From 13263d33b98faae40e9e071e4861c2964fb1c211 Mon Sep 17 00:00:00 2001
From: webfansplz <308241863@qq.com>
Date: Sat, 18 Jun 2022 14:20:10 +0800
Subject: [PATCH 1/2] fix(type): `$watch` callback parameters type

---
 packages/runtime-core/src/componentPublicInstance.ts | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/packages/runtime-core/src/componentPublicInstance.ts b/packages/runtime-core/src/componentPublicInstance.ts
index 1d913673123..4ec2eaf78f8 100644
--- a/packages/runtime-core/src/componentPublicInstance.ts
+++ b/packages/runtime-core/src/componentPublicInstance.ts
@@ -193,9 +193,11 @@ export type ComponentPublicInstance<
   $options: Options & MergedComponentOptionsOverride
   $forceUpdate: () => void
   $nextTick: typeof nextTick
-  $watch(
-    source: string | Function,
-    cb: Function,
+  $watch<T extends string | ((...args: any) => any)>(
+    source: T,
+    cb: T extends (...args: any) => infer R
+      ? (...args: [R, R]) => any
+      : Function,
     options?: WatchOptions
   ): WatchStopHandle
 } & P &

From 12f38aae6370126f7034659978369a10f2402dc8 Mon Sep 17 00:00:00 2001
From: webfansplz <308241863@qq.com>
Date: Sat, 18 Jun 2022 14:33:28 +0800
Subject: [PATCH 2/2] chore: update

---
 .../src/componentPublicInstance.ts             |  2 +-
 test-dts/watch.test-d.ts                       | 18 +++++++++++++++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/packages/runtime-core/src/componentPublicInstance.ts b/packages/runtime-core/src/componentPublicInstance.ts
index 4ec2eaf78f8..1e4c83c96d8 100644
--- a/packages/runtime-core/src/componentPublicInstance.ts
+++ b/packages/runtime-core/src/componentPublicInstance.ts
@@ -197,7 +197,7 @@ export type ComponentPublicInstance<
     source: T,
     cb: T extends (...args: any) => infer R
       ? (...args: [R, R]) => any
-      : Function,
+      : (...args: any) => any,
     options?: WatchOptions
   ): WatchStopHandle
 } & P &
diff --git a/test-dts/watch.test-d.ts b/test-dts/watch.test-d.ts
index 52d26c93c4c..2c16cabd9a4 100644
--- a/test-dts/watch.test-d.ts
+++ b/test-dts/watch.test-d.ts
@@ -1,4 +1,4 @@
-import { ref, computed, watch, expectType } from './index'
+import { ref, computed, watch, expectType, defineComponent } from './index'
 
 const source = ref('foo')
 const source2 = computed(() => source.value)
@@ -75,3 +75,19 @@ watch([someRef, otherRef], values => {
   // no type error
   console.log(value2.a)
 })
+
+// #6135
+defineComponent({
+  data() {
+    return { a: 1 }
+  },
+  created() {
+    this.$watch(
+      () => this.a,
+      (v, ov) => {
+        expectType<number>(v)
+        expectType<number>(ov)
+      }
+    )
+  }
+})