Render a navigation submenu in a left sidebar

sorry, the site's not public yet. but as far as what you'll see rendered to the page, it's pretty simple to describe:

1) the entire site menu is contained in the Primary Links which are printed at the top of the page (i happen to be using nice_menus to display those in a manageable way, but that's beside the point)

2) the sidebar includes a block that only shows the "submenu" of the "section" you're in (in my case, that means "tier 2" links and below in the menu tree)

note that this is subtly different than the original use cases listed above. in my case, whether i'm at 'History', 'history2', or 'history22', i will see the following in my "submenu" in the sidebar:

History
--history1
--history2
----history21
----history22
--history3

here's the code, cleaned up a bit. first, in template.php:

<?php
/**
 * Hack to derive a submenu tree from a larger menu.
 * This is a modified version of Drupal's menu_navigation_links function, that 
 * stops short and returns the multi-level menu tree array, rather than 
 * continuing on to return the single level links array. We can then pass the
 * returned tree through menu_tree_output to get the markup.
 *
 * @param 
 *   $menu_name The name of the menu.
 *
 * @param 
 *   $level Optional, the depth of the menu to be returned.
 *
 * @return
 *   A submenu tree array.
 */
function menu_navigation_tree($menu_name, $level = 0) {
  // Don't even bother querying the menu table if no menu is specified.
  if (empty($menu_name)) {
    return array();
  }

  // Get the menu hierarchy for the current page.
  $tree = menu_tree_page_data($menu_name);

  // Go down the active trail until the right level is reached.
  while ($level-- > 0 && $tree) {
    // Loop through the current level's items until we find one that is in trail.
    while ($item = array_shift($tree)) {
      if ($item['link']['in_active_trail']) {
        // If the item is in the active trail, we continue in the subtree.
        $tree = empty($item['below']) ? array() : $item['below'];
        break;
      }
    }
  }
  return $tree;
}
?>

then, in my sidebar "submenu" block:

<?php
$tree = menu_navigation_tree(variable_get('menu_primary_links_source', 'primary-links'), 1);
print menu_tree_output($tree);
?>
?>

thanks, JohnAlbin.

i use the word "hack" here somewhat loosely -- my code above doesn't feel bad in that it's easy enough to maintain at the theme level. personally, i always prefer that to another contrib module, where i'm less confident i'll be able to maintain it should the developers go away, lose interest, etc.

that said, menu_block looks pretty great, and like you, i'm shocked this module didn't exist before. and clearly this module is maintained by a reputable and invested developer :) thanks for pointing it out.