core-timestampdatetimewidget--blank-by-default--8-4-4.patch

diff --git a/core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php b/core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php
index 1ffa010916..2b1cefb6a5 100644
--- a/core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php
+++ b/core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php
@@ -23,13 +23,56 @@
  */
 class TimestampDatetimeWidget extends WidgetBase {
 
+  /**
+   * {@inheritdoc}
+   */
+  public static function defaultSettings() {
+    return [
+        'default_blank' => FALSE,
+      ] + parent::defaultSettings();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsForm(array $form, FormStateInterface $form_state) {
+    $element['default_blank'] = [
+      '#type' => 'checkbox',
+      '#title' => t('Leave blank by default.'),
+      '#default_value' => $this->getSetting('default_blank'),
+      '#weight' => -1,
+    ];
+    return $element;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsSummary() {
+    $summary = [];
+
+    $default_blank = $this->getSetting('default_blank');
+    $summary[] = t('Blank by default: @default_blank', ['@default_blank' => ($default_blank ? t('Yes') : 'No')]);
+
+    return $summary;
+  }
+
   /**
    * {@inheritdoc}
    */
   public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
     $date_format = DateFormat::load('html_date')->getPattern();
     $time_format = DateFormat::load('html_time')->getPattern();
+
     $default_value = isset($items[$delta]->value) ? DrupalDateTime::createFromTimestamp($items[$delta]->value) : '';
+    // Leave default as blank if the node is new and has setting.
+    if (
+      $this->getSetting('default_blank') &&
+      $form_state->getFormObject()->getEntity()->isNew()
+    ) {
+      $default_value = '';
+    }
+
     $element['value'] = $element + [
       '#type' => 'datetime',
       '#default_value' => $default_value,