Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.348
diff -u -p -r1.348 bootstrap.inc
--- includes/bootstrap.inc	31 Jan 2010 18:31:46 -0000	1.348
+++ includes/bootstrap.inc	4 Feb 2010 23:54:27 -0000
@@ -2081,7 +2081,32 @@ function drupal_autoload_class($class) {
  *   NULL if either of the REGISTRY_* constants is passed in as $type.
  */
 function _registry_check_code($type, $name = NULL) {
-  static $lookup_cache, $cache_update_needed;
+  static $lookup_cache, $cache_update_needed, $database_included;
+
+  // Include all database-related files. This avoids a problem when the db
+  // layer uses class_exists(), which indirectly calls  _registry_check_code()
+  // through the registered autoloader. _registry_check_code() needs to use the
+  // database to do the check properly, so we avoid the circular logic here.
+  $connection_info = Database::getConnectionInfo();
+  $driver = $connection_info['default']['driver'];
+
+  if ($name && preg_match('/_' . $driver . '$/', $name)) {
+    if (!isset($database_included)) {
+      require_once DRUPAL_ROOT . '/includes/database/database.inc';
+      require_once DRUPAL_ROOT . '/includes/database/query.inc';
+      require_once DRUPAL_ROOT . '/includes/database/select.inc';
+      require_once DRUPAL_ROOT . '/includes/database/schema.inc';
+
+      foreach (glob(DRUPAL_ROOT . '/includes/database/' . $driver . '/*.inc') as $include_file) {
+        if (basename($include_file) != 'install.inc') {
+          require_once $include_file;
+        }
+      }
+      $database_included = TRUE;
+    }
+    $function = $type . '_exists';
+    return $function($name);
+  }
 
   if ($type == 'class' && class_exists($name) || $type == 'interface' && interface_exists($name)) {
     return TRUE;
@@ -2124,7 +2149,23 @@ function _registry_check_code($type, $na
   // This function may get called when the default database is not active, but
   // there is no reason we'd ever want to not use the default database for
   // this query.
-  $file = Database::getConnection('default', 'default')->query("SELECT filename FROM {registry} WHERE name = :name AND type = :type", array(
+  $db = Database::getConnection('default', 'default');
+  // Repopulate the registry if it appears empty.
+  if (!$count = $db->query('SELECT 1 FROM {registry}')->fetchField()) {
+    // If Drupal hasn't been fully boostrapped, we need to include common.inc.
+    require_once DRUPAL_ROOT . '/includes/common.inc';
+    require_once DRUPAL_ROOT . '/includes/registry.inc';
+    _registry_update();
+    if (!$count = $db->query('SELECT 1 FROM {registry}')->fetchField()) {
+      // Registry is still empty.
+      return FALSE;
+    }
+  }
+
+  // This function may get called when the default database is not active, but
+  // there is no reason we'd ever want to not use the default database for
+  // this query.
+  $file = $db->query("SELECT filename FROM {registry} WHERE name = :name AND type = :type", array(
       ':name' => $name,
       ':type' => $type,
     ))
Index: includes/registry.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/registry.inc,v
retrieving revision 1.27
diff -u -p -r1.27 registry.inc
--- includes/registry.inc	28 Dec 2009 10:48:51 -0000	1.27
+++ includes/registry.inc	4 Feb 2010 23:54:27 -0000
@@ -52,6 +52,9 @@ function _registry_update() {
       }
     }
   }
+  if (!function_exists('file_scan_directory')) {
+    require_once DRUPAL_ROOT . '/includes/file.inc';
+  }
   foreach (file_scan_directory('includes', '/\.inc$/') as $filename => $file) {
     $files["$filename"] = array('module' => '', 'weight' => 0);
   }