WordPress/wp-admin/includes/menu.php

<?php
/**
 * Build Administration Menu.
 *
 * @package WordPress
 * @subpackage Administration
 */

if ( is_network_admin() ) {

	/**
	 * Fires before the administration menu loads in the Network Admin.
	 *
	 * The hook fires before menus and sub-menus are removed based on user privileges.
	 *
	 * @private
	 * @since 3.1.0
	 */
	do_action( '_network_admin_menu' );
} elseif ( is_user_admin() ) {

	/**
	 * Fires before the administration menu loads in the User Admin.
	 *
	 * The hook fires before menus and sub-menus are removed based on user privileges.
	 *
	 * @private
	 * @since 3.1.0
	 */
	do_action( '_user_admin_menu' );
} else {

	/**
	 * Fires before the administration menu loads in the admin.
	 *
	 * The hook fires before menus and sub-menus are removed based on user privileges.
	 *
	 * @private
	 * @since 2.2.0
	 */
	do_action( '_admin_menu' );
}

// Create list of page plugin hook names.
foreach ($menu as $menu_page) {
	if ( false !== $pos = strpos($menu_page[2], '?') ) {
		// Handle post_type=post|page|foo pages.
		$hook_name = substr($menu_page[2], 0, $pos);
		$hook_args = substr($menu_page[2], $pos + 1);
		wp_parse_str($hook_args, $hook_args);
		// Set the hook name to be the post type.
		if ( isset($hook_args['post_type']) )
			$hook_name = $hook_args['post_type'];
		else
			$hook_name = basename($hook_name, '.php');
		unset($hook_args);
	} else {
		$hook_name = basename($menu_page[2], '.php');
	}
	$hook_name = sanitize_title($hook_name);

	if ( isset($compat[$hook_name]) )
		$hook_name = $compat[$hook_name];
	elseif ( !$hook_name )
		continue;

	$admin_page_hooks[$menu_page[2]] = $hook_name;
}
unset($menu_page, $compat);

$_wp_submenu_nopriv = array();
$_wp_menu_nopriv = array();
// Loop over submenus and remove pages for which the user does not have privs.
foreach ($submenu as $parent => $sub) {
	foreach ($sub as $index => $data) {
		if ( ! current_user_can($data[1]) ) {
			unset($submenu[$parent][$index]);
			$_wp_submenu_nopriv[$parent][$data[2]] = true;
		}
	}
	unset($index, $data);

	if ( empty($submenu[$parent]) )
		unset($submenu[$parent]);
}
unset($sub, $parent);

/*
 * Loop over the top-level menu.
 * Menus for which the original parent is not accessible due to lack of privileges
 * will have the next submenu in line be assigned as the new menu parent.
 */
foreach ( $menu as $id => $data ) {
	if ( empty($submenu[$data[2]]) )
		continue;
	$subs = $submenu[$data[2]];
	$first_sub = array_shift($subs);
	$old_parent = $data[2];
	$new_parent = $first_sub[2];
	/*
	 * If the first submenu is not the same as the assigned parent,
	 * make the first submenu the new parent.
	 */
	if ( $new_parent != $old_parent ) {
		$_wp_real_parent_file[$old_parent] = $new_parent;
		$menu[$id][2] = $new_parent;

		foreach ($submenu[$old_parent] as $index => $data) {
			$submenu[$new_parent][$index] = $submenu[$old_parent][$index];
			unset($submenu[$old_parent][$index]);
		}
		unset($submenu[$old_parent], $index);

		if ( isset($_wp_submenu_nopriv[$old_parent]) )
			$_wp_submenu_nopriv[$new_parent] = $_wp_submenu_nopriv[$old_parent];
	}
}
unset($id, $data, $subs, $first_sub, $old_parent, $new_parent);

if ( is_network_admin() ) {

	/**
	 * Fires before the administration menu loads in the Network Admin.
	 *
	 * @since 3.1.0
	 *
	 * @param string $context Empty context.
	 */
	do_action( 'network_admin_menu', '' );
} elseif ( is_user_admin() ) {

	/**
	 * Fires before the administration menu loads in the User Admin.
	 *
	 * @since 3.1.0
	 *
	 * @param string $context Empty context.
	 */
	do_action( 'user_admin_menu', '' );
} else {

	/**
	 * Fires before the administration menu loads in the admin.
	 *
	 * @since 1.5.0
	 *
	 * @param string $context Empty context.
	 */
	do_action( 'admin_menu', '' );
}

/*
 * Remove menus that have no accessible submenus and require privileges
 * that the user does not have. Run re-parent loop again.
 */
foreach ( $menu as $id => $data ) {
	if ( ! current_user_can($data[1]) )
		$_wp_menu_nopriv[$data[2]] = true;

	/*
	 * If there is only one submenu and it is has same destination as the parent,
	 * remove the submenu.
	 */
	if ( ! empty( $submenu[$data[2]] ) && 1 == count ( $submenu[$data[2]] ) ) {
		$subs = $submenu[$data[2]];
		$first_sub = array_shift($subs);
		if ( $data[2] == $first_sub[2] )
			unset( $submenu[$data[2]] );
	}

	// If submenu is empty...
	if ( empty($submenu[$data[2]]) ) {
		// And user doesn't have privs, remove menu.
		if ( isset( $_wp_menu_nopriv[$data[2]] ) ) {
			unset($menu[$id]);
		}
	}
}
unset($id, $data, $subs, $first_sub);

// Remove any duplicated separators
$separator_found = false;
foreach ( $menu as $id => $data ) {
	if ( 0 == strcmp('wp-menu-separator', $data[4] ) ) {
		if (false == $separator_found) {
			$separator_found = true;
		} else {
			unset($menu[$id]);
			$separator_found = false;
		}
	} else {
		$separator_found = false;
	}
}
unset($id, $data);

function add_cssclass($add, $class) {
	$class = empty($class) ? $add : $class .= ' ' . $add;
	return $class;
}

function add_menu_classes($menu) {

	$first = $lastorder = false;
	$i = 0;
	$mc = count($menu);
	foreach ( $menu as $order => $top ) {
		$i++;

		if ( 0 == $order ) { // dashboard is always shown/single
			$menu[0][4] = add_cssclass('menu-top-first', $top[4]);
			$lastorder = 0;
			continue;
		}

		if ( 0 === strpos($top[2], 'separator') && false !== $lastorder ) { // if separator
			$first = true;
			$c = $menu[$lastorder][4];
			$menu[$lastorder][4] = add_cssclass('menu-top-last', $c);
			continue;
		}

		if ( $first ) {
			$c = $menu[$order][4];
			$menu[$order][4] = add_cssclass('menu-top-first', $c);
			$first = false;
		}

		if ( $mc == $i ) { // last item
			$c = $menu[$order][4];
			$menu[$order][4] = add_cssclass('menu-top-last', $c);
		}

		$lastorder = $order;
	}

	/**
	 * Filter administration menus array with classes added for top-level items.
	 *
	 * @since 2.7.0
	 *
	 * @param array $menu Associative array of administration menu items.
	 */
	return apply_filters( 'add_menu_classes', $menu );
}

uksort($menu, "strnatcasecmp"); // make it all pretty

/**
 * Filter whether to enable custom ordering of the administration menu.
 *
 * See the 'menu_order' filter for reordering menu items.
 *
 * @since 2.8.0
 *
 * @param bool $custom Whether custom ordering is enabled. Default false.
 */
if ( apply_filters( 'custom_menu_order', false ) ) {
	$menu_order = array();
	foreach ( $menu as $menu_item ) {
		$menu_order[] = $menu_item[2];
	}
	unset($menu_item);
	$default_menu_order = $menu_order;

	/**
	 * Filter the order of administration menu items.
	 *
	 * A truthy value must first be passed to the 'custom_menu_order' filter
	 * for this filter to work. Use the following to enable custom menu ordering:
	 *
	 *     add_filter( 'custom_menu_order', '__return_true' );
	 *
	 * @since 2.8.0
	 *
	 * @param array $menu_order An ordered array of menu items.
	 */
	$menu_order = apply_filters( 'menu_order', $menu_order );
	$menu_order = array_flip($menu_order);
	$default_menu_order = array_flip($default_menu_order);

	function sort_menu($a, $b) {
		global $menu_order, $default_menu_order;
		$a = $a[2];
		$b = $b[2];
		if ( isset($menu_order[$a]) && !isset($menu_order[$b]) ) {
			return -1;
		} elseif ( !isset($menu_order[$a]) && isset($menu_order[$b]) ) {
			return 1;
		} elseif ( isset($menu_order[$a]) && isset($menu_order[$b]) ) {
			if ( $menu_order[$a] == $menu_order[$b] )
				return 0;
			return ($menu_order[$a] < $menu_order[$b]) ? -1 : 1;
		} else {
			return ($default_menu_order[$a] <= $default_menu_order[$b]) ? -1 : 1;
		}
	}

	usort($menu, 'sort_menu');
	unset($menu_order, $default_menu_order);
}

// Remove the last menu item if it is a separator.
$last_menu_key = array_keys( $menu );
$last_menu_key = array_pop( $last_menu_key );
if ( !empty( $menu ) && 'wp-menu-separator' == $menu[ $last_menu_key ][ 4 ] )
	unset( $menu[ $last_menu_key ] );
unset( $last_menu_key );

if ( !user_can_access_admin_page() ) {

	/**
	 * Fires when access to an admin page is denied.
	 *
	 * @since 2.5.0
	 */
	do_action( 'admin_page_access_denied' );

	wp_die( __( 'You do not have sufficient permissions to access this page.' ), 403 );
}

$menu = add_menu_classes($menu);