Fix regex char-class parsing (#38)

`/` inside a `[...]` character class is literal, not a terminator.
Track a `cls` flag while scanning the pattern so `/[^/]+$/` and
`/[\]/]/` parse correctly. Closes #38.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: dy

feature/regex.js

@@ -11,13 +11,20 @@
  */
 import { token, skip, err, next, idx, cur } from '../parse.js';
 
-const SLASH = 47, BSLASH = 92;
+const SLASH = 47, BSLASH = 92, LBRACK = 91, RBRACK = 93;
 
 token('/', 140, a => {
   // left operand = division or assignment; `//` `/*` `/?` `/+` = not a regex start
   const c = cur.charCodeAt(idx);
   if (a || c === SLASH || c === 42 || c === 43 || c === 63) return;
-  const pattern = next(c => c === BSLASH ? 2 : c && c !== SLASH); // \x = 2 chars, else 1 until /
+  // \x = 2 chars; `/` inside a [...] class is literal (classes don't nest), else `/` ends pattern
+  let cls = false;
+  const pattern = next(c =>
+    c === BSLASH ? 2 :
+    c === LBRACK ? (cls = true, 1) :
+    c === RBRACK ? (cls = false, 1) :
+    c && (cls || c !== SLASH)
+  );
   cur.charCodeAt(idx) === SLASH || err('Unterminated regex');
   skip();
   const flags = next(c => c === 103 || c === 105 || c === 109 || c === 115 || c === 117 || c === 121); // gimsuy

test/feature/regex.js

@@ -45,6 +45,13 @@ test('regex: in expressions', t => {
   is(run('x.replace(/=>/g, ":")', { x: 'a=>b=>c' }), 'a:b:c')
 })
 
+test('regex: character classes', t => {
+  // `/` inside [...] is literal, not a terminator
+  is(parse('/[^/]+$/'), ['//', '[^/]+$'])
+  is(parse('/[\\]/]/')[1], '[\\]/]')
+  is(run('"a/b".match(/([^/]+)$/)')[1], 'b')
+})
+
 test('regex: JSON serializable', t => {
   const ast = parse('/abc/gi')
   const json = JSON.stringify(ast)