drupal/core/modules/field/field.module

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

use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Language\Language;
use Drupal\Core\Template\Attribute;
use Drupal\field\FieldInterface;
use Drupal\field\FieldInstanceInterface;
use Drupal\Core\Entity\EntityNG;

/*
 * 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 __DIR__ . '/field.crud.inc';
require_once __DIR__ . '/field.info.inc';
require_once __DIR__ . '/field.multilingual.inc';
require_once __DIR__ . '/field.attach.inc';
require_once __DIR__ . '/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'.
 *
 * - @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 deletion of field or field_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, $type) {
  // It is not safe to call field_read_fields() during maintenance mode.
  if ($type == 'module' && module_hook($file->name, 'field_info') && !defined('MAINTENANCE_MODE')) {
    $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_entity_create().
 */
function field_entity_create(EntityInterface $entity) {
  $info = $entity->entityInfo();
  if (!empty($info['fieldable'])) {
    field_populate_default_values($entity, $entity->language()->id);
  }
}

/**
 * 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) {
  // Ensure we are working with a BC mode entity.
  $entity = $entity->getBCEntity();

  $entity_type = $entity->entityType();
  $langcode = $langcode ?: $entity->language()->id;
  foreach (field_info_instances($entity_type, $entity->bundle()) as $field_name => $instance) {
    $field = field_info_field($field_name);
    $field_langcode = field_is_translatable($entity_type, $field) ? $langcode : Language::LANGCODE_NOT_SPECIFIED;
    // We need to preserve existing values.
    if (empty($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();

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

    foreach ($instances as $field_name => $instance) {
      $definition = _field_generate_entity_field_definition($instance->getField());

      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;
}

/**
 * Generates an entity field definition for a configurable field.
 *
 * @param \Drupal\field\FieldInterface $field
 *   The field definition.
 * @param \Drupal\field\FieldInstanceInterface $instance
 *   (Optional) The field instance definition.
 *
 * @return array
 *   The entity field definition.
 */
function _field_generate_entity_field_definition(FieldInterface $field, FieldInstanceInterface $instance = NULL) {
  // @todo: Allow for adding field type settings.
  $definition = array(
    'label' => t('Field !name', array('!name' => $field->id())),
    'type' => 'field_item:' . $field->type,
    'list' => TRUE,
    'configurable' => TRUE,
    'translatable' => !empty($field->translatable),
  );
  if ($instance) {
    $definition['instance'] = $instance;
  }

  return $definition;
}

/**
 * Implements hook_field_widget_info_alter().
 */
function field_field_widget_info_alter(&$info) {
  // Add the Hidden widget to all field types.
  $info['hidden']['field_types'] = array_keys(field_info_field_types());
}

/**
 * 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.settings.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_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]' values for fields.
 */
function field_sync_field_status() {
  $module_handler = Drupal::moduleHandler();
  $state = Drupal::state();

  // Get both deleted and non-deleted field definitions.
  $fields = array();
  foreach (config_get_storage_names_with_prefix('field.field') as $name) {
    $field = Drupal::config($name)->get();
    $fields[$field['uuid']] = $field;
  }
  $deleted_fields = $state->get('field.field.deleted') ?: array();
  $fields += $deleted_fields;

  if (empty($fields)) {
    return;
  }

  // Set the 'module' and 'active' values for the current set of enabled
  // modules.
  $changed = array();
  $modules = $module_handler->getModuleList();
  foreach ($modules as $module => $module_info) {
    // Collect field types and storage backends exposed by the module.
    $field_types = (array) $module_handler->invoke($module, 'field_info');
    $storage_types = (array) $module_handler->invoke($module, 'field_storage_info');

    if ($field_types || $storage_types) {
      foreach ($fields as $uuid => &$field) {
        // Associate field types.
        if (isset($field_types[$field['type']]) && ($field['module'] !== $module || !$field['active'])) {
          $field['module'] = $module;
          $field['active'] = TRUE;
          $changed[$uuid] = $field;
        }
        // Associate storage backends.
        if (isset($storage_types[$field['storage']['type']]) && ($field['storage']['module'] !== $module || !$field['storage']['active'])) {
          $field['storage']['module'] = $module;
          $field['storage']['active'] = TRUE;
          $changed[$uuid] = $field;
        }
      }
    }
  }

  // Set fields with missing field type or storage modules to inactive.
  foreach ($fields as $uuid => &$field) {
    if (!isset($modules[$field['module']]) && $field['active']) {
      $field['active'] = FALSE;
      $changed[$uuid] = $field;
    }
    if (!isset($modules[$field['storage']['module']]) && $field['storage']['active']) {
      $field['storage']['active'] = FALSE;
      $changed[$uuid] = $field;
    }
  }

  // Store the updated field definitions.
  foreach ($changed as $uuid => $field) {
    if (!empty($field['deleted'])) {
      $deleted_fields[$uuid] = $field;
    }
    else {
      Drupal::config('field.field.' . $field['id'])
        ->set('module', $field['module'])
        ->set('active', $field['active'])
        ->set('storage.module', $field['storage']['module'])
        ->set('storage.active', $field['storage']['active'])
        ->save();
    }
  }
  $state->set('field.field.deleted', $deleted_fields);

  field_cache_clear();
}

/**
 * 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;
}

/**
 * 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:
 *     - status: 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(),
      'form_modes' => array(),
    );

    return $settings;
  }
}

/**
 * Returns form mode settings in a given bundle.
 *
 * @param string $entity_type
 *   The type of entity; e.g. 'node' or 'user'.
 * @param string $bundle
 *   The bundle name to return form mode settings for.
 *
 * @return
 *   An array keyed by form mode, with the following key/value pairs:
 *   - status: Boolean specifying whether the form mode uses a dedicated set of
 *     display options (TRUE), or the 'default' options (FALSE). Defaults to
 *     FALSE.
 */
function field_form_mode_settings($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['form_modes'];
    // Include form modes for which nothing has been stored yet, but whose
    // definition in hook_entity_info_alter() specify they should use custom
    // settings by default.
    $form_modes = entity_get_form_modes($entity_type);
    foreach ($form_modes as $form_mode => $form_mode_info) {
      if (!isset($settings[$form_mode]['status']) && $form_mode_info['status']) {
        $settings[$form_mode]['status'] = TRUE;
      }
    }
    $cache[$entity_type][$bundle] = $settings;
  }

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

/**
 * Returns view mode settings in a given bundle.
 *
 * @param $entity_type
 *   The type of entity; e.g. 'node' or 'user'.
 * @param $bundle
 *   The bundle name to return view mode settings for.
 *
 * @return
 *   An array keyed by view mode, with the following key/value pairs:
 *   - status: Boolean specifying whether the view mode uses a dedicated set of
 *     display options (TRUE), or the 'default' options (FALSE). Defaults to
 *     FALSE.
 */
function field_view_mode_settings($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.
    $view_modes = entity_get_view_modes($entity_type);
    foreach ($view_modes as $view_mode => $view_mode_info) {
      if (!isset($settings[$view_mode]['status']) && $view_mode_info['status']) {
        $settings[$view_mode]['status'] = TRUE;
      }
    }
    $cache[$entity_type][$bundle] = $settings;
  }

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

/**
 * 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_htmlcorrector(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();

  // Ensure we are working with a BC mode entity.
  $entity = $entity->getBCEntity();

  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. 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.
 *     - 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();
  $entity_type = $entity->entityType();

  // Return nothing if the field doesn't exist.
  $instance = field_info_instance($entity_type, $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, $view_mode)->getRenderer($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(
      'field_definition' => $instance,
      'view_mode' => $view_mode,
      'prepare' => FALSE,
      'configuration' => $display_options,
    ));
  }

  if ($formatter) {
    $display_langcode = field_language($entity, $field_name, $langcode);

    // Get the items.
    if ($entity->getNGEntity() instanceof EntityNG) {
      $items = $entity->getTranslation($display_langcode)->get($field_name);
      $definition = $entity->getPropertyDefinition($field_name);
    }
    else {
      $definitions = \Drupal::entityManager()->getFieldDefinitions($entity_type, $bundle);
      $definition = $definitions[$field_name];
      $itemsBC = isset($entity->{$field_name}[$display_langcode]) ? $entity->{$field_name}[$display_langcode] : array();
      $items = \Drupal::typedData()->create($definitions[$field_name], $itemsBC, $field_name, $entity);
    }

    // Invoke the formatter's prepareView() and view() methods.
    $id = $entity->id();
    $itemsBC_multi = array($id => $items->getValue());
    $formatter->prepareView(array($id => $entity), $display_langcode, $itemsBC_multi);
    $itemsBC = $itemsBC_multi[$id];
    $result = $formatter->view($entity, $display_langcode, $itemsBC);

    // 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,
      'langcode' => $display_langcode,
    );
    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 with available field items keyed by delta.
 */
function field_get_items(EntityInterface $entity, $field_name, $langcode = NULL) {
  $entity = $entity->getBCEntity();
  $langcode = field_language($entity, $field_name, $langcode);
  return isset($entity->{$field_name}[$langcode]) ? $entity->{$field_name}[$langcode] : array();
}

/**
 * Determines whether the user has access to a given field.
 *
 * @param string $op
 *   The operation to be performed. Possible values:
 *   - edit
 *   - view
 * @param \Drupal\field\FieldInterface $field
 *   The field on which the operation is to be performed.
 * @param $entity_type
 *   The type of $entity; for example, 'node' or 'user'.
 * @param $entity
 *   (optional) The entity for the operation.
 * @param $account
 *   (optional) The account to check, if not given use currently logged in user.
 *
 * @return
 *   TRUE if the operation is allowed; FALSE if the operation is denied.
 */
function field_access($op, FieldInterface $field, $entity_type, $entity = NULL, $account = NULL) {
  global $user;

  if (!isset($account)) {
    $account = $user;
  }

  foreach (module_implements('field_access') as $module) {
    $function = $module . '_field_access';
    $access = $function($op, $field, $entity_type, $entity, $account);
    if ($access === FALSE) {
      return FALSE;
    }
  }
  return TRUE;
}

/**
 * Extracts the bundle name from a bundle object.
 *
 * @param $entity_type
 *   The type of $entity; e.g., 'node' or 'user'.
 * @param $bundle
 *   The bundle object (or string if bundles for this entity type do not exist
 *   as standalone objects).
 *
 * @return
 *   The bundle name.
 */
function field_extract_bundle($entity_type, $bundle) {
  if (is_string($bundle)) {
    return $bundle;
  }

  $info = entity_get_info($entity_type);
  if (is_object($bundle) && isset($info['bundle_keys']['bundle']) && isset($bundle->{$info['bundle_keys']['bundle']})) {
    return $bundle->{$info['bundle_keys']['bundle']};
  }
}

/**
 * Implements hook_page_build().
 */
function field_page_build(&$page) {
  $path = drupal_get_path('module', 'field');
  $page['#attached']['css'][$path . '/css/field.module.css'] = array('every_page' => TRUE);
}

/**
 * Prepares variables for field templates.
 *
 * Default template: field.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - element: A render element representing the field.
 *   - attributes: A string containing the attributes for the wrapping div.
 *   - title_attributes: A string containing the attributes for the title.
 *   - content_attributes: A string containing the attributes for the content's
 *     div.
 */
function template_preprocess_field(&$variables, $hook) {
  $element = $variables['element'];

  // There's some overhead in calling check_plain() so only call it if the label
  // variable is being displayed. Otherwise, set it to NULL to avoid PHP
  // warnings if a theme implementation accesses the variable even when it's
  // supposed to be hidden. If a theme implementation needs to print a hidden
  // label, it needs to supply a preprocess function that sets it to the
  // sanitized element title or whatever else is wanted in its place.
  $variables['label_hidden'] = ($element['#label_display'] == 'hidden');
  $variables['label'] = $variables['label_hidden'] ? NULL : check_plain($element['#title']);

  // We want other preprocess functions and the theme implementation to have
  // fast access to the field item render arrays. The item render array keys
  // (deltas) should always be a subset of the keys in #items, and looping on
  // those keys is faster than calling element_children() or looping on all keys
  // within $element, since that requires traversal of all element properties.
  $variables['items'] = array();
  foreach ($element['#items'] as $delta => $item) {
    if (!empty($element[$delta])) {
      $variables['items'][$delta] = $element[$delta];
    }
  }

  // Add default CSS classes. Since there can be many fields rendered on a page,
  // save some overhead by calling strtr() directly instead of
  // drupal_html_class().
  $variables['field_name_css'] = strtr($element['#field_name'], '_', '-');
  $variables['field_type_css'] = strtr($element['#field_type'], '_', '-');
  $variables['attributes']['class'] = array(
    'field',
    'field-name-' . $variables['field_name_css'],
    'field-type-' . $variables['field_type_css'],
    'field-label-' . $element['#label_display'],
  );
  // Add a "clearfix" class to the wrapper since we float the label and the
  // field items in field.module.css if the label is inline.
  if ($element['#label_display'] == 'inline') {
    $variables['attributes']['class'][] = 'clearfix';
  }

  // Add specific suggestions that can override the default implementation.
  $variables['theme_hook_suggestions'] = array(
    'field__' . $element['#field_type'],
    'field__' . $element['#field_name'],
    'field__' . $element['#bundle'],
    'field__' . $element['#field_name'] . '__' . $element['#bundle'],
  );
}

/**
 * Theme process function for theme_field() and field.html.twig.
 *
 * @see theme_field()
 * @see field.html.twig
 */
function template_process_field(&$variables, $hook) {
  static $default_attributes;
  // The default theme implementation is a function, so template_process() does
  // not automatically run, so we need to flatten the classes and attributes
  // here. For best performance, only instantiate Drupal\Core\Template\Attribute
  // when needed, and note that template_preprocess_field() does not initialize
  // the *_attributes variables.
  if (!isset($default_attributes)) {
    $default_attributes = new Attribute;
  }
  $variables['attributes'] = isset($variables['attributes']) ? new Attribute($variables['attributes']) : clone $default_attributes;
  $variables['title_attributes'] = isset($variables['title_attributes']) ? new Attribute($variables['title_attributes']) : clone($default_attributes);
  $variables['content_attributes'] = isset($variables['content_attributes']) ? new Attribute($variables['content_attributes']) : clone($default_attributes);
  foreach ($variables['items'] as $delta => $item) {
    $variables['item_attributes'][$delta] = isset($variables['item_attributes'][$delta]) ? new Attribute($variables['item_attributes'][$delta]) : clone($default_attributes);
  }
}

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

/**
 * Returns HTML for a field.
 *
 * This is the default theme implementation to display the value of a field.
 * Theme developers who are comfortable with overriding theme functions may do
 * so in order to customize this markup. This function can be overridden with
 * varying levels of specificity. For example, for a field named 'body'
 * displayed on the 'article' content type, any of the following functions will
 * override this default implementation. The first of these functions that
 * exists is used:
 * - THEMENAME_field__body__article()
 * - THEMENAME_field__article()
 * - THEMENAME_field__body()
 * - THEMENAME_field()
 *
 * Theme developers who prefer to customize templates instead of overriding
 * functions may copy the "field.html.twig" from the "modules/field/theme"
 * folder of the Drupal installation to somewhere within the theme's folder and
 * customize it, just like customizing other Drupal templates such as
 * page.html.twig or node.html.twig. However, it takes longer for the server to
 * process templates than to call a function, so for websites with many fields
 * displayed on a page, this can result in a noticeable slowdown of the website.
 * For these websites, developers are discouraged from placing a field.html.twig
 * file into the theme's folder, but may customize templates for specific
 * fields. For example, for a field named 'body' displayed on the 'article'
 * content type, any of the following templates will override this default
 * implementation. The first of these templates that exists is used:
 * - field--body--article.html.twig
 * - field--article.html.twig
 * - field--body.html.twig
 * - field.html.twig
 * So, if the body field on the article content type needs customization, a
 * field--body--article.html.twig file can be added within the theme's folder.
 * Because it's a template, it will result in slightly more time needed to
 * display that field, but it will not impact other fields, and therefore, is
 * unlikely to cause a noticeable change in website performance. A very rough
 * guideline is that if a page is being displayed with more than 100 fields and
 * they are all themed with a template instead of a function, it can add up to
 * 5% to the time it takes to display that page. This is a guideline only and
 * the exact performance impact depends on the server configuration and the
 * details of the website.
 *
 * @param $variables
 *   An associative array containing:
 *   - label_hidden: A boolean indicating whether to show or hide the field
 *     label.
 *   - title_attributes: A string containing the attributes for the title.
 *   - label: The label for the field.
 *   - content_attributes: A string containing the attributes for the content's
 *     div.
 *   - items: An array of field items.
 *   - item_attributes: An array of attributes for each item.
 *   - classes: A string containing the classes for the wrapping div.
 *   - attributes: A string containing the attributes for the wrapping div.
 *
 * @see template_preprocess_field()
 * @see template_process_field()
 * @see field.html.twig
 *
 * @ingroup themeable
 */
function theme_field($variables) {
  $output = '';

  // Render the label, if it's not hidden.
  if (!$variables['label_hidden']) {
    $output .= '<div class="field-label"' . $variables['title_attributes'] . '>' . $variables['label'] . '</div>';
  }

  // Render the items.
  $output .= '<div class="field-items"' . $variables['content_attributes'] . '>';
  foreach ($variables['items'] as $delta => $item) {
    $classes = 'field-item ' . ($delta % 2 ? 'odd' : 'even');
    $output .= '<div class="' . $classes . '"' . $variables['item_attributes'][$delta] . '>' . drupal_render($item) . '</div>';
  }
  $output .= '</div>';

  // Render the top-level DIV.
  $output = '<div' . $variables['attributes'] . '>' . $output . '</div>';

  return $output;
}

/**
 * Assembles a partial entity structure with initial IDs.
 *
 * @param stdClass $ids
 *   An object with the properties entity_type (required), entity_id (required),
 *   revision_id (optional) and bundle (optional).
 *
 * @return \Drupal\Core\Entity\EntityInterface
 *   An entity, initialized with the provided IDs.
 */
function _field_create_entity_from_ids($ids) {
  $id_properties = array();
  $info = entity_get_info($ids->entity_type);
  if (isset($info['entity_keys']['id'])) {
    $id_properties[$info['entity_keys']['id']] = $ids->entity_id;
  }
  if (!empty($info['entity_keys']['revision']) && isset($ids->revision_id)) {
    $id_properties[$info['entity_keys']['revision']] = $ids->revision_id;
  }
  if (!empty($info['entity_keys']['bundle']) && isset($ids->bundle)) {
    $id_properties[$info['entity_keys']['bundle']] = $ids->bundle;
  }
  return entity_create($ids->entity_type, $id_properties);
}

/**
 * Implements hook_hook_info().
 */
function field_hook_info() {
  $hooks['field_views_data'] = array(
    'group' => 'views',
  );
  $hooks['field_views_data_alter'] = array(
    'group' => 'views',
  );

  return $hooks;
}