fix(watch): traverse refs in deep watch (#1939)

ref #1900

packages/runtime-core/__tests__/apiWatch.spec.ts

@@ -574,6 +574,25 @@ describe('api: watch', () => {
     expect(dummy).toEqual([1, 2, 2, false])
   })
 
+  it('watching deep ref', async () => {
+    const count = ref(0)
+    const double = computed(() => count.value * 2)
+    const state = reactive([count, double])
+
+    let dummy
+    watch(
+      () => state,
+      state => {
+        dummy = [state[0].value, state[1].value]
+      },
+      { deep: true }
+    )
+
+    count.value++
+    await nextTick()
+    expect(dummy).toEqual([1, 2])
+  })
+
   it('immediate', async () => {
     const count = ref(0)
     const cb = jest.fn()

packages/runtime-core/src/apiWatch.ts

@@ -329,7 +329,9 @@ function traverse(value: unknown, seen: Set<unknown> = new Set()) {
     return value
   }
   seen.add(value)
-  if (isArray(value)) {
+  if (isRef(value)) {
+    traverse(value.value, seen)
+  } else if (isArray(value)) {
     for (let i = 0; i < value.length; i++) {
       traverse(value[i], seen)
     }