[core] Remove 'use client' from index files

[michaldudak]

Closes #330.

[oliviertassinari]

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".

[michaldudak]

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)

[oliviertassinari]

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

https://github.com/mui/base-ui/blob/43c957dd8d41f78b45cb8d5bb7e915d809298779/packages/mui-base/src/NumberField/NumberFieldGroup.tsx#L1

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

https://github.com/mui/base-ui/blob/43c957dd8d41f78b45cb8d5bb7e915d809298779/packages/mui-base/src/NumberField/index.ts#L1

at the same time.

But I don't know, it might not be that important: https://github.com/vercel/next.js/pull/64467#issuecomment-2067817756 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.

[atomiks]

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.

[mui-bot]

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https://deploy-preview-331--base-ui.netlify.app/

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[michaldudak]

👍 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.

I feel the same. Technically it's the component (or hook) that must be ran on the client. I updated the PR.

[michaldudak]

@atomiks, I'd appreciate a review

[oliviertassinari]

Cool cleanup 👌

but I suppose there shouldn't be a gap between 'use client' as Olivier mentioned

It's subjective. The rational was to do it a single way through the codebase of MUI. I saw the majority was without blank lines so pushed to default with the majority. I think Albert initially introduced the no blank line path.

Now, if you look at the React docs, it's different https://react.dev/reference/rsc/use-client.

For use strict, there is no consistency in https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode. It's also a mix in https://github.com/search?q=org%3Aradix-ui+%27use+client%27&type=code.

No real preference, as long as it's consistent.

[michaldudak]

I personally prefer more whitespace, but it's not a dealbreaker.