[libcxx-commits] [libcxx] [libc++][list] Applied `[[nodiscard]]` (PR #169015)

[via libcxx-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Hristo Hristov (H-G-Hristov)

<details>
<summary>Changes</summary>

`[[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

---
Full diff: https://github.com/llvm/llvm-project/pull/169015.diff


2 Files Affected:

- (modified) libcxx/include/list (+19-19) 
- (modified) libcxx/test/libcxx/diagnostics/list.nodiscard.verify.cpp (+24-2) 


``````````diff
diff --git a/libcxx/include/list b/libcxx/include/list
index 2898a45da0029..518d91dbf1e50 100644
--- a/libcxx/include/list
+++ b/libcxx/include/list
@@ -774,57 +774,57 @@ public:
 
   _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI void assign(size_type __n, const value_type& __x);
 
-  _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;
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return this->__size_; }
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return this->__size_; }
   [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI bool empty() const _NOEXCEPT {
     return __base::empty();
   }
-  _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>(this->__node_alloc_max_size(), numeric_limits<difference_type >::max());
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return __base::begin(); }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return __base::begin(); }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return __base::end(); }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return __base::end(); }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return __base::begin(); }
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return __base::begin(); }
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return __base::end(); }
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return __base::end(); }
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT {
     return __base::begin();
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT { return __base::end(); }
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT { return __base::end(); }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reverse_iterator rbegin() _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reverse_iterator rbegin() _NOEXCEPT {
     return reverse_iterator(end());
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rbegin() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rbegin() const _NOEXCEPT {
     return const_reverse_iterator(end());
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reverse_iterator rend() _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reverse_iterator rend() _NOEXCEPT {
     return reverse_iterator(begin());
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rend() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rend() const _NOEXCEPT {
     return const_reverse_iterator(begin());
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crbegin() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crbegin() const _NOEXCEPT {
     return const_reverse_iterator(end());
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crend() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crend() const _NOEXCEPT {
     return const_reverse_iterator(begin());
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reference front() {
+ [[__nodiscard__]]  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reference front() {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "list::front called on empty list");
     return __base::__end_.__next_->__as_node()->__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_VALID_ELEMENT_ACCESS(!empty(), "list::front called on empty list");
     return __base::__end_.__next_->__as_node()->__get_value();
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reference back() {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI reference back() {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "list::back called on empty list");
     return __base::__end_.__prev_->__as_node()->__get_value();
   }
-  _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reference back() const {
+  [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX26 _LIBCPP_HIDE_FROM_ABI const_reference back() const {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "list::back called on empty list");
     return __base::__end_.__prev_->__as_node()->__get_value();
   }
diff --git a/libcxx/test/libcxx/diagnostics/list.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/list.nodiscard.verify.cpp
index f19224a71f5cc..9e7029b5794d4 100644
--- a/libcxx/test/libcxx/diagnostics/list.nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/diagnostics/list.nodiscard.verify.cpp
@@ -12,7 +12,29 @@
 
 #include <list>
 
+template <typename ListT>
 void test() {
-  std::list<int> list;
-  list.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  ListT list{};
+
+  list.get_allocator(); // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.size();          // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.empty();         // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.max_size();      // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+  list.begin();   // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.end();     // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.cbegin();  // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.cend();    // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.rbegin();  // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.rend();    // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.crbegin(); // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.crend();   // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+  list.front(); // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  list.back();  // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
+}
+
+void test() {
+  test<std::list<int>>();
+  test<const std::list<int>>();
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/169015