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

Previously, the Ruby grammar only recognized %r{} regex literals
in limited contexts, causing patterns like %r{(\.{2}|\A/)} to
break syntax highlighting.

This fix:
- Adds a top-level REGEXP mode to support all %r{} variations globally
- Enables nested brace handling inside %r{...}
- Removes redundant %r handling tied to RE_STARTERS_RE
- Adds a test case to regexes.txt to prevent regression

CHANGES.md

@@ -25,6 +25,7 @@ Core Grammars:
 - enh(json) add json5 support [Kerry Shetline][]
 - fix(css) `unicode-range` parsing, issue #4253 [Kerry Shetline][]
 - fix(csharp) Support digit separators [te-ing][]
+- fix(ruby) support nested content in `%r{}` regex literals outside expression contexts [Jacques Erasmus][]
 
 Documentation:
 
@@ -53,6 +54,7 @@ CONTRIBUTORS
 [Thomas Gorissen]: https://github.com/serrynaimo
 [te-ing]: https://github.com/te-ing
 [Anthony Martin]: https://github.com/anthony-c-martin
+[Jacques Erasmus]: https://github.com/j-erasmus
 
 
 ## Version 11.11.1

src/languages/ruby.js

@@ -227,6 +227,27 @@ export default function(hljs) {
     ]
   };
 
+  const REGEXP = {
+    className: 'regexp',
+    contains: [
+      hljs.BACKSLASH_ESCAPE,
+      SUBST,
+      {
+        begin: /\{/, end: /\}/,
+        contains: ['self', hljs.BACKSLASH_ESCAPE, SUBST],
+        relevance: 0
+      }
+    ],
+    illegal: /\n/,
+    variants: [
+      { begin: /%r\{/, end: /\}[a-z]*/ },
+      { begin: '%r\\(', end: '\\)[a-z]*' },
+      { begin: '%r!', end: '![a-z]*' },
+      { begin: '%r\\[', end: '\\][a-z]*' },
+      { begin: '/', end: '/[a-z]*' }
+    ]
+  };
+
   const PARAMS = {
     variants: [
       {
@@ -324,6 +345,7 @@ export default function(hljs) {
     UPPER_CASE_CONSTANT,
     CLASS_REFERENCE,
     METHOD_DEFINITION,
+    REGEXP,
     {
       // swallow namespace qualifiers before symbols
       begin: hljs.IDENT_RE + '::' },
@@ -372,22 +394,6 @@ export default function(hljs) {
             {
               begin: '/',
               end: '/[a-z]*'
-            },
-            {
-              begin: /%r\{/,
-              end: /\}[a-z]*/
-            },
-            {
-              begin: '%r\\(',
-              end: '\\)[a-z]*'
-            },
-            {
-              begin: '%r!',
-              end: '![a-z]*'
-            },
-            {
-              begin: '%r\\[',
-              end: '\\][a-z]*'
             }
           ]
         }

test/markup/ruby/regexes.expect.txt

@@ -3,3 +3,4 @@ str =~ <span class="hljs-regexp">%r{foo|bar|buz$}</span>
 str =~ <span class="hljs-regexp">%r!foo|bar$!</span>
 str =~ <span class="hljs-regexp">%r[foo|bar$]</span>
 str =~ <span class="hljs-regexp">%r(\(foo|bar\)$)</span>
+str =~ <span class="hljs-regexp">%r{(\.{2}|\A/)}</span>

test/markup/ruby/regexes.txt

@@ -3,3 +3,4 @@ str =~ %r{foo|bar|buz$}
 str =~ %r!foo|bar$!
 str =~ %r[foo|bar$]
 str =~ %r(\(foo|bar\)$)
+str =~ %r{(\.{2}|\A/)}