From bbe8b6b2affb81b12a945d070a79b3e709a5922f Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Sun, 29 Sep 2024 04:22:45 +0800
Subject: [PATCH] `<utility>`: Privatize `pair`'s internal non-Standard
 constructor (#4979)

---
 stl/inc/utility                                       | 11 ++++++-----
 .../tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp |  7 +++++++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/stl/inc/utility b/stl/inc/utility
index c5f9265dcfa..549d8cccd95 100644
--- a/stl/inc/utility
+++ b/stl/inc/utility
@@ -315,11 +315,6 @@ struct pair { // store a pair of values
     }
 #endif // _HAS_CXX23
 
-    template <class _Tuple1, class _Tuple2, size_t... _Indices1, size_t... _Indices2>
-    constexpr pair(_Tuple1& _Val1, _Tuple2& _Val2, index_sequence<_Indices1...>, index_sequence<_Indices2...>)
-        : first(_STD _Tuple_get<_Indices1>(_STD move(_Val1))...),
-          second(_STD _Tuple_get<_Indices2>(_STD move(_Val2))...) {}
-
     template <class... _Types1, class... _Types2>
     _CONSTEXPR20 pair(piecewise_construct_t, tuple<_Types1...> _Val1, tuple<_Types2...> _Val2)
         : pair(_Val1, _Val2, index_sequence_for<_Types1...>{}, index_sequence_for<_Types2...>{}) {}
@@ -466,6 +461,12 @@ struct pair { // store a pair of values
 
     _Ty1 first; // the first stored value
     _Ty2 second; // the second stored value
+
+private:
+    template <class _Tuple1, class _Tuple2, size_t... _Indices1, size_t... _Indices2>
+    constexpr pair(_Tuple1& _Val1, _Tuple2& _Val2, index_sequence<_Indices1...>, index_sequence<_Indices2...>)
+        : first(_STD _Tuple_get<_Indices1>(_STD move(_Val1))...),
+          second(_STD _Tuple_get<_Indices2>(_STD move(_Val2))...) {}
 };
 
 #if _HAS_CXX17
diff --git a/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp b/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
index c1f45849030..7fc2e4102a7 100644
--- a/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
+++ b/tests/std/tests/VSO_0000000_more_pair_tuple_sfinae/test.cpp
@@ -558,6 +558,13 @@ STATIC_ASSERT(!is_constructible_v<tuple<A>, allocator_arg_t, allocator<int>, pai
 STATIC_ASSERT(is_constructible_v<tuple<A, A>, allocator_arg_t, allocator<int>, pair<Ex, Ex>>);
 STATIC_ASSERT(!is_constructible_v<tuple<A, A, A>, allocator_arg_t, allocator<int>, pair<Ex, Ex>>);
 
+// Also test that the internal constructor used for the piecewise_construct_t constructor of pair is not public.
+STATIC_ASSERT(!is_constructible_v<pair<int, int>, tuple<>&, tuple<>&, make_index_sequence<0>, make_index_sequence<0>>);
+STATIC_ASSERT(
+    !is_constructible_v<pair<int, int>, tuple<int>&, tuple<>&, make_index_sequence<1>, make_index_sequence<0>>);
+STATIC_ASSERT(
+    !is_constructible_v<pair<int, int>, tuple<int>&, tuple<int>&, make_index_sequence<1>, make_index_sequence<1>>);
+
 
 pair<int, int> func1() {
     const int x = 17;