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[libc++] Introduce __core_convertible_to and make this paper as a C++26 feature
Signed-off-by: yronglin <[email protected]>
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‎libcxx/include/CMakeLists.txt‎

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@@ -307,6 +307,7 @@ set(files
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__concepts/constructible.h
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__concepts/convertible_to.h
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__concepts/copyable.h
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__concepts/core_convertible_to.h
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__concepts/derived_from.h
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__concepts/destructible.h
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__concepts/different_from.h

‎libcxx/include/__concepts/core_convertible_to.h‎

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#ifndef _LIBCPP___CONCEPTS_CORE_CONVERTIBLE_TO_H
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#define _LIBCPP___CONCEPTS_CORE_CONVERTIBLE_TO_H
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#include <__config>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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#if _LIBCPP_STD_VER >= 20
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// [conv.general]/3 says "E is convertible to T" whenever "T t=E;" is well-formed.
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// We can't test for that, but we can test implicit convertibility by passing it
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// to a function. Unlike std::convertible_to, __core_convertible_to doesn't test
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// static_cast or handle cv void, while accepting move-only types.
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//
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// This is a conceptual __is_core_convertible.
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template <class _Tp, class _Up>
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concept __core_convertible_to = requires {
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// rejects function and array types which are adjusted to pointer types in parameter lists
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static_cast<_Up (*)()>(nullptr)();
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static_cast<void (*)(_Up)>(nullptr)(static_cast<_Tp (*)()>(nullptr)());
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};
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#endif
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___CONCEPTS_CORE_CONVERTIBLE_TO_H

‎libcxx/include/__cxx03/module.modulemap‎

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@@ -1190,6 +1190,7 @@ module cxx03_std_private_concepts_constructible [system] {
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}
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module cxx03_std_private_concepts_convertible_to [system] { header "__concepts/convertible_to.h" }
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module cxx03_std_private_concepts_copyable [system] { header "__concepts/copyable.h" }
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module cxx03_std_private_concepts_core_convertible_to [system] { header "__concepts/core_convertible_to.h" }
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module cxx03_std_private_concepts_derived_from [system] { header "__concepts/derived_from.h" }
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module cxx03_std_private_concepts_destructible [system] {
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header "__concepts/destructible.h"

‎libcxx/include/__expected/expected.h‎

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@@ -10,7 +10,7 @@
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#define _LIBCPP___EXPECTED_EXPECTED_H
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#include <__assert>
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#include <__concepts/boolean_testable.h>
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#include <__concepts/core_convertible_to.h>
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#include <__config>
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#include <__expected/bad_expected_access.h>
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#include <__expected/unexpect.h>
@@ -1141,10 +1141,13 @@ class expected : private __expected_base<_Tp, _Err> {
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// [expected.object.eq], equality operators
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template <class _T2, class _E2>
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_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const expected<_T2, _E2>& __y)
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requires(!is_void_v<_T2>) && requires {
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{ *__x == *__y } -> __boolean_testable;
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{ __x.error() == __y.error() } -> __boolean_testable;
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}
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requires(!is_void_v<_T2>)
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# if _LIBCPP_STD_VER >= 26
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&& requires {
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{ *__x == *__y } -> __core_convertible_to<bool>;
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{ __x.error() == __y.error() } -> __core_convertible_to<bool>;
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}
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# endif
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{
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if (__x.__has_val() != __y.__has_val()) {
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return false;
@@ -1159,18 +1162,22 @@ class expected : private __expected_base<_Tp, _Err> {
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template <class _T2>
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_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const _T2& __v)
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# if _LIBCPP_STD_VER >= 26
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requires(!__is_std_expected<_T2>::value) && requires {
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{ *__x == __v } -> __boolean_testable;
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{ *__x == __v } -> __core_convertible_to<bool>;
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}
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# endif
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{
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return __x.__has_val() && static_cast<bool>(__x.__val() == __v);
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}
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template <class _E2>
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_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const unexpected<_E2>& __e)
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# if _LIBCPP_STD_VER >= 26
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requires requires {
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{ __x.error() == __e.error() } -> __boolean_testable;
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{ __x.error() == __e.error() } -> __core_convertible_to<bool>;
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}
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# endif
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{
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return !__x.__has_val() && static_cast<bool>(__x.__unex() == __e.error());
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}
@@ -1865,9 +1872,12 @@ class expected<_Tp, _Err> : private __expected_void_base<_Err> {
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template <class _T2, class _E2>
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requires is_void_v<_T2>
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_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const expected<_T2, _E2>& __y)
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# if _LIBCPP_STD_VER >= 26
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requires requires {
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{ __x.error() == __y.error() } -> __boolean_testable;
1878+
{ __x.error() == __y.error() } -> __core_convertible_to<bool>;
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}
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# endif
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{
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if (__x.__has_val() != __y.__has_val()) {
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return false;
@@ -1878,9 +1888,12 @@ class expected<_Tp, _Err> : private __expected_void_base<_Err> {
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template <class _E2>
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_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const unexpected<_E2>& __y)
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# if _LIBCPP_STD_VER >= 26
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requires requires {
1882-
{ __x.error() == __y.error() } -> __boolean_testable;
1894+
{ __x.error() == __y.error() } -> __core_convertible_to<bool>;
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}
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# endif
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{
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return !__x.__has_val() && static_cast<bool>(__x.__unex() == __y.error());
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}

‎libcxx/include/module.modulemap.in‎

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@@ -1075,6 +1075,7 @@ module std [system] {
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module constructible { header "__concepts/constructible.h" }
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module convertible_to { header "__concepts/convertible_to.h" }
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module copyable { header "__concepts/copyable.h" }
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module core_convertible_to { header "__concepts/core_convertible_to.h" }
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module derived_from { header "__concepts/derived_from.h" }
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module destructible { header "__concepts/destructible.h" }
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module different_from { header "__concepts/different_from.h" }

‎libcxx/test/std/utilities/expected/expected.expected/equality/equality.T2.pass.cpp‎

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#include "test_macros.h"
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#include "../../types.h"
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#if TEST_STD_VER >= 26
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// https://wg21.link/P3379R0
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static_assert(CanCompare<std::expected<int, int>, int>);
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static_assert(CanCompare<std::expected<int, int>, EqualityComparable>);
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static_assert(!CanCompare<std::expected<int, int>, NonComparable>);
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#endif
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constexpr bool test() {
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// x.has_value()

‎libcxx/test/std/utilities/expected/expected.expected/equality/equality.other_expected.pass.cpp‎

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@@ -26,14 +26,18 @@ static_assert(!CanCompare<NonComparable, NonComparable>);
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static_assert(CanCompare<std::expected<int, int>, std::expected<int, int>>);
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static_assert(CanCompare<std::expected<int, int>, std::expected<short, short>>);
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#if TEST_STD_VER >= 26
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// https://wg21.link/P3379R0
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static_assert(!CanCompare<std::expected<int, int>, std::expected<void, int>>);
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static_assert(CanCompare<std::expected<int, int>, std::expected<int, int>>);
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static_assert(!CanCompare<std::expected<NonComparable, int>, std::expected<NonComparable, int>>);
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static_assert(!CanCompare<std::expected<int, NonComparable>, std::expected<int, NonComparable>>);
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static_assert(!CanCompare<std::expected<NonComparable, int>, std::expected<int, NonComparable>>);
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static_assert(!CanCompare<std::expected<int, NonComparable>, std::expected<NonComparable, int>>);
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#else
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// Note this is true because other overloads in expected<non-void> are unconstrained
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static_assert(CanCompare<std::expected<void, int>, std::expected<int, int>>);
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#endif
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constexpr bool test() {
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// x.has_value() && y.has_value()
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{

‎libcxx/test/std/utilities/expected/expected.expected/equality/equality.unexpected.pass.cpp‎

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#include "test_macros.h"
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#include "../../types.h"
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#if TEST_STD_VER >= 26
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// https://wg21.link/P3379R0
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static_assert(CanCompare<std::expected<EqualityComparable, EqualityComparable>, std::unexpected<int>>);
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static_assert(CanCompare<std::expected<EqualityComparable, int>, std::unexpected<EqualityComparable>>);
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static_assert(!CanCompare<std::expected<EqualityComparable, NonComparable>, std::unexpected<int>>);
27+
#endif
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constexpr bool test() {
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// x.has_value()

‎libcxx/test/std/utilities/expected/expected.void/equality/equality.other_expected.pass.cpp‎

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@@ -26,13 +26,18 @@ static_assert(!CanCompare<Foo, Foo>);
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static_assert(CanCompare<std::expected<void, int>, std::expected<void, int>>);
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static_assert(CanCompare<std::expected<void, int>, std::expected<void, short>>);
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#if TEST_STD_VER >= 26
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// https://wg21.link/P3379R0
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static_assert(!CanCompare<std::expected<void, int>, std::expected<int, int>>);
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static_assert(CanCompare<std::expected<void, int>, std::expected<void, int>>);
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static_assert(CanCompare<std::expected<void, int>, std::expected<void, int>>);
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static_assert(!CanCompare<std::expected<void, NonComparable>, std::expected<void, NonComparable>>);
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static_assert(!CanCompare<std::expected<void, int>, std::expected<void, NonComparable>>);
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static_assert(!CanCompare<std::expected<void, NonComparable>, std::expected<void, int>>);
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#else
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// Note this is true because other overloads in expected<non-void> are unconstrained
39+
static_assert(CanCompare<std::expected<void, int>, std::expected<int, int>>);
40+
#endif
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constexpr bool test() {
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// x.has_value() && y.has_value()

‎llvm/utils/gn/secondary/libcxx/include/BUILD.gn‎

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@@ -382,6 +382,7 @@ if (current_toolchain == default_toolchain) {
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"__concepts/constructible.h",
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"__concepts/convertible_to.h",
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"__concepts/copyable.h",
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"__concepts/core_convertible_to.h",
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"__concepts/derived_from.h",
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"__concepts/destructible.h",
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"__concepts/different_from.h",

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