fix: support using keyword

[Rich-Harris]

Upgrades to the latest version of Acorn, and replaces ecmaVersion: 16 with 'latest' which allows Svelte code to use the using keyword (which is now stage 4, i.e. part of the language).

I didn't think it worthwhile to add a test (would be like having a test for var declarations or whatever) but you can easily see it working in the playground once it deploys.

One thing we could conceivably do is transform components with top-level using such that disposals don't occur until the component is removed. This would mean wrapping everything in an async function that ends with something like this:

return new Promise((fulfil) => {
  $effect(() => fulfil);
});

Personally I'm not sold on the idea — it's a little magical, and would prevent the component from exporting values — but I raise it as a possibility for discussion. If we thought we might want to add that capability in future we could always prevent the usage of top-level using, though that itself might be annoying.

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Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

[changeset-bot]

🦋 Changeset detected

Latest commit: 0fd3921

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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svelte	Patch

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-16190-svelte.vercel.app/

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@16190

[Rich-Harris]

Realised that we don't need to do the whole async dance to get top-level using to work as expected in components — opened #16192 as an alternative

[Rich-Harris]

gonna close this in favour of #16192. the people have spoken