Bug 1540301, part 2 - Make nsXPCWrappedJSClass::CallMethod() into a static method. r=bzbarsky

The first idea here is that |this| is actually the GetClass() of the
|wrapper| argument (the one call site looks like
"GetClass()->CallMethod(this, ...)"), so we can locally reconstruct it
when CallMethod is a static method.

The second idea here is that the only real use of the
nsXPCWrappedJSClass is to grab some data from the nsXPTInterfaceInfo
in a few places. This means that we can take a pointer to the info
early on in the function and use that rather than go through the
nsXPCWrappedJSClass. This in turn means that because the info is
statically allocated we no longer need to do a kungFuDeathGrip on the
wrapper's nsXPCWrappedJSClass.

Differential Revision: https://phabricator.services.mozilla.com/D26215

--HG--
extra : moz-landing-system : lando

js/xpconnect/src/XPCWrappedJS.cpp

@@ -596,7 +596,7 @@ nsXPCWrappedJS::CallMethod(uint16_t methodIndex, const nsXPTMethodInfo* info,
   if (!IsValid()) {
     return NS_ERROR_UNEXPECTED;
   }
-  return GetClass()->CallMethod(this, methodIndex, info, params);
+  return nsXPCWrappedJSClass::CallMethod(this, methodIndex, info, params);
 }
 
 NS_IMETHODIMP

js/xpconnect/src/XPCWrappedJSClass.cpp

@@ -780,6 +780,8 @@ nsresult nsXPCWrappedJSClass::CallMethod(nsXPCWrappedJS* wrapper,
     return NS_ERROR_FAILURE;
   }
 
+  const nsXPTInterfaceInfo* interfaceInfo =
+      wrapper->GetClass()->GetInterfaceInfo();
   JS::RootedId id(cx);
   const char* name;
   nsAutoCString symbolName;
@@ -808,7 +810,7 @@ nsresult nsXPCWrappedJSClass::CallMethod(nsXPCWrappedJS* wrapper,
     // Throw and warn for good measure.
     JS_ReportErrorASCII(cx, "%s", str);
     NS_WARNING(str);
-    return CheckForException(ccx, aes, obj, name, GetInterfaceName());
+    return CheckForException(ccx, aes, obj, name, interfaceInfo->Name());
   }
 
   RootedValue fval(cx);
@@ -860,7 +862,8 @@ nsresult nsXPCWrappedJSClass::CallMethod(nsXPCWrappedJS* wrapper,
     // pass this along to the caller as an exception/result code.
 
     fval = ObjectValue(*obj);
-    if (!mInfo->IsFunction() || JS_TypeOfValue(ccx, fval) != JSTYPE_FUNCTION) {
+    if (!interfaceInfo->IsFunction() ||
+        JS_TypeOfValue(ccx, fval) != JSTYPE_FUNCTION) {
       if (!JS_GetPropertyById(cx, obj, id, &fval)) {
         goto pre_call_clean_up;
       }
@@ -943,9 +946,6 @@ pre_call_clean_up:
   // clean up any 'out' params handed in
   CleanupOutparams(info, nativeParams, /* inOutOnly = */ true, paramCount);
 
-  // Make sure "this" doesn't get deleted during this call.
-  nsCOMPtr<nsIXPCWrappedJSClass> kungFuDeathGrip(this);
-
   if (!readyToDoTheCall) {
     return retval;
   }
@@ -979,14 +979,14 @@ pre_call_clean_up:
       }
 
       XPCConvert::ConstructException(
-          code, sz.get(), GetInterfaceName(), name, nullptr,
+          code, sz.get(), interfaceInfo->Name(), name, nullptr,
           getter_AddRefs(syntheticException), nullptr, nullptr);
       success = false;
     }
   }
 
   if (!success) {
-    return CheckForException(ccx, aes, obj, name, GetInterfaceName(),
+    return CheckForException(ccx, aes, obj, name, interfaceInfo->Name(),
                              syntheticException);
   }
 

js/xpconnect/src/xpcprivate.h

@@ -1634,8 +1634,9 @@ class nsXPCWrappedJSClass final : public nsIXPCWrappedJSClass {
 
   static JSObject* GetRootJSObject(JSContext* cx, JSObject* aJSObj);
 
-  nsresult CallMethod(nsXPCWrappedJS* wrapper, uint16_t methodIndex,
+  static nsresult CallMethod(nsXPCWrappedJS* wrapper, uint16_t methodIndex,
-                      const nsXPTMethodInfo* info, nsXPTCMiniVariant* params);
+                             const nsXPTMethodInfo* info,
+                             nsXPTCMiniVariant* params);
 
   static JSObject* CallQueryInterfaceOnJSObject(JSContext* cx, JSObject* jsobj,
                                                 JS::HandleObject scope,