Support defining getters in Rust

[alexcrichton]

Currently when you export a struct in Rust to JS it only exports public methods, but we should enable the ability to define getters and setters for properties too, for example:

#[wasm_bindgen]
struct Foo { /* ... */ }

#[wasm_bindgen]
impl Foo {
    pub fn new() -> Foo { ... }

    #[wasm_bindgen(getter)]
    pub fn field1(&self) -> u32 { ... }
    #[wasm_bindgen(setter)]
    pub fn set_field1(&mut self, f: u32) { ... }

    #[wasm_bindgen(getter = anotherName)]
    pub fn another_name(&self) { ... }
    #[wasm_bindgen(setter = anotherName)]
    pub fn set_another_name(&mut self, param: u32) { ... }
}

[dtysky]

Any updating?

[alexcrichton]

None yet, but would still be great to implement!

[c410-f3r]

I will work on it. Any tips for this issue, @alexcrichton ?

[alexcrichton]

Sure! I think a rough set of steps for implementing this would be:

1. Update the shared definition of Export between the macro and the CLI. We probably want to delete the is_constructor field and instead include kind: MethodKind<'a>.
2. Next we'll need to update the macro codegen to produce this. An Export is produced here.
3. That'll require updating ast::Export defined here. How that's represented internally I'm not sure, but adding some more booleans is fine.
4. Instances of ast::Export are parsed and constructed here which is where you'd add the attribute parsing code. You'd modify this macro to parse the new attributes.
5. After all that's working you'd need to update the CLI. You'll naturally get compile errors for generating information since the structure of shared::Export changed. I think for this you'd basically follow the rabbit hole of compiler errors and once they're all ironed out in theory it's a working implementation

If you've got any questions though let me know!

[c410-f3r]

@alexcrichton Oh, this is plenty. Thanks!