always-print-script-modules-in-head.php

<?php
/**
 * Plugin Name: Always Print Script Modules in Head
 * Plugin URI: https://gist.github.com/westonruter/f9e67442c674c3176b95cd1ed0e784c1
 * Description: In classic themes script modules are forced to print in the footer since the HEAD is rendered before the rest of the page, so it is not yet known what script modules will be enqueued. This can be fixed with output buffering. This is a demonstration plugin for Core Trac ticket #43258 which adds output buffering for the rendered template.
 * Requires at least: 6.8-beta1
 * Version: 0.1.0
 * Author: Weston Ruter
 * Author URI: https://weston.ruter.net/
 * License: GPLv2 or later
 * License URI: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 * Update URI: https://gist.github.com/westonruter/f9e67442c674c3176b95cd1ed0e784c1
 * GitHub Plugin URI: https://gist.github.com/westonruter/f9e67442c674c3176b95cd1ed0e784c1
 *
 * @package always-print-script-modules-in-head
 */

add_action(
	'after_setup_theme',
	static function () {
		if ( wp_is_block_theme() ) {
			return;
		}

		// Remove the actions which WP_Script_Modules::add_hooks() adds for the footer in classic themes (where block themes can use wp_head).
		remove_action( 'wp_footer', array( wp_script_modules(), 'print_import_map' ) );
		remove_action( 'wp_footer', array( wp_script_modules(), 'print_enqueued_script_modules' ) );
		remove_action( 'wp_footer', array( wp_script_modules(), 'print_script_module_preloads' ) );

		// Print a placeholder for where the script module markup should be located in the head.
		$placeholder = sprintf( '<!--%s:%s-->', 'script_modules', wp_generate_uuid4() );
		add_action(
			'wp_head',
			static function () use ( $placeholder ) {
				echo $placeholder;
			}
		);

		// Capture the script module markup when it is printed at wp_footer.
		$script_module_markup = '';
		add_action(
			'wp_footer',
			static function () use ( &$script_module_markup ) {
				ob_start();
				wp_script_modules()->print_import_map();
				wp_script_modules()->print_enqueued_script_modules();
				wp_script_modules()->print_script_module_preloads();
				$script_module_markup = ob_get_clean();
			}
		);

		// Replace placeholder with the captured script module markup.
		add_filter(
			'wp_template_output_buffer',
			static function ( $buffer ) use ( $placeholder, &$script_module_markup ) {
				return str_replace( $placeholder, $script_module_markup, $buffer );
			}
		);
	},
	11
);