Type hint for \DateTimeInterface instead of \DateTime

app/code/Magento/Backend/Block/Widget/Grid/Column/Filter/Date.php

@@ -131,7 +131,7 @@ public function getHtml()
     public function getEscapedValue($index = null)
     {
         $value = $this->getValue($index);
-        if ($value instanceof \DateTime) {
+        if ($value instanceof \DateTimeInterface) {
             return $this->dateTimeFormatter->formatObject(
                 $value,
                 $this->_localeDate->getDateFormat(\IntlDateFormatter::SHORT)

app/code/Magento/Backend/Block/Widget/Grid/Column/Filter/Datetime.php

@@ -147,7 +147,7 @@ public function getEscapedValue($index = null)
     {
         if ($this->getColumn()->getFilterTime()) {
             $value = $this->getValue($index);
-            if ($value instanceof \DateTime) {
+            if ($value instanceof \DateTimeInterface) {
                 return $this->_localeDate->formatDateTime($value);
             }
             return $value;

app/code/Magento/CatalogRule/Model/ResourceModel/Rule.php

@@ -153,7 +153,7 @@ protected function _afterDelete(\Magento\Framework\Model\AbstractModel $rule)
      * Get catalog rules product price for specific date, website and
      * customer group
      *
-     * @param \DateTime $date
+     * @param \DateTimeInterface $date
      * @param int $wId
      * @param int $gId
      * @param int $pId
@@ -173,13 +173,13 @@ public function getRulePrice($date, $wId, $gId, $pId)
      * Retrieve product prices by catalog rule for specific date, website and customer group
      * Collect data with  product Id => price pairs
      *
-     * @param \DateTime $date
+     * @param \DateTimeInterface $date
      * @param int $websiteId
      * @param int $customerGroupId
      * @param array $productIds
      * @return array
      */
-    public function getRulePrices(\DateTime $date, $websiteId, $customerGroupId, $productIds)
+    public function getRulePrices(\DateTimeInterface $date, $websiteId, $customerGroupId, $productIds)
     {
         $connection = $this->getConnection();
         $select = $connection->select()

app/code/Magento/Eav/Model/Entity/Attribute/Backend/Datetime.php

@@ -76,7 +76,7 @@ public function formatDate($date)
         // unix timestamp given - simply instantiate date object
         if (is_scalar($date) && preg_match('/^[0-9]+$/', $date)) {
             $date = (new \DateTime())->setTimestamp($date);
-        } elseif (!($date instanceof \DateTime)) {
+        } elseif (!($date instanceof \DateTimeInterface)) {
             // normalized format expecting Y-m-d[ H:i:s]  - time is optional
             $date = new \DateTime($date);
         }

app/code/Magento/Indexer/Model/Mview/View/State.php

@@ -140,7 +140,7 @@ public function getUpdated()
     /**
      * Set state updated time
      *
-     * @param string|int|\DateTime $updated
+     * @param string|int|\DateTimeInterface $updated
      * @return $this
      */
     public function setUpdated($updated)

app/code/Magento/Reports/Model/ResourceModel/Report/AbstractReport.php

@@ -188,8 +188,8 @@ protected function _clearTableByDateRange(
      * @param string $table
      * @param string $column
      * @param string $whereColumn
-     * @param null|string|\DateTime $from
-     * @param null|string|\DateTime $to
+     * @param null|string|\DateTimeInterface $from
+     * @param null|string|\DateTimeInterface $to
      * @param [][] $additionalWhere
      * @param string $alias
      * @return \Magento\Framework\DB\Select
@@ -440,12 +440,12 @@ protected function _getTZOffsetTransitions($timezone, $from = null, $to = null)
         $tzTransitions = [];
         try {
             if (!empty($from)) {
-                $from = $from instanceof \DateTime
+                $from = $from instanceof \DateTimeInterface
                     ? $from->getTimestamp()
                     : (new \DateTime($from))->getTimestamp();
             }
 
-            $to = $to instanceof \DateTime
+            $to = $to instanceof \DateTimeInterface
                 ? $to
                 : new \DateTime($to);
             $nextPeriod = $this->getConnection()->formatDate(

app/code/Magento/Reports/Model/ResourceModel/Report/Collection.php

@@ -19,14 +19,14 @@ class Collection extends \Magento\Framework\Data\Collection
     /**
      * From value
      *
-     * @var string
+     * @var \DateTime
      */
     protected $_from;
 
     /**
      * To value
      *
-     * @var string
+     * @var \DateTime
      */
     protected $_to;
 
@@ -114,14 +114,14 @@ public function setPeriod($period)
      * Set interval
      * @codeCoverageIgnore
      *
-     * @param \DateTime $fromDate
-     * @param \DateTime $toDate
+     * @param \DateTimeInterface $fromDate
+     * @param \DateTimeInterface $toDate
      * @return $this
      */
-    public function setInterval($fromDate, $toDate)
+    public function setInterval(\DateTimeInterface $fromDate, \DateTimeInterface $toDate)
     {
-        $this->_from = $fromDate;
-        $this->_to = $toDate;
+        $this->_from = new \DateTime($fromDate->format('Y-m-d'), $fromDate->getTimezone());
+        $this->_to = new \DateTime($toDate->format('Y-m-d'), $toDate->getTimezone());
 
         return $this;
     }

app/code/Magento/Reports/Test/Unit/Model/ResourceModel/Report/CollectionTest.php

@@ -79,8 +79,8 @@ public function testGetStoreIds()
 
     /**
      * @param string $period
-     * @param \DateTime $fromDate
-     * @param \DateTime $toDate
+     * @param \DateTimeInterface $fromDate
+     * @param \DateTimeInterface $toDate
      * @param int $size
      * @dataProvider intervalsDataProvider
      * @return void
@@ -105,8 +105,8 @@ public function testGetPageSize()
 
     /**
      * @param string $period
-     * @param \DateTime $fromDate
-     * @param \DateTime $toDate
+     * @param \DateTimeInterface $fromDate
+     * @param \DateTimeInterface $toDate
      * @param int $size
      * @dataProvider intervalsDataProvider
      * @return void

app/code/Magento/Rule/Model/ResourceModel/AbstractResource.php

@@ -57,7 +57,7 @@ public function _beforeSave(\Magento\Framework\Model\AbstractModel $object)
     private function resolveDate(\Magento\Framework\Model\AbstractModel $object, $dateIdentifier)
     {
         $date = $object->getData($dateIdentifier);
-        if ($date instanceof \DateTime) {
+        if ($date instanceof \DateTimeInterface) {
             $object->setData($dateIdentifier, $date->format('Y-m-d H:i:s'));
         } elseif (!is_string($date) || empty($date)) {
             $object->setData($dateIdentifier, null);

app/code/Magento/Sales/Block/Adminhtml/Order/View/Tab/History.php

@@ -207,7 +207,7 @@ public function getItemComment(array $item)
      *
      * @param string $label
      * @param bool $notified
-     * @param \DateTime $created
+     * @param \DateTimeInterface $created
      * @param string $comment
      * @return array
      */

app/code/Magento/SalesRule/Model/Coupon/Massgenerator.php

@@ -171,7 +171,7 @@ public function generatePool()
             } while ($this->getResource()->exists($code));
 
             $expirationDate = $this->getToDate();
-            if ($expirationDate instanceof \DateTime) {
+            if ($expirationDate instanceof \DateTimeInterface) {
                 $expirationDate = $expirationDate->format('Y-m-d H:i:s');
             }
 

app/code/Magento/Theme/Model/ResourceModel/Design/Collection.php

@@ -60,7 +60,7 @@ public function joinStore()
     /**
      * Add date filter to collection
      *
-     * @param null|int|string|\DateTime $date
+     * @param null|int|string|\DateTimeInterface $date
      * @return $this
      */
     public function addDateFilter($date = null)

app/etc/di.xml

@@ -6,6 +6,7 @@
  */
 -->
 <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
+    <preference for="DateTimeInterface" type="DateTime" />
     <preference for="Psr\Log\LoggerInterface" type="Magento\Framework\Logger\Monolog" />
     <preference for="Magento\Framework\EntityManager\EntityMetadataInterface" type="Magento\Framework\EntityManager\EntityMetadata" />
     <preference for="Magento\Framework\EntityManager\HydratorInterface" type="Magento\Framework\EntityManager\Hydrator" />

lib/internal/Magento/Framework/DB/Adapter/AdapterInterface.php

@@ -667,7 +667,7 @@ public function quoteTableAs($ident, $alias = null, $auto = false);
     /**
      * Format Date to internal database date format
      *
-     * @param int|string|\DateTime $date
+     * @param int|string|\DateTimeInterface $date
      * @param boolean $includeTime
      * @return \Zend_Db_Expr
      */

lib/internal/Magento/Framework/DB/Adapter/Pdo/Mysql.php

@@ -332,7 +332,7 @@ public function getTransactionLevel()
     /**
      * Convert date to DB format
      *
-     * @param int|string|\DateTime $date
+     * @param int|string|\DateTimeInterface $date
      * @return \Zend_Db_Expr
      */
     public function convertDate($date)
@@ -343,7 +343,7 @@ public function convertDate($date)
     /**
      * Convert date and time to DB format
      *
-     * @param   int|string|\DateTime $datetime
+     * @param   int|string|\DateTimeInterface $datetime
      * @return \Zend_Db_Expr
      */
     public function convertDateTime($datetime)
@@ -2746,7 +2746,7 @@ public function addForeignKey(
     /**
      * Format Date to internal database date format
      *
-     * @param int|string|\DateTime $date
+     * @param int|string|\DateTimeInterface $date
      * @param bool $includeTime
      * @return \Zend_Db_Expr
      */

lib/internal/Magento/Framework/Mview/View/StateInterface.php

@@ -113,7 +113,7 @@ public function getUpdated();
     /**
      * Set state updated time
      *
-     * @param string|int|\DateTime $updated
+     * @param string|int|\DateTimeInterface $updated
      * @return \Magento\Framework\Mview\View\StateInterface
      */
     public function setUpdated($updated);

lib/internal/Magento/Framework/Stdlib/DateTime.php

@@ -39,14 +39,14 @@ class DateTime
     /**
      * Format date to internal format
      *
-     * @param string|\DateTime|bool|null $date
+     * @param string|\DateTimeInterface|bool|null $date
      * @param boolean $includeTime
      * @return string|null
      * @api
      */
     public function formatDate($date, $includeTime = true)
     {
-        if ($date instanceof \DateTime) {
+        if ($date instanceof \DateTimeInterface) {
             $format = $includeTime ? self::DATETIME_PHP_FORMAT : self::DATE_PHP_FORMAT;
             return $date->format($format);
         } elseif (empty($date)) {

lib/internal/Magento/Framework/Stdlib/DateTime/DateTime.php

@@ -97,7 +97,7 @@ public function date($format = null, $input = null)
     /**
      * Forms GMT timestamp
      *
-     * @param  int|string $input date in current timezone
+     * @param  int|string|\DateTimeInterface $input date in current timezone
      * @return int
      */
     public function gmtTimestamp($input = null)
@@ -106,6 +106,8 @@ public function gmtTimestamp($input = null)
             return (int)gmdate('U');
         } elseif (is_numeric($input)) {
             $result = $input;
+        } elseif ($input instanceof \DateTimeInterface) {
+            $result = $input->getTimestamp();
         } else {
             $result = strtotime($input);
         }
@@ -128,17 +130,23 @@ public function gmtTimestamp($input = null)
      */
     public function timestamp($input = null)
     {
-        if ($input === null) {
-            $result = $this->gmtTimestamp();
-        } elseif (is_numeric($input)) {
-            $result = $input;
-        } else {
-            $result = strtotime($input);
+        switch (true) {
+            case ($input === null):
+                $result = $this->gmtTimestamp();
+                break;
+            case (is_numeric($input)):
+                $result = $input;
+                break;
+            case ($input instanceof \DateTimeInterface):
+                $result = $input->getTimestamp();
+                break;
+            default:
+                $result = strtotime($input);
         }
+
         $date = $this->_localeDate->date($result);
-        $timestamp = $date->getTimestamp();
-        unset($date);
-        return $timestamp;
+
+        return $date->getTimestamp();
     }
 
     /**

lib/internal/Magento/Framework/Stdlib/DateTime/DateTimeFormatter.php

@@ -64,7 +64,7 @@ public function formatObject($object, $format = null, $locale = null)
     /**
      * Implements what IntlDateFormatter::formatObject() is in PHP 5.5+
      *
-     * @param \IntlCalendar|\DateTime $object
+     * @param \IntlCalendar|\DateTimeInterface $object
      * @param string|int|array|null $format
      * @param string|null $locale
      * @return string

lib/internal/Magento/Framework/Stdlib/DateTime/DateTimeFormatterInterface.php

@@ -13,7 +13,7 @@ interface DateTimeFormatterInterface
     /**
      * Returns a translated and localized date string
      *
-     * @param \IntlCalendar|\DateTime $object
+     * @param \IntlCalendar|\DateTimeInterface $object
      * @param string|int|array|null $format
      * @param string|null $locale
      * @return string

lib/internal/Magento/Framework/Stdlib/DateTime/Timezone.php

@@ -160,20 +160,25 @@ public function date($date = null, $locale = null, $useTimezone = true, $include
             ? $this->getConfigTimezone()
             : date_default_timezone_get();
 
-        if (empty($date)) {
-            return new \DateTime('now', new \DateTimeZone($timezone));
-        } elseif ($date instanceof \DateTime) {
-            return $date->setTimezone(new \DateTimeZone($timezone));
-        } elseif (!is_numeric($date)) {
-            $timeType = $includeTime ? \IntlDateFormatter::SHORT : \IntlDateFormatter::NONE;
-            $formatter = new \IntlDateFormatter(
-                $locale,
-                \IntlDateFormatter::SHORT,
-                $timeType,
-                new \DateTimeZone($timezone)
-            );
-            $date = $formatter->parse($date) ?: (new \DateTime($date))->getTimestamp();
+        switch (true) {
+            case (empty($date)):
+                return new \DateTime('now', new \DateTimeZone($timezone));
+            case ($date instanceof \DateTime):
+                return $date->setTimezone(new \DateTimeZone($timezone));
+            case ($date instanceof \DateTimeImmutable):
+                return new \DateTime($date->format('Y-m-d H:i:s'), $date->getTimezone());
+            case (!is_numeric($date)):
+                $timeType = $includeTime ? \IntlDateFormatter::SHORT : \IntlDateFormatter::NONE;
+                $formatter = new \IntlDateFormatter(
+                    $locale,
+                    \IntlDateFormatter::SHORT,
+                    $timeType,
+                    new \DateTimeZone($timezone)
+                );
+                $date = $formatter->parse($date) ?: (new \DateTime($date))->getTimestamp();
+                break;
         }
+
         return (new \DateTime(null, new \DateTimeZone($timezone)))->setTimestamp($date);
     }
 
@@ -197,7 +202,7 @@ public function formatDate($date = null, $format = \IntlDateFormatter::SHORT, $s
     {
         $formatTime = $showTime ? $format : \IntlDateFormatter::NONE;
 
-        if (!($date instanceof \DateTime)) {
+        if (!($date instanceof \DateTimeInterface)) {
             $date = new \DateTime($date);
         }
 
@@ -260,7 +265,7 @@ public function formatDateTime(
         $timezone = null,
         $pattern = null
     ) {
-        if (!($date instanceof \DateTime)) {
+        if (!($date instanceof \DateTimeInterface)) {
             $date = new \DateTime($date);
         }
 
@@ -296,8 +301,12 @@ public function formatDateTime(
      */
     public function convertConfigTimeToUtc($date, $format = 'Y-m-d H:i:s')
     {
-        if (!($date instanceof \DateTime)) {
-            $date = new \DateTime($date, new \DateTimeZone($this->getConfigTimezone()));
+        if (!($date instanceof \DateTimeInterface)) {
+            if ($date instanceof \DateTimeImmutable) {
+                $date = new \DateTime($date->format('Y-m-d H:i:s'), new \DateTimeZone($this->getConfigTimezone()));
+            } else {
+                $date = new \DateTime($date, new \DateTimeZone($this->getConfigTimezone()));
+            }
         } else {
             if ($date->getTimezone()->getName() !== $this->getConfigTimezone()) {
                 throw new LocalizedException(