[Bug] Log doesn't allow implementation of traits for non-default generic parameter

[Wodann]

Component

primitives

What version of Alloy are you on?

0.6.3

Operating System

Linux

Describe the bug

The Log generic uses a default type = LogData. This means that for any traits that are implemented for Log, the traits are only implemented for Log::<LogData>. Given that Rust does not allow implementation of external traits on external types, this prohibits people from implementing traits on the Log type when using a locally defined CustomLogData.

E.g. when trying to impl alloy_rlp::Encodable for LogData<CustomLogData> this would fail with the compiler error:

only traits defined in the current crate can be implemented for types defined outside of the crate define and implement a trait or new type instead

To solve this, the trait implementations in https://github.com/alloy-rs/core/blob/main/crates/primitives/src/log.rs#L120 should be generic; e.g. impl<LogDataT: SomeTrait> alloy_rlp::Encodable for Log<LogDataT> { .. }.

[prestwich]

without capturing log encoding semantics in primitives, how would you design SomeTrait?

[Wodann]

My proposal would be:

trait ExecutionLogData {
  fn topics(&self) -> &[B256];

  fn data(&self) -> &Bytes;
}

This should provide you with all of the information to implement the current implementations of alloy_rlp::Encodable and alloy_rlp::Decodable.

[prestwich]

The goal of parameterizing over the data is to allow replacing it with deserialized versions and dropping the serialized version.

So this might work for something like trait IntoLogData { fn into(&self) -> LogData }

[Wodann]

Yeah, a simple LogDataT: Into<LogData> would suffice too for the two rlp traits 🙂

[prestwich]

it needs a bit more complexity, as it would require RLP coding which is fallible. so it migh be something more like:

impl<T: TryInto<LogData, Error = alloy_rlp::Error>> alloy_rlp::Encodable for Log<T> { ... }
impl<T: TryInto<LogData, Error = Infallible>> alloy_rlp::Encodable for Log<T> { ... }