Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.925
diff -u -r1.925 common.inc
--- includes/common.inc	18 Jun 2009 21:19:01 -0000	1.925
+++ includes/common.inc	30 Jun 2009 19:24:16 -0000
@@ -2766,6 +2766,10 @@
   // Preprocess can only be set if caching is enabled.
   $options['preprocess'] = $options['cache'] ? $options['preprocess'] : FALSE;
 
+  // Tweak the weight so that files of the same weight are included in the
+  // order of the calls to drupal_add_js().
+  $options['weight'] += count($javascript) / 1000;
+
   if (isset($data)) {
     // Add jquery.js and drupal.js, as well as the basePath setting, the
     // first time a Javascript file is added.
Index: modules/simpletest/tests/common.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/tests/common.test,v
retrieving revision 1.47
diff -u -r1.47 common.test
--- modules/simpletest/tests/common.test	30 Jun 2009 09:39:19 -0000	1.47
+++ modules/simpletest/tests/common.test	30 Jun 2009 19:24:16 -0000
@@ -549,6 +549,46 @@
   }
 
   /**
+   * Test JavaScript ordering.
+   */
+  function testRenderOrder() {
+    // Add a bunch of JavaScript in strange ordering.
+    drupal_add_js('(function($){alert("Weight 5 #1");})(jQuery);', array('type' => 'inline', 'scope' => 'footer', 'weight' => 5));
+    drupal_add_js('(function($){alert("Weight 0 #1");})(jQuery);', array('type' => 'inline', 'scope' => 'footer'));
+    drupal_add_js('(function($){alert("Weight 0 #2");})(jQuery);', array('type' => 'inline', 'scope' => 'footer'));
+    drupal_add_js('(function($){alert("Weight -8 #1");})(jQuery);', array('type' => 'inline', 'scope' => 'footer', 'weight' => -8));
+    drupal_add_js('(function($){alert("Weight -8 #2");})(jQuery);', array('type' => 'inline', 'scope' => 'footer', 'weight' => -8));
+    drupal_add_js('(function($){alert("Weight -8 #3");})(jQuery);', array('type' => 'inline', 'scope' => 'footer', 'weight' => -8));
+    drupal_add_js('(function($){alert("Weight -8 #4");})(jQuery);', array('type' => 'inline', 'scope' => 'footer', 'weight' => -8));
+    drupal_add_js('(function($){alert("Weight 5 #2");})(jQuery);', array('type' => 'inline', 'scope' => 'footer', 'weight' => 5));
+    drupal_add_js('(function($){alert("Weight 0 #3");})(jQuery);', array('type' => 'inline', 'scope' => 'footer'));
+
+    // Construct the expected result from the regex.
+    $expected = array(
+      "-8 #1",
+      "-8 #2",
+      "-8 #3",
+      "-8 #4",
+      "0 #1",
+      "0 #2",
+      "0 #3",
+      "5 #1",
+      "5 #2",
+    );
+
+    // Retrieve the rendered JavaScript and test against the regex.
+    $js = drupal_get_js('footer');
+    $matches = array();
+    if (preg_match_all('/Weight\s([-0-9]+\s[#0-9]+)/', $js, $matches)) {
+      $result = $matches[1];
+    }
+    else {
+      $result = array();
+    }
+    $this->assertIdentical($result, $expected, t('JavaScript is added in the expected weight order.'));
+  }
+
+  /**
    * Test rendering the JavaScript with a file's weight above jQuery's.
    */
   function testRenderDifferentWeight() {