Validate drops of pseudo-royals

Closes #867.

Author: ianfab

src/position.cpp

@@ -1146,6 +1146,9 @@ bool Position::legal(Move m) const {
       if (capture(m) && (var->petrifyOnCaptureTypes & type_of(moved_piece(m))) && (st->pseudoRoyals & from))
           return false;
       Bitboard pseudoRoyals = st->pseudoRoyals & pieces(sideToMove);
+      // Add dropped pseudo-royal
+      if (type_of(m) == DROP && (extinction_piece_types() & type_of(moved_piece(m))))
+          pseudoRoyals |= square_bb(to);
       Bitboard pseudoRoyalsTheirs = st->pseudoRoyals & pieces(~sideToMove);
       if (is_ok(from) && (pseudoRoyals & from))
           pseudoRoyals ^= square_bb(from) ^ kto;

test.py

@@ -120,6 +120,10 @@
 castlingKingPiece = k
 extinctionValue = loss
 extinctionPieceTypes = k
+
+[coregaldrop:coregal]
+pieceDrops = true
+startFen = rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR[Qq] w KQkq - 0 1
 """
 
 sf.load_variant_config(ini_text)
@@ -346,6 +350,11 @@ def test_legal_moves(self):
         result = sf.legal_moves("seirawan", fen, [])
         self.assertIn("c8g4h", result)
 
+        # Drop pseudo-royals into check
+        result = sf.legal_moves("coregaldrop", sf.start_fen("coregaldrop"), [])
+        self.assertIn("Q@a3", result)
+        self.assertNotIn("Q@a6", result)
+
         # In Cannon Shogi the FGC and FSC can also move one square diagonally and, besides,
         # move or capture two squares diagonally, by leaping an adjacent piece. 
         fen = "lnsg1gsnl/1rc1kuab1/p1+A1p1p1p/3P5/6i2/6P2/P1P1P3P/1B1U1ICR1/LNSGKGSNL[] w - - 1 3"