script: Make EventTarget::fire return bool according to spec (#39308)

This is a continuation of #38566, newly discovered when fixing
https://github.com/servo/servo/issues/38616#issuecomment-3261561671.

We add more documentation and return `bool` for the function family of
[event firing](https://dom.spec.whatwg.org/#concept-event-fire).

Testing: No behaviour change.

Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>

components/script/dom/eventtarget.rs

@@ -885,7 +885,7 @@ impl EventTarget {
     }
 
     // https://dom.spec.whatwg.org/#concept-event-fire
-    pub(crate) fn fire_event(&self, name: Atom, can_gc: CanGc) -> DomRoot<Event> {
+    pub(crate) fn fire_event(&self, name: Atom, can_gc: CanGc) -> bool {
         self.fire_event_with_params(
             name,
             EventBubbles::DoesNotBubble,
@@ -896,7 +896,7 @@ impl EventTarget {
     }
 
     // https://dom.spec.whatwg.org/#concept-event-fire
-    pub(crate) fn fire_bubbling_event(&self, name: Atom, can_gc: CanGc) -> DomRoot<Event> {
+    pub(crate) fn fire_bubbling_event(&self, name: Atom, can_gc: CanGc) -> bool {
         self.fire_event_with_params(
             name,
             EventBubbles::Bubbles,
@@ -907,7 +907,7 @@ impl EventTarget {
     }
 
     // https://dom.spec.whatwg.org/#concept-event-fire
-    pub(crate) fn fire_cancelable_event(&self, name: Atom, can_gc: CanGc) -> DomRoot<Event> {
+    pub(crate) fn fire_cancelable_event(&self, name: Atom, can_gc: CanGc) -> bool {
         self.fire_event_with_params(
             name,
             EventBubbles::DoesNotBubble,
@@ -918,11 +918,7 @@ impl EventTarget {
     }
 
     // https://dom.spec.whatwg.org/#concept-event-fire
-    pub(crate) fn fire_bubbling_cancelable_event(
-        &self,
-        name: Atom,
-        can_gc: CanGc,
-    ) -> DomRoot<Event> {
+    pub(crate) fn fire_bubbling_cancelable_event(&self, name: Atom, can_gc: CanGc) -> bool {
         self.fire_event_with_params(
             name,
             EventBubbles::Bubbles,
@@ -940,11 +936,10 @@ impl EventTarget {
         cancelable: EventCancelable,
         composed: EventComposed,
         can_gc: CanGc,
-    ) -> DomRoot<Event> {
+    ) -> bool {
         let event = Event::new(&self.global(), name, bubbles, cancelable, can_gc);
         event.set_composed(composed.into());
-        event.fire(self, can_gc);
-        event
+        event.fire(self, can_gc)
     }
 
     /// <https://dom.spec.whatwg.org/#dom-eventtarget-addeventlistener>

components/script/dom/html/htmlformelement.rs

@@ -1148,7 +1148,7 @@ impl HTMLFormElement {
                 }
             })
             .collect::<Vec<DomRoot<Element>>>();
-        // Step 4
+        // Step 4: If invalid controls is empty, then return a positive result.
         if invalid_controls.is_empty() {
             return Ok(());
         }
@@ -1156,10 +1156,13 @@ impl HTMLFormElement {
         let unhandled_invalid_controls = invalid_controls
             .into_iter()
             .filter_map(|field| {
-                let event = field
+                // Step 6.1: Let notCanceled be the result of firing an event named invalid at
+                // field, with the cancelable attribute initialized to true.
+                let not_canceled = field
                     .upcast::<EventTarget>()
                     .fire_cancelable_event(atom!("invalid"), can_gc);
-                if !event.DefaultPrevented() {
+                // Step 6.2: If notCanceled is true, then add field to unhandled invalid controls.
+                if not_canceled {
                     return Some(field);
                 }
                 None
@@ -1302,6 +1305,7 @@ impl HTMLFormElement {
         Some(form_data.datums())
     }
 
+    /// <https://html.spec.whatwg.org/multipage/#dom-form-reset>
     pub(crate) fn reset(&self, _reset_method_flag: ResetFrom, can_gc: CanGc) {
         // https://html.spec.whatwg.org/multipage/#locked-for-reset
         if self.marked_for_reset.get() {
@@ -1310,10 +1314,13 @@ impl HTMLFormElement {
             self.marked_for_reset.set(true);
         }
 
-        let event = self
+        // https://html.spec.whatwg.org/multipage/#concept-form-reset
+        // Let reset be the result of firing an event named reset at form,
+        // with the bubbles and cancelable attributes initialized to true.
+        let reset = self
             .upcast::<EventTarget>()
             .fire_bubbling_cancelable_event(atom!("reset"), can_gc);
-        if event.DefaultPrevented() {
+        if !reset {
             return;
         }
 

components/script/dom/validation.rs

@@ -1,7 +1,6 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
-use crate::dom::bindings::codegen::Bindings::EventBinding::Event_Binding::EventMethods;
 use crate::dom::bindings::codegen::Bindings::HTMLElementBinding::HTMLElementMethods;
 use crate::dom::bindings::codegen::Bindings::HTMLOrSVGElementBinding::FocusOptions;
 use crate::dom::bindings::inheritance::Castable;
@@ -62,14 +61,15 @@ pub(crate) trait Validatable {
             return true;
         }
 
-        // Step 1.1.
-        let event = self
+        // Step 1.1: Let report be the result of firing an event named invalid at element,
+        // with the cancelable attribute initialized to true.
+        let report = self
             .as_element()
             .upcast::<EventTarget>()
             .fire_cancelable_event(atom!("invalid"), can_gc);
 
         // Step 1.2.
-        if !event.DefaultPrevented() {
+        if report {
             let flags = self.validity_state().invalid_flags();
             println!(
                 "Validation error: {}",