watchEffect typing does not support async callback

[mitar]

Vue version

3.5.26

Link to minimal reproduction

core/packages/reactivity/src/watch.ts

Line 47 in c68bebf

export type OnCleanup = (cleanupFn: () => void) => void

Steps to reproduce

Observe the type defined on OnCleanup which is used by:

export type WatchEffect = (onCleanup: OnCleanup) => void

Observe that the callback cannot return a promise, so async functions are not allowed by typing.

On the other hand, current documentation does use async and even "async" behavior has an important tip at the end of this section.

What is expected?

Type like:

export type WatchEffect = (onCleanup: OnCleanup) => Promise<void> | void

What is actually happening?

When type checking using eslint, it complains:

Promise returned in function argument where a void return was expected
@typescript-eslint/no-misused-promises

System Info

Any additional comments?

This has been previously reported in vuejs/composition-api#648 and based on recent comments it is still problematic.