internal/tracer: correctly set Tracer names in OpenTracing bridge (#4…

…0945)

The existing wrapped OpenTelemetry TracerProvider for bridging
OpenTracing API calls to OpenTelemetryAPI calls discards the name
provided to the `Tracer()` constructor on it, since it uses a fixed
tracer that we provide it.

This change leverages an upstream patch,
open-telemetry/opentelemetry-go#3116 (dependency
update: https://github.com/sourcegraph/sourcegraph/pull/47126), that
allows wrapped tracers to be created on the fly with the provided
parameters, so that we can more accurately see the instrumentation
source.

## Test plan

Via the bridge, we can see that the Tracer used is the bridge tracer:

<img width="1322" alt="image"
src="https://user-images.githubusercontent.com/23356519/186957763-60faee32-e6a5-4bda-bb64-fddb82eacc0d.png">

Via direct usage of OpenTelemetry, we can see that the Tracer used has
the custom name set:

<img width="1448" alt="image"
src="https://user-images.githubusercontent.com/23356519/186957773-c6ff7643-3f89-498d-857b-1dd79b36508d.png">

internal/trace/tracer.go

@@ -24,7 +24,7 @@ func (t Tracer) New(ctx context.Context, family, title string, tags ...Tag) (*Tr
 
 	var otelSpan oteltrace.Span
 	ctx, otelSpan = t.TracerProvider.
-		Tracer("internal/trace").
+		Tracer("sourcegraph/internal/trace").
 		Start(ctx, family,
 			oteltrace.WithAttributes(attribute.String("title", title)),
 			oteltrace.WithAttributes(tagSet(tags).toAttributes()...))

internal/tracer/tracer.go

@@ -130,12 +130,11 @@ func newBridgeTracers(logger log.Logger, provider *oteltracesdk.TracerProvider,
 
 	// Set up otBridgeTracer for converting OpenTracing API calls to OpenTelemetry, and
 	// otelTracerProvider for the inverse.
-	//
-	// TODO: Unfortunately, this wrapped tracer provider discards the name provided to
-	// the Tracer() constructor on it, since it uses a fixed tracer that we provide it.
-	// This is implemented in https://github.com/sourcegraph/sourcegraph/pull/40945
-	otBridgeTracer, otelTracerProvider := otelbridge.NewTracerPair(provider.Tracer("internal/tracer/otel"))
+	otBridgeTracer := otelbridge.NewBridgeTracer()
 	otBridgeTracer.SetTextMapPropagator(compositePropagator)
+	otelTracerProvider := otelbridge.NewTracerProvider(otBridgeTracer, provider)
+	otBridgeTracer.SetOpenTelemetryTracer(
+		otelTracerProvider.Tracer("sourcegraph/internal/tracer.opentracing-bridge"))
 
 	// Set up logging
 	otelLogger := logger.AddCallerSkip(2).Scoped("otel", "OpenTelemetry library")