fix(types): fix defineModel watch type error (#9942)

close #9939

packages/dts-test/watch.test-d.ts

@@ -1,4 +1,11 @@
-import { computed, defineComponent, ref, shallowRef, watch } from 'vue'
+import {
+  computed,
+  defineComponent,
+  defineModel,
+  ref,
+  shallowRef,
+  watch,
+} from 'vue'
 import { expectType } from './utils'
 
 const source = ref('foo')
@@ -106,3 +113,31 @@ defineComponent({
     expectType<Steps>(value)
   })
 }
+
+{
+  // defineModel
+  const bool = defineModel({ default: false })
+  watch(bool, value => {
+    expectType<boolean>(value)
+  })
+
+  const bool1 = defineModel<boolean>()
+  watch(bool1, value => {
+    expectType<boolean | undefined>(value)
+  })
+
+  const msg = defineModel<string>({ required: true })
+  watch(msg, value => {
+    expectType<string>(value)
+  })
+
+  const arr = defineModel<string[]>({ required: true })
+  watch(arr, value => {
+    expectType<string[]>(value)
+  })
+
+  const obj = defineModel<{ foo: string }>({ required: true })
+  watch(obj, value => {
+    expectType<{ foo: string }>(value)
+  })
+}

packages/runtime-core/src/apiWatch.ts

@@ -115,6 +115,13 @@ const INITIAL_WATCHER_VALUE = {}
 
 type MultiWatchSources = (WatchSource<unknown> | object)[]
 
+// overload: single source + cb
+export function watch<T, Immediate extends Readonly<boolean> = false>(
+  source: WatchSource<T>,
+  cb: WatchCallback<T, Immediate extends true ? T | undefined : T>,
+  options?: WatchOptions<Immediate>,
+): WatchStopHandle
+
 // overload: array of multiple sources + cb
 export function watch<
   T extends MultiWatchSources,
@@ -137,13 +144,6 @@ export function watch<
   options?: WatchOptions<Immediate>,
 ): WatchStopHandle
 
-// overload: single source + cb
-export function watch<T, Immediate extends Readonly<boolean> = false>(
-  source: WatchSource<T>,
-  cb: WatchCallback<T, Immediate extends true ? T | undefined : T>,
-  options?: WatchOptions<Immediate>,
-): WatchStopHandle
-
 // overload: watching reactive object w/ cb
 export function watch<
   T extends object,