add test for alias self_ty

tests/ui/traits/next-solver/normalization-shadowing/use_object_if_empty_env.rs

@@ -16,4 +16,21 @@ where
     x
 }
 
+trait Id<'a> {
+    type This: ?Sized;
+}
+impl<T: ?Sized> Id<'_> for T {
+    type This = T;
+}
+
+// Ensure that we properly normalize alias self_ty before evaluating the goal.
+fn alias_foo<T>(x: for<'a> fn(
+    <<dyn Trait<Assoc = T> as Id<'a>>::This as Trait>::Assoc
+)) -> fn(T)
+where
+    dyn Trait<Assoc = T>: Trait,
+{
+    x
+}
+
 fn main() {}