From d0c64d347d1b8c42af2a4d5e30a68867af871834 Mon Sep 17 00:00:00 2001
From: Thomas Delacour <thomasdelacour@Thomass-MacBook-Pro.local>
Date: Sun, 1 Sep 2019 19:43:35 -0400
Subject: [PATCH] ISSUE-23995: lazily generate unique_id for node

---
 components/script/dom/node.rs     | 29 +++++++++++++++++------------
 components/script/dom/raredata.rs |  3 +++
 tests/unit/script/size_of.rs      | 14 +++++++-------
 3 files changed, 27 insertions(+), 19 deletions(-)

diff --git a/components/script/dom/node.rs b/components/script/dom/node.rs
index 8746a30a7e0..4885d87c64b 100644
--- a/components/script/dom/node.rs
+++ b/components/script/dom/node.rs
@@ -152,8 +152,6 @@ pub struct Node {
     /// Must be sent back to the layout thread to be destroyed when this
     /// node is finalized.
     style_and_layout_data: Cell<Option<OpaqueStyleAndLayoutData>>,
-
-    unique_id: UniqueId,
 }
 
 bitflags! {
@@ -1006,7 +1004,20 @@ impl Node {
     }
 
     pub fn unique_id(&self) -> String {
-        self.unique_id.borrow().to_simple().to_string()
+        let mut rare_data = self.ensure_rare_data();
+
+        if rare_data.unique_id.is_none() {
+            let id = UniqueId::new();
+            ScriptThread::save_node_id(id.borrow().to_simple().to_string());
+            rare_data.unique_id = Some(id);
+        }
+        rare_data
+            .unique_id
+            .as_ref()
+            .unwrap()
+            .borrow()
+            .to_simple()
+            .to_string()
     }
 
     pub fn summarize(&self) -> NodeInfo {
@@ -1654,7 +1665,7 @@ impl Node {
 
     #[allow(unrooted_must_root)]
     fn new_(flags: NodeFlags, doc: Option<&Document>) -> Node {
-        let node = Node {
+        Node {
             eventtarget: EventTarget::new_inherited(),
 
             parent_node: Default::default(),
@@ -1671,13 +1682,7 @@ impl Node {
             ranges: WeakRangeVec::new(),
 
             style_and_layout_data: Cell::new(None),
-
-            unique_id: UniqueId::new(),
-        };
-
-        ScriptThread::save_node_id(node.unique_id());
-
-        node
+        }
     }
 
     // https://dom.spec.whatwg.org/#concept-node-adopt
@@ -3122,7 +3127,7 @@ impl<'a> UnbindContext<'a> {
 }
 
 /// A node's unique ID, for devtools.
-struct UniqueId {
+pub struct UniqueId {
     cell: UnsafeCell<Option<Box<Uuid>>>,
 }
 
diff --git a/components/script/dom/raredata.rs b/components/script/dom/raredata.rs
index 2372b0b89ab..8c481425982 100644
--- a/components/script/dom/raredata.rs
+++ b/components/script/dom/raredata.rs
@@ -7,6 +7,7 @@ use crate::dom::customelementregistry::{
     CustomElementDefinition, CustomElementReaction, CustomElementState,
 };
 use crate::dom::mutationobserver::RegisteredObserver;
+use crate::dom::node::UniqueId;
 use crate::dom::shadowroot::ShadowRoot;
 use std::rc::Rc;
 
@@ -22,6 +23,8 @@ pub struct NodeRareData {
     pub containing_shadow_root: Option<Dom<ShadowRoot>>,
     /// Registered observers for this node.
     pub mutation_observers: Vec<RegisteredObserver>,
+    /// Lazily-generated Unique Id for this node.
+    pub unique_id: Option<UniqueId>,
 }
 
 #[derive(Default, JSTraceable, MallocSizeOf)]
diff --git a/tests/unit/script/size_of.rs b/tests/unit/script/size_of.rs
index 1c5bcace945..4ab28494e06 100644
--- a/tests/unit/script/size_of.rs
+++ b/tests/unit/script/size_of.rs
@@ -30,10 +30,10 @@ macro_rules! sizeof_checker (
 
 // Update the sizes here
 sizeof_checker!(size_event_target, EventTarget, 56);
-sizeof_checker!(size_node, Node, 184);
-sizeof_checker!(size_element, Element, 392);
-sizeof_checker!(size_htmlelement, HTMLElement, 408);
-sizeof_checker!(size_div, HTMLDivElement, 408);
-sizeof_checker!(size_span, HTMLSpanElement, 408);
-sizeof_checker!(size_text, Text, 216);
-sizeof_checker!(size_characterdata, CharacterData, 216);
+sizeof_checker!(size_node, Node, 176);
+sizeof_checker!(size_element, Element, 384);
+sizeof_checker!(size_htmlelement, HTMLElement, 400);
+sizeof_checker!(size_div, HTMLDivElement, 400);
+sizeof_checker!(size_span, HTMLSpanElement, 400);
+sizeof_checker!(size_text, Text, 208);
+sizeof_checker!(size_characterdata, CharacterData, 208);