diff --git a/core/lib/Drupal/Core/Form/FormBase.php b/core/lib/Drupal/Core/Form/FormBase.php
index 42ec8befc81cf3f6dd34b0fb0cc8c7f0370ce125..3dfd81c0a9e47e98e4c7ca1dab5434e9378db087 100644
--- a/core/lib/Drupal/Core/Form/FormBase.php
+++ b/core/lib/Drupal/Core/Form/FormBase.php
@@ -48,6 +48,13 @@ abstract class FormBase extends DependencySerialization implements FormInterface
    */
   protected $configFactory;
 
+  /**
+   * The form error handler.
+   *
+   * @var \Drupal\Core\Form\FormErrorInterface
+   */
+  protected $errorHandler;
+
   /**
    * {@inheritdoc}
    */
@@ -214,4 +221,33 @@ protected function container() {
     return \Drupal::getContainer();
   }
 
+  /**
+   * Returns the form error handler.
+   *
+   * @return \Drupal\Core\Form\FormErrorInterface
+   *   The form error handler.
+   */
+  protected function errorHandler() {
+    if (!$this->errorHandler) {
+      $this->errorHandler = \Drupal::service('form_builder');
+    }
+    return $this->errorHandler;
+  }
+
+  /**
+   * Files an error against a form element.
+   *
+   * @param string $name
+   *   The name of the form element.
+   * @param array $form_state
+   *   An associative array containing the current state of the form.
+   * @param string $message
+   *   (optional) The error message to present to the user.
+   *
+   * @see \Drupal\Core\Form\FormErrorInterface::setErrorByName()
+   */
+  protected function setFormError($name, array &$form_state, $message = '') {
+    $this->errorHandler()->setErrorByName($name, $form_state, $message);
+  }
+
 }
diff --git a/core/lib/Drupal/Core/Form/FormErrorInterface.php b/core/lib/Drupal/Core/Form/FormErrorInterface.php
index c642ed3ae3d6ac46a117885ded2dd26e84aa352d..e203908c6848554ec18ef81235180610509e3c1d 100644
--- a/core/lib/Drupal/Core/Form/FormErrorInterface.php
+++ b/core/lib/Drupal/Core/Form/FormErrorInterface.php
@@ -92,15 +92,15 @@ interface FormErrorInterface {
    * would be triggered if the input processing and validation steps were fully
    * skipped.
    *
-   * @param $name
+   * @param string $name
    *   The name of the form element. If the #parents property of your form
    *   element is array('foo', 'bar', 'baz') then you may set an error on 'foo'
    *   or 'foo][bar][baz'. Setting an error on 'foo' sets an error for every
    *   element where the #parents array starts with 'foo'.
    * @param array $form_state
    *   An associative array containing the current state of the form.
-   * @param $message
-   *   The error message to present to the user.
+   * @param string $message
+   *   (optional) The error message to present to the user.
    *
    * @return mixed
    *   Return value is for internal use only. To get a list of errors, use
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
index c47d28fbe0f7b7b9dc5d9edba298a161734747a7..fd952050fc7888637ec3b8f42f0af3ca79b85922 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/FeedFormController.php
@@ -70,10 +70,10 @@ public function validate(array $form, array &$form_state) {
     $result = $feed_storage_controller->getFeedDuplicates($feed);
     foreach ($result as $item) {
       if (strcasecmp($item->title, $feed->label()) == 0) {
-        form_set_error('title', $form_state, $this->t('A feed named %feed already exists. Enter a unique title.', array('%feed' => $feed->label())));
+        $this->setFormError('title', $form_state, $this->t('A feed named %feed already exists. Enter a unique title.', array('%feed' => $feed->label())));
       }
       if (strcasecmp($item->url, $feed->url->value) == 0) {
-        form_set_error('url', $form_state, $this->t('A feed with this URL %url already exists. Enter a unique URL.', array('%url' => $feed->url->value)));
+        $this->setFormError('url', $form_state, $this->t('A feed with this URL %url already exists. Enter a unique URL.', array('%url' => $feed->url->value)));
       }
     }
     parent::validate($form, $form_state);
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php b/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
index f25dc5a860b838477f0f79cbf5ca2bd96e8319ba..8aec75b513bca5cc81d4131266d112915b1e5778 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
@@ -118,7 +118,7 @@ public function validateForm(array &$form, array &$form_state) {
     // If both fields are empty or filled, cancel.
     $file_upload = $this->getRequest()->files->get('files[upload]', NULL, TRUE);
     if (empty($form_state['values']['remote']) == empty($file_upload)) {
-      form_set_error('remote', $form_state, $this->t('You must <em>either</em> upload a file or enter a URL.'));
+      $this->setFormError('remote', $form_state, $this->t('You must <em>either</em> upload a file or enter a URL.'));
     }
   }
 
diff --git a/core/modules/ban/lib/Drupal/ban/Form/BanAdmin.php b/core/modules/ban/lib/Drupal/ban/Form/BanAdmin.php
index f03d2927931b0387e0c0a39c2e1bfe644e9408a8..29ca186ffeb3c99b398f81b1afbb8d72e61ee1da 100644
--- a/core/modules/ban/lib/Drupal/ban/Form/BanAdmin.php
+++ b/core/modules/ban/lib/Drupal/ban/Form/BanAdmin.php
@@ -105,13 +105,13 @@ public function buildForm(array $form, array &$form_state, $default_ip = '') {
   public function validateForm(array &$form, array &$form_state) {
     $ip = trim($form_state['values']['ip']);
     if ($this->ipManager->isBanned($ip)) {
-      form_set_error('ip', $form_state, $this->t('This IP address is already banned.'));
+      $this->setFormError('ip', $form_state, $this->t('This IP address is already banned.'));
     }
     elseif ($ip == $this->getRequest()->getClientIP()) {
-      form_set_error('ip', $form_state, $this->t('You may not ban your own IP address.'));
+      $this->setFormError('ip', $form_state, $this->t('You may not ban your own IP address.'));
     }
     elseif (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_RES_RANGE) == FALSE) {
-      form_set_error('ip', $form_state, $this->t('Enter a valid IP address.'));
+      $this->setFormError('ip', $form_state, $this->t('Enter a valid IP address.'));
     }
   }
 
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockFormController.php b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockFormController.php
index 8b04b7e63a6025542d30afd47d4395d14560b060..11f34c1fe5bd7bdab7b87c6147250f3fd2253740 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockFormController.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/CustomBlockFormController.php
@@ -237,7 +237,7 @@ public function validateForm(array &$form, array &$form_state) {
       // @todo Inject this once https://drupal.org/node/2060865 is in.
       $exists = \Drupal::entityManager()->getStorageController('custom_block')->loadByProperties(array('info' => $form_state['values']['info']));
       if (!empty($exists)) {
-        form_set_error('info', $form_state, t('A block with description %name already exists.', array(
+        $this->setFormError('info', $form_state, $this->t('A block with description %name already exists.', array(
         '%name' => $form_state['values']['info']
       )));
       }
diff --git a/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php b/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
index c51633882434ef09f9bf61c93c4eea9cc0705853..07beef0e4e4d5236f6573fd4484218731aa0fb87 100644
--- a/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
+++ b/core/modules/book/lib/Drupal/book/Form/BookAdminEditForm.php
@@ -96,7 +96,7 @@ public function buildForm(array $form, array &$form_state, NodeInterface $node =
    */
   public function validateForm(array &$form, array &$form_state) {
     if ($form_state['values']['tree_hash'] != $form_state['values']['tree_current_hash']) {
-      form_set_error('', $form_state, $this->t('This book has been modified by another user, the changes could not be saved.'));
+      $this->setFormError('', $form_state, $this->t('This book has been modified by another user, the changes could not be saved.'));
     }
   }
 
diff --git a/core/modules/book/lib/Drupal/book/Form/BookSettingsForm.php b/core/modules/book/lib/Drupal/book/Form/BookSettingsForm.php
index 1bc25a77a5c7dfed3d71a412f36c36077f6d911f..499b70e81de17971d1529f9aef11e28f8f795a35 100644
--- a/core/modules/book/lib/Drupal/book/Form/BookSettingsForm.php
+++ b/core/modules/book/lib/Drupal/book/Form/BookSettingsForm.php
@@ -53,7 +53,7 @@ public function buildForm(array $form, array &$form_state) {
   public function validateForm(array &$form, array &$form_state) {
     $child_type = $form_state['values']['book_child_type'];
     if (empty($form_state['values']['book_allowed_types'][$child_type])) {
-      form_set_error('book_child_type', $form_state, $this->t('The content type for the %add-child link must be one of those selected as an allowed book outline type.', array('%add-child' => $this->t('Add child page'))));
+      $this->setFormError('book_child_type', $form_state, $this->t('The content type for the %add-child link must be one of those selected as an allowed book outline type.', array('%add-child' => $this->t('Add child page'))));
     }
 
     parent::validateForm($form, $form_state);
diff --git a/core/modules/comment/lib/Drupal/comment/CommentFormController.php b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
index 10ac40709be1ee77e4a581f214866fae4159b84f..d0066a89810a456cc8d18e6b51506929ee5ffeac 100644
--- a/core/modules/comment/lib/Drupal/comment/CommentFormController.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
@@ -275,10 +275,10 @@ public function validate(array $form, array &$form_state) {
 
       $date = $form_state['values']['date'];
       if ($date instanceOf DrupalDateTime && $date->hasErrors()) {
-        form_set_error('date', $form_state, $this->t('You have to specify a valid date.'));
+        $this->setFormError('date', $form_state, $this->t('You have to specify a valid date.'));
       }
       if ($form_state['values']['name'] && !$form_state['values']['is_anonymous'] && !$account) {
-        form_set_error('name', $form_state, $this->t('You have to specify a valid author.'));
+        $this->setFormError('name', $form_state, $this->t('You have to specify a valid author.'));
       }
     }
     elseif ($form_state['values']['is_anonymous']) {
@@ -288,7 +288,7 @@ public function validate(array $form, array &$form_state) {
       if ($form_state['values']['name']) {
         $accounts = $this->entityManager->getStorageController('user')->loadByProperties(array('name' => $form_state['values']['name']));
         if (!empty($accounts)) {
-          form_set_error('name', $form_state, $this->t('The name you used belongs to a registered user.'));
+          $this->setFormError('name', $form_state, $this->t('The name you used belongs to a registered user.'));
         }
       }
     }
diff --git a/core/modules/config/lib/Drupal/config/Form/ConfigImportForm.php b/core/modules/config/lib/Drupal/config/Form/ConfigImportForm.php
index 729603498fcfad2f7c9f2b9a1f498dc9a5f5cc8f..bb5f4edbf7bdbc0025c13d08970f0069552e6ecf 100644
--- a/core/modules/config/lib/Drupal/config/Form/ConfigImportForm.php
+++ b/core/modules/config/lib/Drupal/config/Form/ConfigImportForm.php
@@ -79,7 +79,7 @@ public function validateForm(array &$form, array &$form_state) {
       $form_state['values']['import_tarball'] = $file_upload->getRealPath();
     }
     else {
-      form_set_error('import_tarball', $form_state, $this->t('The import tarball could not be uploaded.'));
+      $this->setFormError('import_tarball', $form_state, $this->t('The import tarball could not be uploaded.'));
     }
   }
 
@@ -100,7 +100,7 @@ public function submitForm(array &$form, array &$form_state) {
         $form_state['redirect_route']['route_name'] = 'config.sync';
       }
       catch (\Exception $e) {
-        form_set_error('import_tarball', $form_state, $this->t('Could not extract the contents of the tar file. The error message is <em>@message</em>', array('@message' => $e->getMessage())));
+        $this->setFormError('import_tarball', $form_state, $this->t('Could not extract the contents of the tar file. The error message is <em>@message</em>', array('@message' => $e->getMessage())));
       }
       drupal_unlink($path);
     }
diff --git a/core/modules/config/lib/Drupal/config/Form/ConfigSingleImportForm.php b/core/modules/config/lib/Drupal/config/Form/ConfigSingleImportForm.php
index 24913c78b4ec7bac091cacf5623dfb34212fa74c..edddce32e77e6007b0998293eabae61abb685be1 100644
--- a/core/modules/config/lib/Drupal/config/Form/ConfigSingleImportForm.php
+++ b/core/modules/config/lib/Drupal/config/Form/ConfigSingleImportForm.php
@@ -183,7 +183,7 @@ public function validateForm(array &$form, array &$form_state) {
       $entity_storage = $this->entityManager->getStorageController($form_state['values']['config_type']);
       // If an entity ID was not specified, set an error.
       if (!isset($data[$id_key])) {
-        form_set_error('import', $form_state, $this->t('Missing ID key "@id_key" for this @entity_type import.', array('@id_key' => $id_key, '@entity_type' => $definition['label'])));
+        $this->setFormError('import', $form_state, $this->t('Missing ID key "@id_key" for this @entity_type import.', array('@id_key' => $id_key, '@entity_type' => $definition['label'])));
         return;
       }
       $uuid_key = $definition['entity_keys']['uuid'];
@@ -191,17 +191,17 @@ public function validateForm(array &$form, array &$form_state) {
       if ($entity = $entity_storage->load($data[$id_key])) {
         $this->configExists = $entity;
         if (!isset($data[$uuid_key])) {
-          form_set_error('import', $form_state, $this->t('An entity with this machine name already exists but the import did not specify a UUID.'));
+          $this->setFormError('import', $form_state, $this->t('An entity with this machine name already exists but the import did not specify a UUID.'));
           return;
         }
         if ($data[$uuid_key] !== $entity->uuid()) {
-          form_set_error('import', $form_state, $this->t('An entity with this machine name already exists but the UUID does not match.'));
+          $this->setFormError('import', $form_state, $this->t('An entity with this machine name already exists but the UUID does not match.'));
           return;
         }
       }
       // If there is no entity with a matching ID, check for a UUID match.
       elseif (isset($data[$uuid_key]) && $entity_storage->loadByProperties(array($uuid_key => $data[$uuid_key]))) {
-        form_set_error('import', $form_state, $this->t('An entity with this UUID already exists but the machine name does not match.'));
+        $this->setFormError('import', $form_state, $this->t('An entity with this UUID already exists but the machine name does not match.'));
       }
     }
     else {
diff --git a/core/modules/contact/lib/Drupal/contact/CategoryFormController.php b/core/modules/contact/lib/Drupal/contact/CategoryFormController.php
index d1eb9b4b66afdd3098be5722403eb8c785b116bd..15c7c5d7c26bfaef9f816692c735fa5822cd3f2c 100644
--- a/core/modules/contact/lib/Drupal/contact/CategoryFormController.php
+++ b/core/modules/contact/lib/Drupal/contact/CategoryFormController.php
@@ -84,7 +84,7 @@ public function validate(array $form, array &$form_state) {
     foreach ($recipients as &$recipient) {
       $recipient = trim($recipient);
       if (!valid_email_address($recipient)) {
-        form_set_error('recipients', $form_state, t('%recipient is an invalid e-mail address.', array('%recipient' => $recipient)));
+        $this->setFormError('recipients', $form_state, $this->t('%recipient is an invalid e-mail address.', array('%recipient' => $recipient)));
       }
     }
     $form_state['values']['recipients'] = $recipients;
diff --git a/core/modules/edit/lib/Drupal/edit/Form/EditFieldForm.php b/core/modules/edit/lib/Drupal/edit/Form/EditFieldForm.php
index 9f125a55a87b04f539048647e04d71b01c25a5f2..78ece732014eaf42fae5f4ab299342f78d454d5f 100644
--- a/core/modules/edit/lib/Drupal/edit/Form/EditFieldForm.php
+++ b/core/modules/edit/lib/Drupal/edit/Form/EditFieldForm.php
@@ -7,19 +7,18 @@
 
 namespace Drupal\edit\Form;
 
+use Drupal\Core\Form\FormBase;
 use Symfony\Component\DependencyInjection\ContainerInterface;
-use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityStorageControllerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Form\FormInterface;
 use Drupal\user\TempStoreFactory;
 use Drupal\Core\Entity\EntityChangedInterface;
 
 /**
  * Builds and process a form for editing a single entity field.
  */
-class EditFieldForm implements FormInterface, ContainerInjectionInterface {
+class EditFieldForm extends FormBase {
 
   /**
    * Stores the tempstore factory.
@@ -145,7 +144,7 @@ public function validateForm(array &$form, array &$form_state) {
     if ($changed_field_name = $this->getChangedFieldName($entity)) {
       $changed_field_errors = $entity->$changed_field_name->validate();
       if (count($changed_field_errors)) {
-        form_set_error('changed_field', $form_state, $changed_field_errors[0]->getMessage());
+        $this->setFormError('changed_field', $form_state, $changed_field_errors[0]->getMessage());
       }
     }
   }
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/FieldOverview.php b/core/modules/field_ui/lib/Drupal/field_ui/FieldOverview.php
index b8c9df2e3c159092a600d11f7be05692f5bf7f54..3fbf5c3dd0e5d4c3619291f318eeca97cfe15973 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/FieldOverview.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/FieldOverview.php
@@ -315,12 +315,12 @@ protected function validateAddNew(array $form, array &$form_state) {
     if (array_filter(array($field['label'], $field['field_name'], $field['type']))) {
       // Missing label.
       if (!$field['label']) {
-        form_set_error('fields][_add_new_field][label', $form_state, $this->t('Add new field: you need to provide a label.'));
+        $this->setFormError('fields][_add_new_field][label', $form_state, $this->t('Add new field: you need to provide a label.'));
       }
 
       // Missing field name.
       if (!$field['field_name']) {
-        form_set_error('fields][_add_new_field][field_name', $form_state, $this->t('Add new field: you need to provide a field name.'));
+        $this->setFormError('fields][_add_new_field][field_name', $form_state, $this->t('Add new field: you need to provide a field name.'));
       }
       // Field name validation.
       else {
@@ -333,7 +333,7 @@ protected function validateAddNew(array $form, array &$form_state) {
 
       // Missing field type.
       if (!$field['type']) {
-        form_set_error('fields][_add_new_field][type', $form_state, $this->t('Add new field: you need to select a field type.'));
+        $this->setFormError('fields][_add_new_field][type', $form_state, $this->t('Add new field: you need to select a field type.'));
       }
     }
   }
@@ -359,12 +359,12 @@ protected function validateAddExisting(array $form, array &$form_state) {
       if (array_filter(array($field['label'], $field['field_name']))) {
         // Missing label.
         if (!$field['label']) {
-          form_set_error('fields][_add_existing_field][label', $form_state, $this->t('Re-use existing field: you need to provide a label.'));
+          $this->setFormError('fields][_add_existing_field][label', $form_state, $this->t('Re-use existing field: you need to provide a label.'));
         }
 
         // Missing existing field name.
         if (!$field['field_name']) {
-          form_set_error('fields][_add_existing_field][field_name', $form_state, $this->t('Re-use existing field: you need to select a field.'));
+          $this->setFormError('fields][_add_existing_field][field_name', $form_state, $this->t('Re-use existing field: you need to select a field.'));
         }
       }
     }
diff --git a/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php b/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
index fa2ba128286c5b999daf1b42b7163f67f2b3be5b..2a788cb63f2619ceecde099b31b53f110e9a1ad6 100644
--- a/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
+++ b/core/modules/field_ui/lib/Drupal/field_ui/Form/FieldEditForm.php
@@ -172,7 +172,7 @@ public function validateForm(array &$form, array &$form_state) {
     $cardinality = $form_state['values']['field']['cardinality'];
     $cardinality_number = $form_state['values']['field']['cardinality_number'];
     if ($cardinality === 'number' && empty($cardinality_number)) {
-      form_error($form['field']['cardinality_container']['cardinality_number'], $form_state, $this->t('Number of values is required.'));
+      $this->setFormError('field][cardinality_number', $form_state, $this->t('Number of values is required.'));
     }
   }
 
diff --git a/core/modules/filter/lib/Drupal/filter/FilterFormatFormControllerBase.php b/core/modules/filter/lib/Drupal/filter/FilterFormatFormControllerBase.php
index 002c1d57ddd96279baec93cdfbceb59b10558fe4..5ca05c21d596fbb68c4f4bc1ca58ab42f064340b 100644
--- a/core/modules/filter/lib/Drupal/filter/FilterFormatFormControllerBase.php
+++ b/core/modules/filter/lib/Drupal/filter/FilterFormatFormControllerBase.php
@@ -232,7 +232,7 @@ public function validate(array $form, array &$form_state) {
       ->condition('name', $format_name)
       ->execute();
     if ($format_exists) {
-      form_set_error('name', $form_state, t('Text format names must be unique. A format named %name already exists.', array('%name' => $format_name)));
+      $this->setFormError('name', $form_state, $this->t('Text format names must be unique. A format named %name already exists.', array('%name' => $format_name)));
     }
   }
 
diff --git a/core/modules/image/lib/Drupal/image/Form/ImageStyleEditForm.php b/core/modules/image/lib/Drupal/image/Form/ImageStyleEditForm.php
index 2d1af48baa48c7aa9bbbfd58c570693d869ff40e..c00b00938469aea17addb293784b3c2c75b26d71 100644
--- a/core/modules/image/lib/Drupal/image/Form/ImageStyleEditForm.php
+++ b/core/modules/image/lib/Drupal/image/Form/ImageStyleEditForm.php
@@ -156,7 +156,7 @@ public function form(array $form, array &$form_state) {
    */
   public function effectValidate($form, &$form_state) {
     if (!$form_state['values']['new']) {
-      form_error($form['effects']['new']['new'], $form_state, $this->t('Select an effect to add.'));
+      $this->setFormError('new', $form_state, $this->t('Select an effect to add.'));
     }
   }
 
diff --git a/core/modules/language/lib/Drupal/language/Form/LanguageAddForm.php b/core/modules/language/lib/Drupal/language/Form/LanguageAddForm.php
index 64f3f97c93903fa50de1800e219e5d518f2acf85..bca5523c5f76ebe05fa7ba77b19ab982b7a59ccc 100644
--- a/core/modules/language/lib/Drupal/language/Form/LanguageAddForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/LanguageAddForm.php
@@ -124,11 +124,11 @@ public function validateCustom(array $form, array &$form_state) {
       $this->validateCommon($form['custom_language'], $form_state);
 
       if ($language = language_load($langcode)) {
-        form_error($form['custom_language']['langcode'], $form_state, $this->t('The language %language (%langcode) already exists.', array('%language' => $language->name, '%langcode' => $langcode)));
+        $this->setFormError('langcode', $form_state, $this->t('The language %language (%langcode) already exists.', array('%language' => $language->name, '%langcode' => $langcode)));
       }
     }
     else {
-      form_error($form['predefined_langcode'], $form_state, $this->t('Use the <em>Add language</em> button to save a predefined language.'));
+      $this->setFormError('predefined_langcode', $form_state, $this->t('Use the <em>Add language</em> button to save a predefined language.'));
     }
   }
 
@@ -138,11 +138,11 @@ public function validateCustom(array $form, array &$form_state) {
   public function validatePredefined($form, &$form_state) {
     $langcode = $form_state['values']['predefined_langcode'];
     if ($langcode == 'custom') {
-      form_error($form['predefined_langcode'], $form_state, $this->t('Fill in the language details and save the language with <em>Add custom language</em>.'));
+      $this->setFormError('predefined_langcode', $form_state, $this->t('Fill in the language details and save the language with <em>Add custom language</em>.'));
     }
     else {
       if ($language = language_load($langcode)) {
-        form_error($form['predefined_langcode'], $form_state, $this->t('The language %language (%langcode) already exists.', array('%language' => $language->name, '%langcode' => $langcode)));
+        $this->setFormError('predefined_langcode', $form_state, $this->t('The language %language (%langcode) already exists.', array('%language' => $language->name, '%langcode' => $langcode)));
       }
     }
   }
diff --git a/core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php b/core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php
index 2b20c8d3fd0e4b4c62b26d8821db5d10249513bc..b2adf0a81f7ff6f0bf8eaa33ead638218db8e0a3 100644
--- a/core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php
+++ b/core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php
@@ -70,10 +70,10 @@ public function commonForm(array &$form) {
   public function validateCommon(array $form, array &$form_state) {
     // Ensure sane field values for langcode and name.
     if (!isset($form['langcode_view']) && preg_match('@[^a-zA-Z_-]@', $form_state['values']['langcode'])) {
-      form_error($form['langcode'], $form_state, $this->t('%field may only contain characters a-z, underscores, or hyphens.', array('%field' => $form['langcode']['#title'])));
+      $this->setFormError('langcode', $form_state, $this->t('%field may only contain characters a-z, underscores, or hyphens.', array('%field' => $form['langcode']['#title'])));
     }
     if ($form_state['values']['name'] != check_plain($form_state['values']['name'])) {
-      form_error($form['name'], $form_state, $this->t('%field cannot contain any markup.', array('%field' => $form['name']['#title'])));
+      $this->setFormError('name', $form_state, $this->t('%field cannot contain any markup.', array('%field' => $form['name']['#title'])));
     }
   }
 
diff --git a/core/modules/language/lib/Drupal/language/Form/NegotiationBrowserForm.php b/core/modules/language/lib/Drupal/language/Form/NegotiationBrowserForm.php
index 4a8ec2d7fbe189044cc3259552659ae522b15aef..2271b14cc82620bd2005128ec02494287b532e76 100644
--- a/core/modules/language/lib/Drupal/language/Form/NegotiationBrowserForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/NegotiationBrowserForm.php
@@ -143,10 +143,10 @@ public function validateForm(array &$form, array &$form_state) {
       foreach ($mappings as $key => $data) {
         // Make sure browser_langcode is unique.
         if (array_key_exists($data['browser_langcode'], $unique_values)) {
-          form_set_error('mappings][' . $key . '][browser_langcode', $form_state, $this->t('Browser language codes must be unique.'));
+          $this->setFormError('mappings][' . $key . '][browser_langcode', $form_state, $this->t('Browser language codes must be unique.'));
         }
         elseif (preg_match('/[^a-z\-]/', $data['browser_langcode'])) {
-          form_set_error('mappings][' . $key . '][browser_langcode', $form_state, $this->t('Browser language codes can only contain lowercase letters and a hyphen(-).'));
+          $this->setFormError('mappings][' . $key . '][browser_langcode', $form_state, $this->t('Browser language codes can only contain lowercase letters and a hyphen(-).'));
         }
         $unique_values[$data['browser_langcode']] = $data['drupal_langcode'];
       }
@@ -157,10 +157,10 @@ public function validateForm(array &$form, array &$form_state) {
     if (!empty($data['browser_langcode'])) {
       // Make sure browser_langcode is unique.
       if (array_key_exists($data['browser_langcode'], $unique_values)) {
-        form_set_error('mappings][' . $key . '][browser_langcode', $form_state, $this->t('Browser language codes must be unique.'));
+        $this->setFormError('mappings][' . $key . '][browser_langcode', $form_state, $this->t('Browser language codes must be unique.'));
       }
       elseif (preg_match('/[^a-z\-]/', $data['browser_langcode'])) {
-        form_set_error('mappings][' . $key . '][browser_langcode', $form_state, $this->t('Browser language codes can only contain lowercase letters and a hyphen(-).'));
+        $this->setFormError('mappings][' . $key . '][browser_langcode', $form_state, $this->t('Browser language codes can only contain lowercase letters and a hyphen(-).'));
       }
       $unique_values[$data['browser_langcode']] = $data['drupal_langcode'];
     }
diff --git a/core/modules/language/lib/Drupal/language/Form/NegotiationUrlForm.php b/core/modules/language/lib/Drupal/language/Form/NegotiationUrlForm.php
index 9a6c267bd6241350c966085e380e3386ef8752e3..ac709e30b95218331ffe1fe049087acf58732321 100644
--- a/core/modules/language/lib/Drupal/language/Form/NegotiationUrlForm.php
+++ b/core/modules/language/lib/Drupal/language/Form/NegotiationUrlForm.php
@@ -106,18 +106,18 @@ public function validateForm(array &$form, array &$form_state) {
         if (!$language->default && $form_state['values']['language_negotiation_url_part'] == LANGUAGE_NEGOTIATION_URL_PREFIX) {
           // Throw a form error if the prefix is blank for a non-default language,
           // although it is required for selected negotiation type.
-          form_error($form['prefix'][$langcode], $form_state, t('The prefix may only be left blank for the default language.'));
+          $this->setFormError("prefix][$langcode", $form_state, t('The prefix may only be left blank for the default language.'));
         }
       }
       elseif (strpos($value, '/') !== FALSE) {
         // Throw a form error if the string contains a slash,
         // which would not work.
-        form_error($form['prefix'][$langcode], $form_state, t('The prefix may not contain a slash.'));
+        $this->setFormError("prefix][$langcode", $form_state, t('The prefix may not contain a slash.'));
       }
       elseif (isset($count[$value]) && $count[$value] > 1) {
         // Throw a form error if there are two languages with the same
         // domain/prefix.
-        form_error($form['prefix'][$langcode], $form_state, t('The prefix for %language, %value, is not unique.', array('%language' => $language->name, '%value' => $value)));
+        $this->setFormError("prefix][$langcode", $form_state, t('The prefix for %language, %value, is not unique.', array('%language' => $language->name, '%value' => $value)));
       }
     }
 
@@ -130,13 +130,13 @@ public function validateForm(array &$form, array &$form_state) {
         if (!$language->default && $form_state['values']['language_negotiation_url_part'] == LANGUAGE_NEGOTIATION_URL_DOMAIN) {
           // Throw a form error if the domain is blank for a non-default language,
           // although it is required for selected negotiation type.
-          form_error($form['domain'][$langcode], $form_state, t('The domain may only be left blank for the default language.'));
+          $this->setFormError("domain][$langcode", $form_state, t('The domain may only be left blank for the default language.'));
         }
       }
       elseif (isset($count[$value]) && $count[$value] > 1) {
         // Throw a form error if there are two languages with the same
         // domain/domain.
-        form_error($form['domain'][$langcode], $form_state, t('The domain for %language, %value, is not unique.', array('%language' => $language->name, '%value' => $value)));
+        $this->setFormError("domain][$langcode", $form_state, t('The domain for %language, %value, is not unique.', array('%language' => $language->name, '%value' => $value)));
       }
     }
 
@@ -147,7 +147,7 @@ public function validateForm(array &$form, array &$form_state) {
         // Ensure we have exactly one protocol when checking the hostname.
         $host = 'http://' . str_replace(array('http://', 'https://'), '', $value);
         if (parse_url($host, PHP_URL_HOST) != $value) {
-          form_error($form['domain'][$langcode], $form_state, t('The domain for %language may only contain the domain name, not a protocol and/or port.', array('%language' => $name)));
+          $this->setFormError("domain][$langcode", $form_state, t('The domain for %language may only contain the domain name, not a protocol and/or port.', array('%language' => $name)));
         }
       }
     }
diff --git a/core/modules/locale/lib/Drupal/locale/Form/LocaleSettingsForm.php b/core/modules/locale/lib/Drupal/locale/Form/LocaleSettingsForm.php
index 3d4a4103a6138443851a47b440e481093441b730..630b716521dd9188aa58b9d301542d7908605afb 100644
--- a/core/modules/locale/lib/Drupal/locale/Form/LocaleSettingsForm.php
+++ b/core/modules/locale/lib/Drupal/locale/Form/LocaleSettingsForm.php
@@ -93,7 +93,7 @@ public function validateForm(array &$form, array &$form_state) {
     parent::validateForm($form, $form_state);
 
     if (empty($form['#translation_directory']) && $form_state['values']['use_source'] == LOCALE_TRANSLATION_USE_SOURCE_LOCAL) {
-      form_set_error('use_source', $form_state, t('You have selected local translation source, but no <a href="@url">Interface translation directory</a> was configured.', array('@url' => url('admin/config/media/file-system'))));
+      $this->setFormError('use_source', $form_state, $this->t('You have selected local translation source, but no <a href="@url">Interface translation directory</a> was configured.', array('@url' => url('admin/config/media/file-system'))));
     }
   }
 
diff --git a/core/modules/locale/lib/Drupal/locale/Form/TranslateEditForm.php b/core/modules/locale/lib/Drupal/locale/Form/TranslateEditForm.php
index 24456a8a8d1f71a88d7a23833163846594e7a727..34c93bede91aca338041ce3b611697faf3d9b973 100644
--- a/core/modules/locale/lib/Drupal/locale/Form/TranslateEditForm.php
+++ b/core/modules/locale/lib/Drupal/locale/Form/TranslateEditForm.php
@@ -166,8 +166,8 @@ public function validateForm(array &$form, array &$form_state) {
     foreach ($form_state['values']['strings'] as $lid => $translations) {
       foreach ($translations['translations'] as $key => $value) {
         if (!locale_string_is_safe($value)) {
-          form_set_error("strings][$lid][translations][$key", $form_state, $this->t('The submitted string contains disallowed HTML: %string', array('%string' => $value)));
-          form_set_error("translations][$langcode][$key", $form_state, $this->t('The submitted string contains disallowed HTML: %string', array('%string' => $value)));
+          $this->setFormError("strings][$lid][translations][$key", $form_state, $this->t('The submitted string contains disallowed HTML: %string', array('%string' => $value)));
+          $this->setFormError("translations][$langcode][$key", $form_state, $this->t('The submitted string contains disallowed HTML: %string', array('%string' => $value)));
           watchdog('locale', 'Attempted submission of a translation string with disallowed HTML: %string', array('%string' => $value), WATCHDOG_WARNING);
         }
       }
diff --git a/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkFormController.php b/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkFormController.php
index 7c39219ea5dc273b5b5721dd59aaa2b69f5b970c..bc2c71d03a501470293d30c65cb2860f9f942500 100644
--- a/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkFormController.php
+++ b/core/modules/menu_link/lib/Drupal/menu_link/MenuLinkFormController.php
@@ -234,7 +234,7 @@ public function validate(array $form, array &$form_state) {
       }
     }
     if (!trim($menu_link->link_path) || !drupal_valid_path($menu_link->link_path, TRUE)) {
-      form_set_error('link_path', $form_state, t("The path '@link_path' is either invalid or you do not have access to it.", array('@link_path' => $menu_link->link_path)));
+      $this->setFormError('link_path', $form_state, $this->t("The path '@link_path' is either invalid or you do not have access to it.", array('@link_path' => $menu_link->link_path)));
     }
 
     parent::validate($form, $form_state);
diff --git a/core/modules/node/lib/Drupal/node/NodeFormController.php b/core/modules/node/lib/Drupal/node/NodeFormController.php
index 1153188b58a9a86307013f1e220e338acdca5719..e37eb4134bbcd6524d1d35ca0fe4adff3053a1bf 100644
--- a/core/modules/node/lib/Drupal/node/NodeFormController.php
+++ b/core/modules/node/lib/Drupal/node/NodeFormController.php
@@ -318,7 +318,7 @@ public function validate(array $form, array &$form_state) {
     $node = $this->buildEntity($form, $form_state);
 
     if ($node->id() && (node_last_changed($node->id(), $this->getFormLangcode($form_state)) > $node->getChangedTime())) {
-      form_set_error('changed', $form_state, t('The content on this page has either been modified by another user, or you have already submitted modifications using this form. As a result, your changes cannot be saved.'));
+      $this->setFormError('changed', $form_state, $this->t('The content on this page has either been modified by another user, or you have already submitted modifications using this form. As a result, your changes cannot be saved.'));
     }
 
     // Validate the "authored by" field.
@@ -326,14 +326,14 @@ public function validate(array $form, array &$form_state) {
       // The use of empty() is mandatory in the context of usernames
       // as the empty string denotes the anonymous user. In case we
       // are dealing with an anonymous user we set the user ID to 0.
-      form_set_error('name', $form_state, t('The username %name does not exist.', array('%name' => $form_state['values']['name'])));
+      $this->setFormError('name', $form_state, $this->t('The username %name does not exist.', array('%name' => $form_state['values']['name'])));
     }
 
     // Validate the "authored on" field.
     // The date element contains the date object.
     $date = $node->date instanceof DrupalDateTime ? $node->date : new DrupalDateTime($node->date);
     if ($date->hasErrors()) {
-      form_set_error('date', $form_state, t('You have to specify a valid date.'));
+      $this->setFormError('date', $form_state, $this->t('You have to specify a valid date.'));
     }
 
     // Invoke hook_node_validate() for validation needed by modules.
diff --git a/core/modules/node/lib/Drupal/node/NodeTypeFormController.php b/core/modules/node/lib/Drupal/node/NodeTypeFormController.php
index f48b591c13b4122694620e8cfa382d7036038c20..6d7d7b0ba6d1e21f9892bcf96bd9071fd04820a8 100644
--- a/core/modules/node/lib/Drupal/node/NodeTypeFormController.php
+++ b/core/modules/node/lib/Drupal/node/NodeTypeFormController.php
@@ -182,7 +182,7 @@ public function validate(array $form, array &$form_state) {
     $id = trim($form_state['values']['type']);
     // '0' is invalid, since elsewhere we check it using empty().
     if ($id == '0') {
-      form_set_error('type', $form_state, t("Invalid machine-readable name. Enter a name other than %invalid.", array('%invalid' => $id)));
+      $this->setFormError('type', $form_state, $this->t("Invalid machine-readable name. Enter a name other than %invalid.", array('%invalid' => $id)));
     }
   }
 
diff --git a/core/modules/picture/lib/Drupal/picture/PictureMappingFormController.php b/core/modules/picture/lib/Drupal/picture/PictureMappingFormController.php
index 121f6a780c462826e5bf7e6285e74ffc7237c80c..1e4b106f65fc3dbe5bedb677d2f1298b9433c378 100644
--- a/core/modules/picture/lib/Drupal/picture/PictureMappingFormController.php
+++ b/core/modules/picture/lib/Drupal/picture/PictureMappingFormController.php
@@ -126,7 +126,7 @@ public function validate(array $form, array &$form_state) {
       }
       // Make sure at least one mapping is defined.
       elseif (!$picture_mapping->isNew() && !$picture_mapping->hasMappings()) {
-        form_set_error('mappings', $form_state, $this->t('Please select at least one mapping.'));
+        $this->setFormError('mappings', $form_state, $this->t('Please select at least one mapping.'));
       }
     }
   }
diff --git a/core/modules/search/lib/Drupal/search/Form/SearchBlockForm.php b/core/modules/search/lib/Drupal/search/Form/SearchBlockForm.php
index bb4c9f7e62e8e59454445dfd87aa63c4a2cd6e5b..c943c9338dae79c7d6d38b73e89ed5976c38383b 100644
--- a/core/modules/search/lib/Drupal/search/Form/SearchBlockForm.php
+++ b/core/modules/search/lib/Drupal/search/Form/SearchBlockForm.php
@@ -58,7 +58,7 @@ public function submitForm(array &$form, array &$form_state) {
     // "field is required" because the search keywords field has no title.
     // The error message would also complain about a missing #title field.)
     if ($form_state['values']['search_block_form'] == '') {
-      form_set_error('keys', $form_state, $this->t('Please enter some keywords.'));
+      $this->setFormError('keys', $form_state, $this->t('Please enter some keywords.'));
     }
 
     $form_id = $form['form_id']['#value'];
@@ -72,7 +72,7 @@ public function submitForm(array &$form, array &$form_state) {
       );
     }
     else {
-      form_set_error(NULL, $form_state, $this->t('Search is currently disabled.'), 'error');
+      $this->setFormError('', $form_state, $this->t('Search is currently disabled.'), 'error');
     }
   }
 }
diff --git a/core/modules/search/lib/Drupal/search/Form/SearchForm.php b/core/modules/search/lib/Drupal/search/Form/SearchForm.php
index 69022ddbd2328d669425cfdef73b25315bba1798..fe49f16eba361702354bd83f603ab02b65dbfb5b 100644
--- a/core/modules/search/lib/Drupal/search/Form/SearchForm.php
+++ b/core/modules/search/lib/Drupal/search/Form/SearchForm.php
@@ -112,7 +112,7 @@ public function validateForm(array &$form, array &$form_state) {
   public function submitForm(array &$form, array &$form_state) {
     $keys = $form_state['values']['processed_keys'];
     if ($keys == '') {
-      form_set_error('keys', $form_state, t('Please enter some keywords.'));
+      $this->setFormError('keys', $form_state, $this->t('Please enter some keywords.'));
       // Fall through to the form redirect.
     }
 
diff --git a/core/modules/search/lib/Drupal/search/Form/SearchSettingsForm.php b/core/modules/search/lib/Drupal/search/Form/SearchSettingsForm.php
index 5d2335c7ce10ede22c0800b967ede5760493624e..d7e566fbf08cfc58301dee0ed42a5e771a7c0cad 100644
--- a/core/modules/search/lib/Drupal/search/Form/SearchSettingsForm.php
+++ b/core/modules/search/lib/Drupal/search/Form/SearchSettingsForm.php
@@ -219,7 +219,7 @@ public function validateForm(array &$form, array &$form_state) {
       $new_plugins = array_filter($form_state['values']['active_plugins']);
       $default = $form_state['values']['default_plugin'];
       if (!in_array($default, $new_plugins, TRUE)) {
-        form_set_error('default_plugin', $form_state, $this->t('Your default search plugin is not selected as an active plugin.'));
+        $this->setFormError('default_plugin', $form_state, $this->t('Your default search plugin is not selected as an active plugin.'));
       }
     }
     // Handle per-plugin validation logic.
diff --git a/core/modules/shortcut/lib/Drupal/shortcut/ShortcutSetFormController.php b/core/modules/shortcut/lib/Drupal/shortcut/ShortcutSetFormController.php
index 461f1b426c35a988bbb511cc057cf355ba3816e1..404dd1dbffea5e92f633ab9a1a0055839d357801 100644
--- a/core/modules/shortcut/lib/Drupal/shortcut/ShortcutSetFormController.php
+++ b/core/modules/shortcut/lib/Drupal/shortcut/ShortcutSetFormController.php
@@ -65,7 +65,7 @@ public function validate(array $form, array &$form_state) {
     $entity = $this->entity;
     // Check to prevent a duplicate title.
     if ($form_state['values']['label'] != $entity->label() && shortcut_set_title_exists($form_state['values']['label'])) {
-      form_set_error('label', $form_state, t('The shortcut set %name already exists. Choose another name.', array('%name' => $form_state['values']['label'])));
+      $this->setFormError('label', $form_state, $this->t('The shortcut set %name already exists. Choose another name.', array('%name' => $form_state['values']['label'])));
     }
   }
 
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestSettingsForm.php b/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestSettingsForm.php
index f54dd6cd28b9c717f7e34ee6123c5b97883db103..24bdb85815fb7210380cf5e1af48b04785e77f7f 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestSettingsForm.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestSettingsForm.php
@@ -97,7 +97,7 @@ public function validateForm(array &$form, array &$form_state) {
     // If a password was provided but a username wasn't, the credentials are
     // incorrect, so throw an error.
     if (empty($form_state['values']['simpletest_httpauth_username']) && !empty($form_state['values']['simpletest_httpauth_password'])) {
-      form_set_error('simpletest_httpauth_username', $form_state, $this->t('HTTP authentication credentials must include a username in addition to a password.'));
+      $this->setFormError('simpletest_httpauth_username', $form_state, $this->t('HTTP authentication credentials must include a username in addition to a password.'));
     }
 
     parent::validateForm($form, $form_state);
diff --git a/core/modules/system/lib/Drupal/system/Form/DateFormatFormBase.php b/core/modules/system/lib/Drupal/system/Form/DateFormatFormBase.php
index d8a69b5bd5e554ad0e2a874e69cb904da01bf117..bdce06ba1ba028572dcc15487a6bdb7a8bad41fa 100644
--- a/core/modules/system/lib/Drupal/system/Form/DateFormatFormBase.php
+++ b/core/modules/system/lib/Drupal/system/Form/DateFormatFormBase.php
@@ -191,7 +191,7 @@ public function validate(array $form, array &$form_state) {
     $pattern = trim($form_state['values']['date_format_pattern']);
     foreach ($this->dateFormatStorage->loadMultiple() as $format) {
       if ($format->getPattern() == $pattern && ($this->entity->isNew() || $format->id() != $this->entity->id())) {
-        form_set_error('date_format_pattern', $form_state, t('This format already exists. Enter a unique format string.'));
+        $this->setFormError('date_format_pattern', $form_state, $this->t('This format already exists. Enter a unique format string.'));
         continue;
       }
     }
diff --git a/core/modules/system/lib/Drupal/system/Form/SiteInformationForm.php b/core/modules/system/lib/Drupal/system/Form/SiteInformationForm.php
index fdc180c98487f1a2854d02867666bf3f64c0fb95..34e3584f22f19e86fd56b8d797bc4024aa3c0e39 100644
--- a/core/modules/system/lib/Drupal/system/Form/SiteInformationForm.php
+++ b/core/modules/system/lib/Drupal/system/Form/SiteInformationForm.php
@@ -144,7 +144,7 @@ public function validateForm(array &$form, array &$form_state) {
     }
     // Validate front page path.
     if (!drupal_valid_path($form_state['values']['site_frontpage'])) {
-      form_set_error('site_frontpage', $form_state, t("The path '%path' is either invalid or you do not have access to it.", array('%path' => $form_state['values']['site_frontpage'])));
+      $this->setFormError('site_frontpage', $form_state, $this->t("The path '%path' is either invalid or you do not have access to it.", array('%path' => $form_state['values']['site_frontpage'])));
     }
     // Get the normal paths of both error pages.
     if (!empty($form_state['values']['site_403'])) {
@@ -155,11 +155,11 @@ public function validateForm(array &$form, array &$form_state) {
     }
     // Validate 403 error path.
     if (!empty($form_state['values']['site_403']) && !drupal_valid_path($form_state['values']['site_403'])) {
-      form_set_error('site_403', $form_state, t("The path '%path' is either invalid or you do not have access to it.", array('%path' => $form_state['values']['site_403'])));
+      $this->setFormError('site_403', $form_state, $this->t("The path '%path' is either invalid or you do not have access to it.", array('%path' => $form_state['values']['site_403'])));
     }
     // Validate 404 error path.
     if (!empty($form_state['values']['site_404']) && !drupal_valid_path($form_state['values']['site_404'])) {
-      form_set_error('site_404', $form_state, t("The path '%path' is either invalid or you do not have access to it.", array('%path' => $form_state['values']['site_404'])));
+      $this->setFormError('site_404', $form_state, $this->t("The path '%path' is either invalid or you do not have access to it.", array('%path' => $form_state['values']['site_404'])));
     }
 
     parent::validateForm($form, $form_state);
diff --git a/core/modules/system/lib/Drupal/system/Form/ThemeSettingsForm.php b/core/modules/system/lib/Drupal/system/Form/ThemeSettingsForm.php
index 39d0caac46cb313585d6adf9e7a63f40f85ff8f2..ec7622730f751f7c4da659a92de198b6d3c44819 100644
--- a/core/modules/system/lib/Drupal/system/Form/ThemeSettingsForm.php
+++ b/core/modules/system/lib/Drupal/system/Form/ThemeSettingsForm.php
@@ -332,7 +332,7 @@ public function validateForm(array &$form, array &$form_state) {
         }
         else {
           // File upload failed.
-          form_set_error('logo_upload', $form_state, t('The logo could not be uploaded.'));
+          $this->setFormError('logo_upload', $form_state, $this->t('The logo could not be uploaded.'));
         }
       }
 
@@ -348,7 +348,7 @@ public function validateForm(array &$form, array &$form_state) {
         }
         else {
           // File upload failed.
-          form_set_error('favicon_upload', $form_state, t('The favicon could not be uploaded.'));
+          $this->setFormError('favicon_upload', $form_state, $this->t('The favicon could not be uploaded.'));
         }
       }
 
@@ -357,13 +357,13 @@ public function validateForm(array &$form, array &$form_state) {
       if ($form_state['values']['logo_path']) {
         $path = $this->validatePath($form_state['values']['logo_path']);
         if (!$path) {
-          form_set_error('logo_path', $form_state, t('The custom logo path is invalid.'));
+          $this->setFormError('logo_path', $form_state, $this->t('The custom logo path is invalid.'));
         }
       }
       if ($form_state['values']['favicon_path']) {
         $path = $this->validatePath($form_state['values']['favicon_path']);
         if (!$path) {
-          form_set_error('favicon_path', $form_state, t('The custom favicon path is invalid.'));
+          $this->setFormError('favicon_path', $form_state, $this->t('The custom favicon path is invalid.'));
         }
       }
     }
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/TermFormController.php b/core/modules/taxonomy/lib/Drupal/taxonomy/TermFormController.php
index bbed7fdc931098926dfddfdb8e76626129ccd42c..925d83c5311ff7228f4f731f5297eba49058b26a 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/TermFormController.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/TermFormController.php
@@ -161,7 +161,7 @@ public function validate(array $form, array &$form_state) {
 
     // Ensure numeric values.
     if (isset($form_state['values']['weight']) && !is_numeric($form_state['values']['weight'])) {
-      form_set_error('weight', $form_state, $this->t('Weight value must be numeric.'));
+      $this->setFormError('weight', $form_state, $this->t('Weight value must be numeric.'));
     }
   }
 
diff --git a/core/modules/update/lib/Drupal/update/UpdateSettingsForm.php b/core/modules/update/lib/Drupal/update/UpdateSettingsForm.php
index f72c201d3cd81223672b46ceb96a43649300c0a9..d2d418671d1d77309116a24f82d76869d005c264 100644
--- a/core/modules/update/lib/Drupal/update/UpdateSettingsForm.php
+++ b/core/modules/update/lib/Drupal/update/UpdateSettingsForm.php
@@ -90,10 +90,10 @@ public function validateForm(array &$form, array &$form_state) {
         $form_state['notify_emails'] = $valid;
       }
       elseif (count($invalid) == 1) {
-        form_set_error('update_notify_emails', $form_state, t('%email is not a valid e-mail address.', array('%email' => reset($invalid))));
+        $this->setFormError('update_notify_emails', $form_state, $this->t('%email is not a valid e-mail address.', array('%email' => reset($invalid))));
       }
       else {
-        form_set_error('update_notify_emails', $form_state, t('%emails are not valid e-mail addresses.', array('%emails' => implode(', ', $invalid))));
+        $this->setFormError('update_notify_emails', $form_state, $this->t('%emails are not valid e-mail addresses.', array('%emails' => implode(', ', $invalid))));
       }
     }
 
diff --git a/core/modules/user/lib/Drupal/user/AccountFormController.php b/core/modules/user/lib/Drupal/user/AccountFormController.php
index 1179cdcf70c5747498a857919238110d643d7739..4983b0f0bedda8936ce76fc6c7c4e7d52691a462 100644
--- a/core/modules/user/lib/Drupal/user/AccountFormController.php
+++ b/core/modules/user/lib/Drupal/user/AccountFormController.php
@@ -296,7 +296,7 @@ public function validate(array $form, array &$form_state) {
     // Validate new or changing username.
     if (isset($form_state['values']['name'])) {
       if ($error = user_validate_name($form_state['values']['name'])) {
-        form_set_error('name', $form_state, $error);
+        $this->setFormError('name', $form_state, $error);
       }
       // Cast the user ID as an integer. It might have been set to NULL, which
       // could lead to unexpected results.
@@ -310,7 +310,7 @@ public function validate(array $form, array &$form_state) {
         ->fetchField();
 
         if ($name_taken) {
-          form_set_error('name', $form_state, $this->t('The name %name is already taken.', array('%name' => $form_state['values']['name'])));
+          $this->setFormError('name', $form_state, $this->t('The name %name is already taken.', array('%name' => $form_state['values']['name'])));
         }
       }
     }
@@ -329,10 +329,10 @@ public function validate(array $form, array &$form_state) {
       if ($mail_taken) {
         // Format error message dependent on whether the user is logged in or not.
         if ($GLOBALS['user']->isAuthenticated()) {
-          form_set_error('mail', $form_state, $this->t('The e-mail address %email is already taken.', array('%email' => $mail)));
+          $this->setFormError('mail', $form_state, $this->t('The e-mail address %email is already taken.', array('%email' => $mail)));
         }
         else {
-          form_set_error('mail', $form_state, $this->t('The e-mail address %email is already registered. <a href="@password">Have you forgotten your password?</a>', array('%email' => $mail, '@password' => url('user/password'))));
+          $this->setFormError('mail', $form_state, $this->t('The e-mail address %email is already registered. <a href="@password">Have you forgotten your password?</a>', array('%email' => $mail, '@password' => url('user/password'))));
         }
       }
     }
@@ -347,7 +347,7 @@ public function validate(array $form, array &$form_state) {
 
       $user_schema = drupal_get_schema('users');
       if (drupal_strlen($form_state['values']['signature']) > $user_schema['fields']['signature']['length']) {
-        form_set_error('signature', $form_state, $this->t('The signature is too long: it must be %max characters or less.', array('%max' => $user_schema['fields']['signature']['length'])));
+        $this->setFormError('signature', $form_state, $this->t('The signature is too long: it must be %max characters or less.', array('%max' => $user_schema['fields']['signature']['length'])));
       }
     }
   }
diff --git a/core/modules/user/lib/Drupal/user/Form/UserLoginForm.php b/core/modules/user/lib/Drupal/user/Form/UserLoginForm.php
index 4aad0e91f4fe5298888615bd3874f95ed502583d..46744a4dbbddd4fcdb8efcfb4335fa5f4e493a5b 100644
--- a/core/modules/user/lib/Drupal/user/Form/UserLoginForm.php
+++ b/core/modules/user/lib/Drupal/user/Form/UserLoginForm.php
@@ -118,7 +118,7 @@ public function submitForm(array &$form, array &$form_state) {
   public function validateName(array &$form, array &$form_state) {
     if (!empty($form_state['values']['name']) && user_is_blocked($form_state['values']['name'])) {
       // Blocked in user administration.
-      form_set_error('name', $form_state, $this->t('The username %name has not been activated or is blocked.', array('%name' => $form_state['values']['name'])));
+      $this->setFormError('name', $form_state, $this->t('The username %name has not been activated or is blocked.', array('%name' => $form_state['values']['name'])));
     }
   }
 
@@ -186,15 +186,15 @@ public function validateFinal(array &$form, array &$form_state) {
 
       if (isset($form_state['flood_control_triggered'])) {
         if ($form_state['flood_control_triggered'] == 'user') {
-          form_set_error('name', $form_state, format_plural($flood_config->get('user_limit'), 'Sorry, there has been more than one failed login attempt for this account. It is temporarily blocked. Try again later or <a href="@url">request a new password</a>.', 'Sorry, there have been more than @count failed login attempts for this account. It is temporarily blocked. Try again later or <a href="@url">request a new password</a>.', array('@url' => url('user/password'))));
+          $this->setFormError('name', $form_state, format_plural($flood_config->get('user_limit'), 'Sorry, there has been more than one failed login attempt for this account. It is temporarily blocked. Try again later or <a href="@url">request a new password</a>.', 'Sorry, there have been more than @count failed login attempts for this account. It is temporarily blocked. Try again later or <a href="@url">request a new password</a>.', array('@url' => url('user/password'))));
         }
         else {
           // We did not find a uid, so the limit is IP-based.
-          form_set_error('name', $form_state, $this->t('Sorry, too many failed login attempts from your IP address. This IP address is temporarily blocked. Try again later or <a href="@url">request a new password</a>.', array('@url' => url('user/password'))));
+          $this->setFormError('name', $form_state, $this->t('Sorry, too many failed login attempts from your IP address. This IP address is temporarily blocked. Try again later or <a href="@url">request a new password</a>.', array('@url' => url('user/password'))));
         }
       }
       else {
-        form_set_error('name', $form_state, $this->t('Sorry, unrecognized username or password. <a href="@password">Have you forgotten your password?</a>', array('@password' => url('user/password', array('query' => array('name' => $form_state['values']['name']))))));
+        $this->setFormError('name', $form_state, $this->t('Sorry, unrecognized username or password. <a href="@password">Have you forgotten your password?</a>', array('@password' => url('user/password', array('query' => array('name' => $form_state['values']['name']))))));
         $accounts = $this->userStorage->loadByProperties(array('name' => $form_state['values']['name']));
         if (!empty($accounts)) {
           watchdog('user', 'Login attempt failed for %user.', array('%user' => $form_state['values']['name']));
diff --git a/core/modules/user/lib/Drupal/user/Form/UserPasswordForm.php b/core/modules/user/lib/Drupal/user/Form/UserPasswordForm.php
index 2399a58f902209ad419892d06390cdde09090cf8..07d35e9953989a5100b8922b32a3fac4cc870765 100644
--- a/core/modules/user/lib/Drupal/user/Form/UserPasswordForm.php
+++ b/core/modules/user/lib/Drupal/user/Form/UserPasswordForm.php
@@ -119,7 +119,7 @@ public function validateForm(array &$form, array &$form_state) {
       form_set_value(array('#parents' => array('account')), $account, $form_state);
     }
     else {
-      form_set_error('name', $form_state, $this->t('Sorry, %name is not recognized as a username or an e-mail address.', array('%name' => $name)));
+      $this->setFormError('name', $form_state, $this->t('Sorry, %name is not recognized as a username or an e-mail address.', array('%name' => $name)));
     }
   }
 
diff --git a/core/modules/views_ui/lib/Drupal/views_ui/ViewAddFormController.php b/core/modules/views_ui/lib/Drupal/views_ui/ViewAddFormController.php
index 2c3d19c92010291fc9b180b91d45176db008db04..f02e145c667c411eb07144d3c1ff51009ab344d2 100644
--- a/core/modules/views_ui/lib/Drupal/views_ui/ViewAddFormController.php
+++ b/core/modules/views_ui/lib/Drupal/views_ui/ViewAddFormController.php
@@ -171,7 +171,7 @@ public function validate(array $form, array &$form_state) {
 
     foreach ($errors as $display_errors) {
       foreach ($display_errors as $name => $message) {
-        form_set_error($name, $form_state, $message);
+        $this->setFormError($name, $form_state, $message);
       }
     }
   }
diff --git a/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php b/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php
index 05b011d886a7baacb4deeb629bd68f7ab7202a79..84df38ea5c23e8d762b4d2aff20ea9fbf6035c17 100644
--- a/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php
+++ b/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php
@@ -236,7 +236,7 @@ public function validate(array $form, array &$form_state) {
     $view = $this->entity;
     foreach ($view->getExecutable()->validate() as $display_errors) {
       foreach ($display_errors as $error) {
-        form_set_error('', $form_state, $error);
+        $this->setFormError('', $form_state, $error);
       }
     }
   }