[libc++] P2944R3: Constrained comparisions - tuple

libcxx/include/tuple

@@ -216,6 +216,7 @@ template <class... Types>
 #  include <__compare/common_comparison_category.h>
 #  include <__compare/ordering.h>
 #  include <__compare/synth_three_way.h>
+#  include <__concepts/boolean_testable.h>
 #  include <__config>
 #  include <__cstddef/size_t.h>
 #  include <__fwd/array.h>
@@ -1153,6 +1154,11 @@ struct __tuple_equal<0> {
 };
 
 template <class... _Tp, class... _Up>
+#    if _LIBCPP_STD_VER >= 26
+  requires(__all<requires(const _Tp& __t, const _Up& __u) {
+             { __t == __u } -> __boolean_testable;
+           }...>::value && (sizeof...(_Tp) == sizeof...(_Up)))
+#    endif
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 operator==(const tuple<_Tp...>& __x, const tuple<_Up...>& __y) {
   static_assert(sizeof...(_Tp) == sizeof...(_Up), "Can't compare tuples of different sizes");

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

@@ -16,12 +16,33 @@
 
 // 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