reason and fix for zip traits

thrust/thrust/iterator/zip_iterator.h

@@ -325,14 +325,15 @@ inline _CCCL_HOST_DEVICE zip_iterator<_CUDA_VSTD::tuple<Iterators...>> make_zip_
 
 THRUST_NAMESPACE_END
 
-// TODO(bgruber): libcu++ iterator traits fail for complex zip_iterators in C++17, see e.g.:
-// https://godbolt.org/z/7jb4qG3bb
+// libcu++ iterator traits fail for complex zip_iterators in C++17, see e.g.: https://godbolt.org/z/7jb4qG3bb
+// The reason is that libcu++ backported the C++20 range iterator machinery to C++17, but C++17 has slightly different
+// language rules, especially regarding `void`. We deemed to it too hard to work around the issues.
 #if _CCCL_STD_VER < 2020
 _LIBCUDACXX_BEGIN_NAMESPACE_STD
 template <typename IteratorTuple>
-struct iterator_traits<thrust::zip_iterator<IteratorTuple>>
+struct iterator_traits<THRUST_NS_QUALIFIER::zip_iterator<IteratorTuple>>
 {
-  using It                = thrust::zip_iterator<IteratorTuple>;
+  using It                = THRUST_NS_QUALIFIER::zip_iterator<IteratorTuple>;
   using value_type        = typename It::value_type;
   using reference         = typename It::reference;
   using iterator_category = typename It::iterator_category;