Specialization and lifetime dispatch #40582
Description
I see this briefly mentioned in #31844 but no existing issue tracking the incorrect behavior.
Something in the following code is unsound. It should not be possible to implement make_static.
#![feature(specialization)]
trait FromRef<'a, T: ?Sized> {
fn from_ref(r: &'a T) -> Self;
}
impl<'a, T: ?Sized> FromRef<'a, T> for &'a T {
fn from_ref(r: &'a T) -> Self {
r
}
}
impl<'a, T: ?Sized, R> FromRef<'a, T> for R {
default fn from_ref(_: &'a T) -> Self {
unimplemented!()
}
}
fn main() {
let s = "specialization".to_owned();
println!("{:?}", make_static(s.as_str()));
}
fn make_static<T: ?Sized>(data: &T) -> &'static T {
fn helper<T: ?Sized, R>(data: &T) -> R {
R::from_ref(data)
}
helper(data)
}