Improve lazyloading of comment meta in WP_Query loops.

Lazy-loading logic is moved to a method on `WP_Query`. This makes it possible
for comment feeds to take advantage of metadata lazyloading, in addition to
comments loaded via `comments_template()`.

This new technique parallels the termmeta lazyloading technique introduced in
[34704].

Fixes #34047.

git-svn-id: https://develop.svn.wordpress.org/trunk@34711 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/comment-functions.php

@@ -2452,30 +2452,6 @@ function _prime_comment_caches( $comment_ids, $update_meta_cache = true ) {
 	}
 }
 
-/**
- * Lazy load comment meta when inside of a `WP_Query` loop.
- *
- * @since 4.4.0
- *
- * @param null $check      The `$check` param passed from the 'pre_comment_metadata' hook.
- * @param int  $comment_id ID of the comment whose metadata is being cached.
- * @return null In order not to short-circuit `get_metadata()`.
- */
-function wp_lazyload_comment_meta( $check, $comment_id ) {
-	global $wp_query;
-
-	if ( ! empty( $wp_query->comments ) ) {
-		// Don't use `wp_list_pluck()` to avoid by-reference manipulation.
-		$comment_ids = array();
-		foreach ( $wp_query->comments as $comment ) {
-			$comment_ids[] = $comment->comment_ID;
-		}
-		update_meta_cache( 'comment', $comment_ids );
-	}
-
-	return $check;
-}
-
 //
 // Internal
 //

src/wp-includes/comment-template.php

@@ -1320,6 +1320,10 @@ function comments_template( $file = '/comments.php', $separate_comments = false
 	 * @param int   $post_ID  Post ID.
 	 */
 	$wp_query->comments = apply_filters( 'comments_array', $comments_flat, $post->ID );
+
+	// Set up lazy-loading for comment metadata.
+	add_action( 'get_comment_metadata', array( $wp_query, 'lazyload_comment_meta' ), 10, 2 );
+
 	$comments = &$wp_query->comments;
 	$wp_query->comment_count = count($wp_query->comments);
 	$wp_query->max_num_comment_pages = $comment_query->max_num_pages;

src/wp-includes/default-filters.php

@@ -200,7 +200,6 @@ add_filter( 'nav_menu_meta_box_object', '_wp_nav_menu_meta_box_object'        );
 add_filter( 'pingback_ping_source_uri', 'pingback_ping_source_uri'            );
 add_filter( 'xmlrpc_pingback_error',    'xmlrpc_pingback_error'               );
 add_filter( 'title_save_pre',           'trim'                                );
-add_filter( 'get_comment_metadata',     'wp_lazyload_comment_meta',     10, 2 );
 
 add_filter( 'http_request_host_is_external', 'allowed_http_request_hosts', 10, 2 );
 

src/wp-includes/query.php

@@ -1311,6 +1311,15 @@ class WP_Query {
 	 */
 	public $updated_term_meta_cache = false;
 
+	/**
+	 * Whether the comment meta cache for matched posts has been primed.
+	 *
+	 * @since 4.4.0
+	 * @access protected
+	 * @var bool
+	 */
+	public $updated_comment_meta_cache = false;
+
 	/**
 	 * Cached list of search stopwords.
 	 *
@@ -3682,6 +3691,11 @@ class WP_Query {
 			}
 		}
 
+		// If comments have been fetched as part of the query, make sure comment meta lazy-loading is set up.
+		if ( ! empty( $this->comments ) ) {
+			add_action( 'get_comment_metadata', array( $this, 'lazyload_comment_meta' ), 10, 2 );
+		}
+
 		if ( ! $q['suppress_filters'] ) {
 			/**
 			 * Filter the array of retrieved posts after they've been fetched and
@@ -4816,6 +4830,50 @@ class WP_Query {
 
 		return $check;
 	}
+
+	/**
+	 * Lazy-load comment meta when inside of a `WP_Query` loop.
+	 *
+	 * This method is public so that it can be used as a filter callback. As a rule, there is no need to invoke it
+	 * directly, from either inside or outside the `WP_Query` object.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @param null $check      The `$check` param passed from the 'pre_comment_metadata' hook.
+	 * @param int  $comment_id ID of the comment whose metadata is being cached.
+	 * @return null In order not to short-circuit `get_metadata()`.
+	 */
+	public function lazyload_comment_meta( $check, $comment_id ) {
+		/*
+		 * We only do this once per `WP_Query` instance.
+		 * Can't use `remove_action()` because of non-unique object hashes.
+		 */
+		if ( $this->updated_comment_meta_cache ) {
+			return $check;
+		}
+
+		// Don't use `wp_list_pluck()` to avoid by-reference manipulation.
+		$comment_ids = array();
+		if ( is_array( $this->comments ) ) {
+			foreach ( $this->comments as $comment ) {
+				$comment_ids[] = $comment->comment_ID;
+			}
+		}
+
+		/*
+		 * Only update the metadata cache for comments belonging to these posts if the comment_id passed
+		 * to `get_comment_meta()` matches one of those comments. This prevents a single call to
+		 * `get_comment_meta()` from priming metadata for all `WP_Query` objects.
+		 */
+		if ( in_array( $comment_id, $comment_ids ) ) {
+			update_meta_cache( 'comment', $comment_ids );
+			$this->updated_comment_meta_cache = true;
+		} elseif ( empty( $comment_ids ) ) {
+			$this->updated_comment_meta_cache = true;
+		}
+
+		return $check;
+	}
 }
 
 /**

tests/phpunit/tests/comment/metaCache.php

@@ -121,4 +121,93 @@ class Tests_Comment_Meta_Cache extends WP_UnitTestCase {
 			}
 		}
 	}
+
+	/**
+	 * @group 34047
+	 */
+	public function test_comment_meta_should_be_lazy_loaded_in_comment_feed_queries() {
+		global $wpdb;
+
+		$posts = $this->factory->post->create_many( 2, array( 'post_status' => 'publish' ) );
+
+		$now = time();
+		$comments = array();
+		for ( $i = 0; $i < 5; $i++ ) {
+			$comments[] = $this->factory->comment->create( array(
+				'comment_post_ID' => $posts[0],
+				'comment_date_gmt' => date( 'Y-m-d H:i:s', $now - ( 60 * $i ) ),
+			) );
+		}
+
+		foreach ( $comments as $c ) {
+			add_comment_meta( $c, 'foo', 'bar' );
+		}
+
+		update_option( 'posts_per_rss', 3 );
+
+		$q = new WP_Query( array(
+			'feed' => true,
+			'withcomments' => true,
+		) );
+
+		// First comment will cause the cache to be primed.
+		$num_queries = $wpdb->num_queries;
+		$this->assertSame( 'bar', get_comment_meta( $comments[0], 'foo', 'bar' ) );
+		$num_queries++;
+		$this->assertSame( $num_queries, $wpdb->num_queries );
+
+		// Second comment from the results should not cause more queries.
+		$this->assertSame( 'bar', get_comment_meta( $comments[1], 'foo', 'bar' ) );
+		$this->assertSame( $num_queries, $wpdb->num_queries );
+
+		// A comment from outside the results will not be primed.
+		$this->assertSame( 'bar', get_comment_meta( $comments[4], 'foo', 'bar' ) );
+		$num_queries++;
+		$this->assertSame( $num_queries, $wpdb->num_queries );
+	}
+
+	/**
+	 * @group 34047
+	 */
+	public function test_comment_meta_should_be_lazy_loaded_in_single_post_comment_feed_queries() {
+		global $wpdb;
+
+		$posts = $this->factory->post->create_many( 2, array( 'post_status' => 'publish' ) );
+
+		$now = time();
+		$comments = array();
+		for ( $i = 0; $i < 5; $i++ ) {
+			$comments[] = $this->factory->comment->create( array(
+				'comment_post_ID' => $posts[0],
+				'comment_date_gmt' => date( 'Y-m-d H:i:s', $now - ( 60 * $i ) ),
+			) );
+		}
+
+		foreach ( $comments as $c ) {
+			add_comment_meta( $c, 'foo', 'bar' );
+		}
+
+		update_option( 'posts_per_rss', 3 );
+
+		$q = new WP_Query( array(
+			'feed' => true,
+			'withcomments' => true,
+			'p' => $posts[0],
+		) );
+
+		// First comment will cause the cache to be primed.
+		$num_queries = $wpdb->num_queries;
+		$this->assertSame( 'bar', get_comment_meta( $comments[0], 'foo', 'bar' ) );
+		$num_queries++;
+		$this->assertSame( $num_queries, $wpdb->num_queries );
+
+		// Second comment from the results should not cause more queries.
+		$this->assertSame( 'bar', get_comment_meta( $comments[1], 'foo', 'bar' ) );
+		$this->assertSame( $num_queries, $wpdb->num_queries );
+
+		// A comment from outside the results will not be primed.
+		$this->assertSame( 'bar', get_comment_meta( $comments[4], 'foo', 'bar' ) );
+		$num_queries++;
+		$this->assertSame( $num_queries, $wpdb->num_queries );
+	}
 }