feat: whether to ignore the log API under tracing and record it as event to otel event

[ShyunnY]

Feature Request

Motivation

I'm new to the tracing-opentelemetry crate, and I'm glad to see that this library can be connected to tracing! I had an idea while using it: in the current implementation of tracing-opentelemetry, the content of the log api (info!/warn!/error!...) in the Span scope is attached to the Span as an otel Event.

tracing-opentelemetry/src/layer.rs

Lines 1074 to 1079 in 6b4da4a

	let mut builder_updates = None;
	event.record(&mut SpanEventVisitor {
	event_builder: &mut otel_event,
	span_builder_updates: &mut builder_updates,
	sem_conv_config: self.sem_conv_config,
	});

Consider a problem: sometimes users do not want to attach log records to the Span as an otel event, but get the span of the current context through the Span::current() provided by tracing, and then manually set some operations.

#[instrument]
async fn do_something(username: String) {
    info!("just record some logs. Do not attach these logs to the Event!");

    let span = Span::current();
    span.record("username", &username);
}

Proposal

So should we consider adding a feature or configuration to ignore the events recorded in the log? If there is a better way, I hope you can tell me. Thank you.

Alternatives

[mladedav]

So you want to have no span events and only export empty spans into opentelemetry, right?

I think you can just use tracing's filtering. See filter_fn where you can check metadata.kind.is_span() and filter based on that. Just be sure to set the filter as a layer filter (with_filter on the layer) and not a global filter (with on the whole subscriber).