[libc++][set] Applied [[nodiscard]]#169982
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frederick-vs-ja merged 2 commits intollvm:mainfrom Dec 12, 2025
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`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue. - https://libcxx.llvm.org/CodingGuidelines.htm - https://wg21.link/map
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@llvm/pr-subscribers-libcxx Author: Hristo Hristov (H-G-Hristov) Changes
Full diff: https://github.com/llvm/llvm-project/pull/169982.diff 3 Files Affected:
diff --git a/libcxx/include/set b/libcxx/include/set
index 3d6f571a42a1a..54a24e74ff52e 100644
--- a/libcxx/include/set
+++ b/libcxx/include/set
@@ -701,24 +701,28 @@ public:
_LIBCPP_HIDE_FROM_ABI ~set() { static_assert(sizeof(std::__diagnose_non_const_comparator<_Key, _Compare>()), ""); }
- _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return __tree_.begin(); }
- _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return __tree_.begin(); }
- _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return __tree_.end(); }
- _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return __tree_.end(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return __tree_.begin(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return __tree_.begin(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return __tree_.end(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return __tree_.end(); }
- _LIBCPP_HIDE_FROM_ABI reverse_iterator rbegin() _NOEXCEPT { return reverse_iterator(end()); }
- _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rbegin() const _NOEXCEPT { return const_reverse_iterator(end()); }
- _LIBCPP_HIDE_FROM_ABI reverse_iterator rend() _NOEXCEPT { return reverse_iterator(begin()); }
- _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rend() const _NOEXCEPT { return const_reverse_iterator(begin()); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI reverse_iterator rbegin() _NOEXCEPT { return reverse_iterator(end()); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rbegin() const _NOEXCEPT {
+ return const_reverse_iterator(end());
+ }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI reverse_iterator rend() _NOEXCEPT { return reverse_iterator(begin()); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rend() const _NOEXCEPT {
+ return const_reverse_iterator(begin());
+ }
- _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT { return begin(); }
- _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT { return end(); }
- _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crbegin() const _NOEXCEPT { return rbegin(); }
- _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crend() const _NOEXCEPT { return rend(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT { return begin(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT { return end(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crbegin() const _NOEXCEPT { return rbegin(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crend() const _NOEXCEPT { return rend(); }
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool empty() const _NOEXCEPT { return __tree_.size() == 0; }
- _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __tree_.size(); }
- _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT { return __tree_.max_size(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __tree_.size(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT { return __tree_.max_size(); }
// modifiers:
# ifndef _LIBCPP_CXX03_LANG
@@ -777,10 +781,10 @@ public:
"node_type with incompatible allocator passed to set::insert()");
return __tree_.template __node_handle_insert_unique<node_type>(__hint, std::move(__nh));
}
- _LIBCPP_HIDE_FROM_ABI node_type extract(key_type const& __key) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI node_type extract(key_type const& __key) {
return __tree_.template __node_handle_extract<node_type>(__key);
}
- _LIBCPP_HIDE_FROM_ABI node_type extract(const_iterator __it) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI node_type extract(const_iterator __it) {
return __tree_.template __node_handle_extract<node_type>(__it);
}
template <class _Compare2>
@@ -811,43 +815,47 @@ public:
_LIBCPP_HIDE_FROM_ABI void swap(set& __s) _NOEXCEPT_(__is_nothrow_swappable_v<__base>) { __tree_.swap(__s.__tree_); }
- _LIBCPP_HIDE_FROM_ABI allocator_type get_allocator() const _NOEXCEPT { return __tree_.__alloc(); }
- _LIBCPP_HIDE_FROM_ABI key_compare key_comp() const { return __tree_.value_comp(); }
- _LIBCPP_HIDE_FROM_ABI value_compare value_comp() const { return __tree_.value_comp(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI allocator_type get_allocator() const _NOEXCEPT { return __tree_.__alloc(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI key_compare key_comp() const { return __tree_.value_comp(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI value_compare value_comp() const { return __tree_.value_comp(); }
// set operations:
- _LIBCPP_HIDE_FROM_ABI iterator find(const key_type& __k) { return __tree_.find(__k); }
- _LIBCPP_HIDE_FROM_ABI const_iterator find(const key_type& __k) const { return __tree_.find(__k); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator find(const key_type& __k) { return __tree_.find(__k); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator find(const key_type& __k) const { return __tree_.find(__k); }
# if _LIBCPP_STD_VER >= 14
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI iterator find(const _K2& __k) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator find(const _K2& __k) {
return __tree_.find(__k);
}
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI const_iterator find(const _K2& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator find(const _K2& __k) const {
return __tree_.find(__k);
}
# endif
- _LIBCPP_HIDE_FROM_ABI size_type count(const key_type& __k) const { return __tree_.__count_unique(__k); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type count(const key_type& __k) const {
+ return __tree_.__count_unique(__k);
+ }
# if _LIBCPP_STD_VER >= 14
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI size_type count(const _K2& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type count(const _K2& __k) const {
return __tree_.__count_multi(__k);
}
# endif
# if _LIBCPP_STD_VER >= 20
- _LIBCPP_HIDE_FROM_ABI bool contains(const key_type& __k) const { return find(__k) != end(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool contains(const key_type& __k) const { return find(__k) != end(); }
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI bool contains(const _K2& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool contains(const _K2& __k) const {
return find(__k) != end();
}
# endif // _LIBCPP_STD_VER >= 20
- _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.__lower_bound_unique(__k); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) {
+ return __tree_.__lower_bound_unique(__k);
+ }
- _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const {
return __tree_.__lower_bound_unique(__k);
}
@@ -855,46 +863,48 @@ public:
// match multiple elements.
# if _LIBCPP_STD_VER >= 14
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _K2& __k) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _K2& __k) {
return __tree_.__lower_bound_multi(__k);
}
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _K2& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _K2& __k) const {
return __tree_.__lower_bound_multi(__k);
}
# endif
- _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.__upper_bound_unique(__k); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) {
+ return __tree_.__upper_bound_unique(__k);
+ }
- _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const {
return __tree_.__upper_bound_unique(__k);
}
# if _LIBCPP_STD_VER >= 14
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _K2& __k) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _K2& __k) {
return __tree_.__upper_bound_multi(__k);
}
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _K2& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _K2& __k) const {
return __tree_.__upper_bound_multi(__k);
}
# endif
- _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const key_type& __k) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const key_type& __k) {
return __tree_.__equal_range_unique(__k);
}
- _LIBCPP_HIDE_FROM_ABI pair<const_iterator, const_iterator> equal_range(const key_type& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI pair<const_iterator, const_iterator> equal_range(const key_type& __k) const {
return __tree_.__equal_range_unique(__k);
}
# if _LIBCPP_STD_VER >= 14
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const _K2& __k) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const _K2& __k) {
return __tree_.__equal_range_multi(__k);
}
template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
- _LIBCPP_HIDE_FROM_ABI pair<const_iterator, const_iterator> equal_range(const _K2& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI pair<const_iterator, const_iterator> equal_range(const _K2& __k) const {
return __tree_.__equal_range_multi(__k);
}
# endif
diff --git a/libcxx/test/libcxx/diagnostics/multiset.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/multiset.nodiscard.verify.cpp
new file mode 100644
index 0000000000000..828d2e2897e4b
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/multiset.nodiscard.verify.cpp
@@ -0,0 +1,18 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03
+
+// Check that functions are marked [[nodiscard]]
+
+#include <set>
+
+void test() {
+ std::multiset<int> multiset;
+ multiset.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+}
diff --git a/libcxx/test/libcxx/diagnostics/set.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/set.nodiscard.verify.cpp
index cc6fb55854dac..046b8b06bb587 100644
--- a/libcxx/test/libcxx/diagnostics/set.nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/diagnostics/set.nodiscard.verify.cpp
@@ -8,16 +8,104 @@
// UNSUPPORTED: c++03
-// check that <set> functions are marked [[nodiscard]]
+// Check that functions are marked [[nodiscard]]
#include <set>
-void set_test() {
- std::set<int> set;
- set.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
-}
+#include "test_macros.h"
+
+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::set<int, TransparentCompare> s;
+ const std::set<int, TransparentCompare> cs{};
+
+ s.begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ s.end(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.end(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ s.rbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.rbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ s.rend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.rend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ cs.cbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.cend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.crbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.crend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ s.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ s.size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ s.max_size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ int key = 0;
+
+#if TEST_STD_VER >= 17
+ s.extract(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ s.extract(s.begin()); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+ s.get_allocator(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ s.key_comp(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ s.value_comp(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ s.find(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.find(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if TEST_STD_VER >= 14
+ TransparentKey<int> tkey;
+
+ s.find(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.find(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+ s.count(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if TEST_STD_VER >= 14
+ s.count(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+ s.lower_bound(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.lower_bound(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if TEST_STD_VER >= 14
+ s.lower_bound(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.lower_bound(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+ s.upper_bound(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.upper_bound(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if TEST_STD_VER >= 14
+ s.upper_bound(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.upper_bound(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
-void multiset_test() {
- std::multiset<int> multiset;
- multiset.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ s.equal_range(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.equal_range(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if TEST_STD_VER >= 14
+ s.equal_range(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cs.equal_range(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
}
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`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue. - https://libcxx.llvm.org/CodingGuidelines.htm - https://wg21.link/set
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As of llvm/llvm-project#169982 this will be caught by LLVM, and it's the only such example.
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[[nodiscard]]should be applied to functions where discarding the return value is most likely a correctness issue.