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

[Jonathan Wakely <jwakely@redhat.com>]

On 27/07/17 16:27 +0900, Katsuhiko Nishimra wrote:
From 56c4a18d0d8c8ce7aa1239880138775e4db06645 Mon Sep 17 00:00:00 2001
>From: Katsuhiko Nishimra <ktns.87@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.