fix(compat): ensure functional component is not null in $children

[andreww2012]

In compat mode, if a component is functional, it will be null in $children array. This happens because $children are formed from proxy property which is not set for functional components:

core/packages/runtime-core/src/component.ts

Lines 740 to 746 in 6a8d548

	const isStateful = isStatefulComponent(instance)
	initProps(instance, props, isStateful, isSSR)
	initSlots(instance, children)
	const setupResult = isStateful
	? setupStatefulComponent(instance, isSSR)
	: undefined

Inside setupStatefulComponent:

core/packages/runtime-core/src/component.ts

Line 785 in 6a8d548

instance.proxy = new Proxy(instance.ctx, PublicInstanceProxyHandlers)

The fix is to use component.ctx (which is the proxy's original object) as a fallback when populating $children. I do realize this is not the same object as the wrapped one but this might be sufficient for migration purposes.

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	90.7 kB	34.5 kB	31.1 kB
vue.global.prod.js	148 kB	53.7 kB	48.1 kB

Usages

Name	Size	Gzip	Brotli
createApp	50.8 kB	19.9 kB	18.1 kB
createSSRApp	54.1 kB	21.2 kB	19.3 kB
defineCustomElement	53.1 kB	20.6 kB	18.8 kB
overall	64.5 kB	24.9 kB	22.6 kB