fix: correctly migrate sequence expressions

[paoloricciuti]

Svelte 5 rewrite

Closes #13278

While working on this i noticed that the sequence expression was a problem for $state too. Also while the migration correctly migrate this

$: double = (console.log(double), count * 2);

the resulting code will actually error at runtime because a derived is accessing himself. This however is a bit harder to migrate effectively because either we should move it to state+effect (kinda 🤮) or we should have an external non stateful variable. Regardless i think we should do this in a separate PR.

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[Rich-Harris]

this output doesn't seem right

Suggested change

	let count = ($state((void 0, 0)));
	let count = $state((void 0, 0));

[paoloricciuti]

The migration simply append $state( and ) to the left and right of the init (it was already like this before).

This keeps the code very simple but if you have multiple parentheses spit out some weird code. Eg.

let count = (((0)));

converts to

let count = ((($state(0))));

Because parentheses are basically counted nowhere in the ast.

We can probably fix this with some more complex code to migrate state but I'm not sure is worth it just for the esthetic.

[paoloricciuti]

So basically the point is: the last tells us where the expression is but the expression does not include the parentheses and we can't really be sure of how many parentheses, whitespace, code that the ast doesn't consider are there so the code will be probably much more complex (and even worse for handling the derived)

[Rich-Harris]

i fixed it 😉

[paoloricciuti]

Ugh I need to remember that doing such things is fine...whenever I'm working with some AST i tend to avoid touching strings as much as possible but it's actually totally fine. Thanks and sorry 😉