ErrorConvert is only implemented for InputError

[praveenperera]

Discussed in #498

^{Originally posted by TheNeikos March 25, 2024}
Heya!

I have a function that returns a PResult, but I can't easily use the bits::bits parser because the error traits it requires are not implemented/compatible with PResult's definition:

bits requires that:

• BitError: ParserError<(Input, usize)> + ErrorConvert<ByteError>
• ByteError: ParserError<Input>

But ErrorConvert is only implemented for InputError. Since PResult is the 'main' way of using winnow, this means I have to awkwardly specify the Error type using a turbofish. bits has 5 generics (even if I can infer 4 of them).

So for example an invocation looks like this:

winnow::binary::bits::bits::<_, _, InputError<(_, usize)>, _, _>((
                winnow::binary::bits::pattern(0x0, 1usize),
                winnow::binary::bits::bool,
                winnow::binary::bits::bool,
                winnow::binary::bits::take(2usize)
                    .try_map(<QualityOfService as TryFrom<u8>>::try_from),
                winnow::binary::bits::bool,
                winnow::binary::bits::bool,
                winnow::binary::bits::bool,
            ))
            .parse_next(input)
            .map_err(|_: ErrMode<InputError<_>>| {
                ErrMode::from_error_kind(input, winnow::error::ErrorKind::Slice)
            })?

Now, am I doing something wrong? Or is this just a current limitation?

Thanks for any pointers!

---

Parse Peek

fn parse_header_byte(input: Stream<'_>) -> IResult<Stream<'_>, (bool, bool, bool, bool, bool, u8)> {
    bits::<_, _, InputError<(_, usize)>, _, _>((
        take_bool,
        take_bool,
        take_bool,
        take_bool,
        take_bool,
        take_bits(3_u8),
    ))
    .parse_peek(input)
}

Parse next

fn parse_header_byte(input: &mut Stream<'_>) -> PResult<(bool, bool, bool, bool, bool, u8)> {
    bits::<_, _, InputError<(_, usize)>, _, _>((
        take_bool,
        take_bool,
        take_bool,
        take_bool,
        take_bool,
        take_bits(3_u8),
    ))
    .parse_next(input)
    .map_err(|_: ErrMode<InputError<_>>| {
        ErrMode::from_error_kind(input, winnow::error::ErrorKind::Slice)
    })
}