Disallow friendly king captures in self-capture variants

Author: Belzedar94

src/movegen.cpp

@@ -152,7 +152,10 @@ namespace {
 
     const Bitboard pawns      = pos.pieces(Us, PAWN);
     const Bitboard movable    = pos.board_bb(Us, PAWN) & ~pos.pieces();
-    const Bitboard capturable = pos.board_bb(Us, PAWN) & (allowFriendlyCaptures ? pos.pieces() : pos.pieces(Them));
+    const Bitboard friendlyCapturable = pos.pieces(Us) & ~pos.pieces(Us, KING);
+    const Bitboard capturable = pos.board_bb(Us, PAWN)
+                              & (allowFriendlyCaptures ? (pos.pieces(Them) | friendlyCapturable)
+                                                       :  pos.pieces(Them));
 
     target = Type == EVASIONS ? target : AllSquares;
 
@@ -417,7 +420,7 @@ namespace {
 
         captureTarget = target;
         if (pos.self_capture() && (Type == NON_EVASIONS || Type == CAPTURES))
-            captureTarget |= pos.pieces(Us);
+            captureTarget |= pos.pieces(Us) & ~pos.pieces(Us, KING);
 
         moveList = generate_pawn_moves<Us, Type>(pos, moveList, target);
         for (PieceSet ps = pos.piece_types() & ~(piece_set(PAWN) | KING); ps;)
@@ -476,7 +479,7 @@ namespace {
         Bitboard kingMoves   = pos.moves_from  (Us, KING, ksq) & ~pos.pieces();
         Bitboard kingCaptureMask = Type == EVASIONS ? ~pos.pieces(Us) : captureTarget;
         if (Type == EVASIONS && pos.self_capture())
-            kingCaptureMask |= pos.pieces(Us);
+            kingCaptureMask |= pos.pieces(Us) & ~pos.pieces(Us, KING);
         Bitboard kingQuietMask = Type == EVASIONS ? ~pos.pieces(Us) : target;
         Bitboard b = (kingAttacks & kingCaptureMask) | (kingMoves & kingQuietMask);
         while (b)

src/position.cpp

@@ -1371,8 +1371,15 @@ bool Position::pseudo_legal(const Move m) const {
       return false;
 
   // The destination square cannot be occupied by a friendly piece unless self capture is allowed
-  if ((pieces(us) & to) && !(self_capture() && capture(m)))
-      return false;
+  if (pieces(us) & to)
+  {
+      if (!(self_capture() && capture(m)))
+          return false;
+
+      // Friendly kings are never capturable, even when self-capture is enabled
+      if (type_of(piece_on(to)) == KING)
+          return false;
+  }
 
   // Handle the special case of a pawn move
   if (type_of(pc) == PAWN)