Attribute Macro trace_tools::observe

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Attribute macro for extending functions and futures with the Observe trait.

This instruments the function or future with a tracing span with the trace_tools::observe target, so that it can be filtered by subscribers. It also records the location of the calling code to the span as fields. This is assigned to loc.file, loc.line and loc.col fields, similar to how tokio instruments tasks internally.

As such, tokio tasks, any functions or futures instrumented with tracing, and any functions or futures instrumented with the Observe trait or macro will be wrapped in spans that contain similarly structured information for diagnostics. The only difference should be the span target and the span name (if available).


A future or function can be wrapped in a tracing span with the following:

use trace_tools::observe;

pub async fn say_hello() {

This will generate a span equivalent to the following:

// Location of the function signature.
let location = std::panic::Location::caller();

    "observed", = "say_hello",
    loc.file = location.file(),
    loc.line = location.line(),
    loc.col = location.column(),

The future or function will then run inside the context of the generated span:

let _guard = span.enter();

async move {