[libcxx-commits] [libcxx] [libc++] Fix _CopySegment helper in ranges::copy(join_view, out) when called in a static assertion context (PR #69593)

[Rajveer Singh Bharadwaj via libcxx-commits]

https://github.com/Rajveer100 updated https://github.com/llvm/llvm-project/pull/69593

>From 27992e4a056439be351084e1285fb7ae8383abab Mon Sep 17 00:00:00 2001
From: Rajveer <rajveer.developer at icloud.com>
Date: Thu, 19 Oct 2023 17:08:57 +0530
Subject: [PATCH] [libc++] Fix _CopySegment helper in ranges::copy(join_view,
 out) replacing `const` with `constexpr`

Part of Issue #69083
---
 libcxx/include/__algorithm/copy.h                 | 13 +++++++------
 .../alg.copy/ranges.copy.segmented.pass.cpp       | 15 +++++++++++----
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/libcxx/include/__algorithm/copy.h b/libcxx/include/__algorithm/copy.h
index dfe9898c6480cf8..c25136d79dac562 100644
--- a/libcxx/include/__algorithm/copy.h
+++ b/libcxx/include/__algorithm/copy.h
@@ -35,7 +35,7 @@ template <class _AlgPolicy>
 struct __copy_loop {
   template <class _InIter, class _Sent, class _OutIter>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
-  operator()(_InIter __first, _Sent __last, _OutIter __result) const {
+  operator()(_InIter __first, _Sent __last, _OutIter __result) {
     while (__first != __last) {
       *__result = *__first;
       ++__first;
@@ -51,9 +51,10 @@ struct __copy_loop {
 
     _OutIter& __result_;
 
-    _LIBCPP_HIDE_FROM_ABI _CopySegment(_OutIter& __result) : __result_(__result) {}
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 explicit _CopySegment(_OutIter& __result)
+        : __result_(__result) {}
 
-    _LIBCPP_HIDE_FROM_ABI void
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
     operator()(typename _Traits::__local_iterator __lfirst, typename _Traits::__local_iterator __llast) {
       __result_ = std::__copy<_AlgPolicy>(__lfirst, __llast, std::move(__result_)).second;
     }
@@ -61,7 +62,7 @@ struct __copy_loop {
 
   template <class _InIter, class _OutIter, __enable_if_t<__is_segmented_iterator<_InIter>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
-  operator()(_InIter __first, _InIter __last, _OutIter __result) const {
+  operator()(_InIter __first, _InIter __last, _OutIter __result) {
     std::__for_each_segment(__first, __last, _CopySegment<_InIter, _OutIter>(__result));
     return std::make_pair(__last, std::move(__result));
   }
@@ -72,7 +73,7 @@ struct __copy_loop {
                               !__is_segmented_iterator<_InIter>::value && __is_segmented_iterator<_OutIter>::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
-  operator()(_InIter __first, _InIter __last, _OutIter __result) const {
+  operator()(_InIter __first, _InIter __last, _OutIter __result) {
     using _Traits = __segmented_iterator_traits<_OutIter>;
     using _DiffT  = typename common_type<__iter_diff_t<_InIter>, __iter_diff_t<_OutIter> >::type;
 
@@ -99,7 +100,7 @@ struct __copy_trivial {
   // At this point, the iterators have been unwrapped so any `contiguous_iterator` has been unwrapped to a pointer.
   template <class _In, class _Out, __enable_if_t<__can_lower_copy_assignment_to_memmove<_In, _Out>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
-  operator()(_In* __first, _In* __last, _Out* __result) const {
+  operator()(_In* __first, _In* __last, _Out* __result) {
     return std::__copy_trivial_impl(__first, __last, __result);
   }
 };
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy.segmented.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy.segmented.pass.cpp
index abb9157df9abbbb..50fb479afcd0640 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy.segmented.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy.segmented.pass.cpp
@@ -92,10 +92,7 @@ constexpr void test_join_view() {
   }
 }
 
-int main(int, char**) {
-  test_containers<std::deque<int>, std::deque<int>>();
-  test_containers<std::deque<int>, std::vector<int>>();
-  test_containers<std::vector<int>, std::deque<int>>();
+constexpr bool test_constexpr() {
   test_containers<std::vector<int>, std::vector<int>>();
 
   types::for_each(types::forward_iterator_list<int*>{}, []<class Iter> {
@@ -103,6 +100,16 @@ int main(int, char**) {
     test_join_view<Iter, sentinel_wrapper<Iter>>();
     test_join_view<Iter, sized_sentinel<Iter>>();
   });
+  return true;
+}
+
+int main(int, char**) {
+  test_containers<std::deque<int>, std::deque<int>>();
+  test_containers<std::deque<int>, std::vector<int>>();
+  test_containers<std::vector<int>, std::deque<int>>();
+
+  test_constexpr();
+  static_assert(test_constexpr());
 
   return 0;
 }