regex flags, bad regexs become Words

src/parser/tokenizer2.ts

@@ -390,8 +390,29 @@ export class Scanner {
       if (this.char === c`/` && this.peek() === c`/`) {
         this.next() // skip /
         this.next() // skip /
+
+        // 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
       }
 
       this.next()