Can't mix native transaction with Otel's trace.SpanFromContext

[wzy9607]

Describe the bug

The OTel bridge have the same problem that the opentracing bridge once faced (#235 and opentracing/opentracing-go#192)

apm’s native transaction can't be retrieved by Otel’s trace.SpanFromContext(https://github.com/open-telemetry/opentelemetry-go/blob/b2246d58650bc6db04459353843250ee3bba77fc/trace/context.go#L48).

Since goredis (https://github.com/redis/go-redis/blob/dc8c93ba66777b8f9866542b47cd102f591b5984/extra/redisotel/tracing.go#L90) and maybe other libs use trace.SpanFromContext before starting a Span,
currently it is not possible to mix native apm instrumentation with those lib’s OTel instrumentation.

To Reproduce

package main

import (
	"context"
	"fmt"

	"go.elastic.co/apm/module/apmotel/v2"
	"go.elastic.co/apm/v2"
	"go.elastic.co/apm/v2/apmtest"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/trace"
)

func main() {
	tracer := apmtest.NewRecordingTracer()
	provider, err := apmotel.NewTracerProvider(apmotel.WithAPMTracer(tracer.Tracer))
	if err != nil {
		panic(err)
	}
	otel.SetTracerProvider(provider)

	ctx := context.Background()
	tx := tracer.StartTransaction("test1", "test")
	ctx = apm.ContextWithTransaction(ctx, tx)

	fmt.Printf("apm transaction: %#v\n", apm.TransactionFromContext(ctx))
	sp := trace.SpanFromContext(ctx)
	fmt.Printf("OTel span: %#v\n", sp) // expect to not be otel trace.noopSpan{}
}

Expected behavior

Should be able to retrieve Span using Otel’s trace.SpanFromContext from an apm transaction.

[axw]

Thanks for opening this issue @wzy9607, I agree this would be ideal - I have added it to our backlog of things to look into.

[wzy9607]

I found that apm.TransactionFromContext、apm.SpanFromContext also can't retrieve an Otel span started with by apmotel tracer.

To Reproduce

package main

import (
	"context"
	"fmt"

	"go.elastic.co/apm/module/apmotel/v2"
	"go.elastic.co/apm/v2"
	"go.elastic.co/apm/v2/apmtest"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/trace"
)

func main() {
	tracer := apmtest.NewRecordingTracer()
	provider, err := apmotel.NewTracerProvider(apmotel.WithAPMTracer(tracer.Tracer))
	if err != nil {
		panic(err)
	}
	otel.SetTracerProvider(provider)

	ctx := context.Background()
	ctx, _ = otel.Tracer("test").Start(ctx, "test1")

	fmt.Printf("apm transaction: %#v\n", apm.TransactionFromContext(ctx)) // expect to not be (*apm.Transaction)(nil)
	fmt.Printf("apm span: %#v\n", apm.SpanFromContext(ctx))               // expect to not be (*apm.Span)(nil)
	fmt.Printf("OTel span: %#v\n", trace.SpanFromContext(ctx))            // is &apmotel.span, as expected
}

[dmathieu]

This should be fully fixed by #1450.