Re: [committed] libstdc++: Define __cpp_lib_constexpr_string macro

[Jonathan Wakely <jwakely@redhat.com>]

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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.



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commit 3215d4f5b3d08e0087a88df9e155c779927ace1a
Author: Jonathan Wakely <jwakely@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