tracing: send spans' attributes along with the event ones

[tsionyx]

Implementing #617

Adds a enable_span_attributes() method for the sentry_tracing::SentryLayer that activates the desired behaviour.
The root span's attributes can only be propagated once the traces enabled (e.g. through ClientOptions::traces_sample_rate).

[tsionyx]

use sentry::{
    integrations::tracing::{self as sentry_tracing, EventFilter},
    ClientOptions,
};
use tracing::{span, warn, Level};
use tracing_subscriber::{layer::SubscriberExt as _, util::SubscriberInitExt as _};

const DSN: &str = "MY_DSN";

fn main() {
    let _guard = sentry::init((
        DSN,
        ClientOptions {
            traces_sample_rate: 1.0,
            ..Default::default()
        },
    ));

    let sentry_layer = sentry_tracing::layer()
        .enable_span_attributes()
        .event_filter(|md| match *md.level() {
            Level::ERROR | Level::WARN => EventFilter::Event,
            _ => EventFilter::Ignore,
        });

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

    // create very simple spans hierarchy
    let span = span!(Level::ERROR, "root span", span_int = 42, span_str = "hello");
    span.in_scope(|| {
        span!(
            Level::WARN,
            "child span",
            span_num = 144,
            span_str = "world"
        )
        .in_scope(|| {
            warn!(event_data = 3.1417, "The event message");
        })
    });
}

gives the following output in the dashboard

[Swatinem]

lgtm

[Swatinem]

this breaking change is a bit unfortunate. I’m also a bit surprised why we had Context<S> there in the first place, if it was unused in all of these functions.

[tsionyx]

I updated the type from Option<Context> to impl Into<Option<Context>>. This modification restores the capability to provide either a direct Context or an Option<Context>. As a result, the breaking change has been mitigated.

[Swatinem]

This is a breaking change anyway because this fn signature is gaining a new parameter. So might as well just go directly with an Option, as in impl Into is a bit heavy handed.

[tsionyx]

Since I don't need it anyway, I can remove this new argument from this particular breadcrumb_from_event. I put it here before only to make the uniform-looking signatures.

[tsionyx]

Done, restored the initial breadcrumb_from_event signature.

[codecov]

Codecov Report

Merging #629 (3c65139) into master (c53da38) will decrease coverage by 0.29%.
The diff coverage is 39.70%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #629      +/-   ##
==========================================
- Coverage   73.03%   72.75%   -0.29%     
==========================================
  Files          59       59              
  Lines        6658     6706      +48     
==========================================
+ Hits         4863     4879      +16     
- Misses       1795     1827      +32