attributes: overriding #[instrument] target should also effect ret/err events

[hawkw]

Currently, when an #[instrument] attribute has an overridden target, the events generated by ret and err arguments do not inherit that target:

tracing/tracing-attributes/src/expand.rs

Lines 203 to 217 in 7a9e1e4

	let err_event = match args.err_mode {
	Some(FormatMode::Default) | Some(FormatMode::Display) => {
	Some(quote!(tracing::error!(error = %e)))
	}
	Some(FormatMode::Debug) => Some(quote!(tracing::error!(error = ?e))),
	_ => None,
	};
	let ret_event = match args.ret_mode {
	Some(FormatMode::Display) => Some(quote!(tracing::event!(#level, return = %x))),
	Some(FormatMode::Default) | Some(FormatMode::Debug) => {
	Some(quote!(tracing::event!(#level, return = ?x)))
	}
	_ => None,
	};

For example, if I write

#[tracing::instrument(target = "some_target", ret)
fn do_stuff() -> Something {
    // ...
}

the do_stuff span will have the target "some_target", but the return value event generated by ret will have the current module path as its target, and there is no way to change the return value event's target.

We should probably change this so that the overridden target also applies to the events generated by ret and err. Fortunately, this is probably a pretty straightforward change.

See also #2182 (reply in thread)

[tbraun96]

PR is opened: #2184