Index: includes/module.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/module.inc,v
retrieving revision 1.160
diff -u -p -r1.160 module.inc
--- includes/module.inc	10 Oct 2009 12:12:15 -0000	1.160
+++ includes/module.inc	15 Oct 2009 20:35:43 -0000
@@ -361,6 +361,8 @@ function module_implements($hook, $sort 
   if ($reset) {
     $implementations = array();
     cache_set('module_implements', array());
+    drupal_static_reset('module_hook_info');
+    cache_clear_all('hook_info', 'cache');
     return;
   }
 
@@ -376,18 +378,25 @@ function module_implements($hook, $sort 
   }
 
   if (!isset($implementations[$hook])) {
+    $hook_info = module_hook_info();
     $implementations[$hook] = array();
     $list = module_list(FALSE, FALSE, $sort);
     foreach ($list as $module) {
-      if (module_hook($module, $hook)) {
-        $implementations[$hook][$module] = $module;
+      $include_file = FALSE;
+      if (module_hook($module, $hook) || (isset($hook_info[$hook]['group']) && $include_file = module_load_include('inc', $module, $module . '.' . $hook_info[$hook]['group']) && module_hook($module, $hook))) {
+        $implementations[$hook][$module] = $include_file ? $hook_info[$hook]['group'] : FALSE;
         // We added something to the cache, so write it when we are done.
         $implementations['#write_cache'] = TRUE;
       }
     }
   }
   else {
-    foreach ($implementations[$hook] as $module) {
+    foreach ($implementations[$hook] as $module => $group) {
+      // If this hook implementation is stored in a lazy-loaded file, so include
+      // that file first.
+      if ($group) {
+        module_load_include('inc', $module, "$module.$group");
+      }
       // It is possible that a module removed a hook implementation without the
       // implementations cache being rebuilt yet, so we check module_hook() on
       // each request to avoid undefined function errors.
@@ -400,13 +409,45 @@ function module_implements($hook, $sort 
     }
   }
 
-  // The explicit cast forces a copy to be made. This is needed because
-  // $implementations[$hook] is only a reference to an element of
-  // $implementations and if there are nested foreaches (due to nested node
-  // API calls, for example), they would both manipulate the same array's
-  // references, which causes some modules' hooks not to be called.
-  // See also http://www.zend.com/zend/art/ref-count.php.
-  return (array)$implementations[$hook];
+  return array_keys($implementations[$hook]);
+}
+
+/**
+ * Retrieve a list of what hooks are explicitly declared.
+ */
+function module_hook_info() {
+  $hook_info = &drupal_static(__FUNCTION__, array());
+
+  if (empty($hook_info)) {
+    $cache = cache_get('hook_info');
+    if ($cache === FALSE) {
+      // Rebuild the cache and save it.
+      // We can't use module_invoke_all() here or it would cause an infinite
+      // loop.
+      foreach (module_list() as $module) {
+        $function = $module . '_hook_info';
+        if (function_exists($function)) {
+          $result = $function();
+          if (isset($result) && is_array($result)) {
+            $hook_info = array_merge_recursive($hook_info, $result);
+          }
+        }
+      }
+      // We can't use drupal_alter() for the same reason as above.
+      foreach (module_list() as $module) {
+        $function = $module . '_hook_info_alter';
+        if (function_exists($function)) {
+          $function($hook_info);
+        }
+      }
+      cache_set('hook_info', $hook_info);
+    }
+    else {
+      $hook_info = $cache->data;
+    }
+  }
+
+  return $hook_info;
 }
 
 /**
Index: includes/token.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/token.inc,v
retrieving revision 1.5
diff -u -p -r1.5 token.inc
--- includes/token.inc	25 Aug 2009 02:50:08 -0000	1.5
+++ includes/token.inc	15 Oct 2009 20:35:43 -0000
@@ -153,7 +153,6 @@ function token_scan($text) {
 function token_generate($type, array $tokens, array $data = array(), array $options = array()) {
   $results = array();
   $options += array('sanitize' => TRUE);
-  _token_initialize();
 
   $result = module_invoke_all('tokens', $type, $tokens, $data, $options);
   foreach ($result as $original => $replacement) {
@@ -227,25 +226,8 @@ function token_find_with_prefix(array $t
 function token_info() {
   $data = &drupal_static(__FUNCTION__);
   if (!isset($data)) {
-    _token_initialize();
     $data = module_invoke_all('token_info');
     drupal_alter('token_info', $data);
   }
   return $data;
 }
-
-/**
- * Load modulename.tokens.inc for all enabled modules.
- */
-function _token_initialize() {
-  $initialized = &drupal_static(__FUNCTION__);
-  if (!$initialized) {
-    foreach (module_list() as $module) {
-      $filename = DRUPAL_ROOT . '/' . drupal_get_path('module', $module) . "/$module.tokens.inc";
-      if (file_exists($filename)) {
-        include_once $filename;
-      }
-    }
-    $initialized = TRUE;
-  }
-}
Index: modules/system/system.api.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.api.php,v
retrieving revision 1.90
diff -u -p -r1.90 system.api.php
--- modules/system/system.api.php	15 Oct 2009 17:55:55 -0000	1.90
+++ modules/system/system.api.php	15 Oct 2009 20:38:13 -0000
@@ -12,6 +12,38 @@
  */
 
 /**
+ * Defines one or more hooks that are exposed by a module.
+ *
+ * Normally hooks do not need to be explicitly defined. However, by declaring a
+ * hook explicitly, a module may define a "group" for it. Modules that implement
+ * a hook may then place their implementation in either $module.module or in
+ * $module.$group.inc. If the hook is located in $module.$group.inc, then that
+ * file will be automatically loaded when needed.
+ * In general, hooks that are rarely invoked and/or are very large should be
+ * placed in a separate include file, while hooks that are very short or very
+ * frequently called should be left in the main module file so that they are
+ * always available.
+ *
+ * @return
+ *   An associative array whose keys are hook names and whose values are an
+ *   associative array containing:
+ *   - group: A string defining the group to which the hook belongs. The module
+ *     system will determine whether a file with the name $module.$group.inc
+ *     exists, and automatically load it when required.
+ *
+ * See system_hook_info() for all hook groups defined by Drupal core.
+ */
+function hook_hook_info() {
+  $hooks['token_info'] = array(
+    'group' => 'tokens',
+  );
+  $hooks['tokens'] = array(
+    'group' => 'tokens',
+  );
+  return $hooks;
+}
+
+/**
  * Inform the base system and the Field API about one or more entity types.
  *
  * Inform the system about one or more entity types (i.e., object types that
Index: modules/system/system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.815
diff -u -p -r1.815 system.module
--- modules/system/system.module	15 Oct 2009 17:55:55 -0000	1.815
+++ modules/system/system.module	15 Oct 2009 20:38:01 -0000
@@ -278,6 +278,19 @@ function system_rdf_namespaces() {
 }
 
 /**
+ * Implement hook_hook_info().
+ */
+function system_hook_info() {
+  $hooks['token_info'] = array(
+    'group' => 'tokens',
+  );
+  $hooks['tokens'] = array(
+    'group' => 'tokens',
+  );
+  return $hooks;
+}
+
+/**
  * Implement hook_entity_info().
  */
 function system_entity_info() {