Add links after activity (span) creation

[pyohannes]

Feature Request

A recent experimental addition to the OTel specification introduces a new required AddLink operation on spans, which allows adding span links after a span was created.

This addition is expected to be declared stable soon (@carlosalberto is driving this), there already exist prototypes for C++, Java, and Python. Messaging semantic conventions, which aim at stabilization this year, require this feature.

It should be decided how to make this feature available for .NET users.

Is your feature request related to a problem?

As soon as this feature is declared stable, OTel .NET will need to implement it in order to conform to the specification.

Describe the solution you'd like:

Ideally, there would be an Activity.AddLink method, similar to Activity.AddEvent or Activity.AddTag.

Describe alternatives you've considered.

A workaround would be to create a dedicated child span for each link to be added after a span was created. This is cumbersome, as it will drastically increase the number of spans in some cases and obfuscate resulting traces.

[cijothomas]

Thanks @pyohannes for raising this. The actual change needs to be done in the .NET runtime repo.

@vishweshbankwar This needs to have a corresponding issue in Runtime repo for consideration in .NET 9 timeframe. Could you open that, and link back here?

[vishweshbankwar]

https://github.com/dotnet/runtime/issues/97680

[cijothomas]

Added to 1.10 milestone, as that aligns with .NET 9 release, which already has added support for AddLink. There is probably nothing to be done in this repo except docs/tests maybe, as Links are stored inside Activity.