Script Modules API: Add import map polyfill (#58263)

* Add import map polyfill

* Update issue number

* Update WP folder for the polyfill file

* Update the function with dom injection

* Load it on the footer

* Remove unwanted comma

* Update WP Core folder to be like other polyfills

* Do not load polyfill if there are no modules

* Add an id to the script

* Use WP default functions

* Use load id

* Use stable version

* Sync function with Core

lib/compat/wordpress-6.5/class-wp-script-modules.php

@@ -212,10 +212,37 @@ public function print_script_module_preloads() {
 		 * Prints the import map using a script tag with a type="importmap" attribute.
 		 *
 		 * @since 6.5.0
+		 *
+		 * @global WP_Scripts $wp_scripts The WP_Scripts object for printing the polyfill.
 		 */
 		public function print_import_map() {
 			$import_map = $this->get_import_map();
 			if ( ! empty( $import_map['imports'] ) ) {
+				global $wp_scripts;
+				if ( isset( $wp_scripts ) ) {
+					/*
+					 * In Core, the polyfill is registered with a different approach.
+					 * See: https://github.com/WordPress/wordpress-develop/blob/4b23ba81ddb067110e41d05550de7f2a4f09dad3/src/wp-includes/script-loader.php#L99
+					 */
+					wp_register_script(
+						'wp-polyfill-importmap',
+						gutenberg_url( '/build/modules/importmap-polyfill.min.js' ),
+						array(),
+						'1.8.2',
+						true
+					);
+					wp_print_inline_script_tag(
+						wp_get_script_polyfill(
+							$wp_scripts,
+							array(
+								'HTMLScriptElement.supports && HTMLScriptElement.supports("importmap")' => 'wp-polyfill-importmap',
+							)
+						),
+						array(
+							'id' => 'wp-load-polyfill-importmap',
+						)
+					);
+				}
 				wp_print_inline_script_tag(
 					wp_json_encode( $import_map, JSON_HEX_TAG | JSON_HEX_AMP ),
 					array(

lib/compat/wordpress-6.5/scripts-modules.php

@@ -20,13 +20,14 @@
 	 * @return WP_Script_Modules The main WP_Script_Modules instance.
 	 */
 	function wp_script_modules(): WP_Script_Modules {
-		static $instance = null;
-		if ( is_null( $instance ) ) {
-			$instance = new WP_Script_Modules();
-			$instance->add_hooks();
+		global $wp_script_modules;
+
+		if ( ! ( $wp_script_modules instanceof WP_Script_Modules ) ) {
+			$wp_script_modules = new WP_Script_Modules();
 		}
-		return $instance;
+		return $wp_script_modules;
 	}
+	wp_script_modules()->add_hooks();
 }
 
 if ( ! function_exists( 'wp_register_script_module' ) ) {