Add compose macro button

src/button.rs

@@ -23,10 +23,12 @@ impl From<Modifier> for u8 {
 }
 
 #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[non_exhaustive]
 pub enum Button {
     Mod(Modifier),
     Key(Key),
     ModTap(Key, Modifier),
+    Compose(Key, Key, Option<Key>),
     NextLayer,
     PrevLayer,
     None,
@@ -38,6 +40,8 @@ impl Display for Button {
             Button::Mod(modifier) => Debug::fmt(&modifier, f),
             Button::Key(key) => write!(f, "{key:?}"),
             Button::ModTap(key, modifier) => write!(f, "{key:?}/{modifier}"),
+            Button::Compose(k1, k2, None) => write!(f, "⎄ {k1:?} {k2:?}"),
+            Button::Compose(k1, k2, Some(k3)) => write!(f, "⎄ {k1:?} {k2:?} {k3:?}"),
             Button::NextLayer => write!(f, "↘"),
             Button::PrevLayer => write!(f, "↖"),
             Button::None => write!(f, "Ø"),

src/keys.rs

@@ -2,6 +2,7 @@ use serde::{Deserialize, Serialize};
 
 #[repr(u8)]
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[non_exhaustive]
 // https://usb.org/sites/default/files/hut1_3_0.pdf
 pub enum Key {
     A = 0x04,