MDL-59909 calendar: Try hard not to fail the adhoc task.

Triggering a fatal error in an adhoc task is bad. It will be retried indefinitely.
Even though we are not sure how to get a module instance without a course module record,
it is possible and should not kill the Moodle site.

completion/classes/api.php

@@ -59,7 +59,10 @@ class api {
         if (is_object($instanceorid)) {
             $instance = $instanceorid;
         } else {
-            $instance = $DB->get_record($modulename, array('id' => $instanceorid), '*', MUST_EXIST);
+            $instance = $DB->get_record($modulename, array('id' => $instanceorid), '*', IGNORE_MISSING);
+        }
+        if (!$instance) {
+            return false;
         }
         $course = get_course($instance->course);
 

completion/tests/api_test.php

@@ -72,6 +72,13 @@ class core_completion_api_testcase extends advanced_testcase {
         $this->assertEquals(\core_completion\api::COMPLETION_EVENT_TYPE_DATE_COMPLETION_EXPECTED, $event->eventtype);
         $this->assertEquals($time, $event->timestart);
         $this->assertEquals($time, $event->timesort);
+
+        require_once($CFG->dirroot . '/course/lib.php');
+        // Delete the module.
+        course_delete_module($assign->cmid);
+
+        // Check we don't get a failure when called on a deleted module.
+        \core_completion\api::update_completion_date_event($assign->cmid, 'assign', null, $time);
     }
 
     public function test_update_completion_date_event_update() {

course/lib.php

@@ -1404,7 +1404,9 @@ function course_module_update_calendar_events($modulename, $instance = null, $cm
         if (!isset($cm)) {
             $cm = get_coursemodule_from_instance($modulename, $instance->id, $instance->course);
         }
-        course_module_calendar_event_update_process($instance, $cm);
+        if (!empty($cm)) {
+            course_module_calendar_event_update_process($instance, $cm);
+        }
         return true;
     }
     return false;
@@ -1433,8 +1435,9 @@ function course_module_bulk_update_calendar_events($modulename, $courseid = 0) {
     }
 
     foreach ($instances as $instance) {
-        $cm = get_coursemodule_from_instance($modulename, $instance->id, $instance->course);
-        course_module_calendar_event_update_process($instance, $cm);
+        if ($cm = get_coursemodule_from_instance($modulename, $instance->id, $instance->course)) {
+            course_module_calendar_event_update_process($instance, $cm);
+        }
     }
     return true;
 }

lib/classes/task/refresh_mod_calendar_events_task.php

@@ -44,6 +44,10 @@ class refresh_mod_calendar_events_task extends adhoc_task {
      * Run the task to refresh calendar events.
      */
     public function execute() {
+        global $CFG;
+
+        require_once($CFG->dirroot . '/course/lib.php');
+
         // Specific list of plugins that need to be refreshed. If not set, then all mod plugins will be refreshed.
         $pluginstorefresh = null;
         if (isset($this->get_custom_data()->plugins)) {