[libc++] flat_meow transparent comparator string literals
#133654
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@llvm/pr-subscribers-libcxx Author: Hui (huixie90) ChangesPatch is 37.71 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/133654.diff 31 Files Affected:
diff --git a/libcxx/include/__flat_map/flat_map.h b/libcxx/include/__flat_map/flat_map.h
index f5abfd0985280..76a51bed50744 100644
--- a/libcxx/include/__flat_map/flat_map.h
+++ b/libcxx/include/__flat_map/flat_map.h
@@ -11,16 +11,15 @@
#define _LIBCPP___FLAT_MAP_FLAT_MAP_H
#include <__algorithm/lexicographical_compare_three_way.h>
+#include <__algorithm/lower_bound.h>
#include <__algorithm/min.h>
#include <__algorithm/ranges_adjacent_find.h>
#include <__algorithm/ranges_equal.h>
#include <__algorithm/ranges_inplace_merge.h>
-#include <__algorithm/ranges_lower_bound.h>
-#include <__algorithm/ranges_partition_point.h>
#include <__algorithm/ranges_sort.h>
#include <__algorithm/ranges_unique.h>
-#include <__algorithm/ranges_upper_bound.h>
#include <__algorithm/remove_if.h>
+#include <__algorithm/upper_bound.h>
#include <__assert>
#include <__compare/synth_three_way.h>
#include <__concepts/swappable.h>
@@ -863,6 +862,13 @@ class flat_map {
__containers_.values.erase(__containers_.values.begin() + __dist, __containers_.values.end());
}
+ template <class _Self, class _KeyIter>
+ _LIBCPP_HIDE_FROM_ABI static auto __corresponding_mapped_it(_Self&& __self, _KeyIter&& __key_iter) {
+ return __self.__containers_.values.begin() +
+ static_cast<ranges::range_difference_t<mapped_container_type>>(
+ ranges::distance(__self.__containers_.keys.begin(), __key_iter));
+ }
+
template <bool _WasSorted, class _InputIterator, class _Sentinel>
_LIBCPP_HIDE_FROM_ABI void __append_sort_merge_unique(_InputIterator __first, _Sentinel __last) {
auto __on_failure = std::__make_exception_guard([&]() noexcept { clear() /* noexcept */; });
@@ -903,7 +909,8 @@ class flat_map {
template <class _Self, class _Kp>
_LIBCPP_HIDE_FROM_ABI static auto __key_equal_range(_Self&& __self, const _Kp& __key) {
- auto __it = ranges::lower_bound(__self.__containers_.keys, __key, __self.__compare_);
+ auto __it =
+ std::lower_bound(__self.__containers_.keys.begin(), __self.__containers_.keys.end(), __key, __self.__compare_);
auto __last = __self.__containers_.keys.end();
if (__it == __last || __self.__compare_(__key, *__it)) {
return std::make_pair(__it, __it);
@@ -914,42 +921,30 @@ class flat_map {
template <class _Self, class _Kp>
_LIBCPP_HIDE_FROM_ABI static auto __equal_range_impl(_Self&& __self, const _Kp& __key) {
auto [__key_first, __key_last] = __key_equal_range(__self, __key);
-
- const auto __make_mapped_iter = [&](const auto& __key_iter) {
- return __self.__containers_.values.begin() +
- static_cast<ranges::range_difference_t<mapped_container_type>>(
- ranges::distance(__self.__containers_.keys.begin(), __key_iter));
- };
-
- using __iterator_type = ranges::iterator_t<decltype(__self)>;
- return std::make_pair(__iterator_type(__key_first, __make_mapped_iter(__key_first)),
- __iterator_type(__key_last, __make_mapped_iter(__key_last)));
+ using __iterator_type = ranges::iterator_t<decltype(__self)>;
+ return std::make_pair(__iterator_type(__key_first, __corresponding_mapped_it(__self, __key_first)),
+ __iterator_type(__key_last, __corresponding_mapped_it(__self, __key_last)));
}
template <class _Res, class _Self, class _Kp>
_LIBCPP_HIDE_FROM_ABI static _Res __lower_bound(_Self&& __self, _Kp& __x) {
- return __binary_search<_Res>(__self, ranges::lower_bound, __x);
+ auto __key_iter =
+ std::lower_bound(__self.__containers_.keys.begin(), __self.__containers_.keys.end(), __x, __self.__compare_);
+ auto __mapped_iter = __corresponding_mapped_it(__self, __key_iter);
+ return _Res(std::move(__key_iter), std::move(__mapped_iter));
}
template <class _Res, class _Self, class _Kp>
_LIBCPP_HIDE_FROM_ABI static _Res __upper_bound(_Self&& __self, _Kp& __x) {
- return __binary_search<_Res>(__self, ranges::upper_bound, __x);
- }
-
- template <class _Res, class _Self, class _Fn, class _Kp>
- _LIBCPP_HIDE_FROM_ABI static _Res __binary_search(_Self&& __self, _Fn __search_fn, _Kp& __x) {
- auto __key_iter = __search_fn(__self.__containers_.keys, __x, __self.__compare_);
- auto __mapped_iter =
- __self.__containers_.values.begin() +
- static_cast<ranges::range_difference_t<mapped_container_type>>(
- ranges::distance(__self.__containers_.keys.begin(), __key_iter));
-
+ auto __key_iter =
+ std::upper_bound(__self.__containers_.keys.begin(), __self.__containers_.keys.end(), __x, __self.__compare_);
+ auto __mapped_iter = __corresponding_mapped_it(__self, __key_iter);
return _Res(std::move(__key_iter), std::move(__mapped_iter));
}
template <class _KeyArg, class... _MArgs>
_LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __try_emplace(_KeyArg&& __key, _MArgs&&... __mapped_args) {
- auto __key_it = ranges::lower_bound(__containers_.keys, __key, __compare_);
+ auto __key_it = std::lower_bound(__containers_.keys.begin(), __containers_.keys.end(), __key, __compare_);
auto __mapped_it = __containers_.values.begin() + ranges::distance(__containers_.keys.begin(), __key_it);
if (__key_it == __containers_.keys.end() || __compare_(__key, *__key_it)) {
diff --git a/libcxx/include/__flat_map/flat_multimap.h b/libcxx/include/__flat_map/flat_multimap.h
index ea77fb5d79bd2..7b5c64e0b5262 100644
--- a/libcxx/include/__flat_map/flat_multimap.h
+++ b/libcxx/include/__flat_map/flat_multimap.h
@@ -10,18 +10,16 @@
#ifndef _LIBCPP___FLAT_MAP_FLAT_MULTIMAP_H
#define _LIBCPP___FLAT_MAP_FLAT_MULTIMAP_H
+#include <__algorithm/equal_range.h>
#include <__algorithm/lexicographical_compare_three_way.h>
+#include <__algorithm/lower_bound.h>
#include <__algorithm/min.h>
#include <__algorithm/ranges_equal.h>
-#include <__algorithm/ranges_equal_range.h>
#include <__algorithm/ranges_inplace_merge.h>
#include <__algorithm/ranges_is_sorted.h>
-#include <__algorithm/ranges_lower_bound.h>
-#include <__algorithm/ranges_partition_point.h>
#include <__algorithm/ranges_sort.h>
-#include <__algorithm/ranges_unique.h>
-#include <__algorithm/ranges_upper_bound.h>
#include <__algorithm/remove_if.h>
+#include <__algorithm/upper_bound.h>
#include <__assert>
#include <__compare/synth_three_way.h>
#include <__concepts/convertible_to.h>
@@ -443,7 +441,7 @@ class flat_multimap {
is_move_constructible_v<mapped_type>
_LIBCPP_HIDE_FROM_ABI iterator emplace(_Args&&... __args) {
std::pair<key_type, mapped_type> __pair(std::forward<_Args>(__args)...);
- auto __key_it = ranges::upper_bound(__containers_.keys, __pair.first, __compare_);
+ auto __key_it = std::upper_bound(__containers_.keys.begin(), __containers_.keys.end(), __pair.first, __compare_);
auto __mapped_it = __corresponding_mapped_it(*this, __key_it);
return __flat_map_utils::__emplace_exact_pos(
@@ -473,7 +471,7 @@ class flat_multimap {
// |
// hint
// We want to insert "2" after the last existing "2"
- __key_iter = ranges::upper_bound(__containers_.keys.begin(), __key_iter, __pair.first, __compare_);
+ __key_iter = std::upper_bound(__containers_.keys.begin(), __key_iter, __pair.first, __compare_);
__mapped_iter = __corresponding_mapped_it(*this, __key_iter);
} else {
_LIBCPP_ASSERT_INTERNAL(!__prev_larger && __next_smaller, "this means that the multimap is not sorted");
@@ -485,7 +483,7 @@ class flat_multimap {
// |
// hint
// We want to insert "2" before the first existing "2"
- __key_iter = ranges::lower_bound(__key_iter, __containers_.keys.end(), __pair.first, __compare_);
+ __key_iter = std::lower_bound(__key_iter, __containers_.keys.end(), __pair.first, __compare_);
__mapped_iter = __corresponding_mapped_it(*this, __key_iter);
}
return __flat_map_utils::__emplace_exact_pos(
@@ -804,7 +802,8 @@ class flat_multimap {
template <class _Self, class _Kp>
_LIBCPP_HIDE_FROM_ABI static auto __equal_range_impl(_Self&& __self, const _Kp& __key) {
- auto [__key_first, __key_last] = ranges::equal_range(__self.__containers_.keys, __key, __self.__compare_);
+ auto [__key_first, __key_last] =
+ std::equal_range(__self.__containers_.keys.begin(), __self.__containers_.keys.end(), __key, __self.__compare_);
using __iterator_type = ranges::iterator_t<decltype(__self)>;
return std::make_pair(__iterator_type(__key_first, __corresponding_mapped_it(__self, __key_first)),
@@ -813,14 +812,16 @@ class flat_multimap {
template <class _Res, class _Self, class _Kp>
_LIBCPP_HIDE_FROM_ABI static _Res __lower_bound(_Self&& __self, _Kp& __x) {
- auto __key_iter = ranges::lower_bound(__self.__containers_.keys, __x, __self.__compare_);
+ auto __key_iter =
+ std::lower_bound(__self.__containers_.keys.begin(), __self.__containers_.keys.end(), __x, __self.__compare_);
auto __mapped_iter = __corresponding_mapped_it(__self, __key_iter);
return _Res(std::move(__key_iter), std::move(__mapped_iter));
}
template <class _Res, class _Self, class _Kp>
_LIBCPP_HIDE_FROM_ABI static _Res __upper_bound(_Self&& __self, _Kp& __x) {
- auto __key_iter = ranges::upper_bound(__self.__containers_.keys, __x, __self.__compare_);
+ auto __key_iter =
+ std::upper_bound(__self.__containers_.keys.begin(), __self.__containers_.keys.end(), __x, __self.__compare_);
auto __mapped_iter = __corresponding_mapped_it(__self, __key_iter);
return _Res(std::move(__key_iter), std::move(__mapped_iter));
}
diff --git a/libcxx/include/__flat_set/flat_set.h b/libcxx/include/__flat_set/flat_set.h
index dca06c7236e73..b554d7555997e 100644
--- a/libcxx/include/__flat_set/flat_set.h
+++ b/libcxx/include/__flat_set/flat_set.h
@@ -16,7 +16,6 @@
#include <__algorithm/ranges_adjacent_find.h>
#include <__algorithm/ranges_equal.h>
#include <__algorithm/ranges_inplace_merge.h>
-#include <__algorithm/ranges_partition_point.h>
#include <__algorithm/ranges_sort.h>
#include <__algorithm/ranges_unique.h>
#include <__algorithm/remove_if.h>
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
index 456f12e0c0d29..dd9f6da2dda71 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
@@ -106,6 +106,13 @@ int main(int, char**) {
TEST_IGNORE_NODISCARD m.at(Transparent<int>{3});
assert(transparent_used);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ int& x = m.at("alpha");
+ assert(x == 1);
+ }
return 0;
}
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_transparent.pass.cpp
index 24c08464f3158..3a18990123553 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_transparent.pass.cpp
@@ -94,6 +94,13 @@ int main(int, char**) {
m[ConvertibleTransparent<int>{3}];
assert(transparent_used);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ int& x = m["alpha"];
+ assert(x == 1);
+ }
{
auto index_func = [](auto& m, auto key_arg, auto value_arg) {
using FlatMap = std::decay_t<decltype(m)>;
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key_transparent.pass.cpp
index 3ba30757bf2c7..20e23dc085ffd 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key_transparent.pass.cpp
@@ -139,6 +139,13 @@ int main(int, char**) {
};
test_erase_exception_guarantee(erase_transparent);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ auto n = m.erase("beta");
+ assert(n == 1);
+ }
return 0;
}
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign_transparent.pass.cpp
index 636c4edfe551d..3a1e9eb7482b0 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign_transparent.pass.cpp
@@ -254,6 +254,18 @@ int main(int, char**) {
};
test_emplace_exception_guarantee(insert_or_assign_iter);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ auto [it, inserted] = m.insert_or_assign("alpha", 2);
+ assert(!inserted);
+ assert(it == m.begin());
+ assert(it->second == 2);
+ auto it2 = m.insert_or_assign(m.begin(), "beta2", 2);
+ assert(it2 == m.begin() + 2);
+ assert(it2->second == 2);
+ }
return 0;
}
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_transparent.pass.cpp
index 75cabb70630f3..b6a2abe5e5e01 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_transparent.pass.cpp
@@ -163,5 +163,15 @@ int main(int, char**) {
};
test_emplace_exception_guarantee(insert_func_iter);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ auto [it, inserted] = m.insert({"alpha", 1});
+ assert(!inserted);
+ assert(it == m.begin());
+ auto it2 = m.insert(m.begin(), {"beta2", 2});
+ assert(it2 == m.begin() + 2);
+ }
return 0;
}
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace_transparent.pass.cpp
index 21fda43780967..b8dd590ac808e 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace_transparent.pass.cpp
@@ -160,6 +160,17 @@ int main(int, char**) {
assert(p->second == 3);
assert(transparent_used);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ auto [it1, inserted] = m.try_emplace("charlie", 4);
+ assert(it1 == m.begin() + 2);
+ assert(inserted);
+
+ auto it2 = m.try_emplace(m.begin(), "beta2", 2);
+ assert(it2 == m.begin() + 2);
+ }
{
auto try_emplace = [](auto& m, auto key_arg, auto value_arg) {
using M = std::decay_t<decltype(m)>;
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains_transparent.pass.cpp
index 0493538ab6dad..46863681ae6ef 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains_transparent.pass.cpp
@@ -14,6 +14,7 @@
#include <cassert>
#include <flat_map>
+#include <functional>
#include <string>
#include <utility>
#include <deque>
@@ -67,5 +68,12 @@ int main(int, char**) {
assert(b);
assert(transparent_used);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ assert(m.contains("beta") == true);
+ assert(m.contains("charlie") == false);
+ }
return 0;
}
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count_transparent.pass.cpp
index cd195ff1fa8b4..946ded0b1cfab 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count_transparent.pass.cpp
@@ -15,6 +15,7 @@
#include <cassert>
#include <deque>
#include <flat_map>
+#include <functional>
#include <string>
#include <utility>
@@ -67,6 +68,13 @@ int main(int, char**) {
assert(n == 1);
assert(transparent_used);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ assert(m.count("alpha") == 1);
+ assert(m.count("charlie") == 0);
+ }
return 0;
}
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range_transparent.pass.cpp
index 0198f433bdc4f..9d623823d430e 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range_transparent.pass.cpp
@@ -16,6 +16,7 @@
#include <cassert>
#include <deque>
#include <flat_map>
+#include <functional>
#include <string>
#include <utility>
@@ -95,6 +96,14 @@ int main(int, char**) {
assert(p.first != p.second);
assert(transparent_used);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ auto [first, last] = m.equal_range("beta");
+ assert(first == m.begin() + 1);
+ assert(last == m.begin() + 2);
+ }
return 0;
}
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find_transparent.pass.cpp
index 291577a89fc8f..249732b757662 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find_transparent.pass.cpp
@@ -16,6 +16,7 @@
#include <cassert>
#include <deque>
#include <flat_map>
+#include <functional>
#include <string>
#include <utility>
@@ -83,6 +84,13 @@ int main(int, char**) {
assert(it != m.end());
assert(transparent_used);
}
+ {
+ // std::string and C string literal
+ using M = std::flat_map<std::string, int, std::less<>>;
+ M m{{"alpha", 1}, {"beta", 2}, {"epsilon", 1}, {"eta", 3}, {"gamma", 3}};
+ auto it = m.find("beta");
+ assert(it == m.begin() + 1);
+ }
return 0;
}
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound_transparent.pass.cpp
in...
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|
frederick-vs-ja
approved these changes
Apr 13, 2025
ldionne
approved these changes
May 30, 2025
libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
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Jun 14, 2025
) See discussion in https://cplusplus.github.io/LWG/issue4239 std::flat_map<std::string, int, std::less<>> m; m.try_emplace("abc", 5); // hard error The reason is that we specify in 23.6.8.7 [flat.map.modifiers]/p21 the effect to be as if `ranges::upper_bound` is called. `ranges::upper_bound` requires indirect_strict_weak_order, which requires the comparator to be invocable for all combinations. In this case, it requires const char (&)[4] < const char (&)[4] to be well-formed, which is no longer the case in C++26 after https://wg21.link/P2865R6. This patch uses `std::upper_bound` instead.
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See discussion in https://cplusplus.github.io/LWG/issue4239
The reason is that we specify in 23.6.8.7 [flat.map.modifiers] p21 the effect to be as if
ranges::upper_boundis called.ranges::upper_boundrequires indirect_strict_weak_order, which requires the comparator to be invocable for all combinations. In this case, it requiresconst char (&)[4] < const char (&)[4]to be well-formed, which is no longer the case in C++26 after P2865R6.
We should just use
std::upper_boundinstead.