feat: store error representation in qt-variable

Author: janbritz

classes/constants.php

@@ -36,6 +36,8 @@ class constants {
     public const QT_VAR_SCORING_STATE = '_scoringstate';
     /** @var string */
     public const QT_VAR_RESPONSE = 'qpy_response';
+    /** @var string */
+    public const QT_VAR_ERROR = '_qpy_error';
 
     /** @var string This isn't needed after the action has been processed, so it's not a qt var. */
     public const FORM_DRAFT_AREAS = 'qpy_draft_areas';

question.php

@@ -23,6 +23,7 @@
  */
 
 use qtype_questionpy\constants;
+use qtype_questionpy\exception\request_error;
 use qtype_questionpy\local\api\api;
 use qtype_questionpy\local\api\attempt;
 use qtype_questionpy\local\api\attempt_ui;
@@ -372,7 +373,7 @@ public function summarise_response(array $response) {
             }
         }
 
-        return $summary ?: '-';
+        return $summary;
     }
 
     /**
@@ -427,6 +428,10 @@ public function grade_response(array $response): array {
             $event->trigger();
             debugging($event->get_description(), backtrace: $t->getTrace());
 
+            // Our question behaviour constructs an error message containing this error representation.
+            $error = $t instanceof request_error ? $t->requesterrorcode->value : $t::class . "({$t->getCode()}";
+            $this->get_behaviour()->get_pending_step()->set_qt_var(constants::QT_VAR_ERROR, $error);
+
             // As the server was not able to score the response, we mark this question with manual scoring.
             return [0, question_state::$needsgrading];
         }