Bug 809715 - Use MFBT's IsBaseOf to simplify QS_IS_NODE - r=ehsan

js/xpconnect/src/qsObjectHelper.h

@@ -12,6 +12,7 @@
 #include "nsIDOMNode.h"
 #include "nsINode.h"
 #include "nsWrapperCache.h"
+#include "mozilla/TypeTraits.h"
 
 inline nsISupports*
 ToSupports(nsISupports *p)
@@ -25,40 +26,14 @@ ToCanonicalSupports(nsISupports *p)
     return NULL;
 }
 
-#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 2) || \
-    _MSC_FULL_VER >= 140050215
-
-/* Use a compiler intrinsic if one is available. */
-
-#define QS_CASTABLE_TO(_interface, _class) __is_base_of(_interface, _class)
-
-#else
-
-/* The generic version of this predicate relies on the overload resolution
- * rules.  If |_class| inherits from |_interface|, the |_interface*|
- * overload of DOMCI_CastableTo<_interface>::p() will be chosen, otherwise
- * the |void*| overload will be chosen.  There is no definition of these
- * functions; we determine which overload was selected by inspecting the
- * size of the return type.
- */
-
-template <typename Interface> struct QS_CastableTo {
-    struct false_type { int x[1]; };
-    struct true_type { int x[2]; };
-    static false_type p(void*);
-    static true_type p(Interface*);
+template <typename T>
+struct qsIsNode
+{
+    static const bool value =
+        mozilla::IsBaseOf<nsINode, T>::value ||
+        mozilla::IsBaseOf<nsIDOMNode, T>::value;
 };
 
-#define QS_CASTABLE_TO(_interface, _class)                                     \
-    (sizeof(QS_CastableTo<_interface>::p(static_cast<_class*>(0))) ==          \
-     sizeof(QS_CastableTo<_interface>::true_type))
-
-#endif
-
-#define QS_IS_NODE(_class)                                                     \
-    QS_CASTABLE_TO(nsINode, _class) ||                                         \
-    QS_CASTABLE_TO(nsIDOMNode, _class)
-
 class qsObjectHelper : public xpcObjectHelper
 {
 public:
@@ -66,7 +41,7 @@ public:
     inline
     qsObjectHelper(T *aObject, nsWrapperCache *aCache)
         : xpcObjectHelper(ToSupports(aObject), ToCanonicalSupports(aObject),
-                          aCache, QS_IS_NODE(T))
+                          aCache, qsIsNode<T>::value)
     {}
 
     template <class T>
@@ -74,7 +49,7 @@ public:
     qsObjectHelper(nsCOMPtr<T>& aObject, nsWrapperCache *aCache)
         : xpcObjectHelper(ToSupports(aObject.get()),
                           ToCanonicalSupports(aObject.get()), aCache,
-                          QS_IS_NODE(T))
+                          qsIsNode<T>::value)
     {
         if (mCanonical) {
             // Transfer the strong reference.
@@ -88,7 +63,7 @@ public:
     qsObjectHelper(nsRefPtr<T>& aObject, nsWrapperCache *aCache)
         : xpcObjectHelper(ToSupports(aObject.get()),
                           ToCanonicalSupports(aObject.get()), aCache,
-                          QS_IS_NODE(T))
+                          qsIsNode<T>::value)
     {
         if (mCanonical) {
             // Transfer the strong reference.