fix(ruby): properly highlight %r{} regex literals containing nested patterns

[j-erasmus]

Summary

This fixes an issue where %r{}-style regular expressions in Ruby were not correctly highlighted when they contained nested patterns or complex escape sequences. Patterns like (\.{2}|\A/) would either break highlighting or be ignored entirely due to improper handling of nesting inside %r{}.

Resolves: https://github.com/highlightjs/highlight.js/issues/4281

---

Root Cause

Highlight.js previously treated %r{} regex literals as flat strings. This caused the parser to:

• Fail on nested constructs like {2} (quantifiers)
• Break on position anchors like \A
• Terminate the regex early or skip highlighting entirely

---

Fix

• Introduces a top-level REGEXP mode to match %r{}, %r(), %r[], %r!, etc. anywhere in Ruby code
• Enables nested brace parsing inside %r{} using contains: ['self']
• Removes %r variants from the legacy RE_STARTERS_RE block (which still handles /.../ contexts)
• Keeps other regex behavior intact and scoped

---

Screenshots

• sample file

Before	After

[Yang062]

101142167176

@.***

Jacques Erasmus @.***> 于 2025年7月4日周五 19:49写道：

@.**** commented on this pull request.

In src/languages/ruby.js https://github.com/highlightjs/highlight.js/pull/4286#discussion_r2185158611 :

@@ -227,6 +227,27 @@ export default function(hljs) { ] };

• const REGEXP = {
• className: 'regexp',
• contains: [

•  hljs.BACKSLASH_ESCAPE,
  

•  SUBST,
  

•  {
  

•    begin: /\{/, end: /\}/,
  

@joshgoebel https://github.com/joshgoebel this should now be fixed, I also added some tests to verify these cases.

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[j-erasmus]

@joshgoebel any updates here? I've addressed the comments you left previously. Please take a look/merge when you get a chance 🙇