As mentioned live, there is an attribute [[noreturn]] that could be used to decorate the function, basically to add a consistency check / clarify expectations to whoever passes by.

Looking around the codebase it's already in use in a couple of places, so I guess it has to be supported.

Thanks for the PR! LGTM - but it seems this breaks one of the existing tests.

That's caused by the type check during json deserialization.
seems when the number is positive, 3 in this case, the number is recognized as unsigned number, rather than signed integer. so the test case failed.

Ill continue with this once I pick up the serialization work again next week.

@taniabogatsch This also now fixes the ugly (void)field_id in the JsonDeserializer

Ah, that's a neat solution!