Do not keep map packages loaded on Game start to reduce memory impact

OpenRA.Game/Game.cs

@@ -980,7 +980,7 @@ public static void LoadMap(string launchMap)
 				Order.Command($"state {Session.ClientState.Ready}")
 			};
 
-			var map = ModData.MapCache.SingleOrDefault(m => m.Uid == launchMap || Path.GetFileName(m.Package.Name) == launchMap);
+			var map = ModData.MapCache.SingleOrDefault(m => m.Uid == launchMap || Path.GetFileName(m.PackageName) == launchMap);
 			if (map == null)
 				throw new ArgumentException($"Could not find map '{launchMap}'.");
 

OpenRA.Game/Map/MapCache.cs

@@ -153,6 +153,9 @@ void LoadMapInternal(string map, IReadOnlyPackage package, MapClassification cla
 						var uid = Map.ComputeUID(mapPackage);
 						previews[uid].UpdateFromMap(mapPackage, package, classification, modData.Manifest.MapCompatibility, mapGrid.Type, modDataRules);
 
+						// Freeing the package to save memory if there is a lot of Maps
+						previews[uid].DisposePackage();
+
 						if (oldMap != uid)
 						{
 							LastModifiedMap = uid;

OpenRA.Game/Map/MapDirectoryTracker.cs

@@ -86,7 +86,7 @@ public void UpdateMaps(MapCache mapcache)
 				dirty = false;
 				foreach (var mapAction in mapActionQueue)
 				{
-					var map = mapcache.FirstOrDefault(x => x.Package?.Name == mapAction.Key && x.Status == MapStatus.Available);
+					var map = mapcache.FirstOrDefault(x => x.PackageName == mapAction.Key && x.Status == MapStatus.Available);
 					if (map != null)
 					{
 						if (mapAction.Value == MapAction.Delete)

OpenRA.Game/Map/MapPreview.cs

@@ -174,7 +174,19 @@ public InnerData Clone()
 		readonly ModData modData;
 
 		public readonly string Uid;
-		public IReadOnlyPackage Package { get; private set; }
+		public string PackageName { get; private set; }
+		IReadOnlyPackage package;
+		public IReadOnlyPackage Package
+		{
+			get
+			{
+				package ??= parentPackage.OpenPackage(PackageName, modData.ModFiles);
+				return package;
+			}
+
+			private set => package = value;
+		}
+
 		IReadOnlyPackage parentPackage;
 
 		volatile InnerData innerData;
@@ -286,7 +298,7 @@ public MapPreview(Map map, ModData modData)
 			cache = modData.MapCache;
 
 			Uid = map.Uid;
-			Package = map.Package;
+			PackageName = map.Package.Name;
 
 			var mapPlayers = new MapPlayers(map.PlayerDefinitions);
 			var spawns = new List<CPos>();
@@ -338,7 +350,7 @@ public void UpdateFromMap(IReadOnlyPackage p, IReadOnlyPackage parent, MapClassi
 				yaml = new MiniYaml(null, MiniYaml.FromStream(yamlStream, $"{p.Name}:map.yaml", stringPool: cache.StringPool)).ToDictionary();
 			}
 
-			Package = p;
+			PackageName = p.Name;
 			parentPackage = parent;
 
 			var newData = innerData.Clone();
@@ -587,10 +599,15 @@ public void Invalidate()
 
 		public void Dispose()
 		{
-			if (Package != null)
+			DisposePackage();
+		}
+
+		public void DisposePackage()
+		{
+			if (package != null)
 			{
-				Package.Dispose();
-				Package = null;
+				package.Dispose();
+				package = null;
 			}
 		}
 

OpenRA.Mods.Common/Widgets/Logic/Editor/SaveMapLogic.cs

@@ -247,7 +247,7 @@ public static void SaveMap(ModData modData, World world, Map map, string combine
 			if (map.Package?.Name != combinedPath)
 			{
 				// When creating a new map or when file paths don't match
-				if (modData.MapCache.Any(m => m.Status == MapStatus.Available && m.Package?.Name == combinedPath))
+				if (modData.MapCache.Any(m => m.Status == MapStatus.Available && m.PackageName == combinedPath))
 				{
 					ConfirmationDialogs.ButtonPrompt(modData,
 						title: OverwriteMapFailedTitle,

OpenRA.Mods.Common/Widgets/Logic/MissionBrowserLogic.cs

@@ -141,7 +141,7 @@ public MissionBrowserLogic(Widget widget, ModData modData, World world, Action o
 						.Select(p => new
 						{
 							Preview = p,
-							Index = missionMapPaths.IndexOf(Path.GetFileName(p.Package.Name))
+							Index = missionMapPaths.IndexOf(Path.GetFileName(p.PackageName))
 						})
 						.Where(x => x.Index != -1)
 						.OrderBy(x => x.Index)