Lack of convenient API to start span with a parent context in v2

[Gilthoniel]

Tracer Version(s)

v2.0.0

Go Version(s)

go v1.24.3

Bug Report

We used to use the ChildOf option to inject a parent context extracted from a message or an HTTP request but the option is not deprecated in favor of StartChild but we cannot instantiate the parent span from the parent context and we end up doing this:

if parentSpan, _ := tracer.Extract(MessageCarrier{msg}); parentSpan != nil {
	opts = append(opts, tracer.WithStartSpanConfig(&tracer.StartSpanConfig{
		Parent: parentSpan,
	}))
}

But that seems overkill. I can't find a different way so I'm assuming that's not the right approach but then I have no idea what the right one is.

Or a Parent option when starting the span would be possible ?

Reproduction Code

opts := []tracer.StartSpanOption{
	tracer.Tag("messaging.topic", topic),
	tracer.Tag(ext.SpanKind, ext.SpanKindConsumer),
	tracer.SpanType(ext.SpanTypeMessageConsumer),
}

if parentSpan, _ := tracer.Extract(MessageCarrier{msg}); parentSpan != nil {
	opts = append(opts, tracer.WithStartSpanConfig(&tracer.StartSpanConfig{
		Parent: parentSpan,
	}))
}

span, ctx := tracer.StartSpanFromContext(ctx, "queue.consume", opts...)
defer func() {
	span.Finish(tracer.WithError(err))
}()

Error Logs

No response

Go Env Output

No response

[darccio]

@Gilthoniel Thanks for reaching out! ChildOf was deprecated but it's still available. The way you modified your code is correct, but we agree it can bee a bit cumbersome. We'll discuss your case internally to see how can be improve this specific case.

[skunkworker]

Piggybacking on this issue. The docs here https://github.com/DataDog/dd-trace-go/blob/main/ddtrace/tracer/doc.go. Outline continuing remote traces (without creating a new parent trace). But do not give a v2 replacement.

// Then, on the server side, to continue the trace one would do:
//
//	sctx, err := tracer.Extract(tracer.HTTPHeadersCarrier(req.Header))
//	// ...
//	span := tracer.StartSpan("child.span", tracer.ChildOf(sctx))

Is the method above the only way to "continue" a trace from a given spancontext parent?

[darccio]

@skunkworker You are right. Keep in mind that ChildOf is still available although marked as deprecated.