From 171f5e9c6008bf0dff565991f34b214da016dde0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thorsten=20L=C3=BCnborg?= <t.luenborg@googlemail.com>
Date: Fri, 21 Jan 2022 08:33:18 +0100
Subject: [PATCH] fix(reactivity): mutating a readonly ref nested in a reactive
 object should fail. (#5048)

fix: #5042
---
 packages/reactivity/__tests__/readonly.spec.ts | 11 +++++++++++
 packages/reactivity/src/baseHandlers.ts        |  3 +++
 2 files changed, 14 insertions(+)

diff --git a/packages/reactivity/__tests__/readonly.spec.ts b/packages/reactivity/__tests__/readonly.spec.ts
index 1a7df0804e0..72a873a016e 100644
--- a/packages/reactivity/__tests__/readonly.spec.ts
+++ b/packages/reactivity/__tests__/readonly.spec.ts
@@ -474,4 +474,15 @@ describe('reactivity/readonly', () => {
     expect(rr.foo).toBe(r)
     expect(isReadonly(rr.foo)).toBe(true)
   })
+
+  test('attemptingt to write to a readonly ref nested in a reactive object should fail', () => {
+    const r = ref(false)
+    const ror = readonly(r)
+    const obj = reactive({ ror })
+    try {
+      obj.ror = true
+    } catch (e) {}
+
+    expect(obj.ror).toBe(false)
+  })
 })
diff --git a/packages/reactivity/src/baseHandlers.ts b/packages/reactivity/src/baseHandlers.ts
index 97acf063f67..eed9dc8509f 100644
--- a/packages/reactivity/src/baseHandlers.ts
+++ b/packages/reactivity/src/baseHandlers.ts
@@ -150,6 +150,9 @@ function createSetter(shallow = false) {
     receiver: object
   ): boolean {
     let oldValue = (target as any)[key]
+    if (isReadonly(oldValue) && isRef(oldValue)) {
+      return false
+    }
     if (!shallow && !isReadonly(value)) {
       if (!isShallow(value)) {
         value = toRaw(value)