8-add-legal-move-filter (#16)

works on #8

Reviewed-on: #16
Co-authored-by: Josh <josh@joshuaschuett.com>
Co-committed-by: Josh <josh@joshuaschuett.com>

test/chess_ffi.py

@@ -91,10 +91,12 @@ gen_king_moves    = _bind_opt("gen_king_moves",    *PIECE_SIG)
 ATTACKED_SIG = (C.POINTER(Board), C.c_int, C.c_int)
 INCHECK_ARGS = (C.POINTER(Board), C.c_int)
 ATTACKERS_TO = (C.POINTER(Board), C.c_int, C.c_int)
+GEN_LEGAL_MOVES = (C.POINTER(Board), C.POINTER(Move))
 
 square_attacked = _bind_opt("square_attacked", ATTACKED_SIG, C.c_bool)
 in_check = _bind_opt("in_check", INCHECK_ARGS, C.c_bool)
 attackers_to = _bind_opt("attackers_to", ATTACKERS_TO, C.c_uint64)
+get_legal_moves = _bind_opt("get_legal_moves", GEN_LEGAL_MOVES, C.c_int)
 
 
 # Attack cache tables.
@@ -126,6 +128,10 @@ def gen_moves(board, captures_only=False, cap=256):
     return buf, n
 
 
+def gen_legal_moves(board, out):
+    return int(get_legal_moves(C.byref(board), out))
+
+
 def is_square_attacked(board, sq, by):
     return bool(square_attacked(C.byref(board), int(sq), int(by)))
 

test/test_legal_move_gen.py

@@ -0,0 +1,110 @@
+from test.base import ChessLibTestBase
+from test.chess_ffi import Move
+from test.chess_ffi import Board
+from test.chess_ffi import BLACK
+from test.chess_ffi import is_in_check
+from test.chess_ffi import gen_legal_moves
+from test.chess_ffi import sq
+
+MAX_MOVES = 256
+
+
+class TestLegalMoveGen(ChessLibTestBase):
+    def _gen_legal(self, board):
+        """Support either return-count or out-parameter signatures."""
+        moves = (Move * MAX_MOVES)()
+        n = gen_legal_moves(board, moves)
+        return n, moves
+
+
+    def test_start_position(self):
+        # 20 legal moves from the initial chess position
+        # https://www.chessprogramming.org/Perft_Results#Initial_Position
+        fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
+        b = Board()
+        self.load_fen(fen, board=b)
+
+        n, _ = self._gen_legal(b)
+        self.assertEqual(n, 20, "Start position must have 20 legal moves for White")
+
+
+    def test_kiwipete_depth1_count(self):
+        # Kiwipete: perft(1) = 48
+        # https://www.chessprogramming.org/Perft_Results#Position_2
+        fen = "r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq - 0 1"
+        b = Board(); self.load_fen(fen, board=b)
+
+        n, moves = self._gen_legal(b)
+        self.assertEqual(n, 48, "Kiwipete perft(1) should be 48")
+
+
+    def test_perft_position_3(self):
+        # https://www.chessprogramming.org/Perft_Results#Position_3
+        fen = "8/2p5/3p4/KP5r/1R3p1k/8/4P1P1/8 w - - 0 1"
+        b = Board(); self.load_fen(fen, board=b)
+
+        n, moves = self._gen_legal(b)
+        self.assertEqual(n, 14)
+
+
+    def test_perft_position_4(self):
+        # https://www.chessprogramming.org/Perft_Results#Position_4
+        fen = "r3k2r/Pppp1ppp/1b3nbN/nP6/BBP1P3/q4N2/Pp1P2PP/R2Q1RK1 w kq - 0 1"
+        b = Board(); self.load_fen(fen, board=b)
+
+        n, moves = self._gen_legal(b)
+        self.assertEqual(n, 6)
+
+
+    def test_perft_position_5(self):
+        # https://www.chessprogramming.org/Perft_Results#Position_5
+        fen = "rnbq1k1r/pp1Pbppp/2p5/8/2B5/8/PPP1NnPP/RNBQK2R w KQ - 1 8"
+        b = Board(); self.load_fen(fen, board=b)
+
+        n, moves = self._gen_legal(b)
+        self.assertEqual(n, 44)
+
+    
+    def test_perft_position_6(self):
+        # https://www.chessprogramming.org/Perft_Results#Position_6
+        fen = "r4rk1/1pp1qppp/p1np1n2/2b1p1B1/2B1P1b1/P1NP1N2/1PP1QPPP/R4RK1 w - - 0 10"
+        b = Board(); self.load_fen(fen, board=b)
+
+        n, moves = self._gen_legal(b)
+        self.assertEqual(n, 46)
+
+
+    def test_stalemate_black_to_move(self):
+        # Classic stalemate: Black to move, no legal moves, not in check
+        fen = "7k/5Q2/6K1/8/8/8/8/8 b - - 0 1"
+        b = Board()
+        self.load_fen(fen, board=b)
+
+        moves = (Move * MAX_MOVES)()
+        n = gen_legal_moves(b, moves)
+
+        self.assertEqual(n, 0, "Stalemate should have 0 legal moves")
+        self.assertFalse(is_in_check(b, BLACK), "Side to move must not be in check in stalemate")
+    
+
+    def test_simple_checkmate(self):
+        # Black to move; mated (Qg7# with Kg6 support)
+        fen = "7k/6Q1/6K1/8/8/8/8/8 b - - 0 1"
+        b = Board(); self.load_fen(fen, board=b)
+        moves = (Move * MAX_MOVES)()
+        n = gen_legal_moves(b, moves)
+
+        self.assertEqual(n, 0, "Checkmated side should have 0 legal moves")
+        self.assertTrue(is_in_check(b, BLACK), "Mated side must be in check")
+
+
+    def test_pinned_piece_cannot_move(self):
+            # White knight e2 pinned by rook e8 vs king e1
+            fen = "4r3/8/8/8/8/8/4N3/4K3 w - - 0 1"
+            b = Board(); self.load_fen(fen, board=b)
+            moves = (Move * MAX_MOVES)()
+            n = gen_legal_moves(b, moves)
+
+            for move in moves:
+                # Pinned knight cannot move from it's square.
+                self.assertFalse(getattr(move, "from") == sq("e2"))

test/test_movegen.py

@@ -253,7 +253,7 @@ class TestPseudoMoveGeneration(ChessLibTestBase):
 
     def test_quiet_pawn_promotions_white(self):
         cases = [
-            ("8/PPPPPPPP/8/8/8/8/8/8 w - - 0 1", 8, "all open on 7th rank"),
+            ("8/PPPPPPPP/8/8/8/8/8/8 w - - 0 1", 32, "all open on 7th rank"),
             ("8/8/7P/8/8/8/8/8 w - - 0 1", 0, "no promotions"),
             ("7n/7P/8/8/8/8/8/8 w - - 0 1", 0, "blocked by enemy"),
             ("7N/7P/8/8/8/8/8/8 w - - 0 1", 0, "blocked by friendly"),
@@ -263,8 +263,8 @@ class TestPseudoMoveGeneration(ChessLibTestBase):
 
     def test_capture_pawn_promotions_white(self):
         cases = [
-            ("6n1/7P/8/8/8/8/8/8 w - - 0 1", 1, "one capture"),
-            ("5n1n/6P1/8/8/8/8/8/8 w - - 0 1", 2, "two captures"),
+            ("6n1/7P/8/8/8/8/8/8 w - - 0 1", 4, "one capture"),
+            ("5n1n/6P1/8/8/8/8/8/8 w - - 0 1", 8, "two captures"),
             ("8/7P/8/8/8/8/8/8 w - - 0 1", 0, "no capture"),
         ]
         self.run_subtests(cases, gen_white_pawn_capture_promotions)