vite.config.ts not working with Vite 3 (internal monorepo)

[lmiller1990]

Current behavior

In #22915 we updated to Vite 3. For unknown reasons, I had to change vite.config.ts to vite.config.mjs to make it work. I can't find anything in their release notes about this, though.

I suspect mts will also work, once we update our TypeScript version to 4.7. 4.7 notes on mjs and mts.

Desired behavior

I want to use strongly typed vite.config.

Test code to reproduce

• Change vite.config.mjs to vite.config.ts in packages/{app,launchpad,frontend-shared} (once feat: update to Vite 3 #22915 is merged)
• Run yarn build-prod-ui in packages/{app,launchpad}
• Error

Cypress Version

develop

Other

This only impacts the monorepo, vite.config.ts seems fine for users, I guess it's an issue in our monorepo only, possibly due to old TypeScript version, or some other dependency.