[libcxx-commits] [libcxx] ceea07d - [libc++][forward_list] Applied `[[nodiscard]]` (#169019)

[via libcxx-commits]

Author: Hristo Hristov
Date: 2025-11-24T16:30:17+02:00
New Revision: ceea07daa8a41562fdd884a224afbac1d7346e3e

URL: https://github.com/llvm/llvm-project/commit/ceea07daa8a41562fdd884a224afbac1d7346e3e
DIFF: https://github.com/llvm/llvm-project/commit/ceea07daa8a41562fdd884a224afbac1d7346e3e.diff

LOG: [libc++][forward_list] Applied `[[nodiscard]]` (#169019)

`[[nodiscard]]` should be applied to functions where discarding the
return value is most likely a correctness issue.
- https://libcxx.llvm.org/CodingGuidelines.html#apply-nodiscard-where-relevant

Added: 
    

Modified: 
    libcxx/include/forward_list
    libcxx/test/libcxx/diagnostics/forward_list.nodiscard.verify.cpp

Removed: 
    


################################################################################
diff  --git a/libcxx/include/forward_list b/libcxx/include/forward_list
index 272e52d68f46a..56c45d0d46575 100644
--- a/libcxx/include/forward_list
+++ b/libcxx/include/forward_list
@@ -732,50 +732,52 @@ public:
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI void assign(size_type __n, const value_type& __v);
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI allocator_type get_allocator() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI allocator_type get_allocator() const _NOEXCEPT {
     return allocator_type(this->__alloc_);
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT {
     return iterator(__base::__before_begin()->__next_);
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT {
     return const_iterator(__base::__before_begin()->__next_);
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return iterator(nullptr); }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT {
+    return iterator(nullptr);
+  }
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT {
     return const_iterator(nullptr);
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT {
     return const_iterator(__base::__before_begin()->__next_);
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT {
     return const_iterator(nullptr);
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator before_begin() _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator before_begin() _NOEXCEPT {
     return iterator(__base::__before_begin());
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator before_begin() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator before_begin() const _NOEXCEPT {
     return const_iterator(__base::__before_begin());
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cbefore_begin() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cbefore_begin() const _NOEXCEPT {
     return const_iterator(__base::__before_begin());
   }
 
   [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI bool empty() const _NOEXCEPT {
     return __base::__before_begin()->__next_ == nullptr;
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT {
     return std::min<size_type>(__node_traits::max_size(this->__alloc_), numeric_limits<
diff erence_type>::max());
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reference front() {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reference front() {
     _LIBCPP_ASSERT_NON_NULL(!empty(), "forward_list::front called on an empty list");
     return __base::__before_begin()->__next_->__get_value();
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reference front() const {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reference front() const {
     _LIBCPP_ASSERT_NON_NULL(!empty(), "forward_list::front called on an empty list");
     return __base::__before_begin()->__next_->__get_value();
   }

diff  --git a/libcxx/test/libcxx/diagnostics/forward_list.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/forward_list.nodiscard.verify.cpp
index 7594a1d299a50..671c7f71ab2a2 100644
--- a/libcxx/test/libcxx/diagnostics/forward_list.nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/diagnostics/forward_list.nodiscard.verify.cpp
@@ -13,6 +13,27 @@
 #include <forward_list>
 
 void test() {
-  std::forward_list<int> forward_list;
-  forward_list.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::forward_list<int> fl;
+  const std::forward_list<int> cfl;
+
+  fl.get_allocator(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+  fl.begin();          // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  cfl.begin();         // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  fl.end();            // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  cfl.end();           // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  fl.cbegin();         // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  cfl.cbegin();        // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  fl.cend();           // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  cfl.cend();          // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  fl.before_begin();   // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  cfl.before_begin();  // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  fl.cbefore_begin();  // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  cfl.cbefore_begin(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+  fl.empty();    // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  fl.max_size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+  fl.front();  // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  cfl.front(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
 }