MDL-79307 assignfeedback_editpdf: more informative task failure.

If ghostscript is not correctly configured the task will never
succeed, so error out earlier with a more informative exception
explaining this.

mod/assign/feedback/editpdf/classes/task/convert_submission.php

@@ -20,7 +20,9 @@
 use core\task\manager;
 use assignfeedback_editpdf\document_services;
 use assignfeedback_editpdf\combined_document;
+use assignfeedback_editpdf\pdf;
 use context_module;
+use moodle_exception;
 use assign;
 
 /**
@@ -47,6 +49,13 @@ public function execute() {
             return;
         }
 
+        // Early exit if ghostscript isn't correctly configured.
+        $result = pdf::test_gs_path(false);
+        if ($result->status !== pdf::GSPATH_OK) {
+            $statusstring = get_string('test_' . $result->status, 'assignfeedback_editpdf');
+            throw new moodle_exception('pathtogserror', 'assignfeedback_editpdf', '', $statusstring, $result->status);
+        }
+
         $cm = get_coursemodule_from_instance('assign', $submission->assignment, 0, false, MUST_EXIST);
         $context = context_module::instance($cm->id);
         $assign = new assign($context, null, null);

mod/assign/feedback/editpdf/lang/en/assignfeedback_editpdf.php

@@ -59,6 +59,7 @@
 $string['gotopage'] = 'Go to page';
 $string['green'] = 'Green';
 $string['gsimage'] = 'Ghostscript test image';
+$string['pathtogserror'] = 'The configured path to ghostscript is not correctly set: {$a}';
 $string['pathtogspathdesc'] = 'Please note that annotate PDF requires the path to ghostscript to be set in {$a}.';
 $string['highlight'] = 'Highlight';
 $string['jsrequired'] = 'JavaScript is required to annotate a PDF. Please enable JavaScript in your browser to use this feature.';