So I hear you like Production (to be a trait) :D

OpenRa.Game/Game.cs

@@ -289,7 +289,7 @@ namespace OpenRa.Game
 				new VoicePool("ackno", "affirm1", "noprob", "overout", "ritaway", "roger", "ugotit"),
 				new VoicePool("await1", "ready", "report1", "yessir1"));
 
-		static int2? FindAdjacentTile(Actor a, UnitMovementType umt)
+		public static int2? FindAdjacentTile(Actor a, UnitMovementType umt)
 		{
 			var tiles = Footprint.Tiles(a, a.traits.Get<Traits.Building>());
 			var min = tiles.Aggregate(int2.Min) - new int2(1, 1);
@@ -341,10 +341,12 @@ namespace OpenRa.Game
 
 		public static void BuildUnit(Player player, string name)
 		{
-			var producerTypes = Rules.TechTree.UnitBuiltAt(Rules.UnitInfo[name]);
+			var newUnitType = Rules.UnitInfo[ name ];
+			var producerTypes = Rules.TechTree.UnitBuiltAt( newUnitType );
+			// TODO: choose producer based on "primary building"
 			var producer = world.Actors
-				.FirstOrDefault(a => a.unitInfo != null
+				.Where( x => producerTypes.Contains( x.unitInfo ) && x.Owner == player )
-					&& producerTypes.Contains(a.unitInfo.Name) && a.Owner == player);
+				.FirstOrDefault();
 
 			if (producer == null)
 			{
@@ -352,51 +354,8 @@ namespace OpenRa.Game
 			    return;
 			}
 
-			Actor newActor;
+			if( producer.traits.WithInterface<IProducer>().Any( p => p.Produce( producer, newUnitType ) ) )
-
-			if (producerTypes.Contains("spen") || producerTypes.Contains("syrd"))
-			{
-				var space = FindAdjacentTile(producer, Rules.UnitInfo[name].WaterBound ?
-					UnitMovementType.Float : UnitMovementType.Wheel);	/* hackety hack */
-
-				if (space == null)
-					return;
-
-				newActor = new Actor(name, space.Value, player);
-				var unit = newActor.traits.Get<Unit>();
-				unit.Facing = SharedRandom.Next(256);
-			}
-			else
-			{
-				var productionPoint = (1 / 24f * producer.CenterLocation).ToInt2();
-				if (UnitInfluence.GetUnitAt(productionPoint) != null)
-					return;
-
-				newActor = new Actor(name, (1 / 24f * producer.CenterLocation).ToInt2(), player);
-				var rp = producer.traits.GetOrDefault<RallyPoint>();
-				var dest = rp != null ? rp.rallyPoint : (newActor.Location + new int2(0, 3));
-
-				var unit = newActor.traits.Get<Unit>();
-				var mobile = newActor.traits.GetOrDefault<Mobile>();
-				if( mobile != null )
-				{
-					unit.Facing = 128;
-					newActor.QueueActivity(new Traits.Activities.Move(dest, 1));
-				}
-
-				var heli = newActor.traits.GetOrDefault<Helicopter>();
-				if (heli != null)
-				{
-					unit.Facing = 20;
-					heli.targetLocation = dest;
-				}
-			}
-
-			world.Add(newActor);
 				player.FinishProduction(Rules.UnitCategory[name]);
-
-			if (producer.traits.Contains<RenderWarFactory>())
-				producer.traits.Get<RenderWarFactory>().EjectUnit();
 		}
 	}
 }

OpenRa.Game/GameRules/TechTree.cs

@@ -8,7 +8,7 @@ namespace OpenRa.Game.GameRules
 {
 	class TechTree
 	{
-		readonly Cache<string, List<UnitInfo.BuildingInfo>> producesIndex = new Cache<string, List<UnitInfo.BuildingInfo>>( x => new List<UnitInfo.BuildingInfo>() );
+		readonly Cache<string, List<UnitInfo>> producesIndex = new Cache<string, List<UnitInfo>>( x => new List<UnitInfo>() );
 
 		public TechTree()
 		{
@@ -60,12 +60,12 @@ namespace OpenRa.Game.GameRules
 				.Where(x => Rules.UnitInfo[x].Owner.Contains(player.Race));	/* todo: fix for dual-race scenarios (captured buildings) */
 		}
 
-		public IEnumerable<string> UnitBuiltAt( UnitInfo info )
+		public IEnumerable<UnitInfo> UnitBuiltAt( UnitInfo info )
 		{
 			if( info.BuiltAt.Length != 0 )
-				return info.BuiltAt.Select( x => x.ToLowerInvariant() );
+				return info.BuiltAt.Select( x => Rules.UnitInfo[ x.ToLowerInvariant() ] );
 			else
-				return producesIndex[ Rules.UnitCategory[ info.Name ] ].Select( x => x.Name.ToLowerInvariant() );
+				return producesIndex[ Rules.UnitCategory[ info.Name ] ];
 		}
 	}
 }

OpenRa.Game/OpenRa.Game.csproj

@@ -146,6 +146,7 @@
     <Compile Include="Traits\InfantrySquad.cs" />
     <Compile Include="Traits\McvDeploy.cs" />
     <Compile Include="Traits\Mobile.cs" />
+    <Compile Include="Traits\Production.cs" />
     <Compile Include="Traits\RallyPoint.cs" />
     <Compile Include="Traits\RenderBuilding.cs" />
     <Compile Include="Traits\RenderBuildingOre.cs" />

OpenRa.Game/Traits/Production.cs

@@ -0,0 +1,70 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using OpenRa.Game.GameRules;
+
+namespace OpenRa.Game.Traits
+{
+	class Production : IProducer
+	{
+		public Production( Actor self ) { }
+
+		public virtual int2? CreationLocation( Actor self, UnitInfo producee )
+		{
+			return ( 1 / 24f * self.CenterLocation ).ToInt2();
+		}
+
+		public virtual int CreationFacing( Actor self, Actor newUnit )
+		{
+			if( newUnit.traits.Contains<Helicopter>() )
+				return 20;
+			return 128;
+		}
+
+		public bool Produce( Actor self, UnitInfo producee )
+		{
+			var location = CreationLocation( self, producee );
+			if( location == null || Game.UnitInfluence.GetUnitAt( location.Value ) != null )
+				return false;
+
+			var newUnit = new Actor( producee.Name, location.Value, self.Owner );
+			newUnit.traits.Get<Unit>().Facing = CreationFacing( self, newUnit ); ;
+
+			var rp = self.traits.GetOrDefault<RallyPoint>();
+			if( rp != null )
+			{
+				var mobile = newUnit.traits.GetOrDefault<Mobile>();
+				if( mobile != null )
+					newUnit.QueueActivity( new Traits.Activities.Move( rp.rallyPoint, 1 ) );
+
+				var heli = newUnit.traits.GetOrDefault<Helicopter>();
+				if( heli != null )
+					heli.targetLocation = rp.rallyPoint; // TODO: make Activity.Move work for helis.
+			}
+
+			Game.world.Add( newUnit );
+
+			if( self.traits.Contains<RenderWarFactory>() )
+				self.traits.Get<RenderWarFactory>().EjectUnit();
+
+			return true;
+		}
+	}
+
+	class ProductionSurround : Production
+	{
+		public ProductionSurround( Actor self ) : base( self ) { }
+
+		public override int2? CreationLocation( Actor self, UnitInfo producee )
+		{
+			return Game.FindAdjacentTile( self, producee.WaterBound ?
+			        UnitMovementType.Float : UnitMovementType.Wheel);	/* hackety hack */
+		}
+
+		public override int CreationFacing( Actor self, Actor newUnit )
+		{
+			return Util.GetFacing( newUnit.CenterLocation - self.CenterLocation, 128 );
+		}
+	}
+}

OpenRa.Game/Traits/TraitsInterfaces.cs

@@ -4,6 +4,7 @@ using System.Linq;
 using System.Text;
 using OpenRa.Game.Graphics;
 using IjwFramework.Types;
+using OpenRa.Game.GameRules;
 
 namespace OpenRa.Game.Traits
 {
@@ -19,4 +20,5 @@ namespace OpenRa.Game.Traits
 		Order IssueOrder( Actor self, int2 xy, bool lmb, Actor underCursor );
 		void ResolveOrder( Actor self, Order order );
 	}
+	interface IProducer { bool Produce( Actor self, UnitInfo produceee ); } 
 }

units.ini

@@ -211,20 +211,20 @@ Dimensions=2,2
 Footprint=xx xx
 [WEAP]
 Description=War Factory
-Traits=Building, RenderWarFactory, RallyPoint
+Traits=Building, RenderWarFactory, RallyPoint, Production
 Dimensions=3,2
 Footprint=xxx xxx
 Produces=Vehicle
 RallyPoint=1,3
 [SYRD]
 Description=Shipyard
-Traits=Building, RenderBuilding
+Traits=Building, RenderBuilding, ProductionSurround
 Dimensions=3,3
 Footprint=xxx xxx xxx
 Produces=Ship
 [SPEN]
 Description=Sub Pen
-Traits=Building, RenderBuilding
+Traits=Building, RenderBuilding, ProductionSurround
 Dimensions=3,3
 Footprint=xxx xxx xxx
 Produces=Ship
@@ -276,7 +276,7 @@ Dimensions=1,1
 Footprint=x
 [HPAD]
 Description=Helipad
-Traits=Building, RenderBuilding
+Traits=Building, RenderBuilding, Production
 Dimensions=2,2
 Footprint=xx xx
 Produces=Plane
@@ -302,7 +302,7 @@ Dimensions=2,1
 Footprint=xx
 [AFLD]
 Description=Airstrip
-Traits=Building, RenderBuilding
+Traits=Building, RenderBuilding, Production
 Dimensions=3,2
 Footprint=xxx xxx
 Produces=Plane
@@ -323,21 +323,21 @@ Dimensions=3,2
 Footprint=xxx xxx
 [BARR]
 Description=Soviet Barracks
-Traits=Building, RenderBuilding, RallyPoint
+Traits=Building, RenderBuilding, RallyPoint, Production
 Dimensions=2,2
 Footprint=xx xx
 Produces=Infantry
 RallyPoint=1,3
 [TENT]
 Description=Allied Barracks
-Traits=Building, RenderBuilding, RallyPoint
+Traits=Building, RenderBuilding, RallyPoint, Production
 Dimensions=2,2
 Footprint=xx xx
 Produces=Infantry
 RallyPoint=1,3
 [KENN]
 Description=Kennel
-Traits=Building, RenderBuilding, RallyPoint
+Traits=Building, RenderBuilding, RallyPoint, Production
 Dimensions=1,1
 Footprint=x
 RallyPoint=1,2