MDL-32690: Restore 1.9 backup into 2.X fails on missing assignment type

Solution is as follows:
* Allow unsupported subplugins to convert from Moodle1 to Moodle2
* On Moodle2 restore hide unsupported subplugins
* Graceful error message in assignment of unsupported subplugins

mod/assignment/backup/moodle1/lib.php

@@ -194,7 +194,8 @@ class moodle1_mod_assignment_handler extends moodle1_mod_handler {
         }
 
         if (!isset($this->subpluginhandlers[$subplugin])) {
-            throw new moodle1_convert_exception('unsupported_subplugin', 'assignment_'.$subplugin);
+            // Generic handling, prevents breaking conversion process...
+            $this->subpluginhandlers[$subplugin] = new moodle1_assignment_unsupported_subplugin_handler($this, $subplugin);
         }
 
         return $this->subpluginhandlers[$subplugin];
@@ -236,4 +237,10 @@ abstract class moodle1_assignment_subplugin_handler extends moodle1_submod_handl
 
         //you will probably want to do stuff with $this->xmlwriter here (within your overridden method) to write plugin specific data.
     }
+}
+
+/**
+ * This class handles subplugins that do not exist or that are not supported
+ */
+class moodle1_assignment_unsupported_subplugin_handler extends moodle1_assignment_subplugin_handler {
 }

mod/assignment/backup/moodle2/restore_assignment_stepslib.php

@@ -72,6 +72,11 @@ class restore_assignment_activity_structure_step extends restore_activity_struct
         $newitemid = $DB->insert_record('assignment', $data);
         // immediately after inserting "activity" record, call this
         $this->apply_activity_instance($newitemid);
+
+        // Hide unsupported sub-plugins
+        if (!$this->is_valid_assignment_subplugin($data->assignmenttype)) {
+            $DB->set_field('course_modules', 'visible', 0, array('id' => $this->get_task()->get_moduleid()));
+        }
     }
 
     protected function process_assignment_submission($data) {
@@ -100,4 +105,19 @@ class restore_assignment_activity_structure_step extends restore_activity_struct
         $this->add_related_files('mod_assignment', 'submission', 'assignment_submission');
         $this->add_related_files('mod_assignment', 'response', 'assignment_submission');
     }
+
+    /**
+     * Determine if a sub-plugin is supported or not
+     *
+     * @param string $type
+     * @return bool
+     */
+    protected function is_valid_assignment_subplugin($type) {
+        static $subplugins = null;
+
+        if (is_null($subplugins)) {
+            $subplugins = get_plugin_list('assignment');
+        }
+        return array_key_exists($type, $subplugins);
+    }
 }

mod/assignment/lang/en/assignment.php

@@ -223,3 +223,4 @@ $string['viewfeedback'] = 'View assignment grades and feedback';
 $string['viewmysubmission'] = 'View my submission';
 $string['viewsubmissions'] = 'View {$a} submitted assignments';
 $string['yoursubmission'] = 'Your submission';
+$string['unsupportedsubplugin'] = 'The assignment type of \'{$a}\' is not currently supported. You may wait until the assignment type is made available, or delete the assignment.';

mod/assignment/lib.php

@@ -3948,7 +3948,12 @@ function assignment_extend_settings_navigation(settings_navigation $settings, na
     global $PAGE, $DB, $USER, $CFG;
 
     $assignmentrow = $DB->get_record("assignment", array("id" => $PAGE->cm->instance));
-    require_once "$CFG->dirroot/mod/assignment/type/$assignmentrow->assignmenttype/assignment.class.php";
+
+    $classfile = "$CFG->dirroot/mod/assignment/type/$assignmentrow->assignmenttype/assignment.class.php";
+    if (!file_exists($classfile)) {
+        return;
+    }
+    require_once($classfile);
 
     $assignmentclass = 'assignment_'.$assignmentrow->assignmenttype;
     $assignmentinstance = new $assignmentclass($PAGE->cm->id, $assignmentrow, $PAGE->cm, $PAGE->course);

mod/assignment/mod_form.php

@@ -9,7 +9,7 @@ class mod_assignment_mod_form extends moodleform_mod {
     protected $_assignmentinstance = null;
 
     function definition() {
-        global $CFG, $DB, $PAGE;
+        global $CFG, $DB, $PAGE, $COURSE;
         $mform =& $this->_form;
 
         // this hack is needed for different settings of each subtype
@@ -29,7 +29,11 @@ class mod_assignment_mod_form extends moodleform_mod {
         $mform->setType('type', PARAM_ALPHA);
         $mform->setDefault('type', $type);
 
-        require_once($CFG->dirroot.'/mod/assignment/type/'.$type.'/assignment.class.php');
+        $classfile = $CFG->dirroot.'/mod/assignment/type/'.$type.'/assignment.class.php';
+        if (!file_exists($classfile)) {
+            throw new moodle_exception('unsupportedsubplugin', 'assignment', new moodle_url('/course/view.php', array('id' => $COURSE->id)), $type);
+        }
+        require_once($classfile);
         $assignmentclass = 'assignment_'.$type;
         $assignmentinstance = new $assignmentclass();
 

mod/assignment/view.php

@@ -40,7 +40,11 @@ require_login($course, true, $cm);
 
 $PAGE->requires->js('/mod/assignment/assignment.js');
 
-require ("$CFG->dirroot/mod/assignment/type/$assignment->assignmenttype/assignment.class.php");
+$classfile = "$CFG->dirroot/mod/assignment/type/$assignment->assignmenttype/assignment.class.php";
+if (!file_exists($classfile)) {
+    throw new moodle_exception('unsupportedsubplugin', 'assignment', new moodle_url('/course/view.php', array('id' => $course->id)), $assignment->assignmenttype);
+}
+require ($classfile);
 $assignmentclass = "assignment_$assignment->assignmenttype";
 $assignmentinstance = new $assignmentclass($cm->id, $assignment, $cm, $course);