Vite is treating TypeScript code in .svelte files as JavaScript (ignoring lang="ts")

Describe the bug

I am trying to use Shadcn-Svelte with my Svelte app and when trying to use components, I get errors from vite that seem like vite is interpreting Svelte scripts as JavaScript files, completely ignoring the lang="ts". My configuration files are correct, as they are unmodified from the svelte starter template.

I get errors along the lines of

[plugin:vite-plugin-svelte] .../frontend/src/lib/components/ui/input/input.svelte:2:13 Unexpected token
.../frontend/src/lib/components/ui/input/input.svelte:2:13
1 |  <script lang="ts">
 2 |    import type { HTMLInputAttributes } from "svelte/elements";
                    ^
 3 |    import type { InputEvents } from "./index.ts";
 4 |    import { cn } from "$lib/utils.ts";

Reproduction

bunx create svelte -> bunx shadcn-svelte init -> bunx shadcn-svelte add button

Steps to reproduce

Use the Button component in shadcn-svelte somewhere in Svelte (eg. `+page.svelte)
bun dev and go to localhost:5173

System Info

System:
    OS: Linux 6.1 Debian GNU/Linux 12 (bookworm) 12 (bookworm)
    CPU: (4) x64 Intel(R) Core(TM) i7-4610M CPU @ 3.00GHz
    Memory: 6.58 GB / 15.53 GB
    Container: Yes
    Shell: 5.2.15 - /bin/bash
  Binaries:
    Node: 22.2.0 - ~/.nvm/versions/node/v22.2.0/bin/node
    npm: 10.7.0 - ~/.nvm/versions/node/v22.2.0/bin/npm
    bun: 1.1.10 - ~/.bun/bin/bun
  npmPackages:
    vite: ^5.2.12 => 5.2.12

Used Package Manager

bun

Logs

No response

Validations

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[X] Read the Contributing Guidelines.
[X] Read the docs.
[X] Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
[X] Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
[X] Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
[X] The provided reproduction is a minimal reproducible example of the bug.

vitejs / vite

Vite is treating TypeScript code in .svelte files as JavaScript (ignoring lang="ts") #17445