Comments containing HTML tags can cause unhelpful error messages

[danielj0nes]

Describe the bug

Both single-line and multi-line comments that contain certain HTML tags can break the parser and throw an internal server error.

It wasn’t easy to figure out what caused the issue, either, because Svelte for VS Code and the Vite error message incorrectly reported a missing semicolon.

It would be helpful to at least have a clearer warning or error message in this case.

---

Reproduction

// Adding a tag to this comment, such as this one: <style>
// will now break the parser.
function f(x) {
  ...
}

Vite output:

[plugin:vite-plugin-svelte:preprocess] Error while preprocessing placeholder.svelte
placeholder.svelte:4:30: Missed semicolon

---

System Info

System:
  OS: Linux 6.17 cpe:/o:nixos:nixos:25.11 25.11 (Xantusia)
  CPU: (16) x64 AMD Ryzen 7 PRO 8840U w/ Radeon 780M Graphics
  Memory: 22.89 GB / 30.01 GB
  Container: Yes
  Shell: 5.9 - /run/current-system/sw/bin/zsh

Binaries:
  Node: 22.21.1 - /run/current-system/sw/bin/node
  npm: 10.9.4 - /run/current-system/sw/bin/npm

Browsers:
  Chromium: 142.0.7444.162
  Firefox: 145.0
  Firefox Developer Edition: 145.0

npmPackages:
  svelte: ^5.41.0 => 5.43.6

---

Severity

annoyance