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[libc++][ranges] Applied [[nodiscard]] to as_rvalue_view (#173145)

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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.as.rvalue

Towards #172124
This commit is contained in:
Hristo Hristov 2025-12-23 18:47:37 +02:00 committed by GitHub
parent cbcda2dc08
commit c15a73e96d
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GPG Key ID: B5690EEEBB952194
2 changed files with 71 additions and 8 deletions
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16
libcxx/include/__ranges/as_rvalue_view.h
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@ -48,27 +48,27 @@ public:
_LIBCPP_HIDE_FROM_ABI constexpr explicit as_rvalue_view(_View __base) : __base_(std::move(__base)) {}
_LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
requires copy_constructible<_View>
{
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()
requires(!__simple_view<_View>)
{
return move_iterator(ranges::begin(__base_));
}
_LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
requires range<const _View>
{
return move_iterator(ranges::begin(__base_));
}
_LIBCPP_HIDE_FROM_ABI constexpr auto end()
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end()
requires(!__simple_view<_View>)
{
if constexpr (common_range<_View>) {
@ -78,7 +78,7 @@ public:
}
}
_LIBCPP_HIDE_FROM_ABI constexpr auto end() const
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
requires range<const _View>
{
if constexpr (common_range<const _View>) {
@ -88,13 +88,13 @@ public:
}
}
_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_);

63
libcxx/test/libcxx/ranges/range.adaptors/range.as_rvalue_view/nodiscard.verify.cpp Normal file
View File

@ -0,0 +1,63 @@
//===----------------------------------------------------------------------===//
//
// 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>
#include <utility>
#include "test_range.h"
struct NonSimpleView : std::ranges::view_base {
int* begin() const;
int* end() const;
const int* begin();
const int* end();
constexpr std::size_t size() { return 0; };
};
static_assert(!simple_view<NonSimpleView>);
void test() {
NonSimpleView range;
auto v = std::views::as_rvalue(range);
// [range.as.rvalue.view]
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
v.base();
// 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.as.rvalue.overview]
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::views::as_rvalue(range);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::views::as_rvalue(v);
}