Fix subcell crushing properly.

OpenRA.Game/Traits/World/UnitInfluence.cs

@@ -51,6 +51,15 @@ namespace OpenRA.Traits
 					yield return i.actor;
 		}
 		
+		public IEnumerable<Actor> GetUnitsAt( int2 a, SubCell sub )
+		{
+			if (!map.IsInMap(a)) yield break;
+
+			for( var i = influence[ a.X, a.Y ] ; i != null ; i = i.next )
+				if (!i.actor.Destroyed && (i.subCell == sub || i.subCell == SubCell.FullCell))
+					yield return i.actor;
+		}
+		
 		public bool HasFreeSubCell(int2 a)
 		{
 			if (!AnyUnitsAt(a))
@@ -59,29 +68,6 @@ namespace OpenRA.Traits
 			return new[]{SubCell.TopLeft, SubCell.TopRight, SubCell.Center,
 				SubCell.BottomLeft, SubCell.BottomRight}.Any(b => !AnyUnitsAt(a,b));
 		}
-		
-		// This is only used inside Move, when we *know* that we can enter the cell.
-		// If the cell contains something crushable, a naive check of 'is it empty' will fail.
-		// Infantry can currently only crush crates/mines which take a whole cell, so we will ignore
-		// the SubCell.FullCell case and hope that someone doesn't introduce subcell units
-		// crushing other subcell units in the future.
-		public SubCell GetFreeSubcell(int2 a, SubCell preferred)
-		{
-			if (preferred == SubCell.FullCell)
-				return preferred;
-			
-			return new[]{ preferred, SubCell.TopLeft, SubCell.TopRight, SubCell.Center,
-				SubCell.BottomLeft, SubCell.BottomRight}.First(b => 
-			{
-				var node = influence[ a.X, a.Y ];
-				while (node != null)
-				{
-					if (node.subCell == b) return false;
-					node = node.next;
-				}
-				return true;
-			});
-		}
 
 		public bool AnyUnitsAt(int2 a)
 		{
@@ -90,12 +76,10 @@ namespace OpenRA.Traits
 		
 		public bool AnyUnitsAt(int2 a, SubCell sub)
 		{		
-			var node = influence[ a.X, a.Y ];
-			while (node != null)
-			{
-				if (node.subCell == sub || node.subCell == SubCell.FullCell) return true;
-				node = node.next;
-			}
+			for( var i = influence[ a.X, a.Y ] ; i != null ; i = i.next )
+				if (i.subCell == sub || i.subCell == SubCell.FullCell)
+					return true;
+
 			return false;
 		}
 

OpenRA.Mods.RA/Move/Mobile.cs

@@ -307,7 +307,31 @@ namespace OpenRA.Mods.RA.Move
 				yield return Pair.New(toCell, __toSubCell);
 			}
         }
-
+		
+		public SubCell GetDesiredSubcell(int2 a)
+		{
+			if (!Info.SharesCell)
+				return SubCell.FullCell;
+			
+			// Prioritise the current subcell
+			return new[]{ __fromSubCell, SubCell.TopLeft, SubCell.TopRight, SubCell.Center,
+				SubCell.BottomLeft, SubCell.BottomRight}.First(b => 
+			{
+				var blockingActors = uim.GetUnitsAt(a,b);
+				if (blockingActors.Count() > 0)
+	            {
+	                // Non-sharable unit can enter a cell with shareable units only if it can crush all of them
+	                if (Info.Crushes == null)
+	                    return false;
+	
+	                if (blockingActors.Any(c => !(c.HasTrait<ICrushable>() &&
+	                                             c.TraitsImplementing<ICrushable>().Any(d => d.CrushClasses.Intersect(Info.Crushes).Any()))))
+	                    return false;
+	            }
+				return true;
+			});
+		}
+		
         public bool CanEnterCell(int2 p)
         {
             return CanEnterCell(p, null, true);

OpenRA.Mods.RA/Move/Move.cs

@@ -229,7 +229,7 @@ namespace OpenRA.Mods.RA.Move
 			hasWaited = false;
 			path.RemoveAt( path.Count - 1 );
 			
-			var subCell = self.World.WorldActor.Trait<UnitInfluence>().GetFreeSubcell(nextCell, mobile.__fromSubCell);
+			var subCell = mobile.GetDesiredSubcell(nextCell);
 			return Pair.New(nextCell, subCell);
 		}