From c2be5ab5810ba5e7951d0bf7c1f84922356daf2c Mon Sep 17 00:00:00 2001
From: Marshall Clow <mclow.lists@gmail.com>
Date: Mon, 10 Apr 2017 23:47:47 +0000
Subject: [PATCH] Fix PR#32605: common_type<T> is not SFINAE-friendly

llvm-svn: 299901
---
 libcxx/include/type_traits                                  | 4 +---
 .../meta/meta.trans/meta.trans.other/common_type.pass.cpp   | 6 +++++-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/libcxx/include/type_traits b/libcxx/include/type_traits
index ec158fc081c3..c0922392a66b 100644
--- a/libcxx/include/type_traits
+++ b/libcxx/include/type_traits
@@ -1998,9 +1998,7 @@ struct _LIBCPP_TEMPLATE_VIS common_type {};
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS common_type<_Tp>
-{
-    typedef typename common_type<_Tp, _Tp>::type type;
-};
+    : public common_type<_Tp, _Tp> {};
 
 // bullet 3 - sizeof...(Tp) == 2
 
diff --git a/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/common_type.pass.cpp b/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/common_type.pass.cpp
index 736f74b4c270..db7b4c2f412a 100644
--- a/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/common_type.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.trans/meta.trans.other/common_type.pass.cpp
@@ -45,6 +45,8 @@ namespace std
 
     template <> struct common_type< ::S<long>, long> {};
     template <> struct common_type<long, ::S<long> > {};
+    template <> struct common_type<::X<float> > {};
+    template <> struct common_type<::X<double>, ::X<double> > {};
 }
 
 #if TEST_STD_VER >= 11
@@ -304,5 +306,7 @@ int main()
     static_assert((std::is_same<std::common_type<const int, int>::type,       int>::value), "");
     static_assert((std::is_same<std::common_type<int, const int>::type,       int>::value), "");
     static_assert((std::is_same<std::common_type<const int, const int>::type, int>::value), "");
-    
+
+    static_assert(no_common_type<X<float> >::value, "");
+    static_assert(no_common_type<X<double> >::value, "");
 }