tests/ui/reborrow/custom_mut_coerce_shared.rs

#![feature(reborrow)]
use std::ops::{CoerceShared, Reborrow};

struct CustomMut<'a, T>(&'a mut T);
impl<'a, T> Reborrow for CustomMut<'a, T> {}
impl<'a, T> CoerceShared for CustomMut<'a, T> {
    type Target = CustomRef<'a, T>;
}

struct CustomRef<'a, T>(&'a T);

impl<'a, T> Clone for CustomRef<'a, T> {
    fn clone(&self) -> Self {
        Self(self.0)
    }
}
impl<'a, T> Copy for CustomRef<'a, T> {}

fn method(a: CustomRef<'_, ()>) {}  //~NOTE function defined here

fn main() {
    let a = CustomMut(&mut ());
    method(a);
    //~^ ERROR mismatched types
    //~| NOTE expected `CustomRef<'_, ()>`, found `CustomMut<'_, ()>`
    //~| NOTE arguments to this function are incorrect
    //~| NOTE expected struct `CustomRef<'_, ()>`
}