Refine battlekings gating attack handling

Author: Belzedar94

src/position.cpp

@@ -1277,8 +1277,9 @@ bool Position::legal(Move m) const {
 
       Bitboard attackers = attackers_to(gating_square(m), occ, ~us);
 
-      // Ignore attacks from squares that will be cleared as part of the move
-      attackers &= ~SquareBB[to];
+      // Ignore attacks from enemy pieces that will be removed as part of the move
+      if (capture(m) && piece_on(to) != NO_PIECE)
+          attackers &= ~SquareBB[to];
       if (type_of(m) == EN_PASSANT)
           attackers &= ~SquareBB[capture_square(to)];
 

test.py

@@ -435,7 +435,7 @@ def test_chess_promotion_does_not_gate(self):
         self.assertEqual(fen, "Q7/8/8/8/8/8/7p/7K b - - 0 1")
 
     def test_battlekings_king_spawn_blocked(self):
-        fen = "8/8/8/8/8/3p4/4Q3/8 w - - 0 1"
+        fen = "8/8/8/8/8/4r3/4Q3/4r3 w - - 0 1"
         moves = sf.legal_moves("battlekings", fen, [])
         self.assertFalse(moves)