Use of other Folders under vendor in Magento 2

Question

I am used to Magento 1.x, now It's really confusing to understand the Magento 2.0.x structure.

I am trying to do it. Please help me to understand what is the function of the following folders below vender (Except magento folder)

( bin, braintree, composer, doctrine, fabpot, justinrainbow, league, lusitanian, monolog, oyejorge, pdepend, pelago, phpmd, phpseclib, phpunit, psr, sebastian, seld, sjparkinson, squizlabs, symfony, tedivm, tubalmartin, zendframework )

Is that related to our development? Or those are just some Library files, which need to be keep there?

Answer 1

These PHP libraries are installed as external dependencies via composer and fall into three categories

1. libraries that Magento uses. For example: zendframework, monolog, braintree
2. libraries that the Magento development tools use (bin/magento, the test framework). For example: phpunit, pdepend, phpmd, symfony
3. libraries that composer itself uses. For example: composer, justinrainbow, symfony (yes, again. The symfony console)

"composer" also contains the PSR-4 autoloader generated by composer (autoload.php).

"bin" is special, as it is not a library on its own but contains symlinks to executable scripts from the dependencies (like "phpunit")

Answer 2

The files under the vendor folder are really important as they are part of the software.

If you check the app/autoload.php file you can see the following code:

$vendorDir = require BP . '/app/etc/vendor_path.php';
$vendorAutoload = BP . "/{$vendorDir}/autoload.php";

/* 'composer install' validation */
if (file_exists($vendorAutoload)) {
    $composerAutoloader = include $vendorAutoload;
} else {
    throw new \Exception(
        'Vendor autoload is not found. Please run \'composer install\' under application root directory.'
    );
}

That means the classes declared in the vendor folder are included to Magento via the autoloader.

For example, the logging system in Magento 2 uses the following interface \Psr\Log\LoggerInterface and that class is declared under vendor\psr\log\Psr\Log folder.