From 4d517022cf96de33e9b9c150e34f10548c92252a Mon Sep 17 00:00:00 2001
From: xiaowei-one <meetxiaowei1109@163.com>
Date: Tue, 28 Feb 2023 20:25:53 +0800
Subject: [PATCH] fix: trigger when adding new property with Vue.seta and
 piWatch test

---
 src/v3/apiWatch.ts                     | 13 +++++++++++--
 test/unit/features/v3/apiWatch.spec.ts | 11 +++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/v3/apiWatch.ts b/src/v3/apiWatch.ts
index 141a58eb686..c6208691024 100644
--- a/src/v3/apiWatch.ts
+++ b/src/v3/apiWatch.ts
@@ -218,8 +218,17 @@ function doWatch(
       })
   } else if (isFunction(source)) {
     if (cb) {
-      // getter with cb
-      getter = () => call(source, WATCHER_GETTER)
+      const ob = call(source, WATCHER_GETTER)
+      if (isReactive(ob)){
+        getter = () => {
+          ;(ob as any).__ob__.dep.depend()
+          return ob
+        }
+        deep = true
+      } else {
+        // getter with cb
+        getter = () => ob
+      }
     } else {
       // no cb -> simple effect
       getter = () => {
diff --git a/test/unit/features/v3/apiWatch.spec.ts b/test/unit/features/v3/apiWatch.spec.ts
index c92bc150ae7..e34694a0baa 100644
--- a/test/unit/features/v3/apiWatch.spec.ts
+++ b/test/unit/features/v3/apiWatch.spec.ts
@@ -1200,4 +1200,15 @@ describe('api: watch', () => {
     expect(parentSpy).toHaveBeenCalledTimes(1)
     expect(childSpy).toHaveBeenCalledTimes(1)
   })
+
+  // #12967
+  test('trigger when adding new property with Vue.set', async () => {
+    const spy = vi.fn()
+    const r = reactive({ exist: 5 })
+    watch(() => r, spy, { deep: true })
+    set(r, 'add', 1)
+
+    await nextTick()
+    expect(spy).toHaveBeenCalledTimes(1)
+  })
 })