Analyzer request: Emit a warning for usage of CancellationToken as a parameter in orchestrator functions

[cgillum]

Is your feature request related to a problem? Please describe.
.NET Function Apps allow customers to bind to a CancellationToken parameter to detect when the functions host is being shut down. We recently received a question about whether this should be used for things like the CreateTimer API. My thinking is that customers should never use this CancellationToken parameter in orchestrator function apps. I can't think of a scenario where it would not create problems.

Describe the solution you'd like
It would be great to have an analyzer rule that emits a warning if someone has a CancellationToken parameter in their orchestrator function.

[ConnorMcMahon]

I have definitely had a customer cancel a timer in a loop, and it caused the timer to always immediately return, resulting in an infinite loop in their code.

It was very hard to debug, so I am all for this.

[ConnorMcMahon]

EDIT: I misinterpreted this based on the title to mean all CancellationToken usage in orchestrator functions. I agree we should block this with the analyzer.

I think there are some other cancellation token usage patterns that we want to discourage in orchestrator functions, but we will want to understand what those exact scenarios before we attempt to write an analyzer for them.

Original Text below:

I'm now not 100% positive that we want to emit a warning for all uses of CancellationTokens.

While I can't think of any cases where using a cancellation token would actually be helpful with the orchestration APIs, I'm fairly certain there are many cases where it is harmless. In fact, I think some examples of that are in our own samples/documentation, and we should definitely fix those if the cancellation tokens aren't actually providing value.

Introducing a warning for these harmless cases may cause customers with large code bases to turn off all of the Durable analyzers, as we have seen this happen in the past where we introduced false positives.