[libcxx-commits] [libcxx] [libc++][string] Applied `[[nodiscard]]` to non-member functions (PR #169330)
Hristo Hristov via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Nov 24 08:53:21 PST 2025
https://github.com/H-G-Hristov updated https://github.com/llvm/llvm-project/pull/169330
>From 9612b3bab168b79a57ec0fa0016fc94ba55be0b7 Mon Sep 17 00:00:00 2001
From: Hristo Hristov <hghristov.rmm at gmail.com>
Date: Mon, 24 Nov 2025 16:22:05 +0200
Subject: [PATCH] [libc++][string] Applied `[[nodiscard]]` to non-member
functions
`[[nodiscard]]` should be applied to functions where discarding the return value is most likely a correctness issue.
- https://libcxx.llvm.org/CodingGuidelines.html#apply-nodiscard-where-relevant
---
libcxx/include/string | 99 ++++++++++---------
.../diagnostics/string.nodiscard.verify.cpp | 77 +++++++++++++++
2 files changed, 130 insertions(+), 46 deletions(-)
diff --git a/libcxx/include/string b/libcxx/include/string
index 6b42cb2c7586d..2b3ba6d2d9b62 100644
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -3851,46 +3851,52 @@ swap(basic_string<_CharT, _Traits, _Allocator>& __lhs, basic_string<_CharT, _Tra
__lhs.swap(__rhs);
}
-_LIBCPP_EXPORTED_FROM_ABI int stoi(const string& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_EXPORTED_FROM_ABI long stol(const string& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_EXPORTED_FROM_ABI unsigned long stoul(const string& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_EXPORTED_FROM_ABI long long stoll(const string& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_EXPORTED_FROM_ABI unsigned long long stoull(const string& __str, size_t* __idx = nullptr, int __base = 10);
-
-_LIBCPP_EXPORTED_FROM_ABI float stof(const string& __str, size_t* __idx = nullptr);
-_LIBCPP_EXPORTED_FROM_ABI double stod(const string& __str, size_t* __idx = nullptr);
-_LIBCPP_EXPORTED_FROM_ABI long double stold(const string& __str, size_t* __idx = nullptr);
-
-_LIBCPP_EXPORTED_FROM_ABI string to_string(int __val);
-_LIBCPP_EXPORTED_FROM_ABI string to_string(unsigned __val);
-_LIBCPP_EXPORTED_FROM_ABI string to_string(long __val);
-_LIBCPP_EXPORTED_FROM_ABI string to_string(unsigned long __val);
-_LIBCPP_EXPORTED_FROM_ABI string to_string(long long __val);
-_LIBCPP_EXPORTED_FROM_ABI string to_string(unsigned long long __val);
-_LIBCPP_EXPORTED_FROM_ABI string to_string(float __val);
-_LIBCPP_EXPORTED_FROM_ABI string to_string(double __val);
-_LIBCPP_EXPORTED_FROM_ABI string to_string(long double __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI int stoi(const string& __str, size_t* __idx = nullptr, int __base = 10);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI unsigned long
+stoul(const string& __str, size_t* __idx = nullptr, int __base = 10);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI long stol(const string& __str, size_t* __idx = nullptr, int __base = 10);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI long long
+stoll(const string& __str, size_t* __idx = nullptr, int __base = 10);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI unsigned long long
+stoull(const string& __str, size_t* __idx = nullptr, int __base = 10);
+
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI float stof(const string& __str, size_t* __idx = nullptr);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI double stod(const string& __str, size_t* __idx = nullptr);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI long double stold(const string& __str, size_t* __idx = nullptr);
+
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(int __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(unsigned __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(long __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(unsigned long __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(long long __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(unsigned long long __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(float __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(double __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI string to_string(long double __val);
# if _LIBCPP_HAS_WIDE_CHARACTERS
-_LIBCPP_EXPORTED_FROM_ABI int stoi(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_EXPORTED_FROM_ABI long stol(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_EXPORTED_FROM_ABI unsigned long stoul(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_EXPORTED_FROM_ABI long long stoll(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_EXPORTED_FROM_ABI unsigned long long stoull(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-
-_LIBCPP_EXPORTED_FROM_ABI float stof(const wstring& __str, size_t* __idx = nullptr);
-_LIBCPP_EXPORTED_FROM_ABI double stod(const wstring& __str, size_t* __idx = nullptr);
-_LIBCPP_EXPORTED_FROM_ABI long double stold(const wstring& __str, size_t* __idx = nullptr);
-
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(int __val);
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(unsigned __val);
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(long __val);
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(unsigned long __val);
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(long long __val);
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(unsigned long long __val);
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(float __val);
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(double __val);
-_LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(long double __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI int stoi(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI long stol(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI unsigned long
+stoul(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI long long
+stoll(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI unsigned long long
+stoull(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
+
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI float stof(const wstring& __str, size_t* __idx = nullptr);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI double stod(const wstring& __str, size_t* __idx = nullptr);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI long double stold(const wstring& __str, size_t* __idx = nullptr);
+
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(int __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(unsigned __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(long __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(unsigned long __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(long long __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(unsigned long long __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(float __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(double __val);
+[[__nodiscard__]] _LIBCPP_EXPORTED_FROM_ABI wstring to_wstring(long double __val);
# endif // _LIBCPP_HAS_WIDE_CHARACTERS
template <class _CharT, class _Traits, class _Allocator>
@@ -3899,7 +3905,7 @@ _LIBCPP_TEMPLATE_DATA_VIS const typename basic_string<_CharT, _Traits, _Allocato
template <class _CharT, class _Allocator>
struct __string_hash : public __unary_function<basic_string<_CharT, char_traits<_CharT>, _Allocator>, size_t> {
- _LIBCPP_HIDE_FROM_ABI size_t
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI size_t
operator()(const basic_string<_CharT, char_traits<_CharT>, _Allocator>& __val) const _NOEXCEPT {
return std::__do_string_hash(__val.data(), __val.data() + __val.size());
}
@@ -3970,30 +3976,31 @@ erase_if(basic_string<_CharT, _Traits, _Allocator>& __str, _Predicate __pred) {
// Literal suffixes for basic_string [basic.string.literals]
inline namespace literals {
inline namespace string_literals {
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<char>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<char>
operator""s(const char* __str, size_t __len) {
return basic_string<char>(__str, __len);
}
# if _LIBCPP_HAS_WIDE_CHARACTERS
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<wchar_t>
-operator""s(const wchar_t* __str, size_t __len) {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<wchar_t> operator""s(const wchar_t* __str, size_t __len) {
return basic_string<wchar_t>(__str, __len);
}
# endif
# if _LIBCPP_HAS_CHAR8_T
-inline _LIBCPP_HIDE_FROM_ABI constexpr basic_string<char8_t> operator""s(const char8_t* __str, size_t __len) {
+[[__nodiscard__]] inline
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_string<char8_t> operator""s(const char8_t* __str, size_t __len) {
return basic_string<char8_t>(__str, __len);
}
# endif
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<char16_t>
-operator""s(const char16_t* __str, size_t __len) {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<char16_t> operator""s(const char16_t* __str, size_t __len) {
return basic_string<char16_t>(__str, __len);
}
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<char32_t>
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<char32_t>
operator""s(const char32_t* __str, size_t __len) {
return basic_string<char32_t>(__str, __len);
}
diff --git a/libcxx/test/libcxx/diagnostics/string.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/string.nodiscard.verify.cpp
index f020516a2495a..0ff92cac3a3b2 100644
--- a/libcxx/test/libcxx/diagnostics/string.nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/diagnostics/string.nodiscard.verify.cpp
@@ -130,3 +130,80 @@ void test() {
str.subview(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
#endif
}
+
+void test_nonmembers() {
+ // Numeric conversions
+
+ std::string str;
+
+ std::stoi(str); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stol(str); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stoll(str); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stoull(str); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::stof(str); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stod(str); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stold(str); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::to_string(94); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_string(82U); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_string(94L); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_string(82UL); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_string(94LL); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_string(82ULL); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_string(94.0F); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_string(82.0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_string(94.0L); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+#if !defined(TEST_HAS_NO_WIDE_CHARACTERS)
+
+ std::wstring wstr;
+
+ std::stoi(wstr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stol(wstr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stoll(wstr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stoull(wstr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::stof(wstr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stod(wstr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::stold(wstr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+ std::to_wstring(94); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_wstring(82U); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_wstring(94L); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_wstring(82UL); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_wstring(94LL); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_wstring(82ULL); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_wstring(94.0F); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_wstring(82.0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ std::to_wstring(94.0L); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+#endif
+
+ // std::hash<>
+
+ std::hash<std::string> hash;
+
+ hash(str); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+#if TEST_STD_VER >= 14
+ // string literals
+
+ using namespace std::string_literals;
+
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ ""s; // const char*
+# if !defined(TEST_HAS_NO_WIDE_CHARACTERS)
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ L""s; // const wchar_t*
+# endif
+# if !defined(TEST_HAS_NO_CHAR8_T)
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ u8""s; // const char8_t*
+# endif
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ u""s; // const char16_t*
+ // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+ U""s; // const char32_t*
+#endif
+}
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