field.module

<?php
/**
 * @file
 * Attach custom data fields to Drupal entities.
 */

use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Template\Attribute;

/*
 * Load all public Field API functions. Drupal currently has no
 * mechanism for auto-loading core APIs, so we have to load them on
 * every page request.
 */
require_once DRUPAL_ROOT . '/core/modules/field/field.crud.inc';
require_once DRUPAL_ROOT . '/core/modules/field/field.default.inc';
require_once DRUPAL_ROOT . '/core/modules/field/field.info.inc';
require_once DRUPAL_ROOT . '/core/modules/field/field.multilingual.inc';
require_once DRUPAL_ROOT . '/core/modules/field/field.attach.inc';
require_once DRUPAL_ROOT . '/core/modules/field/field.form.inc';

/**
 * @defgroup field Field API
 * @{
 * Attaches custom data fields to Drupal entities.
 *
 * The Field API allows custom data fields to be attached to Drupal entities and
 * takes care of storing, loading, editing, and rendering field data. Any entity
 * type (node, user, etc.) can use the Field API to make itself "fieldable" and
 * thus allow fields to be attached to it. Other modules can provide a user
 * interface for managing custom fields via a web browser as well as a wide and
 * flexible variety of data type, form element, and display format capabilities.
 *
 * The Field API defines two primary data structures, Field and Instance, and
 * the concept of a Bundle. A Field defines a particular type of data that can
 * be attached to entities. A Field Instance is a Field attached to a single
 * Bundle. A Bundle is a set of fields that are treated as a group by the Field
 * Attach API and is related to a single fieldable entity type.
 *
 * For example, suppose a site administrator wants Article nodes to have a
 * subtitle and photo. Using the Field API or Field UI module, the administrator
 * creates a field named 'subtitle' of type 'text' and a field named 'photo' of
 * type 'image'. The administrator (again, via a UI) creates two Field
 * Instances, one attaching the field 'subtitle' to the 'node' bundle 'article'
 * and one attaching the field 'photo' to the 'node' bundle 'article'. When the
 * node system uses the Field Attach API to load all fields for an Article node,
 * it passes the node's entity type (which is 'node') and content type (which is
 * 'article') as the node's bundle. field_attach_load() then loads the
 * 'subtitle' and 'photo' fields because they are both attached to the 'node'
 * bundle 'article'.
 *
 * Field definitions are represented as an array of key/value pairs.
 *
 * array $field:
 * - id: (integer, read-only) The primary identifier of the field. It is
 *   assigned automatically by field_create_field().
 * - field_name: (string) The name of the field. Each field name is unique
 *   within Field API. When a field is attached to an entity, the field's data
 *   is stored in $entity->$field_name. Maximum length is 32 characters.
 * - type: (string) The type of the field, such as 'text' or 'image'. Field
 *   types are defined by modules that implement hook_field_info().
 * - entity_types: (array) The array of entity types that can hold instances of
 *   this field. If empty or not specified, the field can have instances in any
 *   entity type.
 * - cardinality: (integer) The number of values the field can hold. Legal
 *   values are any positive integer or FIELD_CARDINALITY_UNLIMITED.
 * - translatable: (integer) Whether the field is translatable.
 * - locked: (integer) Whether or not the field is available for editing. If
 *   TRUE, users can't change field settings or create new instances of the
 *   field in the UI. Defaults to FALSE.
 * - module: (string, read-only) The name of the module that implements the
 *   field type.
 * - active: (integer, read-only) TRUE if the module that implements the field
 *   type is currently enabled, FALSE otherwise.
 * - deleted: (integer, read-only) TRUE if this field has been deleted, FALSE
 *   otherwise. Deleted fields are ignored by the Field Attach API. This
 *   property exists because fields can be marked for deletion but only actually
 *   destroyed by a separate garbage-collection process.
 * - columns: (array, read-only) An array of the Field API columns used to store
 *   each value of this field. The column list may depend on field settings; it
 *   is not constant per field type. Field API column specifications are exactly
 *   like Schema API column specifications but, depending onthe field storage
 *   module in use, the name of the column may not represent an actual column in
 *   an SQL database.
 * - indexes: (array) An array of indexes on data columns, using the same
 *   definition format as Schema API index specifications. Only columns that
 *   appear in the 'columns' setting are allowed. Note that field types can
 *   specify default indexes, which can be modified or added to when creating a
 *   field.
 * - foreign keys: (optional) An associative array of relations, using the same
 *   structure as the 'foreign keys' definition of hook_schema(). Note,
 *   however, that the field data is not necessarily stored in SQL. Also, the
 *   possible usage is limited, as you cannot specify another field as
 *   related, only existing SQL tables, such as filter formats.
 * - settings: (array) A sub-array of key/value pairs of field-type-specific
 *   settings. Each field type module defines and documents its own field
 *   settings.
 * - storage: (array) A sub-array of key/value pairs identifying the storage
 *   backend to use for the for the field.
 *   - type: (string) The storage backend used by the field. Storage backends
 *     are defined by modules that implement hook_field_storage_info().
 *   - module: (string, read-only) The name of the module that implements the
 *     storage backend.
 *   - active: (integer, read-only) TRUE if the module that implements the
 *     storage backend is currently enabled, FALSE otherwise.
 *   - settings: (array) A sub-array of key/value pairs of settings. Each
 *     storage backend defines and documents its own settings.
 *
 * Field instance definitions are represented as an array of key/value pairs.
 *
 * array $instance:
 * - id: (integer, read-only) The primary identifier of this field instance. It
 *   is assigned automatically by field_create_instance().
 * - field_id: (integer, read-only) The foreign key of the field attached to the
 *   bundle by this instance. It is populated automatically by
 *   field_create_instance().
 * - field_name: (string) The name of the field attached to the bundle by this
 *   instance.
 * - entity_type: (string) The name of the entity type the instance is attached
 *   to.
 * - bundle: (string) The name of the bundle that the field is attached to.
 * - label: (string) A human-readable label for the field when used with this
 *   bundle. For example, the label will be the title of Form API elements for
 *   this instance.
 * - description: (string)A human-readable description for the field when used
 *   with this bundle. For example, the description will be the help text of
 *   Form API elements for this instance.
 * - required: (integer) TRUE if a value for this field is required when used
 *   with this bundle, FALSE otherwise. Currently, required-ness is only
 *   enforced during Form API operations, not by field_attach_load(),
 *   field_attach_insert(), or field_attach_update().
 * - default_value_function: (string) The name of the function, if any, that
 *   will provide a default value.
 * - default_value: (array) If default_value_function is not set, then fixed
 *   values can be provided.
 * - deleted: (integer, read-only) TRUE if this instance has been deleted, FALSE
 *   otherwise. Deleted instances are ignored by the Field Attach API. This
 *   property exists because instances can be marked for deletion but only
 *   actually destroyed by a separate garbage-collection process.
 * - settings: (array) A sub-array of key/value pairs of field-type-specific
 *   instance settings. Each field type module defines and documents its own
 *   instance settings.
 * - widget: (array) A sub-array of key/value pairs identifying the Form API
 *   input widget for the field when used by this bundle.
 *   - type: (string) The type of the widget, such as text_textfield. Widget
 *     types are defined by modules that implement hook_field_widget_info().
 *   - settings: (array) A sub-array of key/value pairs of widget-type-specific
 *     settings. Each field widget type module defines and documents its own
 *     widget settings.
 *   - weight: (float) The weight of the widget relative to the other elements
 *     in entity edit forms.
 *   - module: (string, read-only) The name of the module that implements the
 *     widget type.
 * - display: (array) A sub-array of key/value pairs identifying the way field
 *   values should be displayed in each of the entity type's view modes, plus
 *   the 'default' mode. For each view mode, Field UI lets site administrators
 *   define whether they want to use a dedicated set of display options or the
 *   'default' options to reduce the number of displays to maintain as they add
 *   new fields. For nodes, on a fresh install, only the 'teaser' view mode is
 *   configured to use custom display options, all other view modes defined use
 *   the 'default' options by default. When programmatically adding field
 *   instances on nodes, it is therefore recommended to at least specify display
 *   options for 'default' and 'teaser'.
 *   - default: (array) A sub-array of key/value pairs describing the display
 *     options to be used when the field is being displayed in view modes that
 *     are not configured to use dedicated display options.
 *     - label: (string) Position of the label. 'inline', 'above' and 'hidden'
 *       are the values recognized by the default 'field' theme implementation.
 *     - type: (string) The type of the display formatter, or 'hidden' for no
 *       display.
 *     - settings: (array) A sub-array of key/value pairs of display options
 *       specific to the formatter.
 *       - weight: (float) The weight of the field relative to the other entity
 *         components displayed in this view mode.
 *       - module: (string, read-only) The name of the module which implements
 *         the display formatter.
 *   - some_mode: A sub-array of key/value pairs describing the display options
 *     to be used when the field is being displayed in the 'some_mode' view
 *     mode. Those options will only be actually applied at run time if the view
 *     mode is not configured to use default settings for this bundle.
 *     - ...
 *   - other_mode:
 *     - ...
 *
 * The (default) render arrays produced for field instances are documented at
 * field_attach_view().
 *
 * Bundles are represented by two strings, an entity type and a bundle name.
 *
 * - @link field_types Field Types API @endlink: Defines field types, widget
 *   types, and display formatters. Field modules use this API to provide field
 *   types like Text and Node Reference along with the associated form elements
 *   and display formatters.
 *
 * - @link field_crud Field CRUD API @endlink: Create, updates, and deletes
 *   fields, bundles (a.k.a. "content types"), and instances. Modules use this
 *   API, often in hook_install(), to create custom data structures.
 *
 * - @link field_attach Field Attach API @endlink: Connects entity types to the
 *   Field API. Field Attach API functions load, store, generate Form API
 *   structures, display, and perform a variety of other functions for field
 *   data connected to individual entities. Fieldable entity types like node and
 *   user use this API to make themselves fieldable.
 *
 * - @link field_info Field Info API @endlink: Exposes information about all
 *   fields, instances, widgets, and related information defined by or with the
 *   Field API.
 *
 * - @link field_storage Field Storage API @endlink: Provides a pluggable back
 *   -end storage system for actual field data. The default implementation,
 *   field_sql_storage.module, stores field data in the local SQL database.
 *
 * - @link field_purge Field API bulk data deletion @endlink: Cleans up after
 *   bulk deletion operations such as field_delete_field() and
 *   field_delete_instance().
 *
 * - @link field_language Field language API @endlink: Provides native
 *   multilingual support for the Field API.
 */

/**
 * Value for field API indicating a field accepts an unlimited number of values.
 */
const FIELD_CARDINALITY_UNLIMITED = -1;

/**
 * Value for field API indicating a widget doesn't accept default values.
 *
 * @see hook_field_widget_info()
 */
const FIELD_BEHAVIOR_NONE = 0x0001;

/**
 * Value for field API concerning widget default and multiple value settings.
 *
 * @see hook_field_widget_info()
 *
 * When used in a widget default context, indicates the widget accepts default
 * values. When used in a multiple value context for a widget that allows the
 * input of one single field value, indicates that the widget will be repeated
 * for each value input.
 */
const FIELD_BEHAVIOR_DEFAULT = 0x0002;

/**
 * Value for field API indicating a widget can receive several field values.
 *
 * @see hook_field_widget_info()
 */
const FIELD_BEHAVIOR_CUSTOM = 0x0004;

/**
 * Load the most recent version of an entity's field data.
 *
 * @see field_attach_load().
 */
const FIELD_LOAD_CURRENT = 'FIELD_LOAD_CURRENT';

/**
 * Load the version of an entity's field data specified in the entity.
 *
 * @see field_attach_load().
 */
const FIELD_LOAD_REVISION = 'FIELD_LOAD_REVISION';

/**
 * Implements hook_help().
 */
function field_help($path, $arg) {
  switch ($path) {
    case 'admin/help#field':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Field module allows custom data fields to be defined for <em>entity</em> types (entities include content items, comments, user accounts, and taxonomy terms). The Field module takes care of storing, loading, editing, and rendering field data. Most users will not interact with the Field module directly, but will instead use the <a href="@field-ui-help">Field UI module</a> user interface. Module developers can use the Field API to make new entity types "fieldable" and thus allow fields to be attached to them. For more information, see the online handbook entry for <a href="@field">Field module</a>.', array('@field-ui-help' => url('admin/help/field_ui'), '@field' => 'http://drupal.org/documentation/modules/field')) . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';
      $output .= '<dt>' . t('Enabling field types') . '</dt>';
      $output .= '<dd>' . t('The Field module provides the infrastructure for fields and field attachment; the field types and input widgets themselves are provided by additional modules. Some of the modules are required; the optional modules can be enabled from the <a href="@modules">Modules administration page</a>. Drupal core includes the following field type modules: Number (required), Text (required), List (required), Taxonomy (optional), Image (optional), and File (optional); the required Options module provides input widgets for other field modules. Additional fields and widgets may be provided by contributed modules, which you can find in the <a href="@contrib">contributed module section of Drupal.org</a>. Currently enabled field and input widget modules:', array('@modules' => url('admin/modules'), '@contrib' => 'http://drupal.org/project/modules', '@options' => url('admin/help/options')));

      // Make a list of all widget and field modules currently enabled, in
      // order by displayed module name (module names are not translated).
      $items = array();
      $info = system_get_info('module');
      $modules = array_merge(module_implements('field_info'), module_implements('field_widget_info'));
      $modules = array_unique($modules);
      sort($modules);
      foreach ($modules as $module) {
        $display = $info[$module]['name'];
        if (module_hook($module, 'help')) {
          $items['items'][] = l($display, 'admin/help/' . $module);
        }
        else {
          $items['items'][] = $display;
        }
      }
      $output .= theme('item_list', $items) . '</dd>';
      $output .= '<dt>' . t('Managing field data storage') . '</dt>';
      $output .= '<dd>' . t('Developers of field modules can either use the default <a href="@sql-store">Field SQL Storage module</a> to store data for their fields, or a contributed or custom module developed using the <a href="@storage-api">field storage API</a>.', array('@storage-api' => 'http://api.drupal.org/api/group/field_storage/8', '@sql-store' => url('admin/help/field_sql_storage'))) . '</dd>';
      $output .= '</dl>';
      return $output;
  }
}

/**
 * Implements hook_theme().
 */
function field_theme() {
  return array(
    'field' => array(
      'render element' => 'element',
    ),
    'field_multiple_value_form' => array(
      'render element' => 'element',
    ),
  );
}

/**
 * Implements hook_cron().
 */
function field_cron() {
  // Refresh the 'active' status of fields.
  field_sync_field_status();

  // Do a pass of purging on deleted Field API data, if any exists.
  $limit = config('field.settings')->get('purge_batch_size');
  field_purge_batch($limit);
}

/**
 * Implements hook_system_info_alter().
 *
 * Goes through a list of all modules that provide a field type and makes them
 * required if there are any active fields of that type.
 */
function field_system_info_alter(&$info, $file, $type) {
  if ($type == 'module' && module_hook($file->name, 'field_info')) {
    $fields = field_read_fields(array('module' => $file->name), array('include_deleted' => TRUE));
    if ($fields) {
      $info['required'] = TRUE;

      // Provide an explanation message (only mention pending deletions if there
      // remains no actual, non-deleted fields)
      $non_deleted = FALSE;
      foreach ($fields as $field) {
        if (empty($field['deleted'])) {
          $non_deleted = TRUE;
          break;
        }
      }
      if ($non_deleted) {
        if (module_exists('field_ui')) {
          $explanation = t('Field type(s) in use - see <a href="@fields-page">Field list</a>', array('@fields-page' => url('admin/reports/fields')));
        }
        else {
          $explanation = t('Fields type(s) in use');
        }
      }
      else {
        $explanation = t('Fields pending deletion');
      }
      $info['explanation'] = $explanation;
    }
  }
}

/**
 * Implements hook_data_type_info() to register data types for all field types.
 */
function field_data_type_info() {
  $field_types = field_info_field_types();
  $items = array();

  // Expose data types for all the field type items.
  // @todo: Make 'field item class' mandatory.
  foreach ($field_types as $type_name => $type_info) {

    if (!empty($type_info['field item class'])) {
      $items[$type_name . '_field'] = array(
        'label' => t('Field !label item', array('!label' => $type_info['label'])),
        'class' => $type_info['field item class'],
        'list class' => !empty($type_info['field class']) ? $type_info['field class'] : '\Drupal\Core\Entity\Field\Type\Field',
      );
    }
  }
  return $items;
}

/**
 * Implements hook_entity_create().
 */
function field_entity_create(EntityInterface $entity) {
  $info = $entity->entityInfo();
  if (!empty($info['fieldable'])) {
    foreach ($entity->getTranslationLanguages() as $langcode => $language) {
      field_populate_default_values($entity, $langcode);
    }
  }
}

/**
 * Inserts a default value for each entity field not having one.
 *
 * @param \Drupal\Core\Entity\EntityInterface $entity
 *   The entity for the operation.
 * @param string $langcode
 *   (optional) The field language code to fill-in with the default value.
 *   Defaults to the entity language.
 */
function field_populate_default_values(EntityInterface $entity, $langcode = NULL) {
  $entity_type = $entity->entityType();
  $langcode = $langcode ?: $entity->language()->langcode;
  foreach (field_info_instances($entity_type, $entity->bundle()) as $field_name => $instance) {
    $field = field_info_field($field_name);
    $field_langcode = field_is_translatable($entity_type, $field) ? $langcode : LANGUAGE_NOT_SPECIFIED;
    // We need to preserve existing values.
    if (empty($entity->{$field_name}) || !array_key_exists($field_langcode, $entity->{$field_name})) {
      $items = field_get_default_value($entity, $field, $instance, $field_langcode);
      if (!empty($items)) {
        $entity->{$field_name}[$field_langcode] = $items;
      }
    }
  }
}

/**
 * Implements hook_entity_field_info() to define all configured fields.
 */
function field_entity_field_info($entity_type) {
  $property_info = array();
  $field_types = field_info_field_types();

  foreach (field_info_instances($entity_type) as $bundle_name => $instances) {
    $optional = $bundle_name != $entity_type;

    foreach ($instances as $field_name => $instance) {
      $field = field_info_field($field_name);

      if (!empty($field_types[$field['type']]['field item class'])) {

        // @todo: Allow for adding field type settings.
        $definition = array(
          'label' => t('Field !name', array('!name' => $field_name)),
          'type' => $field['type'] . '_field',
          'configurable' => TRUE,
          'translatable' => !empty($field['translatable'])
        );

        if ($optional) {
          $property_info['optional'][$field_name] = $definition;
          $property_info['bundle map'][$bundle_name][] = $field_name;
        }
        else {
          $property_info['definitions'][$field_name] = $definition;
        }
      }
    }
  }

  return $property_info;
}

/**
 * Applies language fallback rules to the fields attached to the given entity.
 *
 * Core language fallback rules simply check if fields have a field translation
 * for the requested language code. If so, the requested language is returned,
 * otherwise all the fallback candidates are inspected to see if there is a
 * field translation available in another language.
 * By default this is called by field_field_language_alter(), but this
 * behavior can be disabled by setting the 'field_language_fallback'
 * variable to FALSE.
 *
 * @param $field_langcodes
 *   A reference to an array of language codes keyed by field name.
 * @param \Drupal\Core\Entity\EntityInterface $entity
 *   The entity to be displayed.
 * @param $langcode
 *   The language code $entity has to be displayed in.
 */
function field_language_fallback(&$field_langcodes, EntityInterface $entity, $langcode) {
  // Lazily init fallback candidates to avoid unnecessary calls.
  $fallback_candidates = NULL;

  foreach ($field_langcodes as $field_name => $field_langcode) {
    // If the requested language is defined for the current field use it,
    // otherwise search for a fallback value among the fallback candidates.
    if (isset($entity->{$field_name}[$langcode])) {
      $field_langcodes[$field_name] = $langcode;
    }
    elseif (!empty($entity->{$field_name})) {
      if (!isset($fallback_candidates)) {
        require_once DRUPAL_ROOT . '/core/includes/language.inc';
        $fallback_candidates = language_fallback_get_candidates();
      }
      foreach ($fallback_candidates as $fallback_langcode) {
        if (isset($entity->{$field_name}[$fallback_langcode])) {
          $field_langcodes[$field_name] = $fallback_langcode;
          break;
        }
      }
    }
  }
}

/**
 * Implements hook_cache_flush().
 */
function field_cache_flush() {
  // Request a flush of our cache table.
  return array('field');
}

/**
 * Implements hook_rebuild().
 */
function field_rebuild() {
  // Refresh the 'active' status of fields.
  field_sync_field_status();
}

/**
 * Implements hook_modules_enabled().
 */
function field_modules_enabled($modules) {
  // Refresh the 'active' status of fields.
  field_sync_field_status();
}

/**
 * Implements hook_modules_disabled().
 */
function field_modules_disabled($modules) {
  // Refresh the 'active' status of fields.
  field_sync_field_status();
}

/**
 * Refreshes the 'active' and 'storage_active' columns for fields.
 */
function field_sync_field_status() {
  // Refresh the 'active' and 'storage_active' columns according to the current
  // set of enabled modules.
  $modules = array_keys(drupal_container()->get('module_handler')->getModuleList());
  foreach ($modules as $module_name) {
    field_associate_fields($module_name);
  }
  db_update('field_config')
    ->fields(array('active' => 0))
    ->condition('module', $modules, 'NOT IN')
    ->execute();
  db_update('field_config')
    ->fields(array('storage_active' => 0))
    ->condition('storage_module', $modules, 'NOT IN')
    ->execute();
}

/**
 * Allows a module to update the database for fields and columns it controls.
 *
 * @param $module
 *   The name of the module to update on.
 */
function field_associate_fields($module) {
  // Associate field types.
  $field_types = (array) module_invoke($module, 'field_info');
  if ($field_types) {
    db_update('field_config')
      ->fields(array('module' => $module, 'active' => 1))
      ->condition('type', array_keys($field_types))
      ->execute();
  }
  // Associate storage backends.
  $storage_types = (array) module_invoke($module, 'field_storage_info');
  if ($storage_types) {
    db_update('field_config')
      ->fields(array('storage_module' => $module, 'storage_active' => 1))
      ->condition('storage_type', array_keys($storage_types))
      ->execute();
  }
}

/**
 * Helper function to get the default value for a field on an entity.
 *
 * @param \Drupal\Core\Entity\EntityInterface $entity
 *   The entity for the operation.
 * @param $field
 *   The field structure.
 * @param $instance
 *   The instance structure.
 * @param $langcode
 *   The field language to fill-in with the default value.
 */
function field_get_default_value(EntityInterface $entity, $field, $instance, $langcode = NULL) {
  $items = array();
  if (!empty($instance['default_value_function'])) {
    $function = $instance['default_value_function'];
    $items = $function($entity, $field, $instance, $langcode);
  }
  elseif (!empty($instance['default_value'])) {
    $items = $instance['default_value'];
  }
  return $items;
}

/**
 * Filters out empty field values.
 *
 * @param $field
 *   The field definition.
 * @param $items
 *   The field values to filter.
 *
 * @return
 *   The array of items without empty field values. The function also renumbers
 *   the array keys to ensure sequential deltas.
 */
function _field_filter_items($field, $items) {
  $function = $field['module'] . '_field_is_empty';
  foreach ((array) $items as $delta => $item) {
    // Explicitly break if the function is undefined.
    if ($function($item, $field)) {
      unset($items[$delta]);
    }
  }
  return array_values($items);
}

/**
 * Sorts items in a field according to user drag-and-drop reordering.
 *
 * @param $field
 *   The field definition.
 * @param $items
 *   The field values to sort.
 *
 * @return
 *   The sorted array of field items.
 */
function _field_sort_items($field, $items) {
  if (($field['cardinality'] > 1 || $field['cardinality'] == FIELD_CARDINALITY_UNLIMITED) && isset($items[0]['_weight'])) {
    usort($items, '_field_sort_items_helper');
    foreach ($items as $delta => $item) {
      if (is_array($items[$delta])) {
        unset($items[$delta]['_weight']);
      }
    }
  }
  return $items;
}

/**
 * Callback for usort() within _field_sort_items().
 *
 * Copied form element_sort(), which acts on #weight keys.
 */
function _field_sort_items_helper($a, $b) {
  $a_weight = (is_array($a) ? $a['_weight'] : 0);
  $b_weight = (is_array($b) ? $b['_weight'] : 0);
  return $a_weight - $b_weight;
}

/**
 * Callback for usort() within theme_field_multiple_value_form().
 *
 * Sorts using ['_weight']['#value']
 */
function _field_sort_items_value_helper($a, $b) {
  $a_weight = (is_array($a) && isset($a['_weight']['#value']) ? $a['_weight']['#value'] : 0);
  $b_weight = (is_array($b) && isset($b['_weight']['#value']) ? $b['_weight']['#value'] : 0);
  return $a_weight - $b_weight;
}

/**
 * Gets or sets administratively defined bundle settings.
 *
 * @param string $entity_type
 *   The type of $entity; e.g., 'node' or 'user'.
 * @param string $bundle
 *   The bundle name.
 * @param array|null $settings
 *   (optional) The settings to store, an associative array with the following
 *   elements:
 *   - view_modes: An associative array keyed by view mode, with the following
 *     key/value pairs:
 *     - custom_settings: Boolean specifying whether the view mode uses a
 *       dedicated set of display options (TRUE), or the 'default' options
 *       (FALSE). Defaults to FALSE.
 *   - extra_fields: An associative array containing the form and display
 *     settings for extra fields (also known as pseudo-fields):
 *     - form: An associative array whose keys are the names of extra fields,
 *       and whose values are associative arrays with the following elements:
 *       - weight: The weight of the extra field, determining its position on an
 *         entity form.
 *     - display: An associative array whose keys are the names of extra fields,
 *       and whose values are associative arrays keyed by the name of view
 *       modes. This array must include an item for the 'default' view mode.
 *       Each view mode sub-array contains the following elements:
 *       - weight: The weight of the extra field, determining its position when
 *         an entity is viewed.
 *       - visible: TRUE if the extra field is visible, FALSE otherwise.
 *
 * @return array|null
 *   If no $settings are passed, the current settings are returned.
 */
function field_bundle_settings($entity_type, $bundle, $settings = NULL) {
  if (isset($settings)) {
    variable_set('field_bundle_settings_' . $entity_type . '__' . $bundle, $settings);
    field_info_cache_clear();
  }
  else {
    $settings = variable_get('field_bundle_settings_' . $entity_type . '__' . $bundle, array());
    $settings += array(
      'view_modes' => array(),
      'extra_fields' => array(),
    );
    $settings['extra_fields'] += array(
      'form' => array(),
    );

    return $settings;
  }
}

/**
 * Returns view mode settings in a given bundle.
 *
 * @param $entity_type
 *   The type of entity; e.g. 'node' or 'user'.
 * @param $bundle
 *   The bundle name to return view mode settings for.
 *
 * @return
 *   An array keyed by view mode, with the following key/value pairs:
 *   - custom_settings: Boolean specifying whether the view mode uses a
 *     dedicated set of display options (TRUE), or the 'default' options
 *     (FALSE). Defaults to FALSE.
 */
function field_view_mode_settings($entity_type, $bundle) {
  $cache = &drupal_static(__FUNCTION__, array());

  if (!isset($cache[$entity_type][$bundle])) {
    $bundle_settings = field_bundle_settings($entity_type, $bundle);
    $settings = $bundle_settings['view_modes'];
    // Include view modes for which nothing has been stored yet, but whose
    // definition in hook_entity_info_alter() specify they should use custom
    // settings by default.
    $entity_info = entity_get_info($entity_type);
    foreach ($entity_info['view_modes'] as $view_mode => $view_mode_info) {
      if (!isset($settings[$view_mode]['custom_settings']) && $view_mode_info['custom_settings']) {
        $settings[$view_mode]['custom_settings'] = TRUE;
      }
    }
    $cache[$entity_type][$bundle] = $settings;
  }

  return $cache[$entity_type][$bundle];
}

/**
 * Pre-render callback: Adjusts weights and visibility of non-field elements.
 */
function _field_extra_fields_pre_render($elements) {
  $entity_type = $elements['#entity_type'];
  $bundle = $elements['#bundle'];

  $extra_fields = field_info_extra_fields($entity_type, $bundle, 'form');
  foreach ($extra_fields as $name => $settings) {
    if (isset($elements[$name])) {
      $elements[$name]['#weight'] = $settings['weight'];
    }
  }

  return $elements;
}

/**
 * Clears the field info and field data caches.
 */
function field_cache_clear() {
  cache('field')->deleteAll();
  field_info_cache_clear();
}

/**
 * Filters an HTML string to prevent cross-site-scripting (XSS) vulnerabilities.
 *
 * Like filter_xss_admin(), but with a shorter list of allowed tags.
 *
 * Used for items entered by administrators, like field descriptions, allowed
 * values, where some (mainly inline) mark-up may be desired (so
 * drupal_htmlspecialchars() is not acceptable).
 *
 * @param $string
 *   The string with raw HTML in it.
 *
 * @return
 *   An XSS safe version of $string, or an empty string if $string is not valid
 *   UTF-8.
 */
function field_filter_xss($string) {
  return filter_xss($string, _field_filter_xss_allowed_tags());
}

/**
 * Returns a list of tags allowed by field_filter_xss().
 */
function _field_filter_xss_allowed_tags() {
  return array('a', 'b', 'big',  'code', 'del', 'em', 'i', 'ins',  'pre', 'q', 'small', 'span', 'strong', 'sub', 'sup', 'tt', 'ol', 'ul', 'li', 'p', 'br', 'img');
}

/**
 * Returns a human-readable list of allowed tags for display in help texts.
 */
function _field_filter_xss_display_allowed_tags() {
  return '<' . implode('> <', _field_filter_xss_allowed_tags()) . '>';
}

/**
 * Returns a renderable array for a single field value.
 *
 * @param \Drupal\Core\Entity\EntityInterface $entity
 *   The entity containing the field to display. Must at least contain the ID
 *   key and the field data to display.
 * @param $field_name
 *   The name of the field to display.
 * @param $item
 *   The field value to display, as found in
 *   $entity->field_name[$langcode][$delta].
 * @param $display
 *   Can be either the name of a view mode, or an array of display settings. See
 *   field_view_field() for more information.
 * @param $langcode
 *   (Optional) The language of the value in $item. If not provided, the current
 *   language will be assumed.
 *
 * @return
 *   A renderable array for the field value.
 */
function field_view_value(EntityInterface $entity, $field_name, $item, $display = array(), $langcode = NULL) {
  $output = array();

  if ($field = field_info_field($field_name)) {
    // Determine the langcode that will be used by language fallback.
    $langcode = field_language($entity, $field_name, $langcode);

    // Push the item as the single value for the field, and defer to
    // field_view_field() to build the render array for the whole field.
    $clone = clone $entity;
    $clone->{$field_name}[$langcode] = array($item);
    $elements = field_view_field($clone, $field_name, $display, $langcode);

    // Extract the part of the render array we need.
    $output = isset($elements[0]) ? $elements[0] : array();
    if (isset($elements['#access'])) {
      $output['#access'] = $elements['#access'];
    }
  }

  return $output;
}

/**
 * Returns a renderable array for the value of a single field in an entity.
 *
 * The resulting output is a fully themed field with label and multiple values.
 *
 * This function can be used by third-party modules that need to output an
 * isolated field.
 * - Do not use inside node (or other entities) templates, use
 *   render($content[FIELD_NAME]) instead.
 * - Do not use to display all fields in an entity, use
 *   field_attach_prepare_view() and field_attach_view() instead.
 * - The field_view_value() function can be used to output a single formatted
 *   field value, without label or wrapping field markup.
 *
 * The function takes care of invoking the prepare_view steps. It also respects
 * field access permissions.
 *
 * @param \Drupal\Core\Entity\EntityInterface $entity
 *   The entity containing the field to display.
 * @param $field_name
 *   The name of the field to display.
 * @param $display_options
 *   Can be either:
 *   - The name of a view mode. The field will be displayed according to the
 *     display settings specified for this view mode in the $instance
 *     definition for the field in the entity's bundle. If no display settings
 *     are found for the view mode, the settings for the 'default' view mode
 *     will be used.
 *   - An array of display options. The following key/value pairs are allowed:
 *     - label: (string) Position of the label. The default 'field' theme
 *       implementation supports the values 'inline', 'above' and 'hidden'.
 *       Defaults to 'above'.
 *     - type: (string) The formatter to use. Defaults to the
 *       'default_formatter' for the field type, specified in hook_field_info().
 *       The default formatter will also be used if the requested formatter is
 *       not available.
 *     - settings: (array) Settings specific to the formatter. Defaults to the
 *       formatter's default settings, specified in hook_field_formatter_info().
 *     - weight: (float) The weight to assign to the renderable element.
 *       Defaults to 0.
 * @param $langcode
 *   (Optional) The language code the field values are to be shown in. The
 *   site's current language fallback logic will be applied when no values are
 *   available for the given language code. If no language code is provided the
 *   current language will be used.
 *
 * @return
 *   A renderable array for the field value.
 *
 * @see field_view_value()
 */
function field_view_field(EntityInterface $entity, $field_name, $display_options = array(), $langcode = NULL) {
  $output = array();
  $bundle = $entity->bundle();

  // Return nothing if the field doesn't exist.
  $instance = field_info_instance($entity->entityType(), $field_name, $bundle);
  if (!$instance) {
    return $output;
  }

  // Get the formatter object.
  if (is_string($display_options)) {
    $view_mode = $display_options;
    $formatter = entity_get_render_display($entity, $view_mode)->getFormatter($field_name);
  }
  else {
    $view_mode = '_custom';
    // hook_field_attach_display_alter() needs to receive the 'prepared'
    // $display_options, so we cannot let preparation happen internally.
    $field = field_info_field($field_name);
    $formatter_manager = drupal_container()->get('plugin.manager.field.formatter');
    $display_options = $formatter_manager->prepareConfiguration($field['type'], $display_options);
    $formatter = $formatter_manager->getInstance(array(
      'instance' => $instance,
      'view_mode' => $view_mode,
      'prepare' => FALSE,
      'configuration' => $display_options,
    ));
  }

  if ($formatter) {
    $display_langcode = field_language($entity, $field_name, $langcode);
    $items = $entity->{$field_name}[$display_langcode];

    // Invoke prepare_view steps if needed.
    if (empty($entity->_field_view_prepared)) {
      $id = $entity->id();

      // First let the field types do their preparation.
      $options = array('field_name' => $field_name, 'langcode' => $display_langcode);
      $null = NULL;
      _field_invoke_multiple('prepare_view', $entity->entityType(), array($id => $entity), $null, $null, $options);

      // Then let the formatter do its own specific massaging.
      $items_multi = array($id => $entity->{$field_name}[$display_langcode]);
      $formatter->prepareView(array($id => $entity), $display_langcode, $items_multi);
      $items = $items_multi[$id];
    }

    // Build the renderable array.
    $result = $formatter->view($entity, $display_langcode, $items);

    // Invoke hook_field_attach_view_alter() to let other modules alter the
    // renderable array, as in a full field_attach_view() execution.
    $context = array(
      'entity' => $entity,
      'view_mode' => $view_mode,
      'display_options' => $display_options,
    );
    drupal_alter('field_attach_view', $result, $context);

    if (isset($result[$field_name])) {
      $output = $result[$field_name];
    }
  }

  return $output;
}

/**
 * Returns the field items in the language they currently would be displayed.
 *
 * @param \Drupal\Core\Entity\EntityInterface $entity
 *   The entity containing the data to be displayed.
 * @param $field_name
 *   The field to be displayed.
 * @param $langcode
 *   (optional) The language code $entity->{$field_name} has to be displayed in.
 *   Defaults to the current language.
 *
 * @return
 *   An array of field items keyed by delta if available, FALSE otherwise.
 */
function field_get_items(EntityInterface $entity, $field_name, $langcode = NULL) {
  $langcode = field_language($entity, $field_name, $langcode);
  return isset($entity->{$field_name}[$langcode]) ? $entity->{$field_name}[$langcode] : FALSE;