Issue #3013290 by blacklabel_tom: Dead links on the rest module help page /admin/help/rest

core/modules/rest/rest.module

@@ -20,7 +20,7 @@ function rest_help($route_name, RouteMatchInterface $route_match) {
       $output .= '<h3>' . t('Uses') . '</h3>';
       $output .= '<dl>';
       $output .= '<dt>' . t('Installing supporting modules') . '</dt>';
-      $output .= '<dd>' . t('In order to use REST on a web site, you need to install modules that provide serialization and authentication services. You can use the Core module <a href=":hal">HAL</a> for serialization and <a href=":basic_auth">HTTP Basic Authentication</a> for authentication, or install a contributed or custom module.', [':hal' => (\Drupal::moduleHandler()->moduleExists('hal')) ? \Drupal::url('help.page', ['name' => 'hal']) : '#', ':basic_auth' => (\Drupal::moduleHandler()->moduleExists('basic_auth')) ? \Drupal::url('help.page', ['name' => 'basic_auth']) : '#']) . '</dd>';
+      $output .= '<dd>' . t('In order to use REST on a web site, you need to install modules that provide serialization and authentication services. You can use the Core module <a href=":hal">HAL</a> for serialization and <a href=":basic_auth">HTTP Basic Authentication</a> for authentication, or install a contributed or custom module.', [':hal' => (\Drupal::moduleHandler()->moduleExists('hal')) ? \Drupal::url('help.page', ['name' => 'hal']) : 'https://www.drupal.org/docs/8/core/modules/hal/overview', ':basic_auth' => (\Drupal::moduleHandler()->moduleExists('basic_auth')) ? \Drupal::url('help.page', ['name' => 'basic_auth']) : 'https://www.drupal.org/docs/8/core/modules/basic_auth/overview']) . '</dd>';
       $output .= '<dt>' . t('Enabling REST support for an entity type') . '</dt>';
       $output .= '<dd>' . t('REST support for content types (provided by the <a href=":node">Node</a> module) is enabled by default. To enable support for other content entity types, you can use a <a href=":config" target="blank">process based on configuration editing</a> or the contributed <a href=":restui">REST UI module</a>.', [':node' => (\Drupal::moduleHandler()->moduleExists('node')) ? \Drupal::url('help.page', ['name' => 'node']) : '#', ':config' => 'https://www.drupal.org/documentation/modules/rest', ':restui' => 'https://www.drupal.org/project/restui']) . '</dd>';
       $output .= '<dd>' . t('You will also need to grant anonymous users permission to perform each of the REST operations you want to be available, and set up authentication properly to authorize web requests.') . '</dd>';