fix(spy): support deep partial in vi.mocked (#8152) (#9493)

Author: j2h30728

docs/api/vi.md

@@ -264,7 +264,7 @@ function mocked<T>(
 
 Type helper for TypeScript. Just returns the object that was passed.
 
-When `partial` is `true` it will expect a `Partial<T>` as a return value. By default, this will only make TypeScript believe that the first level values are mocked. You can pass down `{ deep: true }` as a second argument to tell TypeScript that the whole object is mocked, if it actually is.
+When `partial` is `true` it will expect a `Partial<T>` as a return value. By default, this will only make TypeScript believe that the first level values are mocked. You can pass down `{ deep: true }` as a second argument to tell TypeScript that the whole object is mocked, if it actually is. You can pass down `{ partial: true, deep: true }` to make nested objects also partial recursively.
 
 ```ts [example.ts]
 export function add(x: number, y: number): number {
@@ -274,6 +274,10 @@ export function add(x: number, y: number): number {
 export function fetchSomething(): Promise<Response> {
   return fetch('https://vitest.dev/')
 }
+
+export function getUser(): { name: string; address: { city: string; zip: string } } {
+  return { name: 'John', address: { city: 'New York', zip: '10001' } }
+}
 ```
 
 ```ts [example.test.ts]
@@ -291,6 +295,13 @@ test('mock return value with only partially correct typing', async () => {
   vi.mocked(example.fetchSomething, { partial: true }).mockResolvedValue({ ok: false })
   // vi.mocked(example.someFn).mockResolvedValue({ ok: false }) // this is a type error
 })
+
+test('mock return value with deep partial typing', async () => {
+  vi.mocked(example.getUser, { partial: true, deep: true }).mockReturnValue({
+    address: { city: 'Los Angeles' },
+  })
+  expect(example.getUser().address.city).toBe('Los Angeles')
+})
 ```
 
 ### vi.importActual

packages/spy/src/types.ts

@@ -406,6 +406,37 @@ export type PartialMock<T extends Procedure | Constructable = Procedure> = Mock<
   >
 >
 
+type DeepPartial<T> = T extends Procedure
+  ? T
+  : T extends Array<infer U>
+    ? Array<DeepPartial<U>>
+    : T extends object
+      ? { [K in keyof T]?: DeepPartial<T[K]> }
+      : T
+
+type DeepPartialMaybePromise<T> = T extends Promise<Awaited<T>>
+  ? Promise<DeepPartial<Awaited<T>>>
+  : DeepPartial<T>
+
+type DeepPartialResultFunction<T> = T extends Constructable
+  ? ({
+    new (...args: ConstructorParameters<T>): InstanceType<T>
+  })
+  | ({
+    (this: InstanceType<T>, ...args: ConstructorParameters<T>): void
+  })
+  : T extends Procedure
+    ? (...args: Parameters<T>) => DeepPartialMaybePromise<ReturnType<T>>
+    : T
+
+type DeepPartialMock<T extends Procedure | Constructable = Procedure> = Mock<
+  DeepPartialResultFunction<
+    T extends Mock
+      ? NonNullable<ReturnType<T['getMockImplementation']>>
+      : T
+  >
+>
+
 export type MaybeMockedConstructor<T> = T extends Constructable
   ? Mock<T>
   : T
@@ -417,7 +448,7 @@ export type PartiallyMockedFunction<T extends Procedure | Constructable> = Parti
 }
 export type MockedFunctionDeep<T extends Procedure | Constructable> = Mock<T>
   & MockedObjectDeep<T>
-export type PartiallyMockedFunctionDeep<T extends Procedure | Constructable> = PartialMock<T>
+export type PartiallyMockedFunctionDeep<T extends Procedure | Constructable> = DeepPartialMock<T>
   & MockedObjectDeep<T>
 export type MockedObject<T> = MaybeMockedConstructor<T> & {
   [K in Methods<T>]: T[K] extends Procedure ? MockedFunction<T[K]> : T[K];

packages/vitest/src/integrations/vi.ts

@@ -320,7 +320,7 @@ export interface VitestUtils {
    * Type helper for TypeScript. Just returns the object that was passed.
    *
    * When `partial` is `true` it will expect a `Partial<T>` as a return value. By default, this will only make TypeScript believe that
-   * the first level values are mocked. You can pass down `{ deep: true }` as a second argument to tell TypeScript that the whole object is mocked, if it actually is.
+   * the first level values are mocked. You can pass down `{ partial: true, deep: true }` to make nested objects also partial recursively.
    * @example
    * ```ts
    * import example from './example.js'

test/core/test/vi.spec.ts

@@ -108,6 +108,40 @@ describe('testing vi utils', () => {
       vi.mocked(fetchSomething).mockResolvedValue(new Response(null))
       vi.mocked(fetchSomething, { partial: true }).mockResolvedValue({ ok: false })
     }
+
+    // #8152
+    if (0) {
+      interface NestedObject {
+        level1: {
+          level2: {
+            value: string
+            count: number
+          }
+          name: string
+        }
+        items: string[]
+      }
+
+      const mockNestedFactory = vi.fn<() => NestedObject>()
+
+      vi.mocked(mockNestedFactory, { partial: true, deep: true }).mockReturnValue({
+        level1: { level2: {} },
+      })
+      vi.mocked(mockNestedFactory, { partial: true, deep: true }).mockReturnValue({
+        level1: {},
+      })
+      vi.mocked(mockNestedFactory, { partial: true, deep: true }).mockReturnValue({})
+      vi.mocked(mockNestedFactory, { partial: true, deep: true }).mockReturnValue({
+        items: ['a', 'b'],
+      })
+
+      const mockNestedAsyncFactory = vi.fn<() => Promise<NestedObject>>()
+
+      vi.mocked(mockNestedAsyncFactory, { partial: true, deep: true }).mockResolvedValue({
+        level1: { level2: {} },
+      })
+      vi.mocked(mockNestedAsyncFactory, { partial: true, deep: true }).mockResolvedValue({})
+    }
   })
 
   test('vi.mocked with classes', () => {