Query: Prevent ID only queries erroring when starting the loop.

Ensure only full post objects are passed to `update_post_author_caches()` when called within `WP_Query::the_post()`. This prevents an error when starting the Loop for Queries initiated with a subset of fields or IDs only.

Props konyoldeath, dd32, lozula, TimothyBlynJacobs, spacedmonkey, mxbclang, peterwilsoncc.
Fixes #56948.


Built from https://develop.svn.wordpress.org/trunk@54771


git-svn-id: http://core.svn.wordpress.org/trunk@54323 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-query.php

@@ -3586,7 +3586,15 @@ class WP_Query {
 		global $post;
 
 		if ( ! $this->in_the_loop ) {
-			update_post_author_caches( $this->posts );
+			// Only prime the post cache for queries limited to the ID field.
+			$post_ids = array_filter( $this->posts, 'is_numeric' );
+			// Exclude any falsey values, such as 0.
+			$post_ids = array_filter( $post_ids );
+			if ( $post_ids ) {
+				_prime_post_caches( $post_ids, $this->query_vars['update_post_term_cache'], $this->query_vars['update_post_meta_cache'] );
+			}
+			$post_objects = array_map( 'get_post', $this->posts );
+			update_post_author_caches( $post_objects );
 		}
 
 		$this->in_the_loop = true;

wp-includes/post.php

@@ -7461,6 +7461,15 @@ function update_post_caches( &$posts, $post_type = 'post', $update_term_cache =
  * @param WP_Post[] $posts Array of post objects.
  */
 function update_post_author_caches( $posts ) {
+	/*
+	 * cache_users() is a pluggable function so is not available prior
+	 * to the `plugins_loaded` hook firing. This is to ensure against
+	 * fatal errors when the function is not available.
+	 */
+	if ( ! function_exists( 'cache_users' ) ) {
+		return;
+	}
+
 	$author_ids = wp_list_pluck( $posts, 'post_author' );
 	$author_ids = array_map( 'absint', $author_ids );
 	$author_ids = array_unique( array_filter( $author_ids ) );

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.2-alpha-54770';
+$wp_version = '6.2-alpha-54771';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.