feat: allow $state in return statements

[Ocean-OS]

This allows $state calls to be returned from a function, returning a proxy (if the argument can be proxied). I don't know if we should warn on arguments that aren't proxiable, I'm leaning towards 'no' since that would probably be unnecessary.

Closes #14316

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[changeset-bot]

🦋 Changeset detected

Latest commit: 8f71584

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-15589-svelte.vercel.app/

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@15589

[naylour]

Yes

[Ocean-OS]

I'm not sure if this should also apply to implicit returns in arrow functions, does anyone have any input on that?

[benmccann]

it would be good to have a test, which would also help illuminate what is being supported

[Ocean-OS]

it would be good to have a test, which would also help illuminate what is being supported

I'll add the test in a bit. This PR allows you to return a $state call, like so:

function fn() {
    //...
    return $state(obj); 
} 

In this example, $state gets compiled to $.proxy, proxying the object.
Since the only purpose for this is proxying, $state.raw cannot be used in the same way.

[Hugos68]

This is cool but I fail to see what use cases require you to directly return $state. If you need to return $state it's usually because you are creating a reactive module. In which you would never return directly:

function reactive() {
    const value = $state(...);
    // Mutations/Side effects here
    return value;
}

I struggle to see where you would directly return $state in a meaningful manner.