MDL-77464 questions: regrading was losing question_attempt metadata

This is very similar to MDL-77090, but at the time, I missed that this
also needed to be handled. (Question metadata is, I think, only used
by the quiz 'Try another question like this one' feature.)

mod/quiz/tests/behat/attempt_redo_questions.feature

@@ -55,6 +55,10 @@ Feature: Allow students to redo questions in a practice quiz, without starting a
     Then I should see "Finished regrading (1/1)"
     And I should see "Regrade completed"
     And I press "Continue"
+    # Regrade a second time, to ensure the first regrade did not corrupt any data.
+    And I press "Regrade all"
+    And I should see "Finished regrading (1/1)"
+    And I should see "Regrade completed"
 
   @javascript
   Scenario: Start attempt, teacher edits question, redo picks up latest non-draft version

question/engine/questionattempt.php

@@ -1472,11 +1472,16 @@ protected function get_attempt_state_data_to_regrade_with_version(question_attem
         if ($this->get_question(false) === $otherversion) {
             return $oldstep->get_all_data();
         } else {
+            // Update the data belonging to the question type by asking the question to do it.
             $attemptstatedata = $this->get_question(false)->update_attempt_state_data_for_new_version(
                     $oldstep, $otherversion);
 
-            foreach ($oldstep->get_behaviour_data() as $name => $value) {
-                $attemptstatedata['-' . $name] = $value;
+            // Then copy over all the behaviour and metadata variables.
+            // This terminology is explained in the class comment on {@see question_attempt_step}.
+            foreach ($oldstep->get_all_data() as $name => $value) {
+                if (substr($name, 0, 1) === '-' || substr($name, 0, 2) === ':_') {
+                    $attemptstatedata[$name] = $value;
+                }
             }
             return $attemptstatedata;
         }

question/engine/tests/walkthrough_test.php

@@ -134,7 +134,7 @@ public function test_action_author_with_display_options_testcase() {
      */
     public function test_regrading_an_interactive_attempt_while_in_progress() {
 
-        // Start at attempt at a matching question.
+        // Start an attempt at a matching question.
         $q = test_question_maker::make_question('match');
         $this->start_attempt_at_question($q, 'interactive', 1);
         $this->save_quba();
@@ -156,4 +156,36 @@ public function test_regrading_an_interactive_attempt_while_in_progress() {
         $this->check_step_count(1);
         $this->check_current_output($this->get_tries_remaining_expectation(1));
     }
+
+    /**
+     * @covers \question_usage_by_activity::regrade_question
+     * @covers \question_attempt::regrade
+     * @covers \question_attempt::get_attempt_state_data_to_regrade_with_version
+     */
+    public function test_regrading_does_not_lose_metadata() {
+
+        // Start an attempt at a matching question.
+        $q = test_question_maker::make_question('match');
+        $this->start_attempt_at_question($q, 'interactive', 1);
+        // Like in process_redo_question in mod_quiz.
+        $this->quba->set_question_attempt_metadata($this->slot, 'originalslot', 42);
+        $this->save_quba();
+
+        // Verify.
+        $this->check_current_state(question_state::$todo);
+        $this->check_current_mark(null);
+        $this->check_step_count(1);
+        $this->check_current_output($this->get_tries_remaining_expectation(1));
+
+        // Regrade the attempt.
+        $reloadedquestion = clone($q);
+        $this->quba->regrade_question($this->slot, false, null, $reloadedquestion);
+
+        // Verify.
+        $this->check_current_state(question_state::$todo);
+        $this->check_current_mark(null);
+        $this->check_step_count(1);
+        $this->check_current_output($this->get_tries_remaining_expectation(1));
+        $this->assertEquals(42, $this->quba->get_question_attempt_metadata($this->slot, 'originalslot'));
+    }
 }