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H-G-HristovH-G-Hristov
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[libc++][bitset] Applied [[nodiscard]]
`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue. - https://libcxx.llvm.org/CodingGuidelines.html - https://wg21.link/bitset
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‎libcxx/include/bitset‎

Lines changed: 24 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -681,45 +681,54 @@ public:
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// element access:
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# ifdef _LIBCPP_ABI_BITSET_VECTOR_BOOL_CONST_SUBSCRIPT_RETURN_BOOL
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bool operator[](size_t __p) const {
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bool operator[](size_t __p) const {
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_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__p < _Size, "bitset::operator[] index out of bounds");
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return __base::__make_ref(__p);
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}
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# else
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __const_reference operator[](size_t __p) const {
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __const_reference operator[](size_t __p) const {
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_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__p < _Size, "bitset::operator[] index out of bounds");
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return __base::__make_ref(__p);
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}
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# endif
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 reference operator[](size_t __p) {
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 reference operator[](size_t __p) {
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_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__p < _Size, "bitset::operator[] index out of bounds");
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return __base::__make_ref(__p);
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}
698-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long to_ulong() const { return __base::to_ulong(); }
699-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long to_ullong() const {
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long to_ulong() const {
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return __base::to_ulong();
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}
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long to_ullong() const {
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return __base::to_ullong();
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}
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template <class _CharT, class _Traits, class _Allocator>
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 basic_string<_CharT, _Traits, _Allocator>
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 basic_string<_CharT, _Traits, _Allocator>
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to_string(_CharT __zero = _CharT('0'), _CharT __one = _CharT('1')) const;
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template <class _CharT, class _Traits>
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 basic_string<_CharT, _Traits, allocator<_CharT> >
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
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_LIBCPP_CONSTEXPR_SINCE_CXX23 basic_string<_CharT, _Traits, allocator<_CharT> >
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to_string(_CharT __zero = _CharT('0'), _CharT __one = _CharT('1')) const;
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template <class _CharT>
709-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 basic_string<_CharT, char_traits<_CharT>, allocator<_CharT> >
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[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
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_LIBCPP_CONSTEXPR_SINCE_CXX23 basic_string<_CharT, char_traits<_CharT>, allocator<_CharT> >
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to_string(_CharT __zero = _CharT('0'), _CharT __one = _CharT('1')) const;
711-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 basic_string<char, char_traits<char>, allocator<char> >
715+
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI
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_LIBCPP_CONSTEXPR_SINCE_CXX23 basic_string<char, char_traits<char>, allocator<char> >
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to_string(char __zero = '0', char __one = '1') const;
713-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 size_t count() const _NOEXCEPT;
714-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR size_t size() const _NOEXCEPT { return _Size; }
718+
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 size_t count() const _NOEXCEPT;
719+
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR size_t size() const _NOEXCEPT { return _Size; }
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool operator==(const bitset& __rhs) const _NOEXCEPT;
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# if _LIBCPP_STD_VER <= 17
717722
_LIBCPP_HIDE_FROM_ABI bool operator!=(const bitset& __rhs) const _NOEXCEPT;
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# endif
719-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool test(size_t __pos) const;
720-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool all() const _NOEXCEPT { return __base::all(); }
721-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool any() const _NOEXCEPT { return __base::any(); }
722-
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool none() const _NOEXCEPT { return !any(); }
724+
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool test(size_t __pos) const;
725+
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool all() const _NOEXCEPT {
726+
return __base::all();
727+
}
728+
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool any() const _NOEXCEPT {
729+
return __base::any();
730+
}
731+
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool none() const _NOEXCEPT { return !any(); }
723732
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bitset operator<<(size_t __pos) const _NOEXCEPT;
724733
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bitset operator>>(size_t __pos) const _NOEXCEPT;
725734

‎libcxx/test/libcxx/utilities/template.bitset/nodiscard.verify.cpp‎

Lines changed: 48 additions & 0 deletions
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@@ -0,0 +1,48 @@
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// UNSUPPORTED: c++03
10+
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// <bitset>
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// Check that functions are marked [[nodiscard]]
14+
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#include <bitset>
16+
17+
#include "test_macros.h"
18+
#include "test_allocator.h"
19+
20+
void test() {
21+
std::bitset<10> bs;
22+
const std::bitset<10> cbs;
23+
24+
bs[0]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
25+
cbs[0]; // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
26+
bs.to_ulong(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
27+
bs.to_ullong(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
28+
29+
struct CharTraits : public std::char_traits<char> {};
30+
31+
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
32+
bs.to_string<char, CharTraits, test_allocator<char>>();
33+
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
34+
bs.to_string<char, CharTraits>();
35+
#if !defined(TEST_HAS_NO_WIDE_CHARACTERS)
36+
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
37+
bs.to_string<wchar_t>();
38+
#endif
39+
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
40+
bs.to_string();
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42+
bs.count(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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bs.size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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bs.test(0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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bs.all(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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bs.any(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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bs.none(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
48+
}

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