Decouple API from SDK

[MrAlias]

• Remove all SDK dependencies from the API package (not including the instrumentation package).
  • Remove SDK benchmarks in the global package. When it makes sense (the metric SDK move the benchmark to the SDK).
  • Remove SDK benchmarks from the kv package. Instead test overhead of the package functions directly.
  • Use the api/trace/testtrace package instead of the SDK in the global/internal/trace_test.go tests.
• Update the api/trace/testtrace package to include a Provider and extensible functionality in how it records spans.

[jmacd]

That had to be tiresome! Thank you.
This will make testing API changes so much easier, not to have a cyclic dependency on the SDK.

[lizthegrey]

I assume after this we'll add a separate go.mod for api?

[MrAlias]

I assume after this we'll add a separate go.mod for api?

Sort of. The idea is to add a go.mod for the sdk/ subdirectory and have the API be the main entry point to go.opentelemetry.io/otel (#964). How the restructuring of the api package will look is still not 100% nailed down, but the separation of the SDK is the main goal (#940). Still need to resolve the instrumentation package issues prior to the new SDK package (https://github.com/open-telemetry/opentelemetry-go/issues/976, #974)

[lizthegrey]

I assume after this we'll add a separate go.mod for api?

Sort of. The idea is to add a go.mod for the sdk/ subdirectory and have the API be the main entry point to go.opentelemetry.io/otel (#964). How the restructuring of the api package will look is still not 100% nailed down, but the separation of the SDK is the main goal (#940). Still need to resolve the instrumentation package issues prior to the new SDK package (#976, #974)

Ah, got it. I'd prefer that we go ahead and do that work before we cut another minor release version

[Aneurysm9]

This isn't a very useful example anymore, perhaps it would be best to simply delete it or move it into a README.md.

[MrAlias]

This is going to be included in the godocs and I think it is a decent example of how to use it for a new users:

Additionally, with it actually existing as Go code it is validated with the compiler resulting in valid code. This is something I noticed was not true in some other places where we tried to keep code in docs (1, 2, ...)

[MrAlias]

That said, I'm not super tied to this example if we want to remove or expand it.

[Aneurysm9]

I suppose that does remain a decent example. Out of context it looks off, but I'm not against keeping it.