[libcxx-commits] [libcxx] [libc+][ranges] Applied `[[nodiscard]]` to `repeat_view` (PR #173712)
Hristo Hristov via libcxx-commits
libcxx-commits at lists.llvm.org
Sat Dec 27 00:21:23 PST 2025
https://github.com/H-G-Hristov updated https://github.com/llvm/llvm-project/pull/173712
>From 75a3b5605f4d647d8c7d45bbd2a8ab92743e4f25 Mon Sep 17 00:00:00 2001
From: Hristo Hristov <hghristov.rmm at gmail.com>
Date: Sat, 27 Dec 2025 10:17:42 +0200
Subject: [PATCH] [libc+][ranges] Applied `[[nodiscard]]` to `repeat_view`
`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue.
- https://libcxx.llvm.org/CodingGuidelines.html
- https://wg21.link/range.repeat
Towards #172124
---
libcxx/include/__ranges/repeat_view.h | 27 +++++----
.../range.repeat.view/nodiscard.verify.cpp | 58 +++++++++++++++++++
2 files changed, 75 insertions(+), 10 deletions(-)
create mode 100644 libcxx/test/libcxx/ranges/range.factories/range.repeat.view/nodiscard.verify.cpp
diff --git a/libcxx/include/__ranges/repeat_view.h b/libcxx/include/__ranges/repeat_view.h
index 56b09701c8090..9192183f48013 100644
--- a/libcxx/include/__ranges/repeat_view.h
+++ b/libcxx/include/__ranges/repeat_view.h
@@ -108,17 +108,21 @@ class _LIBCPP_ABI_LLVM18_NO_UNIQUE_ADDRESS repeat_view : public view_interface<r
__bound_ >= 0, "The behavior is undefined if Bound is not unreachable_sentinel_t and bound is negative");
}
- _LIBCPP_HIDE_FROM_ABI constexpr __iterator begin() const { return __iterator(std::addressof(*__value_)); }
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __iterator begin() const {
+ return __iterator(std::addressof(*__value_));
+ }
- _LIBCPP_HIDE_FROM_ABI constexpr __iterator end() const
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __iterator end() const
requires(!same_as<_Bound, unreachable_sentinel_t>)
{
return __iterator(std::addressof(*__value_), __bound_);
}
- _LIBCPP_HIDE_FROM_ABI constexpr unreachable_sentinel_t end() const noexcept { return unreachable_sentinel; }
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr unreachable_sentinel_t end() const noexcept {
+ return unreachable_sentinel;
+ }
- _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
requires(!same_as<_Bound, unreachable_sentinel_t>)
{
return std::__to_unsigned_like(__bound_);
@@ -152,7 +156,7 @@ class repeat_view<_Tp, _Bound>::__iterator {
_LIBCPP_HIDE_FROM_ABI __iterator() = default;
- _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& operator*() const noexcept { return *__value_; }
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& operator*() const noexcept { return *__value_; }
_LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator++() {
++__current_;
@@ -192,7 +196,9 @@ class repeat_view<_Tp, _Bound>::__iterator {
return *this;
}
- _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& operator[](difference_type __n) const noexcept { return *(*this + __n); }
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& operator[](difference_type __n) const noexcept {
+ return *(*this + __n);
+ }
_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const __iterator& __x, const __iterator& __y) {
return __x.__current_ == __y.__current_;
@@ -202,22 +208,23 @@ class repeat_view<_Tp, _Bound>::__iterator {
return __x.__current_ <=> __y.__current_;
}
- _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(__iterator __i, difference_type __n) {
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(__iterator __i, difference_type __n) {
__i += __n;
return __i;
}
- _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(difference_type __n, __iterator __i) {
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(difference_type __n, __iterator __i) {
__i += __n;
return __i;
}
- _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator-(__iterator __i, difference_type __n) {
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator-(__iterator __i, difference_type __n) {
__i -= __n;
return __i;
}
- _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type operator-(const __iterator& __x, const __iterator& __y) {
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type
+ operator-(const __iterator& __x, const __iterator& __y) {
return static_cast<difference_type>(__x.__current_) - static_cast<difference_type>(__y.__current_);
}
diff --git a/libcxx/test/libcxx/ranges/range.factories/range.repeat.view/nodiscard.verify.cpp b/libcxx/test/libcxx/ranges/range.factories/range.repeat.view/nodiscard.verify.cpp
new file mode 100644
index 0000000000000..2b1d149919ad1
--- /dev/null
+++ b/libcxx/test/libcxx/ranges/range.factories/range.repeat.view/nodiscard.verify.cpp
@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++23
+
+// Check that functions are marked [[nodiscard]]
+
+#include <ranges>
+
+void test() {
+ auto uv = std::views::repeat(49);
+ auto v = std::views::repeat(94, 82);
+
+ // [range.repeat.view]
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ v.begin();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ v.end();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ uv.end();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ v.size();
+
+ // [range.repeat.iterator]
+
+ auto it = v.begin();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ it[0];
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ it + 1;
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ 1 + it;
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ it - 1;
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ it - it;
+
+ // [range.repeat.overview]
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::repeat(47);
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::repeat(94, 82);
+}
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