From ef432bda777d8c73e7d66b4d70bb7a5f3d2aa60f Mon Sep 17 00:00:00 2001
From: Evan You <yyx990803@gmail.com>
Date: Mon, 11 Dec 2023 18:40:25 +0800
Subject: [PATCH] refactor(reactivity): improve nested readonly ref set check

ref #9094
---
 packages/reactivity/src/baseHandlers.ts | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/packages/reactivity/src/baseHandlers.ts b/packages/reactivity/src/baseHandlers.ts
index 7a73a09acdd..3876db4cdf2 100644
--- a/packages/reactivity/src/baseHandlers.ts
+++ b/packages/reactivity/src/baseHandlers.ts
@@ -174,17 +174,19 @@ class MutableReactiveHandler extends BaseReactiveHandler {
     receiver: object
   ): boolean {
     let oldValue = (target as any)[key]
-    if (isReadonly(oldValue) && isRef(oldValue) && !isRef(value)) {
-      return false
-    }
     if (!this._shallow) {
+      const isOldValueReadonly = isReadonly(oldValue)
       if (!isShallow(value) && !isReadonly(value)) {
         oldValue = toRaw(oldValue)
         value = toRaw(value)
       }
       if (!isArray(target) && isRef(oldValue) && !isRef(value)) {
-        oldValue.value = value
-        return true
+        if (isOldValueReadonly) {
+          return false
+        } else {
+          oldValue.value = value
+          return true
+        }
       }
     } else {
       // in shallow mode, objects are set as-is regardless of reactive or not