WIP [libc++]P2944R3: Constrained comparisions - variant and tuple

libcxx/include/tuple

@@ -1161,9 +1161,16 @@ struct __tuple_equal<0> {
 };
 
 template <class... _Tp, class... _Up>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Tp& __t, const _Up& __u) {
+            { __t == __u } -> __boolean_testable;
+          } && ...) && (sizeof...(_Tp) == sizeof...(_Up))
+#    endif
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 operator==(const tuple<_Tp...>& __x, const tuple<_Up...>& __y) {
+#    if _LIBCPP_STD_VER < 26
   static_assert(sizeof...(_Tp) == sizeof...(_Up), "Can't compare tuples of different sizes");
+#    endif
   return __tuple_equal<sizeof...(_Tp)>()(__x, __y);
 }
 

libcxx/include/variant

@@ -242,6 +242,7 @@ namespace std {
 #  include <__type_traits/is_assignable.h>
 #  include <__type_traits/is_constructible.h>
 #  include <__type_traits/is_convertible.h>
+#  include <__type_traits/is_core_convertible.h>
 #  include <__type_traits/is_destructible.h>
 #  include <__type_traits/is_nothrow_assignable.h>
 #  include <__type_traits/is_nothrow_constructible.h>
@@ -1453,6 +1454,11 @@ struct __convert_to_bool {
 };
 
 template <class... _Types>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t == __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
 _LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const variant<_Types...>& __lhs, const variant<_Types...>& __rhs) {
   using __variant_detail::__visitation::__variant;
   if (__lhs.index() != __rhs.index())
@@ -1485,6 +1491,11 @@ operator<=>(const variant<_Types...>& __lhs, const variant<_Types...>& __rhs) {
 #    endif // _LIBCPP_STD_VER >= 20
 
 template <class... _Types>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t != __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
 _LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const variant<_Types...>& __lhs, const variant<_Types...>& __rhs) {
   using __variant_detail::__visitation::__variant;
   if (__lhs.index() != __rhs.index())
@@ -1495,6 +1506,11 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator!=(const variant<_Types...>& __lhs,
 }
 
 template <class... _Types>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t < __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
 _LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const variant<_Types...>& __lhs, const variant<_Types...>& __rhs) {
   using __variant_detail::__visitation::__variant;
   if (__rhs.valueless_by_exception())
@@ -1509,6 +1525,11 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const variant<_Types...>& __lhs,
 }
 
 template <class... _Types>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t > __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
 _LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const variant<_Types...>& __lhs, const variant<_Types...>& __rhs) {
   using __variant_detail::__visitation::__variant;
   if (__lhs.valueless_by_exception())
@@ -1523,6 +1544,11 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const variant<_Types...>& __lhs,
 }
 
 template <class... _Types>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t <= __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
 _LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const variant<_Types...>& __lhs, const variant<_Types...>& __rhs) {
   using __variant_detail::__visitation::__variant;
   if (__lhs.valueless_by_exception())
@@ -1537,6 +1563,11 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const variant<_Types...>& __lhs,
 }
 
 template <class... _Types>
+#    if _LIBCPP_STD_VER >= 26
+  requires(requires(const _Types& __t) {
+    { __t >= __t } -> __core_convertible_to<bool>;
+  } && ...)
+#    endif
 _LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const variant<_Types...>& __lhs, const variant<_Types...>& __rhs) {
   using __variant_detail::__visitation::__variant;
   if (__rhs.valueless_by_exception())

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.rel/eq.pass.cpp

@@ -16,12 +16,31 @@
 
 // UNSUPPORTED: c++03
 
-#include <tuple>
-#include <string>
+#include <array>
 #include <cassert>
+#include <tuple>
 
+#include "test_comparisons.h"
 #include "test_macros.h"
 
+#if TEST_STD_VER >= 26
+
+// Test SFINAE.
+
+static_assert(std::equality_comparable<std::tuple<EqualityComparable>>);
+static_assert(std::equality_comparable<std::tuple<EqualityComparable, EqualityComparable>>);
+
+static_assert(!std::equality_comparable<std::tuple<NonComparable>>);
+static_assert(!std::equality_comparable<std::tuple<EqualityComparable, NonComparable>>);
+static_assert(!std::equality_comparable<std::tuple<NonComparable, EqualityComparable>>);
+static_assert(!std::equality_comparable_with<std::tuple<EqualityComparable>, std::tuple<NonComparable>>);
+static_assert(!std::equality_comparable_with<std::tuple<NonComparable>, std::tuple<EqualityComparable>>);
+// Size mismatch.
+static_assert(!std::equality_comparable_with<std::tuple<EqualityComparable>, std::tuple<EqualityComparable, EqualityComparable>>);
+static_assert(!std::equality_comparable_with<std::tuple<EqualityComparable, EqualityComparable>, std::tuple<EqualityComparable>>);
+
+#endif
+
 int main(int, char**)
 {
     {

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.rel/size_incompatible_comparison.verify.cpp

@@ -21,9 +21,15 @@
 
 #include <tuple>
 
+#include "test_macros.h"
+
+#if TEST_STD_VER >= 26
+// expected-no-diagnostics
+#else
 void f(std::tuple<int> t1, std::tuple<int, long> t2) {
   // We test only the core comparison operators and trust that the others
   // fall back on the same implementations prior to C++20.
   static_cast<void>(t1 == t2); // expected-error@*:* {{}}
   static_cast<void>(t1 < t2); // expected-error@*:* {{}}
 }
+#endif

libcxx/test/std/utilities/variant/variant.relops/relops.pass.cpp

@@ -39,8 +39,57 @@
 #include <utility>
 #include <variant>
 
+#include "test_comparisons.h"
 #include "test_macros.h"
 
+#if TEST_STD_VER >= 26
+
+// Test SFINAE.
+
+// ==
+static_assert(HasOperatorEqual<std::variant<EqualityComparable>>);
+static_assert(HasOperatorEqual<std::variant<EqualityComparable, int, long>>);
+
+static_assert(!HasOperatorEqual<std::variant<NonComparable>>);
+static_assert(!HasOperatorEqual<std::variant<NonComparable, EqualityComparable>>);
+
+// >
+static_assert(HasOperatorGreaterThan<std::variant<ThreeWayComparable>>);
+static_assert(HasOperatorGreaterThan<std::variant<ThreeWayComparable, int, long>>);
+
+static_assert(!HasOperatorGreaterThan<std::variant<NonComparable>>);
+static_assert(!HasOperatorGreaterThan<std::variant<NonComparable, ThreeWayComparable>>);
+
+// >=
+static_assert(HasOperatorGreaterThanEqual<std::variant<ThreeWayComparable>>);
+static_assert(HasOperatorGreaterThanEqual<std::variant<ThreeWayComparable, int, long>>);
+
+static_assert(!HasOperatorGreaterThanEqual<std::variant<NonComparable>>);
+static_assert(!HasOperatorGreaterThanEqual<std::variant<NonComparable, ThreeWayComparable>>);
+
+// <
+static_assert(HasOperatorLessThan<std::variant<ThreeWayComparable>>);
+static_assert(HasOperatorLessThan<std::variant<ThreeWayComparable, int, long>>);
+
+static_assert(!HasOperatorLessThan<std::variant<NonComparable>>);
+static_assert(!HasOperatorLessThan<std::variant<NonComparable, ThreeWayComparable>>);
+
+// <=
+static_assert(HasOperatorLessThanEqual<std::variant<ThreeWayComparable>>);
+static_assert(HasOperatorLessThanEqual<std::variant<ThreeWayComparable, int, long>>);
+
+static_assert(!HasOperatorLessThanEqual<std::variant<NonComparable>>);
+static_assert(!HasOperatorLessThanEqual<std::variant<NonComparable, ThreeWayComparable>>);
+
+// !=
+static_assert(HasOperatorNotEqual<std::variant<EqualityComparable>>);
+static_assert(HasOperatorNotEqual<std::variant<EqualityComparable, int, long>>);
+
+static_assert(!HasOperatorNotEqual<std::variant<NonComparable>>);
+static_assert(!HasOperatorNotEqual<std::variant<NonComparable, EqualityComparable>>);
+
+#endif
+
 #ifndef TEST_HAS_NO_EXCEPTIONS
 struct MakeEmptyT {
   MakeEmptyT() = default;

libcxx/test/support/test_comparisons.h

@@ -268,6 +268,70 @@ struct PartialOrder {
   }
 };
 
-#endif
+template <typename T1, typename T2 = T1>
+concept HasOperatorEqual = requires(T1 t1, T2 t2) { t1 == t2; };
+
+template <typename T1, typename T2 = T1>
+concept HasOperatorGreaterThan = requires(T1 t1, T2 t2) { t1 > t2; };
+
+template <typename T1, typename T2 = T1>
+concept HasOperatorGreaterThanEqual = requires(T1 t1, T2 t2) { t1 >= t2; };
+template <typename T1, typename T2 = T1>
+concept HasOperatorLessThan = requires(T1 t1, T2 t2) { t1 < t2; };
+
+template <typename T1, typename T2 = T1>
+concept HasOperatorLessThanEqual = requires(T1 t1, T2 t2) { t1 <= t2; };
+
+template <typename T1, typename T2 = T1>
+concept HasOperatorNotEqual = requires(T1 t1, T2 t2) { t1 != t2; };
+
+template <typename T1, typename T2 = T1>
+concept HasOperatorSpaceship = requires(T1 t1, T2 t2) { t1 <=> t2; };
+
+struct NonComparable {};
+static_assert(!std::equality_comparable<NonComparable>);
+static_assert(!HasOperatorEqual<NonComparable>);
+static_assert(!HasOperatorGreaterThan<NonComparable>);
+static_assert(!HasOperatorGreaterThanEqual<NonComparable>);
+static_assert(!HasOperatorLessThan<NonComparable>);
+static_assert(!HasOperatorLessThanEqual<NonComparable>);
+static_assert(!HasOperatorNotEqual<NonComparable>);
+static_assert(!HasOperatorSpaceship<NonComparable>);
+
+class EqualityComparable {
+public:
+  constexpr EqualityComparable(int value) : value_{value} {};
+
+  friend constexpr bool operator==(const EqualityComparable&, const EqualityComparable&) noexcept = default;
+
+private:
+  int value_;
+};
+static_assert(std::equality_comparable<EqualityComparable>);
+static_assert(HasOperatorEqual<EqualityComparable>);
+static_assert(HasOperatorNotEqual<EqualityComparable>);
+
+class ThreeWayComparable {
+public:
+  constexpr ThreeWayComparable(int value) : value_{value} {};
+
+  friend constexpr bool operator==(const ThreeWayComparable&, const ThreeWayComparable&) noexcept = default;
+  friend constexpr std::strong_ordering
+  operator<=>(const ThreeWayComparable&, const ThreeWayComparable&) noexcept = default;
+
+private:
+  int value_;
+};
+static_assert(std::equality_comparable<ThreeWayComparable>);
+static_assert(std::three_way_comparable<ThreeWayComparable>);
+static_assert(HasOperatorEqual<ThreeWayComparable>);
+static_assert(HasOperatorGreaterThan<ThreeWayComparable>);
+static_assert(HasOperatorGreaterThanEqual<ThreeWayComparable>);
+static_assert(HasOperatorLessThan<ThreeWayComparable>);
+static_assert(HasOperatorLessThanEqual<ThreeWayComparable>);
+static_assert(HasOperatorNotEqual<ThreeWayComparable>);
+static_assert(HasOperatorSpaceship<ThreeWayComparable>);
+
+#endif // TEST_STD_VER >= 20
 
 #endif // TEST_COMPARISONS_H