Void spans

[tokio-rs]

Void spans

[hawkw]

Feature Request

Crates

tracing-core?

I think this would be a change in tracing rather than tracing-core; the Span type is from tracing :)

[...]
The solution outlined above works okay, but it'd be nicer if there existed a sort of "void" Span that was free to produce, and that did nothing when entered. Ideally I would also not need to give Metadata for it, since it shouldn't ever be used.

I think we could implement this rather easily, actually. It could look like this:

impl Span { 
    // ...
 
    pub fn none() -> Self {
        let meta = $crate::callsite! {
            name: "no span"
            kind: Kind::SPAN,
            target: ""
            level: Level::TRACE,
            fields: 
        }.metadata();
        Self {
            meta,
            inner: None,
        }
    }

    // ...
}

We could then hack the log support to not log for spans originating at the empty callsite.

We would need to make sure the documentation clearly distinguishes between Span::new_disabled and Span::none.

Name is, of course, open to bikeshedding.

[hawkw]

As an alternative, we could also move the metadata field optional. I think that might be the right approach. It'd make life easier for a Span::current function in the case that we're not currently in a span; otherwise, we'd have to return Option<Span>. And, since it's a reference, it shouldn't make the struct bigger to add an option.

[jonhoo]

I think this would be a change in tracing rather than tracing-core; the Span type is from tracing :)

Updated!