Implement Serialize/Deserialize for ActionStage (TraceMachina#1186)

Implements Serialize/Deserialize for ActionStage to allow for storage
and retrieval from stores such as Redis.

towards: TraceMachina#1182

nativelink-error/src/lib.rs

@@ -441,3 +441,17 @@ impl From<Code> for std::io::ErrorKind {
         }
     }
 }
+
+// Allows for mapping this type into a generic serialization error.
+impl serde::ser::Error for Error {
+    fn custom<T: std::fmt::Display>(msg: T) -> Self {
+        Self::new(Code::InvalidArgument, msg.to_string())
+    }
+}
+
+// Allows for mapping this type into a generic deserialization error.
+impl serde::de::Error for Error {
+    fn custom<T: std::fmt::Display>(msg: T) -> Self {
+        Self::new(Code::InvalidArgument, msg.to_string())
+    }
+}

nativelink-util/src/action_messages.rs

@@ -29,6 +29,7 @@ use nativelink_proto::google::rpc::Status;
 use prost::bytes::Bytes;
 use prost::Message;
 use prost_types::Any;
+use serde::ser::Error as SerdeError;
 use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
@@ -746,7 +747,7 @@ impl Default for ActionResult {
 // TODO(allada) Remove the need for clippy argument by making the ActionResult and ProtoActionResult
 // a Box.
 /// The execution status/stage. This should match `ExecutionStage::Value` in `remote_execution.proto`.
-#[derive(PartialEq, Debug, Clone)]
+#[derive(PartialEq, Debug, Clone, Serialize, Deserialize)]
 #[allow(clippy::large_enum_variant)]
 pub enum ActionStage {
     /// Stage is unknown.
@@ -762,9 +763,22 @@ pub enum ActionStage {
     /// Worker completed the work with result.
     Completed(ActionResult),
     /// Result was found from cache, don't decode the proto just to re-encode it.
+    #[serde(serialize_with = "serialize_proto_result", skip_deserializing)]
+    // The serialization step decodes this to an ActionResult which is serializable.
+    // Since it will always be serialized as an ActionResult, we do not need to support
+    // deserialization on this type at all.
+    // In theory, serializing this should never happen so performance shouldn't be affected.
     CompletedFromCache(ProtoActionResult),
 }
 
+fn serialize_proto_result<S>(v: &ProtoActionResult, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: serde::Serializer,
+{
+    let s = ActionResult::try_from(v.clone()).map_err(S::Error::custom)?;
+    s.serialize(serializer)
+}
+
 impl ActionStage {
     pub const fn has_action_result(&self) -> bool {
         match self {
@@ -1075,7 +1089,7 @@ where
 
 /// Current state of the action.
 /// This must be 100% compatible with `Operation` in `google/longrunning/operations.proto`.
-#[derive(PartialEq, Debug, Clone)]
+#[derive(PartialEq, Debug, Clone, Serialize, Deserialize)]
 pub struct ActionState {
     pub stage: ActionStage,
     pub id: OperationId,