How to add multiple tracers to the registry?

[paymog]

Is there a canonical way to add multiple tracers to the registry where each tracer might be conditionally created based on some evn vars? I've been fighting with the compiler for over an hour to try get this but haven't found a solution. Here's some sample code that's a bit close but still doesn't compile

fn setup_otel(logger: &Logger) {
    let mut tracing_registry = tracing_subscriber::registry();
    let mut otel_layers = Vec::new();

    if let (Some(otel_endpoint), Some(port)) = (
        ENV_VARS.datadog_otel_host.clone(),
        ENV_VARS.datadog_otel_port.clone(),
    ) {
        global::set_text_map_propagator(opentelemetry_datadog::DatadogPropagator::new());
        let unwrapped_endpoint = construct_otel_endpoint(otel_endpoint, port);

        let ddog_tracer = opentelemetry_datadog::DatadogPipelineBuilder::default()
            .with_service_name("graph-node")
            .with_agent_endpoint(unwrapped_endpoint)
            .install_batch(opentelemetry_sdk::runtime::Tokio)
            .unwrap_or_else(|err| {
                error!(logger, "Failed to initialize Datadog tracer: {}", err);
                std::process::exit(1);
            });

        let datadog_layer = tracing_opentelemetry::layer().with_tracer(ddog_tracer);
        otel_layers.push(datadog_layer);
    }

    if true { // TODO use env vars to configure this tracer
        global::set_text_map_propagator(opentelemetry_jaeger_propagator::Propagator::new());
        let jaeger_tracer = opentelemetry_jaeger::new_agent_pipeline()
            .with_service_name("graph-node")
            .install_simple()
            .unwrap_or_else(|err| {
                error!(logger, "Failed to initialize Jaeger tracer: {}", err);
                std::process::exit(1);
            });

        let jaeger_layer = tracing_opentelemetry::layer().with_tracer(jaeger_tracer);
        otel_layers.push(jaeger_layer);
    }

    // Compose all layers into the subscriber
    for layer in otel_layers {
        tracing_registry = tracing_registry.with(layer)
    }

    tracing_registry
        .try_init()
        .unwrap_or_else(|err| {
            error!(logger, "Failed to initialize tracing: {}", err);
        });

    info!(logger, "Otel setup complete");
}

Unfortunately, I can't build the tracing registry in the for loop and run into the following compiler error

    |
738 |     let mut tracing_registry = tracing_subscriber::registry();
    |                                ------------------------------ expected due to this value
...
777 |         tracing_registry = tracing_registry.with(layer)
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `Registry`, found `Layered<OpenTelemetryLayer<..., ...>, ...>`
    |
    = note: expected struct `tracing_subscriber::Registry`
               found struct `Layered<OpenTelemetryLayer<tracing_subscriber::Registry, opentelemetry_sdk::trace::Tracer>, tracing_subscriber::Registry>`

[stormshield-fabs]

I'd suggest taking a look at tracing's Runtime configuration with layers documentation.

For your use case, I think the easier route is to go with Options but you can keep your current approach using a Vec by erasing the type of the layers with Layer::boxed.