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Preserve castling rights for promoted kings on a SuicideBoard #1202

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Preserve castling rights for promoted kings on a SuicideBoard #1202

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4ad3be3
Preserve castling rights for promoted kings
jacksonthall22 Aug 7, 2026
14311a1
Merge pull request #1 from hyprchs/jacksonthall22/antichess-castling-…
jacksonthall22 Aug 8, 2026
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5 changes: 3 additions & 2 deletions chess/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2462,6 +2462,7 @@ def push(self, move: Move) -> None:
from_bb = BB_SQUARES[move.from_square]
to_bb = BB_SQUARES[move.to_square]

effective_promoted = self._effective_promoted()
promoted = bool(self.promoted & from_bb)
piece_type = self._remove_piece_at(move.from_square)
assert piece_type is not None, f"push() expects move to be pseudo-legal, but got {move} in {self.board_fen()}"
Expand All @@ -2470,12 +2471,12 @@ def push(self, move: Move) -> None:

# Update castling rights.
self.castling_rights &= ~to_bb & ~from_bb
if piece_type == KING and not self._effective_promoted() & from_bb:
if piece_type == KING and not effective_promoted & from_bb:
if self.turn == WHITE:
self.castling_rights &= ~BB_RANK_1
else:
self.castling_rights &= ~BB_RANK_8
elif captured_piece_type == KING and not self._effective_promoted() & to_bb:
elif captured_piece_type == KING and not effective_promoted & to_bb:
if self.turn == WHITE and square_rank(move.to_square) == RANK_8:
self.castling_rights &= ~BB_RANK_8
elif self.turn == BLACK and square_rank(move.to_square) == RANK_1:
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10 changes: 10 additions & 0 deletions test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4469,6 +4469,16 @@ def test_king_promotions(self):
self.assertEqual(board.san(d1K), "d1=K")
self.assertEqual(board.parse_san("d1=K"), d1K)

def test_promoted_king_move_preserves_castling_rights(self):
board = chess.variant.SuicideBoard("6k1/8/8/8/8/8/1K~6/R3K2R w KQ - 0 1")
move = chess.Move.from_uci("b2b3")
self.assertTrue(board.is_valid())
self.assertIn(move, board.legal_moves)

board.push(move)

self.assertEqual(board.castling_xfen(), "KQ")


class AtomicTestCase(unittest.TestCase):

Expand Down