feat: include script and svelte:options attributes in ast

[jrmajor]

In Svelte 4 AST, script tags (root.instance and root.module) do not have attributes, and prettier-plugin-svelte has to extract them using regex (https://github.com/sveltejs/prettier-plugin-svelte/blob/b120c4de5faa6ca6fa0c6867d6048e1dd1b958ca/src/lib/extractAttributes.ts).

With Svelte 5 (modern AST), the same now applies to svelte:options tag. However, unlike script, it can also have expression attributes:

<!-- only string attributes are allowed on `script` -->
<script lang="ts" context="module"></script>
<!-- svelte:options allows expressions in attributes -->
<svelte:options immutable={true}>

Currently, extractAttributes can only handle string attributes. If we included attributes for these elements in AST, we could remove this function altogether, instead of improving it to also parse expression attributes.

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[Rich-Harris]

this seems very sensible to me — @dummdidumm any thoughts on this from a language-tools perspective?

[dummdidumm]

We can't allow expression attributes on the script tag because generics accepts a typescript generic, which could look like this generics="T extends { foo: number}" which should be treated literally and not as an expression.
Adding the attributes itself would probably be ok, though the regex to blank script/style tags would probably not benefit from it (because that needs to happen before the parser).
Maybe it helps to open a very drafty PR over at prettier-plugin-svelte so we can more clearly see what the potential benefits are

[Rich-Harris]

which should be treated literally and not as an expression

But we could do that, no? The parser would treat that as a text attribute regardless of the {...} because it's a <script>

[jrmajor]

We can't allow expression attributes on the script tag because generics accepts a typescript generic, which could look like this generics="T extends { foo: number}" which should be treated literally and not as an expression.

I've added a test for that, and it seems it's trated literally:

{
	"type": "Attribute",
	"start": 132,
	"end": 168,
	"name": "generics",
	"value": [
		{
			"start": 142,
			"end": 167,
			"type": "Text",
			"raw": "T extends { foo: number }",
			"data": "T extends { foo: number }"
		}
	]
}

Maybe it helps to open a very drafty PR over at prettier-plugin-svelte so we can more clearly see what the potential benefits are

I'll check how it works in sveltejs/prettier-plugin-svelte#436.

[jrmajor]

Maybe it helps to open a very drafty PR over at prettier-plugin-svelte so we can more clearly see what the potential benefits are

I'll check how it works in sveltejs/prettier-plugin-svelte#436.

It worked, I was able to delete extractAttributes.ts and remove lines where it was used. It also fixed the test that were failing because expressions in svelte:options weren't correctly parsed. Can't push that unfortunately, because I had to use file:../svelte/packages/svelte version constraint for svelte.

[dummdidumm]

Push it anyway 😁 it's fine if the PR fails in CI for a few days, we just don't merge until this goes in.

[jrmajor]

@dummdidumm Here you go: sveltejs/prettier-plugin-svelte@10fedea (#436).

[Rich-Harris]

thank you!