How to configure logging in Symfony?

@aubrey 

Configuring logging in Symfony involves a few steps:

1. Install a logging library: Symfony uses the PSR-3 logging interface, which means you can use any logging library that implements this interface. Some popular choices include Monolog, Log4PHP, and KLogger. You can install your chosen library using Composer.
2. Configure the logger: To configure the logger, you'll need to add some configuration to your config/packages/dev and/or config/packages/prod files (depending on whether you're configuring logging for development or production). Here's an example configuration for Monolog:

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# config/packages/dev/monolog.yaml
monolog:
    handlers:
        main:
            type: stream
            path: '%kernel.logs_dir%/%kernel.environment%.log'
            level: debug

This configuration tells Monolog to log messages to a file in the logs directory, with a filename that includes the current environment (dev or prod). It also sets the logging level to debug, which means that messages with a severity of debug, info, notice, warning, error, critical, and alert will be logged.

1. Use the logger: Once the logger is configured, you can use it in your code by injecting it as a dependency or using the LoggerAwareTrait. Here's an example of how to use the logger in a Symfony controller:

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use PsrLogLoggerInterface;

class MyController
{
    private $logger;

    public function __construct(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }

    public function index()
    {
        $this->logger->info('Hello, world!');
        // ...
    }
}

In this example, the logger is injected into the controller's constructor, and the info method is called to log a message. You can use any of the logging methods defined by the PSR-3 interface, such as debug, info, notice, warning, error, critical, and alert.

That's a basic overview of how to configure logging in Symfony. There are many more options available, such as configuring multiple log handlers, filtering messages based on severity or context, and more. Check the documentation of your chosen logging library for more information.