Automatic code highlighting broken in fullscreen code view

[oskar1 (Oskar)]

Priority/Severity:
Low
Platform:
Chrome 124, Ubuntu 22
Version:
Discourse v3.3.0.beta2-dev
Description:
Discourse performs automatic code highlighting with hljs, even when no language was specified. This feature works in normal topic view, but not when viewing the code in fullscreen.
Reproducible steps:

1. Create a topic with a code block, without specifying the language

System.out.println("hello world");

2. View the topic and see that hljs detected a language and applies highlighting.
3. Click the fullscreen button at the top right of the code block.
4. See that hljs language detection failed and no highlighting is applied

Here are some screenshots in one big image, because of new user restrictions .

[pmusaraj (Penar Musaraj)]

Thanks for the report, @oskar1, I can confirm this bug locally. (It’s harder to reproduce this on meta because we use text not auto as the default code lang on meta.)

We will take a look at fixing this soon.

[Arkshine]

I think the issue is here :

https://github.com/discourse/discourse/blob/main/app/assets/javascripts/discourse/app/lib/highlight-syntax.js#L36-L52

You have lang-auto class name applied with markdown code and automatically removed here so the library can guess the language.

However, when you go fullscreen, lang-auto is no longer in the element, and you have only language-<detected-language-here> class name here. Thus, lang is undefined.

A maybe fix could be here – if lang-auto is not found, look for language-<..>

const m = className.match(/^lang-(.+)$/);
→
const m = className.match(/^`(?:lang|language)-(.+)$/);

[pmusaraj (Penar Musaraj)]

Happy to review a PR if you’d like to submit one @Arkshine, you’ve done a good part of the work already .

[Arkshine]

I made a PR . Hopefully, the tests are good enough!

https://github.com/discourse/discourse/pull/26710

[pmusaraj (Penar Musaraj)]

Thanks @Arkshine, fix looks great, will merge it once tests pass in CI.