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libstdc++: Define __cpp_lib_constexpr_string macro

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As noted in r11-1339-gb6ab9ecd550227684643b41e9e33a4d3466724d8 we define
a non-standard __cpp_lib_constexpr_char_traits feature test macro to
indicate support for P0426R1 and P1032R1. At some point last year the
__cpp_lib_constexpr_string macro was retconned to indicate support for
those papers. This adds the new macro (which we didn't previously
define, because it referred to P0980R1 "Making std::string constexpr"
which we don't support).

libstdc++-v3/ChangeLog:

	* include/bits/basic_string.h (__cpp_lib_constexpr_string): Define.
	* include/std/version (__cpp_lib_constexpr_string): Define.
	* testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc:
	Check for __cpp_lib_constexpr_string.
	* testsuite/21_strings/char_traits/requirements/constexpr_functions_c++20.cc:
	Likewise.
	* testsuite/21_strings/char_traits/requirements/version.cc: New test.
This commit is contained in:
Jonathan Wakely 2021-04-28 15:56:04 +01:00
parent 43a35b26e2
commit 3da80ed7ef
5 changed files with 41 additions and 4 deletions
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9
libstdc++-v3/include/bits/basic_string.h
View file

@ -48,11 +48,18 @@
# include <string_view>
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus == 201703L
// Support P0426R1 changes to char_traits in C++17.
# define __cpp_lib_constexpr_string 201611L
#else
// Also support P1032R1 in C++20 (but not P0980R1 yet).
# define __cpp_lib_constexpr_string 201811L
#endif
#if _GLIBCXX_USE_CXX11_ABI
_GLIBCXX_BEGIN_NAMESPACE_CXX11
/**

2
libstdc++-v3/include/std/version
View file

@ -131,6 +131,7 @@
#define __cpp_lib_clamp 201603
#if __cplusplus == 201703L // N.B. updated value in C++20
# define __cpp_lib_constexpr_char_traits 201611L
# define __cpp_lib_constexpr_string 201611L
#endif
#define __cpp_lib_enable_shared_from_this 201603
#define __cpp_lib_execution 201902L // FIXME: should be 201603L
@ -219,6 +220,7 @@
#define __cpp_lib_constexpr_iterator 201811L
#define __cpp_lib_constexpr_memory 201811L
#define __cpp_lib_constexpr_numeric 201911L
#define __cpp_lib_constexpr_string 201811L
#define __cpp_lib_constexpr_string_view 201811L
#define __cpp_lib_constexpr_tuple 201811L
#define __cpp_lib_constexpr_utility 201811L

11
libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc
View file

@ -73,12 +73,17 @@ template<typename CT>
return true;
}
#ifndef __cpp_lib_constexpr_string
# error Feature-test macro for constexpr char_traits is missing
#elif __cpp_lib_constexpr_string < (__cplusplus == 201703 ? 201611 : 201811)
# error Feature-test macro for constexpr char_traits has the wrong value
#endif
// We also provide this non-standard macro for P0426R1 (and P1032R1 in C++20).
#ifndef __cpp_lib_constexpr_char_traits
# error Feature-test macro for constexpr char_traits is missing
#elif __cpp_lib_constexpr_char_traits < 201611
#elif __cpp_lib_constexpr_char_traits != (__cplusplus == 201703 ? 201611 : 201811)
# error Feature-test macro for constexpr char_traits has the wrong value
#elif __cpp_lib_constexpr_char_traits > 201611 && __cplusplus == 201703
# error Feature-test macro for constexpr char_traits has wrong value for C++17
#endif
static_assert( test_assign<std::char_traits<char>>() );

7
libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++20.cc
View file

@ -30,6 +30,13 @@ template<typename CT>
return s1[0]==char_type{1} && s1[1]==char_type{1} && s1[2]==char_type{2};
}
#ifndef __cpp_lib_constexpr_string
# error Feature-test macro for constexpr char_traits is missing
#elif __cpp_lib_constexpr_string < 201811
# error Feature-test macro for constexpr char_traits has the wrong value
#endif
// We also provide this non-standard macro for P0426R1 and P1032R1.
#ifndef __cpp_lib_constexpr_char_traits
# error Feature-test macro for constexpr char_traits is missing
#elif __cpp_lib_constexpr_char_traits != 201811

16
libstdc++-v3/testsuite/21_strings/char_traits/requirements/version.cc Normal file
View file

@ -0,0 +1,16 @@
// { dg-do compile { target c++17 } }
#include <version>
#ifndef __cpp_lib_constexpr_string
# error Feature-test macro for constexpr char_traits is missing in <version>
#elif __cpp_lib_constexpr_string < (__cplusplus == 201703 ? 201611 : 201811)
# error Feature-test macro for constexpr char_traits has the wrong value in <version>
#endif
// We also provide this non-standard macro for P0426R1 and P1032R1.
#ifndef __cpp_lib_constexpr_char_traits
# error Feature-test macro for constexpr char_traits is missing in <version>
#elif __cpp_lib_constexpr_char_traits != (__cplusplus == 201703 ? 201611 : 201811)
# error Feature-test macro for constexpr char_traits has the wrong value in <version>
#endif