WIP: Serde Data Format for JsValue

[jrop]

This PR provides a custom serde data format for serializing/deserializing Rust data structures into/from JsValue.

Serialization Example:

#[derive(Serialize)]
struct Test {
    int: u32,
    seq: Vec<&'static str>,
}

let test = Test {
    int: 1,
    seq: vec!["a", "b"],
};
let mut map = HashMap::new();
map.insert("int".into(), JsValue::Int(1));
map.insert(
    "seq".into(),
    JsValue::Array(vec![
        JsValue::String("a".into()),
        JsValue::String("b".into()),
    ]),
);
let expected = JsValue::Object(map);
assert_eq!(to_js_value(&test).unwrap(), expected);

Deserialization Example:

#[derive(Deserialize)]
struct Test {
    int: u32,
    seq: Vec<&'static str>,
}
// deserialization example:
let mut map = HashMap::new();
map.insert("int".into(), JsValue::Int(1));
map.insert(
    "seq".into(),
    JsValue::Array(vec![
        JsValue::String("a".into()),
        JsValue::String("b".into()),
    ]),
);
let j = JsValue::Object(map);
let expected = Test {
    int: 1,
    seq: vec!["a".to_owned(), "b".to_owned()],
};
assert_eq!(expected, from_js_value(&j).unwrap());

I've been slowly working on this for a while, and -- while it is definitely not finished yet -- I thought I would open this PR and gather early feedback. I have been wanting this for quickjs-rs in my own projects, so I'm curious to see if we can 1) get this reviewed and incorporate early feedback, 2) I can work more on the outstanding items listed below, 3) merge!

TODO:

• Cull the Error enum (initially copied from the sample serde data-format: it has more error conditions than we likely care about)
• Add more tests
• SerializeTupleStruct
• JsValue::Date
• JsValue::BigInt
• Split the implementation into a few files (right now it is in one monolithic file)
• Feature-gate serde

#10 #64

[jrop]

I took a swing at serde implementations for JsValue::Date, and I think the only way to make it work would be to create a "wrapper" type around DateTime:

1. struct QuickJsDateTime(chrono::DateTime<Utc>)
2. impl Deref (Target=DateTime<Utc>) for QuickJsDateTime
3. impl Serialize for QuickJsDateTime
4. impl Deserialize for QuickJsDateTime
5. Change JsValue::Date(DateTime<Utc>) => JsValue::Date(QuickJsDateTime)

This would still have all of the convenience, but give us the freedom to have all of the necessary trait implementations that we will need to make this work.

@theduke I would appreciate your feedback on this conjecture!

[semirix]

@theduke @jrop Any news on this? I would really benefit from this functionality being merged.

[jrop]

@semirix I have not spent anymore time on this for various reasons. 1) I would like @theduke to weigh in if this PR looks good so far and if my proposed changes going forward are acceptable before I spend more time on this (Some of the changes I proposed introduce potential API breakage). 2) I have been short on time as of late, due to other responsibilities.

I agree that I would love to have this integrated. It would be very useful.