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

On Mon, Jul 31, 2017 at 03:53:42PM +0100, Jonathan Wakely wrote:
> 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.

I see. Actually I've guessed so, and thank you for clarifying it.
I'm attaching a replacing patch. Please take a look at it.

From 1b22cc531027832cf1eb50b73354f1730edbba54 Mon Sep 17 00:00:00 2001
From: Katsuhiko Nishimra <>
Date: Tue, 1 Aug 2017 20:36:58 +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 with clang++
6.0.0-svn309616-1~exp1 and g++ 7.1.0-11 on Debian unstable.
 libstdc++-v3/include/std/type_traits | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 390b6f40a..ee9c75baf 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2894,9 +2894,9 @@ template <typename _From, typename _To>
 #if __GNUC__ >= 7
-#elif defined __has_builtin
+#elif defined(__is_identifier)
 // For non-GNU compilers:
-# if __has_builtin(__is_aggregate)
+# if ! __is_identifier(__is_aggregate)
 # endif

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