MDL-67947 questions: questions_in_use should ask all components

Previously it was only checking mods.

lang/en/question.php

@@ -287,7 +287,7 @@ $string['questiondoesnotexist'] = 'This question does not exist';
 $string['questionname'] = 'Question name';
 $string['questionno'] = 'Question {$a}';
 $string['questionsaveerror'] = 'Errors occur during saving question - ({$a})';
-$string['questionsinuse'] = '(* Questions marked by an asterisk are already in use in some quizzes. These questions will not be deleted from these quizzes but only from the category list.)';
+$string['questionsinuse'] = '(* Questions marked with an asterisk are used somewhere, for example in a quiz. Therefore, if you proceed, these questions will not really be deleted, they will just be hidden.)';
 $string['questionsmovedto'] = 'Questions still in use moved to "{$a}" in the parent course category.';
 $string['questionsrescuedfrom'] = 'Questions saved from context {$a}.';
 $string['questionsrescuedfrominfo'] = 'These questions (some of which may be hidden) were saved when context {$a} was deleted because they are still used by some quizzes or other activities.';

lib/questionlib.php

@@ -119,34 +119,35 @@ function question_save_qtype_order($neworder, $config = null) {
  * @return boolean whether any of these questions are being used by any part of Moodle.
  */
 function questions_in_use($questionids) {
-    global $CFG;
 
+    // Are they used by the core question system?
     if (question_engine::questions_in_use($questionids)) {
         return true;
     }
 
-    foreach (core_component::get_plugin_list('mod') as $module => $path) {
-        $lib = $path . '/lib.php';
-        if (is_readable($lib)) {
-            include_once($lib);
+    // Check if any plugins are using these questions.
+    $callbacksbytype = get_plugins_with_function('questions_in_use');
+    foreach ($callbacksbytype as $callbacks) {
+        foreach ($callbacks as $function) {
+            if ($function($questionids)) {
+                return true;
+            }
+        }
+    }
 
-            $fn = $module . '_questions_in_use';
-            if (function_exists($fn)) {
-                if ($fn($questionids)) {
-                    return true;
-                }
-            } else {
+    // Finally check legacy callback.
+    $legacycallbacks = get_plugin_list_with_function('mod', 'question_list_instances');
+    foreach ($legacycallbacks as $plugin => $function) {
+        debugging($plugin . ' implements deprecated method ' . $function .
+                '. ' . $plugin . '_questions_in_use should be implemented instead.', DEBUG_DEVELOPER);
 
-                // Fallback for legacy modules.
-                $fn = $module . '_question_list_instances';
-                if (function_exists($fn)) {
-                    foreach ($questionids as $questionid) {
-                        $instances = $fn($questionid);
-                        if (!empty($instances)) {
-                            return true;
-                        }
-                    }
-                }
+        if (isset($callbacksbytype['mod'][substr($plugin, 4)])) {
+            continue; // Already done.
+        }
+
+        foreach ($questionids as $questionid) {
+            if (!empty($function($questionid))) {
+                return true;
             }
         }
     }

question/upgrade.txt

 This files describes API changes for code that uses the question API.
 
+=== 3.9 ==
+
+For years, the ..._questions_in_use callback has been the right way for plugins to
+tell the core question system if questions are required. Previously this callback
+only worked in mods. Now it works in all plugins.
+
+At the same time, if you are still relying on the legacy ..._question_list_instances
+callback for this, you will now get a debugging warning telling you to upgrade.
+
 === 3.8 ===
 
 If you have customised the display of the question bank (using $CFG->questionbankcolumns)