Jetpack Sync: Ensure duplicate Sync modules are not loaded (#38503)

* Jetpack Sync: Ensure duplicate Sync modules are removed

projects/packages/sync/README.md

@@ -69,6 +69,8 @@ the following modules will be enabled no matter the configuration:
 - `Automattic\\Jetpack\\Sync\\Modules\\Stats`
 - `Automattic\\Jetpack\\Sync\\Modules\\Updates`
 
+**Attention**: Sync currently only supports configuring the list of [default Sync modules](https://github.com/Automattic/jetpack/blob/trunk/projects/packages/sync/src/class-modules.php#L25). Any modules that Sync already loads conditionally, such as `WooCommerce` or `Search` are **NOT** configurable.
+
 ##### `jetpack_sync_options_whitelist` / `jetpack_sync_options_contentless`
 
 **Controlled by the Sync Options Module, which is required.**

projects/packages/sync/changelog/fix-sync-custom-config-modules-loaded-twice

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Jetpack Sync: Ensure duplicate Sync modules are not loaded

projects/packages/sync/src/class-modules.php

@@ -123,6 +123,8 @@ public static function initialize_modules() {
 		 */
 		$modules = apply_filters( 'jetpack_sync_modules', self::DEFAULT_SYNC_MODULES );
 
+		$modules = array_unique( $modules );
+
 		$modules = array_map( array( __CLASS__, 'load_module' ), $modules );
 
 		return array_map( array( __CLASS__, 'set_module_defaults' ), $modules );

projects/packages/sync/src/class-package-version.php

@@ -12,7 +12,7 @@
  */
 class Package_Version {
 
-	const PACKAGE_VERSION = '3.3.0';
+	const PACKAGE_VERSION = '3.3.1-alpha';
 
 	const PACKAGE_SLUG = 'sync';
 

projects/packages/sync/tests/php/test-modules.php

@@ -0,0 +1,63 @@
+<?php // phpcs:ignore WordPress.Files.FileName.InvalidClassFileName
+
+namespace Automattic\Jetpack\Sync;
+
+use WorDBless\BaseTestCase;
+
+/**
+ * Unit tests for the Automattic\Jetpack\Sync\Modules class.
+ *
+ * @package automattic/jetpack-sync
+ */
+class Test_Modules extends BaseTestCase {
+
+	/**
+	 * Runs before every test in this class.
+	 */
+	public function set_up() {
+		// Reset private static properties after each test.
+		$reflection_class = new \ReflectionClass( '\Automattic\Jetpack\Sync\Modules' );
+		try {
+			$reflection_class->setStaticPropertyValue( 'initialized_modules', null );
+		} catch ( \ReflectionException $e ) { // PHP 7 compat
+			$configured = $reflection_class->getProperty( 'initialized_modules' );
+			$configured->setAccessible( true );
+			$configured->setValue( null );
+		}
+	}
+
+	/**
+	 * Runs after every test in this class.
+	 */
+	public function tear_down() {
+		remove_filter( 'jetpack_sync_modules', array( $this, 'add_posts_module' ) );
+	}
+
+	/**
+	 * Tests get_modules with duplicate modules.
+	 */
+	public function test_get_modules_will_remove_duplicates() {
+		add_filter( 'jetpack_sync_modules', array( $this, 'add_posts_module' ) );
+
+		$modules        = Modules::get_modules();
+		$module_classes = array();
+		foreach ( $modules as $module ) {
+			$module_classes[] = get_class( $module );
+		}
+
+		$this->assertSame( Modules::DEFAULT_SYNC_MODULES, $module_classes );
+	}
+
+	/**
+	 * Adds Sync Posts module to Sync's module list.
+	 *
+	 * @param array $sync_modules The list of sync modules declared prior to this filter.
+	 *
+	 * @return array A list of sync modules that now includes Posts modules.
+	 */
+	public function add_posts_module( array $sync_modules ) {
+		$sync_modules[] = 'Automattic\\Jetpack\\Sync\\Modules\\Posts';
+
+		return $sync_modules;
+	}
+}