Throw a more detailed error message when creating invalid frozen actors

OpenRA.Mods.Common/Traits/Modifiers/FrozenUnderFog.cs

@@ -18,11 +18,17 @@ using OpenRA.Traits;
 namespace OpenRA.Mods.Common.Traits
 {
 	[Desc("This actor will remain visible (but not updated visually) under fog, once discovered.")]
-	public class FrozenUnderFogInfo : ITraitInfo, Requires<BuildingInfo>, IDefaultVisibilityInfo
+	public class FrozenUnderFogInfo : ITraitInfo, Requires<BuildingInfo>, IDefaultVisibilityInfo, IRulesetLoaded
 	{
 		[Desc("Players with these stances can always see the actor.")]
 		public readonly Stance AlwaysVisibleStances = Stance.Ally;
 
+		void IRulesetLoaded<ActorInfo>.RulesetLoaded(Ruleset rules, ActorInfo info)
+		{
+			if (!info.HasTraitInfo<SelectableInfo>() && !info.HasTraitInfo<IAutoSelectionSizeInfo>())
+				throw new YamlException("Cannot create a frozen actor for actor type '{0}' with empty bounds (no selection size given).".F(info.Name));
+		}
+
 		public object Create(ActorInitializer init) { return new FrozenUnderFog(init, this); }
 	}
 
@@ -61,7 +67,7 @@ namespace OpenRA.Mods.Common.Traits
 			footprint = footprintCells.SelectMany(c => map.ProjectedCellsCovering(c.ToMPos(map))).ToArray();
 		}
 
-		public void Created(Actor self)
+		void INotifyCreated.Created(Actor self)
 		{
 			frozenStates = new PlayerDictionary<FrozenState>(self.World, (player, playerIndex) =>
 			{