class EditEntityFieldAccessCheck

edit.services.yml in drupal/core/modules/edit/edit.services.yml

drupal/core/modules/edit/edit.services.yml

access_check.edit.entity_field in drupal/core/modules/edit/edit.services.yml

Drupal\edit\Access\EditEntityFieldAccessCheck

class EditEntityFieldAccessCheck implements AccessCheckInterface, EditEntityFieldAccessCheckInterface {

  /**
   * Implements AccessCheckInterface::applies().
   */
  public function applies(Route $route) {
    return array_key_exists('_access_edit_entity_field', $route
      ->getRequirements());
  }

  /**
   * Implements AccessCheckInterface::access().
   */
  public function access(Route $route, Request $request) {

    // @todo Request argument validation and object loading should happen
    //   elsewhere in the request processing pipeline:
    //   http://drupal.org/node/1798214.
    $this
      ->validateAndUpcastRequestAttributes($request);
    return $this
      ->accessEditEntityField($request->attributes
      ->get('entity'), $request->attributes
      ->get('field_name'));
  }

  /**
   * Implements EntityFieldAccessCheckInterface::accessEditEntityField().
   */
  public function accessEditEntityField(EntityInterface $entity, $field_name) {
    return $entity
      ->access('update') && field_access('edit', $field_name, $entity
      ->entityType(), $entity);
  }

  /**
   * Validates and upcasts request attributes.
   */
  protected function validateAndUpcastRequestAttributes(Request $request) {

    // Load the entity.
    if (!is_object($entity = $request->attributes
      ->get('entity'))) {
      $entity_id = $entity;
      $entity_type = $request->attributes
        ->get('entity_type');
      if (!$entity_type || !entity_get_info($entity_type)) {
        throw new NotFoundHttpException();
      }
      $entity = entity_load($entity_type, $entity_id);
      if (!$entity) {
        throw new NotFoundHttpException();
      }
      $request->attributes
        ->set('entity', $entity);
    }

    // Validate the field name and language.
    $field_name = $request->attributes
      ->get('field_name');
    if (!$field_name || !field_info_instance($entity
      ->entityType(), $field_name, $entity
      ->bundle())) {
      throw new NotFoundHttpException();
    }
    $langcode = $request->attributes
      ->get('langcode');
    if (!$langcode || field_valid_language($langcode) !== $langcode) {
      throw new NotFoundHttpException();
    }
  }

}