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.


git-svn-id: https://develop.svn.wordpress.org/trunk@52437 602fd350-edb4-49c9-b593-d223f7449a82

src/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' );

src/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;

tests/phpunit/tests/oembed/template.php

@@ -309,13 +309,14 @@ class Tests_Embed_Template extends WP_UnitTestCase {
 	public function test_add_host_js() {
 		remove_all_filters( 'embed_oembed_html' );
 
+		// This function is now a no-op.
 		wp_oembed_add_host_js();
 
-		$this->assertEquals( 10, has_filter( 'embed_oembed_html', 'wp_maybe_enqueue_oembed_host_js' ) );
+		$this->assertFalse( has_filter( 'embed_oembed_html', 'wp_maybe_enqueue_oembed_host_js' ) );
 	}
 
 	/** @covers ::wp_maybe_enqueue_oembed_host_js() */
-	function test_wp_maybe_enqueue_oembed_host_js() {
+	public function test_wp_maybe_enqueue_oembed_host_js() {
 		$scripts = wp_scripts();
 
 		$this->assertFalse( $scripts->query( 'wp-embed', 'enqueued' ) );
@@ -330,6 +331,19 @@ class Tests_Embed_Template extends WP_UnitTestCase {
 		$this->assertTrue( $scripts->query( 'wp-embed', 'enqueued' ) );
 	}
 
+	/** @covers ::wp_maybe_enqueue_oembed_host_js() */
+	public function test_wp_maybe_enqueue_oembed_host_js_without_wp_head_action() {
+		$scripts = wp_scripts();
+
+		remove_action( 'wp_head', 'wp_oembed_add_host_js' );
+		$this->assertFalse( $scripts->query( 'wp-embed', 'enqueued' ) );
+
+		$post_embed = '<blockquote class="wp-embedded-content" data-secret="S24AQCJW9i"><a href="https://make.wordpress.org/core/2016/03/11/embeds-changes-in-wordpress-4-5/">Embeds Changes in WordPress 4.5</a></blockquote><iframe class="wp-embedded-content" sandbox="allow-scripts" security="restricted" style="position: absolute; clip: rect(1px, 1px, 1px, 1px);" title="&#8220;Embeds Changes in WordPress 4.5&#8221; &#8212; Make WordPress Core" src="https://make.wordpress.org/core/2016/03/11/embeds-changes-in-wordpress-4-5/embed/#?secret=S24AQCJW9i" data-secret="S24AQCJW9i" width="600" height="338" frameborder="0" marginwidth="0" marginheight="0" scrolling="no"></iframe>';
+
+		wp_maybe_enqueue_oembed_host_js( $post_embed );
+		$this->assertFalse( $scripts->query( 'wp-embed', 'enqueued' ) );
+	}
+
 	/**
 	 * Confirms that no ampersands exist in src/wp-includes/js/wp-embed.js.
 	 *