In `wp_list_comments()`, update the comment meta cache when the comments derive from `WP_Query` and the new `->comment_meta_cached` prop is `false`.

There are no uses of `wp_list_comments()` in Core where `$comments` are passed as the 2nd argument.

Adds unit tests.

Props wonderboymusic, bradt.
Fixes #16894.


git-svn-id: https://develop.svn.wordpress.org/trunk@33925 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/comment-template.php

@@ -2116,6 +2116,12 @@ function wp_list_comments( $args = array(), $comments = null ) {
 		} else {
 			$_comments = $wp_query->comments;
 		}
+
+		if ( ! $wp_query->comment_meta_cached ) {
+			$comment_ids = wp_list_pluck( $_comments, 'comment_ID' );
+			update_meta_cache( 'comment', $comment_ids );
+			$wp_query->comment_meta_cached = true;
+		}
 	}
 
 	if ( '' === $r['per_page'] && get_option('page_comments') )

src/wp-includes/query.php

@@ -1292,6 +1292,15 @@ class WP_Query {
 	 */
 	 public $thumbnails_cached = false;
 
+	/**
+	 * Set if comment meta has already been cached
+	 *
+	 * @since 4.4.0
+	 * @access public
+	 * @var bool
+	 */
+	 public $comment_meta_cached = false;
+
 	/**
 	 * Cached list of search stopwords.
 	 *

tests/phpunit/tests/comment/metaCache.php

@@ -0,0 +1,64 @@
+<?php
+
+class Tests_Meta_Cache extends WP_UnitTestCase {
+	protected $i = 0;
+	protected $queries = 0;
+
+	public function test_comment_meta_cache() {
+		$post_id = $this->factory->post->create( array(
+			'post_status' => 'publish'
+		) );
+
+		$comment_ids = $this->factory->comment->create_post_comments( $post_id, 10 );
+
+		foreach ( $comment_ids as $cid ) {
+			update_comment_meta( $cid, 'sauce', 'fire' );
+		}
+
+		$post = get_post( $post_id );
+
+		$this->assertEquals( $post->comment_count, count( $comment_ids ) );
+
+		$this->go_to( get_permalink( $post_id ) );
+
+		$this->assertTrue( is_single() );
+		$this->assertTrue( have_posts() );
+
+		global $wp_query;
+
+		while ( have_posts() ) {
+			the_post();
+
+			$comment_args = array(
+				'order'   => 'ASC',
+				'orderby' => 'comment_date_gmt',
+				'status'  => 'approve',
+				'post_id' => get_the_ID(),
+			);
+
+			$comments = get_comments( $comment_args );
+
+			// This is beyond awful
+			$wp_query->comments = $comments;
+
+			wp_list_comments( array(
+				'echo' => false,
+				'callback' => array( $this, '_comment_callback' )
+			) );
+		}
+	}
+
+	public function _comment_callback( $comment ) {
+		global $wpdb;
+
+		get_comment_meta( $comment->comment_ID, 'sauce' );
+
+		if ( 0 === $this->i ) {
+			$this->queries = $wpdb->num_queries;
+		} else {
+			$this->assertEquals( $this->queries, $wpdb->num_queries );
+		}
+
+		$this->i++;
+	}
+}