[libc++][unordered_multimap] Applied [[nodiscard]]
#171659
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@llvm/pr-subscribers-libcxx Author: Hristo Hristov (H-G-Hristov) Changes
Full diff: https://github.com/llvm/llvm-project/pull/171659.diff 2 Files Affected:
diff --git a/libcxx/include/unordered_map b/libcxx/include/unordered_map
index 2afc8805cb4c7..dc1dc6451de0b 100644
--- a/libcxx/include/unordered_map
+++ b/libcxx/include/unordered_map
@@ -1798,20 +1798,20 @@ public:
_LIBCPP_HIDE_FROM_ABI unordered_multimap& operator=(initializer_list<value_type> __il);
# endif // _LIBCPP_CXX03_LANG
- _LIBCPP_HIDE_FROM_ABI allocator_type get_allocator() const _NOEXCEPT {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI allocator_type get_allocator() const _NOEXCEPT {
return allocator_type(__table_.__node_alloc());
}
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool empty() const _NOEXCEPT { return __table_.size() == 0; }
- _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __table_.size(); }
- _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT { return __table_.max_size(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __table_.size(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT { return __table_.max_size(); }
- _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return __table_.begin(); }
- _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return __table_.end(); }
- _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return __table_.begin(); }
- _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return __table_.end(); }
- _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT { return __table_.begin(); }
- _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT { return __table_.end(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return __table_.begin(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return __table_.end(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return __table_.begin(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return __table_.end(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT { return __table_.begin(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT { return __table_.end(); }
_LIBCPP_HIDE_FROM_ABI iterator insert(const value_type& __x) { return __table_.__emplace_multi(__x); }
@@ -1879,10 +1879,10 @@ public:
"node_type with incompatible allocator passed to unordered_multimap::insert()");
return __table_.template __node_handle_insert_multi<node_type>(__hint.__i_, 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 __table_.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 __table_.template __node_handle_extract<node_type>(__it.__i_);
}
@@ -1916,71 +1916,71 @@ public:
__table_.swap(__u.__table_);
}
- _LIBCPP_HIDE_FROM_ABI hasher hash_function() const { return __table_.hash_function().hash_function(); }
- _LIBCPP_HIDE_FROM_ABI key_equal key_eq() const { return __table_.key_eq().key_eq(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI hasher hash_function() const { return __table_.hash_function().hash_function(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI key_equal key_eq() const { return __table_.key_eq().key_eq(); }
- _LIBCPP_HIDE_FROM_ABI iterator find(const key_type& __k) { return __table_.find(__k); }
- _LIBCPP_HIDE_FROM_ABI const_iterator find(const key_type& __k) const { return __table_.find(__k); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator find(const key_type& __k) { return __table_.find(__k); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator find(const key_type& __k) const { return __table_.find(__k); }
# if _LIBCPP_STD_VER >= 20
template <class _K2, enable_if_t<__is_transparent_v<hasher, _K2> && __is_transparent_v<key_equal, _K2>>* = nullptr>
- _LIBCPP_HIDE_FROM_ABI iterator find(const _K2& __k) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI iterator find(const _K2& __k) {
return __table_.find(__k);
}
template <class _K2, enable_if_t<__is_transparent_v<hasher, _K2> && __is_transparent_v<key_equal, _K2>>* = nullptr>
- _LIBCPP_HIDE_FROM_ABI const_iterator find(const _K2& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_iterator find(const _K2& __k) const {
return __table_.find(__k);
}
# endif // _LIBCPP_STD_VER >= 20
- _LIBCPP_HIDE_FROM_ABI size_type count(const key_type& __k) const { return __table_.__count_multi(__k); }
+ _[[__nodiscard__]] LIBCPP_HIDE_FROM_ABI size_type count(const key_type& __k) const { return __table_.__count_multi(__k); }
# if _LIBCPP_STD_VER >= 20
template <class _K2, enable_if_t<__is_transparent_v<hasher, _K2> && __is_transparent_v<key_equal, _K2>>* = nullptr>
- _LIBCPP_HIDE_FROM_ABI size_type count(const _K2& __k) const {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type count(const _K2& __k) const {
return __table_.__count_multi(__k);
}
# endif // _LIBCPP_STD_VER >= 20
# 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 <class _K2, enable_if_t<__is_transparent_v<hasher, _K2> && __is_transparent_v<key_equal, _K2>>* = nullptr>
- _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 pair<iterator, iterator> equal_range(const key_type& __k) {
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const key_type& __k) {
return __table_.__equal_range_multi(__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 __table_.__equal_range_multi(__k);
}
# if _LIBCPP_STD_VER >= 20
template <class _K2, enable_if_t<__is_transparent_v<hasher, _K2> && __is_transparent_v<key_equal, _K2>>* = nullptr>
- _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 __table_.__equal_range_multi(__k);
}
template <class _K2, enable_if_t<__is_transparent_v<hasher, _K2> && __is_transparent_v<key_equal, _K2>>* = nullptr>
- _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 __table_.__equal_range_multi(__k);
}
# endif // _LIBCPP_STD_VER >= 20
- _LIBCPP_HIDE_FROM_ABI size_type bucket_count() const _NOEXCEPT { return __table_.bucket_count(); }
- _LIBCPP_HIDE_FROM_ABI size_type max_bucket_count() const _NOEXCEPT { return __table_.max_bucket_count(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type bucket_count() const _NOEXCEPT { return __table_.bucket_count(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type max_bucket_count() const _NOEXCEPT { return __table_.max_bucket_count(); }
- _LIBCPP_HIDE_FROM_ABI size_type bucket_size(size_type __n) const { return __table_.bucket_size(__n); }
- _LIBCPP_HIDE_FROM_ABI size_type bucket(const key_type& __k) const { return __table_.bucket(__k); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type bucket_size(size_type __n) const { return __table_.bucket_size(__n); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_type bucket(const key_type& __k) const { return __table_.bucket(__k); }
- _LIBCPP_HIDE_FROM_ABI local_iterator begin(size_type __n) { return __table_.begin(__n); }
- _LIBCPP_HIDE_FROM_ABI local_iterator end(size_type __n) { return __table_.end(__n); }
- _LIBCPP_HIDE_FROM_ABI const_local_iterator begin(size_type __n) const { return __table_.cbegin(__n); }
- _LIBCPP_HIDE_FROM_ABI const_local_iterator end(size_type __n) const { return __table_.cend(__n); }
- _LIBCPP_HIDE_FROM_ABI const_local_iterator cbegin(size_type __n) const { return __table_.cbegin(__n); }
- _LIBCPP_HIDE_FROM_ABI const_local_iterator cend(size_type __n) const { return __table_.cend(__n); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI local_iterator begin(size_type __n) { return __table_.begin(__n); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI local_iterator end(size_type __n) { return __table_.end(__n); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_local_iterator begin(size_type __n) const { return __table_.cbegin(__n); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_local_iterator end(size_type __n) const { return __table_.cend(__n); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_local_iterator cbegin(size_type __n) const { return __table_.cbegin(__n); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI const_local_iterator cend(size_type __n) const { return __table_.cend(__n); }
- _LIBCPP_HIDE_FROM_ABI float load_factor() const _NOEXCEPT { return __table_.load_factor(); }
- _LIBCPP_HIDE_FROM_ABI float max_load_factor() const _NOEXCEPT { return __table_.max_load_factor(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI float load_factor() const _NOEXCEPT { return __table_.load_factor(); }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI float max_load_factor() const _NOEXCEPT { return __table_.max_load_factor(); }
_LIBCPP_HIDE_FROM_ABI void max_load_factor(float __mlf) { __table_.max_load_factor(__mlf); }
_LIBCPP_HIDE_FROM_ABI void rehash(size_type __n) { __table_.__rehash_multi(__n); }
_LIBCPP_HIDE_FROM_ABI void reserve(size_type __n) { __table_.__reserve_multi(__n); }
diff --git a/libcxx/test/libcxx/diagnostics/unordered_multimap.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/unordered_multimap.nodiscard.verify.cpp
new file mode 100644
index 0000000000000..c4786a50d38f4
--- /dev/null
+++ b/libcxx/test/libcxx/diagnostics/unordered_multimap.nodiscard.verify.cpp
@@ -0,0 +1,103 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++11
+
+// Check that functions are marked [[nodiscard]]
+
+#include <unoredered_map>
+#include <utility>
+
+#include "test_macros.h"
+
+struct TransparentKey {};
+
+struct StoredKey {
+ friend bool operator==(StoredKey const&, StoredKey const&) { return true; }
+ friend bool operator==(StoredKey const&, TransparentKey const&) { return true; }
+};
+
+struct TransparentKeyHash {
+ using is_transparent = void;
+
+ constexpr std::size_t operator()(TransparentKey const&) const { return 0; }
+ constexpr std::size_t operator()(StoredKey const&) const { return 0; }
+};
+
+void test() {
+ std::unordered_map<int, int> m;
+ const std::unordered_map<int, int> cm;
+
+ m.get_allocator(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ m.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.max_size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ m.begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.end(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.end(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.cbegin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.cend(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ int key = 0;
+
+#if TEST_STD_VER >= 17
+ m.extract(0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.extract(m.begin()); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+ m.hash_function(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.key_eq(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ m.find(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.find(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if TEST_STD_VER >= 20
+ std::unordered_map<StoredKey, int, TransparentKeyHash, std::equal_to<>> tm;
+ const std::unordered_map<StoredKey, int, TransparentKeyHash, std::equal_to<>> ctm;
+
+ TransparentKey tkey;
+
+ tm.find(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ctm.find(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+#if TEST_STD_VER >= 20
+ m.count(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.count(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ tm.contains(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ctm.contains(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+ m.equal_range(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.equal_range(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if TEST_STD_VER >= 20
+ tm.equal_range(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ctm.equal_range(tkey); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
+
+ m.bucket_count(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.max_bucket_count(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ int size = 0;
+
+ m.bucket_size(size); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.bucket(key); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ m.begin(size); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.end(size); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.begin(size); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.end(size); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.cbegin(size); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ cm.cend(size); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ m.load_factor(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ m.max_load_factor(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+}
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✅ With the latest revision this PR passed the C/C++ code formatter. |
H-G-Hristov
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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/unord.multimap
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H-G-Hristov
changed the title
[[nodiscard]][[nodiscard]]
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frederick-vs-ja
approved these changes
Dec 15, 2025
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/169/builds/18033 Here is the relevant piece of the build log for the reference |
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[[nodiscard]]should be applied to functions where discarding the return value is most likely a correctness issue.