Function fail 

pub fn fail<Input, Output, Error>(
    i: &mut Input,
) -> Result<Output, ErrMode<Error>>
where
    Input: Stream,
    Error: ParserError<Input>,

A parser which always fails.

For example, it can be used as the last alternative in alt to control the error message given.

Example

use winnow::combinator::fail;

let s = "string";
assert_eq!(fail::<_, &str, _>.parse_peek(s), Err(ErrMode::Backtrack(InputError::new(s, ErrorKind::Fail))));