Missing type inference for expect(...).toEqual<T>(...)

Describe the bug

Type inference for expect(x).toEqual(y) is lacking.

That is, you can pass x and y of incompatible types without getting a type inspection.

Compared with type inference for assert.deepStrictEqual(x,y), which works as expected, and correctly gives a type inspection if the type of y is not assignable to the type of x.

You can of course manually type-hint as e.g. expect(x).toEqual<Y>(y), and this might be more appropriate and explicit in some cases - however, it is inconsistent with assert.deepStrictEqual, which does support inference.

(It also slows you down when writing tests, since you won't get auto-completions for y, e.g. when y is an object literal type, unless you manually provide the type yourself.)

Reproduction

Here's an example:

import { test, expect, assert } from "vitest"

type Foo = {
    hello: 'world'
}

function makeFoo(): Foo {
    return { hello: 'world' }
}

test(`can parse PTN place notations`, () => {
  expect(makeFoo()).toEqual({ nope: 'wrong' }) // 👎

  expect(makeFoo()).toEqual<Foo>({ nope: 'wrong' }) // 👍

  assert.deepStrictEqual(makeFoo(), { nope: 'wrong' }) // 👍
})

You can see it failing in this TS playground.

System Info

System:
    OS: Linux 6.6 Ubuntu 22.04.4 LTS 22.04.4 LTS (Jammy Jellyfish)
    CPU: (24) x64 AMD Ryzen 9 7900 12-Core Processor
    Memory: 12.68 GB / 15.49 GB
    Container: Yes
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 18.20.5 - ~/.nvm/versions/node/v18.20.5/bin/node
    npm: 10.8.2 - ~/.nvm/versions/node/v18.20.5/bin/npm
    pnpm: 9.15.2 - ~/.nvm/versions/node/v18.20.5/bin/pnpm
    bun: 1.0.0 - ~/.bun/bin/bun
  npmPackages:
    vitest: ^3.2.4 => 3.2.4

Used Package Manager

npm

Validations

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

Start with the TypeScript playground reproduction and compare the inferred types for expect(...).toEqual(...) with assert.deepStrictEqual(...). Trace the type declarations behind expect and toEqual; done when incompatible argument types are rejected and object-literal completions work without an explicit generic type.