diff -u b/core/modules/field/field.api.php b/core/modules/field/field.api.php
--- b/core/modules/field/field.api.php
+++ b/core/modules/field/field.api.php
@@ -711,11 +711,11 @@
 /**
  * Perform alterations on Field API widget types.
  *
- * @param $info
+ * @param array $info
  *   Array of informations on existing widget types, as collected by the
  *   annotation discovery mechanism.
  */
-function hook_field_widget_info_alter(&$info) {
+function hook_field_widget_info_alter(array &$info) {
   // Add a setting to a widget type.
   $info['text_textfield']['settings'] += array(
     'mymodule_additional_setting' => 'default value',
diff -u b/core/modules/field/field.info.inc b/core/modules/field/field.info.inc
--- b/core/modules/field/field.info.inc
+++ b/core/modules/field/field.info.inc
@@ -451,12 +451,12 @@
 /**
  * Returns information about field widgets from AnnotatedClassDiscovery.
  *
- * @param $widget_type
+ * @param string $widget_type
  *   (optional) A widget type name. If omitted, all widget types will be
  *   returned.
  *
- * @return
- *   Either a single widget type description, as provided by class annotations
+ * @return array
+ *   Either a single widget type description, as provided by class annotations,
  *   or an array of all existing widget types, keyed by widget type name.
  */
 function field_info_widget_types($widget_type = NULL) {
diff -u b/core/modules/field/lib/Drupal/field/FieldInstance.php b/core/modules/field/lib/Drupal/field/FieldInstance.php
--- b/core/modules/field/lib/Drupal/field/FieldInstance.php
+++ b/core/modules/field/lib/Drupal/field/FieldInstance.php
@@ -15,6 +15,8 @@
   public $definition;
 
   /**
+   * The widget object used for this instance.
+   * 
    * @var Drupal\field\Plugin\Type\Widget\WidgetInterface
    */
   protected $widget;