Fix missing temporal dimension to dislodge checks

MultiversalDiplomacy/Adjudicate/Decision/MovementDecisions.cs

@@ -84,7 +84,7 @@ public class MovementDecisions
             // Create a dislodge decision for this unit.
             List<MoveOrder> incoming = orders
                 .OfType<MoveOrder>()
-                .Where(move => move.Province == order.Unit.Province)
+                .Where(order.IsIncoming)
                 .ToList();
             this.IsDislodged[order.Unit] = new(order, incoming);
 
@@ -108,9 +108,7 @@ public class MovementDecisions
                 // Find competing moves.
                 List<MoveOrder> competing = orders
                     .OfType<MoveOrder>()
-                    .Where(other
-                        => other != move
-                        && other.Province == move.Province)
+                    .Where(move.IsCompeting)
                     .ToList();
 
                 // Create the move-related decisions.

MultiversalDiplomacy/Orders/MoveOrder.cs

@@ -34,9 +34,20 @@ public class MoveOrder : UnitOrder
         this.Location = location;
     }
 
+    /// <summary>
+    /// Returns whether another move order is in a head-to-head battle with this order.
+    /// </summary>
     public bool IsOpposing(MoveOrder other)
         => this.Season == other.Unit.Season
         && other.Season == this.Unit.Season
         && this.Province == other.Unit.Province
         && other.Province == this.Unit.Province;
+
+    /// <summary>
+    /// Returns whether another move order has the same destination as this order.
+    /// </summary>
+    public bool IsCompeting(MoveOrder other)
+        => this != other
+        && this.Season == other.Season
+        && this.Province == other.Province;
 }

MultiversalDiplomacy/Orders/UnitOrder.cs

@@ -16,4 +16,12 @@ public abstract class UnitOrder : Order
     {
         this.Unit = unit;
     }
+
+    /// <summary>
+    /// Returns whether a move order is moving into this order's unit's province.
+    /// </summary>
+    public bool IsIncoming(MoveOrder other)
+        => this != other
+        && other.Season == this.Unit.Season
+        && other.Province == this.Unit.Province;
 }

MultiversalDiplomacyTests/Is.cs

@@ -3,23 +3,57 @@ using MultiversalDiplomacy.Adjudicate.Decision;
 
 namespace MultiversalDiplomacyTests;
 
+/// <summary>
+/// Multiversal Diplomacy assertion constraint extension provider. "NotX" constraints are provided
+/// because properties can't be added to Is.Not via extension.
+/// </summary>
 public class Is : NUnit.Framework.Is
 {
+    /// <summary>
+    /// Returns a constraint that checks for a positive order validation.
+    /// </summary>
     public static OrderValidationConstraint Valid
         => new(true, ValidationReason.Valid);
 
+    /// <summary>
+    /// Returns a constraint that checks for a negative order validation.
+    /// </summary>
     public static OrderValidationConstraint Invalid(ValidationReason expected)
         => new(false, expected);
 
+    /// <summary>
+    /// Returns a constraint that checks for a positive <see cref="IsDislodged"/> decision.
+    /// </summary>
     public static OrderBinaryAdjudicationConstraint<IsDislodged> Dislodged
         => new(true);
 
+    /// <summary>
+    /// Returns a constraint that checks for a negative <see cref="IsDislodged"/> decision.
+    /// </summary>
     public static OrderBinaryAdjudicationConstraint<IsDislodged> NotDislodged
         => new(false);
 
+    /// <summary>
+    /// Returns a constraint that checks for a positive <see cref="DoesMove"/> decision.
+    /// </summary>
     public static OrderBinaryAdjudicationConstraint<DoesMove> Victorious
         => new(true);
 
+    /// <summary>
+    /// Returns a constraint that checks for a negative <see cref="DoesMove"/> decision.
+    /// </summary>
     public static OrderBinaryAdjudicationConstraint<DoesMove> Repelled
         => new(false);
+
+    /// <summary>
+    /// Returns a constraint that checks for a positive <see cref="GivesSupport"/> decision.
+    /// </summary>
+    public static OrderBinaryAdjudicationConstraint<GivesSupport> NotCut
+        => new(true);
+
+    /// <summary>
+    /// Returns a constraint that checks for a negative <see cref="GivesSupport"/> decision.
+    /// </summary>
+    public static OrderBinaryAdjudicationConstraint<GivesSupport> Cut
+        => new(false);
 }

MultiversalDiplomacyTests/TestCaseBuilder.cs

@@ -133,7 +133,13 @@ public class TestCaseBuilder
         /// <summary>
         /// Make the support order target an army.
         /// </summary>
-        public ISupportTypeContext Army(string provinceName, string? powerName = null);
+        /// <param name="season">
+        /// The unit season. If not specified, defaults to the same season as the ordered unit.
+        /// </param>
+        public ISupportTypeContext Army(
+            string provinceName,
+            Season? season = null,
+            string? powerName = null);
 
         /// <summary>
         /// Make the support order target a fleet.
@@ -157,7 +163,14 @@ public class TestCaseBuilder
         /// <summary>
         /// Give the unit an order to support the target's move order.
         /// </summary>
-        public IOrderDefinedContext<SupportMoveOrder> MoveTo(string provinceName, string? coast = null);
+        /// <param name="season">
+        /// The target's destination season. If not specified, defaults to the same season as the
+        /// target (not the ordered unit).
+        /// </param>
+        public IOrderDefinedContext<SupportMoveOrder> MoveTo(
+            string provinceName,
+            Season? season = null,
+            string? coast = null);
     }
 
     /// <summary>
@@ -506,14 +519,18 @@ public class TestCaseBuilder
             this.UnitContext = unitContext;
         }
 
-        public ISupportTypeContext Army(string provinceName, string? powerName = null)
+        public ISupportTypeContext Army(
+            string provinceName,
+            Season? season = null,
+            string? powerName = null)
         {
             Power power = powerName == null
                 ? this.PowerContext.Power
                 : this.Builder.World.GetPower(powerName);
             Location location = this.Builder.World.GetLand(provinceName);
+            Season destSeason = season ?? this.SeasonContext.Season;
             Unit unit = this.Builder.GetOrBuildUnit(
-                power, location, this.SeasonContext.Season, UnitType.Army);
+                power, location, destSeason, UnitType.Army);
             return new SupportTypeContext(this, unit);
         }
 
@@ -559,16 +576,20 @@ public class TestCaseBuilder
             return new OrderDefinedContext<SupportHoldOrder>(this.UnitContext, order);
         }
 
-        public IOrderDefinedContext<SupportMoveOrder> MoveTo(string provinceName, string? coast = null)
+        public IOrderDefinedContext<SupportMoveOrder> MoveTo(
+            string provinceName,
+            Season? season = null,
+            string? coast = null)
         {
             Location destination = this.Target.Type == UnitType.Army
                 ? this.Builder.World.GetLand(provinceName)
                 : this.Builder.World.GetWater(provinceName, coast);
+            Season targetDestSeason = season ?? this.Target.Season;
             SupportMoveOrder order = new SupportMoveOrder(
                 this.PowerContext.Power,
                 this.UnitContext.Unit,
                 this.Target,
-                this.SeasonContext.Season,
+                targetDestSeason,
                 destination);
             this.Builder.OrderList.Add(order);
             return new OrderDefinedContext<SupportMoveOrder>(this.UnitContext, order);

MultiversalDiplomacyTests/TimeTravelTest.cs

@@ -50,4 +50,54 @@ public class TimeTravelTest
         Unit aMun1 = world.GetUnitAt("Mun", fork.Coord);
         Assert.That(aMun1.Past, Is.EqualTo(originalUnit));
     }
+
+    [Test]
+    public void SupportToRepelledPastMoveForksTimeline()
+    {
+        TestCaseBuilder setup = new(World.WithStandardMap(), MovementPhaseAdjudicator.Instance);
+
+        // Fail to dislodge on the first turn, then support the move so it succeeds.
+        setup[(0, 0)]
+            .GetReference(out Season s0)
+            ["Germany"]
+                .Army("Mun").MovesTo("Tyr").GetReference(out var mun0)
+            ["Austria"]
+                .Army("Tyr").Holds().GetReference(out var tyr0);
+
+        setup.ValidateOrders();
+        Assert.That(mun0, Is.Valid);
+        Assert.That(tyr0, Is.Valid);
+        setup.AdjudicateOrders();
+        Assert.That(mun0, Is.Repelled);
+        Assert.That(tyr0, Is.NotDislodged);
+        setup.UpdateWorld();
+
+        setup[(1, 0)]
+            ["Germany"]
+                .Army("Mun").Supports.Army("Mun", season: s0).MoveTo("Tyr").GetReference(out var mun1)
+            ["Austria"]
+                .Army("Tyr").Holds();
+
+        // Confirm that history is changed.
+        setup.ValidateOrders();
+        Assert.That(mun1, Is.Valid);
+        setup.AdjudicateOrders();
+        Assert.That(mun1, Is.NotCut);
+        Assert.That(mun0, Is.Victorious);
+        Assert.That(tyr0, Is.Dislodged);
+
+        // Confirm that an alternate future is created.
+        World world = setup.UpdateWorld();
+        Season fork = world.GetSeason(1, 1);
+        Unit tyr1 = world.GetUnitAt("Tyr", fork.Coord);
+        Assert.That(
+            tyr1.Past,
+            Is.EqualTo(mun0.Order.Unit),
+            "Expected A Mun 0:0 to advance to Tyr 1:1");
+        Assert.That(
+            world.RetreatingUnits.Count,
+            Is.EqualTo(1),
+            "Expected A Tyr 0:0 to be in retreat");
+        Assert.That(world.RetreatingUnits.First().Unit, Is.EqualTo(tyr0.Order.Unit));
+    }
 }