@subalias said in #3:
> I didn't choose any castling option. The Lichess FEN generator correctly removes White's kingside option itself, but not the queenside option. If you try to include kingside castling, you can't. Besides this being inconsistent, the generator should never generate an invalid FEN, even if the user makes a mistake. Invalid FENs shouldn't be accepted as input, either.
In this position, there is no white rook on the right side of the white king, so kingside castling is certainly impossible even in chess960, so it is automatically disabled. But if queenside castling would get automatically disabled, then it would be impossible to input some chess960 positions, so it's up to the user to set up castling rights correctly.
Of course, if you input a position that is only legal in chess960, then this position cannot be handled by programs that do not deal with chess960. I would call this a feature and not a bug.
However, the way Lichess implements this isn't enough to handle *all* chess960 scenarios, because if both rooks are on the same side of the king (i.e. one rook has moved), then the castling right always refers to the rook that's farther away from the king, and I think there's no way to give the castling right to the other rook. I think something like X-FEN would be necessary for that.
