From a211e271ee8c328e68afc0fe5ab86fabd7e4a320 Mon Sep 17 00:00:00 2001
From: edison <daiwei521@126.com>
Date: Sat, 7 Aug 2021 09:44:45 +0800
Subject: [PATCH] fix(v-memo): ensure track block when returning cached vnode
 (#4270)

fix #4253
---
 .../transforms/__snapshots__/vMemo.spec.ts.snap  |  4 ++--
 packages/compiler-core/src/transforms/vFor.ts    |  2 +-
 packages/runtime-core/src/helpers/withMemo.ts    | 16 +++++++++-------
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/packages/compiler-core/__tests__/transforms/__snapshots__/vMemo.spec.ts.snap b/packages/compiler-core/__tests__/transforms/__snapshots__/vMemo.spec.ts.snap
index 7e654286290..349eb97a468 100644
--- a/packages/compiler-core/__tests__/transforms/__snapshots__/vMemo.spec.ts.snap
+++ b/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\\")
       ]))
diff --git a/packages/compiler-core/src/transforms/vFor.ts b/packages/compiler-core/src/transforms/vFor.ts
index 5d3049f0c95..c6d444ed8dc 100644
--- a/packages/compiler-core/src/transforms/vFor.ts
+++ b/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`),
diff --git a/packages/runtime-core/src/helpers/withMemo.ts b/packages/runtime-core/src/helpers/withMemo.ts
index e3ac03bb0be..43b1fc282bc 100644
--- a/packages/runtime-core/src/helpers/withMemo.ts
+++ b/packages/runtime-core/src/helpers/withMemo.ts
@@ -7,11 +7,7 @@ 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()
@@ -19,11 +15,17 @@ export function withMemo(
   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
 }