dom: Implement current window event.

components/script/dom/event.rs

@@ -690,12 +690,15 @@ fn inner_invoke(
             object.remove_listener_if_once(&event.type_(), &event_listener);
         }
 
-        // Step 2.6-2.8
-        // FIXME(#25478): we need to get the global that the event
-        // listener is going to be called on, then if it's a Window
-        // set its .event to the event, remembering the previous
-        // value of its .event. This allows events to just use
-        // the word "event" instead of taking the event as an argument.
+        // Step 2.6
+        let global = listener.associated_global();
+
+        // Step 2.7-2.8
+        let current_event = if let Some(window) = global.downcast::<Window>() {
+            window.set_current_event(Some(event))
+        } else {
+            None
+        };
 
         // Step 2.9 TODO: EventListener passive option not implemented
 
@@ -712,8 +715,9 @@ fn inner_invoke(
         // Step 2.11 TODO: passive not implemented
 
         // Step 2.12
-        // TODO This is where we put back the .event we
-        // had before step 2.6.
+        if let Some(window) = global.downcast::<Window>() {
+            window.set_current_event(current_event.as_ref().map(|e| &**e));
+        }
 
         // Step 2.13: short-circuit instead of going to next listener
         if event.stop_immediate.get() {

components/script/dom/eventtarget.rs

@@ -150,6 +150,23 @@ pub enum CompiledEventListener {
 }
 
 impl CompiledEventListener {
+    #[allow(unsafe_code)]
+    pub fn associated_global(&self) -> DomRoot<GlobalScope> {
+        let obj = match self {
+            CompiledEventListener::Listener(listener) => listener.callback(),
+            CompiledEventListener::Handler(CommonEventHandler::EventHandler(handler)) => {
+                handler.callback()
+            },
+            CompiledEventListener::Handler(CommonEventHandler::ErrorEventHandler(handler)) => {
+                handler.callback()
+            },
+            CompiledEventListener::Handler(CommonEventHandler::BeforeUnloadEventHandler(
+                handler,
+            )) => handler.callback(),
+        };
+        unsafe { GlobalScope::from_object(obj) }
+    }
+
     // https://html.spec.whatwg.org/multipage/#the-event-handler-processing-algorithm
     pub fn call_or_handle_event(
         &self,

components/script/dom/webidls/Window.webidl

@@ -180,6 +180,10 @@ partial interface Window {
    Selection? getSelection();
 };
 
+// https://dom.spec.whatwg.org/#interface-window-extensions
+partial interface Window {
+  [Replaceable] readonly attribute any event; // historical
+};
 
 dictionary WindowPostMessageOptions : PostMessageOptions {
    USVString targetOrigin = "/";

components/script/dom/window.rs

@@ -83,6 +83,7 @@ use euclid::default::{Point2D as UntypedPoint2D, Rect as UntypedRect};
 use euclid::{Point2D, Rect, Scale, Size2D, Vector2D};
 use ipc_channel::ipc::IpcSender;
 use ipc_channel::router::ROUTER;
+use js::conversions::ToJSValConvertible;
 use js::jsapi::Heap;
 use js::jsapi::JSAutoRealm;
 use js::jsapi::JSObject;
@@ -340,6 +341,9 @@ pub struct Window {
     /// those values will cause the marker to be set to false.
     #[ignore_malloc_size_of = "Rc is hard"]
     layout_marker: DomRefCell<Rc<Cell<bool>>>,
+
+    /// https://dom.spec.whatwg.org/#window-current-event
+    current_event: DomRefCell<Option<Dom<Event>>>,
 }
 
 impl Window {
@@ -1334,9 +1338,34 @@ impl WindowMethods for Window {
     fn GetSelection(&self) -> Option<DomRoot<Selection>> {
         self.document.get().and_then(|d| d.GetSelection())
     }
+
+    // https://dom.spec.whatwg.org/#dom-window-event
+    #[allow(unsafe_code)]
+    fn Event(&self, cx: JSContext) -> JSVal {
+        rooted!(in(*cx) let mut rval = UndefinedValue());
+        if let Some(ref event) = *self.current_event.borrow() {
+            unsafe {
+                event
+                    .reflector()
+                    .get_jsobject()
+                    .to_jsval(*cx, rval.handle_mut());
+            }
+        }
+        rval.get()
+    }
 }
 
 impl Window {
+    pub(crate) fn set_current_event(&self, event: Option<&Event>) -> Option<DomRoot<Event>> {
+        let current = self
+            .current_event
+            .borrow()
+            .as_ref()
+            .map(|e| DomRoot::from_ref(&**e));
+        *self.current_event.borrow_mut() = event.map(|e| Dom::from_ref(e));
+        current
+    }
+
     /// https://html.spec.whatwg.org/multipage/#window-post-message-steps
     fn post_message_impl(
         &self,
@@ -2375,6 +2404,7 @@ impl Window {
             event_loop_waker,
             visible: Cell::new(true),
             layout_marker: DomRefCell::new(Rc::new(Cell::new(true))),
+            current_event: DomRefCell::new(None),
         });
 
         unsafe { WindowBinding::Wrap(JSContext::from_ptr(runtime.cx()), win) }

tests/wpt/metadata/dom/events/event-global.html.ini

@@ -1,19 +1,6 @@
 [event-global.html]
-  [event exists on window, which is initially set to undefined]
-    expected: FAIL
-
-  [window.event is only defined during dispatch]
-    expected: FAIL
-
   [window.event is undefined if the target is in a shadow tree (event dispatched outside shadow tree)]
     expected: FAIL
 
   [window.event is undefined if the target is in a shadow tree (event dispatched inside shadow tree)]
     expected: FAIL
-
-  [window.event is set to the current event during dispatch]
-    expected: FAIL
-
-  [window.event is set to the current event, which is the event passed to dispatch]
-    expected: FAIL
-

tests/wpt/metadata/dom/idlharness.window.js.ini

@@ -152,9 +152,6 @@
   [AbortSignal interface object length]
     expected: FAIL
 
-  [Window interface: attribute event]
-    expected: FAIL
-
   [AbortController interface: new AbortController() must inherit property "abort()" with the proper type]
     expected: FAIL