Faulty Warning in Opentracing Shim

[Jarch09]

Description

Currently, the opentracing shim is issuing a warning (SDK should have deferred the context setup, see the documentation of go.opentelemetry.io/otel/bridge/opentracing/migration) even if everything is being done correctly.

Steps To Reproduce

1. BridgeTracer.StartSpan calls WrapperTracer.Start: https://github.com/open-telemetry/opentelemetry-go/blob/main/bridge/opentracing/bridge.go#L429
2. WrapperTracer.Start calls the underlying opentelemetry tracer.Start: https://github.com/open-telemetry/opentelemetry-go/blob/main/bridge/opentracing/wrapper.go#L79 ... among other effects, this adds the opentelemetry span to the context
3. Therefore, even if we successfully SkipContextSetup, we have a new context object
4. Therefore, the context comparison in BridgeTracer.StartSpan always fails even if we've "set up everything correctly" - this results in the warning: SDK should have deferred the context setup, see the documentation of go.opentelemetry.io/otel/bridge/opentracing/migration (link)

Expected behavior

I think this check / warning is meant to verify that the opentracing span hasn't been added to the context yet.

If this is the intent, we could check to see if the opentracing span is in the context:

if ot.SpanFromContext(checkCtx2) != nil {
    // issue warning
}

[dmathieu]

Thank you for reporting this. I have opened a fix in #3029.