Consider publishing dual format with CommonJS compatibility

[otakustay]

Clear and concise description of the problem

We are moving to "moduleResolution": "nodenext" with TypeScript 4.6 nightly build, but for some ecosystem reasons we are unable to introduce "type": "module" to our packages.

Although vite as a CLI runs without any problem, the import {expect} from 'vitest' statement can be errored from TypeScript in IDE:

Module 'vitest' cannot be imported using this construct. The specifier only resolves to an ES module, which cannot be imported synchronously. Use dynamic import instead.ts(1471)

This has no actual negative effects to us since we don't transpile .test.ts, but a red error is always there whenever we open our tests files.

Suggested solution

Consider publish both CJS and ESM formats and having exports field in package.json also references to CJS files.

Alternative

No response

Additional context

No response

Validations

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[aleclarson]

I think Vitest could simply publish a stub CJS module to appease TypeScript here?

When Vitest runs the test file, it will be compiled with the module entry point of Vitest, so it shouldn't cause any problems.

[aleclarson]

Scratch that. Looks like the issue is "type": "module" in Vitest's package.json

I can confirm that removing the type: module line fixes the TypeScript error. Can we publish Vitest without it, or would that cause problems?

edit: Ah, removing type: module means we'll have to publish the dist files with .mjs extension.