fix(reactivity): assigning array.length while observing a symbol property

[skirtles-code]

Example 1: SFC Playground

<script setup>
import { reactive } from 'vue'

const s = Symbol()
const a = reactive([1])

setTimeout(() => {
  a.length = 0
}, 100)
</script>

<template>
  {{ a }} {{ a[s] }}
</template>

Chrome:

Uncaught TypeError: Cannot convert a Symbol value to a number

Firefox:

Uncaught TypeError: can't convert symbol to number

Assigning the length of a reactive array will trigger this error if we are also observing a symbol-keyed property on the same array. The logic for assigning the length iterates through all observed properties, but doesn't take into account the possibility that a key could be a symbol.

This can also be triggered by pop(), shift() and splice(), which set the length internally.

I originally encountered this problem in a question on Vue Land, where somebody was using the stringify function from yaml. That function checks for a special symbol as part of the conversion process. Just checking for the symbol is enough to add a dependency, it doesn't matter whether the property exists:

Example 2: SFC Playground

---

The same examples using the deploy preview of this PR:

• Example 1
• Example 2

[yingpengsha]

I need this change, but no one seems to care except us.

[nawbc]

@yyx990803 cc

[yisar]

@yyx990803 cc

[yingpengsha]

Hi, Evan @yyx990803
The reason I need this change is that I am trying to apply @vue/reactivity to solid-js using the enableExternalSource of solid-js. At the same time, I think this change will not bring too many side effects. I hope this change can be approved.

[yingpengsha]

@sxzz PTAL

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	85.9 kB (+7 B)	32.7 kB (+3 B)	29.5 kB (+16 B)
vue.global.prod.js	132 kB (+7 B)	49.4 kB (+2 B)	44.3 kB (-30 B)

Usages

Name	Size	Gzip	Brotli
createApp	47.9 kB (+7 B)	18.9 kB (+6 B)	17.2 kB (+33 B)
createSSRApp	50.7 kB (+7 B)	20 kB (+5 B)	18.2 kB (-2 B)
defineCustomElement	50.3 kB (+7 B)	19.6 kB (+3 B)	17.9 kB (-24 B)
overall	61.2 kB (+7 B)	23.7 kB (+2 B)	21.5 kB (-6 B)