use sentry_tracing multiple times?

[avioletheart]

i have a function such as this:

pub fn init_logging(component: &str) {
    let sentry_layer = sentry_tracing::layer().event_filter(|md| match md.level() {
        &tracing::Level::ERROR => EventFilter::Event,
        _ => EventFilter::Ignore,
    });

    if config.json_log {
        tracing_subscriber::registry()
            .with(json_subscriber::layer())
            .with(sentry_layer)
            .with(EnvFilter::from_default_env())
            .init();
    } else {
        tracing_subscriber::registry()
            .with(tracing_subscriber::fmt::layer())
            .with(sentry_layer)
            .init();
    }
}

if i remove the sentry_layer in one of the two branches, it works. but with the code above the compile fails with an odd error:

error[E0277]: the trait bound `SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>: __tracing_subscriber_Layer<Layered<tracing_subscriber::fmt::Layer<Registry>, Registry>>` is not satisfied
    --> crates/libpk/src/lib.rs:39:19
     |
39   |             .with(sentry_layer)
     |              ---- ^^^^^^^^^^^^ the trait `__tracing_subscriber_Layer<Layered<tracing_subscriber::fmt::Layer<Registry>, Registry>>` is not implemented for `SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>`
     |              |
     |              required by a bound introduced by this call
     |
     = help: the trait `Layer<Layered<tracing_subscriber::fmt::Layer<Registry>, _>>` is not implemented for `SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>`
             but trait `Layer<Layered<json_subscriber::fmt::Layer, _>>` is implemented for it
     = help: for that trait implementation, expected `json_subscriber::fmt::Layer`, found `tracing_subscriber::fmt::Layer<Registry>`
note: required by a bound in `with`
    --> /root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/tracing-subscriber-0.3.18/src/layer/mod.rs:1503:12
     |
1501 |     fn with<L>(self, layer: L) -> Layered<L, Self>
     |        ---- required by a bound in this associated function
1502 |     where
1503 |         L: Layer<Self>,
     |            ^^^^^^^^^^^ required by this bound in `__tracing_subscriber_SubscriberExt::with`

error[E0599]: the method `init` exists for struct `Layered<SentryLayer<Layered<Layer, Registry>>, Layered<Layer<Registry>, Registry>>`, but its trait bounds were not satisfied
  --> crates/libpk/src/lib.rs:40:14
   |
37 | /         tracing_subscriber::registry()
38 | |             .with(tracing_subscriber::fmt::layer())
39 | |             .with(sentry_layer)
40 | |             .init();
   | |             -^^^^ method cannot be called due to unsatisfied trait bounds
   | |_____________|
   |
   |
  ::: /root/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/tracing-subscriber-0.3.18/src/layer/layered.rs:22:1
   |
22 |   pub struct Layered<L, I, S = I> {
   |   ------------------------------- doesn't satisfy `_: Into<Dispatch>` or `_: SubscriberInitExt`
   |
   = note: the following trait bounds were not satisfied:
           `Layered<SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>, Layered<tracing_subscriber::fmt::Layer<Registry>, Registry>>: Into<tracing::Dispatch>`
           which is required by `Layered<SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>, Layered<tracing_subscriber::fmt::Layer<Registry>, Registry>>: SubscriberInitExt`
           `&Layered<SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>, Layered<tracing_subscriber::fmt::Layer<Registry>, Registry>>: Into<tracing::Dispatch>`
           which is required by `&Layered<SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>, Layered<tracing_subscriber::fmt::Layer<Registry>, Registry>>: SubscriberInitExt`
           `&mut Layered<SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>, Layered<tracing_subscriber::fmt::Layer<Registry>, Registry>>: Into<tracing::Dispatch>`
           which is required by `&mut Layered<SentryLayer<Layered<json_subscriber::fmt::Layer, Registry>>, Layered<tracing_subscriber::fmt::Layer<Registry>, Registry>>: SubscriberInitExt`

what is the correct way of doing this?

[lcian]

Hey @avioletheart, I should spend some time investigating why that doesn't work, I'm not sure if there's something that might need a fix on our end.

However, if you reorder the layers and put the sentry layer first, your example compiles fine.
e.g. like this:

pub fn init_logging(component: &str) {
    let sentry_layer = sentry_tracing::layer().event_filter(|md| match md.level() {
        &tracing::Level::ERROR => EventFilter::Event,
        _ => EventFilter::Ignore,
    });

    if config.json_log {
        tracing_subscriber::registry()
            .with(sentry_layer)
            .with(json_subscriber::layer())
            .with(EnvFilter::from_default_env())
            .init();
    } else {
        tracing_subscriber::registry()
            .with(sentry_layer)
            .with(tracing_subscriber::fmt::layer())
            .init();
    }
}

Does that work for your usecase?

[avioletheart]

huh, so it does work, i swear i'd tried that. thanks!

[lcian]

Nice!
I'll keep this open so that I remember to look into it again.
I'm not sure if this behaviour is intended or if we're maybe missing some impls on SentryLayer that should be there so that it can be applied in whatever order.

[lcian]

This seems to be a special case that happens only when applying different layers conditionally.
Normally, the layer can be applied in whatever position.
Please open a new issue if you're blocked by this and we'll look into it again.