Compile error when compiling for split keyboard without additional features

[zUnixorn]

Description of the issue

When compiling for a split keyboard and not having any of the "simple-backlight", "simple-backlight-matrix", "rgb-backlight-matrix", "underglow" features enabled, I get a the following compile error:

error[E0084]: unsupported representation for zero-variant enum
  --> rumcake/rumcake/src/split/mod.rs:49:1
   |
49 | #[repr(u8)]
   | ^^^^^^^^^^^
50 | pub enum MessageToPeripheral {
   | ---------------------------- zero-variant enum

Two possible fixes I thought of, would be either wrapping the repr(u8) on MessageToPeripheral in a cfg_attr:

#[cfg_attr(any(
    feature = "simple-backlight", 
    feature = "simple-backlight-matrix", 
    feature = "rgb-backlight-matrix", 
    feature = "underglow"
), repr(u8))]

or by adding a dummy variant to the enum, so it always has at least one variant, regardless enabled of features.

Hardware

Shouldn't work with other MCUs either, but in this case I tested it on an RP2040 and nRF52840 (split-template)

Version of rumcake used

0.1.0 (a73d77b)

Minimum Reproducible Example

You can just use the split example and change the rev of rumcake to a73d77b

How to Reproduce

1. use split example
2. change the rev of rumcake to a73d77b
3. compile
4. observe compile error

Expected Behaviour

compile without errors when not specifying any additional features

[Univa]

Good catch, I have pushed up a fix, using cfg_attr.