expect().resolves does not accept a function

[IIIMADDINIII]

Describe the bug

Mostly a the same as #6643 but now Jest supports functions with resolves: jestjs/jest#15713

If you call await expect(async () => { ... }).rejects.toThrow(), this will work as expected. However, change this to await expect(async () => { ... }).resolves.not.toThrow() and the test fails with the following error:

TypeError: You must provide a Promise to expect() when using .resolves, not 'function'.

vitest/packages/expect/src/jest-expect.ts

Lines 1149 to 1162 in cba2036

	const obj = utils.flag(this, 'object')
	const wrapper = typeof obj === 'function' ? obj() : obj // for jest compat
	if (utils.flag(this, 'poll')) {
	throw new SyntaxError(
	`expect.poll() is not supported in combination with .rejects`,
	)
	}
	if (typeof wrapper?.then !== 'function') {
	throw new TypeError(
	`You must provide a Promise to expect() when using .rejects, not '${typeof wrapper}'.`,
	)
	}

vitest/packages/expect/src/jest-expect.ts

Lines 1077 to 1089 in cba2036

	const obj = utils.flag(this, 'object')
	if (utils.flag(this, 'poll')) {
	throw new SyntaxError(
	`expect.poll() is not supported in combination with .resolves`,
	)
	}
	if (typeof obj?.then !== 'function') {
	throw new TypeError(
	`You must provide a Promise to expect() when using .resolves, not '${typeof obj}'.`,
	)
	}

Reproduction

https://stackblitz.com/edit/vitest-dev-vitest-9omsvx?file=test%2Fbasic.test.ts

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: 22.22.0 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @vitest/ui: 4.1.5 => 4.1.5 
    vite: 8.0.10 => 8.0.10 
    vitest: 4.1.5 => 4.1.5

Used Package Manager

npm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[hi-ogawa]

I've thought rejects supporting the function was Jest's feature creep or unintended oversight, then we inherited and resolves not supporting function is designed as intended (both Jest initially and Vitest now).

That said, personally I like passing function to rejects, so I vote for generalizing to resolves too.