"Alternate Names" aka pseudo-prerequisites. E7 and MSLO can be built again.

OpenRa.Game/Chrome.cs

@@ -751,9 +751,7 @@ namespace OpenRa.Game
 			if (!Rules.TechTree.CanBuild(info, Game.LocalPlayer, buildings))
 			{
 				var prereqs = buildable.Prerequisites
-					.Select(a => Rules.NewUnitInfo[a.ToLowerInvariant()].Traits.Get<BuildableInfo>())
-					.Where( u => u.Owner.Any( o => o == Game.LocalPlayer.Race ) )
-					.Select( a => a.Description );
+					.Select( a => Description( a ) );
 				renderer.DrawText("Requires {0}".F( string.Join( ", ", prereqs.ToArray() ) ), p.ToInt2(),
 					Color.White);
 			}
@@ -765,6 +763,14 @@ namespace OpenRa.Game
 			}
 		}
 
+		private static string Description( string a )
+		{
+			if( a[ 0 ] == '@' )
+				return "any " + a.Substring( 1 );
+			else
+				return Rules.NewUnitInfo[ a.ToLowerInvariant() ].Traits.Get<BuildableInfo>().Description;
+		}
+
 		void DrawSupportPowers()
 		{
 			var numPowers = Game.LocalPlayer.SupportPowers.Values

OpenRa.Game/GameRules/TechTree.cs

@@ -25,7 +25,13 @@ namespace OpenRa.Game.GameRules
 		{
 			var ret = new Cache<string, List<Actor>>( x => new List<Actor>() );
 			foreach( var b in Game.world.Actors.Where( x => x.Owner == player && x.Info != null && x.Info.Traits.Contains<BuildingInfo>() ) )
+			{
 				ret[ b.Info.Name ].Add( b );
+				var buildable = b.Info.Traits.GetOrDefault<BuildableInfo>();
+				if( buildable != null )
+					foreach( var alt in buildable.AlternateName )
+						ret[ alt ].Add( b );
+			}
 			return ret;
 		}
 

OpenRa.Game/Traits/Buildable.cs

@@ -16,6 +16,7 @@ namespace OpenRa.Game.Traits
 		public readonly string Description = "";
 		public readonly string LongDesc = "";
 		public readonly string Icon = null;
+		public readonly string[] AlternateName = { };
 	}
 
 	class Buildable { }