Fix serde support for larger ZeroNodes

Cargo.toml

@@ -5,6 +5,9 @@ license = "MIT OR Apache-2.0"
 authors = ["Dirkjan Ochtman <dirkjan@ochtman.nl>"]
 edition = "2018"
 
+[features]
+with-serde = ["serde", "serde-big-array"]
+
 [dependencies]
 ahash = "0.6.1"
 indicatif = { version = "0.15", optional = true }
@@ -13,3 +16,4 @@ ordered-float = "2.0"
 rand = { version = "0.8", features = ["small_rng"] }
 rayon = "1.5"
 serde = { version = "1.0.118", features = ["derive"], optional = true }
+serde-big-array = { version = "0.3.1", optional = true }

src/lib.rs

@@ -12,6 +12,8 @@ use rand::{Rng, SeedableRng};
 use rayon::iter::{IntoParallelRefMutIterator, ParallelIterator};
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
+#[cfg(feature = "serde")]
+use serde_big_array::big_array;
 
 /// Parameters for building the `Hnsw`
 #[derive(Default)]
@@ -622,9 +624,12 @@ struct ZeroNode {
     /// The nearest neighbors on this layer
     ///
     /// This is always kept in sorted order (near to far).
+    #[serde(with = "BigArray")]
     nearest: [PointId; M * 2],
 }
 
+big_array! { BigArray; }
+
 impl Default for ZeroNode {
     fn default() -> ZeroNode {
         ZeroNode { nearest: [PointId::invalid(); M * 2] }