feat: return errors from resource.New

[dstrelau]

Which problem is this PR solving?

When using detectors with mis-matched Schema URLs, resource.New will return an error. Previously, this was dropped and consequently it looked like configuration worked but many resource attributes would be missing in the resulting telemetry.

With the recent addition of #48, this error is much easier to hit. For example, the detectors built into opentelemetry-go import semconv v1.17.0 but this project pulls in v1.18.0. This means that adding something like otelconfig.WithResourceOption(resource.WithHost()) results in a mis-configured OTel and no error to warn you what happened.

This is all … very bad. This PR is really the bare minimum that needs to be done here. That is, it at least causes a runtime error so that you can tell what's going on — but it doesn't solve the problem that you fundamentally cannot use this library with any other library that doesn't happen to use semconv v1.18.0. There are a number of open issues in OTel and adjacent repositories regarding this problem, which probably warrant further investigation into a long-term sustainable solution.

Short description of the changes

Return the err from resource.New up through the stack. Update tests to expect this.

⚠️ I guess technically this could be considered a backwards incompatible change, in that folks may have configurations that are "working" today but will throw an error after this change. I put that in scare quotes though because it's not really working — it's just not throwing an error. I feel like actually returning an appropriate error here and letting folks know their configuration is likely not working as expected is the right choice.

How to verify that this has the expected result

There's a new test that specifically uses a detector with a different schema URL.

[cartermp]

Ahhhh this 'ole bucket of fun. I ended up documenting things to fail loudly because of this:

When using detectors with mis-matched Schema URLs, resource.New will return an error.

In the docs: https://opentelemetry.io/docs/instrumentation/go/manual/#setup

func newTraceProvider(exp sdktrace.SpanExporter) *sdktrace.TracerProvider {
	// Ensure default SDK resources and the required service name are set.
	r, err := resource.Merge(
		resource.Default(),
		resource.NewWithAttributes(
			semconv.SchemaURL,
			semconv.ServiceName("ExampleService"),
		),
	)

	if err != nil {
		panic(err)
	}

	return sdktrace.NewTracerProvider(
		sdktrace.WithBatcher(exp),
		sdktrace.WithResource(r),
	)
}

TBH I can't think of a better way to handle this, since there's no other way to actually get the right instrumentation.

[dstrelau]

It does look like this is on the minds of the OTel folks: open-telemetry/opentelemetry-go#4364

[JamieDanielson]

Thank you for this! I'll follow this up with some version updates and a couple more tests to hopefully make this a bit less painful to manage.