Create new setting to control default, and set correct value in db for existing records.

add_form.php

@@ -125,10 +125,16 @@ class mod_attendance_add_form extends moodleform {
                             array('maxfiles' => EDITOR_UNLIMITED_FILES, 'noclean' => true, 'context' => $modcontext));
         $mform->setType('sdescription', PARAM_RAW);
 
+        if (!empty($pluginconfig->enablecalendar)) {
             $mform->addElement('checkbox', 'calendarevent', '', get_string('calendarevent', 'attendance'));
             $mform->addHelpButton('calendarevent', 'calendarevent', 'attendance');
-        // XXX - this should be modified to use a different config setting if we keep enablecalendar's current meaning
+            if (isset($pluginconfig->calendarevent_default)) {
-        $mform->setDefault('calendarevent', get_config('attendance', 'enablecalendar'));
+                $mform->setDefault('calendarevent', $pluginconfig->calendarevent_default);
+            }
+        } else {
+            $mform->addElement('hidden', 'calendarevent', 0);
+            $mform->setType('calendarevent', PARAM_INT);
+        }
 
         // If warnings allow selector for reporting.
         if (!empty(get_config('attendance', 'enablewarnings'))) {

db/upgrade.php

@@ -517,6 +517,10 @@ function xmldb_attendance_upgrade($oldversion=0) {
             XMLDB_NOTNULL, null, '1', 'caleventid');
         if (!$dbman->field_exists($table, $field)) {
             $dbman->add_field($table, $field);
+            if (empty(get_config('attendance', 'enablecalendar'))) {
+                // Calendar disabled on this site, set calendarevent for existing records to 0;
+                $DB->execute("UPDATE {attendance_sessions} set calendarevent = 0");
+            }
         }
         upgrade_mod_savepoint(true, 2018051402, 'attendance');
     }

settings.php

@@ -105,6 +105,9 @@ if ($ADMIN->fulltree) {
     $description = new lang_string('defaultsessionsettings_help', 'mod_attendance');
     $settings->add(new admin_setting_heading('defaultsessionsettings', $name, $description));
 
+    $settings->add(new admin_setting_configcheckbox('attendance/calendarevent_default',
+        get_string('calendarevent', 'attendance'), '', 1));
+
     $settings->add(new admin_setting_configcheckbox('attendance/absenteereport_default',
         get_string('includeabsentee', 'attendance'), '', 1));
 

update_form.php

@@ -113,10 +113,13 @@ class mod_attendance_update_form extends moodleform {
                            array('rows' => 1, 'columns' => 80), $defopts);
         $mform->setType('sdescription', PARAM_RAW);
 
+        if (!empty(get_config('attendance', 'enablecalendar'))) {
             $mform->addElement('checkbox', 'calendarevent', '', get_string('calendarevent', 'attendance'));
             $mform->addHelpButton('calendarevent', 'calendarevent', 'attendance');
-        // XXX - this should be modified to use a different config setting if we keep enablecalendar's current meaning
+        } else {
-        // $mform->setDefault('calendarevent', get_config('attendance', 'enablecalendar'));
+            $mform->addElement('hidden', 'calendarevent', 0);
+            $mform->setType('calendarevent', PARAM_INT);
+        }
 
         // If warnings allow selector for reporting.
         if (!empty(get_config('attendance', 'enablewarnings'))) {