Code shared from the Rust Playground

playground.rs

#![feature(dropck_eyepatch)] 

use std::{fmt, rc::Rc};

struct PeekOnDrop<T: fmt::Debug>(T);

unsafe impl<#[may_dangle] T: fmt::Debug> Drop for PeekOnDrop<T> {
    fn drop(&mut self) {
        println!("{:?}", self.0);
    }   
}

struct SelfRef<'a> {
   value: Box<u8>,
   rc: Option<Rc<PeekOnDrop<&'a u8>>>,
}

fn main() {
    let mut sr = SelfRef {
        rc: None,
        value: Box::new(1),
    };
    
    sr.rc = Some(Rc::new(PeekOnDrop(&*sr.value)));
}