Support TraceStates on SamplingResults

[spencerwilson]

Spec v0.7.0 added the expectation that SamplingResult includes a TraceState. Current spec text: A SamplingResult contains...

A Tracestate that will be associated with the Span through the new SpanContext. If the sampler returns an empty Tracestate here, the Tracestate will be cleared, so samplers SHOULD normally return the passed-in Tracestate if they do not intend to change it.

Task: Support ^ by adding a property traceState?: TraceState to SamplingResult (src). Backwards compatibility: If a SamplingResult lacks traceState, assume the value is "current trace state; no changes". Update Tracer to implement the trace state updating described by the spec.

References:

• Allow samplers to modify tracestate opentelemetry-specification#988
• Follow up for #988. opentelemetry-specification#1036

[legendecas]

I moved this issue since this is part of the SDK (though the Sampler interface is not moved to this repo yet, tracking in #2961).

[dyladan]

thanks. I was just looking through our labels and we don't have a "required by spec" label. this isn't really a bug because it is working as designed, but the spec changed. Create a new label? Can probably consolidate spec-v1 and spec-v1.1 labels into it.

[legendecas]

Create a new label? Can probably consolidate spec-v1 and spec-v1.1 labels into it.

Both SGTM. Though, I don't find the semver-minor to be very clear as it has reached 1.9.0 already and our API package is not following the semantics.

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[legendecas]

Not stale, need to be addressed after landing #3088.