Preserve player definition order in MapPlayers

OpenRA.Game/Map/MapPlayers.cs

@@ -22,15 +22,16 @@ namespace OpenRA
 		// 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 readonly OrderedDictionary<string, PlayerReference> Players;
 
 		public MapPlayers()
 			: this([]) { }
 
 		public MapPlayers(IEnumerable<MiniYamlNode> playerDefinitions)
 		{
-			Players = playerDefinitions.Select(pr => new PlayerReference(new MiniYaml(pr.Key, pr.Value.Nodes)))
+			Players = new OrderedDictionary<string, PlayerReference>(playerDefinitions
-				.ToDictionary(player => player.Name);
+				.Select(pr => new PlayerReference(new MiniYaml(pr.Key, pr.Value.Nodes)))
+				.Select(player => KeyValuePair.Create(player.Name, player)));
 		}
 
 		public MapPlayers(Ruleset rules, int playerCount)
@@ -38,7 +39,7 @@ namespace OpenRA
 			var firstFaction = rules.Actors[SystemActors.World].TraitInfos<FactionInfo>()
 				.First(f => f.Selectable).InternalName;
 
-			Players = new Dictionary<string, PlayerReference>
+			Players = new OrderedDictionary<string, PlayerReference>
 			{
 				{
 					"Neutral", new PlayerReference

OpenRA.Mods.Common/Traits/World/EditorActorLayer.cs

@@ -307,7 +307,7 @@ namespace OpenRA.Mods.Common.Traits
 		{
 			var newCount = previews.Count(p => p.Info.Name == PlayerSpawnName);
 			var playersChanged = false;
-			foreach (var kv in Players.Players)
+			foreach (var kv in Players.Players.ToList())
 			{
 				if (!kv.Key.StartsWith("Multi", StringComparison.Ordinal))
 					continue;

OpenRA.Test/OpenRA.Game/MapPlayersTest.cs

@@ -0,0 +1,37 @@
+#region Copyright & License Information
+/*
+ * Copyright (c) The OpenRA Developers and Contributors
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using NUnit.Framework;
+
+namespace OpenRA.Test
+{
+	[TestFixture]
+	sealed class MapPlayersTest
+	{
+		[TestCase(TestName = "Players keep their definition order when removed and re-added")]
+		public void PlayersKeepDefinitionOrder()
+		{
+			var players = new MapPlayers();
+			string[] names = ["Neutral", "Creeps", "Multi0", "Multi1", "Multi2"];
+			foreach (var name in names)
+				players.Players.Add(name, null);
+
+			// The map editor removes and re-adds all spawn players when updating multiple spawns at once.
+			for (var i = 2; i < names.Length; i++)
+				players.Players.Remove(names[i]);
+
+			for (var i = 2; i < names.Length; i++)
+				players.Players.Add(names[i], null);
+
+			Assert.That(players.Players.Keys, Is.EqualTo(names));
+		}
+	}
+}