Add RequiresMods tag to the mod Manifest

List required mods and their versions to enable mod dependencies on another mods.
Also used for identifying the engine version by `modchooser`'s version.

OpenRA.Game/Game.cs

@@ -253,6 +253,13 @@ namespace OpenRA
 				RunAfterDelay(Settings.Server.NatDiscoveryTimeout, UPnP.StoppingNatDiscovery);
 		}
 
+		public static bool IsModInstalled(string modId)
+		{
+			return Manifest.AllMods[modId].RequiresMods.All(mod => ModMetadata.AllMods.ContainsKey(mod.Key)
+				&& ModMetadata.AllMods[mod.Key].Version == mod.Value
+				&& IsModInstalled(mod.Key));
+		}
+
 		public static void InitializeMod(string mod, Arguments args)
 		{
 			// Clear static state if we have switched mods
@@ -276,8 +283,8 @@ namespace OpenRA
 				ModData.Dispose();
 			ModData = null;
 
-			// Fall back to default if the mod doesn't exist
+			// Fall back to default if the mod doesn't exist or has missing prerequisites.
-			if (!ModMetadata.AllMods.ContainsKey(mod))
+			if (!ModMetadata.AllMods.ContainsKey(mod) || !IsModInstalled(mod))
 				mod = new GameSettings().Mod;
 
 			Console.WriteLine("Loading mod: {0}", mod);

OpenRA.Game/Manifest.cs

@@ -32,6 +32,8 @@ namespace OpenRA
 	// Describes what is to be loaded in order to run a mod
 	public class Manifest
 	{
+		public static readonly Dictionary<string, Manifest> AllMods = LoadMods();
+
 		public readonly ModMetadata Mod;
 		public readonly string[]
 			Folders, Rules, ServerTraits,
@@ -44,6 +46,7 @@ namespace OpenRA
 		public readonly MiniYaml LoadScreen;
 		public readonly MiniYaml LobbyDefaults;
 
+		public readonly Dictionary<string, string> RequiresMods;
 		public readonly Dictionary<string, Pair<string, int>> Fonts;
 
 		public readonly string[] SpriteFormats = { };
@@ -51,7 +54,7 @@ namespace OpenRA
 		readonly string[] reservedModuleNames = { "Metadata", "Folders", "MapFolders", "Packages", "Rules",
 			"Sequences", "VoxelSequences", "Cursors", "Chrome", "Assemblies", "ChromeLayout", "Weapons",
 			"Voices", "Notifications", "Music", "Translations", "TileSets", "ChromeMetrics", "Missions",
-			"ServerTraits", "LoadScreen", "LobbyDefaults", "Fonts", "SupportsMapsFrom", "SpriteFormats" };
+			"ServerTraits", "LoadScreen", "LobbyDefaults", "Fonts", "SupportsMapsFrom", "SpriteFormats", "RequiresMods" };
 
 		readonly TypeDictionary modules = new TypeDictionary();
 		readonly Dictionary<string, MiniYaml> yaml;
@@ -98,6 +101,8 @@ namespace OpenRA
 					return Pair.New(nd["Font"].Value, Exts.ParseIntegerInvariant(nd["Size"].Value));
 				});
 
+			RequiresMods = yaml["RequiresMods"].ToDictionary(my => my.Value);
+
 			// Allow inherited mods to import parent maps.
 			var compat = new List<string>();
 			compat.Add(mod);
@@ -174,5 +179,29 @@ namespace OpenRA
 
 			return module;
 		}
+
+		static Dictionary<string, Manifest> LoadMods()
+		{
+			var basePath = Platform.ResolvePath(".", "mods");
+			var mods = Directory.GetDirectories(basePath)
+				.Select(x => x.Substring(basePath.Length + 1));
+
+			var ret = new Dictionary<string, Manifest>();
+			foreach (var mod in mods)
+			{
+				try
+				{
+					var manifest = new Manifest(mod);
+					ret.Add(mod, manifest);
+				}
+				catch (Exception ex)
+				{
+					Log.Write("debug", "An exception occured while trying to load mod {0}:", mod);
+					Log.Write("debug", ex.ToString());
+				}
+			}
+
+			return ret;
+		}
 	}
 }

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

@@ -27,6 +27,7 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 		readonly Dictionary<string, Sprite> previews = new Dictionary<string, Sprite>();
 		readonly Dictionary<string, Sprite> logos = new Dictionary<string, Sprite>();
 		readonly Cache<ModMetadata, bool> modInstallStatus;
+		readonly Cache<string, bool> modPrerequisitesFulfilled;
 		readonly Widget modChooserPanel;
 		readonly ButtonWidget loadButton;
 		readonly SheetBuilder sheetBuilder;
@@ -38,6 +39,9 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 		[ObjectCreator.UseCtor]
 		public ModBrowserLogic(Widget widget)
 		{
+			modInstallStatus = new Cache<ModMetadata, bool>(IsModInstalled);
+			modPrerequisitesFulfilled = new Cache<string, bool>(Game.IsModInstalled);
+
 			modChooserPanel = widget;
 			loadButton = modChooserPanel.Get<ButtonWidget>("LOAD_BUTTON");
 			loadButton.OnClick = () => LoadMod(selectedMod);
@@ -93,8 +97,6 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 				catch (Exception) { }
 			}
 
-			modInstallStatus = new Cache<ModMetadata, bool>(IsModInstalled);
-
 			ModMetadata initialMod;
 			ModMetadata.AllMods.TryGetValue(Game.Settings.Game.PreviousMod, out initialMod);
 			SelectMod(initialMod != null && initialMod.Id != "modchooser" ? initialMod : ModMetadata.AllMods["ra"]);
@@ -157,6 +159,8 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 				modOffset = selectedIndex - 4;
 
 			loadButton.Text = modInstallStatus[mod] ? "Load Mod" : "Install Assets";
+
+			loadButton.Text = modPrerequisitesFulfilled[mod.Id] ? loadButton.Text : "Prerequisites missing!";
 		}
 
 		void LoadMod(ModMetadata mod)

mods/cnc/mod.yaml

@@ -4,6 +4,9 @@ Metadata:
 	Version: {DEV_VERSION}
 	Author: the OpenRA Developers
 
+RequiresMods:
+	modchooser: {DEV_VERSION}
+
 Folders:
 	.
 	./mods/cnc

mods/d2k/mod.yaml

@@ -4,6 +4,9 @@ Metadata:
 	Version: {DEV_VERSION}
 	Author: the OpenRA Developers
 
+RequiresMods:
+	modchooser: {DEV_VERSION}
+
 Folders:
 	.
 	./mods/d2k

mods/modchooser/mod.yaml

@@ -4,6 +4,8 @@ Metadata:
 	Author: The OpenRA Developers
 	Hidden: true
 
+RequiresMods:
+
 Folders:
 	.
 	./mods/modchooser

mods/ra/mod.yaml

@@ -4,6 +4,9 @@ Metadata:
 	Version: {DEV_VERSION}
 	Author: the OpenRA Developers
 
+RequiresMods:
+	modchooser: {DEV_VERSION}
+
 Folders:
 	.
 	./mods/ra

mods/ts/mod.yaml

@@ -4,6 +4,9 @@ Metadata:
 	Version: {DEV_VERSION}
 	Author: the OpenRA Developers
 
+RequiresMods:
+	modchooser: {DEV_VERSION}
+
 Folders:
 	.
 # Tiberian Sun