Bug 1303302 - Add IsDestructible trait in TypeTraits and use it for refcounted type static check. r=froydnj

MozReview-Commit-ID: G3YFhrJngq0

--HG--
extra : rebase_source : da0aa325eb7772c1a156440ed46be9d0d429c91e

mfbt/TypeTraits.h

@@ -572,6 +572,27 @@ struct IsUnsignedHelper<T, false, false, NoCV> : FalseType {};
 template<typename T>
 struct IsUnsigned : detail::IsUnsignedHelper<T> {};
 
+namespace detail {
+
+struct DoIsDestructibleImpl
+{
+  template<typename T, typename = decltype(DeclVal<T&>().~T())>
+  static TrueType test(int);
+  template<typename T>
+  static FalseType test(...);
+};
+
+template<typename T>
+struct IsDestructibleImpl : public DoIsDestructibleImpl
+{
+  typedef decltype(test<T>(0)) Type;
+};
+
+} // namespace detail
+
+template<typename T>
+struct IsDestructible : public detail::IsDestructibleImpl<T>::Type {};
+
 /* 20.9.5 Type property queries [meta.unary.prop.query] */
 
 /* 20.9.6 Relationships between types [meta.rel] */

mfbt/tests/TestTypeTraits.cpp

@@ -31,6 +31,7 @@ using mozilla::IsRvalueReference;
 using mozilla::IsSame;
 using mozilla::IsSigned;
 using mozilla::IsUnsigned;
+using mozilla::IsDestructible;
 using mozilla::MakeSigned;
 using mozilla::MakeUnsigned;
 using mozilla::RemoveExtent;
@@ -352,6 +353,27 @@ static_assert(!IsSigned<NotIntConstructible>::value,
 static_assert(!IsUnsigned<NotIntConstructible>::value,
               "non-arithmetic types are not unsigned");
 
+class PublicDestructible
+{
+public:
+  ~PublicDestructible();
+};
+class PrivateDestructible
+{
+private:
+  ~PrivateDestructible();
+};
+class TrivialDestructible
+{
+};
+
+static_assert(IsDestructible<PublicDestructible>::value,
+              "public destructible class is destructible");
+static_assert(!IsDestructible<PrivateDestructible>::value,
+              "private destructible class is not destructible");
+static_assert(IsDestructible<TrivialDestructible>::value,
+              "trivial destructible class is destructible");
+
 namespace CPlusPlus11IsBaseOf {
 
 // Adapted from C++11 § 20.9.6.

xpcom/glue/nsISupportsImpl.h

@@ -29,59 +29,10 @@
 #include "mozilla/MacroForEach.h"
 #include "mozilla/TypeTraits.h"
 
-#if defined(__clang__)
-   // bug 1028428 shows that at least in FreeBSD 10.0 with Clang 3.4 and libc++ 3.4,
-   // std::is_destructible is buggy in that it returns false when it should return true
-   // on ipc::SharedMemory. On the other hand, all Clang versions currently in use
-   // seem to handle the fallback just fine.
-#  define MOZ_CAN_USE_IS_DESTRUCTIBLE_FALLBACK
-#elif defined(__GNUC__)
-   // GCC 4.7 has buggy std::is_destructible.
-#  if MOZ_USING_LIBSTDCXX
-#    define MOZ_HAVE_STD_IS_DESTRUCTIBLE
-#  endif
-   // Some GCC versions have an ICE when using destructors in decltype().
-   // Works on GCC 4.8 at least.
-#  define MOZ_CAN_USE_IS_DESTRUCTIBLE_FALLBACK
-#endif
-
-#ifdef MOZ_HAVE_STD_IS_DESTRUCTIBLE
-#  include <type_traits>
-#  define MOZ_IS_DESTRUCTIBLE(X) (std::is_destructible<X>::value)
-#elif defined MOZ_CAN_USE_IS_DESTRUCTIBLE_FALLBACK
-  namespace mozilla {
-    struct IsDestructibleFallbackImpl
-    {
-      template<typename T, typename = decltype(DeclVal<T>().~T())>
-      static TrueType Test(int);
-
-      template<typename>
-      static FalseType Test(...);
-
-      template<typename T>
-      struct Selector
-      {
-        typedef decltype(Test<T>(0)) type;
-      };
-    };
-
-    template<typename T>
-    struct IsDestructibleFallback
-      : IsDestructibleFallbackImpl::Selector<T>::type
-    {
-    };
-  } // namespace mozilla
-#  define MOZ_IS_DESTRUCTIBLE(X) (mozilla::IsDestructibleFallback<X>::value)
-#endif
-
-#ifdef MOZ_IS_DESTRUCTIBLE
 #define MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(X) \
-  static_assert(!MOZ_IS_DESTRUCTIBLE(X), \
+  static_assert(!mozilla::IsDestructible<X>::value, \
                 "Reference-counted class " #X " should not have a public destructor. " \
                 "Make this class's destructor non-public");
-#else
-#define MOZ_ASSERT_TYPE_OK_FOR_REFCOUNTING(X)
-#endif
 
 inline nsISupports*
 ToSupports(nsISupports* aSupports)