It doesn't matter that it's 'kind of unusual', even though I contend that it isn't. Even if, for the sake of argument, we assume that it is, that doesn't change my point.
My point is that the whole point of Rust is supposedly that it
>is a systems programming language that runs blazingly fast, prevents segfaults, and guarantees thread safety.
except that when you look at any of the examples of code that really would benefit from the compiler's help, the compiler just throws its hands in the air and goes 'it's all up to you now'.
The problem is that Rust doesn't let you make a single assumption and let the compiler prove the safety of the code using that assumption. It just has a valve that you can hit that removes all guarantees.
If you could say 'this code is safe assuming that this FFI function doesn't exhibit undefined behaviour, please check that for me' or write a proof that says 'this actually is safe, because this pointer can only ever point into this valid memory or this valid memory, and this is why' then the compiler would still be useful.
Whether 'this work' (which is not just creating data structures, but anything that the compiler doesn't understand, which is much broader than just creating data structures) is unusual or not, IMO the whole appeal of Rust is that it makes doing that work easy. But it doesn't.
Rust just doesn't seem worth it, doesn't seem worth rewriting whole ecosystems of code. It doesn't give any actual safety.