Magento 2.2-rc3.0 and problem with including path for lib/internal directory.

[sergei-sss]

Preconditions

1. Magento 2.2-rc3.0

Steps to reproduce

1. Upload any library to the lib/internal directory, in our case - GeoIP and MaxMind libraries.
2. Use the same libraries as you are can currently using in magento 2.1.x:

use GeoIp2\Database\Reader as GeoIP2Reader;
...
$reader = new GeoIP2Reader($dbPath, ['en']);

Expected result

1. $reader is the object of the Reader class

Actual result

1. Error: GeoIp2\Database\Reader class not found

It seems that for magento 2.2 in Magento\Framework\Autoload\Populator::populateMappings()
the following adding include path for lib/internal was removed.
We use the lib/internal directory for libraries in our “ready-to-paste” package version, and now we are confused.
Is it bug? Or we currently need to add libraries to the new “generated” directory (it seems improbable).

[orlangur]

This is intentional change in 0b659d2#diff-b5d0ee8c97c7abd7e3fa29b9a27d1780L220.

The best way to solve is to install all libraries using Composer and do not rely on include_path just like Magento does. If it is not possible, you can simply restore this config in your custom composer.json.