fix: Add files and group properties to HTMLInputAttributes

[dvcol]

This adds missing files and group properties to match the respective bind:files and bind:group.

Unless I'm mistaken, it seems that the files and group attributes are missing from the HTMLInputAttributes type in element.d.ts.

The typings for the binding 'bind:group' and 'bind:files' are present (as seen here) but the individual properties aren't.

Note that the bindings exists on the deprecated SvelteInputProps, so maybe this is intentional somehow ?

Closes issue #14579

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[Rich-Harris]

Ah, interesting — hadn't noticed the prop typing issue. The fix you propose definitely makes sense for files since setting files works.

For group it's slightly less clear-cut — the types here would imply that you could do this (note the lack of bind)...

<!-- is checked when `choice === 'one'` -->
<input type="radio" group={choice} value="one" />

...but you can't, it just (uselessly/confusingly) sets a group attribute on the element. So now I'm wondering if it's better to let the types lie a little bit, or change the behaviour of group so that the above works (which would be a can of worms when considering spread attributes).

[dummdidumm]

I vote for "lie a bit" - I cannot imagine someone tripping up on that in practise.

[dvcol]

What about making it condition on the input type ?

interface HTMLInputAttributes<Type extends HTMLInputTypeAttribute | undefined | null = undefined> extends HTMLAttributes<HTMLInputElement> {
	...
	group?: Type extends 'checkbox' | 'radio' ? any | undefined | null : never;
        ...
}

However, doesn't this issues also exist for other specific bindings, like checked and indeterminate ?

[paoloricciuti]

What about making it condition on the input type ?

interface HTMLInputAttributes<Type extends HTMLInputTypeAttribute | undefined | null = undefined> extends HTMLAttributes<HTMLInputElement> {
	...
	group?: Type extends 'checkbox' | 'radio' ? any | undefined | null : never;
        ...
}

However, doesn't this issues also exist for other specific bindings, like checked and indeterminate ?

This wouldn't solve the issue @Rich-Harris is talking about tho

[dvcol]

Not completely, but it would restrict it to the checkbox and radio inputs, lessen the lie in some way ?

[Rich-Harris]

I don't think it's possible — unless I'm missing something there's nowhere for us to pass the right type argument, so Type will always be undefined which causes this:

I'm good with 'lie a bit' too so I'll merge this as-is. Thanks!

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