When deep copying objects in C# by hand, how can you ensure that all the fields/properties are copied?

I have a class with 20 primitive fields and 9 Lists/Dictionaries of primitive types. This class is used in performance-critical code that utilizes an object pool. The copy routine is used to copy state from one object to a newly rented object from the object pool. The routine performs a deep copy to ensure that the Lists/Dictionaries are not shared.

While debugging, I found out that I had missed one of the fields in the copy routine. I spent 6 hours tracking down the error.

How can I ensure that all class fields are being copied correctly and fail compilation if the copy method is not updated when new fields are added? Or is there some other approach that would make the copy routine less brittle?

I can't use MemberwiseClone() because I don't want to allocate. Runtime reflection is not an option since it could hurt performance. I have similar performance concerns around Serialization/Deserialization (and the highest voted SO approach of using BinaryFormatter is now deprecated). While manual copying is the fastest option, it makes the code brittle and hard to maintain. What's the best approach to improve code maintainability in this scenario?

> Runtime reflection is not an option since it could hurt performance.

That may well be a constraint for your production code, but I doubt that it's a constraint for your test code.

Failing the build may be hard to achieve - no doubt feasible with Roslyn code analyzers, but at least tricky - but I'd expect it to be relatively straightforward to write a unit test that invokes the copy operation and then compares the results using reflection.