Allow bare objects to be passed to functions taking exported types

[hamza1311]

Motivation

At the moment, when calling a function exported by wasm-bindgen, there's no way to convert to Rust structs without creating a class instance of the exported wasm-bindgen type.

Calling without creating a class instance is needed in cases where a class instance cannot be created, such as when interfacing with existing code is needed.

Proposed Solution

Given the following code

#[wasm_bindgen]
pub struct Data {
    key_id: String,
    name: String,
}

#[wasm_bindgen]
pub fn do_work(data: Data) -> String {
    format!(r#"
        key_id: {}
        name: {}
    "#, data.key_id, data.name)
}

The following call should be possible

do_work({
  key_id: 'key_id',
  name: 'name',
})

See #3468 (comment)

Alternatives

Use imported types with duck typing. Type imports with duck typing don't always work though. In my case, this is shared code and I need everything to also be usable from rust

[jkomyno]

Alternative projects that integrate wasm_bindgen to support creating structs in place (i.e., what OP referred to as "duck typing") are:

• tsify
• serde_wasm_bindgen

[Liamolucko]

There's also the older issue #2645 open about this.

[daxpedda]

Closing this in favor of #2645 then.