How to rename inner types when encoding/decoding foreign structs using serde?

[yizhepku]

Suppose I have a Rust struct like this:

#[derive(Serialize, Deserialize)]
#[serde(rename = "Elixir.MyPackage.Event")]
struct Event {
    name: String,
    duration: std::time::Duration,
}

And we create an instance like this:

Event { name: "foo".to_string(), duration: std::time::Duration::from_secs(10) }

Currently, rustler will convert it to this:

%{
  :__struct__ => MyPackage.Event,
  :name => "foo",
  :duration => %{:__struct__ => "Duration", "nanos" => 0, "secs" => 10}
}

Is there a way to map std::time::Duration to Elixir.MyPackage.Duration instead?

[yizhepku]

I got it working with a simple hack in src/serde/ser.rs:

fn serialize_struct(
    self,
    name: &'static str,
    len: usize,
) -> Result<Self::SerializeStruct, Self::Error> {
    let name = format!("Elixir.MyPackage.{name}"); // <---- SUPER HACK
    let name_term = util::str_to_term(&self.env, &name).or(Err(Error::InvalidStructName))?;
    Ok(MapSerializer::new(self, Some(len), Some(name_term)))
}

Do the same for src/serde/de.rs:

#[inline]
fn deserialize_struct<V>(
    self,
    name: &'static str,
    _fields: &'static [&'static str],
    visitor: V,
) -> Result<V::Value, Self::Error>
where
    V: Visitor<'de>,
{
    let name = format!("Elixir.Temporex.Core.{name}"); // <---- SUPER HACK
    let struct_name_term = util::validate_struct(&self.term, Some(&name))?;
    let iter = MapIterator::new(self.term).ok_or(Error::ExpectedStruct)?;
    visitor.visit_map(MapDeserializer::new(iter, Some(struct_name_term)))
}

With this hack, I also don't need #[serde(rename="...")] anymore. Perhaps it's useful as a general feature?