[libc++][list] Applied [[nodiscard]]

[H-G-Hristov]

[[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

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Hristo Hristov (H-G-Hristov)

Changes

[[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 --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>>(); } 

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