[jeffbee]

I see signs that Google itself is using preserve_none internally, since the public protobuf repo has PROTOBUF_CC (Calling Convention) but it is defined as nothing

  #define PROTOBUF_CC

Is there any chance of this getting out into the wild or is it too dangerous for us mortals?

[haberman]

Since preserve_none is Clang-only and only available on recent compilers, it would introduce an ABI hazard between the core library and generated code. We don't want to cause crashes if you compile protobuf with one compiler and generated code with another.

Also, until quite recently preserve_none was incompatible with the sanitizers, but I believe this may have been fixed by: https://github.com/llvm/llvm-project/pull/81048