Port modern callback handling code from Gecko, and copy related WebIDL parser bits too.

15 files changed, 420 insertions, 222 deletions

diff --git a/src/components/script/dom/bindings/callback.rs b/src/components/script/dom/bindings/callback.rs
index 8a29c382ca9..deebc53d6e3 100644
--- a/src/components/script/dom/bindings/callback.rs
+++ b/src/components/script/dom/bindings/callback.rs
@@ -2,13 +2,13 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use dom::bindings::trace::trace_object;
-use dom::bindings::utils::Reflectable;
+use dom::bindings::js::JSRef;
+use dom::bindings::trace::Traceable;
+use dom::bindings::utils::{Reflectable, global_object_for_js_object};
 use js::jsapi::{JSContext, JSObject, JS_WrapObject, JS_ObjectIsCallable};
-use js::jsapi::{JS_GetProperty, JSTracer};
+use js::jsapi::JS_GetProperty;
 use js::jsval::{JSVal, UndefinedValue};
 
-use std::cast;
 use std::ptr;
 
 use serialize::{Encodable, Encoder};
@@ -24,42 +24,61 @@ pub enum ExceptionHandling {
     RethrowExceptions
 }
 
-#[deriving(Clone,Eq)]
-pub struct CallbackInterface {
-    pub callback: *mut JSObject
+#[deriving(Clone,Eq,Encodable)]
+pub struct CallbackFunction {
+    object: CallbackObject
 }
 
-impl<S: Encoder<E>, E> Encodable<S, E> for CallbackInterface {
-    fn encode(&self, s: &mut S) -> Result<(), E> {
-        unsafe {
-            let tracer: *mut JSTracer = cast::transmute(s);
-            trace_object(tracer, "callback", self.callback);
+impl CallbackFunction {
+    pub fn new(callback: *mut JSObject) -> CallbackFunction {
+        CallbackFunction {
+            object: CallbackObject {
+                callback: Traceable::new(callback)
+            }
         }
-        Ok(())
     }
 }
 
+#[deriving(Clone,Eq,Encodable)]
+pub struct CallbackInterface {
+    object: CallbackObject
+}
+
+#[deriving(Clone,Eq,Encodable)]
+struct CallbackObject {
+    callback: Traceable<*mut JSObject>,
+}
+
 pub trait CallbackContainer {
+    fn new(callback: *mut JSObject) -> Self;
     fn callback(&self) -> *mut JSObject;
 }
 
-impl CallbackContainer for CallbackInterface {
-    fn callback(&self) -> *mut JSObject {
-        self.callback
+impl CallbackInterface {
+    pub fn callback(&self) -> *mut JSObject {
+        *self.object.callback
+    }
+}
+
+impl CallbackFunction {
+    pub fn callback(&self) -> *mut JSObject {
+        *self.object.callback
     }
 }
 
 impl CallbackInterface {
     pub fn new(callback: *mut JSObject) -> CallbackInterface {
         CallbackInterface {
-            callback: callback
+            object: CallbackObject {
+                callback: Traceable::new(callback)
+            }
         }
     }
 
     pub fn GetCallableProperty(&self, cx: *mut JSContext, name: &str) -> Result<JSVal, ()> {
         let mut callable = UndefinedValue();
         unsafe {
-            if name.to_c_str().with_ref(|name| JS_GetProperty(cx, self.callback, name, &mut callable)) == 0 {
+            if name.to_c_str().with_ref(|name| JS_GetProperty(cx, self.callback(), name, &mut callable)) == 0 {
                 return Err(());
             }
 
@@ -73,14 +92,9 @@ impl CallbackInterface {
     }
 }
 
-pub fn GetJSObjectFromCallback<T: CallbackContainer>(callback: &T) -> *mut JSObject {
-    callback.callback()
-}
-
-pub fn WrapCallThisObject<T: 'static + CallbackContainer + Reflectable>(cx: *mut JSContext,
-                                                                        _scope: *mut JSObject,
-                                                                        p: Box<T>) -> *mut JSObject {
-    let mut obj = GetJSObjectFromCallback(p);
+pub fn WrapCallThisObject<T: Reflectable>(cx: *mut JSContext,
+                                          p: &JSRef<T>) -> *mut JSObject {
+    let mut obj = p.reflector().get_jsobject();
     assert!(obj.is_not_null());
 
     unsafe {
@@ -98,7 +112,9 @@ pub struct CallSetup {
 }
 
 impl CallSetup {
-    pub fn new(cx: *mut JSContext, handling: ExceptionHandling) -> CallSetup {
+    pub fn new<T: CallbackContainer>(callback: &T, handling: ExceptionHandling) -> CallSetup {
+        let win = global_object_for_js_object(callback.callback()).root();
+        let cx = win.deref().get_cx();
         CallSetup {
             cx: cx,
             handling: handling
diff --git a/src/components/script/dom/bindings/codegen/CodegenRust.py b/src/components/script/dom/bindings/codegen/CodegenRust.py
index 9fca81cd287..a6da30bad29 100644
--- a/src/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/src/components/script/dom/bindings/codegen/CodegenRust.py
@@ -7,9 +7,10 @@
 import os
 import string
 import operator
+import itertools
 
 from WebIDL import *
-from Configuration import Descriptor
+from Configuration import getTypesFromDescriptor, getTypesFromDictionary, getTypesFromCallback, Descriptor
 
 AUTOGENERATED_WARNING_COMMENT = \
     "/* THIS FILE IS AUTOGENERATED - DO NOT EDIT */\n\n"
@@ -406,6 +407,7 @@ def getJSToNativeConversionTemplate(type, descriptorProvider, failureCode=None,
                                     isEnforceRange=False,
                                     isClamp=False,
                                     exceptionCode=None,
+                                    allowTreatNonObjectAsNull=False,
                                     isCallbackReturnValue=False,
                                     sourceDescription="value"):
     """
@@ -439,6 +441,9 @@ def getJSToNativeConversionTemplate(type, descriptorProvider, failureCode=None,
     If isClamp is true, we're converting an integer and clamping if the
     value is out of range.
 
+    If allowTreatNonObjectAsNull is true, then [TreatNonObjectAsNull]
+    extended attributes on nullable callback functions will be honored.
+
     The return value from this function is a tuple consisting of four things:
 
     1)  A string representing the conversion code.  This will have template
@@ -500,6 +505,14 @@ def getJSToNativeConversionTemplate(type, descriptorProvider, failureCode=None,
                  '%s' % (firstCap(sourceDescription), typeName,
                          exceptionCode))),
             post="\n")
+    def onFailureNotCallable(failureCode):
+        return CGWrapper(
+            CGGeneric(
+                failureCode or
+                ('//XXXjdm ThrowErrorMessage(cx, MSG_NOT_CALLABLE, "%s");\n'
+                 '%s' % (firstCap(sourceDescription), exceptionCode))),
+            post="\n")
+
 
     # A helper function for handling null default values. Checks that the
     # default value, if it exists, is null.
@@ -699,23 +712,39 @@ def getJSToNativeConversionTemplate(type, descriptorProvider, failureCode=None,
 
     if type.isCallback():
         assert not isEnforceRange and not isClamp
+        assert not type.treatNonCallableAsNull()
+        assert not type.treatNonObjectAsNull() or type.nullable()
+        assert not type.treatNonObjectAsNull() or not type.treatNonCallableAsNull()
 
-        if isMember:
-            raise TypeError("Can't handle member callbacks; need to sort out "
-                            "rooting issues")
-        # XXXbz we're going to assume that callback types are always
-        # nullable and always have [TreatNonCallableAsNull] for now.
-        haveCallable = "${val}.is_object() && JS_ObjectIsCallable(cx, ${val}.to_object()) != 0"
-        if defaultValue is not None:
-            assert(isinstance(defaultValue, IDLNullValue))
-            haveCallable = "${haveValue} && " + haveCallable
-        return (
-            "if (%s) {\n"
-            "  ${val}.to_object()\n"
-            "} else {\n"
-            "  ptr::mut_null()\n"
-            "}" % haveCallable,
-            CGGeneric("*mut JSObject"), needsRooting)
+        declType = CGGeneric('%s::%s' % (type.unroll().module(), type.unroll().identifier.name))
+
+        conversion = CGCallbackTempRoot(declType.define())
+
+        if type.nullable():
+            declType = CGTemplatedType("Option", declType)
+            conversion = CGWrapper(conversion, pre="Some(", post=")")
+
+        if allowTreatNonObjectAsNull and type.treatNonObjectAsNull():
+            if not isDefinitelyObject:
+                haveObject = "${val}.is_object()"
+                if defaultValue is not None:
+                    assert isinstance(defaultValue, IDLNullValue)
+                    haveObject = "${haveValue} && " + haveObject
+                template = CGIfElseWrapper(haveObject,
+                                           conversion,
+                                           CGGeneric("None")).define()
+            else:
+                template = conversion
+        else:
+            template = CGIfElseWrapper("JS_ObjectIsCallable(cx, ${val}.to_object()) != 0",
+                                       conversion,
+                                       onFailureNotCallable(failureCode)).define()
+            template = wrapObjectTemplate(
+                template,
+                isDefinitelyObject,
+                type,
+                failureCode)
+        return (template, declType, needsRooting)
 
     if type.isAny():
         assert not isEnforceRange and not isClamp
@@ -874,7 +903,8 @@ class CGArgumentConverter(CGThing):
             defaultValue=argument.defaultValue,
             treatNullAs=argument.treatNullAs,
             isEnforceRange=argument.enforceRange,
-            isClamp=argument.clamp)
+            isClamp=argument.clamp,
+            allowTreatNonObjectAsNull=argument.allowTreatNonCallableAsNull())
 
         if argument.optional and not argument.defaultValue:
             declType = CGWrapper(declType, pre="Option<", post=">")
@@ -913,7 +943,7 @@ def typeNeedsCx(type, retVal=False):
         return any(typeNeedsCx(t) for t in type.unroll().flatMemberTypes)
     if retVal and type.isSpiderMonkeyInterface():
         return True
-    return type.isCallback() or type.isAny() or type.isObject()
+    return type.isAny() or type.isObject()
 
 def typeRetValNeedsRooting(type):
     if type is None:
@@ -958,9 +988,11 @@ def getRetvalDeclarationForType(returnType, descriptorProvider):
             result = CGWrapper(result, pre="Option<", post=">")
         return result
     if returnType.isCallback():
-        # XXXbz we're going to assume that callback types are always
-        # nullable for now.
-        return CGGeneric("*mut JSObject")
+        result = CGGeneric('%s::%s' % (returnType.unroll().module(),
+                                       returnType.unroll().identifier.name))
+        if returnType.nullable():
+            result = CGWrapper(result, pre="Option<", post=">")
+        return result
     if returnType.isAny():
         return CGGeneric("JSVal")
     if returnType.isObject() or returnType.isSpiderMonkeyInterface():
@@ -1347,12 +1379,8 @@ class CGIfWrapper(CGWrapper):
                            post="\n}")
 
 class CGTemplatedType(CGWrapper):
-    def __init__(self, templateName, child, isConst=False, isReference=False):
-        const = "const " if isConst else ""
-        pre = "%s%s<" % (const, templateName)
-        ref = "&" if isReference else ""
-        post = ">%s" % ref
-        CGWrapper.__init__(self, child, pre=pre, post=post)
+    def __init__(self, templateName, child):
+        CGWrapper.__init__(self, child, pre=templateName + "<", post=">")
 
 class CGNamespace(CGWrapper):
     def __init__(self, namespace, child, public=False):
@@ -1573,23 +1601,32 @@ class CGGeneric(CGThing):
     def define(self):
         return self.text
 
-def getTypes(descriptor):
+class CGCallbackTempRoot(CGGeneric):
+    def __init__(self, name):
+        val = "%s::new(tempRoot)" % name
+        define = """{
+  let tempRoot = ${val}.to_object();
+  %s
+}""" % val
+        CGGeneric.__init__(self, define)
+
+
+def getAllTypes(descriptors, dictionaries, callbacks):
     """
-    Get all argument and return types for all members of the descriptor
+    Generate all the types we're dealing with.  For each type, a tuple
+    containing type, descriptor, dictionary is yielded.  The
+    descriptor and dictionary can be None if the type does not come
+    from a descriptor or dictionary; they will never both be non-None.
     """
-    members = [m for m in descriptor.interface.members]
-    if descriptor.interface.ctor():
-        members.append(descriptor.interface.ctor())
-    signatures = [s for m in members if m.isMethod() for s in m.signatures()]
-    types = []
-    for s in signatures:
-        assert len(s) == 2
-        (returnType, arguments) = s
-        types.append(returnType)
-        types.extend([a.type for a in arguments])
-
-    types.extend(a.type for a in members if a.isAttr())
-    return types
+    for d in descriptors:
+        for t in getTypesFromDescriptor(d):
+            yield (t, d, None)
+    for dictionary in dictionaries:
+        for t in getTypesFromDictionary(dictionary):
+            yield (t, None, dictionary)
+    for callback in callbacks:
+        for t in getTypesFromCallback(callback):
+            yield (t, None, None)
 
 def SortedTuples(l):
     """
@@ -1606,24 +1643,23 @@ def SortedDictValues(d):
     # We're only interested in the values.
     return (i[1] for i in d)
 
-def UnionTypes(descriptors):
+def UnionTypes(descriptors, dictionaries, callbacks, config):
     """
-    Returns a tuple containing a set of header filenames to include, a set of
-    tuples containing a type declaration and a boolean if the type is a struct
-    for member types of the unions and a CGList containing CGUnionStructs for
-    every union.
+    Returns a CGList containing CGUnionStructs for every union.
     """
 
     # Now find all the things we'll need as arguments and return values because
     # we need to wrap or unwrap them.
     unionStructs = dict()
-    for d in descriptors:
-        for t in getTypes(d):
-            t = t.unroll()
-            if t.isUnion():
-                name = str(t)
-                if not name in unionStructs:
-                    unionStructs[name] = CGList([CGUnionStruct(t, d), CGUnionConversionStruct(t, d)])
+    for (t, descriptor, dictionary) in getAllTypes(descriptors, dictionaries, callbacks):
+        assert not descriptor or not dictionary
+        t = t.unroll()
+        if not t.isUnion():
+            continue
+        name = str(t)
+        if not name in unionStructs:
+            provider = descriptor or config.getDescriptorProvider()
+            unionStructs[name] = CGList([CGUnionStruct(t, provider), CGUnionConversionStruct(t, provider)])
 
     return CGList(SortedDictValues(unionStructs), "\n\n")
 
@@ -2309,15 +2345,19 @@ class FakeArgument():
     A class that quacks like an IDLArgument.  This is used to make
     setters look like method calls or for special operations.
     """
-    def __init__(self, type, interfaceMember):
+    def __init__(self, type, interfaceMember, allowTreatNonObjectAsNull=False):
         self.type = type
         self.optional = False
         self.variadic = False
         self.defaultValue = None
+        self._allowTreatNonObjectAsNull = allowTreatNonObjectAsNull
         self.treatNullAs = interfaceMember.treatNullAs
         self.enforceRange = False
         self.clamp = False
 
+    def allowTreatNonCallableAsNull(self):
+        return self._allowTreatNonObjectAsNull
+
 class CGSetterCall(CGPerSignatureCall):
     """
     A class to generate a native object setter call for a particular IDL
@@ -2325,7 +2365,7 @@ class CGSetterCall(CGPerSignatureCall):
     """
     def __init__(self, argsPre, argType, nativeMethodName, descriptor, attr):
         CGPerSignatureCall.__init__(self, None, argsPre,
-                                    [FakeArgument(argType, attr)],
+                                    [FakeArgument(argType, attr, allowTreatNonObjectAsNull=True)],
                                     nativeMethodName, False, descriptor, attr,
                                     setter=True)
     def wrap_return_value(self):
@@ -2710,9 +2750,22 @@ class CGUnionStruct(CGThing):
         enumValues = [
             "    e%s(%s)," % (v["name"], v["typeName"]) for v in templateVars
         ]
-        return ("pub enum %s {\n"
-                "%s\n"
-                "}\n") % (self.type, "\n".join(enumValues))
+        enumConversions = [
+            "            e%s(ref inner) => inner.to_jsval(cx)," % v["name"] for v in templateVars
+        ]
+        return ("""pub enum %s {
+%s
+}
+
+impl ToJSValConvertible for %s {
+    fn to_jsval(&self, cx: *mut JSContext) -> JSVal {
+        match *self {
+%s
+        }
+  }
+}
+""") % (self.type, "\n".join(enumValues),
+        self.type, "\n".join(enumConversions))
 
 
 class CGUnionConversionStruct(CGThing):
@@ -4170,14 +4223,17 @@ class CGBindingRoot(CGThing):
                          for d in dictionaries])
 
         # Do codegen for all the callbacks.
-        cgthings.extend(CGCallbackFunction(c, config.getDescriptorProvider())
+        cgthings.extend(CGList([CGCallbackFunction(c, config.getDescriptorProvider()),
+                                CGCallbackFunctionImpl(c)], "\n")
                         for c in mainCallbacks)
 
         # Do codegen for all the descriptors
         cgthings.extend([CGDescriptor(x) for x in descriptors])
 
         # Do codegen for all the callback interfaces.
-        cgthings.extend([CGCallbackInterface(x) for x in callbackDescriptors])
+        cgthings.extend(CGList([CGCallbackInterface(x),
+                                CGCallbackFunctionImpl(x)], "\n")
+                        for x in callbackDescriptors)
 
         # And make sure we have the right number of newlines at the end
         curr = CGWrapper(CGList(cgthings, "\n\n"), post="\n\n")
@@ -4236,7 +4292,7 @@ class CGBindingRoot(CGThing):
             'dom::bindings::utils::VoidVal',
             'dom::bindings::utils::get_dictionary_property',
             'dom::bindings::trace::JSTraceable',
-            'dom::bindings::callback::{CallbackContainer,CallbackInterface}',
+            'dom::bindings::callback::{CallbackContainer,CallbackInterface,CallbackFunction}',
             'dom::bindings::callback::{CallSetup,ExceptionHandling}',
             'dom::bindings::callback::{WrapCallThisObject}',
             'dom::bindings::conversions::{FromJSValConvertible, ToJSValConvertible}',
@@ -4322,8 +4378,9 @@ class CGNativeMember(ClassMethod):
         elif type.isPrimitive() and type.tag() in builtinNames:
             result = CGGeneric(builtinNames[type.tag()])
             if type.nullable():
-                result = CGTemplatedType("Nullable", result)
-            typeDecl, template = result.define(), "return ${declName};"
+                raise TypeError("Nullable primitives are not supported here.")
+
+            typeDecl, template = result.define(), "return Ok(${declName});"
         elif type.isDOMString():
             if isMember:
                 # No need for a third element in the isMember case
@@ -4363,9 +4420,9 @@ class CGNativeMember(ClassMethod):
                 ("already_AddRefed<%s>" % type.unroll().identifier.name,
                  "return ${declName}.forget();")
         elif type.isAny():
-            typeDecl, template = "JS::Value", "return ${declName};"
+            typeDecl, template = "JSVal", "return Ok(${declName});"
         elif type.isObject():
-            typeDecl, template = "*JSObject", "return ${declName};"
+            typeDecl, template = "JSObject*", "return ${declName};"
         elif type.isSpiderMonkeyInterface():
             if type.nullable():
                 returnCode = "return ${declName}.IsNull() ? nullptr : ${declName}.Value().Obj();"
@@ -4462,7 +4519,7 @@ class CGNativeMember(ClassMethod):
         if type.isUnion():
             if type.nullable():
                 type = type.inner
-            return str(type), True, True
+            return str(type), False, True
 
         if type.isGeckoInterface() and not type.isCallbackInterface():
             iface = type.unroll().inner
@@ -4492,10 +4549,7 @@ class CGNativeMember(ClassMethod):
             return type.name, True, True
 
         if type.isDOMString():
-            if isMember:
-                declType = "nsString"
-            else:
-                declType = "nsAString"
+            declType = "DOMString"
             return declType, True, False
 
         if type.isByteString():
@@ -4528,7 +4582,7 @@ class CGNativeMember(ClassMethod):
             if isMember:
                 declType = "JS::Value"
             else:
-                declType = "JS::Handle<JS::Value>"
+                declType = "JSVal"
             return declType, False, False
 
         if type.isObject():
@@ -4570,7 +4624,7 @@ class CGNativeMember(ClassMethod):
             # Note: All variadic args claim to be optional, but we can just use
             # empty arrays to represent them not being present.
             decl = CGTemplatedType("Option", decl)
-            ref = True
+            ref = False
         return (decl, ref)
 
     def getArg(self, arg):
@@ -4581,7 +4635,7 @@ class CGNativeMember(ClassMethod):
                                       arg.optional and not arg.defaultValue,
                                       "Variadic" if arg.variadic else False)
         if ref:
-            decl = CGWrapper(decl, pre="const ", post="&")
+            decl = CGWrapper(decl, pre="&")
 
         return Argument(decl.define(), arg.identifier.name)
 
@@ -4649,39 +4703,37 @@ class CGCallback(CGClass):
 
         # And now insert our template argument.
         argsWithoutThis = list(args)
-        args.insert(0, Argument("Box<T>",  "thisObj"))
+        args.insert(0, Argument("&JSRef<T>",  "thisObj"))
 
         # And the self argument
         method.args.insert(0, Argument(None, "&self"))
         args.insert(0, Argument(None, "&self"))
         argsWithoutThis.insert(0, Argument(None, "&self"))
 
-        setupCall = ("let s = CallSetup::new(cx_for_dom_object(${cxProvider}), aExceptionHandling);\n"
+        setupCall = ("let s = CallSetup::new(self, aExceptionHandling);\n"
                      "if s.GetContext().is_null() {\n"
                      "  return Err(FailureUnknown);\n"
                      "}\n")
 
         bodyWithThis = string.Template(
             setupCall+
-            "let thisObjJS = WrapCallThisObject(s.GetContext(), ptr::mut_null() /*XXXjdm proper scope*/, thisObj);\n"
+            "let thisObjJS = WrapCallThisObject(s.GetContext(), thisObj);\n"
             "if thisObjJS.is_null() {\n"
             "  return Err(FailureUnknown);\n"
             "}\n"
             "return ${methodName}(${callArgs});").substitute({
                 "callArgs" : ", ".join(argnamesWithThis),
                 "methodName": 'self.' + method.name,
-                "cxProvider": 'thisObj'
                 })
         bodyWithoutThis = string.Template(
             setupCall +
             "return ${methodName}(${callArgs});").substitute({
                 "callArgs" : ", ".join(argnamesWithoutThis),
                 "methodName": 'self.' + method.name,
-                "cxProvider": args[2].name #XXXjdm There's no guarantee that this is a DOM object
                 })
         return [ClassMethod(method.name+'_', method.returnType, args,
                             bodyInHeader=True,
-                            templateArgs=["T: 'static+CallbackContainer+Reflectable"],
+                            templateArgs=["T: Reflectable"],
                             body=bodyWithThis,
                             visibility='pub'),
                 ClassMethod(method.name+'__', method.returnType, argsWithoutThis,
@@ -4707,15 +4759,27 @@ class CGCallbackFunction(CGCallback):
                             methods=[CallCallback(callback, descriptorProvider)])
 
     def getConstructors(self):
-        return CGCallback.getConstructors(self) + [
-            ClassConstructor(
-            [Argument("CallbackFunction*", "aOther")],
-            bodyInHeader=True,
-            visibility="pub",
-            explicit=True,
-            baseConstructors=[
-                "CallbackFunction(aOther)"
-                ])]
+        return CGCallback.getConstructors(self)
+
+class CGCallbackFunctionImpl(CGGeneric):
+    def __init__(self, callback):
+        impl = string.Template("""impl CallbackContainer for ${type} {
+    fn new(callback: *mut JSObject) -> ${type} {
+        ${type}::new(callback)
+    }
+
+    fn callback(&self) -> *mut JSObject {
+        self.parent.callback()
+    }
+}
+
+impl ToJSValConvertible for ${type} {
+    fn to_jsval(&self, cx: *mut JSContext) -> JSVal {
+        self.callback().to_jsval(cx)
+    }
+}
+""").substitute({"type": callback.name})
+        CGGeneric.__init__(self, impl)
 
 class CGCallbackInterface(CGCallback):
     def __init__(self, descriptor):
@@ -4817,7 +4881,7 @@ class CallbackMember(CGNativeMember):
         return CGList([
             CGGeneric(pre),
             CGWrapper(CGIndenter(CGGeneric(body)),
-                      pre="with_compartment(cx, self.parent.callback, || {\n",
+                      pre="with_compartment(cx, self.parent.callback(), || {\n",
                       post="})")
         ], "\n").define()
 
@@ -4876,19 +4940,10 @@ class CallbackMember(CGNativeMember):
         else:
             jsvalIndex = "%d" % i
             if arg.optional and not arg.defaultValue:
-                argval += ".Value()"
-        if arg.type.isDOMString():
-            # XPConnect string-to-JS conversion wants to mutate the string.  So
-            # let's give it a string it can mutate
-            # XXXbz if we try to do a sequence of strings, this will kinda fail.
-            result = "mutableStr"
-            prepend = "nsString mutableStr(%s);\n" % argval
-        else:
-            result = argval
-            prepend = ""
+                argval += ".clone().unwrap()"
 
-        conversion = prepend + wrapForType("*argv.get_mut(%s)" % jsvalIndex,
-                result=result,
+        conversion = wrapForType("*argv.get_mut(%s)" % jsvalIndex,
+                result=argval,
                 successCode="continue;" if arg.variadic else "break;")
         if arg.variadic:
             conversion = string.Template(
@@ -4899,12 +4954,12 @@ class CallbackMember(CGNativeMember):
         elif arg.optional and not arg.defaultValue:
             conversion = (
                 CGIfWrapper(CGGeneric(conversion),
-                            "%s.WasPassed()" % arg.identifier.name).define() +
+                            "%s.is_some()" % arg.identifier.name).define() +
                 " else if (argc == %d) {\n"
                 "  // This is our current trailing argument; reduce argc\n"
-                "  --argc;\n"
+                "  argc -= 1;\n"
                 "} else {\n"
-                "  argv[%d] = JS::UndefinedValue();\n"
+                "  *argv.get_mut(%d) = UndefinedValue();\n"
                 "}" % (i+1, i))
         return conversion
 
@@ -4946,7 +5001,7 @@ class CallbackMember(CGNativeMember):
             })
 
     def getArgcDecl(self):
-        return CGGeneric("let argc = %su32;" % self.argCountStr);
+        return CGGeneric("let mut argc = %su32;" % self.argCountStr);
 
     @staticmethod
     def ensureASCIIName(idlObject):
@@ -4999,7 +5054,7 @@ class CallCallback(CallbackMethod):
         return "aThisObj"
 
     def getCallableDecl(self):
-        return "JS::Rooted<JS::Value> callable(cx, JS::ObjectValue(*mCallback));\n"
+        return "let callable = ObjectValue(unsafe {&*self.parent.callback()});\n";
 
 class CallbackOperationBase(CallbackMethod):
     """
@@ -5012,11 +5067,11 @@ class CallbackOperationBase(CallbackMethod):
 
     def getThisObj(self):
         if not self.singleOperation:
-            return "self.parent.callback"
+            return "self.parent.callback()"
         # This relies on getCallableDecl declaring a boolean
         # isCallable in the case when we're a single-operation
         # interface.
-        return "if isCallable { aThisObj } else { self.parent.callback }"
+        return "if isCallable { aThisObj } else { self.parent.callback() }"
 
     def getCallableDecl(self):
         replacements = {
@@ -5030,11 +5085,11 @@ class CallbackOperationBase(CallbackMethod):
         if not self.singleOperation:
             return 'JS::Rooted<JS::Value> callable(cx);\n' + getCallableFromProp
         return (
-            'let isCallable = unsafe { JS_ObjectIsCallable(cx, self.parent.callback) != 0 };\n'
+            'let isCallable = unsafe { JS_ObjectIsCallable(cx, self.parent.callback()) != 0 };\n'
             'let callable =\n' +
             CGIndenter(
                 CGIfElseWrapper('isCallable',
-                                CGGeneric('unsafe { ObjectValue(&*self.parent.callback) }'),
+                                CGGeneric('unsafe { ObjectValue(&*self.parent.callback()) }'),
                                 CGGeneric(getCallableFromProp))).define() + ';\n')
 
 class CallbackOperation(CallbackOperationBase):
@@ -5242,12 +5297,16 @@ class GlobalGenRoots():
     @staticmethod
     def UnionTypes(config):
 
-        curr = UnionTypes(config.getDescriptors())
+        curr = UnionTypes(config.getDescriptors(),
+                          config.getDictionaries(),
+                          config.getCallbacks(),
+                          config)
 
         curr = CGImports(curr, [], [
             'dom::bindings::utils::unwrap_jsmanaged',
             'dom::bindings::codegen::PrototypeList',
             'dom::bindings::conversions::FromJSValConvertible',
+            'dom::bindings::conversions::ToJSValConvertible',
             'dom::bindings::conversions::Default',
             'dom::bindings::error::throw_not_in_union',
             'dom::bindings::js::JS',
diff --git a/src/components/script/dom/bindings/codegen/Configuration.py b/src/components/script/dom/bindings/codegen/Configuration.py
index 1272867f542..42d3b56f91c 100644
--- a/src/components/script/dom/bindings/codegen/Configuration.py
+++ b/src/components/script/dom/bindings/codegen/Configuration.py
@@ -76,7 +76,11 @@ class Configuration:
     @staticmethod
     def _filterForFile(items, webIDLFile=""):
         """Gets the items that match the given filters."""
+        if not webIDLFile:
+            return items
+
         return filter(lambda x: x.filename() == webIDLFile, items)
+
     def getDictionaries(self, webIDLFile=""):
         return self._filterForFile(self.dictionaries, webIDLFile=webIDLFile)
     def getCallbacks(self, webIDLFile=""):
@@ -269,3 +273,54 @@ class Descriptor(DescriptorProvider):
             throws = member.getExtendedAttribute(throwsAttr)
         maybeAppendInfallibleToAttrs(attrs, throws)
         return attrs
+
+# Some utility methods
+def getTypesFromDescriptor(descriptor):
+    """
+    Get all argument and return types for all members of the descriptor
+    """
+    members = [m for m in descriptor.interface.members]
+    if descriptor.interface.ctor():
+        members.append(descriptor.interface.ctor())
+    members.extend(descriptor.interface.namedConstructors)
+    signatures = [s for m in members if m.isMethod() for s in m.signatures()]
+    types = []
+    for s in signatures:
+        assert len(s) == 2
+        (returnType, arguments) = s
+        types.append(returnType)
+        types.extend(a.type for a in arguments)
+
+    types.extend(a.type for a in members if a.isAttr())
+    return types
+
+def getFlatTypes(types):
+    retval = set()
+    for type in types:
+        type = type.unroll()
+        if type.isUnion():
+            retval |= set(type.flatMemberTypes)
+        else:
+            retval.add(type)
+    return retval
+
+def getTypesFromDictionary(dictionary):
+    """
+    Get all member types for this dictionary
+    """
+    types = []
+    curDict = dictionary
+    while curDict:
+        types.extend([m.type for m in curDict.members])
+        curDict = curDict.parent
+    return types
+
+def getTypesFromCallback(callback):
+    """
+    Get the types this callback depends on: its return type and the
+    types of its arguments.
+    """
+    sig = callback.signatures()[0]
+    types = [sig[0]] # Return type
+    types.extend(arg.type for arg in sig[1]) # Arguments
+    return types
diff --git a/src/components/script/dom/bindings/codegen/parser/WebIDL.py b/src/components/script/dom/bindings/codegen/parser/WebIDL.py
index bee73d5c489..5740a21ca52 100644
--- a/src/components/script/dom/bindings/codegen/parser/WebIDL.py
+++ b/src/components/script/dom/bindings/codegen/parser/WebIDL.py
@@ -464,6 +464,10 @@ class IDLInterface(IDLObjectWithScope):
         self._callback = False
         self._finished = False
         self.members = []
+        # namedConstructors needs deterministic ordering because bindings code
+        # outputs the constructs in the order that namedConstructors enumerates
+        # them.
+        self.namedConstructors = list()
         self.implementedInterfaces = set()
         self._consequential = False
         self._isPartial = True
@@ -696,6 +700,9 @@ class IDLInterface(IDLObjectWithScope):
             if identifier == "TreatNonCallableAsNull":
                 raise WebIDLError("TreatNonCallableAsNull cannot be specified on interfaces",
                                   [attr.location, self.location])
+            if identifier == "TreatNonObjectAsNull":
+                raise WebIDLError("TreatNonObjectAsNull cannot be specified on interfaces",
+                                  [attr.location, self.location])
             elif identifier == "NoInterfaceObject":
                 if not attr.noArguments():
                     raise WebIDLError("[NoInterfaceObject] must take no arguments",
@@ -1049,11 +1056,12 @@ class IDLType(IDLObject):
         assert False # Override me!
 
     def treatNonCallableAsNull(self):
-        if not (self.nullable() and self.tag() == IDLType.Tags.callback):
-            raise WebIDLError("Type %s cannot be TreatNonCallableAsNull" % self,
-                              [self.location])
+        assert self.tag() == IDLType.Tags.callback
+        return self.nullable() and self.inner._treatNonCallableAsNull
 
-        return hasattr(self, "_treatNonCallableAsNull")
+    def treatNonObjectAsNull(self):
+        assert self.tag() == IDLType.Tags.callback
+        return self.nullable() and self.inner._treatNonObjectAsNull
 
     def markTreatNonCallableAsNull(self):
         assert not self.treatNonCallableAsNull()
@@ -2189,6 +2197,7 @@ class IDLArgument(IDLObjectWithIdentifier):
         self._isComplete = False
         self.enforceRange = False
         self.clamp = False
+        self._allowTreatNonCallableAsNull = False
 
         assert not variadic or optional
 
@@ -2215,6 +2224,8 @@ class IDLArgument(IDLObjectWithIdentifier):
                     raise WebIDLError("[EnforceRange] and [Clamp] are mutually exclusive",
                                       [self.location]);
                 self.enforceRange = True
+            elif identifier == "TreatNonCallableAsNull":
+                self._allowTreatNonCallableAsNull = True
             else:
                 raise WebIDLError("Unhandled extended attribute on an argument",
                                   [attribute.location])
@@ -2247,6 +2258,9 @@ class IDLArgument(IDLObjectWithIdentifier):
                                                                self.location)
             assert self.defaultValue
 
+    def allowTreatNonCallableAsNull(self):
+        return self._allowTreatNonCallableAsNull
+
     def _getDependentObjects(self):
         deps = set([self.type])
         if self.defaultValue:
@@ -2269,6 +2283,12 @@ class IDLCallbackType(IDLType, IDLObjectWithScope):
             for argument in arguments:
                 argument.resolve(self)
 
+        self._treatNonCallableAsNull = False
+        self._treatNonObjectAsNull = False
+
+    def module(self):
+        return self.location.filename().split('/')[-1].split('.webidl')[0] + 'Binding'
+
     def isCallback(self):
         return True
 
@@ -2308,6 +2328,21 @@ class IDLCallbackType(IDLType, IDLObjectWithScope):
         return (other.isPrimitive() or other.isString() or other.isEnum() or
                 other.isNonCallbackInterface() or other.isDate())
 
+    def addExtendedAttributes(self, attrs):
+        unhandledAttrs = []
+        for attr in attrs:
+            if attr.identifier() == "TreatNonCallableAsNull":
+                self._treatNonCallableAsNull = True
+            elif attr.identifier() == "TreatNonObjectAsNull":
+                self._treatNonObjectAsNull = True
+            else:
+                unhandledAttrs.append(attr)
+        if self._treatNonCallableAsNull and self._treatNonObjectAsNull:
+            raise WebIDLError("Cannot specify both [TreatNonCallableAsNull] "
+                              "and [TreatNonObjectAsNull]", [self.location])
+        if len(unhandledAttrs) != 0:
+            IDLType.addExtendedAttributes(self, unhandledAttrs)
+
     def _getDependentObjects(self):
         return set([self._returnType] + self._arguments)
 
diff --git a/src/components/script/dom/bindings/conversions.rs b/src/components/script/dom/bindings/conversions.rs
index e1a155fa457..867e07ade30 100644
--- a/src/components/script/dom/bindings/conversions.rs
+++ b/src/components/script/dom/bindings/conversions.rs
@@ -328,6 +328,12 @@ impl<'a, T: Reflectable> ToJSValConvertible for JSRef<'a, T> {
     }
 }
 
+impl<'a, T: Reflectable> ToJSValConvertible for JS<T> {
+    fn to_jsval(&self, cx: *mut JSContext) -> JSVal {
+        self.reflector().to_jsval(cx)
+    }
+}
+
 impl<T: ToJSValConvertible> ToJSValConvertible for Option<T> {
     fn to_jsval(&self, cx: *mut JSContext) -> JSVal {
         match self {
@@ -350,7 +356,11 @@ impl<X: Default, T: FromJSValConvertible<X>> FromJSValConvertible<()> for Option
 }
 
 impl ToJSValConvertible for *mut JSObject {
-    fn to_jsval(&self, _cx: *mut JSContext) -> JSVal {
-        ObjectOrNullValue(*self)
+    fn to_jsval(&self, cx: *mut JSContext) -> JSVal {
+        let mut wrapped = ObjectOrNullValue(*self);
+        unsafe {
+            assert!(JS_WrapValue(cx, &mut wrapped) != 0);
+        }
+        wrapped
     }
 }
diff --git a/src/components/script/dom/bindings/trace.rs b/src/components/script/dom/bindings/trace.rs
index d18f6a64448..26decbc450a 100644
--- a/src/components/script/dom/bindings/trace.rs
+++ b/src/components/script/dom/bindings/trace.rs
@@ -110,6 +110,7 @@ impl<T> DerefMut<T> for Untraceable<T> {
 /// Encapsulates a type that can be traced but is boxed in a type we don't control
 /// (such as RefCell). Wrap a field in Traceable and implement the Encodable trait
 /// for that new concrete type to achieve magic compiler-derived trace hooks.
+#[deriving(Eq, Clone)]
 pub struct Traceable<T> {
     inner: T
 }
diff --git a/src/components/script/dom/document.rs b/src/components/script/dom/document.rs
index 68ea97d1335..f6f67f93747 100644
--- a/src/components/script/dom/document.rs
+++ b/src/components/script/dom/document.rs
@@ -2,6 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+use dom::bindings::codegen::EventHandlerBinding::EventHandlerNonNull;
 use dom::bindings::codegen::InheritTypes::{DocumentDerived, EventCast, HTMLElementCast};
 use dom::bindings::codegen::InheritTypes::{HTMLHeadElementCast, TextCast, ElementCast};
 use dom::bindings::codegen::InheritTypes::{DocumentTypeCast, HTMLHtmlElementCast, NodeCast};
@@ -45,7 +46,7 @@ use servo_util::namespace::{Namespace, Null};
 use servo_util::str::{DOMString, null_str_as_empty_ref};
 
 use collections::hashmap::HashMap;
-use js::jsapi::{JSObject, JSContext};
+use js::jsapi::JSContext;
 use std::ascii::StrAsciiExt;
 use url::{Url, from_str};
 
@@ -326,8 +327,8 @@ pub trait DocumentMethods {
     fn Applets(&self) -> Temporary<HTMLCollection>;
     fn Location(&mut self) -> Temporary<Location>;
     fn Children(&self) -> Temporary<HTMLCollection>;
-    fn GetOnload(&self, _cx: *mut JSContext) -> *mut JSObject;
-    fn SetOnload(&mut self, _cx: *mut JSContext, listener: *mut JSObject);
+    fn GetOnload(&self) -> Option<EventHandlerNonNull>;
+    fn SetOnload(&mut self, listener: Option<EventHandlerNonNull>);
 }
 
 impl<'a> DocumentMethods for JSRef<'a, Document> {
@@ -808,12 +809,12 @@ impl<'a> DocumentMethods for JSRef<'a, Document> {
         HTMLCollection::children(&*window, NodeCast::from_ref(self))
     }
 
-    fn GetOnload(&self, _cx: *mut JSContext) -> *mut JSObject {
+    fn GetOnload(&self) -> Option<EventHandlerNonNull> {
         let eventtarget: &JSRef<EventTarget> = EventTargetCast::from_ref(self);
         eventtarget.get_event_handler_common("load")
     }
 
-    fn SetOnload(&mut self, _cx: *mut JSContext, listener: *mut JSObject) {
+    fn SetOnload(&mut self, listener: Option<EventHandlerNonNull>) {
         let eventtarget: &mut JSRef<EventTarget> = EventTargetCast::from_mut_ref(self);
         eventtarget.set_event_handler_common("load", listener)
     }
diff --git a/src/components/script/dom/eventdispatcher.rs b/src/components/script/dom/eventdispatcher.rs
index cc5eb66f577..11db1eb7b2b 100644
--- a/src/components/script/dom/eventdispatcher.rs
+++ b/src/components/script/dom/eventdispatcher.rs
@@ -50,7 +50,7 @@ pub fn dispatch_event<'a, 'b>(target: &JSRef<'a, EventTarget>,
                 for listener in listeners.iter() {
                     //FIXME: this should have proper error handling, or explicitly
                     //       drop the exception on the floor
-                    assert!(listener.HandleEvent__(event, ReportExceptions).is_ok());
+                    assert!(listener.HandleEvent_(&**cur_target, event, ReportExceptions).is_ok());
 
                     if event.deref().stop_immediate {
                         break;
@@ -80,7 +80,7 @@ pub fn dispatch_event<'a, 'b>(target: &JSRef<'a, EventTarget>,
             for listener in listeners.iter() {
                 //FIXME: this should have proper error handling, or explicitly drop the
                 //       exception on the floor.
-                assert!(listener.HandleEvent__(event, ReportExceptions).is_ok());
+                assert!(listener.HandleEvent_(target, event, ReportExceptions).is_ok());
                 if event.deref().stop_immediate {
                     break;
                 }
@@ -99,7 +99,7 @@ pub fn dispatch_event<'a, 'b>(target: &JSRef<'a, EventTarget>,
                     for listener in listeners.iter() {
                         //FIXME: this should have proper error handling or explicitly
                         //       drop exceptions on the floor.
-                        assert!(listener.HandleEvent__(event, ReportExceptions).is_ok());
+                        assert!(listener.HandleEvent_(&**cur_target, event, ReportExceptions).is_ok());
 
                         if event.deref().stop_immediate {
                             break;
diff --git a/src/components/script/dom/eventtarget.rs b/src/components/script/dom/eventtarget.rs
index b0b8a9bad33..db92255cb59 100644
--- a/src/components/script/dom/eventtarget.rs
+++ b/src/components/script/dom/eventtarget.rs
@@ -4,18 +4,21 @@
 
 use dom::bindings::callback::CallbackContainer;
 use dom::bindings::codegen::BindingDeclarations::EventListenerBinding::EventListener;
+use dom::bindings::codegen::EventHandlerBinding::EventHandlerNonNull;
 use dom::bindings::error::{Fallible, InvalidState};
 use dom::bindings::js::JSRef;
 use dom::bindings::utils::{Reflectable, Reflector};
 use dom::event::Event;
 use dom::eventdispatcher::dispatch_event;
-use dom::node::{Node, NodeTypeId, window_from_node};
+use dom::node::NodeTypeId;
 use dom::xmlhttprequest::XMLHttpRequestId;
 use dom::virtualmethods::VirtualMethods;
-use js::jsapi::{JSObject, JS_CompileUCFunction, JS_GetFunctionObject, JS_CloneFunctionObject};
+use js::jsapi::{JS_CompileUCFunction, JS_GetFunctionObject, JS_CloneFunctionObject};
+use js::jsapi::{JSContext, JSObject};
 use servo_util::str::DOMString;
 use libc::{c_char, size_t};
 use std::ptr;
+use url::Url;
 
 use collections::hashmap::HashMap;
 
@@ -92,11 +95,14 @@ pub trait EventTargetHelpers {
                                  listener: Option<EventListener>);
     fn get_inline_event_listener(&self, ty: DOMString) -> Option<EventListener>;
     fn set_event_handler_uncompiled(&mut self,
-                                    content: &JSRef<Node>,
+                                    cx: *mut JSContext,
+                                    url: Url,
+                                    scope: *mut JSObject,
                                     ty: &str,
                                     source: DOMString);
-    fn set_event_handler_common(&mut self, ty: &str, listener: *mut JSObject);
-    fn get_event_handler_common(&self, ty: &str) -> *mut JSObject;
+    fn set_event_handler_common<T: CallbackContainer>(&mut self, ty: &str,
+                                                      listener: Option<T>);
+    fn get_event_handler_common<T: CallbackContainer>(&self, ty: &str) -> Option<T>;
 }
 
 impl<'a> EventTargetHelpers for JSRef<'a, EventTarget> {
@@ -132,7 +138,7 @@ impl<'a> EventTargetHelpers for JSRef<'a, EventTarget> {
             None => {
                 if listener.is_some() {
                     entries.push(EventListenerEntry {
-                        phase: Capturing, //XXXjdm no idea when inline handlers should run
+                        phase: Bubbling,
                         listener: Inline(listener.unwrap()),
                     });
                 }
@@ -151,12 +157,11 @@ impl<'a> EventTargetHelpers for JSRef<'a, EventTarget> {
     }
 
     fn set_event_handler_uncompiled(&mut self,
-                                    content: &JSRef<Node>,
+                                    cx: *mut JSContext,
+                                    url: Url,
+                                    scope: *mut JSObject,
                                     ty: &str,
                                     source: DOMString) {
-        let win = window_from_node(content).root();
-        let cx = win.deref().get_cx();
-        let url = win.deref().get_url();
         let url = url.to_str().to_c_str();
         let name = ty.to_c_str();
         let lineno = 0; //XXXjdm need to get a real number here
@@ -177,20 +182,22 @@ impl<'a> EventTargetHelpers for JSRef<'a, EventTarget> {
                 assert!(fun.is_not_null());
                 JS_GetFunctionObject(fun)
             }})});
-        let scope = win.deref().reflector().get_jsobject();
         let funobj = unsafe { JS_CloneFunctionObject(cx, handler, scope) };
         assert!(funobj.is_not_null());
-        self.set_event_handler_common(ty, funobj)
+        self.set_event_handler_common(ty, Some(EventHandlerNonNull::new(funobj)))
     }
 
-    fn set_event_handler_common(&mut self, ty: &str, listener: *mut JSObject) {
-        let listener = EventListener::new(listener);
-        self.set_inline_event_listener(ty.to_owned(), Some(listener));
+    fn set_event_handler_common<T: CallbackContainer>(
+        &mut self, ty: &str, listener: Option<T>)
+    {
+        let event_listener = listener.map(|listener|
+                                          EventListener::new(listener.callback()));
+        self.set_inline_event_listener(ty.to_owned(), event_listener);
     }
 
-    fn get_event_handler_common(&self, ty: &str) -> *mut JSObject {
+    fn get_event_handler_common<T: CallbackContainer>(&self, ty: &str) -> Option<T> {
         let listener = self.get_inline_event_listener(ty.to_owned());
-        listener.map(|listener| listener.parent.callback()).unwrap_or(ptr::mut_null())
+        listener.map(|listener| CallbackContainer::new(listener.parent.callback()))
     }
 }
 
diff --git a/src/components/script/dom/htmlbodyelement.rs b/src/components/script/dom/htmlbodyelement.rs
index 7f0b8efc66b..6ba82e252f0 100644
--- a/src/components/script/dom/htmlbodyelement.rs
+++ b/src/components/script/dom/htmlbodyelement.rs
@@ -3,10 +3,12 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use dom::bindings::codegen::BindingDeclarations::HTMLBodyElementBinding;
+use dom::bindings::codegen::EventHandlerBinding::EventHandlerNonNull;
 use dom::bindings::codegen::InheritTypes::{HTMLBodyElementDerived, HTMLElementCast};
-use dom::bindings::codegen::InheritTypes::{EventTargetCast, NodeCast};
+use dom::bindings::codegen::InheritTypes::EventTargetCast;
 use dom::bindings::error::ErrorResult;
 use dom::bindings::js::{JSRef, Temporary};
+use dom::bindings::utils::Reflectable;
 use dom::document::Document;
 use dom::element::HTMLBodyElementTypeId;
 use dom::eventtarget::{EventTarget, NodeTargetTypeId, EventTargetHelpers};
@@ -14,7 +16,6 @@ use dom::htmlelement::HTMLElement;
 use dom::node::{Node, ElementNodeTypeId, window_from_node};
 use dom::virtualmethods::VirtualMethods;
 use dom::window::WindowMethods;
-use js::jsapi::{JSContext, JSObject};
 use servo_util::str::DOMString;
 
 #[deriving(Encodable)]
@@ -54,8 +55,8 @@ pub trait HTMLBodyElementMethods {
     fn SetBgColor(&self, _bg_color: DOMString) -> ErrorResult;
     fn Background(&self) -> DOMString;
     fn SetBackground(&self, _background: DOMString) -> ErrorResult;
-    fn GetOnunload(&self, cx: *mut JSContext) -> *mut JSObject;
-    fn SetOnunload(&mut self, cx: *mut JSContext, listener: *mut JSObject);
+    fn GetOnunload(&self) -> Option<EventHandlerNonNull>;
+    fn SetOnunload(&mut self, listener: Option<EventHandlerNonNull>);
 }
 
 impl<'a> HTMLBodyElementMethods for JSRef<'a, HTMLBodyElement> {
@@ -107,14 +108,14 @@ impl<'a> HTMLBodyElementMethods for JSRef<'a, HTMLBodyElement> {
         Ok(())
     }
 
-    fn GetOnunload(&self, cx: *mut JSContext) -> *mut JSObject {
+    fn GetOnunload(&self) -> Option<EventHandlerNonNull> {
         let win = window_from_node(self).root();
-        win.deref().GetOnunload(cx)
+        win.deref().GetOnunload()
     }
 
-    fn SetOnunload(&mut self, cx: *mut JSContext, listener: *mut JSObject) {
+    fn SetOnunload(&mut self, listener: Option<EventHandlerNonNull>) {
         let mut win = window_from_node(self).root();
-        win.SetOnunload(cx, listener)
+        win.SetOnunload(listener)
     }
 }
 
@@ -131,11 +132,22 @@ impl<'a> VirtualMethods for JSRef<'a, HTMLBodyElement> {
         }
 
         if name.starts_with("on") {
-            //XXXjdm This should only forward a subset of event handler names
+            static forwarded_events: &'static [&'static str] =
+                &["onfocus", "onload", "onscroll", "onafterprint", "onbeforeprint",
+                  "onbeforeunload", "onhashchange", "onlanguagechange", "onmessage",
+                  "onoffline", "ononline", "onpagehide", "onpageshow", "onpopstate",
+                  "onstorage", "onresize", "onunload", "onerror"];
             let mut window = window_from_node(self).root();
-            let mut evtarget: &mut JSRef<EventTarget> = EventTargetCast::from_mut_ref(&mut *window);
-            let content: &mut JSRef<Node> = NodeCast::from_mut_ref(self);
-            evtarget.set_event_handler_uncompiled(content,
+            let (cx, url, reflector) = (window.get_cx(),
+                                        window.get_url(),
+                                        window.reflector().get_jsobject());
+            let evtarget: &mut JSRef<EventTarget> =
+                if forwarded_events.iter().any(|&event| name.as_slice() == event) {
+                    EventTargetCast::from_mut_ref(&mut *window)
+                } else {
+                    EventTargetCast::from_mut_ref(self)
+                };
+            evtarget.set_event_handler_uncompiled(cx, url, reflector,
                                                   name.slice_from(2).to_owned(),
                                                   value);
         }
diff --git a/src/components/script/dom/htmlelement.rs b/src/components/script/dom/htmlelement.rs
index c5f3fd3ed48..85d2d2bee67 100644
--- a/src/components/script/dom/htmlelement.rs
+++ b/src/components/script/dom/htmlelement.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use dom::bindings::codegen::BindingDeclarations::HTMLElementBinding;
+use dom::bindings::codegen::EventHandlerBinding::EventHandlerNonNull;
 use dom::bindings::codegen::InheritTypes::{ElementCast, HTMLFrameSetElementDerived};
 use dom::bindings::codegen::InheritTypes::{HTMLElementDerived, HTMLBodyElementDerived};
 use dom::bindings::codegen::InheritTypes::EventTargetCast;
@@ -14,11 +15,10 @@ use dom::eventtarget::{EventTarget, NodeTargetTypeId};
 use dom::node::{Node, ElementNodeTypeId, window_from_node};
 use dom::virtualmethods::VirtualMethods;
 use dom::window::WindowMethods;
-use js::jsapi::{JSContext, JSObject};
+use js::jsapi::JSContext;
 use js::jsval::{JSVal, NullValue};
 use servo_util::namespace;
 use servo_util::str::DOMString;
-use std::ptr;
 
 #[deriving(Encodable)]
 pub struct HTMLElement {
@@ -90,8 +90,8 @@ pub trait HTMLElementMethods {
     fn OffsetLeft(&self) -> i32;
     fn OffsetWidth(&self) -> i32;
     fn OffsetHeight(&self) -> i32;
-    fn GetOnload(&self, cx: *mut JSContext) -> *mut JSObject;
-    fn SetOnload(&mut self, cx: *mut JSContext, listener: *mut JSObject);
+    fn GetOnload(&self) -> Option<EventHandlerNonNull>;
+    fn SetOnload(&mut self, listener: Option<EventHandlerNonNull>);
 }
 
 impl<'a> HTMLElementMethods for JSRef<'a, HTMLElement> {
@@ -212,19 +212,19 @@ impl<'a> HTMLElementMethods for JSRef<'a, HTMLElement> {
         0
     }
 
-    fn GetOnload(&self, cx: *mut JSContext) -> *mut JSObject {
+    fn GetOnload(&self) -> Option<EventHandlerNonNull> {
         if self.is_body_or_frameset() {
             let win = window_from_node(self).root();
-            win.deref().GetOnload(cx)
+            win.deref().GetOnload()
         } else {
-            ptr::mut_null()
+            None
         }
     }
 
-    fn SetOnload(&mut self, cx: *mut JSContext, listener: *mut JSObject) {
+    fn SetOnload(&mut self, listener: Option<EventHandlerNonNull>) {
         if self.is_body_or_frameset() {
             let mut win = window_from_node(self).root();
-            win.SetOnload(cx, listener)
+            win.SetOnload(listener)
         }
     }
 }
diff --git a/src/components/script/dom/testbinding.rs b/src/components/script/dom/testbinding.rs
index 115fbcadaa5..4b753785e10 100644
--- a/src/components/script/dom/testbinding.rs
+++ b/src/components/script/dom/testbinding.rs
@@ -5,7 +5,7 @@
 use dom::bindings::js::{JS, JSRef, Temporary};
 use dom::bindings::codegen::BindingDeclarations::TestBindingBinding::TestEnum;
 use dom::bindings::codegen::BindingDeclarations::TestBindingBinding::TestEnumValues::_empty;
-use dom::bindings::codegen::UnionTypes::{HTMLElementOrLong, StringOrFormData};
+use dom::bindings::codegen::UnionTypes::{HTMLElementOrLong, EventOrString};
 use dom::bindings::str::ByteString;
 use dom::bindings::utils::{Reflector, Reflectable};
 use dom::blob::Blob;
@@ -136,7 +136,7 @@ pub trait TestBindingMethods {
     fn PassEnum(&self, _: TestEnum) {}
     fn PassInterface(&self, _: &JSRef<Blob>) {}
     fn PassUnion(&self, _: HTMLElementOrLong) {}
-    fn PassUnion2(&self, _: StringOrFormData) {}
+    fn PassUnion2(&self, _: EventOrString) {}
     fn PassAny(&self, _: *mut JSContext, _: JSVal) {}
 
     fn PassNullableBoolean(&self, _: Option<bool>) {}
@@ -155,7 +155,7 @@ pub trait TestBindingMethods {
     // fn PassNullableEnum(&self, _: Option<TestEnum>) {}
     fn PassNullableInterface(&self, _: Option<JSRef<Blob>>) {}
     fn PassNullableUnion(&self, _: Option<HTMLElementOrLong>) {}
-    fn PassNullableUnion2(&self, _: Option<StringOrFormData>) {}
+    fn PassNullableUnion2(&self, _: Option<EventOrString>) {}
     fn PassNullableAny(&self, _: *mut JSContext, _: Option<JSVal>) {}
 
     fn PassOptionalBoolean(&self, _: Option<bool>) {}
@@ -174,7 +174,7 @@ pub trait TestBindingMethods {
     fn PassOptionalEnum(&self, _: Option<TestEnum>) {}
     fn PassOptionalInterface(&self, _: Option<JSRef<Blob>>) {}
     fn PassOptionalUnion(&self, _: Option<HTMLElementOrLong>) {}
-    fn PassOptionalUnion2(&self, _: Option<StringOrFormData>) {}
+    fn PassOptionalUnion2(&self, _: Option<EventOrString>) {}
     fn PassOptionalAny(&self, _: *mut JSContext, _: Option<JSVal>) {}
 
     fn PassOptionalNullableBoolean(&self, _: Option<Option<bool>>) {}
@@ -193,7 +193,7 @@ pub trait TestBindingMethods {
     // fn PassOptionalNullableEnum(&self, _: Option<Option<TestEnum>>) {}
     fn PassOptionalNullableInterface(&self, _: Option<Option<JSRef<Blob>>>) {}
     fn PassOptionalNullableUnion(&self, _: Option<Option<HTMLElementOrLong>>) {}
-    fn PassOptionalNullableUnion2(&self, _: Option<Option<StringOrFormData>>) {}
+    fn PassOptionalNullableUnion2(&self, _: Option<Option<EventOrString>>) {}
 
     fn PassOptionalBooleanWithDefault(&self, _: bool) {}
     fn PassOptionalByteWithDefault(&self, _: i8) {}
@@ -223,7 +223,7 @@ pub trait TestBindingMethods {
     // fn PassOptionalNullableEnumWithDefault(&self, _: Option<TestEnum>) {}
     fn PassOptionalNullableInterfaceWithDefault(&self, _: Option<JSRef<Blob>>) {}
     fn PassOptionalNullableUnionWithDefault(&self, _: Option<HTMLElementOrLong>) {}
-    fn PassOptionalNullableUnion2WithDefault(&self, _: Option<StringOrFormData>) {}
+    fn PassOptionalNullableUnion2WithDefault(&self, _: Option<EventOrString>) {}
     fn PassOptionalAnyWithDefault(&self, _: *mut JSContext, _: JSVal) {}
 
     fn PassOptionalNullableBooleanWithNonNullDefault(&self, _: Option<bool>) {}
diff --git a/src/components/script/dom/webidls/EventHandler.webidl b/src/components/script/dom/webidls/EventHandler.webidl
index ee760bcd05b..dd922cc3f75 100644
--- a/src/components/script/dom/webidls/EventHandler.webidl
+++ b/src/components/script/dom/webidls/EventHandler.webidl
@@ -11,11 +11,11 @@
  * and create derivative works of this document.
  */
 
-//[TreatNonObjectAsNull] //XXXjdm webidl.py assertion
+[TreatNonObjectAsNull]
 callback EventHandlerNonNull = any (Event event);
 typedef EventHandlerNonNull? EventHandler;
 
-//[TreatNonObjectAsNull] //XXXjdm webidl.py assertion
+[TreatNonObjectAsNull]
 callback OnErrorEventHandlerNonNull = boolean ((Event or DOMString) event, optional DOMString source, optional unsigned long lineno, optional unsigned long column, optional any error);
 typedef OnErrorEventHandlerNonNull? OnErrorEventHandler;
 
diff --git a/src/components/script/dom/webidls/TestBinding.webidl b/src/components/script/dom/webidls/TestBinding.webidl
index 101e4d554e5..467abce3328 100644
--- a/src/components/script/dom/webidls/TestBinding.webidl
+++ b/src/components/script/dom/webidls/TestBinding.webidl
@@ -70,7 +70,7 @@ interface TestBinding {
            attribute TestEnum enumAttribute;
            attribute Blob interfaceAttribute;
   //         attribute (HTMLElement or long) unionAttribute;
-  //         attribute (DOMString or FormData) union2Attribute;
+  //         attribute (Event or DOMString) union2Attribute;
            attribute any anyAttribute;
 
            attribute boolean? booleanAttributeNullable;
@@ -89,7 +89,7 @@ interface TestBinding {
   readonly attribute TestEnum? enumAttributeNullable;
            attribute Blob? interfaceAttributeNullable;
   //         attribute (HTMLElement or long)? unionAttributeNullable;
-  //         attribute (DOMString or FormData)? union2AttributeNullable;
+  //         attribute (Event or DOMString)? union2AttributeNullable;
 
   void receiveVoid();
   boolean receiveBoolean();
@@ -137,7 +137,7 @@ interface TestBinding {
   void passEnum(TestEnum arg);
   void passInterface(Blob arg);
   void passUnion((HTMLElement or long) arg);
-  void passUnion2((DOMString or FormData) data);
+  void passUnion2((Event or DOMString) data);
   void passAny(any arg);
 
   void passNullableBoolean(boolean? arg);
@@ -156,7 +156,7 @@ interface TestBinding {
   // void passNullableEnum(TestEnum? arg);
   void passNullableInterface(Blob? arg);
   void passNullableUnion((HTMLElement or long)? arg);
-  void passNullableUnion2((DOMString or FormData)? data);
+  void passNullableUnion2((Event or DOMString)? data);
 
   void passOptionalBoolean(optional boolean arg);
   void passOptionalByte(optional byte arg);
@@ -174,7 +174,7 @@ interface TestBinding {
   void passOptionalEnum(optional TestEnum arg);
   void passOptionalInterface(optional Blob arg);
   void passOptionalUnion(optional (HTMLElement or long) arg);
-  void passOptionalUnion2(optional (DOMString or FormData) data);
+  void passOptionalUnion2(optional (Event or DOMString) data);
   void passOptionalAny(optional any arg);
 
   void passOptionalNullableBoolean(optional boolean? arg);
@@ -193,7 +193,7 @@ interface TestBinding {
   // void passOptionalNullableEnum(optional TestEnum? arg);
   void passOptionalNullableInterface(optional Blob? arg);
   void passOptionalNullableUnion(optional (HTMLElement or long)? arg);
-  void passOptionalNullableUnion2(optional (DOMString or FormData)? data);
+  void passOptionalNullableUnion2(optional (Event or DOMString)? data);
 
   void passOptionalBooleanWithDefault(optional boolean arg = false);
   void passOptionalByteWithDefault(optional byte arg = 0);
@@ -207,7 +207,7 @@ interface TestBinding {
   void passOptionalStringWithDefault(optional DOMString arg = "");
   void passOptionalEnumWithDefault(optional TestEnum arg = "foo");
   // void passOptionalUnionWithDefault(optional (HTMLElement or long) arg = 9);
-  // void passOptionalUnion2WithDefault(optional(DOMString or FormData)? data = "foo");
+  // void passOptionalUnion2WithDefault(optional(Event or DOMString)? data = "foo");
 
   void passOptionalNullableBooleanWithDefault(optional boolean? arg = null);
   void passOptionalNullableByteWithDefault(optional byte? arg = null);
@@ -223,7 +223,7 @@ interface TestBinding {
   // void passOptionalNullableEnumWithDefault(optional TestEnum? arg = null);
   void passOptionalNullableInterfaceWithDefault(optional Blob? arg = null);
   void passOptionalNullableUnionWithDefault(optional (HTMLElement or long)? arg = null);
-  void passOptionalNullableUnion2WithDefault(optional (DOMString or FormData)? data = null);
+  void passOptionalNullableUnion2WithDefault(optional (Event or DOMString)? data = null);
   void passOptionalAnyWithDefault(optional any arg = null);
 
   void passOptionalNullableBooleanWithNonNullDefault(optional boolean? arg = false);
@@ -240,5 +240,5 @@ interface TestBinding {
   void passOptionalNullableStringWithNonNullDefault(optional DOMString? arg = "");
   // void passOptionalNullableEnumWithNonNullDefault(optional TestEnum? arg = "foo");
   // void passOptionalNullableUnionWithNonNullDefault(optional (HTMLElement or long)? arg = 7);
-  // void passOptionalNullableUnion2WithNonNullDefault(optional (DOMString or FormData)? data = "foo");
+  // void passOptionalNullableUnion2WithNonNullDefault(optional (Event or DOMString)? data = "foo");
 };
diff --git a/src/components/script/dom/window.rs b/src/components/script/dom/window.rs
index ecb08928832..0c71edb69a0 100644
--- a/src/components/script/dom/window.rs
+++ b/src/components/script/dom/window.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use dom::bindings::codegen::BindingDeclarations::WindowBinding;
+use dom::bindings::codegen::EventHandlerBinding::{OnErrorEventHandlerNonNull, EventHandlerNonNull};
 use dom::bindings::codegen::InheritTypes::EventTargetCast;
 use dom::bindings::js::{JS, JSRef, Temporary, OptionalSettable};
 use dom::bindings::trace::{Traceable, Untraceable};
@@ -24,7 +25,7 @@ use servo_util::str::DOMString;
 use servo_util::task::{spawn_named};
 use servo_util::url::parse_url;
 
-use js::jsapi::{JSContext, JSObject};
+use js::jsapi::JSContext;
 use js::jsapi::{JS_GC, JS_GetRuntime};
 use js::jsval::{NullValue, JSVal};
 
@@ -141,12 +142,12 @@ pub trait WindowMethods {
     fn Window(&self) -> Temporary<Window>;
     fn Self(&self) -> Temporary<Window>;
     fn Performance(&mut self) -> Temporary<Performance>;
-    fn GetOnload(&self, _cx: *mut JSContext) -> *mut JSObject;
-    fn SetOnload(&mut self, _cx: *mut JSContext, listener: *mut JSObject);
-    fn GetOnunload(&self, _cx: *mut JSContext) -> *mut JSObject;
-    fn SetOnunload(&mut self, _cx: *mut JSContext, listener: *mut JSObject);
-    fn GetOnerror(&self, _cx: *mut JSContext) -> *mut JSObject;
-    fn SetOnerror(&mut self, _cx: *mut JSContext, listener: *mut JSObject);
+    fn GetOnload(&self) -> Option<EventHandlerNonNull>;
+    fn SetOnload(&mut self, listener: Option<EventHandlerNonNull>);
+    fn GetOnunload(&self) -> Option<EventHandlerNonNull>;
+    fn SetOnunload(&mut self, listener: Option<EventHandlerNonNull>);
+    fn GetOnerror(&self) -> Option<OnErrorEventHandlerNonNull>;
+    fn SetOnerror(&mut self, listener: Option<OnErrorEventHandlerNonNull>);
     fn Debug(&self, message: DOMString);
     fn Gc(&self);
 }
@@ -275,32 +276,32 @@ impl<'a> WindowMethods for JSRef<'a, Window> {
         Temporary::new(self.performance.get_ref().clone())
     }
 
-    fn GetOnload(&self, _cx: *mut JSContext) -> *mut JSObject {
+    fn GetOnload(&self) -> Option<EventHandlerNonNull> {
         let eventtarget: &JSRef<EventTarget> = EventTargetCast::from_ref(self);
         eventtarget.get_event_handler_common("load")
     }
 
-    fn SetOnload(&mut self, _cx: *mut JSContext, listener: *mut JSObject) {
+    fn SetOnload(&mut self, listener: Option<EventHandlerNonNull>) {
         let eventtarget: &mut JSRef<EventTarget> = EventTargetCast::from_mut_ref(self);
         eventtarget.set_event_handler_common("load", listener)
     }
 
-    fn GetOnunload(&self, _cx: *mut JSContext) -> *mut JSObject {
+    fn GetOnunload(&self) -> Option<EventHandlerNonNull> {
         let eventtarget: &JSRef<EventTarget> = EventTargetCast::from_ref(self);
         eventtarget.get_event_handler_common("unload")
     }
 
-    fn SetOnunload(&mut self, _cx: *mut JSContext, listener: *mut JSObject) {
+    fn SetOnunload(&mut self, listener: Option<EventHandlerNonNull>) {
         let eventtarget: &mut JSRef<EventTarget> = EventTargetCast::from_mut_ref(self);
         eventtarget.set_event_handler_common("unload", listener)
     }
 
-    fn GetOnerror(&self, _cx: *mut JSContext) -> *mut JSObject {
+    fn GetOnerror(&self) -> Option<OnErrorEventHandlerNonNull> {
         let eventtarget: &JSRef<EventTarget> = EventTargetCast::from_ref(self);
         eventtarget.get_event_handler_common("error")
     }
 
-    fn SetOnerror(&mut self, _cx: *mut JSContext, listener: *mut JSObject) {
+    fn SetOnerror(&mut self, listener: Option<OnErrorEventHandlerNonNull>) {
         let eventtarget: &mut JSRef<EventTarget> = EventTargetCast::from_mut_ref(self);
         eventtarget.set_event_handler_common("error", listener)
     }
@@ -429,6 +430,7 @@ impl<'a> PrivateWindowHelpers for JSRef<'a, Window> {
         handle
     }
 }
+
 impl Window {
     pub fn new(cx: *mut JSContext,
                page: Rc<Page>,