Fix LWG Issue 2141: common_type trait produces reference types

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@192142 91177308-0d34-0410-b5e6-96231b3b80d8

include/type_traits

@@ -719,6 +719,31 @@ template <class _Tp, size_t _Np> struct _LIBCPP_TYPE_VIS_ONLY remove_all_extents
 template <class _Tp> using remove_all_extents_t = typename remove_all_extents<_Tp>::type;
 #endif
 
+// decay
+
+template <class _Tp>
+struct _LIBCPP_TYPE_VIS_ONLY decay
+{
+private:
+    typedef typename remove_reference<_Tp>::type _Up;
+public:
+    typedef typename conditional
+                     <
+                         is_array<_Up>::value,
+                         typename remove_extent<_Up>::type*,
+                         typename conditional
+                         <
+                              is_function<_Up>::value,
+                              typename add_pointer<_Up>::type,
+                              typename remove_cv<_Up>::type
+                         >::type
+                     >::type type;
+};
+
+#if _LIBCPP_STD_VER > 11
+template <class _Tp> using decay_t = typename decay<_Tp>::type;
+#endif
+
 // is_abstract
 
 namespace __is_abstract_imp
@@ -1356,7 +1381,7 @@ template <class ..._Tp> struct common_type;
 template <class _Tp>
 struct _LIBCPP_TYPE_VIS_ONLY common_type<_Tp>
 {
-    typedef _Tp type;
+    typedef typename decay<_Tp>::type type;
 };
 
 template <class _Tp, class _Up>
@@ -1367,7 +1392,7 @@ private:
     static _Up&& __u();
     static bool __f();
 public:
-    typedef typename remove_reference<decltype(__f() ? __t() : __u())>::type type;
+    typedef typename decay<decltype(__f() ? __t() : __u())>::type type;
 };
 
 template <class _Tp, class _Up, class ..._Vp>
@@ -1546,29 +1571,6 @@ public:
 
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
-template <class _Tp>
-struct _LIBCPP_TYPE_VIS_ONLY decay
-{
-private:
-    typedef typename remove_reference<_Tp>::type _Up;
-public:
-    typedef typename conditional
-                     <
-                         is_array<_Up>::value,
-                         typename remove_extent<_Up>::type*,
-                         typename conditional
-                         <
-                              is_function<_Up>::value,
-                              typename add_pointer<_Up>::type,
-                              typename remove_cv<_Up>::type
-                         >::type
-                     >::type type;
-};
-
-#if _LIBCPP_STD_VER > 11
-template <class _Tp> using decay_t = typename decay<_Tp>::type;
-#endif
-
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
 template <class _Tp>

test/utilities/meta/meta.trans/meta.trans.other/common_type.pass.cpp

@@ -22,6 +22,20 @@ int main()
     static_assert((std::is_same<std::common_type_t<char>, char>::value), "");
 #endif
 
+    static_assert((std::is_same<std::common_type<               int>::type, int>::value), "");
+    static_assert((std::is_same<std::common_type<const          int>::type, int>::value), "");
+    static_assert((std::is_same<std::common_type<      volatile int>::type, int>::value), "");
+    static_assert((std::is_same<std::common_type<const volatile int>::type, int>::value), "");
+
+    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), "");
+    static_assert((std::is_same<std::common_type<volatile long,    int>::type, long>::value), "");
+    static_assert((std::is_same<std::common_type<const long, const int>::type, long>::value), "");
+
     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

test/utilities/meta/meta.unary/meta.unary.prop/is_trivialially_copyable.pass.cpp

@@ -19,8 +19,8 @@ void test_is_trivially_copyable()
 {
     static_assert( std::is_trivially_copyable<T>::value, "");
     static_assert( std::is_trivially_copyable<const T>::value, "");
-    static_assert( std::is_trivially_copyable<volatile T>::value, "");
+    static_assert(!std::is_trivially_copyable<volatile T>::value, "");
-    static_assert( std::is_trivially_copyable<const volatile T>::value, "");
+    static_assert(!std::is_trivially_copyable<const volatile T>::value, "");
 }
 
 template <class T>

www/cxx1y_status.html

@@ -184,7 +184,7 @@
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2231">2231</a></td><td>DR 704 removes complexity guarantee for clear()</td><td>Bristol</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2235">2235</a></td><td>Undefined behavior without proper requirements on basic_string constructors</td><td>Bristol</td><td>Complete</td></tr>
     <tr><td></td><td></td><td></td><td></td></tr>
-	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2141">2141</a></td><td>common_type trait produces reference types</td><td>Chicago</td><td></td></tr>
+	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2141">2141</a></td><td>common_type trait produces reference types</td><td>Chicago</td><td>Complete</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2235">2235</a></td><td>Undefined behavior without proper requirements on basic_string constructors</td><td>Chicago</td><td></td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2246">2246</a></td><td>unique_ptr assignment effects w.r.t. deleter</td><td>Chicago</td><td></td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2247">2247</a></td><td>Type traits and std::nullptr_t</td><td>Chicago</td><td>Complete</td></tr>