1 files changed, 35 insertions, 0 deletions
diff --git a/tests/ui/coherence/warn-when-cycle-is-error-in-coherence.rs b/tests/ui/coherence/warn-when-cycle-is-error-in-coherence.rs
new file mode 100644
index 000000000..01f7d6ce9
--- /dev/null
+++ b/tests/ui/coherence/warn-when-cycle-is-error-in-coherence.rs
@@ -0,0 +1,35 @@
+#![deny(coinductive_overlap_in_coherence)]
+
+use std::borrow::Borrow;
+use std::cmp::Ordering;
+use std::marker::PhantomData;
+
+#[derive(PartialEq, Default)]
+pub(crate) struct Interval<T>(PhantomData<T>);
+
+// This impl overlaps with the `derive` unless we reject the nested
+// `Interval<?1>: PartialOrd<Interval<?1>>` candidate which results
+// in a - currently inductive - cycle.
+impl<T, Q> PartialEq<Q> for Interval<T>
+//~^ ERROR implementations of `PartialEq<Interval<_>>` for `Interval<_>` will conflict in the future
+//~| WARN this was previously accepted by the compiler but is being phased out
+where
+    T: Borrow<Q>,
+    Q: ?Sized + PartialOrd,
+{
+    fn eq(&self, _: &Q) -> bool {
+        true
+    }
+}
+
+impl<T, Q> PartialOrd<Q> for Interval<T>
+where
+    T: Borrow<Q>,
+    Q: ?Sized + PartialOrd,
+{
+    fn partial_cmp(&self, _: &Q) -> Option<Ordering> {
+        None
+    }
+}
+
+fn main() {}