[libcxx-commits] [libcxx] [libc++][pstl] Applied `[[nodiscard]]` (PR #174015)
Hristo Hristov via libcxx-commits
libcxx-commits at lists.llvm.org
Tue Dec 30 12:06:18 PST 2025
https://github.com/H-G-Hristov created https://github.com/llvm/llvm-project/pull/174015
`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue.
- https://libcxx.llvm.org/CodingGuidelines.html
Towards #172124
>From 37da65adf609c5ef44eb7570a30716977a5508c2 Mon Sep 17 00:00:00 2001
From: Hristo Hristov <hghristov.rmm at gmail.com>
Date: Tue, 30 Dec 2025 22:05:50 +0200
Subject: [PATCH] [libc++][pstl] Applied `[[nodiscard]]`
`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue.
- https://libcxx.llvm.org/CodingGuidelines.html
Towards #172124
---
libcxx/include/__algorithm/pstl.h | 18 ++++-----
.../diagnostics/pstl.nodiscard.verify.cpp | 40 ++++++++++++++-----
2 files changed, 40 insertions(+), 18 deletions(-)
diff --git a/libcxx/include/__algorithm/pstl.h b/libcxx/include/__algorithm/pstl.h
index eea07e2b96b64..7169dd85df602 100644
--- a/libcxx/include/__algorithm/pstl.h
+++ b/libcxx/include/__algorithm/pstl.h
@@ -115,7 +115,7 @@ template <class _ExecutionPolicy,
class _Predicate,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI __iterator_difference_type<_ForwardIterator>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI __iterator_difference_type<_ForwardIterator>
count_if(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
_LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(
_ForwardIterator, "count_if(first, last, pred) requires [first, last) to be ForwardIterators");
@@ -129,7 +129,7 @@ template <class _ExecutionPolicy,
class _Tp,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI __iterator_difference_type<_ForwardIterator>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI __iterator_difference_type<_ForwardIterator>
count(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
_LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(
_ForwardIterator, "count(first, last, val) requires [first, last) to be ForwardIterators");
@@ -144,7 +144,7 @@ template <class _ExecutionPolicy,
class _Pred,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI bool
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool
equal(_ExecutionPolicy&& __policy,
_ForwardIterator1 __first1,
_ForwardIterator1 __last1,
@@ -166,7 +166,7 @@ template <class _ExecutionPolicy,
class _ForwardIterator2,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI bool
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool
equal(_ExecutionPolicy&& __policy, _ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2) {
_LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator1, "equal requires ForwardIterators");
_LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator2, "equal requires ForwardIterators");
@@ -185,7 +185,7 @@ template <class _ExecutionPolicy,
class _Pred,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI bool
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool
equal(_ExecutionPolicy&& __policy,
_ForwardIterator1 __first1,
_ForwardIterator1 __last1,
@@ -209,7 +209,7 @@ template <class _ExecutionPolicy,
class _ForwardIterator2,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI bool
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool
equal(_ExecutionPolicy&& __policy,
_ForwardIterator1 __first1,
_ForwardIterator1 __last1,
@@ -259,7 +259,7 @@ template <class _ExecutionPolicy,
class _Predicate,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI _ForwardIterator
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _ForwardIterator
find_if(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
_LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator, "find_if requires ForwardIterators");
using _Implementation = __pstl::__dispatch<__pstl::__find_if, __pstl::__current_configuration, _RawPolicy>;
@@ -272,7 +272,7 @@ template <class _ExecutionPolicy,
class _Predicate,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI _ForwardIterator
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _ForwardIterator
find_if_not(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
_LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator, "find_if_not requires ForwardIterators");
using _Implementation = __pstl::__dispatch<__pstl::__find_if_not, __pstl::__current_configuration, _RawPolicy>;
@@ -285,7 +285,7 @@ template <class _ExecutionPolicy,
class _Tp,
class _RawPolicy = __remove_cvref_t<_ExecutionPolicy>,
enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI _ForwardIterator
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI _ForwardIterator
find(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
_LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator, "find requires ForwardIterators");
using _Implementation = __pstl::__dispatch<__pstl::__find, __pstl::__current_configuration, _RawPolicy>;
diff --git a/libcxx/test/libcxx/diagnostics/pstl.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/pstl.nodiscard.verify.cpp
index a16e07168f700..712c0deb68c83 100644
--- a/libcxx/test/libcxx/diagnostics/pstl.nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/diagnostics/pstl.nodiscard.verify.cpp
@@ -6,23 +6,45 @@
//
//===----------------------------------------------------------------------===//
-// Check that PSTL algorithms are marked [[nodiscard]] as a conforming extension
+// REQUIRES: std-at-least-c++17
// UNSUPPORTED: libcpp-has-no-incomplete-pstl
-// UNSUPPORTED: c++03, c++11, c++14
-
-// clang-format off
+// Check that PSTL algorithms are marked [[nodiscard]]
#include <algorithm>
#include <execution>
#include <iterator>
void test() {
- int a[] = {1};
+ int a[] = {1};
+ int b[] = {1};
auto pred = [](auto) { return false; };
- std::all_of(std::execution::par, std::begin(a), std::end(a), pred); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
- std::any_of(std::execution::par, std::begin(a), std::end(a), pred); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
- std::none_of(std::execution::par, std::begin(a), std::end(a), pred); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
- std::is_partitioned(std::execution::par, std::begin(a), std::end(a), pred); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::all_of(std::execution::par, std::begin(a), std::end(a), pred);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::any_of(std::execution::par, std::begin(a), std::end(a), pred);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::none_of(std::execution::par, std::begin(a), std::end(a), pred);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::count_if(std::execution::par, std::begin(a), std::end(a), pred);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::count(std::execution::par, std::begin(a), std::end(a), 1);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::equal(std::execution::par, std::begin(a), std::end(a), std::begin(b), pred);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::equal(std::execution::par, std::begin(a), std::end(a), std::begin(b));
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::equal(std::execution::par, std::begin(a), std::end(a), std::begin(b), std::end(b), pred);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::equal(std::execution::par, std::begin(a), std::end(a), std::begin(b), std::end(b));
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::find_if(std::execution::par, std::begin(a), std::end(a), pred);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::find_if_not(std::execution::par, std::begin(a), std::end(a), pred);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::find(std::execution::par, std::begin(a), std::end(a), 1);
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::is_partitioned(std::execution::par, std::begin(a), std::end(a), pred);
}
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