Code showing the difficulty to create a symlinkable base for a plugin in WordPress 3.4.x

symlinkable-plugin-base.php

<?php
class Symlinkable_Plugin_Base {
  var $plugin_file;
  var $plugin_id;
  function __construct( $args = array() ) {

    global $pagenow;

    if ( 'plugins.php' == $pagenow && isset( $_GET['action'] ) && isset( $_GET['plugin'] ) ) {
      global $plugin;
      if ( ! isset( $plugin ) ) {
        /*
         * This plugin is being activated
         */
        $this->plugin_id = filter_input( INPUT_GET, 'plugin', FILTER_SANITIZE_STRING );
        $this->plugin_file = WP_PLUGIN_DIR . '/' . $this->plugin_id;
      } else {
        /*
         * Another plugin is being activated
         */
        $this->plugin_file = WP_PLUGIN_DIR . '/' . $plugin;
        $this->plugin_id = $plugin;
      }
      add_action( 'plugins_loaded', array( $this, 'plugins_loaded' ) );
      add_action( "activate_{$this->plugin_id}", array( $this, 'activate_plugin' ), 0 );
      register_activation_hook( $this->plugin_id, array( $this, 'activate' ) );
    } else if ( 'plugins.php' == $pagenow && isset( $_GET['action'] ) &&  'delete-selected' == $_GET['action']
          && isset( $_POST['verify-delete'] ) &&  '1' == $_POST['verify-delete']
          && isset( $_POST['checked'] ) && count( $_POST['checked'] ) ) {
      if ( preg_match( '#^uninstall_(.*?)$#', current_filter(), $match ) ) {
        $this->plugin_file = $match[1];
      } else {
        // What a hack! I really need help from WordPress core here!!! :)
        $backtrace = debug_backtrace();
        foreach( $backtrace as $index => $call ) {
          if ( preg_match( '#/wp-admin/includes/plugin.php$#', $call['file'] ) ) {
            $this->plugin_file = $backtrace[$index-1]['file'];
            break;
          }
        }
      }
      $this->plugin_id = basename( dirname( $this->plugin_file ) ) . '/' . basename( $this->plugin_file );
    } else {
      /**
       * Grab the plugin file name from one the global values set when the plugin is included.
       * @see: http://wordpress.stackexchange.com/questions/15202/plugins-in-symlinked-directories
       * @see: http://wordpress.stackexchange.com/a/15204/89
       */
      global $mu_plugin, $network_plugin, $plugin;
      if ( isset( $mu_plugin ) ) {
        $this->plugin_file = $mu_plugin;
      } else if ( isset( $network_plugin ) ) {
        $this->plugin_file = $network_plugin;
      } else if ( isset( $plugin ) ) {
        $this->plugin_file = $plugin;
      } else {
        trigger_error( sprintf( __( 'Plugin %s only works when loaded by WordPress.' ), $this->plugin_id ) );
        exit;
      }
      $this->plugin_id = basename( dirname( $this->plugin_file ) ) . '/' . basename( $this->plugin_file );
      require_once( ABSPATH . 'wp-admin/includes/plugin.php' );
      if ( ! is_plugin_active( $this->plugin_id ) ) {
        trigger_error( sprintf( __( 'Plugin %s is not an active plugin or is not installed in a subdirectory of %s.' ),
          $this->plugin_name,
          WP_PLUGIN_DIR
        ));
        exit;
      }
      register_deactivation_hook( $this->plugin_id, array( $this, 'deactivate' ) );
    }

    register_uninstall_hook( $this->plugin_id, array( parent::plugin_class, 'uninstall' ) );

  }

}