From 1a54b610d60aaa22f2c488f0e599873f9a6f9104 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Wed, 4 Sep 2024 12:59:03 +0800
Subject: [PATCH] `<algorithm>`: Relax const-ness requirements on
 `ranges::_Meow_bound_unchecked` (#4927)

---
 stl/inc/algorithm                             |  8 +++----
 .../P0896R4_ranges_alg_inplace_merge/test.cpp | 22 +++++++++++++++++++
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/stl/inc/algorithm b/stl/inc/algorithm
index c0b1c0e84a..3f54cd75ef 100644
--- a/stl/inc/algorithm
+++ b/stl/inc/algorithm
@@ -7031,9 +7031,9 @@ namespace ranges {
 
     template <class _It, class _Ty, class _Pr, class _Pj>
     _NODISCARD constexpr _It _Lower_bound_unchecked(
-        _It _First, iter_difference_t<_It> _Count, const _Ty& _Val, _Pr _Pred, _Pj _Proj) {
+        _It _First, iter_difference_t<_It> _Count, _Ty&& _Val, _Pr _Pred, _Pj _Proj) {
         _STL_INTERNAL_STATIC_ASSERT(forward_iterator<_It>);
-        _STL_INTERNAL_STATIC_ASSERT(indirect_strict_weak_order<_Pr, const _Ty*, projected<_It, _Pj>>);
+        _STL_INTERNAL_STATIC_ASSERT(indirect_strict_weak_order<_Pr, add_pointer_t<_Ty>, projected<_It, _Pj>>);
 
         using _Diff = iter_difference_t<_It>;
 
@@ -7082,9 +7082,9 @@ namespace ranges {
 
     template <class _It, class _Ty, class _Pr, class _Pj>
     _NODISCARD constexpr _It _Upper_bound_unchecked(
-        _It _First, iter_difference_t<_It> _Count, const _Ty& _Val, _Pr _Pred, _Pj _Proj) {
+        _It _First, iter_difference_t<_It> _Count, _Ty&& _Val, _Pr _Pred, _Pj _Proj) {
         _STL_INTERNAL_STATIC_ASSERT(forward_iterator<_It>);
-        _STL_INTERNAL_STATIC_ASSERT(indirect_strict_weak_order<_Pr, const _Ty*, projected<_It, _Pj>>);
+        _STL_INTERNAL_STATIC_ASSERT(indirect_strict_weak_order<_Pr, add_pointer_t<_Ty>, projected<_It, _Pj>>);
 
         using _Diff = iter_difference_t<_It>;
 
diff --git a/tests/std/tests/P0896R4_ranges_alg_inplace_merge/test.cpp b/tests/std/tests/P0896R4_ranges_alg_inplace_merge/test.cpp
index bb0314722b..3a9f6a495a 100644
--- a/tests/std/tests/P0896R4_ranges_alg_inplace_merge/test.cpp
+++ b/tests/std/tests/P0896R4_ranges_alg_inplace_merge/test.cpp
@@ -4,9 +4,11 @@
 #include <algorithm>
 #include <cassert>
 #include <concepts>
+#include <cstddef>
 #include <ranges>
 #include <span>
 #include <utility>
+#include <vector>
 
 #include <range_algorithm_support.hpp>
 
@@ -56,6 +58,26 @@ struct instantiator {
     }
 };
 
+// Test GH-4863: <algorithm>: ranges::inplace_merge doesn't seem to be able to utilize ranges::upper_bound
+void test_gh_4863() { // COMPILE-ONLY
+    {
+        vector<int> v;
+        auto cmp = [](int&, int&) { return false; };
+        ranges::sort(v, cmp);
+        ranges::inplace_merge(v, v.begin(), cmp);
+    }
+    {
+        struct S {
+            operator nullptr_t() {
+                return nullptr;
+            }
+        };
+        vector<int> v;
+        auto cmp = [](const nullptr_t&, const nullptr_t&) { return false; };
+        ranges::inplace_merge(v, v.begin(), cmp, [](int) { return S{}; });
+    }
+}
+
 int main() {
     test_bidi<instantiator, P>();
 }