Allow WordPress-MU plugins to be loaded automatically from a sub directory

subdir-loader.php

<?php

    /**
     * Plugin Name: MU plugins subdirectory loader
     * Plugin URI: http://code.ctlt.ubc.ca
     * Description: Enables the loading of plugins sitting in mu-plugins (as folders)
     * Version: 0.1
     * Author: iamfriendly, CTLT
     * Author URI: http://ubc.ca/
     *
     */

    class CTLT_Load_MU_Plugins_In_SubDir
    {

        // The transient name
        static $transientName = 'mu_plugins_in_sub_dir';

        /**
         * Set up our actions and filters
         *
         * @author Richard Tape <@richardtape>
         * @package CTLT_Load_MU_Plugins_In_SubDir
         * @since 1.0
         * @param null
         * @return null
         */

        public function __construct()
        {

            // Load the plugins
            add_action( 'muplugins_loaded', array( $this, 'muplugins_loaded__requirePlugins' ) );

            // Adjust the MU plugins list table to show which plugins are MU
            add_action( 'after_plugin_row_subdir-loader.php', array( $this, 'after_plugin_row__addRows' ) );

        }/* __construct() */


        /**
         * Will clear cache when visiting the plugin page in /wp-admin/.
         * Will also clear cache if a previously detected mu-plugin was deleted.
         *
         * @author Richard Tape <@richardtape>
         * @package CTLT_Load_MU_Plugins_In_SubDir
         * @since 1.0
         * @param null
         * @return (array) $plugins - an array of plugins in sub directories in the WPMU plugins dir
         */
        
        public static function WPMUPluginFilesInSubDirs()
        {

            // Do we have a pre-existing cache of the plugins? This checks in %prefix%_sitemeta
            $plugins = get_site_transient( static::$transientName );

            // If we do have a cache, let's check the plugin still exists
            if( $plugins !== false )
            {

                foreach( $plugins as $pluginFile )
                {

                    if( !is_readable( WPMU_PLUGIN_DIR . '/' . $pluginFile ) )
                    {

                        $plugins = false;
                        break;

                    }

                }

            }

            if( $plugins !== false ){
                return $plugins;
            }


            // Check we have access to get_plugins()
            if( !function_exists( 'get_plugins' ) ) {
                require ABSPATH . 'wp-admin/includes/plugin.php';
            }

            // Start fresh
            $plugins = array();

            foreach( get_plugins( '/../mu-plugins' ) as $pluginFile => $pluginData )
            {

                // skip files directly at root (WP already handles these)
                if( dirname( $pluginFile ) != '.' ){
                    $plugins[] = $pluginFile; 
                }

            }

            // OK, set the transient and...
            set_site_transient( static::$transientName, $plugins );

            // ...ship
            return $plugins;

        }/* WPMUPluginFilesInSubDirs() */

        

        /**
         * Delete the transient if we're on an individual site's plugins page
         * Require each of the MU plugins
         *
         * @author Richard Tape <@richardtape>
         * @package CTLT_Load_MU_Plugins_In_SubDir
         * @since 1.0
         * @param null
         * @return null
         */
        
        public function muplugins_loaded__requirePlugins()
        {

            // delete cache when viewing the plugins page in the dashboard
            if( isset( $_SERVER['REQUEST_URI'] ) && strpos( $_SERVER['REQUEST_URI'], '/wp-admin/plugins.php' ) !== false ){
                delete_site_transient( static::$transientName );
            }

            // Now load each plugin in a subdir
            foreach( static::WPMUPluginFilesInSubDirs() as $pluginFile ){
                require WPMU_PLUGIN_DIR . '/' . $pluginFile;
            }

        }/* muplugins_loaded__requirePlugins() */


        /**
         * Quick and dirty way to display which plugins are MU and slightly adjust their layout 
         * to show which ones are subdir or not
         *
         * @author Richard Tape <@richardtape>
         * @package CTLT_Load_MU_Plugins_In_SubDir
         * @since 1.0
         * @param null
         * @return null
         */
        
        public function after_plugin_row__addRows()
        {

            foreach( static::WPMUPluginFilesInSubDirs() as $pluginFile )
            {

                // Super stripped down version of WP_Plugins_List_Table
                $data   = get_plugin_data( WPMU_PLUGIN_DIR . '/' . $pluginFile );
                $name   = empty( $data['Plugin Name'] ) ? $pluginFile : $data['Plugin Name'];
                $desc   = empty( $data['Description'] ) ? '&nbsp;' : $data['Description'];
                $id     = sanitize_title( $name );

                echo static::getPluginRowMarkup( $id, $name, $desc );

            }

        }/* after_plugin_row__addRows() */


        /**
         * Helper function to output a table row in the MU plugins list
         *
         * @author Richard Tape <@richardtape>
         * @package CTLT_Load_MU_Plugins_In_SubDir
         * @since 1.0
         * @param (string) $id - plugin ID (slug of the $name)
         * @param (string) $name - Name of the plugin
         * @param (string) $desc - The plugin's description
         * @return (string) the <tr> markup for this plugin
         */
        
        public static function getPluginRowMarkup( $id, $name, $desc )
        {

            $output = '
                <tr id="' . $id . '" class="active">
                    <th scope="row" class="check-column"></th>
                    <td class="plugin-title"><strong style="padding-left: 10px;">+&nbsp;&nbsp;' . $name . '</strong></td>
                    <td class="column-description desc">
                        <div class="plugin-description"><p>' . $desc . '</p></div>
                    </td>
                </tr>
            ';

            return $output;

        }/* getPluginRowMarkup() */
        

    }/* class CTLT_Load_MU_Plugins_In_SubDir */

    global $CTLT_Load_MU_Plugins_In_SubDir;
    $CTLT_Load_MU_Plugins_In_SubDir = new CTLT_Load_MU_Plugins_In_SubDir();

Thank you it still works after 9 years