From 97974855cc5cb44400e5bb955ec4c72e27c0ffaf Mon Sep 17 00:00:00 2001
From: Thorsten Luenborg <t.luenborg@googlemail.com>
Date: Sun, 5 Dec 2021 12:58:11 +0100
Subject: [PATCH] fix(reactivity): mutating a readonly ref nested in a reactive
 object should fail.

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 185bb310759..25b71cc02e5 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 0fa1c4bc2ea..65595d4ce55 100644
--- a/packages/reactivity/src/baseHandlers.ts
+++ b/packages/reactivity/src/baseHandlers.ts
@@ -147,6 +147,9 @@ function createSetter(shallow = false) {
     receiver: object
   ): boolean {
     let oldValue = (target as any)[key]
+    if (isReadonly(oldValue) && isRef(oldValue)) {
+      return false
+    }
     if (!shallow && !isReadonly(value)) {
       value = toRaw(value)
       oldValue = toRaw(oldValue)