Add RemoveNegativeSequenceLength update rule

OpenRA.Mods.Common/UpdateRules/Rules/20221203/RemoveNegativeSequenceLength.cs

@@ -0,0 +1,92 @@
+#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 System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenRA.Mods.Common.UpdateRules.Rules
+{
+	public class RemoveNegativeSequenceLength : UpdateRule
+	{
+		public override string Name => "Negative sequence length is no longer allowed.";
+
+		public override string Description => "Negative sequence length is no longer allowed, define individual frames in reverse instead.";
+
+		List<MiniYamlNode> resolvedImagesNodes;
+
+		public override IEnumerable<string> BeforeUpdateSequences(ModData modData, List<MiniYamlNode> resolvedImagesNodes)
+		{
+			this.resolvedImagesNodes = resolvedImagesNodes;
+			yield break;
+		}
+
+		readonly Queue<Action> actionQueue = new();
+
+		static MiniYamlNode GetNode(string key, MiniYamlNode node, MiniYamlNode defaultNode)
+		{
+			return node.LastChildMatching(key, includeRemovals: false) ?? defaultNode?.LastChildMatching(key, includeRemovals: false);
+		}
+
+		public override IEnumerable<string> UpdateSequenceNode(ModData modData, MiniYamlNode sequenceNode)
+		{
+			var defaultNode = sequenceNode.LastChildMatching("Defaults");
+			var defaultLengthNode = defaultNode == null ? null : GetNode("Length", defaultNode, null);
+			foreach (var node in sequenceNode.Value.Nodes)
+			{
+				var lengthNode = node.LastChildMatching("Length");
+				if (lengthNode != null && lengthNode.IsRemoval())
+					continue;
+
+				lengthNode ??= defaultLengthNode;
+				if (lengthNode == null || lengthNode.Value.Value == "*")
+					continue;
+
+				var length = FieldLoader.GetValue<int>(lengthNode.Key, lengthNode.Value.Value);
+				if (length >= 0)
+					continue;
+
+				var resolvedImage = resolvedImagesNodes.First(n => n.Key == sequenceNode.Key);
+				var resolvedNode = resolvedImage.LastChildMatching(node.Key);
+				var resolvedDefaultNode = resolvedNode.Value.Value == "Defaults" ? null : resolvedImage.LastChildMatching("Defaults");
+
+				var startNode = GetNode("Start", node, defaultNode) ?? GetNode("Start", resolvedNode, resolvedDefaultNode);
+				if (startNode == null)
+				{
+					actionQueue.Enqueue(() => node.RemoveNodes("Length"));
+					continue;
+				}
+
+				var facingsNode = GetNode("Facings", node, defaultNode) ?? GetNode("Facings", resolvedNode, resolvedDefaultNode);
+				var facings = facingsNode == null ? 1 : FieldLoader.GetValue<int>(facingsNode.Key, facingsNode.Value.Value);
+
+				length = -length * facings;
+				var start = FieldLoader.GetValue<int>(startNode.Key, startNode.Value.Value) - 1;
+
+				var frames = new int[length];
+				for (var i = 0; i < length; i++)
+					frames[i] = start - i;
+
+				actionQueue.Enqueue(() =>
+				{
+					node.RemoveNodes("Start");
+					node.RemoveNodes("Length");
+					node.AddNode("Frames", frames);
+				});
+			}
+
+			while (actionQueue.Count != 0)
+				actionQueue.Dequeue().Invoke();
+
+			yield break;
+		}
+	}
+}

OpenRA.Mods.Common/UpdateRules/UpdatePath.cs

@@ -97,6 +97,7 @@ namespace OpenRA.Mods.Common.UpdateRules
 				new RenameMcvCrateAction(),
 				new RemoveSequenceHasEmbeddedPalette(),
 				new RenameContrailWidth(),
+				new RemoveNegativeSequenceLength(),
 			})
 		};