List mu-plugins from subfolders

features/plugin.feature

@@ -751,6 +751,31 @@ Feature: Manage WordPress plugins
       | name    | title             | description                                    |
       | test-mu | Test mu-plugin    | Test mu-plugin description                     |
 
+  Scenario: Listing mu-plugins should include plugins from subfolders
+    Given a WP install
+    And a wp-content/mu-plugins/test-mu-root.php file:
+      """
+      <?php
+      // Plugin Name: Test MU Root
+      // Description: Test mu-plugin in root
+      // Version: 1.0.0
+      """
+    And a wp-content/mu-plugins/subfolder-plugin/subfolder-plugin.php file:
+      """
+      <?php
+      /**
+       * Plugin Name: Subfolder MU Plugin
+       * Description: Test mu-plugin in subfolder
+       * Version: 2.0.0
+       */
+      """
+
+    When I run `wp plugin list --status=must-use --fields=name,title,version`
+    Then STDOUT should be a table containing rows:
+      | name              | title                 | version |
+      | test-mu-root      | Test MU Root          | 1.0.0   |
+      | subfolder-plugin  | Subfolder MU Plugin   | 2.0.0   |
+
   @require-wp-5.5
   Scenario: Listing plugins should include name and auto_update
     Given a WP install

src/Plugin_Command.php

@@ -239,7 +239,25 @@ protected function status_single( $args ) {
 	protected function get_all_items() {
 		$items = $this->get_item_list();
 
-		foreach ( get_mu_plugins() as $file => $mu_plugin ) {
+		// Get all mu-plugins including those in subfolders.
+		// get_mu_plugins() only returns PHP files directly in the mu-plugins directory.
+		// To also get plugins in subfolders, we use get_plugins() with a relative path.
+		$mu_plugins = get_mu_plugins();
+		if ( defined( 'WPMU_PLUGIN_DIR' ) ) {
+			// Get plugins from mu-plugins subfolders using the relative path approach.
+			// This is the standard WordPress method to access plugins in the mu-plugins directory.
+			$mu_plugins_subfolder = get_plugins( '/../' . basename( WPMU_PLUGIN_DIR ) );
+			// Merge subfolder plugins with root-level mu-plugins.
+			// No duplicates possible: get_mu_plugins() returns 'plugin.php' (root only)
+			// while get_plugins() returns 'subfolder/plugin.php' (different keys).
+			foreach ( $mu_plugins_subfolder as $file => $plugin_data ) {
+				if ( ! isset( $mu_plugins[ $file ] ) ) {
+					$mu_plugins[ $file ] = $plugin_data;
+				}
+			}
+		}
+
+		foreach ( $mu_plugins as $file => $mu_plugin ) {
 			$mu_version = '';
 			if ( ! empty( $mu_plugin['Version'] ) ) {
 				$mu_version = $mu_plugin['Version'];