Monolog Logging Service 4.1.1

use Monolog\Helper\Log;
Log::info('an info message', ['context' => 'foo']);
Log::error('an error message', ['data' => 'bar']);

$logger = \XF::app()->get('monolog')->newChannel('myaddon');
$logger->warning('a warning message', ['context' => 'foo']);

use Monolog\Logger;

$monolog = \XF::app()->get('monolog');
$streamhandler = $monolog->stream(); // return our default stream handler for logging to a file
                            //(or create your own!)

/** @var Monolog\Logger $logger */
$logger = $monolog->logger('myaddon');
$logger->pushHandler($streamhandler); // push our stream handler onto the handler stack
// you can apply any other customisations you like here as well by adding custom handlers, formatters or processors

$logger->critical('a critical message', ['context' => 'foo']);