SpanExporter is no longer dyn compatible

[tisonkun]

• https://github.com/fast/fastrace/actions/runs/14009742598/job/39228048469?pr=70
• build: upgrade for opentelemetry 0.29 fast/fastrace#70

This doesn't seems desired, although it's included in the changelog:

Breaking: Updated the SpanExporter trait method signature

#2685

[tisonkun]

fast/fastrace@f521d90

Add a DynSpanExporter at downstream can work it around somehow. Not sure if it's desired.

[cijothomas]

Thanks for reporting and for fixing the changelog we missed!

The PR shows how other exporters have adjusted to the new model, see if that can be borrowed.

[tisonkun]

@cijothomas I can see that in PR #2685 other references add a new generic param to avoid dyn. I try it in fast/fastrace@46aafdb but unfortunately it breaks our contract with users that they need not to care about the generic - type erase must happen in some level inside. So we add DynSpanExporter to bridge it.

If the upstream decide to hold #2685, I can live with it. Just leave this issue for other library developers that have to migrate:

trait DynSpanExporter: Send + Sync + Debug {
    fn export(
        &self,
        batch: Vec<SpanData>,
    ) -> Pin<Box<dyn Future<Output = OTelSdkResult> + Send + '_>>;
}

impl<T: SpanExporter> DynSpanExporter for T {
    fn export(
        &self,
        batch: Vec<SpanData>,
    ) -> Pin<Box<dyn Future<Output = OTelSdkResult> + Send + '_>> {
        Box::pin(SpanExporter::export(self, batch))
    }
}

and then you can use Box<dyn DynSpanExporter>. Other methods can be forwarded also, just in Fastrace we use only export.

[tisonkun]

Closed as information delivered.