Auto merge of #17614 - cbrewster:custom_element_reactions, r=jdm

Implement custom element reactions

<!-- Please describe your changes on the following line: -->
Initial work for implementing custom element reactions: https://html.spec.whatwg.org/multipage/custom-elements.html#custom-element-reactions

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #17433 (github issue number if applicable).

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

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1 files changed, 27 insertions, 2 deletions

diff --git a/components/script/dom/node.rs b/components/script/dom/node.rs
index 333b47c3a2c..1c25567cb2d 100644
--- a/components/script/dom/node.rs
+++ b/components/script/dom/node.rs
@@ -30,6 +30,7 @@ use dom::bindings::str::{DOMString, USVString};
 use dom::bindings::xmlname::namespace_from_domstring;
 use dom::characterdata::{CharacterData, LayoutCharacterDataHelpers};
 use dom::cssstylesheet::CSSStyleSheet;
+use dom::customelementregistry::CallbackReaction;
 use dom::document::{Document, DocumentSource, HasBrowsingContext, IsHTMLDocument};
 use dom::documentfragment::DocumentFragment;
 use dom::documenttype::DocumentType;
@@ -66,6 +67,7 @@ use ref_slice::ref_slice;
 use script_layout_interface::{HTMLCanvasData, OpaqueStyleAndLayoutData, SVGSVGData};
 use script_layout_interface::{LayoutElementType, LayoutNodeType, TrustedNodeAddress};
 use script_layout_interface::message::Msg;
+use script_thread::ScriptThread;
 use script_traits::DocumentActivity;
 use script_traits::UntrustedNodeAddress;
 use selectors::matching::{matches_selector_list, MatchingContext, MatchingMode};
@@ -313,6 +315,10 @@ impl Node {
             // e.g. when removing a <form>.
             vtable_for(&&*node).unbind_from_tree(&context);
             node.style_and_layout_data.get().map(|d| node.dispose(d));
+            // https://dom.spec.whatwg.org/#concept-node-remove step 14
+            if let Some(element) = node.as_custom_element() {
+                ScriptThread::enqueue_callback_reaction(&*element, CallbackReaction::Disconnected);
+            }
         }
 
         self.owner_doc().content_and_heritage_changed(self, NodeDamage::OtherNodeDamage);
@@ -322,6 +328,15 @@ impl Node {
     pub fn to_untrusted_node_address(&self) -> UntrustedNodeAddress {
         UntrustedNodeAddress(self.reflector().get_jsobject().get() as *const c_void)
     }
+
+    pub fn as_custom_element(&self) -> Option<Root<Element>> {
+        self.downcast::<Element>()
+            .and_then(|element| if element.get_custom_element_definition().is_some() {
+                Some(Root::from_ref(element))
+            } else {
+                None
+            })
+    }
 }
 
 pub struct QuerySelectorIterator {
@@ -1401,13 +1416,20 @@ impl Node {
         let old_doc = node.owner_doc();
         // Step 2.
         node.remove_self();
+        // Step 3.
         if &*old_doc != document {
-            // Step 3.
+            // Step 3.1.
             for descendant in node.traverse_preorder() {
                 descendant.set_owner_doc(document);
             }
-            // Step 4.
             for descendant in node.traverse_preorder() {
+                // Step 3.2.
+                if let Some(element) = node.as_custom_element() {
+                    ScriptThread::enqueue_callback_reaction(&*element,
+                        CallbackReaction::Adopted(old_doc.clone(), Root::from_ref(document)));
+                }
+
+                // Step 3.3.
                 vtable_for(&descendant).adopting_steps(&old_doc);
             }
         }
@@ -1615,6 +1637,9 @@ impl Node {
             // Step 7.1.
             parent.add_child(*kid, child);
             // Step 7.2: insertion steps.
+            if let Some(element) = kid.as_custom_element() {
+                ScriptThread::enqueue_callback_reaction(&*element, CallbackReaction::Connected);
+            }
         }
         if let SuppressObserver::Unsuppressed = suppress_observers {
             vtable_for(&parent).children_changed(