Композитор не загружайте класс
composer dumpautoload -o
Alberto Peripolli
composer dumpautoload -orequire __DIR__ . '/vendor/autoload.php';
$log = new Monolog\Logger('name');
$log->pushHandler(new Monolog\Handler\StreamHandler('app.log', Monolog\Logger::WARNING));
$log->addWarning('Foo');composer require name-of-package