fix(slot): slots should be deep cloned, fix vuejs#7975

src/core/instance/render.js

@@ -11,7 +11,7 @@ import {
 import { createElement } from '../vdom/create-element'
 import { installRenderHelpers } from './render-helpers/index'
 import { resolveSlots } from './render-helpers/resolve-slots'
-import VNode, { createEmptyVNode } from '../vdom/vnode'
+import VNode, { cloneVNodes, createEmptyVNode } from '../vdom/vnode'
 
 import { isUpdatingChildComponent } from './lifecycle'
 
@@ -62,11 +62,16 @@ export function renderMixin (Vue: Class<Component>) {
     const vm: Component = this
     const { render, _parentVnode } = vm.$options
 
-    // reset _rendered flag on slots for duplicate slot check
-    if (process.env.NODE_ENV !== 'production') {
+    if (vm._isMounted) {
+      // if the parent didn't update, the slot nodes will be the ones from
+      // last render. They need to be cloned to ensure "freshness" for this render.
       for (const key in vm.$slots) {
-        // $flow-disable-line
-        vm.$slots[key]._rendered = false
+        const slot = vm.$slots[key]
+        // _rendered is a flag added by renderSlot, but may not be present
+        // if the slot is passed from manually written render functions
+        if (slot._rendered || (slot[0] && slot[0].elm)) {
+          vm.$slots[key] = cloneVNodes(slot, true /* deep */)
+        }
       }
     }
 

src/core/vdom/vnode.js

@@ -85,15 +85,16 @@ export function createTextVNode (val: string | number) {
 // used for static nodes and slot nodes because they may be reused across
 // multiple renders, cloning them avoids errors when DOM manipulations rely
 // on their elm reference.
-export function cloneVNode (vnode: VNode): VNode {
+export function cloneVNode (vnode: VNode, deep?: boolean): VNode {
+  const componentOptions = vnode.componentOptions
   const cloned = new VNode(
     vnode.tag,
     vnode.data,
     vnode.children,
     vnode.text,
     vnode.elm,
     vnode.context,
-    vnode.componentOptions,
+    componentOptions,
     vnode.asyncFactory
   )
   cloned.ns = vnode.ns
@@ -105,5 +106,23 @@ export function cloneVNode (vnode: VNode): VNode {
   cloned.fnScopeId = vnode.fnScopeId
   cloned.asyncMeta = vnode.asyncMeta
   cloned.isCloned = true
+
+  if (deep) {
+    if (vnode.children) {
+      cloned.children = cloneVNodes(vnode.children, true)
+    }
+    if (componentOptions && componentOptions.children) {
+      componentOptions.children = cloneVNodes(componentOptions.children, true)
+    }
+  }
   return cloned
 }
+
+export function cloneVNodes (vnodes: Array<VNode>, deep?: boolean): Array<VNode> {
+  const len = vnodes.length
+  const res = new Array(len)
+  for (let i = 0; i < len; i++) {
+    res[i] = cloneVNode(vnodes[i], deep)
+  }
+  return res
+}

test/unit/features/component/component-slot.spec.js

@@ -886,4 +886,61 @@ describe('Component slot', () => {
       expect(vm.$el.textContent).toBe('foo')
     }).then(done)
   })
+
+  // #7975
+  it('should update named slot correctly when its position in the tree changed', done => {
+    const ChildComponent = {
+      template: '<b>{{ message }}</b>',
+      props: ['message']
+    }
+
+    let parentVm
+    const ParentComponent = {
+      template: `
+        <div>
+          <span v-if="alter">
+            <span><slot name="foo" /></span>
+          </span>
+          <span v-else>
+            <slot name="foo" />
+          </span>
+        </div>
+      `,
+      data () {
+        return {
+          alter: true
+        }
+      },
+      mounted () {
+        parentVm = this
+      }
+    }
+
+    const vm = new Vue({
+      template: `
+        <parent-component>
+          <span slot="foo">
+            <child-component :message="message" />
+          </span>
+        </parent-component>
+      `,
+      components: {
+        ChildComponent,
+        ParentComponent
+      },
+      data () {
+        return {
+          message: 1
+        }
+      }
+    }).$mount()
+
+    expect(vm.$el.firstChild.innerHTML).toBe('<span><span><b>1</b></span></span>')
+    parentVm.alter = false
+    waitForUpdate(() => {
+      vm.message = 2
+    }).then(() => {
+      expect(vm.$el.firstChild.innerHTML).toBe('<span><b>2</b></span>')
+    }).then(done)
+  })
 })