On 28/04/21 16:14 +0100, Jonathan Wakely wrote:
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.
I messed up the __cpp_lib_constexpr_string macro by copy&pasting from
the __cpp_lib_constexpr_char_traits one, which is defined inside a
#ifdef __cplusplus >= 201702 block. But for __cpp_lib_constexpr_string
it isn't so the #else means that we define it to 201811L for
everything newer *or* older than C++17.
I also noticed that __cpp_lib_semaphore wasn't defined consistently,
as it's failing on AIX.
Fixed on trunk by this patch. Tested x86_64-linux and powerpc-aix.
I'll backport this to the relevant branches too.
commit 3215d4f5b3d08e0087a88df9e155c779927ace1a
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Fri Apr 30 20:32:05 2021
libstdc++: Fix inconsistent feature test macros
The __cpp_lib_constexpr_string and __cpp_lib_semaphore feature test
macros are not defined consistently in <version> and the relevant header
for the feature.
libstdc++-v3/ChangeLog:
* include/bits/basic_string.h (__cpp_lib_constexpr_string):
Only define for C++17 and later.
* include/std/version (__cpp_lib_semaphore): Fix condition
to match the one in <semaphore>.
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 41d781c698e..fba7c6f3354 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -55,7 +55,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus == 201703L
// Support P0426R1 changes to char_traits in C++17.
# define __cpp_lib_constexpr_string 201611L
-#else
+#elif __cplusplus > 201703L
// Also support P1032R1 in C++20 (but not P0980R1 yet).
# define __cpp_lib_constexpr_string 201811L
#endif
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 09e67a40d0c..ea0e18a3f9d 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -241,7 +241,7 @@
#if __cpp_lib_concepts
# define __cpp_lib_ranges 201911L
#endif
-#if __cpp_lib_atomic_wait
+#if __cpp_lib_atomic_wait || _GLIBCXX_HAVE_POSIX_SEMAPHORE
# define __cpp_lib_semaphore 201907L
#endif
#define __cpp_lib_shift 201806L
