struct S;
struct T;

impl From<&S> for T {
    fn from(_s: &S) -> T {
        T
    }
}

impl From<&mut S> for T {
    fn from(s: &mut S) -> T {
        (&*s).into()
    }
}

fn main() {
    let s = &mut S;
    let t: T = s.into();
}