diff --git a/core/modules/aggregator/src/Form/OpmlFeedAdd.php b/core/modules/aggregator/src/Form/OpmlFeedAdd.php
index d084bff..0ba285a 100644
--- a/core/modules/aggregator/src/Form/OpmlFeedAdd.php
+++ b/core/modules/aggregator/src/Form/OpmlFeedAdd.php
@@ -99,8 +99,8 @@ public function buildForm(array $form, FormStateInterface $form_state) {
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
     // If both fields are empty or filled, cancel.
-    $file_upload = $this->getRequest()->files->get('files[upload]', NULL, TRUE);
-    if ($form_state->isValueEmpty('remote') == empty($file_upload)) {
+    $all_files = $this->getRequest()->files->get('files', []);
+    if ($form_state->isValueEmpty('remote') == empty($all_files['upload'])) {
       $form_state->setErrorByName('remote', $this->t('<em>Either</em> upload a file or enter a URL.'));
     }
   }
diff --git a/core/modules/config/src/Form/ConfigImportForm.php b/core/modules/config/src/Form/ConfigImportForm.php
index c0f606b..f95b7a5 100644
--- a/core/modules/config/src/Form/ConfigImportForm.php
+++ b/core/modules/config/src/Form/ConfigImportForm.php
@@ -67,13 +67,16 @@ public function buildForm(array $form, FormStateInterface $form_state) {
    * {@inheritdoc}
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
-    $file_upload = $this->getRequest()->files->get('files[import_tarball]', NULL, TRUE);
-    if ($file_upload && $file_upload->isValid()) {
-      $form_state->setValue('import_tarball', $file_upload->getRealPath());
-    }
-    else {
-      $form_state->setErrorByName('import_tarball', $this->t('The file could not be uploaded.'));
+    $all_files = $this->getRequest()->files->get('files', []);
+    if (!empty($all_files['import_tarball'])) {
+      $file_upload = $all_files['import_tarball'];
+      if ($file_upload->isValid()) {
+        $form_state->setValue('import_tarball', $file_upload->getRealPath());
+        return;
+      }
     }
+
+    $form_state->setErrorByName('import_tarball', $this->t('The file could not be uploaded.'));
   }
 
   /**
diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 0e5b057..bbf3bff 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -709,11 +709,12 @@ function file_save_upload($form_field_name, $validators = array(), $destination
   $user = \Drupal::currentUser();
   static $upload_cache;
 
-  $file_upload = \Drupal::request()->files->get("files[$form_field_name]", NULL, TRUE);
+  $all_files = \Drupal::request()->files->get('files', array());
   // Make sure there's an upload to process.
-  if (empty($file_upload)) {
+  if (empty($all_files[$form_field_name])) {
     return NULL;
   }
+  $file_upload = $all_files[$form_field_name];
 
   // Return cached objects without processing since the file will have
   // already been processed and the paths in $_FILES will be invalid.
@@ -1168,10 +1169,11 @@ function file_managed_file_submit($form, FormStateInterface $form_state) {
  */
 function file_managed_file_save_upload($element, FormStateInterface $form_state) {
   $upload_name = implode('_', $element['#parents']);
-  $file_upload = \Drupal::request()->files->get("files[$upload_name]", NULL, TRUE);
-  if (empty($file_upload)) {
+  $all_files = \Drupal::request()->files->get('files', array());
+  if (empty($all_files[$upload_name])) {
     return FALSE;
   }
+  $file_upload = $all_files[$upload_name];
 
   $destination = isset($element['#upload_location']) ? $element['#upload_location'] : NULL;
   if (isset($destination) && !file_prepare_directory($destination, FILE_CREATE_DIRECTORY)) {
diff --git a/core/modules/link/src/Plugin/Validation/Constraint/LinkAccessConstraintValidator.php b/core/modules/link/src/Plugin/Validation/Constraint/LinkAccessConstraintValidator.php
index f2a5f83..b4be911 100644
--- a/core/modules/link/src/Plugin/Validation/Constraint/LinkAccessConstraintValidator.php
+++ b/core/modules/link/src/Plugin/Validation/Constraint/LinkAccessConstraintValidator.php
@@ -7,7 +7,7 @@
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidatorInterface;
-use Symfony\Component\Validator\ExecutionContextInterface;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
 /**
  * Validates the LinkAccess constraint.
@@ -17,7 +17,7 @@ class LinkAccessConstraintValidator implements ConstraintValidatorInterface, Con
   /**
    * Stores the validator's state during validation.
    *
-   * @var \Symfony\Component\Validator\ExecutionContextInterface
+   * @var \Symfony\Component\Validator\Context\ExecutionContextInterface
    */
   protected $context;
 
diff --git a/core/modules/link/src/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidator.php b/core/modules/link/src/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidator.php
index e85de58..8934c31 100644
--- a/core/modules/link/src/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidator.php
+++ b/core/modules/link/src/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidator.php
@@ -5,7 +5,7 @@
 use Drupal\Component\Utility\UrlHelper;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidatorInterface;
-use Symfony\Component\Validator\ExecutionContextInterface;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
 /**
  * Validates the LinkExternalProtocols constraint.
@@ -15,7 +15,7 @@ class LinkExternalProtocolsConstraintValidator implements ConstraintValidatorInt
   /**
    * Stores the validator's state during validation.
    *
-   * @var \Symfony\Component\Validator\ExecutionContextInterface
+   * @var \Symfony\Component\Validator\Context\ExecutionContextInterface
    */
   protected $context;
 
diff --git a/core/modules/link/src/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidator.php b/core/modules/link/src/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidator.php
index 86c3866..c68069b 100644
--- a/core/modules/link/src/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidator.php
+++ b/core/modules/link/src/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidator.php
@@ -7,7 +7,7 @@
 use Symfony\Component\Routing\Exception\RouteNotFoundException;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidatorInterface;
-use Symfony\Component\Validator\ExecutionContextInterface;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
 /**
  * Validates the LinkNotExistingInternal constraint.
@@ -17,7 +17,7 @@ class LinkNotExistingInternalConstraintValidator implements ConstraintValidatorI
   /**
    * Stores the validator's state during validation.
    *
-   * @var \Symfony\Component\Validator\ExecutionContextInterface
+   * @var \Symfony\Component\Validator\Context\ExecutionContextInterface
    */
   protected $context;
 
diff --git a/core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraint.php b/core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraint.php
index 3fe76a6..f2010fa 100644
--- a/core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraint.php
+++ b/core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraint.php
@@ -5,7 +5,7 @@
 use Drupal\link\LinkItemInterface;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidatorInterface;
-use Symfony\Component\Validator\ExecutionContextInterface;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
 /**
  * Validation constraint for links receiving data allowed by its settings.
@@ -20,7 +20,7 @@ class LinkTypeConstraint extends Constraint implements ConstraintValidatorInterf
   public $message = "The path '@uri' is invalid.";
 
   /**
-   * @var \Symfony\Component\Validator\ExecutionContextInterface
+   * @var \Symfony\Component\Validator\Context\ExecutionContextInterface
    */
   protected $context;
 
diff --git a/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkAccessConstraintValidatorTest.php b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkAccessConstraintValidatorTest.php
index 9e4623e..8271c59 100644
--- a/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkAccessConstraintValidatorTest.php
+++ b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkAccessConstraintValidatorTest.php
@@ -29,7 +29,7 @@ class LinkAccessConstraintValidatorTest extends UnitTestCase {
    * @dataProvider providerValidate
    */
   public function testValidate($value, $user, $valid) {
-    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context = $this->getMock('Symfony\Component\Validator\Context\ExecutionContextInterface');
 
     if ($valid) {
       $context->expects($this->never())
diff --git a/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
index 771b307..a326b57 100644
--- a/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
+++ b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
@@ -19,7 +19,7 @@ class LinkExternalProtocolsConstraintValidatorTest extends UnitTestCase {
    * @dataProvider providerValidate
    */
   public function testValidate($value, $valid) {
-    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context = $this->getMock('Symfony\Component\Validator\Context\ExecutionContextInterface');
 
     if ($valid) {
       $context->expects($this->never())
@@ -77,7 +77,7 @@ public function testValidateWithMalformedUri() {
       ->method('getUrl')
       ->willThrowException(new \InvalidArgumentException());
 
-    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context = $this->getMock('Symfony\Component\Validator\Context\ExecutionContextInterface');
     $context->expects($this->never())
       ->method('addViolation');
 
@@ -97,7 +97,7 @@ public function testValidateIgnoresInternalUrls() {
       ->method('getUrl')
       ->willReturn(Url::fromRoute('example.test'));
 
-    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context = $this->getMock('Symfony\Component\Validator\Context\ExecutionContextInterface');
     $context->expects($this->never())
       ->method('addViolation');
 
diff --git a/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidatorTest.php b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidatorTest.php
index 69776fd..2f0f7b5 100644
--- a/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidatorTest.php
+++ b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidatorTest.php
@@ -19,7 +19,7 @@ class LinkNotExistingInternalConstraintValidatorTest extends UnitTestCase {
    * @dataProvider providerValidate
    */
   public function testValidate($value, $valid) {
-    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context = $this->getMock('Symfony\Component\Validator\Context\ExecutionContextInterface');
 
     if ($valid) {
       $context->expects($this->never())
@@ -94,7 +94,7 @@ public function testValidateWithMalformedUri() {
       ->method('getUrl')
       ->willThrowException(new \InvalidArgumentException());
 
-    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context = $this->getMock('Symfony\Component\Validator\Context\ExecutionContextInterface');
     $context->expects($this->never())
       ->method('addViolation');
 
diff --git a/core/modules/update/src/Form/UpdateManagerInstall.php b/core/modules/update/src/Form/UpdateManagerInstall.php
index 5524f9e..f06b53a 100644
--- a/core/modules/update/src/Form/UpdateManagerInstall.php
+++ b/core/modules/update/src/Form/UpdateManagerInstall.php
@@ -122,8 +122,8 @@ public function buildForm(array $form, FormStateInterface $form_state) {
    * {@inheritdoc}
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
-    $uploaded_file = $this->getRequest()->files->get('files[project_upload]', NULL, TRUE);
-    if (!($form_state->getValue('project_url') xor !empty($uploaded_file))) {
+    $all_files = $this->getRequest()->files->get('files', []);
+    if (!($form_state->getValue('project_url') xor !empty($all_files['project_upload']))) {
       $form_state->setErrorByName('project_url', $this->t('You must either provide a URL or upload an archive file to install.'));
     }
   }
diff --git a/core/modules/user/src/Plugin/Validation/Constraint/UserMailRequired.php b/core/modules/user/src/Plugin/Validation/Constraint/UserMailRequired.php
index 5905e12..246628a 100644
--- a/core/modules/user/src/Plugin/Validation/Constraint/UserMailRequired.php
+++ b/core/modules/user/src/Plugin/Validation/Constraint/UserMailRequired.php
@@ -4,7 +4,7 @@
 
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidatorInterface;
-use Symfony\Component\Validator\ExecutionContextInterface;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
 /**
  * Checks if the user's email address is provided if required.
@@ -31,7 +31,7 @@ class UserMailRequired extends Constraint implements ConstraintValidatorInterfac
   public $message = '@name field is required.';
 
   /**
-   * @var \Symfony\Component\Validator\ExecutionContextInterface
+   * @var \Symfony\Component\Validator\Context\ExecutionContextInterface
    */
   protected $context;
 
diff --git a/core/modules/user/tests/src/Unit/Plugin/Validation/Constraint/ProtectedUserFieldConstraintValidatorTest.php b/core/modules/user/tests/src/Unit/Plugin/Validation/Constraint/ProtectedUserFieldConstraintValidatorTest.php
index d29c8c5..0370461 100644
--- a/core/modules/user/tests/src/Unit/Plugin/Validation/Constraint/ProtectedUserFieldConstraintValidatorTest.php
+++ b/core/modules/user/tests/src/Unit/Plugin/Validation/Constraint/ProtectedUserFieldConstraintValidatorTest.php
@@ -47,7 +47,7 @@ public function testValidate($items, $expected_violation, $name = FALSE) {
 
     // If a violation is expected, then the context's addViolation method will
     // be called, otherwise it should not be called.
-    $context = $this->getMock('Symfony\Component\Validator\ExecutionContextInterface');
+    $context = $this->getMock('Symfony\Component\Validator\Context\ExecutionContextInterface');
 
     if ($expected_violation) {
       $context->expects($this->once())