feat: more efficient code generation when referencing globals

[Rich-Harris]

Noticed this while reviewing #12692 — there's some low-hanging fruit here. When referencing built-ins in templates...

<p>{location.href}</p>
<p>{btoa('hello world')}</p>

...we currently create effects (or deriveds, in the case of component props):

$.template_effect(() => $.set_text(text_1, btoa('hello world')));
$.template_effect(() => $.set_text(text, location.href));

If we make the perfectly reasonable assumption that globals don't reference Svelte state, we can do this instead:

text.nodeValue = location.href;
text_1.nodeValue = btoa('hello world');

This assumption would break if someone did something stupid...

globalThis.foo = () => somestate;

...but if people do that they will have their Svelte license revoked.

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests and linting

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

[changeset-bot]

🦋 Changeset detected

Latest commit: 33bf522

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

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[ottomated]

If this only applied to built-in globals, it would still be better in the most common case but prevent the assumption from ever breaking (I agree it's uncommon, but I could see it happening in two cases: a svelte app embedded into another page, or communication with a browser extension)

[Rich-Harris]

It doesn't really — someone could happily do const location = $state(...); globalThis.location = location and it would still break stuff. The trick is to not do that!