Add setting ['composer_autoload']

Supersedes PR bcit-ci#3132

Author: narfbg

application/config/config.php

@@ -121,7 +121,6 @@
 */
 $config['enable_hooks'] = FALSE;
 
-
 /*
 |--------------------------------------------------------------------------
 | Class Extension Prefix
@@ -136,6 +135,27 @@
 */
 $config['subclass_prefix'] = 'MY_';
 
+/*
+|--------------------------------------------------------------------------
+| Composer auto-loading
+|--------------------------------------------------------------------------
+|
+| Enabling this setting will tell CodeIgniter to look for a Composer
+| package auto-loader script in application/vendor/autoload.php.
+|
+|	$config['composer_autoload'] = TRUE;
+|
+| Or if you have your vendor/ directory located somewhere else, you
+| can opt to set a specific path as well:
+|
+|	$config['composer_autoload'] = '/path/to/vendor/autoload.php';
+|
+| For more information about Composer, please visit http://getcomposer.org/
+|
+| Note: This will NOT disable or override the CodeIgniter-specific
+|	autoloading (application/config/autoload.php)
+*/
+$config['composer_autoload'] = FALSE;
 
 /*
 |--------------------------------------------------------------------------

system/core/CodeIgniter.php

@@ -447,6 +447,23 @@ function &get_instance()
 		$params = array_slice($URI->rsegments, 2);
 	}
 
+/*
+ * ------------------------------------------------------
+ *  Should we use a Composer autoloader?
+ * ------------------------------------------------------
+ */
+	if (($composer_autoload = config_item('composer_autoload')) !== FALSE)
+	{
+		if ($composer_autoload === TRUE && file_exists(APPPATH.'vendor/autoload.php'))
+		{
+			require_once(APPPATH.'vendor/autoload.php');
+		}
+		elseif (file_exists($composer_autoload))
+		{
+			require_once($composer_autoload);
+		}
+	}
+
 /*
  * ------------------------------------------------------
  *  Is there a "pre_controller" hook?

user_guide_src/source/changelog.rst

@@ -61,6 +61,7 @@ Release Date: Not Released
    -  Added availability checks where usage of dangerous functions like ``eval()`` and ``exec()`` is required.
    -  Added support for changing the file extension of log files using ``$config['log_file_extension']``.
    -  Added support for turning newline standardization on/off via ``$config['standardize_newlines']`` and set it to FALSE by default.
+   -  Added configuration setting ``$config['composer_autoload']`` to enable loading of a `Composer <https://getcomposer.org/>`_ auto-loader.
 
 -  Helpers
 

user_guide_src/source/general/autoloader.rst

@@ -20,4 +20,8 @@ file and add the item you want loaded to the autoload array. You'll
 find instructions in that file corresponding to each type of item.
 
 .. note:: Do not include the file extension (.php) when adding items to
-	the autoload array.
+	the autoload array.
+
+Additionally, if you want CodeIgniter to use a `Composer <https://getcomposer.org/>`_
+auto-loader, just set ``$config['composer_autoload']`` to ``TRUE`` or
+a custom path in **application/config/config.php**.