Review spec for tracing

[codeboten]

Part of the work for GA is to review tracing API spec and ensure our implementation is correct

[codeboten]

• is_valid is currently a method on the SpanContext, the spec defines it as a bool flag https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/api.md#spancontext is_valid is currently a method on the SpanContext, the spec defines it as a bool flag  #996

[lzchen]

• API to add links to span https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/api.md#span API to add links to span #994
• SDK - check ended span on lazy event add https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/api.md#span-operations Check ended span on lazy event add #995

[ocelotl]

• The Tracer SHOULD provide methods to get the currently active Span

• We currently have a CURRENT_SPAN attribute in the API Tracer class, is this misleading? The Tracer must delegate to the Context to get the currently active Span and to mark a given Span as active.

• The instances of SpanContext should be immutable The instances of SpanContext should be immutable #1002

• Implementations SHOULD NOT provide access to a Span's attributes besides its SpanContext SDK SHOULD NOT provide access to a Span's attributes besides its SpanContext #1001

• Implementations MUST NOT allow callers to create Spans directly Implementations MUST NOT allow callers to create Spans directly #1000

• Implementations SHOULD preserve the order in which they are set Implementations SHOULD preserve the order in which attributes are set #999

• If overwriting of values is supported, null attributes that have been previously set results in the attribute being cleared and the key being dropped from the attribute set null attributes that have been previously set results in the attribute being cleared and the key being dropped from the attribute set #998

• Callers must not be able to set Span Attributes, Links or Events after the end time has been set Callers must not be able to set Span Attributes, Links or Events after the end time has been set #997

[codeboten]

* The `Tracer` SHOULD provide methods to get the currently active Span

Currently we have get_current_span in the trace module, it was a tracer method before this change #552

It looks like this spec issue is planning on changing this, i won't open an issue to track it

[lzchen]

open-telemetry/oteps#134

[lzchen]

Possible big change: open-telemetry/opentelemetry-specification#875

[codeboten]

Closing this one, let's open up individual issues for all future changes.