pub mod remote { pub struct Inner(pub Box<u8>); } pub mod remote_inner_heap_size { use heapsz::HeapSize; use super::remote; pub fn heap_size(t: &remote::Inner) -> usize { t.0.heap_size() } } #[derive(heapsz_derive::HeapSize)] pub struct With { #[heap_size(with = "remote_inner_heap_size")] pub inner: remote::Inner, } fn main() {}