Add an Autoloader based on the Plugin Directory, for autoloading of utilities

mu-plugins/autoloader/class-autoloader.php

@@ -0,0 +1,93 @@
+<?php
+namespace WordPressdotorg\Autoload;
+
+/**
+ * An Autoloader which respects WordPress's filename standards.
+ *
+ * @package WordPressdotorg\MU_Plugins\Utilities\Autoloader
+ */
+class Autoloader {
+
+	/**
+	 * Namespace separator.
+	 */
+	const NS_SEPARATOR = '\\';
+
+	/**
+	 * The prefix to compare classes against.
+	 *
+	 * @var string
+	 * @access protected
+	 */
+	protected $prefix;
+
+	/**
+	 * Length of the prefix string.
+	 *
+	 * @var int
+	 * @access protected
+	 */
+	protected $prefix_length;
+
+	/**
+	 * Path to the file to be loaded.
+	 *
+	 * @var string
+	 * @access protected
+	 */
+	protected $path;
+
+	/**
+	 * Constructor.
+	 *
+	 * @param string $prefix Prefix all classes have in common.
+	 * @param string $path   Path to the files to be loaded.
+	 */
+	public function __construct( $prefix, $path ) {
+		$this->prefix        = $prefix;
+		$this->prefix_length = strlen( $prefix );
+		$this->path          = rtrim( $path . '/' ) . '/';
+	}
+
+	/**
+	 * Loads a class if it starts with `$this->prefix`.
+	 *
+	 * @param string $class The class to be loaded.
+	 */
+	public function load( $class ) {
+		if ( strpos( $class, $this->prefix . self::NS_SEPARATOR ) !== 0 ) {
+			return;
+		}
+
+		// Strip prefix from the start (ala PSR-4)
+		$class = substr( $class, $this->prefix_length + 1 );
+		$class = strtolower( $class );
+		$file  = '';
+
+		if ( false !== ( $last_ns_pos = strripos( $class, self::NS_SEPARATOR ) ) ) {
+			$namespace = substr( $class, 0, $last_ns_pos );
+			$namespace = str_replace( '_', '-', $namespace );
+			$class     = substr( $class, $last_ns_pos + 1 );
+			$file      = str_replace( self::NS_SEPARATOR, DIRECTORY_SEPARATOR, $namespace ) . DIRECTORY_SEPARATOR;
+		}
+
+		$file .= 'class-' . str_replace( '_', '-', $class ) . '.php';
+
+		$path = $this->path . $file;
+
+		if ( file_exists( $path ) ) {
+			require $path;
+		}
+	}
+}
+
+/**
+ * Registers Autoloader's autoload function.
+ *
+ * @param string $prefix
+ * @param string $path
+ */
+function register_class_path( $prefix, $path ) {
+	$loader = new Autoloader( $prefix, $path );
+	spl_autoload_register( array( $loader, 'load' ) );
+}

mu-plugins/loader.php

@@ -1,11 +1,20 @@
 <?php
+namespace WordPressdotorg\MU_Plugins;
+use WordPressdotorg\Autoload;
 
 /**
  * Load mu-plugins.
  *
  * `utilities/` aren't loaded automatically since they're not used globally.
  */
 
+// Load and register the Autoloader.
+if ( ! class_exists( '\WordPressdotorg\Autoload\Autoloader', false ) ) {
+	require_once __DIR__ . '/autoloader/class-autoloader.php';
+}
+
+Autoload\register_class_path( __NAMESPACE__, __DIR__ );
+
 require_once __DIR__ . '/helpers/helpers.php';
 require_once __DIR__ . '/blocks/global-header-footer/blocks.php';
 require_once __DIR__ . '/blocks/horizontal-slider/horizontal-slider.php';