dom: Optimize IFrameCollection::validate (#38196)

The `IFrameCollection` was previously rebuilt too often. This PR tries
to address the todo, to only rebuild the IFrameCollection when
necessary.

Testing: `CSS Selector Invalidation: :has() invalidation should not be
O(n^2)` wpt-test changed status from timeout to failed.
Fixes: #38131 (IFrameCollection::validate accounts for 30% of script
time in DOM heavy scenarios)


Co-authored-by: sharpshooter_pt <ibluegalaxy_taoj@163.com>

Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

components/script/dom/document.rs

@@ -3349,6 +3349,10 @@ impl Document {
         self.iframes.borrow_mut()
     }
 
+    pub(crate) fn invalidate_iframes_collection(&self) {
+        self.iframes.borrow_mut().invalidate();
+    }
+
     pub(crate) fn get_dom_interactive(&self) -> Option<CrossProcessInstant> {
         self.dom_interactive.get()
     }
@@ -4145,7 +4149,7 @@ impl Document {
             scripts: Default::default(),
             anchors: Default::default(),
             applets: Default::default(),
-            iframes: Default::default(),
+            iframes: RefCell::new(IFrameCollection::new()),
             style_shared_lock: {
                 /// Per-process shared lock for author-origin stylesheets
                 ///

components/script/dom/htmliframeelement.rs

@@ -43,7 +43,7 @@ use crate::dom::element::{
 use crate::dom::eventtarget::EventTarget;
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::htmlelement::HTMLElement;
-use crate::dom::node::{Node, NodeDamage, NodeTraits, UnbindContext};
+use crate::dom::node::{BindContext, Node, NodeDamage, NodeTraits, UnbindContext};
 use crate::dom::trustedhtml::TrustedHTML;
 use crate::dom::virtualmethods::VirtualMethods;
 use crate::dom::windowproxy::WindowProxy;
@@ -813,6 +813,13 @@ impl VirtualMethods for HTMLIFrameElement {
         }
     }
 
+    fn bind_to_tree(&self, context: &BindContext, can_gc: CanGc) {
+        if let Some(s) = self.super_type() {
+            s.bind_to_tree(context, can_gc);
+        }
+        self.owner_document().invalidate_iframes_collection();
+    }
+
     fn unbind_from_tree(&self, context: &UnbindContext, can_gc: CanGc) {
         self.super_type().unwrap().unbind_from_tree(context, can_gc);
 
@@ -865,5 +872,7 @@ impl VirtualMethods for HTMLIFrameElement {
         // a new iframe. Without this, the constellation gets very
         // confused.
         self.destroy_nested_browsing_context();
+
+        self.owner_document().invalidate_iframes_collection();
     }
 }

components/script/iframe_collection.rs

@@ -2,7 +2,6 @@
  * 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 std::cell::Cell;
 use std::default::Default;
 
 use base::id::BrowsingContextId;
@@ -29,25 +28,31 @@ pub(crate) struct IFrame {
 #[derive(Default, JSTraceable, MallocSizeOf)]
 #[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
 pub(crate) struct IFrameCollection {
-    /// The version of the [`Document`] that this collection refers to. When the versions
-    /// do not match, the collection will need to be rebuilt.
-    document_version: Cell<u64>,
     /// The `<iframe>`s in the collection.
     iframes: Vec<IFrame>,
+    /// When true, the collection will need to be rebuilt.
+    invalid: bool,
 }
 
 impl IFrameCollection {
+    pub(crate) fn new() -> Self {
+        Self {
+            iframes: vec![],
+            invalid: true,
+        }
+    }
+
+    pub(crate) fn invalidate(&mut self) {
+        self.invalid = true;
+    }
+
     /// Validate that the collection is up-to-date with the given [`Document`]. If it isn't up-to-date
     /// rebuild it.
     pub(crate) fn validate(&mut self, document: &Document) {
-        // TODO: Whether the DOM has changed at all can lead to rebuilding this collection
-        // when it isn't necessary. A better signal might be if any `<iframe>` nodes have
-        // been connected or disconnected.
-        let document_node = DomRoot::from_ref(document.upcast::<Node>());
-        let document_version = document_node.inclusive_descendants_version();
-        if document_version == self.document_version.get() {
+        if !self.invalid {
             return;
         }
+        let document_node = DomRoot::from_ref(document.upcast::<Node>());
 
         // Preserve any old sizes, but only for `<iframe>`s that already have a
         // BrowsingContextId and a set size.
@@ -75,7 +80,7 @@ impl IFrameCollection {
                 }
             })
             .collect();
-        self.document_version.set(document_version);
+        self.invalid = false;
     }
 
     pub(crate) fn get(&self, browsing_context_id: BrowsingContextId) -> Option<&IFrame> {

tests/wpt/meta/css/selectors/invalidation/has-complexity.html.ini

@@ -1,4 +1,18 @@
 [has-complexity.html]
-  expected: TIMEOUT
   [Before appending 25000 elements]
     expected: FAIL
+
+  [After appending 25000 elements. This should not time out.]
+    expected: FAIL
+
+  [After appending another 25000 elements. This should not time out.]
+    expected: FAIL
+
+  [After appending div with 25000 elements. This should not time out.]
+    expected: FAIL
+
+  [After removing div with 25000 elements. This should not time out.]
+    expected: FAIL
+
+  [After removing 25000 elements one-by-one. This should not time out.]
+    expected: FAIL