Ensure SimplePie is initialized fully.

Author: peterwilsoncc

src/wp-includes/feed.php

@@ -805,6 +805,9 @@ function fetch_feed( $url ) {
 	if ( ! class_exists( 'SimplePie\SimplePie', false ) ) {
 		require_once ABSPATH . WPINC . '/class-simplepie.php';
 	}
+	require_once ABSPATH . WPINC . '/class-wp-feed-cache-transient.php';
+	require_once ABSPATH . WPINC . '/class-wp-simplepie-file.php';
+	require_once ABSPATH . WPINC . '/class-wp-simplepie-sanitize-kses.php';
 
 	if ( is_array( $url ) && count( $url ) <= 1 ) {
 		$url = array_shift( $url );
@@ -816,15 +819,22 @@ function fetch_feed( $url ) {
 		$items = SimplePie\SimplePie::merge_items( $feeds );
 
 		$feed = new SimplePie\SimplePie();
+		$feed->get_registry()->register( SimplePie\Sanitize::class, 'WP_SimplePie_Sanitize_KSES', true );
+		$feed->sanitize = new WP_SimplePie_Sanitize_KSES();
+		if ( method_exists( 'SimplePie_Cache', 'register' ) ) {
+			SimplePie_Cache::register( 'wp_transient', 'WP_Feed_Cache_Transient' );
+			$feed->set_cache_location( 'wp_transient' );
+		} else {
+			// Back-compat for SimplePie 1.2.x.
+			require_once ABSPATH . WPINC . '/class-wp-feed-cache.php';
+			$feed->set_cache_class( 'WP_Feed_Cache' );
+		}
+		$feed->get_registry()->register( SimplePie\File::class, 'WP_SimplePie_File', true );
 		$feed->init();
 		$feed->data['items'] = $items;
 		return $feed;
 	}
 
-	require_once ABSPATH . WPINC . '/class-wp-feed-cache-transient.php';
-	require_once ABSPATH . WPINC . '/class-wp-simplepie-file.php';
-	require_once ABSPATH . WPINC . '/class-wp-simplepie-sanitize-kses.php';
-
 	$feed = new SimplePie\SimplePie();
 
 	$feed->get_registry()->register( SimplePie\Sanitize::class, 'WP_SimplePie_Sanitize_KSES', true );