fix(queryClient): make sure that setQueryData can return undefined from the updater function on type level

the only runtime tests we had didn't use the previous value, so the generic defaults to unknown; the TS error becomes apparent when providing a generic to setQueryData

Author: TkDodo

src/core/queryClient.ts

@@ -128,7 +128,7 @@ export class QueryClient {
 
   setQueryData<TData>(
     queryKey: QueryKey,
-    updater: Updater<TData | undefined, TData> | undefined,
+    updater: Updater<TData | undefined, TData | undefined>,
     options?: SetDataOptions
   ): TData | undefined {
     const query = this.queryCache.find<TData>(queryKey)

src/core/tests/queryClient.test.tsx

@@ -311,8 +311,8 @@ describe('queryClient', () => {
 
     test('should not update query data if updater returns undefined', () => {
       const key = queryKey()
-      queryClient.setQueryData(key, 'qux')
-      queryClient.setQueryData(key, () => undefined)
+      queryClient.setQueryData<string>(key, 'qux')
+      queryClient.setQueryData<string>(key, () => undefined)
       expect(queryClient.getQueryData(key)).toBe('qux')
     })