Adding #[wasm_bindgen] to Builder

[thorlucas]

Hi,

Is it possible to add this macro to the builder? Maybe just behind a feature flag.

Thanks,

[TedDriggs]

Is it necessary in that situation to add it to the setter methods as well?

[thorlucas]

I believe it only needs to be implemented on any methods that must be available from JavaScript.

[TedDriggs]

On the surface this sounds possible, but I have some concerns around how it will play with other features:

• Will it work with &mut self setters?
• Will it work with #[builder(setter(into))] setters, which have type parameters in their arguments?
• Will it work with the new each setters?

It's important to me that new features largely interoperate with other existing features; documentation of proc-macros is still difficult, so having too many edge cases would make the crate very hard to use.

I currently have other time commitments that prevent me from working on this, but if someone else wants to take on the implementation and testing I'll happily review the results.

[TedDriggs]

I don't see good answers to the above questions on the horizon, and don't think derive_builder can take on the test burden of making this fully supported.

That said, I also don't see as many Builder-style APIs in JS; much more often, I see APIs that take an Options plain JS object and use that to initialize the class. I might suggest using the builder for construction in Rust, but then having another function that is #[wasm_bindgen] that takes a JsObject and initializes your type from that.

One could even make a proc-macro for it, e.g. #[derive(OptionsConstructor)] - that would be able to handle the parsing of the object and mapping of its properties to fields on the target struct.

[TedDriggs]

This is now actually possible using #[builder_setter_attr(wasm_bindgen)], but you'll have to be careful not to use features that break WASM (e.g. generics, &mut self, etc.) - derive_builder will not do any testing of compatibility between the options you've chosen for your builder and additional attributes you choose to apply.