[RadioGroup] Create new RadioGroup component

[atomiks]

• I have followed (at least) the PR section of the contributing guide.

Closes #26

[mui-bot]

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[michaldudak]

We don't have to enforce strings here. Let's make it any or unknown as in Tabs.

[atomiks]

A hidden <input> is rendered for the whole RadioGroup root which requires the native DOM type:

{props.name && (
  <input type="hidden" name={props.name} value={checkedItem ?? ''} required={required} />
)}

So we can allow string or number. I don't think anything else needs to be allowed anyway?

[michaldudak]

Similarly to the Select, we can allow arbitrary values here and expose a prop to control how it's serialized.

[atomiks]

What valid use cases are there for something other than a string or number?

[colmtuite]

@atomiks The docs demo is missing the "indicator", I think that's one (or perhaps the main?) point of confusion. There should be (whatever "should" means) a little dot inside the circle when it's selected. Like this https://helios.hashicorp.design/assets/components/form/radio-card/radio-card-states-2acdd2c7a5775a7479f7c497d3947804.png

[atomiks]

@colmtuite that's just one particular design though. The indicator can be anything, such as a plain filled-in white circle which is an outline when unchecked.

[colmtuite]

@atomiks I don't see the keepMounted prop documented in the component API, am I missing/misunderstanding something?

[mj12albert]

@atomiks is Composite/CompositeItem intended to be a successor to the current useCompoundParent/Item?

At least for Slider I think this could be a completely replacement for it if we could pass arbitrary metadata into these parameters (for slider it's the id of the associated input element)

BTW the only other component also using useCompound is Tabs, which uses useCompound in a similar way that Accordion needs, I'll try using CompositeList/Item for Accordion first ~

[atomiks]

Yes, it's a replacement for both them & FloatingList. It can be modified wherever necessary for different components