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\Serialization\Yaml;
use Drupal\Component\Serialization\Exception\InvalidDataTypeException;
use Drupal\Component\Utility\Crypt;
use Drupal\Component\Utility\Number;
use Drupal\Component\Utility\SortArray;
use Drupal\Component\Utility\String;
use Drupal\Component\Utility\Tags;
use Drupal\Component\Utility\UrlHelper;
use Drupal\Core\Cache\Cache;
use Drupal\Core\Language\Language;
use Drupal\Core\Site\Settings;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\Request;
use Drupal\Core\PhpStorage\PhpStorageFactory;
use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Datetime\DrupalDateTime;
use Drupal\Core\EventSubscriber\HtmlViewSubscriber;
use Drupal\Core\Routing\GeneratorNotInitializedException;
use Drupal\Core\Template\Attribute;
use Drupal\Core\Render\Element;
use Drupal\Core\Session\AnonymousUserSession;

/**
 * @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
 *   $my_substring = drupal_substr($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.
 *
 * This is the ETX (End of text) character and is used as a minimal means to
 * separate singular and plural variants in source and translation text. It
 * was found to be the most compatible delimiter for the supported databases.
 */
const LOCALE_PLURAL_DELIMITER = "\03";

/**
 * Adds content to a specified region.
 *
 * @param $region
 *   Page region the content is added to.
 * @param $data
 *   Content to be added.
 */
function drupal_add_region_content($region = NULL, $data = NULL) {
  static $content = array();

  if (isset($region) && isset($data)) {
    $content[$region][] = $data;
  }
  return $content;
}

/**
 * Gets assigned content for a given region.
 *
 * @param $region
 *   A specified region to fetch content for. If NULL, all regions will be
 *   returned.
 * @param $delimiter
 *   Content to be inserted between imploded array elements.
 */
function drupal_get_region_content($region = NULL, $delimiter = ' ') {
  $content = drupal_add_region_content();
  if (isset($region)) {
    if (isset($content[$region]) && is_array($content[$region])) {
      return implode($delimiter, $content[$region]);
    }
  }
  else {
    foreach (array_keys($content) as $region) {
      if (is_array($content[$region])) {
        $content[$region] = implode($delimiter, $content[$region]);
      }
    }
    return $content;
  }
}

/**
 * Gets the name of the currently active installation profile.
 *
 * When this function is called during Drupal's initial installation process,
 * the name of the profile that's about to be installed is stored in the global
 * installation state. At all other times, the "install_profile" setting will be
 * available in settings.php.
 *
 * @return string|null $profile
 *   The name of the installation profile or NULL if no installation profile is
 *   currently active. This is the case for example during the first steps of
 *   the installer or during unit tests.
 */
function drupal_get_profile() {
  global $install_state;

  if (drupal_installation_attempted()) {
    // If the profile has been selected return it.
    if (isset($install_state['parameters']['profile'])) {
      $profile = $install_state['parameters']['profile'];
    }
    else {
      $profile = NULL;
    }
  }
  else {
    // Fall back to NULL, if there is no 'install_profile' setting.
    $profile = Settings::get('install_profile');
  }

  return $profile;
}

/**
 * Adds output to the HEAD tag of the HTML page.
 *
 * This function can be called as long as the headers aren't sent. Pass no
 * arguments (or NULL for both) to retrieve the currently stored elements.
 *
 * @param $data
 *   A renderable array. If the '#type' key is not set then 'html_tag' will be
 *   added as the default '#type'.
 * @param $key
 *   A unique string key to allow implementations of hook_html_head_alter() to
 *   identify the element in $data. Required if $data is not NULL.
 *
 * @return
 *   An array of all stored HEAD elements.
 *
 * @see drupal_pre_render_html_tag()
 */
function drupal_add_html_head($data = NULL, $key = NULL) {
  $stored_head = &drupal_static(__FUNCTION__);

  if (!isset($stored_head)) {
    // Make sure the defaults, including Content-Type, come first.
    $stored_head = _drupal_default_html_head();
  }

  if (isset($data) && isset($key)) {
    if (!isset($data['#type'])) {
      $data['#type'] = 'html_tag';
    }
    $stored_head[$key] = $data;
  }
  return $stored_head;
}

/**
 * Returns elements that are always displayed in the HEAD tag of the HTML page.
 */
function _drupal_default_html_head() {
  // Add default elements. Make sure the Content-Type comes first because the
  // IE browser may be vulnerable to XSS via encoding attacks from any content
  // that comes before this META tag, such as a TITLE tag.
  $elements['system_meta_content_type'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'charset' => 'utf-8',
    ),
    // Security: This always has to be output first.
    '#weight' => -1000,
  );
  // Show Drupal and the major version number in the META GENERATOR tag.
  // Get the major version.
  list($version, ) = explode('.', \Drupal::VERSION);
  $elements['system_meta_generator'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
      'name' => 'Generator',
      'content' => 'Drupal ' . $version . ' (http://drupal.org)',
    ),
  );
  // Also send the generator in the HTTP header.
  $elements['system_meta_generator']['#attached']['drupal_add_http_header'][] = array('X-Generator', $elements['system_meta_generator']['#attributes']['content']);
  return $elements;
}

/**
 * Retrieves output to be displayed in the HEAD tag of the HTML page.
 */
function drupal_get_html_head() {
  $elements = drupal_add_html_head();
  \Drupal::moduleHandler()->alter('html_head', $elements);
  return drupal_render($elements);
}

/**
 * Adds a feed URL for the current page.
 *
 * This function can be called as long the HTML header hasn't been sent.
 *
 * @param $url
 *   An internal system path or a fully qualified external URL of the feed.
 * @param $title
 *   The title of the feed.
 */
function drupal_add_feed($url = NULL, $title = '') {
  $stored_feed_links = &drupal_static(__FUNCTION__, array());

  if (isset($url)) {
    $feed_icon = array(
      '#theme' => 'feed_icon',
      '#url' => $url,
      '#title' => $title,
    );

    $feed_icon['#attached']['drupal_add_html_head_link'][][] = array(
      'rel' => 'alternate',
      'type' => 'application/rss+xml',
      'title' => $title,
      // Force the URL to be absolute, for consistency with other <link> tags
      // output by Drupal.
      'href' => url($url, array('absolute' => TRUE)),
    );

    $stored_feed_links[$url] = drupal_render($feed_icon);
  }
  return $stored_feed_links;
}

/**
 * Gets the feed URLs for the current page.
 *
 * @param $delimiter
 *   A delimiter to split feeds by.
 */
function drupal_get_feeds($delimiter = "\n") {
  $feeds = drupal_add_feed();
  return implode($feeds, $delimiter);
}

/**
 * @defgroup http_handling HTTP handling
 * @{
 * Functions to properly handle HTTP responses.
 */

/**
 * Prepares a 'destination' URL query parameter for use with url().
 *
 * 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
 *   An associative array containing the key:
 *   - destination: The path provided via the destination query string or, if
 *     not available, the current path.
 *
 * @see current_path()
 */
function drupal_get_destination() {
  $destination = &drupal_static(__FUNCTION__);

  if (isset($destination)) {
    return $destination;
  }

  $query = \Drupal::request()->query;
  if ($query->has('destination')) {
    $destination = array('destination' => $query->get('destination'));
  }
  else {
    $path = current_path();
    $query = UrlHelper::buildQuery(UrlHelper::filterQueryParameters($query->all()));
    if ($query != '') {
      $path .= '?' . $query;
    }
    $destination = array('destination' => $path);
  }
  return $destination;
}

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

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

/**
 * Verifies the syntax of the given e-mail address.
 *
 * This uses the
 * @link http://php.net/manual/filter.filters.validate.php PHP e-mail validation filter. @endlink
 *
 * @param $mail
 *   A string containing an e-mail address.
 *
 * @return
 *   TRUE if the address is in a valid format.
 */
function valid_email_address($mail) {
  return (bool)filter_var($mail, FILTER_VALIDATE_EMAIL);
}

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

/**
 * @defgroup sanitization Sanitization functions
 * @{
 * Functions to sanitize values.
 *
 * See http://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
 *   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 $attributes array passed to Drupal\Core\Template\Attribute,
 *   because Drupal\Core\Template\Attribute expects those values to be
 *   plain-text strings. To pass a filtered URI to
 *   Drupal\Core\Template\Attribute, call
 *   \Drupal\Component\Utility\UrlHelper::stripDangerousProtocols() instead.
 *
 * @see \Drupal\Component\Utility\UrlHelper::stripDangerousProtocols()
 * @see \Drupal\Component\Utility\String::checkPlain()
 */
function check_url($uri) {
  return String::checkPlain(UrlHelper::stripDangerousProtocols($uri));
}

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

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

/**
 * Formats an RSS channel.
 *
 * Arbitrary elements may be added using the $args associative array.
 */
function format_rss_channel($title, $link, $description, $items, $langcode = NULL, $args = array()) {
  $langcode = $langcode ? $langcode : \Drupal::languageManager()->getCurrentLanguage(Language::TYPE_CONTENT)->id;

  $output = "<channel>\n";
  $output .= ' <title>' . String::checkPlain($title) . "</title>\n";
  $output .= ' <link>' . check_url($link) . "</link>\n";

  // The RSS 2.0 "spec" doesn't indicate HTML can be used in the description.
  // We strip all HTML tags, but need to prevent double encoding from properly
  // escaped source data (such as &amp becoming &amp;amp;).
  $output .= ' <description>' . String::checkPlain(decode_entities(strip_tags($description))) . "</description>\n";
  $output .= ' <language>' . String::checkPlain($langcode) . "</language>\n";
  $output .= format_xml_elements($args);
  $output .= $items;
  $output .= "</channel>\n";

  return $output;
}

/**
 * Formats a single RSS item.
 *
 * Arbitrary elements may be added using the $args associative array.
 */
function format_rss_item($title, $link, $description, $args = array()) {
  $output = "<item>\n";
  $output .= ' <title>' . String::checkPlain($title) . "</title>\n";
  $output .= ' <link>' . check_url($link) . "</link>\n";
  $output .= ' <description>' . String::checkPlain($description) . "</description>\n";
  $output .= format_xml_elements($args);
  $output .= "</item>\n";

  return $output;
}

/**
 * Formats XML elements.
 *
 * @param $array
 *   An array where each item represents an element and is either a:
 *   - (key => value) pair (<key>value</key>)
 *   - Associative array with fields:
 *     - 'key': element name
 *     - 'value': element contents
 *     - 'attributes': associative array of element attributes
 *
 * In both cases, 'value' can be a simple string, or it can be another array
 * with the same format as $array itself for nesting.
 */
function format_xml_elements($array) {
  $output = '';
  foreach ($array as $key => $value) {
    if (is_numeric($key)) {
      if ($value['key']) {
        $output .= ' <' . $value['key'];
        if (isset($value['attributes']) && is_array($value['attributes'])) {
          $output .= new Attribute($value['attributes']);
        }

        if (isset($value['value']) && $value['value'] != '') {
          $output .= '>' . (is_array($value['value']) ? format_xml_elements($value['value']) : String::checkPlain($value['value'])) . '</' . $value['key'] . ">\n";
        }
        else {
          $output .= " />\n";
        }
      }
    }
    else {
      $output .= ' <' . $key . '>' . (is_array($value) ? format_xml_elements($value) : String::checkPlain($value)) . "</$key>\n";
    }
  }
  return $output;
}

/**
 * Formats a string containing a count of items.
 *
 * This function ensures that the string is pluralized correctly. Since t() is
 * called by this function, make sure not to pass already-localized strings to
 * it.
 *
 * For example:
 * @code
 *   $output = format_plural($node->comment_count, '1 comment', '@count comments');
 * @endcode
 *
 * Example with additional replacements:
 * @code
 *   $output = format_plural($update_count,
 *     'Changed the content type of 1 post from %old-type to %new-type.',
 *     'Changed the content type of @count posts from %old-type to %new-type.',
 *     array('%old-type' => $info->old_type, '%new-type' => $info->new_type));
 * @endcode
 *
 * @param $count
 *   The item count to display.
 * @param $singular
 *   The string for the singular case. Make sure it is clear this is singular,
 *   to ease translation (e.g. use "1 new comment" instead of "1 new"). Do not
 *   use @count in the singular string.
 * @param $plural
 *   The string for the plural case. Make sure it is clear this is plural, to
 *   ease translation. Use @count in place of the item count, as in
 *   "@count new comments".
 * @param $args
 *   An associative array of replacements to make after translation. Instances
 *   of any key in this array are replaced with the corresponding value.
 *   Based on the first character of the key, the value is escaped and/or
 *   themed. See format_string(). Note that you do not need to include @count
 *   in this array; this replacement is done automatically for the plural case.
 * @param $options
 *   An associative array of additional options. See t() for allowed keys.
 *
 * @return
 *   A translated string.
 *
 * @see t()
 * @see format_string()
 * @see \Drupal\Core\StringTranslation\TranslationManager->formatPlural()
 *
 * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
 *   Use \Drupal::translation()->formatPlural().
 */
function format_plural($count, $singular, $plural, array $args = array(), array $options = array()) {
  return \Drupal::translation()->formatPlural($count, $singular, $plural, $args, $options);
}

/**
 * Parses a given byte count.
 *
 * @param $size
 *   A size expressed as a number of bytes with optional SI or IEC binary unit
 *   prefix (e.g. 2, 3K, 5MB, 10G, 6GiB, 8 bytes, 9mbytes).
 *
 * @return
 *   An integer representation of the size in bytes.
 */
function parse_size($size) {
  $unit = preg_replace('/[^bkmgtpezy]/i', '', $size); // Remove the non-unit characters from the size.
  $size = preg_replace('/[^0-9\.]/', '', $size); // Remove the non-numeric characters from the size.
  if ($unit) {
    // Find the position of the unit in the ordered string which is the power of magnitude to multiply a kilobyte by.
    return round($size * pow(DRUPAL_KILOBYTE, stripos('bkmgtpezy', $unit[0])));
  }
  else {
    return round($size);
  }
}

/**
 * Generates a string representation for the given byte count.
 *
 * @param $size
 *   A size in bytes.
 * @param $langcode
 *   Optional language code to translate to a language other than what is used
 *   to display the page.
 *
 * @return
 *   A translated string representation of the size.
 */
function format_size($size, $langcode = NULL) {
  if ($size < DRUPAL_KILOBYTE) {
    return format_plural($size, '1 byte', '@count bytes', array(), array('langcode' => $langcode));
  }
  else {
    $size = $size / DRUPAL_KILOBYTE; // Convert bytes to kilobytes.
    $units = array(
      t('@size KB', array(), array('langcode' => $langcode)),
      t('@size MB', array(), array('langcode' => $langcode)),
      t('@size GB', array(), array('langcode' => $langcode)),
      t('@size TB', array(), array('langcode' => $langcode)),
      t('@size PB', array(), array('langcode' => $langcode)),
      t('@size EB', array(), array('langcode' => $langcode)),
      t('@size ZB', array(), array('langcode' => $langcode)),
      t('@size YB', array(), array('langcode' => $langcode)),
    );
    foreach ($units as $unit) {
      if (round($size, 2) >= DRUPAL_KILOBYTE) {
        $size = $size / DRUPAL_KILOBYTE;
      }
      else {
        break;
      }
    }
    return str_replace('@size', round($size, 2), $unit);
  }
}

/**
 * Formats a time interval with the requested granularity.
 *
 * @param $interval
 *   The length of the interval in seconds.
 * @param $granularity
 *   How many different units to display in the string.
 * @param $langcode
 *   Optional language code to translate to a language other than
 *   what is used to display the page.
 *
 * @return
 *   A translated string representation of the interval.
 *
 * @see \Drupal\Core\Datetime\Date::formatInterval()
 *
 * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
 *   Use \Drupal::service('date')->formatInterval().
 */
function format_interval($interval, $granularity = 2, $langcode = NULL) {
  return \Drupal::service('date')->formatInterval($interval, $granularity, $langcode);
}

/**
 * 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 module in
 *     hook_date_format_types(), if it's been assigned a format.
 *   - 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 $langcode
 *   (optional) Language code to translate to. Defaults to the language used to
 *   display the page.
 *
 * @return
 *   A translated date string in the requested format.
 *
 * @see \Drupal\Component\Datetime\Date::format()
 */
function format_date($timestamp, $type = 'medium', $format = '', $timezone = NULL, $langcode = NULL) {
  return \Drupal::service('date')->format($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);
}

/**
 * Translates a formatted date string.
 *
 * Callback for preg_replace_callback() within format_date().
 */
function _format_date_callback(array $matches = NULL, $new_langcode = NULL) {
  // We cache translations to avoid redundant and rather costly calls to t().
  static $cache, $langcode;

  if (!isset($matches)) {
    $langcode = $new_langcode;
    return;
  }

  $code = $matches[1];
  $string = $matches[2];

  if (!isset($cache[$langcode][$code][$string])) {
    $options = array(
      'langcode' => $langcode,
    );

    if ($code == 'F') {
      $options['context'] = 'Long month name';
    }

    if ($code == '') {
      $cache[$langcode][$code][$string] = $string;
    }
    else {
      $cache[$langcode][$code][$string] = t($string, array(), $options);
    }
  }
  return $cache[$langcode][$code][$string];
}

/**
 * Retrieves the correct datetime format type for this system.
 *
 * This value is sometimes required when the format type needs to be determined
 * before a date can be created.
 *
 * @return string
 *   A string as defined in \DrupalComponent\Datetime\DateTimePlus.php: either
 *   'intl' or 'php', depending on whether IntlDateFormatter is available.
 */
function datetime_default_format_type() {
  static $drupal_static_fast;
  if (!isset($drupal_static_fast)) {
    $drupal_static_fast['format_type'] = &drupal_static(__FUNCTION__);
  }
  $format_type = &$drupal_static_fast['format_type'];

  if (!isset($format_type)) {
    $date = new DrupalDateTime();
    $format_type = $date->canUseIntl() ? DrupalDateTime::INTL : DrupalDateTime::PHP;
  }
  return $format_type;
}

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

/**
 * Generates an internal or external URL.
 *
 * When creating links in modules, consider whether l() could be a better
 * alternative than url().
 *
 * @see \Drupal\Core\Routing\UrlGeneratorInterface::generateFromPath().
 */
function url($path = NULL, array $options = array()) {
  $generator = \Drupal::urlGenerator();
  try {
    $url = $generator->generateFromPath($path, $options);
  }
  catch (GeneratorNotInitializedException $e) {
    // Fallback to using globals.
    // @todo Remove this once there is no code that calls url() when there is
    //   no request.
    global $base_url, $base_path, $script_path;
    $generator->setBasePath($base_path);
    $generator->setBaseUrl($base_url . '/');
    $generator->setScriptPath($script_path);
    $url = $generator->generateFromPath($path, $options);
  }
  return $url;
}

/**
 * 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.
 *
 * @see drupal_add_http_header()
 */
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) : '';
}

/**
 * Formats an internal or external URL link as an HTML anchor tag.
 *
 * This function correctly handles aliased paths and adds an 'active' class
 * attribute to links that point to the current page (for theming), so all
 * internal links output by modules should be generated by this function if
 * possible.
 *
 * However, for links enclosed in translatable text you should use t() and
 * embed the HTML anchor tag directly in the translated string. For example:
 * @code
 * t('Visit the <a href="@url">settings</a> page', array('@url' => url('admin')));
 * @endcode
 * This keeps the context of the link title ('settings' in the example) for
 * translators.
 *
 * This function does not support generating links from internal routes. For
 * that use \Drupal\Core\Utility\LinkGenerator::generate(), which is exposed via
 * the 'link_generator' service. It requires an internal route name and does not
 * support external URLs. Using Drupal 7 style system paths should be avoided if
 * possible but l() should still be used when rendering links to external URLs.
 *
 * @param string|array $text
 *   The link text for the anchor tag as a translated string or render array.
 * @param string $path
 *   The internal path or external URL being linked to, such as "node/34" or
 *   "http://example.com/foo". After the url() function is called to construct
 *   the URL from $path and $options, the resulting URL is passed through
 *   \Drupal\Component\Utility\String::checkPlain() before it is inserted into
 *   the HTML anchor tag, to ensure well-formed HTML. See url() for more
 *   information and notes.
 * @param array $options
 *   An associative array of additional options. Defaults to an empty array. It
 *   may contain the following elements.
 *   - 'attributes': An associative array of HTML attributes to apply to the
 *     anchor tag. If element 'class' is included, it must be an array; 'title'
 *     must be a string; other elements are more flexible, as they just need
 *     to work as an argument for the constructor of the class
 *     Drupal\Core\Template\Attribute($options['attributes']).
 *   - 'html' (default FALSE): Whether $text is HTML or just plain-text. For
 *     example, to make an image tag into a link, this must be set to TRUE, or
 *     you will see the escaped HTML image tag. $text is not sanitized if
 *     'html' is TRUE. The calling function must ensure that $text is already
 *     safe.
 *   - 'language': An optional language object. If the path being linked to is
 *     internal to the site, $options['language'] is used to determine whether
 *     the link is "active", or pointing to the current page (the language as
 *     well as the path must match). This element is also used by url().
 *   - 'set_active_class': Whether l() should compare the $path, language and
 *     query options to the current URL to determine whether the link is
 *     "active". Defaults to FALSE. If TRUE, an "active" class will be applied
 *     to the link. It is important to use this sparingly since it is usually
 *     unnecessary and requires extra processing.
 *     For anonymous users, the "active" class will be calculated on the server,
 *     because most sites serve each anonymous user the same cached page anyway.
 *     For authenticated users, the "active" class will be calculated on the
 *     client (through JavaScript), only data- attributes are added to links to
 *     prevent breaking the render cache. The JavaScript is added in
 *     system_page_build().
 *   - Additional $options elements used by the url() function.
 *
 * @return string
 *   An HTML string containing a link to the given path.
 *
 * @see url()
 * @see system_page_build()
 */
function l($text, $path, array $options = array()) {
  // Start building a structured representation of our link to be altered later.
  $variables = array(
    'text' => is_array($text) ? drupal_render($text) : $text,
    'path' => $path,
    'options' => $options,
  );

  // Merge in default options.
  $variables['options'] += array(
    'attributes' => array(),