v-once on template with only text children inside a v-for does not work

[xiangyuecn]

Version

2.6.10

Reproduction link

https://codepen.io/xiangyuecn/pen/eYmmPNP

Steps to reproduce

1. Look at the test code running interface. OnceMsg area should have been static, but it is not!
2. Look at the Test 3 part of the test code. It's exactly the same as the Test 2 part, but their performance is not the same.
3. Similar to this kind of code, they are the same, but the results are different:

<div>
	<template v-once>[{{ getTime() }}] {{ name }}</template>
	<span v-once>[{{ getTime() }}] {{ name }}</span>
</div>

<div v-for="obj,idx in logs" :key="idx">
	<div>
		<template v-once>[{{ getTime() }}] {{ obj.msg }}</template>
		<span v-once>[{{ getTime() }}] {{ obj.msg }}</span>
	</div>
</div>

Use <template v-once> because I don't want to use more than one span, which will damage the DOM structure.

What is expected?

<template v-once> in v-for should be consistent with <template v-once> not in v-for, OnceMsg area should have been static.

What is actually happening?

<template v-once> in v-for and <template v-once> not in v-for are inconsistent, The leftmost time of OnceMsg area will change with the cycle.

[posva]

Seems to be a duplicate of #8021 with PR at #8499

[xiangyuecn]

@posva You may not understand the difference between this question and #8021. When I submitted this question, I have studied 8021. 8021 has no substantive relationship with my question.

I have done the code test of clone #8499 PR, which has fixed the 8021 problem, but this PR has no effect on my problem.

---

Please pay special attention: My question is v-once of template node tag, 8021 is the v-once of component template text.

My problem can be solved by setting a layer of tag(e.g:span、div) for developers, and 8021 component structure can't handle it like this.

Please compare the difference between Test 3 and Test 4 in my test code.

---

I found that there is no issue in the issues list that is the same as the issue I found. If you understand the issue I said clearly, please open the issue, or give the reason why it can't be opened again.

[xiangyuecn]

@posva Oh man, you changed my title. But I found that you didn't write it. Refer to my test code Test 5.

${/*Test 5:Non text only children are working, but may not*/""}
<span>
  <template v-once>[{{ getTime() }}] <span>{{ obj.msg }}</span></template> ${/*It works*/""}
  <span>Other</span>
  <template v-once>[{{ getTime() }}] <span>{{ obj.msg }}</span></template> ${/*It doesn't work*/""}
  <span>Other</span>
</span>

Please change the title again.