rust-cpython: mark unsafe functions as such It wasn't trivial to fix leak_immutable() to be safe since we have to allow immutable operations (e.g. iter()) on the leaked reference. So let's mark it unsafe for now. Callers must take care of the returned object to guarantee the memory safety. I'll revisit this later. I think $leaked<T: 'static> could have a function that converts itself into $leaked<U: 'static> with a given FnOnce(&T) -> &U, where T is $inner_struct, and U is $iterator_type for example.