Svelte 5: Inaccurate source maps when `lang="ts"` is enabled

Why this is a good first issue

Source map accuracy issue specific to TypeScript in Svelte 5.

AI Summary

The issue involves inaccurate source maps when using TypeScript in Svelte 5, particularly affecting terminal output and error pages. The problem appears related to preprocessing configurations, possibly involving Vite. While the reproduction is clear, the fix may require understanding both Svelte's and Vite's source map handling.

Issue Description

Describe the bug

Source maps are seemingly inaccurate when lang="ts" is enabled on the <script> tag. This only occurs when using TS in Svelte 5. Removing lang="ts" fixes the issue.

When presented with the following Svelte code:

Errors locations are accurate in the IDE (as shown above), but are off in both the terminal output, and the error page.

Reproduction

https://github.com/AdrianGonz97/svelte-5-ts-source-maps-reproduction

Logs

No response

System Info

  System:
    OS: Linux 5.15 Ubuntu 20.04.5 LTS (Focal Fossa)
    CPU: (24) x64 AMD Ryzen 9 5900X 12-Core Processor
    Memory: 7.95 GB / 31.30 GB
    Container: Yes
    Shell: 5.8 - /usr/bin/zsh
  Binaries:
    Node: 20.10.0 - ~/.volta/tools/image/node/20.10.0/bin/node
    Yarn: 1.22.21 - ~/.volta/tools/image/yarn/1.22.21/bin/yarn
    npm: 10.2.3 - ~/.volta/tools/image/node/20.10.0/bin/npm
    pnpm: 8.10.5 - ~/.volta/bin/pnpm
    bun: 1.0.2 - ~/.bun/bin/bun
  npmPackages:
    svelte: ^5.0.0-next.26 => 5.0.0-next.26

Severity

annoyance

GitHub Labels

bug