aftermath works again, and Inherits... might works.

OpenRa.FileFormats/MiniYaml.cs

@@ -54,5 +54,37 @@ namespace OpenRa.FileFormats
 			}
 			return levels[ 0 ];
 		}
+
+		public static Dictionary<string, MiniYaml> Merge( Dictionary<string, MiniYaml> a, Dictionary<string, MiniYaml> b )
+		{
+			if( a.Count == 0 )
+				return b;
+			if( b.Count == 0 )
+				return a;
+
+			var ret = new Dictionary<string, MiniYaml>();
+
+			var keys = a.Keys.Union( b.Keys ).ToList();
+
+			foreach( var key in keys )
+			{
+				MiniYaml aa, bb;
+				a.TryGetValue( key, out aa );
+				b.TryGetValue( key, out bb );
+				ret.Add( key, Merge( aa, bb ) );
+			}
+
+			return ret;
+		}
+
+		public static MiniYaml Merge( MiniYaml a, MiniYaml b )
+		{
+			if( a == null )
+				return b;
+			if( b == null )
+				return a;
+
+			return new MiniYaml( a.Value ?? b.Value, Merge( a.Nodes, b.Nodes ) );
+		}
 	}
 }

OpenRa.Game/GameRules/NewUnitInfo.cs

@@ -8,24 +8,31 @@ namespace OpenRa.Game.GameRules
 {
 	class NewUnitInfo
 	{
-		public readonly string Parent;
 		public readonly TypeDictionary Traits = new TypeDictionary();
 		public readonly string Name;
 
-		public NewUnitInfo( string name, MiniYaml node )
+		public NewUnitInfo( string name, MiniYaml node, Dictionary<string, MiniYaml> allUnits )
 		{
 			Name = name;
 
-			// todo: make inheritance actually work
-			MiniYaml inherit;
-			if( node.Nodes.TryGetValue( "Inherits", out inherit ) )
-			{
-				Parent = inherit.Value;
-				node.Nodes.Remove( "Inherits" );
+			foreach( var t in MergeWithParent( node, allUnits ).Nodes )
+				if( t.Key != "Inherits" )
+					Traits.Add( LoadTraitInfo( t.Key, t.Value ) );
 		}
 
-			foreach (var t in node.Nodes)
-				Traits.Add(LoadTraitInfo(t.Key, t.Value));
+		static MiniYaml MergeWithParent( MiniYaml node, Dictionary<string, MiniYaml> allUnits )
+		{
+			MiniYaml inherits;
+			node.Nodes.TryGetValue( "Inherits", out inherits );
+			if( inherits.Value == null || string.IsNullOrEmpty( inherits.Value ) )
+				return node;
+
+			MiniYaml parent;
+			allUnits.TryGetValue( inherits.Value, out parent );
+			if( parent == null )
+				return node;
+
+			return MiniYaml.Merge( node, MergeWithParent( parent, allUnits ) );
 		}
 
 		static ITraitInfo LoadTraitInfo(string traitName, MiniYaml my)

OpenRa.Game/GameRules/Rules.cs

@@ -90,9 +90,13 @@ namespace OpenRa.Game
 			SupportPowerInfo = new InfoLoader<SupportPowerInfo>(
 				Pair.New<string, Func<string, SupportPowerInfo>>("SupportPower", _ => new SupportPowerInfo()));
 
+			var yamlRules = MiniYaml.FromFile("ra.yaml");
+			if( useAftermath )
+				yamlRules = MiniYaml.Merge( MiniYaml.FromFile( "aftermath.yaml" ), yamlRules );
+
 			NewUnitInfo = new Dictionary<string, NewUnitInfo>();
-			foreach (var kv in MiniYaml.FromFile("ra.yaml"))
-				NewUnitInfo.Add(kv.Key.ToLowerInvariant(), new NewUnitInfo(kv.Key.ToLowerInvariant(), kv.Value));
+			foreach( var kv in yamlRules )
+				NewUnitInfo.Add(kv.Key.ToLowerInvariant(), new NewUnitInfo(kv.Key.ToLowerInvariant(), kv.Value, yamlRules));
 
 			TechTree = new TechTree();
 			Map = new Map( AllRules );