[tabs] `onValueChange` does not fire when the initially selected tab is picked by the `Tabs` component

[ciampo]

Bug report

Current behavior

When tabs and tabpanels are not given a value, and Tabs.Root is not provided with a value or defaultValue, the component automatically picks the first tab as the selected tab (hence why defaultValue has a default value of 0).

When this happens, the onValueChange callback does not fire, even if the selected tab changed, caused by an external factor (from the POV of the consumer).

Expected behavior

I'd expect the onValueChange callback to fire when the component internally picks a selected tab.

Reproducible example

https://codesandbox.io/p/sandbox/elated-microservice-wl4sl2

Notice how alert doesn't fire initially, while it fires for every subsequent user interaction.

Base UI version

1.0.0-beta.0

Which browser are you using?

Chrome

Which OS are you using?

Mac OS

Which assistive tech are you using (if applicable)?

N/A

Additional context

I understand this may be an opinionated take — in any case, whatever is decided, it shoud be applied to all components whenever a value changes for reasons out of the consumer's control (and not just tabs).

[michaldudak]

@ciampo, things changed a bit in the meantime, as values are mandatory on Tabs and TabPanels, but I think the issue is still valid.

Does #3758 fix your use case?

[ciampo]

Hey @michaldudak , I took a look at #3758 and it does fix this bug 🎉

Thank you for working on it!