Print wp_oembed_add_discovery_links() at wp_head priority 4 if still hooked at priority 10

Author: westonruter

src/wp-includes/default-filters.php

@@ -704,7 +704,8 @@
 add_action( 'rest_api_init', 'wp_oembed_register_route' );
 add_filter( 'rest_pre_serve_request', '_oembed_rest_pre_serve_request', 10, 4 );
 
-add_action( 'wp_head', 'wp_oembed_add_discovery_links' );
+add_action( 'wp_head', 'wp_oembed_add_discovery_links', 4 ); // Printed after feed_links() and feed_links_extra().
+add_action( 'wp_head', 'wp_oembed_add_discovery_links' ); // Unhooked the first time that wp_oembed_add_discovery_links() runs for back-compat.
 add_action( 'wp_head', 'wp_oembed_add_host_js' ); // Back-compat for sites disabling oEmbed host JS by removing action.
 add_filter( 'embed_oembed_html', 'wp_maybe_enqueue_oembed_host_js' );
 

src/wp-includes/embed.php

@@ -332,8 +332,17 @@ function wp_oembed_register_route() {
  *
  * @since 4.4.0
  * @since 6.8.0 Output was adjusted to only embed if the post supports it.
+ * @since 6.9.0 Now runs first at `wp_head` priority 4, with a fallback to priority 10.
  */
 function wp_oembed_add_discovery_links() {
+	// For back-compat, short-circuit if a plugin has removed the action at the original priority.
+	if ( ! has_action( 'wp_head', 'wp_oembed_add_discovery_links', 10 ) ) {
+		return;
+	}
+
+	// Prevent running again at the original priority.
+	remove_action( 'wp_head', 'wp_oembed_add_discovery_links' );
+
 	$output = '';
 
 	if ( is_singular() && is_post_embeddable() ) {