Failed to execute 'insertBefore' on 'Node' with v-else

[cexbrayat]

Version

3.0.0-alpha.2

Reproduction link

https://github.com/chz/vue-next-test

Steps to reproduce

Add a component with:

<input id="role-input" v-model="user.role" />
<div id="else">
      <div v-if="user.role === 'ADMIN'">
        <h2>Admin</h2>
      </div>
      <div v-else>
        <h2 id="hello">Hello</h2>
      </div>
      <div id="other">other</div>
</div>

import { defineComponent, reactive } from 'vue';

export default defineComponent({
  name: 'VElse',
  setup() {
    return {
      user: reactive({
        role: 'ADMIN',
        name: 'Cédric'
      })
  }
});

then enter a different value in the input

What is expected?

The v-else node should be inserted

What is actually happening?

A error is thrown:

DOMException: Failed to execute 'insertBefore' on 'Node': The node before which the new node is to be inserted is not a child of this node.
    at insert (webpack-internal:///./node_modules/@vue/runtime-dom/dist/runtime-dom.esm-bundler.js:175:20)
    at mountElement (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:2002:9)
    at processElement (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:1955:13)
    at patch (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:1920:21)
    at patchBlockChildren (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:2125:13)
    at patchElement (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:2091:13)
    at processElement (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:1958:13)
    at patch (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:1920:21)
    at componentEffect (webpack-internal:///./node_modules/@vue/runtime-core/dist/runtime-core.esm-bundler.js:2387:17)
    at run (webpack-internal:///./node_modules/@vue/reactivity/dist/reactivity.esm-bundler.js:115:20)

---

This is very similar than #604 that should have been fixed in alpha.2.
Replacing fallbackContainer by hostParentNode(oldVNode.el) in patchBlockChildren does fix the issue, so the condition is still not perfect.