Improve the Cow

crates/bevy_reflect/src/serde/de.rs

@@ -211,6 +211,13 @@ impl<'de> Visitor<'de> for U32Visitor {
     }
 }
 
+/// Helper struct for deserializing strings without allocating (when possible).
+///
+/// Based on [this comment](https://github.com/bevyengine/bevy/pull/6894#discussion_r1045069010).
+#[derive(Deserialize)]
+#[serde(transparent)]
+struct BorrowableCowStr<'a>(#[serde(borrow)] Cow<'a, str>);
+
 /// A general purpose deserializer for reflected types.
 ///
 /// This will return a [`Box<dyn Reflect>`] containing the deserialized data.
@@ -274,8 +281,9 @@ impl<'a, 'de> Visitor<'de> for UntypedReflectDeserializerVisitor<'a> {
         A: MapAccess<'de>,
     {
         let type_name = map
-            .next_key::<Cow<'de, str>>()?
-            .ok_or_else(|| Error::invalid_length(0, &"at least one entry"))?;
+            .next_key::<BorrowableCowStr>()?
+            .ok_or_else(|| Error::invalid_length(0, &"at least one entry"))?
+            .0;
 
         let registration = self.registry.get_with_name(&type_name).ok_or_else(|| {
             Error::custom(format_args!("No registration found for `{type_name}`"))

crates/bevy_scene/src/serde.rs

@@ -353,7 +353,7 @@ impl<'a, 'de> Visitor<'de> for ComponentVisitor<'a> {
     {
         let mut added = HashSet::new();
         let mut components = Vec::new();
-        while let Some(key) = map.next_key::<Cow<'de, str>>()? {
+        while let Some(BorrowableCowStr(key)) = map.next_key()? {
             if !added.insert(key.clone()) {
                 return Err(Error::custom(format!("duplicate component: `{key}`")));
             }
@@ -385,6 +385,13 @@ impl<'a, 'de> Visitor<'de> for ComponentVisitor<'a> {
     }
 }
 
+/// Helper struct for deserializing strings without allocating (when possible).
+///
+/// Based on [this comment](https://github.com/bevyengine/bevy/pull/6894#discussion_r1045069010).
+#[derive(Deserialize)]
+#[serde(transparent)]
+struct BorrowableCowStr<'a>(#[serde(borrow)] Cow<'a, str>);
+
 #[cfg(test)]
 mod tests {
     use crate::serde::{SceneDeserializer, SceneSerializer};