Functional component not rendering named slot (following #8871)

Version

2.5.17

Reproduction link

https://codesandbox.io/s/p9mx85qpz0

Steps to reproduce

nothing in particular.

What is expected?

It should display Hello World

What is actually happening?

It displays Hello

---

Following https://github.com/vuejs/vue/issues/8871 I made App.vue non-functional:

If you make Child.vue non-functional it works: https://codesandbox.io/s/pw5lzx2w90

If you use default (not named) slots it works: https://codesandbox.io/s/04jrp3y4ln

[murr4y]

Responded on the Vue Forum as well, is this maybe the same issue as in #7587?

It works by using a scoped slot: https://codesandbox.io/s/0p96w8o1pw

[posva]

In this specific scenario, the Parent component should be written like this:

  render(h, context) {
    context.data.scopedSlots = {
      username: () => h('span', {}, 'World')
    }
    return h(Child, context.data, [])
  },

I think we may need to adapt the functional component to allow passing a child with a slot attribute:

  render(h, context) {
    context.data.scopedSlots = {
      username: () => h('span', {}, 'World')
    }
    return h(Child, context.data, [
      h('span', { slot: 'username' }, 'World')
    ])
  },

@nickmessing I imagine the jsx plugin transforms into this because it has no way of knowing if Child is functional or not