fix(v-memo): ensure track block when returning cached vnode (#4270)

fix #4253

Author: edison1105

packages/compiler-core/__tests__/transforms/__snapshots__/vMemo.spec.ts.snap

@@ -37,7 +37,7 @@ export function render(_ctx, _cache) {
   return (_openBlock(), _createElementBlock(\\"div\\", null, [
     (_openBlock(true), _createElementBlock(_Fragment, null, _renderList(_ctx.list, ({ x, y }, __, ___, _cached) => {
       const _memo = ([x, y === z])
-      if (_cached && _cached.key === x && _isMemoSame(_cached.memo, _memo)) return _cached
+      if (_cached && _cached.key === x && _isMemoSame(_cached, _memo)) return _cached
       const _item = (_openBlock(), _createElementBlock(\\"span\\", { key: x }, \\"foobar\\"))
       _item.memo = _memo
       return _item
@@ -53,7 +53,7 @@ export function render(_ctx, _cache) {
   return (_openBlock(), _createElementBlock(\\"div\\", null, [
     (_openBlock(true), _createElementBlock(_Fragment, null, _renderList(_ctx.list, ({ x, y }, __, ___, _cached) => {
       const _memo = ([x, y === _ctx.z])
-      if (_cached && _cached.key === x && _isMemoSame(_cached.memo, _memo)) return _cached
+      if (_cached && _cached.key === x && _isMemoSame(_cached, _memo)) return _cached
       const _item = (_openBlock(), _createElementBlock(\\"div\\", { key: x }, [
         _createElementVNode(\\"span\\", null, \\"foobar\\")
       ]))

packages/compiler-core/src/transforms/vFor.ts

@@ -209,7 +209,7 @@ export const transformFor = createStructuralDirectiveTransform(
               ...(keyExp ? [` && _cached.key === `, keyExp] : []),
               ` && ${context.helperString(
                 IS_MEMO_SAME
-              )}(_cached.memo, _memo)) return _cached`
+              )}(_cached, _memo)) return _cached`
             ]),
             createCompoundExpression([`const _item = `, childBlock as any]),
             createSimpleExpression(`_item.memo = _memo`),

packages/runtime-core/src/helpers/withMemo.ts

@@ -7,23 +7,25 @@ export function withMemo(
   index: number
 ) {
   const cached = cache[index] as VNode | undefined
-  if (cached && isMemoSame(cached.memo!, memo)) {
-    // make sure to let parent block track it when returning cached
-    if (isBlockTreeEnabled > 0 && currentBlock) {
-      currentBlock.push(cached)
-    }
+  if (cached && isMemoSame(cached, memo)) {
     return cached
   }
   const ret = render()
   ret.memo = memo
   return (cache[index] = ret)
 }
 
-export function isMemoSame(prev: any[], next: any[]) {
+export function isMemoSame(cached: VNode, memo: any[]) {
+  const prev: any[] = cached.memo!
   for (let i = 0; i < prev.length; i++) {
-    if (prev[i] !== next[i]) {
+    if (prev[i] !== memo[i]) {
       return false
     }
   }
+
+  // make sure to let parent block track it when returning cached
+  if (isBlockTreeEnabled > 0 && currentBlock) {
+    currentBlock.push(cached)
+  }
   return true
 }