[WIP] Implement EIP-7495: StableContainer

ssz/Cargo.toml

@@ -14,7 +14,7 @@ categories = ["cryptography::cryptocurrencies"]
 name = "ssz"
 
 [dev-dependencies]
-ethereum_ssz_derive = { version = "0.5.4", path = "../ssz_derive" }
+ethereum_ssz_derive = { path = "../ssz_derive" }
 
 [dependencies]
 ethereum-types = "0.14.1"

ssz/src/decode/impls.rs

@@ -249,14 +249,18 @@ impl Decode for NonZeroUsize {
 
 impl<T: Decode> Decode for Option<T> {
     fn is_ssz_fixed_len() -> bool {
-        false
+        T::is_ssz_fixed_len()
     }
+
+    fn ssz_fixed_len() -> usize {
+        T::ssz_fixed_len()
+    }
+
     fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
-        let (selector, body) = split_union_bytes(bytes)?;
-        match selector.into() {
-            0u8 => Ok(None),
-            1u8 => <T as Decode>::from_ssz_bytes(body).map(Option::Some),
-            other => Err(DecodeError::UnionSelectorInvalid(other)),
+        if bytes.is_empty() {
+            Ok(None)
+        } else {
+            T::from_ssz_bytes(bytes).map(Some)
         }
     }
 }

ssz/src/encode/impls.rs

@@ -206,28 +206,28 @@ impl_encode_for_tuples! {
 
 impl<T: Encode> Encode for Option<T> {
     fn is_ssz_fixed_len() -> bool {
-        false
+        T::is_ssz_fixed_len()
+    }
+
+    fn ssz_fixed_len() -> usize {
+        T::ssz_fixed_len()
     }
+
     fn ssz_append(&self, buf: &mut Vec<u8>) {
-        match self {
-            Option::None => {
-                let union_selector: u8 = 0u8;
-                buf.push(union_selector);
-            }
-            Option::Some(ref inner) => {
-                let union_selector: u8 = 1u8;
-                buf.push(union_selector);
-                inner.ssz_append(buf);
+        match &self {
+            None => {}
+            Some(_) => {
+                if let Some(inner) = self.as_ref() {
+                    inner.ssz_append(buf);
+                }
             }
         }
     }
+
     fn ssz_bytes_len(&self) -> usize {
-        match self {
-            Option::None => 1usize,
-            Option::Some(ref inner) => inner
-                .ssz_bytes_len()
-                .checked_add(1)
-                .expect("encoded length must be less than usize::max_value"),
+        match &self {
+            None => 0,
+            Some(inner) => inner.ssz_bytes_len(),
         }
     }
 }
@@ -607,9 +607,9 @@ mod tests {
     #[test]
     fn ssz_encode_option_u8() {
         let opt: Option<u8> = None;
-        assert_eq!(opt.as_ssz_bytes(), vec![0]);
+        assert_eq!(opt.as_ssz_bytes(), vec![]);
         let opt: Option<u8> = Some(2);
-        assert_eq!(opt.as_ssz_bytes(), vec![1, 2]);
+        assert_eq!(opt.as_ssz_bytes(), vec![2]);
     }
 
     #[test]

ssz/tests/tests.rs

@@ -57,7 +57,9 @@ mod round_trip {
     fn option_vec_h256() {
         let items: Vec<Option<Vec<H256>>> = vec![
             None,
-            Some(vec![]),
+            // Some(vec![]) serializes the same as None so it is impossible to differentiate them.
+            // Is this a bug?
+            Some(vec![H256::zero()]),
             Some(vec![H256::zero(), H256::from([1; 32]), H256::random()]),
         ];
 

ssz_derive/Cargo.toml

@@ -19,6 +19,7 @@ syn = "1.0.42"
 proc-macro2 = "1.0.23"
 quote = "1.0.7"
 darling = "0.13.0"
+ssz_types = { git = "https://github.com/macladson/ssz_types", branch = "stable-container" }
 
 [dev-dependencies]
-ethereum_ssz = { path = "../ssz" }
+ethereum_ssz = { git = "https://github.com/macladson/ethereum_ssz", branch = "stable-container" }