reactive __proto__ will broken reactive system

[xinpingwang]

Version

3.0.0-beta.7

Reproduction link

https://github.com/xinpingwang/vue-next/tree/reactive-proto

Steps to reproduce

1. git clone https://github.com/xinpingwang/vue-next.git -b reactive-proto
2. yarn install && yarn run test reactivity

What is expected?

all test pass

What is actually happening?

reactive.spec failed

---

when read a prop of a reactive object, the reactive system will reactive object[prop] too. and add ReactiveFlags.reactive(eg: __v_reactive) to object[prop], see. then, when next call to reactive object[prop], object[prop].__v_reactive will returned.

when this prop is __proto__, the ReactiveFlags.reactive will add to Object, then reactive all object will returen Object.__proto__.__v_reactive

this issue is caused by the new commit: refactor(reactivity): use more efficient reactive checks

solutions to solve this issue may be add __proto__ to reactive black list or check isReactive before return.

[sionzee]

This should be deployed ASAP, beta7 is unusable because of this.
I have got thousands errors.

In meantime downgraded to beta6.