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|
//! Regression test for https://github.com/rust-lang/rust/issues/62211
//!
//! The old implementation of defaults did not check whether the provided
//! default actually fulfills all bounds on the assoc. type, leading to
//! unsoundness, demonstrated here as a use-after-free.
//!
//! Note that the underlying cause of this is still not yet fixed.
//! See: https://github.com/rust-lang/rust/issues/33017
#![feature(associated_type_defaults)]
use std::{
fmt::Display,
ops::{AddAssign, Deref},
};
trait UncheckedCopy: Sized {
// This Output is said to be Copy. Yet we default to Self
// and it's accepted, not knowing if Self ineed is Copy
type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
//~^ ERROR the trait bound `Self: Copy` is not satisfied
//~| ERROR the trait bound `Self: Deref` is not satisfied
//~| ERROR cannot add-assign `&'static str` to `Self`
//~| ERROR `Self` doesn't implement `std::fmt::Display`
// We said the Output type was Copy, so we can Copy it freely!
fn unchecked_copy(other: &Self::Output) -> Self::Output {
(*other)
}
fn make_origin(s: Self) -> Self::Output {
s.into()
}
}
impl<T> UncheckedCopy for T {}
fn bug<T: UncheckedCopy>(origin: T) {
let origin = T::make_origin(origin);
let mut copy = T::unchecked_copy(&origin);
// assert we indeed have 2 strings pointing to the same buffer.
assert_eq!(origin.as_ptr(), copy.as_ptr());
// Drop the origin. Any use of `copy` is UB.
drop(origin);
copy += "This is invalid!";
println!("{}", copy);
}
fn main() {
bug(String::from("hello!"));
}
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