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[libc++][flat_set] Applied [[nodiscard]] #169739

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Nov 27, 2025
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[libc++][flat_set] Applied [[nodiscard]] #169739

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88 changes: 51 additions & 37 deletions libcxx/include/__flat_set/flat_set.h
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Original file line number Diff line number Diff line change
Expand Up @@ -339,38 +339,42 @@ class flat_set {
}

// iterators
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator begin() noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator begin() noexcept {
return iterator(std::as_const(__keys_).begin());
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator begin() const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator begin() const noexcept {
return const_iterator(__keys_.begin());
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator end() noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator end() noexcept {
return iterator(std::as_const(__keys_).end());
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator end() const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator end() const noexcept {
return const_iterator(__keys_.end());
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reverse_iterator rbegin() noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reverse_iterator rbegin() noexcept {
return reverse_iterator(end());
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator rbegin() const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator rbegin() const noexcept {
return const_reverse_iterator(end());
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reverse_iterator rend() noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reverse_iterator rend() noexcept {
return reverse_iterator(begin());
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator rend() const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator rend() const noexcept {
return const_reverse_iterator(begin());
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator cbegin() const noexcept { return begin(); }
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator cend() const noexcept { return end(); }
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator crbegin() const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator cbegin() const noexcept {
return begin();
}
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator cend() const noexcept {
return end();
}
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator crbegin() const noexcept {
return const_reverse_iterator(end());
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator crend() const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator crend() const noexcept {
return const_reverse_iterator(begin());
}

Expand All @@ -379,9 +383,13 @@ class flat_set {
return __keys_.empty();
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type size() const noexcept { return __keys_.size(); }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type size() const noexcept {
return __keys_.size();
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type max_size() const noexcept { return __keys_.max_size(); }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type max_size() const noexcept {
return __keys_.max_size();
}

// [flat.set.modifiers], modifiers
template <class... _Args>
Expand Down Expand Up @@ -466,7 +474,7 @@ class flat_set {
insert(sorted_unique, __il.begin(), __il.end());
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 container_type extract() && {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 container_type extract() && {
auto __guard = std::__make_scope_guard([&]() noexcept { clear() /* noexcept */; });
auto __ret = std::move(__keys_);
return __ret;
Expand Down Expand Up @@ -528,111 +536,117 @@ class flat_set {
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void clear() noexcept { __keys_.clear(); }

// observers
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 key_compare key_comp() const { return __compare_; }
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 value_compare value_comp() const { return __compare_; }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 key_compare key_comp() const { return __compare_; }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 value_compare value_comp() const {
return __compare_;
}

// set operations
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator find(const key_type& __x) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator find(const key_type& __x) {
return __find_impl(*this, __x);
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator find(const key_type& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator find(const key_type& __x) const {
return __find_impl(*this, __x);
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator find(const _Kp& __x) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator find(const _Kp& __x) {
return __find_impl(*this, __x);
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator find(const _Kp& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator find(const _Kp& __x) const {
return __find_impl(*this, __x);
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type count(const key_type& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type count(const key_type& __x) const {
return contains(__x) ? 1 : 0;
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type count(const _Kp& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type count(const _Kp& __x) const {
return contains(__x) ? 1 : 0;
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool contains(const key_type& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool contains(const key_type& __x) const {
return find(__x) != end();
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool contains(const _Kp& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool contains(const _Kp& __x) const {
return find(__x) != end();
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator lower_bound(const key_type& __x) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator lower_bound(const key_type& __x) {
const auto& __keys = __keys_;
return iterator(std::lower_bound(__keys.begin(), __keys.end(), __x, __compare_));
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator lower_bound(const key_type& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator
lower_bound(const key_type& __x) const {
return const_iterator(std::lower_bound(__keys_.begin(), __keys_.end(), __x, __compare_));
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator lower_bound(const _Kp& __x) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator lower_bound(const _Kp& __x) {
const auto& __keys = __keys_;
return iterator(std::lower_bound(__keys.begin(), __keys.end(), __x, __compare_));
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator lower_bound(const _Kp& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator lower_bound(const _Kp& __x) const {
return const_iterator(std::lower_bound(__keys_.begin(), __keys_.end(), __x, __compare_));
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator upper_bound(const key_type& __x) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator upper_bound(const key_type& __x) {
const auto& __keys = __keys_;
return iterator(std::upper_bound(__keys.begin(), __keys.end(), __x, __compare_));
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator upper_bound(const key_type& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator
upper_bound(const key_type& __x) const {
return const_iterator(std::upper_bound(__keys_.begin(), __keys_.end(), __x, __compare_));
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator upper_bound(const _Kp& __x) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator upper_bound(const _Kp& __x) {
const auto& __keys = __keys_;
return iterator(std::upper_bound(__keys.begin(), __keys.end(), __x, __compare_));
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator upper_bound(const _Kp& __x) const {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator upper_bound(const _Kp& __x) const {
return const_iterator(std::upper_bound(__keys_.begin(), __keys_.end(), __x, __compare_));
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, iterator> equal_range(const key_type& __x) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, iterator>
equal_range(const key_type& __x) {
return __equal_range_impl(*this, __x);
}

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<const_iterator, const_iterator>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<const_iterator, const_iterator>
equal_range(const key_type& __x) const {
return __equal_range_impl(*this, __x);
}

template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, iterator> equal_range(const _Kp& __x) {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, iterator>
equal_range(const _Kp& __x) {
return __equal_range_impl(*this, __x);
}
template <class _Kp>
requires __is_transparent_v<_Compare>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<const_iterator, const_iterator>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<const_iterator, const_iterator>
equal_range(const _Kp& __x) const {
return __equal_range_impl(*this, __x);
}
Expand Down
2 changes: 1 addition & 1 deletion libcxx/test/libcxx/diagnostics/flat_map.nodiscard.verify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@

// <flat_map>

// [[nodiscard]] bool empty() const noexcept;
// Check that functions are marked [[nodiscard]]

#include <flat_map>
#include <utility>
Expand Down
88 changes: 83 additions & 5 deletions libcxx/test/libcxx/diagnostics/flat_set.nodiscard.verify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6,15 +6,93 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
// REQUIRES: std-at-least-c++23

// <flat_set>

// [[nodiscard]] bool empty() const noexcept;
// Check that functions are marked [[nodiscard]]

#include <flat_set>
#include <utility>

void f() {
std::flat_set<int> c;
c.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
template <typename T>
struct TransparentKey {
T t;

constexpr explicit operator T() const { return t; }
};

struct TransparentCompare {
using is_transparent = void; // This makes the comparator transparent

template <typename T>
constexpr bool operator()(const T& t, const TransparentKey<T>& transparent) const {
return t < transparent.t;
}

template <typename T>
constexpr bool operator()(const TransparentKey<T>& transparent, const T& t) const {
return transparent.t < t;
}

template <typename T>
constexpr bool operator()(const T& t1, const T& t2) const {
return t1 < t2;
}
};

void test() {
std::flat_set<int, TransparentCompare> fs;
const std::flat_set<int, TransparentCompare> cfs;

fs.begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.end(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.end(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.rbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.rbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.rend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.rend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.cbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.cend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.crbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.crend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

fs.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.max_size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

std::move(fs).extract(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

fs.key_comp(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.value_comp(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

int key = 0;
TransparentKey<int> tkey;

fs.find(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.find(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.find(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.find(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

fs.count(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.count(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

fs.contains(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.contains(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

fs.lower_bound(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.lower_bound(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.lower_bound(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.lower_bound(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

fs.upper_bound(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.upper_bound(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.upper_bound(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.upper_bound(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

fs.equal_range(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.equal_range(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
fs.equal_range(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
cfs.equal_range(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
}
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