common.inc

<?php

/**
 * @file
 * Common functions that many Drupal modules will need to reference.
 *
 * The functions that are critical and need to be available even when serving
 * a cached page are instead located in bootstrap.inc.
 */

use Drupal\Component\Serialization\Json;
use Drupal\Component\Utility\Bytes;
use Drupal\Component\Utility\Html;
use Drupal\Component\Utility\SortArray;
use Drupal\Component\Utility\UrlHelper;
use Drupal\Core\Cache\Cache;
use Drupal\Core\Render\Markup;
use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\PhpStorage\PhpStorageFactory;
use Drupal\Core\StringTranslation\PluralTranslatableMarkup;
use Drupal\Core\Render\BubbleableMetadata;
use Drupal\Core\Render\Element;

/**
 * @defgroup php_wrappers PHP wrapper functions
 * @{
 * Functions that are wrappers or custom implementations of PHP functions.
 *
 * Certain PHP functions should not be used in Drupal. Instead, Drupal's
 * replacement functions should be used.
 *
 * For example, for improved or more secure UTF8-handling, or RFC-compliant
 * handling of URLs in Drupal.
 *
 * For ease of use and memorizing, all these wrapper functions use the same name
 * as the original PHP function, but prefixed with "drupal_". Beware, however,
 * that not all wrapper functions support the same arguments as the original
 * functions.
 *
 * You should always use these wrapper functions in your code.
 *
 * Wrong:
 * @code
 *   $my_substring = substr($original_string, 0, 5);
 * @endcode
 *
 * Correct:
 * @code
 *   $my_substring = Unicode::substr($original_string, 0, 5);
 * @endcode
 *
 * @}
 */

/**
 * Return status for saving which involved creating a new item.
 */
const SAVED_NEW = 1;

/**
 * Return status for saving which involved an update to an existing item.
 */
const SAVED_UPDATED = 2;

/**
 * Return status for saving which deleted an existing item.
 */
const SAVED_DELETED = 3;

/**
 * The default aggregation group for CSS files added to the page.
 */
const CSS_AGGREGATE_DEFAULT = 0;

/**
 * The default aggregation group for theme CSS files added to the page.
 */
const CSS_AGGREGATE_THEME = 100;

/**
 * The default weight for CSS rules that style HTML elements ("base" styles).
 */
const CSS_BASE = -200;

/**
 * The default weight for CSS rules that layout a page.
 */
const CSS_LAYOUT = -100;

/**
 * The default weight for CSS rules that style design components (and their associated states and themes.)
 */
const CSS_COMPONENT = 0;

/**
 * The default weight for CSS rules that style states and are not included with components.
 */
const CSS_STATE = 100;

/**
 * The default weight for CSS rules that style themes and are not included with components.
 */
const CSS_THEME = 200;

/**
 * The default group for JavaScript settings added to the page.
 */
const JS_SETTING = -200;

/**
 * The default group for JavaScript and jQuery libraries added to the page.
 */
const JS_LIBRARY = -100;

/**
 * The default group for module JavaScript code added to the page.
 */
const JS_DEFAULT = 0;

/**
 * The default group for theme JavaScript code added to the page.
 */
const JS_THEME = 100;

/**
 * The delimiter used to split plural strings.
 *
 * @deprecated in Drupal 8.0.x-dev, will be removed before Drupal 9.0.0.
 *   Use \Drupal\Core\StringTranslation\PluralTranslatableMarkup::DELIMITER
 *   instead.
 */
const LOCALE_PLURAL_DELIMITER = PluralTranslatableMarkup::DELIMITER;

/**
 * Prepares a 'destination' URL query parameter.
 *
 * Used to direct the user back to the referring page after completing a form.
 * By default the current URL is returned. If a destination exists in the
 * previous request, that destination is returned. As such, a destination can
 * persist across multiple pages.
 *
 * @return array
 *   An associative array containing the key:
 *   - destination: The value of the current request's 'destination' query
 *     parameter, if present. This can be either a relative or absolute URL.
 *     However, for security, redirection to external URLs is not performed.
 *     If the query parameter isn't present, then the URL of the current
 *     request is returned.
 *
 * @see \Drupal\Core\EventSubscriber\RedirectResponseSubscriber::checkRedirectUrl()
 *
 * @ingroup form_api
 *
 * @deprecated in Drupal 8.0.x-dev, will be removed before Drupal 9.0.0.
 *   Use the redirect.destination service.
 */
function drupal_get_destination() {
  return \Drupal::destination()->getAsArray();
}

/**
 * @defgroup validation Input validation
 * @{
 * Functions to validate user input.
 */

/**
 * Verifies the syntax of the given email address.
 *
 * @param string $mail
 *   A string containing an email address.
 *
 * @return bool
 *   TRUE if the address is in a valid format.
 *
 * @deprecated in Drupal 8.0.x-dev, will be removed before Drupal 9.0.0.
 *   Use \Drupal::service('email.validator')->isValid().
 */
function valid_email_address($mail) {
  return \Drupal::service('email.validator')->isValid($mail);
}

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

/**
 * @defgroup sanitization Sanitization functions
 * @{
 * Functions to sanitize values.
 *
 * See https://www.drupal.org/writing-secure-code for information
 * on writing secure code.
 */

/**
 * Strips dangerous protocols from a URI and encodes it for output to HTML.
 *
 * @param $uri
 *   A plain-text URI that might contain dangerous protocols.
 *
 * @return string
 *   A URI stripped of dangerous protocols and encoded for output to an HTML
 *   attribute value. Because it is already encoded, it should not be set as a
 *   value within a $attributes array passed to Drupal\Core\Template\Attribute,
 *   because Drupal\Core\Template\Attribute expects those values to be
 *   plain-text strings. To pass a filtered URI to
 *   Drupal\Core\Template\Attribute, call
 *   \Drupal\Component\Utility\UrlHelper::stripDangerousProtocols() instead.
 *
 * @see \Drupal\Component\Utility\UrlHelper::stripDangerousProtocols()
 * @see \Drupal\Component\Utility\UrlHelper::filterBadProtocol()
 *
 * @deprecated in Drupal 8.0.x-dev, will be removed before Drupal 9.0.0.
 *   Use UrlHelper::stripDangerousProtocols() or UrlHelper::filterBadProtocol()
 *   instead. UrlHelper::stripDangerousProtocols() can be used in conjunction
 *   with \Drupal\Component\Utility\SafeMarkup::format() and an @variable
 *   placeholder which will perform the necessary escaping.
 *   UrlHelper::filterBadProtocol() is functionality equivalent to check_url()
 *   apart from the fact it is protected from double escaping bugs. Note that
 *   this method no longer marks its output as safe.
 *
 */
function check_url($uri) {
  return Html::escape(UrlHelper::stripDangerousProtocols($uri));
}

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

/**
 * @defgroup format Formatting
 * @{
 * Functions to format numbers, strings, dates, etc.
 */

/**
 * Generates a string representation for the given byte count.
 *
 * @param $size
 *   A size in bytes.
 * @param $langcode
 *   Optional language code to translate to a language other than what is used
 *   to display the page.
 *
 * @return \Drupal\Core\StringTranslation\TranslatableMarkup
 *   A translated string representation of the size.
 */
function format_size($size, $langcode = NULL) {
  if ($size < Bytes::KILOBYTE) {
    return \Drupal::translation()->formatPlural($size, '1 byte', '@count bytes', array(), array('langcode' => $langcode));
  }
  else {
    $size = $size / Bytes::KILOBYTE; // Convert bytes to kilobytes.
    $units = ['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
    foreach ($units as $unit) {
      if (round($size, 2) >= Bytes::KILOBYTE) {
        $size = $size / Bytes::KILOBYTE;
      }
      else {
        break;
      }
    }
    $args = ['@size' => round($size, 2)];
    $options = ['langcode' => $langcode];
    switch ($unit) {
      case 'KB':
        return new TranslatableMarkup('@size KB', $args, $options);
      case 'MB':
        return new TranslatableMarkup('@size MB', $args, $options);
      case 'GB':
        return new TranslatableMarkup('@size GB', $args, $options);
      case 'TB':
        return new TranslatableMarkup('@size TB', $args, $options);
      case 'PB':
        return new TranslatableMarkup('@size PB', $args, $options);
      case 'EB':
        return new TranslatableMarkup('@size EB', $args, $options);
      case 'ZB':
        return new TranslatableMarkup('@size ZB', $args, $options);
      case 'YB':
        return new TranslatableMarkup('@size YB', $args, $options);
    }
  }
}

/**
 * Formats a date, using a date type or a custom date format string.
 *
 * @param $timestamp
 *   A UNIX timestamp to format.
 * @param $type
 *   (optional) The format to use, one of:
 *   - One of the built-in formats: 'short', 'medium',
 *     'long', 'html_datetime', 'html_date', 'html_time',
 *     'html_yearless_date', 'html_week', 'html_month', 'html_year'.
 *   - The name of a date type defined by a date format config entity.
 *   - The machine name of an administrator-defined date format.
 *   - 'custom', to use $format.
 *   Defaults to 'medium'.
 * @param $format
 *   (optional) If $type is 'custom', a PHP date format string suitable for
 *   input to date(). Use a backslash to escape ordinary text, so it does not
 *   get interpreted as date format characters.
 * @param $timezone
 *   (optional) Time zone identifier, as described at
 *   http://php.net/manual/timezones.php Defaults to the time zone used to
 *   display the page.
 * @param $langcode
 *   (optional) Language code to translate to. Defaults to the language used to
 *   display the page.
 *
 * @return
 *   A translated date string in the requested format.
 *
 * @see \Drupal\Core\Datetime\DateFormatter::format()
 *
 * @deprecated in Drupal 8.0.0, will be removed before Drupal 9.0.0.
 *   Use \Drupal::service('date.formatter')->format().
 */
function format_date($timestamp, $type = 'medium', $format = '', $timezone = NULL, $langcode = NULL) {
  return \Drupal::service('date.formatter')->format($timestamp, $type, $format, $timezone, $langcode);
}

/**
 * Returns an ISO8601 formatted date based on the given date.
 *
 * @param $date
 *   A UNIX timestamp.
 *
 * @return string
 *   An ISO8601 formatted date.
 */
function date_iso8601($date) {
  // The DATE_ISO8601 constant cannot be used here because it does not match
  // date('c') and produces invalid RDF markup.
  return date('c', $date);
}

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

/**
 * Formats an attribute string for an HTTP header.
 *
 * @param $attributes
 *   An associative array of attributes such as 'rel'.
 *
 * @return
 *   A ; separated string ready for insertion in a HTTP header. No escaping is
 *   performed for HTML entities, so this string is not safe to be printed.
 */
function drupal_http_header_attributes(array $attributes = array()) {
  foreach ($attributes as $attribute => &$data) {
    if (is_array($data)) {
      $data = implode(' ', $data);
    }
    $data = $attribute . '="' . $data . '"';
  }
  return $attributes ? ' ' . implode('; ', $attributes) : '';
}

/**
 * Attempts to set the PHP maximum execution time.
 *
 * This function is a wrapper around the PHP function set_time_limit().
 * When called, set_time_limit() restarts the timeout counter from zero.
 * In other words, if the timeout is the default 30 seconds, and 25 seconds
 * into script execution a call such as set_time_limit(20) is made, the
 * script will run for a total of 45 seconds before timing out.
 *
 * If the current time limit is not unlimited it is possible to decrease the
 * total time limit if the sum of the new time limit and the current time spent
 * running the script is inferior to the original time limit. It is inherent to
 * the way set_time_limit() works, it should rather be called with an
 * appropriate value every time you need to allocate a certain amount of time
 * to execute a task than only once at the beginning of the script.
 *
 * Before calling set_time_limit(), we check if this function is available
 * because it could be disabled by the server administrator. We also hide all
 * the errors that could occur when calling set_time_limit(), because it is
 * not possible to reliably ensure that PHP or a security extension will
 * not issue a warning/error if they prevent the use of this function.
 *
 * @param $time_limit
 *   An integer specifying the new time limit, in seconds. A value of 0
 *   indicates unlimited execution time.
 *
 * @ingroup php_wrappers
 */
function drupal_set_time_limit($time_limit) {
  if (function_exists('set_time_limit')) {
    $current = ini_get('max_execution_time');
    // Do not set time limit if it is currently unlimited.
    if ($current != 0) {
      @set_time_limit($time_limit);
    }
  }
}

/**
 * Returns the base URL path (i.e., directory) of the Drupal installation.
 *
 * base_path() adds a "/" to the beginning and end of the returned path if the
 * path is not empty. At the very least, this will return "/".
 *
 * Examples:
 * - http://example.com returns "/" because the path is empty.
 * - http://example.com/drupal/folder returns "/drupal/folder/".
 */
function base_path() {
  return $GLOBALS['base_path'];
}

/**
 * Deletes old cached CSS files.
 *
 * @deprecated in Drupal 8.x, will be removed before Drupal 9.0.
 *   Use \Drupal\Core\Asset\AssetCollectionOptimizerInterface::deleteAll().
 */
function drupal_clear_css_cache() {
  \Drupal::service('asset.css.collection_optimizer')->deleteAll();
}

/**
 * Constructs an array of the defaults that are used for JavaScript assets.
 *
 * @param $data
 *   (optional) The default data parameter for the JavaScript asset array.
 *
 * @see hook_js_alter()
 */
function drupal_js_defaults($data = NULL) {
  return array(
    'type' => 'file',
    'group' => JS_DEFAULT,
    'weight' => 0,
    'scope' => 'header',
    'cache' => TRUE,
    'preprocess' => TRUE,
    'attributes' => array(),
    'version' => NULL,
    'data' => $data,
    'browsers' => array(),
  );
}

/**
 * Adds JavaScript to change the state of an element based on another element.
 *
 * A "state" means a certain property on a DOM element, such as "visible" or
 * "checked". A state can be applied to an element, depending on the state of
 * another element on the page. In general, states depend on HTML attributes and
 * DOM element properties, which change due to user interaction.
 *
 * Since states are driven by JavaScript only, it is important to understand
 * that all states are applied on presentation only, none of the states force
 * any server-side logic, and that they will not be applied for site visitors
 * without JavaScript support. All modules implementing states have to make
 * sure that the intended logic also works without JavaScript being enabled.
 *
 * #states is an associative array in the form of:
 * @code
 * array(
 *   STATE1 => CONDITIONS_ARRAY1,
 *   STATE2 => CONDITIONS_ARRAY2,
 *   ...
 * )
 * @endcode
 * Each key is the name of a state to apply to the element, such as 'visible'.
 * Each value is a list of conditions that denote when the state should be
 * applied.
 *
 * Multiple different states may be specified to act on complex conditions:
 * @code
 * array(
 *   'visible' => CONDITIONS,
 *   'checked' => OTHER_CONDITIONS,
 * )
 * @endcode
 *
 * Every condition is a key/value pair, whose key is a jQuery selector that
 * denotes another element on the page, and whose value is an array of
 * conditions, which must bet met on that element:
 * @code
 * array(
 *   'visible' => array(
 *     JQUERY_SELECTOR => REMOTE_CONDITIONS,
 *     JQUERY_SELECTOR => REMOTE_CONDITIONS,
 *     ...
 *   ),
 * )
 * @endcode
 * All conditions must be met for the state to be applied.
 *
 * Each remote condition is a key/value pair specifying conditions on the other
 * element that need to be met to apply the state to the element:
 * @code
 * array(
 *   'visible' => array(
 *     ':input[name="remote_checkbox"]' => array('checked' => TRUE),
 *   ),
 * )
 * @endcode
 *
 * For example, to show a textfield only when a checkbox is checked:
 * @code
 * $form['toggle_me'] = array(
 *   '#type' => 'checkbox',
 *   '#title' => t('Tick this box to type'),
 * );
 * $form['settings'] = array(
 *   '#type' => 'textfield',
 *   '#states' => array(
 *     // Only show this field when the 'toggle_me' checkbox is enabled.
 *     'visible' => array(
 *       ':input[name="toggle_me"]' => array('checked' => TRUE),
 *     ),
 *   ),
 * );
 * @endcode
 *
 * The following states may be applied to an element:
 * - enabled
 * - disabled
 * - required
 * - optional
 * - visible
 * - invisible
 * - checked
 * - unchecked
 * - expanded
 * - collapsed
 *
 * The following states may be used in remote conditions:
 * - empty
 * - filled
 * - checked
 * - unchecked
 * - expanded
 * - collapsed
 * - value
 *
 * The following states exist for both elements and remote conditions, but are
 * not fully implemented and may not change anything on the element:
 * - relevant
 * - irrelevant
 * - valid
 * - invalid
 * - touched
 * - untouched
 * - readwrite
 * - readonly
 *
 * When referencing select lists and radio buttons in remote conditions, a
 * 'value' condition must be used:
 * @code
 *   '#states' => array(
 *     // Show the settings if 'bar' has been selected for 'foo'.
 *     'visible' => array(
 *       ':input[name="foo"]' => array('value' => 'bar'),
 *     ),
 *   ),
 * @endcode
 *
 * @param $elements
 *   A renderable array element having a #states property as described above.
 *
 * @see form_example_states_form()
 */
function drupal_process_states(&$elements) {
  $elements['#attached']['library'][] = 'core/drupal.states';
  // Elements of '#type' => 'item' are not actual form input elements, but we
  // still want to be able to show/hide them. Since there's no actual HTML input
  // element available, setting #attributes does not make sense, but a wrapper
  // is available, so setting #wrapper_attributes makes it work.
  $key = ($elements['#type'] == 'item') ? '#wrapper_attributes' : '#attributes';
  $elements[$key]['data-drupal-states'] = Json::encode($elements['#states']);
}

/**
 * Assists in attaching the tableDrag JavaScript behavior to a themed table.
 *
 * Draggable tables should be used wherever an outline or list of sortable items
 * needs to be arranged by an end-user. Draggable tables are very flexible and
 * can manipulate the value of form elements placed within individual columns.
 *
 * To set up a table to use drag and drop in place of weight select-lists or in
 * place of a form that contains parent relationships, the form must be themed
 * into a table. The table must have an ID attribute set and it
 * may be set as follows:
 * @code
 * $table = array(
 *   '#type' => 'table',
 *   '#header' => $header,
 *   '#rows' => $rows,
 *   '#attributes' => array(
 *     'id' => 'my-module-table',
 *   ),
 * );
 * return drupal_render($table);
 * @endcode
 *
 * In the theme function for the form, a special class must be added to each
 * form element within the same column, "grouping" them together.
 *
 * In a situation where a single weight column is being sorted in the table, the
 * classes could be added like this (in the theme function):
 * @code
 * $form['my_elements'][$delta]['weight']['#attributes']['class'] = array('my-elements-weight');
 * @endcode
 *
 * Each row of the table must also have a class of "draggable" in order to
 * enable the drag handles:
 * @code
 * $row = array(...);
 * $rows[] = array(
 *   'data' => $row,
 *   'class' => array('draggable'),
 * );
 * @endcode
 *
 * When tree relationships are present, the two additional classes
 * 'tabledrag-leaf' and 'tabledrag-root' can be used to refine the behavior:
 * - Rows with the 'tabledrag-leaf' class cannot have child rows.
 * - Rows with the 'tabledrag-root' class cannot be nested under a parent row.
 *
 * Calling drupal_attach_tabledrag() would then be written as such:
 * @code
 * drupal_attach_tabledrag('my-module-table', array(
 *   'action' => 'order',
 *   'relationship' => 'sibling',
 *   'group' => 'my-elements-weight',
 * );
 * @endcode
 *
 * In a more complex case where there are several groups in one column (such as
 * the block regions on the admin/structure/block page), a separate subgroup
 * class must also be added to differentiate the groups.
 * @code
 * $form['my_elements'][$region][$delta]['weight']['#attributes']['class'] = array('my-elements-weight', 'my-elements-weight-' . $region);
 * @endcode
 *
 * The 'group' option is still 'my-element-weight', and the additional
 * 'subgroup' option will be passed in as 'my-elements-weight-' . $region. This
 * also means that you'll need to call drupal_attach_tabledrag() once for every
 * region added.
 *
 * @code
 * foreach ($regions as $region) {
 *   drupal_attach_tabledrag('my-module-table', array(
 *     'action' => 'order',
 *     'relationship' => 'sibling',
 *     'group' => 'my-elements-weight',
 *     'subgroup' => 'my-elements-weight-' . $region,
 *   ));
 * }
 * @endcode
 *
 * In a situation where tree relationships are present, adding multiple
 * subgroups is not necessary, because the table will contain indentations that
 * provide enough information about the sibling and parent relationships. See
 * MenuForm::BuildOverviewForm for an example creating a table
 * containing parent relationships.
 *
 * @param $element
 *   A form element to attach the tableDrag behavior to.
 * @param array $options
 *   These options are used to generate JavaScript settings necessary to
 *   configure the tableDrag behavior appropriately for this particular table.
 *   An associative array containing the following keys:
 *   - 'table_id': String containing the target table's id attribute.
 *     If the table does not have an id, one will need to be set,
 *     such as <table id="my-module-table">.
 *   - 'action': String describing the action to be done on the form item.
 *      Either 'match' 'depth', or 'order':
 *     - 'match' is typically used for parent relationships.
 *     - 'order' is typically used to set weights on other form elements with
 *       the same group.
 *     - 'depth' updates the target element with the current indentation.
 *   - 'relationship': String describing where the "action" option
 *     should be performed. Either 'parent', 'sibling', 'group', or 'self':
 *     - 'parent' will only look for fields up the tree.
 *     - 'sibling' will look for fields in the same group in rows above and
 *       below it.
 *     - 'self' affects the dragged row itself.
 *     - 'group' affects the dragged row, plus any children below it (the entire
 *       dragged group).
 *   - 'group': A class name applied on all related form elements for this action.
 *   - 'subgroup': (optional) If the group has several subgroups within it, this
 *     string should contain the class name identifying fields in the same
 *     subgroup.
 *   - 'source': (optional) If the $action is 'match', this string should contain
 *     the classname identifying what field will be used as the source value
 *     when matching the value in $subgroup.
 *   - 'hidden': (optional) The column containing the field elements may be
 *     entirely hidden from view dynamically when the JavaScript is loaded. Set
 *     to FALSE if the column should not be hidden.
 *   - 'limit': (optional) Limit the maximum amount of parenting in this table.
 *
 * @see MenuForm::BuildOverviewForm()
 */
function drupal_attach_tabledrag(&$element, array $options) {
  // Add default values to elements.
  $options = $options + array(
    'subgroup' => NULL,
    'source' => NULL,
    'hidden' => TRUE,
    'limit' => 0
  );

  $group = $options['group'];

  $tabledrag_id = &drupal_static(__FUNCTION__);
  $tabledrag_id = (!isset($tabledrag_id)) ? 0 : $tabledrag_id + 1;

  // If a subgroup or source isn't set, assume it is the same as the group.
  $target = isset($options['subgroup']) ? $options['subgroup'] : $group;
  $source = isset($options['source']) ? $options['source'] : $target;
  $element['#attached']['drupalSettings']['tableDrag'][$options['table_id']][$group][$tabledrag_id] = array(
    'target' => $target,
    'source' => $source,
    'relationship' => $options['relationship'],
    'action' => $options['action'],
    'hidden' => $options['hidden'],
    'limit' => $options['limit'],
  );

  $element['#attached']['library'][] = 'core/drupal.tabledrag';
}

/**
 * Deletes old cached JavaScript files and variables.
 *
 * @deprecated in Drupal 8.x, will be removed before Drupal 9.0.
 *   Use \Drupal\Core\Asset\AssetCollectionOptimizerInterface::deleteAll().
 */
function drupal_clear_js_cache() {
  \Drupal::service('asset.js.collection_optimizer')->deleteAll();
}

/**
 * Pre-render callback: Renders a link into #markup.
 *
 * @deprecated in Drupal 8.x, will be removed before Drupal 9.0.
 *   Use \Drupal\Core\Render\Element\Link::preRenderLink().
 */
function drupal_pre_render_link($element) {
  return Element\Link::preRenderLink($element);
}

/**
 * Pre-render callback: Collects child links into a single array.
 *
 * This function can be added as a pre_render callback for a renderable array,
 * usually one which will be themed by links.html.twig. It iterates through all
 * unrendered children of the element, collects any #links properties it finds,
 * merges them into the parent element's #links array, and prevents those
 * children from being rendered separately.
 *
 * The purpose of this is to allow links to be logically grouped into related
 * categories, so that each child group can be rendered as its own list of
 * links if drupal_render() is called on it, but calling drupal_render() on the
 * parent element will still produce a single list containing all the remaining
 * links, regardless of what group they were in.
 *
 * A typical example comes from node links, which are stored in a renderable
 * array similar to this:
 * @code
 * $build['links'] = array(
 *   '#theme' => 'links__node',
 *   '#pre_render' => array('drupal_pre_render_links'),
 *   'comment' => array(
 *     '#theme' => 'links__node__comment',
 *     '#links' => array(
 *       // An array of links associated with node comments, suitable for
 *       // passing in to links.html.twig.
 *     ),
 *   ),
 *   'statistics' => array(
 *     '#theme' => 'links__node__statistics',
 *     '#links' => array(
 *       // An array of links associated with node statistics, suitable for
 *       // passing in to links.html.twig.
 *     ),
 *   ),
 *   'translation' => array(
 *     '#theme' => 'links__node__translation',
 *     '#links' => array(
 *       // An array of links associated with node translation, suitable for
 *       // passing in to links.html.twig.
 *     ),
 *   ),
 * );
 * @endcode
 *
 * In this example, the links are grouped by functionality, which can be
 * helpful to themers who want to display certain kinds of links independently.
 * For example, adding this code to node.html.twig will result in the comment
 * links being rendered as a single list:
 * @code
 * {{ content.links.comment }}
 * @endcode
 *
 * (where a node's content has been transformed into $content before handing
 * control to the node.html.twig template).
 *
 * The pre_render function defined here allows the above flexibility, but also
 * allows the following code to be used to render all remaining links into a
 * single list, regardless of their group:
 * @code
 * {{ content.links }}
 * @endcode
 *
 * In the above example, this will result in the statistics and translation
 * links being rendered together in a single list (but not the comment links,
 * which were rendered previously on their own).
 *
 * Because of the way this function works, the individual properties of each
 * group (for example, a group-specific #theme property such as
 * 'links__node__comment' in the example above, or any other property such as
 * #attributes or #pre_render that is attached to it) are only used when that
 * group is rendered on its own. When the group is rendered together with other
 * children, these child-specific properties are ignored, and only the overall
 * properties of the parent are used.
 */
function drupal_pre_render_links($element) {
  $element += array('#links' => array(), '#attached' => array());
  foreach (Element::children($element) as $key) {
    $child = &$element[$key];
    // If the child has links which have not been printed yet and the user has
    // access to it, merge its links in to the parent.
    if (isset($child['#links']) && empty($child['#printed']) && Element::isVisibleElement($child)) {
      $element['#links'] += $child['#links'];
      // Mark the child as having been printed already (so that its links
      // cannot be mistakenly rendered twice).
      $child['#printed'] = TRUE;
    }
    // Merge attachments.
    if (isset($child['#attached'])) {
      $element['#attached'] = BubbleableMetadata::mergeAttachments($element['#attached'], $child['#attached']);
    }
  }
  return $element;
}

/**
 * Renders final HTML given a structured array tree.
 *
 * @deprecated as of Drupal 8.0.x, will be removed before Drupal 9.0.0. Use the
 *   'renderer' service instead.
 *
 * @see \Drupal\Core\Render\RendererInterface::renderRoot()
 */
function drupal_render_root(&$elements) {
  return \Drupal::service('renderer')->renderRoot($elements);
}

/**
 * Renders HTML given a structured array tree.
 *
 * @deprecated as of Drupal 8.0.x, will be removed before Drupal 9.0.0. Use the
 *   'renderer' service instead.
 *
 * @see \Drupal\Core\Render\RendererInterface::render()
 */
function drupal_render(&$elements, $is_recursive_call = FALSE) {
  return \Drupal::service('renderer')->render($elements, $is_recursive_call);
}

/**
 * Renders children of an element and concatenates them.
 *
 * @param array $element
 *   The structured array whose children shall be rendered.
 * @param array $children_keys
 *   (optional) If the keys of the element's children are already known, they
 *   can be passed in to save another run of
 *   \Drupal\Core\Render\Element::children().
 *
 * @return string|\Drupal\Component\Render\MarkupInterface
 *   The rendered HTML of all children of the element.
 *
 * @deprecated in Drupal 8.0.x and will be removed before 9.0.0. Avoid early
 *   rendering when possible or loop through the elements and render them as
 *   they are available.
 *
 * @see drupal_render()
 */
function drupal_render_children(&$element, $children_keys = NULL) {
  if ($children_keys === NULL) {
    $children_keys = Element::children($element);
  }
  $output = '';
  foreach ($children_keys as $key) {
    if (!empty($element[$key])) {
      $output .= drupal_render($element[$key]);
    }
  }
  return Markup::create($output);
}

/**
 * Renders an element.
 *
 * This function renders an element. The top level element is shown with show()
 * before rendering, so it will always be rendered even if hide() had been
 * previously used on it.
 *
 * @param $element
 *   The element to be rendered.
 *
 * @return
 *   The rendered element.
 *
 * @see \Drupal\Core\Render\RendererInterface
 * @see show()
 * @see hide()
 */
function render(&$element) {
  if (!$element && $element !== 0) {
    return NULL;
  }
  if (is_array($element)) {
    // Early return if this element was pre-rendered (no need to re-render).
    if (isset($element['#printed']) && $element['#printed'] == TRUE && isset($element['#markup']) && strlen($element['#markup']) > 0) {
      return $element['#markup'];
    }
    show($element);
    return \Drupal::service('renderer')->render($element);
  }
  else {
    // Safe-guard for inappropriate use of render() on flat variables: return
    // the variable as-is.
    return $element;
  }
}

/**
 * Hides an element from later rendering.
 *
 * The first time render() or drupal_render() is called on an element tree,
 * as each element in the tree is rendered, it is marked with a #printed flag
 * and the rendered children of the element are cached. Subsequent calls to
 * render() or drupal_render() will not traverse the child tree of this element
 * again: they will just use the cached children. So if you want to hide an
 * element, be sure to call hide() on the element before its parent tree is
 * rendered for the first time, as it will have no effect on subsequent
 * renderings of the parent tree.
 *
 * @param $element
 *   The element to be hidden.
 *
 * @return
 *   The element.
 *
 * @see render()
 * @see show()
 */
function hide(&$element) {
  $element['#printed'] = TRUE;
  return $element;
}

/**
 * Shows a hidden element for later rendering.
 *
 * You can also use render($element), which shows the element while rendering
 * it.
 *
 * The first time render() or drupal_render() is called on an element tree,
 * as each element in the tree is rendered, it is marked with a #printed flag
 * and the rendered children of the element are cached. Subsequent calls to
 * render() or drupal_render() will not traverse the child tree of this element
 * again: they will just use the cached children. So if you want to show an
 * element, be sure to call show() on the element before its parent tree is
 * rendered for the first time, as it will have no effect on subsequent
 * renderings of the parent tree.
 *
 * @param $element
 *   The element to be shown.
 *
 * @return
 *   The element.
 *
 * @see render()
 * @see hide()
 */
function show(&$element) {
  $element['#printed'] = FALSE;
  return $element;
}

/**
 * Retrieves the default properties for the defined element type.
 *
 * @param $type
 *   An element type as defined by an element plugin.