1 files changed, 101 insertions, 0 deletions
diff --git a/third_party/rust/slab/src/serde.rs b/third_party/rust/slab/src/serde.rs
new file mode 100644
index 0000000000..7ffe8e0da3
--- /dev/null
+++ b/third_party/rust/slab/src/serde.rs
@@ -0,0 +1,101 @@
+use core::fmt;
+use core::marker::PhantomData;
+
+use serde::de::{Deserialize, Deserializer, MapAccess, Visitor};
+use serde::ser::{Serialize, SerializeMap, Serializer};
+
+use super::{Entry, Slab};
+
+impl<T> Serialize for Slab<T>
+where
+    T: Serialize,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let mut map_serializer = serializer.serialize_map(Some(self.len()))?;
+        for (key, value) in self {
+            map_serializer.serialize_key(&key)?;
+            map_serializer.serialize_value(value)?;
+        }
+        map_serializer.end()
+    }
+}
+
+struct SlabVisitor<T>(PhantomData<T>);
+
+impl<'de, T> Visitor<'de> for SlabVisitor<T>
+where
+    T: Deserialize<'de>,
+{
+    type Value = Slab<T>;
+
+    fn expecting(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "a map")
+    }
+
+    fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+    where
+        A: MapAccess<'de>,
+    {
+        let mut slab = Slab::with_capacity(map.size_hint().unwrap_or(0));
+
+        // same as FromIterator impl
+        let mut vacant_list_broken = false;
+        let mut first_vacant_index = None;
+        while let Some((key, value)) = map.next_entry()? {
+            if key < slab.entries.len() {
+                // iterator is not sorted, might need to recreate vacant list
+                if let Entry::Vacant(_) = slab.entries[key] {
+                    vacant_list_broken = true;
+                    slab.len += 1;
+                }
+                // if an element with this key already exists, replace it.
+                // This is consistent with HashMap and BtreeMap
+                slab.entries[key] = Entry::Occupied(value);
+            } else {
+                if first_vacant_index.is_none() && slab.entries.len() < key {
+                    first_vacant_index = Some(slab.entries.len());
+                }
+                // insert holes as necessary
+                while slab.entries.len() < key {
+                    // add the entry to the start of the vacant list
+                    let next = slab.next;
+                    slab.next = slab.entries.len();
+                    slab.entries.push(Entry::Vacant(next));
+                }
+                slab.entries.push(Entry::Occupied(value));
+                slab.len += 1;
+            }
+        }
+        if slab.len == slab.entries.len() {
+            // no vacant entries, so next might not have been updated
+            slab.next = slab.entries.len();
+        } else if vacant_list_broken {
+            slab.recreate_vacant_list();
+        } else if let Some(first_vacant_index) = first_vacant_index {
+            let next = slab.entries.len();
+            match &mut slab.entries[first_vacant_index] {
+                Entry::Vacant(n) => *n = next,
+                _ => unreachable!(),
+            }
+        } else {
+            unreachable!()
+        }
+
+        Ok(slab)
+    }
+}
+
+impl<'de, T> Deserialize<'de> for Slab<T>
+where
+    T: Deserialize<'de>,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_map(SlabVisitor(PhantomData))
+    }
+}