Prevent saving and starting a map when max player count is exceeded.

OpenRA.Game/Map/Map.cs

@@ -336,9 +336,6 @@ namespace OpenRA
 				throw new InvalidDataException($"Map format {MapFormat} is not supported.\n File: {package.Name}");
 
 			PlayerDefinitions = MiniYaml.NodesOrEmpty(yaml, "Players");
-			if (PlayerDefinitions.Count > 64)
-				throw new InvalidDataException($"Maps must not define more than 64 players.\n File: {package.Name}");
-
 			ActorDefinitions = MiniYaml.NodesOrEmpty(yaml, "Actors");
 
 			Grid = modData.Manifest.Get<MapGrid>();

OpenRA.Game/Map/MapPlayers.cs

@@ -17,6 +17,10 @@ namespace OpenRA
 {
 	public class MapPlayers
 	{
+		// Player masks are represented using a 64 bit integer
+		// The "Everyone" player for spectators is created at runtime,
+		// reducing the available player count for maps by 1.
+		public const int MaximumPlayerCount = 63;
 		public readonly Dictionary<string, PlayerReference> Players;
 
 		public MapPlayers()

OpenRA.Game/Server/MapStatusCache.cs

@@ -88,6 +88,12 @@ namespace OpenRA.Server
 					status = Session.MapStatus.Incompatible;
 				}
 
+				if (map.Players.Players.Count > MapPlayers.MaximumPlayerCount)
+				{
+					Log.Write("server", "Failed to load `{0}`: Player count exceeds maximum ({1}/{2}).", map.Title, map.Players.Players.Count, MapPlayers.MaximumPlayerCount);
+					status = Session.MapStatus.Incompatible;
+				}
+
 				cache[map] = status;
 
 				if ((status & Session.MapStatus.Validating) != 0)