Generated wasmBindings initialization doesn't expect exceptions

[egor-ryashin]

During the build process the following code is generated in html file:

<script type="module">
import init, * as bindings from '/bevy-demo-58cf2fdc11fbdbe3.js';
const wasm = await init({ module_or_path: '/bevy-demo-58cf2fdc11fbdbe3_bg.wasm' });


window.wasmBindings = bindings;


dispatchEvent(new CustomEvent("TrunkApplicationStarted", {detail: {wasm}}));

</script>

But the init method can throw exceptions which breaks wasmBindings initialization. It's common to think that an exception itself means a broken state that shouldn't be used further but actually some libraries think throwing exception does mean a successful initialization:

(index):136 Error stack: Error: Using exceptions for control flow, don't mind me. This isn't actually an error!
    at imports.wbg.__wbindgen_throw (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32.js:1708:15)
    at bevy_demo.wasm.wasm_bindgen::throw_str::hf2c30ede6cf4503f (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32_bg.wasm:wasm-function[86081]:0x197660f)
    at bevy_demo.wasm.winit::platform_impl::web::web_sys::throw::hb0947f5ee7e3478c (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32_bg.wasm:wasm-function[84214]:0x196dae3)
    at bevy_demo.wasm.winit::platform_impl::web::event_loop::EventLoop<T>::run::ha55cc005230eefa7 (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32_bg.wasm:wasm-function[35226]:0x1765908)
    at bevy_demo.wasm.bevy_winit::state::winit_runner::h0a8699fee68b727a (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32_bg.wasm:wasm-function[2126]:0x80769e)
    at bevy_demo.wasm.core::ops::function::FnOnce::call_once{{vtable.shim}}::h0bf45ed5d82b2040 (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32_bg.wasm:wasm-function[48332]:0x1891bd7)
    at bevy_demo.wasm.bevy_app::app::App::run::h54dc5d2aa39ddf98 (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32_bg.wasm:wasm-function[10409]:0xffe335)
    at bevy_demo.wasm.bevy_demo::main::hfc3b979dc39b6105 (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32_bg.wasm:wasm-function[1706]:0x709ea4)
    at bevy_demo.wasm.main (http://127.0.0.1:7701/bevy-demo-aa55efd8f2bb1a32_bg.wasm:wasm-function[45805]:0x186d0da)

Anyway, I think without catching that exception properly that library keeps wasmBindings uninitialized.

Updated. This code generates the exception: https://github.com/rust-windowing/winit/blob/2486f0f1a1d00ac9e5936a5222b2cfe90ceeca02/src/platform_impl/web/event_loop/mod.rs#L41

[ctron]

It's common to think that an exception itself means a broken state that shouldn't be used further but actually some libraries think throwing exception does mean a successful initialization:

True indeed. I am not sure what to do here. Throwing an exception in the init method basically means that we don't know the state. Assuming "all good" seems wrong.

I think what could be done is to move the assignment up (before the init call). Catch the exception, and dispatch a different event (TrunkApplicationStartupFailed). So the user could deal with this.