Issue #2650854 by acke, esolitos: ImmutableConfigException on "File settings" form

Author: esolitos

src/Form/FileSettingsForm.php

@@ -5,14 +5,15 @@
  */
 
 namespace Drupal\file_entity\Form;
-use Drupal\Core\Form\FormBase;
+
+use Drupal\Core\Form\ConfigFormBase;
 use Drupal\Core\Form\FormStateInterface;
 
 /**
  * Class FileSettingsForm
  * @package Drupal\file_entity\Form
  */
-class FileSettingsForm extends FormBase {
+class FileSettingsForm extends ConfigFormBase {
 
   /**
    * Returns a unique string identifying the form.
@@ -24,6 +25,15 @@ public function getFormId() {
     return 'file_settings';
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEditableConfigNames() {
+    return [
+      'file_entity.settings',
+    ];
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -33,7 +43,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#title' => t('Maximum upload size'),
       '#default_value' => \Drupal::config('file_entity.settings')->get('max_filesize'),
       '#description' => t('Enter a value like "512" (bytes), "80 KB" (kilobytes) or "50 MB" (megabytes) in order to restrict the allowed file size. If left empty the file sizes will be limited only by PHP\'s maximum post and file upload sizes (current max limit <strong>%limit</strong>).', array('%limit' => format_size(file_upload_max_size()))),
-      '#element_validate' => '\Drupal\file\Plugin\Field\FieldType\FileItem::validateMaxFilesize',
+      '#element_validate' => ['\Drupal\file\Plugin\Field\FieldType\FileItem::validateMaxFilesize'],
       '#size' => 10,
     );
 
@@ -42,7 +52,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#title' => t('Default allowed file extensions'),
       '#default_value' => \Drupal::config('file_entity.settings')->get('default_allowed_extensions'),
       '#description' => t('Separate extensions with a space or comma and do not include the leading dot.'),
-      '#element_validate' => '\Drupal\file\Plugin\Field\FieldType\FileItem::validateExtensions',
+      '#element_validate' => ['\Drupal\file\Plugin\Field\FieldType\FileItem::validateExtensions'],
       '#maxlength' => NULL,
     );