Introduce AirAttackType

Aircraft attack behavior (currently FlyBy or Hover)
is now controlled via this instead of the CanHover boolean.

OpenRA.Mods.Common/UpdateRules/Rules/20190314/AddAirAttackTypes.cs

@@ -0,0 +1,74 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2019 The OpenRA Developers (see AUTHORS)
+ * 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 AddAirAttackTypes : UpdateRule
+	{
+		public override string Name { get { return "Add AttackType field to AttackAircraft"; } }
+		public override string Description
+		{
+			get
+			{
+				return "Aircraft attack behavior now depends on AttackAircraft.AttackType\n"
+					+ "instead of Aircraft.CanHover.";
+			}
+		}
+
+		readonly List<Tuple<string, string>> hoveringActors = new List<Tuple<string, string>>();
+
+		public override IEnumerable<string> AfterUpdate(ModData modData)
+		{
+			var message = "Aircraft attack behavior (Hover or Strafe) is now controlled via AttackAircraft.AttackType.\n"
+				+ "Aircraft with CanHover: true will now also need AttackType: Hover on AttackAircraft\n"
+				+ "to maintain position while attacking as before.\n"
+				+ "The following places might need manual changes:\n"
+				+ UpdateUtils.FormatMessageList(hoveringActors.Select(n => n.Item1 + " (" + n.Item2 + ")"));
+
+			if (hoveringActors.Any())
+				yield return message;
+
+			hoveringActors.Clear();
+		}
+
+		public override IEnumerable<string> UpdateActorNode(ModData modData, MiniYamlNode actorNode)
+		{
+			var aircraftTraits = actorNode.ChildrenMatching("Aircraft");
+			var attackAircraftTraits = actorNode.ChildrenMatching("AttackAircraft");
+			foreach (var attackAircraft in attackAircraftTraits)
+			{
+				var isHover = false;
+				foreach (var aircraft in aircraftTraits)
+				{
+					var canHoverNode = aircraft.LastChildMatching("CanHover");
+					if (canHoverNode != null)
+						isHover = canHoverNode.NodeValue<bool>();
+
+					if (isHover)
+						break;
+				}
+
+				// It's still possible that CanHover: true is inherited, so let modders check manually if 'false',
+				// otherwise add AttackType: Hover.
+				if (!isHover)
+					hoveringActors.Add(Tuple.Create(actorNode.Key, actorNode.Location.Filename));
+				else
+					attackAircraft.AddNode("AttackType", "Hover");
+			}
+
+			yield break;
+		}
+	}
+}