Make STL components not dependent on is_trivial(_v) (#5202)

Co-authored-by: Stephan T. Lavavej <[email protected]>

stl/inc/__msvc_string_view.hpp

@@ -1344,9 +1344,10 @@ class basic_string_view { // wrapper for any kind of contiguous character buffer
         "Bad char_traits for basic_string_view; N4950 [string.view.template.general]/1 "
         "\"The program is ill-formed if traits::char_type is not the same type as charT.\"");
 
-    static_assert(!is_array_v<_Elem> && is_trivial_v<_Elem> && is_standard_layout_v<_Elem>,
-        "The character type of basic_string_view must be a non-array trivial standard-layout type. See N4950 "
-        "[strings.general]/1.");
+    static_assert(!is_array_v<_Elem> && is_trivially_copyable_v<_Elem> && is_trivially_default_constructible_v<_Elem>
+                      && is_standard_layout_v<_Elem>,
+        "The character type of basic_string_view must be a non-array trivially copyable standard-layout type T where "
+        "is_trivially_default_constructible_v<T> is true. See N5001 [strings.general]/1.");
 
     using traits_type            = _Traits;
     using value_type             = _Elem;

stl/inc/execution

@@ -500,7 +500,8 @@ struct _Parallel_choose_max_chunk {
 
 template <class _Ty>
 struct alignas(_Ty) alignas(size_t) alignas(_Atomic_counter_t) _Circular_buffer { // work stealing deque extent type
-    static_assert(is_trivial_v<_Ty>, "Work stealing deques work only with trivial operations");
+    static_assert(is_trivially_copyable_v<_Ty> && is_trivially_default_constructible_v<_Ty>,
+        "Work stealing deques work only with trivial operations");
 
     size_t _Log_size;
     _Atomic_counter_t _Ref_count;

stl/inc/filesystem

@@ -352,19 +352,12 @@ namespace filesystem {
 
     inline constexpr _Is_slash_oper _Is_slash{};
 
-    template <class _Ty>
-    _NODISCARD _Ty _Unaligned_load(const void* _Ptr) { // load a _Ty from _Ptr
-        static_assert(is_trivial_v<_Ty>, "Unaligned loads require trivial types");
-        _Ty _Tmp;
-        _CSTD memcpy(&_Tmp, _Ptr, sizeof(_Tmp));
-        return _Tmp;
-    }
-
     _NODISCARD inline bool _Is_drive_prefix(const wchar_t* const _First) {
         // test if _First points to a prefix of the form X:
         // pre: _First points to at least 2 wchar_t instances
         // pre: Little endian
-        auto _Value = _Unaligned_load<unsigned int>(_First);
+        unsigned int _Value;
+        _CSTD memcpy(&_Value, _First, sizeof(_Value)); // load from possibly unaligned address
         _Value &= 0xFFFF'FFDFu; // transform lowercase drive letters into uppercase ones
         _Value -= (static_cast<unsigned int>(L':') << (sizeof(wchar_t) * CHAR_BIT)) | L'A';
         return _Value < 26;

stl/inc/memory

@@ -2246,7 +2246,8 @@ struct _NODISCARD _Reverse_destroy_multidimensional_n_guard {
 
 template <class _Ty, size_t _Size>
 void _Uninitialized_copy_multidimensional(const _Ty (&_In)[_Size], _Ty (&_Out)[_Size]) {
-    if constexpr (is_trivial_v<_Ty>) {
+    using _Item = remove_all_extents_t<_Ty>;
+    if constexpr (conjunction_v<is_trivially_copy_constructible<_Item>, is_trivially_destructible<_Item>>) {
         _STD _Copy_memmove_n(_In, _Size, _Out);
     } else if constexpr (is_array_v<_Ty>) {
         _Reverse_destroy_multidimensional_n_guard<_Ty> _Guard{_Out, 0};
@@ -2610,7 +2611,8 @@ struct _NODISCARD _Reverse_destroy_multidimensional_n_al_guard {
 template <class _Ty, size_t _Size, class _Alloc>
 void _Uninitialized_copy_multidimensional_al(const _Ty (&_In)[_Size], _Ty (&_Out)[_Size], _Alloc& _Al) {
     using _Item = remove_all_extents_t<_Ty>;
-    if constexpr (conjunction_v<is_trivial<_Ty>, _Uses_default_construct<_Alloc, _Item*, const _Item&>>) {
+    if constexpr (conjunction_v<is_trivially_copy_constructible<_Item>, is_trivially_destructible<_Item>,
+                      _Uses_default_construct<_Alloc, _Item*, const _Item&>>) {
         _STD _Copy_memmove_n(_In, _Size, _Out);
     } else if constexpr (is_array_v<_Ty>) {
         _Reverse_destroy_multidimensional_n_al_guard<_Ty, _Alloc> _Guard{_Out, 0, _Al};

stl/inc/type_traits

@@ -2299,7 +2299,7 @@ _NODISCARD inline size_t _Fnv1a_append_bytes(size_t _Val, const unsigned char* c
 template <class _Ty>
 _NODISCARD size_t _Fnv1a_append_range(const size_t _Val, const _Ty* const _First,
     const _Ty* const _Last) noexcept { // accumulate range [_First, _Last) into partial FNV-1a hash _Val
-    static_assert(is_trivial_v<_Ty>, "Only trivial types can be directly hashed.");
+    static_assert(is_trivially_copyable_v<_Ty>, "Only trivially copyable types can be directly hashed.");
     const auto _Firstb = reinterpret_cast<const unsigned char*>(_First);
     const auto _Lastb  = reinterpret_cast<const unsigned char*>(_Last);
     return _Fnv1a_append_bytes(_Val, _Firstb, static_cast<size_t>(_Lastb - _Firstb));
@@ -2308,7 +2308,7 @@ _NODISCARD size_t _Fnv1a_append_range(const size_t _Val, const _Ty* const _First
 template <class _Kty>
 _NODISCARD size_t _Fnv1a_append_value(
     const size_t _Val, const _Kty& _Keyval) noexcept { // accumulate _Keyval into partial FNV-1a hash _Val
-    static_assert(is_trivial_v<_Kty>, "Only trivial types can be directly hashed.");
+    static_assert(is_trivially_copyable_v<_Kty>, "Only trivially copyable types can be directly hashed.");
     return _Fnv1a_append_bytes(_Val, &reinterpret_cast<const unsigned char&>(_Keyval), sizeof(_Kty));
 }
 
@@ -2320,7 +2320,7 @@ _NODISCARD size_t _Hash_representation(const _Kty& _Keyval) noexcept { // bitwis
 template <class _Kty>
 _NODISCARD size_t _Hash_array_representation(
     const _Kty* const _First, const size_t _Count) noexcept { // bitwise hashes the representation of an array
-    static_assert(is_trivial_v<_Kty>, "Only trivial types can be directly hashed.");
+    static_assert(is_trivially_copyable_v<_Kty>, "Only trivially copyable types can be directly hashed.");
     return _Fnv1a_append_bytes(
         _FNV_offset_basis, reinterpret_cast<const unsigned char*>(_First), _Count * sizeof(_Kty));
 }

stl/inc/xstring

@@ -538,9 +538,10 @@ private:
         "N4950 [string.require]/3 requires that the supplied "
         "char_traits character type match the string's character type.");
 
-    static_assert(!is_array_v<_Elem> && is_trivial_v<_Elem> && is_standard_layout_v<_Elem>,
-        "The character type of basic_string must be a non-array trivial standard-layout type. See N4950 "
-        "[strings.general]/1.");
+    static_assert(!is_array_v<_Elem> && is_trivially_copyable_v<_Elem> && is_trivially_default_constructible_v<_Elem>
+                      && is_standard_layout_v<_Elem>,
+        "The character type of basic_string must be a non-array trivially copyable standard-layout type T where "
+        "is_trivially_default_constructible_v<T> is true. See N5001 [strings.general]/1.");
 
 public:
     using traits_type    = _Traits;
@@ -573,12 +574,13 @@ private:
     //   _String_val::_Bx::_Ptr (type is pointer)
     //   _String_val::_Mysize   (type is size_type)
     //   _String_val::_Myres    (type is size_type)
-    // N4950 [strings.general]/1 says _Elem must be trivial standard-layout, so memcpy is safe.
+    // N5001 [strings.general]/1 says _Elem must be trivially copyable standard-layout, so memcpy is safe.
     // We need to ask if pointer is safe to memcpy.
     // size_type must be an unsigned integral type so memcpy is safe.
     // We also need to disable memcpy if the user has supplied _Traits, since
     //   they can observe traits::assign and similar.
-    static constexpr bool _Can_memcpy_val = _Is_specialization_v<_Traits, char_traits> && is_trivial_v<pointer>;
+    static constexpr bool _Can_memcpy_val =
+        _Is_specialization_v<_Traits, char_traits> && is_trivially_copyable_v<pointer>;
     // This offset skips over the _Container_base members, if any
     static constexpr size_t _Memcpy_val_offset = _Size_after_ebco_v<_Container_base>;
     static constexpr size_t _Memcpy_val_size   = sizeof(_Scary_val) - _Memcpy_val_offset;

tests/std/tests/GH_000431_copy_move_family/test.cpp

@@ -37,7 +37,8 @@ struct TrivialStruct {
         return i == right.i;
     }
 };
-STATIC_ASSERT(is_trivial_v<TrivialStruct>);
+STATIC_ASSERT(is_trivially_copyable_v<TrivialStruct>);
+STATIC_ASSERT(is_trivially_default_constructible_v<TrivialStruct>);
 
 struct TriviallyCopyableStruct {
     int i;
@@ -49,7 +50,7 @@ struct TriviallyCopyableStruct {
     }
 };
 STATIC_ASSERT(is_trivially_copyable_v<TriviallyCopyableStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyCopyableStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyCopyableStruct>);
 
 struct TriviallyMovableStruct {
     int i;
@@ -65,7 +66,7 @@ struct TriviallyMovableStruct {
     }
 };
 STATIC_ASSERT(is_trivially_copyable_v<TriviallyMovableStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyMovableStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyMovableStruct>);
 
 enum int_enum : int {};
 enum char_enum : char {};

tests/std/tests/GH_000431_iter_copy_move_cat/test.compile.pass.cpp

@@ -170,14 +170,15 @@ void test_iter_cat_for_containers() {
 struct TrivialStruct {
     int i;
 };
-STATIC_ASSERT(is_trivial_v<TrivialStruct>);
+STATIC_ASSERT(is_trivially_copyable_v<TrivialStruct>);
+STATIC_ASSERT(is_trivially_default_constructible_v<TrivialStruct>);
 
 struct TriviallyCopyableStruct {
     int i;
     TriviallyCopyableStruct();
 };
 STATIC_ASSERT(is_trivially_copyable_v<TriviallyCopyableStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyCopyableStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyCopyableStruct>);
 
 struct TriviallyMovableStruct {
     int i;
@@ -188,7 +189,7 @@ struct TriviallyMovableStruct {
     TriviallyMovableStruct& operator=(TriviallyMovableStruct&&)      = default;
 };
 STATIC_ASSERT(is_trivially_copyable_v<TriviallyMovableStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyMovableStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyMovableStruct>);
 
 struct TriviallyConstructibleStruct {
     int i;
@@ -204,7 +205,7 @@ STATIC_ASSERT(is_trivially_move_constructible_v<TriviallyConstructibleStruct>);
 STATIC_ASSERT(!is_trivially_copy_assignable_v<TriviallyConstructibleStruct>);
 STATIC_ASSERT(!is_trivially_move_assignable_v<TriviallyConstructibleStruct>);
 STATIC_ASSERT(!is_trivially_copyable_v<TriviallyConstructibleStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyConstructibleStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyConstructibleStruct>);
 
 struct TriviallyAssignableStruct {
     int i;
@@ -220,7 +221,7 @@ STATIC_ASSERT(!is_trivially_move_constructible_v<TriviallyAssignableStruct>);
 STATIC_ASSERT(is_trivially_copy_assignable_v<TriviallyAssignableStruct>);
 STATIC_ASSERT(is_trivially_move_assignable_v<TriviallyAssignableStruct>);
 STATIC_ASSERT(!is_trivially_copyable_v<TriviallyAssignableStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyAssignableStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyAssignableStruct>);
 
 struct TriviallyCopyConstructibleStruct {
     int i;
@@ -236,7 +237,7 @@ STATIC_ASSERT(!is_trivially_move_constructible_v<TriviallyCopyConstructibleStruc
 STATIC_ASSERT(!is_trivially_copy_assignable_v<TriviallyCopyConstructibleStruct>);
 STATIC_ASSERT(!is_trivially_move_assignable_v<TriviallyCopyConstructibleStruct>);
 STATIC_ASSERT(!is_trivially_copyable_v<TriviallyCopyConstructibleStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyCopyConstructibleStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyCopyConstructibleStruct>);
 
 struct TriviallyCopyAssignableStruct {
     int i;
@@ -253,7 +254,7 @@ STATIC_ASSERT(!is_trivially_move_constructible_v<TriviallyCopyAssignableStruct>)
 STATIC_ASSERT(is_trivially_copy_assignable_v<TriviallyCopyAssignableStruct>);
 STATIC_ASSERT(!is_trivially_move_assignable_v<TriviallyCopyAssignableStruct>);
 STATIC_ASSERT(!is_trivially_copyable_v<TriviallyCopyAssignableStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyCopyAssignableStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyCopyAssignableStruct>);
 
 struct TriviallyMoveConstructibleStruct {
     int i;
@@ -269,7 +270,7 @@ STATIC_ASSERT(is_trivially_move_constructible_v<TriviallyMoveConstructibleStruct
 STATIC_ASSERT(!is_trivially_copy_assignable_v<TriviallyMoveConstructibleStruct>);
 STATIC_ASSERT(!is_trivially_move_assignable_v<TriviallyMoveConstructibleStruct>);
 STATIC_ASSERT(!is_trivially_copyable_v<TriviallyMoveConstructibleStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyMoveConstructibleStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyMoveConstructibleStruct>);
 
 struct TriviallyMoveAssignableStruct {
     int i;
@@ -285,7 +286,7 @@ STATIC_ASSERT(!is_trivially_move_constructible_v<TriviallyMoveAssignableStruct>)
 STATIC_ASSERT(!is_trivially_copy_assignable_v<TriviallyMoveAssignableStruct>);
 STATIC_ASSERT(is_trivially_move_assignable_v<TriviallyMoveAssignableStruct>);
 STATIC_ASSERT(!is_trivially_copyable_v<TriviallyMoveAssignableStruct>);
-STATIC_ASSERT(!is_trivial_v<TriviallyMoveAssignableStruct>);
+STATIC_ASSERT(!is_trivially_default_constructible_v<TriviallyMoveAssignableStruct>);
 
 struct EmptyBase {};
 

tests/std/tests/P0009R18_mdspan_layout_left/test.cpp

@@ -19,9 +19,10 @@ constexpr void check_members(const extents<IndexType, Extents...>& ext, index_se
     using Ext     = extents<IndexType, Extents...>;
     using Mapping = layout_left::mapping<Ext>;
 
-    // layout_left meets the layout mapping policy requirements and is a trivial type
+    // layout_left meets the requirements of N5001 [mdspan.layout.policy.overview]/1
     static_assert(check_layout_mapping_policy_requirements<layout_left, Ext>());
-    static_assert(is_trivial_v<layout_left>);
+    static_assert(is_trivially_copyable_v<layout_left>);
+    static_assert(is_trivially_default_constructible_v<layout_left>);
 
     // layout_left::mapping<Ext> is a trivially copyable type that models regular for each Ext
     static_assert(is_trivially_copyable_v<Mapping>);

tests/std/tests/P0009R18_mdspan_layout_right/test.cpp

@@ -19,9 +19,10 @@ constexpr void check_members(const extents<IndexType, Extents...>& ext, index_se
     using Ext     = extents<IndexType, Extents...>;
     using Mapping = layout_right::mapping<Ext>;
 
-    // layout_right meets the layout mapping policy requirements and is a trivial type
+    // layout_right meets the requirements of N5001 [mdspan.layout.policy.overview]/1
     static_assert(check_layout_mapping_policy_requirements<layout_right, Ext>());
-    static_assert(is_trivial_v<layout_right>);
+    static_assert(is_trivially_copyable_v<layout_right>);
+    static_assert(is_trivially_default_constructible_v<layout_right>);
 
     // layout_right::mapping<Ext> is a trivially copyable type that models regular for each Ext
     static_assert(is_trivially_copyable_v<Mapping>);

tests/std/tests/P0009R18_mdspan_layout_stride/test.cpp

@@ -105,9 +105,10 @@ constexpr void do_check_members(const extents<IndexType, Extents...>& ext,
     using Strides = array<IndexType, sizeof...(Extents)>;
     using Mapping = layout_stride::mapping<Ext>;
 
-    // layout_stride meets the layout mapping policy requirements and is a trivial type
+    // layout_stride meets the requirements of N5001 [mdspan.layout.policy.overview]/1
     static_assert(check_layout_mapping_policy_requirements<layout_stride, Ext>());
-    static_assert(is_trivial_v<layout_stride>);
+    static_assert(is_trivially_copyable_v<layout_stride>);
+    static_assert(is_trivially_default_constructible_v<layout_stride>);
 
     // layout_stride::mapping<Ext> is a trivially copyable type that models regular for each Ext
     static_assert(is_trivially_copyable_v<Mapping>);

tests/std/tests/P0009R18_mdspan_mdspan/test.cpp

@@ -337,7 +337,8 @@ struct TrivialAccessor {
 };
 
 static_assert(check_accessor_policy_requirements<TrivialAccessor<int>>());
-static_assert(is_trivial_v<TrivialAccessor<int>>);
+static_assert(is_trivially_copyable_v<TrivialAccessor<int>>);
+static_assert(is_trivially_default_constructible_v<TrivialAccessor<int>>);
 
 template <class Ext, class Layout, template <class> class AccessorTemplate>
 constexpr void check_modeled_concepts_and_member_types() {

tests/std/tests/P0323R12_expected/test.cpp

@@ -173,7 +173,8 @@ namespace test_unexpected {
 namespace test_unexpect {
     auto copy = unexpect;
     static_assert(is_same_v<decltype(copy), unexpect_t>);
-    static_assert(is_trivial_v<unexpect_t>);
+    static_assert(is_trivially_copyable_v<unexpect_t>);
+    static_assert(is_trivially_default_constructible_v<unexpect_t>);
     static_assert(is_empty_v<unexpect_t>);
 } // namespace test_unexpect
 

tests/std/tests/P0513R0_poisoning_the_hash/test.cpp

@@ -52,7 +52,7 @@ constexpr bool standard_hash_enabled() {
         && is_trivially_move_constructible_v<hash<T>> //
         && is_trivially_copy_assignable_v<hash<T>> //
         && is_trivially_move_assignable_v<hash<T>> //
-        && is_trivial_v<hash<T>> // as a consequence of the above
+        && is_trivially_copyable_v<hash<T>> //
         && is_same_v<typename hash<T>::argument_type, T> //
         && is_same_v<typename hash<T>::result_type, size_t> //
         && (noexcept(hash<T>{}(declval<const T&>())) == NoExcept) //

tests/std/tests/P0896R4_P1614R2_comparisons/test.cpp

@@ -52,7 +52,8 @@ constexpr bool is_trivially_constexpr() {
 
     // Not required, but likely portable nonetheless:
     STATIC_ASSERT(std::is_empty_v<T>);
-    STATIC_ASSERT(std::is_trivial_v<T>);
+    STATIC_ASSERT(std::is_trivially_copyable_v<T>);
+    STATIC_ASSERT(std::is_trivially_default_constructible_v<T>);
     STATIC_ASSERT(std::is_trivially_copy_constructible_v<T>);
     STATIC_ASSERT(std::is_trivially_move_constructible_v<T>);
     STATIC_ASSERT(std::is_trivially_copy_assignable_v<T>);

tests/std/tests/P0896R4_ranges_algorithm_machinery/test.compile.pass.cpp

@@ -547,7 +547,8 @@ namespace dangling_test {
 namespace result_test {
     using ranges::in_found_result, ranges::in_fun_result, ranges::in_in_result, ranges::in_out_result,
         ranges::in_in_out_result, ranges::in_out_out_result, ranges::min_max_result;
-    using std::is_aggregate_v, std::is_convertible_v, std::is_trivial_v;
+    using std::is_aggregate_v, std::is_convertible_v, std::is_trivially_copyable_v,
+        std::is_trivially_default_constructible_v;
 
     // Validate the result types are:
     // * aggregates
@@ -559,14 +560,23 @@ namespace result_test {
     static_assert(is_aggregate_v<in_out_out_result<int, int, int>>);
     static_assert(is_aggregate_v<min_max_result<int>>);
 
-    // * trivial when parameter types are trivial
-    static_assert(is_trivial_v<in_found_result<int>>);
-    static_assert(is_trivial_v<in_fun_result<int, int>>);
-    static_assert(is_trivial_v<in_in_result<int, int>>);
-    static_assert(is_trivial_v<in_out_result<int, int>>);
-    static_assert(is_trivial_v<in_in_out_result<int, int, int>>);
-    static_assert(is_trivial_v<in_out_out_result<int, int, int>>);
-    static_assert(is_trivial_v<min_max_result<int>>);
+    // * trivially copyable when parameter types are trivially copyable
+    static_assert(is_trivially_copyable_v<in_found_result<int>>);
+    static_assert(is_trivially_copyable_v<in_fun_result<int, int>>);
+    static_assert(is_trivially_copyable_v<in_in_result<int, int>>);
+    static_assert(is_trivially_copyable_v<in_out_result<int, int>>);
+    static_assert(is_trivially_copyable_v<in_in_out_result<int, int, int>>);
+    static_assert(is_trivially_copyable_v<in_out_out_result<int, int, int>>);
+    static_assert(is_trivially_copyable_v<min_max_result<int>>);
+
+    // * trivially default constructible when parameter types are trivially default constructible
+    static_assert(is_trivially_default_constructible_v<in_found_result<int>>);
+    static_assert(is_trivially_default_constructible_v<in_fun_result<int, int>>);
+    static_assert(is_trivially_default_constructible_v<in_in_result<int, int>>);
+    static_assert(is_trivially_default_constructible_v<in_out_result<int, int>>);
+    static_assert(is_trivially_default_constructible_v<in_in_out_result<int, int, int>>);
+    static_assert(is_trivially_default_constructible_v<in_out_out_result<int, int, int>>);
+    static_assert(is_trivially_default_constructible_v<min_max_result<int>>);
 
     // * usable with structured bindings
     constexpr bool test_bindings_in_found_result() {