modules and themes to dynamically attach further assets to a library
 * when it is added to the page; e.g., to add JavaScript settings.
 *
 * This hook is only invoked once per library and page.
 *
 * @param array $library
 *   The JavaScript/CSS library that is being added.
 * @param string $name
 *   The name of the library.
 *
 * @see _drupal_add_library()
 */
function hook_library_alter(array &$library, $name) {
  if ($name == 'core/jquery.ui.datepicker') {
    // Note: If the added assets do not depend on additional request-specific
    // data supplied here, consider to statically register it directly via
    // hook_library_info_alter() already.
    $library['dependencies'][] = 'locale/drupal.locale.datepicker';

    $language_interface = \Drupal::languageManager()->getCurrentLanguage();
    $settings['jquery']['ui']['datepicker'] = array(
      'isRTL' => $language_interface->direction == LanguageInterface::DIRECTION_RTL,
      'firstDay' => \Drupal::config('system.date')->get('first_day'),
    );
    $library['js'][] = array(
      'type' => 'setting',
      'data' => $settings,
    );
  }
}

/**
 * Alter CSS files before they are output on the page.
 *
 * @param $css
 *   An array of all CSS items (files and inline CSS) being requested on the page.
 *
 * @see _drupal_add_css()
 * @see drupal_get_css()
 */
function hook_css_alter(&$css) {
  // Remove defaults.css file.
  unset($css[drupal_get_path('module', 'system') . '/defaults.css']);
}

/**
 * Alter the Ajax command data that is sent to the client.
 *
 * @param \Drupal\Core\Ajax\CommandInterface[] $data
 *   An array of all the rendered commands that will be sent to the client.
 *
 * @see \Drupal\Core\Ajax\AjaxResponse::ajaxRender()
 */
function hook_ajax_render_alter(array &$data) {
  // Inject any new status messages into the content area.
  $status_messages = array('#theme' => 'status_messages');
  $command = new \Drupal\Core\Ajax\PrependCommand('#block-system-main .content', drupal_render($status_messages));
  $data[] = $command->render();
}

/**
 * Add elements to a page before it is rendered.
 *
 * Use this hook when you want to add elements at the page level. For your
 * additions to be printed, they have to be placed below a top level array key
 * of the $page array that has the name of a region of the active theme.
 *
 * By default, valid region keys are 'page_top', 'header', 'sidebar_first',
 * 'content', 'sidebar_second' and 'page_bottom'. To get a list of all regions
 * of the active theme, use system_region_list($theme). Note that $theme is a
 * global variable.
 *
 * If you want to alter the elements added by other modules or if your module
 * depends on the elements of other modules, use hook_page_alter() instead which
 * runs after this hook.
 *
 * @param $page
 *   Nested array of renderable elements that make up the page.
 *
 * @see hook_page_alter()
 * @see DefaultHtmlFragmentRenderer::render()
 */
function hook_page_build(&$page) {
  $path = drupal_get_path('module', 'foo');
  // Add JavaScript/CSS assets to all pages.
  // @see drupal_process_attached()
  $page['#attached']['js'][$path . '/foo.js'] = array('every_page' => TRUE);
  $page['#attached']['css'][$path . '/foo.base.css'] = array('every_page' => TRUE);
  $page['#attached']['css'][$path . '/foo.theme.css'] = array('every_page' => TRUE);

  // Add a special CSS file to a certain page only.
  if (drupal_is_front_page()) {
    $page['#attached']['css'][] = $path . '/foo.front.css';
  }

  // Append a standard disclaimer to the content region on a node detail page.
  if (\Drupal::request()->attributes->get('node')) {
    $page['content']['disclaimer'] = array(
      '#markup' => t('Acme, Inc. is not responsible for the contents of this sample code.'),
      '#weight' => 25,
    );
  }
}

/**
 * Alters all the menu links discovered by the menu link plugin manager.
 *
 * @param array $links
 *   The link definitions to be altered.
 *
 * @return array
 *   An array of discovered menu links. Each link has a key that is the machine
 *   name, which must be unique. By default, use the route name as the
 *   machine name. In cases where multiple links use the same route name, such
 *   as two links to the same page in different menus, or two links using the
 *   same route name but different route parameters, the suggested machine name
 *   patten is the route name followed by a dot and a unique suffix. For
 *   example, an additional logout link might have a machine name of
 *   user.logout.navigation, and default links provided to edit the article and
 *   page content types could use machine names
 *   entity.node_type.edit_form.article and entity.node_type.edit_form.page.
 *   Since the machine name may be arbitrary, you should never write code that
 *   assumes it is identical to the route name.
 *
 *   The value corresponding to each machine name key is an associative array
 *   that may contain the following key-value pairs:
 *   - title: (required) The untranslated title of the menu link.
 *   - description: The untranslated description of the link.
 *   - route_name: (optional) The route name to be used to build the path.
 *     Either a route_name or a link_path must be provided.
 *   - route_parameters: (optional) The route parameters to build the path.
 *   - link_path: (optional) If you have an external link use link_path instead
 *     of providing a route_name.
 *   - parent: (optional) The machine name of the link that is this link's menu
 *     parent.
 *   - weight: (optional) An integer that determines the relative position of
 *     items in the menu; higher-weighted items sink. Defaults to 0. Menu items
 *     with the same weight are ordered alphabetically.
 *   - menu_name: (optional) The machine name of a menu to put the link in, if
 *     not the default Tools menu.
 *   - expanded: (optional) If set to TRUE, and if a menu link is provided for
 *     this menu item (as a result of other properties), then the menu link is
 *     always expanded, equivalent to its 'always expanded' checkbox being set
 *     in the UI.
 *   - options: (optional) An array of options to be passed to l() when
 *     generating a link from this menu item.
 *
 * @ingroup menu
 */
function hook_menu_links_discovered_alter(&$links) {
  // Change the weight and title of the user.logout link.
  $links['user.logout']['weight'] = -10;
  $links['user.logout']['title'] = 'Logout';
}

/**
 * Alter tabs and actions displayed on the page before they are rendered.
 *
 * This hook is invoked by menu_local_tasks(). The system-determined tabs and
 * actions are passed in by reference. Additional tabs or actions may be added.
 *
 * Each tab or action is an associative array containing:
 * - #theme: The theme function to use to render.
 * - #link: An associative array containing:
 *   - title: The localized title of the link.
 *   - href: The system path to link to.
 *   - localized_options: An array of options to pass to l().
 * - #weight: The link's weight compared to other links.
 * - #active: Whether the link should be marked as 'active'.
 *
 * @param array $data
 *   An associative array containing:
 *   - actions: A list of of actions keyed by their href, each one being an
 *     associative array as described above.
 *   - tabs: A list of (up to 2) tab levels that contain a list of of tabs keyed
 *     by their href, each one being an associative array as described above.
 * @param string $route_name
 *   The route name of the page.
 */
function hook_menu_local_tasks(&$data, $route_name) {
  // Add an action linking to node/add to all pages.
  $data['actions']['node/add'] = array(
    '#theme' => 'menu_local_action',
    '#link' => array(
      'title' => t('Add content'),
      'href' => 'node/add',
      'localized_options' => array(
        'attributes' => array(
          'title' => t('Add content'),
        ),
      ),
    ),
  );

  // Add a tab linking to node/add to all pages.
  $data['tabs'][0]['node/add'] = array(
    '#theme' => 'menu_local_task',
    '#link' => array(
      'title' => t('Example tab'),
      'href' => 'node/add',
      'localized_options' => array(
        'attributes' => array(
          'title' => t('Add content'),
        ),
      ),
    ),
  );
}

/**
 * Alter tabs and actions displayed on the page before they are rendered.
 *
 * This hook is invoked by menu_local_tasks(). The system-determined tabs and
 * actions are passed in by reference. Existing tabs or actions may be altered.
 *
 * @param array $data
 *   An associative array containing tabs and actions. See
 *   hook_menu_local_tasks() for details.
 * @param string $route_name
 *   The route name of the page.
 *
 * @see hook_menu_local_tasks()
 *
 * @ingroup menu
 */
function hook_menu_local_tasks_alter(&$data, $route_name) {
}

/**
 * Alter local actions plugins.
 *
 * @param array $local_actions
 *   The array of local action plugin definitions, keyed by plugin ID.
 *
 * @see \Drupal\Core\Menu\LocalActionInterface
 * @see \Drupal\Core\Menu\LocalActionManager
 *
 * @ingroup menu
 */
function hook_menu_local_actions_alter(&$local_actions) {
}

/**
 * Alter local tasks plugins.
 *
 * @param array $local_tasks
 *   The array of local tasks plugin definitions, keyed by plugin ID.
 *
 * @see \Drupal\Core\Menu\LocalTaskInterface
 * @see \Drupal\Core\Menu\LocalTaskManager
 */
function hook_local_tasks_alter(&$local_tasks) {
  // Remove a specified local task plugin.
  unset($local_tasks['example_plugin_id']);
}

/**
 * Alter contextual links before they are rendered.
 *
 * This hook is invoked by
 * \Drupal\Core\Menu\ContextualLinkManager::getContextualLinkPluginsByGroup().
 * The system-determined contextual links are passed in by reference. Additional
 * links may be added and existing links can be altered.
 *
 * Each contextual link contains the following entries:
 * - title: The localized title of the link.
 * - route_name: The route name of the link.
 * - route_parameters: The route parameters of the link.
 * - localized_options: An array of options to pass to url().
 * - (optional) weight: The weight of the link, which is used to sort the links.
 *
 *
 * @param array $links
 *   An associative array containing contextual links for the given $group,
 *   as described above. The array keys are used to build CSS class names for
 *   contextual links and must therefore be unique for each set of contextual
 *   links.
 * @param string $group
 *   The group of contextual links being rendered.
 * @param array $route_parameters.
 *   The route parameters passed to each route_name of the contextual links.
 *   For example:
 *   @code
 *   array('node' => $node->id())
 *   @endcode
 *
 * @see \Drupal\Core\Menu\ContextualLinkManager
 *
 * @ingroup menu
 */
function hook_contextual_links_alter(array &$links, $group, array $route_parameters) {
  if ($group == 'menu') {
    // Dynamically use the menu name for the title of the menu_edit contextual
    // link.
    $menu = \Drupal::entityManager()->getStorage('menu')->load($route_parameters['menu']);
    $links['menu_edit']['title'] = t('Edit menu: !label', array('!label' => $menu->label()));
  }
}

/**
 * Alter the plugin definition of contextual links.
 *
 * @param array $contextual_links
 *   An array of contextual_links plugin definitions, keyed by contextual link
 *   ID. Each entry contains the following keys:
 *     - title: The displayed title of the link
 *     - route_name: The route_name of the contextual link to be displayed
 *     - group: The group under which the contextual links should be added to.
 *       Possible values are e.g. 'node' or 'menu'.
 *
 * @see \Drupal\Core\Menu\ContextualLinkManager
 */
function hook_contextual_links_plugins_alter(array &$contextual_links) {
  $contextual_links['menu_edit']['title'] = 'Edit the menu';
}

/**
 * Perform alterations before a page is rendered.
 *
 * Use this hook when you want to remove or alter elements at the page
 * level, or add elements at the page level that depend on an other module's
 * elements (this hook runs after hook_page_build().
 *
 * If you are making changes to entities such as forms, menus, or user
 * profiles, use those objects' native alter hooks instead (hook_form_alter(),
 * for example).
 *
 * The $page array contains top level elements for each block region:
 * @code
 *   $page['page_top']
 *   $page['header']
 *   $page['sidebar_first']
 *   $page['content']
 *   $page['sidebar_second']
 *   $page['page_bottom']
 * @endcode
 *
 * The 'content' element contains the main content of the current page, and its
 * structure will vary depending on what module is responsible for building the
 * page. Some legacy modules may not return structured content at all: their
 * pre-rendered markup will be located in $page['content']['main']['#markup'].
 *
 * Pages built by Drupal's core Node module use a standard structure:
 *
 * @code
 *   // Node body.
 *   $page['content']['system_main']['nodes'][$nid]['body']
 *   // Array of links attached to the node (add comments, read more).
 *   $page['content']['system_main']['nodes'][$nid]['links']
 *   // The node entity itself.
 *   $page['content']['system_main']['nodes'][$nid]['#node']
 *   // The results pager.
 *   $page['content']['system_main']['pager']
 * @endcode
 *
 * Blocks may be referenced by their module/delta pair within a region:
 * @code
 *   // The login block in the first sidebar region.
 *   $page['sidebar_first']['user_login']['#block'];
 * @endcode
 *
 * @param $page
 *   Nested array of renderable elements that make up the page.
 *
 * @see hook_page_build()
 * @see DefaultHtmlFragmentRenderer::render()
 */
function hook_page_alter(&$page) {
  // Add help text to the user login block.
  $page['sidebar_first']['user_login']['help'] = array(
    '#weight' => -10,
    '#markup' => t('To post comments or add content, you first have to log in.'),
  );
}

/**
 * Perform alterations before a form is rendered.
 *
 * One popular use of this hook is to add form elements to the node form. When
 * altering a node form, the node entity can be retrieved by invoking
 * $form_state->getFormObject()->getEntity().
 *
 * In addition to hook_form_alter(), which is called for all forms, there are
 * two more specific form hooks available. The first,
 * hook_form_BASE_FORM_ID_alter(), allows targeting of a form/forms via a base
 * form (if one exists). The second, hook_form_FORM_ID_alter(), can be used to
 * target a specific form directly.
 *
 * The call order is as follows: all existing form alter functions are called
 * for module A, then all for module B, etc., followed by all for any base
 * theme(s), and finally for the theme itself. The module order is determined
 * by system weight, then by module name.
 *
 * Within each module, form alter hooks are called in the following order:
 * first, hook_form_alter(); second, hook_form_BASE_FORM_ID_alter(); third,
 * hook_form_FORM_ID_alter(). So, for each module, the more general hooks are
 * called first followed by the more specific.
 *
 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
 *   The current state of the form. The arguments that
 *   \Drupal::formBuilder()->getForm() was originally called with are available
 *   in the array $form_state->getBuildInfo()['args'].
 * @param $form_id
 *   String representing the name of the form itself. Typically this is the
 *   name of the function that generated the form.
 *
 * @see hook_form_BASE_FORM_ID_alter()
 * @see hook_form_FORM_ID_alter()
 * @see forms_api_reference.html
 */
function hook_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  if (isset($form['type']) && $form['type']['#value'] . '_node_settings' == $form_id) {
    $upload_enabled_types = \Drupal::config('mymodule.settings')->get('upload_enabled_types');
    $form['workflow']['upload_' . $form['type']['#value']] = array(
      '#type' => 'radios',
      '#title' => t('Attachments'),
      '#default_value' => in_array($form['type']['#value'], $upload_enabled_types) ? 1 : 0,
      '#options' => array(t('Disabled'), t('Enabled')),
    );
    // Add a custom submit handler to save the array of types back to the config file.
    $form['actions']['submit']['#submit'][] = 'mymodule_upload_enabled_types_submit';
  }
}

/**
 * Provide a form-specific alteration instead of the global hook_form_alter().
 *
 * Modules can implement hook_form_FORM_ID_alter() to modify a specific form,
 * rather than implementing hook_form_alter() and checking the form ID, or
 * using long switch statements to alter multiple forms.
 *
 * Form alter hooks are called in the following order: hook_form_alter(),
 * hook_form_BASE_FORM_ID_alter(), hook_form_FORM_ID_alter(). See
 * hook_form_alter() for more details.
 *
 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
 *   The current state of the form. The arguments that
 *   \Drupal::formBuilder()->getForm() was originally called with are available
 *   in the array $form_state->getBuildInfo()['args'].
 * @param $form_id
 *   String representing the name of the form itself. Typically this is the
 *   name of the function that generated the form.
 *
 * @see hook_form_alter()
 * @see hook_form_BASE_FORM_ID_alter()
 * @see \Drupal\Core\Form\FormBuilderInterface::prepareForm()
 * @see forms_api_reference.html
 */
function hook_form_FORM_ID_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  // Modification for the form with the given form ID goes here. For example, if
  // FORM_ID is "user_register_form" this code would run only on the user
  // registration form.

  // Add a checkbox to registration form about agreeing to terms of use.
  $form['terms_of_use'] = array(
    '#type' => 'checkbox',
    '#title' => t("I agree with the website's terms and conditions."),
    '#required' => TRUE,
  );
}

/**
 * Provide a form-specific alteration for shared ('base') forms.
 *
 * By default, when \Drupal::formBuilder()->getForm() is called, Drupal looks
 * for a function with the same name as the form ID, and uses that function to
 * build the form. In contrast, base forms allow multiple form IDs to be mapped
 * to a single base (also called 'factory') form function.
 *
 * Modules can implement hook_form_BASE_FORM_ID_alter() to modify a specific
 * base form, rather than implementing hook_form_alter() and checking for
 * conditions that would identify the shared form constructor.
 *
 * To identify the base form ID for a particular form (or to determine whether
 * one exists) check the $form_state. The base form ID is stored under
 * $form_state->getBuildInfo()['base_form_id'].
 *
 * Form alter hooks are called in the following order: hook_form_alter(),
 * hook_form_BASE_FORM_ID_alter(), hook_form_FORM_ID_alter(). See
 * hook_form_alter() for more details.
 *
 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
 *   The current state of the form.
 * @param $form_id
 *   String representing the name of the form itself. Typically this is the
 *   name of the function that generated the form.
 *
 * @see hook_form_alter()
 * @see hook_form_FORM_ID_alter()
 * @see \Drupal\Core\Form\FormBuilderInterface::prepareForm()
 */
function hook_form_BASE_FORM_ID_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  // Modification for the form with the given BASE_FORM_ID goes here. For
  // example, if BASE_FORM_ID is "node_form", this code would run on every
  // node form, regardless of node type.

  // Add a checkbox to the node form about agreeing to terms of use.
  $form['terms_of_use'] = array(
    '#type' => 'checkbox',
    '#title' => t("I agree with the website's terms and conditions."),
    '#required' => TRUE,
  );
}

/**
 * Alter an email message created with the drupal_mail() function.
 *
 * hook_mail_alter() allows modification of email messages created and sent
 * with drupal_mail(). Usage examples include adding and/or changing message
 * text, message fields, and message headers.
 *
 * Email messages sent using functions other than drupal_mail() will not
 * invoke hook_mail_alter(). For example, a contributed module directly
 * calling the drupal_mail_system()->mail() or PHP mail() function
 * will not invoke this hook. All core modules use drupal_mail() for
 * messaging, it is best practice but not mandatory in contributed modules.
 *
 * @param $message
 *   An array containing the message data. Keys in this array include:
 *  - 'id':
 *     The drupal_mail() id of the message. Look at module source code or
 *     drupal_mail() for possible id values.
 *  - 'to':
 *     The address or addresses the message will be sent to. The
 *     formatting of this string must comply with RFC 2822.
 *  - 'from':
 *     The address the message will be marked as being from, which is
 *     either a custom address or the site-wide default email address.
 *  - 'subject':
 *     Subject of the email to be sent. This must not contain any newline
 *     characters, or the email may not be sent properly.
 *  - 'body':
 *     An array of strings containing the message text. The message body is
 *     created by concatenating the individual array strings into a single text
 *     string using "\n\n" as a separator.
 *  - 'headers':
 *     Associative array containing mail headers, such as From, Sender,
 *     MIME-Version, Content-Type, etc.
 *  - 'params':
 *     An array of optional parameters supplied by the caller of drupal_mail()
 *     that is used to build the message before hook_mail_alter() is invoked.
 *  - 'language':
 *     The language object used to build the message before hook_mail_alter()
 *     is invoked.
 *  - 'send':
 *     Set to FALSE to abort sending this email message.
 *
 * @see drupal_mail()
 */
function hook_mail_alter(&$message) {
  if ($message['id'] == 'modulename_messagekey') {
    if (!example_notifications_optin($message['to'], $message['id'])) {
      // If the recipient has opted to not receive such messages, cancel
      // sending.
      $message['send'] = FALSE;
      return;
    }
    $message['body'][] = "--\nMail sent out from " . \Drupal::config('system.site')->get('name');
  }
}

/**
 * Alter the registry of modules implementing a hook.
 *
 * This hook is invoked during \Drupal::moduleHandler()->getImplementations().
 * A module may implement this hook in order to reorder the implementing
 * modules, which are otherwise ordered by the module's system weight.
 *
 * Note that hooks invoked using \Drupal::moduleHandler->alter() can have
 * multiple variations(such as hook_form_alter() and hook_form_FORM_ID_alter()).
 * \Drupal::moduleHandler->alter() will call all such variants defined by a
 * single module in turn. For the purposes of hook_module_implements_alter(),
 * these variants are treated as a single hook. Thus, to ensure that your
 * implementation of hook_form_FORM_ID_alter() is called at the right time,
 * you will have to change the order of hook_form_alter() implementation in
 * hook_module_implements_alter().
 *
 * @param $implementations
 *   An array keyed by the module's name. The value of each item corresponds
 *   to a $group, which is usually FALSE, unless the implementation is in a
 *   file named $module.$group.inc.
 * @param $hook
 *   The name of the module hook being implemented.
 */
function hook_module_implements_alter(&$implementations, $hook) {
  if ($hook == 'rdf_mapping') {
    // Move my_module_rdf_mapping() to the end of the list.
    // \Drupal::moduleHandler()->getImplementations()
    // iterates through $implementations with a foreach loop which PHP iterates
    // in the order that the items were added, so to move an item to the end of
    // the array, we remove it and then add it.
    $group = $implementations['my_module'];
    unset($implementations['my_module']);
    $implementations['my_module'] = $group;
  }
}

/**
 * Perform alterations to the breadcrumb built by the BreadcrumbManager.
 *
 * @param array $breadcrumb
 *   An array of breadcrumb link a tags, returned by the breadcrumb manager
 *   build method, for example
 *   @code
 *     array('<a href="/">Home</a>');
 *   @endcode
 * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
 *   The current route match.
 * @param array $context
 *   May include the following key:
 *   - builder: the instance of
 *     \Drupal\Core\Breadcrumb\BreadcrumbBuilderInterface that constructed this
 *     breadcrumb, or NULL if no builder acted based on the current attributes.
 */
function hook_system_breadcrumb_alter(array &$breadcrumb, \Drupal\Core\Routing\RouteMatchInterface $route_match, array $context) {
  // Add an item to the end of the breadcrumb.
  $breadcrumb[] = Drupal::l(t('Text'), 'example_route_name');
}

/**
 * Alter the information parsed from module and theme .info.yml files
 *
 * This hook is invoked in _system_rebuild_module_data() and in
 * _system_rebuild_theme_data(). A module may implement this hook in order to
 * add to or alter the data generated by reading the .info.yml file with
 * \Drupal\Core\Extension\InfoParser.
 *
 * @param array $info
 *   The .info.yml file contents, passed by reference so that it can be altered.
 * @param \Drupal\Core\Extension\Extension $file
 *   Full information about the module or theme.
 * @param string $type
 *   Either 'module' or 'theme', depending on the type of .info.yml file that
 *   was passed.
 */
function hook_system_info_alter(array &$info, \Drupal\Core\Extension\Extension $file, $type) {
  // Only fill this in if the .info.yml file does not define a 'datestamp'.
  if (empty($info['datestamp'])) {
    $info['datestamp'] = $file->getMTime();
  }
}

/**
 * Provide online user help.
 *
 * By implementing hook_help(), a module can make documentation available to
 * the user for the module as a whole, or for specific pages. Help for
 * developers should usually be provided via function header comments in the
 * code, or in special API example files.
 *
 * The page-specific help information provided by this hook appears as a system
 * help block on that page. The module overview help information is displayed
 * by the Help module. It can be accessed from the page at admin/help or from
 * the Extend page.
 *
 * For detailed usage examples of:
 * - Module overview help, see content_translation_help(). Module overview
 *   help should follow
 *   @link https://drupal.org/node/632280 the standard help template. @endlink
 * - Page-specific help using only routes, see book_help().
 * - Page-specific help using routes and $request, see block_help().
 *
 * @param string $route_name
 *   For page-specific help, use the route name as identified in the
 *   module's routing.yml file. For module overview help, the route name
 *   will be in the form of "help.page.$modulename".
 * @param Drupal\Core\Routing\RouteMatchInterface $route_match
 *   The current route match. This can be used to generate different help
 *   output for different pages that share the same route.
 *
 * @return string
 *   A localized string containing the help text.
 */
function hook_help($route_name, \Drupal\Core\Routing\RouteMatchInterface $route_match) {
  switch ($route_name) {
    // Main module help for the block module.
    case 'help.page.block':
      return '<p>' . t('Blocks are boxes of content rendered into an area, or region, of a web page. The default theme Bartik, for example, implements the regions "Sidebar first", "Sidebar second", "Featured", "Content", "Header", "Footer", etc., and a block may appear in any one of these areas. The <a href="!blocks">blocks administration page</a> provides a drag-and-drop interface for assigning a block to a region, and for controlling the order of blocks within regions.', array('!blocks' => \Drupal::url('block.admin_display'))) . '</p>';

    // Help for another path in the block module.
    case 'block.admin_display':
      return '<p>' . t('This page provides a drag-and-drop interface for assigning a block to a region, and for controlling the order of blocks within regions. Since not all themes implement the same regions, or display regions in the same way, blocks are positioned on a per-theme basis. Remember that your changes will not be saved until you click the <em>Save blocks</em> button at the bottom of the page.') . '</p>';
  }
}

/**
 * Register a module or theme's theme implementations.
 *
 * The implementations declared by this hook have several purposes:
 * - They can specify how a particular render array is to be rendered as HTML.
 *   This is usually the case if the theme function is assigned to the render
 *   array's #theme property.
 * - They can return HTML for default calls to _theme().
 * - They can return HTML for calls to _theme() for a theme suggestion.
 *
 * @param array $existing
 *   An array of existing implementations that may be used for override
 *   purposes. This is primarily useful for themes that may wish to examine