MDL-39980 question engine: Attempt on last loses response files

When doing Each attempt builds on last, we need to copy any response
files into a draft file area, and then re-save them.

While writing the unit test for this, I had to deal with a todo in the
question engine so that questions with files in the response could be
unit-tested.

I also found an fixed a bug with qtype_essay_question::is_same_response
and fixed some notices in the existing essay/manual graded unit tests.

question/engine/datalib.php

@@ -1379,6 +1379,35 @@ class question_file_loader implements question_response_files {
     public function get_files() {
         return $this->step->get_qt_files($this->name, $this->contextid);
     }
+
+    /**
+     * Copy these files into a draft area, and return the corresponding
+     * {@link question_file_saver} that can save them again.
+     *
+     * This is used by {@link question_attempt::start_based_on()}, which is used
+     * (for example) by the quizzes 'Each attempt builds on last' feature.
+     *
+     * @return question_file_saver that can re-save these files again.
+     */
+    public function get_question_file_saver() {
+
+        // Value will be either a plain MD5 hash, or some real content, followed
+        // by an MD5 hash in a HTML comment. We only want the value in the latter case.
+        if (preg_match('/\s*<!-- File hash: [0-9a-zA-Z]{32} -->\s*$/', $this->value)) {
+            $value = preg_replace('/\s*<!-- File hash: [0-9a-zA-Z]{32} -->\s*$/', '', $this->value);
+
+        } else if (preg_match('/^[0-9a-zA-Z]{32}$/', $this->value)) {
+            $value = null;
+
+        } else {
+            throw new coding_exception('$value passed to question_file_loader::get_question_file_saver' .
+                    ' was not of the expected form.');
+        }
+
+        list($draftid, $text) = $this->step->prepare_response_files_draft_itemid_with_text(
+                $this->name, $this->contextid, $value);
+        return new question_file_saver($draftid, 'question', 'response_' . $this->name, $text);
+    }
 }
 
 

question/engine/questionattempt.php

@@ -923,7 +923,13 @@ class question_attempt {
      * @return array name => value pairs.
      */
     protected function get_resume_data() {
-        return $this->behaviour->get_resume_data();
+        $resumedata = $this->behaviour->get_resume_data();
+        foreach ($resumedata as $name => $value) {
+            if ($value instanceof question_file_loader) {
+                $resumedata[$name] = $value->get_question_file_saver();
+            }
+        }
+        return $resumedata;
     }
 
     /**
@@ -975,11 +981,12 @@ class question_attempt {
      */
     protected function process_response_files($name, $draftidname, $postdata = null, $text = null) {
         if ($postdata) {
-            // There can be no files with test data (at the moment).
-            return null;
+            // For simulated posts, get the draft itemid from there.
+            $draftitemid = $this->get_submitted_var($draftidname, PARAM_INT, $postdata);
+        } else {
+            $draftitemid = file_get_submitted_draft_itemid($draftidname);
         }
 
-        $draftitemid = file_get_submitted_draft_itemid($draftidname);
         if (!$draftitemid) {
             return null;
         }

question/engine/questionattemptstep.php

@@ -106,7 +106,7 @@ class question_attempt_step {
         global $USER;
 
         if (!is_array($data)) {
-            echo format_backtrace(debug_backtrace());
+            throw new coding_exception('$data must be an array when constructing a question_attempt_step.');
         }
         $this->state = question_state::$unprocessed;
         $this->data = $data;