Prime users cache in WP_Query and post REST API controller.

For a call to `WP_Query` or a post REST API request that contains posts from multiple authors, call the `cache_users` function, to ensure that all user data for post authors is primed in 
a single database query. This results in far fewer database queries on multiple author sites. 

Props spacedmonkey, timothyblynjacobs, peterwilsoncc.
Fixes #55716.

Built from https://develop.svn.wordpress.org/trunk@53482


git-svn-id: http://core.svn.wordpress.org/trunk@53071 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-query.php

@@ -3434,6 +3434,9 @@ class WP_Query {
 	 */
 	public function the_post() {
 		global $post;
+		if ( ! $this->in_the_loop ) {
+			update_post_author_caches( $this->posts );
+		}
 		$this->in_the_loop = true;
 
 		if ( -1 == $this->current_post ) { // Loop has just started.

wp-includes/pluggable.php

@@ -132,6 +132,8 @@ if ( ! function_exists( 'cache_users' ) ) :
 	function cache_users( $user_ids ) {
 		global $wpdb;
 
+		update_meta_cache( 'user', $user_ids );
+
 		$clean = _get_non_cached_ids( $user_ids, 'users' );
 
 		if ( empty( $clean ) ) {
@@ -141,13 +143,9 @@ if ( ! function_exists( 'cache_users' ) ) :
 		$list = implode( ',', $clean );
 
 		$users = $wpdb->get_results( "SELECT * FROM $wpdb->users WHERE ID IN ($list)" );
-
-		$ids = array();
 		foreach ( $users as $user ) {
 			update_user_caches( $user );
-			$ids[] = $user->ID;
 		}
-		update_meta_cache( 'user', $ids );
 	}
 endif;
 

wp-includes/post.php

@@ -7474,6 +7474,20 @@ function update_post_caches( &$posts, $post_type = 'post', $update_term_cache =
 	}
 }
 
+/**
+ * Prime post author user caches.
+ *
+ * @since 6.1.0
+ *
+ * @param WP_Post[] $posts Array of Post objects
+ */
+function update_post_author_caches( $posts ) {
+	$author_ids = wp_list_pluck( $posts, 'post_author' );
+	$author_ids = array_map( 'absint', $author_ids );
+	$author_ids = array_unique( array_filter( $author_ids ) );
+	cache_users( $author_ids );
+}
+
 /**
  * Updates metadata cache for list of post IDs.
  *

wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php

@@ -369,6 +369,8 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 
 		$posts = array();
 
+		update_post_author_caches( $query_result );
+
 		foreach ( $query_result as $post ) {
 			if ( ! $this->check_read_permission( $post ) ) {
 				continue;

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53481';
+$wp_version = '6.1-alpha-53482';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.