make common_type SFINAE-friendly and support void. Patch from Agustin Berge.

This patch also fixes PR22135. (https://llvm.org/bugs/show_bug.cgi?id=22135)
See the review for more information: http://reviews.llvm.org/D6964

llvm-svn: 246977

1 files changed, 54 insertions, 4 deletions

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 91bf7e7654e..e8611253c5d 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
@@ -13,11 +13,39 @@
 
 #include <type_traits>
 
+#include "test_macros.h"
+
+struct E {};
+
+template <class T>
+struct X { explicit X(T const&){} };
+
+template <class T>
+struct S { explicit S(T const&){} };
+
+namespace std
+{
+    template <typename T>
+    struct common_type<T, ::S<T> >
+    {
+        typedef S<T> type;
+    };
+}
+
+#if TEST_STD_VER >= 11
+template <class T, class U, class = void>
+struct no_common_type : std::true_type {};
+
+template <class T, class U>
+struct no_common_type<T, U, typename std::conditional<false,
+    typename std::common_type<T, U>::type, void>::type> : std::false_type {};
+#endif // TEST_STD_VER >= 11
+
 int main()
 {
     static_assert((std::is_same<std::common_type<int>::type, int>::value), "");
     static_assert((std::is_same<std::common_type<char>::type, char>::value), "");
-#if _LIBCPP_STD_VER > 11
+#if TEST_STD_VER > 11
     static_assert((std::is_same<std::common_type_t<int>,   int>::value), "");
     static_assert((std::is_same<std::common_type_t<char>, char>::value), "");
 #endif
@@ -29,7 +57,7 @@ int main()
 
     static_assert((std::is_same<std::common_type<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<long,       const int>::type, long>::value), "");
     static_assert((std::is_same<std::common_type<const long,       int>::type, long>::value), "");
     static_assert((std::is_same<std::common_type<long,    volatile int>::type, long>::value), "");
@@ -38,15 +66,37 @@ int main()
 
     static_assert((std::is_same<std::common_type<double, char>::type, double>::value), "");
     static_assert((std::is_same<std::common_type<short, char>::type, int>::value), "");
-#if _LIBCPP_STD_VER > 11
+#if TEST_STD_VER > 11
     static_assert((std::is_same<std::common_type_t<double, char>, double>::value), "");
     static_assert((std::is_same<std::common_type_t<short, char>, int>::value), "");
 #endif
 
     static_assert((std::is_same<std::common_type<double, char, long long>::type, double>::value), "");
     static_assert((std::is_same<std::common_type<unsigned, char, long long>::type, long long>::value), "");
-#if _LIBCPP_STD_VER > 11
+#if TEST_STD_VER > 11
     static_assert((std::is_same<std::common_type_t<double, char, long long>, double>::value), "");
     static_assert((std::is_same<std::common_type_t<unsigned, char, long long>, long long>::value), "");
 #endif
+
+    static_assert((std::is_same<std::common_type<               void>::type, void>::value), "");
+    static_assert((std::is_same<std::common_type<const          void>::type, void>::value), "");
+    static_assert((std::is_same<std::common_type<      volatile void>::type, void>::value), "");
+    static_assert((std::is_same<std::common_type<const volatile void>::type, void>::value), "");
+
+    static_assert((std::is_same<std::common_type<void,       const void>::type, void>::value), "");
+    static_assert((std::is_same<std::common_type<const void,       void>::type, void>::value), "");
+    static_assert((std::is_same<std::common_type<void,    volatile void>::type, void>::value), "");
+    static_assert((std::is_same<std::common_type<volatile void,    void>::type, void>::value), "");
+    static_assert((std::is_same<std::common_type<const void, const void>::type, void>::value), "");
+
+#if TEST_STD_VER >= 11
+    static_assert((no_common_type<void, int>::value), "");
+    static_assert((no_common_type<int, void>::value), "");
+    static_assert((no_common_type<int, E>::value), "");
+    static_assert((no_common_type<int, X<int> >::value), "");
+#endif // TEST_STD_VER >= 11
+
+    static_assert((std::is_same<std::common_type<int, S<int> >::type, S<int> >::value), "");
+    static_assert((std::is_same<std::common_type<int, S<int>, S<int> >::type, S<int> >::value), "");
+    static_assert((std::is_same<std::common_type<int, int, S<int> >::type, S<int> >::value), "");
 }