Improve typing

Author: sirlancelot

src/types.ts

@@ -82,3 +82,11 @@ export type Mock<TFunc extends AnyMockable> = TFunc extends AnyConstructor
   : TFunc extends AnyFunction
     ? MockedFunction<TFunc>
     : never
+
+/** Produce a union of progressively longer tuples based on the input tuple */
+export type PartialArguments<
+  Tuple extends any[],
+  _Previous extends any[] = [],
+> = Tuple extends [infer First, ...infer Rest]
+  ? [..._Previous, First] | PartialArguments<Rest, [..._Previous, First]>
+  : never

src/vitest-when.ts

@@ -8,6 +8,7 @@ import type {
   MockInstance,
   NormalizeMockable,
   ParametersOf,
+  PartialArguments,
   ReturnTypeOf,
   WithMatchers,
 } from './types.ts'
@@ -24,7 +25,7 @@ export interface StubWrapper<TFunc extends AnyMockable> {
 
 export interface StubWrapperFlexible<TFunc extends AnyMockable> {
   calledWith<TArgs extends ParametersOf<TFunc>>(
-    ...args: Partial<WithMatchers<TArgs>>
+    ...args: PartialArguments<WithMatchers<TArgs>>
   ): Stub<TFunc>
 }
 

test/typing.test-d.ts

@@ -57,6 +57,13 @@ describe('vitest-when type signatures', () => {
     >()
   })
 
+  it('should ensure correct type of previous arguments', () => {
+    subject
+      .when(extraArguments, { ignoreExtraArgs: true })
+      /* @ts-expect-error: first arg is not correct */
+      .calledWith(undefined, 2)
+  })
+
   it('returns mock type for then resolve', () => {
     const result = subject.when(simpleAsync).calledWith(1).thenResolve('hello')