fix invalid source maps on HMR

turbopack/crates/turbo-tasks-fs/src/rope.rs

@@ -372,6 +372,22 @@ pub mod ser_as_string {
     }
 }
 
+pub mod ser_option_as_string {
+    use serde::{ser::Error, Serializer};
+
+    use super::Rope;
+
+    /// Serializes a Rope into a string.
+    pub fn serialize<S: Serializer>(rope: &Option<Rope>, serializer: S) -> Result<S::Ok, S::Error> {
+        if let Some(rope) = rope {
+            let s = rope.to_str().map_err(Error::custom)?;
+            serializer.serialize_some(&s)
+        } else {
+            serializer.serialize_none()
+        }
+    }
+}
+
 impl PartialEq for Rope {
     // Ropes with similar contents are equals, regardless of their structure.
     fn eq(&self, other: &Self) -> bool {

turbopack/crates/turbopack-browser/src/ecmascript/merged/update.rs

@@ -77,25 +77,25 @@ struct EcmascriptModuleEntry {
     #[serde(with = "turbo_tasks_fs::rope::ser_as_string")]
     code: Rope,
     url: String,
-    map: Option<String>,
+    #[serde(with = "turbo_tasks_fs::rope::ser_option_as_string")]
+    map: Option<Rope>,
 }
 
 impl EcmascriptModuleEntry {
     async fn from_code(id: &ModuleId, code: Vc<Code>, chunk_path: &str) -> Result<Self> {
         let map = match &*code.generate_source_map().await? {
             Some(map) => {
-                let map = map.await?.to_source_map().await?;
-                let mut map_str = vec![];
-                (*map).to_writer(&mut map_str)?;
-                Some(String::from_utf8(map_str)?)
+                let map = map.to_rope().await?;
+                // Cloning a rope is cheap.
+                Some(map.clone_value())
             }
             None => None,
         };
 
         Ok(Self::new(id, code.await?, map, chunk_path))
     }
 
-    fn new(id: &ModuleId, code: ReadRef<Code>, map: Option<String>, chunk_path: &str) -> Self {
+    fn new(id: &ModuleId, code: ReadRef<Code>, map: Option<Rope>, chunk_path: &str) -> Self {
         /// serde_qs can't serialize a lone enum when it's [serde::untagged].
         #[derive(Serialize)]
         struct Id<'a> {