Added support for complex messages in function arguments

Runtime/Messages/MessageComponent.cs

@@ -258,11 +258,11 @@ public class Function : MessageComponent
       public readonly string name;
 
       // The argument of the function
-      public readonly string argument;
+      public readonly Message argument;
 
 
       // Constructor
-      public Function(string name, string argument = null)
+      public Function(string name, Message argument = null)
       {
         this.name = name;
         this.argument = argument;

Runtime/Messages/MessageFormatter.cs

@@ -134,7 +134,9 @@ string MessageComponent.IVisitor<string, MessageEnvironment>.VisitSelectFormatCo
     // Visit a function component
     string MessageComponent.IVisitor<string, MessageEnvironment>.VisitFunctionComponent(MessageComponent.Function component, MessageEnvironment env)
     {
-      if (_functionExecutor.TryExecuteFunction(component.name, component.argument, out var value))
+      var argument = component.argument != null ? Format(component.argument, env) : null;
+
+      if (_functionExecutor.TryExecuteFunction(component.name, argument, out var value))
         return Format(new Message(value), env);
       else
         throw new MessageException($"Function \"{component.name}\" could not be found");

Runtime/Messages/MessageParser.cs

@@ -18,6 +18,7 @@ public enum ContextType
     {
       Plural,
       Select,
+      Function,
     }
 
 
@@ -188,7 +189,10 @@ private static MessageComponent ParseFunctionComponent(Scanner scanner, Stack<Co
         return new MessageComponent.Function(name);
       scanner.SkipWhile(Scanner.IsWhitespace);
 
-      var argument = ParseString(scanner, contexts);
+      contexts.Push(ContextType.Function);
+      var argument = new Message(ParseComponents(scanner, contexts));
+      contexts.Pop();
+
       return new MessageComponent.Function(name, argument);
     }