New lint: js_sys::Promise returning functions should be must_use

[silvanshade]

It seems that functions and methods which return js_sys::Promise (e.g., when creating bindings with wasm-bindgen) should probably always be marked as #[must_use]. If you invoke something which returns a Promise and then just discard it, the computation does nothing.

In order to do something useful you either have to pass the resulting Promise on to some other JS computation or convert it to a JsFuture and .await it in some async context.

There could be a lint which suggests that #[must_use] should be added for these cases to remind the user to consume the Promise.

Does this sound like something that would be appropriate as a clippy lint?

[ghost]

Why not just apply #[must_use] to js_sys::Promise?

[silvanshade]

Oh I didn’t realize you could apply #[must_use] directly to types. If that works it would be a better solution.