[cfe-dev] [PATCH] libstdc++: Support std::is_aggregate on clang++ (was clang++: std::is_aggregate unusable with clang-5.0/libstdc++-7)

[Tim Song via cfe-dev]

On Mon, Jul 31, 2017 at 10:53 AM, Jonathan Wakely <jwakely at redhat.com> wrote:
> On 27/07/17 16:27 +0900, Katsuhiko Nishimra wrote:
>>
>> From 56c4a18d0d8c8ce7aa1239880138775e4db06645 Mon Sep 17 00:00:00 2001
>> From: Katsuhiko Nishimra <ktns.87 at gmail.com>
>> Date: Thu, 27 Jul 2017 16:03:54 +0900
>> Subject: [PATCH] libstdc++: Support std::is_aggregate on clang++
>>
>> Currently, libstdc++ tries to detect __is_aggregate built-in macro using
>> __has_builtin, but this fails on clang++ because __has_builtin on
>> clang++ detects only built-in functions, not built-in macros. This patch
>> adds a test using __is_identifier. Tested on clang++
>> 5.0.0-svn308422-1~exp1 and g++ 7.1.0-10 from Debian unstable.
>> ---
>> libstdc++-v3/include/std/type_traits | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/libstdc++-v3/include/std/type_traits
>> b/libstdc++-v3/include/std/type_traits
>> index 390b6f40a..e7ec402fb 100644
>> --- a/libstdc++-v3/include/std/type_traits
>> +++ b/libstdc++-v3/include/std/type_traits
>> @@ -2894,6 +2894,11 @@ template <typename _From, typename _To>
>>
>> #if __GNUC__ >= 7
>> # define _GLIBCXX_HAVE_BUILTIN_IS_AGGREGATE 1
>> +#elif defined(__is_identifier)
>> +// For clang
>> +# if ! __is_identifier(__is_aggregate)
>> +#  define _GLIBCXX_HAVE_BUILTIN_IS_AGGREGATE 1
>> +# endif
>> #elif defined __has_builtin
>> // For non-GNU compilers:
>> # if __has_builtin(__is_aggregate)
>
>
> This __has_bultin check only exists for Clang, so should be replaced
> by the correct __is_identifier check, not left there in addition to
> it.
>
>

https://clang.llvm.org/docs/LanguageExtensions.html#checks-for-type-trait-primitives
seems to suggest using __has_extension instead.