[libcxx-commits] [libcxx] [libc++] Implement LWG4072: std::optional comparisons: constrain harder (PR #209968)
Dan Shan via libcxx-commits
libcxx-commits at lists.llvm.org
Sun Aug 2 06:47:56 PDT 2026
https://github.com/HumanThe2nd updated https://github.com/llvm/llvm-project/pull/209968
>From 246e54199dca725addfb8c4d8ea5c446bd7801b2 Mon Sep 17 00:00:00 2001
From: Dan <danielshan824 at gmail.com>
Date: Fri, 31 Jul 2026 09:06:01 -0400
Subject: [PATCH] [libc++][optional] Constrain heterogeneous comparison
operators for nested optional
---
libcxx/include/__optional/comparison.h | 65 ++++++++++++-------
.../optional.comp_with_t/equal.pass.cpp | 3 +
.../optional.comp_with_t/greater.pass.cpp | 3 +
.../greater_equal.pass.cpp | 3 +
.../optional.comp_with_t/less_equal.pass.cpp | 3 +
.../optional.comp_with_t/less_than.pass.cpp | 3 +
.../optional.comp_with_t/not_equal.pass.cpp | 3 +
7 files changed, 59 insertions(+), 24 deletions(-)
diff --git a/libcxx/include/__optional/comparison.h b/libcxx/include/__optional/comparison.h
index ba5cddb1acbfb..20e7c68632ce2 100644
--- a/libcxx/include/__optional/comparison.h
+++ b/libcxx/include/__optional/comparison.h
@@ -13,6 +13,7 @@
#include <__compare/ordering.h>
#include <__compare/three_way_comparable.h>
#include <__config>
+#include <__optional/common.h>
#include <__optional/nullopt_t.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/is_constructible.h>
@@ -201,7 +202,8 @@ _LIBCPP_HIDE_FROM_ABI constexpr strong_ordering operator<=>(const optional<_Tp>&
template <
class _Tp,
class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>,
+ enable_if_t<!__is_std_optional_v<_Up> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>,
int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const optional<_Tp>& __x, const _Up& __v) {
if (__x.has_value())
@@ -212,7 +214,8 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const optional<_Tp>& __x, const
template <
class _Tp,
class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>,
+ enable_if_t<!__is_std_optional_v<_Tp> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() == std::declval<const _Up&>()), bool>,
int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const _Tp& __v, const optional<_Up>& __x) {
if (__x.has_value())
@@ -223,7 +226,8 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const _Tp& __v, const optional<_
template <
class _Tp,
class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>,
+ enable_if_t<!__is_std_optional_v<_Up> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>,
int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const optional<_Tp>& __x, const _Up& __v) {
if (__x.has_value())
@@ -234,7 +238,8 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const optional<_Tp>& __x, const
template <
class _Tp,
class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>,
+ enable_if_t<!__is_std_optional_v<_Tp> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() != std::declval<const _Up&>()), bool>,
int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const _Tp& __v, const optional<_Up>& __x) {
if (__x.has_value())
@@ -242,20 +247,24 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const _Tp& __v, const optional<_
return true;
}
-template < class _Tp,
- class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>,
- int> = 0>
+template <
+ class _Tp,
+ class _Up,
+ enable_if_t<!__is_std_optional_v<_Up> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>,
+ int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const optional<_Tp>& __x, const _Up& __v) {
if (__x.has_value())
return *__x < __v;
return true;
}
-template < class _Tp,
- class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>,
- int> = 0>
+template <
+ class _Tp,
+ class _Up,
+ enable_if_t<!__is_std_optional_v<_Tp> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() < std::declval<const _Up&>()), bool>,
+ int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const _Tp& __v, const optional<_Up>& __x) {
if (__x.has_value())
return __v < *__x;
@@ -265,7 +274,8 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const _Tp& __v, const optional<_U
template <
class _Tp,
class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>,
+ enable_if_t<!__is_std_optional_v<_Up> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>,
int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const optional<_Tp>& __x, const _Up& __v) {
if (__x.has_value())
@@ -276,7 +286,8 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const optional<_Tp>& __x, const
template <
class _Tp,
class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>,
+ enable_if_t<!__is_std_optional_v<_Tp> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() <= std::declval<const _Up&>()), bool>,
int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const _Tp& __v, const optional<_Up>& __x) {
if (__x.has_value())
@@ -284,20 +295,24 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const _Tp& __v, const optional<_
return false;
}
-template < class _Tp,
- class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>,
- int> = 0>
+template <
+ class _Tp,
+ class _Up,
+ enable_if_t<!__is_std_optional_v<_Up> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>,
+ int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const optional<_Tp>& __x, const _Up& __v) {
if (__x.has_value())
return *__x > __v;
return false;
}
-template < class _Tp,
- class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>,
- int> = 0>
+template <
+ class _Tp,
+ class _Up,
+ enable_if_t<!__is_std_optional_v<_Tp> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() > std::declval<const _Up&>()), bool>,
+ int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const _Tp& __v, const optional<_Up>& __x) {
if (__x.has_value())
return __v > *__x;
@@ -307,7 +322,8 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const _Tp& __v, const optional<_U
template <
class _Tp,
class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>,
+ enable_if_t<!__is_std_optional_v<_Up> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>,
int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const optional<_Tp>& __x, const _Up& __v) {
if (__x.has_value())
@@ -318,7 +334,8 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const optional<_Tp>& __x, const
template <
class _Tp,
class _Up,
- enable_if_t<__is_core_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>,
+ enable_if_t<!__is_std_optional_v<_Tp> &&
+ __is_core_convertible_v<decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()), bool>,
int> = 0>
_LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const _Tp& __v, const optional<_Up>& __x) {
if (__x.has_value())
diff --git a/libcxx/test/std/utilities/optional/optional.comp_with_t/equal.pass.cpp b/libcxx/test/std/utilities/optional/optional.comp_with_t/equal.pass.cpp
index 54965b270dcce..1a3c9b7b869fe 100644
--- a/libcxx/test/std/utilities/optional/optional.comp_with_t/equal.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.comp_with_t/equal.pass.cpp
@@ -35,6 +35,9 @@ static_assert(HasOperatorEqual<std::optional<EqualityComparable>, EqualityCompar
static_assert(!HasOperatorEqual<std::optional<NonComparable>, NonComparable>);
static_assert(!HasOperatorEqual<std::optional<EqualityComparable>, NonComparable>);
+static_assert(!HasOperatorEqual<std::optional<void*>, std::optional<int>>);
+static_assert(!HasOperatorEqual<std::optional<int>, std::optional<void*>>);
+
#endif
using std::optional;
diff --git a/libcxx/test/std/utilities/optional/optional.comp_with_t/greater.pass.cpp b/libcxx/test/std/utilities/optional/optional.comp_with_t/greater.pass.cpp
index b63b85b000930..919cda73d88a3 100644
--- a/libcxx/test/std/utilities/optional/optional.comp_with_t/greater.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.comp_with_t/greater.pass.cpp
@@ -34,6 +34,9 @@ static_assert(!HasOperatorGreaterThan<NonComparable, std::optional<NonComparable
static_assert(!HasOperatorGreaterThan<NonComparable, std::optional<ThreeWayComparable>>);
static_assert(!HasOperatorGreaterThan<ThreeWayComparable, std::optional<NonComparable>>);
+static_assert(!HasOperatorGreaterThan<std::optional<void*>, std::optional<int>>);
+static_assert(!HasOperatorGreaterThan<std::optional<int>, std::optional<void*>>);
+
#endif
using std::optional;
diff --git a/libcxx/test/std/utilities/optional/optional.comp_with_t/greater_equal.pass.cpp b/libcxx/test/std/utilities/optional/optional.comp_with_t/greater_equal.pass.cpp
index bb1a8c551d3d5..d8626203f3b3c 100644
--- a/libcxx/test/std/utilities/optional/optional.comp_with_t/greater_equal.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.comp_with_t/greater_equal.pass.cpp
@@ -34,6 +34,9 @@ static_assert(!HasOperatorGreaterThanEqual<NonComparable, std::optional<NonCompa
static_assert(!HasOperatorGreaterThanEqual<NonComparable, std::optional<ThreeWayComparable>>);
static_assert(!HasOperatorGreaterThanEqual<ThreeWayComparable, std::optional<NonComparable>>);
+static_assert(!HasOperatorGreaterThanEqual<std::optional<void*>, std::optional<int>>);
+static_assert(!HasOperatorGreaterThanEqual<std::optional<int>, std::optional<void*>>);
+
#endif
using std::optional;
diff --git a/libcxx/test/std/utilities/optional/optional.comp_with_t/less_equal.pass.cpp b/libcxx/test/std/utilities/optional/optional.comp_with_t/less_equal.pass.cpp
index 8b08ec3deea5a..45c5a050ecab9 100644
--- a/libcxx/test/std/utilities/optional/optional.comp_with_t/less_equal.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.comp_with_t/less_equal.pass.cpp
@@ -34,6 +34,9 @@ static_assert(!HasOperatorLessThanEqual<NonComparable, std::optional<NonComparab
static_assert(!HasOperatorLessThanEqual<NonComparable, std::optional<ThreeWayComparable>>);
static_assert(!HasOperatorLessThanEqual<ThreeWayComparable, std::optional<NonComparable>>);
+static_assert(!HasOperatorLessThanEqual<std::optional<void*>, std::optional<int>>);
+static_assert(!HasOperatorLessThanEqual<std::optional<int>, std::optional<void*>>);
+
#endif
using std::optional;
diff --git a/libcxx/test/std/utilities/optional/optional.comp_with_t/less_than.pass.cpp b/libcxx/test/std/utilities/optional/optional.comp_with_t/less_than.pass.cpp
index 3ef23a3224520..1933fb80796ae 100644
--- a/libcxx/test/std/utilities/optional/optional.comp_with_t/less_than.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.comp_with_t/less_than.pass.cpp
@@ -34,6 +34,9 @@ static_assert(!HasOperatorLessThan<NonComparable, std::optional<NonComparable>>)
static_assert(!HasOperatorLessThan<NonComparable, std::optional<ThreeWayComparable>>);
static_assert(!HasOperatorLessThan<ThreeWayComparable, std::optional<NonComparable>>);
+static_assert(!HasOperatorLessThan<std::optional<void*>, std::optional<int>>);
+static_assert(!HasOperatorLessThan<std::optional<int>, std::optional<void*>>);
+
#endif
using std::optional;
diff --git a/libcxx/test/std/utilities/optional/optional.comp_with_t/not_equal.pass.cpp b/libcxx/test/std/utilities/optional/optional.comp_with_t/not_equal.pass.cpp
index 97fb8ee447393..a272ecb2cc9c7 100644
--- a/libcxx/test/std/utilities/optional/optional.comp_with_t/not_equal.pass.cpp
+++ b/libcxx/test/std/utilities/optional/optional.comp_with_t/not_equal.pass.cpp
@@ -35,6 +35,9 @@ static_assert(HasOperatorNotEqual<std::optional<EqualityComparable>, EqualityCom
static_assert(!HasOperatorNotEqual<std::optional<NonComparable>, NonComparable>);
static_assert(!HasOperatorNotEqual<std::optional<EqualityComparable>, NonComparable>);
+static_assert(!HasOperatorNotEqual<std::optional<void*>, std::optional<int>>);
+static_assert(!HasOperatorNotEqual<std::optional<int>, std::optional<void*>>);
+
#endif
using std::optional;
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