Returning a struct from a closure results in "__wrap is not a function" on that struct

[jacobgardner]

I'm on wasm-bindgen@0.2.31 and getting "__wrap is not a function" when calling a closure which returns a struct that is not used anywhere else.

Here's the smallest example of the bug, I could make:

type ClosureType = FnMut() -> BadStruct;

#[wasm_bindgen]
pub struct ClosureHandle(Closure<ClosureType>);

#[wasm_bindgen]
pub struct BadStruct {}

#[wasm_bindgen]
pub fn closure_returner() -> Result<Object, JsValue> {
    let o = Object::new();

    let some_fn = Closure::wrap(Box::new(move || BadStruct {}) as Box<ClosureType>);
    Reflect::set(
        &o,
        &JsValue::from("someKey"),
        &some_fn.as_ref().unchecked_ref(),
    )
    .map_err(|_| "Unable to set property")?;
    Reflect::set(
        &o,
        &JsValue::from("handle"),
        &JsValue::from(ClosureHandle(some_fn)),
    )
    .map_err(|_| "Unable to set closure handle")?;

    Ok(o)
}

Typescript:

import("../../lib-web/pkg").then(module => {
    const c = module.closure_returner();
    c.someKey(); // Error occurs here
});

Currently this works as a workaround:

#[wasm_bindgen]
pub fn _dont_call() -> BadStruct {
    unimplemented!();
}

Edit: Related to #949, but not exactly the same.

[alexcrichton]

Thanks for the report! This should be fixed in #1175