How to dynamically record fields on an event?

[AndiDog]

The event! macro dispatches the event immediately, not allowing to record anything on it before it gets sent off (or logged).

Let's say I have a serde_json::Value object representing some web server request, and want to log all the request fields as JSON:

# nested
{"message": "Received request on web server", "request": {"param1": "a", "param2": "b"}}

# or flat
{"message": "Received request on web server", "request.param1": "a", "request.param2": "b"}

This cannot be done with event!(Level::INFO, ?request, "Received request on web server") syntax since that would turn the request into a string (here: using Debug trait).

I'm thinking of something like this:

let ev = event_but_do_not_dispatch!("Received request on web server");
ev.record(...);
ev.observe_with_current_collector();

See also #2198

[AndiDog]

Just saw #1906. Is there a way to convert serde_json::Value easily to valuable::Valuable? Then it would be possible to event!(v = tracing::field::valuable(&some_json_value), ...).