fix(type): align watch types with vue3 (#927)

src/apis/watch.ts

@@ -32,18 +32,16 @@ export type WatchCallback<V = any, OV = any> = (
   onInvalidate: InvalidateCbRegistrator
 ) => any
 
-type MapSources<T> = {
-  [K in keyof T]: T[K] extends WatchSource<infer V> ? V : never
-}
-
-type MapOldSources<T, Immediate> = {
+declare type MapSources<T, Immediate> = {
   [K in keyof T]: T[K] extends WatchSource<infer V>
     ? Immediate extends true
       ? V | undefined
       : V
     : never
 }
 
+type MultiWatchSources = (WatchSource<unknown> | object)[]
+
 export interface WatchOptionsBase {
   flush?: FlushMode
   // onTrack?: ReactiveEffectOptions['onTrack'];
@@ -204,8 +202,8 @@ function patchWatcherTeardown(watcher: VueWatcher, runCleanup: () => void) {
 
 function createWatcher(
   vm: ComponentInstance,
-  source: WatchSource<unknown> | WatchSource<unknown>[] | WatchEffect,
-  cb: WatchCallback<any> | null,
+  source: WatchSource | WatchSource[] | WatchEffect,
+  cb: WatchCallback | null,
   options: WatchOptions
 ): () => void {
   if (__DEV__ && !cb) {
@@ -416,27 +414,47 @@ export function watchSyncEffect(effect: WatchEffect) {
   return watchEffect(effect, { flush: 'sync' })
 }
 
-// overload #1: array of multiple sources + cb
-// Readonly constraint helps the callback to correctly infer value types based
-// on position in the source array. Otherwise the values will get a union type
-// of all possible value types.
+// overload #1 + #2 + #3: array of multiple sources + cb
+
+// overload #1: In readonly case the first overload must be spread tuple type.
+// In otherwise members in tuple can not get the correct types.
+export function watch<
+  T extends Readonly<MultiWatchSources>,
+  Immediate extends Readonly<boolean> = false
+>(
+  sources: [...T],
+  cb: WatchCallback<MapSources<T, false>, MapSources<T, Immediate>>,
+  options?: WatchOptions<Immediate>
+): WatchStopHandle
+
+// overload #2: for not spread readonly tuple
+export function watch<
+  T extends Readonly<MultiWatchSources>,
+  Immediate extends Readonly<boolean> = false
+>(
+  sources: T,
+  cb: WatchCallback<MapSources<T, false>, MapSources<T, Immediate>>,
+  options?: WatchOptions<Immediate>
+): WatchStopHandle
+
+// overload #3: for not readonly multiSources
 export function watch<
-  T extends Readonly<WatchSource<unknown>[]>,
+  T extends MultiWatchSources,
   Immediate extends Readonly<boolean> = false
 >(
   sources: [...T],
-  cb: WatchCallback<MapSources<T>, MapOldSources<T, Immediate>>,
+  cb: WatchCallback<MapSources<T, false>, MapSources<T, Immediate>>,
   options?: WatchOptions<Immediate>
 ): WatchStopHandle
 
-// overload #2: single source + cb
+// overload #4: 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 #3: watching reactive object w/ cb
+// overload #5: watching reactive object w/ cb
 export function watch<
   T extends object,
   Immediate extends Readonly<boolean> = false

test-dts/watch.test-d.tsx

@@ -10,17 +10,44 @@ watch(source, (value, oldValue) => {
   expectType<string>(oldValue)
 })
 
-watch([source, source2, source3], (values, oldValues) => {
-  expectType<(string | number)[]>(values)
-  expectType<(string | number)[]>(oldValues)
-})
+// spread array
+watch(
+  [source, source2, source3],
+  ([source1, source2, source3], [oldSource1, oldSource2, oldSource3]) => {
+    expectType<string>(source1)
+    expectType<string>(source2)
+    expectType<number>(source3)
+    expectType<string>(oldSource1)
+    expectType<string>(oldSource2)
+    expectType<number>(oldSource3)
+  }
+)
 
 // const array
-watch([source, source2, source3], (values, oldValues) => {
+watch([source, source2, source3] as const, (values, oldValues) => {
   expectType<Readonly<[string, string, number]>>(values)
   expectType<Readonly<[string, string, number]>>(oldValues)
+  expectType<string>(values[0])
+  expectType<string>(values[1])
+  expectType<number>(values[2])
+  expectType<string>(oldValues[0])
+  expectType<string>(oldValues[1])
+  expectType<number>(oldValues[2])
 })
 
+// const spread array
+watch(
+  [source, source2, source3] as const,
+  ([source1, source2, source3], [oldSource1, oldSource2, oldSource3]) => {
+    expectType<string>(source1)
+    expectType<string>(source2)
+    expectType<number>(source3)
+    expectType<string>(oldSource1)
+    expectType<string>(oldSource2)
+    expectType<number>(oldSource3)
+  }
+)
+
 // immediate watcher's oldValue will be undefined on first run.
 watch(
   source,
@@ -42,7 +69,7 @@ watch(
 
 // const array
 watch(
-  [source, source2, source3],
+  [source, source2, source3] as const,
   (values, oldValues) => {
     expectType<Readonly<[string, string, number]>>(values)
     expectType<

test/v3/runtime-core/apiWatch.spec.ts

@@ -143,7 +143,7 @@ describe('api: watch', () => {
     const status = ref(false)
 
     let dummy
-    watch([() => state.count, status], (vals, oldVals) => {
+    watch([() => state.count, status] as const, (vals, oldVals) => {
       dummy = [vals, oldVals]
       const [count] = vals
       const [, oldStatus] = oldVals