Move the Perft trait into the position crate, and let the perft binary call into
that.
Amend Position::make_move to return a bool in the Ok case that indicates whether
the position has been seen before. Use this to decide whether to continue
recursing during the Perft run. I haven't seen that this makes a difference in
the counts returned by Perft yet.
UCI uses a move format it calls "long algebraic". They look like either "e2e4"
for a regular move, or "h7h8q" for a promotion. Implement parsing these move
strings as a two step process. First define an AlgebraicMoveComponents struct
in the moves crate that implements FromStr. This struct reads out an origin
square, a target square, and an optional promotion shape from a string. Then,
implement a pair of methods on Position that take the move components struct
and return a fully encoded Move struct with them.
This process is required because the algebraic string is not enough by itself to
know what kind of move was made. The current position is required to understand
that.
Implement Shape::is_promotable().
Add a NULL move to the Move struct. I'm not sure what this is used for yet, but
the UCI spec specifically calls out a string that encodes a null move, so I added
it. It may end up being unused!
Do a little bit of cleanup in the core crate as well. Use deeper imports (import
std::fmt instead of requring the fully qualified type path) and remove some
unnecessary From implementations.
This commit is also the first instance (I think) of defining an errors module
in lib.rs for the core crate that holds the various error types the crate exports.
A small Python script that reads a JSON list of positions and their known Perft
node counts to a certain depth, then invokes the Perft program for each position
and validates the output.
Peter Ellis Jones shared such a JSON list on GitHub. Import that file.
The move I observed in my testing was a castling move, which doesn't set target
and origin squares because those are provided by the castling parameters struct
from the board crate.
Fix the missing squares on castle moves by looking up castling parameters and
populating them. This requires Move::castle() to take a Color in addition to the
Wing. Update all the call sites.
I've lived with this warning for a long time because I didn't really understand
it.
```
warning: `chessfriend_core` (lib) generated 1 warning (run `cargo fix --lib -p chessfriend_core` to apply 1 suggestion)
warning: creating a shared reference to mutable static is discouraged
--> bitboard/src/library.rs:66:9
```
I was able to fix this by creating a new type with a single OnceLock attribute.
The OnceLock acts as a cell, making it mutable, even if self is not. So, you can
declare the MoveLibraryWrapper non-mutable static, but still initialize the
library inside the Cell.
This thing isn't used by any of the "modern" code I've written. It was difficult
to write, but kinda neat architecturally. It made a lot of invalid configurations
of moves into build-time errors. Anyway…
Remove several of the tests that relied on it, but that hadn't been updated to
use the newer code either.
Instead of generating e.p. moves in a separate pass, check whether each capture
move (left and right) targets the en passant square. If so, yield an e.p. capture
otherwise just a regular capture.
En passant state should be cleared after any move that isn't a double push.
To support this fix, rename advance_clocks to advance_board_state and let it take
an Option<Square>. Every supporting make_move method calls this method to update
board state when the make is done. So this is the ideal place to also update
e.p. state.
Remove the <n> argument from this method. I think it was a bad idea to begin with
but at the time I was looking for an expedient solution for getting neighbor
squares 2 squares away.
Overhaul bounds checking in this method so horizontal (west and east) bounds are
checked in addition to vertical (north and south) bounds. For the diagonal
directions in particular, it was easy to generate some bogus neighbor squares
because this method didn't check for wrapping when calculating horizontal
neighbors.
Clippy complained that all the properties of the AllPiecesMoveGenerator struct
had the same suffix. It suggested I remove the _move_generator suffix. So I did.
The move generators should only generate moves that can be made, so calling
make_move() and unmake_move() should never give an error during legal move
generation. Both of these calls assert that the result is not an Err(). Improve
the error messaging so that they log the move, the current board position, and
the error message. Highlight the squares relevant to the move (origin, target,
and capture) when printing the board.
Found another bug in the pawn move generator related to en passant moves. The
generator was emitting e.p. captures even when no pawn was available to capture
on that target square.
The solution was to include the e.p. square in the enemies list, effectively
treating the e.p. target as if it were occupied by an enemy piece, and then remove
it from the capture bitboards before move generation.
Include a couple tests to exercise this functionality.
As moves are made, keep track of the hashes of those board position. When moves
are unmade, pop seen hashes from the HashSet.
Reformat the imports in position.rs.
Move this file over to position/tests. That makes it an integration test, technically.
Update it to comply with the current API conventions. This is a pretty radical
change from when I first wrote these!
In the process of running these tests, I found a bug in my PawnMoveGenerator where
it was generating the origin squares for en passant captures incorrectly. Fix
those bugs and write two new tests to exercise those code paths.
One of the test_board! variants was setting .active_color instead of using the
setter. This is a build failure. Fix it.
Move the assert_move_list! macro to the moves crate. This is a more natural home
for it. Additionally, add assert_move_list_contains! and assert_move_list_does_not_contain!
to generate assertions that a collection of moves (anything that implements
.contains()) has or doesn't have a set of moves. Also remove formatted_move_list!,
which is no longer used.
All that done, make the tests pass!
This change builds on several previous changes to implement Zobrist hashing of the
board. This hash can be updated incrementally as changes are made to the board.
In order to do that, various properties of the Board struct had to made internal.
In the setters and various mutating members of Board, the hash is updated as
state changes.
The entire hashing mechanism is optional. If no ZobristState is provided when the
Board is created, the hash is never computed.
Plumb the Zobrist state through Position as well so that clients of Position (the
ultimate interface for interacting with the chess engine) can provide global
state to the whole engine.
The explorer crate gives an example of how this works. Some global state is
computed during initialization and then passed to the Position when it's created.
Make the struct fields private and export getters and various setters for
manipulating the data.
Update all the references to these fields to use the getters and setters instead.
Make the struct attribute private, and export two new methods. A getter, active_color(),
and a setter, set_active_color().
Update all references to the attribute to use the methods.
When place_piece() is called with PlacePieceStrategy::Replace, return the replaced
piece in the Ok() variant of the Result as an Option<Piece>.
Plumb this new return type through Board and Position.
I've been bothered by certain instances where the color has already been unwrapped
from an Option<Color> but a subsequent call takes an Option, so you have to rewrap
it to call the method. I might be overthinking this…
For the Board::*_color_is_in_check set of methods, try out this naming convention:
active_color_is_in_check()
: Operates directly on the Board's active color, no unwrapping required
color_is_in_check()
: Takes an Option<Color> and unwraps it with the active color if None is given
unwrapped_color_is_in_check()
: Takes a Color and operates on it. This method is called by the two above, but
is also public.
Instead of inheriting the MakeMove and UnmakeMove traits by being a BoardProvider,
implement bespoke versions of these two methods. This gives Position a chance to
do some of its own work (tracking captures, move records, etc) when making a move.
Pass the move record by reference to the unmake_move() method. Saves a copy.
Export the Result types for MakeMove and UnmakeMove.
