Introduce a ConfigException

lib/configexception.php

@@ -0,0 +1,22 @@
+<?php
+
+if (!defined('GNUSOCIAL')) { exit(1); }
+
+/**
+ * Class for configuration exceptions
+ *
+ * Subclass of ServerException for when the site's configuration is malformed.
+ *
+ * @category Exception
+ * @package  GNUsocial
+ * @author   Mikael Nordfeldth <mmn@hethane.se>
+ * @license  https://www.fsf.org/licensing/licenses/agpl-3.0.html GNU Affero General Public License version 3.0
+ * @link     https://gnu.io/social
+ */
+
+class ConfigException extends ServerException
+{
+    public function __construct($message=null) {
+        parent::__construct($message, 500);
+    }
+}

lib/gnusocial.php

@@ -432,9 +432,13 @@ class GNUsocial
         if (common_config('htmlpurifier', 'Cache.DefinitionImpl') === 'Serializer'
                 && !is_dir(common_config('htmlpurifier', 'Cache.SerializerPath'))) {
             if (!mkdir(common_config('htmlpurifier', 'Cache.SerializerPath'))) {
-                throw new ServerException('Could not create HTMLPurifier cache dir: '._ve(common_config('htmlpurifier', 'Cache.SerializerPath')));
+                throw new ConfigException('Could not create HTMLPurifier cache dir: '._ve(common_config('htmlpurifier', 'Cache.SerializerPath')));
             }
         }
+
+        if (!is_array(common_config('public', 'autosource'))) {
+            throw new ConfigException('Configuration option public/autosource is not an array.');
+        }
     }
 
     /**