Register validated commands without registry copies

registry.go

@@ -9,19 +9,27 @@ func (a *App) Register(commands ...Command) error {
 		return fmt.Errorf("cannot register commands on a nil app")
 	}
 
-	updated := make(map[string]*commandNode, len(a.commands)+len(commands))
-	for name, node := range a.commands {
-		updated[name] = node
-	}
+	pending := make(map[string]*commandNode, len(commands))
 	for _, command := range commands {
 		if err := validateCommandDeclaration(command); err != nil {
 			return err
 		}
-		if _, exists := updated[command.name]; exists {
+		if _, exists := a.commands[command.name]; exists {
 			return fmt.Errorf("command path %q is already registered", command.name)
 		}
-		updated[command.name] = &commandNode{command: cloneCommand(command)}
+		if _, exists := pending[command.name]; exists {
+			return fmt.Errorf("command path %q is already registered", command.name)
+		}
+		pending[command.name] = &commandNode{command: cloneCommand(command)}
+	}
+	if len(pending) == 0 {
+		return nil
+	}
+	if a.commands == nil {
+		a.commands = make(map[string]*commandNode, len(pending))
+	}
+	for name, node := range pending {
+		a.commands[name] = node
 	}
-	a.commands = updated
 	return nil
 }