1 files changed, 54 insertions, 0 deletions
diff --git a/src/test/ui/associated-types/defaults-unsound-62211-2.rs b/src/test/ui/associated-types/defaults-unsound-62211-2.rs
new file mode 100644
index 000000000..c13ec776a
--- /dev/null
+++ b/src/test/ui/associated-types/defaults-unsound-62211-2.rs
@@ -0,0 +1,54 @@
+//! 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 and ICEs, the latter being demonstrated here.
+//!
+//! 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(());
+}