fix(reactivity): mutating a readonly ref nested in a reactive object should fail.

fix: #5042

Author: LinusBorg

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)
+  })
 })

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)