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Support language and diff highlighting together #2025
Description
Support for both language and diff highlighting together is a popular feature request, as can be seen from the discussion github-linguist/linguist#5758 on the Linguist repo and this Stack Overflow question.
This feature has already been implemented on other markdown-powered sites. The most straightforward syntax would be:
՝՝՝diff js
let fileIcon = document.querySelector("li.file-entry > span.icon");
+fileIcon.classList.remove("icon-file-text");
const disposable = addIconToElement(fileIcon, "/path/to/file.txt");
՝՝՝Currently, this ignores the “js” part and only applies the “diff” syntax highlighting.
Activity
github-actions commentedon Mar 17, 2026
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
hb20007 commentedon Mar 17, 2026
Bump
zkoppert commentedon Apr 24, 2026
Thanks for the report.
After investigating, this is about combining language-specific syntax highlighting with diff highlighting. Syntax highlighting is handled by github/linguist (step 3 of the rendering pipeline), not by this repository.
This repo (
github/markup) only handles step 1: converting markup formats to raw HTML. Check out this part of the README for a fuller picture:For syntax highlighting and code block rendering feedback, GitHub's feedback discussions or the linguist repo would be better venues.
Closing as out of scope for this repository.
hb20007 commentedon Apr 24, 2026
@zkoppert According to a comment by the linguist repo maintainer,
zkoppert commentedon May 5, 2026
Reopening this — I'm sorry for the runaround and for not understanding this better the first time. I know that's not a great experience and I'd like to get this back on track.
After digging into the code, the linguist maintainer's comment is right: this does start in
github/markup.Here's my understanding: in
lib/github/markup/markdown.rb, CommonMarker is invoked with:GITHUB_PRE_LANGbut without thefull_info_stringoption. That means when you write```diff js, CommonMarker outputs:The
jstoken is discarded entirely at this stage — before the syntax highlighting engine ever sees it. CommonMarker already supports preserving it viafull_info_string, which would output something like<pre lang="diff" data-meta="js">— but we don't enable it.A full implementation would also require the internal highlighting engine to recognize that preserved token and apply dual highlighting (language syntax + diff markers). The good news is that
suggestionblocks in PR reviews already do exactly this — so the capability exists internally, it just isn't wired up for fenced code blocks.Linguist doesn't need changes — it only provides grammars, and grammars for both
diffand all supported languages already exist.Sorry again for the misdirection. This is a valid feature request for this repo.
beedell-roke commentedon May 22, 2026
talk.commonmark.org/t/4903/2would be useful to remediate, for the sake of allowing explicit sub-syntax specification in any potential implementation.github-actions commentedon Jul 22, 2026
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
hb20007 commentedon Jul 22, 2026
Still relevant
github-actions commentedon Sep 22, 2026
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
Neirda24 commentedon Sep 22, 2026
still relevant. never mark it as stale