src/test/ui/associated-types/defaults-unsound-62211-2.rs

   1 //! Regression test for https://github.com/rust-lang/rust/issues/62211
   2 //!
   3 //! The old implementation of defaults did not check whether the provided
   4 //! default actually fulfills all bounds on the assoc. type, leading to
   5 //! unsoundness and ICEs, the latter being demonstrated here.
   6 //!
   7 //! Note that the underlying cause of this is still not yet fixed.
   8 //! See: https://github.com/rust-lang/rust/issues/33017
   9
  10 #![feature(associated_type_defaults)]
  11
  12 use std::{
  13     fmt::Display,
  14     ops::{AddAssign, Deref}
  15 };
  16
  17
  18 trait UncheckedCopy: Sized {
  19     // This Output is said to be Copy. Yet we default to Self
  20     // and it's accepted, not knowing if Self ineed is Copy
  21     type Output: Copy
  22     //~^ ERROR the trait bound `Self: Copy` is not satisfied
  23     + Deref<Target = str>
  24     //~^ ERROR the trait bound `Self: Deref` is not satisfied
  25     + AddAssign<&'static str>
  26     //~^ ERROR cannot add-assign `&'static str` to `Self`
  27     + From<Self>
  28     + Display = Self;
  29     //~^ ERROR `Self` doesn't implement `std::fmt::Display`
  30
  31     // We said the Output type was Copy, so we can Copy it freely!
  32     fn unchecked_copy(other: &Self::Output) -> Self::Output {
  33         (*other)
  34     }
  35
  36     fn make_origin(s: Self) -> Self::Output {
  37         s.into()
  38     }
  39 }
  40
  41 impl<T> UncheckedCopy for T {}
  42 //~^ ERROR `T` doesn't implement `std::fmt::Display`
  43 //~| ERROR the trait bound `T: Deref` is not satisfied
  44 //~| ERROR cannot add-assign `&'static str` to `T`
  45 //~| ERROR the trait bound `T: Copy` is not satisfied
  46
  47 fn bug<T: UncheckedCopy>(origin: T) {
  48     let origin = T::make_origin(origin);
  49     let mut copy = T::unchecked_copy(&origin);
  50
  51     // assert we indeed have 2 strings pointing to the same buffer.
  52     assert_eq!(origin.as_ptr(), copy.as_ptr());
  53
  54     // Drop the origin. Any use of `copy` is UB.
  55     drop(origin);
  56
  57     copy += "This is invalid!";
  58     println!("{}", copy);
  59 }
  60
  61 fn main() {
  62     bug(());
  63 }