Tweak Compose button

src/button.rs

@@ -28,11 +28,26 @@ pub enum Button {
     Mod(Modifier),
     Key(Key),
     ModTap(Key, Modifier),
-    Compose(Key, Key, Option<Key>),
+    Compose2(CompShift, Key, CompShift, Key),
+    Compose3(CompShift, Key, CompShift, Key, CompShift, Key),
     Layer(LayerShift, LayerDir, u16),
     None,
 }
 
+/// Whether a key should be shift modified as part of a compose chain.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
+pub enum CompShift {
+    /// Do not shift the key.
+    #[default]
+    Lower,
+
+    /// Shift the key.
+    Upper,
+
+    /// Shift the key if shift is being held down.
+    Variable,
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub enum LayerDir {
     Left,
@@ -49,12 +64,22 @@ pub enum LayerShift {
 
 impl Display for Button {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let cs = |cs: &CompShift| match cs {
+            CompShift::Lower => "",
+            CompShift::Upper => "⇧",
+            CompShift::Variable => "⇧?",
+        };
+
         match self {
             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::Compose2(cs1, k1, cs2, k2) => {
-            Button::Compose(k1, k2, Some(k3)) => write!(f, "⎄ {k1:?} {k2:?} {k3:?}"),
+                write!(f, "⎄ {}{k1:?} {}{k2:?}", cs(cs1), cs(cs2))
+            }
+            Button::Compose3(cs1, k1, cs2, k2, cs3, k3) => {
+                write!(f, "⎄ {}{k1:?} {}{k2:?} {}{k3:?}", cs(cs1), cs(cs2), cs(cs3))
+            }
             Button::Layer(..) => write!(f, "Lr"),
             Button::None => write!(f, "Ø"),
         }