Add test for nalgebra hang in coherence

tests/ui/traits/coherence-alias-hang.rs

@@ -0,0 +1,23 @@
+//@ check-pass
+
+// Regression test for nalgebra hang <https://github.com/rust-lang/rust/issues/130056>.
+
+#![feature(lazy_type_alias)]
+#![allow(incomplete_features)]
+
+type Id<T: ?Sized> = T;
+trait NotImplemented {}
+
+struct W<T: ?Sized, U: ?Sized>(*const T, *const U);
+trait Trait {
+    type Assoc: ?Sized;
+}
+impl<T: ?Sized + Trait> Trait for W<T, T> {
+    type Assoc = W<T::Assoc, Id<T::Assoc>>;
+}
+
+trait Overlap<T: ?Sized> {}
+impl<T: ?Sized> Overlap<T> for W<T, T> {}
+impl<T: ?Sized + Trait + NotImplemented> Overlap<T::Assoc> for T {}
+
+fn main() {}