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fix(atomic): validate en passant with variant rules #1215

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fix(atomic): validate en passant with variant rules #1215

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5 changes: 5 additions & 0 deletions chess/variant.py
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Original file line number Diff line number Diff line change
Expand Up @@ -298,6 +298,11 @@ def generate_legal_moves(self, from_mask: chess.Bitboard = chess.BB_ALL, to_mask
if self.is_legal(move):
yield move

def generate_legal_ep(self, from_mask: chess.Bitboard = chess.BB_ALL, to_mask: chess.Bitboard = chess.BB_ALL) -> Iterator[chess.Move]:
for move in self.generate_pseudo_legal_ep(from_mask, to_mask):
if self.is_legal(move):
yield move

def status(self) -> chess.Status:
status = super().status()
status &= ~chess.STATUS_OPPOSITE_CHECK
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26 changes: 26 additions & 0 deletions test.py
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Expand Up @@ -4551,6 +4551,32 @@ def test_atomic_en_passant(self):
board.push_san("cxb6+")
self.assertEqual(board.fen(), "rn2kb1r/2p1p2p/p2q1pp1/3P4/Q7/4P3/PP3P1P/R3K3 b Qkq - 0 11")

# Exploding the opponent's king makes en passant legal even though
# the capturing king would otherwise remain in check.
board = chess.variant.AtomicBoard("rn3b2/8/p7/1kp5/3p2P1/P2K1P2/2P5/2R2B2 w - - 0 1")
board.push_uci("c2c4")
move = chess.Move.from_uci("d4c3")
self.assertTrue(board.is_legal(move))
self.assertIn(move, board.generate_legal_moves())
self.assertIn(move, board.generate_legal_ep())
self.assertIn(move, board.generate_legal_captures())
self.assertTrue(board.has_legal_en_passant())
self.assertEqual(board.fen().split()[3], "c3")
self.assertEqual(board.epd().split()[3], "c3")

# Exploding the capturing king makes en passant illegal, even if the
# usual check test considers the king safe after the explosion.
board = chess.variant.AtomicBoard("8/R7/8/6P1/2p1kP2/2K4N/3P4/8 w - - 0 1")
board.push_uci("d2d4")
move = chess.Move.from_uci("c4d3")
self.assertFalse(board.is_legal(move))
self.assertNotIn(move, board.generate_legal_moves())
self.assertNotIn(move, board.generate_legal_ep())
self.assertNotIn(move, board.generate_legal_captures())
self.assertFalse(board.has_legal_en_passant())
self.assertEqual(board.fen().split()[3], "-")
self.assertEqual(board.epd().split()[3], "-")

# Test the explosion radius.
board = chess.variant.AtomicBoard("3kK3/8/8/2NNNNN1/2NN1pN1/2NN1NN1/2NNPNN1/2NNNNN1 w - - 0 1")
board.push_san("e4")
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