Global fields to always log on any event in tracing_subscriber

[nduchenk]

Hi everyone.
Is it possible somehow add global fields that will be logged on each event using tracing_subscriber crate ?

This is what I have for layer:

    let layer = tracing_subscriber::fmt::layer()
        .json()
        .with_timer(UtcTime::rfc_3339())
        .flatten_event(true)
        .with_target(true)
        .with_current_span(false)
        .with_span_events(FmtSpan::NONE)
        .with_filter(EnvFilter::from_str("info").unwrap_or_default());

    tracing_subscriber::registry().with(layer).init();

macro call:
info!(test = 1, test = 2, "Test message");
gives next message:
{"timestamp":"2022-09-23T09:05:40.716435Z","level":"INFO","message":"Test message","test":1,"test":2,"target":"test"}

What I want is to make any macro call for any LEVEL in any place to produce additional fields:
so the same call:
info!(test = 1, test = 2, "Test message");
will produce next message:
{"timestamp":"2022-09-23T09:05:40.716435Z","level":"INFO","message":"Test message","test":1,"test":2,"target":"test", "global_field_0": "global_field_value_0", "global_field_1": "global_field_value_1"}.

Will appreciate on suggestions on how to do it.

I see there is an open issue:

Allow configuring a formatter with extra fields to include

[nduchenk]

It seems the solution will be to write my own struct that implements Layer.

[Michael-F-Bryan]

What about creating a span at the top of your main() containing all the global fields? That way they'll be inherited by every message like normal.

[nduchenk]

Hi, sorry for late reply. I've just implemented trait FormatEvent from tracing_subscriber and use my implementation with tracing_subscriber::fmt::layer(). So I can add/remove/rename fields.
If I use span from main function those additional fields will be recorded in current_span or in a span_list and I need them to be on the same level as all other fields in event.