From 874669fd54e17d483ee5d27930a53e328ad79d55 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser@berlin.de>
Date: Sat, 17 May 2025 19:45:21 +0200
Subject: [PATCH] [libc++] Fix set::operator= when instantiating with a
 std::pair

---
 libcxx/include/__tree                                  |  4 ++--
 .../associative/set/set.cons/copy_assign.pass.cpp      | 10 ++++++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index 1903533898481..403cfe1ba4036 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -1281,7 +1281,7 @@ private:
   }
   _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__tree&, false_type) _NOEXCEPT {}
 
-  template <class _From, __enable_if_t<__is_pair_v<__remove_cvref_t<_From> >, int> = 0>
+  template <class _From, class _ValueT = _Tp, __enable_if_t<__is_tree_value_type<_ValueT>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI static void __assign_value(__get_node_value_type_t<value_type>& __lhs, _From&& __rhs) {
     using __key_type = typename _NodeTypes::key_type;
 
@@ -1291,7 +1291,7 @@ private:
     __lhs.second                         = std::forward<_From>(__rhs).second;
   }
 
-  template <class _To, class _From, class _ValueT = _Tp, __enable_if_t<!__is_pair_v<__remove_cvref_t<_From> >, int> = 0>
+  template <class _To, class _From, class _ValueT = _Tp, __enable_if_t<!__is_tree_value_type<_ValueT>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI static void __assign_value(_To& __lhs, _From&& __rhs) {
     __lhs = std::forward<_From>(__rhs);
   }
diff --git a/libcxx/test/std/containers/associative/set/set.cons/copy_assign.pass.cpp b/libcxx/test/std/containers/associative/set/set.cons/copy_assign.pass.cpp
index e21e07734d888..f154f5d8b994c 100644
--- a/libcxx/test/std/containers/associative/set/set.cons/copy_assign.pass.cpp
+++ b/libcxx/test/std/containers/associative/set/set.cons/copy_assign.pass.cpp
@@ -80,5 +80,15 @@ int main(int, char**) {
     assert(*std::next(mo.begin(), 2) == 3);
   }
 
+  { // Test with std::pair, since we have some special handling for pairs inside __tree
+    std::pair<int, int> arr[] = {
+        std::make_pair(1, 2), std::make_pair(2, 3), std::make_pair(3, 4), std::make_pair(4, 5)};
+    std::set<std::pair<int, int> > a(arr, arr + 4);
+    std::set<std::pair<int, int> > b;
+
+    b = a;
+    assert(a == b);
+  }
+
   return 0;
 }