The compiler has very limited "proof" capabilities even in principle, especially wrt. unsafe{} code. From a principled POV it would be nice to be able to provide a formal, compiler-checked proof that some block of code that has to rely on "unsafe" operations doesn't actually violate the language safety guarantees and can be wrapped safely. But this will have to depend on a formal model of "unsafe" itself which is still lacking. And it wouldn't even help for things like FFI, which involves calls into outside code for which the semantics are not formally known.