Version

3.0.4

Reproduction link

https://github.com/pgy108103/vue3_vite_issue_sample

Steps to reproduce

Change hasTransition flage in todo.vue, you will see that.

What is expected?

I want transition elements to be used with components that use slotted()

What is actually happening?

As title.

const setScopeId = (
    el: RendererElement,
    scopeId: string | false | null,
    vnode: VNode,
    parentComponent: ComponentInternalInstance | null
  ) => {
    if (scopeId) {
      hostSetScopeId(el, scopeId)
    }
    if (parentComponent) {
      const treeOwnerId = parentComponent.type.__scopeId
      // vnode's own scopeId and the current patched component's scopeId is
      // different - this is a slot content node.
      if (treeOwnerId && treeOwnerId !== scopeId) {
        hostSetScopeId(el, treeOwnerId + '-s')
      }
      //.....
    }
  }

caused by: scopeId is incorrectly set, causing css to not take effect.

if slot's parentComponent is Transition or KeepAlive.parentComponent.type.__scopeId is null,but parentComponent.subTree.scopeId has the correct value.

@edison1105 Your fix does not solve the real cause. And there are problems according to your changes, let's say if the Transition has an out-in mode, then the subtree may be undefined. I made another PR, see https://github.com/vuejs/vue-next/pull/3150

@edison1105 Your fix does not solve the real cause. And there are problems according to your changes, let's say if the Transition has an out-in mode, then the subtree may be undefined. I made another PR, see #3150

Nice to know this and I will close my PR.

Update: the root cause of this is flawed implementation of :slotted scoped id logic. Currently, the following fails:

<Comp>
  <slot/>
</Comp>

<style scoped>
:slotted(*) { color: red }
</style>

#3150 only special cases internal components like Transition, but the ideal behavior is for :slotted to be able to affect elements inside <slot/> regardless of whether it's passed to another component's slot.

I'm working on a fix for this but it requires a pretty substantial refactor and may take a while.