Issue #6351: Fix jquery.ui focus conflict for CKEditor form elements.

By @indigoxela, @quicksketch, and @herbdool.

core/modules/ckeditor5/ckeditor5.module

@@ -168,6 +168,19 @@ function ckeditor5_library_info() {
   return $libraries;
 }
 
+/**
+ * Implements hook_library_info_alter().
+ */
+function ckeditor5_library_info_alter(&$libraries, $module) {
+  if ($module == 'system' && isset($libraries['ui.dialog'])) {
+    // Override jquery.ui dialog _allowInteraction method to allow interaction
+    // for editor form elements from within jquery dialogs.
+    // @see https://bugs.jqueryui.com/ticket/9087/
+    $path = backdrop_get_path('module', 'ckeditor5') . '/js/ckeditor5-dialog-fix.js';
+    $libraries['ui.dialog']['js'][$path] = array();
+  }
+}
+
 /**
  * Implements hook_theme().
  */

core/modules/ckeditor5/js/ckeditor5-dialog-fix.js

@@ -0,0 +1,28 @@
+/**
+ * @file
+ * Fix conflict with jquery.ui focusin event handling in dialogs.
+ */
+(function ($) {
+
+  'use strict';
+
+  /**
+   * Override the _allowInteraction() extension point.
+   *
+   * @see https://api.jqueryui.com/dialog/#method-_allowInteraction
+   * @see https://bugs.jqueryui.com/ticket/9087/
+   */
+  $.widget('ui.dialog', $.ui.dialog, {
+    _allowInteraction: function _allowInteraction(event) {
+      // The CKEditor 5 balloon toolbar is outside the modal container, by
+      // specifying CKEditor elements as allowed-interaction outside the modal,
+      // the balloon buttons can be clicked. All editor form elements, like
+      // buttons in balloon toolbars get the "ck" class.
+      if ($(event.target).hasClass('ck')) {
+        return true;
+      }
+      return this._super(event);
+    }
+  });
+
+})(jQuery);