[regexp] Disallow '\' in capture names

src/regexp/regexp-parser.cc

Index: src/regexp/regexp-parser.cc
diff --git a/src/regexp/regexp-parser.cc b/src/regexp/regexp-parser.cc
index 68c5a6d2633cd31ee8ee17c0487ec87ea44d7b7d..3e5998719436e1cfe743e694b2eaf526b46bc377 100644
--- a/src/regexp/regexp-parser.cc
+++ b/src/regexp/regexp-parser.cc
@@ -789,6 +789,12 @@ const ZoneVector<uc16>* RegExpParser::ParseCaptureGroupName() {
       }
     }
 
+    // The backslash char is misclassified as both ID_Start and ID_Continue.
+    if (c == '\\') {
+      ReportError(CStrVector("Invalid capture group name"));
+      return nullptr;
+    }
+
     if (at_start) {
       if (!IdentifierStart::Is(c)) {
         ReportError(CStrVector("Invalid capture group name"));