As I understand things, it's possible to use Base UI components without having to add "use client" (as a user of Base UI). For example, https://deploy-preview-331--base-ui.netlify.app/base-ui/react-number-field/ imported by a server component seems to work just fine (@mui/system is heading to work, and React.useId works with server components).

Now, sure, developers would need to add events to make use of those Base UI, so need "use client" in their code. But this might only happen higher up, meaning when developers use the design systems built with Base UI. I suspect that adding "use client" in each component file could help with the DX, delaying the time when developers hit an error that requires them to add "use client".

Sorry, I don't quite understand what you're proposing above.

I suspect that adding "use client" in each component file could help with the DX

We must add "use client" in our component files as we use APIs not supported by RSC (context, event handlers)

The point I was trying to make is that, for example:

Doesn't have "use client" but it is seems that it should. Removing

at the same time.

But I don't know, it might not be that important: vercel/next.js#64467 (comment) if it's fixed in Next.js latest canary. All in all, 👍 to add use client at the lowest level possible, even if it leads to duplication. It feels clearer, but I can't find strong arguments either way.

Is this only necessary when using the star (*) export?

In our new API, we export each component individually. Only the types use the star (might need export type *).

Error: It's currently unsupported to use "export *" in a client boundary. Please use named exports instead.