[libc++] Simplify tuple_cat further

Author: philnik777

libcxx/include/CMakeLists.txt

@@ -782,7 +782,6 @@ set(files
   __tuple/sfinae_helpers.h
   __tuple/tuple_element.h
   __tuple/tuple_like.h
-  __tuple/tuple_like_ext.h
   __tuple/tuple_like_no_subrange.h
   __tuple/tuple_size.h
   __tuple/tuple_types.h

libcxx/include/__tuple/tuple_like_ext.h

@@ -2115,7 +2115,6 @@ module std [system] {
     module ignore                   { header "__tuple/ignore.h" }
     module sfinae_helpers           { header "__tuple/sfinae_helpers.h" }
     module tuple_element            { header "__tuple/tuple_element.h" }
-    module tuple_like_ext           { header "__tuple/tuple_like_ext.h" }
     module tuple_like_no_subrange   { header "__tuple/tuple_like_no_subrange.h" }
     module tuple_like               { header "__tuple/tuple_like.h" }
     module tuple_size               { header "__tuple/tuple_size.h" }

libcxx/include/module.modulemap.in

@@ -1273,15 +1273,19 @@ operator<=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y) {
 template <class... _Tuples>
 struct __tuple_cat_return_impl;
 
-template <class _Tuple>
-struct __tuple_cat_return_impl<_Tuple> {
-  using type _LIBCPP_NODEBUG = _Tuple;
+template <class... _Types>
+struct __tuple_cat_return_impl<tuple<_Types...>> {
+  using type _LIBCPP_NODEBUG = tuple<_Types...>;
 };
 
-template <class... _Types0, template <class...> class _Tuple, class... _Types1, class... _Tuples>
-struct __tuple_cat_return_impl<tuple<_Types0...>, _Tuple<_Types1...>, _Tuples...>
+template <class... _Types0, class... _Types1, class... _Tuples>
+struct __tuple_cat_return_impl<tuple<_Types0...>, tuple<_Types1...>, _Tuples...>
     : __tuple_cat_return_impl<tuple<_Types0..., _Types1...>, _Tuples...> {};
 
+template <class... _Types0, class _Tp, class _Up, class... _Tuples>
+struct __tuple_cat_return_impl<tuple<_Types0...>, pair<_Tp, _Up>, _Tuples...>
+    : __tuple_cat_return_impl<tuple<_Types0..., _Tp, _Up>, _Tuples...> {};
+
 template <class, class, class>
 struct __tuple_cat_array;
 
@@ -1369,11 +1373,7 @@ __tuple_cat_select_element_wise(_TupleSrc&& __src, __index_sequence<_Indices...>
   return _TupleDst(std::get<_Indices>(std::forward<_TupleSrc>(__src))...);
 }
 
-template <class _Tuple0,
-          class... _Tuples,
-          __enable_if_t<
-              _And<__tuple_like_ext<__remove_cvref_t<_Tuple0>>, __tuple_like_ext<__remove_cvref_t<_Tuples>>...>::value,
-              int> = 0>
+template <class _Tuple0, class... _Tuples>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 __tuple_cat_return_t<_Tuple0, _Tuples...>
 tuple_cat(_Tuple0&& __t0, _Tuples&&... __tpls) {
   using _T0 _LIBCPP_NODEBUG          = __libcpp_remove_reference_t<_Tuple0>;