when reporting the 'info' to the GUI and the PV contains less then 'depth' moves due to a TT hit the engine now tries to restore the rest of the PV from the TT.

Author: lithander

MinimalChess/Playmaker.cs

@@ -7,8 +7,7 @@ public static class Playmaker
         internal static IEnumerable<(Move Move, Board Board)> Play(Board position, int depth, KillerMoves killers, History history)
         {
             //1. Captures Mvv-Lva, PV excluded
-            Move bestMove = Transpositions.GetBestMove(position);
-            if (bestMove != default)
+            if (Transpositions.GetBestMove(position, out Move bestMove))
             {
                 var nextPosition = new Board(position, bestMove);
                 yield return (bestMove, nextPosition);

MinimalChess/Transpositions.cs

@@ -103,12 +103,10 @@ public static void Store(ulong zobristHash, int depth, SearchWindow window, int
             }
         }
 
-        internal static Move GetBestMove(Board position)
+        public static bool GetBestMove(Board position, out Move bestMove)
         {
-            if (Index(position.ZobristHash, out int index))
-                return _table[index].BestMove;
-
-            return default;
+            bestMove = Index(position.ZobristHash, out int index) ? _table[index].BestMove : default;
+            return bestMove != default;
         }
 
         public static bool GetScore(ulong zobristHash, int depth, SearchWindow window, out int score)

MinimalChessEngine/Engine.cs

@@ -1,4 +1,5 @@
-using MinimalChess;
+using System;
+using MinimalChess;
 using System.Collections.Generic;
 using System.Threading;
 
@@ -133,8 +134,34 @@ private bool CanSearchDeeper()
 
         private void Collect()
         {
-            Uci.Info(_search.Depth, (int)SideToMove * _search.Score, _search.NodesVisited, _time.Elapsed, _search.PrincipalVariation);
             _best = _search.PrincipalVariation[0];
+
+            Uci.Info(
+                depth:  _search.Depth, 
+                score:  (int)SideToMove * _search.Score, 
+                nodes:  _search.NodesVisited, 
+                timeMs: _time.Elapsed, 
+                pv:     GetPrintablePV(_search.PrincipalVariation, _search.Depth)
+            );
+        }
+
+        private Move[] GetPrintablePV(Move[] pv, int depth)
+        {
+            List<Move> result = new(pv);
+            //Try to extend from TT to reach the desired depth?
+            if (result.Count < depth)
+            {
+                Board position = new Board(_board);
+                foreach (Move move in pv)
+                    position.Play(move);
+
+                while (result.Count < depth && Transpositions.GetBestMove(position, out Move move))
+                {
+                    position.Play(move);
+                    result.Add(move);
+                }
+            }
+            return result.ToArray();
         }
     }
 }