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Implement LWG-3836 std::expected<bool, E1> conversion constructor expected(const expected<U, G>&) should take precedence over expected(U&&) with operator bool #3587

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 6 commits into from
Mar 28, 2023
Merged

Implement LWG-3836 std::expected<bool, E1> conversion constructor expected(const expected<U, G>&) should take precedence over expected(U&&) with operator bool #3587

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4bb5821
Implement LWG-3836 for `optional` and add test coverage
frederick-vs-ja Mar 23, 2023
585e878
Implement LWG-3836 for `expected` and add test coverage
frederick-vs-ja Mar 23, 2023
65a68d9
Missing clang-format
frederick-vs-ja Mar 23, 2023
ca824fa
Fix `optional` test case for C++17
frederick-vs-ja Mar 23, 2023
7e2e1cf
Skip one libc++ test
frederick-vs-ja Mar 23, 2023
92a86f0
Fix copy-pasta
frederick-vs-ja Mar 23, 2023
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21 changes: 12 additions & 9 deletions stl/inc/expected
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Expand Up @@ -238,14 +238,15 @@ public:
// clang-format on

template <class _Uty, class _UErr>
static constexpr bool _Allow_unwrapping = !is_constructible_v<_Ty, expected<_Uty, _UErr>&> //
&& !is_constructible_v<_Ty, expected<_Uty, _UErr>> //
&& !is_constructible_v<_Ty, const expected<_Uty, _UErr>&> //
&& !is_constructible_v<_Ty, const expected<_Uty, _UErr>> //
&& !is_convertible_v<expected<_Uty, _UErr>&, _Ty> //
&& !is_convertible_v<expected<_Uty, _UErr>&&, _Ty> //
&& !is_convertible_v<const expected<_Uty, _UErr>&, _Ty> //
&& !is_convertible_v<const expected<_Uty, _UErr>&&, _Ty> //
static constexpr bool _Allow_unwrapping = disjunction_v<is_same<remove_cv_t<_Ty>, bool>,
negation<disjunction<is_constructible<_Ty, expected<_Uty, _UErr>&>, //
is_constructible<_Ty, expected<_Uty, _UErr>>, //
is_constructible<_Ty, const expected<_Uty, _UErr>&>, //
is_constructible<_Ty, const expected<_Uty, _UErr>>, //
is_convertible<expected<_Uty, _UErr>&, _Ty>, //
is_convertible<expected<_Uty, _UErr>&&, _Ty>, //
is_convertible<const expected<_Uty, _UErr>&, _Ty>, //
is_convertible<const expected<_Uty, _UErr>&&, _Ty>>>> //
&& !is_constructible_v<unexpected<_Err>, expected<_Uty, _UErr>&> //
&& !is_constructible_v<unexpected<_Err>, expected<_Uty, _UErr>> //
&& !is_constructible_v<unexpected<_Err>, const expected<_Uty, _UErr>&> //
Expand Down Expand Up @@ -280,7 +281,9 @@ public:

template <class _Uty = _Ty>
requires (!is_same_v<remove_cvref_t<_Uty>, in_place_t> && !is_same_v<remove_cvref_t<_Uty>, expected>
&& !_Is_specialization_v<remove_cvref_t<_Uty>, unexpected> && is_constructible_v<_Ty, _Uty>)
&& !_Is_specialization_v<remove_cvref_t<_Uty>, unexpected>
&& (!is_same_v<remove_cv_t<_Ty>, bool> || !_Is_specialization_v<remove_cvref_t<_Uty>, expected>)
&& is_constructible_v<_Ty, _Uty>)
constexpr explicit(!is_convertible_v<_Uty, _Ty>)
expected(_Uty&& _Other) noexcept(is_nothrow_constructible_v<_Ty, _Uty>) // strengthened
: _Value(_STD forward<_Uty>(_Other)), _Has_value(true) {}
Expand Down
16 changes: 10 additions & 6 deletions stl/inc/optional
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Expand Up @@ -239,19 +239,23 @@ public:

template <class _Ty2>
using _AllowDirectConversion = bool_constant<conjunction_v<negation<is_same<_Remove_cvref_t<_Ty2>, optional>>,

@strega-nil-ms nicole mazzuca (strega-nil-ms) Mar 24, 2023

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Pre-existing, but why is this doing a bool_constant<conjunction_v rather than just conjunction; no change requested.

@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) Mar 24, 2023

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I think there's some attempt here to improve throughput by "smashing" a complicated type to either true_type or false_type but looking at this again, I am unsure whether we are actually achieving anything here. In cases below (e.g. _AllowUnwrappingAssignment) we are introducing a new struct instead of simply a using, and there appears to be no short-circuit benefit to doing so. I'll record a todo on my list, but I would prefer to avoid touching this existing code in <optional> until Casey returns as there is no urgent need.

negation<is_same<_Remove_cvref_t<_Ty2>, in_place_t>>, is_constructible<_Ty, _Ty2>>>;
negation<is_same<_Remove_cvref_t<_Ty2>, in_place_t>>,
negation<conjunction<is_same<remove_cv_t<_Ty>, bool>, _Is_specialization<_Remove_cvref_t<_Ty2>, optional>>>,
is_constructible<_Ty, _Ty2>>>;

template <class _Ty2 = _Ty, enable_if_t<_AllowDirectConversion<_Ty2>::value, int> = 0>
constexpr explicit(!is_convertible_v<_Ty2, _Ty>)
optional(_Ty2&& _Right) noexcept(is_nothrow_constructible_v<_Ty, _Ty2>) // strengthened
: _Mybase(in_place, _STD forward<_Ty2>(_Right)) {}

template <class _Ty2>
struct _AllowUnwrapping : bool_constant<!disjunction_v<is_same<_Ty, _Ty2>, is_constructible<_Ty, optional<_Ty2>&>,
is_constructible<_Ty, const optional<_Ty2>&>,
is_constructible<_Ty, const optional<_Ty2>>, is_constructible<_Ty, optional<_Ty2>>,
is_convertible<optional<_Ty2>&, _Ty>, is_convertible<const optional<_Ty2>&, _Ty>,
is_convertible<const optional<_Ty2>, _Ty>, is_convertible<optional<_Ty2>, _Ty>>> {};
struct _AllowUnwrapping
: bool_constant<disjunction_v<is_same<remove_cv_t<_Ty>, bool>,
negation<disjunction<is_same<_Ty, _Ty2>, is_constructible<_Ty, optional<_Ty2>&>,
is_constructible<_Ty, const optional<_Ty2>&>, is_constructible<_Ty, const optional<_Ty2>>,
is_constructible<_Ty, optional<_Ty2>>, is_convertible<optional<_Ty2>&, _Ty>,
is_convertible<const optional<_Ty2>&, _Ty>, is_convertible<const optional<_Ty2>, _Ty>,
is_convertible<optional<_Ty2>, _Ty>>>>> {};

template <class _Ty2,
enable_if_t<conjunction_v<_AllowUnwrapping<_Ty2>, is_constructible<_Ty, const _Ty2&>>, int> = 0>
Expand Down
3 changes: 3 additions & 0 deletions tests/libcxx/expected_results.txt
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Expand Up @@ -120,6 +120,9 @@ std/language.support/support.limits/support.limits.general/format.version.compil
# libc++ doesn't implement LWG-3670
std/ranges/range.factories/range.iota.view/iterator/member_typedefs.compile.pass.cpp FAIL

# libc++ doesn't implement LWG-3836
std/utilities/expected/expected.expected/ctor/ctor.u.pass.cpp FAIL

# libc++ doesn't implement LWG-3857
std/strings/string.view/string.view.cons/from_range.pass.cpp FAIL
std/strings/string.view/string.view.cons/from_string1.compile.fail.cpp FAIL
Expand Down
26 changes: 26 additions & 0 deletions tests/std/tests/P0220R1_optional/test.cpp
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Expand Up @@ -8148,6 +8148,30 @@ namespace msvc {
STATIC_ASSERT(!is_constructible_v<O, const in_place_t&>);
} // namespace lwg2842

namespace lwg3836 {
STATIC_ASSERT(std::is_convertible_v<std::optional<int>, std::optional<bool>>);
STATIC_ASSERT(std::is_convertible_v<const std::optional<int>&, std::optional<bool>>);

#if _HAS_CXX20
#define CONSTEXPR20 constexpr
#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
#define CONSTEXPR20 inline
#endif // ^^^ !_HAS_CXX20 ^^^
CONSTEXPR20 bool run_test() {
std::optional<int> oi = 0;
std::optional<bool> ob = oi;
assert(!ob.value());
assert(!std::optional<bool>{std::optional<int>{0}}.value());

return true;
}
#undef CONSTEXPR20

#if _HAS_CXX20
STATIC_ASSERT(run_test());
#endif // _HAS_CXX20
} // namespace lwg3836

namespace vso406124 {
// Defend against regression of VSO-406124
void run_test() {
Expand Down Expand Up @@ -8334,6 +8358,8 @@ int main() {
nonmembers::make_optional_explicit_init_list::run_test();
nonmembers::swap_::run_test();

msvc::lwg3836::run_test();

msvc::vso406124::run_test();
msvc::vso508126::run_test();
msvc::vso614907::run_test();
Expand Down
8 changes: 8 additions & 0 deletions tests/std/tests/P0323R12_expected/test.cpp
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Expand Up @@ -662,6 +662,14 @@ namespace test_expected {
test_constructors<IsNothrowConstructible::Not, IsExplicitConstructible::Yes>();
test_constructors<IsNothrowConstructible::Yes, IsExplicitConstructible::Not>();
test_constructors<IsNothrowConstructible::Yes, IsExplicitConstructible::Yes>();

// LWG-3836
struct BaseError {};
struct DerivedError : BaseError {};

std::expected<bool, DerivedError> e1(false);
std::expected<bool, BaseError> e2(e1);
Comment on lines +670 to +671

@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) Mar 24, 2023

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No change requested: This test is already using namespace std;. Not worth resetting testing as this test has already accumulated ~20 occurrences; I'll clean this up later, no reason to pollute this PR.

assert(!e2.value());
}

template <IsNothrowCopyConstructible nothrowCopyConstructible, IsNothrowMoveConstructible nothrowMoveConstructible,
Expand Down