From 4ce9db9ce82d039ac9daba6b2f931294dd488ba7 Mon Sep 17 00:00:00 2001
From: Boone Gorges <boonebgorges@gmail.com>
Date: Wed, 5 Nov 2014 01:00:24 +0000
Subject: [PATCH] In `wp_insert_term()`, clean up accidental duplicate terms
 after insert.

In [30056], the UNIQUE index was removed from the 'slug' column of `wp_terms`.
While we have numerous checks in place to avoid the creation of unwanted
duplicate term+term_taxonomy pairs, it's possible that in certain edge cases -
such as during the lag caused by database replication, or a race condition
involving near-simultaneous creation of more than one term - we'll end up
unwittingly inserting two identical rows.

The current changeset minimizes this risk by introducing a failsafe mechanism
into `wp_insert_term()`. After a term and term_taxonomy are INSERTed, we check
to see whether the term just created is a duplicate of an existing term; if so,
we delete the new one and keep the old one. This prevents problems caused by
replication lag, because SELECT queries that take place after an INSERT will
hit the master database; it mitigates race conditions by enforcing that the
term that was created first (ie, the one with the lowest `term_id`) is
always the "canonical" one.

Props nacin, markjaquith.
See #22023, #5809.
Built from https://develop.svn.wordpress.org/trunk@30238


git-svn-id: http://core.svn.wordpress.org/trunk@30238 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/taxonomy.php | 18 ++++++++++++++++++
 wp-includes/version.php  |  2 +-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/wp-includes/taxonomy.php b/wp-includes/taxonomy.php
index 75e5c6a08e..d5f5f33ade 100644
--- a/wp-includes/taxonomy.php
+++ b/wp-includes/taxonomy.php
@@ -2902,6 +2902,24 @@ function wp_insert_term( $term, $taxonomy, $args = array() ) {
 	$wpdb->insert( $wpdb->term_taxonomy, compact( 'term_id', 'taxonomy', 'description', 'parent') + array( 'count' => 0 ) );
 	$tt_id = (int) $wpdb->insert_id;
 
+	/*
+	 * Sanity check: if we just created a term with the same parent + taxonomy + slug but a higher term_id than
+	 * an existing term, then we have unwittingly created a duplicate term. Delete the dupe, and use the term_id
+	 * and term_taxonomy_id of the older term instead. Then return out of the function so that the "create" hooks
+	 * are not fired.
+	 */
+	$duplicate_term = $wpdb->get_row( $wpdb->prepare( "SELECT t.term_id, tt.term_taxonomy_id FROM $wpdb->terms t INNER JOIN $wpdb->term_taxonomy tt ON ( tt.term_id = t.term_id ) WHERE t.slug = %s AND tt.parent = %d AND tt.taxonomy = %s AND t.term_id < %d AND tt.term_taxonomy_id != %d", $slug, $parent, $taxonomy, $term_id, $tt_id ) );
+	if ( $duplicate_term ) {
+		$wpdb->delete( $wpdb->terms, array( 'term_id' => $term_id ) );
+		$wpdb->delete( $wpdb->term_taxonomy, array( 'term_taxonomy_id' => $tt_id ) );
+
+		$term_id = (int) $duplicate_term->term_id;
+		$tt_id   = (int) $duplicate_term->term_taxonomy_id;
+
+		clean_term_cache( $term_id, $taxonomy );
+		return array( 'term_id' => $term_id, 'term_taxonomy_id' => $tt_id );
+	}
+
 	/**
 	 * Fires immediately after a new term is created, before the term cache is cleaned.
 	 *
diff --git a/wp-includes/version.php b/wp-includes/version.php
index e6314f906b..9cea8be0d7 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.1-alpha-30237';
+$wp_version = '4.1-alpha-30238';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.