Use Task.FromResult to return already computed results

[BillWagner]

I'm not sure how well to enforce this, because the anti-patterns are very diverse, and subtle.

During coded reviews I've seen code (often in mocks for tests) that use some form of task construction and execution (like Task.Run()) to produce a result when Task.FromResult() would have been much cleaner.

[sharwell]

The obvious case is an async method that returns a result, but does not await anything.

[jaredpar]

Another obvious case is when the contents of the lambda body passed to Run are constant. In that case there isn't really a plausible argument for scheduling a task to return a constant value. Task.FromResult is a much better option

[andrewmurphyio]

@jaredpar that doesn't work when you're using a dictionary to cache a result