fn main() {
let ok = r"ab\[c";
let bad = "ab\[c";
//~^ ERROR unknown character escape: `[`
//~| HELP for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
//~| HELP if you meant to write a literal backslash (perhaps escaping in a regular expression), consider a raw string literal
}