From a3b02e0c6a7847eb837b4f274318bfba404aef90 Mon Sep 17 00:00:00 2001
From: ScottVerbeek <scottverbeek@catalyst-au.net>
Date: Thu, 20 Jul 2023 09:38:06 +1000
Subject: [PATCH] MDL-77381 question engine: don't query empty arrays

---
 question/engine/datalib.php                   |  4 +-
 .../tests/datalib_reporting_queries_test.php  | 48 +++++++++++++++++++
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/question/engine/datalib.php b/question/engine/datalib.php
index 2f0208a54c4..c671c4fa1e8 100644
--- a/question/engine/datalib.php
+++ b/question/engine/datalib.php
@@ -560,7 +560,9 @@ ORDER BY
      * @return array of records. See the SQL in this function to see the fields available.
      */
     public function load_questions_usages_latest_steps(qubaid_condition $qubaids, $slots = null, $fields = null) {
-        if ($slots !== null) {
+        if ($slots === []) {
+            return [];
+        } else if ($slots !== null) {
             [$slottest, $params] = $this->db->get_in_or_equal($slots, SQL_PARAMS_NAMED, 'slot');
             $slotwhere = " AND qa.slot {$slottest}";
         } else {
diff --git a/question/engine/tests/datalib_reporting_queries_test.php b/question/engine/tests/datalib_reporting_queries_test.php
index 993e8866368..268c2724054 100644
--- a/question/engine/tests/datalib_reporting_queries_test.php
+++ b/question/engine/tests/datalib_reporting_queries_test.php
@@ -16,6 +16,8 @@
 
 namespace core_question;
 
+use mod_quiz\quiz_attempt;
+use mod_quiz\quiz_settings;
 use qubaid_list;
 use question_bank;
 use question_engine;
@@ -332,4 +334,50 @@ class datalib_reporting_queries_test extends \qbehaviour_walkthrough_test_base {
             'state'          => (string) question_state::$gaveup,
         ), $state);
     }
+
+    /**
+     * Test that a Quiz with only description questions wont break \quiz_statistics\task\recalculate.
+     *
+     * @covers \quiz_statistics\task\recalculate::execute()
+     * @return void
+     */
+    public function test_quiz_with_description_questions_recalculate_statistics() {
+        $this->resetAfterTest();
+
+        // Create course with quiz module.
+        $course = $this->getDataGenerator()->create_course();
+        $quizgenerator = $this->getDataGenerator()->get_plugin_generator('mod_quiz');
+        $layout = '1';
+        $quiz = $quizgenerator->create_instance([
+            'course' => $course->id,
+            'grade' => 0.0, 'sumgrades' => 1,
+            'layout' => $layout
+        ]);
+
+        // Add question of type description to quiz.
+        $questiongenerator = $this->getDataGenerator()->get_plugin_generator('core_question');
+        $cat = $questiongenerator->create_question_category();
+        $question = $questiongenerator->create_question('description', null, ['category' => $cat->id]);
+        quiz_add_quiz_question($question->id, $quiz);
+
+        // Create attempt.
+        $user = $this->getDataGenerator()->create_user();
+        $quizobj = quiz_settings::create($quiz->id, $user->id);
+        $quba = question_engine::make_questions_usage_by_activity('mod_quiz', $quizobj->get_context());
+        $quba->set_preferred_behaviour($quizobj->get_quiz()->preferredbehaviour);
+        $timenow = time();
+        $attempt = quiz_create_attempt($quizobj, 1, null, $timenow, false, $user->id);
+        quiz_start_new_attempt($quizobj, $quba, $attempt, 1, $timenow);
+        quiz_attempt_save_started($quizobj, $quba, $attempt);
+
+        // Submit attempt.
+        $attemptobj = quiz_attempt::create($attempt->id);
+        $attemptobj->process_submitted_actions($timenow, false);
+        $attemptobj->process_finish($timenow, false);
+
+        // Calculate the statistics.
+        $this->expectOutputRegex('~.*Calculations completed.*~');
+        $statisticstask = new \quiz_statistics\task\recalculate();
+        $statisticstask->execute();
+    }
 }