Chess

-----------------------------

New features:

* Allow offering a draw to XBoard engines using
``chess.engine.Protocol.play(..., draw_offered=True)``.
* Now detects insufficient material in Horde. Thanks stevepapazis!

Changes:

* ``chess.engine.popen_engine(..., setpgrp=True)`` on Windows now merges
``CREATE_NEW_PROCESS_GROUP`` into ``creationflags`` instead of overriding.
On Unix it now uses ``start_new_session`` instead of calling ``setpgrp`` in
``preexec_fn``.
* Declare that ``chess.svg`` produces SVG Tiny 1.2, and prepare SVG 2 forwards
compatibility.

Bugfixes:

* Fix slightly off-center pawns in ``chess.svg``.
* Fix typing error in Python 3.10 (due to added ``int.bit_count``).

----------------------------

Bugfixes:

* Fixed typing of ``chess.pgn.Mainline.__reversed__()``. It is now a generator,
and ``chess.pgn.ReverseMainline`` has been **removed**.
This is a breaking change but a required bugfix.
* Implement UCI **ponderhit** for consecutive calls to
``chess.engine.Protocol.play(..., ponder=True)``. Previously, the pondering
search was always stopped and restarted.
* Provide the full move stack, not just the position, for UCI pondering.
* Fixed XBoard level in sudden death games.
* Ignore trailing space after ponder move sent by UCI engine.
Previously, such a move would be rejected.
* Prevent cancelling engine commands after they have already been cancelled or
completed. Some internals (``chess.engine.BaseCommand``) have been changed to
accomplish this.

New features:

* Added ``chess.Board.outcome()``.
* Implement and accept usermove feature for XBoard engines.

Special thanks to MarkZH for many of the engine related changes in this
release!

-----------------------------

New features:

* Let ``chess.pgn.GameNode.eval()`` accept PGN comments like
``[%eval 2.5,11]``, meaning 250 centipawns at depth 11.
Use ``chess.pgn.GameNode.eval_depth()`` and
``chess.pgn.GameNode.set_eval(..., depth)`` to get and set the depth.
* Read and write PGN comments with millisecond precision like
``[%clk 1:23:45.678]``.

Changes:

* Recover from invalid UTF-8 sent by an UCI engine, by ignoring that
(and only that) line.

-----------------------------

Bugfixes:

* Fixed unintended collisions and optimized ``chess.Piece.__hash__()``.
* Fixed false-positive ``chess.STATUS_IMPOSSIBLE_CHECK`` if checkers are
aligned with other king.

Changes:

* Also detect ``chess.STATUS_IMPOSSIBLE_CHECK`` if checker is aligned with
en passant square and king.

New features:

* Implemented Lichess winning chance model for ``chess.engine.Score``:
``score.wdl(model="lichess")``.

-----------------------------

Bugfixes:

* Added a new reason for ``board.status()`` to be invalid:
``chess.STATUS_IMPOSSIBLE_CHECK``. This detects positions where two sliding
pieces are giving check while also being aligned with the king
on the same rank, file, or diagonal. Such positions are impossible to reach,
break Stockfish, and maybe other engines.

----------------------------

Bugfixes:

* ``chess.pgn.read_game()`` now properly detects variant games with Chess960
castling rights (as well as mislabeled Standard Chess960 games). Previously,
all castling moves in such games were rejected.