[Forwardport] Correct return type of methods and typo correction.

app/code/Magento/Backend/App/AbstractAction.php

@@ -217,6 +217,7 @@ public function dispatch(\Magento\Framework\App\RequestInterface $request)
             $this->_view->loadLayout(['default', 'adminhtml_denied'], true, true, false);
             $this->_view->renderLayout();
             $this->_request->setDispatched(true);
+
             return $this->_response;
         }
 
@@ -226,6 +227,11 @@ public function dispatch(\Magento\Framework\App\RequestInterface $request)
 
         $this->_processLocaleSettings();
 
+        // Need to preload isFirstPageAfterLogin (see https://github.com/magento/magento2/issues/15510)
+        if ($this->_auth->isLoggedIn()) {
+            $this->_auth->getAuthStorage()->isFirstPageAfterLogin();
+        }
+
         return parent::dispatch($request);
     }
 

app/code/Magento/Backend/Block/GlobalSearch.php

@@ -31,6 +31,7 @@ public function getWidgetInitOptions()
                 'filterProperty' => 'name',
                 'preventClickPropagation' => false,
                 'minLength' => 2,
+                'submitInputOnEnter' => false,
             ]
         ];
     }

app/code/Magento/Braintree/Gateway/Response/CancelDetailsHandler.php

@@ -0,0 +1,43 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Braintree\Gateway\Response;
+
+use Magento\Braintree\Gateway\SubjectReader;
+use Magento\Payment\Gateway\Response\HandlerInterface;
+use Magento\Sales\Model\Order\Payment;
+
+/**
+ * Handles response details for order cancellation request.
+ */
+class CancelDetailsHandler implements HandlerInterface
+{
+    /**
+     * @var SubjectReader
+     */
+    private $subjectReader;
+
+    /**
+     * @param SubjectReader $subjectReader
+     */
+    public function __construct(SubjectReader $subjectReader)
+    {
+        $this->subjectReader = $subjectReader;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function handle(array $handlingSubject, array $response)
+    {
+        $paymentDO = $this->subjectReader->readPayment($handlingSubject);
+        /** @var Payment $orderPayment */
+        $orderPayment = $paymentDO->getPayment();
+        $orderPayment->setIsTransactionClosed(true);
+        $orderPayment->setShouldCloseParentTransaction(true);
+    }
+}

app/code/Magento/Braintree/Gateway/SubjectReader.php

@@ -43,19 +43,20 @@ public function readPayment(array $subject)
     }
 
     /**
-     * Reads transaction from subject
+     * Reads transaction from the subject.
      *
      * @param array $subject
-     * @return \Braintree\Transaction
+     * @return Transaction
+     * @throws \InvalidArgumentException if the subject doesn't contain transaction details.
      */
     public function readTransaction(array $subject)
     {
         if (!isset($subject['object']) || !is_object($subject['object'])) {
-            throw new \InvalidArgumentException('Response object does not exist');
+            throw new \InvalidArgumentException('Response object does not exist.');
         }
 
         if (!isset($subject['object']->transaction)
-            && !$subject['object']->transaction instanceof Transaction
+            || !$subject['object']->transaction instanceof Transaction
         ) {
             throw new \InvalidArgumentException('The object is not a class \Braintree\Transaction.');
         }

app/code/Magento/Braintree/Gateway/Validator/CancelResponseValidator.php

@@ -0,0 +1,90 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Braintree\Gateway\Validator;
+
+use Braintree\Error\ErrorCollection;
+use Braintree\Error\Validation;
+use Magento\Payment\Gateway\Validator\AbstractValidator;
+use Magento\Payment\Gateway\Validator\ResultInterface;
+use Magento\Payment\Gateway\Validator\ResultInterfaceFactory;
+use Magento\Braintree\Gateway\SubjectReader;
+
+/**
+ * Decorates the general response validator to handle specific cases.
+ *
+ * This validator decorates the general response validator to handle specific cases like
+ * an expired or already voided on Braintree side authorization transaction.
+ */
+class CancelResponseValidator extends AbstractValidator
+{
+    /**
+     * @var int
+     */
+    private static $acceptableTransactionCode = 91504;
+
+    /**
+     * @var GeneralResponseValidator
+     */
+    private $generalResponseValidator;
+
+    /**
+     * @var SubjectReader
+     */
+    private $subjectReader;
+
+    /**
+     * @param ResultInterfaceFactory $resultFactory
+     * @param GeneralResponseValidator $generalResponseValidator
+     * @param SubjectReader $subjectReader
+     */
+    public function __construct(
+        ResultInterfaceFactory $resultFactory,
+        GeneralResponseValidator $generalResponseValidator,
+        SubjectReader $subjectReader
+    ) {
+        parent::__construct($resultFactory);
+        $this->generalResponseValidator = $generalResponseValidator;
+        $this->subjectReader = $subjectReader;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function validate(array $validationSubject): ResultInterface
+    {
+        $result = $this->generalResponseValidator->validate($validationSubject);
+        if (!$result->isValid()) {
+            $response = $this->subjectReader->readResponseObject($validationSubject);
+            if ($this->isErrorAcceptable($response->errors)) {
+                $result = $this->createResult(true, [__('Transaction is cancelled offline.')]);
+            }
+        }
+
+        return $result;
+    }
+
+    /**
+     * Checks if error collection has an acceptable error code.
+     *
+     * @param ErrorCollection $errorCollection
+     * @return bool
+     */
+    private function isErrorAcceptable(ErrorCollection $errorCollection): bool
+    {
+        $errors = $errorCollection->deepAll();
+        // there is should be only one acceptable error
+        if (count($errors) > 1) {
+            return false;
+        }
+
+        /** @var Validation $error */
+        $error = array_pop($errors);
+
+        return (int)$error->code === self::$acceptableTransactionCode;
+    }
+}

app/code/Magento/Braintree/Test/Unit/Gateway/Response/CancelDetailsHandlerTest.php

@@ -0,0 +1,61 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Braintree\Test\Unit\Gateway\Response;
+
+use Magento\Braintree\Gateway\Response\CancelDetailsHandler;
+use Magento\Braintree\Gateway\SubjectReader;
+use Magento\Payment\Gateway\Data\OrderAdapterInterface;
+use Magento\Payment\Gateway\Data\PaymentDataObject;
+use Magento\Sales\Model\Order\Payment;
+use PHPUnit\Framework\TestCase;
+use PHPUnit_Framework_MockObject_MockObject as MockObject;
+
+/**
+ * Tests \Magento\Braintree\Gateway\Response\CancelDetailsHandler.
+ */
+class CancelDetailsHandlerTest extends TestCase
+{
+    /**
+     * @var CancelDetailsHandler
+     */
+    private $handler;
+
+    /**
+     * @inheritdoc
+     */
+    protected function setUp()
+    {
+        $this->handler = new CancelDetailsHandler(new SubjectReader());
+    }
+
+    /**
+     * Checks a case when cancel handler closes the current and parent transactions.
+     *
+     * @return void
+     */
+    public function testHandle(): void
+    {
+        /** @var OrderAdapterInterface|MockObject $order */
+        $order = $this->getMockForAbstractClass(OrderAdapterInterface::class);
+        /** @var Payment|MockObject $payment */
+        $payment = $this->getMockBuilder(Payment::class)
+            ->disableOriginalConstructor()
+            ->setMethods(['setOrder'])
+            ->getMock();
+
+        $paymentDO = new PaymentDataObject($order, $payment);
+        $response = [
+            'payment' => $paymentDO,
+        ];
+
+        $this->handler->handle($response, []);
+
+        self::assertTrue($payment->getIsTransactionClosed(), 'The current transaction should be closed.');
+        self::assertTrue($payment->getShouldCloseParentTransaction(), 'The parent transaction should be closed.');
+    }
+}