Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @therealprof (or someone else) soon.

Please see the contribution instructions for more information.

I think having Ord for StandardId and ExtendedId makes perfect sense.
For can::Id the question is if Ord should be implement according to CAN bus arbitration rules. In that case the automatic derive would not work.

Does that mean that
Id::Standard(StandardId::ZERO) > Id::Standard(StandardId::MAX) should be true? Thus small number meaning important means "large"? :)

In that case, would it not make more sense if the ordering was the same for all three types?

Unfortunately arbitration rules are a bit more complex than that if I understand the CAN specification correctly.
When two messages are transmitted at the same time the ID with the first dominant bit (0bit) wins.
To compare standard and extended ids you would need to shift the standard ID by 18bits to align them with the MSB of the extended ID and also account for the IDE bit.

Example:
Std(0) < Ext(0) < Ext(1337) < Std(1) < Ext(555555) < Std(4)

Oh, ok thanks
I will have a closer look at the protocol :)

So something more like

impl Ord for Id {
    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
        let split_id = |id: &Id| {
            let (standard_id_part, ide_bit, extended_id_part) = match id {
                Id::Standard(StandardId(x)) => (*x, 0, 0),
                Id::Extended(x) => (
                    x.standard_id().0,
                    1,
                    x.0 & ((1 << 18) - 1), // Bit ID-17 to ID-0
                ),
            };
            (standard_id_part, ide_bit, extended_id_part)
        };

        split_id(self).cmp(&split_id(other))
    }
}

Looks good to me now. Can you please fix the two tests too:

failures:
    can::id::tests::cmp_extended
    can::id::tests::cmp_standard

I hope I have put the documentation in the right place. Otherwise please let me know.

The failing test have been removed, they were forgotten left overs from my first attempt

Anything more I can do?

Build succeeded:

• ci-linux (1.54.0, x86_64-unknown-linux-gnu)
• ci-linux (stable, thumbv6m-none-eabi)
• ci-linux (stable, thumbv7m-none-eabi)
• ci-linux (stable, x86_64-unknown-linux-gnu)
• ci-linux-test (1.54.0, x86_64-unknown-linux-gnu)
• ci-linux-test (stable)
• fmt