Issue #3458183 by catch, Spokje: Deprecate $variables['teaser']

core/modules/node/node.module

@@ -476,8 +476,11 @@ function node_theme_suggestions_node(array $variables) {
  */
 function template_preprocess_node(&$variables) {
   $variables['view_mode'] = $variables['elements']['#view_mode'];
-  // Provide a distinct $teaser boolean.
+
+  // The teaser variable is deprecated.
+  $variables['deprecations']['teaser'] = "'teaser' is deprecated in drupal:11.1.0 and is removed in drupal:12.0.0. Use 'view_mode' instead. See https://www.drupal.org/node/3458185";
   $variables['teaser'] = $variables['view_mode'] == 'teaser';
+
   $variables['node'] = $variables['elements']['#node'];
   /** @var \Drupal\node\NodeInterface $node */
   $node = $variables['node'];

core/modules/node/templates/node.html.twig

@@ -54,7 +54,6 @@
  * - title_suffix: Additional output populated by modules, intended to be
  *   displayed after the main title tag that appears in the template.
  * - view_mode: View mode; for example, "teaser" or "full".
- * - teaser: Flag for the teaser state. Will be true if view_mode is 'teaser'.
  * - page: Flag for the full page state. Will be true if view_mode is 'full'.
  * - readmore: Flag for more state. Will be true if the teaser content of the
  *   node cannot hold the main body content.

core/themes/olivero/olivero.theme

@@ -97,7 +97,7 @@ function olivero_preprocess_maintenance_page(&$variables) {
 function olivero_preprocess_node(&$variables) {
   // Remove the "Add new comment" link on teasers or when the comment form is
   // displayed on the page.
-  if ($variables['teaser'] || !empty($variables['content']['comments']['comment_form'])) {
+  if ($variables['view_mode'] === 'teaser' || !empty($variables['content']['comments']['comment_form'])) {
     unset($variables['content']['links']['comment']['#links']['comment-add']);
   }