Auto merge of #25468 - gterzian:add_generic_to_frozen_array, r=Manishearth

Add generic to frozen array

<!-- Please describe your changes on the following line: -->

https://github.com/servo/servo/pull/25467#discussion_r364575071

Depends on https://github.com/servo/servo/pull/25467

---
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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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4 files changed, 36 insertions, 13 deletions

diff --git a/components/script/dom/bindings/utils.rs b/components/script/dom/bindings/utils.rs
index e344e9ae279..56b2112e498 100644
--- a/components/script/dom/bindings/utils.rs
+++ b/components/script/dom/bindings/utils.rs
@@ -10,10 +10,8 @@ use crate::dom::bindings::codegen::PrototypeList::{MAX_PROTO_CHAIN_LENGTH, PROTO
 use crate::dom::bindings::conversions::{jsstring_to_str, private_from_proto_check};
 use crate::dom::bindings::error::throw_invalid_this;
 use crate::dom::bindings::inheritance::TopTypeId;
-use crate::dom::bindings::root::DomRoot;
 use crate::dom::bindings::str::DOMString;
 use crate::dom::bindings::trace::trace_object;
-use crate::dom::messageport::MessagePort;
 use crate::dom::windowproxy;
 use crate::script_runtime::JSContext as SafeJSContext;
 use js::conversions::{jsstr_to_string, ToJSValConvertible};
@@ -126,12 +124,9 @@ impl Clone for DOMJSClass {
 unsafe impl Sync for DOMJSClass {}
 
 /// Returns a JSVal representing a frozen array of ports
-pub fn message_ports_to_frozen_array(
-    message_ports: &[DomRoot<MessagePort>],
-    cx: SafeJSContext,
-) -> JSVal {
+pub fn to_frozen_array<T: ToJSValConvertible>(convertibles: &[T], cx: SafeJSContext) -> JSVal {
     rooted!(in(*cx) let mut ports = UndefinedValue());
-    unsafe { message_ports.to_jsval(*cx, ports.handle_mut()) };
+    unsafe { convertibles.to_jsval(*cx, ports.handle_mut()) };
 
     rooted!(in(*cx) let obj = ports.to_object());
     unsafe { JS_FreezeObject(*cx, RawHandleObject::from(obj.handle())) };
diff --git a/components/script/dom/extendablemessageevent.rs b/components/script/dom/extendablemessageevent.rs
index 6131363fd99..a1433ec6269 100644
--- a/components/script/dom/extendablemessageevent.rs
+++ b/components/script/dom/extendablemessageevent.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 https://mozilla.org/MPL/2.0/. */
 
+use crate::dom::bindings::cell::DomRefCell;
 use crate::dom::bindings::codegen::Bindings::ExtendableMessageEventBinding;
 use crate::dom::bindings::codegen::Bindings::ExtendableMessageEventBinding::ExtendableMessageEventMethods;
 use crate::dom::bindings::error::Fallible;
@@ -10,7 +11,7 @@ use crate::dom::bindings::reflector::reflect_dom_object;
 use crate::dom::bindings::root::{Dom, DomRoot};
 use crate::dom::bindings::str::DOMString;
 use crate::dom::bindings::trace::RootedTraceableBox;
-use crate::dom::bindings::utils::message_ports_to_frozen_array;
+use crate::dom::bindings::utils::to_frozen_array;
 use crate::dom::event::Event;
 use crate::dom::eventtarget::EventTarget;
 use crate::dom::extendableevent::ExtendableEvent;
@@ -32,6 +33,8 @@ pub struct ExtendableMessageEvent {
     origin: DOMString,
     lastEventId: DOMString,
     ports: Vec<Dom<MessagePort>>,
+    #[ignore_malloc_size_of = "mozjs"]
+    frozen_ports: DomRefCell<Option<Heap<JSVal>>>,
 }
 
 impl ExtendableMessageEvent {
@@ -49,6 +52,7 @@ impl ExtendableMessageEvent {
                 .into_iter()
                 .map(|port| Dom::from_ref(&*port))
                 .collect(),
+            frozen_ports: DomRefCell::new(None),
         }
     }
 
@@ -141,11 +145,22 @@ impl ExtendableMessageEventMethods for ExtendableMessageEvent {
 
     /// https://w3c.github.io/ServiceWorker/#extendablemessage-event-ports
     fn Ports(&self, cx: JSContext) -> JSVal {
+        if let Some(ports) = &*self.frozen_ports.borrow() {
+            return ports.get();
+        }
+
         let ports: Vec<DomRoot<MessagePort>> = self
             .ports
             .iter()
             .map(|port| DomRoot::from_ref(&**port))
             .collect();
-        message_ports_to_frozen_array(ports.as_slice(), cx)
+        let frozen_ports = to_frozen_array(ports.as_slice(), cx);
+
+        // Cache the Js value.
+        let heap_val = Heap::default();
+        heap_val.set(frozen_ports);
+        *self.frozen_ports.borrow_mut() = Some(heap_val);
+
+        frozen_ports
     }
 }
diff --git a/components/script/dom/messageevent.rs b/components/script/dom/messageevent.rs
index 0bb2ea1fd7a..54a6f2ee588 100644
--- a/components/script/dom/messageevent.rs
+++ b/components/script/dom/messageevent.rs
@@ -13,7 +13,7 @@ use crate::dom::bindings::reflector::reflect_dom_object;
 use crate::dom::bindings::root::{Dom, DomRoot};
 use crate::dom::bindings::str::DOMString;
 use crate::dom::bindings::trace::RootedTraceableBox;
-use crate::dom::bindings::utils::message_ports_to_frozen_array;
+use crate::dom::bindings::utils::to_frozen_array;
 use crate::dom::event::Event;
 use crate::dom::eventtarget::EventTarget;
 use crate::dom::globalscope::GlobalScope;
@@ -61,6 +61,8 @@ pub struct MessageEvent {
     source: DomRefCell<Option<SrcObject>>,
     lastEventId: DomRefCell<DOMString>,
     ports: DomRefCell<Vec<Dom<MessagePort>>>,
+    #[ignore_malloc_size_of = "mozjs"]
+    frozen_ports: DomRefCell<Option<Heap<JSVal>>>,
 }
 
 impl MessageEvent {
@@ -82,6 +84,7 @@ impl MessageEvent {
                     .map(|port| Dom::from_ref(&*port))
                     .collect(),
             ),
+            frozen_ports: DomRefCell::new(None),
         }
     }
 
@@ -238,13 +241,24 @@ impl MessageEventMethods for MessageEvent {
 
     /// <https://html.spec.whatwg.org/multipage/#dom-messageevent-ports>
     fn Ports(&self, cx: JSContext) -> JSVal {
+        if let Some(ports) = &*self.frozen_ports.borrow() {
+            return ports.get();
+        }
+
         let ports: Vec<DomRoot<MessagePort>> = self
             .ports
             .borrow()
             .iter()
             .map(|port| DomRoot::from_ref(&**port))
             .collect();
-        message_ports_to_frozen_array(ports.as_slice(), cx)
+        let frozen_ports = to_frozen_array(ports.as_slice(), cx);
+
+        // Cache the Js value.
+        let heap_val = Heap::default();
+        heap_val.set(frozen_ports);
+        *self.frozen_ports.borrow_mut() = Some(heap_val);
+
+        frozen_ports
     }
 
     /// <https://html.spec.whatwg.org/multipage/#dom-messageevent-initmessageevent>
@@ -268,6 +282,7 @@ impl MessageEventMethods for MessageEvent {
             .into_iter()
             .map(|port| Dom::from_ref(&*port))
             .collect();
+        *self.frozen_ports.borrow_mut() = None;
         self.event
             .init_event(Atom::from(type_), bubbles, cancelable);
     }
diff --git a/tests/wpt/metadata/html/webappapis/scripting/events/messageevent-constructor.https.html.ini b/tests/wpt/metadata/html/webappapis/scripting/events/messageevent-constructor.https.html.ini
index 73cfb17b2a2..e2ef27deb9d 100644
--- a/tests/wpt/metadata/html/webappapis/scripting/events/messageevent-constructor.https.html.ini
+++ b/tests/wpt/metadata/html/webappapis/scripting/events/messageevent-constructor.https.html.ini
@@ -1,7 +1,5 @@
 [messageevent-constructor.https.html]
   type: testharness
-  [ports attribute should be a FrozenArray]
-    expected: FAIL
 
   [All parameters to initMessageEvent should be mandatory]
     expected: FAIL