fix(core - patch)：when before patch: old keys like [a, b, c ...] new …

[sam0212]

…keys like [d, b, b, e, ....], when patch the second key "b" Vnode by new children, the vnodeToMove will be undefined, so need add a condition for vnodeToMove

fix an error when diff patch, when before patch: old keys like [a, b, c ...] new keys like [d, b, b, e, ....], when patch the second key "b" Vnode by new children, the vnodeToMove will be undefined, so need add a condition for vnodeToMove

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the main branch for v2.x (or to a previous version branch)
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

[sam0212]

// PatchChild.vue <template> <div> {{ data.key }} </div> </template> <script> export default { props: { data: { type: Object, required: true, }, }, }; </script>

// Wrapper.vue <template> <div> <div> <PatchChild v-for="item in list" :key="item.key" :data="item" /> </div> <div><button @click="changeList">changeList</button></div> </div> </template> <script> import PatchChild from './PatchChild.vue'; export default { components: { PatchChild, }, data() { return { list: [ { key: 'A', }, { key: 'B', }, { key: 'C', }, ], }; }, methods: { changeList() { this.list = [ { key: 'D', }, { key: 'B', }, { key: 'B', }, { key: 'E', }, ]; }, }, }; </script>

[posva]

Keys cannot be repeated. Normally there is already an error for this but this shouldn’t be « fixed ». It’s supposed not to work