Fire slot change events when the slot content changes (#35137)

* Add the onslotchange attribute to ShadowRoot

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

* Add spec comments to MutationObserver::queue_mutation_observer_microtask

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

* Add DomRefCell::take

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

* Add spec comments to notify_mutation_observers

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

* Fire slotchange events when a slot changes

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

* ./mach fmt

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

* Fix check for when to dispatch slot events

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

* Potentially fire slot change events in Node::remove

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

* Update WPT expectations

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

* ./mach fmt

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

* Bump stylo

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

* Move "signal a slot change" into ScriptThread impl

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

---------

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

1 files changed, 34 insertions, 0 deletions

diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 13558b81832..c232fb9fe51 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -128,6 +128,7 @@ use crate::dom::element::Element;
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::htmlanchorelement::HTMLAnchorElement;
 use crate::dom::htmliframeelement::HTMLIFrameElement;
+use crate::dom::htmlslotelement::HTMLSlotElement;
 use crate::dom::mutationobserver::MutationObserver;
 use crate::dom::node::{Node, NodeTraits, ShadowIncluding};
 use crate::dom::performanceentry::PerformanceEntry;
@@ -259,6 +260,9 @@ pub struct ScriptThread {
     /// The unit of related similar-origin browsing contexts' list of MutationObserver objects
     mutation_observers: DomRefCell<Vec<Dom<MutationObserver>>>,
 
+    /// <https://dom.spec.whatwg.org/#signal-slot-list>
+    signal_slots: DomRefCell<Vec<Dom<HTMLSlotElement>>>,
+
     /// A handle to the WebGL thread
     #[no_trace]
     webgl_chan: Option<WebGLPipeline>,
@@ -508,6 +512,26 @@ impl ScriptThread {
         })
     }
 
+    pub(crate) fn add_signal_slot(observer: &HTMLSlotElement) {
+        with_script_thread(|script_thread| {
+            script_thread
+                .signal_slots
+                .borrow_mut()
+                .push(Dom::from_ref(observer));
+        })
+    }
+
+    pub(crate) fn take_signal_slots() -> Vec<DomRoot<HTMLSlotElement>> {
+        with_script_thread(|script_thread| {
+            script_thread
+                .signal_slots
+                .take()
+                .into_iter()
+                .map(|slot| slot.as_rooted())
+                .collect()
+        })
+    }
+
     pub(crate) fn mark_document_with_no_blocked_loads(doc: &Document) {
         with_script_thread(|script_thread| {
             script_thread
@@ -914,6 +938,7 @@ impl ScriptThread {
             closed_pipelines: DomRefCell::new(HashSet::new()),
             mutation_observer_microtask_queued: Default::default(),
             mutation_observers: Default::default(),
+            signal_slots: Default::default(),
             system_font_service,
             webgl_chan: state.webgl_chan,
             #[cfg(feature = "webxr")]
@@ -3718,6 +3743,15 @@ impl ScriptThread {
             )
         }
     }
+
+    /// <https://dom.spec.whatwg.org/#signal-a-slot-change>
+    pub(crate) fn signal_a_slot_change(slot: &HTMLSlotElement) {
+        // Step 1. Append slot to slot’s relevant agent’s signal slots.
+        ScriptThread::add_signal_slot(slot);
+
+        // Step 2. Queue a mutation observer microtask.
+        MutationObserver::queue_mutation_observer_microtask();
+    }
 }
 
 impl Drop for ScriptThread {