Upgrade syn, Migrate SerializeHierarchy to PathSerialize, PathDeserialize, PathIntrospect

[schmidma]

Introduced Changes

This PR upgrades the syn crate to the newest release, which included several breaking changes.

While porting our derive macros (approx_derive and serialize_hierarchy_derive), which heavily depend on syn, I came up with a newer, cleaner way to express the functionality of our path serialization -> Now called path_serde.

Instead of a single trait for all the necessary functionality, I define 3 new traits.

pub trait PathSerialize {
    fn serialize_path<S>(&self, path: &str, serializer: S) -> Result<S::Ok, Error<S::Error>>
    where
        S: Serializer;
}

pub trait PathDeserialize {
    fn deserialize_path<'de, D>(
        &mut self,
        path: &str,
        deserializer: D,
    ) -> Result<(), Error<D::Error>>
    where
        D: Deserializer<'de>;
}

pub trait PathIntrospect {
    fn get_fields() -> BTreeSet<String> {
        let mut fields = BTreeSet::default();
        Self::extend_with_fields(&mut fields, "");
        fields
    }

    fn extend_with_fields(fields: &mut BTreeSet<String>, prefix: &str);
}

All usages are subsequently adjusted to fit the new separation. Trait bounds can be more specific, and the exists(path: String) function was removed as it is duplication of a get_fields().contains(path) call.

ToDo / Known Issues

• documentation

Ideas for Next Iterations (Not This PR)

• clean up implementation of communication
• guess the bounds for generics in derive of path_serde traits
• non-leaf additional fields. This allows something like VisionTop.main.image.rbg.jpeg. Currently the conversion to rgb is implicitly done when converting to jpeg

How to Test

hopefully only compilation...
But better test the communication server with twix or fanta etc...

[knoellle]

😅

[knoellle]

LGTM