⏫ Forwardport of #12061 to 2.3-develop branch

Applied pull request patch https://github.com/magento/magento2/pull/12061.patch (created by @atishgoswami) based on commit(s):
  1. b30eda5
  2. 9e63c27
  3. bd8758d
  4. 75379cf

app/code/Magento/Contact/Controller/Index/Post.php

@@ -9,12 +9,13 @@
 use Magento\Contact\Model\ConfigInterface;
 use Magento\Contact\Model\MailInterface;
 use Magento\Framework\App\Action\Context;
-use Magento\Framework\App\ObjectManager;
 use Magento\Framework\App\Request\DataPersistorInterface;
 use Magento\Framework\Controller\Result\Redirect;
 use Magento\Framework\Exception\LocalizedException;
 use Magento\Framework\HTTP\PhpEnvironment\Request;
 use Psr\Log\LoggerInterface;
+use Magento\Framework\App\ObjectManager;
+use Magento\Framework\DataObject;
 
 class Post extends \Magento\Contact\Controller\Index
 {
@@ -56,7 +57,7 @@ public function __construct(
         $this->context = $context;
         $this->mail = $mail;
         $this->dataPersistor = $dataPersistor;
-        $this->logger = $logger ?: \Magento\Framework\App\ObjectManager::getInstance()->get(LoggerInterface::class);
+        $this->logger = $logger ?: ObjectManager::getInstance()->get(LoggerInterface::class);
     }
 
     /**
@@ -71,45 +72,33 @@ public function execute()
         }
         try {
             $this->sendEmail($this->validatedParams());
-            $this->messageManager->addSuccess(
+            $this->messageManager->addSuccessMessage(
                 __('Thanks for contacting us with your comments and questions. We\'ll respond to you very soon.')
             );
-            $this->getDataPersistor()->clear('contact_us');
+            $this->dataPersistor->clear('contact_us');
         } catch (LocalizedException $e) {
             $this->messageManager->addErrorMessage($e->getMessage());
-            $this->getDataPersistor()->set('contact_us', $this->getRequest()->getParams());
+            $this->dataPersistor->set('contact_us', $this->getRequest()->getParams());
         } catch (\Exception $e) {
             $this->logger->critical($e);
             $this->messageManager->addErrorMessage(
                 __('An error occurred while processing your form. Please try again later.')
             );
-            $this->getDataPersistor()->set('contact_us', $this->getRequest()->getParams());
+            $this->dataPersistor->set('contact_us', $this->getRequest()->getParams());
         }
         return $this->resultRedirectFactory->create()->setPath('contact/index');
     }
 
-    /**
-     * Get Data Persistor
-     *
-     * @return DataPersistorInterface
-     */
-    private function getDataPersistor()
-    {
-        if ($this->dataPersistor === null) {
-            $this->dataPersistor = ObjectManager::getInstance()
-                ->get(DataPersistorInterface::class);
-        }
-
-        return $this->dataPersistor;
-    }
-
     /**
      * @param array $post Post data from contact form
      * @return void
      */
     private function sendEmail($post)
     {
-        $this->mail->send($post['email'], ['data' => new \Magento\Framework\DataObject($post)]);
+        $this->mail->send(
+            $post['email'],
+            ['data' => new DataObject($post)]
+        );
     }
 
     /**

app/code/Magento/Contact/Model/Mail.php

@@ -6,9 +6,10 @@
 namespace Magento\Contact\Model;
 
 use Magento\Framework\Mail\Template\TransportBuilder;
-use Magento\Framework\App\ObjectManager;
 use Magento\Framework\Translate\Inline\StateInterface;
 use Magento\Store\Model\StoreManagerInterface;
+use Magento\Framework\App\ObjectManager;
+use Magento\Framework\App\Area;
 
 class Mail implements MailInterface
 {
@@ -49,8 +50,7 @@ public function __construct(
         $this->contactsConfig = $contactsConfig;
         $this->transportBuilder = $transportBuilder;
         $this->inlineTranslation = $inlineTranslation;
-        $this->storeManager = $storeManager ?:
-            ObjectManager::getInstance()->get(StoreManagerInterface::class);
+        $this->storeManager = $storeManager ?: ObjectManager::getInstance()->get(StoreManagerInterface::class);
     }
 
     /**
@@ -71,7 +71,7 @@ public function send($replyTo, array $variables)
                 ->setTemplateIdentifier($this->contactsConfig->emailTemplate())
                 ->setTemplateOptions(
                     [
-                        'area' => 'frontend',
+                        'area' => Area::AREA_FRONTEND,
                         'store' => $this->storeManager->getStore()->getId()
                     ]
                 )

dev/tests/integration/testsuite/Magento/Contact/Controller/IndexTest.php

@@ -24,7 +24,7 @@ public function testPostAction()
         $this->assertRedirect($this->stringContains('contact/index'));
         $this->assertSessionMessages(
             $this->contains(
-                "Thanks for contacting us with your comments and questions. We'll respond to you very soon."
+                "Thanks for contacting us with your comments and questions. We'll respond to you very soon."
             ),
             \Magento\Framework\Message\MessageInterface::TYPE_SUCCESS
         );