Regression test for rust-lang#58813

(Update: Fixed test; revision is meant to introduce compile-failure, w/o ICE.)

Author: pnkfelix

src/test/incremental/cyclic-trait-hierarchy.rs

@@ -0,0 +1,14 @@
+// Adapated from rust-lang/rust#58813
+
+// revisions: rpass1 cfail2
+
+#[cfg(rpass1)]
+pub trait T2 { }
+#[cfg(cfail2)]
+pub trait T2: T1 { }
+//[cfail2]~^ ERROR cycle detected when computing the supertraits of `T2`
+//[cfail2]~| ERROR cycle detected when computing the supertraits of `T2`
+
+pub trait T1: T2 { }
+
+fn main() { }