Is it possible to control the tracing::instrument(ret) level, to make it different from the span's?

[scullionw]

#[tracing::instrument(ret, level = "debug")]
pub fn myfn(context: String) -> String {
    warn!("careful!");

    todo!()
}

i would like the return value to be logged on the "DEBUG" level only, to cut back on the logging noise. However, I want the warn!(...) log here to have the instrumented context attached to it. Right now, the context is only attached when the level is debug.

[hawkw]

This isn't currently possible, but it would be a good feature request! We could add something like

#[tracing::instrument(ret(level = "debug"), level = "warn")]
fn whatever() -> ... {
   ...
}

to allow changing the level for the ret event.

We would probably want to do it by adding a ret(level = "<level>") rather than just ret = "<level>" to future-proof the macro interface, so that we can add additional configuration arguments beyond setting the return event's level.

I think this should be a fairly straightforward change, at least for someone who's familiar with procedural macros, if you're interested in implementing it?

[davidbarsky]

@hawkw I think I answered something similar, but I think I threw out a bikeshed a month or two back: #2290 (reply in thread). Do you have any thoughts on that approach?

[shekhirin]

For future generations: yes, it is possible since 0.1.24

tracing/tracing-attributes/CHANGELOG.md

Lines 92 to 103 in c297a37

	# 0.1.24 (April 24th, 2023)
	This release of `tracing-attributes` adds support for passing an optional
	`level` to the `err` and `ret` arguments to `#[instrument]`, allowing the level
	of the generated return-value event to be overridden. For example,
	```rust
	#[instrument(err(level = "info"))]
	fn my_great_function() -> Result<(), &'static str> {
	// ...
	}
	```