resource.WithoutBuiltin() is ineffective if used by itself within resource.New()

[RichieSams]

Description

resource.WithoutBuiltin() is ineffective if used by itself within resource.New()
resource.New() will return nil, which downstream code treats as "no config, give me the defaults".

For example, prometheus.InstallNewPipeline(), will in turn call controller.New(). If the resource passed to controller.New() is nil, then controller.New() will assume that you want the defaults. AKA, all the things we wanted to remove with resource.WithoutBuiltin()

Environment

• OS: Linux (but shouldn't matter)
• Architecture: x64 (but shouldn't matter)
• Go Version: 1.16
• opentelemetry-go version: v0.19.0

Steps To Reproduce

Example code:

res, err := resource.New(
	context.Background(),
	resource.WithoutBuiltin(),
)
if err != nil {
	return nil, fmt.Errorf("Failed to initialize Prometheus exporter - %w", err)
}

// Create the metrics route
metricsHandler, err := prometheus.InstallNewPipeline(prometheus.Config{}, controller.WithResource(res))
if err != nil {
	return nil, fmt.Errorf("Failed to initialize Prometheus exporter - %w", err)
}

All prometheus metrics created will have all the built-in labels added. (Service, sdk, etc.)

Workaround

type NullDetector struct{}

// Detect implements Detector
func (NullDetector) Detect(ctx context.Context) (*resource.Resource, error) {
	return nil, nil
}

res, err := resource.New(
	context.Background(),
	resource.WithoutBuiltin(),
	resource.WithDetectors(&telemetry.NullDetector{}),
)
if err != nil {
	return nil, fmt.Errorf("Failed to initialize Prometheus exporter - %w", err)
}

// Create the metrics route
metricsHandler, err := prometheus.InstallNewPipeline(prometheus.Config{}, controller.WithResource(res))
if err != nil {
	return nil, fmt.Errorf("Failed to initialize Prometheus exporter - %w", err)
}

Expected behavior

Passing resource.WithoutBuiltin() to resource.New(), should result in no built-in labels being added.

Possible solution

resource.WithoutBuiltin() should both nil out all the built-in detectors, but also add a NullDetector, so that we're guaranteed to have a single "valid" detector on return.

[Aneurysm9]

I think this might be addressed by #1810, can you take a look and see if that would meet your needs?

[RichieSams]

Oh great. That's exactly the solve.