Some changes on the dependency injection engine based on feedback:

- `wc_get_container` declares a return type now.
- The autoloader now runs before `autoload_packages.php` is included.
- The autloader now excludes the namespaces for Admin, Blocs, Rest API.
- `private $container` in `Container` is now declared as being
  of type `\League\Container\Container`.
- The underlying container is registered with `share` instead of `add`.
- All methods in `AbstractServiceProvider` now allow passing a concrete.
- `AbstractServiceProvider::addWithAutoArguments` now checks if an
  argument has a default value, and registers the argument so that
  that value is supplied when constructing the object.
- `Proxies` class renamed to `ProxiesServiceProvider`.
- The methods to call code in `LegacyProxy` now use `call_user_func_array`.

src/Autoloader.php

@@ -7,8 +7,6 @@
 
 namespace Automattic\WooCommerce;
 
-use PHPUnit\Exception;
-
 defined( 'ABSPATH' ) || exit;
 
 /**
@@ -23,6 +21,12 @@ class Autoloader {
 	 */
 	private function __construct() {}
 
+	const NON_CORE_WOO_NAMESPACES = array(
+		'Automattic\\WooCommerce\\Admin\\',
+		'Automattic\\WooCommerce\\Blocks\\',
+		'Automattic\\WooCommerce\\RestApi\\',
+	);
+
 	/**
 	 * Require the autoloader and return the result.
 	 *
@@ -38,23 +42,32 @@ class Autoloader {
 			return false;
 		}
 
+		self::registerPsr4Autoloader();
+
 		$autoloader_result = require $autoloader;
 		if ( ! $autoloader_result ) {
 			return false;
 		}
 
-		self::registerPsr4Autoloader();
-
 		return $autoloader_result;
 	}
 
 	/**
 	 * Define a PSR4 autoloader for the dependency injection engine to work.
 	 * Function grabbed from https://container.thephpleague.com/3.x
+	 *
+	 * TODO: Assess if this is still needed after https://github.com/Automattic/jetpack/pull/15106 is merged.
+	 *       If it still is, remove this notice. If it isn't, remove the method.
 	 */
 	protected static function registerPsr4Autoloader() {
 		spl_autoload_register(
 			function ( $class ) {
+				foreach ( self::NON_CORE_WOO_NAMESPACES as $non_core_namespace ) {
+					if ( $non_core_namespace === substr( $class, 0, strlen( $non_core_namespace ) ) ) {
+						return;
+					}
+				}
+
 				$prefix   = 'Automattic\\WooCommerce\\';
 				$base_dir = __DIR__ . '/';
 				$len      = strlen( $prefix );
@@ -64,9 +77,7 @@ class Autoloader {
 				}
 				$relative_class = substr( $class, $len );
 				$file           = $base_dir . str_replace( '\\', '/', $relative_class ) . '.php';
-				if ( file_exists( $file ) ) {
-					require $file;
-				}
+				require $file;
 			}
 		);
 	}

src/Container.php

@@ -7,7 +7,7 @@
 
 namespace Automattic\WooCommerce;
 
-use Automattic\WooCommerce\Tools\DependencyManagement\ServiceProviders as ServiceProviders;
+use Automattic\WooCommerce\Tools\DependencyManagement\ServiceProviders\ProxiesServiceProvider;
 
 /**
  * PSR11 compliant dependency injection container for WooCommerce.
@@ -34,13 +34,13 @@ final class Container implements \Psr\Container\ContainerInterface {
 	 * @var string[]
 	 */
 	private $service_providers = array(
-		ServiceProviders\Proxies::class,
+		ProxiesServiceProvider::class,
 	);
 
 	/**
 	 * The underlying container.
 	 *
-	 * @var \Psr\Container\ContainerInterface
+	 * @var \League\Container\Container
 	 */
 	private $container;
 
@@ -53,7 +53,7 @@ final class Container implements \Psr\Container\ContainerInterface {
 		// Add ourselves as the shared instance of ContainerInterface,
 		// register everything else using service providers.
 
-		$this->container->add( \Psr\Container\ContainerInterface::class, $this );
+		$this->container->share( \Psr\Container\ContainerInterface::class, $this );
 
 		foreach ( $this->service_providers as $service_provider_class ) {
 			$this->container->addServiceProvider( $service_provider_class );

src/Tools/DependencyManagement/AbstractServiceProvider.php

@@ -7,6 +7,7 @@
 
 namespace Automattic\WooCommerce\Tools\DependencyManagement;
 
+use League\Container\Argument\RawArgument;
 use League\Container\Definition\DefinitionInterface;
 use League\Container\Definition\Definition;
 
@@ -27,21 +28,24 @@ abstract class AbstractServiceProvider extends \League\Container\ServiceProvider
 	/**
 	 * Register a class in the container and use reflection to guess the constructor arguments.
 	 *
+	 * WARNING: this method uses reflection, so please have performance in mind when using it.
+	 *
 	 * @param string $class_name Class name to register.
+	 * @param mixed  $concrete   The concrete to register. Can be a shared instance, a factory callback, or a class name.
 	 * @param bool   $shared Whether to register the class as shared (`get` always returns the same instance) or not.
 	 *
 	 * @return DefinitionInterface The generated container definition.
 	 *
 	 * @throws \Exception Error when reflecting the class, or class constructor is not public, or an argument has no valid type hint.
 	 */
-	public function addWithAutoArguments( string $class_name, bool $shared = false ) : DefinitionInterface {
+	public function addWithAutoArguments( string $class_name, $concrete = null, bool $shared = false ) : DefinitionInterface {
 		try {
 			$reflector = new \ReflectionClass( $class_name );
 		} catch ( \ReflectionException $ex ) {
 			throw new \Exception( get_class( $this ) . "::addWithAutoArguments: error when reflecting class '$class_name': {$ex->getMessage()}" );
 		}
 
-		$definition = new Definition( $class_name, null );
+		$definition = new Definition( $class_name, $concrete );
 
 		$constructor = $reflector->getConstructor();
 
@@ -52,12 +56,17 @@ abstract class AbstractServiceProvider extends \League\Container\ServiceProvider
 
 			$constructor_arguments = $constructor->getParameters();
 			foreach ( $constructor_arguments as $argument ) {
-				$argument_class = $argument->getClass();
-				if ( is_null( $argument_class ) ) {
-					throw new \Exception( get_class( $this ) . "::addWithAutoArguments: constructor argument '{$argument->getName()}' of class '$class_name' doesn't have a type hint or has one that doesn't specify a class." );
-				}
+				if ( $argument->isDefaultValueAvailable() ) {
+					$default_value = $argument->getDefaultValue();
+					$definition->addArgument( new RawArgument( $default_value ) );
+				} else {
+					$argument_class = $argument->getClass();
+					if ( is_null( $argument_class ) ) {
+						throw new \Exception( get_class( $this ) . "::addWithAutoArguments: constructor argument '{$argument->getName()}' of class '$class_name' doesn't have a type hint or has one that doesn't specify a class." );
+					}
 
-				$definition->addArgument( $argument_class->name );
+					$definition->addArgument( $argument_class->name );
+				}
 			}
 		}
 
@@ -72,14 +81,17 @@ abstract class AbstractServiceProvider extends \League\Container\ServiceProvider
 	 * Register a class in the container and use reflection to guess the constructor arguments.
 	 * The class is registered as shared, so `get` on the container always returns the same instance.
 	 *
+	 * WARNING: this method uses reflection, so please have performance in mind when using it.
+	 *
 	 * @param string $class_name Class name to register.
+	 * @param mixed  $concrete   The concrete to register. Can be a shared instance, a factory callback, or a class name.
 	 *
 	 * @return DefinitionInterface The generated container definition.
 	 *
 	 * @throws \Exception Error when reflecting the class, or class constructor is not public, or an argument has no valid type hint.
 	 */
-	public function shareWithAutoArguments( string $class_name ) : DefinitionInterface {
-		return $this->addWithAutoArguments( $class_name, true );
+	public function shareWithAutoArguments( string $class_name, $concrete = null ) : DefinitionInterface {
+		return $this->addWithAutoArguments( $class_name, $concrete, true );
 	}
 
 	/**
@@ -104,6 +116,6 @@ abstract class AbstractServiceProvider extends \League\Container\ServiceProvider
 	 * @return DefinitionInterface The generated container definition.
 	 */
 	public function share( string $id, $concrete = null ) : DefinitionInterface {
-		return $this->getContainer()->share( $id, $concrete );
+		return $this->add( $id, $concrete, true );
 	}
 }

src/Tools/DependencyManagement/ServiceProviders/ProxiesServiceProvider.php

@@ -13,7 +13,7 @@ use Automattic\WooCommerce\Tools\Proxies as ProxyClasses;
 /**
  * Service provider for the classes in the Automattic\WooCommerce\Tools\Proxies namespace.
  */
-class Proxies extends AbstractServiceProvider {
+class ProxiesServiceProvider extends AbstractServiceProvider {
 
 	/**
 	 * The classes/interfaces that are serviced by this service provider.

src/Tools/Proxies/LegacyProxy.php

@@ -96,7 +96,7 @@ class LegacyProxy {
 	 * @return mixed The result from the function.
 	 */
 	public function callFunction( $function_name, ...$parameters ) {
-		return call_user_func( $function_name, ...$parameters );
+		return call_user_func_array( $function_name, $parameters );
 	}
 
 	/**
@@ -110,6 +110,6 @@ class LegacyProxy {
 	 * @return mixed The result from the method.
 	 */
 	public function callStatic( $class_name, $method_name, ...$parameters ) {
-		return $class_name::$method_name( ...$parameters );
+		return call_user_func_array( "$class_name::$method_name", $parameters );
 	}
 }

woocommerce.php

@@ -53,7 +53,7 @@ function WC() { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.Fu
  *
  * @return \Psr\Container\ContainerInterface The WooCommerce PSR11 container.
  */
-function wc_get_container() {
+function wc_get_container() : \Psr\Container\ContainerInterface {
 	return $GLOBALS['wc_container'];
 }