Add ball deferral & met level leniency for gen3/4

Fixes some issues reported via discord

PKHeX.Core/Legality/Encounters/Generator/ByGeneration/EncounterGenerator3.cs

@@ -21,6 +21,29 @@ public sealed class EncounterGenerator3 : IEncounterGenerator
         return GetEncounters(pk, chain, info);
     }
 
+    private enum DeferralType
+    {
+        None,
+        PIDIV,
+        Tile,
+        Ball,
+        SlotNumber,
+    }
+
+    private struct Deferral
+    {
+        public DeferralType Type;
+        public IEncounterable? Encounter;
+
+        public void Update(DeferralType type, IEncounterable enc)
+        {
+            if (Type >= type)
+                return;
+            Type = type;
+            Encounter = enc;
+        }
+    }
+
     public IEnumerable<IEncounterable> GetEncounters(PKM pk, EvoCriteria[] chain, LegalInfo info)
     {
         if (chain.Length == 0)
@@ -29,8 +52,7 @@ public sealed class EncounterGenerator3 : IEncounterGenerator
         info.PIDIV = MethodFinder.Analyze(pk);
         var game = pk.Version;
         var iterator = new EncounterEnumerator3(pk, chain, game);
-        IEncounterable? deferType = null;
+        Deferral defer = default;
-        EncounterSlot3? deferSlot = null;
         var leadQueue = new LeadEncounterQueue<EncounterSlot3>();
 
         bool emerald = pk.E;
@@ -43,7 +65,12 @@ public sealed class EncounterGenerator3 : IEncounterGenerator
             var e = enc.Encounter;
             if (!IsTypeCompatible(e, pk, info.PIDIV.Type))
             {
-                deferType ??= e;
+                defer.Update(DeferralType.PIDIV, e);
+                continue;
+            }
+            if (!IsBallCompatible(e, pk))
+            {
+                defer.Update(DeferralType.Ball, e);
                 continue;
             }
             if (e is not EncounterSlot3 slot)
@@ -76,7 +103,7 @@ public sealed class EncounterGenerator3 : IEncounterGenerator
             var lead = LeadFinder.GetLeadInfo3(slot, info.PIDIV, evo, emerald, gender, pk.Format);
             if (!lead.IsValid())
             {
-                deferSlot ??= slot;
+                defer.Update(DeferralType.SlotNumber, slot);
                 continue;
             }
             leadQueue.Insert(lead, slot);
@@ -90,19 +117,22 @@ public sealed class EncounterGenerator3 : IEncounterGenerator
         if (leadQueue.List.Count != 0)
             yield break;
 
-        // Error will be flagged later if this is chosen.
+        // Errors will be flagged later for those not manually handled below.
-        if (deferSlot != null)
+        if (defer.Encounter is not { } lastResort)
-        {
+            yield break;
-            info.ManualFlag = EncounterYieldFlag.InvalidFrame;
+        if (defer.Type is DeferralType.PIDIV)
-            yield return deferSlot;
-        }
-        else if (deferType != null)
-        {
             info.ManualFlag = EncounterYieldFlag.InvalidPIDIV;
-            yield return deferType;
+        else if (defer.Type is DeferralType.Tile)
-        }
+            info.ManualFlag = EncounterYieldFlag.InvalidFrame;
+        yield return lastResort;
     }
 
+    private static bool IsBallCompatible(IFixedBall e, PKM pk) => e.FixedBall switch
+    {
+        Ball.Safari when pk.Ball is (byte)Ball.Safari => true,
+        _ => pk.Ball is not (byte)Ball.Safari,
+    };
+
     private static bool IsTypeCompatible(IEncounterTemplate enc, PKM pk, PIDType type)
     {
         if (enc is IRandomCorrelation r)

PKHeX.Core/Legality/Encounters/Generator/ByGeneration/EncounterGenerator4.cs

@@ -26,14 +26,35 @@ public sealed class EncounterGenerator4 : IEncounterGenerator
             yield return enc;
     }
 
+    private enum DeferralType
+    {
+        None,
+        PIDIV,
+        Tile,
+        Ball,
+        SlotNumber,
+    }
+
+    private struct Deferral
+    {
+        public DeferralType Type;
+        public IEncounterable? Encounter;
+
+        public void Update(DeferralType type, IEncounterable enc)
+        {
+            if (Type >= type)
+                return;
+            Type = type;
+            Encounter = enc;
+        }
+    }
+
     public IEnumerable<IEncounterable> GetEncounters(PKM pk, EvoCriteria[] chain, LegalInfo info)
     {
         info.PIDIV = MethodFinder.Analyze(pk);
         var game = pk.Version;
         var iterator = new EncounterEnumerator4(pk, chain, game);
-        EncounterSlot4? deferSlot = null;
+        Deferral defer = default;
-        IEncounterable? deferTile = null;
-        IEncounterable? deferType = null;
         var leadQueue = new LeadEncounterQueue<EncounterSlot4>();
 
         foreach (var enc in iterator)
@@ -41,16 +62,24 @@ public sealed class EncounterGenerator4 : IEncounterGenerator
             var e = enc.Encounter;
             if (!IsTileCompatible(e, pk))
             {
-                deferTile ??= e;
+                defer.Update(DeferralType.Tile, e);
                 continue;
             }
             if (!IsTypeCompatible(e, pk, info.PIDIV.Type))
             {
-                deferType ??= e;
+                defer.Update(DeferralType.PIDIV, e);
+                continue;
+            }
+            if (!IsBallCompatible(e, pk))
+            {
+                defer.Update(DeferralType.Ball, e);
                 continue;
             }
             if (e is not EncounterSlot4 slot)
             {
+                if (pk.Ball is (byte)Ball.Safari or (byte)Ball.Sport)
+                    defer.Update(DeferralType.Ball, e);
+                else
                     yield return e;
                 continue;
             }
@@ -59,7 +88,7 @@ public sealed class EncounterGenerator4 : IEncounterGenerator
             var lead = LeadFinder.GetLeadInfo4(pk, slot, info.PIDIV, evo);
             if (!lead.IsValid())
             {
-                deferSlot ??= slot;
+                defer.Update(DeferralType.SlotNumber, slot);
                 continue;
             }
             leadQueue.Insert(lead, slot);
@@ -73,23 +102,23 @@ public sealed class EncounterGenerator4 : IEncounterGenerator
         if (leadQueue.List.Count != 0)
             yield break;
 
-        // Error will be flagged later if this is chosen.
+        // Errors will be flagged later for those not manually handled below.
-        if (deferTile != null)
+        if (defer.Encounter is not { } lastResort)
-        {
+            yield break;
-            yield return deferTile;
+        if (defer.Type is DeferralType.PIDIV)
-        }
-        else if (deferSlot != null)
-        {
-            info.ManualFlag = EncounterYieldFlag.InvalidFrame;
-            yield return deferSlot;
-        }
-        else if (deferType != null)
-        {
             info.ManualFlag = EncounterYieldFlag.InvalidPIDIV;
-            yield return deferType;
+        else if (defer.Type is DeferralType.Tile)
-        }
+            info.ManualFlag = EncounterYieldFlag.InvalidFrame;
+        yield return lastResort;
     }
 
+    private static bool IsBallCompatible(IFixedBall e, PKM pk) => e.FixedBall switch
+    {
+        Ball.Safari when pk.Ball is (byte)Ball.Safari => true,
+        Ball.Sport when pk.Ball is (byte)Ball.Sport => true,
+        _ => pk.Ball is not ((byte)Ball.Safari or (byte)Ball.Sport),
+    };
+
     private static bool IsTileCompatible(IEncounterTemplate enc, PKM pk)
     {
         if (pk is not IGroundTile e)

PKHeX.Core/Legality/Evolutions/EvolutionChain.cs

@@ -91,6 +91,8 @@ public static class EvolutionChain
             return [];
 
         var chain = result[..count];
+        if (IsMetLost(pk, enc)) // Original met level lost, need to be more permissive on evos.
+            EvolutionUtil.ConditionEncounterNoMet(chain);
         return chain.ToArray();
     }
 
@@ -121,6 +123,13 @@ public static class EvolutionChain
         return count;
     }
 
+    private static bool IsMetLost(PKM pk, EvolutionOrigin enc) => enc.Generation switch
+    {
+        >= 5 => false,
+        <= 2 => pk is not ICaughtData2 { MetLevel: not 0 },
+           _ => enc.Generation != pk.Format,
+    };
+
     private static int DevolveFrom(Span<EvoCriteria> result, PKM pk, EvolutionOrigin enc, EntityContext context, ushort encSpecies, bool discard)
     {
         var group = EvolutionGroupUtil.GetGroup(context);

PKHeX.Core/Legality/Evolutions/EvolutionGroup/EvolutionUtil.cs

@@ -163,4 +163,16 @@ internal static class EvolutionUtil
         }
         return i;
     }
+
+    public static void ConditionEncounterNoMet(Span<EvoCriteria> chain)
+    {
+        // Allow for under-leveled evolutions for purposes of finding an under-leveled evolved encounter.
+        // e.g. a level 5 Silcoon encounter slot (normally needs level 7).
+        for (int i = 0; i < chain.Length - 1; i++)
+        {
+            ref var evo = ref chain[i];
+            if (evo.Method.IsLevelUpRequired())
+                evo = evo with { LevelMin = (byte)(chain[i + 1].LevelMin + evo.LevelUpRequired) };
+        }
+    }
 }