MDL-55937 assign: Check for group submission caps when userid=0

mod/assign/locallib.php

@@ -2831,7 +2831,12 @@ class assign {
             $item = $this->get_submission($submissionid);
 
             // Check permissions.
-            $this->require_view_submission($item->userid);
+            if (empty($item->userid)) {
+                // Group submission.
+                $this->require_view_group_submission($item->groupid);
+            } else {
+                $this->require_view_submission($item->userid);
+            }
             $o .= $this->get_renderer()->render(new assign_header($this->get_instance(),
                                                               $this->get_context(),
                                                               $this->show_intro(),
@@ -3026,6 +3031,18 @@ class assign {
         return '';
     }
 
+    /**
+     * Throw an error if the permissions to view this users' group submission are missing.
+     *
+     * @param int $groupid Group id.
+     * @throws required_capability_exception
+     */
+    public function require_view_group_submission($groupid) {
+        if (!$this->can_view_group_submission($groupid)) {
+            throw new required_capability_exception($this->context, 'mod/assign:viewgrades', 'nopermission', '');
+        }
+    }
+
     /**
      * Throw an error if the permissions to view this users submission are missing.
      *