PHP spl_autoload_register not being called in certain locations Google API PHP

Question

I wanted to integrate my app with google callendar.
I added google PHP API to libraries/Google.

libraries/Google/autoload.php is:

define ('GOOGLE_LIB_PATH', BASE_P . 'libraries/Google/');

set_include_path(
    get_include_path() . PATH_SEPARATOR . GOOGLE_LIB_PATH
);
spl_autoload_register(
    function ($className) {

      $classPath = explode('_', $className);
      if ($classPath[0] != 'Google') {
        return;
      }
      // Drop 'Google', and maximum class file path depth in this project is 3.
      $classPath = array_slice($classPath, 1, 2);

      $filePath = GOOGLE_LIB_PATH . implode('/', $classPath) . '.php';
      echo $filePath .'<br>';
      if (file_exists($filePath)) {
        require_once($filePath);
      }
    }
);

Output is:

/home/users/page/libraries/Google/Service/Calendar.php
/home/users/page/libraries/Google/Service.php
/home/users/page/libraries/Google/Service/Resource.php
/home/users/page/libraries/Google/Client.php
/home/users/page/libraries/Google/Collection.php
/home/users/page/libraries/Google/Model.php

Fatal error: Class 'Google_Config' not found in /home/users/page/libraries/Google/Client.php on line 77

After adding one call it starts loading config, but stops at other

define ('GOOGLE_LIB_PATH', BASE_P . 'libraries/Google/');

set_include_path(
    get_include_path() . PATH_SEPARATOR . GOOGLE_LIB_PATH
);
spl_autoload_register(
    function ($className) {
    // same as above
    }
);
$x = new Google_Config; // Added this line

Output is:

/home/users/page/libraries/Google/Config.php
/home/users/page/libraries/Google/Service/Calendar.php
/home/users/page/libraries/Google/Service.php
/home/users/page/libraries/Google/Service/Resource.php
/home/users/page/libraries/Google/Client.php
/home/users/page/libraries/Google/Collection.php
/home/users/page/libraries/Google/Model.php

Fatal error: Class 'Google_Auth_OAuth2' not found in /home/users/page/libraries/Google/Client.php on line 614

Autoloader seems to work only when it wants. Or is there any magic I do not know about?

PHP Version 5.4.36-0+tld0
Tried Class "Google_Config" not found and Spl_autoload_register() not working on server

Edit: BASE_P is defined as: dirname(__FILE__).'/' in main dir.

Edit2: Tried including classes manually. Autoloader stops working always after: libraries/Google/Model.php is loaded. But if I load Model.php before everything else (right after registering autoloader) it does not seem to break autoloader. But it still stops after few autoloads.

Answer 1

It's an old project, and I finally found a culprit:

function __autoload($class_name) {
    $dir = dirname(__FILE__).'/';
    if (file_exists($dir.'classes/'. $class_name . '.php'))
        require_once $dir.'classes/'. $class_name . '.php';

}

Changing it to:

spl_autoload_register(
    function ($class_name) {

    $dir = dirname(__FILE__).'/';

    if (file_exists($dir.'classes/'. $class_name . '.php'))
        require_once $dir.'classes/'. $class_name . '.php';

);

Fixed the other autoloader.

Moral? Never mix __autoload() and spl_autoload_register()
Basically never use __autoload() as it is deprecated and like this example shows, it can break things.
(or will probably be as stated http://php.net/manual/en/language.oop5.autoload.php)

Hope it will help someone someday.