Type error on mockImplementation with call signature in object type

[freakzlike]

Describe the bug

I have a function type with additional properties:

export interface Handler {
  (v: number): number;
  other(v: number): number;
}

When I try to use mockImplementation on the call signature, I receive the following type error

mockedHandler.mockImplementation((v) => v * 1);
// Property 'other' is missing in type '(v: number) => number' but required in type 'Handler'

There was no error in v1. Now with v2, I have to pass the whole object even though other is not used and not working.
I expect that only the call signature type is required for mockImplementation

As additional help I found a helper to extract the call signature from an object type:

type CallSignature<T extends (...a: any[]) => unknown> = (...a: Parameters<T>) => ReturnType<T>

const onlyCall: CallSignature<Handler> = (v) => v * 2

Reproduction

https://stackblitz.com/edit/vitest-dev-vitest-8ikkec?file=test%2Fbasic.test.ts&view=editor

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.20.3 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @vitest/ui: latest => 2.0.3 
    vite: latest => 5.3.4 
    vitest: latest => 2.0.3

Used Package Manager

pnpm

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• The provided reproduction is a minimal reproducible example of the bug.

[is-jonreeves]

Incase it helps narrow things down, we are also getting a bunch of similar typescript errors after upgrading from 2.0.2 to 2.0.3.

[hi-ogawa]

I think OP's vi.mocked + mockImplementation was already broken in v2.0.0.

@is-jonreeves If you are seeing a issue specific to 2.0.2 -> 2.0.3 (thus due to #6086), then it would be great if you can provide a reproduction.

[is-jonreeves]

I tested 2.0.4 and it appears to have also resolved my issue. Thanks!

---

For what it's worth... I re-tried downgrading to 2.0.3 to make sure I wasn't mistaken, and there is definitely a type error over there.

Downgrading to 2.0.3:

npm i -D [email protected] @vitest/[email protected] @vitest/[email protected]

Simplest example I could find in our code:

const mockedSelectIsUnlicensed = vi.spyOn(sessionSlice, 'selectIsUnlicensed');
...
mockedSelectIsUnlicensed.mockImplementation(() => true); // <--- complains in 2.0.3 even though type is correct

Type error in 2.0.3 (not in 2.0.2 or 2.0.4):

Type '() => true' is not assignable to type '{ clearCache: () => void; resultsCount: () => number; resetResultsCount: () => void; }'

I don't have a full example I can share, but if it helps, the usecase is a real redux store where we have used vi.spyOn to override an exported selector.