Implement Event propagation across shadow roots (#34884)

* Implement Event.composed flag

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Allow composed events to pass shadow boundaries

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Update WPT expectations

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

---------

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

components/script/animations.rs

@@ -506,6 +506,7 @@ impl Animations {
             let parent = EventInit {
                 bubbles: true,
                 cancelable: false,
+                composed: false,
             };
 
             let property_or_animation_name =

components/script/dom/event.rs

@@ -73,6 +73,9 @@ pub(crate) struct Event {
     /// <https://dom.spec.whatwg.org/#dom-event-bubbles>
     bubbles: Cell<bool>,
 
+    /// <https://dom.spec.whatwg.org/#dom-event-composed>
+    composed: Cell<bool>,
+
     /// <https://dom.spec.whatwg.org/#dom-event-istrusted>
     is_trusted: Cell<bool>,
 
@@ -129,6 +132,7 @@ impl Event {
             stop_immediate_propagation: Cell::new(false),
             cancelable: Cell::new(false),
             bubbles: Cell::new(false),
+            composed: Cell::new(false),
             is_trusted: Cell::new(false),
             dispatch: Cell::new(false),
             initialized: Cell::new(false),
@@ -169,6 +173,8 @@ impl Event {
         can_gc: CanGc,
     ) -> DomRoot<Event> {
         let event = Event::new_uninitialized_with_proto(global, proto, can_gc);
+
+        // NOTE: The spec doesn't tell us to call init event here, it just happens to do what we need.
         event.init_event(type_, bool::from(bubbles), bool::from(cancelable));
         event
     }
@@ -622,10 +628,68 @@ impl Event {
         self.set_trusted(true);
         target.dispatch_event(self, can_gc)
     }
+
+    /// <https://dom.spec.whatwg.org/#inner-event-creation-steps>
+    fn inner_creation_steps(
+        global: &GlobalScope,
+        proto: Option<HandleObject>,
+        init: &EventBinding::EventInit,
+        can_gc: CanGc,
+    ) -> DomRoot<Event> {
+        // Step 1. Let event be the result of creating a new object using eventInterface.
+        // If realm is non-null, then use that realm; otherwise, use the default behavior defined in Web IDL.
+        let event = Event::new_uninitialized_with_proto(global, proto, can_gc);
+
+        // Step 2. Set event’s initialized flag.
+        event.initialized.set(true);
+
+        // Step 3. Initialize event’s timeStamp attribute to the relative high resolution
+        // coarse time given time and event’s relevant global object.
+        // NOTE: This is done inside Event::new_inherited
+
+        // Step 3. For each member → value in dictionary, if event has an attribute whose
+        // identifier is member, then initialize that attribute to value.#
+        event.bubbles.set(init.bubbles);
+        event.cancelable.set(init.cancelable);
+        event.composed.set(init.composed);
+
+        // Step 5. Run the event constructing steps with event and dictionary.
+        // NOTE: Event construction steps may be defined by subclasses
+
+        // Step 6. Return event.
+        event
+    }
+
+    /// Implements the logic behind the [get the parent](https://dom.spec.whatwg.org/#get-the-parent)
+    /// algorithm for shadow roots.
+    pub(crate) fn should_pass_shadow_boundary(&self, shadow_root: &ShadowRoot) -> bool {
+        debug_assert!(self.dispatching());
+
+        // > A shadow root’s get the parent algorithm, given an event, returns null if event’s composed flag
+        // > is unset and shadow root is the root of event’s path’s first struct’s invocation target;
+        // > otherwise shadow root’s host.
+        if self.Composed() {
+            return true;
+        }
+
+        let path = self.path.borrow();
+        let first_invocation_target = &path
+            .first()
+            .expect("Event path is empty despite event currently being dispatched")
+            .invocation_target
+            .as_rooted();
+
+        // The spec doesn't tell us what should happen if the invocation target is not a node
+        let Some(target_node) = first_invocation_target.downcast::<Node>() else {
+            return false;
+        };
+
+        &*target_node.GetRootNode(&GetRootNodeOptions::empty()) != shadow_root.upcast::<Node>()
+    }
 }
 
 impl EventMethods<crate::DomTypeHolder> for Event {
-    /// <https://dom.spec.whatwg.org/#dom-event-event>
+    /// <https://dom.spec.whatwg.org/#concept-event-constructor>
     fn Constructor(
         global: &GlobalScope,
         proto: Option<HandleObject>,
@@ -633,16 +697,15 @@ impl EventMethods<crate::DomTypeHolder> for Event {
         type_: DOMString,
         init: &EventBinding::EventInit,
     ) -> Fallible<DomRoot<Event>> {
-        let bubbles = EventBubbles::from(init.bubbles);
+        // Step 1. Let event be the result of running the inner event creation steps with
-        let cancelable = EventCancelable::from(init.cancelable);
+        // this interface, null, now, and eventInitDict.
-        Ok(Event::new_with_proto(
+        let event = Event::inner_creation_steps(global, proto, init, can_gc);
-            global,
+
-            proto,
+        // Step 2. Initialize event’s type attribute to type.
-            Atom::from(type_),
+        *event.type_.borrow_mut() = Atom::from(type_);
-            bubbles,
+
-            cancelable,
+        // Step 3. Return event.
-            can_gc,
+        Ok(event)
-        ))
     }
 
     /// <https://dom.spec.whatwg.org/#dom-event-eventphase>
@@ -805,6 +868,11 @@ impl EventMethods<crate::DomTypeHolder> for Event {
         self.canceled.get() == EventDefault::Prevented
     }
 
+    /// <https://dom.spec.whatwg.org/#dom-event-composed>
+    fn Composed(&self) -> bool {
+        self.composed.get()
+    }
+
     /// <https://dom.spec.whatwg.org/#dom-event-preventdefault>
     fn PreventDefault(&self) {
         if self.cancelable.get() {

components/script/dom/eventtarget.rs

@@ -805,12 +805,14 @@ impl EventTarget {
             }
         }
 
-        if self.downcast::<ShadowRoot>().is_some() {
+        if let Some(shadow_root) = self.downcast::<ShadowRoot>() {
-            // FIXME: Handle event composed flag here
+            if event.should_pass_shadow_boundary(shadow_root) {
-            // We currently assume that events are never composed (so events may never
+                let host = shadow_root.Host();
-            // cross a shadow boundary)
+                return Some(DomRoot::from_ref(host.upcast::<EventTarget>()));
+            } else {
                 return None;
             }
+        }
 
         if let Some(node) = self.downcast::<Node>() {
             // FIXME: Handle slottables here

components/script/dom/webidls/Event.webidl

@@ -34,6 +34,7 @@ interface Event {
   undefined preventDefault();
   [Pure]
   readonly attribute boolean defaultPrevented;
+  readonly attribute boolean composed;
 
   [LegacyUnforgeable]
   readonly attribute boolean isTrusted;
@@ -46,4 +47,5 @@ interface Event {
 dictionary EventInit {
   boolean bubbles = false;
   boolean cancelable = false;
+  boolean composed = false;
 };

tests/wpt/meta/dom/events/event-global-extra.window.js.ini

@@ -1,3 +0,0 @@
-[event-global-extra.window.html]
-  [window.event should not be affected by nodes moving post-dispatch]
-    expected: FAIL

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

@@ -1,7 +1,3 @@
 [event-global.html]
-  expected: TIMEOUT
-  [window.event is undefined if the target is in a shadow tree (event dispatched inside shadow tree)]
-    expected: TIMEOUT
-
   [window.event is undefined inside window.onerror if the target is in a shadow tree (ErrorEvent dispatched inside shadow tree)]
     expected: FAIL

tests/wpt/meta/dom/idlharness.any.js.ini

@@ -5,15 +5,6 @@
   expected: ERROR
 
 [idlharness.any.worker.html]
-  [Event interface: attribute composed]
-    expected: FAIL
-
-  [Event interface: new Event("foo") must inherit property "composed" with the proper type]
-    expected: FAIL
-
-  [Event interface: new CustomEvent("foo") must inherit property "composed" with the proper type]
-    expected: FAIL
-
   [AbortController interface: attribute signal]
     expected: FAIL
 

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

@@ -8,9 +8,6 @@
   [AbortSignal must be primary interface of new AbortController().signal]
     expected: FAIL
 
-  [Event interface: attribute composed]
-    expected: FAIL
-
   [AbortSignal interface: existence and properties of interface prototype object's @@unscopables property]
     expected: FAIL
 
@@ -32,9 +29,6 @@
   [AbortSignal interface object name]
     expected: FAIL
 
-  [Event interface: new CustomEvent("foo") must inherit property "composed" with the proper type]
-    expected: FAIL
-
   [EventTarget interface: new AbortController().signal must inherit property "removeEventListener(DOMString, EventListener?, optional (EventListenerOptions or boolean))" with the proper type]
     expected: FAIL
 
@@ -116,9 +110,6 @@
   [AbortSignal interface: existence and properties of interface prototype object]
     expected: FAIL
 
-  [Event interface: new Event("foo") must inherit property "composed" with the proper type]
-    expected: FAIL
-
   [Element interface: operation remove()]
     expected: FAIL
 
@@ -146,9 +137,6 @@
   [Document interface: operation append((Node or DOMString)...)]
     expected: FAIL
 
-  [Event interface: document.createEvent("Event") must inherit property "composed" with the proper type]
-    expected: FAIL
-
   [DocumentType interface: operation remove()]
     expected: FAIL
 

tests/wpt/meta/shadow-dom/Extensions-to-Event-Interface.html.ini

@@ -1,16 +1,4 @@
 [Extensions-to-Event-Interface.html]
-  [composed on EventInit must default to false]
-    expected: FAIL
-
-  [composed on EventInit must set the composed flag]
-    expected: FAIL
-
-  [The event must propagate out of open mode shadow boundaries when the composed flag is set]
-    expected: FAIL
-
-  [The event must propagate out of closed mode shadow boundaries when the composed flag is set]
-    expected: FAIL
-
   [The event must not propagate out of open mode shadow tree of the target but must propagate out of inner shadow trees when the scoped flag is set]
     expected: FAIL
 

tests/wpt/meta/shadow-dom/capturing-and-bubbling-event-listeners-across-shadow-trees.html.ini

@@ -1,10 +1,4 @@
 [capturing-and-bubbling-event-listeners-across-shadow-trees.html]
-  [Capturing event listeners should be invoked before bubbling event listeners when an event is dispatched inside a shadow tree]
-    expected: FAIL
-
-  [Capturing event listeners should be invoked before bubbling event listeners when an event is dispatched inside a doubly nested shadow tree]
-    expected: FAIL
-
   [Capturing event listeners should be invoked before bubbling event listeners when an event is dispatched via a slot]
     expected: FAIL
 

tests/wpt/meta/shadow-dom/event-composed-path-after-dom-mutation.html.ini

@@ -1,7 +0,0 @@
-[event-composed-path-after-dom-mutation.html]
-  expected: TIMEOUT
-  [Event.composedPath() should return the same result even if DOM is mutated (1/2)]
-    expected: TIMEOUT
-
-  [Event.composedPath() should return the same result even if DOM is mutated (2/2)]
-    expected: TIMEOUT

tests/wpt/meta/shadow-dom/event-composed-path.html.ini

@@ -1,22 +1,4 @@
 [event-composed-path.html]
-  [Event Path with an open ShadowRoot.]
-    expected: FAIL
-
-  [Event Path with a closed ShadowRoot.]
-    expected: FAIL
-
-  [Event Path with nested ShadowRoots: open > open.]
-    expected: FAIL
-
-  [Event Path with nested ShadowRoots: open > closed.]
-    expected: FAIL
-
-  [Event Path with nested ShadowRoots: closed > open.]
-    expected: FAIL
-
-  [Event Path with nested ShadowRoots: closed > closed.]
-    expected: FAIL
-
   [Event Path with a slot in an open Shadow Root.]
     expected: FAIL
 

tests/wpt/meta/shadow-dom/event-composed.html.ini

@@ -1,13 +1,4 @@
 [event-composed.html]
-  [A new events composed value should be set to false by default.]
-    expected: FAIL
-
-  [Users should be able to set a composed value.]
-    expected: FAIL
-
-  [An event should not be scoped if composed is specified]
-    expected: FAIL
-
   [A synthetic MouseEvent with composed=true should not be scoped]
     expected: FAIL
 

tests/wpt/meta/shadow-dom/event-dispatch-order.tentative.html.ini

@@ -1,3 +0,0 @@
-[event-dispatch-order.tentative.html]
-  [Event dispatch order: capture listerns should be called in capturing phase at a shadow host]
-    expected: FAIL

tests/wpt/meta/shadow-dom/event-inside-shadow-tree.html.ini

@@ -1,36 +0,0 @@
-[event-inside-shadow-tree.html]
-  [Firing an event inside a grand child of a detached open mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside a grand child of a detached closed mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside a grand child of an in-document open mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside a grand child of an in-document closed mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside a detached open mode shadow tree inside open mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside a detached open mode shadow tree inside closed mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside a detached closed mode shadow tree inside open mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside a detached closed mode shadow tree inside closed mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside an in-document open mode shadow tree inside open mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside an in-document open mode shadow tree inside closed mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside an in-document closed mode shadow tree inside open mode shadow tree]
-    expected: FAIL
-
-  [Firing an event inside an in-document closed mode shadow tree inside closed mode shadow tree]
-    expected: FAIL

tests/wpt/meta/shadow-dom/event-post-dispatch.html.ini

@@ -1,13 +1,4 @@
 [event-post-dispatch.html]
-  [Event properties post dispatch with an open ShadowRoot (composed: true).]
-    expected: FAIL
-
-  [Event properties post dispatch with a closed ShadowRoot (composed: true).]
-    expected: FAIL
-
-  [Event properties post dispatch with nested ShadowRoots (composed: true).]
-    expected: FAIL
-
   [Event properties post dispatch with relatedTarget in the same shadow tree. (composed: true)]
     expected: FAIL