Default slot content should not be evaluated when the parent is providing it

[Rolanddoda]

Version

2.6.10

Reproduction link

https://codesandbox.io/s/kk445knpx3

Steps to reproduce

In the Child.vue we have a slot with a default slot content. In the Parent.vue we override the default content of the child.

What is expected?

IMO the content of the slot in child component should not be evaluated since the content provided from the parent will be used.

What is actually happening?

The content of the parent it renders which is what I expect.

The default content of the Child.vue it's evaluated even if it not renders. That's why you see in the console: Cannot read property 'length' of null

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Maybe that's not a bug and instead it's the intentional behavior, but it doesn't make sense to me, to evaluate something that will not render.

[posva]

I would say this is a bug as we should be able to pass a function to the slot function (_t) so the default slot content is only evaluated if no slot is provided.

I thought a workaround would be using a v-for to make it lazy, but it doesn't work

[Rolanddoda]

Thanks for the quick response @posva .