Merge pull request #8 from Belzedar94/codex/iron-pieces

Add iron/uncapturable pieces support (Fixes fairy-stockfish#606)

Author: Belzedar94

.github/copilot-instructions.md .github/AGENTS.md.github/copilot-instructions.md renamed to .github/AGENTS.md

@@ -419,6 +419,7 @@ Variant* VariantParser<DoCheck>::parse(Variant* v) {
     parse_attribute("blastOnCapture", v->blastOnCapture);
     parse_attribute("blastImmuneTypes", v->blastImmuneTypes, v->pieceToChar);
     parse_attribute("mutuallyImmuneTypes", v->mutuallyImmuneTypes, v->pieceToChar);
+    parse_attribute("ironPieceTypes", v->ironPieceTypes, v->pieceToChar);
     parse_attribute("petrifyOnCaptureTypes", v->petrifyOnCaptureTypes, v->pieceToChar);
     parse_attribute("petrifyBlastPieces", v->petrifyBlastPieces);
     parse_attribute("doubleStep", v->doubleStep);

src/parser.cpp

@@ -1210,6 +1210,14 @@ bool Position::legal(Move m) const {
   )
   return false;
 
+  // Iron pieces: any attempt to capture them is illegal (but they can capture normally)
+  if (capture(m)) {
+      Square csq = (type_of(m) == EN_PASSANT) ? capture_square(to) : to;
+      Piece  cpc = piece_on(csq);
+      if (cpc != NO_PIECE && (iron_piece_types() & type_of(cpc)))
+          return false;
+  }
+
   // En passant captures are a tricky special case. Because they are rather
   // uncommon, we do it simply by testing whether the king is attacked after
   // the move is made.

src/position.cpp

@@ -142,6 +142,7 @@ class Position {
   bool blast_on_capture() const;
   PieceSet blast_immune_types() const;
   PieceSet mutually_immune_types() const;
+  PieceSet iron_piece_types() const;
   EndgameEval endgame_eval() const;
   Bitboard double_step_region(Color c) const;
   Bitboard triple_step_region(Color c) const;
@@ -518,6 +519,11 @@ inline PieceSet Position::mutually_immune_types() const {
   return var->mutuallyImmuneTypes;
 }
 
+inline PieceSet Position::iron_piece_types() const {
+  assert(var != nullptr);
+  return var->ironPieceTypes;
+}
+
 inline EndgameEval Position::endgame_eval() const {
   assert(var != nullptr);
   return !count_in_hand(ALL_PIECES) && (var->endgameEval != EG_EVAL_CHESS || count<KING>() == 2) ? var->endgameEval : NO_EG_EVAL;

src/position.h

@@ -66,6 +66,8 @@ struct Variant {
   bool blastOnCapture = false;
   PieceSet blastImmuneTypes = NO_PIECE_SET;
   PieceSet mutuallyImmuneTypes = NO_PIECE_SET;
+  // Iron pieces: attempts to capture these piece types are illegal
+  PieceSet ironPieceTypes = NO_PIECE_SET;
   PieceSet petrifyOnCaptureTypes = NO_PIECE_SET;
   bool petrifyBlastPieces = false;
   bool doubleStep = true;

src/variant.h

@@ -185,6 +185,7 @@
 # blastOnCapture: captures explode all adjacent non-pawn pieces (e.g., atomic chess) [bool] (default: false)
 # blastImmuneTypes: pieces completely immune to explosions (even at ground zero) [PieceSet] (default: none)
 # mutuallyImmuneTypes: pieces that can't capture another piece of same types (e.g., kings (commoners) in atomar) [PieceSet] (default: none)
+# ironPieceTypes: pieces that are uncapturable (attempting to capture them is illegal) [PieceSet] (default: none)
 # petrifyOnCaptureTypes: defined pieces are turned into wall squares when capturing [PieceSet] (default: -)
 # petrifyBlastPieces: if petrify and blast combined, should pieces destroyed in the blast be petrified? [bool] (default: false)
 # doubleStep: enable pawn double step [bool] (default: true)
@@ -2045,3 +2046,7 @@ flagRegionWhite = *10
 flagRegionBlack = *1
 immobilityIllegal = true
 mandatoryPiecePromotion = true
+
+# Iron pieces demo: pawns are uncapturable; everything else behaves normally.
+[iron-pawns:chess]
+ironPieceTypes = p