[libc++][PSTL] Fix std::copy frontend dispatching

[philnik]

Try to fix CI

[Mordante]

LGTM modulo nits

libcxx/test/libcxx/algorithms/pstl.robust_against_customization_points_not_working.pass.cpp

295

Since the function is not nodiscard and shouldn't be.

libcxx/include/__algorithm/pstl_copy.h

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___ALGORITHM_PSTL_COPY_H
 #define _LIBCPP___ALGORITHM_PSTL_COPY_H
 
 #include <__algorithm/copy_n.h>
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
 #include <__algorithm/pstl_transform.h>
 #include <__config>
 #include <__functional/identity.h>
 #include <__iterator/iterator_traits.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/is_constant_evaluated.h>
 #include <__type_traits/is_execution_policy.h>
 #include <__type_traits/is_trivially_copyable.h>
 #include <__type_traits/remove_cvref.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 // TODO: Use the std::copy/move shenanigans to forward to std::memmove
 
+template <class>
+void __pstl_copy();
+
 template <class _ExecutionPolicy,
           class _ForwardIterator,
           class _ForwardOutIterator,
-          enable_if_t<is_execution_policy_v<__remove_cvref_t<_ExecutionPolicy>>, int> = 0>
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
 _LIBCPP_HIDE_FROM_ABI _ForwardOutIterator
 copy(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _ForwardOutIterator __result) {
-  return std::transform(__policy, __first, __last, __result, __identity());
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_copy),
+      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last, _ForwardOutIterator __g_result) {
+        return std::transform(__policy, __g_first, __g_last, __g_result, __identity());
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__result));
 }
 
+template <class>
+void __pstl_copy_n();
+
 template <class _ExecutionPolicy,
           class _ForwardIterator,
           class _ForwardOutIterator,
           class _Size,
-          enable_if_t<is_execution_policy_v<__remove_cvref_t<_ExecutionPolicy>>, int> = 0>
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
 _LIBCPP_HIDE_FROM_ABI _ForwardOutIterator
 copy_n(_ExecutionPolicy&& __policy, _ForwardIterator __first, _Size __n, _ForwardOutIterator __result) {
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_copy_n),
+      [&__policy](_ForwardIterator __g_first, _Size __g_n, _ForwardOutIterator __g_result) {
         if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value)
-    return std::copy(__policy, __first, __first + __n, __result);
+          return std::copy(__policy, __g_first, __g_first + __g_n, __g_result);
         else
-    return std::copy_n(__first, __n, __result);
+          return std::copy_n(__g_first, __g_n, __g_result);
+      },
+      std::move(__first),
+      __n,
+      std::move(__result));
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
 
 #endif // _LIBCPP___ALGORITHM_PSTL_COPY_H

libcxx/test/libcxx/algorithms/pstl.robust_against_customization_points_not_working.pass.cpp

 
 template <class, class ForwardIterator, class Pred>
 bool __pstl_all_of(TestBackend, ForwardIterator, ForwardIterator, Pred) {
   assert(!pstl_all_of_called);
   pstl_all_of_called = true;
   return true;
 }
 
+bool pstl_copy_called = false;
+
+template <class, class ForwardIterator, class ForwardOutIterator>
+ForwardIterator __pstl_copy(TestBackend, ForwardIterator, ForwardIterator, ForwardOutIterator) {
+  assert(!pstl_copy_called);
+  pstl_copy_called = true;
+  return 0;
+}
+
+bool pstl_copy_n_called = false;
+
+template <class, class ForwardIterator, class Size, class ForwardOutIterator>
+ForwardIterator __pstl_copy_n(TestBackend, ForwardIterator, Size, ForwardOutIterator) {
+  assert(!pstl_copy_n_called);
+  pstl_copy_n_called = true;
+  return 0;
+}
+
 bool pstl_count_called = false;
 
 template <class, class ForwardIterator, class T>
 typename std::iterator_traits<ForwardIterator>::difference_type
 __pstl_count(TestBackend, ForwardIterator, ForwardIterator, const T&) {
   assert(!pstl_count_called);
   pstl_count_called = true;
   return 0;
int main(int, char**) {
   auto pred = [](auto&&...) { return true; };
 
   (void)std::any_of(TestPolicy{}, std::begin(a), std::end(a), pred);
   assert(std::pstl_any_of_called);
   (void)std::all_of(TestPolicy{}, std::begin(a), std::end(a), pred);
   assert(std::pstl_all_of_called);
   (void)std::none_of(TestPolicy{}, std::begin(a), std::end(a), pred);
   assert(std::pstl_none_of_called);
+  (void)std::copy(TestPolicy{}, std::begin(a), std::end(a), std::begin(a));
+  assert(std::pstl_copy_called);
+  (void)std::copy_n(TestPolicy{}, std::begin(a), 1, std::begin(a));
+  assert(std::pstl_copy_n_called);
   (void)std::count(TestPolicy{}, std::begin(a), std::end(a), 0);
   assert(std::pstl_count_called);
   (void)std::count_if(TestPolicy{}, std::begin(a), std::end(a), pred);
   assert(std::pstl_count_if_called);
   (void)std::fill(TestPolicy{}, std::begin(a), std::end(a), 0);
   assert(std::pstl_fill_called);
   (void)std::fill_n(TestPolicy{}, std::begin(a), std::size(a), 0);
   assert(std::pstl_fill_n_called);