[libcxx-commits] [libcxx] 0347c30 - [libc++][ranges] Applied `[[nodiscard]]` to `take_view` (#173738)
via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Dec 29 08:44:39 PST 2025
Author: Hristo Hristov
Date: 2025-12-29T18:44:35+02:00
New Revision: 0347c30f6878206e14842f260bcb58e435766d6f
URL: https://github.com/llvm/llvm-project/commit/0347c30f6878206e14842f260bcb58e435766d6f
DIFF: https://github.com/llvm/llvm-project/commit/0347c30f6878206e14842f260bcb58e435766d6f.diff
LOG: [libc++][ranges] Applied `[[nodiscard]]` to `take_view` (#173738)
`[[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.take
Towards #172124
Added:
libcxx/test/libcxx/ranges/range.adaptors/range.take/nodiscard.verify.cpp
Modified:
libcxx/include/__ranges/take_view.h
Removed:
################################################################################
diff --git a/libcxx/include/__ranges/take_view.h b/libcxx/include/__ranges/take_view.h
index 85723dc5e36b6..13cb4a285d9df 100644
--- a/libcxx/include/__ranges/take_view.h
+++ b/libcxx/include/__ranges/take_view.h
@@ -75,15 +75,15 @@ class take_view : public view_interface<take_view<_View>> {
_LIBCPP_ASSERT_UNCATEGORIZED(__count >= 0, "count has to be greater than or equal to zero");
}
- _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>)
{
if constexpr (sized_range<_View>) {
@@ -99,7 +99,7 @@ class take_view : public view_interface<take_view<_View>> {
}
}
- _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
requires range<const _View>
{
if constexpr (sized_range<const _View>) {
@@ -115,7 +115,7 @@ class take_view : public view_interface<take_view<_View>> {
}
}
- _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end()
requires(!__simple_view<_View>)
{
if constexpr (sized_range<_View>) {
@@ -129,7 +129,7 @@ class take_view : public view_interface<take_view<_View>> {
}
}
- _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
requires range<const _View>
{
if constexpr (sized_range<const _View>) {
@@ -143,14 +143,14 @@ class take_view : public view_interface<take_view<_View>> {
}
}
- _LIBCPP_HIDE_FROM_ABI constexpr auto size()
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size()
requires sized_range<_View>
{
auto __n = ranges::size(__base_);
return ranges::min(__n, static_cast<decltype(__n)>(__count_));
}
- _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
requires sized_range<const _View>
{
auto __n = ranges::size(__base_);
@@ -178,7 +178,7 @@ class take_view<_View>::__sentinel {
requires _Const && convertible_to<sentinel_t<_View>, sentinel_t<_Base>>
: __end_(std::move(__s.__end_)) {}
- _LIBCPP_HIDE_FROM_ABI constexpr sentinel_t<_Base> base() const { return __end_; }
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr sentinel_t<_Base> base() const { return __end_; }
_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const _Iter<_Const>& __lhs, const __sentinel& __rhs) {
return __lhs.count() == 0 || __lhs.base() == __rhs.__end_;
diff --git a/libcxx/test/libcxx/ranges/range.adaptors/range.take/nodiscard.verify.cpp b/libcxx/test/libcxx/ranges/range.adaptors/range.take/nodiscard.verify.cpp
new file mode 100644
index 0000000000000..621b20b29e3a1
--- /dev/null
+++ b/libcxx/test/libcxx/ranges/range.adaptors/range.take/nodiscard.verify.cpp
@@ -0,0 +1,143 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// <ranges>
+
+// Check that functions are marked [[nodiscard]]
+
+#include <ranges>
+#include <vector>
+#include <utility>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+
+void test() {
+ // [range.take.view]
+
+ {
+ std::vector<int> range;
+
+ auto v = std::views::take(range, 0);
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ v.base();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::move(v).base();
+
+ // 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}}
+ std::as_const(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}}
+ std::as_const(v).end();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ v.size();
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::as_const(v).size();
+ }
+
+ // [range.take.sentinel]
+
+ {
+ struct MoveOnlyView : std::ranges::view_base {
+ int* ptr_;
+
+ constexpr explicit MoveOnlyView(int* ptr) : ptr_(ptr) {}
+ MoveOnlyView(MoveOnlyView&&) = default;
+ MoveOnlyView& operator=(MoveOnlyView&&) = default;
+
+ constexpr int* begin() const { return ptr_; }
+ constexpr sentinel_wrapper<int*> end() const { return sentinel_wrapper<int*>{ptr_ + 8}; }
+ };
+
+ int arr[]{94, 82, 49};
+ auto v = std::views::take(MoveOnlyView{arr}, 0);
+
+ auto st = v.end();
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::as_const(st).base();
+ }
+
+ // [range.take.overview]
+
+ { // The `empty_view` case.
+ auto emptyView = std::views::empty<int>;
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::take(emptyView, 0);
+ }
+
+ { // The `span | basic_string_view | subrange` case.
+ int arr[]{94, 82, 49};
+ auto subrange = std::ranges::subrange(arr, arr + 3);
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::take(subrange, 3);
+ }
+
+ { // The `iota_view` case.
+ auto iota = std::views::iota(94, 47);
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::take(iota, 3);
+ }
+
+#if TEST_STD_VER >= 23
+ { // The `repeat_view` "_RawRange models sized_range" case.
+ auto repeat = std::ranges::repeat_view<int, int>(94, 8);
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::take(repeat, 3);
+ }
+
+ { // The `repeat_view` "otherwise" case.
+
+ auto repeat = std::ranges::repeat_view<int>(94);
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::take(repeat, 3);
+ }
+#endif // TEST_STD_VER >= 23
+
+ { // The "otherwise" case.
+ struct SizedView : std::ranges::view_base {
+ int* begin_ = nullptr;
+ int* end_ = nullptr;
+ constexpr SizedView(int* begin, int* end) : begin_(begin), end_(end) {}
+
+ constexpr auto begin() const { return forward_iterator<int*>(begin_); }
+ constexpr auto end() const { return sized_sentinel<forward_iterator<int*>>(forward_iterator<int*>(end_)); }
+ };
+ static_assert(std::ranges::forward_range<SizedView>);
+ static_assert(std::ranges::sized_range<SizedView>);
+ static_assert(std::ranges::view<SizedView>);
+
+ int arr[]{94, 82, 49};
+
+ SizedView view{arr, arr + 3};
+ auto subrange = std::ranges::subrange(view.begin(), view.end());
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::take(subrange, 3);
+ }
+
+ {
+ struct X {};
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::views::take(X{});
+ }
+}
More information about the libcxx-commits
mailing list