Issue #3376376: HelpSectionManager::clearCachedDefinitions breaks the update system

core/modules/help/help.module

@@ -148,7 +148,7 @@ function _help_search_update(array $extensions = []): void {
     return;
   }
 
-  if (\Drupal::service('update.update_hook_registry')->getInstalledVersion('help') >= 10100) {
+  if (_help_is_fully_installed()) {
     // Ensure that topics for extensions that have been uninstalled are removed
     // and that the index state variable is updated.
     $help_search = \Drupal::service('plugin.manager.search')->createInstance('help_search');
@@ -156,3 +156,15 @@ function _help_search_update(array $extensions = []): void {
     $help_search->updateIndexState();
   }
 }
+
+/**
+ * Checks whether the help module installation is complete.
+ *
+ * @return bool
+ *
+ * @see \help_update_10200()
+ */
+function _help_is_fully_installed(): bool {
+  return \Drupal::service('update.update_hook_registry')
+    ->getInstalledVersion('help') >= 10200;
+}

core/modules/help/src/HelpSectionManager.php

@@ -57,8 +57,7 @@ class HelpSectionManager extends DefaultPluginManager {
    */
   public function clearCachedDefinitions() {
     parent::clearCachedDefinitions();
-    $version = \Drupal::service('update.update_hook_registry')->getInstalledVersion('help');
-    if ($this->searchManager && $version >= 10100) {
+    if ($this->searchManager && _help_is_fully_installed()) {
       // Rebuild the index on cache clear so that new help topics are indexed
       // and any changes due to help topics edits or translation changes are
       // picked up.