Prune garbage collected SharedShapes

boa_engine/src/object/shape/shared_shape/forward_transition.rs

@@ -55,4 +55,24 @@ impl ForwardTransition {
         };
         transitions.get(key).cloned()
     }
+
+    /// Prunes the [`WeakGc`]s that have been garbage collected.
+    pub(super) fn prune_property_transitions(&self) {
+        let mut this = self.inner.borrow_mut();
+        let Some(transitions) = this.properties.as_deref_mut() else {
+            return;
+        };
+
+        transitions.retain(|_, v| v.is_upgradable());
+    }
+
+    /// Prunes the [`WeakGc`]s that have been garbage collected.
+    pub(super) fn prune_prototype_transitions(&self) {
+        let mut this = self.inner.borrow_mut();
+        let Some(transitions) = this.prototypes.as_deref_mut() else {
+            return;
+        };
+
+        transitions.retain(|_, v| v.is_upgradable());
+    }
 }

boa_engine/src/object/shape/shared_shape/mod.rs

@@ -192,6 +192,8 @@ impl SharedShape {
             if let Some(inner) = shape.upgrade() {
                 return Self { inner };
             }
+
+            self.forward_transitions().prune_prototype_transitions();
         }
         let new_inner_shape = Inner {
             forward_transitions: ForwardTransition::default(),
@@ -217,6 +219,8 @@ impl SharedShape {
             if let Some(inner) = shape.upgrade() {
                 return Self { inner };
             }
+
+            self.forward_transitions().prune_property_transitions();
         }
 
         let property_table = self.property_table().add_property_deep_clone_if_needed(
@@ -266,6 +270,8 @@ impl SharedShape {
                     action,
                 };
             }
+
+            self.forward_transitions().prune_property_transitions();
         }
 
         // The attribute change transitions, didn't change from accessor to data property or vice-versa.

boa_gc/src/pointers/ephemeron.rs

@@ -31,6 +31,13 @@ impl<K: Trace + ?Sized, V: Trace + Clone> Ephemeron<K, V> {
         // `inner_ptr`.
         unsafe { self.inner_ptr.get().as_ref().value().cloned() }
     }
+
+    /// Checks if the [`Ephemeron`] has a value.
+    pub fn has_value(&self) -> bool {
+        // SAFETY: this is safe because `Ephemeron` is tracked to always point to a valid pointer
+        // `inner_ptr`.
+        unsafe { self.inner_ptr.get().as_ref().value().is_some() }
+    }
 }
 
 impl<K: Trace + ?Sized, V: Trace> Ephemeron<K, V> {

boa_gc/src/pointers/weak.rs

@@ -23,6 +23,11 @@ impl<T: Trace> WeakGc<T> {
     pub fn upgrade(&self) -> Option<Gc<T>> {
         self.inner.value()
     }
+
+    /// Check if the [`WeakGc`] can be upgraded.
+    pub fn is_upgradable(&self) -> bool {
+        self.inner.has_value()
+    }
 }
 
 impl<T: Trace> Clone for WeakGc<T> {