Ability to call rust function using js "this" and "args" using a utility trait.

[Swiiz]

Engine utility feature request
Ability to call rust function using js "this" and "args" using a utility trait.
This is often needed when creating classes.

Example code

impl Class for MyClass {
    const NAME: &'static str = "MyClass";

    fn data_constructor(
        _: &boa_engine::prelude::JsValue,
        _: &[boa_engine::prelude::JsValue],
        _: &mut boa_engine::prelude::Context,
    ) -> boa_engine::JsResult<Self> {
        Ok(Self {  })
    }

    fn init(class: &mut ClassBuilder<'_>) -> boa_engine::JsResult<()> {
        class.method(
            js_string!("myFunc"),
            0,
            NativeFunction::from_fn_ptr(|this, args, context| MyClass::my_func.call_from_js(this, args, context)));

        Ok(())
    }
}

impl MyClass {
    fn my_func(&mut self, name: String, age: u32) -> JsValue {
        println!("{name} {age}");
        JsValue::Undefined
    }
}

A basic implementation would look like:

pub trait FuncFromJs<Receiver, _Marker> {
    fn call_from_js(&self, this: &JsValue, args: &[JsValue], context: &mut Context) -> JsResult<JsValue>;
}

macro_rules! impl_funcfromjs {
    ($($i:tt $t:tt),+) => {
        #[allow(non_snake_case)]
        impl<Func, Receiver: NativeObject, $($t: TryFromJs),+> FuncFromJs<&Receiver, ($($t),+,)> for Func where Func: Fn(&Receiver, $($t),+) -> JsValue {
            fn call_from_js(&self, this: &JsValue, args: &[JsValue], context: &mut Context) -> JsResult<JsValue> {
                let ($($t),+,) = ($($t::try_from_js(&args[$i], context).unwrap()),+,);
                let _self = this.as_object().unwrap().downcast_ref::<Receiver>().unwrap();
                Ok(self(&_self, $($t),+))
            }
        }

        #[allow(non_snake_case)]
        impl<Func, Receiver: NativeObject, $($t: TryFromJs),+> FuncFromJs<&mut Receiver, ($($t),+,)> for Func where Func: Fn(&mut Receiver, $($t),+) -> JsValue {
            fn call_from_js(&self, this: &JsValue, args: &[JsValue], context: &mut Context) -> JsResult<JsValue> {
                let ($($t),+,) = ($($t::try_from_js(&args[$i], context).unwrap()),+,);
                let mut _self = this.as_object().unwrap().downcast_mut::<Receiver>().unwrap();
                Ok(self(&mut _self, $($t),+))
            }
        }
    };
}

impl_funcfromjs!(0 A);
impl_funcfromjs!(0 A, 1 B);
impl_funcfromjs!(0 A, 1 B, 2 C);
impl_funcfromjs!(0 A, 1 B, 2 C, 3 D);
impl_funcfromjs!(0 A, 1 B, 2 C, 3 D, 4 E);
impl_funcfromjs!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F);
impl_funcfromjs!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G);
impl_funcfromjs!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G, 7 H);