:key placed in <template> with one element is not used

[ota-meshi]

Version

3.0.0-rc.6

Reproduction link

DEMO on Vue3 template explorer

Steps to reproduce

Check the compilation results of Case2 and Case4.

<div>
  <!-- Case1 -- The key is attached to _Fragment.-->
  <template v-for="item in list" :key="item.id1">
    <MyButton :foo="item">One</MyButton>
    <MyButton :foo="item">Two</MyButton>
  </template>
  <!-- Case2 -- The key is not attached to _Fragment. -->
  <template v-for="item in list" :key="item.id2">
    <MyButton :foo="item">One</MyButton>
  </template>
  <!-- Case3 -- The key is attached to div. -->
  <div v-for="item in list" :key="item.id3">
    <MyButton :foo="item">One</MyButton>
  </div>
  <!-- Case4 -- The key is not attached to _Fragment. -->
  <template v-for="item in list" :key="item.id4">
    <div>
      <MyButton :foo="item">One</MyButton>
    </div>
  </template>
</div>

What is expected?

I expected {key: item.id2} and {key: item.id4} to be attached somewhere.

What is actually happening?

{key: item.id2} and {key: item.id4} are not attached anywhere.

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• Console warning when using a v-if on an element inside a v-for on a template #1734 (comment)