[libcxx-commits] [libcxx] [libc++][string] Applied `[[nodiscard]]` to non-member functions (PR #169330)

[via libcxx-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Hristo Hristov (H-G-Hristov)

<details>
<summary>Changes</summary>

`[[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

---
Full diff: https://github.com/llvm/llvm-project/pull/169330.diff


2 Files Affected:

- (modified) libcxx/include/string (+53-46) 
- (modified) libcxx/test/libcxx/diagnostics/string.nodiscard.verify.cpp (+52) 


``````````diff
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..03966016f231b 100644
--- a/libcxx/test/libcxx/diagnostics/string.nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/diagnostics/string.nodiscard.verify.cpp
@@ -130,3 +130,55 @@ 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}}
+
+  // 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
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/169330