Update to Drupal 8.2.0. For more information, see https://www.drupal.org/project/drupal/releases/8.2.0

core/modules/datetime_range/src/DateTimeRangeTrait.php

@@ -0,0 +1,78 @@
+<?php
+
+namespace Drupal\datetime_range;
+
+use Drupal\Core\Datetime\DrupalDateTime;
+use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
+
+/**
+ * Provides friendly methods for datetime range.
+ */
+trait DateTimeRangeTrait {
+
+  /**
+   * Creates a render array from a date object.
+   *
+   * @param \Drupal\Core\Datetime\DrupalDateTime $date
+   *   A date object.
+   *
+   * @return array
+   *   A render array.
+   */
+  protected function buildDate(DrupalDateTime $date) {
+    if ($this->getFieldSetting('datetime_type') == DateTimeItem::DATETIME_TYPE_DATE) {
+      // A date without time will pick up the current time, use the default.
+      datetime_date_default_time($date);
+    }
+    $this->setTimeZone($date);
+
+    $build = [
+      '#plain_text' => $this->formatDate($date),
+      '#cache' => [
+        'contexts' => [
+          'timezone',
+        ],
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Creates a render array from a date object with ISO date attribute.
+   *
+   * @param \Drupal\Core\Datetime\DrupalDateTime $date
+   *   A date object.
+   *
+   * @return array
+   *   A render array.
+   */
+  protected function buildDateWithIsoAttribute(DrupalDateTime $date) {
+    if ($this->getFieldSetting('datetime_type') == DateTimeItem::DATETIME_TYPE_DATE) {
+      // A date without time will pick up the current time, use the default.
+      datetime_date_default_time($date);
+    }
+
+    // Create the ISO date in Universal Time.
+    $iso_date = $date->format("Y-m-d\TH:i:s") . 'Z';
+
+    $this->setTimeZone($date);
+
+    $build = [
+      '#theme' => 'time',
+      '#text' => $this->formatDate($date),
+      '#html' => FALSE,
+      '#attributes' => [
+        'datetime' => $iso_date,
+      ],
+      '#cache' => [
+        'contexts' => [
+          'timezone',
+        ],
+      ],
+    ];
+
+    return $build;
+  }
+
+}