From 7bc6b530f28ab13fa410cc09d8e072a3cd51aaf7 Mon Sep 17 00:00:00 2001
From: Ryan Boren <ryan@git.wordpress.org>
Date: Wed, 5 Aug 2009 16:43:51 +0000
Subject: [PATCH] rel=canonical for singular pages. see #10115

git-svn-id: https://develop.svn.wordpress.org/trunk@11777 602fd350-edb4-49c9-b593-d223f7449a82
---
 wp-includes/default-filters.php |  1 +
 wp-includes/link-template.php   | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/wp-includes/default-filters.php b/wp-includes/default-filters.php
index 2519d7aa12..6fb6482b8a 100644
--- a/wp-includes/default-filters.php
+++ b/wp-includes/default-filters.php
@@ -178,6 +178,7 @@ add_action('wp_head', 'noindex', 1);
 add_action('wp_head', 'wp_print_styles', 8);
 add_action('wp_head', 'wp_print_head_scripts', 9);
 add_action('wp_head', 'wp_generator');
+add_action('wp_head', 'rel_canonical');
 add_action('wp_footer', 'wp_print_footer_scripts');
 if(!defined('DOING_CRON'))
 	add_action('sanitize_comment_cookies', 'wp_cron');
diff --git a/wp-includes/link-template.php b/wp-includes/link-template.php
index 96453aabcb..e6d9f78d9b 100644
--- a/wp-includes/link-template.php
+++ b/wp-includes/link-template.php
@@ -1806,4 +1806,22 @@ function plugins_url($path = '', $plugin = '') {
 	return apply_filters('plugins_url', $url, $path, $plugin);
 }
 
+/**
+ * Output rel=canonical for singular queries
+ *
+ * @package WordPress
+ * @since 2.9.0
+*/
+function rel_canonical() {
+	if ( !is_singular() )
+		return;
+
+	global $wp_the_query;
+	if ( !$id = $wp_the_query->get_queried_object_id() )
+		return;
+
+	$link = get_permalink( $id );
+	echo "<link rel='canonical' href='$link' />\n";
+}
+
 ?>