Re: [pushed] c++: C++26 constexpr cast from void* [PR110344]

[Marek Polacek <polacek@redhat.com>]

On Tue, Jun 27, 2023 at 11:29:34PM -0400, Jason Merrill via Gcc-patches wrote:
> Tested x86_64-pc-linux-gnu, applying to trunk.
> 
> -- 8< --
> 
> P2768 allows static_cast from void* to ob* in constant evaluation if the
> pointer does in fact point to an object of the appropriate type.
> cxx_fold_indirect_ref already does the work of finding such an object if it
> happens to be a subobject rather than the outermost object at that address,
> as in constexpr-voidptr2.C.

This patch seems to have broken a lot of tests when running with
GXX_TESTSUITE_STDS=98,11,14,17,20,23,26.  cpp0x/constexpr-cast2.C
probably just needs not to expect certain errors in C++26, and
cpp2a/constexpr-new*.C may need code to handle &heap (?).
 
> 	P2768
> 	PR c++/110344
> 
> gcc/c-family/ChangeLog:
> 
> 	* c-cppbuiltin.cc (c_cpp_builtins): Update __cpp_constexpr.
> 
> gcc/cp/ChangeLog:
> 
> 	* constexpr.cc (cxx_eval_constant_expression): In C++26, allow cast
> 	from void* to the type of a pointed-to object.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp26/constexpr-voidptr1.C: New test.
> 	* g++.dg/cpp26/constexpr-voidptr2.C: New test.
> 	* g++.dg/cpp26/feat-cxx26.C: New test.
> ---
>  gcc/c-family/c-cppbuiltin.cc                  |   8 +-
>  gcc/cp/constexpr.cc                           |  11 +
>  .../g++.dg/cpp26/constexpr-voidptr1.C         |  35 +
>  .../g++.dg/cpp26/constexpr-voidptr2.C         |  15 +
>  gcc/testsuite/g++.dg/cpp26/feat-cxx26.C       | 597 ++++++++++++++++++
>  5 files changed, 665 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/g++.dg/cpp26/constexpr-voidptr1.C
>  create mode 100644 gcc/testsuite/g++.dg/cpp26/constexpr-voidptr2.C
>  create mode 100644 gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
> 
> diff --git a/gcc/c-family/c-cppbuiltin.cc b/gcc/c-family/c-cppbuiltin.cc
> index 5d64625fcd7..6bd4c1261a7 100644
> --- a/gcc/c-family/c-cppbuiltin.cc
> +++ b/gcc/c-family/c-cppbuiltin.cc
> @@ -1075,12 +1075,18 @@ c_cpp_builtins (cpp_reader *pfile)
>  	  cpp_define (pfile, "__cpp_size_t_suffix=202011L");
>  	  cpp_define (pfile, "__cpp_if_consteval=202106L");
>  	  cpp_define (pfile, "__cpp_auto_cast=202110L");
> -	  cpp_define (pfile, "__cpp_constexpr=202211L");
> +	  if (cxx_dialect <= cxx23)
> +	    cpp_define (pfile, "__cpp_constexpr=202211L");
>  	  cpp_define (pfile, "__cpp_multidimensional_subscript=202211L");
>  	  cpp_define (pfile, "__cpp_named_character_escapes=202207L");
>  	  cpp_define (pfile, "__cpp_static_call_operator=202207L");
>  	  cpp_define (pfile, "__cpp_implicit_move=202207L");
>  	}
> +      if (cxx_dialect > cxx23)
> +	{
> +	  /* Set feature test macros for C++26.  */
> +	  cpp_define (pfile, "__cpp_constexpr=202306L");
> +	}
>        if (flag_concepts)
>          {
>  	  if (cxx_dialect >= cxx20)
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index 432b3a275e8..cca0435bafc 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -7681,6 +7681,17 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
>  	    && !is_std_construct_at (ctx->call)
>  	    && !is_std_allocator_allocate (ctx->call))
>  	  {
> +	    /* P2738 (C++26): a conversion from a prvalue P of type "pointer to
> +	       cv void" to a pointer-to-object type T unless P points to an
> +	       object whose type is similar to T.  */
> +	    if (cxx_dialect > cxx23)
> +	      if (tree ob
> +		  = cxx_fold_indirect_ref (ctx, loc, TREE_TYPE (type), op))
> +		{
> +		  r = build1 (ADDR_EXPR, type, ob);
> +		  break;
> +		}
> +
>  	    /* Likewise, don't error when casting from void* when OP is
>  	       &heap uninit and similar.  */
>  	    tree sop = tree_strip_nop_conversions (op);
> diff --git a/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr1.C b/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr1.C
> new file mode 100644
> index 00000000000..ce0ccbef5f9
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr1.C
> @@ -0,0 +1,35 @@
> +// PR c++/110344
> +// { dg-do compile { target c++26 } }
> +
> +#include <string_view>
> +struct Sheep {
> +  constexpr std::string_view speak() const noexcept { return "Baaaaaa"; }
> +};
> +struct Cow {
> +  constexpr std::string_view speak() const noexcept { return "Mooo"; }
> +};
> +class Animal_View {
> +private:
> +  const void *animal;
> +  std::string_view (*speak_function)(const void *);
> +public:
> +  template <typename Animal>
> +  constexpr Animal_View(const Animal &a)
> +    : animal{&a}, speak_function{[](const void *object) {
> +				   return static_cast<const Animal *>(object)->speak();
> +				 }} {}
> +  constexpr std::string_view speak() const noexcept {
> +    return speak_function(animal);
> +  }
> +};
> +// This is the key bit here. This is a single concrete function
> +// that can take anything that happens to have the "Animal_View"
> +// interface
> +constexpr std::string_view do_speak(Animal_View av) { return av.speak(); }
> +int main() {
> +  // A Cow is a cow. The only think that makes it special
> +  // is that it has a "std::string_view speak() const" member
> +  constexpr Cow cow;
> +  constexpr auto result = do_speak(cow);
> +  return static_cast<int>(result.size());
> +}
> diff --git a/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr2.C b/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr2.C
> new file mode 100644
> index 00000000000..e746301e9f9
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr2.C
> @@ -0,0 +1,15 @@
> +// PR c++/110344
> +// { dg-do compile { target c++26 } }
> +
> +struct A { int i; };
> +struct B { A a; };
> +
> +constexpr int f()
> +{
> +  B b { 42 };
> +  void *p = &b;
> +  A* ap = static_cast<A*>(p);
> +  return ap->i;
> +}
> +
> +static_assert (f() == 42);
> diff --git a/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C b/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
> new file mode 100644
> index 00000000000..0977d964fe0
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp26/feat-cxx26.C
> @@ -0,0 +1,597 @@
> +// { dg-options "-std=c++26 -I${srcdir}/g++.dg/cpp1y -I${srcdir}/g++.dg/cpp1y/testinc" }
> +
> +//  C++98 features:
> +
> +#ifndef __cpp_rtti
> +#  error "__cpp_rtti"
> +#elif  __cpp_rtti != 199711
> +#  error "__cpp_rtti != 199711"
> +#endif
> +
> +#ifndef __cpp_exceptions
> +#  error "__cpp_exceptions"
> +#elif  __cpp_exceptions != 199711
> +#  error "__cpp_exceptions != 199711"
> +#endif
> +
> +//  C++11 features:
> +
> +#ifndef __cpp_raw_strings
> +#  error "__cpp_raw_strings"
> +#elif __cpp_raw_strings != 200710
> +#  error "__cpp_raw_strings != 200710"
> +#endif
> +
> +#ifndef __cpp_unicode_literals
> +#  error "__cpp_unicode_literals"
> +#elif __cpp_unicode_literals != 200710
> +#  error "__cpp_unicode_literals != 200710"
> +#endif
> +
> +#ifndef __cpp_user_defined_literals
> +#  error "__cpp_user_defined_literals"
> +#elif __cpp_user_defined_literals != 200809
> +#  error "__cpp_user_defined_literals != 200809"
> +#endif
> +
> +#ifndef __cpp_lambdas
> +#  error "__cpp_lambdas"
> +#elif __cpp_lambdas != 200907
> +#  error "__cpp_lambdas != 200907"
> +#endif
> +
> +#ifndef __cpp_range_based_for
> +#  error "__cpp_range_based_for"
> +#elif __cpp_range_based_for != 201603
> +#  error "__cpp_range_based_for != 201603"
> +#endif
> +
> +#ifndef __cpp_decltype
> +#  error "__cpp_decltype"
> +#elif __cpp_decltype != 200707
> +#  error "__cpp_decltype != 200707"
> +#endif
> +
> +#ifndef __cpp_attributes
> +#  error "__cpp_attributes"
> +#elif __cpp_attributes != 200809
> +#  error "__cpp_attributes != 200809"
> +#endif
> +
> +#ifndef __cpp_rvalue_references
> +#  error "__cpp_rvalue_references"
> +#elif __cpp_rvalue_references != 200610
> +#  error "__cpp_rvalue_references != 200610"
> +#endif
> +
> +#ifndef __cpp_variadic_templates
> +#  error "__cpp_variadic_templates"
> +#elif __cpp_variadic_templates != 200704
> +#  error "__cpp_variadic_templates != 200704"
> +#endif
> +
> +#ifndef __cpp_initializer_lists
> +#  error "__cpp_initializer_lists"
> +#elif __cpp_initializer_lists != 200806
> +#  error "__cpp_initializer_lists != 200806"
> +#endif
> +
> +#ifndef __cpp_delegating_constructors
> +#  error "__cpp_delegating_constructors"
> +#elif __cpp_delegating_constructors != 200604
> +#  error "__cpp_delegating_constructors != 200604"
> +#endif
> +
> +#ifndef __cpp_nsdmi
> +#  error "__cpp_nsdmi"
> +#elif __cpp_nsdmi != 200809
> +#  error "__cpp_nsdmi != 200809"
> +#endif
> +
> +#ifndef __cpp_inheriting_constructors
> +#  error "__cpp_inheriting_constructors"
> +#elif  __cpp_inheriting_constructors!= 201511
> +#  error "__cpp_inheriting_constructors != 201511"
> +#endif
> +
> +#ifndef __cpp_ref_qualifiers
> +#  error "__cpp_ref_qualifiers"
> +#elif __cpp_ref_qualifiers != 200710
> +#  error "__cpp_ref_qualifiers != 200710"
> +#endif
> +
> +#ifndef __cpp_alias_templates
> +#  error "__cpp_alias_templates"
> +#elif __cpp_alias_templates != 200704
> +#  error "__cpp_alias_templates != 200704"
> +#endif
> +
> +#ifndef __cpp_threadsafe_static_init
> +#  error "__cpp_threadsafe_static_init"
> +#elif __cpp_threadsafe_static_init != 200806
> +#  error "__cpp_threadsafe_static_init != 200806"
> +#endif
> +
> +//  C++14 features:
> +
> +#ifndef __cpp_binary_literals
> +#  error "__cpp_binary_literals"
> +#elif __cpp_binary_literals != 201304
> +#  error "__cpp_binary_literals != 201304"
> +#endif
> +
> +#ifndef __cpp_init_captures
> +#  error "__cpp_init_captures"
> +#elif __cpp_init_captures != 201803
> +#  error "__cpp_init_captures != 201803"
> +#endif
> +
> +#ifndef __cpp_generic_lambdas
> +#  error "__cpp_generic_lambdas"
> +#elif __cpp_generic_lambdas != 201707
> +#  error "__cpp_generic_lambdas != 201707"
> +#endif
> +
> +#ifndef __cpp_constexpr
> +#  error "__cpp_constexpr"
> +#elif __cpp_constexpr != 202306L
> +#  error "__cpp_constexpr != 202306L"
> +#endif
> +
> +#ifndef __cpp_decltype_auto
> +#  error "__cpp_decltype_auto"
> +#elif __cpp_decltype_auto != 201304
> +#  error "__cpp_decltype_auto != 201304"
> +#endif
> +
> +#ifndef __cpp_return_type_deduction
> +#  error "__cpp_return_type_deduction"
> +#elif __cpp_return_type_deduction != 201304
> +#  error "__cpp_return_type_deduction != 201304"
> +#endif
> +
> +#ifndef __cpp_aggregate_nsdmi
> +#  error "__cpp_aggregate_nsdmi"
> +#elif __cpp_aggregate_nsdmi != 201304
> +#  error "__cpp_aggregate_nsdmi != 201304"
> +#endif
> +
> +#ifndef __cpp_variable_templates
> +#  error "__cpp_variable_templates"
> +#elif __cpp_variable_templates != 201304
> +#  error "__cpp_variable_templates != 201304"
> +#endif
> +
> +#ifndef __cpp_digit_separators
> +#  error "__cpp_digit_separators"
> +#elif __cpp_digit_separators != 201309
> +#  error "__cpp_digit_separators != 201309"
> +#endif
> +
> +#ifndef __cpp_sized_deallocation
> +#  error "__cpp_sized_deallocation"
> +#elif __cpp_sized_deallocation != 201309
> +#  error "__cpp_sized_deallocation != 201309"
> +#endif
> +
> +//  GNU VLA support:
> +
> +#ifndef __cpp_runtime_arrays
> +#  error "__cpp_runtime_arrays"
> +#elif __cpp_runtime_arrays != 198712
> +#  error "__cpp_runtime_arrays != 198712"
> +#endif
> +
> +//  C++11 attributes:
> +
> +#ifdef __has_cpp_attribute
> +#  if ! __has_cpp_attribute(noreturn)
> +#    error "__has_cpp_attribute(noreturn)"
> +#  elif __has_cpp_attribute(noreturn) != 200809
> +#    error "__has_cpp_attribute(noreturn) != 200809"
> +#  endif
> +#else
> +#  error "__has_cpp_attribute"
> +#endif
> +
> +//  Attribute carries_dependency not in yet.
> +//#ifdef __has_cpp_attribute
> +//#  if ! __has_cpp_attribute(carries_dependency)
> +//#    error "__has_cpp_attribute(carries_dependency)"
> +//#  elif __has_cpp_attribute(carries_dependency) != 200809
> +//#    error "__has_cpp_attribute(carries_dependency) != 200809"
> +//#  endif
> +//#else
> +//#  error "__has_cpp_attribute"
> +//#endif
> +
> +//  C++14 attributes:
> +
> +#ifdef __has_cpp_attribute
> +#  if ! __has_cpp_attribute(deprecated)
> +#    error "__has_cpp_attribute(deprecated)"
> +#  elif __has_cpp_attribute(deprecated) != 201309
> +#    error "__has_cpp_attribute(deprecated) != 201309"
> +#  endif
> +#else
> +#  error "__has_cpp_attribute"
> +#endif
> +
> +//  Include checks:
> +
> +//  Check for __has_include macro.
> +#ifndef __has_include
> +#  error "__has_include"
> +#endif
> +
> +//  Try known bracket header (use operator).
> +#if __has_include (<complex>)
> +#else
> +#  error "<complex>"
> +#endif
> +
> +//  Define and use a macro to invoke the operator.
> +#define sluggo(TXT) __has_include(TXT)
> +
> +#if sluggo(<complex>)
> +#else
> +#  error "<complex>"
> +#endif
> +
> +#if ! sluggo(<complex>)
> +#  error "<complex>"
> +#else
> +#endif
> +
> +//  Quoted complex.h should find at least the bracket version.
> +#if __has_include("complex.h")
> +#else
> +#  error "complex.h"
> +#endif
> +
> +//  Try known local quote header.
> +#if __has_include("complex_literals.h")
> +#else
> +#  error "\"complex_literals.h\""
> +#endif
> +
> +//  Try nonexistent bracket header.
> +#if __has_include(<stuff>)
> +#  error "<stuff>"
> +#else
> +#endif
> +
> +//  Try nonexistent quote header.
> +#if __has_include("phlegm")
> +#  error "\"phlegm\""
> +#else
> +#endif
> +
> +//  Test __has_include_next.
> +#if __has_include("phoobhar.h")
> +#  include "phoobhar.h"
> +#else
> +#  error "__has_include(\"phoobhar.h\")"
> +#endif
> +
> +//  Try a macro.
> +#define COMPLEX_INC "complex.h"
> +#if __has_include(COMPLEX_INC)
> +#else
> +#  error COMPLEX_INC
> +#endif
> +
> +//  Realistic use of __has_include.
> +#if __has_include(<array>)
> +#  define STD_ARRAY 1
> +#  include <array>
> +  template<typename _Tp, std::size_t _Num>
> +    using array = std::array<_Tp, _Num>;
> +#elif __has_include(<tr1/array>)
> +#  define TR1_ARRAY 1
> +#  include <tr1/array>
> +  template<typename _Tp, std::size_t _Num>
> +    typedef std::tr1::array<_Tp, _Num> array;
> +#endif
> +
> +// C++17 features:
> +
> +#ifndef __cpp_unicode_characters
> +#  error "__cpp_unicode_characters"
> +#elif __cpp_unicode_characters != 201411
> +#  error "__cpp_unicode_characters != 201411"
> +#endif
> +
> +#ifndef __cpp_static_assert
> +#  error "__cpp_static_assert"
> +#elif __cpp_static_assert != 201411
> +#  error "__cpp_static_assert != 201411"
> +#endif
> +
> +#ifndef __cpp_namespace_attributes
> +#  error "__cpp_namespace_attributes"
> +#elif __cpp_namespace_attributes != 201411
> +#  error "__cpp_namespace_attributes != 201411"
> +#endif
> +
> +#ifndef __cpp_enumerator_attributes
> +#  error "__cpp_enumerator_attributes"
> +#elif __cpp_enumerator_attributes != 201411
> +#  error "__cpp_enumerator_attributes != 201411"
> +#endif
> +
> +#ifndef __cpp_nested_namespace_definitions
> +#  error "__cpp_nested_namespace_definitions"
> +#elif __cpp_nested_namespace_definitions != 201411
> +#  error "__cpp_nested_namespace_definitions != 201411"
> +#endif
> +
> +#ifndef __cpp_fold_expressions
> +#  error "__cpp_fold_expressions"
> +#elif __cpp_fold_expressions != 201603
> +#  error "__cpp_fold_expressions != 201603"
> +#endif
> +
> +#ifndef __cpp_nontype_template_args
> +#  error "__cpp_nontype_template_args"
> +#elif __cpp_nontype_template_args != 201911
> +#  error "__cpp_nontype_template_args != 201911"
> +#endif
> +
> +#ifndef __cpp_hex_float
> +#  error "__cpp_hex_float"
> +#elif __cpp_hex_float != 201603
> +#  error "__cpp_hex_float != 201603"
> +#endif
> +
> +#ifndef __cpp_aggregate_bases
> +#  error "__cpp_aggregate_bases"
> +#elif __cpp_aggregate_bases != 201603
> +#  error "__cpp_aggregate_bases != 201603"
> +#endif
> +
> +#ifndef __cpp_deduction_guides
> +#  error "__cpp_deduction_guides"
> +#elif __cpp_deduction_guides != 201907
> +#  error "__cpp_deduction_guides != 201907"
> +#endif
> +
> +#ifndef __cpp_if_constexpr
> +#  error "__cpp_if_constexpr"
> +#elif __cpp_if_constexpr != 201606
> +#  error "__cpp_if_constexpr != 201606"
> +#endif
> +
> +#ifndef __cpp_aligned_new
> +#  error "__cpp_aligned_new"
> +#elif __cpp_aligned_new != 201606
> +#  error "__cpp_aligned_new != 201606"
> +#endif
> +
> +#ifndef __cpp_template_auto
> +#  error "__cpp_template_auto"
> +#elif __cpp_template_auto != 201606
> +#  error "__cpp_template_auto != 201606"
> +#endif
> +
> +#ifndef __cpp_inline_variables
> +#  error "__cpp_inline_variables"
> +#elif __cpp_inline_variables != 201606
> +#  error "__cpp_inline_variables != 201606"
> +#endif
> +
> +#ifndef __cpp_capture_star_this
> +#  error "__cpp_capture_star_this"
> +#elif __cpp_capture_star_this != 201603
> +#  error "__cpp_capture_star_this != 201603"
> +#endif
> +
> +#ifndef __cpp_noexcept_function_type
> +#  error "__cpp_noexcept_function_type"
> +#elif __cpp_noexcept_function_type != 201510
> +#  error "__cpp_noexcept_function_type != 201510"
> +#endif
> +
> +#ifndef __cpp_structured_bindings
> +#  error "__cpp_structured_bindings"
> +#elif __cpp_structured_bindings != 201606
> +#  error "__cpp_structured_bindings != 201606"
> +#endif
> +
> +#ifndef __cpp_template_template_args
> +#  error "__cpp_template_template_args"
> +#elif __cpp_template_template_args != 201611
> +#  error "__cpp_template_template_args != 201611"
> +#endif
> +
> +#ifndef __cpp_variadic_using
> +#  error "__cpp_variadic_using"
> +#elif __cpp_variadic_using != 201611
> +#  error "__cpp_variadic_using != 201611"
> +#endif
> +
> +#ifndef __cpp_guaranteed_copy_elision
> +#  error "__cpp_guaranteed_copy_elision"
> +#elif __cpp_guaranteed_copy_elision != 201606
> +#  error "__cpp_guaranteed_copy_elision != 201606"
> +#endif
> +
> +#ifndef __cpp_nontype_template_parameter_auto
> +#  error "__cpp_nontype_template_parameter_auto"
> +#elif __cpp_nontype_template_parameter_auto != 201606
> +#  error "__cpp_nontype_template_parameter_auto != 201606"
> +#endif
> +
> +// C++20 features:
> +
> +#ifndef __cpp_conditional_explicit
> +#  error "__cpp_conditional_explicit"
> +#elif __cpp_conditional_explicit != 201806
> +#  error "__cpp_conditional_explicit != 201806"
> +#endif
> +
> +#ifndef __cpp_nontype_template_parameter_class
> +#  error "__cpp_nontype_template_parameter_class"
> +#elif __cpp_nontype_template_parameter_class != 201806
> +#  error "__cpp_nontype_template_parameter_class != 201806"
> +#endif
> +
> +#ifndef __cpp_impl_destroying_delete
> +#  error "__cpp_impl_destroying_delete"
> +#elif __cpp_impl_destroying_delete != 201806
> +#  error "__cpp_impl_destroying_delete != 201806"
> +#endif
> +
> +#ifndef __cpp_constinit
> +#  error "__cpp_constinit"
> +#elif __cpp_constinit != 201907
> +#  error "__cpp_constinit != 201907"
> +#endif
> +
> +#ifndef __cpp_constexpr_dynamic_alloc
> +#  error "__cpp_constexpr_dynamic_alloc"
> +#elif __cpp_constexpr_dynamic_alloc != 201907
> +#  error "__cpp_constexpr_dynamic_alloc != 201907"
> +#endif
> +
> +#ifndef __cpp_aggregate_paren_init
> +#  error "__cpp_aggregate_paren_init"
> +#elif __cpp_aggregate_paren_init != 201902
> +#  error "__cpp_aggregate_paren_init != 201902"
> +#endif
> +
> +#ifndef __cpp_char8_t
> +#  error "__cpp_char8_t"
> +#elif __cpp_char8_t != 202207
> +#  error "__cpp_char8_t != 202207"
> +#endif
> +
> +#ifndef __cpp_designated_initializers
> +#  error "__cpp_designated_initializers"
> +#elif __cpp_designated_initializers != 201707
> +#  error "__cpp_designated_initializers != 201707"
> +#endif
> +
> +#ifndef __cpp_constexpr_in_decltype
> +#  error "__cpp_constexpr_in_decltype"
> +#elif __cpp_constexpr_in_decltype != 201711
> +#  error "__cpp_constexpr_in_decltype != 201711"
> +#endif
> +
> +#ifndef __cpp_consteval
> +#  error "__cpp_consteval"
> +#elif __cpp_consteval != 201811
> +#  error "__cpp_consteval != 201811"
> +#endif
> +
> +#ifndef __cpp_concepts
> +#  error "__cpp_concepts"
> +#elif __cpp_concepts != 202002
> +#  error "__cpp_concepts != 202002"
> +#endif
> +
> +#ifndef __cpp_using_enum
> +#  error "__cpp_using_enum"
> +#elif __cpp_using_enum != 201907
> +#  error "__cpp_using_enum != 201907"
> +#endif
> +
> +// C++20 attributes:
> +
> +#ifdef __has_cpp_attribute
> +
> +#  if ! __has_cpp_attribute(maybe_unused)
> +#    error "__has_cpp_attribute(maybe_unused)"
> +#  elif __has_cpp_attribute(maybe_unused) != 201603
> +#    error "__has_cpp_attribute(maybe_unused) != 201603"
> +#  endif
> +
> +#  if ! __has_cpp_attribute(nodiscard)
> +#    error "__has_cpp_attribute(nodiscard)"
> +#  elif __has_cpp_attribute(nodiscard) != 201907
> +#    error "__has_cpp_attribute(nodiscard) != 201907"
> +#  endif
> +
> +#  if ! __has_cpp_attribute(fallthrough)
> +#    error "__has_cpp_attribute(fallthrough)"
> +#  elif __has_cpp_attribute(fallthrough) != 201603
> +#    error "__has_cpp_attribute(fallthrough) != 201603"
> +#  endif
> +
> +#  if ! __has_cpp_attribute(no_unique_address)
> +#    error "__has_cpp_attribute(no_unique_address)"
> +#  elif __has_cpp_attribute(no_unique_address) != 201803
> +#    error "__has_cpp_attribute(no_unique_address) != 201803"
> +#  endif
> +
> +#  if ! __has_cpp_attribute(likely)
> +#    error "__has_cpp_attribute(likely)"
> +#  elif __has_cpp_attribute(likely) != 201803
> +#    error "__has_cpp_attribute(likely) != 201803"
> +#  endif
> +
> +#  if ! __has_cpp_attribute(unlikely)
> +#    error "__has_cpp_attribute(unlikely)"
> +#  elif __has_cpp_attribute(unlikely) != 201803
> +#    error "__has_cpp_attribute(unlikely) != 201803"
> +#  endif
> +
> +#else
> +#  error "__has_cpp_attribute"
> +#endif
> +
> +// C++23 features:
> +
> +#ifndef __cpp_size_t_suffix
> +#  error "__cpp_size_t_suffix"
> +#elif __cpp_size_t_suffix != 202011
> +#  error "__cpp_size_t_suffix != 202011"
> +#endif
> +
> +#ifndef __cpp_if_consteval
> +#  error "__cpp_if_consteval"
> +#elif __cpp_if_consteval != 202106
> +#  error "__cpp_if_consteval != 202106"
> +#endif
> +
> +#ifndef __cpp_multidimensional_subscript
> +#  error "__cpp_multidimensional_subscript"
> +#elif __cpp_multidimensional_subscript != 202211
> +#  error "__cpp_multidimensional_subscript != 202211"
> +#endif
> +
> +#ifndef __cpp_named_character_escapes
> +#  error "__cpp_named_character_escapes"
> +#elif __cpp_named_character_escapes != 202207
> +#  error "__cpp_named_character_escapes != 202207"
> +#endif
> +
> +#ifndef __cpp_static_call_operator
> +#  error "__cpp_static_call_operator"
> +#elif __cpp_static_call_operator != 202207
> +#  error "__cpp_static_call_operator != 202207"
> +#endif
> +
> +#ifndef __cpp_implicit_move
> +#  error "__cpp_implicit_move"
> +#elif __cpp_implicit_move != 202207
> +#  error "__cpp_implicit_move != 202207"
> +#endif
> +
> +#ifndef __cpp_auto_cast
> +#  error "__cpp_auto_cast"
> +#elif __cpp_auto_cast != 202110
> +#  error "__cpp_auto_cast != 202110"
> +#endif
> +
> +//  C++23 attributes:
> +
> +#ifdef __has_cpp_attribute
> +#  if ! __has_cpp_attribute(assume)
> +#    error "__has_cpp_attribute(assume)"
> +#  elif __has_cpp_attribute(assume) != 202207
> +#    error "__has_cpp_attribute(assume) != 202207"
> +#  endif
> +#else
> +#  error "__has_cpp_attribute"
> +#endif
> 
> base-commit: ebe7c586f62b1c5218b19c3c6853163287b3c887
> prerequisite-patch-id: 8aff665478d425e404ede05fed4c0e4106a063f2
> -- 
> 2.39.3
> 

Marek