fn main() {
    let ok = "{{everything fine}}";
    let bad = "\{it is wrong\}";
    //~^  ERROR unknown character escape: {
    //~^^  HELP if used in a formatting string, curly braces are escaped with `{{` and `}}`
    //~^^^ ERROR unknown character escape: }
    //~^^^^  HELP if used in a formatting string, curly braces are escaped with `{{` and `}}`
}