diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/EntityReferenceFieldFormatter.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/EntityReferenceFieldFormatter.php
index 0e43086..92bf745 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/EntityReferenceFieldFormatter.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/EntityReferenceFieldFormatter.php
@@ -3,7 +3,7 @@
 namespace Drupal\Core\Field\Plugin\Field\FieldFormatter;
 
 use Drupal\Core\Entity\EntityDisplayBase;
-use Drupal\Core\Entity\EntityFieldManager;
+use Drupal\Core\Entity\EntityFieldManagerInterface;
 use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Field\BaseFieldDefinition;
@@ -60,14 +60,18 @@ class EntityReferenceFieldFormatter extends EntityReferenceFormatterBase impleme
   /**
    * The list of supported fields, prepared as options (machine_name => label).
    *
-   * @var array
+   * @var string[]
    */
   protected $availableFieldOptions;
 
   /**
    * The list of available formatters, keyed by field type.
    *
-   * @var array
+   * Each element of this array is an associative array, where keys are
+   * formatter machine names, and the values are formatter human-readable
+   * labels.
+   *
+   * @var array[]
    */
   protected $availableFormatterOptions;
 
@@ -94,7 +98,7 @@ public static function create(ContainerInterface $container, array $configuratio
    * Constructs a EntityReferenceReferencedEntityFieldFormatter object.
    *
    * @param string $plugin_id
-   *   The plugin_id for the formatter.
+   *   The formatter's plugin ID.
    * @param mixed $plugin_definition
    *   The plugin implementation definition.
    * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
@@ -107,7 +111,7 @@ public static function create(ContainerInterface $container, array $configuratio
    *   The view mode.
    * @param array $third_party_settings
    *   Any third party settings.
-   * @param \Drupal\Core\Entity\EntityFieldManager $entity_field_manager
+   * @param \Drupal\Core\Entity\EntityFieldManagerInterface $entity_field_manager
    *   The entity field manager.
    * @param \Drupal\Core\Field\FormatterPluginManager $formatter_plugin_manager
    *   The formatter plugin manager.
@@ -116,7 +120,7 @@ public static function create(ContainerInterface $container, array $configuratio
    * @param \Drupal\Core\Entity\EntityTypeBundleInfoInterface $entity_type_bundle_info
    *   The entity type bundle info.
    */
-  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, EntityFieldManager $entity_field_manager, FormatterPluginManager $formatter_plugin_manager, EntityTypeManagerInterface $entity_type_manager, EntityTypeBundleInfoInterface $entity_type_bundle_info) {
+  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, EntityFieldManagerInterface $entity_field_manager, FormatterPluginManager $formatter_plugin_manager, EntityTypeManagerInterface $entity_type_manager, EntityTypeBundleInfoInterface $entity_type_bundle_info) {
     parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
     $this->entityFieldManager = $entity_field_manager;
     $this->formatterPluginManager = $formatter_plugin_manager;
@@ -193,7 +197,6 @@ protected function getAvailableFieldOptions() {
     foreach ($target_bundles as $bundle) {
       // Fetch all fields present on each target bundle.
       $bundle_field_names = [];
-      /** @var \Drupal\Core\Field\FieldDefinitionInterface $field_definition */
       foreach ($this->entityFieldManager->getFieldDefinitions($entity_type_id, $bundle) as $field_machine_name => $field_definition) {
         // We use ::isDisplayConfigurable() to filter out the base fields that
         // should not be exposed to the user. The only exception to this is the
@@ -243,14 +246,14 @@ protected function getAvailableFormatterOptions(FieldStorageDefinitionInterface
   /**
    * Ajax callback for field name change.
    */
-  public static function onFieldNameChange(array $form, FormStateInterface $form_state) {
+  public static function onFieldNameChange(array &$form, FormStateInterface $form_state) {
     return $form['fields'][$form_state->get('plugin_settings_edit')]['plugin']['settings_edit_form']['settings'];
   }
 
   /**
    * Ajax callback for formatter type change.
    */
-  public static function onFormatterTypeChange(array $form, FormStateInterface $form_state) {
+  public static function onFormatterTypeChange(array &$form, FormStateInterface $form_state) {
     return $form['fields'][$form_state->get('plugin_settings_edit')]['plugin']['settings_edit_form']['settings']['settings'];
   }
 
@@ -330,7 +333,7 @@ public function settingsForm(array $form, FormStateInterface $form_state) {
         $settings_form = $formatter->settingsForm([], $form_state);
       }
       else {
-        drupal_set_message('Could not instantiate the formatter plugin, please choose a different formatter.', 'error');
+        drupal_set_message($this->t('Could not instantiate the formatter plugin, please choose a different formatter.'), 'error');
       }
       $form['settings'] = $settings_form;
       $form['settings']['#prefix'] = '<div id="field-formatter-settings-ajax">';
@@ -348,7 +351,7 @@ public function settingsSummary() {
 
     $field_name = $this->getFieldName();
     $formatter_type = $this->getFormatterType($field_name['machine_name']);
-    $summary[] = $this->t('Displaying the field "%field_name", using the formatter "%type".', [
+    $summary[] = $this->t('Displaying the field %field_name, using the formatter %type.', [
       '%field_name' => $field_name['label'],
       '%type' => $formatter_type['label'],
     ]);
@@ -369,20 +372,18 @@ public function settingsSummary() {
    *   The value of the setting, or NULL if absent.
    */
   public function getSetting($key, FormStateInterface $form_state = NULL) {
-    if (!$form_state) {
-      return parent::getSetting($key);
-    }
-
-    $field_name = $this->fieldDefinition->getName();
-    $form_state_key = [
-      'fields',
-      $field_name,
-      'settings_edit_form',
-      'settings',
-      $key,
-    ];
-    if ($form_state->hasValue($form_state_key)) {
-      return $form_state->getValue($form_state_key);
+    if ($form_state) {
+      $field_name = $this->fieldDefinition->getName();
+      $form_state_key = [
+        'fields',
+        $field_name,
+        'settings_edit_form',
+        'settings',
+        $key,
+      ];
+      if ($form_state->hasValue($form_state_key)) {
+        return $form_state->getValue($form_state_key);
+      }
     }
 
     return parent::getSetting($key);
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceFieldFormatterTest.php b/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceFieldFormatterTest.php
index 16058db..22c3713 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceFieldFormatterTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceFieldFormatterTest.php
@@ -9,7 +9,7 @@
 use Drupal\simpletest\NodeCreationTrait;
 
 /**
- * Tests the output of entity reference autocomplete widgets.
+ * Tests the "entity_reference_field" formatter.
  *
  * @group entity_reference
  */
@@ -85,7 +85,7 @@ protected function setUp() {
   }
 
   /**
-   * Tests the Referenced Entity Field formatter configuration.
+   * Tests the formatter's configuration and output.
    */
   public function testEntityReferenceFieldFormatter() {
     $page = $this->getSession()->getPage();
@@ -96,7 +96,7 @@ public function testEntityReferenceFieldFormatter() {
     $page->selectFieldOption('fields[field_related_content][type]', 'entity_reference_field');
     $result = $assert_session->waitForElementVisible('css', '.field-plugin-summary-cell .ajax-new-content');
     $this->assertNotEmpty($result);
-    $assert_session->pageTextContains('Displaying the field "Title", using the formatter "Plain text".');
+    $assert_session->pageTextContains('Displaying the field Title, using the formatter Plain text.');
 
     // Save without choosing anything and verify that the child title is shown
     // by default.
@@ -132,7 +132,7 @@ public function testEntityReferenceFieldFormatter() {
     $page->pressButton('Update');
     $result = $assert_session->waitForElementVisible('css', '.field-plugin-summary-cell .ajax-new-content');
     $this->assertNotEmpty($result);
-    $assert_session->pageTextContains('Displaying the field "Body", using the formatter "Default".');
+    $assert_session->pageTextContains('Displaying the field Body, using the formatter Default.');
     $page->pressButton('Save');
 
     $this->drupalGet('/node/' . $this->testParentNode->id());