children not update

[tangjinzhou]

Version

3.0.0-beta.21

Reproduction link

https://jsbin.com/kazolagosa/edit?html,output

Steps to reproduce

slot not update when use two v-if.
we can use v-else-if or key to slove it. but bring mental burden to users. hahah

What is expected?

slot update

What is actually happening?

slot not update

[tangjinzhou]

https://vue-next-template-explorer.netlify.app/#%7B%22src%22%3A%22%3Ch1%20v-if%3D%5C%22x%5C%22%3Etest1%3C%2Fh1%3E%5Cn%3Ch1%20v-if%3D%5C%22y%5C%22%3Etest2%3C%2Fh1%3E%5Cn%22%2C%22ssr%22%3Afalse%2C%22options%22%3A%7B%22mode%22%3A%22module%22%2C%22prefixIdentifiers%22%3Afalse%2C%22optimizeImports%22%3Afalse%2C%22hoistStatic%22%3Afalse%2C%22cacheHandlers%22%3Afalse%2C%22scopeId%22%3Anull%2C%22ssrCssVars%22%3A%22%7B%20color%20%7D%22%2C%22optimizeBindings%22%3Afalse%7D%7D Same key

[tangjinzhou]

@yyx990803 @HcySunYang
This is not just a key issue, even if the same key, the child node should be updated.
Like:

<span v-if="value%2 === 0" key="1">world</span>
<span v-if="value%2 !== 0" key="1">hello</span>

[HcySunYang]

To be honest, this is a wrong usage.
if the users specify the key manually, it is possible to break the block-tree assumption, should we prevent users from doing that? Or give a warning? 🤔

[tangjinzhou]

This is a very conventional way of use. If using v-if v-if is not common, but v-if v-else is a common way of using it.
Like：
https://jsbin.com/lotusikiru/edit?html,output

<span v-if="value%2 === 0" key="1">world</span>
<span v-else key="1">hello</span>

If let users understand patchFlag, this is a big mental burden（心智负担😓）.

[underfin]

Look like we need do some static analysis for same keys element and add corresponding patchFlag to it.

[yyx990803]

In Vue 3 you should never do this. There's no convincing reason to force the same key on two branches. We should throw warnings if the user tries to do this.