1 files changed, 39 insertions, 0 deletions
diff --git a/src/test/ui/associated-types/param-env-normalize-cycle.rs b/src/test/ui/associated-types/param-env-normalize-cycle.rs
new file mode 100644
index 000000000..12db595ed
--- /dev/null
+++ b/src/test/ui/associated-types/param-env-normalize-cycle.rs
@@ -0,0 +1,39 @@
+// Minimized case from typenum that didn't compile because:
+// - We tried to normalize the ParamEnv of the second impl
+// - This requires trying to normalize `GrEq<Self, Square<Square<U>>>`
+// - This requires proving `Square<Square<U>>: Sized` so that the first impl
+//   applies
+// - This requires Providing `Square<Square<U>>` is well-formed, so that we
+//   can use the `Sized` bound on `Mul::Output`
+// - This requires proving `Square<U>: Mul`
+// - But first we tried normalizing the whole obligation, including the
+//   ParamEnv, which leads to a cycle error.
+
+// check-pass
+
+trait PrivateSquareRoot {}
+
+pub trait Mul<Rhs = Self> {
+    type Output;
+}
+
+pub trait IsGreaterOrEqual<Rhs> {
+    type Output;
+}
+
+pub type Square<A> = <A as Mul>::Output;
+pub type GrEq<A, B> = <A as IsGreaterOrEqual<B>>::Output;
+
+impl<A, B> IsGreaterOrEqual<B> for A {
+    type Output = ();
+}
+
+impl<U> PrivateSquareRoot for U
+where
+    U: Mul,
+    Square<U>: Mul,
+    GrEq<Self, Square<Square<U>>>: Sized,
+{
+}
+
+fn main() {}