block castling out of check

js/pacosako.js

@@ -504,19 +504,31 @@ class Game {
          if (from === (side === DARK ? 'e8' : 'e1')) {
             const row = from[1];
 
+            /* memoize isInCheck(); may not need it and don't want to look twice */
+            /* with any other piece this would be recursive, but kings can't capture */
+            let inCheck = () => {
+               const check = this.isInCheck(side);
+               inCheck = () => check;
+               return check;
+            };
+
             if (this._castling[side].king &&
                   board.isEmpty('f' + row) &&
                   board.isEmpty('g' + row)) {
+               if (!inCheck()) {
                   yield 'g' + row;
                }
+            }
 
             if (this._castling[side].queen &&
                   board.isEmpty('d' + row) &&
                   board.isEmpty('c' + row) &&
                   board.isEmpty('b' + row)) {
+               if (!inCheck()) {
                   yield 'c' + row;
                }
             }
+         }
       } else if (type === QUEEN) {
          for (const dir of ANY_DIR) {
             yield* board.scanPath(side, from, canCapture, dir[0], dir[1], 8);
@@ -609,6 +621,9 @@ class Game {
       /* start with the opponent's unpaired pieces, the ones that can capture */
       let queue = [];
       for (const from of sim._board.findPieces(other, true, false)) {
+         /* this next condition is needed to avoid recursion through legalMoves() */
+         /* kings can't capture anything anyway, so they can be skipped */
+         if (sim._board.getPiece(other, from) !== KING) {
             if (sim.isLegalMove(other, from, king, true)) {
                /* this piece can directly capture the king */
                return true;
@@ -616,6 +631,7 @@ class Game {
 
             queue.push({ game: sim, from });
          }
+      }
 
       /* arbitrary limit, but a human player would probably miss a 7-move chain too */
       const moveLimit = this._moves.length + 6;