engine: enhance debug output

src/board.rs

@@ -233,7 +233,7 @@ pub fn draw(board: &Board, f: &mut dyn std::io::Write) {
         }
         writeln!(f, "{} {}", r + 1, rank).unwrap();
     }
-    writeln!(f, "  abcdefgh").unwrap();
+    write!(f, "  abcdefgh").unwrap();
 }
 
 /// Storage for precomputed board pieces stats.
@@ -274,6 +274,19 @@ impl BoardStats {
     }
 }
 
+impl std::fmt::Display for BoardStats {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(
+            f,
+            "{}P {}B {}N {}R {}Q {}K {}dp {}bp {}ip {}m",
+            self.num_pawns, self.num_bishops, self.num_knights, self.num_rooks,
+            self.num_queens, self.num_kings,
+            self.num_doubled_pawns, self.num_backward_pawns, self.num_isolated_pawns,
+            self.mobility
+        )
+    }
+}
+
 /// Create two new BoardStats objects from the board, for white and black.
 ///
 /// See `compute_stats_into` for details.

src/engine.rs

@@ -54,6 +54,22 @@ impl std::fmt::Debug for Node {
     }
 }
 
+impl std::fmt::Display for Node {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        let mut s = vec!();
+        board::draw(&self.board, &mut s);
+        let board_drawing = String::from_utf8_lossy(&s).to_string();
+        write!(
+            f,
+            "* Board:\n{}\n\
+             * Game state:\n{}\n\
+             * White statistics:\n{}\n\
+             * Black statistics:\n{}",
+            board_drawing, self.game_state, self.stats.0, self.stats.1
+        )
+    }
+}
+
 /// Engine communication mode.
 enum Mode {
     /// No mode, sit here and do nothing.

src/notation.rs

@@ -75,6 +75,10 @@ pub fn parse_fen_fields(fields: &[&str]) -> Option<Fen> {
     })
 }
 
+pub fn en_passant_to_string(ep: Option<board::Pos>) -> String {
+    ep.and_then(|p| Some(board::pos_string(&p))).unwrap_or("-".to_string())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/rules.rs

@@ -1,6 +1,7 @@
 //! Functions to determine legal moves.
 
 use crate::board::*;
+use crate::notation;
 
 /// Characteristics of the state of a game.
 ///
@@ -30,6 +31,21 @@ impl GameState {
     }
 }
 
+impl std::fmt::Display for GameState {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(
+            f,
+            "- color: {}\n\
+             - castling: {:04b}\n\
+             - en_passant: {}\n\
+             - halfmove: {}\n\
+             - fullmove: {}",
+            self.color, self.castling, notation::en_passant_to_string(self.en_passant),
+            self.halfmove, self.fullmove
+        )
+    }
+}
+
 pub const CASTLING_WH_K: u8    = 0b00000001;
 pub const CASTLING_WH_Q: u8    = 0b00000010;
 pub const CASTLING_WH_MASK: u8 = 0b00000011;