Version

2.6.14

Reproduction link

Slot fallback broken running in 2.6.12:
https://jsfiddle.net/hirokiosame/dotsp9ak/

Slot fallback working in 2.6.14:
https://jsfiddle.net/hirokiosame/eb16s0hx/

Steps to reproduce

1. Build the following component with vue-template-compiler v2.6.14:

<template>	<div>	test component	<slot>	- slot fallback works!	</slot>	</div> </template>

2. Run component in a Vue.js v2.6.12 app:

<template> <test-component /> </template> <script> import TestComponent from './TestComponent.js';  export default {  components: { 	TestComponent,  }, } </script>

What is expected?

For a component built with vue-template-compiler v2.6.14 to be backwards compatible with a Vue.js v2.6.12 runtime.

It's not only no longer working, it actually displays "undefined" in place of the slot fallback.

Since there is no new feature being leveraged, I think it's expected for behavior to be preserved.

What is actually happening?

Slot fallback not working in component built with vue-template-compiler v2.6.14, but running in a Vue.js 2.6.12 app