fix: allow whitespace in legacy onMount check

[rdunk]

I have an application using [email protected] alongside @sveltejs/[email protected], it seems like the is_legacy check introduced in #13140 is failing (assuming legacy refers to <= Svelte 4) as the result of onMount.toString() includes a linebreak in the function body.

This PR modifies the regex to account for whitespace within the curly braces.

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[teemingc]

I can't reproduce the issue that you're describing. Can you open a new issue with a minimal reproduction?

[rdunk]

I have a minimal repro here: https://github.com/rdunk/svelte-legacy-check-repro, but on further inspection it seems to only fail with the combination of [email protected], [email protected] and @sveltejs/[email protected]. Looking through release notes, perhaps Svelte 4 and the compatible version of the vite plugin (3.x) are incompatible with Vite 6?

Let me know if not and I'll open an issue and properly report.

[teemingc]

Yeah, they're incompatible. I think you might need Svelte 5 and vite-plugin-svelte 4 to use Vite 6

[rdunk]

OK, thanks for confirming. In that case I'll close this PR as I'm only able to reproduce when using Vite 6. Thanks for the help!