Add WAGTAIL_SLIM_SIDEBAR = False setting to switch back to legacy sidebar

docs/reference/settings.rst

@@ -217,6 +217,15 @@ If a user has not uploaded a profile picture, Wagtail will look for an avatar li
 
 Changes whether the Submit for Moderation button is displayed in the action menu.
 
+``WAGTAIL_SLIM_SIDEBAR``
+------------------------
+
+.. code-block:: python
+
+  WAGTAIL_SLIM_SIDEBAR = False
+
+Disables Wagtail’s slim sidebar to use the legacy sidebar instead.
+
 Comments
 ========
 

wagtail/admin/templatetags/wagtailadmin_tags.py

@@ -769,7 +769,7 @@ def locales():
 
 @register.simple_tag()
 def slim_sidebar_enabled():
-    return 'legacy-sidebar' not in getattr(settings, 'WAGTAIL_EXPERIMENTAL_FEATURES', [])
+    return getattr(settings, 'WAGTAIL_SLIM_SIDEBAR', True)
 
 
 @register.simple_tag(takes_context=True)

wagtail/admin/tests/test_menu.py

@@ -32,7 +32,7 @@ class TestMenuRendering(TestCase, WagtailTestUtils):
         response = self.client.get(reverse('wagtailadmin_home'))
         self.assertContains(response, 'sidebar-collapsed')
 
-    @override_settings(WAGTAIL_EXPERIMENTAL_FEATURES={'legacy-sidebar'})
+    @override_settings(WAGTAIL_SLIM_SIDEBAR=False)
     def test_not_collapsed_with_legacy(self):
         '''Sidebar should only remember its collapsed state with the slim implementation.'''
         # Sidebar should not be collapsed because the feature flag is not enabled