Issue #3285054 by lauriii, Wim Leers: Add ckeditor5-stylesheets: false to Claro and Olivero (and fix it)

core/modules/ckeditor5/ckeditor5.module

@@ -639,7 +639,7 @@ function _ckeditor5_theme_css($theme = NULL): array {
   }
   if (isset($theme) && $theme_path = \Drupal::service('extension.list.theme')->getPath($theme)) {
     $info = \Drupal::service('extension.list.theme')->getExtensionInfo($theme);
-    if (isset($info['ckeditor5-stylesheets'])) {
+    if (isset($info['ckeditor5-stylesheets']) && $info['ckeditor5-stylesheets'] !== FALSE) {
       $css = $info['ckeditor5-stylesheets'];
       foreach ($css as $key => $url) {
         // CSS url is external or relative to Drupal root.

core/modules/ckeditor5/tests/src/Functional/AddedStylesheetsTest.php

@@ -83,6 +83,7 @@ class AddedStylesheetsTest extends BrowserTestBase {
       'use text format llama',
       'administer themes',
       'view the administration theme',
+      'administer filters',
     ]);
     $this->drupalLogin($this->adminUser);
   }
@@ -102,6 +103,11 @@ class AddedStylesheetsTest extends BrowserTestBase {
     $this->drupalGet('node/add/article');
     $assert_session->responseNotContains('test_ckeditor_stylesheets_relative/css/yokotsoko.css');
 
+    // Confirm that the missing ckeditor5-stylesheets configuration can be
+    // bypassed.
+    $this->drupalGet('admin/config/content/formats/manage/llama');
+    $assert_session->pageTextNotContains('ckeditor_stylesheets configured without a corresponding ckeditor5-stylesheets configuration.');
+
     // Install a theme with ckeditor5-stylesheets configured. Do this manually
     // to confirm `library_info` cache tags are invalidated.
     $this->drupalGet('admin/appearance');

core/themes/claro/claro.info.yml

@@ -173,6 +173,8 @@ ckeditor_stylesheets:
   - css/theme/ckeditor-frame.css
   - css/classy/components/media-embed-error.css
 
+ckeditor5-stylesheets: false
+
 regions:
   header: 'Header'
   pre_content: 'Pre-content'

core/themes/olivero/olivero.info.yml

@@ -90,3 +90,5 @@ ckeditor_stylesheets:
   - css/components/table.css
   - css/components/text-content.css
   - css/theme/ckeditor-frame.css
+
+ckeditor5-stylesheets: false