validate regex before creating rule

app/dashboard/views/domain_detail.py

@@ -451,6 +451,20 @@ def domain_detail_auto_create(custom_domain_id):
                             )
                         )
 
+                    try:
+                        re.compile(new_auto_create_rule_form.regex.data)
+                    except:
+                        flash(
+                            f"Invalid regex {new_auto_create_rule_form.regex.data}",
+                            "error",
+                        )
+                        return redirect(
+                            url_for(
+                                "dashboard.domain_detail_auto_create",
+                                custom_domain_id=custom_domain.id,
+                            )
+                        )
+
                     rule = AutoCreateRule.create(
                         custom_domain_id=custom_domain.id,
                         order=int(new_auto_create_rule_form.order.data),