Add wrapping fn for `Fn(&str) -> IResult<&str, T>` parsers

[eignnx]

As far as I can tell, some nom parsers (like re_find!) aren't generic enough, and must accept &str input. This means you can't pass them a LocatedSpan.

It would be nice if there were a function that accepted one of those parsers and "lifted" it into a LocatedSpan -> LocatedSpan parser.

Here's as far as I got trying to implement this function:

type Span<'a> = LocatedSpan<&'a str>;

fn wrap<'input, T>(
    parser: impl Fn(&'input str) -> IResult<&'input str, T>,
) -> impl Fn(Span<'input>) -> IResult<Span<'input>, T> {
    |input: Span<'input>| {
        let (rest, pos) = position(input)?;
        // In the following line, how do we map the error?
        let (rest, res) = parser(rest.fragment()).map_err(|e| e)?;
        let rest = unsafe {
            // How should the offset and line be updated here?
            Span::new_from_raw_offset(pos.location_offset(), pos.location_line(), rest, ())
        };
        Ok((rest, res))
    }

The end result is that this function could be used like so:

fn some_parser(input: Span) -> IResult<Span, Whatever> {
    let re = |input: &str| re_find!(input, "<some regex here>");
    wrap(re)(input)
}

[rljacobson]

Is this still relevant in nom 6.0.0-alpha1? It might be easier just to wait for the new version of nom.

[MTRNord]

Any update on this? The string example from nom sadly doesnt work with nom_locate :/