feat(tracker/gioui): user-defined keybindings.yml override defaults

The behaviour of the user-defined keybindings.yml was changed.
It now documents just the changes from the default keybindings.
An empty line with no action means "unbind the key".

tracker/gioui/keybindings.yml

@@ -1,3 +1,11 @@
+# You can place your custom keybindings.yml in the Sointu config directory e.g.
+# AppData\Roaming\sointu\keybindings.yml on Windows. There, you can override the
+# default keybindings with your own. The format is the same as below. A
+# keybinding without any action means unbinding the key. For example, the line
+#
+# - {key: "A"}
+#
+# will stop the A key from sending NoteOff events.
 - {key: "C", shortcut: true, action: "Copy"}
 - {key: "V", shortcut: true, action: "Paste"}
 - {key: "A", shortcut: true, action: "SelectAll"}

tracker/gioui/keyevent.go

@@ -60,10 +60,9 @@ func loadDefaultKeyBindings() []KeyBinding {
 }
 
 func init() {
-	keyBindings := loadCustomKeyBindings()
+	keyBindings := loadDefaultKeyBindings()
-	if keyBindings == nil {
+	keyBindings = append(keyBindings, loadCustomKeyBindings()...)
-		keyBindings = loadDefaultKeyBindings()
+
-	}
 	for _, kb := range keyBindings {
 		var mods key.Modifiers
 		if kb.Shortcut {
@@ -84,8 +83,17 @@ func init() {
 		if kb.Super {
 			mods |= key.ModSuper
 		}
-		keyBindingMap[key.Event{Name: key.Name(kb.Key), Modifiers: mods, State: key.Press}] = kb.Action
+
-		if _, ok := keyActionMap[KeyAction(kb.Action)]; !ok {
+		keyEvent := key.Event{Name: key.Name(kb.Key), Modifiers: mods, State: key.Press}
+		action, ok := keyBindingMap[keyEvent] // if this key has been previously bound, remove it from the hint map
+		if ok {
+			delete(keyActionMap, KeyAction(action))
+		}
+		if kb.Action == "" { // unbind
+			delete(keyBindingMap, keyEvent)
+		} else { // bind
+			keyBindingMap[keyEvent] = kb.Action
+			// last binding of the some action wins for displaying the hint
 			modString := strings.Replace(mods.String(), "-", "+", -1)
 			text := kb.Key
 			if modString != "" {