Fix bugs with en passant

src/Chess/board.nim

@@ -133,12 +133,15 @@ proc doMove(self: ChessBoard, move: Move)
 proc pretty*(self: ChessBoard): string
 proc spawnPiece(self: ChessBoard, location: Location, piece: Piece)
 proc updateAttackedSquares(self: ChessBoard)
+proc updateSlidingAttacks(self: ChessBoard)
 proc getPinnedDirections(self: ChessBoard, loc: Location): seq[Location]
 proc getAttacks*(self: ChessBoard, loc: Location): Attacked
 proc getSlidingAttacks(self: ChessBoard, loc: Location): tuple[attacks: Attacked, pins: Attacked]
 proc inCheck*(self: ChessBoard, color: PieceColor = None): bool
 proc toFEN*(self: ChessBoard): string
 proc undoLastMove*(self: ChessBoard)
+proc movePiece(self: ChessBoard, move: Move, attack: bool = true)
+proc removePiece(self: ChessBoard, location: Location, attack: bool = true)
 
 
 proc extend[T](self: var seq[T], other: openarray[T]) {.inline.} = 
@@ -847,27 +850,21 @@ proc generatePawnMoves(self: ChessBoard, location: Location): seq[Move] =
         if target.isValid():
             let otherPiece = self.grid[target]
             if target == self.position.enPassantSquare and self.grid[enPassantPawn].color == piece.color.opposite():
-                # Ensure en passant doesn't create a check
+                # En passant may be possible
-                let king = self.getKing(piece.color)
+                let targetPawn = self.grid[enPassantPawn]
-                var ok = true
+                # Remove both pieces and see if the king ends up in check
-                if king.row == location.row:
+                self.removePiece(enPassantPawn, attack=false)
-                    var current = location
+                self.removePiece(location, attack=false)
-                    while true:
+                self.updateAttackedSquares()
-                        current = current + piece.color.rightSide()
+                if not self.inCheck(piece.color):
-                        if not current.isValid():
+                    # King is not in check after en passant: move is legal
-                            break
-                        let p = self.grid[current.row, current.col]
-                        if p.color == piece.color:
-                            break
-                        if p.color == None:
-                            continue
-                        # Bishops can't create checks through en passant (neither can knights)
-                        if p.color == piece.color.opposite() and p.kind in [Queen, Rook]:
-                            ok = false
-                            break
-                if ok:
                     directions.add(diagonal)
+                # Reset what we just did and reupdate the attack metadata
+                self.spawnPiece(location, piece)
+                self.spawnPiece(enPassantPawn, targetPawn)
+                self.updateAttackedSquares()
             elif otherPiece.color == piece.color.opposite() and otherPiece.kind != King:  # Can't capture the king!
+                # A capture may be possible
                 directions.add(diagonal)
     # Check for pins
     let pinned = self.getPinnedDirections(location)
@@ -924,8 +921,9 @@ proc generateSlidingMoves(self: ChessBoard, location: Location): seq[Move] =
             if direction in pinned:
                 newDirections.add(direction)
         directions = newDirections
-    let checked = self.inCheck()
+    let 
-    let resolutions = if not checked: @[] else: self.getCheckResolutions(piece.color)
+        checked = self.inCheck()
+        resolutions = if not checked: @[] else: self.getCheckResolutions(piece.color)
     for direction in directions:
         # Slide in this direction as long as it's possible
         var
@@ -1333,9 +1331,10 @@ proc updateSlidingAttacks(self: ChessBoard) =
 proc updateAttackedSquares(self: ChessBoard) =
     ## Updates internal metadata about which squares
     ## are attacked
-    
     self.position.attacked.white.setLen(0)
     self.position.attacked.black.setLen(0)
+    self.position.pinned.white.setLen(0)
+    self.position.pinned.black.setLen(0)
     # Pawns
     self.updatePawnAttacks()
     # Sliding pieces
@@ -1687,8 +1686,6 @@ proc undoLastMove*(self: ChessBoard) =
 
 proc isLegal(self: ChessBoard, move: Move): bool {.inline.} =
     ## Returns whether the given move is legal
-    if self.grid[move.startSquare.row, move.startSquare.col].color != self.getActiveColor():
-        return false
     return move in self.generateMoves(move.startSquare)
 
 
@@ -2047,6 +2044,8 @@ proc handleMoveCommand(board: ChessBoard, command: seq[string]): Move {.discarda
             move.flags = move.flags or CastleLong.uint16
         elif move.targetSquare == move.startSquare + shortCastleKing():
             move.flags = move.flags or CastleShort.uint16
+    if move.targetSquare == board.getEnPassantTarget():
+        move.flags = move.flags or EnPassant.uint16
     result = board.makeMove(move)
     if result == emptyMove():
         echo &"Error: move: {moveString} is illegal"
@@ -2095,7 +2094,7 @@ proc handlePositionCommand(board: var ChessBoard, command: seq[string]) =
             try:
                 tempBoard = newChessboardFromFEN(fenString)
             except ValueError:
-                echo &"Error: position: {getCurrentExceptionMsg()}"
+                echo &"error: position: {getCurrentExceptionMsg()}"
                 return
             if args.len() > 0:
                 var i = 0
@@ -2113,6 +2112,9 @@ proc handlePositionCommand(board: var ChessBoard, command: seq[string]) =
             echo board
         of "pretty":
             echo board.pretty()
+        else:
+            echo &"error: position: unknown subcommand '{command[1]}'"
+            return
 
 
 proc handleUCICommand(board: var ChessBoard, command: seq[string]) =
@@ -2154,7 +2156,8 @@ const HELP_TEXT = """Nimfish help menu:
     - ep: Print the current en passant target
     - pretty: Shorthand for "position pretty"
     - print: Shorthand for "position print"
-    - fen: Shorthand for "position fen" (print only!)
+    - fen: Shorthand for "position fen"
+    - pos <args>: Shorthand for "position <args>"
     - get <square>: Get the piece on the given square
     - uci: enter UCI mode (WIP)
 """
@@ -2189,7 +2192,7 @@ proc main: int =
                     echo HELP_TEXT
                 of "go":
                     handleGoCommand(board, cmd)
-                of "position":
+                of "position", "pos":
                     handlePositionCommand(board, cmd)
                 of "move":
                     handleMoveCommand(board, cmd)