v-model compiling fails when used with functional components

[miljan-aleksic]

Version

15.7.0

Reproduction link

https://codesandbox.io/s/r58jr04jlo

Steps to reproduce

Click on the checkbox.

What is expected?

The checkbox should be selected without throwing js errors.

What is actually happening?

It's issuing an error becasue the compiled js code assumes it's a stateful component and tries to use _vm.$set().

[posva]

Marking as both as I don't know if this was intended to work in the first place

[yyx990803]

While I think this should technically work, I strongly suggest staying away from such usage.

1. Functional component being able to mutate parent state is very implicit and not a good pattern.

2. <template functional> is likely going away in v3. (See Functional and async components API change rfcs#27)

I'll close this as a wontfix.