perf(turbopack): Implement ShrinkToFit for AutoMap (#79218)

kdy1 · mischnic · web-flow · commit 62de494f3c28 · 2025-05-15T16:48:37.000Z
### What?

Implement `ShrinkToFit` for `AutoMap`, which can be used in a `Vc`

### Why?

For consistency and to reduce max RSS

---------

Co-authored-by: Niklas Mischkulnig &lt;4586894+mischnic@users.noreply.github.com&gt;
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/turbopack/crates/turbo-tasks-auto-hash-map/Cargo.toml b/turbopack/crates/turbo-tasks-auto-hash-map/Cargo.toml
@@ -13,3 +13,4 @@ hashbrown = { workspace = true, features = ["serde"]}
 rustc-hash = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
 smallvec = { workspace = true }
+shrink-to-fit = { workspace = true, features = ["hashbrown"] }
diff --git a/turbopack/crates/turbo-tasks-auto-hash-map/src/map.rs b/turbopack/crates/turbo-tasks-auto-hash-map/src/map.rs
@@ -12,6 +12,7 @@ use serde::{
     de::{MapAccess, Visitor},
     ser::SerializeMap,
 };
+use shrink_to_fit::ShrinkToFit;
 use smallvec::SmallVec;
 
 use crate::{MAX_LIST_SIZE, MIN_HASH_SIZE};
@@ -900,6 +901,25 @@ where
     }
 }
 
+impl<K, V, H, const I: usize> ShrinkToFit for AutoMap<K, V, H, I>
+where
+    K: Eq + Hash,
+    V: Eq,
+    H: BuildHasher + Default,
+{
+    fn shrink_to_fit(&mut self) {
+        if self.len() < MIN_HASH_SIZE {
+            self.convert_to_list();
+        }
+
+        match self {
+            AutoMap::List(list) => list.shrink_to_fit(),
+            AutoMap::Map(map) => {
+                hashbrown::HashMap::shrink_to_fit(map);
+            }
+        }
+    }
+}
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/turbopack/crates/turbo-tasks-auto-hash-map/src/set.rs b/turbopack/crates/turbo-tasks-auto-hash-map/src/set.rs
@@ -6,6 +6,7 @@ use std::{
 
 use rustc_hash::FxHasher;
 use serde::{Deserialize, Serialize};
+use shrink_to_fit::ShrinkToFit;
 
 use crate::AutoMap;
 
@@ -240,6 +241,16 @@ where
     }
 }
 
+impl<K, H, const I: usize> ShrinkToFit for AutoSet<K, H, I>
+where
+    K: Eq + Hash,
+    H: BuildHasher + Default,
+{
+    fn shrink_to_fit(&mut self) {
+        self.map.shrink_to_fit();
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
