Support [Add<T>] for type T

src/gaemstone/ECS/Game.cs

@@ -6,7 +6,7 @@ namespace gaemstone.ECS;
 /// Entity for storing global game state and configuration.
 /// Parameters can use <see cref="GameAttribute"/> to source this entity.
 /// </summary>
-[Entity]
+[Entity, Add<Game>]
 public struct Game {  }
 
 /// <summary> Equivalent to <see cref="SourceAttribute{Game}"/>. </summary>

src/gaemstone/ECS/Universe+Modules.cs

@@ -189,20 +189,18 @@ internal class ModuleInfo
 			var builder = path.IsAbsolute ? Universe.New(path) : Entity.NewChild(path);
 			if (!type.Has<PrivateAttribute>()) builder.Symbol(path.Name);
 
-			foreach (var attr in type.GetMultiple<AddEntityAttribute>())
-				builder.Add(Universe.LookupOrThrow(attr.Entity));
-			foreach (var attr in type.GetMultiple<AddRelationAttribute>())
-				builder.Add(Universe.LookupOrThrow(attr.Relation), Universe.LookupOrThrow(attr.Target));
-
 			var entity = builder.Build();
 
-			if (type.Has<SingletonAttribute>())
-				entity.Add(entity);
+			EntityRef Lookup(Type toLookup)
+				=> (type != toLookup) ? Universe.LookupOrThrow(toLookup) : entity;
+			foreach (var attr in type.GetMultiple<AddEntityAttribute>())
+				entity.Add(Lookup(attr.Entity));
+			foreach (var attr in type.GetMultiple<AddRelationAttribute>())
+				entity.Add(Lookup(attr.Relation), Lookup(attr.Target));
 
-			if (type.Has<ComponentAttribute>())
-				entity.CreateComponent(proxyType);
-			else
-				entity.CreateLookup(proxyType);
+			if (type.Has<SingletonAttribute>()) entity.Add(entity);
+			if (type.Has<ComponentAttribute>()) entity.CreateComponent(proxyType);
+			else                                entity.CreateLookup(proxyType);
 		}
 	}