Add general and source code attributes to spans

[tsloughter]

https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/semantic_conventions/span-general.md#source-code-attributes

[bullno1]

I kinda need this too.

This is only possible in macro right?

[tsloughter]

Correct, it would need to be done in the macros for with_span and start_span.

[bullno1]

https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/semantic_conventions/span-general.md#general-thread-attributes

On the topic of thread.id attribute, erlang:system_info(scheduler_id) is suggested.
While this is kind of correct, I'm not sure how useful it is compared to say: self().
But formatting self() can have some overhead that is not always desirable.

[bullno1]

On the same topic code.function also requires some string/binary construction from ?FUNCTION_NAME and ?FUNCTION_ARITY.
It's probably negligible but it's not nothing, even in the non-recording case.

There are 2 ways to go about this:

• Just format anyway.
• Introduce some sort of "lazy attributes" that's only evaluated by the span processor. {'$lazy', fun()}?

[tsloughter]

I think just format (lists:concat(?FUNCTION_NAME, "/", ?FUNCTION_ARITY)) it anyway and we should look at proposing ?FUNCTION_NAME_STRING that includes arity to OTP.