allow functional components to return multiple VNodes (fix #8191)

[zevdg]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
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Does this PR introduce a breaking change? (check one)

• Yes
• No

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• New/updated tests are included

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Other information:

[zevdg]

fixes #8191

[ktsn]

Thanks. Can we add a test case for this?

[zevdg]

Silly me. I assumed that since vue was preliminary a Javascript project, it wouldn't have the typescript toolchain installed, and therefore wouldn't be able to test the types. I'll add a test for this to yarn test:types.

[HerringtonDarkholme]

@ktsn @LinusBorg Is this a public API ? I checked the doc here https://vuejs.org/v2/api/#render and here https://vuejs.org/v2/api/#render. But it seems nowhere mentions multiple root.

[zevdg]

The most official source I've seen on the topic has been a core team member here suggesting it as an option at #7088 (comment)

Given that articles like https://zendev.com/2018/05/07/multi-root-vue-components.html are starting to pop up, it probably ought to be added to https://vuejs.org/v2/guide/render-function.html#Functional-Components. I'm surprised it wasn't already.

[LinusBorg]

@HerringtonDarkholme It's definitely official API. It's one of the reasons functional components were created in the first place.

But looking at the current documentation, it's not mentioned (anymore?)

/cc @chrisvfritz

[chrisvfritz]

Oh, I thought I did mention it. I'll add it. 👍

[zevdg]

is there anything holding this up?

[zevdg]

poking this again, is there anything else I need to do to get this merged?

[LinusBorg]

Please be patient, we are currently wrapping up work on other core projects and will return attention back to the core repository shortly.

[zevdg]

No worries. Thanks for the update :-)

[luxalpa]

3 months later, what's holding this up?

Also this requires possible return value undefined (or null?) as far as I see, since functional components can also return nothing.