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[libc++] Mini-cleanup for [[nodiscard]] #172275

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[libc++] Mini-cleanup for [[nodiscard]] #172275

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004fa4b
Remove incorrect `[[nodiscard]]` from compound assignment operators
frederick-vs-ja Dec 15, 2025
79cf27e
Add missing `[[nodiscard]]` to `mdspan::size`
frederick-vs-ja Dec 15, 2025
d0b7b2e
Enable verifying `[[nodiscard]]` in C++03 for various components
frederick-vs-ja Dec 15, 2025
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6 changes: 3 additions & 3 deletions libcxx/include/__filesystem/copy_options.h
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Expand Up @@ -50,15 +50,15 @@ enum class copy_options : unsigned short {
return static_cast<copy_options>(~static_cast<unsigned short>(__lhs));
}

[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline copy_options& operator&=(copy_options& __lhs, copy_options __rhs) {
_LIBCPP_HIDE_FROM_ABI inline copy_options& operator&=(copy_options& __lhs, copy_options __rhs) {
return __lhs = __lhs & __rhs;
}

[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline copy_options& operator|=(copy_options& __lhs, copy_options __rhs) {
_LIBCPP_HIDE_FROM_ABI inline copy_options& operator|=(copy_options& __lhs, copy_options __rhs) {
return __lhs = __lhs | __rhs;
}

[[nodiscard]] _LIBCPP_HIDE_FROM_ABI inline copy_options& operator^=(copy_options& __lhs, copy_options __rhs) {
_LIBCPP_HIDE_FROM_ABI inline copy_options& operator^=(copy_options& __lhs, copy_options __rhs) {
return __lhs = __lhs ^ __rhs;
}
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@philnik777 philnik777 Dec 15, 2025

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Please add a regression test. I wasn't able to find any tests for these functions, so it'd be appreciated if they were added. That would probably have caught this.

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@frederick-vs-ja frederick-vs-ja Dec 15, 2025

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Now I'm adding it to libcxx/test/std/input.output/filesystems/fs.enum/enum.copy_options.pass.cpp.


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2 changes: 1 addition & 1 deletion libcxx/include/__mdspan/mdspan.h
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Expand Up @@ -214,7 +214,7 @@ class mdspan {
}(make_index_sequence<rank()>()));
}

_LIBCPP_HIDE_FROM_ABI constexpr size_type size() const noexcept {
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr size_type size() const noexcept {
// Could leave this as only checked in debug mode: semantically size() is never
// guaranteed to be related to any accessible range
_LIBCPP_ASSERT_UNCATEGORIZED(
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2 changes: 1 addition & 1 deletion libcxx/test/libcxx/containers/views/mdspan/mdspan/assert.size.pass.cpp
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Expand Up @@ -43,7 +43,7 @@ int main(int, char**) {
assert(map.required_span_size() == static_cast<signed char>(12));
// 100 x 3 exceeds 256
{
TEST_LIBCPP_ASSERT_FAILURE(([=] { mds.size(); }()), "mdspan: size() is not representable as size_type");
TEST_LIBCPP_ASSERT_FAILURE(([=] { (void)mds.size(); }()), "mdspan: size() is not representable as size_type");
}
}
return 0;
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2 changes: 2 additions & 0 deletions libcxx/test/libcxx/containers/views/mdspan/nodiscard.verify.cpp
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Expand Up @@ -33,6 +33,8 @@ void test() {
mdsp.static_extent(0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
mdsp.extent(0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

mdsp.size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

mdsp.extents(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
mdsp.data_handle(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
mdsp.mapping(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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8 changes: 6 additions & 2 deletions libcxx/test/libcxx/diagnostics/algorithm.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <algorithm> functions are marked [[nodiscard]]

// clang-format off
Expand Down Expand Up @@ -188,11 +186,13 @@ void test() {
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::max(1, 2, std::greater<int>());

#if TEST_STD_VER >= 11
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::max({1, 2, 3});

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::max({1, 2, 3}, std::greater<int>());
#endif

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::min_element(std::begin(arr), std::end(arr));
Expand All @@ -206,11 +206,13 @@ void test() {
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::min(1, 2, std::greater<int>());

#if TEST_STD_VER >= 11
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::min({1, 2, 3});

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::min({1, 2, 3}, std::greater<int>());
#endif

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::minmax_element(std::begin(arr), std::end(arr));
Expand All @@ -224,11 +226,13 @@ void test() {
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::minmax(1, 2, std::greater<int>());

#if TEST_STD_VER >= 11
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::minmax({1, 2, 3});

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::minmax({1, 2, 3}, std::greater<int>());
#endif

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::mismatch(std::begin(arr), std::end(arr), std::begin(arr));
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6 changes: 2 additions & 4 deletions libcxx/test/libcxx/diagnostics/array.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <array> functions are marked [[nodiscard]]

#include <array>
Expand All @@ -18,7 +16,7 @@
template <std::size_t N>
void test_members() {
std::array<int, N> a;
const std::array<int, N> ca{};
const std::array<int, N> ca = {};

a.begin(); // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
ca.begin(); // expected-warning 2 {{ignoring return value of function declared with 'nodiscard' attribute}}
Expand Down Expand Up @@ -57,7 +55,7 @@ void test_members() {

template <typename ArrT>
void test_get() {
std::array<int, 94> a{};
std::array<int, 94> a = {};

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get<0>(a);
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2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/cstdlib.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// We don't control the implementation of the stdlib.h functions on windows
// UNSUPPORTED: windows

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2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/deque.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <deque> functions are marked [[nodiscard]]

#include <deque>
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2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/forward_list.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <forward_list> functions are marked [[nodiscard]]

#include <forward_list>
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8 changes: 4 additions & 4 deletions libcxx/test/libcxx/diagnostics/functional.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <functional> functions are marked [[nodiscard]]

#include <cstddef>
Expand All @@ -20,7 +18,7 @@ void test() {

// Function wrappers

#if !defined(TEST_HAS_NO_RTTI)
#if TEST_STD_VER >= 11 && !defined(TEST_HAS_NO_RTTI)
std::function<void(int)> f;
const std::function<void(int)> cf;

Expand Down Expand Up @@ -48,14 +46,16 @@ void test() {
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::bind_front([](int a) { return a; }, 94);
#endif
#if TEST_STD_VER >= 11
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::bind([](int a) { return a; }, 94);
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::bind<float>([](int a) { return a; }, 94);
#endif

// Reference wrappers

std::reference_wrapper<int> rw{i};
std::reference_wrapper<int> rw = i;
rw.get(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}

std::ref(i); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/limits.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <limits> functions are marked [[nodiscard]]

#include <limits>
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2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/list.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <list> functions are marked [[nodiscard]]

#include <list>
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22 changes: 10 additions & 12 deletions libcxx/test/libcxx/diagnostics/mutex.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// UNSUPPORTED: no-threads

// check that <mutex> functions are marked [[nodiscard]]
Expand Down Expand Up @@ -47,23 +45,23 @@ void test() {
std::unique_lock<M> other;

// clang-format off
std::unique_lock<M>{}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>{m}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>{m, std::defer_lock}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>{m, std::try_to_lock}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>{m, std::adopt_lock}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>{m, time_point}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>{m, duration}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>(std::move(other)); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>(); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
(std::unique_lock<M>)(m); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>(m, std::defer_lock_t()); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>(m, std::try_to_lock_t()); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>(m, std::adopt_lock_t()); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>(m, time_point); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>(m, duration); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::unique_lock<M>(std::move(other)); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
// clang-format on
}

// std::lock_guard
{
std::mutex m;
// clang-format off
std::lock_guard<std::mutex>{m}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::lock_guard<std::mutex>{m, std::adopt_lock}; // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
(std::lock_guard<std::mutex>)(m); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
std::lock_guard<std::mutex>(m, std::adopt_lock_t()); // expected-warning {{ignoring temporary created by a constructor declared with 'nodiscard' attribute}}
// clang-format on
}
}
2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/new.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <array> functions are marked [[nodiscard]]

// clang-format off
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4 changes: 1 addition & 3 deletions libcxx/test/libcxx/diagnostics/queue.nodiscard.verify.cpp
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Expand Up @@ -6,16 +6,14 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <queue> functions are marked [[nodiscard]]

#include <queue>

void test() {
{
std::queue<int> q;
const std::queue<int> cq{};
const std::queue<int> cq;

q.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
q.size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
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2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/stack.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <stack> functions are marked [[nodiscard]]

#include <stack>
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2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/string.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <string> functions are marked [[nodiscard]]

#include <string>
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4 changes: 1 addition & 3 deletions libcxx/test/libcxx/diagnostics/string_view.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <string_view> functions are marked [[nodiscard]]

#include <string_view>
Expand Down Expand Up @@ -126,7 +124,7 @@ void test_nonmembers() {

std::hash<std::string_view> hash;
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
hash(std::string_view{});
hash(std::string_view());

#if TEST_STD_VER >= 14
// string_view literals
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2 changes: 0 additions & 2 deletions libcxx/test/libcxx/diagnostics/utility.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <utility> functions are marked [[nodiscard]]

#include <utility>
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14 changes: 6 additions & 8 deletions libcxx/test/libcxx/diagnostics/vector.nodiscard.verify.cpp
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Expand Up @@ -6,8 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03

// check that <vector> functions are marked [[nodiscard]]

#include <type_traits>
Expand Down Expand Up @@ -44,11 +42,11 @@ void test_non_vector_bool() {
}

void instantiate() {
test<std::vector<int>>();
test<const std::vector<int>>();
test<std::vector<bool>>();
test<const std::vector<bool>>();
test<std::vector<int> >();
test<const std::vector<int> >();
test<std::vector<bool> >();
test<const std::vector<bool> >();

test_non_vector_bool<std::vector<int>>();
test_non_vector_bool<const std::vector<int>>();
test_non_vector_bool<std::vector<int> >();
test_non_vector_bool<const std::vector<int> >();
}
7 changes: 4 additions & 3 deletions libcxx/test/libcxx/thread/nodiscard.verify.cpp
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Expand Up @@ -6,7 +6,6 @@
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03
// UNSUPPORTED: no-threads

// Check that functions are marked [[nodiscard]]
Expand Down Expand Up @@ -65,7 +64,7 @@ void test() {
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
m.try_lock();
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
m.try_lock_for(std::chrono::nanoseconds{82});
m.try_lock_for(std::chrono::nanoseconds(82));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
m.try_lock_until(timePoint);
}
Expand All @@ -75,7 +74,7 @@ void test() {
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
m.try_lock();
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
m.try_lock_for(std::chrono::nanoseconds{82});
m.try_lock_for(std::chrono::nanoseconds(82));
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
m.try_lock_until(timePoint);
}
Expand All @@ -86,8 +85,10 @@ void test() {

// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::try_lock(m1, m2);
#if TEST_STD_VER >= 11
// expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
std::try_lock(m1, m2, m3);
#endif
}

// Condition variables
Expand Down
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