[libc+] Applied [[nodiscard]] to Allocators

Towards #172124

Author: H-G-Hristov

libcxx/include/__memory/addressof.h

@@ -19,32 +19,34 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX17 _LIBCPP_NO_CFI _LIBCPP_HIDE_FROM_ABI _Tp* addressof(_Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX17 _LIBCPP_NO_CFI _LIBCPP_HIDE_FROM_ABI _Tp*
+addressof(_Tp& __x) _NOEXCEPT {
   return __builtin_addressof(__x);
 }
 
 #if __has_feature(objc_arc)
 // Objective-C++ Automatic Reference Counting uses qualified pointers
 // that require special addressof() signatures.
 template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI __strong _Tp* addressof(__strong _Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI __strong _Tp* addressof(__strong _Tp& __x) _NOEXCEPT {
   return &__x;
 }
 
 #  if __has_feature(objc_arc_weak)
 template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI __weak _Tp* addressof(__weak _Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI __weak _Tp* addressof(__weak _Tp& __x) _NOEXCEPT {
   return &__x;
 }
 #  endif
 
 template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI __autoreleasing _Tp* addressof(__autoreleasing _Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI __autoreleasing _Tp* addressof(__autoreleasing _Tp& __x) _NOEXCEPT {
   return &__x;
 }
 
 template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI __unsafe_unretained _Tp* addressof(__unsafe_unretained _Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI __unsafe_unretained _Tp*
+addressof(__unsafe_unretained _Tp& __x) _NOEXCEPT {
   return &__x;
 }
 #endif

libcxx/include/__memory/allocator.h

@@ -120,18 +120,19 @@ class allocator
     typedef allocator<_Up> other;
   };
 
-  _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI pointer address(reference __x) const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI pointer address(reference __x) const _NOEXCEPT {
     return std::addressof(__x);
   }
-  _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI const_pointer address(const_reference __x) const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI const_pointer
+  address(const_reference __x) const _NOEXCEPT {
     return std::addressof(__x);
   }
 
   [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 _Tp* allocate(size_t __n, const void*) {
     return allocate(__n);
   }
 
-  _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT {
+  [[__nodiscard__]] _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT {
     return size_type(~0) / sizeof(_Tp);
   }
 

libcxx/include/__memory/is_sufficiently_aligned.h

@@ -23,7 +23,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 #if _LIBCPP_STD_VER >= 26
 
 template <size_t _Alignment, class _Tp>
-_LIBCPP_HIDE_FROM_ABI bool is_sufficiently_aligned(_Tp* __ptr) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_sufficiently_aligned(_Tp* __ptr) {
   return reinterpret_cast<uintptr_t>(__ptr) % _Alignment == 0;
 }
 

libcxx/include/__memory/raw_storage_iterator.h

@@ -67,7 +67,7 @@ class _LIBCPP_DEPRECATED_IN_CXX17 raw_storage_iterator
     return __t;
   }
 #  if _LIBCPP_STD_VER >= 14
-  _LIBCPP_HIDE_FROM_ABI _OutputIterator base() const { return __x_; }
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _OutputIterator base() const { return __x_; }
 #  endif
 };
 

libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp

@@ -10,6 +10,7 @@
 
 // check that <memory> functions are marked [[nodiscard]]
 
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_RAW_STORAGE_ITERATOR
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
 
@@ -20,7 +21,13 @@
 #include "test_macros.h"
 
 void test() {
+  int i = 0;
+
+  std::addressof(i); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
   std::get_temporary_buffer<int>(0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if _LIBCPP_STD_VER >= 26
+  std::is_sufficiently_aligned<2>(&i); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
 }
 
 void test_allocator_traits() {
@@ -32,11 +39,26 @@ void test_allocator_traits() {
 
 void test_allocator() {
   std::allocator<int> allocator;
-  allocator.allocate(1);          // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
 #if TEST_STD_VER <= 17
+  int i = 0;
+  const int ci = 0;
+
+  allocator.address(i);           // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  allocator.address(ci);          // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  allocator.allocate(1);          // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
   allocator.allocate(1, nullptr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  allocator.max_size();              // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
 #endif
 #if TEST_STD_VER >= 23
   allocator.allocate_at_least(1); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
 #endif
 }
+
+#if TEST_STD_VER >= 14
+void test_raw_storage_iterator() {
+  std::raw_storage_iterator<int*, int> it(nullptr);
+
+  it.base(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+}
+#endif