CodeIgniter + Composer + PHP 5.2 ou PHP 5.3

composer.json

{
    "require": {
        "rogeriopradoj/codeigniter": "*",
         "xrstf/composer-php52": "*"
    },
    "require-dev": {
        "phpunit/phpunit": "*",
        "squizlabs/php_codesniffer": "*"
    },
    "scripts": {
        "post-install-cmd": [
            "xrstf\\Composer52\\Generator::onPostInstallCmd"
        ],
        "post-update-cmd": [
            "xrstf\\Composer52\\Generator::onPostInstallCmd"
        ],
        "post-autoload-dump": [
            "xrstf\\Composer52\\Generator::onPostInstallCmd"
        ]
    }
}

config--bootstrap.php

<?php

ini_set('default_charset', 'utf-8');
date_default_timezone_set('America/Sao_Paulo');

/*
 *---------------------------------------------------------------
 * APPLICATION ENVIRONMENT
 *---------------------------------------------------------------
 *
 * You can load different configurations depending on your
 * current environment. Setting the environment also influences
 * things like logging and error reporting.
 *
 * This can be set to anything, but default usage is:
 *
 *     development
 *     testing
 *     production
 *
 * NOTE: If you change these, also change the error_reporting() code below
 *
 */
    define('ENVIRONMENT', $environment);
/*
 *---------------------------------------------------------------
 * ERROR REPORTING
 *---------------------------------------------------------------
 *
 * Different environments will require different levels of error reporting.
 * By default development will show errors but testing and live will hide them.
 */

if (defined('ENVIRONMENT'))
{
    switch (ENVIRONMENT)
    {
        case 'development':
            error_reporting(-1);
            ini_set('display_errors', '1');
        break;
    
        case 'testing':
        case 'production':
            error_reporting(0);
            ini_set('display_errors', '0');
        break;

        default:
            exit('The application environment is not set correctly.');
    }
}

/*
 *---------------------------------------------------------------
 * SYSTEM FOLDER NAME
 *---------------------------------------------------------------
 *
 * This variable must contain the name of your "system" folder.
 * Include the path if the folder is not in the same  directory
 * as this file.
 *
 */
    $system_path = realpath(dirname(__FILE__) . '/../vendor/rogeriopradoj/codeigniter/system');

/*
 *---------------------------------------------------------------
 * APPLICATION FOLDER NAME
 *---------------------------------------------------------------
 *
 * If you want this front controller to use a different "application"
 * folder then the default one you can set its name here. The folder
 * can also be renamed or relocated anywhere on your server.  If
 * you do, use a full server path. For more info please see the user guide:
 * http://codeigniter.com/user_guide/general/managing_apps.html
 *
 * NO TRAILING SLASH!
 *
 */
    $application_folder = realpath(dirname(__FILE__) . '/../src/application');

/*
 * --------------------------------------------------------------------
 * DEFAULT CONTROLLER
 * --------------------------------------------------------------------
 *
 * Normally you will set your default controller in the routes.php file.
 * You can, however, force a custom routing by hard-coding a
 * specific controller class/function here.  For most applications, you
 * WILL NOT set your routing here, but it's an option for those
 * special instances where you might want to override the standard
 * routing in a specific front controller that shares a common CI installation.
 *
 * IMPORTANT:  If you set the routing here, NO OTHER controller will be
 * callable. In essence, this preference limits your application to ONE
 * specific controller.  Leave the function name blank if you need
 * to call functions dynamically via the URI.
 *
 * Un-comment the $routing array below to use this feature
 *
 */
    // The directory name, relative to the "controllers" folder.  Leave blank
    // if your controller is not in a sub-folder within the "controllers" folder
    // $routing['directory'] = '';

    // The controller class file name.  Example:  Mycontroller
    // $routing['controller'] = '';

    // The controller function you wish to be called.
    // $routing['function'] = '';


/*
 * -------------------------------------------------------------------
 *  CUSTOM CONFIG VALUES
 * -------------------------------------------------------------------
 *
 * The $assign_to_config array below will be passed dynamically to the
 * config class when initialized. This allows you to set custom config
 * items or override any default config values found in the config.php file.
 * This can be handy as it permits you to share one application between
 * multiple front controller files, with each file containing different
 * config values.
 *
 * Un-comment the $assign_to_config array below to use this feature
 *
 */
    // $assign_to_config['name_of_config_item'] = 'value of config item';


// Composer autoload
if (version_compare(phpversion(), '5.3.0', '<')) {
    //echo nl2br(phpversion() . PHP_EOL);
    require_once 'vendor/autoload_52.php';
} else {
    //echo nl2br(phpversion() . PHP_EOL);
    require_once 'vendor/autoload.php';
}

// --------------------------------------------------------------------
// END OF USER CONFIGURABLE SETTINGS.  DO NOT EDIT BELOW THIS LINE
// --------------------------------------------------------------------

/*
 * ---------------------------------------------------------------
 *  Resolve the system path for increased reliability
 * ---------------------------------------------------------------
 */

    // Set the current directory correctly for CLI requests
    if (defined('STDIN'))
    {
        chdir(dirname(__FILE__));
    }

    if (realpath($system_path) !== FALSE)
    {
        $system_path = realpath($system_path).'/';
    }

    // ensure there's a trailing slash
    $system_path = rtrim($system_path, '/').'/';

    // Is the system path correct?
    if ( ! is_dir($system_path))
    {
        exit("Your system folder path does not appear to be set correctly. Please open the following file and correct this: ".pathinfo(__FILE__, PATHINFO_BASENAME));
    }

/*
 * -------------------------------------------------------------------
 *  Now that we know the path, set the main path constants
 * -------------------------------------------------------------------
 */
    // The name of THIS file
    define('SELF', pathinfo(__FILE__, PATHINFO_BASENAME));

    // The PHP file extension
    // this global constant is deprecated.
    define('EXT', '.php');

    // Path to the system folder
    define('BASEPATH', str_replace("\\", "/", $system_path));

    // Path to the front controller (this file)
    //define('FCPATH', str_replace(SELF, '', __FILE__));
    $fcpath = str_replace(SELF, '', __FILE__) . '../';
    define('FCPATH', $fcpath);

    // Name of the "system folder"
    define('SYSDIR', trim(strrchr(trim(BASEPATH, '/'), '/'), '/'));


    // The path to the "application" folder
    if (is_dir($application_folder))
    {
        define('APPPATH', $application_folder.'/');
    }
    else
    {
        if ( ! is_dir(BASEPATH.$application_folder.'/'))
        {
            exit("Your application folder path does not appear to be set correctly. Please open the following file and correct this: ".SELF);
        }

        define('APPPATH', BASEPATH.$application_folder.'/');
    }

/*
 * --------------------------------------------------------------------
 * LOAD THE BOOTSTRAP FILE
 * --------------------------------------------------------------------
 *
 * And away we go...
 *
 */
require_once BASEPATH.'core/CodeIgniter.php';

dev.php

<?php

// https://github.com/symfony/symfony-standard/blob/1c7180239027832cda2140448a5022578d18a437/web/app_dev.php
if (isset($_SERVER['HTTP_CLIENT_IP'])
    || isset($_SERVER['HTTP_X_FORWARDED_FOR'])
    || !in_array(@$_SERVER['REMOTE_ADDR'], array('127.0.0.1', 'fe80::1', '::1'))
) {
    header('HTTP/1.0 403 Forbidden');
    exit('Você não está autorizado a acessar esse arquivo. Verifique '.basename(__FILE__).' para mais informações.');
}

$environment = 'development';

require_once realpath(dirname(__FILE__) . '/config/bootstrap.php');

index.php

<?php
$environment = 'production';

require_once realpath(dirname(__FILE__) . '/config/bootstrap.php');