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[libc++][ranges] Applied [[nodiscard]] to common_view (#173176)

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`[[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/ranges
- https://wg21.link/range.common

Towards #172124
This commit is contained in:
Hristo Hristov 2025-12-23 18:47:53 +02:00 committed by GitHub
parent c15a73e96d
commit b6bf708a05
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GPG key ID: B5690EEEBB952194
2 changed files with 68 additions and 7 deletions
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14
libcxx/include/__ranges/common_view.h
View file

@ -56,16 +56,16 @@ public:
return __base_;
}
_LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
_LIBCPP_HIDE_FROM_ABI constexpr auto begin() {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin() {
if constexpr (random_access_range<_View> && sized_range<_View>)
return ranges::begin(__base_);
else
return common_iterator<iterator_t<_View>, sentinel_t<_View>>(ranges::begin(__base_));
}
_LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
requires range<const _View>
{
if constexpr (random_access_range<const _View> && sized_range<const _View>)
@ -74,14 +74,14 @@ public:
return common_iterator<iterator_t<const _View>, sentinel_t<const _View>>(ranges::begin(__base_));
}
_LIBCPP_HIDE_FROM_ABI constexpr auto end() {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end() {
if constexpr (random_access_range<_View> && sized_range<_View>)
return ranges::begin(__base_) + ranges::size(__base_);
else
return common_iterator<iterator_t<_View>, sentinel_t<_View>>(ranges::end(__base_));
}
_LIBCPP_HIDE_FROM_ABI constexpr auto end() const
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
requires range<const _View>
{
if constexpr (random_access_range<const _View> && sized_range<const _View>)
@ -90,13 +90,13 @@ public:
return common_iterator<iterator_t<const _View>, sentinel_t<const _View>>(ranges::end(__base_));
}
_LIBCPP_HIDE_FROM_ABI constexpr auto size()
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size()
requires sized_range<_View>
{
return ranges::size(__base_);
}
_LIBCPP_HIDE_FROM_ABI constexpr auto size() const
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
requires sized_range<const _View>
{
return ranges::size(__base_);

61
libcxx/test/libcxx/ranges/range.adaptors/range.common.view/nodiscard.verify.cpp Normal file
View file

@ -0,0 +1,61 @@
//===----------------------------------------------------------------------===//
//
// 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++20
// Check that functions are marked [[nodiscard]]
#include <ranges>
#include <utility>
struct NonCommonView : std::ranges::view_base {
int* begin() const;
const int* end() const;
int* base();
int* begin();
const int* end();
constexpr std::size_t size() const { return 0; };
};
static_assert(!std::ranges::common_range<NonCommonView>);
void test() {
NonCommonView range;
auto v = std::views::common(range);
// [range.common.view]
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::move(v).base();
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
v.begin();
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::as_const(v).begin();
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
v.end();
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::as_const(v).end();
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
v.size();
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::as_const(v).size();
// [range.common.overview]
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::views::common(v);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::views::common(range);
}