Merge branch 'trunk' into ticket/20564

# Conflicts:
#	src/wp-includes/blocks/footnotes.php

src/wp-includes/blocks/footnotes.php

@@ -126,3 +126,76 @@ function wp_get_footnotes_from_revision( $revision_field, $field, $revision ) {
 	return $footnotes_html;
 }
 add_filter( '_wp_post_revision_field_footnotes', 'wp_get_footnotes_from_revision', 10, 3 );
+
+/**
+ * The REST API autosave endpoint doesn't save meta, so we can use the
+ * `wp_creating_autosave` when it updates an exiting autosave, and
+ * `_wp_put_post_revision` when it creates a new autosave.
+ *
+ * @since 6.3.0
+ *
+ * @param int|array $autosave The autosave ID or array.
+ */
+function _wp_rest_api_autosave_meta( $autosave ) {
+	// Ensure it's a REST API request.
+	if ( ! defined( 'REST_REQUEST' ) || ! REST_REQUEST ) {
+		return;
+	}
+
+	$body = rest_get_server()->get_raw_data();
+	$body = json_decode( $body, true );
+
+	if ( ! isset( $body['meta']['footnotes'] ) ) {
+		return;
+	}
+
+	// `wp_creating_autosave` passes the array,
+	// `_wp_put_post_revision` passes the ID.
+	$id = is_int( $autosave ) ? $autosave : $autosave['ID'];
+
+	if ( ! $id ) {
+		return;
+	}
+
+	update_post_meta( $id, 'footnotes', $body['meta']['footnotes'] );
+}
+// See https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L391C1-L391C1.
+add_action( 'wp_creating_autosave', '_wp_rest_api_autosave_meta' );
+// See https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L398.
+// Then https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/revision.php#L367.
+add_action( '_wp_put_post_revision', '_wp_rest_api_autosave_meta' );
+
+/**
+ * This is a workaround for the autosave endpoint returning early if the
+ * revision field are equal. The problem is that "footnotes" is not real
+ * revision post field, so there's nothing to compare against.
+ *
+ * This trick sets the "footnotes" field (value doesn't matter), which will
+ * cause the autosave endpoint to always update the latest revision. That should
+ * be fine, it should be ok to update the revision even if nothing changed. Of
+ * course, this is temporary fix.
+ *
+ * @since 6.3.0
+ *
+ * @param WP_Post         $prepared_post The prepared post object.
+ * @param WP_REST_Request $request       The request object.
+ *
+ * See https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L365-L384.
+ * See https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L219.
+ */
+function _wp_rest_api_force_autosave_difference( $prepared_post, $request ) {
+	// We only want to be altering POST requests.
+	if ( $request->get_method() !== 'POST' ) {
+		return $prepared_post;
+	}
+
+	// Only alter requests for the '/autosaves' route.
+	if ( substr( $request->get_route(), -strlen( '/autosaves' ) ) !== '/autosaves' ) {
+		return $prepared_post;
+	}
+
+	$prepared_post->footnotes = '[]';
+	return $prepared_post;
+}
+
+add_filter( 'rest_pre_insert_post', '_wp_rest_api_force_autosave_difference', 10, 2 );