fix: clone slot nodes for render fn usage as well

fix #7041

Author: yyx990803

src/core/instance/render-helpers/resolve-slots.js

@@ -44,7 +44,7 @@ export function resolveSlots (
 }
 
 function isWhitespace (node: VNode): boolean {
-  return node.isComment || node.text === ' '
+  return (node.isComment && !node.asyncFactory) || node.text === ' '
 }
 
 export function resolveScopedSlots (

src/core/instance/render.js

@@ -66,7 +66,9 @@ export function renderMixin (Vue: Class<Component>) {
       // last render. They need to be cloned to ensure "freshness" for this render.
       for (const key in vm.$slots) {
         const slot = vm.$slots[key]
-        if (slot._rendered) {
+        // _rendered is a flag added by renderSlot, but may not be present
+        // if the slot is passed from manually written render functions
+        if (slot._rendered || (slot[0] && slot[0].elm)) {
           vm.$slots[key] = cloneVNodes(slot, true /* deep */)
         }
       }

src/platforms/web/runtime/components/transition.js

@@ -82,7 +82,7 @@ export default {
   abstract: true,
 
   render (h: Function) {
-    let children: ?Array<VNode> = this.$options._renderChildren
+    let children: any = this.$slots.default
     if (!children) {
       return
     }

test/unit/modules/vdom/patch/edge-cases.spec.js

@@ -246,4 +246,25 @@ describe('vdom patch: edge cases', () => {
     vm.$el.children[0].click()
     expect(spy).toHaveBeenCalled()
   })
+
+  // #7041
+  it('transition children with only deep bindings should be patched on update', done => {
+    const vm = new Vue({
+      template: `
+      <div>
+        <transition>
+          <div :style="style"></div>
+        </transition>
+      </div>
+      `,
+      data: () => ({
+        style: { color: 'red' }
+      })
+    }).$mount()
+    expect(vm.$el.children[0].style.color).toBe('red')
+    vm.style.color = 'green'
+    waitForUpdate(() => {
+      expect(vm.$el.children[0].style.color).toBe('green')
+    }).then(done)
+  })
 })