script: delay Mutation initialization (#35291)

Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>

components/script/dom/attr.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use std::borrow::ToOwned;
+use std::cell::LazyCell;
 use std::mem;
 
 use devtools_traits::AttrInfo;
@@ -157,11 +158,11 @@ impl Attr {
         let namespace = self.namespace().clone();
         let old_value = DOMString::from(&**self.value());
         let new_value = DOMString::from(&*value);
-        let mutation = Mutation::Attribute {
+        let mutation = LazyCell::new(|| Mutation::Attribute {
             name: name.clone(),
             namespace: namespace.clone(),
             old_value: Some(old_value.clone()),
-        };
+        });
 
         MutationObserver::queue_a_mutation_record(owner.upcast::<Node>(), mutation);
 

components/script/dom/characterdata.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 //! DOM bindings for `CharacterData`.
+use std::cell::LazyCell;
 
 use dom_struct::dom_struct;
 
@@ -100,9 +101,9 @@ impl CharacterData {
 
     // Queue a MutationObserver record before changing the content.
     fn queue_mutation_record(&self) {
-        let mutation = Mutation::CharacterData {
+        let mutation = LazyCell::new(|| Mutation::CharacterData {
             old_value: self.data.borrow().clone(),
-        };
+        });
         MutationObserver::queue_a_mutation_record(self.upcast::<Node>(), mutation);
     }
 }

components/script/dom/element.rs

@@ -5,7 +5,7 @@
 //! Element nodes.
 
 use std::borrow::Cow;
-use std::cell::Cell;
+use std::cell::{Cell, LazyCell};
 use std::default::Default;
 use std::ops::Deref;
 use std::rc::Rc;
@@ -1557,11 +1557,11 @@ impl Element {
     pub(crate) fn push_attribute(&self, attr: &Attr) {
         let name = attr.local_name().clone();
         let namespace = attr.namespace().clone();
-        let mutation = Mutation::Attribute {
+        let mutation = LazyCell::new(|| Mutation::Attribute {
             name: name.clone(),
             namespace: namespace.clone(),
             old_value: None,
-        };
+        });
 
         MutationObserver::queue_a_mutation_record(&self.node, mutation);
 
@@ -1749,11 +1749,11 @@ impl Element {
             let name = attr.local_name().clone();
             let namespace = attr.namespace().clone();
             let old_value = DOMString::from(&**attr.value());
-            let mutation = Mutation::Attribute {
+            let mutation = LazyCell::new(|| Mutation::Attribute {
                 name: name.clone(),
                 namespace: namespace.clone(),
                 old_value: Some(old_value.clone()),
-            };
+            });
 
             MutationObserver::queue_a_mutation_record(&self.node, mutation);
 

components/script/dom/mutationobserver.rs

@@ -2,6 +2,7 @@
  * 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::LazyCell;
 use std::rc::Rc;
 
 use dom_struct::dom_struct;
@@ -146,7 +147,12 @@ impl MutationObserver {
     }
 
     /// <https://dom.spec.whatwg.org/#queueing-a-mutation-record>
-    pub(crate) fn queue_a_mutation_record(target: &Node, attr_type: Mutation) {
+    pub(crate) fn queue_a_mutation_record<'a, F>(
+        target: &Node,
+        attr_type: LazyCell<Mutation<'a>, F>,
+    ) where
+        F: FnOnce() -> Mutation<'a>,
+    {
         if !target.global().as_window().get_exists_mut_observer() {
             return;
         }
@@ -165,7 +171,7 @@ impl MutationObserver {
                     continue;
                 }
 
-                match attr_type {
+                match *attr_type {
                     Mutation::Attribute {
                         ref name,
                         ref namespace,
@@ -239,7 +245,7 @@ impl MutationObserver {
         // Step 4
         for (observer, paired_string) in interested_observers {
             // Steps 4.1-4.7
-            let record = match attr_type {
+            let record = match *attr_type {
                 Mutation::Attribute {
                     ref name,
                     ref namespace,

components/script/dom/node.rs

@@ -5,7 +5,7 @@
 //! The core DOM types. Defines the basic DOM hierarchy as well as all the HTML elements.
 
 use std::borrow::Cow;
-use std::cell::{Cell, UnsafeCell};
+use std::cell::{Cell, LazyCell, UnsafeCell};
 use std::default::Default;
 use std::ops::Range;
 use std::slice::from_ref;
@@ -2130,12 +2130,12 @@ impl Node {
             // Step 5.
             vtable_for(node).children_changed(&ChildrenMutation::replace_all(new_nodes.r(), &[]));
 
-            let mutation = Mutation::ChildList {
+            let mutation = LazyCell::new(|| Mutation::ChildList {
                 added: None,
                 removed: Some(new_nodes.r()),
                 prev: None,
                 next: None,
-            };
+            });
             MutationObserver::queue_a_mutation_record(node, mutation);
 
             new_nodes.r()
@@ -2208,12 +2208,12 @@ impl Node {
                 child,
             ));
 
-            let mutation = Mutation::ChildList {
+            let mutation = LazyCell::new(|| Mutation::ChildList {
                 added: Some(new_nodes),
                 removed: None,
                 prev: previous_sibling.as_deref(),
                 next: child,
-            };
+            });
             MutationObserver::queue_a_mutation_record(parent, mutation);
         }
 
@@ -2287,12 +2287,12 @@ impl Node {
         ));
 
         if !removed_nodes.is_empty() || !added_nodes.is_empty() {
-            let mutation = Mutation::ChildList {
+            let mutation = LazyCell::new(|| Mutation::ChildList {
                 added: Some(added_nodes),
                 removed: Some(removed_nodes.r()),
                 prev: None,
                 next: None,
-            };
+            });
             MutationObserver::queue_a_mutation_record(parent, mutation);
         }
         parent.owner_doc().remove_script_and_layout_blocker();
@@ -2405,12 +2405,12 @@ impl Node {
             ));
 
             let removed = [node];
-            let mutation = Mutation::ChildList {
+            let mutation = LazyCell::new(|| Mutation::ChildList {
                 added: None,
                 removed: Some(&removed),
                 prev: old_previous_sibling.as_deref(),
                 next: old_next_sibling.as_deref(),
-            };
+            });
             MutationObserver::queue_a_mutation_record(parent, mutation);
         }
         parent.owner_doc().remove_script_and_layout_blocker();
@@ -3072,12 +3072,12 @@ impl NodeMethods<crate::DomTypeHolder> for Node {
             reference_child,
         ));
         let removed = removed_child.map(|r| [r]);
-        let mutation = Mutation::ChildList {
+        let mutation = LazyCell::new(|| Mutation::ChildList {
             added: Some(nodes),
             removed: removed.as_ref().map(|r| &r[..]),
             prev: previous_sibling.as_deref(),
             next: reference_child,
-        };
+        });
 
         MutationObserver::queue_a_mutation_record(self, mutation);