Warnings for clippy::unnecessary_cast for default values

[martiege]

Thank you for this great package! I've been using it with success, but it generates some warnings for clippy::unnecessary_cast, e.g.

 28 |   #[bitfield(u16)]
    |  ____________^
 29 | | #[derive(PartialEq, Eq)]
 30 | | pub struct HardwareVersion {
 31 | |     #[bits(4, access = RO)]
 32 | |     pub hardware_version: u8,
 33 | |
 34 | |     #[bits(12, default = 0_u16)]
    | |______________________________^ help: try: `0_u16`

[wrenger]

Ah interesting. The cast is usually only necessary if the bitfield type differs from the struct field type.

[martiege]

Yes, the strange thing is that explicitly casting does remove the warning for some data structures, but not from others...

This gives the warning:

#[bitfield(u16)]
#[derive(PartialEq, Eq)]
pub struct HardwareVersion {
    #[bits(4, access=RO)]
    pub hardware_version: u8,

    #[bits(12, default=0_u16)]
    __: u16,
}

While this does not:

#[bitfield(u16)]
#[derive(PartialEq, Eq)]
pub struct CalibrationDataChars {
    #[bits(10, access=RO)]
    pub calibration_data_chars: u16,

    #[bits(6, default=0_u8)]
    __: u8,
}

And just for fun, this gives the warning (but specifically for u16, not u8 as the empty bits should be):

#[bitfield(u16)]
#[derive(PartialEq, Eq)]
pub struct CalibrationDataChars {
    #[bits(10, access=RO)]
    pub calibration_data_chars: u16,

    #[bits(6, default=0)]
    __: u8,
}

I'm guessing this happens due to some internal way this structure is represented. The fact that the first data structure is a u16 bitfield, and the empty bits are also u16, while the second structure is a u16, and the empty bits are u8, is also likely related somehow.