Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.1013
diff -u -p -r1.1013 common.inc
--- includes/common.inc	11 Oct 2009 06:05:53 -0000	1.1013
+++ includes/common.inc	13 Oct 2009 00:16:14 -0000
@@ -2578,13 +2578,71 @@ function drupal_attributes(array $attrib
  *   an HTML string containing a link to the given path.
  */
 function l($text, $path, array $options = array()) {
+  global $theme;
+  static $theme_function = 'theme_link', $initialized;
+
+  $variables = array(
+    'text' => $text,
+    'path' => $path,
+    'options' => $options,
+  );
+
+  // If the theme system is not initialized yet, then theme('link') cannot be
+  // called and it needs to be called directly. Also, since l() is called very
+  // often during a single page request, we statically cache the theme function
+  // to directly invoke them in subsequent calls.
+  if (!isset($initialized) && isset($theme)) {
+    $initialized = TRUE;
+    // Theme hooks can define include files, but those only need to be loaded
+    // once per request. A single call to theme() is fine, but subsequent
+    // invocations of l() will avoid this overhead.
+    $return = theme('link', $variables);
+
+    // Retrieve the theme function. Because preprocessing and processing does
+    // not make sense here, we skip them.
+    $registry = theme_get_registry();
+    if (isset($registry) && isset($registry['link']['function']) && function_exists($registry['link']['function'])) {
+      $theme_function = $registry['link']['function'];
+    }
+  }
+  // In subsequent calls to l(), we mimic theme('link') using the cached data.
+  else {
+    $return = $theme_function($variables);
+  }
+
+  return $return;
+}
+
+/**
+ * Format an internal Drupal link.
+ *
+ * @param $variables
+ *   An associative array containing:
+ *   - text: The link text to output.
+ *   - path: The URL path component to link to.
+ *   - options: (optional) An array of options to pass to url().
+ *   See l() for more information.
+ * 
+ * @return
+ *   A HTML string containing a link to the given path.
+ * 
+ * @ingroup themeable
+ * 
+ * @todo If it is impossible to call l() before the theme system is initialized,
+ *   then move this function into theme.inc.
+ */
+function theme_link($variables) {
   global $language_url;
 
+  $text = $variables['text'];
+  $path = $variables['path'];
+  $options = $variables['options'];
+
   // Merge in defaults.
   $options += array(
-      'attributes' => array(),
-      'html' => FALSE,
-    );
+    'attributes' => array(),
+    'html' => FALSE,
+  );
 
   // Append active class.
   if (($path == $_GET['q'] || ($path == '<front>' && drupal_is_front_page())) &&
@@ -4857,6 +4915,9 @@ function drupal_common_theme() {
     'status_messages' => array(
       'arguments' => array('display' => NULL),
     ),
+    'link' => array(
+      'arguments' => array('text' => NULL, 'path' => NULL, 'options' => array()),
+    ),
     'links' => array(
       'arguments' => array('links' => NULL, 'attributes' => array('class' => array('links')), 'heading' => array()),
     ),
Index: modules/simpletest/tests/common.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/tests/common.test,v
retrieving revision 1.83
diff -u -p -r1.83 common.test
--- modules/simpletest/tests/common.test	11 Oct 2009 02:14:43 -0000	1.83
+++ modules/simpletest/tests/common.test	13 Oct 2009 00:05:28 -0000
@@ -4,7 +4,7 @@
 /**
  * Tests for URL generation functions.
  */
-class CommonURLUnitTest extends DrupalUnitTestCase {
+class CommonURLUnitTest extends DrupalWebTestCase {
   public static function getInfo() {
     return array(
       'name' => 'URL generation tests',