Wrap errors for embedded-hal trait implementations

[markus-k]

The current implementations of the OutputPin, InputPin and StatefulOutputPin traits require that PortDriver::Error implements embedded_hal::digital::Error, which is never going to be the case. Thus, these traits are never usable.

Here is a small example that should result in lots of compiler errors because of unsatisfied trait bounds:

use embedded_hal::digital::{InputPin, OutputPin};

fn main() {
    let mut expander =
        port_expander::Tca6408a::new(embedded_hal_mock::eh1::i2c::Mock::new(&[]), false);
    let pins = expander.split();

    let mut pin0 = pins.io0.into_output().unwrap();
    let pin1 = pins.io1.into_input().unwrap();

    println!("Is pin1 low? {}", pin1.is_low().unwrap());
    print_it(pin1).unwrap();

    pin0.set_low().unwrap();
    set_it_high(pin0).unwrap();
}

fn set_it_high<P>(mut pin: P) -> Result<(), P::Error>
where
    P: OutputPin,
{
    pin.set_high()?;

    Ok(())
}

fn print_it<P>(mut pin: P) -> Result<(), P::Error>
where
    P: InputPin,
{
    println!("Pin: {}", pin.is_high()?);

    Ok(())
}

This change wraps the error type used in ErrorKind::Error in a wrapper struct PinError<BE> which implements embedded_hal::digital::Error. Like this all upstream errors that are core::fmt::Debug should be compatible with embedded-hal.

The return types for Pin::set_high() and OutputPin::set_high() are different now, since the returned error from the Pin implementation do not wrap errors in PinError. This could cause problems, so maybe it's a good idea to wrap these errors as well?

[Rahix]

Ouch, you are totally right... Thanks for the fix.

The return types for Pin::set_high() and OutputPin::set_high() are different now, since the returned error from the Pin implementation do not wrap errors in PinError. This could cause problems, so maybe it's a good idea to wrap these errors as well?

I'd rather have both methods return the same type. So the inherent methods should also return PinError.

[markus-k]

Alright, I agree thats better. I have updated the PR.

[Rahix]

Thanks!