Fix various issues with WP_Adjacent_Post:

* Performance / number of queries.
 * Incorrect results caused by sticky posts.
 * Back compat for filters, which had used "WHERE" while WP_Query does not; and fixing table references.

props ethitter.
fixes #26937.

Built from https://develop.svn.wordpress.org/trunk@27635


git-svn-id: http://core.svn.wordpress.org/trunk@27478 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/link-template.php

@@ -1243,7 +1243,7 @@ class WP_Adjacent_Post {
 	}
 
 	/**
-	 * Allow direct access to adjacent post from the class instance itself
+	 * Allow direct access to adjacent post from the class instance itself.
 	 *
 	 * @param string $property Property to get.
 	 * @return mixed String when adjacent post is found and post property exists. Null when no adjacent post is found.
@@ -1296,9 +1296,15 @@ class WP_Adjacent_Post {
 			'post_type'           => 'post',
 			'orderby'             => 'date',
 			'order'               => 'previous' === $this->adjacent ? 'DESC' : 'ASC',
+			'ignore_sticky_posts' => true,
+			'date_query'          => array(),
+
+			// Performance considerations:
 			'no_found_rows'          => true,
 			'cache_results'          => true,
-			'date_query'       => array(),
+			'update_post_term_cache' => false,
+			'update_post_meta_cache' => false,
+			'split_the_query'        => wp_using_ext_object_cache(),
 		);
 
 		$tax_query = array();
@@ -1388,14 +1394,37 @@ class WP_Adjacent_Post {
 		 */
 		remove_filter( 'posts_clauses', array( $this, 'filter' ) );
 
-		/*
+		/**
-		 * The `join` and `where` filters are identical in their parameters,
+		 * If no legacy filter callbacks are registered, proceed no further.
-		 * so we can use the same approach for both.
 		 */
-		foreach ( array( 'join', 'where' ) as $clause ) {
+		if ( ! has_filter( 'get_' . $this->adjacent . '_post_join' ) && ! has_filter( 'get_' . $this->adjacent . '_post_where' ) && ! has_filter( 'get_' . $this->adjacent . '_post_sort' ) ) {
-			if ( has_filter( 'get_' . $this->adjacent . '_post_' . $clause ) ) {
+			return $clauses;
-				$clauses[ $clause ] = $this->filter_join_and_where( $clauses[ $clause ], $clause );
 		}
+
+		/**
+		 * Posts table must be aliased as `p` for backwards compatibility with query previously generated by `get_adjacent_post()`.
+		 */
+		$clauses = array_map( array( $this, 'alias_posts_table' ), $clauses );
+
+		/**
+		 * Apply the legacy `join` filter.
+		 */
+		if ( has_filter( 'get_' . $this->adjacent . '_post_join' ) ) {
+			$clauses['join'] = $this->filter_join( $clauses['join'] );
+		}
+
+		/**
+		 * Posts table must be aliased as `p` for backwards compatibility with query previously generated by `get_adjacent_post()`.
+		 * No filter on the table name exists, so we have to leverage the next applied filter, that for the `join` clause.
+		 * We wait to apply this until after the legacy filter is applied so that the legacy filter doesn't remove the alias.
+		 */
+		$clauses['join'] = 'AS p ' . $clauses['join'];
+
+		/**
+		 * Apply the legacy `where` filter.
+		 */
+		if ( has_filter( 'get_' . $this->adjacent . '_post_where' ) ) {
+			$clauses['where'] = $this->filter_where( $clauses['where'] );
 		}
 
 		/*
@@ -1411,18 +1440,69 @@ class WP_Adjacent_Post {
 	}
 
 	/**
-	 * Apply the deprecated `join` or `where` clause filter to the clauses built by WP_Query.
+	 * Alias posts table as `p` to match query previously built by `get_adjacent_post()`.
 	 *
-	 * @param string $value
+	 * @global $wpdb
-	 * @param string $clause
+	 * @param string  Clause to alias
 	 * @return string
 	 */
-	protected function filter_join_and_where( $value, $clause ) {
+	protected function alias_posts_table( $clause ) {
+		global $wpdb;
+
+		return str_replace( $wpdb->posts, 'p', $clause );
+	}
+
+	/**
+	 * Apply the deprecated `join` clause filter to the clause built by WP_Query.
+	 *
+	 * @param string $join
+	 * @return string
+	 */
+	protected function filter_join( $join ) {
 		/**
-		 * @todo Minimal hook docs
 		 * @deprecated 3.9.0
 		 */
-		return apply_filters( 'get_' . $this->adjacent . '_post_' . $clause, $value, $this->in_same_term, $this->excluded_terms );
+		return apply_filters( 'get_' . $this->adjacent . '_post_join', $join, $this->in_same_term, $this->excluded_terms );
+	}
+
+	/**
+	 * Apply the deprecated `where` clause filter to the clause built by WP_Query.
+	 *
+	 * @param string $join
+	 * @return string
+	 */
+	protected function filter_where( $where ) {
+		$where = trim( $where );
+
+		// The legacy filter passed the entire clause, including the `WHERE`, while WP_Query's filter does not.
+		// We prepend the `WHERE` for the benefit of legacy callbacks that look for it.
+		if ( 0 !== stripos( $where, 'where' ) ) {
+			$where = 'WHERE 1=1 ' . $where;
+		}
+
+		/**
+		 * @deprecated 3.9.0
+		 */
+		$where = apply_filters( 'get_' . $this->adjacent . '_post_where', $where, $this->in_same_term, $this->excluded_terms );
+
+		$where = trim( $where );
+
+		// The legacy filter passed the entire clause, including the `WHERE`, while WP_Query's filter does not.
+		// Removing the `WHERE` is necessary as we've added it above, and the legacy filter could include it in the returned string.
+		if ( 0 === stripos( $where, 'where 1=1' ) ) {
+			$where = substr( $where, 9 );
+		} elseif ( 0 === stripos( $where, 'where' ) ) {
+			$where = substr( $where, 5 );
+		}
+
+		$where = trim( $where );
+
+		// WP_Query expects that the string returned begins with `AND`, as it is prepended with "1=1" when the clauses are joined
+		if ( 0 !== stripos( $where, 'and' ) ) {
+			$where = 'AND ' . $where;
+		}
+
+		return $where;
 	}
 
 	/**