From 52e100cab31659bf2461db635c42cf25169cc19e Mon Sep 17 00:00:00 2001
From: Chris Wanstrath <2+defunkt@users.noreply.github.com>
Date: Tue, 25 Nov 2025 16:00:06 -0800
Subject: [PATCH] regex flags, bad regexs become Words

---
 src/parser/tokenizer2.ts | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/parser/tokenizer2.ts b/src/parser/tokenizer2.ts
index f0a8502..317c580 100644
--- a/src/parser/tokenizer2.ts
+++ b/src/parser/tokenizer2.ts
@@ -390,7 +390,28 @@ export class Scanner {
       if (this.char === c`/` && this.peek() === c`/`) {
         this.next() // skip /
         this.next() // skip /
-        this.push(TokenType.Regex)
+
+        // read regex flags
+        while (this.char > 0 && isIdentStart(this.char))
+          this.next()
+
+        // validate regex
+        const to = this.pos - getCharSize(this.char)
+        const regexText = this.input.slice(this.start, to)
+        const [_, pattern, flags] = regexText.match(/^\/\/(.*)\/\/([gimsuy]*)$/) || []
+
+        if (pattern) {
+          try {
+            new RegExp(pattern, flags)
+            this.push(TokenType.Regex)
+            break
+          } catch (e) {
+            // invalid regex - fall through to Word
+          }
+        }
+
+        // invalid regex is treated as Word
+        this.push(TokenType.Word)
         break
       }