Add missing type hints in fields codegen

[apohrebniak]

I noticed that having

#[derive(defmt::Format)]
struct Foo {
  u16: u16,
  u32: u32,
  u64: u64,
  u128: u128,
}

cargo expand generates:

impl defmt::Format for Foo
where
    u64: defmt::Format,
    u128: defmt::Format,
{
    fn _format_tag() -> defmt::Str {
        {
            defmt::export::make_istr({
                #[link_section = ".defmt.{\"package\":\"examples\",\"tag\":\"defmt_derived\",\"data\":\"Foo {{ u16: {=u16:?}, u32: {=u32:?}, u64: {=?:?}, u128: {=?:?} }}\",\"disambiguator\":\"6889995364419830437\",\"crate_name\":\"stm32f411x_scsi_bbb\"}"]
                #[export_name = "{\"package\":\"examples\",\"tag\":\"defmt_derived\",\"data\":\"Foo {{ u16: {=u16:?}, u32: {=u32:?}, u64: {=?:?}, u128: {=?:?} }}\",\"disambiguator\":\"6889995364419830437\",\"crate_name\":\"stm32f411x_scsi_bbb\"}"]
                static S: u8 = 0;
                &S as *const u8 as u16
            })
        }
    }
    fn _format_data(&self) {
        match self {
            Self {
                u16,
                u32,
                u64,
                u128,
            } => {
                defmt::export::u16(u16);
                defmt::export::u32(u32);
                defmt::export::fmt(u64);
                defmt::export::fmt(u128);
            }
        }
    }
}

the important bit here is that there're missing type hints for u64 and u128. Therefore

    let foo = Foo {
        u16: 0xCAFE,
        u32: 0xCAFE,
        u64: 0xCAFE,
        u128: 0xCAFE,
    };
    defmt::info!("{:#X}", foo);

outputs INFO Foo { u16: 0xCAFE, u32: 0xCAFE, u64: 51966, u128: 51966 }.

This PR adds those missing hints, so the output is correct:
INFO Foo { u16: 0xCAFE, u32: 0xCAFE, u64: 0xCAFE, u128: 0xCAFE }

[Urhengulas]

Thank you!

[jonathanpallant]

Is this a breaking change? We're altering how a struct is encoded over the wire using our default formatter, and changing how the values get formatted by default on the host side. Although arguably, we're just fixing a mistake and it should always have been like this.

[Urhengulas]

Is this a breaking change? We're altering how a struct is encoded over the wire using our default formatter, and changing how the values get formatted by default on the host side. Although arguably, we're just fixing a mistake and it should always have been like this.

I don't think that this is breaking. We do not change the wire format. And all derive(defmt::Format) that worked before will still work.