feat(transition): compat with keep-alive

packages/runtime-core/src/componentSlots.ts

@@ -1,8 +1,9 @@
 import { ComponentInternalInstance, currentInstance } from './component'
 import { VNode, NormalizedChildren, normalizeVNode, VNodeChild } from './vnode'
-import { isArray, isFunction } from '@vue/shared'
+import { isArray, isFunction, EMPTY_OBJ } from '@vue/shared'
 import { ShapeFlags } from './shapeFlags'
 import { warn } from './warning'
+import { isKeepAlive } from './components/KeepAlive'
 
 export type Slot = (...args: any[]) => VNode[]
 
@@ -65,7 +66,7 @@ export function resolveSlots(
     }
   } else if (children !== null) {
     // non slot object children (direct value) passed to a component
-    if (__DEV__) {
+    if (__DEV__ && !isKeepAlive(instance.vnode)) {
       warn(
         `Non-function value encountered for default slot. ` +
           `Prefer function slots for better performance.`
@@ -74,7 +75,5 @@ export function resolveSlots(
     const normalized = normalizeSlotValue(children)
     slots = { default: () => normalized }
   }
-  if (slots !== void 0) {
-    instance.slots = slots
-  }
+  instance.slots = slots || EMPTY_OBJ
 }