When switching between two of the same components with slot using v-else, I get a render error

[cypressious]

Version

2.6.6

Reproduction link

https://codesandbox.io/s/4l3wn6r3nx

Steps to reproduce

Check the checkbox to trigger the error

What is expected?

The value "2" should be rendered

What is actually happening?

[Vue warn]: Error in render: "TypeError: item.a is undefined"

found in

---> <HelloWorld> at /src/components/HelloWorld.vue
       <App> at /src/App.vue
         <Root>

and "1" is still being rendered.

---

I have two of the same components next to each other and switch between them using v-else.

This used to work in earlier versions of Vue but in 2.6.6 I get this unexpected render error. It appears as if component 1 is being rendered with the properties of component 2.

[LinusBorg]

Since you didn't key the two component instances, the same instance will be re-used, and that's fine in itself.

But it seems that the optimizations for (scoped) slots that we introduced in 2.6 have an unwanted side-effect here, namely that also the scoped slot is re-used / cached when the instance is "switched".

A workaround would be to add a key to at least one of the two component instances.