MDL-59666 mod_assign: Add validation for grading due date

mod/assign/lang/en/assign.php

@@ -252,6 +252,8 @@ $string['grading'] = 'Grading';
 $string['gradingchangessaved'] = 'The grade changes were saved';
 $string['gradingduedate'] = 'Remind me to grade by';
 $string['gradingduedate_help'] = 'The expected date that marking of the submissions should be completed by. This date is used to prioritise dashboard notifications for teachers.';
+$string['gradingdueduedatevalidation'] = 'Remind me to grade by date cannot be earlier than the due date.';
+$string['gradingduefromdatevalidation'] = 'Remind me to grade by date cannot be earlier than the allow submissions from date.';
 $string['gradechangessaveddetail'] = 'The changes to the grade and feedback were saved';
 $string['gradingmethodpreview'] = 'Grading criteria';
 $string['gradingoptions'] = 'Options';

mod/assign/mod_form.php

@@ -238,6 +238,14 @@ class mod_assign_mod_form extends moodleform_mod {
                 $errors['cutoffdate'] = get_string('cutoffdatefromdatevalidation', 'assign');
             }
         }
+        if ($data['gradingduedate']) {
+            if ($data['allowsubmissionsfromdate'] && $data['allowsubmissionsfromdate'] > $data['gradingduedate']) {
+                $errors['gradingduedate'] = get_string('gradingduefromdatevalidation', 'assign');
+            }
+            if ($data['duedate'] && $data['duedate'] > $data['gradingduedate']) {
+                $errors['gradingduedate'] = get_string('gradingdueduedatevalidation', 'assign');
+            }
+        }
         if ($data['blindmarking'] && $data['attemptreopenmethod'] == ASSIGN_ATTEMPT_REOPEN_METHOD_UNTILPASS) {
             $errors['attemptreopenmethod'] = get_string('reopenuntilpassincompatiblewithblindmarking', 'assign');
         }