[libc++] P3247R2: Deprecate is_trivial(_v) (#130573)

frederick-vs-ja · web-flow · commit ab95005a0523 · 2025-04-09T07:40:01.000+08:00
Requirements on character-like types are updated unconditionally,
because `basic_string` does requires the default-constructibility. It
might be possible to make `basic_string_view` support classes with
non-public trivial default constructor, but this doesn't seem sensible.

libcxxabi's `ItaniumDemangle.h` is also updated to avoid deprecated
features.
diff --git a/libcxx/docs/ReleaseNotes/21.rst b/libcxx/docs/ReleaseNotes/21.rst
@@ -45,6 +45,7 @@ Implemented Papers
 - P2562R1: ``constexpr`` Stable Sorting (`Github <https://github.com/llvm/llvm-project/issues/105360>`__)
 - P0472R3: Put std::monostate in <utility> (`Github <https://github.com/llvm/llvm-project/issues/127874>`__)
 - P1222R4: A Standard ``flat_set`` (`Github <https://github.com/llvm/llvm-project/issues/105193>`__)
+- P3247R2: Deprecate the notion of trivial types (`Github <https://github.com/llvm/llvm-project/issues/118387>`__)
 
 Improvements and New Features
 -----------------------------
@@ -65,6 +66,8 @@ Deprecations and Removals
 
 - ``std::is_pod`` and ``std::is_pod_v`` are deprecated in C++20 and later.
 
+- ``std::is_trivial`` and ``std::is_trivial_v`` are deprecated in C++26 and later.
+
 Upcoming Deprecations and Removals
 ----------------------------------
 
diff --git a/libcxx/docs/Status/Cxx2cPapers.csv b/libcxx/docs/Status/Cxx2cPapers.csv
@@ -94,7 +94,7 @@
 "`P1928R15 <https://wg21.link/P1928R15>`__","``std::simd`` — merge data-parallel types from the Parallelism TS 2","2024-11 (Wrocław)","","",""
 "`P3325R5 <https://wg21.link/P3325R5>`__","A Utility for Creating Execution Environments","2024-11 (Wrocław)","","",""
 "`P3068R6 <https://wg21.link/P3068R6>`__","Allowing exception throwing in constant-evaluation","2024-11 (Wrocław)","","",""
-"`P3247R2 <https://wg21.link/P3247R2>`__","Deprecate the notion of trivial types","2024-11 (Wrocław)","","",""
+"`P3247R2 <https://wg21.link/P3247R2>`__","Deprecate the notion of trivial types","2024-11 (Wrocław)","|Complete|","21",""
 "","","","","",""
 "`P3074R7 <https://wg21.link/P3074R7>`__","trivial unions (was ``std::uninitialized``)","2025-02 (Hagenberg)","","",""
 "`P1494R5 <https://wg21.link/P1494R5>`__","Partial program correctness","2025-02 (Hagenberg)","","",""
diff --git a/libcxx/include/__config b/libcxx/include/__config
@@ -742,8 +742,10 @@ typedef __char32_t char32_t;
 
 #  if _LIBCPP_STD_VER >= 26
 #    define _LIBCPP_DEPRECATED_IN_CXX26 _LIBCPP_DEPRECATED
+#    define _LIBCPP_DEPRECATED_IN_CXX26_(m) _LIBCPP_DEPRECATED_(m)
 #  else
 #    define _LIBCPP_DEPRECATED_IN_CXX26
+#    define _LIBCPP_DEPRECATED_IN_CXX26_(m)
 #  endif
 
 #  if _LIBCPP_HAS_CHAR8_T
diff --git a/libcxx/include/__iterator/aliasing_iterator.h b/libcxx/include/__iterator/aliasing_iterator.h
@@ -14,7 +14,8 @@
 #include <__iterator/iterator_traits.h>
 #include <__memory/addressof.h>
 #include <__memory/pointer_traits.h>
-#include <__type_traits/is_trivial.h>
+#include <__type_traits/is_trivially_constructible.h>
+#include <__type_traits/is_trivially_copyable.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -45,7 +46,8 @@ struct __aliasing_iterator_wrapper {
     using reference         = value_type&;
     using pointer           = value_type*;
 
-    static_assert(is_trivial<value_type>::value);
+    static_assert(is_trivially_default_constructible<value_type>::value);
+    static_assert(is_trivially_copyable<value_type>::value);
     static_assert(sizeof(__base_value_type) == sizeof(value_type));
 
     _LIBCPP_HIDE_FROM_ABI __iterator() = default;
diff --git a/libcxx/include/__type_traits/is_char_like_type.h b/libcxx/include/__type_traits/is_char_like_type.h
@@ -12,7 +12,8 @@
 #include <__config>
 #include <__type_traits/conjunction.h>
 #include <__type_traits/is_standard_layout.h>
-#include <__type_traits/is_trivial.h>
+#include <__type_traits/is_trivially_constructible.h>
+#include <__type_traits/is_trivially_copyable.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -21,7 +22,8 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _CharT>
-using _IsCharLikeType _LIBCPP_NODEBUG = _And<is_standard_layout<_CharT>, is_trivial<_CharT> >;
+using _IsCharLikeType _LIBCPP_NODEBUG =
+    _And<is_standard_layout<_CharT>, is_trivially_default_constructible<_CharT>, is_trivially_copyable<_CharT> >;
 
 _LIBCPP_END_NAMESPACE_STD
 
diff --git a/libcxx/include/__type_traits/is_trivial.h b/libcxx/include/__type_traits/is_trivial.h
@@ -19,11 +19,14 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp>
-struct _LIBCPP_TEMPLATE_VIS _LIBCPP_NO_SPECIALIZATIONS is_trivial : public integral_constant<bool, __is_trivial(_Tp)> {
-};
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX26_(
+    "Consider using is_trivially_copyable<T>::value && is_trivially_default_constructible<T>::value instead.")
+    _LIBCPP_NO_SPECIALIZATIONS is_trivial : public integral_constant<bool, __is_trivial(_Tp)> {};
 
 #if _LIBCPP_STD_VER >= 17
 template <class _Tp>
+_LIBCPP_DEPRECATED_IN_CXX26_(
+    "Consider using is_trivially_copyable_v<T> && is_trivially_default_constructible_v<T> instead.")
 _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool is_trivial_v = __is_trivial(_Tp);
 #endif
 
diff --git a/libcxx/include/string b/libcxx/include/string
@@ -632,7 +632,8 @@ basic_string<char32_t> operator""s( const char32_t *str, size_t len );
 #  include <__type_traits/is_nothrow_constructible.h>
 #  include <__type_traits/is_same.h>
 #  include <__type_traits/is_standard_layout.h>
-#  include <__type_traits/is_trivial.h>
+#  include <__type_traits/is_trivially_constructible.h>
+#  include <__type_traits/is_trivially_copyable.h>
 #  include <__type_traits/is_trivially_relocatable.h>
 #  include <__type_traits/remove_cvref.h>
 #  include <__type_traits/void_t.h>
@@ -788,7 +789,9 @@ public:
 
   static_assert(!is_array<value_type>::value, "Character type of basic_string must not be an array");
   static_assert(is_standard_layout<value_type>::value, "Character type of basic_string must be standard-layout");
-  static_assert(is_trivial<value_type>::value, "Character type of basic_string must be trivial");
+  static_assert(is_trivially_default_constructible<value_type>::value,
+                "Character type of basic_string must be trivially default constructible");
+  static_assert(is_trivially_copyable<value_type>::value, "Character type of basic_string must be trivially copyable");
   static_assert(is_same<_CharT, typename traits_type::char_type>::value,
                 "traits_type::char_type must be the same type as CharT");
   static_assert(is_same<typename allocator_type::value_type, value_type>::value,
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
@@ -235,7 +235,8 @@ namespace std {
 #  include <__type_traits/is_convertible.h>
 #  include <__type_traits/is_same.h>
 #  include <__type_traits/is_standard_layout.h>
-#  include <__type_traits/is_trivial.h>
+#  include <__type_traits/is_trivially_constructible.h>
+#  include <__type_traits/is_trivially_copyable.h>
 #  include <__type_traits/remove_cvref.h>
 #  include <__type_traits/remove_reference.h>
 #  include <__type_traits/type_identity.h>
@@ -302,7 +303,10 @@ public:
 
   static_assert(!is_array<value_type>::value, "Character type of basic_string_view must not be an array");
   static_assert(is_standard_layout<value_type>::value, "Character type of basic_string_view must be standard-layout");
-  static_assert(is_trivial<value_type>::value, "Character type of basic_string_view must be trivial");
+  static_assert(is_trivially_default_constructible<value_type>::value,
+                "Character type of basic_string_view must be trivially default constructible");
+  static_assert(is_trivially_copyable<value_type>::value,
+                "Character type of basic_string_view must be trivially copyable");
   static_assert(is_same<_CharT, typename traits_type::char_type>::value,
                 "traits_type::char_type must be the same type as CharT");
 
diff --git a/libcxx/include/type_traits b/libcxx/include/type_traits
@@ -93,7 +93,7 @@ namespace std
     template <class T> struct is_unbounded_array;               // since C++20
 
     // Member introspection:
-    template <class T> struct is_trivial;
+    template <class T> struct is_trivial;                       // deprecated in C++26
     template <class T> struct is_pod;                           // deprecated in C++20
     template <class T> struct is_trivially_copyable;
     template <class T> struct is_standard_layout;
@@ -323,7 +323,7 @@ namespace std
       template <class T> inline constexpr bool is_volatile_v
         = is_volatile<T>::value;                                // since C++17
       template <class T> inline constexpr bool is_trivial_v
-        = is_trivial<T>::value;                                 // since C++17
+        = is_trivial<T>::value;                                 // since C++17; deprecated in C++26
       template <class T> inline constexpr bool is_trivially_copyable_v
         = is_trivially_copyable<T>::value;                      // since C++17
       template <class T> inline constexpr bool is_standard_layout_v
diff --git a/libcxx/test/libcxx/memory/allocator_void.trivial.compile.pass.cpp b/libcxx/test/libcxx/memory/allocator_void.trivial.compile.pass.cpp
@@ -20,7 +20,7 @@ typedef std::allocator<void> A1;
 struct A2 : std::allocator<void> { };
 
 static_assert(std::is_trivially_default_constructible<A1>::value, "");
-static_assert(std::is_trivial<A1>::value, "");
+static_assert(std::is_trivially_copyable<A1>::value, "");
 
 static_assert(std::is_trivially_default_constructible<A2>::value, "");
-static_assert(std::is_trivial<A2>::value, "");
+static_assert(std::is_trivially_copyable<A2>::value, "");
diff --git a/libcxx/test/libcxx/utilities/memory/util.smartptr/util.smartptr.shared/libcxx.control_block_layout.pass.cpp b/libcxx/test/libcxx/utilities/memory/util.smartptr/util.smartptr.shared/libcxx.control_block_layout.pass.cpp
@@ -123,7 +123,9 @@ void test() {
 
   // Make sure both types have the same triviality (that has ABI impact since
   // it determined how objects are passed). Both should be non-trivial.
-  static_assert(std::is_trivial<New>::value == std::is_trivial<Old>::value, "");
+  static_assert(std::is_trivially_copyable<New>::value == std::is_trivially_copyable<Old>::value, "");
+  static_assert(
+      std::is_trivially_default_constructible<New>::value == std::is_trivially_default_constructible<Old>::value, "");
 }
 
 // Object types to store in the control block
diff --git a/libcxx/test/libcxx/utilities/utility/private_constructor_tag.compile.pass.cpp b/libcxx/test/libcxx/utilities/utility/private_constructor_tag.compile.pass.cpp
@@ -18,4 +18,5 @@
 #include <__utility/private_constructor_tag.h>
 #include <type_traits>
 
-static_assert(std::is_trivial<std::__private_constructor_tag>::value, "");
+static_assert(std::is_trivially_copyable<std::__private_constructor_tag>::value, "");
+static_assert(std::is_trivially_default_constructible<std::__private_constructor_tag>::value, "");
diff --git a/libcxx/test/std/depr/depr.c.headers/stddef_h.compile.pass.cpp b/libcxx/test/std/depr/depr.c.headers/stddef_h.compile.pass.cpp
@@ -43,8 +43,9 @@ static_assert((std::is_same<decltype(nullptr), nullptr_t>::value), "");
 static_assert(sizeof(nullptr_t) == sizeof(void*), "");
 #if TEST_STD_VER >= 11
 #  if TEST_STD_VER >= 20
-// P0767
-static_assert(std::is_trivial<max_align_t>::value, "");
+// P0767R1 and P3247R2
+static_assert(std::is_trivially_copyable<max_align_t>::value, "");
+static_assert(std::is_trivially_default_constructible<max_align_t>::value, "");
 static_assert(std::is_standard_layout<max_align_t>::value, "");
 #  else
 static_assert(std::is_pod<max_align_t>::value, "");
diff --git a/libcxx/test/std/language.support/support.types/byte.pass.cpp b/libcxx/test/std/language.support/support.types/byte.pass.cpp
@@ -16,7 +16,9 @@
 // It is a distinct type for accessing the bits that ultimately make up object storage.
 
 #if TEST_STD_VER > 17
-static_assert( std::is_trivial<std::byte>::value, "" );   // P0767
+static_assert(std::is_trivially_copyable<std::byte>::value, "");
+static_assert(std::is_trivially_default_constructible<std::byte>::value, "");
+static_assert(std::is_standard_layout<std::byte>::value, "");
 #else
 static_assert( std::is_pod<std::byte>::value, "" );
 #endif
diff --git a/libcxx/test/std/language.support/support.types/max_align_t.compile.pass.cpp b/libcxx/test/std/language.support/support.types/max_align_t.compile.pass.cpp
@@ -16,7 +16,8 @@
 
 #include "test_macros.h"
 
-static_assert(std::is_trivial<std::max_align_t>::value, "");
+static_assert(std::is_trivially_copyable<std::max_align_t>::value, "");
+static_assert(std::is_trivially_default_constructible<std::max_align_t>::value, "");
 static_assert(std::is_standard_layout<std::max_align_t>::value, "");
 #if TEST_STD_VER <= 17
 static_assert(std::is_pod<std::max_align_t>::value, "");
diff --git a/libcxx/test/std/library/description/conventions/customization.point.object/cpo.compile.pass.cpp b/libcxx/test/std/library/description/conventions/customization.point.object/cpo.compile.pass.cpp
@@ -23,7 +23,8 @@ template <class CPO, class... Args>
 constexpr bool test(CPO& o, Args&&...) {
   static_assert(std::is_const_v<CPO>);
   static_assert(std::is_class_v<CPO>);
-  static_assert(std::is_trivial_v<CPO>);
+  static_assert(std::is_trivially_copyable_v<CPO>);
+  static_assert(std::is_trivially_default_constructible_v<CPO>);
 
   auto p = o;
   using T = decltype(p);
diff --git a/libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp b/libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp
@@ -36,7 +36,8 @@ template <class CPO, class... Args>
 constexpr bool test(CPO& o, Args&&...) {
   static_assert(std::is_const_v<CPO>);
   static_assert(std::is_class_v<CPO>);
-  static_assert(std::is_trivial_v<CPO>);
+  static_assert(std::is_trivially_copyable_v<CPO>);
+  static_assert(std::is_trivially_default_constructible_v<CPO>);
 
   auto p = o;
   using T = decltype(p);
diff --git a/libcxx/test/std/ranges/range.req/range.view/view_base.compile.pass.cpp b/libcxx/test/std/ranges/range.req/range.view/view_base.compile.pass.cpp
@@ -16,7 +16,8 @@
 #include <type_traits>
 
 static_assert(std::is_empty_v<std::ranges::view_base>);
-static_assert(std::is_trivial_v<std::ranges::view_base>);
+static_assert(std::is_trivially_copyable_v<std::ranges::view_base>);
+static_assert(std::is_trivially_default_constructible_v<std::ranges::view_base>);
 
 // Make sure we can inherit from it, as it's intended (that wouldn't be the
 // case if e.g. it was marked as final).
diff --git a/libcxx/test/std/strings/basic.string/char.bad.verify.cpp b/libcxx/test/std/strings/basic.string/char.bad.verify.cpp
@@ -6,14 +6,25 @@
 //
 //===----------------------------------------------------------------------===//
 
+// XFAIL: FROZEN-CXX03-HEADERS-FIXME
+
 // <string>
 //   ... manipulating sequences of any non-array trivial standard-layout types.
 
 #include <string>
+#include <type_traits>
 #include "test_traits.h"
 
-struct NotTrivial {
-  NotTrivial() : value(3) {}
+struct NotTriviallyCopyable {
+  int value;
+  NotTriviallyCopyable& operator=(const NotTriviallyCopyable& other) {
+    value = other.value;
+    return *this;
+  }
+};
+
+struct NotTriviallyDefaultConstructible {
+  NotTriviallyDefaultConstructible() : value(3) {}
   int value;
 };
 
@@ -37,10 +48,17 @@ void f() {
   }
 
   {
-    // not trivial
-    static_assert(!std::is_trivial<NotTrivial>::value, "");
-    std::basic_string<NotTrivial, test_traits<NotTrivial> > s;
-    // expected-error-re@*:* {{static assertion failed{{.*}}Character type of basic_string must be trivial}}
+    // not trivially copyable
+    static_assert(!std::is_trivially_copyable<NotTriviallyCopyable>::value, "");
+    std::basic_string<NotTriviallyCopyable, test_traits<NotTriviallyCopyable> > s;
+    // expected-error-re@*:* {{static assertion failed{{.*}}Character type of basic_string must be trivially copyable}}
+  }
+
+  {
+    // not trivially default constructible
+    static_assert(!std::is_trivially_default_constructible<NotTriviallyDefaultConstructible>::value, "");
+    std::basic_string<NotTriviallyDefaultConstructible, test_traits<NotTriviallyDefaultConstructible> > s;
+    // expected-error-re@*:* {{static assertion failed{{.*}}Character type of basic_string must be trivially default constructible}}
   }
 
   {
diff --git a/libcxx/test/std/strings/string.view/char.bad.verify.cpp b/libcxx/test/std/strings/string.view/char.bad.verify.cpp
@@ -14,10 +14,19 @@
 //   ... manipulating sequences of any non-array trivial standard-layout types.
 
 #include <string>
+#include <type_traits>
 #include "../basic.string/test_traits.h"
 
-struct NotTrivial {
-  NotTrivial() : value(3) {}
+struct NotTriviallyCopyable {
+  int value;
+  NotTriviallyCopyable& operator=(const NotTriviallyCopyable& other) {
+    value = other.value;
+    return *this;
+  }
+};
+
+struct NotTriviallyDefaultConstructible {
+  NotTriviallyDefaultConstructible() : value(3) {}
   int value;
 };
 
@@ -41,10 +50,17 @@ int main(int, char**) {
   }
 
   {
-    //  not trivial
-    static_assert(!std::is_trivial<NotTrivial>::value, "");
-    std::basic_string_view<NotTrivial, test_traits<NotTrivial> > sv;
-    //  expected-error-re@string_view:* {{static assertion failed{{.*}}Character type of basic_string_view must be trivial}}
+    //  not trivially copyable
+    static_assert(!std::is_trivially_copyable<NotTriviallyCopyable>::value, "");
+    std::basic_string_view<NotTriviallyCopyable, test_traits<NotTriviallyCopyable> > s;
+    // expected-error-re@*:* {{static assertion failed{{.*}}Character type of basic_string_view must be trivially copyable}}
+  }
+
+  {
+    //  not trivially default constructible
+    static_assert(!std::is_trivially_default_constructible<NotTriviallyDefaultConstructible>::value, "");
+    std::basic_string_view<NotTriviallyDefaultConstructible, test_traits<NotTriviallyDefaultConstructible> > sv;
+    //  expected-error-re@string_view:* {{static assertion failed{{.*}}Character type of basic_string_view must be trivially default constructible}}
   }
 
   {
diff --git a/libcxx/test/std/time/time.zone/time.zone.zonedtraits/types.compile.pass.cpp b/libcxx/test/std/time/time.zone/time.zone.zonedtraits/types.compile.pass.cpp
@@ -24,10 +24,14 @@
 
 // This test test whether non-specialized versions exhibit the expected
 // behavior. (Note these specializations are not really useful.)
-static_assert(std::is_trivial_v<std::chrono::zoned_traits<int>>);
-static_assert(std::is_trivial_v<std::chrono::zoned_traits<float>>);
-static_assert(std::is_trivial_v<std::chrono::zoned_traits<void*>>);
+static_assert(std::is_trivially_copyable_v<std::chrono::zoned_traits<int>>);
+static_assert(std::is_trivially_copyable_v<std::chrono::zoned_traits<float>>);
+static_assert(std::is_trivially_copyable_v<std::chrono::zoned_traits<void*>>);
+static_assert(std::is_trivially_default_constructible_v<std::chrono::zoned_traits<int>>);
+static_assert(std::is_trivially_default_constructible_v<std::chrono::zoned_traits<float>>);
+static_assert(std::is_trivially_default_constructible_v<std::chrono::zoned_traits<void*>>);
 
 struct foo {};
 static_assert(std::is_empty_v<std::chrono::zoned_traits<foo>>);
-static_assert(std::is_trivial_v<std::chrono::zoned_traits<foo>>);
+static_assert(std::is_trivially_copyable_v<std::chrono::zoned_traits<foo>>);
+static_assert(std::is_trivially_default_constructible_v<std::chrono::zoned_traits<foo>>);
diff --git a/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/aligned_storage.pass.cpp b/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/aligned_storage.pass.cpp
diff --git a/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/aligned_union.pass.cpp b/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/aligned_union.pass.cpp
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_trivial.deprecated.verify.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_trivial.deprecated.verify.cpp
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_trivial.pass.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_trivial.pass.cpp
diff --git a/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp b/libcxx/test/std/utilities/tuple/tuple.general/ignore.pass.cpp
diff --git a/libcxx/test/support/nasty_string.h b/libcxx/test/support/nasty_string.h
diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h
