[libcxx-commits] [libcxx] [libc++] Add [[nodiscard]] to std::prev and std::next (PR #109550)

[Marc Auberer via libcxx-commits]

https://github.com/marcauberer created https://github.com/llvm/llvm-project/pull/109550

Add `[[nodiscard]]` attribute to `std::prev` and `std::next`. Those are potential pitfalls for users who might think they mutate the iterator.

>From eed6911ccd65e7a145d6d28ec933dec79390028c Mon Sep 17 00:00:00 2001
From: Marc Auberer <marc.auberer at chillibits.com>
Date: Sat, 21 Sep 2024 22:47:15 +0200
Subject: [PATCH] [libc++] Add [[nodiscard]] to std::prev and std::next

---
 libcxx/include/__iterator/next.h | 8 ++++----
 libcxx/include/__iterator/prev.h | 6 +++---
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/libcxx/include/__iterator/next.h b/libcxx/include/__iterator/next.h
index fb6c8ea6d75508..4064bcec4e183b 100644
--- a/libcxx/include/__iterator/next.h
+++ b/libcxx/include/__iterator/next.h
@@ -43,25 +43,25 @@ next(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n =
 namespace ranges {
 struct __next {
   template <input_or_output_iterator _Ip>
-  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const {
     ++__x;
     return __x;
   }
 
   template <input_or_output_iterator _Ip>
-  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
     ranges::advance(__x, __n);
     return __x;
   }
 
   template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp>
-  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, _Sp __bound_sentinel) const {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, _Sp __bound_sentinel) const {
     ranges::advance(__x, __bound_sentinel);
     return __x;
   }
 
   template <input_or_output_iterator _Ip, sentinel_for<_Ip> _Sp>
-  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Sp __bound_sentinel) const {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Sp __bound_sentinel) const {
     ranges::advance(__x, __n, __bound_sentinel);
     return __x;
   }
diff --git a/libcxx/include/__iterator/prev.h b/libcxx/include/__iterator/prev.h
index e950d8dc414717..0b88d33d924cfe 100644
--- a/libcxx/include/__iterator/prev.h
+++ b/libcxx/include/__iterator/prev.h
@@ -42,19 +42,19 @@ prev(_InputIter __x, typename iterator_traits<_InputIter>::difference_type __n =
 namespace ranges {
 struct __prev {
   template <bidirectional_iterator _Ip>
-  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x) const {
     --__x;
     return __x;
   }
 
   template <bidirectional_iterator _Ip>
-  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n) const {
     ranges::advance(__x, -__n);
     return __x;
   }
 
   template <bidirectional_iterator _Ip>
-  _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const {
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip operator()(_Ip __x, iter_difference_t<_Ip> __n, _Ip __bound_iter) const {
     ranges::advance(__x, -__n, __bound_iter);
     return __x;
   }