comparison core/includes/form.inc @ 0:c75dbcec494b

Initial commit from drush-created site

+<?php
+
+/**
+ * @file
+ * Functions for form and batch generation and processing.
+ */
+
+use Drupal\Component\Utility\UrlHelper;
+use Drupal\Core\Render\Element;
+use Drupal\Core\Render\Element\RenderElement;
+use Drupal\Core\Template\Attribute;
+use Drupal\Core\Url;
+use Symfony\Component\HttpFoundation\RedirectResponse;
+
+/**
+ * Prepares variables for select element templates.
+ *
+ * Default template: select.html.twig.
+ *
+ * It is possible to group options together; to do this, change the format of
+ * $options to an associative array in which the keys are group labels, and the
+ * values are associative arrays in the normal $options format.
+ *
+ * @param $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #title, #value, #options, #description, #extra,
+ *     #multiple, #required, #name, #attributes, #size.
+ */
+function template_preprocess_select(&$variables) {
+  $element = $variables['element'];
+  Element::setAttributes($element, ['id', 'name', 'size']);
+  RenderElement::setAttributes($element, ['form-select']);
+
+  $variables['attributes'] = $element['#attributes'];
+  $variables['options'] = form_select_options($element);
+}
+
+/**
+ * Converts an options form element into a structured array for output.
+ *
+ * This function calls itself recursively to obtain the values for each optgroup
+ * within the list of options and when the function encounters an object with
+ * an 'options' property inside $element['#options'].
+ *
+ * @param array $element
+ *   An associative array containing the following key-value pairs:
+ *   - #multiple: Optional Boolean indicating if the user may select more than
+ *     one item.
+ *   - #options: An associative array of options to render as HTML. Each array
+ *     value can be a string, an array, or an object with an 'option' property:
+ *     - A string or integer key whose value is a translated string is
+ *       interpreted as a single HTML option element. Do not use placeholders
+ *       that sanitize data: doing so will lead to double-escaping. Note that
+ *       the key will be visible in the HTML and could be modified by malicious
+ *       users, so don't put sensitive information in it.
+ *     - A translated string key whose value is an array indicates a group of
+ *       options. The translated string is used as the label attribute for the
+ *       optgroup. Do not use placeholders to sanitize data: doing so will lead
+ *       to double-escaping. The array should contain the options you wish to
+ *       group and should follow the syntax of $element['#options'].
+ *     - If the function encounters a string or integer key whose value is an
+ *       object with an 'option' property, the key is ignored, the contents of
+ *       the option property are interpreted as $element['#options'], and the
+ *       resulting HTML is added to the output.
+ *   - #value: Optional integer, string, or array representing which option(s)
+ *     to pre-select when the list is first displayed. The integer or string
+ *     must match the key of an option in the '#options' list. If '#multiple' is
+ *     TRUE, this can be an array of integers or strings.
+ * @param array|null $choices
+ *   (optional) Either an associative array of options in the same format as
+ *   $element['#options'] above, or NULL. This parameter is only used internally
+ *   and is not intended to be passed in to the initial function call.
+ *
+ * @return mixed[]
+ *   A structured, possibly nested, array of options and optgroups for use in a
+ *   select form element.
+ *   - label: A translated string whose value is the text of a single HTML
+ *     option element, or the label attribute for an optgroup.
+ *   - options: Optional, array of options for an optgroup.
+ *   - selected: A boolean that indicates whether the option is selected when
+ *     rendered.
+ *   - type: A string that defines the element type. The value can be 'option'
+ *     or 'optgroup'.
+ *   - value: A string that contains the value attribute for the option.
+ */
+function form_select_options($element, $choices = NULL) {
+  if (!isset($choices)) {
+    if (empty($element['#options'])) {
+      return [];
+    }
+    $choices = $element['#options'];
+  }
+  // array_key_exists() accommodates the rare event where $element['#value'] is NULL.
+  // isset() fails in this situation.
+  $value_valid = isset($element['#value']) || array_key_exists('#value', $element);
+  $value_is_array = $value_valid && is_array($element['#value']);
+  // Check if the element is multiple select and no value has been selected.
+  $empty_value = (empty($element['#value']) && !empty($element['#multiple']));
+  $options = [];
+  foreach ($choices as $key => $choice) {
+    if (is_array($choice)) {
+      $options[] = [
+        'type' => 'optgroup',
+        'label' => $key,
+        'options' => form_select_options($element, $choice),
+      ];
+    }
+    elseif (is_object($choice) && isset($choice->option)) {
+      $options = array_merge($options, form_select_options($element, $choice->option));
+    }
+    else {
+      $option = [];
+      $key = (string) $key;
+      $empty_choice = $empty_value && $key == '_none';
+      if ($value_valid && ((!$value_is_array && (string) $element['#value'] === $key || ($value_is_array && in_array($key, $element['#value']))) || $empty_choice)) {
+        $option['selected'] = TRUE;
+      }
+      else {
+        $option['selected'] = FALSE;
+      }
+      $option['type'] = 'option';
+      $option['value'] = $key;
+      $option['label'] = $choice;
+      $options[] = $option;
+    }
+  }
+  return $options;
+}
+
+/**
+ * Returns the indexes of a select element's options matching a given key.
+ *
+ * This function is useful if you need to modify the options that are
+ * already in a form element; for example, to remove choices which are
+ * not valid because of additional filters imposed by another module.
+ * One example might be altering the choices in a taxonomy selector.
+ * To correctly handle the case of a multiple hierarchy taxonomy,
+ * #options arrays can now hold an array of objects, instead of a
+ * direct mapping of keys to labels, so that multiple choices in the
+ * selector can have the same key (and label). This makes it difficult
+ * to manipulate directly, which is why this helper function exists.
+ *
+ * This function does not support optgroups (when the elements of the
+ * #options array are themselves arrays), and will return FALSE if
+ * arrays are found. The caller must either flatten/restore or
+ * manually do their manipulations in this case, since returning the
+ * index is not sufficient, and supporting this would make the
+ * "helper" too complicated and cumbersome to be of any help.
+ *
+ * As usual with functions that can return array() or FALSE, do not
+ * forget to use === and !== if needed.
+ *
+ * @param $element
+ *   The select element to search.
+ * @param $key
+ *   The key to look for.
+ *
+ * @return
+ *   An array of indexes that match the given $key. Array will be
+ *   empty if no elements were found. FALSE if optgroups were found.
+ */
+function form_get_options($element, $key) {
+  $keys = [];
+  foreach ($element['#options'] as $index => $choice) {
+    if (is_array($choice)) {
+      return FALSE;
+    }
+    elseif (is_object($choice)) {
+      if (isset($choice->option[$key])) {
+        $keys[] = $index;
+      }
+    }
+    elseif ($index == $key) {
+      $keys[] = $index;
+    }
+  }
+  return $keys;
+}
+
+/**
+ * Prepares variables for fieldset element templates.
+ *
+ * Default template: fieldset.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #attributes, #children, #description, #id, #title,
+ *     #value.
+ */
+function template_preprocess_fieldset(&$variables) {
+  $element = $variables['element'];
+  Element::setAttributes($element, ['id']);
+  RenderElement::setAttributes($element);
+  $variables['attributes'] = isset($element['#attributes']) ? $element['#attributes'] : [];
+  $variables['prefix'] = isset($element['#field_prefix']) ? $element['#field_prefix'] : NULL;
+  $variables['suffix'] = isset($element['#field_suffix']) ? $element['#field_suffix'] : NULL;
+  $variables['title_display'] = isset($element['#title_display']) ? $element['#title_display'] : NULL;
+  $variables['children'] = $element['#children'];
+  $variables['required'] = !empty($element['#required']) ? $element['#required'] : NULL;
+
+  if (isset($element['#title']) && $element['#title'] !== '') {
+    $variables['legend']['title'] = ['#markup' => $element['#title']];
+  }
+
+  $variables['legend']['attributes'] = new Attribute();
+  // Add 'visually-hidden' class to legend span.
+  if ($variables['title_display'] == 'invisible') {
+    $variables['legend_span']['attributes'] = new Attribute(['class' => ['visually-hidden']]);
+  }
+  else {
+    $variables['legend_span']['attributes'] = new Attribute();
+  }
+
+  if (!empty($element['#description'])) {
+    $description_id = $element['#attributes']['id'] . '--description';
+    $description_attributes['id'] = $description_id;
+    $variables['description']['attributes'] = new Attribute($description_attributes);
+    $variables['description']['content'] = $element['#description'];
+
+    // Add the description's id to the fieldset aria attributes.
+    $variables['attributes']['aria-describedby'] = $description_id;
+  }
+
+  // Suppress error messages.
+  $variables['errors'] = NULL;
+}
+
+/**
+ * Prepares variables for details element templates.
+ *
+ * Default template: details.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #attributes, #children, #open,
+ *     #description, #id, #title, #value, #optional.
+ */
+function template_preprocess_details(&$variables) {
+  $element = $variables['element'];
+  $variables['attributes'] = $element['#attributes'];
+  $variables['summary_attributes'] = new Attribute();
+  if (!empty($element['#title'])) {
+    $variables['summary_attributes']['role'] = 'button';
+    if (!empty($element['#attributes']['id'])) {
+      $variables['summary_attributes']['aria-controls'] = $element['#attributes']['id'];
+    }
+    $variables['summary_attributes']['aria-expanded'] = !empty($element['#attributes']['open']) ? 'true' : 'false';
+    $variables['summary_attributes']['aria-pressed'] = $variables['summary_attributes']['aria-expanded'];
+  }
+  $variables['title'] = (!empty($element['#title'])) ? $element['#title'] : '';
+  $variables['description'] = (!empty($element['#description'])) ? $element['#description'] : '';
+  $variables['children'] = (isset($element['#children'])) ? $element['#children'] : '';
+  $variables['value'] = (isset($element['#value'])) ? $element['#value'] : '';
+  $variables['required'] = !empty($element['#required']) ? $element['#required'] : NULL;
+
+  // Suppress error messages.
+  $variables['errors'] = NULL;
+}
+
+/**
+ * Prepares variables for radios templates.
+ *
+ * Default template: radios.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #title, #value, #options, #description, #required,
+ *     #attributes, #children.
+ */
+function template_preprocess_radios(&$variables) {
+  $element = $variables['element'];
+  $variables['attributes'] = [];
+  if (isset($element['#id'])) {
+    $variables['attributes']['id'] = $element['#id'];
+  }
+  if (isset($element['#attributes']['title'])) {
+    $variables['attributes']['title'] = $element['#attributes']['title'];
+  }
+  $variables['children'] = $element['#children'];
+}
+
+/**
+ * Prepares variables for checkboxes templates.
+ *
+ * Default template: checkboxes.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #children, #attributes.
+ */
+function template_preprocess_checkboxes(&$variables) {
+  $element = $variables['element'];
+  $variables['attributes'] = [];
+  if (isset($element['#id'])) {
+    $variables['attributes']['id'] = $element['#id'];
+  }
+  if (isset($element['#attributes']['title'])) {
+    $variables['attributes']['title'] = $element['#attributes']['title'];
+  }
+  $variables['children'] = $element['#children'];
+}
+
+/**
+ * Prepares variables for vertical tabs templates.
+ *
+ * Default template: vertical-tabs.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties and children of
+ *     the details element. Properties used: #children.
+ */
+function template_preprocess_vertical_tabs(&$variables) {
+  $element = $variables['element'];
+  $variables['children'] = (!empty($element['#children'])) ? $element['#children'] : '';
+}
+
+/**
+ * Prepares variables for input templates.
+ *
+ * Default template: input.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #attributes.
+ */
+function template_preprocess_input(&$variables) {
+  $element = $variables['element'];
+  // Remove name attribute if empty, for W3C compliance.
+  if (isset($variables['attributes']['name']) && empty((string) $variables['attributes']['name'])) {
+    unset($variables['attributes']['name']);
+  }
+  $variables['children'] = $element['#children'];
+}
+
+/**
+ * Prepares variables for form templates.
+ *
+ * Default template: form.html.twig.
+ *
+ * @param $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #action, #method, #attributes, #children
+ */
+function template_preprocess_form(&$variables) {
+  $element = $variables['element'];
+  if (isset($element['#action'])) {
+    $element['#attributes']['action'] = UrlHelper::stripDangerousProtocols($element['#action']);
+  }
+  Element::setAttributes($element, ['method', 'id']);
+  if (empty($element['#attributes']['accept-charset'])) {
+    $element['#attributes']['accept-charset'] = "UTF-8";
+  }
+  $variables['attributes'] = $element['#attributes'];
+  $variables['children'] = $element['#children'];
+}
+
+/**
+ * Prepares variables for textarea templates.
+ *
+ * Default template: textarea.html.twig.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #title, #value, #description, #rows, #cols, #maxlength,
+ *     #placeholder, #required, #attributes, #resizable.
+ */
+function template_preprocess_textarea(&$variables) {
+  $element = $variables['element'];
+  $attributes = ['id', 'name', 'rows', 'cols', 'maxlength', 'placeholder'];
+  Element::setAttributes($element, $attributes);
+  RenderElement::setAttributes($element, ['form-textarea']);
+  $variables['wrapper_attributes'] = new Attribute();
+  $variables['attributes'] = new Attribute($element['#attributes']);
+  $variables['value'] = $element['#value'];
+  $variables['resizable'] = !empty($element['#resizable']) ? $element['#resizable'] : NULL;
+  $variables['required'] = !empty($element['#required']) ? $element['#required'] : NULL;
+}
+
+/**
+ * Returns HTML for a form element.
+ * Prepares variables for form element templates.
+ *
+ * Default template: form-element.html.twig.
+ *
+ * In addition to the element itself, the DIV contains a label for the element
+ * based on the optional #title_display property, and an optional #description.
+ *
+ * The optional #title_display property can have these values:
+ * - before: The label is output before the element. This is the default.
+ *   The label includes the #title and the required marker, if #required.
+ * - after: The label is output after the element. For example, this is used
+ *   for radio and checkbox #type elements. If the #title is empty but the field
+ *   is #required, the label will contain only the required marker.
+ * - invisible: Labels are critical for screen readers to enable them to
+ *   properly navigate through forms but can be visually distracting. This
+ *   property hides the label for everyone except screen readers.
+ * - attribute: Set the title attribute on the element to create a tooltip
+ *   but output no label element. This is supported only for checkboxes
+ *   and radios in
+ *   \Drupal\Core\Render\Element\CompositeFormElementTrait::preRenderCompositeFormElement().
+ *   It is used where a visual label is not needed, such as a table of
+ *   checkboxes where the row and column provide the context. The tooltip will
+ *   include the title and required marker.
+ *
+ * If the #title property is not set, then the label and any required marker
+ * will not be output, regardless of the #title_display or #required values.
+ * This can be useful in cases such as the password_confirm element, which
+ * creates children elements that have their own labels and required markers,
+ * but the parent element should have neither. Use this carefully because a
+ * field without an associated label can cause accessibility challenges.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #title, #title_display, #description, #id, #required,
+ *     #children, #type, #name.
+ */
+function template_preprocess_form_element(&$variables) {
+  $element = &$variables['element'];
+
+  // This function is invoked as theme wrapper, but the rendered form element
+  // may not necessarily have been processed by
+  // \Drupal::formBuilder()->doBuildForm().
+  $element += [
+    '#title_display' => 'before',
+    '#wrapper_attributes' => [],
+    '#label_attributes' => [],
+  ];
+  $variables['attributes'] = $element['#wrapper_attributes'];
+
+  // Add element #id for #type 'item'.
+  if (isset($element['#markup']) && !empty($element['#id'])) {
+    $variables['attributes']['id'] = $element['#id'];
+  }
+
+  // Pass elements #type and #name to template.
+  if (!empty($element['#type'])) {
+    $variables['type'] = $element['#type'];
+  }
+  if (!empty($element['#name'])) {
+    $variables['name'] = $element['#name'];
+  }
+
+  // Pass elements disabled status to template.
+  $variables['disabled'] = !empty($element['#attributes']['disabled']) ? $element['#attributes']['disabled'] : NULL;
+
+  // Suppress error messages.
+  $variables['errors'] = NULL;
+
+  // If #title is not set, we don't display any label.
+  if (!isset($element['#title'])) {
+    $element['#title_display'] = 'none';
+  }
+
+  $variables['title_display'] = $element['#title_display'];
+
+  $variables['prefix'] = isset($element['#field_prefix']) ? $element['#field_prefix'] : NULL;
+  $variables['suffix'] = isset($element['#field_suffix']) ? $element['#field_suffix'] : NULL;
+
+  $variables['description'] = NULL;
+  if (!empty($element['#description'])) {
+    $variables['description_display'] = $element['#description_display'];
+    $description_attributes = [];
+    if (!empty($element['#id'])) {
+      $description_attributes['id'] = $element['#id'] . '--description';
+    }
+    $variables['description']['attributes'] = new Attribute($description_attributes);
+    $variables['description']['content'] = $element['#description'];
+  }
+
+  // Add label_display and label variables to template.
+  $variables['label_display'] = $element['#title_display'];
+  $variables['label'] = ['#theme' => 'form_element_label'];
+  $variables['label'] += array_intersect_key($element, array_flip(['#id', '#required', '#title', '#title_display']));
+  $variables['label']['#attributes'] = $element['#label_attributes'];
+
+  $variables['children'] = $element['#children'];
+}
+
+/**
+ * Prepares variables for form label templates.
+ *
+ * Form element labels include the #title and a #required marker. The label is
+ * associated with the element itself by the element #id. Labels may appear
+ * before or after elements, depending on form-element.html.twig and
+ * #title_display.
+ *
+ * This function will not be called for elements with no labels, depending on
+ * #title_display. For elements that have an empty #title and are not required,
+ * this function will output no label (''). For required elements that have an
+ * empty #title, this will output the required marker alone within the label.
+ * The label will use the #id to associate the marker with the field that is
+ * required. That is especially important for screenreader users to know
+ * which field is required.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - element: An associative array containing the properties of the element.
+ *     Properties used: #required, #title, #id, #value, #description.
+ */
+function template_preprocess_form_element_label(&$variables) {
+  $element = $variables['element'];
+  // If title and required marker are both empty, output no label.
+  if (isset($element['#title']) && $element['#title'] !== '') {
+    $variables['title'] = ['#markup' => $element['#title']];
+  }
+
+  // Pass elements title_display to template.
+  $variables['title_display'] = $element['#title_display'];
+
+  // A #for property of a dedicated #type 'label' element as precedence.
+  if (!empty($element['#for'])) {
+    $variables['attributes']['for'] = $element['#for'];
+    // A custom #id allows the referenced form input element to refer back to
+    // the label element; e.g., in the 'aria-labelledby' attribute.
+    if (!empty($element['#id'])) {
+      $variables['attributes']['id'] = $element['#id'];
+    }
+  }
+  // Otherwise, point to the #id of the form input element.
+  elseif (!empty($element['#id'])) {
+    $variables['attributes']['for'] = $element['#id'];
+  }
+
+  // Pass elements required to template.
+  $variables['required'] = !empty($element['#required']) ? $element['#required'] : NULL;
+}
+
+/**
+ * @defgroup batch Batch operations
+ * @{
+ * Creates and processes batch operations.
+ *
+ * Functions allowing forms processing to be spread out over several page
+ * requests, thus ensuring that the processing does not get interrupted
+ * because of a PHP timeout, while allowing the user to receive feedback
+ * on the progress of the ongoing operations.
+ *
+ * The API is primarily designed to integrate nicely with the Form API
+ * workflow, but can also be used by non-Form API scripts (like update.php)
+ * or even simple page callbacks (which should probably be used sparingly).
+ *
+ * Example:
+ * @code
+ * $batch = array(
+ *   'title' => t('Exporting'),
+ *   'operations' => array(
+ *     array('my_function_1', array($account->id(), 'story')),
+ *     array('my_function_2', array()),
+ *   ),
+ *   'finished' => 'my_finished_callback',
+ *   'file' => 'path_to_file_containing_myfunctions',
+ * );
+ * batch_set($batch);
+ * // Only needed if not inside a form _submit handler.
+ * // Setting redirect in batch_process.
+ * batch_process('node/1');
+ * @endcode
+ *
+ * Note: if the batch 'title', 'init_message', 'progress_message', or
+ * 'error_message' could contain any user input, it is the responsibility of
+ * the code calling batch_set() to sanitize them first with a function like
+ * \Drupal\Component\Utility\Html::escape() or
+ * \Drupal\Component\Utility\Xss::filter(). Furthermore, if the batch operation
+ * returns any user input in the 'results' or 'message' keys of $context, it
+ * must also sanitize them first.
+ *
+ * Sample callback_batch_operation():
+ * @code
+ * // Simple and artificial: load a node of a given type for a given user
+ * function my_function_1($uid, $type, &$context) {
+ *   // The $context array gathers batch context information about the execution (read),
+ *   // as well as 'return values' for the current operation (write)
+ *   // The following keys are provided :
+ *   // 'results' (read / write): The array of results gathered so far by
+ *   //   the batch processing, for the current operation to append its own.
+ *   // 'message' (write): A text message displayed in the progress page.
+ *   // The following keys allow for multi-step operations :
+ *   // 'sandbox' (read / write): An array that can be freely used to
+ *   //   store persistent data between iterations. It is recommended to
+ *   //   use this instead of $_SESSION, which is unsafe if the user
+ *   //   continues browsing in a separate window while the batch is processing.
+ *   // 'finished' (write): A float number between 0 and 1 informing
+ *   //   the processing engine of the completion level for the operation.
+ *   //   1 (or no value explicitly set) means the operation is finished
+ *   //   and the batch processing can continue to the next operation.
+ *
+ *   $nodes = \Drupal::entityTypeManager()->getStorage('node')
+ *     ->loadByProperties(['uid' => $uid, 'type' => $type]);
+ *   $node = reset($nodes);
+ *   $context['results'][] = $node->id() . ' : ' . Html::escape($node->label());
+ *   $context['message'] = Html::escape($node->label());
+ * }
+ *
+ * // A more advanced example is a multi-step operation that loads all rows,
+ * // five by five.
+ * function my_function_2(&$context) {
+ *   if (empty($context['sandbox'])) {
+ *     $context['sandbox']['progress'] = 0;
+ *     $context['sandbox']['current_id'] = 0;
+ *     $context['sandbox']['max'] = db_query('SELECT COUNT(DISTINCT id) FROM {example}')->fetchField();
+ *   }
+ *   $limit = 5;
+ *   $result = db_select('example')
+ *     ->fields('example', array('id'))
+ *     ->condition('id', $context['sandbox']['current_id'], '>')
+ *     ->orderBy('id')
+ *     ->range(0, $limit)
+ *     ->execute();
+ *   foreach ($result as $row) {
+ *     $context['results'][] = $row->id . ' : ' . Html::escape($row->title);
+ *     $context['sandbox']['progress']++;
+ *     $context['sandbox']['current_id'] = $row->id;
+ *     $context['message'] = Html::escape($row->title);
+ *   }
+ *   if ($context['sandbox']['progress'] != $context['sandbox']['max']) {
+ *     $context['finished'] = $context['sandbox']['progress'] / $context['sandbox']['max'];
+ *   }
+ * }
+ * @endcode
+ *
+ * Sample callback_batch_finished():
+ * @code
+ * function my_finished_callback($success, $results, $operations) {
+ *   // The 'success' parameter means no fatal PHP errors were detected. All
+ *   // other error management should be handled using 'results'.
+ *   if ($success) {
+ *     $message = \Drupal::translation()->formatPlural(count($results), 'One post processed.', '@count posts processed.');
+ *   }
+ *   else {
+ *     $message = t('Finished with an error.');
+ *   }
+ *   drupal_set_message($message);
+ *   // Providing data for the redirected page is done through $_SESSION.
+ *   foreach ($results as $result) {
+ *     $items[] = t('Loaded node %title.', array('%title' => $result));
+ *   }
+ *   $_SESSION['my_batch_results'] = $items;
+ * }
+ * @endcode
+ */
+
+/**
+ * Adds a new batch.
+ *
+ * Batch operations are added as new batch sets. Batch sets are used to spread
+ * processing (primarily, but not exclusively, forms processing) over several
+ * page requests. This helps to ensure that the processing is not interrupted
+ * due to PHP timeouts, while users are still able to receive feedback on the
+ * progress of the ongoing operations. Combining related operations into
+ * distinct batch sets provides clean code independence for each batch set,
+ * ensuring that two or more batches, submitted independently, can be processed
+ * without mutual interference. Each batch set may specify its own set of
+ * operations and results, produce its own UI messages, and trigger its own
+ * 'finished' callback. Batch sets are processed sequentially, with the progress
+ * bar starting afresh for each new set.
+ *
+ * @param $batch_definition
+ *   An associative array defining the batch, with the following elements (all
+ *   are optional except as noted):
+ *   - operations: (required) Array of operations to be performed, where each
+ *     item is an array consisting of the name of an implementation of
+ *     callback_batch_operation() and an array of parameter.
+ *     Example:
+ *     @code
+ *     array(
+ *       array('callback_batch_operation_1', array($arg1)),
+ *       array('callback_batch_operation_2', array($arg2_1, $arg2_2)),
+ *     )
+ *     @endcode
+ *   - title: A safe, translated string to use as the title for the progress
+ *     page. Defaults to t('Processing').
+ *   - init_message: Message displayed while the processing is initialized.
+ *     Defaults to t('Initializing.').
+ *   - progress_message: Message displayed while processing the batch. Available
+ *     placeholders are @current, @remaining, @total, @percentage, @estimate and
+ *     @elapsed. Defaults to t('Completed @current of @total.').
+ *   - error_message: Message displayed if an error occurred while processing
+ *     the batch. Defaults to t('An error has occurred.').
+ *   - finished: Name of an implementation of callback_batch_finished(). This is
+ *     executed after the batch has completed. This should be used to perform
+ *     any result massaging that may be needed, and possibly save data in
+ *     $_SESSION for display after final page redirection.
+ *   - file: Path to the file containing the definitions of the 'operations' and
+ *     'finished' functions, for instance if they don't reside in the main
+ *     .module file. The path should be relative to base_path(), and thus should
+ *     be built using drupal_get_path().
+ *   - library: An array of batch-specific CSS and JS libraries.
+ *   - url_options: options passed to the \Drupal\Core\Url object when
+ *     constructing redirect URLs for the batch.
+ *   - progressive: A Boolean that indicates whether or not the batch needs to
+ *     run progressively. TRUE indicates that the batch will run in more than
+ *     one run. FALSE (default) indicates that the batch will finish in a single
+ *     run.
+ *   - queue: An override of the default queue (with name and class fields
+ *     optional). An array containing two elements:
+ *     - name: Unique identifier for the queue.
+ *     - class: The name of a class that implements
+ *       \Drupal\Core\Queue\QueueInterface, including the full namespace but not
+ *       starting with a backslash. It must have a constructor with two
+ *       arguments: $name and a \Drupal\Core\Database\Connection object.
+ *       Typically, the class will either be \Drupal\Core\Queue\Batch or
+ *       \Drupal\Core\Queue\BatchMemory. Defaults to Batch if progressive is
+ *       TRUE, or to BatchMemory if progressive is FALSE.
+ */
+function batch_set($batch_definition) {
+  if ($batch_definition) {
+    $batch =& batch_get();
+
+    // Initialize the batch if needed.
+    if (empty($batch)) {
+      $batch = [
+        'sets' => [],
+        'has_form_submits' => FALSE,
+      ];
+    }
+
+    // Base and default properties for the batch set.
+    $init = [
+      'sandbox' => [],
+      'results' => [],
+      'success' => FALSE,
+      'start' => 0,
+      'elapsed' => 0,
+    ];
+    $defaults = [
+      'title' => t('Processing'),
+      'init_message' => t('Initializing.'),
+      'progress_message' => t('Completed @current of @total.'),
+      'error_message' => t('An error has occurred.'),
+    ];
+    $batch_set = $init + $batch_definition + $defaults;
+
+    // Tweak init_message to avoid the bottom of the page flickering down after
+    // init phase.
+    $batch_set['init_message'] .= '<br/>&nbsp;';
+
+    // The non-concurrent workflow of batch execution allows us to save
+    // numberOfItems() queries by handling our own counter.
+    $batch_set['total'] = count($batch_set['operations']);
+    $batch_set['count'] = $batch_set['total'];
+
+    // Add the set to the batch.
+    if (empty($batch['id'])) {
+      // The batch is not running yet. Simply add the new set.
+      $batch['sets'][] = $batch_set;
+    }
+    else {
+      // The set is being added while the batch is running. Insert the new set
+      // right after the current one to ensure execution order, and store its
+      // operations in a queue.
+      $index = $batch['current_set'] + 1;
+      $slice1 = array_slice($batch['sets'], 0, $index);
+      $slice2 = array_slice($batch['sets'], $index);
+      $batch['sets'] = array_merge($slice1, [$batch_set], $slice2);
+      _batch_populate_queue($batch, $index);
+    }
+  }
+}
+
+/**
+ * Processes the batch.
+ *
+ * This function is generally not needed in form submit handlers;
+ * Form API takes care of batches that were set during form submission.
+ *
+ * @param \Drupal\Core\Url|string $redirect
+ *   (optional) Either path or Url object to redirect to when the batch has
+ *   finished processing. Note that to simply force a batch to (conditionally)
+ *   redirect to a custom location after it is finished processing but to
+ *   otherwise allow the standard form API batch handling to occur, it is not
+ *   necessary to call batch_process() and use this parameter. Instead, make
+ *   the batch 'finished' callback return an instance of
+ *   \Symfony\Component\HttpFoundation\RedirectResponse, which will be used
+ *   automatically by the standard batch processing pipeline (and which takes
+ *   precedence over this parameter).
+ *   User will be redirected to the page that started the batch if this argument
+ *   is omitted and no redirect response was returned by the 'finished'
+ *   callback. Any query arguments will be automatically persisted.
+ * @param \Drupal\Core\Url $url
+ *   (optional) URL of the batch processing page. Should only be used for
+ *   separate scripts like update.php.
+ * @param $redirect_callback
+ *   (optional) Specify a function to be called to redirect to the progressive
+ *   processing page.
+ *
+ * @return \Symfony\Component\HttpFoundation\RedirectResponse|null
+ *   A redirect response if the batch is progressive. No return value otherwise.
+ */
+function batch_process($redirect = NULL, Url $url = NULL, $redirect_callback = NULL) {
+  $batch =& batch_get();
+
+  if (isset($batch)) {
+    // Add process information
+    $process_info = [
+      'current_set' => 0,
+      'progressive' => TRUE,
+      'url' => isset($url) ? $url : Url::fromRoute('system.batch_page.html'),
+      'source_url' => Url::fromRouteMatch(\Drupal::routeMatch())->mergeOptions(['query' => \Drupal::request()->query->all()]),
+      'batch_redirect' => $redirect,
+      'theme' => \Drupal::theme()->getActiveTheme()->getName(),
+      'redirect_callback' => $redirect_callback,
+    ];
+    $batch += $process_info;
+
+    // The batch is now completely built. Allow other modules to make changes
+    // to the batch so that it is easier to reuse batch processes in other
+    // environments.
+    \Drupal::moduleHandler()->alter('batch', $batch);
+
+    // Assign an arbitrary id: don't rely on a serial column in the 'batch'
+    // table, since non-progressive batches skip database storage completely.
+    $batch['id'] = db_next_id();
+
+    // Move operations to a job queue. Non-progressive batches will use a
+    // memory-based queue.
+    foreach ($batch['sets'] as $key => $batch_set) {
+      _batch_populate_queue($batch, $key);
+    }
+
+    // Initiate processing.
+    if ($batch['progressive']) {
+      // Now that we have a batch id, we can generate the redirection link in
+      // the generic error message.
+      /** @var \Drupal\Core\Url $batch_url */
+      $batch_url = $batch['url'];
+      /** @var \Drupal\Core\Url $error_url */
+      $error_url = clone $batch_url;
+      $query_options = $error_url->getOption('query');
+      $query_options['id'] = $batch['id'];
+      $query_options['op'] = 'finished';
+      $error_url->setOption('query', $query_options);
+
+      $batch['error_message'] = t('Please continue to <a href=":error_url">the error page</a>', [':error_url' => $error_url->toString(TRUE)->getGeneratedUrl()]);
+
+      // Clear the way for the redirection to the batch processing page, by
+      // saving and unsetting the 'destination', if there is any.
+      $request = \Drupal::request();
+      if ($request->query->has('destination')) {
+        $batch['destination'] = $request->query->get('destination');
+        $request->query->remove('destination');
+      }
+
+      // Store the batch.
+      \Drupal::service('batch.storage')->create($batch);
+
+      // Set the batch number in the session to guarantee that it will stay alive.
+      $_SESSION['batches'][$batch['id']] = TRUE;
+
+      // Redirect for processing.
+      $query_options = $error_url->getOption('query');
+      $query_options['op'] = 'start';
+      $query_options['id'] = $batch['id'];
+      $batch_url->setOption('query', $query_options);
+      if (($function = $batch['redirect_callback']) && function_exists($function)) {
+        $function($batch_url->toString(), ['query' => $query_options]);
+      }
+      else {
+        return new RedirectResponse($batch_url->setAbsolute()->toString(TRUE)->getGeneratedUrl());
+      }
+    }
+    else {
+      // Non-progressive execution: bypass the whole progressbar workflow
+      // and execute the batch in one pass.
+      require_once __DIR__ . '/batch.inc';
+      _batch_process();
+    }
+  }
+}
+
+/**
+ * Retrieves the current batch.
+ */
+function &batch_get() {
+  // Not drupal_static(), because Batch API operates at a lower level than most
+  // use-cases for resetting static variables, and we specifically do not want a
+  // global drupal_static_reset() resetting the batch information. Functions
+  // that are part of the Batch API and need to reset the batch information may
+  // call batch_get() and manipulate the result by reference. Functions that are
+  // not part of the Batch API can also do this, but shouldn't.
+  static $batch = [];
+  return $batch;
+}
+
+/**
+ * Populates a job queue with the operations of a batch set.
+ *
+ * Depending on whether the batch is progressive or not, the
+ * Drupal\Core\Queue\Batch or Drupal\Core\Queue\BatchMemory handler classes will
+ * be used. The name and class of the queue are added by reference to the
+ * batch set.
+ *
+ * @param $batch
+ *   The batch array.
+ * @param $set_id
+ *   The id of the set to process.
+ */
+function _batch_populate_queue(&$batch, $set_id) {
+  $batch_set = &$batch['sets'][$set_id];
+
+  if (isset($batch_set['operations'])) {
+    $batch_set += [
+      'queue' => [
+        'name' => 'drupal_batch:' . $batch['id'] . ':' . $set_id,
+        'class' => $batch['progressive'] ? 'Drupal\Core\Queue\Batch' : 'Drupal\Core\Queue\BatchMemory',
+      ],
+    ];
+
+    $queue = _batch_queue($batch_set);
+    $queue->createQueue();
+    foreach ($batch_set['operations'] as $operation) {
+      $queue->createItem($operation);
+    }
+
+    unset($batch_set['operations']);
+  }
+}
+
+/**
+ * Returns a queue object for a batch set.
+ *
+ * @param $batch_set
+ *   The batch set.
+ *
+ * @return
+ *   The queue object.
+ */
+function _batch_queue($batch_set) {
+  static $queues;
+
+  if (!isset($queues)) {
+    $queues = [];
+  }
+
+  if (isset($batch_set['queue'])) {
+    $name = $batch_set['queue']['name'];
+    $class = $batch_set['queue']['class'];
+
+    if (!isset($queues[$class][$name])) {
+      $queues[$class][$name] = new $class($name, \Drupal::database());
+    }
+    return $queues[$class][$name];
+  }
+}
+
+/**
+ * @} End of "defgroup batch".
+ */