Added Cancel() to Mobile.CurrentAction. Added QueueAction to Mobile. Made Order.Apply use queue rather than SetNextAction.

OpenRa.Game/Game.cs

@@ -192,7 +192,9 @@ namespace OpenRa.Game
 				throw new InvalidOperationException("BuildUnit without suitable production structure!");
 
 			var unit = new Actor(name, (1/24f * producer.CenterLocation).ToInt2(), player);
-			unit.Order(unit.Location + new int2(0, 3)).Apply(false);
+			var mobile = unit.traits.Get<Mobile>();
+			mobile.facing = 128;
+			mobile.SetNextAction( new Traits.Mobile.MoveTo( unit.Location + new int2( 0, 3 ) ) );
 
 			world.AddFrameEndTask(_ => world.Add(unit));
 

OpenRa.Game/MoveOrder.cs

@@ -33,7 +33,7 @@ namespace OpenRa.Game
 			if (Game.LocalPlayer == Unit.Owner)
 				Game.PlaySound("ackno.r00", false);
 			var mobile = Unit.traits.Get<Traits.Mobile>();
-			mobile.SetNextAction( new Traits.Mobile.MoveTo( Destination ) );
+			mobile.QueueAction( new Traits.Mobile.MoveTo( Destination ) );
 		}
 	}
 }

OpenRa.Game/Traits/McvDeploy.cs

@@ -35,7 +35,9 @@ namespace OpenRa.Game.Traits
 		public override void Apply( bool leftMouseButton )
 		{
 			if( leftMouseButton ) return;
-			Unit.traits.Get<Mobile>().SetNextAction( new Mobile.Turn( 96 ) { NextAction = new DeployAction() } );
+			var mobile = Unit.traits.Get<Mobile>();
+			mobile.QueueAction( new Mobile.Turn( 96 ) );
+			mobile.QueueAction( new DeployAction() );
 		}
 
 		class DeployAction : Mobile.CurrentAction
@@ -50,6 +52,12 @@ namespace OpenRa.Game.Traits
 					Game.world.Add( new Actor( "fact", self.Location - new int2( 1, 1 ), self.Owner ) );
 				} );
 			}
+
+			public void Cancel( Actor self, Mobile mobile )
+			{
+				// Cancel can't happen between this being moved to the head of the list, and it being Ticked.
+				throw new InvalidOperationException( "DeployMcvAction: Cancel() should never occur." );
+			}
 		}
 	}
 }

OpenRa.Game/Traits/Mobile.cs

@@ -32,6 +32,21 @@ namespace OpenRa.Game.Traits
 				currentAction.NextAction = nextAction;
 		}
 
+		public void QueueAction( CurrentAction nextAction )
+		{
+			if( currentAction == null )
+			{
+				currentAction = nextAction;
+				return;
+			}
+			var act = currentAction;
+			while( act.NextAction != null )
+			{
+				act = act.NextAction;
+			}
+			act.NextAction = nextAction;
+		}
+
 		public void Tick(Actor self)
 		{
 			if( currentAction != null )
@@ -51,15 +66,16 @@ namespace OpenRa.Game.Traits
 	
 		public interface CurrentAction
 		{
-			CurrentAction NextAction { set; }
+			CurrentAction NextAction { get; set; }
 			void Tick( Actor self, Mobile mobile );
+			void Cancel( Actor self, Mobile mobile );
 		}
 
 		public class Turn : CurrentAction
 		{
 			public CurrentAction NextAction { get; set; }
 
-			public readonly int desiredFacing;
+			public int desiredFacing;
 
 			public Turn( int desiredFacing )
 			{
@@ -77,6 +93,12 @@ namespace OpenRa.Game.Traits
 				}
 				Util.TickFacing( ref mobile.facing, desiredFacing, self.unitInfo.ROT );
 			}
+
+			public void Cancel( Actor self, Mobile mobile )
+			{
+				desiredFacing = mobile.facing;
+				NextAction = null;
+			}
 		}
 
 		public class MoveTo : CurrentAction
@@ -211,6 +233,12 @@ namespace OpenRa.Game.Traits
 				OnComplete = null;
 				mobile.fromCell = mobile.toCell;
 			}
+
+			public void Cancel( Actor self, Mobile mobile )
+			{
+				path.Clear();
+				NextAction = null;
+			}
 		}
 	}
 }