Mario Vercellotti · federico prato
--- a/src/AccessByTaxonomyService.php
+++ b/src/AccessByTaxonomyService.php
+      $form_state->clearErrors();
+      $response->addCommand(
+        new MessageCommand(
+          $access_by_taxonomy_service->translationManager->translate('To preview access changes, please fix these validation errors: <strong>:errors</strong>', [':errors' => implode(' ', $errors)]),
+          '#access_by_taxonomy_status_messages',
+          ['type' => 'warning'],
+          TRUE
+        )
+      );
+
+      // Since we validated the form, and there were errors, we need to delete
+      // error messages, because we don't want them to be displayed twice
+      // when the user reloads the page or navigates away from the page:
+      /** @var \Drupal\Core\Messenger\MessengerInterface $messenger */
+      $messenger = \Drupal::service('messenger');
+      $messenger->deleteByType('error');
--- a/src/AccessByTaxonomyService.php
+++ b/src/AccessByTaxonomyService.php
+    // form and test form state.
+    $test_form = $form;
+    $test_form_state = $form_state;

    /** @var \Drupal\Core\Entity\ContentEntityFormInterface $form_object */
-    $form_object = $form_state->getFormObject();
+    $form_object = $test_form_state->getFormObject();
+
+    try {
+      // Validate the form:
+      $form_object->validateForm($test_form, $test_form_state);
+    }
+    // Validation could trigger more errors depending on special validation
+    // needed for some of the fields in the form. We are not interested in those
+    // errors, so we catch them and ignore them.
+    catch (\Exception) {