Add instrumentation for the "go.opentelemetry.io/otel/trace".nonRecordingSpan

[MrAlias]

A common instrumentation pattern for tracing is to return the the TracerProvider from the span held in a context:

import (
	"net/http"

	"go.opentelemetry.io/otel/trace"
)

func handler(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	tracer := trace.SpanFromContext(ctx).TracerProvider().Tracer("tracer")
	ctx, span := tracer.Start(ctx, "span")
	defer span.End()
	/* ... */
}

When using the instrumentation of the global trace API, this span will not be recorded.

Describe the solution you'd like

The span created in this above code should be captured by auto-instrumentation. Meaning the nonRecordingSpan should be instrumented.

[MrAlias]

This was only partially resolved by #1405. If a global span is already active in the context this will work, as demonstrated in #1405. However, if there is no active span a no-op span is still created and is not instrumented.

We need to provide the same enablement logic as the global API for the trace.SpanFromContext function.

[MrAlias]

My initial idea was to update the noopSpan.TracerProvider method:

https://github.com/open-telemetry/opentelemetry-go/blob/784638358b3d39412703a13fe0bd6aa0908ffe45/trace/noop.go#L84-L85

Similar to open-telemetry/opentelemetry-go#5920 we could call a private method with a *bool. For example:

--- a/trace/noop.go
+++ b/trace/noop.go
@@ -6,6 +6,7 @@ package trace // import "go.opentelemetry.io/otel/trace"
 import (
        "context"

+       "go.opentelemetry.io/auto/sdk"
        "go.opentelemetry.io/otel/attribute"
        "go.opentelemetry.io/otel/codes"
        "go.opentelemetry.io/otel/trace/embedded"
@@ -82,4 +83,22 @@ func (noopSpan) AddLink(Link) {}
 func (noopSpan) SetName(string) {}

 // TracerProvider returns a no-op TracerProvider.
-func (noopSpan) TracerProvider() TracerProvider { return noopTracerProvider{} }
+func (s noopSpan) TracerProvider() TracerProvider {
+       return s.tracerProvider(autoInstEnabled)
+}
+
+// autoInstEnabled defines if the auto-instrumentation SDK is enabled.
+//
+// The auto-instrumentation is expected to overwrite this value to true when it
+// attaches to the process.
+var autoInstEnabled = new(bool)
+
+// tracerProvider return a noopTracerProvider if autoEnabled is false,
+// otherwise it will return a TracerProvider from the sdk package used in
+// auto-instrumentation.
+func (noopSpan) tracerProvider(autoEnabled *bool) TracerProvider {
+       if *autoEnabled {
+               return sdk.TracerProvider()
+       }
+       return noopTracerProvider{}
+}

This will not work because it will create an import cycle.

[MrAlias]

copying the auto/sdk to some go.opentelemetry.io/otel/trace/internal package would also have the same import cycle issue.

[MrAlias]

open-telemetry/opentelemetry-go#6203 has merged. We can no instrument that copy of the SDK to support this.

[MrAlias]

Blocked by either a release of opentelemetry-go or the resolution of #1753. Currently, when trying to test the added probe the comparison of 1.34.1-0.20250205150531-85fab8be9320 > 1.34.0 is returning false which means the probe package constraint will not work.