diff --git a/core/lib/Drupal/Core/Entity/ContentEntityConfirmFormBase.php b/core/lib/Drupal/Core/Entity/ContentEntityConfirmFormBase.php
index 3583ad4..f3a23a7 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityConfirmFormBase.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityConfirmFormBase.php
@@ -121,6 +121,7 @@ public function delete(array $form, FormStateInterface $form_state) {}
   public function validateForm(array &$form, FormStateInterface $form_state) {
     // Override the default validation implementation as it is not necessary
     // nor possible to validate an entity in a confirmation form.
+    return $this->buildEntity($form, $form_state);
   }
 
 }
diff --git a/core/lib/Drupal/Core/Entity/ContentEntityForm.php b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
index bcbcc31..cbeea5f 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityForm.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
@@ -64,18 +64,6 @@ public function form(array $form, FormStateInterface $form_state) {
 
   /**
    * {@inheritdoc}
-   *
-   * Note that extending classes should not override this method to add entity
-   * validation logic, but define further validation constraints using the
-   * entity validation API and/or provide a new validation constraint if
-   * necessary. This is the only way to ensure that the validation logic
-   * is correctly applied independently of form submissions; e.g., for REST
-   * requests.
-   * For more information about entity validation, see
-   * https://www.drupal.org/node/2015613.
-   *
-   * @return \Drupal\Core\Entity\ContentEntityTypeInterface
-   *   The built entity.
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
     parent::validateForm($form, $form_state);
diff --git a/core/lib/Drupal/Core/Entity/ContentEntityFormInterface.php b/core/lib/Drupal/Core/Entity/ContentEntityFormInterface.php
index 4f130dc..52023a2 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityFormInterface.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityFormInterface.php
@@ -61,4 +61,21 @@ public function getFormLangcode(FormStateInterface $form_state);
    */
   public function isDefaultFormLangcode(FormStateInterface $form_state);
 
+  /**
+   * {@inheritdoc}
+   *
+   * Note that extending classes should not override this method to add entity
+   * validation logic, but define further validation constraints using the
+   * entity validation API and/or provide a new validation constraint if
+   * necessary. This is the only way to ensure that the validation logic
+   * is correctly applied independently of form submissions; e.g., for REST
+   * requests.
+   * For more information about entity validation, see
+   * https://www.drupal.org/node/2015613.
+   *
+   * @return \Drupal\Core\Entity\ContentEntityTypeInterface
+   *   The built entity.
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state);
+
 }
diff --git a/core/modules/action/src/ActionFormBase.php b/core/modules/action/src/ActionFormBase.php
index 96bb63d..9afb094 100644
--- a/core/modules/action/src/ActionFormBase.php
+++ b/core/modules/action/src/ActionFormBase.php
@@ -123,8 +123,8 @@ protected function actions(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     if ($this->plugin instanceof PluginFormInterface) {
       $this->plugin->validateConfigurationForm($form, $form_state);
diff --git a/core/modules/block/src/BlockForm.php b/core/modules/block/src/BlockForm.php
index 08d7508..2ba16be 100644
--- a/core/modules/block/src/BlockForm.php
+++ b/core/modules/block/src/BlockForm.php
@@ -273,8 +273,8 @@ protected function actions(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     // The Block Entity form puts all block plugin form elements in the
     // settings form element, so just pass that to the block for validation.
diff --git a/core/modules/block_content/src/BlockContentForm.php b/core/modules/block_content/src/BlockContentForm.php
index 379e576..ec267cc 100644
--- a/core/modules/block_content/src/BlockContentForm.php
+++ b/core/modules/block_content/src/BlockContentForm.php
@@ -224,7 +224,8 @@ public function save(array $form, FormStateInterface $form_state) {
    * {@inheritdoc}
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
-    if ($this->entity->isNew()) {
+    $entity = parent::validateForm($form, $form_state);
+    if ($entity->isNew()) {
       $exists = $this->blockContentStorage->loadByProperties(array('info' => $form_state->getValue(['info', 0, 'value'])));
       if (!empty($exists)) {
         $form_state->setErrorByName('info', $this->t('A block with description %name already exists.', array(
@@ -232,6 +233,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
         )));
       }
     }
+    return $entity;
   }
 
 }
diff --git a/core/modules/contact/src/ContactFormEditForm.php b/core/modules/contact/src/ContactFormEditForm.php
index 3300c59..c545b0e 100644
--- a/core/modules/contact/src/ContactFormEditForm.php
+++ b/core/modules/contact/src/ContactFormEditForm.php
@@ -112,8 +112,8 @@ public function form(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     // Validate and each email recipient.
     $recipients = explode(',', $form_state->getValue('recipients'));
diff --git a/core/modules/contact/src/MessageForm.php b/core/modules/contact/src/MessageForm.php
index d77e3d3..27352c7 100644
--- a/core/modules/contact/src/MessageForm.php
+++ b/core/modules/contact/src/MessageForm.php
@@ -168,6 +168,7 @@ public function actions(array $form, FormStateInterface $form_state) {
     $elements = parent::actions($form, $form_state);
     $elements['submit']['#value'] = $this->t('Send message');
     $elements['preview'] = array(
+      '#type' => 'submit',
       '#value' => $this->t('Preview'),
       '#submit' => array('::submitForm', '::preview'),
     );
diff --git a/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php b/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
index d6d801b..350a2e9 100644
--- a/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
+++ b/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
@@ -38,8 +38,8 @@ public function buildForm(array $form, FormStateInterface $form_state, $entity_t
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     $form_state->setValueForElement($form['id'], $this->targetEntityTypeId . '.' . $form_state->getValue('id'));
   }
diff --git a/core/modules/field_ui/src/Form/FieldConfigEditForm.php b/core/modules/field_ui/src/Form/FieldConfigEditForm.php
index 8a3cd54..b759739 100644
--- a/core/modules/field_ui/src/Form/FieldConfigEditForm.php
+++ b/core/modules/field_ui/src/Form/FieldConfigEditForm.php
@@ -150,8 +150,8 @@ protected function actions(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     if (isset($form['default_value'])) {
       $item = $form['#entity']->get($this->entity->getName());
diff --git a/core/modules/field_ui/src/Form/FieldStorageConfigEditForm.php b/core/modules/field_ui/src/Form/FieldStorageConfigEditForm.php
index 58c4ea9..adafcc7 100644
--- a/core/modules/field_ui/src/Form/FieldStorageConfigEditForm.php
+++ b/core/modules/field_ui/src/Form/FieldStorageConfigEditForm.php
@@ -146,8 +146,8 @@ protected function actions(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     // Validate field cardinality.
     if ($form_state->getValue('cardinality') === 'number' && !$form_state->getValue('cardinality_number')) {
diff --git a/core/modules/filter/src/FilterFormatFormBase.php b/core/modules/filter/src/FilterFormatFormBase.php
index cbc68d6..be5fc56 100644
--- a/core/modules/filter/src/FilterFormatFormBase.php
+++ b/core/modules/filter/src/FilterFormatFormBase.php
@@ -204,8 +204,8 @@ public function exists($format_id) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     // @todo Move trimming upstream.
     $format_format = trim($form_state->getValue('format'));
diff --git a/core/modules/forum/src/Form/Overview.php b/core/modules/forum/src/Form/Overview.php
index 24f5142..dae7fb5 100644
--- a/core/modules/forum/src/Form/Overview.php
+++ b/core/modules/forum/src/Form/Overview.php
@@ -86,9 +86,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
     // Remove the alphabetical reset.
     unset($form['actions']['reset_alphabetical']);
 
-    // The form needs to have submit and validate handlers set explicitly.
     // Use the existing taxonomy overview submit handler.
-    $form['#submit'] = array('::submitForm');
     $form['terms']['#empty'] = $this->t('No containers or forums available. <a href="@container">Add container</a> or <a href="@forum">Add forum</a>.', array(
       '@container' => $this->url('forum.add_container'),
       '@forum' => $this->url('forum.add_forum')
diff --git a/core/modules/node/src/NodeTypeForm.php b/core/modules/node/src/NodeTypeForm.php
index 6dfc669..ff757f9 100644
--- a/core/modules/node/src/NodeTypeForm.php
+++ b/core/modules/node/src/NodeTypeForm.php
@@ -204,8 +204,8 @@ protected function actions(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     $id = trim($form_state->getValue('type'));
     // '0' is invalid, since elsewhere we check it using empty().
diff --git a/core/modules/responsive_image/src/ResponsiveImageStyleForm.php b/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
index 365f7a5..171450b 100644
--- a/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
+++ b/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
@@ -133,7 +133,8 @@ public function form(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
     // Only validate on edit.
     if ($form_state->hasValue('keyed_styles')) {
       // Check if another breakpoint group is selected.
diff --git a/core/modules/search/src/Form/SearchPageFormBase.php b/core/modules/search/src/Form/SearchPageFormBase.php
index 95afb4b..c41fd5b 100644
--- a/core/modules/search/src/Form/SearchPageFormBase.php
+++ b/core/modules/search/src/Form/SearchPageFormBase.php
@@ -144,8 +144,8 @@ public function exists($id) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     // Ensure each path is unique.
     $path = $this->entityQuery->get('search_page')
diff --git a/core/modules/system/src/Form/DateFormatFormBase.php b/core/modules/system/src/Form/DateFormatFormBase.php
index c843ba2..fa1ac33 100644
--- a/core/modules/system/src/Form/DateFormatFormBase.php
+++ b/core/modules/system/src/Form/DateFormatFormBase.php
@@ -155,8 +155,8 @@ public function form(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     // The machine name field should already check to see if the requested
     // machine name is available. Regardless of machine_name or human readable
diff --git a/core/modules/taxonomy/src/TermForm.php b/core/modules/taxonomy/src/TermForm.php
index daa2868..e168987 100644
--- a/core/modules/taxonomy/src/TermForm.php
+++ b/core/modules/taxonomy/src/TermForm.php
@@ -94,8 +94,8 @@ public function form(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     // Ensure numeric values.
     if ($form_state->hasValue('weight') && !is_numeric($form_state->getValue('weight'))) {
diff --git a/core/modules/user/src/AccountForm.php b/core/modules/user/src/AccountForm.php
index 16ab69f..f8f94a4 100644
--- a/core/modules/user/src/AccountForm.php
+++ b/core/modules/user/src/AccountForm.php
@@ -354,9 +354,9 @@ public function buildEntity(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
+  public function validateForm(array &$form, FormStateInterface $form_state) {
     /** @var \Drupal\user\UserInterface $account */
-    $account = parent::validate($form, $form_state);
+    $account = parent::validateForm($form, $form_state);
 
     // Skip the protected user field constraint if the user came from the
     // password recovery page.
diff --git a/core/modules/views_ui/src/ViewAddForm.php b/core/modules/views_ui/src/ViewAddForm.php
index 9750094..0b41235 100644
--- a/core/modules/views_ui/src/ViewAddForm.php
+++ b/core/modules/views_ui/src/ViewAddForm.php
@@ -162,7 +162,7 @@ protected function actions(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
+  public function validateForm(array &$form, FormStateInterface $form_state) {
     $wizard_type = $form_state->getValue(array('show', 'wizard_key'));
     $wizard_instance = $this->wizardManager->createInstance($wizard_type);
     $form_state->set('wizard', $wizard_instance->getPluginDefinition());
diff --git a/core/modules/views_ui/src/ViewDuplicateForm.php b/core/modules/views_ui/src/ViewDuplicateForm.php
index 36f1a7f..ccc1a49 100644
--- a/core/modules/views_ui/src/ViewDuplicateForm.php
+++ b/core/modules/views_ui/src/ViewDuplicateForm.php
@@ -58,7 +58,6 @@ protected function actions(array $form, FormStateInterface $form_state) {
     $actions['submit'] = array(
       '#type' => 'submit',
       '#value' => $this->t('Duplicate'),
-      '#submit' => array('::submitForm'),
     );
     return $actions;
   }
diff --git a/core/modules/views_ui/src/ViewEditForm.php b/core/modules/views_ui/src/ViewEditForm.php
index 2fc7fc4..672c5f1 100644
--- a/core/modules/views_ui/src/ViewEditForm.php
+++ b/core/modules/views_ui/src/ViewEditForm.php
@@ -258,8 +258,8 @@ protected function actions(array $form, FormStateInterface $form_state) {
   /**
    * {@inheritdoc}
    */
-  public function validate(array $form, FormStateInterface $form_state) {
-    parent::validate($form, $form_state);
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
 
     $view = $this->entity;
     if ($view->isLocked()) {