tor-browser

commit 04b013b47241e496684d5f7eb4368c0898166d87
parent cfbe87ee22857758128bf11690eb33f7c6662a18
Author: Denis Palmeiro <dpalmeiro@mozilla.com>
Date:   Tue, 30 Dec 2025 15:43:09 +0000

Bug 2006172: Compare style attributes by value instead of just pointer identity when style sharing.  r=emilio,firefox-style-system-reviewers

Inline styles set by JS (i.e. element.style.display = "block") allocate new
PropertyDeclarationBlock pointers causing identical inline styles to have
different pointers.

Differential Revision: https://phabricator.services.mozilla.com/D277605

Diffstat:
M
servo/components/style/properties/declaration_block.rs
 | 
9
+++++++++
M
servo/components/style/sharing/checks.rs
 | 
13
+++++++++++--
M
servo/components/style/sharing/mod.rs
 | 
2
+-

3 files changed, 21 insertions(+), 3 deletions(-)
diff --git a/servo/components/style/properties/declaration_block.rs b/servo/components/style/properties/declaration_block.rs
@@ -261,6 +261,15 @@ pub struct PropertyDeclarationBlock {
     property_ids: PropertyDeclarationIdSet,
 }
 
+impl PartialEq for PropertyDeclarationBlock {
+    fn eq(&self, other: &Self) -> bool {
+        // property_ids must be equal if declarations are equal, so we don't
+        // need to compare them explicitly.
+        self.declarations == other.declarations
+            && self.declarations_importance == other.declarations_importance
+    }
+}
+
 /// Iterator over `(PropertyDeclaration, Importance)` pairs.
 pub struct DeclarationImportanceIterator<'a> {
     iter: Zip<Iter<'a, PropertyDeclaration>, smallbitvec::Iter<'a>>,
diff --git a/servo/components/style/sharing/checks.rs b/servo/components/style/sharing/checks.rs
@@ -53,10 +53,13 @@ where
     true
 }
 
-/// Whether two elements have the same same style attribute (by pointer identity).
+/// Whether two elements have the same style attribute.
+///
+/// First checks pointer identity (fast path), then falls back to value comparison.
 pub fn have_same_style_attribute<E>(
     target: &mut StyleSharingTarget<E>,
     candidate: &mut StyleSharingCandidate<E>,
+    shared_context: &SharedStyleContext,
 ) -> bool
 where
     E: TElement,
@@ -64,7 +67,13 @@ where
     match (target.style_attribute(), candidate.style_attribute()) {
         (None, None) => true,
         (Some(_), None) | (None, Some(_)) => false,
-        (Some(a), Some(b)) => &*a as *const _ == &*b as *const _,
+        (Some(a), Some(b)) => {
+            if std::ptr::eq(&*a, &*b) {
+                return true;
+            }
+            let guard = shared_context.guards.author;
+            *a.read_with(guard) == *b.read_with(guard)
+        },
     }
 }
 
diff --git a/servo/components/style/sharing/mod.rs b/servo/components/style/sharing/mod.rs
@@ -847,7 +847,7 @@ impl<E: TElement> StyleSharingCache<E> {
             return None;
         }
 
-        if !checks::have_same_style_attribute(target, candidate) {
+        if !checks::have_same_style_attribute(target, candidate, shared_context) {
             trace!("Miss: Style Attr");
             return None;
         }