MDL-20154 quiz: Remove unused random questions

When a random question is removed from a quiz, and it is not
in use elsewhere, it should be deleted.

Conflicts:
	mod/quiz/editlib.php
	mod/quiz/lib.php

mod/quiz/editlib.php

@@ -76,6 +76,12 @@ function quiz_remove_question($quiz, $questionid) {
     $DB->set_field('quiz', 'questions', $quiz->questions, array('id' => $quiz->id));
     $DB->delete_records('quiz_question_instances',
             array('quiz' => $quiz->instance, 'question' => $questionid));
+
+    $qtype = $DB->get_field('question', 'qtype', array('id' => $questionid));
+    if ($qtype === 'random') {
+        // This function automatically checks if the question is in use, and won't delete if it is.
+        question_delete_question($questionid);
+    }
 }
 
 /**

mod/quiz/lib.php

@@ -170,7 +170,20 @@ function quiz_delete_instance($id) {
     quiz_delete_all_attempts($quiz);
     quiz_delete_all_overrides($quiz);
 
+    // Look for random questions that may no longer be used when this quiz is gone.
+    $sql = "SELECT q.id
+              FROM {quiz_question_instances} instance
+              JOIN {question} q ON q.id = instance.question
+             WHERE instance.quiz = ? AND q.qtype = ?";
+    $questionids = $DB->get_fieldset_sql($sql, array($quiz->id, 'random'));
+
+    // We need to do this before we try and delete randoms, otherwise they would still be 'in use'.
     $DB->delete_records('quiz_question_instances', array('quiz' => $quiz->id));
+
+    foreach ($questionids as $questionid) {
+        question_delete_question($questionid);
+    }
+
     $DB->delete_records('quiz_feedback', array('quizid' => $quiz->id));
 
     quiz_access_manager::delete_settings($quiz);