setAtom uses stale pending on atom unmount

[dmaskasky]

Bug Description

This potentially causes atom listeners and pending unmount functions to not be called.

const store = createStore()
const a = atom(0)
const b = atom(0, (_, set, update: number) => set(a, update))
b.onMount = (setAtom) => () => setAtom(1)
const aListener = vi.fn()
store.sub(a, aListener)
const unsub = store.sub(b, () => {})
aListener.mockClear()
unsub()
expect(store.get(a)).toBe(1)
expect(aListener).toHaveBeenCalledTimes(1) // received 0

Resolved with

#2811

[dai-shi]

I thought we had a test to cover such case, but obviously there wasn't. Thanks for the catch.

Wait, it's a aListener that should be fired. No, we haven't covered this case before. Yeah, this is reasonable. It's a bug.