Bug 313309 - Table-driven QI part 3 - use weak statics for interface IDs, r=shaver. This will break VC6 and gcc2.9x, which is ok

xpcom/base/nsISupportsBase.h

@@ -66,6 +66,8 @@
 class NS_NO_VTABLE nsISupports {
 public:
 
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISUPPORTS_IID)
+
   /**
    * @name Methods
    */
@@ -101,5 +103,9 @@ public:
 
   //@}
 };
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsISupports, NS_ISUPPORTS_IID)
+
 /*@}*/
+
 #endif

xpcom/glue/nsID.h

@@ -134,13 +134,23 @@ typedef nsID nsIID;
   const nsIID _name = _iidspec
 
 /**
- * A macro to build the static const IID accessor method
+ * A macro to build the static const IID accessor method. The Dummy
+ * template parameter only exists so that the kIID symbol will be linked
+ * properly (weak symbol on linux, gnu_linkonce on mac, multiple-definitions
+ * merged on windows). Dummy should always be instantiated as "int".
  */
 
 #define NS_DECLARE_STATIC_IID_ACCESSOR(the_iid)                         \
-  static const nsIID& GetIID() {static const nsIID iid = the_iid; return iid;}
+  template <class Dummy>                                                \
+  struct COMTypeInfo                                                    \
+  {                                                                     \
+    static const nsIID kIID NS_HIDDEN;                                  \
+  };                                                                    \
+  static const nsIID& GetIID() {return COMTypeInfo<int>::kIID;}
 
-#define NS_DEFINE_STATIC_IID_ACCESSOR(the_interface, the_iid)
+#define NS_DEFINE_STATIC_IID_ACCESSOR(the_interface, the_iid)           \
+  template <class Dummy>                                                \
+  const nsIID the_interface::COMTypeInfo<Dummy>::kIID NS_HIDDEN = the_iid;
 
 /**
  * A macro to build the static const CID accessor method
@@ -149,7 +159,7 @@ typedef nsID nsIID;
 #define NS_DEFINE_STATIC_CID_ACCESSOR(the_cid) \
   static const nsID& GetCID() {static const nsID cid = the_cid; return cid;}
 
-#define NS_GET_IID(T) nsCOMTypeInfo<T>::GetIID()
-#define NS_GET_TEMPLATE_IID(T) NS_GET_IID(T)
+#define NS_GET_IID(T) (::T::COMTypeInfo<int>::kIID)
+#define NS_GET_TEMPLATE_IID(T) (T::template COMTypeInfo<int>::kIID)
 
 #endif

xpcom/glue/nsISupportsUtils.h

@@ -190,26 +190,6 @@ ns_if_addref( T expr )
 #define NS_ISUPPORTS_CAST(__unambiguousBase, __expr) \
   NS_STATIC_CAST(nsISupports*, NS_STATIC_CAST(__unambiguousBase, __expr))
 
-extern "C++" {
-// ...because some one is accidentally including this file inside
-// an |extern "C"|
-
-class nsISupports;
-
-template <class T>
-struct nsCOMTypeInfo
-{
-    static const nsIID& GetIID() { return T::GetIID(); }
-};
-
-NS_SPECIALIZE_TEMPLATE
-struct nsCOMTypeInfo<nsISupports>
-{
-    static const nsIID& GetIID() {
-        static const nsIID iid_NS_ISUPPORTS_IID = NS_ISUPPORTS_IID; return iid_NS_ISUPPORTS_IID;
-    }
-};
-
 // a type-safe shortcut for calling the |QueryInterface()| member function
 template <class T, class DestinationType>
 inline
@@ -223,6 +203,4 @@ CallQueryInterface( T* aSource, DestinationType** aDestination )
                                    NS_REINTERPRET_CAST(void**, aDestination));
 }
 
-} // extern "C++"
-
 #endif /* __nsISupportsUtils_h */