fix(patch): static tree as same vnode(#8021)

src/core/vdom/patch.js

@@ -44,7 +44,7 @@ function sameVnode (a, b) {
         isTrue(a.isAsyncPlaceholder) &&
         a.asyncFactory === b.asyncFactory &&
         isUndef(b.asyncFactory.error)
-      )
+      ) || sameStaticVnode(a, b)
     )
   )
 }
@@ -57,6 +57,12 @@ function sameInputType (a, b) {
   return typeA === typeB || isTextInputType(typeA) && isTextInputType(typeB)
 }
 
+function sameStaticVnode (a, b) {
+  return isTrue(a.isStatic) &&
+  isTrue(b.isStatic) &&
+  (isTrue(b.isCloned) || isTrue(b.isOnce))
+}
+
 function createKeyToOldIdx (children, beginIdx, endIdx) {
   let i, key
   const map = {}
@@ -518,10 +524,9 @@ export function createPatchFunction (backend) {
     // note we only do this if the vnode is cloned -
     // if the new node is not cloned it means the render functions have been
     // reset by the hot-reload-api and we need to do a proper re-render.
-    if (isTrue(vnode.isStatic) &&
-      isTrue(oldVnode.isStatic) &&
-      vnode.key === oldVnode.key &&
-      (isTrue(vnode.isCloned) || isTrue(vnode.isOnce))
+    if (
+      sameStaticVnode(oldVnode, vnode) &&
+      vnode.key === oldVnode.key
     ) {
       vnode.componentInstance = oldVnode.componentInstance
       return

test/unit/features/directives/once.spec.js

@@ -176,6 +176,42 @@ describe('Directive v-once', () => {
     }).then(done)
   })
 
+  it('should work inside v-for in component', done => {
+    const vm = new Vue({
+      data: {
+        comp: 'comp1',
+        list: [
+          { id: 0 }
+        ]
+      },
+      components: {
+        comp1: {
+          template: '<span>comp1</span>'
+        },
+        comp2: {
+          template: '<span>comp2</span>'
+        }
+      },
+      template: `
+        <div>
+          <div v-for="i in list" :key="i.id">
+            <component :is='comp' v-once></component>
+          </div>
+        </div>
+      `
+    }).$mount()
+
+    expect(vm.$el.textContent).toBe('comp1')
+
+    vm.comp = 'comp2'
+    waitForUpdate(() => {
+      expect(vm.$el.textContent).toBe('comp1')
+      vm.list.push({ id: 1 })
+    }).then(() => {
+      expect(vm.$el.textContent).toBe('comp1comp2')
+    }).then(done)
+  })
+
   it('should work inside v-for with v-if', done => {
     const vm = new Vue({
       data: {