Added a proof of concept for initialData making TData never undefined

packages/react-query-persist-client/src/__tests__/PersistQueryClientProvider.test.tsx

@@ -6,6 +6,7 @@ import {
   useQuery,
   UseQueryResult,
   useQueries,
+  DefinedUseQueryResult,
 } from '@tanstack/react-query'
 import {
   createQueryClient,
@@ -200,7 +201,7 @@ describe('PersistQueryClientProvider', () => {
 
   test('should show initialData while restoring', async () => {
     const key = queryKey()
-    const states: UseQueryResult<string>[] = []
+    const states: DefinedUseQueryResult<string>[] = []
 
     const queryClient = createQueryClient()
     await queryClient.prefetchQuery(key, () => Promise.resolve('hydrated'))

packages/react-query/src/__tests__/useQuery.test.tsx

@@ -19,6 +19,7 @@ import {
   QueryFunction,
   QueryFunctionContext,
   UseQueryOptions,
+  DefinedUseQueryResult,
 } from '..'
 import { ErrorBoundary } from 'react-error-boundary'
 
@@ -142,7 +143,7 @@ describe('useQuery', () => {
         ) => Promise<TQueryFnData>,
         options?: Omit<
           UseQueryOptions<TQueryFnData, TError, TData, TQueryKey>,
-          'queryKey' | 'queryFn'
+          'queryKey' | 'queryFn' | 'initialData'
         >,
       ) => useQuery(qk, () => fetcher(qk[1], 'token'), options)
       const test = useWrappedQuery([''], async () => '1')
@@ -159,7 +160,7 @@ describe('useQuery', () => {
         fetcher: () => Promise<TQueryFnData>,
         options?: Omit<
           UseQueryOptions<TQueryFnData, TError, TData, TQueryKey>,
-          'queryKey' | 'queryFn'
+          'queryKey' | 'queryFn' | 'initialData'
         >,
       ) => useQuery(qk, fetcher, options)
       const testFuncStyle = useWrappedFuncStyleQuery([''], async () => true)
@@ -1295,7 +1296,7 @@ describe('useQuery', () => {
 
   it('should use query function from hook when the existing query does not have a query function', async () => {
     const key = queryKey()
-    const results: UseQueryResult<string>[] = []
+    const results: DefinedUseQueryResult<string>[] = []
 
     queryClient.setQueryData(key, 'set')
 
@@ -1712,7 +1713,7 @@ describe('useQuery', () => {
 
   it('should not show initial data from next query if keepPreviousData is set', async () => {
     const key = queryKey()
-    const states: UseQueryResult<number>[] = []
+    const states: DefinedUseQueryResult<number>[] = []
 
     function Page() {
       const [count, setCount] = React.useState(0)
@@ -3025,7 +3026,7 @@ describe('useQuery', () => {
 
   it('should fetch if initial data is set', async () => {
     const key = queryKey()
-    const states: UseQueryResult<string>[] = []
+    const states: DefinedUseQueryResult<string>[] = []
 
     function Page() {
       const state = useQuery(key, () => 'data', {
@@ -3055,7 +3056,7 @@ describe('useQuery', () => {
 
   it('should not fetch if initial data is set with a stale time', async () => {
     const key = queryKey()
-    const states: UseQueryResult<string>[] = []
+    const states: DefinedUseQueryResult<string>[] = []
 
     function Page() {
       const state = useQuery(key, () => 'data', {
@@ -3085,7 +3086,7 @@ describe('useQuery', () => {
 
   it('should fetch if initial data updated at is older than stale time', async () => {
     const key = queryKey()
-    const states: UseQueryResult<string>[] = []
+    const states: DefinedUseQueryResult<string>[] = []
 
     const oneSecondAgo = Date.now() - 1000
 
@@ -3123,7 +3124,7 @@ describe('useQuery', () => {
 
   it('should fetch if "initial data updated at" is exactly 0', async () => {
     const key = queryKey()
-    const states: UseQueryResult<string>[] = []
+    const states: DefinedUseQueryResult<string>[] = []
 
     function Page() {
       const state = useQuery(key, () => 'data', {
@@ -3154,7 +3155,7 @@ describe('useQuery', () => {
 
   it('should keep initial data when the query key changes', async () => {
     const key = queryKey()
-    const states: UseQueryResult<{ count: number }>[] = []
+    const states: DefinedUseQueryResult<{ count: number }>[] = []
 
     function Page() {
       const [count, setCount] = React.useState(0)
@@ -3629,7 +3630,7 @@ describe('useQuery', () => {
 
   it('should mark query as fetching, when using initialData', async () => {
     const key = queryKey()
-    const results: UseQueryResult<string>[] = []
+    const results: DefinedUseQueryResult<string>[] = []
 
     function Page() {
       const result = useQuery(key, () => 'serverData', { initialData: 'data' })
@@ -3648,7 +3649,7 @@ describe('useQuery', () => {
 
   it('should initialize state properly, when initialData is falsy', async () => {
     const key = queryKey()
-    const results: UseQueryResult<number>[] = []
+    const results: DefinedUseQueryResult<number>[] = []
 
     function Page() {
       const result = useQuery(key, () => 1, { initialData: 0 })
@@ -3668,7 +3669,7 @@ describe('useQuery', () => {
   // // See https://github.com/tannerlinsley/react-query/issues/214
   it('data should persist when enabled is changed to false', async () => {
     const key = queryKey()
-    const results: UseQueryResult<string>[] = []
+    const results: DefinedUseQueryResult<string>[] = []
 
     function Page() {
       const [shouldFetch, setShouldFetch] = React.useState(true)

packages/react-query/src/__tests__/useQuery.types.test.tsx

@@ -0,0 +1,157 @@
+import { useQuery } from '../useQuery'
+
+export type Equal<X, Y> = (<T>() => T extends X ? 1 : 2) extends <
+  T,
+>() => T extends Y ? 1 : 2
+  ? true
+  : false
+
+export type Expect<T extends true> = T
+
+const doNotExecute = (_func: () => void) => true
+
+describe('initialData', () => {
+  describe('Config object overload', () => {
+    it('TData should always be defined when initialData is provided as an object', () => {
+      doNotExecute(() => {
+        const { data } = useQuery({
+          queryFn: () => {
+            return {
+              wow: true,
+            }
+          },
+          initialData: {
+            wow: true,
+          },
+        })
+
+        const result: Expect<Equal<{ wow: boolean }, typeof data>> = true
+        return result
+      })
+    })
+
+    it('TData should always be defined when initialData is provided as a function which ALWAYS returns the data', () => {
+      doNotExecute(() => {
+        const { data } = useQuery({
+          queryFn: () => {
+            return {
+              wow: true,
+            }
+          },
+          initialData: () => ({
+            wow: true,
+          }),
+        })
+
+        const result: Expect<Equal<{ wow: boolean }, typeof data>> = true
+        return result
+      })
+    })
+
+    it('TData should have undefined in the union when initialData is NOT provided', () => {
+      doNotExecute(() => {
+        const { data } = useQuery({
+          queryFn: () => {
+            return {
+              wow: true,
+            }
+          },
+        })
+
+        const result: Expect<Equal<{ wow: boolean } | undefined, typeof data>> =
+          true
+        return result
+      })
+    })
+
+    it('TData should have undefined in the union when initialData is provided as a function which can return undefined', () => {
+      doNotExecute(() => {
+        const { data } = useQuery({
+          queryFn: () => {
+            return {
+              wow: true,
+            }
+          },
+          initialData: () => undefined as { wow: boolean } | undefined,
+        })
+
+        const result: Expect<Equal<{ wow: boolean } | undefined, typeof data>> =
+          true
+        return result
+      })
+    })
+  })
+
+  describe('Query key overload', () => {
+    it('TData should always be defined when initialData is provided', () => {
+      doNotExecute(() => {
+        const { data } = useQuery(['key'], {
+          queryFn: () => {
+            return {
+              wow: true,
+            }
+          },
+          initialData: {
+            wow: true,
+          },
+        })
+
+        const result: Expect<Equal<{ wow: boolean }, typeof data>> = true
+        return result
+      })
+    })
+
+    it('TData should have undefined in the union when initialData is NOT provided', () => {
+      doNotExecute(() => {
+        const { data } = useQuery(['key'], {
+          queryFn: () => {
+            return {
+              wow: true,
+            }
+          },
+        })
+
+        const result: Expect<Equal<{ wow: boolean } | undefined, typeof data>> =
+          true
+        return result
+      })
+    })
+  })
+
+  describe('Query key and func', () => {
+    it('TData should always be defined when initialData is provided', () => {
+      doNotExecute(() => {
+        const { data } = useQuery(
+          ['key'],
+          () => {
+            return {
+              wow: true,
+            }
+          },
+          {
+            initialData: {
+              wow: true,
+            },
+          },
+        )
+
+        const result: Expect<Equal<{ wow: boolean }, typeof data>> = true
+        return result
+      })
+    })
+
+    it('TData should have undefined in the union when initialData is NOT provided', () => {
+      doNotExecute(() => {
+        const { data } = useQuery(['key'], () => {
+          return {
+            wow: true,
+          }
+        })
+
+        const result: Expect<Equal<{ wow: boolean } | undefined, typeof data>> =
+          true
+        return result
+      })
+    })
+  })
+})

packages/react-query/src/types.ts

@@ -65,6 +65,11 @@ export type UseQueryResult<
   TError = unknown,
 > = UseBaseQueryResult<TData, TError>
 
+export type DefinedUseQueryResult<TData = unknown, TError = unknown> = Omit<
+  UseQueryResult<TData, TError>,
+  'data'
+> & { data: TData }
+
 export type UseInfiniteQueryResult<
   TData = unknown,
   TError = unknown,