Why does setting the log level programmatically not work? with_max_level not working?

[bluenote10]

I'm trying for a while to set the log level programmatically. The very first lines of my main function are:

tracing_subscriber::fmt::fmt()
    .with_max_level(tracing::Level::DEBUG)
    .compact()
    .finish();

tracing::info!("Test info level");
tracing::debug!("Test debug level");

I would have expected to see these traces on stdout, but there is nothing. Is this a bug or am I misunderstanding something here?

[hawkw]

You aren't setting the Subscriber as the default. The fmt::SubscriberBuilder::finish method you're calling returns a new fmt::Subscriber, but it doesn't actually configure tracing to use that Subscriber to collect traces. Try passing the returned fmt::Subscriber to tracing::subscriber::set_global_default, or call SubscriberBuilder::init() rather than SubscriberBuilder::finish (which calls set_global_default for you), and then your code should work the way you expect.

We should probably add #[must_use] annotations to either the finish method or the fmt::Subscriber type, so that this code would have generated a warning telling you you're not using the returned subscriber...then, the problem would have hopefully been a lot more obvious.