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[libc++][variant] Applied [[nodiscard]] #172058

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[libc++][variant] Applied [[nodiscard]] #172058

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36 changes: 19 additions & 17 deletions libcxx/include/variant
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Original file line number Diff line number Diff line change
Expand Up @@ -288,7 +288,7 @@ _LIBCPP_BEGIN_UNVERSIONED_NAMESPACE_STD

class _LIBCPP_EXPORTED_FROM_ABI bad_variant_access : public exception {
public:
const char* what() const _NOEXCEPT override;
[[__nodiscard__]] const char* what() const _NOEXCEPT override;
};

_LIBCPP_END_UNVERSIONED_NAMESPACE_STD
Expand Down Expand Up @@ -1282,11 +1282,11 @@ public:
return __impl_.template __emplace<_Ip>(__il, std::forward<_Args>(__args)...);
}

_LIBCPP_HIDE_FROM_ABI constexpr bool valueless_by_exception() const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool valueless_by_exception() const noexcept {
return __impl_.valueless_by_exception();
}

_LIBCPP_HIDE_FROM_ABI constexpr size_t index() const noexcept { return __impl_.index(); }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr size_t index() const noexcept { return __impl_.index(); }

template < bool _Dummy = true,
enable_if_t< __all<(__dependent_type<is_move_constructible<_Types>, _Dummy>::value &&
Expand Down Expand Up @@ -1329,7 +1329,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool __holds_alternative(const variant<_Types...
}

template <class _Tp, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr bool holds_alternative(const variant<_Types...>& __v) noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool holds_alternative(const variant<_Types...>& __v) noexcept {
return std::__holds_alternative<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

Expand All @@ -1343,55 +1343,57 @@ _LIBCPP_HIDE_FROM_ABI constexpr auto&& __generic_get(_Vp&& __v) {
}

template <size_t _Ip, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr variant_alternative_t<_Ip, variant<_Types...>>& get(variant<_Types...>& __v) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr variant_alternative_t<_Ip, variant<_Types...>>&
get(variant<_Types...>& __v) {
static_assert(_Ip < sizeof...(_Types));
static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
return std::__generic_get<_Ip>(__v);
}

template <size_t _Ip, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr variant_alternative_t<_Ip, variant<_Types...>>&& get(variant<_Types...>&& __v) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr variant_alternative_t<_Ip, variant<_Types...>>&&
get(variant<_Types...>&& __v) {
static_assert(_Ip < sizeof...(_Types));
static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
return std::__generic_get<_Ip>(std::move(__v));
}

template <size_t _Ip, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr const variant_alternative_t<_Ip, variant<_Types...>>&
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const variant_alternative_t<_Ip, variant<_Types...>>&
get(const variant<_Types...>& __v) {
static_assert(_Ip < sizeof...(_Types));
static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
return std::__generic_get<_Ip>(__v);
}

template <size_t _Ip, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr const variant_alternative_t<_Ip, variant<_Types...>>&&
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const variant_alternative_t<_Ip, variant<_Types...>>&&
get(const variant<_Types...>&& __v) {
static_assert(_Ip < sizeof...(_Types));
static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
return std::__generic_get<_Ip>(std::move(__v));
}

template <class _Tp, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr _Tp& get(variant<_Types...>& __v) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp& get(variant<_Types...>& __v) {
static_assert(!is_void_v<_Tp>);
return std::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

template <class _Tp, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr _Tp&& get(variant<_Types...>&& __v) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp&& get(variant<_Types...>&& __v) {
static_assert(!is_void_v<_Tp>);
return std::get<__find_exactly_one_t<_Tp, _Types...>::value>(std::move(__v));
}

template <class _Tp, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr const _Tp& get(const variant<_Types...>& __v) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& get(const variant<_Types...>& __v) {
static_assert(!is_void_v<_Tp>);
return std::get<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

template <class _Tp, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr const _Tp&& get(const variant<_Types...>&& __v) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const _Tp&& get(const variant<_Types...>&& __v) {
static_assert(!is_void_v<_Tp>);
return std::get<__find_exactly_one_t<_Tp, _Types...>::value>(std::move(__v));
}
Expand All @@ -1403,29 +1405,29 @@ _LIBCPP_HIDE_FROM_ABI constexpr auto* __generic_get_if(_Vp* __v) noexcept {
}

template <size_t _Ip, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<variant_alternative_t<_Ip, variant<_Types...>>>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<variant_alternative_t<_Ip, variant<_Types...>>>
get_if(variant<_Types...>* __v) noexcept {
static_assert(_Ip < sizeof...(_Types));
static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
return std::__generic_get_if<_Ip>(__v);
}

template <size_t _Ip, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<const variant_alternative_t<_Ip, variant<_Types...>>>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<const variant_alternative_t<_Ip, variant<_Types...>>>
get_if(const variant<_Types...>* __v) noexcept {
static_assert(_Ip < sizeof...(_Types));
static_assert(!is_void_v<variant_alternative_t<_Ip, variant<_Types...>>>);
return std::__generic_get_if<_Ip>(__v);
}

template <class _Tp, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<_Tp> get_if(variant<_Types...>* __v) noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<_Tp> get_if(variant<_Types...>* __v) noexcept {
static_assert(!is_void_v<_Tp>);
return std::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}

template <class _Tp, class... _Types>
_LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<const _Tp> get_if(const variant<_Types...>* __v) noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr add_pointer_t<const _Tp> get_if(const variant<_Types...>* __v) noexcept {
static_assert(!is_void_v<_Tp>);
return std::get_if<__find_exactly_one_t<_Tp, _Types...>::value>(__v);
}
Expand Down Expand Up @@ -1606,7 +1608,7 @@ struct hash< __enable_hash_helper<variant<_Types...>, remove_const_t<_Types>...>
using result_type _LIBCPP_DEPRECATED_IN_CXX17 = size_t;
# endif

_LIBCPP_HIDE_FROM_ABI size_t operator()(const variant<_Types...>& __v) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI size_t operator()(const variant<_Types...>& __v) const {
using __variant_detail::__visitation::__variant;
size_t __res =
__v.valueless_by_exception()
Expand Down
74 changes: 74 additions & 0 deletions libcxx/test/libcxx/utilities/variant/nodiscard.verify.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,74 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// REQUIRES: std-at-least-c++17

// Check that functions are marked [[nodiscard]]

#include <variant>

#include <test_macros.h>

void test() {
{
std::bad_variant_access ex;

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
ex.what();
}

{
struct First {};
struct Second {};

std::variant<First, Second> v;
const std::variant<First, Second> cv;

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
cv.valueless_by_exception();

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
cv.index();

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::holds_alternative<First>(v);

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(v);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(cv);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(std::move(v));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(std::move(cv));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<First>(v);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<First>(cv);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<First>(std::move(v));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<First>(std::move(cv));

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get_if<0>(&v);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get_if<0>(&cv);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get_if<First>(&v);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get_if<First>(&cv);
}

{
std::hash< std::variant<int, float>> hash;

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
hash(std::variant<int, float>{});
}
}
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