Preallocate property tables during deserialization (#464)

rbx_binary/src/deserializer/state.rs

@@ -295,13 +295,24 @@ impl<'db, R: Read> DeserializerState<'db, R> {
         let mut referents = vec![0; number_instances as usize];
         chunk.read_referent_array(&mut referents)?;
 
+        let prop_capacity = self
+            .deserializer
+            .database
+            .classes
+            .get(type_name.as_str())
+            .map(|class| class.default_properties.len())
+            .unwrap_or(0);
+
         // TODO: Check object_format and check for service markers if it's 1?
 
         for &referent in &referents {
             self.instances_by_ref.insert(
                 referent,
                 Instance {
-                    builder: InstanceBuilder::new(&type_name),
+                    builder: InstanceBuilder::with_property_capacity(
+                        type_name.as_str(),
+                        prop_capacity,
+                    ),
                     children: Vec::new(),
                 },
             );

rbx_dom_weak/CHANGELOG.md

@@ -93,6 +93,9 @@ where
 ### Other changes
 * Added `UstrMapExt`, a helper trait providing convenience methods `UstrMap::new` and `UstrMap::with_capacity`.
 * Added re-exports for `ustr` (a convenience function for creating `Ustr`s), `Ustr`, `UstrMap`, and `UstrSet`.
+* Added `InstanceBuilder::with_property_capacity`, which can preallocate an `InstanceBuilder`'s property table. [#464]
+
+[#464]: https://github.com/rojo-rbx/rbx-dom/pull/464
 
 ## 2.9.0 (2024-08-22)
 * Added `WeakDom::descendants` and `WeakDom::descendants_of` to support iterating through the descendants of a DOM. ([#431])

rbx_dom_weak/src/instance.rs

@@ -57,6 +57,21 @@ impl InstanceBuilder {
         }
     }
 
+    /// Create a new `InstanceBuilder` with the given ClassName and with a
+    /// property table with at least enough space for the given capacity.
+    pub fn with_property_capacity<S: Into<Ustr>>(class: S, capacity: usize) -> Self {
+        let class = class.into();
+        let name = class.to_string();
+
+        InstanceBuilder {
+            referent: Ref::new(),
+            name,
+            class,
+            properties: UstrMap::with_capacity(capacity),
+            children: Vec::new(),
+        }
+    }
+
     /// Create a new `InstanceBuilder` with all values set to empty.
     pub fn empty() -> Self {
         InstanceBuilder {

rbx_xml/src/deserializer.rs

@@ -447,7 +447,15 @@ fn deserialize_instance<R: Read>(
 
     trace!("Class {} with referent {:?}", class_name, referent);
 
-    let builder = InstanceBuilder::new(class_name);
+    let prop_capacity = state
+        .options
+        .database
+        .classes
+        .get(class_name.as_str())
+        .map(|class| class.default_properties.len())
+        .unwrap_or(0);
+
+    let builder = InstanceBuilder::with_property_capacity(class_name, prop_capacity);
     let instance_id = state.tree.insert(parent_id, builder);
 
     if let Some(referent) = referent {