[@vue/runtime-core] Child component setup() does not update parent state

[Jexordexan]

Version

3.0.0-alpha.7

Reproduction link

https://codesandbox.io/s/vue-3-reactive-error-spk7o

Steps to reproduce

Create some reactive state in setup() and render it
Allow a child component to access the state (I used provide/inject, but this could be a global store)
Child changes state in its setup()
Observe the state in the parent doesn't update until the next change

What is expected?

The parent reacts and shows the state

What is actually happening?

The state in the parent doesn't display change made by child component

---

I did some digging and found the cause of the bug. Basically the child's setup() is running within the renderEffect of the parent, and the renderEffect never re-runs after changes are made. There is some logic in the addRunners function that skips adding the activeEffect to be run.

This is functionally the same as:

const data = reactive([])

const childSetup = () => data.push('update')

effect(() => {
  console.log(data.length) // --> 0
  childSetup() // changes state internally, effect never re-runs
})

I realize now that I'm changing state within an "effect" that is dependent on that state, which is a bad idea! I was just confused by the level of abstraction away from whats going on. So I'm not sure it is really a bug, but its something I was not expecting and felt broken.