Resolve #3463119 "Abort validation"

Closes #3463119

src/Plugin/Filter/FilterMarkdown.php

@@ -419,9 +419,33 @@ class FilterMarkdown extends FilterBase implements ContainerFactoryPluginInterfa
       $parserElement['id']['#description'] = $this->moreInfo($parserElement['id']['#description'], $url);
     }
 
+    // When the markdown filter is not enabled, not all required information for
+    // to validate the settings is available. In this case, clear the settings
+    // as they are not needed anyway when the markdown filter is disabled.
+    $element['#element_validate'][] = [$this, 'subformValidate'];
+
     return $element;
   }
 
+  /**
+   * Removes the markdown settings when the markdown filter is disabled.
+   *
+   * @param array $element
+   *   The element being validated.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current form state.
+   */
+  public function subformValidate(array $element, FormStateInterface $form_state) {
+    $markdown = &$form_state->getValue(['filters', 'markdown']);
+
+    // Check if markdown is enabled. If it is not, do not attempt to save any
+    // settings to avoid validation issues.
+    if (empty($markdown['status'])) {
+      // Do not save any settings.
+      unset($markdown['settings']);
+    }
+  }
+
   /**
    * The AJAX callback used to return the parser ajax wrapper.
    */