sv migrate svelte-5 uses Typescript syntax in bare <script> tags

[twm]

Describe the bug

I ran npx sv migrate svelte-5 and found that it injected Typescript syntax (interface) into bare <script> tags, resulting in errors like this:

.../halo/src/routes/+layout.svelte:8:23
Error: Type annotations can only be used in TypeScript files. (js)

    let { children }: Props = $props()
</script>

I was able to resolve this by adding lang="ts" to the <script> tags.

Reproduction

Run npx sv migrate svelte-5 on twm/halo@e26f3e6

When I did so I got [email protected]

Logs

No response

System Info

I ran this command but the output was garbage — it thought there was a container (nope!) and failed to identify the installed browsers correctly. I'm on Ubuntu 24.04 x86-64.

Severity

annoyance