fix: ensure migrate keeps inline/trailing comments in $props type definition and produces non-broken code

[rgon]

Fixes #14140

Keeps inline comments when migrating types, as we already do with other statement types L783

    export let step: number | null = null // In-line comments are now kept

    interface Props {
	step: number | null; // In-line comments are now kept
    }

Added tests for Typescript and JSDoc migration. In the latter, the comments are merged with leading comments. See tests/migrate/jsdoc-with-comments/output.svelte

[changeset-bot]

🦋 Changeset detected

Latest commit: e00d318

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

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[dummdidumm]

Thank you! Could you add a changeset? Then we're good to merge

[pkg-pr-new]

pnpm add https://pkg.pr.new/svelte@14143

commit: e00d318

[rgon]

Changeset added!

[paoloricciuti]

Just one comment...while a bit weird unfortunately you can't assume trailing comments are only line comment. For example this

<script>
	export let name = 'world'; /*
	* this is a trailing comment too
	**/
</script>

migrate to broken code

<script>
	/**
	 * @typedef {Object} Props
	 * @property {string} [name] - * this is a trailing comment too
*
	 */

	/** @type {Props} */
	let { name = 'world' } = $props();
	* this is a trailing comment too
	**/
</script>

although to be fair it's broken in today migration too...but the comment should probably undergo the same "cleaning" process we apply to the leadingComments

[rgon]

@paoloricciuti Nice catch! Absolutely fair to fix it while we're at it and add tests, especially when it produces broken code.

I have modified this PR with the fix (and reworked comment parsing a bit so that it's exactly like leadingComments) and added tests for the use case you mentioned.

Adding a new patch fix to the changeset as well, since the issue predates my PR (and arguably is more important than the original issue!).

[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14143-svelte.vercel.app/

this is an automated message

[paoloricciuti]

@rgon if you can fix linting we are good to merge

[paoloricciuti]

The linting issues aren't in any of my touched files:

It was a small issue in the migrate file...let's wait on all greens and i'll merge

[rgon]

@paoloricciuti thanks, I got a bit confused with the sites/svelte-5-preview warnings when running lint on the entire pnpm workspace, since it runs on parallel and merges the log. Was about to push a fix

[paoloricciuti]

Thanks! 🚀