From 90100ff8831cb7e834afd6823527a4e846b5eba0 Mon Sep 17 00:00:00 2001
From: audrasjb <audrasjb@git.wordpress.org>
Date: Tue, 4 Jan 2022 15:23:59 +0000
Subject: [PATCH] Embeds: Fix oEmbed host script enqueueing on block-based
 themes.

This change fixes oEmbed host script enqueueing on front-end when using block themes.

It deprecates `wp_oembed_add_host_js` in favor of `wp_maybe_enqueue_oembed_host_js`. The action is still triggered in `default-filters.php` to ensure backward compatibility for websites that are removing the action. There is now a `has_action()` check in `wp_maybe_enqueue_oembed_host_js()` to see if `wp_oembed_add_host_js()` has not been unhooked from running at the `wp_head` action.

Follow-up to [52132], [52151], [52153], [52325].

Props swissspidy, westonruter, flixos90, kafleg.
Fixes #44632.

Built from https://develop.svn.wordpress.org/trunk@52437


git-svn-id: http://core.svn.wordpress.org/trunk@52029 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/default-filters.php |  3 ++-
 wp-includes/embed.php           | 24 ++++++++++++++++++++----
 wp-includes/version.php         |  2 +-
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/wp-includes/default-filters.php b/wp-includes/default-filters.php
index 94c9436ee9..d9663946d6 100644
--- a/wp-includes/default-filters.php
+++ b/wp-includes/default-filters.php
@@ -642,7 +642,8 @@ 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_host_js' );
+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' );
 
 add_action( 'embed_head', 'enqueue_embed_scripts', 1 );
 add_action( 'embed_head', 'print_emoji_detection_script' );
diff --git a/wp-includes/embed.php b/wp-includes/embed.php
index ec39b03422..7efee7107d 100644
--- a/wp-includes/embed.php
+++ b/wp-includes/embed.php
@@ -356,11 +356,23 @@ function wp_oembed_add_discovery_links() {
 /**
  * Adds the necessary JavaScript to communicate with the embedded iframes.
  *
+ * This function is no longer used directly. For back-compat it exists exclusively as a way to indicate that the oEmbed
+ * host JS _should_ be added. In `default-filters.php` there remains this code:
+ *
+ *     add_action( 'wp_head', 'wp_oembed_add_host_js' )
+ *
+ * Historically a site has been able to disable adding the oEmbed host script by doing:
+ *
+ *     remove_action( 'wp_head', 'wp_oembed_add_host_js' )
+ *
+ * In order to ensure that such code still works as expected, this function remains. There is now a `has_action()` check
+ * in `wp_maybe_enqueue_oembed_host_js()` to see if `wp_oembed_add_host_js()` has not been unhooked from running at the
+ * `wp_head` action.
+ *
  * @since 4.4.0
+ * @deprecated 5.9.0 Use {@see wp_maybe_enqueue_oembed_host_js()} instead.
  */
-function wp_oembed_add_host_js() {
-	add_filter( 'embed_oembed_html', 'wp_maybe_enqueue_oembed_host_js' );
-}
+function wp_oembed_add_host_js() {}
 
 /**
  * Enqueue the wp-embed script if the provided oEmbed HTML contains a post embed.
@@ -374,7 +386,11 @@ function wp_oembed_add_host_js() {
  * @return string Embed markup (without modifications).
  */
 function wp_maybe_enqueue_oembed_host_js( $html ) {
-	if ( preg_match( '/<blockquote\s[^>]*?wp-embedded-content/', $html ) ) {
+	if (
+		has_action( 'wp_head', 'wp_oembed_add_host_js' )
+		&&
+		preg_match( '/<blockquote\s[^>]*?wp-embedded-content/', $html )
+	) {
 		wp_enqueue_script( 'wp-embed' );
 	}
 	return $html;
diff --git a/wp-includes/version.php b/wp-includes/version.php
index d8d7c96d69..7e5185087a 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-beta4-52436';
+$wp_version = '5.9-beta4-52437';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.