Issue #2076321 by yched, Mac_Weber, pcambra: Link "title" validation should use a static method

core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php

@@ -133,6 +133,8 @@ protected static function getUserEnteredStringAsUri($string) {
   }
 
   /**
+   * Form element validation handler for the 'uri' element.
+   *
    * Disallows saving inaccessible or untrusted URLs.
    */
   public static function validateUriElement($element, FormStateInterface $form_state, $form) {
@@ -149,6 +151,18 @@ public static function validateUriElement($element, FormStateInterface $form_sta
     }
   }
 
+  /**
+   * Form element validation handler for the 'title' element.
+   *
+   * Conditionally requires the link title if a URL value was filled in.
+   */
+  public static function validateTitleElement(&$element, FormStateInterface $form_state, $form) {
+    if ($element['uri']['#value'] !== '' && $element['title']['#value'] === '') {
+      $element['title']['#required'] = TRUE;
+      $form_state->setError($element['title'], t('!name field is required.', array('!name' => $element['title']['#title'])));
+    }
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -207,7 +221,7 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
     // non-empty. Omit the validation on the field edit form, since the field
     // settings cannot be saved otherwise.
     if (!$this->isDefaultValueWidget($form_state) && $this->getFieldSetting('title') == DRUPAL_REQUIRED) {
-      $element['#element_validate'][] = array($this, 'validateTitle');
+      $element['#element_validate'][] = array(get_called_class(), 'validateTitleElement');
     }
 
     // Exposing the attributes array in the widget is left for alternate and more
@@ -311,18 +325,6 @@ public function settingsSummary() {
     return $summary;
   }
 
-  /**
-   * Form element validation handler; Validates the title property.
-   *
-   * Conditionally requires the link title if a URL value was filled in.
-   */
-  public function validateTitle(&$element, FormStateInterface $form_state, $form) {
-    if ($element['uri']['#value'] !== '' && $element['title']['#value'] === '') {
-      $element['title']['#required'] = TRUE;
-      $form_state->setError($element['title'], $this->t('!name field is required.', array('!name' => $element['title']['#title'])));
-    }
-  }
-
   /**
    * {@inheritdoc}
    */