New (2.6 ) slot syntax results in slots not added to vm.$slots, breaking existing render functions

[K900]

Version

2.6.1

Reproduction link

https://jsfiddle.net/3kpf9u54/4/

Steps to reproduce

1. Observe the contents of the <template> displayed
2. Change the code from <template slot="content"> to <template #content> or <template v-slot:content> and observe the contents stop being displayed
3. Change the render function code from this.$slots.content to this.$scopedSlots.content() and observe the contents be displayed again

What is expected?

Contents are displayed all the time; old render functions don't break when used with new syntax

What is actually happening?

New syntax forces slots into being scoped, breaking existing render functions

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I'm actually not sure if this is intentional or not, but it breaks Vuetify, and probably other things too. Assuming this is intentional, it makes writing functional components more difficult, as you have to either:

1. check both this.$slots (for Vue pre-2.6) and this.$scopedSlots (for Vue post-2.6)
2. only check this.$scopedSlots and ask Vue pre-2.6 users to add slot-scope everywhere so all slots become scoped
3. only check this.$slots and ask Vue post-2.6 users to use the legacy syntax

[KaelWD]

but it breaks Vuetify

We were going to release a new minor version with $slots replaced by $scopedSlots, this change breaks v-slot (and slot-scope) use with dialog and menu activators

[KaelWD]

The plan was 3 for vuetify 1.4/1.5, then release vuetify 1.6 with a minimum vue version of 2.6 so old templates would still work.

Simple codepen demonstrating the problem: https://codepen.io/anon/pen/xMLreR?editors=1010
2.6.0: https://codepen.io/anon/pen/xMLreR?editors=1010

[KaelWD]

So I found this, which I guess works for those edge cases: https://codepen.io/anon/pen/BMddNv?editors=1010

[K900]

@KaelWD This is now fixed in upstream Vue, and it seems your change actually makes things worse now :(

[yyx990803]

Note: this has been reverted (exposing scoped slots on $slots) as it is technically a breaking change.

The original issue, however, is not since the new syntax is opt-in. Users can keep using the old syntax while waiting for libraries to properly migrate to use this.$scopedSlots in all cases.

[K900]

This is definitely an interesting problem, and one I don't really see a good solution for... I guess there's not much we can do now that this behavior is stable, except wait for the ecosystem to catch up :(

[yyx990803]

In 0e8560d I've made it so that only slots using the new v-slot syntax without scope are exposed on this.$slots. This should ensure intended behavior without affecting existing usage of legacy slots.